3.5. Surface morphology

Figure 19. shows the surface morphology of the Si-face of 4H-silicon carbide before and after the etching at the chlorine trifluoride gas concentration of 100 % and at the flow rate of 0.1 slm. The etching was performed at the substrate temperatures of (b) 570, (c) 620, (d) 770, (e) 970, (f) 1270, (g) 1370 and (h) 1570 K. The etched depth was 5-18 µm.

Figure 19 (a) /\$+3/z0\$!z/1."!z)+.,\$+(+#5z+"z0\$!z%w"!z+"zGw/%(%+\*z.% !z/1/0.0!z!¥ fore the etching. Figure 19 (b) shows that there are many small pits after the etching at 570 K. At 620 K, the pits are very large, nearly 50 µm in diameter, as shown in Figure 19 (c). With the increasing temperature, the pits tends to become small and shallow, as shown in Figures 19 (d) - (h). The pit diameter after etching at 770 K, shown in Figure 19 (d), is nearly DCzMz+"z0\$0z0zIECz\_z/\$+3\*z%\*z%#1.!zDLzcd^z%#1.!zDLzc!dz/\$+3/z0\$0z0\$!z,%0z %)!0!.z!¥ comes even smaller and the pit density decreases at 970 K. This trend is very clear at the temperatures higher than 1270 K, as shown in Figures 19 (f), (g) and (h). Figure 19 (g) shows that the pit density significantly decreases at 1370 K. The sharp-shaped pits, presented at the lower temperatures, are not there, on the silicon carbide surface after the etching at 1570 K, as shown in Figure 19 (h).

Figure 20. Surface morphology of Si-face 4H-silicon carbide surface (a) before and after etching at the total gas flow rate of 0.2 slm, 1370 K and various chlorine trifluoride gas concentrations of (b) 100, (c) 50, (d) 20, (e) 10 and (f) 1%,

Although there are many large pits at the chlorine trifluoride gas concentration of 100%, as shown in Figure 20 (b), they become significantly small and less at 20%, as shown in Figure 20 (d). Figure 20 (e) shows that the surface etched at 10% is flat with only a small number of

centration of 1% diluted in ambient nitrogen at the substrate temperature of 1570 K and at the total flow rate of 4

From Figures 19 and 20, the Si-face 4H-silicon carbide surface after etching tends to be flat 3%0\$z 0\$!z%\*.!/%\*#z 0!),!.01.!z\* z !.!/%\*#z\$(+.%\*!z 0.%"(1+.% !z#/z+\*!\*0.0%+\*^z+(¥

=L;@=<>GJEAFMKAF?L@=;@DGJAF=LJA>DMGJA<=?9K;GFs

Etching of Silicon Carbide Using Chlorine Trifluoride Gas

http://dx.doi.org/10.5772/50387

117

pits. At 1%, most of the surface is flat, except for scratches, as shown in Figure 20 (f).

Figure 21. ")H@GLG?J9H@G>/A>9;=G>\$KADA;GF;9J:A<=

slm. (a): plan view, (b): A-A' cross section, and (c): B-B' cross section.

for 5 min.

Figure 19. /MJ>9;=EGJH@GDG?QG>/A>9;=G>\$KADA;GF;9J:A<=9:=>GJ=9F<9>L=JL@==L;@AF?MKAF?;@DGJAF=LJA>DMGJs ide gas at the concentration of 100 %, at the substrate temperature of (b) 570, (c) 620, (d) 770, (e) 970, (f) 1270, (g) 9F<@'9F<9LL@=>DGOJ9L=G>KDE0@==L;@=<<=HL@AKeE

!40\_z0\$!z%\*"(1!\*!z+"z\$(+.%\*!z0.%"(1+.% !z#/z+\*!\*0.0%+\*z+\*z0\$!z/1."!z)+.,\$+(+#5z%/z!4¥ plained. Figure 20 shows the surface morphology of the Si-face 4H-silicon carbide surface taken by the optical microscope before and after the etching for 5 min at the total flow rate +"zC^Ez/()\_z0z0\$!z/1/0.0!z0!),!.01.!z+"zDFJCzz\* z0z2.%+1/z\$(+.%\*!z0.%"(1+.% !z#/z+\*¥ centrations. Figure 20 (a) shows the surface morphology of the Si-face of 4H-silicon carbide before the etching.

3.5. Surface morphology

116 Physics and Technology of Silicon Carbide Devices

as shown in Figure 19 (h).

before the etching.

Figure 19. shows the surface morphology of the Si-face of 4H-silicon carbide before and after the etching at the chlorine trifluoride gas concentration of 100 % and at the flow rate of 0.1 slm. The etching was performed at the substrate temperatures of (b) 570, (c) 620, (d) 770, (e)

Figure 19 (a) /\$+3/z0\$!z/1."!z)+.,\$+(+#5z+"z0\$!z%w"!z+"zGw/%(%+\*z.% !z/1/0.0!z!¥ fore the etching. Figure 19 (b) shows that there are many small pits after the etching at 570 K. At 620 K, the pits are very large, nearly 50 µm in diameter, as shown in Figure 19 (c). With the increasing temperature, the pits tends to become small and shallow, as shown in Figures 19 (d) - (h). The pit diameter after etching at 770 K, shown in Figure 19 (d), is nearly DCzMz+"z0\$0z0zIECz\_z/\$+3\*z%\*z%#1.!zDLzcd^z%#1.!zDLzc!dz/\$+3/z0\$0z0\$!z,%0z %)!0!.z!¥ comes even smaller and the pit density decreases at 970 K. This trend is very clear at the temperatures higher than 1270 K, as shown in Figures 19 (f), (g) and (h). Figure 19 (g) shows that the pit density significantly decreases at 1370 K. The sharp-shaped pits, presented at the lower temperatures, are not there, on the silicon carbide surface after the etching at 1570 K,

Figure 19. /MJ>9;=EGJH@GDG?QG>/A>9;=G>\$KADA;GF;9J:A<=9:=>GJ=9F<9>L=JL@==L;@AF?MKAF?;@DGJAF=LJA>DMGJs ide gas at the concentration of 100 %, at the substrate temperature of (b) 570, (c) 620, (d) 770, (e) 970, (f) 1270, (g)

!40\_z0\$!z%\*"(1!\*!z+"z\$(+.%\*!z0.%"(1+.% !z#/z+\*!\*0.0%+\*z+\*z0\$!z/1."!z)+.,\$+(+#5z%/z!4¥ plained. Figure 20 shows the surface morphology of the Si-face 4H-silicon carbide surface taken by the optical microscope before and after the etching for 5 min at the total flow rate +"zC^Ez/()\_z0z0\$!z/1/0.0!z0!),!.01.!z+"zDFJCzz\* z0z2.%+1/z\$(+.%\*!z0.%"(1+.% !z#/z+\*¥ centrations. Figure 20 (a) shows the surface morphology of the Si-face of 4H-silicon carbide

9F<@'9F<9LL@=>DGOJ9L=G>KDE0@==L;@=<<=HL@AKeE

970, (f) 1270, (g) 1370 and (h) 1570 K. The etched depth was 5-18 µm.

Figure 20. Surface morphology of Si-face 4H-silicon carbide surface (a) before and after etching at the total gas flow rate of 0.2 slm, 1370 K and various chlorine trifluoride gas concentrations of (b) 100, (c) 50, (d) 20, (e) 10 and (f) 1%, for 5 min.

Although there are many large pits at the chlorine trifluoride gas concentration of 100%, as shown in Figure 20 (b), they become significantly small and less at 20%, as shown in Figure 20 (d). Figure 20 (e) shows that the surface etched at 10% is flat with only a small number of pits. At 1%, most of the surface is flat, except for scratches, as shown in Figure 20 (f).

Figure 21. ")H@GLG?J9H@G>/A>9;=G>\$KADA;GF;9J:A<= =L;@=<>GJEAFMKAF?L@=;@DGJAF=LJA>DMGJA<=?9K;GFs centration of 1% diluted in ambient nitrogen at the substrate temperature of 1570 K and at the total flow rate of 4 slm. (a): plan view, (b): A-A' cross section, and (c): B-B' cross section.

From Figures 19 and 20, the Si-face 4H-silicon carbide surface after etching tends to be flat 3%0\$z 0\$!z%\*.!/%\*#z 0!),!.01.!z\* z !.!/%\*#z\$(+.%\*!z 0.%"(1+.% !z#/z+\*!\*0.0%+\*^z+(¥ lowing this trend, the Si-face 4H-silicon carbide surface is etched at 1570 K at the chlorine trifluoride gas concentration of 1% for 0.5 min. Figure 21 shows the AFM photograph of the etched surface. Figures 21 (a), (b) and (c) are the plan view, A-A' cross section and B-B' cross section, respectively. Although the etched depth is only about 0.03 µm, it can reveal the trend of the surface, causing pit or not. As shown in Figure 21 (a), this surface does not show \*5z!0\$z,%0az%#1.!/zEDzcdz\* zcdz/\$+3/z\*+z,!.%+ %(z/\$,!z.!"(!0%\*#z0\$!zGw/%(%+\*z.¥ bide crystal step [42]. The root-mean-square (RMS) roughness are 0.1 and 0.2 nm on A-A' (%\*!z\* zwjz(%\*!\_z.!/,!0%2!(5\_z3\$%\$z.!z+),.(!z0+z0\$0z+"z0\$!z,+(%/\$! zGw/%(%+\*z.¥ bide substrate surface. Thus, the shallow etching for removing thin layer, such as damaged layer, is possible with maintaining the specular surface of the Si-face of 4H-silicon carbide.

face 4H-silicon carbide surface before and after the etching for 5 min at the various chlorine trifluoride gas concentrations of (b) 100, (c) 50, (d) 20, (e) 10 and (f) 1% at the total flow rate

Etching of Silicon Carbide Using Chlorine Trifluoride Gas

http://dx.doi.org/10.5772/50387

119

Figure 23. Surface morphology of C-face 4H-silicon carbide surface before and after etching at the total gas flow rate of 0.2 slm, 1370 K and various chlorine trifluoride gas concentrations for 5 min. (a) before etching, (b) 100, (c) 50, (d)

centration of 1% diluted in ambient nitrogen at the substrate temperature of 1570 K and at the total flow rate of 4

=L;@=<>GJEAFMKAF?L@=;@DGJAF=LJA>DMGJA<=?9K;GFs

=9F<>!L;@=<<=HL@AKeE

Figure 24. ")H@GLG?J9H@G>>9;=G>\$KADA;GF;9J:A<=

slm. (a): plan view, (b): A-A' cross section, and (c): B-B' cross section.

of 0.2 slm. The substrate temperature is fixed at 1370 K. The etched depth is 3-84 µm.

Figure 22. shows the surface morphology of the C-face of 4H-silicon carbide before and after the etching at the chlorine trifluoride gas concentration of 100 %, at (b) 570, (c) 620, (d) 770, (e) 1070, (f) 1270, (g) 1370 and (h) 1570 K and at the flow rate of 0.1 slm. The etched depth is 10-30 µm. Figure 22 (a) is the C-face 4H-silicon carbide surface before the etching.

Figure 22. /MJ>9;=EGJH@GDG?QG>>9;=G>\$KADA;GF;9J:A<=9:=>GJ=9F<9>L=JL@==L;@AF?MKAF?;@DGJAF=LJA>DMGJs ide gas at the concentration of 100 %, at the substrate temperature of (b) 570, (c) 620, (d) 770, (e) 1070, (f) 1270, (g) 9F<@'9F<9LL@=>DGOJ9L=G>KDE!L;@=<<=HL@AKeE

\$!.!z%/z0\$!z"(0z/1."!z"0!.z0\$!z!0\$%\*#z0zHJCz\_z/z/\$+3\*z%\*z%#1.!zEEzcd\_z!1/!z+"z/%#¥ nificantly small etching rate. However, Figure 22 (c) shows that pits are produced at 620 K. The surface etched at the temperatures between 770 K and 1270 K have many small pits, as /\$+3\*z%\*z%#1.!/z EE^z c d\_z c!dz \* z c"d^z%#1.!/z EEz c#dz \* z c\$dz/\$+3z 0\$0z 0\$!z,%0z %)!0!.z !¥ creases at the temperatures higher than 1370 K. The surface etched at 1570 K shows a flat surface as shown in Figure 22 (h).

Next, the influence of the chlorine trifluoride gas concentration on the surface morphology of the C-face of 4H-silicon carbide is explained. Figure 23 shows the morphology of the C- face 4H-silicon carbide surface before and after the etching for 5 min at the various chlorine trifluoride gas concentrations of (b) 100, (c) 50, (d) 20, (e) 10 and (f) 1% at the total flow rate of 0.2 slm. The substrate temperature is fixed at 1370 K. The etched depth is 3-84 µm.

lowing this trend, the Si-face 4H-silicon carbide surface is etched at 1570 K at the chlorine trifluoride gas concentration of 1% for 0.5 min. Figure 21 shows the AFM photograph of the etched surface. Figures 21 (a), (b) and (c) are the plan view, A-A' cross section and B-B' cross section, respectively. Although the etched depth is only about 0.03 µm, it can reveal the trend of the surface, causing pit or not. As shown in Figure 21 (a), this surface does not show \*5z!0\$z,%0az%#1.!/zEDzcdz\* zcdz/\$+3/z\*+z,!.%+ %(z/\$,!z.!"(!0%\*#z0\$!zGw/%(%+\*z.¥ bide crystal step [42]. The root-mean-square (RMS) roughness are 0.1 and 0.2 nm on A-A'

bide substrate surface. Thus, the shallow etching for removing thin layer, such as damaged layer, is possible with maintaining the specular surface of the Si-face of 4H-silicon carbide.

Figure 22. shows the surface morphology of the C-face of 4H-silicon carbide before and after the etching at the chlorine trifluoride gas concentration of 100 %, at (b) 570, (c) 620, (d) 770, (e) 1070, (f) 1270, (g) 1370 and (h) 1570 K and at the flow rate of 0.1 slm. The etched depth is

Figure 22. /MJ>9;=EGJH@GDG?QG>>9;=G>\$KADA;GF;9J:A<=9:=>GJ=9F<9>L=JL@==L;@AF?MKAF?;@DGJAF=LJA>DMGJs ide gas at the concentration of 100 %, at the substrate temperature of (b) 570, (c) 620, (d) 770, (e) 1070, (f) 1270, (g)

\$!.!z%/z0\$!z"(0z/1."!z"0!.z0\$!z!0\$%\*#z0zHJCz\_z/z/\$+3\*z%\*z%#1.!zEEzcd\_z!1/!z+"z/%#¥ nificantly small etching rate. However, Figure 22 (c) shows that pits are produced at 620 K. The surface etched at the temperatures between 770 K and 1270 K have many small pits, as /\$+3\*z%\*z%#1.!/z EE^z c d\_z c!dz \* z c"d^z%#1.!/z EEz c#dz \* z c\$dz/\$+3z 0\$0z 0\$!z,%0z %)!0!.z !¥ creases at the temperatures higher than 1370 K. The surface etched at 1570 K shows a flat

Next, the influence of the chlorine trifluoride gas concentration on the surface morphology of the C-face of 4H-silicon carbide is explained. Figure 23 shows the morphology of the C-

9F<@'9F<9LL@=>DGOJ9L=G>KDE!L;@=<<=HL@AKeE

surface as shown in Figure 22 (h).

10-30 µm. Figure 22 (a) is the C-face 4H-silicon carbide surface before the etching.

jz(%\*!\_z.!/,!0%2!(5\_z3\$%\$z.!z+),.(!z0+z0\$0z+"z0\$!z,+(%/\$! zGw/%(%+\*z.¥

(%\*!z\* z-

w-

118 Physics and Technology of Silicon Carbide Devices

Figure 23. Surface morphology of C-face 4H-silicon carbide surface before and after etching at the total gas flow rate of 0.2 slm, 1370 K and various chlorine trifluoride gas concentrations for 5 min. (a) before etching, (b) 100, (c) 50, (d) =9F<>!L;@=<<=HL@AKeE

Figure 24. ")H@GLG?J9H@G>>9;=G>\$KADA;GF;9J:A<= =L;@=<>GJEAFMKAF?L@=;@DGJAF=LJA>DMGJA<=?9K;GFs centration of 1% diluted in ambient nitrogen at the substrate temperature of 1570 K and at the total flow rate of 4 slm. (a): plan view, (b): A-A' cross section, and (c): B-B' cross section.

%#1.!zEFzcdz/\$+3/z0\$0z0\$!zw"!zGw/%(%+\*z.% !z/1."!z\$/z(.#!z\* z/\$((+3z,%0/z"¥ ter etching at the chlorine trifluoride gas concentration of 100%. As shown in Figure 23 (c), the etch pits become shallow at the chlorine trifluoride gas concentration of 50%. Figures 23 (d), (e) and (f) /\$+3z0\$0z0\$!z!0\$! z/1."!z%/z!\*0%.!(5z"(0z0z0\$!z\$(+.%\*!z0.%"(1+.% !z#/z+\*¥ centrations less than 20%. Particularly, the surface etched at 1% is flat, as shown in Figure 23 (f). Overall, the trend in the etched surface morphology of the C-face of 4H-silicon carbide is /%)%(.z0+z0\$0z+"z0\$!z%w"!z+"zGw/%(%+\*z.% !\_z(0\$+1#\$z0\$!z,%0z/%6!z+"z0\$!zw"!z%/z/)((¥ er than that of Si-face.

Assuming that the etchant gas concentration is the same in the perfect region and at the weak spot, the pit depth is expressed in Eq. (8), taking into account that ]S is very small.

) <sup>=</sup>*V*E(exp( ]

Here, assuming that *V* <sup>E</sup> shown in Figure 14 %/z0\$!z!0\$%\*#z.0!z%\*z0\$!z,!."!0z.!#%+\*\_z0\$!z\*+.¥ malized pit depth, *h*, is evaluated and shown in Figure 25. The *h* value is defined using the

> *V*E

)*Pitdepth* MAX

=

( *<sup>V</sup>*E,

In Figure 25, the *h* value at the temperatures lower than 500 K is very small; it significantly increases near 700 K. After showing its maximum, the *h* value gradually decreases with the increasing substrate temperature. Near 1600 K, the *h* value is significantly smaller than the maximum value. This trend qualitatively agrees with that of the 4H-silicon carbide surface !0\$! z1/%\*#z\$(+.%\*!z0.%"(1+.% !z#/^z\$1/\_z0\$!z/1."!z)+.,\$+(+#5z0.!\* z+2!.z3% !z0!),!.¥

Figure 25. Normalized pit depth and temperature-dependent surface morphology behavior following the rate theory.

) 1) *V*<sup>E</sup>

]

Etching of Silicon Carbide Using Chlorine Trifluoride Gas

(8)

http://dx.doi.org/10.5772/50387

(9)

121

*Pitdepth* <sup>=</sup>*V*E( *<sup>k</sup>*<sup>W</sup> *k*<sup>P</sup>

where *V* E is the etching rate in the perfect region.

maximum value of the pit depth, in Eq. (9).

*k*P

*<sup>h</sup>* <sup>=</sup> *Pitdepth Pitdepth* MAX

ature range can be understood mainly by the rate process.

%)%(.z0+z0\$!z%w"!zGw/%(%+\*z.% !z/1."!\_z0\$!zw"!zGw/%(%+\*z.% !z/1."!z%/z!0\$¥ ed at 1570 K at the chlorine trifluoride gas concentration of 1% for 0.5 min. Figures 24 (a), (b) and (c) are the AFM photographs of the plan view, A-A' cross section and B-B' cross section, respectively. The etched depth is near 0.03 µm. Figure 24 (a) does not show any shape like an etch pit; Figures 24 (b) and (c) show no periodical shape reflecting the 4H-silicon carbide crystal step [42f^z\$!z
z.+1#\$\*!//z%/zC^Gz\* zC^Fz\*)z+\*zwjz(%\*!z\* zwjz(%\*!\_z.!/,!0%2!¥ ly, which are comparable to that of the polished 4H-silicon carbide substrate surface. Thus, the shallow etching without producing any trace of pit shape is possible, for the C-face of 4H-silicon carbide.

#### 3.6. Surface morphology behavior and its rate process

Entire surface morphology behavior changing with the substrate temperature for Si-face and w"!z +"z Gz /%(%+\*z .% !z%/z /1)).%6! z /z c%dz 2!.5z /)((z \$\*#!z 0z 2!.5z(+3z 0!),!.¥ tures (lower than 570 K), (ii) significant pit formation between 570 K and 1270 K, and (iii) pit formation reduced at high temperatures (higher than 1370 K).

The process of pit formation is described following the rate theory, assuming that the etch pit is formed due to the difference of the etching rate between the perfect crystal region and the weak spot having any kinds of damage and crystalline defect [10].

The rate constant of the etching in the perfect crystal region, *k* P, is assumed to be expressed in Eq. (6).

$$k\_P = A \exp\left(-\frac{E}{RT}\right) \tag{6}$$

where *A* is the pre-exponential factor, *E* is the activation energy, *R* is the gas constant, and *T* is the substrate temperature. In contrast to this, the weak spot, which has larger etching rate to cause pit, is assumed to have the slightly smaller activation energy than that in the perfect region. The rate constant at the weak spot, *k* W, is assumed to be expressed in Eq. (7), using 0\$!z %""!.!\*!z+"z0\$!z0%20%+\*z!\*!.#5z".+)z0\$0z%\*z0\$!z,!."!0z.!#%+\*\_z*E*.

$$k\_W = A \exp\left(-\frac{E - \Delta E}{RT}\right) \tag{7}$$

Assuming that the etchant gas concentration is the same in the perfect region and at the weak spot, the pit depth is expressed in Eq. (8), taking into account that ]S is very small.

$$\text{Pit}\,\text{depth} = V\_{\text{E}} \left( \frac{k\_{\text{W}} - k\_{\text{P}}}{k\_{\text{P}}} \right) = V\_{\text{E}} \left( \exp\left(\frac{\Delta E}{RT}\right) - 1 \right) \cong V\_{\text{E}} \frac{\Delta E}{RT} \tag{8}$$

where *V* E is the etching rate in the perfect region.

%#1.!zEFzcdz/\$+3/z0\$0z0\$!zw"!zGw/%(%+\*z.% !z/1."!z\$/z(.#!z\* z/\$((+3z,%0/z"¥ ter etching at the chlorine trifluoride gas concentration of 100%. As shown in Figure 23 (c), the etch pits become shallow at the chlorine trifluoride gas concentration of 50%. Figures 23 (d), (e) and (f) /\$+3z0\$0z0\$!z!0\$! z/1."!z%/z!\*0%.!(5z"(0z0z0\$!z\$(+.%\*!z0.%"(1+.% !z#/z+\*¥ centrations less than 20%. Particularly, the surface etched at 1% is flat, as shown in Figure 23 (f). Overall, the trend in the etched surface morphology of the C-face of 4H-silicon carbide is /%)%(.z0+z0\$0z+"z0\$!z%w"!z+"zGw/%(%+\*z.% !\_z(0\$+1#\$z0\$!z,%0z/%6!z+"z0\$!zw"!z%/z/)((¥

%)%(.z0+z0\$!z%w"!zGw/%(%+\*z.% !z/1."!\_z0\$!zw"!zGw/%(%+\*z.% !z/1."!z%/z!0\$¥ ed at 1570 K at the chlorine trifluoride gas concentration of 1% for 0.5 min. Figures 24 (a), (b) and (c) are the AFM photographs of the plan view, A-A' cross section and B-B' cross section, respectively. The etched depth is near 0.03 µm. Figure 24 (a) does not show any shape like an etch pit; Figures 24 (b) and (c) show no periodical shape reflecting the 4H-silicon carbide

ly, which are comparable to that of the polished 4H-silicon carbide substrate surface. Thus, the shallow etching without producing any trace of pit shape is possible, for the C-face of

Entire surface morphology behavior changing with the substrate temperature for Si-face and w"!z +"z Gz /%(%+\*z .% !z%/z /1)).%6! z /z c%dz 2!.5z /)((z \$\*#!z 0z 2!.5z(+3z 0!),!.¥ tures (lower than 570 K), (ii) significant pit formation between 570 K and 1270 K, and (iii) pit

The process of pit formation is described following the rate theory, assuming that the etch pit is formed due to the difference of the etching rate between the perfect crystal region and

The rate constant of the etching in the perfect crystal region, *k* P, is assumed to be expressed

where *A* is the pre-exponential factor, *E* is the activation energy, *R* is the gas constant, and *T* is the substrate temperature. In contrast to this, the weak spot, which has larger etching rate to cause pit, is assumed to have the slightly smaller activation energy than that in the perfect region. The rate constant at the weak spot, *k* W, is assumed to be expressed in Eq. (7), using

*<sup>k</sup>*<sup>P</sup> <sup>=</sup> *<sup>A</sup>*exp( *<sup>E</sup>*

*<sup>k</sup>*<sup>W</sup> <sup>=</sup> *<sup>A</sup>*exp( *<sup>E</sup>* ]*<sup>E</sup>*

w-

*RT* ) (6)

*RT* ) (7)

jz(%\*!\_z.!/,!0%2!¥

crystal step [42f^z\$!z
z.+1#\$\*!//z%/zC^Gz\* zC^Fz\*)z+\*zwjz(%\*!z\* z-

3.6. Surface morphology behavior and its rate process

formation reduced at high temperatures (higher than 1370 K).

the weak spot having any kinds of damage and crystalline defect [10].

0\$!z %""!.!\*!z+"z0\$!z0%20%+\*z!\*!.#5z".+)z0\$0z%\*z0\$!z,!."!0z.!#%+\*\_z*E*.

er than that of Si-face.

120 Physics and Technology of Silicon Carbide Devices

4H-silicon carbide.

in Eq. (6).

Here, assuming that *V* <sup>E</sup> shown in Figure 14 %/z0\$!z!0\$%\*#z.0!z%\*z0\$!z,!."!0z.!#%+\*\_z0\$!z\*+.¥ malized pit depth, *h*, is evaluated and shown in Figure 25. The *h* value is defined using the maximum value of the pit depth, in Eq. (9).

$$h = \frac{\text{Pit} \, depth}{\text{Pit} \, depth\_{\text{MAX}}} = \frac{\frac{V\_{\text{E}}}{T}}{\left(\frac{V\_{\text{E}\_r}}{T}\right)\_{\text{Pit} \, depth\_{\text{MAX}}}} \tag{9}$$

In Figure 25, the *h* value at the temperatures lower than 500 K is very small; it significantly increases near 700 K. After showing its maximum, the *h* value gradually decreases with the increasing substrate temperature. Near 1600 K, the *h* value is significantly smaller than the maximum value. This trend qualitatively agrees with that of the 4H-silicon carbide surface !0\$! z1/%\*#z\$(+.%\*!z0.%"(1+.% !z#/^z\$1/\_z0\$!z/1."!z)+.,\$+(+#5z0.!\* z+2!.z3% !z0!),!.¥ ature range can be understood mainly by the rate process.

Figure 25. Normalized pit depth and temperature-dependent surface morphology behavior following the rate theory.

### 3.7. Etch pits and crystalline defect

AFM photographs of the pit shape formed by the chlorine trifluoride gas are shown in %#¥ ure 26. Figures 26 (a) and (b) show the pits on the Si-face and C-face, respectively, after the etching using the chlorine trifluoride gas (100%) at atmospheric pressure for 3 min at 870 K and 0.3 slm. Figure 26 (c) is the etch pit of Figure 26 (a), the edge of which is traced using dotted line.

Figure 27. Comparison between the X-ray topograph and the etched Si-face 4H-silicon carbide surface. (a) X-ray topograph of the Si-face 4H silicon carbide surface, and (b) the Si-face 4H-silicon carbide surface etched using chlorine trifluoride gas at 100% and at 700 K for 60 min. Arrows in this figure indicate the spot in the X-ray topograph and the

Figure 28. GEH9JAKGF:=LO==FL@=4J9QLGHG?J9H@9F<L@==L;@=<>9;=\$KADA;GF;9J:A<=KMJ>9;=94J9QLGHGs

fluoride gas at 100% and at 700 K for 60 min. Arrows in this figure indicate the spot in the X-ray topograph and the

/z %\* %0! z 1/%\*#z 3\$%0!z ..+3/\_z 0\$!.!z .!z )\*5z !0\$z ,%0/\_z 0\$!z ,+/%0%+\*/z +"z 3\$%\$z +..!¥ spond to those of the spots in the X-ray topograph. The dimension of spot in Figure 28 (a) is larger than that in Figure 27 (a); the diameter of etch pits in Figure 28 (b) is about 250 µm which is similarly larger than that in Figure 27 (b), about 40 µ)^z'%\*#z%\*0+z+1\*0z0\$!z.!¥ port [44] about the dimension of etch pits formed by KOH, Figures 28 (a) and (b) may show 0\$!z/.!3z %/(+0%+\*az%#1.!/zEJz cdz\* z cdz)5z/\$+3z 0\$!z 0\$.! %\*#z! #!z %/(+0%+\*^z-

1/!z0\$!z!0\$%\*#z0!\$\*%-1!z1/%\*#z0\$!z\$(+.%\*!z0.%"(1+.% !z#/z)5z.!2!(z0\$!z.5/0((%\*!z !¥ fects, like the KOH technique [44], the relationship between etch pits and various crystalline

9F<:L@=>9;=\$KADA;GF;9J:A<=KMJ>9;==L;@=<MKAF?;@DGJAF=LJAs

Etching of Silicon Carbide Using Chlorine Trifluoride Gas

http://dx.doi.org/10.5772/50387

123

!¥

etch pit at the etched surface.

?J9H@G>L@=/A>9;=\$KADA;GF;9J:A<=KMJ>9;=

defects should be further studied.

etch pit at the etched surface.

Figure 26. Etch pits on (a) Si-face and (b) C-face (870 K, chlorine trifluoride: 100 %, 0.3 slm). (c) is the magnification of the pit in (a), the edge of which is traced using dotted line.

Figures 26 (a) and (c) reveals a nearly hexagonal edge shape having a flat-shaped bottom. Its diameter and depth are about 0.03 mm and 2000-3000 nm, respectively. The many pits that exist over the entire surface are shown to have the same edge and bottom shape as that shown in Figure 26 (a). Figure 26 (b) shows the pit shape on the C-face. This surface is very flat and smooth having only a very small number of circular shaped pits, which are very shallow with a diameter of 0.01 mm and a depth of about 200 nm.

\*5z!0\$z,%0/z0z0\$!zGw/%(%+\*z.% !z/1."!\_z,.+ 1! z5z0\$!z!0\$%\*#z1/%\*#z\$(+.%\*!z0.%¥ fluoride gas, are expected to show a relationship with various crystalline defects, when the etching condition is appropriate. Thus, the Si-face and C-face 4H-silicon carbide surface are !0\$! z1/%\*#z\$(+.%\*!z0.%"(1+.% !z#/z0zDCCMz\* z0zJCCzz/+z0\$0z0\$!z,%0z !,0\$z!+)!z)4¥ imum value, as predicted by Figure 25. Additionally, the etch pits are compared with the Xray topograph, because the X-ray topograph is suitable in order to evaluate an origin of etch pit [42, 43].

Figures 27 (a) and 28 (a) are the X-ray topograph of the Si-face and C-face 4H-silicon carbide surface, respectively. Figures 27 (b) and 28 (b) are the photograph of Si-face and C-face 4Hsilicon carbide surface, respectively, etched using the chlorine trifluoride gas at 100% and at 700 K for 60 min. White arrows in these figures indicate the position of the spots in the X-ray topograph and the etch pits at the etched surface.

3.7. Etch pits and crystalline defect

122 Physics and Technology of Silicon Carbide Devices

the pit in (a), the edge of which is traced using dotted line.

topograph and the etch pits at the etched surface.

shallow with a diameter of 0.01 mm and a depth of about 200 nm.

dotted line.

pit [42, 43].

AFM photographs of the pit shape formed by the chlorine trifluoride gas are shown in %#¥ ure 26. Figures 26 (a) and (b) show the pits on the Si-face and C-face, respectively, after the etching using the chlorine trifluoride gas (100%) at atmospheric pressure for 3 min at 870 K and 0.3 slm. Figure 26 (c) is the etch pit of Figure 26 (a), the edge of which is traced using

Figure 26. Etch pits on (a) Si-face and (b) C-face (870 K, chlorine trifluoride: 100 %, 0.3 slm). (c) is the magnification of

Figures 26 (a) and (c) reveals a nearly hexagonal edge shape having a flat-shaped bottom. Its diameter and depth are about 0.03 mm and 2000-3000 nm, respectively. The many pits that exist over the entire surface are shown to have the same edge and bottom shape as that shown in Figure 26 (a). Figure 26 (b) shows the pit shape on the C-face. This surface is very flat and smooth having only a very small number of circular shaped pits, which are very

\*5z!0\$z,%0/z0z0\$!zGw/%(%+\*z.% !z/1."!\_z,.+ 1! z5z0\$!z!0\$%\*#z1/%\*#z\$(+.%\*!z0.%¥ fluoride gas, are expected to show a relationship with various crystalline defects, when the etching condition is appropriate. Thus, the Si-face and C-face 4H-silicon carbide surface are !0\$! z1/%\*#z\$(+.%\*!z0.%"(1+.% !z#/z0zDCCMz\* z0zJCCzz/+z0\$0z0\$!z,%0z !,0\$z!+)!z)4¥ imum value, as predicted by Figure 25. Additionally, the etch pits are compared with the Xray topograph, because the X-ray topograph is suitable in order to evaluate an origin of etch

Figures 27 (a) and 28 (a) are the X-ray topograph of the Si-face and C-face 4H-silicon carbide surface, respectively. Figures 27 (b) and 28 (b) are the photograph of Si-face and C-face 4Hsilicon carbide surface, respectively, etched using the chlorine trifluoride gas at 100% and at 700 K for 60 min. White arrows in these figures indicate the position of the spots in the X-ray

Figure 27. Comparison between the X-ray topograph and the etched Si-face 4H-silicon carbide surface. (a) X-ray topograph of the Si-face 4H silicon carbide surface, and (b) the Si-face 4H-silicon carbide surface etched using chlorine trifluoride gas at 100% and at 700 K for 60 min. Arrows in this figure indicate the spot in the X-ray topograph and the etch pit at the etched surface.

Figure 28. GEH9JAKGF:=LO==FL@=4J9QLGHG?J9H@9F<L@==L;@=<>9;=\$KADA;GF;9J:A<=KMJ>9;=94J9QLGHGs ?J9H@G>L@=/A>9;=\$KADA;GF;9J:A<=KMJ>9;= 9F<:L@=>9;=\$KADA;GF;9J:A<=KMJ>9;==L;@=<MKAF?;@DGJAF=LJAs fluoride gas at 100% and at 700 K for 60 min. Arrows in this figure indicate the spot in the X-ray topograph and the etch pit at the etched surface.

/z %\* %0! z 1/%\*#z 3\$%0!z ..+3/\_z 0\$!.!z .!z )\*5z !0\$z ,%0/\_z 0\$!z ,+/%0%+\*/z +"z 3\$%\$z +..!¥ spond to those of the spots in the X-ray topograph. The dimension of spot in Figure 28 (a) is larger than that in Figure 27 (a); the diameter of etch pits in Figure 28 (b) is about 250 µm which is similarly larger than that in Figure 27 (b), about 40 µ)^z'%\*#z%\*0+z+1\*0z0\$!z.!¥ port [44] about the dimension of etch pits formed by KOH, Figures 28 (a) and (b) may show 0\$!z/.!3z %/(+0%+\*az%#1.!/zEJz cdz\* z cdz)5z/\$+3z 0\$!z 0\$.! %\*#z! #!z %/(+0%+\*^z-!¥ 1/!z0\$!z!0\$%\*#z0!\$\*%-1!z1/%\*#z0\$!z\$(+.%\*!z0.%"(1+.% !z#/z)5z.!2!(z0\$!z.5/0((%\*!z !¥ fects, like the KOH technique [44], the relationship between etch pits and various crystalline defects should be further studied.

Because of the functions to produce the specular surface and to reveal the crystalline defects, chlorine trifluoride gas is expected to be more useful than the other wet and dry techniques [41], for silicon carbide industrial process.

!40\_z0\$!z !\*/%05z\* z!\$2%+.z+"z!0\$z,%0z,.+ 1! z+\*z0\$!zw"!z+"zGw/%(%+\*z.% !z/1¥ /0.0!z1/%\*#z\$(+.%\*!z0.%"(1+.% !z#/z0z2.%+1/z0!),!.01.!/z3!.!z!2(10! ^z\$!z!0\$z,%0z+¥ tained using the chlorine trifluoride gas at 713 K for 10 min at 100% was observed and shown in Figure 29. The diameter of etch pits was near 10 µm, which was considered to be assigned to screw dislocations, following the previous study [28].

Because the etch pit density (EPD) changed with the substrate temperature [28], the etching was performed at various temperatures around 713 K. The etch pit density obtained in an area of 500 x 500 µm2 at various substrate temperatures is shown in Figure 30^z0z0\$!z0!)¥ peratures below 673 K, the etch pit density was very small. At 683 K, the etch pit density increase to the value near 2 x 104 cm-2. At 713K, the etch pit density showed the maximum value of 4 x 104 cm-2. Although the etch pit density decreased at the temperatures higher than 723 K, its value maintained near 104 cm-2.

\$!z!0\$z,%0z !\*/%05z+0%\*! z0zJDFzz+%\*% ! z3%0\$z0\$!z2(1!/z3% !(5z!,0! z/z0\$!z1.¥ rent dislocation density level of 4H silicon carbide. Thus, the etch pit density of C-face of Gw/%(%+\*z .% !z +0%\*! z%\*z 0\$%/z /01 5z%/z !,0(!z \* z%/z!4,!0! z 0+z /\$+3z z .!(0%+\*¥ ship with the crystal quality. The etch pits obtained in this study were classified to the large circular-shaped and small oval-shaped pits, which ratio were 90% and 10%, respectively, at the etching temperature of 713 K. The former is considered to be assigned to the threading screw dislocation, and the latter can be the threading edge dislocation.

Figure 30. !L;@HAL<=FKALQGF>9;=\$KADA;GF;9J:A<=KMJ>9;=HJG<M;=<:Q;@DGJAF=LJA>DMGJA<=?9K9LN9JAGMKKM:s

Etching of Silicon Carbide Using Chlorine Trifluoride Gas

http://dx.doi.org/10.5772/50387

125

Figure 31. Comparison of etch pits (a) before and (b) after additional etching. White arrows indicate the etch pits.

 \*z+. !.z0+z/\$+3z0\$0z0\$!z+.%#%\*z+"z0\$!/!z!0\$z,%0z3/z//%#\*! z0+z0\$!z.5/0((%\*!z%),!."!¥ tion, the etched surface was further etched using the same etching condition. Figure 31 (a)

strate temperatures.

Figure 29. Etch pits produced on C-face 4H-silicon carbide surface by 100% chlorine trifluoride gas at 713 K for 10 min

Because of the functions to produce the specular surface and to reveal the crystalline defects, chlorine trifluoride gas is expected to be more useful than the other wet and dry techniques

!40\_z0\$!z !\*/%05z\* z!\$2%+.z+"z!0\$z,%0z,.+ 1! z+\*z0\$!zw"!z+"zGw/%(%+\*z.% !z/1¥ /0.0!z1/%\*#z\$(+.%\*!z0.%"(1+.% !z#/z0z2.%+1/z0!),!.01.!/z3!.!z!2(10! ^z\$!z!0\$z,%0z+¥ tained using the chlorine trifluoride gas at 713 K for 10 min at 100% was observed and shown in Figure 29. The diameter of etch pits was near 10 µm, which was considered to be

Because the etch pit density (EPD) changed with the substrate temperature [28], the etching was performed at various temperatures around 713 K. The etch pit density obtained in an

peratures below 673 K, the etch pit density was very small. At 683 K, the etch pit density

\$!z!0\$z,%0z !\*/%05z+0%\*! z0zJDFzz+%\*% ! z3%0\$z0\$!z2(1!/z3% !(5z!,0! z/z0\$!z1.¥ rent dislocation density level of 4H silicon carbide. Thus, the etch pit density of C-face of Gw/%(%+\*z .% !z +0%\*! z%\*z 0\$%/z /01 5z%/z !,0(!z \* z%/z!4,!0! z 0+z /\$+3z z .!(0%+\*¥ ship with the crystal quality. The etch pits obtained in this study were classified to the large circular-shaped and small oval-shaped pits, which ratio were 90% and 10%, respectively, at the etching temperature of 713 K. The former is considered to be assigned to the threading

Figure 29. Etch pits produced on C-face 4H-silicon carbide surface by 100% chlorine trifluoride gas at 713 K for 10 min

cm-2.

at various substrate temperatures is shown in Figure 30^z0z0\$!z0!)¥

cm-2. Although the etch pit density decreased at the temperatures higher

cm-2. At 713K, the etch pit density showed the maximum

[41], for silicon carbide industrial process.

124 Physics and Technology of Silicon Carbide Devices

area of 500 x 500 µm2

value of 4 x 104

increase to the value near 2 x 104

than 723 K, its value maintained near 104

assigned to screw dislocations, following the previous study [28].

screw dislocation, and the latter can be the threading edge dislocation.

Figure 30. !L;@HAL<=FKALQGF>9;=\$KADA;GF;9J:A<=KMJ>9;=HJG<M;=<:Q;@DGJAF=LJA>DMGJA<=?9K9LN9JAGMKKM:s strate temperatures.

Figure 31. Comparison of etch pits (a) before and (b) after additional etching. White arrows indicate the etch pits.

 \*z+. !.z0+z/\$+3z0\$0z0\$!z+.%#%\*z+"z0\$!/!z!0\$z,%0z3/z//%#\*! z0+z0\$!z.5/0((%\*!z%),!."!¥ tion, the etched surface was further etched using the same etching condition. Figure 31 (a) shows the nine etch pits observed on the C-face of 4H silicon carbide after the etching at 713 K for 10 min using the 100 % chlorine trifluoride gas. Their diameter was about 10 – 15 µm. This substrate was additionally etched at 713 K at the 100 % chlorine trifluoride gas. Figure 31 (b) shows the surface, 80 µm of which surface was etched off by the additional etching. Figure 31 (b) shows the large and shallow nine etch pits, which were overlapped 3%0\$z!\$z+0\$!.^z\$!z\*1)!.z\* z0\$!z,+/%0%+\*z+"z!0\$z,%0z!\*0!.z%\*z%#1.!^zFDzcdz+..!/,+\* ¥ ed to those in Figure 31 (a), respectively. Thus, over the depth of 80 µm, the origin to cause 0\$!z!0\$z,%0z3/z+\*(1 ! z0+z!4%/0az0\$!z+.%#%\*z+1( z!z0\$!z %/(+0%+\*\_z/1\$z/z0\$!z0\$.! ¥ ing dislocation, existing normal to the substrate surface.

and Mr. Shinji Iizuka of Kanto Denka Kogyo Co., Ltd., and Dr. Tomohisa Kato, Dr. Hajime Okumura and Dr. Kazuo Arai of National Institutes of Advanced Science and Technology. Mr. N. Okumura of Keyence Co., Ltd., is very much appreciated for the surface roughness evaluation. X-ray topography experiment has been performed under the approval of the

Etching of Silicon Carbide Using Chlorine Trifluoride Gas

http://dx.doi.org/10.5772/50387

127

Department of Chemical and Energy Engineering, Yokohama National University, Japan

[1] Gogotsi, Y., Welz, S., Ersoy, D. A., & Mc Nallan, M. J. (2001). *Nature*, 411(6835), 283.

[6] Mehregany, M., Zorman, C. A., Roy, S., Fleischman, A. J., Wu, C. H., & Rajan, N.

[7] Stoldt, C. R., Carraro, C., Ashurst, W. R., Gao, D., Howe, R. T., & Maboudian, R.

[9] Ashurst, W. R., Wijesundara, M. B. J., Carraro, C., & Maboudian, R. (2004). *Tribology*

[10] Shimura, F. (1989). Semiconductor Silicon Crystal Technology. 244, Academic Press,

[12] Schmid, U., Eickoff, M., Richter, C., Kroetz, G., & Schmitt-Landsiedel, D. (2001). (r

[8] Rajan, N., Mehregany, M., Zorman, C. A., Stefanescu, S., & Kicher, T. P. (1999).

HV\*\*&HVr

)/,r

[2] Vyshnyakova, K., Yushin, G., Pereselentseva, L., & Gogotsi, Y. (2006). (.HV

[3] Zinovev, A. V., Moore, J. F., Hryn, J., & Pellin, M. J. (2006). *Surf. Sci*, 600, 2242.

[5] Chai, C., Yang, Y., Li, Y., & Jia, H. (2003). *Optical Materials*, 23, 103.

[11] Kim, B., Kim, S., Ann, S., & Lee, B. (2003). *Thin Solid Film*, 434, 276.

Photon Factory Program Advisory Committee (Proposal No. 2006G286).

Address all correspondence to: habuka1@ynu.ac.jp

[4] Cooke, M. (2005, Dec). *III-Vs Review*, 18, 40.

(2000). *International Materials Reviews*, 45, 85.

*nal of Microelectromechanical Systems*, 8, 251.

(2002). *Sensors and Actuators a-Physical*, 97-98, 410.

Author details

Hitoshi Habuka\*

References

*ramic Tech.*, 3, 485.

*Letters*, 17, 195.

San Diego, USA.

*sors and Actuators A*, 94, 87.

\$!z.!/1(0/z+0%\*! z%\*z0\$%/z/01 5z%\* %0!z0\$0z0\$!z,%0/z1/! z5z0\$!z!0\$%\*#z1/%\*#z\$(+.¥ ine trifluoride gas at around 713 K has the origin of crystalline imperfection, such as the 0\$.! %\*#z %/(+0%+\*^z+3!2!.\_z0\$!z%\*0!.,.!00%+\*z+"z!0\$z,%0/z3%0\$z.!/,!0z0+z0\$!z1\* !.(5¥ ing dislocation type should be further carefully performed by a comparative investigation [28]. Additionally, the density and shape of etch pit by this technique should be further clarified and verified through many characterization.
