3. Results and discussion

#### 3.1. A model of an carbon implanted silicon layer and the mechanism of the low temperature formation of Si- and SiC crystallites

In Fig.1 the calculated profile of carbon atom distribution in Si constructed basing on data Rp \* zYp from [21] are presented. The Gaussian profile (Fig.1, curve 1) was calculated for the implantation of carbon ions with energy 40 keV and dose 3.534×1017 cm-2, when the carbon concentration in the distribution peak is equal to stoichiometric composition of SiC, i.e. NC/NSi = 1, where NC/NSi is the ratio of the concentrations of C and Si atoms. The curve 2 in Fig.1 shows the calculated profile, corresponding to dose D = 3.56×1017 cm-2 of carbon ions used in this investigation.

#### *3.1.1. LO-phonons and their applications to analysis of an implanted layer*

As it is well known [45, 66], during interaction of electromagnetic waves with an infinite .5/0(z(00%!\_z0\$!z0.\*/2!./(z+,0%(z+/%((0%+\*/zcw,\$+\*+\*/dz+"z0+)/z.!z!4%0! ^z \*z+2!.¥ whelming majority of previous investigations, the synthesis of silicon carbide was identified 5z\$!(,z+"z/,!0.z+"z0.\*/2!./(z+,0%(z,\$+\*+\*/^z+z00!),0/z3/z) !z0+z !0!0z0\$!z(+\*#%¥ tudinal optical oscillations (LO-phonons) of atoms of lattice for a Gaussian concentration profiles of carbon in spite of that majority of studies in the field of ion synthesis of silicon carbide was carried out using these profiles. [3] found that an absorption at wave number 980 cm-1 is observed, if the angle of incidence of irradiation on the sample surface deviate from perpendicularity. Implantation of carbon ions with energies of 24 and 40 keV and a dose of 4.3 × 1017 cm-2 carried out at room temperature into a (111) oriented Si plate of p-type conductivity. Annealing was performed in a vacuum at temperatures of 900 and 1100°C for 30 minutes. The presence in the transmission spectrum of bands associated with the LO-and TO-phonons made possible to calculate such parameters of SiC, as high frequency, X, and the low-frequency dielectric constant, 0, attenuation coefficient of the phonons, the effective \$.#!z\*/e and the force constant . So, the detection of LO-phonons may be used to obtain %0%+\*(z%\*"+.)0%+\*z+10zz/0.101.!z+"z%+\*z%),(\*0! z(5!.^z
+.!2!.\_z0\$!z".!-1!\*5z2(¥ ues of both the transversal- and longitudinal oscillations permit to determine the parameters of efficient charge which is a quantitative criterion of a compound polarity. The efficient charge value permits to calculate a mobility of free charge carriers.

Figure 1. The calculated profiles of distribution of carbon atoms in Si constructed basing on data of Rp and `.p from

In Figs.2 and 3 the IR transmission spectra of both (100)- and (111) oriented silicon samples implanted by carbon ions with energy 40 kev and dose 3.56×1017 cm-2\_z"0!.z%/+\$.+\*+1/z\*¥ \*!(%\*#z+2!.z 0\$!z 0!),!.01.!z.\*#!zECCwDGCC[\_z.!z,.!/!\*0! ^z\$!z/,!0.z0z+0\$z,!.,!\*¥ dicular incidence of infrared rays on the sample surface and at an angle of 73° with respect to the normal to the surface were measured. In Fig.4 the wave number values in maximum of IR transmission versus the annealing temperature are presented. The curves on this figure were constructed using the experimental data presented on Figs.2 and 3. The curves for TOphonons were constructed basing on the infrared transmission spectra measured by using of

Figs. 2 and 3 show the appearance of an IR absorption peak at 965-970 cm-1 in the spectra from samples inclined to IR irradiation at an angle of 73° with respect to the normal to the sample surface. This absorption peak begins to be appeared after annealing at 1000°C for both types of substrate orientation together with the main peak at 797-800 cm-1z3\$%\$z+..!¥

length of this peak, its amplitude and synchronous modification together with the peak for transversal optical oscillation of SiC during annealing as well, the peak at 965-970 cm-1 was //+%0! z3%0\$z(+\*#%01 %\*(z+,0%(z,\$+\*+\*/z+"z/%(%+\*z.% !^z\$!z0!),!.01.!z+"zw,\$+¥ non appearance is about 300°C higher, than that for TO-phonons of SiC (700°C). It may be 1/! z5z/)((\*!//z+"z0\$!zw,\$+\*+\*z,!'z),(%01 !z\* \_z%\*z+\*/!-1!\*!z+"z0\$%/\_z5z %""%¥

For (100) oriented substrates, the increase of the annealing temperature over the range DCCCP1350°C leads a linearly increase of LO-phonon wavelength at minimum of amplitude from 930 to 965 cm-1 \* \_z0\$!\*z32!(!\*#0\$z%\*.!/%\*#z%/z/01.0! ^z/z"+.zcDDDdz+.%!\*0! z/1¥

/%\*#z +\*z 0\$!z 2(1!/z +"z 32!¥

Ion Synthesis of SiC and Its Instability at High Temperatures

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53

[21]. The energy of carbon ions is 40 keV, dose 3.534×1017;q-2 (curve 1) and 3.56×1017;q-2 (curve 2).

perpendicular incidence of the infrared rays on the sample surface.

/,+\* /z 0+z 0\$!z 0.\*/2!./(z +,0%(z 0+)%z +/%((0%+\*z +"z %^z -

culties of their registration.

 "zz0\$%'\*!//z+"z%+\*z/5\*0\$!/%6! z"%()z%/z(!//z+.z+),.(!z3%0\$zz32!z(!\*#0\$z+"z0\$!z!(!0.+¥ )#\*!0%z. %0%+\*z%\*% !\*0z+\*z"%()n/z/1."!\_z0\$!z(%)%00%+\*/z.!(0! z3%0\$z0\$!z+\* %0%+\*z+"z%\*¥ finity of crystal lattice are lifted. As a result, one can to observe the longitudinal optical oscillations of lattice atoms at definite geometrical conditions of experiments [66f^z \*z0\$%/z.!¥ lation, the special experiments to observe these phonons were carried out. For this purpose, the IR transmisssion spectra versus an angle of incidence of electromagnetic radiation on sample surface with step of 5° were measured.

3. Results and discussion

52 Physics and Technology of Silicon Carbide Devices

used in this investigation.

temperature formation of Si- and SiC crystallites

3.1. A model of an carbon implanted silicon layer and the mechanism of the low

*3.1.1. LO-phonons and their applications to analysis of an implanted layer*

charge value permits to calculate a mobility of free charge carriers.

sample surface with step of 5° were measured.

In Fig.1 the calculated profile of carbon atom distribution in Si constructed basing on data Rp \* zYp from [21] are presented. The Gaussian profile (Fig.1, curve 1) was calculated for the implantation of carbon ions with energy 40 keV and dose 3.534×1017 cm-2, when the carbon concentration in the distribution peak is equal to stoichiometric composition of SiC, i.e. NC/NSi = 1, where NC/NSi is the ratio of the concentrations of C and Si atoms. The curve 2 in Fig.1 shows the calculated profile, corresponding to dose D = 3.56×1017 cm-2 of carbon ions

As it is well known [45, 66], during interaction of electromagnetic waves with an infinite .5/0(z(00%!\_z0\$!z0.\*/2!./(z+,0%(z+/%((0%+\*/zcw,\$+\*+\*/dz+"z0+)/z.!z!4%0! ^z \*z+2!.¥ whelming majority of previous investigations, the synthesis of silicon carbide was identified 5z\$!(,z+"z/,!0.z+"z0.\*/2!./(z+,0%(z,\$+\*+\*/^z+z00!),0/z3/z) !z0+z !0!0z0\$!z(+\*#%¥ tudinal optical oscillations (LO-phonons) of atoms of lattice for a Gaussian concentration profiles of carbon in spite of that majority of studies in the field of ion synthesis of silicon carbide was carried out using these profiles. [3] found that an absorption at wave number 980 cm-1 is observed, if the angle of incidence of irradiation on the sample surface deviate from perpendicularity. Implantation of carbon ions with energies of 24 and 40 keV and a dose of 4.3 × 1017 cm-2 carried out at room temperature into a (111) oriented Si plate of p-type conductivity. Annealing was performed in a vacuum at temperatures of 900 and 1100°C for 30 minutes. The presence in the transmission spectrum of bands associated with the LO-and TO-phonons made possible to calculate such parameters of SiC, as high frequency, X, and the low-frequency dielectric constant, 0, attenuation coefficient of the phonons, the effective \$.#!z\*/e and the force constant . So, the detection of LO-phonons may be used to obtain %0%+\*(z%\*"+.)0%+\*z+10zz/0.101.!z+"z%+\*z%),(\*0! z(5!.^z
+.!2!.\_z0\$!z".!-1!\*5z2(¥ ues of both the transversal- and longitudinal oscillations permit to determine the parameters of efficient charge which is a quantitative criterion of a compound polarity. The efficient

 "zz0\$%'\*!//z+"z%+\*z/5\*0\$!/%6! z"%()z%/z(!//z+.z+),.(!z3%0\$zz32!z(!\*#0\$z+"z0\$!z!(!0.+¥ )#\*!0%z. %0%+\*z%\*% !\*0z+\*z"%()n/z/1."!\_z0\$!z(%)%00%+\*/z.!(0! z3%0\$z0\$!z+\* %0%+\*z+"z%\*¥ finity of crystal lattice are lifted. As a result, one can to observe the longitudinal optical oscillations of lattice atoms at definite geometrical conditions of experiments [66f^z \*z0\$%/z.!¥ lation, the special experiments to observe these phonons were carried out. For this purpose, the IR transmisssion spectra versus an angle of incidence of electromagnetic radiation on

Figure 1. The calculated profiles of distribution of carbon atoms in Si constructed basing on data of Rp and `.p from [21]. The energy of carbon ions is 40 keV, dose 3.534×1017;q-2 (curve 1) and 3.56×1017;q-2 (curve 2).

In Figs.2 and 3 the IR transmission spectra of both (100)- and (111) oriented silicon samples implanted by carbon ions with energy 40 kev and dose 3.56×1017 cm-2\_z"0!.z%/+\$.+\*+1/z\*¥ \*!(%\*#z+2!.z 0\$!z 0!),!.01.!z.\*#!zECCwDGCC[\_z.!z,.!/!\*0! ^z\$!z/,!0.z0z+0\$z,!.,!\*¥ dicular incidence of infrared rays on the sample surface and at an angle of 73° with respect to the normal to the surface were measured. In Fig.4 the wave number values in maximum of IR transmission versus the annealing temperature are presented. The curves on this figure were constructed using the experimental data presented on Figs.2 and 3. The curves for TOphonons were constructed basing on the infrared transmission spectra measured by using of perpendicular incidence of the infrared rays on the sample surface.

Figs. 2 and 3 show the appearance of an IR absorption peak at 965-970 cm-1 in the spectra from samples inclined to IR irradiation at an angle of 73° with respect to the normal to the sample surface. This absorption peak begins to be appeared after annealing at 1000°C for both types of substrate orientation together with the main peak at 797-800 cm-1z3\$%\$z+..!¥ /,+\* /z 0+z 0\$!z 0.\*/2!./(z +,0%(z 0+)%z +/%((0%+\*z +"z %^z -/%\*#z +\*z 0\$!z 2(1!/z +"z 32!¥ length of this peak, its amplitude and synchronous modification together with the peak for transversal optical oscillation of SiC during annealing as well, the peak at 965-970 cm-1 was //+%0! z3%0\$z(+\*#%01 %\*(z+,0%(z,\$+\*+\*/z+"z/%(%+\*z.% !^z\$!z0!),!.01.!z+"zw,\$+¥ non appearance is about 300°C higher, than that for TO-phonons of SiC (700°C). It may be 1/! z5z/)((\*!//z+"z0\$!zw,\$+\*+\*z,!'z),(%01 !z\* \_z%\*z+\*/!-1!\*!z+"z0\$%/\_z5z %""%¥ culties of their registration.

For (100) oriented substrates, the increase of the annealing temperature over the range DCCCP1350°C leads a linearly increase of LO-phonon wavelength at minimum of amplitude from 930 to 965 cm-1 \* \_z0\$!\*z32!(!\*#0\$z%\*.!/%\*#z%/z/01.0! ^z/z"+.zcDDDdz+.%!\*0! z/1¥ strates, unlinearly increase of LO-phonon wavelength in the range 955P970 cm-1 up to 1400°C is observed. Thus, the formation of SiC crystallites, i.e. the intensive formation of Si z0!0.\$! .(z+\* /z+"z\*!!//.5z(!\*#0\$z\* z+\* z\*#(!/\_z%\*z0\$!z/!z+"zcDDDdz+.%!\*0! z/1¥ strate is not completed up to the silicon melting point, as for (100) oriented substrate that is completed at 1350°C. The difference between the LO-phonon curves behaviour for (100) and (111) oriented substrates indicates on the differences in the crystallization mecanism. One can see an influence of silicon substrate orientation on SiC crystallization in the implanted layer from the TO-phonon curve also (Fig.4).

In some investigations no changes in the IR transmission spectra after annealing at 700°C [8], 850°C [14], 875°C [11], 900°C [26], 1100°C [2fz3!.!z+/!.2! ^z\$0z3/z!4,(%\*! z5z"%\*¥ ishing of the -SiC formation process. Really, that may be correct, if we are based on the analysis of TO-phonon curve only. However, as is seen from Fig.4, the TO-phonon curves show the saturated absorption and give no addititional information over the temperature range of 900–1400°C, as the LO-phonon curves undergo the substantial changes at these temperatures indicating on the structural changes in the ion implanted layer. Thus, one can conclude that the observation and measurement of LO-phonon peak are important for an

Ion Synthesis of SiC and Its Instability at High Temperatures

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As it is known [38], the TO- and LO-phonons frequences are bounded with the equation:

Where 0 and Xz.!z0\$!z(+3w".!-1!\*5z\* z0\$!z\$%#\$w".!-1!\*5z %!(!0.%z+\*/0\*0/\_z.!/,!¥

where ¢0 is the resonance frequency, N = 4.84×1022 cm-3 is the concentration of ion pairs, Mn

The dimensionless parameter, \_z3\$%\$z%/z,.+,+.0%+\*(z0+z0\$!z/+.,0%+\*z-1\*0%05\_z%/z !0!.¥

The values of 0, e\*/e and determined from the equations (1)—(3) are equal to 9.82, 0.89, and 0.25, respectively. The value of X has been chosen to be equal to 6.7, because according to [45] the sufficiently great dispersion of this value leads an insignificant changes. So, both the detection and the measuring of LO-phonons have been permited to determine some

c<sup>0</sup> c 4j

) = 1.396×10-23 g is the reduced mass of ion pair, TO = 2.395×10-13 cm-1 is the

(1)

55

(2)

(3)

h*LO* h*TO* =( c0 c ) 1/2

tively. The effective charge e\*/e is determined from the equation [54]:

c0c 4j ) 1/2 ( *M <sup>n</sup> N* ) 1/2 ( 3q<sup>0</sup> c + 2 )

> ) 1/2 ( 3 c + 2 )

k =

j(c0c)*M <sup>n</sup>*h*TO* 2 *N e* <sup>2</sup>

*e*\* *<sup>e</sup>* =(

(

analysis of crystallization process.

= (M+M-

)/(M++M-

mined from the equation:

frequency of TO-phonon irradiation.

characteristics of synthesized film.

Figure 2. The IR transmission spectra of (100) oriented Si samples implanted by +C12 ions (E = 40 kev, D = 3.56×1017 cm-2 9>L=JAKG;@JGFGMK9FF=9DAF?GN=JL@=L=EH=J9LMJ=J9F?=f9if:jf

In some investigations no changes in the IR transmission spectra after annealing at 700°C [8], 850°C [14], 875°C [11], 900°C [26], 1100°C [2fz3!.!z+/!.2! ^z\$0z3/z!4,(%\*! z5z"%\*¥ ishing of the -SiC formation process. Really, that may be correct, if we are based on the analysis of TO-phonon curve only. However, as is seen from Fig.4, the TO-phonon curves show the saturated absorption and give no addititional information over the temperature range of 900–1400°C, as the LO-phonon curves undergo the substantial changes at these temperatures indicating on the structural changes in the ion implanted layer. Thus, one can conclude that the observation and measurement of LO-phonon peak are important for an analysis of crystallization process.

strates, unlinearly increase of LO-phonon wavelength in the range 955P970 cm-1 up to 1400°C is observed. Thus, the formation of SiC crystallites, i.e. the intensive formation of Si z0!0.\$! .(z+\* /z+"z\*!!//.5z(!\*#0\$z\* z+\* z\*#(!/\_z%\*z0\$!z/!z+"zcDDDdz+.%!\*0! z/1¥ strate is not completed up to the silicon melting point, as for (100) oriented substrate that is completed at 1350°C. The difference between the LO-phonon curves behaviour for (100) and (111) oriented substrates indicates on the differences in the crystallization mecanism. One can see an influence of silicon substrate orientation on SiC crystallization in the implanted

Figure 2. The IR transmission spectra of (100) oriented Si samples implanted by +C12 ions (E = 40 kev, D = 3.56×1017

9>L=JAKG;@JGFGMK9FF=9DAF?GN=JL@=L=EH=J9LMJ=J9F?=f9if:jf

layer from the TO-phonon curve also (Fig.4).

54 Physics and Technology of Silicon Carbide Devices

cm-2

As it is known [38], the TO- and LO-phonons frequences are bounded with the equation:

$$\frac{\nu\_{LO}}{\nu\_{TO}} = \left(\frac{\varepsilon\_0}{\varepsilon\_{\infty}}\right)^{1/2} \tag{1}$$

Where 0 and Xz.!z0\$!z(+3w".!-1!\*5z\* z0\$!z\$%#\$w".!-1!\*5z %!(!0.%z+\*/0\*0/\_z.!/,!¥ tively. The effective charge e\*/e is determined from the equation [54]:

$$\begin{aligned} \frac{e^\*}{c} &= \left(\frac{\varepsilon\_{\varepsilon\_{\infty}} - 1/2}{\frac{4\pi}{\varepsilon\_{\infty}}}\right) \left(\frac{\mathcal{M}\_s}{\mathcal{N}\_{\varepsilon\_{\infty}} + 2}\right) \\ &\underbrace{\frac{\pi^{(\varepsilon\_0 - \varepsilon\_{\infty})\mathcal{M}\_s \cdot \frac{\varepsilon\_{\infty}}{\varepsilon\_{\infty}}}{2}}\_{\text{(\%}} (\frac{\mathcal{D}}{\mathcal{E}\_{\varepsilon\_{\infty}} + 2})} \\ \end{aligned} \tag{2}$$

where ¢0 is the resonance frequency, N = 4.84×1022 cm-3 is the concentration of ion pairs, Mn = (M+M- )/(M++M- ) = 1.396×10-23 g is the reduced mass of ion pair, TO = 2.395×10-13 cm-1 is the frequency of TO-phonon irradiation.

The dimensionless parameter, \_z3\$%\$z%/z,.+,+.0%+\*(z0+z0\$!z/+.,0%+\*z-1\*0%05\_z%/z !0!.¥ mined from the equation:

$$
\rho = \frac{\varepsilon\_0 - \varepsilon\_\infty}{4\pi} \tag{3}
$$

The values of 0, e\*/e and determined from the equations (1)—(3) are equal to 9.82, 0.89, and 0.25, respectively. The value of X has been chosen to be equal to 6.7, because according to [45] the sufficiently great dispersion of this value leads an insignificant changes. So, both the detection and the measuring of LO-phonons have been permited to determine some characteristics of synthesized film.

Figure 3. The IR transmission spectra of (111) oriented Si samples implanted by +C12 ions (E = 40 kev, D = 3.56x1017 cm²), after isochronous annealing over the temperature range 200–1400°C: a) α = 90°; b) β = 73°.

Figure 4. Wave numbers of IR transmission minimum for TO- and LO-phonon peaks of SiC versus an annealing temperature for carbon implanted silicon layers on Si substrates (E = 40 kev, D = 3.56x10'7 cm³): 1 - Si(000); 2 - Si(111).

#### 3.1.2. The IR transmission analysis of ion-implanted layer on (100) and (111) oriented silicon

In Figs.5a and b, the values of amplitude and halfwidth (FWHM) of the IR transmission peak, respectively, versus an incidence angle of the intrared radiation on the carbon implanted (100) oriented silicon samples, are presented. These data were obtained after isochronous annealing of samples over the range 200-1200℃ for 30 min with the step of 200℃. Beginning from an angle a = 50° (Fig.5a), almost linear decreasing of TO-phonon peak amplitude and simultaneous increasing of LO-phonon peak amplitude are observed. The changes of LO- and TO-phonons peak amplitudes are correlated with one another.

The halfwidth (FWHM) changes of the peak have a more complicated dependence from the incidence angle of the infrared radiation on the sample surface (Fig.5b). This dependence has no correlation with the data in Fig.5a. The half-width of the peak is usually dependent on the quality of the crystal structure of the film and should not depend on the angle of incidence of IR radiation. Apparently, the decreasing of halfwidth of the TO-phonon peak can be explained by the presence of non-tetrahedral Si-C-bonds of a certain type, which are oriented in the space of the film in such a way that with increasing angle a above 35° they cease to absorb infrared radiation at frequencies near 800 cm³. This is equivalent to the effect of decay of these bonds, since it leads to a decrease in the amplitude and the narrowing of the TO-phonon peak, but can not testify about improving the structure of the layer. This is also accompanied by the appearance of deformed LO-phonon peak in the frequency range near 950 cm+. With the increase of the angle a up to 73°, the narrowing of LO-phonon peak and an increase in its amplitude are taken place. The interpretation of these results requires further investigation.

corresponded to LO-phonons have been not measured due to of their infinitesimal. Further 0\$!z 0z +0%\*! z "+.z z ,!.,!\* %1(.z%\*% !\*!z +"z w.5/z +\*z /),(!z /1."!z 3%((z !z %/¥ cussed, as an analysis of the curve 2 is difficult due to the absence of the reflection data. As %/z/!!\*z".+)z%#^zIzc1.2!zDd\_z0\$!z"+1.z,!'/z0zICC\_zDCCC\_zDECCz\* zDFHC[z.!z!2% !\*0(5z+¥ /!.2! \_z3\$%\$\_z/!!)%\*#(5\_z.!z.!(0! z3%0\$z"+1.z,\$5/%(z,.+!//!/z+1.%\*#z%\*z%+\*z%),(\*0¥ ed layer in four temperature ranges. The same maxima are observed for curve 2 in approximately the same temperature ranges. On this curve a fifth maximum at 200°C is also

Ion Synthesis of SiC and Its Instability at High Temperatures

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59

 0z%/z\*!!//.5z0+z\*+0!\_z0\$0z%\*z)+/0z,.!2%+1/z%\*2!/0%#0%+\*/\_z)%\*(5\_z0\$!z%\*"+.)0%+\*/z+..!¥ sponding to the peak in range 900-1000°C are obtained using the dependences of halfwidth and a shift in frequency of an absorption maximum from the annealing temperature. The physical processes corresponded to the peaks of both 600 and 1200-1400°C have not been studied in detail, partly, due to the hard access of the temperature range of 1200-1400°C and, partly, due to weak defined processes at 600°C. It follows from the Fig.6 that the change of area of SiC-peak takes place over the whole temperature range from 20°C up to 1400°C.

In Fig.7 the values of IR transmission amplitude for TO-phonons of SiC at wavenumber 800 cm-1 and for LO-phonons of SiC versus an annealing temperature for spectra presented in Figs.2 and 3 (curves 1, 1' P for the perpendicular incidence of IR rays on sample, the curves 2, 2', 3, 3' P for an angle of 73°), are shown. When constructing these dependences we have believed that the IR transmission amplitude at 800 cm-1 is proportional to the concentration of tetrahedral oriented SiPC-bonds of atoms incorporated into crystallites of SiC. All factors which can affect on a broadening of peak corresponding to an infinitely thin ideal film of SiC have been neglected. This approximation is to some extent, may distort the true picture of the physical phenomena occurring in ion-implanted layer. However, this assumption is very important in a qualitative sense, since it allows understanding the general course of the process and separating a region of the IR transmission peak [30] due to the contribution of crystallites of SiC in the area value, from a region due to the optically active clusters. As seen in Fig.7, the overall shape of the curves 1 and 2 for the TO-phonons is about the same and has a number of features, in particular, at 1300°C, which is also found on the curve 3 for the LO-phonons. The changes of amplitude take place over the all temperature range from 20 1,z0+zDGCC[^z\$!.!z.!z %""!.!\*!/z%\*z0\$!z.5/0((%60%+\*z,.+!//!/z+"z.+\*z%),(\*0! z/%(%¥

In Fig.8 0\$!z\$("w3% 0\$z+"z0\$!zw,\$+\*+\*z,!'z+"z%z0z,!.,!\* %1(.z%\*% !\*!z+"z z. %¥ tion on sample surface for spectra shown in Figs.2 (curve 1 P for substrate Si(100)) and 3 (curve 1' Pz"+.z/1/0.0!z%cDDDdd\_z2!./1/z\*z\*\*!(%\*#z0!),!.01.!\_z%/z,.!/!\*0! ^z\$!z\*(+¥ gous dependences have been presented in previous papers [8, 47, 26f^z+3!2!.\_z0\$!z0!),!.¥ 01.!z.\*#!z3/z\*..+3!.z\* \_z0\$!.!"+.!\_z0\$!z)4%)z0zDECCz\* zDFHC[z3!.!z\*+0z"+1\* ^ To explain these effects let us consider the ideal case again. We assume that the broadening of the absorption band due to different processes is absent and, therefore each frequency in 0\$!z 0.\*/)%//%+\*z/,!0.1)z+..!/,+\* /z 0+z+\*!z+.z+0\$!.z+\* z!03!!\*z 0\$!z0+)/z+"z 0\$!z%)¥ planted layer. On this basis, we can see that, immediately after the implantation the contour of the transmission curve covers a wide range of frequencies, i. e. in ion-implanted layer

con layers for the orientation of the substrate (100) and (111).

observed.

Figure 5. Amplitude (a) and halfwidth (FWHM) (b) of TO- and LO-phonons peaks of SiC of the IR transmission versus the incidence angle of IR radiation on the surface of the carbon implanted Si.

In previous IR investigations of implanted by 12C+ ions silicon layers, a shift in frequency of an absorption maximum versus the annealing temperature, and also the changes of half-3% 0\$z\* z),(%01 !z+"z,!'z3!.!z+/!.2! ^z\*(56%\*#z0\$!z z0.\*/)%//%+\*z/,!0.z,.!/!\*0¥ ed in Figs.2 and 3, one can see not only the changes of these parameters. A base-line to each spectrum (Fig.2, 1350°C) was drawn. As is seen, the areas of obtained figures are changed, too (Fig.6). In our opinion, the area under the IR transmission curve is associated with the number of absorbing objects in the ion-implanted layer and better shows the transformation of these objects during isochronal annealing. As the object may be not only the crystallites of SiC, but also the another types of infrared active compounds of carbon atoms with carbon or silicon atoms, and silicon atoms one with another, which one can unify under one common appellation - clusters.

Basing on the mentioned above, the IR transmission spectra (Figs.2 and 3) were analyzed in detail accordingly to all listed points. In Fig.6 an area of the IR transmission peak (see Fig.2) associated with TO-phonons of SiC obtained both at perpendicular incidence of infrared rays on the sample surface (curve 1) and at an angle of 73° with respect to the normal to the sample surface (curve 2), versus the annealing temperature are presented. Area values can be determined by direct measurement or by using the expression (Fig.2, 1350°C):

$$A = \frac{1}{2}(T\_1 + T\_2)(\nu\_2 - \nu\_1) - \left[\pi(\nu)d\nu \approx \frac{1}{2}(T\_1 + T\_2)(\nu\_2 - \nu\_1) - \sum \pi(\nu)\delta\nu\tag{4}$$

where A P total absorption (or transmission) in relative units in the wave number range 1TT2\_z¡cdzP transmission at frequency \_z1 and T2zP the values of IR transmission at wave \*1)!./z1z\* z2, respectively, zP step of measurements, equal to 2.5 or 5 cm-1. The areas corresponded to LO-phonons have been not measured due to of their infinitesimal. Further 0\$!z 0z +0%\*! z "+.z z ,!.,!\* %1(.z%\*% !\*!z +"z w.5/z +\*z /),(!z /1."!z 3%((z !z %/¥ cussed, as an analysis of the curve 2 is difficult due to the absence of the reflection data. As %/z/!!\*z".+)z%#^zIzc1.2!zDd\_z0\$!z"+1.z,!'/z0zICC\_zDCCC\_zDECCz\* zDFHC[z.!z!2% !\*0(5z+¥ /!.2! \_z3\$%\$\_z/!!)%\*#(5\_z.!z.!(0! z3%0\$z"+1.z,\$5/%(z,.+!//!/z+1.%\*#z%\*z%+\*z%),(\*0¥ ed layer in four temperature ranges. The same maxima are observed for curve 2 in approximately the same temperature ranges. On this curve a fifth maximum at 200°C is also observed.

and an increase in its amplitude are taken place. The interpretation of these results requires

Figure 5. Amplitude (a) and halfwidth (FWHM) (b) of TO- and LO-phonons peaks of SiC of the IR transmission versus

an absorption maximum versus the annealing temperature, and also the changes of half-3% 0\$z\* z),(%01 !z+"z,!'z3!.!z+/!.2! ^z\*(56%\*#z0\$!z z0.\*/)%//%+\*z/,!0.z,.!/!\*0¥ ed in Figs.2 and 3, one can see not only the changes of these parameters. A base-line to each spectrum (Fig.2, 1350°C) was drawn. As is seen, the areas of obtained figures are changed, too (Fig.6). In our opinion, the area under the IR transmission curve is associated with the number of absorbing objects in the ion-implanted layer and better shows the transformation of these objects during isochronal annealing. As the object may be not only the crystallites of SiC, but also the another types of infrared active compounds of carbon atoms with carbon or silicon atoms, and silicon atoms one with another, which one can unify under one common

Basing on the mentioned above, the IR transmission spectra (Figs.2 and 3) were analyzed in detail accordingly to all listed points. In Fig.6 an area of the IR transmission peak (see Fig.2) associated with TO-phonons of SiC obtained both at perpendicular incidence of infrared rays on the sample surface (curve 1) and at an angle of 73° with respect to the normal to the sample surface (curve 2), versus the annealing temperature are presented. Area values can

where A P total absorption (or transmission) in relative units in the wave number range 1TT2\_z¡cdzP transmission at frequency \_z1 and T2zP the values of IR transmission at wave \*1)!./z1z\* z2, respectively, zP step of measurements, equal to 2.5 or 5 cm-1. The areas

be determined by direct measurement or by using the expression (Fig.2, 1350°C):

m(h)*d*h -1 ions silicon layers, a shift in frequency of

<sup>2</sup> (*T*<sup>1</sup> <sup>+</sup> *<sup>T</sup>*2)(h<sup>2</sup> h1) <sup>m</sup>(h)bh (4)

the incidence angle of IR radiation on the surface of the carbon implanted Si.

In previous IR investigations of implanted by 12C+

further investigation.

58 Physics and Technology of Silicon Carbide Devices

appellation - clusters.

*<sup>A</sup>*<sup>=</sup> <sup>1</sup>

<sup>2</sup> (*T*<sup>1</sup> <sup>+</sup> *<sup>T</sup>*2)(h<sup>2</sup> h1)-

 0z%/z\*!!//.5z0+z\*+0!\_z0\$0z%\*z)+/0z,.!2%+1/z%\*2!/0%#0%+\*/\_z)%\*(5\_z0\$!z%\*"+.)0%+\*/z+..!¥ sponding to the peak in range 900-1000°C are obtained using the dependences of halfwidth and a shift in frequency of an absorption maximum from the annealing temperature. The physical processes corresponded to the peaks of both 600 and 1200-1400°C have not been studied in detail, partly, due to the hard access of the temperature range of 1200-1400°C and, partly, due to weak defined processes at 600°C. It follows from the Fig.6 that the change of area of SiC-peak takes place over the whole temperature range from 20°C up to 1400°C.

In Fig.7 the values of IR transmission amplitude for TO-phonons of SiC at wavenumber 800 cm-1 and for LO-phonons of SiC versus an annealing temperature for spectra presented in Figs.2 and 3 (curves 1, 1' P for the perpendicular incidence of IR rays on sample, the curves 2, 2', 3, 3' P for an angle of 73°), are shown. When constructing these dependences we have believed that the IR transmission amplitude at 800 cm-1 is proportional to the concentration of tetrahedral oriented SiPC-bonds of atoms incorporated into crystallites of SiC. All factors which can affect on a broadening of peak corresponding to an infinitely thin ideal film of SiC have been neglected. This approximation is to some extent, may distort the true picture of the physical phenomena occurring in ion-implanted layer. However, this assumption is very important in a qualitative sense, since it allows understanding the general course of the process and separating a region of the IR transmission peak [30] due to the contribution of crystallites of SiC in the area value, from a region due to the optically active clusters. As seen in Fig.7, the overall shape of the curves 1 and 2 for the TO-phonons is about the same and has a number of features, in particular, at 1300°C, which is also found on the curve 3 for the LO-phonons. The changes of amplitude take place over the all temperature range from 20 1,z0+zDGCC[^z\$!.!z.!z %""!.!\*!/z%\*z0\$!z.5/0((%60%+\*z,.+!//!/z+"z.+\*z%),(\*0! z/%(%¥ con layers for the orientation of the substrate (100) and (111).

In Fig.8 0\$!z\$("w3% 0\$z+"z0\$!zw,\$+\*+\*z,!'z+"z%z0z,!.,!\* %1(.z%\*% !\*!z+"z z. %¥ tion on sample surface for spectra shown in Figs.2 (curve 1 P for substrate Si(100)) and 3 (curve 1' Pz"+.z/1/0.0!z%cDDDdd\_z2!./1/z\*z\*\*!(%\*#z0!),!.01.!\_z%/z,.!/!\*0! ^z\$!z\*(+¥ gous dependences have been presented in previous papers [8, 47, 26f^z+3!2!.\_z0\$!z0!),!.¥ 01.!z.\*#!z3/z\*..+3!.z\* \_z0\$!.!"+.!\_z0\$!z)4%)z0zDECCz\* zDFHC[z3!.!z\*+0z"+1\* ^

To explain these effects let us consider the ideal case again. We assume that the broadening of the absorption band due to different processes is absent and, therefore each frequency in 0\$!z 0.\*/)%//%+\*z/,!0.1)z+..!/,+\* /z 0+z+\*!z+.z+0\$!.z+\* z!03!!\*z 0\$!z0+)/z+"z 0\$!z%)¥ planted layer. On this basis, we can see that, immediately after the implantation the contour of the transmission curve covers a wide range of frequencies, i. e. in ion-implanted layer there are many different bonds that absorb at different frequencies. If one attributes the frequency of 800 cm³ to the tetrahedral oriented Si-C-bond of length of 0.194 nm (bond characteristic of the silicon carbide), so in the implanted layer there are the systems with the bond lengths of both larger and smaller than this. In general, the presence of different bond lengths between the atoms of the ion-implanted layer is completely natural because atoms can stop at different distances from each other in the process of implantation.

In our case, the most interesting bonds are the single-, double- and triple silicon-silicon (Si-Si, Si=Si, Si=Sì), silicon-carbon (Si-C, Si=C, Si=C) and carbon-carbon (C-C, C=C, C=C) bonds presented in Fig.9. Simple covalent bond C-C, formed by the overlap of two sp3-hybrid electron clouds along the line connecting the centers of atoms, is o-bond. One of the electron pairs in the double C=C bond forms o-bond, and the second bond is formed by p-electrons with the clouds in the form of "eight", which overlapping, form a 7-bond. Triple C=C bond is a combination of one o-bond and two 7-bonds [22]. The lengths of single bonds are shown in proportion to ones which are characteristic for these bonds in a tetrahedral orientation, although they can have various values in the ion implanted layer. And in the case of double and triple bonds they may be either higher or lower than the values given. The length of a single bond of the same type of atoms was taken equal to twice the covalent radius of atoms, and the length of the Si-C-bond was taken as half the sum of double the values of covalent radii of Si- and C without correction for their ionicity. The lengths of double and triple bonds were taken at 0.021 and 0.034 nm shorter than a single bond, respectively. Triple bond between two atoms can be represented by two tetrahedra sharing a common face, and for the double bond - by two tetrahedra sharing a common edge [44].

Figure 6. An area of the IR transmission peak for TO-phonons of SiC at perpendicular incidence of the radiation on the sample surface (curves 1, 1 ) and at 73º from a normal (curves 2, 2') for spectra presented in Figs.2 (curves 1, 2 - substrate Si(100)) and 3 (curves 1', 2' - substrate Si(111)), versus an annealing temperature.

Figure 7. The IR transmission amplitude values for TO-phonons of SiC (curves 1, 1', 2, 2') at 800 cm' and for LO-phonons of SiC (curves 3, 3') at perpendicular incidence of the radiation on the sample surface (curves 1, 1') and at 73° from a normal (curves 2, 2', 3, 3') to surface for spectra presented in Figs.2 (curves 1, 2, 3 - substrate Si(100)) and 3 (curves 1', 2', 3' - substrate Si(111)), versus an annealing temperature.

Figure 8. Half-width of the TO-phonon peak of SiC at perpendicular incidence of IR radiation on sample surface for spectra presented in Figs.2 (curve 1 – substrate Si(100)) and 3 (curve 1' – substrate Si(111)), versus an annealing temperature.

Types of bond Binding

sented above.

of carbon.

nomenon is of interest.

*The temperature range 20-600°C*

energy, kJ mole-1

Table 1. The values of binding energy for nine types of bond.

Types of bond Binding

Si–Si 187 Si–C 290 C–C 344 Si=Si <374 Si=C <580 C=C 615 /Au/A <561 /Au <870 u 812

energy, 7R9;81-1

By analogy, reasonable to assume that clusters Si=Si, SiZSi, Si=C, SiZC per bond also has less energy than clusters with single Si–Si and Si–C bonds. Consequently, the energy of double and triple bonds Si=C, Si=Si, SiZC and SiZSi must be less than the sum of the energies of two or three single Si–Si and Si–C bonds, as is shown in Table 1. It is evident that the most strongly bonds are the carbon-carbon and then carbon-silicon and silicon-silicon clusters. Let us consider the special features of the curves on Figs.6–8 /%\*#z+\*z0\$!z//1),0%+\*/z,.!¥

It is known [65] that a typical recrystallization temperature of amorphous silicon lies in the temperature range 500–600°C. When the dose of the implanted carbon ions is much higher than the amorphization threshold and, the implanted atoms combining with the silicon 0+)/z \*z "+.)z 0\$!z%\*(1/%+\*/z +"z\*!3z +),+1\* /z +"z +\*/% !.(!z 2+(1)!\_z 0\$!z .5/0((%6¥ tion of silicon, in the case of a Gaussian distribution profile of implanted atoms, starts at the /1."!z\* z0\$!z%\*0!."!zo %/01.! z(5!.zxz/1/0.0!oz\* z#+!/z%\*z0\$!z %.!0%+\*z0+z0\$!z)4%¥ )1)z+"z0\$!z.+\*z %/0.%10%+\*z3%0\$z%\*.!/%\*#z\*\*!(%\*#z0!),!.01.!^z\$!z/%(%+\*z.5/0((%¥ tes are formed in regions where the concentration of silicon atoms exceeds the concentration

The values of concentration ratio NC/NSi (Fig.1) are small on the edges of distribution and, a significant number of silicon atoms falls at each implanted carbon atom. In this temperature range, such combinations of clusters in ion-implanted layer are decaying which consist mainly of bonds of SiPSi, Si=Si and elongated SiP\_z/z0\$!5z\$2!z0\$!z(+3!/0z!\*!.#5z %//+%¥ 0%+\*z)+\*#z0\$!z05,!/z+"z+\* /z(%/0! z+2!^z/z !5z+"z0\$!z(1/0!./\_z3!z)!\*z/1\$z.!#.+1,¥ ing of the atoms in system and the change the lengths of chemical bonds and angles between them, which lead to the most energetically favorable state of system. In such state there is a system of atoms with tetrahedrally oriented bonds, which are the most stable and 1.(!^z((z+0\$!.z05,!/z+"z+\* /z\* z0\$!%.z#!+)!0.%(z..\*#!)!\*0/z.!z!\*!.#5z1\*,.+"%0¥

As it is seen from curves 1 and 1' in the Figs. 6 and 7, the increasing of both an area of SiCpeak of IR transmission and its amplitude at 800 cm-1 takes place over the temperature range ECP600°C, i.e. the formation of SiC crystallites takes place at temperatures significantly less 0\$0z%0z%/z\*!!//.5z"+.z0\$!z%z"+.)0%+\*z5zz0\$!.)(z#.+30\$^z\$!z)!\$\*%/)z+"z0\$%/z,\$!¥

ble; they are insufficiently stable and can decay during annealing.

Types of bond Binding

Ion Synthesis of SiC and Its Instability at High Temperatures

energy, 7R9;81-1

http://dx.doi.org/10.5772/ 51389

63

Figure 9. Various types of bonds between silicon, carbon atoms or their combination.

In the process of implantation of carbon into silicon vast majority of the covalent bonds of the substrate, starting with the amorphization threshold, are not covalent, because of violation of bond lengths and angles between them. However, among the formed Si–C-bonds there are tetrahedral bonds, the distances and angles between atoms of which correspond exactly to the crystallites of silicon carbide. This is confirmed by the presence of absorption at 800 cm-1 and 5z0\$!z.!/1(0/z+"z0\$!z10\$+./zeEIfz3\$+z% !\*0%"%! z5z!(!0.+\*z %"".0%+\*z0\$!z,.!/!\*!z+"z/%(%¥ con carbide crystallites immediately after the implantation of carbon into silicon.

We believe that the ion-implanted layer consists mainly of various combinations of the nine types of bonds, shown in Fig. 9. Moreover, it is possible the presence in the implanted layer +"z0\$!z/%\*#(!z!(+\*#0! z+\* /\_z/!/-1%\_z".!!zco \*#(%\*#odz\* z\$5.% %6! z+\* /\_z/z3!((z/z.!/¥ +\*\*!/z\* z+0\$!.z\$%#\$!.z+. !.z%\*0!.0%+\*/z/z3!((^z-5z)'%\*#z0\$!/!z//1),0%+\*/\_z3!z,.+¥ ceed not only from the contour of the spectrum of infrared transmission, covering a wide range of frequencies. We are basing also on the ability of carbon and silicon atoms to form besides single bonds also double and triple bonds [29, 44, 64, 46]. In paper [27], an aggregate of carbon atoms was named as a cluster. In this paper, as a cluster we have in mind all the nine types of bonds and combinations thereof, from which are formed during annealing a three-dimensional clusters and crystallites of Si and SiC.

Table 1 presents the values of the binding energy for all nine types of bonds, shown in %#¥ ure 9. The sum of the energies of two and three single C–C bonds are equal to 688 and 1032 kJ mole-1, respectively, such that by 73 and 220 kJ mole-1 higher than energy values of the C=C and CZC bonds listed in Table 1. This suggests that the structures of the C=C and CZ bonds for one bond has less energy than the structures with a single C–C bonds.


By analogy, reasonable to assume that clusters Si=Si, SiZSi, Si=C, SiZC per bond also has less energy than clusters with single Si–Si and Si–C bonds. Consequently, the energy of double and triple bonds Si=C, Si=Si, SiZC and SiZSi must be less than the sum of the energies of two or three single Si–Si and Si–C bonds, as is shown in Table 1. It is evident that the most strongly bonds are the carbon-carbon and then carbon-silicon and silicon-silicon clusters.

Let us consider the special features of the curves on Figs.6–8 /%\*#z+\*z0\$!z//1),0%+\*/z,.!¥ sented above.

#### *The temperature range 20-600°C*

Figure 9. Various types of bonds between silicon, carbon atoms or their combination.

62 Physics and Technology of Silicon Carbide Devices

+\*\*!/z\* z+0\$!.z\$%#\$!.z+. !.z%\*0!.0%+\*/z/z3!((^z-

three-dimensional clusters and crystallites of Si and SiC.

In the process of implantation of carbon into silicon vast majority of the covalent bonds of the substrate, starting with the amorphization threshold, are not covalent, because of violation of bond lengths and angles between them. However, among the formed Si–C-bonds there are tetrahedral bonds, the distances and angles between atoms of which correspond exactly to the crystallites of silicon carbide. This is confirmed by the presence of absorption at 800 cm-1 and 5z0\$!z.!/1(0/z+"z0\$!z10\$+./zeEIfz3\$+z% !\*0%"%! z5z!(!0.+\*z %"".0%+\*z0\$!z,.!/!\*!z+"z/%(%¥

We believe that the ion-implanted layer consists mainly of various combinations of the nine types of bonds, shown in Fig. 9. Moreover, it is possible the presence in the implanted layer +"z0\$!z/%\*#(!z!(+\*#0! z+\* /\_z/!/-1%\_z".!!zco \*#(%\*#odz\* z\$5.% %6! z+\* /\_z/z3!((z/z.!/¥

ceed not only from the contour of the spectrum of infrared transmission, covering a wide range of frequencies. We are basing also on the ability of carbon and silicon atoms to form besides single bonds also double and triple bonds [29, 44, 64, 46]. In paper [27], an aggregate of carbon atoms was named as a cluster. In this paper, as a cluster we have in mind all the nine types of bonds and combinations thereof, from which are formed during annealing a

Table 1 presents the values of the binding energy for all nine types of bonds, shown in %#¥ ure 9. The sum of the energies of two and three single C–C bonds are equal to 688 and 1032 kJ mole-1, respectively, such that by 73 and 220 kJ mole-1 higher than energy values of the C=C and CZC bonds listed in Table 1. This suggests that the structures of the C=C and CZ

bonds for one bond has less energy than the structures with a single C–C bonds.

5z)'%\*#z0\$!/!z//1),0%+\*/\_z3!z,.+¥

con carbide crystallites immediately after the implantation of carbon into silicon.

It is known [65] that a typical recrystallization temperature of amorphous silicon lies in the temperature range 500–600°C. When the dose of the implanted carbon ions is much higher than the amorphization threshold and, the implanted atoms combining with the silicon 0+)/z \*z "+.)z 0\$!z%\*(1/%+\*/z +"z\*!3z +),+1\* /z +"z +\*/% !.(!z 2+(1)!\_z 0\$!z .5/0((%6¥ tion of silicon, in the case of a Gaussian distribution profile of implanted atoms, starts at the /1."!z\* z0\$!z%\*0!."!zo %/01.! z(5!.zxz/1/0.0!oz\* z#+!/z%\*z0\$!z %.!0%+\*z0+z0\$!z)4%¥ )1)z+"z0\$!z.+\*z %/0.%10%+\*z3%0\$z%\*.!/%\*#z\*\*!(%\*#z0!),!.01.!^z\$!z/%(%+\*z.5/0((%¥ tes are formed in regions where the concentration of silicon atoms exceeds the concentration of carbon.

The values of concentration ratio NC/NSi (Fig.1) are small on the edges of distribution and, a significant number of silicon atoms falls at each implanted carbon atom. In this temperature range, such combinations of clusters in ion-implanted layer are decaying which consist mainly of bonds of SiPSi, Si=Si and elongated SiP\_z/z0\$!5z\$2!z0\$!z(+3!/0z!\*!.#5z %//+%¥ 0%+\*z)+\*#z0\$!z05,!/z+"z+\* /z(%/0! z+2!^z/z !5z+"z0\$!z(1/0!./\_z3!z)!\*z/1\$z.!#.+1,¥ ing of the atoms in system and the change the lengths of chemical bonds and angles between them, which lead to the most energetically favorable state of system. In such state there is a system of atoms with tetrahedrally oriented bonds, which are the most stable and 1.(!^z((z+0\$!.z05,!/z+"z+\* /z\* z0\$!%.z#!+)!0.%(z..\*#!)!\*0/z.!z!\*!.#5z1\*,.+"%0¥ ble; they are insufficiently stable and can decay during annealing.

As it is seen from curves 1 and 1' in the Figs. 6 and 7, the increasing of both an area of SiCpeak of IR transmission and its amplitude at 800 cm-1 takes place over the temperature range ECP600°C, i.e. the formation of SiC crystallites takes place at temperatures significantly less 0\$0z%0z%/z\*!!//.5z"+.z0\$!z%z"+.)0%+\*z5zz0\$!.)(z#.+30\$^z\$!z)!\$\*%/)z+"z0\$%/z,\$!¥ nomenon is of interest.

In the system "implanted layer Pz/1/0.0!o\_z0\$!z,\$+\*+\*/z.!z#!\*!.0! z%\*z0\$!z,.+!//z+"z\*¥ \*!(%\*#^z\$%/z/5/0!)z%/zz/%\*#(!z!\*0%05z\* \_z%0z%/z.!/+\*(!z 0+z//1)!z 0\$0z!03!!\*z 0\$!z%)¥ planted layer and the substrate there is a continuous interaction of phonons. Since the thickness of the substrate is much greater than the thickness of the implanted layer, then, with respect to the layer, the substrate can act as a huge reservoir of phonons, which able, 1!z 0+z%0/z\$!0z,%05\_z .!!%2!z+.z !(%2!.z 0\$!z,\$+\*+\*/z 0+z 0\$!z%),(\*0! z(5!.^z/z 0\$!z%)¥ planted layer is thermodynamically nonequilibrium system, the process of interaction of phonons with the atoms will go towards reducing the free energy of the system. During each collision of a phonon with cluster of the implanted layer, the phonon absorption will occur if the energy of the system will decrease.

\*!.#5z.!(!/! z 1.%\*#z0\$!z !5z+"z(1/0!./\_z%/z0.\*/"!..! z0+z0\$!z(00%!\_z3\$%\$z\*z1)1¥ late and transfer it to another cluster, followed by the formation of energetically favorable system, in this case, the crystallites of Si and SiC. It is also possible direct transfer of energy of the decaying SiPSi-cluster to other types of clusters. In this temperature range, mainly, weakly bound SiPSi-clusters can decay during the interaction with phonons. More energy .!-1%.!/z"+.z0\$!z"+.)0%+\*z+"z.5/0((%0!/z+"z%z\* z%^z\$%/z!\*!.#5z%/z0.\*/"!.! z0+z0\$!z.!0¥ ing atoms by the lattice. The considered above mechanism of formation of crystallites of Si \* z%\_z0\$!z/+w((! z+2!.w..%!.z)!\$\*%/)\_z3\$!\*z0\$!z%\*0!.0%\*#z0+)/z+2!.+)!z0\$!z!\*¥ ergy barrier of height E En, is shown in Fig.10^z\$%/z)!\$\*%/)z+"z "+.)0%+\*z+"z 0!0.\$!¥ drally oriented bonds SiPSi and SiPC from an energy point of view is advantageous for the crystal lattice, since it thereby reduces its free energy.

Figure 10. Illustration of the over-barrier mechanism of the formation of the tetrahedral oriented bonds

Figure 11. X-ray diffraction patterns of the SiC0.12 layer after implantation (a) and average sizes of crystallites in the (111)

Peak area immediately after implantation is not zero, i. e. a part of the carbon atoms is included into composition of the optically active clusters (Fig.6). If we assume that, after annealing at 1000-1250°C almost all carbon atoms are optically active and optically inactive clusters broke 1,\_z3!z/!!z0\$0z%))! %0!(5z"0!.z0\$!z%),(\*00%+\*z+"z.+\*z%\*0+z0\$!zcDCCdz\* zcDDDdz+.%!\*0¥ ed silicon at least 65% and 60% of carbon atoms were concentrated in optically inactive clusters, .!/,!0%2!(5\_z%"z0\$!z%),(\*00%+\*z3/z..%! z+10z5zz +/!z/1""%%!\*0z0+z+0%\*z0\$!z/0+%\$%+)!0¥ ric concentration (E = 40 keV, D = 3.56×1017 cm-2). A number of carbon atoms is included into

]/A>GJD9Q=J/A0.12

Ion Synthesis of SiC and Its Instability at High Temperatures

http://dx.doi.org/10.5772/ 51389

65

]/A>GJD9Q=J/A0.12).

HD9F=9>L=JAEHD9FL9LAGF9F<9FF=9DAF?:]/A>GJD9Q=J/A0.03

All possible mechanisms of the tetrahedral oriented SiPSi- and SiPC-bonds formation should !z!\*!.#5z,.+"%0(!z"+.z0\$!z.5/0((%\*!z(00%!z0+z !.!/!z".!!z!\*!.#5z+"z/5/0!)^z\$!z"+.)¥ tion of crystallites of Si and SiC in the range 20P600°C occurs mainly due to the decay of clusters such as the longest SiPSi- and SiPC-bonds, but also partly due to the disintegration of other types of clusters. A number of studies have shown [5, 26], that immediately after the implantation, the presence of a minute quantity of SiC crystallites with hexagonal structure is observed in the ion implanted layer and, they are transformed into w%z0z0\$!z0!),!.¥ ture of 400°C and higher. It is impossible to identify the presence of Si crystallites due to their optical inactivity in this range of the infrared absorption. However, their presence is \*+0z%\*z +10\_z/z)1\$z(!//z!\*!.#5z%/z.!-1%.! z0+z!4,!\* z"+.z0\$!%.z"+.)0%+\*z0\$\*z"+.z0\$!z"+.¥ mation of SiC crystallites at the implementation of over-barrier mechanism. As we showed earlier, in layers SiC0.03 with a low carbon concentration the crystallites of Si increase their /%6!/z".+)zEz0+zFz\*)z%\*z0\$!z.\*#!zECPJCC[zc%#^DDd^

Ion Synthesis of SiC and Its Instability at High Temperatures http://dx.doi.org/10.5772/ 51389 65

In the system "implanted layer Pz/1/0.0!o\_z0\$!z,\$+\*+\*/z.!z#!\*!.0! z%\*z0\$!z,.+!//z+"z\*¥ \*!(%\*#^z\$%/z/5/0!)z%/zz/%\*#(!z!\*0%05z\* \_z%0z%/z.!/+\*(!z 0+z//1)!z 0\$0z!03!!\*z 0\$!z%)¥ planted layer and the substrate there is a continuous interaction of phonons. Since the thickness of the substrate is much greater than the thickness of the implanted layer, then, with respect to the layer, the substrate can act as a huge reservoir of phonons, which able, 1!z 0+z%0/z\$!0z,%05\_z .!!%2!z+.z !(%2!.z 0\$!z,\$+\*+\*/z 0+z 0\$!z%),(\*0! z(5!.^z/z 0\$!z%)¥ planted layer is thermodynamically nonequilibrium system, the process of interaction of phonons with the atoms will go towards reducing the free energy of the system. During each collision of a phonon with cluster of the implanted layer, the phonon absorption will

\*!.#5z.!(!/! z 1.%\*#z0\$!z !5z+"z(1/0!./\_z%/z0.\*/"!..! z0+z0\$!z(00%!\_z3\$%\$z\*z1)1¥ late and transfer it to another cluster, followed by the formation of energetically favorable system, in this case, the crystallites of Si and SiC. It is also possible direct transfer of energy of the decaying SiPSi-cluster to other types of clusters. In this temperature range, mainly, weakly bound SiPSi-clusters can decay during the interaction with phonons. More energy .!-1%.!/z"+.z0\$!z"+.)0%+\*z+"z.5/0((%0!/z+"z%z\* z%^z\$%/z!\*!.#5z%/z0.\*/"!.! z0+z0\$!z.!0¥ ing atoms by the lattice. The considered above mechanism of formation of crystallites of Si \* z%\_z0\$!z/+w((! z+2!.w..%!.z)!\$\*%/)\_z3\$!\*z0\$!z%\*0!.0%\*#z0+)/z+2!.+)!z0\$!z!\*¥ ergy barrier of height E En, is shown in Fig.10^z\$%/z)!\$\*%/)z+"z "+.)0%+\*z+"z 0!0.\$!¥ drally oriented bonds SiPSi and SiPC from an energy point of view is advantageous for the

All possible mechanisms of the tetrahedral oriented SiPSi- and SiPC-bonds formation should !z!\*!.#5z,.+"%0(!z"+.z0\$!z.5/0((%\*!z(00%!z0+z !.!/!z".!!z!\*!.#5z+"z/5/0!)^z\$!z"+.)¥ tion of crystallites of Si and SiC in the range 20P600°C occurs mainly due to the decay of clusters such as the longest SiPSi- and SiPC-bonds, but also partly due to the disintegration of other types of clusters. A number of studies have shown [5, 26], that immediately after the implantation, the presence of a minute quantity of SiC crystallites with hexagonal structure is observed in the ion implanted layer and, they are transformed into w%z0z0\$!z0!),!.¥ ture of 400°C and higher. It is impossible to identify the presence of Si crystallites due to their optical inactivity in this range of the infrared absorption. However, their presence is \*+0z%\*z +10\_z/z)1\$z(!//z!\*!.#5z%/z.!-1%.! z0+z!4,!\* z"+.z0\$!%.z"+.)0%+\*z0\$\*z"+.z0\$!z"+.¥ mation of SiC crystallites at the implementation of over-barrier mechanism. As we showed earlier, in layers SiC0.03 with a low carbon concentration the crystallites of Si increase their

occur if the energy of the system will decrease.

64 Physics and Technology of Silicon Carbide Devices

crystal lattice, since it thereby reduces its free energy.

/%6!/z".+)zEz0+zFz\*)z%\*z0\$!z.\*#!zECPJCC[zc%#^DDd^

Figure 10. Illustration of the over-barrier mechanism of the formation of the tetrahedral oriented bonds

Figure 11. X-ray diffraction patterns of the SiC0.12 layer after implantation (a) and average sizes of crystallites in the (111) HD9F=9>L=JAEHD9FL9LAGF9F<9FF=9DAF?:]/A>GJD9Q=J/A0.03 ]/A>GJD9Q=J/A0.12 ]/A>GJD9Q=J/A0.12).

Peak area immediately after implantation is not zero, i. e. a part of the carbon atoms is included into composition of the optically active clusters (Fig.6). If we assume that, after annealing at 1000-1250°C almost all carbon atoms are optically active and optically inactive clusters broke 1,\_z3!z/!!z0\$0z%))! %0!(5z"0!.z0\$!z%),(\*00%+\*z+"z.+\*z%\*0+z0\$!zcDCCdz\* zcDDDdz+.%!\*0¥ ed silicon at least 65% and 60% of carbon atoms were concentrated in optically inactive clusters, .!/,!0%2!(5\_z%"z0\$!z%),(\*00%+\*z3/z..%! z+10z5zz +/!z/1""%%!\*0z0+z+0%\*z0\$!z/0+%\$%+)!0¥ ric concentration (E = 40 keV, D = 3.56×1017 cm-2). A number of carbon atoms is included into stable types of optically inactive clusters which stable up to melting point of silicon. It is known [44], that the optically inactive objects consist of the clusters and their chains that lie in one plane. The formation of clusters and chains of planar systems of nets may be due to energy +\*/% !.0%+\*/^z+.z!4),(!\_z%\*zeHfz0\$!z"+.)0%+\*z+"z(0!.\*0%\*#z(5!./z+"z/%\*#(!z.5/0(z/%(%¥ con with amorphous silicon precipitates enriched with carbon in the ion-implanted layer, attributed to the fact that the system in such a way reduces its free energy.

follows also from decrease of peak halfwidth (Fig.8)z%\*z0!),!.01.!z.\*#!zECxGCC[^z 0/z%\*¥ crease in range 400–600°C may be associated with intensive restructuring of Si–Si bonds of amorphous silicon before recrystallization at the surface and near the substrate, where the concentration of carbon is low. The increase in peak area of the TO-phonon SiC in this range (Fig. 6, curves 1, 1 ') is caused by an increase in the number of tetrahedral bonds and close to

Ion Synthesis of SiC and Its Instability at High Temperatures

@LLH

<P<GAGJ?


No significant differences between the properties of the films on the substrate orientation (100) and (111) in this temperature range were observed, except for the fact that the area of SiCpeak and amplitude at 800 cm-1 are slightly higher for the orientation (111), which indicates a higher number of tetrahedral bonds of SiC and a smaller number of optically inactive clusters.

Figure 12. EHDALM<=G>%.LJ9FKEAKKAGF>GJN9JAGMKO9N=FME:=JN9DM=KN=JKMK9F9FF=9DAF?L=EH=J9LMJ=w

The area under IR spectrum curve is decreased in this temperature range (Fig.6) due to the decay of the optical active clusters absorbing at the frequencies close to 700 and 750 cm-1 (Fig.12). As shown in previous studies (Fig. 13d, e), this is due to the decay of elongated Si Pw+\* /z%\*z0\$!z(5!./z3%0\$zz(+3z+\*!\*0.0%+\*z+"z.+\*^z\*z%\*0!\*/%2!z,.+!//z+"z %/%\*0!¥ gration of these bonds occurs in layers SiC0.4 and SiC0.12z!03!!\*z 0\$!z/1."!z\* z 0\$!z)4%¥ mum of the carbon distribution. In addition of the decay of the optical active non-

\$!z%\*0!\*/%2!z.!..\*#!)!\*0z+"z(1/0!./z%/z\$.0!.%6! z"+.z0\$%/z0!),!.01.!z.\*#!^z/zz.!¥ sult of multiple collisions the atoms of clusters, successively passing from the initialthrough the intermediate states to the most energy favorable end position, form the tetrahedrally oriented bonds of Si- and SiC crystallites. A significant change of halfwidth of

9F<v;E-1.

x;E-1

0!0.\$! .(z%Pw+\* /\_z/!!)%\*#(5\_z !"+.)! z%w%z+\* /z.!z %/%\*0!#.0! \_z0++^

cm-1

`;E-1

*The temperature range 600-800°C*

y;E-1

them, which absorbs in the range 750-850 cm-1 (Fig.12, curves 1, 3, 5).

Spatial pattern of ion-implanted layer is difficult to model, since a Gaussian distribution profile of implanted atoms is characterized by the change by depth of the concentration of carbon atoms NC/NSi and, thus, the mechanism of physical processes from one layer to layer is changed. We can construct a flat infrared inactive net in the middle of layer where NC/NSi = 1. Flat optical inactive net consisting of C and Si atoms, linked by single, double and triple bonds, may also contain free ("dangling") bonds of the silicon and carbon atoms. These bonds may connect to atoms of the other flat net or on the association of the atoms which do \*+0z(%!z%\*z+\*!z,(\*!^z\$!z0+)/z3\$%\$z +z\*+0z(%!z%\*z+\*!z,(\*!\_z\*z"+.)z\*z//+%0%+\*z+"z+,¥ tically active clusters.

With increasing annealing temperature at first the decay of elongated single bonds at two atoms united by a triple bond, is taken place. These pairs of atoms inhibit the diffusion of 0+)/z%\*z0\$!z(5!.^z\$!\*\_z0\$!z!\*!.#!0%((5z1\*"2+.(!z/%\*#(!z+\* /z+"z0+)/z.!z %/%\*0!#.0¥ ed in the planar nets of clusters. The subsequent increase in annealing temperature would lead to the disintegration of the planar nets forming a number free carbon and silicon atoms, as well as pairs of Si and C atoms, linked together by multiple bonds. Free carbon and silicon 0+)/z\*z)+2!z+\*z/\$+.0z %/0\*!/z\* z&+%\*z0+z"+.)z0\$!z.5/0((%0!z%z+.z%\_z3\$%\$z%/z,.+"%0¥ ble from an energy point of view and, as a result, the energy of system is decreased.

In addition to the planar nets of clusters, the ion-implanted layer may contain long chains of clusters, which are also optically inactive. The chains can be formed by alternating different types of bonds, and their degradation temperature may be different. There are also local clusters non-interacting with the surrounding atoms and consisting of three-, four- and more atoms linked together by double bonds. They are most stable clusters due to the full richness of their bonds. Perhaps these clusters are not disintegrated up to the melting point of layer.

In Fig.12z 0\$!z z 0.\*/)%//%+\*z),(%01 !z2!./1/z 0\$!z\*\*!(%\*#z 0!),!.01.!z"+.z %""!.!\*0z".!¥ quencies is shown. It is evident that clusters absorbing at frequencies of 850 and 900 cm-1, in 0\$!z.\*#!zECxICC[z % z\*+0z %/%\*0!#.0! \_z/z0\$!%.z),(%01 !z.!)%\*/z1\*\$\*#! ^z\$!z,+/%¥ tion of minimum of IR transmission peak does not change and is located at 757 cm-1 (Fig.4). This indicates the dominant role of one type of clusters, which absorb at 757 cm-1^z\$!z%\*¥ .!/!z+"z0\$!z),(%01 !z+"z0\$!z,!'zc%#^zDE\_z1.2!zFdz%\* %0!/z\*z%\*.!/!z%\*z0\$!z+\*!\*0.¥ tion of these clusters with increasing annealing temperature. At the same time the concentration of clusters, which absorb at 700 cm-1 and correspond to the elongated single bond, is simultaneously increased. The energy of both the formation and decay of these bonds is a least one (E = hd\_z/z0\$!5z/+.z0\$!z. %0%+\*z+"z(+3!/0z".!-1!\*%!/z)+\*#z+\*¥ sidered. It follows from Fig.7 (curve 1) and 12 (curve 1), that the bonds being very similar to tetrahedral bonds of SiC which absorbs at 800 cm-1, are formed in the implanted layer. That follows also from decrease of peak halfwidth (Fig.8)z%\*z0!),!.01.!z.\*#!zECxGCC[^z 0/z%\*¥ crease in range 400–600°C may be associated with intensive restructuring of Si–Si bonds of amorphous silicon before recrystallization at the surface and near the substrate, where the concentration of carbon is low. The increase in peak area of the TO-phonon SiC in this range (Fig. 6, curves 1, 1 ') is caused by an increase in the number of tetrahedral bonds and close to them, which absorbs in the range 750-850 cm-1 (Fig.12, curves 1, 3, 5).

No significant differences between the properties of the films on the substrate orientation (100) and (111) in this temperature range were observed, except for the fact that the area of SiCpeak and amplitude at 800 cm-1 are slightly higher for the orientation (111), which indicates a higher number of tetrahedral bonds of SiC and a smaller number of optically inactive clusters.

Figure 12. EHDALM<=G>%.LJ9FKEAKKAGF>GJN9JAGMKO9N=FME:=JN9DM=KN=JKMK9F9FF=9DAF?L=EH=J9LMJ=w cm-1 `;E-1 y;E-1 x;E-1 9F<v;E-1.

#### *The temperature range 600-800°C*

stable types of optically inactive clusters which stable up to melting point of silicon. It is known [44], that the optically inactive objects consist of the clusters and their chains that lie in one plane. The formation of clusters and chains of planar systems of nets may be due to energy +\*/% !.0%+\*/^z+.z!4),(!\_z%\*zeHfz0\$!z"+.)0%+\*z+"z(0!.\*0%\*#z(5!./z+"z/%\*#(!z.5/0(z/%(%¥ con with amorphous silicon precipitates enriched with carbon in the ion-implanted layer,

Spatial pattern of ion-implanted layer is difficult to model, since a Gaussian distribution profile of implanted atoms is characterized by the change by depth of the concentration of carbon atoms NC/NSi and, thus, the mechanism of physical processes from one layer to layer is changed. We can construct a flat infrared inactive net in the middle of layer where NC/NSi = 1. Flat optical inactive net consisting of C and Si atoms, linked by single, double and triple bonds, may also contain free ("dangling") bonds of the silicon and carbon atoms. These bonds may connect to atoms of the other flat net or on the association of the atoms which do \*+0z(%!z%\*z+\*!z,(\*!^z\$!z0+)/z3\$%\$z +z\*+0z(%!z%\*z+\*!z,(\*!\_z\*z"+.)z\*z//+%0%+\*z+"z+,¥

With increasing annealing temperature at first the decay of elongated single bonds at two atoms united by a triple bond, is taken place. These pairs of atoms inhibit the diffusion of 0+)/z%\*z0\$!z(5!.^z\$!\*\_z0\$!z!\*!.#!0%((5z1\*"2+.(!z/%\*#(!z+\* /z+"z0+)/z.!z %/%\*0!#.0¥ ed in the planar nets of clusters. The subsequent increase in annealing temperature would lead to the disintegration of the planar nets forming a number free carbon and silicon atoms, as well as pairs of Si and C atoms, linked together by multiple bonds. Free carbon and silicon 0+)/z\*z)+2!z+\*z/\$+.0z %/0\*!/z\* z&+%\*z0+z"+.)z0\$!z.5/0((%0!z%z+.z%\_z3\$%\$z%/z,.+"%0¥

In addition to the planar nets of clusters, the ion-implanted layer may contain long chains of clusters, which are also optically inactive. The chains can be formed by alternating different types of bonds, and their degradation temperature may be different. There are also local clusters non-interacting with the surrounding atoms and consisting of three-, four- and more atoms linked together by double bonds. They are most stable clusters due to the full richness of their bonds. Perhaps these clusters are not disintegrated up to the melting point

In Fig.12z 0\$!z z 0.\*/)%//%+\*z),(%01 !z2!./1/z 0\$!z\*\*!(%\*#z 0!),!.01.!z"+.z %""!.!\*0z".!¥ quencies is shown. It is evident that clusters absorbing at frequencies of 850 and 900 cm-1, in 0\$!z.\*#!zECxICC[z % z\*+0z %/%\*0!#.0! \_z/z0\$!%.z),(%01 !z.!)%\*/z1\*\$\*#! ^z\$!z,+/%¥ tion of minimum of IR transmission peak does not change and is located at 757 cm-1 (Fig.4). This indicates the dominant role of one type of clusters, which absorb at 757 cm-1^z\$!z%\*¥ .!/!z+"z0\$!z),(%01 !z+"z0\$!z,!'zc%#^zDE\_z1.2!zFdz%\* %0!/z\*z%\*.!/!z%\*z0\$!z+\*!\*0.¥ tion of these clusters with increasing annealing temperature. At the same time the concentration of clusters, which absorb at 700 cm-1 and correspond to the elongated single bond, is simultaneously increased. The energy of both the formation and decay of these bonds is a least one (E = hd\_z/z0\$!5z/+.z0\$!z. %0%+\*z+"z(+3!/0z".!-1!\*%!/z)+\*#z+\*¥ sidered. It follows from Fig.7 (curve 1) and 12 (curve 1), that the bonds being very similar to tetrahedral bonds of SiC which absorbs at 800 cm-1, are formed in the implanted layer. That

ble from an energy point of view and, as a result, the energy of system is decreased.

attributed to the fact that the system in such a way reduces its free energy.

tically active clusters.

66 Physics and Technology of Silicon Carbide Devices

of layer.

The area under IR spectrum curve is decreased in this temperature range (Fig.6) due to the decay of the optical active clusters absorbing at the frequencies close to 700 and 750 cm-1 (Fig.12). As shown in previous studies (Fig. 13d, e), this is due to the decay of elongated Si Pw+\* /z%\*z0\$!z(5!./z3%0\$zz(+3z+\*!\*0.0%+\*z+"z.+\*^z\*z%\*0!\*/%2!z,.+!//z+"z %/%\*0!¥ gration of these bonds occurs in layers SiC0.4 and SiC0.12z!03!!\*z 0\$!z/1."!z\* z 0\$!z)4%¥ mum of the carbon distribution. In addition of the decay of the optical active non-0!0.\$! .(z%Pw+\* /\_z/!!)%\*#(5\_z !"+.)! z%w%z+\* /z.!z %/%\*0!#.0! \_z0++^

\$!z%\*0!\*/%2!z.!..\*#!)!\*0z+"z(1/0!./z%/z\$.0!.%6! z"+.z0\$%/z0!),!.01.!z.\*#!^z/zz.!¥ sult of multiple collisions the atoms of clusters, successively passing from the initialthrough the intermediate states to the most energy favorable end position, form the tetrahedrally oriented bonds of Si- and SiC crystallites. A significant change of halfwidth of the Si-C-peak of IR spectrum begins for film on (100) oriented substrate (Fig.8). In case of (111) oriented silicon substrate the same is taken place some later. A certain increase of the concentration of clusters absorbing on the wavenumbers ranged from 850 to 900 cm1 (Fig. 12, curves 4, 5) is simultaneously taken place. The ordering of layer structure in region near the substrate is taken place, too.

Figure 13. Effect of the annealing temperature on the IR transmission amplitude at wavenumbers of (1-ロ) 700 cm³, (2-Δ) 750 cm³] (3-Ο) 800 cm³, (4-▲) 850 cm³, and (5-■) 900 cm³ under normal incidence of IR radiation on the sample surface: a) SiC14; b) SiC095; c) SiC07; d) SiC0.4; e) SiC0.12; f) SiC003:

#### The temperature range 800-1000°C

Accordingly to Figs. 6-8 and 12 almost whole ion implanted layer takes place in the process of crystallization of Si and SiC in this temperature range. The probability of over-barrier mechanism of the formation of Si- and SiC crystallites, seemingly, is increased as is seen from the significant increase of the IR transmission amplitude at 800 cm² (Fig.7, curves 1, 1 ). The flat net of clusters and the chains of them in a great extent are disintegrated. The intensive decay of the infrared active non-tetrahedral Si-C-bonds is taken place and, the sesquialteral- and, partially, the double silicon bonds simultaneously with the infrared inactive single bonds can disintegrated as well. Seemingly, the energy of the phonons may be sufficient for the disintegration of the infrared inactive C-Si-, C-C- and even C=Si-bonds. Simultaneously, the formation of the most energy favorable tetrahedrally oriented bonds of Si- and SiC-crystallites is taken place (Figs. 6, 7, curves 1, 1'; Fig.12, curve 3). The continious process of the formation of the infrared active clusters absorbing on the frequencies close to 700–800 cm² is taken place in the layer and, the concentration of these clusters with the increasing of the annealing temperature is increased. The absorption at 800 cm3 begins significantly predominate over the ones at another frequencies. That leads to the significant increase of the IR transmission amplitude at this frequency in comparison with the increase of amplitude at another ones (Fig.12, curve 3) and, that is perceived as a frequency shift of the IR absorption maximum (Fig.4). The increase of concentration of clusters absorbing on frequencies higher than 800 cm-1 is observed, too (Fig. 12, curves 4, 5).

So, the increase of the area under the IR transmission curve in the temperature range 800-1000°C is caused, mainly, by the absorption at frequency of 800 cm², i.e. by bonds characteristic to the SiC-crystallites and, by bonds absorbing on frequencies both more and less than 800 cm+ as well. In the case of the (100) oriented substrate the number of tetrahedral Si -C-bonds reached at 1000°C some maximum and does not change up to 1200°C, whereas in the case of orientation (111) it increases going smoothly in the range 900-1300°C. Comparison with the data in Fig.13 shows that such flat areas of curves at these temperatures are typical for the layers SiC 7, and especially for SiC 4. The total dose of implanted ions of carbon in the case of SiCq7 was D(SiCn) = 4.54×107 cm2, and D(SiCq4) = 2.72×1017 cm3, and is comparable to the dose of carbon ions with an energy of 40 keV for the considered Gaussian distribution of carbon: D (40 keV) = 3.56×10¹7 cm². The halfwidth of IR-spectrum maximum (Fig.8) in the range 800-1000°C is rapidly decreased. That is an evidence of a significant ordering of the ion implanted layer structure caused by the formation of Si- and SiC-crystallites. It goes more intensively in case of (100) orientation of substrate.

#### The temperature range 1000-1100°C

In spite of the fact that the formation of new SiC crystallites in the implanted layer at these temperatures is not taken place (Fig.7, curve 1, 1'; Fig.12 and 16, curves 3), the decrease of area of SiC-peak of IR transmission curve is significant (Fig.6, curves 1, 1'). As it was shown earlier (Fig.11), the dimensions of Si- and SiC-crystallites are enlarged with the increase of the annealing temperature. Thereby, we believe that in this temperature range the uniting of small crystallites of Si and SiC in the larger ones is taken place, resulting the frequency shift of LO-phonon peak in IR spectrum to a higher frequency (Fig. 4), as well as the growth of its amplitude (Fig. 7, curve 3). When combining the crystallites, in the area of their union the decay of the both optically active and inactive clusters is taken place. This explains the decrease in the amplitude of the infrared transmittance for clusters absorbing at frequencies of 800-900 cm2 (Fig. 12) and the corresponding decrease in the area (Fig. 6). Apparently, this temperature is insufficient for the decay of clusters C=Si and, as a result the formation of new SiC crystallites is not observed. However, a volume of polycrystalline Si is continuously increased due to the disintegration of Si-Si, Si=Si bonds in regions with low concentration of carbon (Fig.1, regions I and II).

In the case of the substrate orientation Si(111), the SiC-peak area is reduced to a lesser extent, and is larger after annealing at 1100°C than the peak area for the substrate Si(100) due to the fact that the number of tetrahedral bonds and crystallites continues to grow.

The temperature range 1100-1200°C

Both the area of Si–C-peak (Fig. 6) and its half-width (Fig. 8) increase in this temperature interval, while the volume of the polycrystalline SiC is unchanged (Fig. 12, curve 3 and Fig. 7, curve 1), as the further growth of SiC crystallite size due to their association (Fig. 4, curves of LO-phonons) is taken place. The growth of the area and half-width of Si–C-peak are caused by the formation of new optically active clusters absorbing at frequencies of 750-900 cm-1 (%#^z DEdz 1!z 0+z 0\$!z !5z +"z /0(!z (1/0!./^z /z z .!/1(0\_z 0\$!z %+\*w%),(\*0! z (5!.z !¥ grades the structure (increase in half-width of the peak).

*The temperature range 1300-1350°C*

*The temperature range 1350-1400°C*

the peak half-width of IR spectrum.

occur intense desorption processes of carbon.

annealing at 1350°C is most close to the dispersive one.

*A shape of IR transmission peak*

Despite the increase in the desorption of carbon, the area of SiC-peak (Fig. 6), as well as the amplitude at all frequencies of spectra are increased in case of the film on the substrate Si(100) (Fig. 12, curves 1-5). The atoms of clusters, which formed due to the destruction of defective .5/0((%0!/z+"z%z%\*z0\$!z,.!2%+1/z0!),!.01.!z.\*#!\_z.!w1\*%0!z#%\*z%\*z"+.)z+"z0\$!z.5/0((%¥ tes of SiC, as well as in form of optically active clusters, which absorb at frequencies near 800 cm-1^z \*z %0%+\*\_z/0(!z(1/0!./z3%0\$z%R\_z%Zz\* zRz+\* /z.!z %/%\*0!#.0! zc%#^zLd^ Growth of SiC crystallite size leads to a frequency shift of LO-phonons peak in the shortwavelength region (Fig. 4). Since in an isolated system unacceptable the processes occurring with increasing free energy, the uniting of two crystallites occurs, if is accompanied by a gain %\*z!\*!.#5z%\*z+),.%/+\*z3%0\$z0\$!z!\*!.#5z!4,!\* ! z%\*z0\$!%.z !5^z \*z0\$!z/!z+"z0\$!z+.%!\*0¥ tion of the substrate Si(111) a decrease of the area of SiC-peak (Fig. 6, curve 1'), as well as the

Ion Synthesis of SiC and Its Instability at High Temperatures

http://dx.doi.org/10.5772/ 51389

71

amplitude at 800 cm-1 (Fig. 7, curve 1') occur due to increased desorption of carbon.

Although at these temperatures the decay of optically inactive clusters, formation of both new crystallites and optically active SiC-clusters should be the greatest, nevertheless the growth of area and the amplitude of the SiC-peak of IR spectrum is not observed. On the contrary, they decrease (Fig. 6 and 7), which can be explained to the dominant influence of sublimation and desorption of carbon. The volume of polycrystalline SiC is also reduced, which is accompanied by a decrease in the amplitude of LO-phonons (Fig. 7\_z1.2!zFd^zz"1.¥ ther ordering of the structure of ion-implanted layer occurs, as evidenced by the decrease in

In conclusion, it is necessary to note that the quantity of absorbing SiPC-bonds in the silicon layer with Gaussian distribution of implanted carbon reaches a maximum at 1000°C for (100) oriented substrate and, at 1000 and 1250°C for (111) oriented substrate (Fig. 6). Most of the carbon atoms combine with atoms of silicon, forming the tetrahedrally oriented bonds of SiC (Fig. 12, curve 3). Seemingly, there are flat nets and chains of clusters (%#^zLd\_z3\$%\$z+\*¥ /%/0z)%\*(5z+"z+\* /z%x%\_z%zRz%\_zx%\_zxz\* \_z0\$%/z0!),!.01.!z%/z/1""%%!\*0z"+.z0\$!%.z !¥ cay. Some significant part of the carbon atoms form bonds of higher order, which decay at temperatures of 1200-1400°C and above. At high temperatures, 1300-1400°C (Figs. 6 and 7)

All presented spectra (Fig.2) \$2!z/\$,!z %""!.!\*0z".+)z/%),(5z %/,!./%2!z/,!0.1)zc0\$!+.!0¥ ically calculated). The transmission band both left and right from the transmission peak are perceptible asymmetric and, one can not describe it's shape by a simple analytical function. \$!z/\$,!z/5))!0.5z%/z !.!/! z3%0\$z0\$!z\*\*!(%\*#z0!),!.01.!z%\*.!/%\*#z\* \_z%0z%/z)%\*¥ %)(z%\*z0\$!z0!),!.01.!z.\*#!zDFCCxDFHC[^z\$!z"1.0\$!.z%\*.!/!z+"z0\$!z\*\*!(%\*#z0!),!.¥ ture leads to the increase of asymmetry, too. The contour of the transmission peak for TOphonons at perpendicular incidence of electromagnetic radiation on sample surface after

#### *The temperature range 1200-1250°C*

No significant changes in the formation of new infrared active clusters over this range are taken place. The decaying clusters with short SiPC-bonds, absorbing at frequencies of KCCP900 cm-1 (Fig. 12, curves 1-3) are converted into clusters with long bonds, absorbing at 700 and 800 cm-1 (Fig. 12, curves 4 and 5). Therefore, the area of SiPC-peak is not changed (Fig.6) for both orientations of substrate (100) and (111). The annealing temperature 1250°C may be sufficient for the decay of sesqui- and double SiPw+\* /^z/zz.!/1(0\_z0\$!z+\*!\*0.¥ tion of tetrahedrally oriented SiPC-bonds increases, the atoms are combined into crystallites of SiC, and the amplitude of the IR spectrum at 800 cm-1 increases (Fig. 12, curve 3). There is z"1.0\$!.z/0.!)(%\*%\*#z+"z0\$!z/0.101.!z+"z0\$!z%+\*w%),(\*0! z(5!.zc%#^zKd\_z+0\$z 1!z0+z0\$!z"+.¥ mation of new crystallites of SiC, as well as due to an increase in their size (Fig. 4, curve of LO-phonons).

#### *The temperature range 1250-1300°C*

Seemengly, there may be competing processes here. Firstly, in the case of the substrate Si(100) in this interval there is a decay of a large number of tetrahedral bonds (Fig. 7, curve 1), which is the main reason for reducing the area of SiC-peak at 1300°C (Fig. 6, curve 1). At the same time the amplitude of the LO-phonon is decreased (Fig. 7, curve 3) and the halfwidth of the peak is increased (Fig. 8, curve 1), indicating a deterioration of the structure. In contrast, in the case of the substrate Si(111) the peak area (Fig. 6, curve 1') and the amplitude at 800 cm-1 (Fig. 7, curve 1') are increased, and this is accompanied by a decrease in the halfwidth of the TO-phonon peak and an increase in amplitude of the LO-phonon peak (Fig. 7, curve 3'), i.e. by the improving of the layer structure. We assume that there may be two dominant mechanism of the influence of substrate orientation on the layer structure at high temperatures. During the recrystallization of the damaged layer in the interface "the SiC film – Si substrate", both a destruction of the silicon crystallites and the uniting of their atoms with the substrate are taken place. The difference of the recrystallization of the substrate Si(100) may be the appearance of forces and conditions for the destruction of the defective crystallites of silicon carbide. This leads to a decrease in amplitude at 800 cm-1 and increase the half-width of the peak due to the appearance of non-tetrahedral SiPC-bonds. The second )!\$\*%/)z)5z!z//+%0! z3%0\$z %""!.!\*0z+\*!\*0.0%+\*/z+"z.+\*z\*!.z0\$!z/1."!z+"z/%(¥ icon. After implantation into (100) oriented Si substrate, the carbon-riched surface layer is much thicker than in case of Si(111) substrate, so the sublimation and desorption of carbon at high temperatures will lead to a significant decrease in the amplitude values of the SiCpeak at all frequencies. Ie, the experiments to study an influence of substrate orientation on the desorption of implanted carbon are necessary.

#### *The temperature range 1300-1350°C*

Both the area of Si–C-peak (Fig. 6) and its half-width (Fig. 8) increase in this temperature interval, while the volume of the polycrystalline SiC is unchanged (Fig. 12, curve 3 and Fig. 7, curve 1), as the further growth of SiC crystallite size due to their association (Fig. 4, curves of LO-phonons) is taken place. The growth of the area and half-width of Si–C-peak are caused by the formation of new optically active clusters absorbing at frequencies of 750-900 cm-1 (%#^z DEdz 1!z 0+z 0\$!z !5z +"z /0(!z (1/0!./^z /z z .!/1(0\_z 0\$!z %+\*w%),(\*0! z (5!.z !¥

No significant changes in the formation of new infrared active clusters over this range are taken place. The decaying clusters with short SiPC-bonds, absorbing at frequencies of KCCP900 cm-1 (Fig. 12, curves 1-3) are converted into clusters with long bonds, absorbing at 700 and 800 cm-1 (Fig. 12, curves 4 and 5). Therefore, the area of SiPC-peak is not changed (Fig.6) for both orientations of substrate (100) and (111). The annealing temperature 1250°C may be sufficient for the decay of sesqui- and double SiPw+\* /^z/zz.!/1(0\_z0\$!z+\*!\*0.¥ tion of tetrahedrally oriented SiPC-bonds increases, the atoms are combined into crystallites of SiC, and the amplitude of the IR spectrum at 800 cm-1 increases (Fig. 12, curve 3). There is z"1.0\$!.z/0.!)(%\*%\*#z+"z0\$!z/0.101.!z+"z0\$!z%+\*w%),(\*0! z(5!.zc%#^zKd\_z+0\$z 1!z0+z0\$!z"+.¥ mation of new crystallites of SiC, as well as due to an increase in their size (Fig. 4, curve of

Seemengly, there may be competing processes here. Firstly, in the case of the substrate Si(100) in this interval there is a decay of a large number of tetrahedral bonds (Fig. 7, curve 1), which is the main reason for reducing the area of SiC-peak at 1300°C (Fig. 6, curve 1). At the same time the amplitude of the LO-phonon is decreased (Fig. 7, curve 3) and the halfwidth of the peak is increased (Fig. 8, curve 1), indicating a deterioration of the structure. In contrast, in the case of the substrate Si(111) the peak area (Fig. 6, curve 1') and the amplitude at 800 cm-1 (Fig. 7, curve 1') are increased, and this is accompanied by a decrease in the halfwidth of the TO-phonon peak and an increase in amplitude of the LO-phonon peak (Fig. 7, curve 3'), i.e. by the improving of the layer structure. We assume that there may be two dominant mechanism of the influence of substrate orientation on the layer structure at high temperatures. During the recrystallization of the damaged layer in the interface "the SiC film – Si substrate", both a destruction of the silicon crystallites and the uniting of their atoms with the substrate are taken place. The difference of the recrystallization of the substrate Si(100) may be the appearance of forces and conditions for the destruction of the defective crystallites of silicon carbide. This leads to a decrease in amplitude at 800 cm-1 and increase the half-width of the peak due to the appearance of non-tetrahedral SiPC-bonds. The second )!\$\*%/)z)5z!z//+%0! z3%0\$z %""!.!\*0z+\*!\*0.0%+\*/z+"z.+\*z\*!.z0\$!z/1."!z+"z/%(¥ icon. After implantation into (100) oriented Si substrate, the carbon-riched surface layer is much thicker than in case of Si(111) substrate, so the sublimation and desorption of carbon at high temperatures will lead to a significant decrease in the amplitude values of the SiCpeak at all frequencies. Ie, the experiments to study an influence of substrate orientation on

grades the structure (increase in half-width of the peak).

*The temperature range 1200-1250°C*

70 Physics and Technology of Silicon Carbide Devices

*The temperature range 1250-1300°C*

the desorption of implanted carbon are necessary.

LO-phonons).

Despite the increase in the desorption of carbon, the area of SiC-peak (Fig. 6), as well as the amplitude at all frequencies of spectra are increased in case of the film on the substrate Si(100) (Fig. 12, curves 1-5). The atoms of clusters, which formed due to the destruction of defective .5/0((%0!/z+"z%z%\*z0\$!z,.!2%+1/z0!),!.01.!z.\*#!\_z.!w1\*%0!z#%\*z%\*z"+.)z+"z0\$!z.5/0((%¥ tes of SiC, as well as in form of optically active clusters, which absorb at frequencies near 800 cm-1^z \*z %0%+\*\_z/0(!z(1/0!./z3%0\$z%R\_z%Zz\* zRz+\* /z.!z %/%\*0!#.0! zc%#^zLd^ Growth of SiC crystallite size leads to a frequency shift of LO-phonons peak in the shortwavelength region (Fig. 4). Since in an isolated system unacceptable the processes occurring with increasing free energy, the uniting of two crystallites occurs, if is accompanied by a gain %\*z!\*!.#5z%\*z+),.%/+\*z3%0\$z0\$!z!\*!.#5z!4,!\* ! z%\*z0\$!%.z !5^z \*z0\$!z/!z+"z0\$!z+.%!\*0¥ tion of the substrate Si(111) a decrease of the area of SiC-peak (Fig. 6, curve 1'), as well as the amplitude at 800 cm-1 (Fig. 7, curve 1') occur due to increased desorption of carbon.

#### *The temperature range 1350-1400°C*

Although at these temperatures the decay of optically inactive clusters, formation of both new crystallites and optically active SiC-clusters should be the greatest, nevertheless the growth of area and the amplitude of the SiC-peak of IR spectrum is not observed. On the contrary, they decrease (Fig. 6 and 7), which can be explained to the dominant influence of sublimation and desorption of carbon. The volume of polycrystalline SiC is also reduced, which is accompanied by a decrease in the amplitude of LO-phonons (Fig. 7\_z1.2!zFd^zz"1.¥ ther ordering of the structure of ion-implanted layer occurs, as evidenced by the decrease in the peak half-width of IR spectrum.

In conclusion, it is necessary to note that the quantity of absorbing SiPC-bonds in the silicon layer with Gaussian distribution of implanted carbon reaches a maximum at 1000°C for (100) oriented substrate and, at 1000 and 1250°C for (111) oriented substrate (Fig. 6). Most of the carbon atoms combine with atoms of silicon, forming the tetrahedrally oriented bonds of SiC (Fig. 12, curve 3). Seemingly, there are flat nets and chains of clusters (%#^zLd\_z3\$%\$z+\*¥ /%/0z)%\*(5z+"z+\* /z%x%\_z%zRz%\_zx%\_zxz\* \_z0\$%/z0!),!.01.!z%/z/1""%%!\*0z"+.z0\$!%.z !¥ cay. Some significant part of the carbon atoms form bonds of higher order, which decay at temperatures of 1200-1400°C and above. At high temperatures, 1300-1400°C (Figs. 6 and 7) occur intense desorption processes of carbon.

#### *A shape of IR transmission peak*

All presented spectra (Fig.2) \$2!z/\$,!z %""!.!\*0z".+)z/%),(5z %/,!./%2!z/,!0.1)zc0\$!+.!0¥ ically calculated). The transmission band both left and right from the transmission peak are perceptible asymmetric and, one can not describe it's shape by a simple analytical function. \$!z/\$,!z/5))!0.5z%/z !.!/! z3%0\$z0\$!z\*\*!(%\*#z0!),!.01.!z%\*.!/%\*#z\* \_z%0z%/z)%\*¥ %)(z%\*z0\$!z0!),!.01.!z.\*#!zDFCCxDFHC[^z\$!z"1.0\$!.z%\*.!/!z+"z0\$!z\*\*!(%\*#z0!),!.¥ ture leads to the increase of asymmetry, too. The contour of the transmission peak for TOphonons at perpendicular incidence of electromagnetic radiation on sample surface after annealing at 1350°C is most close to the dispersive one.

2%+1/(5\_z0\$!z/5))!0.5z+"z z0.\*/)%//%+\*z+\*0+1.z%/z.!(0! z3%0\$z0\$!z,.!/!\*!z+"z0\$!z%\*¥ frared active clusters in the ion implanted layer, and the concentration of clusters is minimal when the asymmetry is minimal, i.e. at 1350°C. In this relation, a largest area of SiC-peak corresponds to maximum amplitude of absorption at wavenumber 800 cm-1 (Figs.7 and 8). As is seen from amplitude values in Fig.12 (curves 1, 2, 4, 5), there is a certain quantity of the non-tetrahedral optical active clusters at 1350°C. Seemingly, a presence of very stable optical inactive clusters, which are not disintegrated even at the melting point of Si, is possible.

3.2.1 Influences of annealing, sputtering and the film composition changes during high dose implantation on the thickness and shape of the distribution profile of carbon atoms

Fig. 14 shows the calculated profile NC(Gibbons) of distribution of carbon atoms through the depth of silicon for the energies and doses of ions according to Table 2, which is the sum of Gaussian distributions constructed with the use of Rp(E) and Yp(E) by [21fzcdz%\*z+. ¥

1/2 exp

Figure 14. distribution profiles in Si produced by ion implantation (see Table 2). (a) SiC0.7; (b) SiC0.95; NC(Gibbons) is the profiles calculated according to [21], where NC(Gibbons) = NC(40 keV) + NC(20 keV) + NC(10 keV) + NC(5 keV) + NC(3 keV). NC(20°C), NC(1250°C) and NO(1250°C) are the Auger profiles of carbon and oxygen, respectively, in a layer after

Fig. 14 also shows the experimental curves (Fig. 14, curves NC(20°C), NC(1250°C) and NOcDEHC[dd\_z+0%\*! z5z1#!.z!(!0.+\*z/,!0.+/+,5\_z/\$+3%\*#z 0\$!z.0%+z+"z 0\$!z+\*!\*0.¥ tions of carbon and oxygen atoms to silicon (NC/NSizzO/NSidz0\$.+1#\$z0\$!z !,0\$z+"z0\$!z/)¥ ple after implantation (20°C) and annealing at 1250°C for 30 min in an argon atmosphere containing some oxygen. These distributions are constructed through a depth, taking into +1\*0z0\$!z+\* %0%+\*z0\$0z0\$!z\*1)!.z+"z.+\*z0+)/z%\*z/%(%+\*z\* \_z+\*/!-1!\*0(5\_z0\$!z%\*0!¥

(*x Rp*)<sup>2</sup> 2]*Rp*

<sup>2</sup> (5)

Ion Synthesis of SiC and Its Instability at High Temperatures

http://dx.doi.org/10.5772/ 51389

73

ance with the expression:

where x – the distance from the surface.

high-dose implantation and annealing at 1250°C for 30 min.

*N* (*x*)=

*D* ]*Rp*(2j)

### *Measurement of a conduction type of carbon implanted silicon layer*

The (100) oriented substrates of n- and p-Si of dimensions 7×5×0.3 mm3 with resistivities 4PH z have been implanted by carbon ions with values of energy 40 keV and dose 3.56×1017 cm-2z0+z !0!.)%\*!zz05,!z+"z+\* 10%+\*^z"0!.z%),(\*00%+\*\_z0\$!z/),(!/z\$2!z!!\*z%/+\$.+¥ nously annealed in vacuum over the temperature range from 200 up to 1200°C with step 200°C for 30 min. A surface layer of the annealed samples have been removed by etching in an acid mixture HF:HNO3 in composition of 1:10. A type of conduction of the implanted surface has been determined using thermo-emf after each 0.5 mm along both horisontal and vertical directions. The thermo-emf have fixed with approximately equiprobability the both n- and p-type of conduction on n-Si substrates, while on the p-Si substrates the thermo-emf have shown the p-type of conduction only. We believe that p-type of conduction on the n-Si substrates is provided by the SiC crystallites. The conduction of the Si crystallites is similar to the conduction of the substrate. If the substrate is p-Si, so the both Si- and SiC-crystallites \$2!z 0\$!z,w05,!z +"z +\* 10%+\*^z +\_z 0\$!z /5\*0\$!/%6! z %w.5/0((%0!/z \$2!z,w05,!z +"z +\* 1¥ tion independently from the type of substrate.

#### 3.2. Investigation of high-temperature instability of solid SiC films synthesized by ion implantation

/z/00! z%\*z,.#.,\$zE\_z"+.z+\*/0.10%+\*z+"zz.!0\*#1(.z,.+"%(!z+"z0\$!z %/0.%10%+\*z+"z.¥ bon atoms in the silicon, the implantation of carbon ions of different energies and doses in the second group of single-crystal silicon wafers of n- and p-type conductivity was carried out sequentially in the order according to Table 2. The doses of ions were chosen in such a way to obtain a layer SiC0.7 with the ratio of the concentrations of carbon and silicon atoms through a depth of about NC/NSizRzC^J^z+/0%),(\*00%+\*z\*\*!(%\*#z+"z0\$!z/),(!/z3/z,!.¥ formed in a vacuum in the temperature range 200-1200°C for 30 min with a step 200°C. In some cases, to compare also were analyzed the samples with films SiC0.95.


Table 2. Values of energy, E, dose, D, projected range, Rp! 9F<KLJ9??DAF? a.p(E), for 12C+ ions in Si, used for constructing a rectangular distribution profiles SiC0.7 and SiC0.95.

#### 3.2.1 Influences of annealing, sputtering and the film composition changes during high dose implantation on the thickness and shape of the distribution profile of carbon atoms

Fig. 14 shows the calculated profile NC(Gibbons) of distribution of carbon atoms through the depth of silicon for the energies and doses of ions according to Table 2, which is the sum of Gaussian distributions constructed with the use of Rp(E) and Yp(E) by [21fzcdz%\*z+. ¥ ance with the expression:

$$N(\mathbf{x}) = \frac{D}{\Delta R\_p (2\pi)^{1/2}} \exp\mathbf{f} - \frac{(\mathbf{x} - R\_p)^2}{2\Delta R\_p^{-2}} \mathbf{J} \tag{5}$$

where x – the distance from the surface.

2%+1/(5\_z0\$!z/5))!0.5z+"z z0.\*/)%//%+\*z+\*0+1.z%/z.!(0! z3%0\$z0\$!z,.!/!\*!z+"z0\$!z%\*¥ frared active clusters in the ion implanted layer, and the concentration of clusters is minimal when the asymmetry is minimal, i.e. at 1350°C. In this relation, a largest area of SiC-peak corresponds to maximum amplitude of absorption at wavenumber 800 cm-1 (Figs.7 and 8). As is seen from amplitude values in Fig.12 (curves 1, 2, 4, 5), there is a certain quantity of the non-tetrahedral optical active clusters at 1350°C. Seemingly, a presence of very stable optical inactive clusters, which are not disintegrated even at the melting point of Si, is possible.

The (100) oriented substrates of n- and p-Si of dimensions 7×5×0.3 mm3 with resistivities 4PH z have been implanted by carbon ions with values of energy 40 keV and dose 3.56×1017 cm-2z0+z !0!.)%\*!zz05,!z+"z+\* 10%+\*^z"0!.z%),(\*00%+\*\_z0\$!z/),(!/z\$2!z!!\*z%/+\$.+¥ nously annealed in vacuum over the temperature range from 200 up to 1200°C with step 200°C for 30 min. A surface layer of the annealed samples have been removed by etching in an acid mixture HF:HNO3 in composition of 1:10. A type of conduction of the implanted surface has been determined using thermo-emf after each 0.5 mm along both horisontal and vertical directions. The thermo-emf have fixed with approximately equiprobability the both n- and p-type of conduction on n-Si substrates, while on the p-Si substrates the thermo-emf have shown the p-type of conduction only. We believe that p-type of conduction on the n-Si substrates is provided by the SiC crystallites. The conduction of the Si crystallites is similar to the conduction of the substrate. If the substrate is p-Si, so the both Si- and SiC-crystallites \$2!z 0\$!z,w05,!z +"z +\* 10%+\*^z +\_z 0\$!z /5\*0\$!/%6! z %w.5/0((%0!/z \$2!z,w05,!z +"z +\* 1¥

3.2. Investigation of high-temperature instability of solid SiC films synthesized by ion

E, keV 40 20 10 5 3 D(SiC0.7), 1017 cm-2 2.80 0.96 0.495 0.165 0.115 D(SiC0.95), 1017 cm-2 4.48 1.54 0.792 0.264 0.184

> Rp(E), nm 93.0 47.0 24.0 12.3 7.5 a.p(E), nm 34.0 21.0 13.0 7.0 4.3

> > a.p(E), for 12C+ ions in Si, used for

9F<KLJ9??DAF?

some cases, to compare also were analyzed the samples with films SiC0.95.

/z/00! z%\*z,.#.,\$zE\_z"+.z+\*/0.10%+\*z+"zz.!0\*#1(.z,.+"%(!z+"z0\$!z %/0.%10%+\*z+"z.¥ bon atoms in the silicon, the implantation of carbon ions of different energies and doses in the second group of single-crystal silicon wafers of n- and p-type conductivity was carried out sequentially in the order according to Table 2. The doses of ions were chosen in such a way to obtain a layer SiC0.7 with the ratio of the concentrations of carbon and silicon atoms through a depth of about NC/NSizRzC^J^z+/0%),(\*00%+\*z\*\*!(%\*#z+"z0\$!z/),(!/z3/z,!.¥ formed in a vacuum in the temperature range 200-1200°C for 30 min with a step 200°C. In

*Measurement of a conduction type of carbon implanted silicon layer*

72 Physics and Technology of Silicon Carbide Devices

tion independently from the type of substrate.

Table 2. Values of energy, E, dose, D, projected range, Rp!

constructing a rectangular distribution profiles SiC0.7 and SiC0.95.

implantation

NC(Gibbons) profile [21]

Figure 14. distribution profiles in Si produced by ion implantation (see Table 2). (a) SiC0.7; (b) SiC0.95; NC(Gibbons) is the profiles calculated according to [21], where NC(Gibbons) = NC(40 keV) + NC(20 keV) + NC(10 keV) + NC(5 keV) + NC(3 keV). NC(20°C), NC(1250°C) and NO(1250°C) are the Auger profiles of carbon and oxygen, respectively, in a layer after high-dose implantation and annealing at 1250°C for 30 min.

Fig. 14 also shows the experimental curves (Fig. 14, curves NC(20°C), NC(1250°C) and NOcDEHC[dd\_z+0%\*! z5z1#!.z!(!0.+\*z/,!0.+/+,5\_z/\$+3%\*#z 0\$!z.0%+z+"z 0\$!z+\*!\*0.¥ tions of carbon and oxygen atoms to silicon (NC/NSizzO/NSidz0\$.+1#\$z0\$!z !,0\$z+"z0\$!z/)¥ ple after implantation (20°C) and annealing at 1250°C for 30 min in an argon atmosphere containing some oxygen. These distributions are constructed through a depth, taking into +1\*0z0\$!z+\* %0%+\*z0\$0z0\$!z\*1)!.z+"z.+\*z0+)/z%\*z/%(%+\*z\* \_z+\*/!-1!\*0(5\_z0\$!z%\*0!¥ grals and the area under the curves NC(Gibbons) and NC(20°C) must be equal one another at a first approximation. The areas under the curves were equal to SG = S20°C = -(*NC* / *NSi*)*dx* = 90 units (or 100%), and after annealing at 1250°C: S1250°CzRzJDz1\*%0/zc+.zJL^GMdz 1!z0+z0\$!z"+.)¥ tion of silicon oxide layer. When evaluating the number of carbon atoms in a thin surface region (8 nm), where NC/NSi is very great due to the low content of silicon atoms (NSi<< 5×1022 cm-3), an approximation was made that the NC/NSi does not exceed 2.3 (Ngraphite = 11.6×1022 cm-3 and Nsilicon = 5×1022 cm-3). At the same time, the area under the profile curve for the region x> 22.2 nm were estimated SG = 78 units, S20°C = 66 units and S1250°C = 65 units. That is, the areas under the profile curves before and after annealing for x > 22.2 nm are almost equal, but less than calculated value, since part of the carbon atoms after implantation was concentrated near the surface (x <8 nm), and during annealing occur desorption of carbon from the layer (x<22.2 nm) and the formation of silicon oxide. The interface "the SiC film - Si substrate" in the experiment was more abrupt than it was expected. After annealing for 30 )%\*10!/\_z()+/0zECMz+"z0\$!z0+0(z\*1)!.z+"z.+\*z0+)/z !/+.! z".+)z0\$!z.+\*w.%\$z/1.¥ face layer of the film. Fig. 14 shows that the average concentration of carbon and oxygen were: NC/NSi = 0.7 in the depth 22.2 < x < 110 nm and the NO/NSizS 3.0 at the surface layer x < 22.2 nm. In this case there is penetration of oxygen atoms into the layer up to 30 nm.

another (NC(3 keV) and NC(5 keV) in the direction of NCcDCz'!dd^z/zz.!/1(0\_z/%#\*%"%\*0z%\*¥

It is seen in Fig.14b that the average concentration of carbon and oxygen were: NC/NSi = 0.95 in the depth of the layer from 20 to 110 nm and the NO/NSizS 2.33 at the surface layer up to a depth of about 20 nm. At the same time observed the penetration of oxygen up to 80 nm to

and after annealing at 1250°C: S1250°Cz Rz DCFz1\*%0/z c+.z JD^FMd^z\$1/\_z%0z ,,!./z 0\$0z "0!.z \*¥ nealing for 30 minutes, almost 30% of the carbon atoms desorbed from the surface layer of 0\$!z "%()^z0z 0\$!z /)!z 0%)!z 0\$!z ,,!.\*!z +"z z(5!.z +"z +45#!\*z 0+)/z 0z 0\$!z /1."!z%/z .!¥ vealed. The area under the profile curve for the region x > 25 nm were estimated SG = 121 units, S20°C = 99 units and S1250°C = 95 units. i.e., the area under the curves of the profile before \* z"0!.z\*\*!(%\*#z"+.z.!#%+\*z4zUzEHz\*)z.!z/%)%(.z%\*z)#\*%01 !\_z10z#%\*z(!//z0\$\*z(1¥ (0! z+\*!\_z/%\*!z,.0z+"z0\$!z.+\*z0+)/z"0!.z%),(\*00%+\*z3/z+\*!\*0.0! z\*!.z0\$!z/1.¥ face (x < 19 nm), and after annealing, there was desorption of carbon from layer (x <25 nm) \* z 0\$!z "+.)0%+\*z+"z/%(%+\*z+4% !^z\$!z%\*0!."!zo0\$!z%z "%()zxz%z/1/0.0!oz%\*z 0\$!z!4,!.%¥

\$!z,.!/!\*!z+"zz/\$.,z%\*0!."!zo0\$!z%z"%()zxz%z/1/0.0!oz,!.)%0/z0+z/1,,+/!z0\$0z%/z,+/¥ /%(!z0+z+0%\*z,.+)%/%\*#z.!/1(0/z+\*z0\$!z)!/1.!)!\*0z+"z"%()z0\$%'\*!//z5zw.5z.!"(!0+)!¥ try, although this method is typically used for films deposited with a very sharp interface "a film - substrate" and for ion-implanted layers usually does not apply. The parameters of the SiC0.7 film by this method were investigated at small grazing angles z5z.!+. %\*#z0\$!z\*¥ gular dependence of the reflection coefficient using two spectral lines CuK (0.154 nm) and CuK (0.139 nm) on the installation "ComplexXRay C6" [61]. The oscillations of intensity were observed, assigned to the interference of X-ray reflections in the layers SiC0.7 and SiO2

The first maximum of reflection with intensity I1zRzLFECJz,1(/!/z0z\*z\*#(!z+"zEzRzC^GDK[ is observed (Fig. 15). The angle of total external reflection is evaluated as an angle where the intensity is equal to a half of the first maximum (I = I1/2 = 46603 pulses), ie 2 = 0.449°, or = 0.2245° = 3.918 mrad. Using the Henke program is determined that this value of +..!¥

increases again up to I2 RzJIKFDz,1(/!/z\* z0\$0z%\* %0!/z0\$!z,.!/!\*!z+"zz)+.!z !\*/!z/0.1¥ ture. If the intensity falls up to the value I = I2/2 = 38415 pulses, the value 2c = 0.486°, the critical angle is equal to c = 0.243° = 4.241 mrad, which corresponds to a density 2.77 g/cm3

second increase in intensity up to I3 = 34416 pulse which corresponds to a denser structure. If the intensity falls up to the value I = I3/2 = 17208 pulse, the value 2<sup>c</sup> = 0.526°, and c =

\$!z(5!.z0\$%'\*!//z%/z !0!.)%\*! z5z0\$!z"+.)1(zE z/%\*zzRz\_z+.z0'%\*#z%\*0+z+1\*0z0\$!z/)(( 2(1!/z+"z`z zRzuEzz\*)\_z3\$!.!zzwz0\$!z32!(!\*#0\$z+"z1 (0.154 nm) or CuK (0.139 nm)

. Further, with increasing of the incidence angle, the intensity of reflection

(*NC* / *NSi*)*dx* = 144 units (or 100%),

http://dx.doi.org/10.5772/ 51389

75

Ion Synthesis of SiC and Its Instability at High Temperatures

, which is close to the density of cristobalite

. As shown in Fig. 15, then there is a

\_z3\$%\$z%/z(+/!z0+z0\$!z !\*/%¥

crease in the concentration of carbon in the surface layer is observed.

the depth. It was found for a layer SiC0.95 that SG = S20°C = -

ment also was sharper than the expected one.

sponds to the value of film density 2.37 g/cm3

and is close to the density of quartz (SiO2) 2.65 g/cm3

0.263° = 4.590 mrad. This corresponds to a density = 3.25 g/cm3

.

(Fig. 15).

(SiO2) 2.32 g/cm3

ty of silicon carbide - 3.2 g/cm3

Some difference between the shape of the experimental and calculated curves of the profile is observed (Fig. 14). The distribution NC(Gibbons) was made without taking into account the effects of sputtering and composition changes in the layer by high dose implantation. Accounting for the effect of surface sputtering during high dose of implantation of carbon ions (E = 40 keV, D = 2.8×1017 cm-2) allows to assume the displacement of profile further into the layer with increasing dose, to some expansion of the profile and, consequently, to reduce the carbon concentration at the peak of the distribution in comparison with the calculated 2(1!^z+3!2!.\_z\$\*#%\*#z0\$!z+),+/%0%+\*z+"z0\$!z/%\*#(!w.5/0(z/%(%+\*z/1/0.0!z1,z0+zz)%4¥ ture of C and Si atoms during the implantation suggests the formation of a significant amount of double and tripple Si–C- and C–C-bonds, which are more strong than the Si–Sibonds, as well as the formation of stable carbon and carbon-silicon clusters. This results a decrease of Rpcdz\* zYp(E) during implantation.

The decrease of Rpcdz !.!/!/z0\$!z%\*"(1!\*!z+"z/1."!z/,100!.%\*#z+\*z0\$!z,+/%0%+\*z+"z0\$!z %/¥ tribution maximum of carbon atoms, i.e., the maximum should remain nearly on the same depth. Moreover, the decrease of pcdz3%((z%\*.!/!z0\$!z.+\*z+\*!\*0.0%+\*z0z0\$!z)4%¥ mum of peak and a more sharp decrease in concentration in the direction to the substrate and to the surface. This will cause a decrease in the depth of the interface "film SiC – the substrate Si», which becomes more sharp with increasing dose, as well as an occurrence of !,.!//%+\*z!03!!\*z,!'/zGCz\* zECz'!\_z\* z,+//%(5z!03!!\*zECz\* zDCz'!^z\$!z,,!.¥ ance of depression between peaks 40 and 20 keV in Fig. 14 for layers SiC0.7 and SiC0.95 may be due to these reasons.

The surface sputtering during the implantation of carbon ions with energies of 10, 5 and 3 keV is more intense with decreasing ion energy. This should lead to an increase in carbon concentration near the surface due to shift of the distribution maxima of these ions one to another (NC(3 keV) and NC(5 keV) in the direction of NCcDCz'!dd^z/zz.!/1(0\_z/%#\*%"%\*0z%\*¥ crease in the concentration of carbon in the surface layer is observed.

grals and the area under the curves NC(Gibbons) and NC(20°C) must be equal one another at

units (or 100%), and after annealing at 1250°C: S1250°CzRzJDz1\*%0/zc+.zJL^GMdz 1!z0+z0\$!z"+.)¥ tion of silicon oxide layer. When evaluating the number of carbon atoms in a thin surface region (8 nm), where NC/NSi is very great due to the low content of silicon atoms (NSi<< 5×1022 cm-3), an approximation was made that the NC/NSi does not exceed 2.3 (Ngraphite = 11.6×1022 cm-3 and Nsilicon = 5×1022 cm-3). At the same time, the area under the profile curve for the region x> 22.2 nm were estimated SG = 78 units, S20°C = 66 units and S1250°C = 65 units. That is, the areas under the profile curves before and after annealing for x > 22.2 nm are almost equal, but less than calculated value, since part of the carbon atoms after implantation was concentrated near the surface (x <8 nm), and during annealing occur desorption of carbon from the layer (x<22.2 nm) and the formation of silicon oxide. The interface "the SiC film - Si substrate" in the experiment was more abrupt than it was expected. After annealing for 30 )%\*10!/\_z()+/0zECMz+"z0\$!z0+0(z\*1)!.z+"z.+\*z0+)/z !/+.! z".+)z0\$!z.+\*w.%\$z/1.¥ face layer of the film. Fig. 14 shows that the average concentration of carbon and oxygen were: NC/NSi = 0.7 in the depth 22.2 < x < 110 nm and the NO/NSizS 3.0 at the surface layer x <

22.2 nm. In this case there is penetration of oxygen atoms into the layer up to 30 nm.

decrease of Rpcdz\* zYp(E) during implantation.

due to these reasons.

Some difference between the shape of the experimental and calculated curves of the profile is observed (Fig. 14). The distribution NC(Gibbons) was made without taking into account the effects of sputtering and composition changes in the layer by high dose implantation. Accounting for the effect of surface sputtering during high dose of implantation of carbon ions (E = 40 keV, D = 2.8×1017 cm-2) allows to assume the displacement of profile further into the layer with increasing dose, to some expansion of the profile and, consequently, to reduce the carbon concentration at the peak of the distribution in comparison with the calculated 2(1!^z+3!2!.\_z\$\*#%\*#z0\$!z+),+/%0%+\*z+"z0\$!z/%\*#(!w.5/0(z/%(%+\*z/1/0.0!z1,z0+zz)%4¥ ture of C and Si atoms during the implantation suggests the formation of a significant amount of double and tripple Si–C- and C–C-bonds, which are more strong than the Si–Sibonds, as well as the formation of stable carbon and carbon-silicon clusters. This results a

The decrease of Rpcdz !.!/!/z0\$!z%\*"(1!\*!z+"z/1."!z/,100!.%\*#z+\*z0\$!z,+/%0%+\*z+"z0\$!z %/¥ tribution maximum of carbon atoms, i.e., the maximum should remain nearly on the same depth. Moreover, the decrease of pcdz3%((z%\*.!/!z0\$!z.+\*z+\*!\*0.0%+\*z0z0\$!z)4%¥ mum of peak and a more sharp decrease in concentration in the direction to the substrate and to the surface. This will cause a decrease in the depth of the interface "film SiC – the substrate Si», which becomes more sharp with increasing dose, as well as an occurrence of !,.!//%+\*z!03!!\*z,!'/zGCz\* zECz'!\_z\* z,+//%(5z!03!!\*zECz\* zDCz'!^z\$!z,,!.¥ ance of depression between peaks 40 and 20 keV in Fig. 14 for layers SiC0.7 and SiC0.95 may be

The surface sputtering during the implantation of carbon ions with energies of 10, 5 and 3 keV is more intense with decreasing ion energy. This should lead to an increase in carbon concentration near the surface due to shift of the distribution maxima of these ions one to

(*NC* / *NSi*)*dx* = 90

a first approximation. The areas under the curves were equal to SG = S20°C = -

74 Physics and Technology of Silicon Carbide Devices

It is seen in Fig.14b that the average concentration of carbon and oxygen were: NC/NSi = 0.95 in the depth of the layer from 20 to 110 nm and the NO/NSizS 2.33 at the surface layer up to a depth of about 20 nm. At the same time observed the penetration of oxygen up to 80 nm to

the depth. It was found for a layer SiC0.95 that SG = S20°C = -(*NC* / *NSi*)*dx* = 144 units (or 100%), and after annealing at 1250°C: S1250°Cz Rz DCFz1\*%0/z c+.z JD^FMd^z\$1/\_z%0z ,,!./z 0\$0z "0!.z \*¥ nealing for 30 minutes, almost 30% of the carbon atoms desorbed from the surface layer of 0\$!z "%()^z0z 0\$!z /)!z 0%)!z 0\$!z ,,!.\*!z +"z z(5!.z +"z +45#!\*z 0+)/z 0z 0\$!z /1."!z%/z .!¥ vealed. The area under the profile curve for the region x > 25 nm were estimated SG = 121 units, S20°C = 99 units and S1250°C = 95 units. i.e., the area under the curves of the profile before \* z"0!.z\*\*!(%\*#z"+.z.!#%+\*z4zUzEHz\*)z.!z/%)%(.z%\*z)#\*%01 !\_z10z#%\*z(!//z0\$\*z(1¥ (0! z+\*!\_z/%\*!z,.0z+"z0\$!z.+\*z0+)/z"0!.z%),(\*00%+\*z3/z+\*!\*0.0! z\*!.z0\$!z/1.¥ face (x < 19 nm), and after annealing, there was desorption of carbon from layer (x <25 nm) \* z 0\$!z "+.)0%+\*z+"z/%(%+\*z+4% !^z\$!z%\*0!."!zo0\$!z%z "%()zxz%z/1/0.0!oz%\*z 0\$!z!4,!.%¥ ment also was sharper than the expected one.

\$!z,.!/!\*!z+"zz/\$.,z%\*0!."!zo0\$!z%z"%()zxz%z/1/0.0!oz,!.)%0/z0+z/1,,+/!z0\$0z%/z,+/¥ /%(!z0+z+0%\*z,.+)%/%\*#z.!/1(0/z+\*z0\$!z)!/1.!)!\*0z+"z"%()z0\$%'\*!//z5zw.5z.!"(!0+)!¥ try, although this method is typically used for films deposited with a very sharp interface "a film - substrate" and for ion-implanted layers usually does not apply. The parameters of the SiC0.7 film by this method were investigated at small grazing angles z5z.!+. %\*#z0\$!z\*¥ gular dependence of the reflection coefficient using two spectral lines CuK (0.154 nm) and CuK (0.139 nm) on the installation "ComplexXRay C6" [61]. The oscillations of intensity were observed, assigned to the interference of X-ray reflections in the layers SiC0.7 and SiO2 (Fig. 15).

The first maximum of reflection with intensity I1zRzLFECJz,1(/!/z0z\*z\*#(!z+"zEzRzC^GDK[ is observed (Fig. 15). The angle of total external reflection is evaluated as an angle where the intensity is equal to a half of the first maximum (I = I1/2 = 46603 pulses), ie 2 = 0.449°, or = 0.2245° = 3.918 mrad. Using the Henke program is determined that this value of +..!¥ sponds to the value of film density 2.37 g/cm3 , which is close to the density of cristobalite (SiO2) 2.32 g/cm3 . Further, with increasing of the incidence angle, the intensity of reflection increases again up to I2 RzJIKFDz,1(/!/z\* z0\$0z%\* %0!/z0\$!z,.!/!\*!z+"zz)+.!z !\*/!z/0.1¥ ture. If the intensity falls up to the value I = I2/2 = 38415 pulses, the value 2c = 0.486°, the critical angle is equal to c = 0.243° = 4.241 mrad, which corresponds to a density 2.77 g/cm3 and is close to the density of quartz (SiO2) 2.65 g/cm3 . As shown in Fig. 15, then there is a second increase in intensity up to I3 = 34416 pulse which corresponds to a denser structure. If the intensity falls up to the value I = I3/2 = 17208 pulse, the value 2<sup>c</sup> = 0.526°, and c = 0.263° = 4.590 mrad. This corresponds to a density = 3.25 g/cm3 \_z3\$%\$z%/z(+/!z0+z0\$!z !\*/%¥ ty of silicon carbide - 3.2 g/cm3 .

\$!z(5!.z0\$%'\*!//z%/z !0!.)%\*! z5z0\$!z"+.)1(zE z/%\*zzRz\_z+.z0'%\*#z%\*0+z+1\*0z0\$!z/)(( 2(1!/z+"z`z zRzuEzz\*)\_z3\$!.!zzwz0\$!z32!(!\*#0\$z+"z1 (0.154 nm) or CuK (0.139 nm) . %0%+\*\_z\* zE av was determined as an average from several (j - i) peaks (Table 3). To determine the thickness, four narrow peak of SiC, and two broad bands of SiO2, probably from two different phases - cristobalite and quartz (Fig. 15), were used. The second broad band consists of 3 bands. The thickness of the resulting system (SiO2zPz%0.7zPz%dz3/z+10zDCCz\*)^ 57255 pulses, which indicates the occurrence of a more dense structure. If the intensity falls

up to the value I = I2/2 = 28627 pulses, the value 2<sup>c</sup> = 0.510°, the critical angle is equal to c =

Figure 16. X-ray reflectometry of parameters of the films SiC0.95, synthesized by multiple implantation of carbon ions

To determine the thickness of the layers, four narrow peaks of SiC, and two broad bands of

65 N 0N

M:9

M av+- Mj J- Mi ,-

SiC 1.066 0.690 4 0.094 0.15405 93.9 SiO2 2.19 1.426 2 0.382 0.15405 23.1

Table 4. Determination of the thickness of the layers in the system (SiO2.33]/A0.95]/A:Q4J9QJ=>D=;LGE=LJQ

The thickness of the system (SiO2.33 P SiC0.95 P Si) was 117 nm, which was comparable to the

estimated thickness of the film. SiO2 peaks are visible not clearly. Perhaps this is because the

, which is close to the density of

http://dx.doi.org/10.5772/ 51389

77

Ion Synthesis of SiC and Its Instability at High Temperatures

0.255° = 4.451 mrad. This corresponds to a density 3.06 g/cm3

with energies of 40, 20, 10, 5 and 3 keV into silicon after annealing at 1150°C.

M<sup>i</sup> j – i

annealing temperature was taken at 100°C lower (1150°C).

.

silicon carbide - 3.2 g/cm3

SiO2 (Fig. 16) were used.

 M<sup>j</sup> -

Layer -

Figure 15. X-ray reflectometry using two spectral lines CuKi (0.154 nm) and CuK<sup>j</sup> (0.139 nm) ("ComplexXRay C6") of parameters of the SiC0.7 films, synthesized by multiple implantation of carbon ions with energies of 40, 20, 10, 5 and 3 keV into silicon, after annealing at 1250°C.


Table 3. Determination of the thickness of the layers in the system (SiO3]/A0.7]/A:Q4J9QJ=>D=;LGE=LJQ9;;GJ<AF? =IM9LAGF<rKAFkl

Similar measurements for the SiC0.95z(5!.z(/+z(! z0+z0\$!z+/!.20%+\*z+"z0\$!z%\*0!\*/%05z+/%((¥ tions of X-ray reflections. The first maximum of reflection with intensity I1 = 98703 pulses at \*z\*#(!z+"zEzRzC^FLI[z%/z+/!.2! zc%#^zDId^z\$!z.%0%(z\*#(!z+"z0+0(z!40!.\*(z.!"(!0%+\*z%/ evaluated as an angle where I = I1uEzRzGLFHEz,1(/!/\_z10z%\*z0\$%/z/!z%\*z0\$!z,+/%0%+\*z+"zz)%\*%¥ )1)z zRzHFLIDz,1(/!\_z%^!^zEczRzC^GHK[\_z\* zzRzC^EEL[zRzF^LJLz). ^z\$%/z\*#(!z+..!/,+\* /z0+ 0\$!z"%()z !\*/%05zE^GIz#u)<sup>3</sup> , which is close to the density of optical glass 2.51 g/cm3 . Further, with increasing of incidence angle, the intensity of reflection is again increased up to I2 = 57255 pulses, which indicates the occurrence of a more dense structure. If the intensity falls up to the value I = I2/2 = 28627 pulses, the value 2<sup>c</sup> = 0.510°, the critical angle is equal to c = 0.255° = 4.451 mrad. This corresponds to a density 3.06 g/cm3 , which is close to the density of silicon carbide - 3.2 g/cm3 .

. %0%+\*\_z\* zE av was determined as an average from several (j - i) peaks (Table 3). To determine the thickness, four narrow peak of SiC, and two broad bands of SiO2, probably from two different phases - cristobalite and quartz (Fig. 15), were used. The second broad band consists of 3 bands. The thickness of the resulting system (SiO2zPz%0.7zPz%dz3/z+10zDCCz\*)^

Figure 15. X-ray reflectometry using two spectral lines CuKi (0.154 nm) and CuK<sup>j</sup> (0.139 nm) ("ComplexXRay C6") of parameters of the SiC0.7 films, synthesized by multiple implantation of carbon ions with energies of 40, 20, 10, 5 and 3

65 N 0N

M:9

. Further,

M av+- Mj J- Mi ,-

SiC 1.138 0.598 4 0.135 0.15405 65.4 SiO2 3.154 2.012 3 0.38 0.15405 23.2 SiO2 2.012 1.178 1 0.83 0.15405 10.6

Table 3. Determination of the thickness of the layers in the system (SiO3]/A0.7]/A:Q4J9QJ=>D=;LGE=LJQ9;;GJ<AF?

Similar measurements for the SiC0.95z(5!.z(/+z(! z0+z0\$!z+/!.20%+\*z+"z0\$!z%\*0!\*/%05z+/%((¥ tions of X-ray reflections. The first maximum of reflection with intensity I1 = 98703 pulses at \*z\*#(!z+"zEzRzC^FLI[z%/z+/!.2! zc%#^zDId^z\$!z.%0%(z\*#(!z+"z0+0(z!40!.\*(z.!"(!0%+\*z%/ evaluated as an angle where I = I1uEzRzGLFHEz,1(/!/\_z10z%\*z0\$%/z/!z%\*z0\$!z,+/%0%+\*z+"zz)%\*%¥ )1)z zRzHFLIDz,1(/!\_z%^!^zEczRzC^GHK[\_z\* zzRzC^EEL[zRzF^LJLz). ^z\$%/z\*#(!z+..!/,+\* /z0+

with increasing of incidence angle, the intensity of reflection is again increased up to I2 =

, which is close to the density of optical glass 2.51 g/cm3

keV into silicon, after annealing at 1250°C.

76 Physics and Technology of Silicon Carbide Devices

M<sup>i</sup> j – i

 M<sup>j</sup> -

0\$!z"%()z !\*/%05zE^GIz#u)<sup>3</sup>

Layer -

=IM9LAGF<rKAFkl

Figure 16. X-ray reflectometry of parameters of the films SiC0.95, synthesized by multiple implantation of carbon ions with energies of 40, 20, 10, 5 and 3 keV into silicon after annealing at 1150°C.

To determine the thickness of the layers, four narrow peaks of SiC, and two broad bands of SiO2 (Fig. 16) were used.


Table 4. Determination of the thickness of the layers in the system (SiO2.33]/A0.95]/A:Q4J9QJ=>D=;LGE=LJQ

The thickness of the system (SiO2.33 P SiC0.95 P Si) was 117 nm, which was comparable to the estimated thickness of the film. SiO2 peaks are visible not clearly. Perhaps this is because the annealing temperature was taken at 100°C lower (1150°C).

#### 3.2.2 The study of the high-temperature instability of solid SiCg films synthesized by ion implantation

In Fig. 17, the IR transmission spectra of the homogeneous SiCaz films, synthesized on substrates of Si(100) with resistivity 4-5 Ohm cm (a) and Si(111) with resistivity 10 Ohm cm (b), subjected to isothermal annealing at the temperature 1200℃ for several hours in an atmosphere of inert gas (Ar), are presented. Comparing these two figures (a) and (b), one can see that the nature of the SiC films formed on substrates with different crystallographic orientations, are different. This difference manifests itself in the amplitudes and half-widths of the peaks corresponding to the excitation of both transverse and longitudinal optical lattice oscillations of SiC (TO- and LO-phonons).

Figure 17. The dependence of the IR transmission spectra of implanted by \*C¹ ions Si on the annealing time at the temperature 1200°C: a) n-Si, the orientation of substrate Si(100), b) p-Si, the orientation of substrate Si(111),

After annealing at 1200°C for 30 min in the IR spectra an intense peak at 800 cm+ which associated with the TO phonons of SiC, as well as a peak at 960 cm³ corresponding to the LOphonons of SiC, are observed. It is seen that in contrast to the spectra of film on (100) oriented Si substrate, the transmission spectra of oscillation modes of SiC of film on the (111) oriented silicon substrate are more blurred and the level of the transmission spectra of the two modes are superimposed on each other, and does not achieve the initial zero level in the wave number, equal to 915 cm². This is caused by the half-width of these peaks (Fig. 17 and 18).

The narrowing of the peak (Fig. 18) up to 40 cm - occurs as a result of intensive formation of the tetrahedrally oriented Si-C-bonds absorbing at 800 cm -1, as well as the decay of bonds which absorb at frequencies different from the value of 800 cm². Since the tetrahedral bond corresponds to the crystalline phase of silicon carbide, the narrowing of the IR spectrum with a minimum at 800 cm² is associated with the process of ordering of the implanted layer. As is seen from Fig. 18, for the SiCo7 layer the narrowing of the peak is more intense with increasing time of isothermal annealing up to 6.5 hours in the case of the (111) oriented substrate in comparison with (100) orientation. After annealing for 8.5 hours or more a further narrowing of the peak is slowing, indicating a complete processes of SiC lattice ordering. Thus, it was established that the annealing duration of the less than 6.5 hours at 1200°C is insufficient to form the structure of silicon carbide.

As is seen from Figs. 17 and 19, the amplitude values of the peaks with increasing of annealing time at 1200°C are reduced. This indicates a decrease in the total volume of silicon car bide due to disintegration of SiC and desorption of carbon. Since the amplitude of the SiCpeak of infrared transmission is proportional to the concentration of Si-C-bonds, the measurements of its value were made in the spectra after isothermal annealing at the temperature of 1200°C (Fig. 19). For (100) oriented silicon substrate of n-type conductivity, the amplitude of the TO- and LO-phonon peaks of the infrared transmission (Fig. 19, curves 2 and 4) after annealing for 0.5-6.5 hours were higher than the same for (111) oriented silicon, and then the decay of SiC in this layer becomes more intense. However, as is seen from Figs. 17 and 19, after annealing for 11.5 and 13.5 hours the disintegration of silicon carbide is almost finished for the SiC of layer on the (111) substrate, while for the (100) orientation is observed after annealing during up to 15.5 hours.

Figure 18. Dependence of the half-width of the TO-phonons peak of SiC of IR spectra on the at the temperature of 1200°C for SiCo3 layers: 1 - Si(111) substrate, 2 - Si(100) substrate.

It should be also noted that the signal from the LO-phonons in the spectra of both types of substrate disappears earlier (Fig. 19) than the signal from the TO-phonons, and in particular, at (111) orientation of substrate. Thus, a gradual decrease in the amplitudes of the TO-and LO-phonon peaks of SiC in the IR transmission spectra of ion-synthesized SiC films at the

increasing time of high-temperature annealing indicates the decay of the SiC structure, i.e. the instability of these films to such regime of treatment.

Figure 20. 0@=9EHDALM<=G>L@=AF>J9J=<LJ9FKEALL9F;=9L>AP=<O9N=FME:=JKN=JKMKL@=<MJ9LAGFG>AKGL@=JE9D9FF=9Ds ing of the SiC0.7 layer (angle of incidence of infrared rays on the sample is 73° from the normal): 1 – 700 cm-1, 2 – 750 cm-1, 3 – 800 cm-1, 4 – 850 cm-1, 5 – 900 cm-1; a) the substrate orientation Si (100), b) the substrate orientation Si (111).

Ion Synthesis of SiC and Its Instability at High Temperatures

http://dx.doi.org/10.5772/ 51389

81

This process is clearly demonstrated on the time dependence of the area of SiC-peak, which is proportional to the total number of optically active Si–C-bonds (Fig. 21). Although the peak amplitude at the minimum of IR transmission (Fig.19, curve 2) and at 800 cm-1 (Fig.20, curve 3) for the Si substrates with (100) orientation are higher than in the case of (111) orientation, the value of area of SiC-peak for (111) was higher after annealing for 0.5 hours. This is due to

Figure 21. The area of the TO-phonon peak of SiC in spectra of the IR transmission versus the annealing time at the temperature of 1200°C for the SiC0.7 layers (angle of incidence of infrared rays on the sample surface - 73° from the

3% 0\$z+"z0\$!z,!'z1/! z5zz/%#\*%"%\*0z)+1\*0z+"z+,0%((5z0%2!z%Pw+\* /z(+/!z0+ tetrahedrally oriented, which absorb at 750 and 850 cm-1 and, probably due to the smaller amount of stable carbon silicon clusters in the film on (111) oriented silicon substrate. It is not contradict to the data for the SiC layer with Gaussian distribution of carbon in silicon, for which was shown that immediately after the implantation of carbon into the (100) and (111) oriented silicon at least 65% and 60% of carbon atoms are concentrated in optically inactive clusters, respectively (see 3.1.2, Fig. 6 "The temperature range 20-600°C"). The strong carbon

normal): 1 - the orientation of the substrate Si(111), 2 – the orientation of the substrate Si(100).

a greater half-

Figure 19. EHDALM<=G>0+9F<(+H@GFGFH=9CKG>/AG>%.LJ9FKEAKKAGFN=JKMKL@=9FF=9DAF?LAE=9LL@=L=EH=J9s ture of 1200°C for SiC0.7 layers on silicon substrates of (100) and (111) orientation: 1 – Si(111), TO-phonon peak; 2 - Si(100), TO-phonon peak; 3 - Si(111), LO-phonon peak; 4 - Si(100), LO-phonon peak.

Since the amplitude of the infrared transmission at the wavenumber 800 cm-1 is proportional 0+z0\$!z+\*!\*0.0%+\*z+"z0\$!z0!0.\$! .((5z+.%!\*0! z%xw+\* /\_z%0/z)#\*%01 !/z3!.!z)!/¥ ured in the spectra after isothermal annealing at the temperature of 1200°C (Fig. 20, curve 3). Assuming that the amplitude at any frequency is proportional to the number of the Si–C- +\* /z3\$%\$z/+.z0z0\$%/z".!-1!\*5\_z0\$!z),(%01 !/z"+.z0\$!zw,\$+\*+\*/z3%0\$z32!\*1)¥ bers 700, 750, 850 and 900 cm-1 (Fig. 20) in the case of incidence of IR radiation to the sample surface at an angle of 73° to the normal were also measured.

It is seen in Fig. 20a, b (curves 3) that after annealing at 1200°C for 0.5 hour of the SiC0.7 film on the Si (100) substrate, the amplitude at wavenumber 800 cm-1 is higher than the same for the Si(111) substrate (70 and 58%), indicating a higher content of the tetrahedrally oriented %w+\* /^z 0z%/z(/+z/!!\*z0\$0z0\$!z\*1)!.z+"z%w+\* /z3\$%\$z.!z(+/!z0+z0!0.\$! .(z+.%!\*0¥ tion and absorb at 750 and 850 cm-1\_z%\*z0\$!z/!z+"z0\$!z/1/0.0!z%zcDCCdz%/z(+3!.z"0!.z\*\*!(¥ ing for 0.5 h (Fig. 20, curves 2 and 4) in comparison with the substrate Si(111) due to their more intense transformation into the tetrahedral SiC-bonds. The nonlinear nature of the curve 3 in 0\$!z.!#%+\*zC^HzPzK^Hz\$+1./z)5z!z 1!z0+z0\$!z"+.)0%+\*z+"z0!0.\$! .((5z+.%!\*0! z%w+\* /z%\* the layer simultaneously with their decay at the surface. The saturation of this process after \*\*!(%\*#z 1.%\*#zI^Hz\$+1./z.!/1(0/z%\*zz"/0!.z !.!/!z%\*z0\$!z\*1)!.z+"z+\* /z 1.%\*#z"1.¥ ther annealing.

Ion Synthesis of SiC and Its Instability at High Temperatures http://dx.doi.org/10.5772/ 51389 81

increasing time of high-temperature annealing indicates the decay of the SiC structure, i.e.

Figure 19. EHDALM<=G>0+9F<(+H@GFGFH=9CKG>/AG>%.LJ9FKEAKKAGFN=JKMKL@=9FF=9DAF?LAE=9LL@=L=EH=J9s ture of 1200°C for SiC0.7 layers on silicon substrates of (100) and (111) orientation: 1 – Si(111), TO-phonon peak; 2 -

Since the amplitude of the infrared transmission at the wavenumber 800 cm-1 is proportional 0+z0\$!z+\*!\*0.0%+\*z+"z0\$!z0!0.\$! .((5z+.%!\*0! z%xw+\* /\_z%0/z)#\*%01 !/z3!.!z)!/¥ ured in the spectra after isothermal annealing at the temperature of 1200°C (Fig. 20, curve 3). Assuming that the amplitude at any frequency is proportional to the number of the Si–C- +\* /z3\$%\$z/+.z0z0\$%/z".!-1!\*5\_z0\$!z),(%01 !/z"+.z0\$!zw,\$+\*+\*/z3%0\$z32!\*1)¥ bers 700, 750, 850 and 900 cm-1 (Fig. 20) in the case of incidence of IR radiation to the sample

It is seen in Fig. 20a, b (curves 3) that after annealing at 1200°C for 0.5 hour of the SiC0.7 film on the Si (100) substrate, the amplitude at wavenumber 800 cm-1 is higher than the same for the Si(111) substrate (70 and 58%), indicating a higher content of the tetrahedrally oriented %w+\* /^z 0z%/z(/+z/!!\*z0\$0z0\$!z\*1)!.z+"z%w+\* /z3\$%\$z.!z(+/!z0+z0!0.\$! .(z+.%!\*0¥ tion and absorb at 750 and 850 cm-1\_z%\*z0\$!z/!z+"z0\$!z/1/0.0!z%zcDCCdz%/z(+3!.z"0!.z\*\*!(¥ ing for 0.5 h (Fig. 20, curves 2 and 4) in comparison with the substrate Si(111) due to their more intense transformation into the tetrahedral SiC-bonds. The nonlinear nature of the curve 3 in 0\$!z.!#%+\*zC^HzPzK^Hz\$+1./z)5z!z 1!z0+z0\$!z"+.)0%+\*z+"z0!0.\$! .((5z+.%!\*0! z%w+\* /z%\* the layer simultaneously with their decay at the surface. The saturation of this process after \*\*!(%\*#z 1.%\*#zI^Hz\$+1./z.!/1(0/z%\*zz"/0!.z !.!/!z%\*z0\$!z\*1)!.z+"z+\* /z 1.%\*#z"1.¥

Si(100), TO-phonon peak; 3 - Si(111), LO-phonon peak; 4 - Si(100), LO-phonon peak.

surface at an angle of 73° to the normal were also measured.

ther annealing.

the instability of these films to such regime of treatment.

80 Physics and Technology of Silicon Carbide Devices

Figure 20. 0@=9EHDALM<=G>L@=AF>J9J=<LJ9FKEALL9F;=9L>AP=<O9N=FME:=JKN=JKMKL@=<MJ9LAGFG>AKGL@=JE9D9FF=9Ds ing of the SiC0.7 layer (angle of incidence of infrared rays on the sample is 73° from the normal): 1 – 700 cm-1, 2 – 750 cm-1, 3 – 800 cm-1, 4 – 850 cm-1, 5 – 900 cm-1; a) the substrate orientation Si (100), b) the substrate orientation Si (111).

This process is clearly demonstrated on the time dependence of the area of SiC-peak, which is proportional to the total number of optically active Si–C-bonds (Fig. 21). Although the peak amplitude at the minimum of IR transmission (Fig.19, curve 2) and at 800 cm-1 (Fig.20, curve 3) for the Si substrates with (100) orientation are higher than in the case of (111) orientation, the value of area of SiC-peak for (111) was higher after annealing for 0.5 hours. This is due to a greater half-

Figure 21. The area of the TO-phonon peak of SiC in spectra of the IR transmission versus the annealing time at the temperature of 1200°C for the SiC0.7 layers (angle of incidence of infrared rays on the sample surface - 73° from the normal): 1 - the orientation of the substrate Si(111), 2 – the orientation of the substrate Si(100).

3% 0\$z+"z0\$!z,!'z1/! z5zz/%#\*%"%\*0z)+1\*0z+"z+,0%((5z0%2!z%Pw+\* /z(+/!z0+ tetrahedrally oriented, which absorb at 750 and 850 cm-1 and, probably due to the smaller amount of stable carbon silicon clusters in the film on (111) oriented silicon substrate. It is not contradict to the data for the SiC layer with Gaussian distribution of carbon in silicon, for which was shown that immediately after the implantation of carbon into the (100) and (111) oriented silicon at least 65% and 60% of carbon atoms are concentrated in optically inactive clusters, respectively (see 3.1.2, Fig. 6 "The temperature range 20-600°C"). The strong carbon clusters prevent the crystallization of SiC, and they are less susceptible to oxidation and prevent 0\$!z,!\*!0.0%+\*z+"z+45#!\*z%\*0+z0\$!z%w(5!.^z\$!z%z"%()z+\*zcDCCdz/1/0.0!z\$/z)+.!z-1\*0%¥ ty of stable clusters after implantation and, as a result the smaller value of area of SiC-peak \* z/)((!.z)+1\*0z+"z+,0%((5z0%2!z%Pw+\* /z"0!.z\*\*!(%\*#z"+.zC^Hz\$+1./z\* \_z%0z(!// /1/!,0%(!z0+z+4% 0%+\*z0zDECC[zxzDH^Hz\$zc%\*/0! z+"zDF^Hz\$z"+.zcDDDdz%z/1/0.0!d^z\$!z.!(0%2!(5 rapid decay of close to tetrahedral Si-C bonds (Fig. 20b, curves 2 and 4) led to the decrease 3%0\$z\$%#\$!.z/,!! z+"z0\$!z\*1)!.z+"z+,0%((5z0%2!z%Pw+\* /z%\*z0\$!z/!z+"zcDDDdz+.%!\*0¥ 0%+\*z+"z%z/1/0.0!^z \*z#!\*!.(z 0\$!z !,!\* !\*!z+"z 0\$!z.! 10%+\*z+"z+,0%((5z0%2!z%Pw bonds on the annealing time is linear. This implies that the rapid decay of close to tetrahedral %Pw+\* /z3/z+1..%\*#\_z)%\*(5\_z 1!z0+z0\$!%.z0.\*/"+.)0%+\*z%\*0+zz0!0.\$! .(z+\* ^z\$! linear dependence indicates the homogeneity of the layer, and a rectangular profile of the %/0.%10%+\*z+"z.+\*z0+)/z%\*z/%(%+\*\_z/z3!((z/z0\$!z"0z0\$0z0\$!z !5z.0!z+"z/%(%+\*z.¥ bide does not depend on the depth of the oxidation front. Some decrease in the slope of angle of the curves at the end of the annealing is occurring due to oxidation of the interface "the SiC film – Si substrate".

In our opinion, the frequency shifts of SiC-peak upward indicate a decrease in crystallite size of SiC. We have previously identified size effects, which manifested in the influence of the crystallite sizes of silicon carbide on its optical properties. It was shown (Fig.23) that the differences of the SiC0.03, SiC0.12 and SiC0.4 layers with low carbon concentration from the SiC1.4, SiC0.95 and SiC0.7 layers with high carbon concentration are manifested in the absence +"zw,\$+\*+\*z,!'z+"z %z%\*z 0\$!z z 0.\*/)%//%+\*z /,!0.z \* z%\*z z /\$%"0z 0z DCCC[z+"z)%\*%¥ mum SiC-peak for TO-phonons in the region of wave numbers higher than 800 cm-1\_z\$.¥ teristic for the tetrahedral bonds of crystalline SiC, which is caused by small sizes of SiC .5/0((%0!/zcV 3 nm) and by an increase of contribution in the IR absorption of their surfaces,

Ion Synthesis of SiC and Its Instability at High Temperatures

http://dx.doi.org/10.5772/ 51389

83

Figure 23. 39N=FME:=JG>L@=%.LJ9FKEAKAGFH=9C>GJ0+9F<(+H@GFGFK/A9K9>MF;LAGFG>L@=9FF=9DAF?L=Es

In this case (Fig. 22), the increase of annealing duration of SiC0,7 layer leads to both the shift of the minimum of the IR transmission peak up to 820 cm-1\_z\* z0\$!z.! 10%+\*z+"z0\$!z),(%¥ tude of the LO-phonon peaks and their subsequent disappearance, although SiC0.7z%/z+\*/% ¥ ered as the layer with a high concentration of carbon. At the same time more intense process of the shift of the minimum of SiC-peak occurs after annealing for longer than 8.5 hours, 3\$%\$z(! /z0+z0\$!z %/,,!.\*!z+"z0\$!z,!'z+"zw,\$+\*+\*/^z\$%/z\*z+1.z3\$!\*z0\$!z,!\*!¥ tration of oxygen deep into the layers, their interaction with the carbon atoms on the surface of the crystallites of silicon carbide with the formation of molecules of CO/CO2. Desorption of carbon atoms causes a decrease in the size of the SiC crystallites and their disintegration. With increasing duration of annealing, the homogeneous SiC0.7 layer entirely transforms into

perature: 1 - SiC1.4, 2 - SiC0.95, 3 - SiC0.7, 4 - SiC0.4, 5 - SiC0.12, 6 - SiC0.03.

\* z0\$!z/1."!/z+"z%z.5/0((%0!/z+\*0%\*%\*#z/0.+\*#z/\$+.0z%Pw+\* /z/z3!((^

The value of the wave number of the minimum of SiC-peak of the infrared transmission (the position of the minimum of peak) defines a prevailing kind of optically active bonds which absorb at this wavenumber at this temperature. For the considered layers after annealing at DECC[z"+.zC^Hz\$\_z0\$!z0.\*/)%//%+\*z,!'/z3%0\$z2(1!/z+"z)%\*%)1)z0z32!\*1)!./zKCFz\* KCIz)-1, characteristic of crystalline silicon carbide, are observed (Fig. 22). It was found that with increasing annealing time, the position of the peak minimum varies smoothly and moved in the direction of the wave number increase (Fig. 17 and 22).

Figure 22. Wave number of the minimum of SiC-peak of IR transmission versus the annealing time at 1200°p for the SiC0.7 layers on silicon substrates of (100) and (111) orientations: 1 - Si (111), TO-phonons, 2 - Si(100), TO-phonons, 3 - Si(111), LO-phonons, 4 - Si(100), the LO-phonons.

In our opinion, the frequency shifts of SiC-peak upward indicate a decrease in crystallite size of SiC. We have previously identified size effects, which manifested in the influence of the crystallite sizes of silicon carbide on its optical properties. It was shown (Fig.23) that the differences of the SiC0.03, SiC0.12 and SiC0.4 layers with low carbon concentration from the SiC1.4, SiC0.95 and SiC0.7 layers with high carbon concentration are manifested in the absence +"zw,\$+\*+\*z,!'z+"z %z%\*z 0\$!z z 0.\*/)%//%+\*z /,!0.z \* z%\*z z /\$%"0z 0z DCCC[z+"z)%\*%¥ mum SiC-peak for TO-phonons in the region of wave numbers higher than 800 cm-1\_z\$.¥ teristic for the tetrahedral bonds of crystalline SiC, which is caused by small sizes of SiC .5/0((%0!/zcV 3 nm) and by an increase of contribution in the IR absorption of their surfaces, \* z0\$!z/1."!/z+"z%z.5/0((%0!/z+\*0%\*%\*#z/0.+\*#z/\$+.0z%Pw+\* /z/z3!((^

clusters prevent the crystallization of SiC, and they are less susceptible to oxidation and prevent 0\$!z,!\*!0.0%+\*z+"z+45#!\*z%\*0+z0\$!z%w(5!.^z\$!z%z"%()z+\*zcDCCdz/1/0.0!z\$/z)+.!z-1\*0%¥ ty of stable clusters after implantation and, as a result the smaller value of area of SiC-peak \* z/)((!.z)+1\*0z+"z+,0%((5z0%2!z%Pw+\* /z"0!.z\*\*!(%\*#z"+.zC^Hz\$+1./z\* \_z%0z(!// /1/!,0%(!z0+z+4% 0%+\*z0zDECC[zxzDH^Hz\$zc%\*/0! z+"zDF^Hz\$z"+.zcDDDdz%z/1/0.0!d^z\$!z.!(0%2!(5 rapid decay of close to tetrahedral Si-C bonds (Fig. 20b, curves 2 and 4) led to the decrease 3%0\$z\$%#\$!.z/,!! z+"z0\$!z\*1)!.z+"z+,0%((5z0%2!z%Pw+\* /z%\*z0\$!z/!z+"zcDDDdz+.%!\*0¥ 0%+\*z+"z%z/1/0.0!^z \*z#!\*!.(z 0\$!z !,!\* !\*!z+"z 0\$!z.! 10%+\*z+"z+,0%((5z0%2!z%Pw bonds on the annealing time is linear. This implies that the rapid decay of close to tetrahedral %Pw+\* /z3/z+1..%\*#\_z)%\*(5\_z 1!z0+z0\$!%.z0.\*/"+.)0%+\*z%\*0+zz0!0.\$! .(z+\* ^z\$! linear dependence indicates the homogeneity of the layer, and a rectangular profile of the %/0.%10%+\*z+"z.+\*z0+)/z%\*z/%(%+\*\_z/z3!((z/z0\$!z"0z0\$0z0\$!z !5z.0!z+"z/%(%+\*z.¥ bide does not depend on the depth of the oxidation front. Some decrease in the slope of angle of the curves at the end of the annealing is occurring due to oxidation of the interface "the SiC

The value of the wave number of the minimum of SiC-peak of the infrared transmission (the position of the minimum of peak) defines a prevailing kind of optically active bonds which absorb at this wavenumber at this temperature. For the considered layers after annealing at DECC[z"+.zC^Hz\$\_z0\$!z0.\*/)%//%+\*z,!'/z3%0\$z2(1!/z+"z)%\*%)1)z0z32!\*1)!./zKCFz\* KCIz)-1, characteristic of crystalline silicon carbide, are observed (Fig. 22). It was found that with increasing annealing time, the position of the peak minimum varies smoothly and moved

Figure 22. Wave number of the minimum of SiC-peak of IR transmission versus the annealing time at 1200°p for the SiC0.7 layers on silicon substrates of (100) and (111) orientations: 1 - Si (111), TO-phonons, 2 - Si(100), TO-phonons, 3 -

in the direction of the wave number increase (Fig. 17 and 22).

Si(111), LO-phonons, 4 - Si(100), the LO-phonons.

film – Si substrate".

82 Physics and Technology of Silicon Carbide Devices

Figure 23. 39N=FME:=JG>L@=%.LJ9FKEAKAGFH=9C>GJ0+9F<(+H@GFGFK/A9K9>MF;LAGFG>L@=9FF=9DAF?L=Es perature: 1 - SiC1.4, 2 - SiC0.95, 3 - SiC0.7, 4 - SiC0.4, 5 - SiC0.12, 6 - SiC0.03.

In this case (Fig. 22), the increase of annealing duration of SiC0,7 layer leads to both the shift of the minimum of the IR transmission peak up to 820 cm-1\_z\* z0\$!z.! 10%+\*z+"z0\$!z),(%¥ tude of the LO-phonon peaks and their subsequent disappearance, although SiC0.7z%/z+\*/% ¥ ered as the layer with a high concentration of carbon. At the same time more intense process of the shift of the minimum of SiC-peak occurs after annealing for longer than 8.5 hours, 3\$%\$z(! /z0+z0\$!z %/,,!.\*!z+"z0\$!z,!'z+"zw,\$+\*+\*/^z\$%/z\*z+1.z3\$!\*z0\$!z,!\*!¥ tration of oxygen deep into the layers, their interaction with the carbon atoms on the surface of the crystallites of silicon carbide with the formation of molecules of CO/CO2. Desorption of carbon atoms causes a decrease in the size of the SiC crystallites and their disintegration. With increasing duration of annealing, the homogeneous SiC0.7 layer entirely transforms into SiO2, and then goes the oxidation of the interface "SiC film – Si substrate", in which the car bon concentration decreases uniformly with depth according to a Gaussian law. Thus, the concentration of carbon in the remaining layer begins to decrease. This leads to the appearance of phenomenon which is characteristic for the SiCo12 SiCo03 layers, namely, to shift of the minimum of the IR transmission peak up to 820 cm+, and to a decrease of the amplitude of the LO-phonon peak and their subsequent disappearance. Thus, size effects are confirmed, published by us in 2011.

### 3.3. Parameters of SiC and C films on Si substrates synthesized by magnetron and ionbeam sputtering

#### 3.3.1. Parameters of C films on Si substrates synthesized by by magnetron sputtering

Carbon thin films were obtained by reactive magnetron sputtering using an ARC 2000 system. A graphite target with a diameter ~50 mm and a thickness of 3 mm was used. The magnetron sputtering mode parameters were: cathode voltage U = 470 V, the ion beam current Ion = 35 mA and the argon pressure inside the chamber ~1 Pa. The carbon films were deposited on a set of cleaned silicon substrates. The temperature of the substrate was 75°C.

The presence of a sharp interface "C film - Si substrate" permits to investigate the thickness and density of the film by X-ray reflectometry (CompleXRay C6) by recording the angular dependence of the reflection coefficient using two spectral lines CuK。 (0.154 nm) and CuKo (0.139 nm). The oscillations of intensity were observed, assigned to the interference of X-ray reflections from the boundaries of carbon layer (Fig. 24).

It is known that the density of graphite is 2.2 g/cm³ and the density of diamond - 3.51 g/cm³. Since the density of the resulting film was 3.32 g/cm³ (Table 5 and Fig.24), we concluded that the diamond-like carbon film was synthesized.


Table 5. Determination of the density of the carbon layer by X-ray reflectometry and using the Henke program.

To determine the thickness, five narrow peaks of C, and a broad band of C were used (Fig. 24, table 5).


Table 6. Determination of the thickness of the layers in the system (C - C - Si) by X-ray reflectometry.

Simulation using the Henke program (http://henke.lbl.gov/optical\_constants/) [24] allows to obtain a theoretical curve, which is close to the experimental (Fig.25). The main parameters of the layer system, which allow to obtain an acceptable agreement of experimental and theoretical curves, were:


Thus, diamond-like carbon film of thickness d = 84 nm, density o = 3.3 g/cm³, and surface roughness of o = 1.5 nm on a silicon surface by magnetron sputtering was synthesized.

Figure 24. X-ray reflectometry using two spectral lines CuK, (0.139 nm) (CompleXRay C6) of parameters of carbon films synthesized by magnetron sputtering: a) sample B.

Figure 25. Simulation using the Henke program [24] of experimental results obtained by X-ray reflectometry of parameters of carbon films synthesized by magnetron sputtering.

#### 3.3.2. Parameters of SiC films on Si substrates synthesized by by ion-beam sputtering

SiC films were prepared by ion-beam sputtering. For the simultaneous deposition on silicon substrates of C and Si atoms, a two-component target consisting of the overlapping wafers of silicon and graphite was used. Sputtering of the target was carried out in an argon atmosphere. The formation of Ar ion beam was happening in the ring electrode system (a hollow cathode and an anode), and magnets with crossed electrical and magnetic fields. Discharge power was 108 W (2.7 kV, 40 mA), argon pressure in the chamber 5.9×102 Pa, substrate temperature - 20℃. Samples with SiC films were annealed at 1250℃ in an argon atmosphere for 30 min.

The presence of a sharp interface "the SiC film - Si substrate" permits to investigate the thickness and density of the film by X-ray reflectometry ("ComplexXRay C6"). The oscillations of intensity were observed, assigned to the interference of X-ray reflections from the boundaries of silicon carbide layer (Fig. 26). It is known that the density of graphite is 2.2 g/cm³, and of silicon - 2.33 g/cm³, of silicon carbide - 3.2 g/cm³ and of diamond - 3.51 g/cm³. Since the density of the obtained film was 3.03 g/cm³ (Table 6 and Fig.26), we concluded, that the film close to silicon carbide, was synthesized. The film contains approximately [(3.03-2.33)/ (3.2-2.33)] × 100% = 80.5% SiC, and [(3.2-3.03)/(3.2-2.33)] × 100% = 19.5% Si, i.e., about 80 atoms of C refer per 100 atoms of Si and the SiCgs layer was formed.


Table 7. Determination of the SiC layer by X-ray reflectometry and using the Henke program.

To determine the film thickness the position of maxima of five narrow peaks of SIC was used (Fig.26).


Table 8. Determination of the thickness of the layer in the system (SiC – Si) by X-ray reflectometry.

Simulation using the Henke program (http://henke.lbl.gov/optical\_constants/) [24] allows obtaining a theoretical curve, which is close to the experimental (Fig.27). The main parameters of the layer system, which allow to obtain an acceptable agreement of experimental and theoretical curves, were:


Figure 26. X-ray reflectometry using two spectral lines CuK, (0.139 nm) (CompleXRay C6) parameters of silicon carbide films synthesized by ion-beam sputtering of the two-component target of silicon and graphite.

The film thickness d = 160 nm is different from the values of 180 nm, obtained from the average distance between the peaks 20 ... The reasons for the differences require further studies.

Thus, the silicon carbide film of thickness d = 160 nm, the density o = 3.03 g/cm³, and surface roughness of σ = 0.4 nm on the silicon surface by ion-beam sputtering of the two-component target of silicon and graphite was synthesized.

Figure 27. Simulation using the Henke program [24] of experimental results obtained by X-ray reflectometry of parameters of SiC films synthesized by ion-beam sputtering of the two-component target of silicon and graphite.

#### Conclusion

	- 20-600°C the formation of tetrahedrally oriented Si-C-bonds due to disintegration of clusters which consist mainly of the Si-Si, Si=Si and elongated Si-C-bonds;
	- 600-800°C the formation of Si crystallites and tetrahedrally oriented Si-C-bonds due to disintegration of strained Si-Si bonds and Si-C-bonds, which absorb at frequencies close to 700 and 750 cm², recrystallization starts near the substrate and the surface and goes to the middle of layer;
	- · 800-1000°C begins to dominate the absorption at 800 cm², and near it, due to formation of tetrahedrally oriented bonds of the SiC crystallites, as well as bonds close to tetrahedral;
	- 1000–1100°C the growth of the crystallite size through consolidation of small crystallites of Si and SiC; decay of Si-C-bonds absorbing at 850 and 900 cm³;
