**4.2 Growing of fianite layers on silicon and gallium arsenide**

obtained by magnetron sputtering were of the best structural perfection [39].

The growth of fianite films on silicon and gallium arsenide substrates was carried out with the purpose to evaluate the prospects of using less expansive and more large Si and GaAs substrates with fianite sublayer instead of monolithic fianite substrates because, currently, maximum size of the latter is 50 mm. Another purpose was determination of an opportunity to use fianite not only as a substrate but also as insulating layers material alternative to SiO2, SiC, Si3N4, protecting and insulating layers, as well as a gate dielectric for multi-layer "semiconductor-dielectric" structures. Producing of such substrates will allow integrating GaN-based optoelectronics with a well-developed silicon electronics and gallium arsenide electronics and optoelectronics. Magnetron and laser sputtering were used for deposition of fianite films on silicon and gallium arsenide fianite films on porous Si and GaAs.

With the purpose to improve quality of fianite films and its adhesion to Si and GaAs substrates opportunities of the use of porous layers of the material were studied.

The following results were obtained:


High mechanical and chemical stability of fianite and absence of pores confirmed the prospects of its application as protective and stabilizing coatings substrates.

#### **4.2.1 Magnetron sputtering technique**

Magnetron systems are related to diode-type sputtering systems. The sputtering occurred due to bombardment of a target surface by gas ions (usually Ar) forming in plasma of anomalous glow discharge. A material ions knocked out the target subjected to the bombardment are captured by magnetic field and maintained complex cycloidal movement by closed trajectory in vicinity of the target surface. High sputtering rate, which is a feature

Various techniques can be used for the producing of fianite films on silicon and other semiconductors, including magnetron [39, 40, 44-46], laser and electron-beam [47-49] sputtering, molecular-beam epitaxy (MBE), as well as gas-phase chemicаl deposition [50]. The choice of a specific technique is determined by further designation of a fianite film, possibility to produce the film of maximum structural perfection, as well as technologic potentialities of a technique. So, MBE technique is more suitable for deposition of the thinnest fianite film for the use as a gate dielectric. Magnetron and laser sputtering are more favorable for fianite layers used as buffer layers with subsequent growing semiconductor films, including АIIIBV compounds. In [39] fianite films were deposited on Si and GaAs substrates using magnetron, laser and electron-beam sputtering techniques. The films

The growth of fianite films on silicon and gallium arsenide substrates was carried out with the purpose to evaluate the prospects of using less expansive and more large Si and GaAs substrates with fianite sublayer instead of monolithic fianite substrates because, currently, maximum size of the latter is 50 mm. Another purpose was determination of an opportunity to use fianite not only as a substrate but also as insulating layers material alternative to SiO2, SiC, Si3N4, protecting and insulating layers, as well as a gate dielectric for multi-layer "semiconductor-dielectric" structures. Producing of such substrates will allow integrating GaN-based optoelectronics with a well-developed silicon electronics and gallium arsenide electronics and optoelectronics. Magnetron and laser sputtering were used for deposition of

With the purpose to improve quality of fianite films and its adhesion to Si and GaAs





High mechanical and chemical stability of fianite and absence of pores confirmed the

Magnetron systems are related to diode-type sputtering systems. The sputtering occurred due to bombardment of a target surface by gas ions (usually Ar) forming in plasma of anomalous glow discharge. A material ions knocked out the target subjected to the bombardment are captured by magnetic field and maintained complex cycloidal movement by closed trajectory in vicinity of the target surface. High sputtering rate, which is a feature

prospects of its application as protective and stabilizing coatings substrates.

obtained by magnetron sputtering were of the best structural perfection [39].

fianite films on silicon and gallium arsenide fianite films on porous Si and GaAs.

substrates opportunities of the use of porous layers of the material were studied.

**4.2 Growing of fianite layers on silicon and gallium arsenide** 

The following results were obtained:

and p-conductivity types were developed;

adhesion of fianite with GaAs layers;

subsequent growth of АIIIN films.

**4.2.1 Magnetron sputtering technique** 

substrates of 18x18 mm size were established;

of magnetron systems, is achieved by an increase of the ion current density due to localization of plasma by means of high transverse magnetic field. The increase of sputtering at simultaneous decrease actuation gas pressure allows a significant decreasing contamination of the films by alien gas impurities. Fianite was grown up on Si and GaAs substrates using unbalanced magnetron system. Fianite crystals were used as a target. Si substrate subjected to the sputtering was heated by IR radiance. Preparation of the substrates included degreasing, removing of the oxide and passivating of the surface in ammonium-peroxide solution. Optimization of the conditions of the growth of fianite films on Si substrates was carried out by varying of the sputtering rate, temperature of the substrate and residual gas pressure.

Bombardment of the target leads to dissociation of zirconium and yttrium oxides to ZrO, Zr, YO, Y, O2. That is why such parameters as sputtering rate and residual gas pressure considerably influence on stoichiometry of the resulting film. Energy of the evaporating particles is rather low (0.5-10 eV), so for the epitaxial growth of fianite film a high temperature of Si substrate and optimal rate of the condensate supply are necessary.

## **4.2.2 Laser sputtering technique**

Experimental installation for deposition of fianite films was a sputtering system composed by vacuum device and eximer laser. The system has been designed and manufactured in IPM RAS.

Operational oxygen pressure was maintained by vacuum system supplied with a mechanical pump and СНА-2 letting system. Evaporation of the target was performed by LPX200 eximer laser radiation working on KrF mixture. Wavelength of the radiation was 248 nm, pulse duration 27 ns, the pulse energy 350 MJ (pulse power 1.3×107W), repetition frequency 50 Hz. Optical system providing a focusing of the laser beam on the target surface consisted of qurtz prisms and 30 cm focal distance lens. The laser beam spot on the target surface was 1×4mm2. The energy density on the target surface was ~10 J/сm2. The distance between the target and substrate was 60 mm. Cylindrical targets of 15-20 mm diameter and 10-30 mm length were used in the installation. In order to prevent local overheating of a target and to provide uniform material drift rotation and axial movement of the target was used. Possibility of conducting pre- and post-growth annealing under oxygen atmosphere at 10 Pа – 100 kPa pressure and at up to 750ºС temperature is a peculiarity of the installation.

Ceramic target of (ZrO2)1-x(Y2O3)x with x=0.1 composition was used for deposition of fianite films. The deposition was carried out on Si and GaAs substrates heated to 600-800ºС temperature under oxygen atmosphere at approximately 10 Pа. The growth rate of YSZ films was about 0.02 nm per pulse. Contactless heater of substrates (heating by irradiance) was an original peculiarity of the sputtering system. The heater comprises vertically positioned quartz tube (of 30 mm inner diameter) supplied with refractory stainless steel heating coil on its outer surface with up to 1 kW power of the heater. Monitoring and maintenance of the assigned temperature (with 5С precision) were carried out using precise regulating device and Pt-Rh thermocouple positioned under the heating coil. A substrate was fitted in a holder and positioned inside of the quartz tube. Loading of substrates and oxygen supply was maintained through the upper end of the tube.

Fianite in Photonics 157

First, silicon surface readily undergoes to transformation into SiO2 amorphous layer due to either interaction with oxygen-containing fianite film, or oxidative atmosphere usually used at the fianite growth. As it has been shown by calculations, fianite should not react with silicon substrate to form SiO2, which has low dielectric constant value, at a direct contact [51]. However, in practice, it is very difficult to avoid formation of this layer at the fianite deposition or subsequent high-thermal treatment [52,53]. Therefore, a development of special technological tools is necessary. One of the routes to solve the problem has been suggested by the authors [54]. Thin Zr or Y layer was deposited on Si substrate before fianite deposition. The metals absorb oxygen from SiO2 layer because free energy of both fianite and Y2O3 formation is lower than of SiO2 one [55]. That leads to a decrease of the layer

Second, oxygen from the fianite layer readily diffuses to a silicon substrate or reacts with silicon surface. Secondary phases occurring as a result of the reaction disturb silicon crystal lattice and hinder a perfect growth. Under these circumstances, the fianite layers on Si substrates are of amorphous or polycrystalline structure. At the development of gate dielectric technology these issues are of peculiar importance because thickness of the last

Therefore, the above data show that the problem of deposition of fianite layers on Si substrates is of great interest. The problem of improvement of quality of the layers seems to be very urgent because of a number of principal difficulties occurring due to peculiarities of physic-chemical properties of the materials considered resulting in reactions at the growth and subsequent thermal treatment stages. The synthesis of perfect fianite layers on Si requires a development of special methods to decrease the influence of amorphous SiO2

To choose the most appropriate method and conditions of fianite film etching, we have tried out the main methods of etching used in microelectronics technologies: liquid (wet),

For fianite film liquid etching (by analogy with ZrO2) the following etchants were used: - etchant HCl:HF:H2O (10:1:5). Fianite films were found to be resistant to this etchant;

a b

thickness.

layer is about some nanometers.

layer at the substrate-layer interface.

**4.3.1 Liquid etching** 

**4.3 Development of the techniques of fianite films etching** 

plasmachemical, and ion-beam methods of etching.



Fig. 19. scanning spectra for (422)reflection of YSZ substrate (а) and the film (b)

Technology of growth of dielectric fianite films using the laser sputtering consists of the following stages:


The substrate heater is switched off and the substrate is cooled to room temperature.

#### **4.2.3 Initial stages of deposition and structure of fianite buffer layers on Si and GaAs substrates**

The application of fianite as a buffer layer will allow a solution route to another very important problem – epitaxy of AIIIN compounds on Si and GaAs substrates having large dimensions, high quality and low net cost.

Single crystalline heteroepitaxial fianite layers of 1000 A thickness were grown on silicon substrates of up to 50 mm diameter in vacuum chamber at p 2102 Pa pressure, sputtering rate Vs 60 А/min and substrate temperature Т<sup>s</sup> 800С.

The studies have shown that the layer became continuous as from 100 A thickness.

X-ray structural studies of ZrO2-Y2O3/Si structures have shown that the fianite film is single phased and consisted of two layers with different rocking curve values: 0,20 for the upper layer and 0,96 for the lower one. Epitaxial relation between the film and the substrate was (100) [100]Si//(100)[100]ZrO2-Y2O3. The relation was established using diffraction measurements under following regimes: /2 scanning (simultaneous rotation of the detector and sample over goniometer axis) and - scanning (rotation of the plate in a proper plane at fixed detector position). The former regime was used to determine orientation of the composition plane, the latter – mutual orientation of unit cells of the film and the substrate in the composition plane.

Spectra of the - scanning of (ZrO2-Y2O3)/Si structure for the asymmetric (422) reflection of the film (b) and the substrate (a) are shown in Fig. 19.

The absence of additional peaks and high peak maximum-to-background ratio (103) are the evidence for ZrO2-Y2O3 layer is a perfect single crystal film. The fianite buffer layers grown on Si and GaAs were used for AIIIN compounds epitaxy.

## **4.2.4 Some difficulties in deposition of the fianite layers on silicon**

Growth of fianite-on-silicon structures of high quality featuring with sharp interfaces is associated with significant difficulties because of a number of principal problems.

Technology of growth of dielectric fianite films using the laser sputtering consists of the

1. A substrate is loaded to the sputtering system and vacuum chamber is evacuated up

5. The eximer laser (the pulse energy 350 MJ, repetition frequency 50 Hz) is switched on

6. Followed by the achievement of assigned thickness of the film the laser is switched off. 7. Followed by the end of the film growth the chamber is filled with oxygen up to the

**4.2.3 Initial stages of deposition and structure of fianite buffer layers on Si and GaAs** 

The application of fianite as a buffer layer will allow a solution route to another very important problem – epitaxy of AIIIN compounds on Si and GaAs substrates having large

Single crystalline heteroepitaxial fianite layers of 1000 A thickness were grown on silicon substrates of up to 50 mm diameter in vacuum chamber at p 2102 Pa pressure, sputtering

X-ray structural studies of ZrO2-Y2O3/Si structures have shown that the fianite film is single phased and consisted of two layers with different rocking curve values: 0,20 for the upper layer and 0,96 for the lower one. Epitaxial relation between the film and the substrate was (100) [100]Si//(100)[100]ZrO2-Y2O3. The relation was established using diffraction measurements under following regimes: /2 scanning (simultaneous rotation of the detector and sample over goniometer axis) and - scanning (rotation of the plate in a proper plane at fixed detector position). The former regime was used to determine orientation of the composition plane, the latter – mutual orientation of unit cells of the film and the

Spectra of the - scanning of (ZrO2-Y2O3)/Si structure for the asymmetric (422) reflection of

The absence of additional peaks and high peak maximum-to-background ratio (103) are the evidence for ZrO2-Y2O3 layer is a perfect single crystal film. The fianite buffer layers grown

Growth of fianite-on-silicon structures of high quality featuring with sharp interfaces is

associated with significant difficulties because of a number of principal problems.

The studies have shown that the layer became continuous as from 100 A thickness.

The substrate heater is switched off and the substrate is cooled to room temperature.

following stages:

to 1 Pa residual pressure.

and the sputtering is started.

dimensions, high quality and low net cost.

substrate in the composition plane.

rate Vs 60 А/min and substrate temperature Т<sup>s</sup> 800С.

the film (b) and the substrate (a) are shown in Fig. 19.

on Si and GaAs were used for AIIIN compounds epitaxy.

**4.2.4 Some difficulties in deposition of the fianite layers on silicon** 

pressure required. 8. The structure is annealed.

**substrates** 

2. Letting-to-oxygen is done up to the pressure required. 3. Rotational movement drive of the target is switched on. 4. A substrate is heated up to deposition temperature.

Fig. 19. scanning spectra for (422)reflection of YSZ substrate (а) and the film (b)

First, silicon surface readily undergoes to transformation into SiO2 amorphous layer due to either interaction with oxygen-containing fianite film, or oxidative atmosphere usually used at the fianite growth. As it has been shown by calculations, fianite should not react with silicon substrate to form SiO2, which has low dielectric constant value, at a direct contact [51]. However, in practice, it is very difficult to avoid formation of this layer at the fianite deposition or subsequent high-thermal treatment [52,53]. Therefore, a development of special technological tools is necessary. One of the routes to solve the problem has been suggested by the authors [54]. Thin Zr or Y layer was deposited on Si substrate before fianite deposition. The metals absorb oxygen from SiO2 layer because free energy of both fianite and Y2O3 formation is lower than of SiO2 one [55]. That leads to a decrease of the layer thickness.

Second, oxygen from the fianite layer readily diffuses to a silicon substrate or reacts with silicon surface. Secondary phases occurring as a result of the reaction disturb silicon crystal lattice and hinder a perfect growth. Under these circumstances, the fianite layers on Si substrates are of amorphous or polycrystalline structure. At the development of gate dielectric technology these issues are of peculiar importance because thickness of the last layer is about some nanometers.

Therefore, the above data show that the problem of deposition of fianite layers on Si substrates is of great interest. The problem of improvement of quality of the layers seems to be very urgent because of a number of principal difficulties occurring due to peculiarities of physic-chemical properties of the materials considered resulting in reactions at the growth and subsequent thermal treatment stages. The synthesis of perfect fianite layers on Si requires a development of special methods to decrease the influence of amorphous SiO2 layer at the substrate-layer interface.

#### **4.3 Development of the techniques of fianite films etching**

To choose the most appropriate method and conditions of fianite film etching, we have tried out the main methods of etching used in microelectronics technologies: liquid (wet), plasmachemical, and ion-beam methods of etching.

#### **4.3.1 Liquid etching**

For fianite film liquid etching (by analogy with ZrO2) the following etchants were used:


Fianite in Photonics 159

substances. Any work with such substances requires availability of specific production or laboratory premises, equipping of which is allowed only in specific industrial areas and causes additional labour and financial costs. That is why further researches were devoted to

This method is based on material scattering under ion bombardment. The sample (fianitesemiconductor structure) was fixed on a holder. The holder was cooled to avoid overheating. Ions were generated in a direct current discharge in a separate "ion" gun, were

A fianite film of 1000 Å was etched through a photoresist mask with the help of ion-beam

The fianite films were studied by means of scanning electron microscopy, ellipsometry and CV-parameters measurement techniques. The films parameters were found as

The capacity-voltage (CV) characteristics of the structures supplied with fianite films

Capacity measurements provide evaluation of dielectric properties of the films under the study: dielectric constant *ε* and dielectric loss *tgδ.* The application of multifrequency device allows determination of frequency dependencies of dielectric constant and high-frequency loss in dielectric films. Since the dielectric film is deposited on semiconductor a MIS structure (metal-insulator-semiconductor) is formed, so the CV-measurement provides additional information concerning the semiconductor and the dielectric-semiconductor interface, namely, type of the semiconductor conductivity (n- or p) and concentration of the dopant, flat band barrier voltage Vfb, density of boundary states and a charge induced in the

The device used for CV- measurements allowed determining of capacity and high-frequency conductivity of the structures, as well as its dependency on the applied voltage. The measurements were carried out at 500 KHz and 1 MHz frequencies. Direct potential bias range was ±40 V. Thermally sputtered Al of 1 mm surface diameter was used as the

"Al-fianite-Si" MIS structure parameters: flat band barrier voltage – 4 V for 180 nm film and

fianite film etching using ion-beam method.

**4.4 Characterization of the fianite films** 



focused and accelerated towards the samples treated.

deposited on *p*-Si and *n*-Si substrates were measured.

contacts. The results obtained are shown in Fig. 20.

1.5 V for 20 nm film; density of boundary state charge~ +1012 см-2.


**4.4.1 The capacity-voltage characteristic measurements of fianite-on-silicon"** 

**4.3.3 Ion-beam etching** 

etching during 35 minutes.

follows:

**structures** 

dielectric.

The film was found to be chemically resistant to all of the above listed reagents. So we tried out all the most chemically active reagents that traditionally are used for dielectric film liquid etching in photosensitive devices production. On the one hand, this evidences resistivity of photosensitive devices with fianite protective layers to corrosive medium exposure. On the other hand, such properties cause technological difficulties. To settle the problem, we have searched for other methods of etching.

## **4.3.2 Plasmachemical etching**

In case of plasmochemical etching, a mask of 1.3 µm thick FP91-20-1 photoresist hardened at 120oC during 20 minutes was used. A diode type plant was used. The discharge power was between 200 and 350 Wt, discharge frequency was 105 KHz. Temperature inside the reaction chamber was varied from 20oC to 90oC, etching time – from 10 to 35 minutes. Mixtures of CCL2F2+Ar, CCL2F2+He, and CCL2F2+O2 of various percentages were used as reagent gases. The pressure in the processing chamber during samples etching varied from 0.2 to 0.85 mBar. The samples surface texture after etching depends upon the etchant, the process conditions, and the preliminary surface treatment. Prior to etching, the samples were treated with Ar and He ions. Loose texture surface was observed on the samples; such texture had been formed probably by precipitation of products of reaction on the sample surface. Water vapor and oxygen may be absorbed on the reactor surface and slow down etching till they completely react with the working gas. The period of etching slow down may be decreased by eliminating of the said factors with the help of a "loading lock". For this purpose, another construction of the plant was chosen that applied the reactive-ion technology of film etching with the loading lock. Use of such plant made it possible to combine glow discharge plasma and the chemical medium providing etching. The medium consists of charged particles, radicals and neutral particles participating in chemical reactions on the film surface. Volatile products are formed in the medium. Positive ions being accelerated in the interelectrode space bombard the surface of plates thus finishing material removing.

The following conditions of the process of fianite film etching were examined:


Adding of O2 to chloride bearing plasma increases concentration of Cl and suppresses polymer film forming on the sample surface. Adding of inert gases stabilizes plasma. Stabilization may be achieved due to thermal properties of the discharge gas used, especially in case of helium adding.

Unfortunately, in this method the rate of film etching was found to be low; besides, the problem of mask selection occurred. That is why, the studied technologies of plasmachemical and reactive-ion etching for fianite films are rather inefficient. But they may be used for gold contacts etching.

Of cause, capabilities of the investigated technologies may be expanded by use of more active reagents, such as CCl4BC3*.* But, such reagents are referred to extremely hazardous

The film was found to be chemically resistant to all of the above listed reagents. So we tried out all the most chemically active reagents that traditionally are used for dielectric film liquid etching in photosensitive devices production. On the one hand, this evidences resistivity of photosensitive devices with fianite protective layers to corrosive medium exposure. On the other hand, such properties cause technological difficulties. To settle the

In case of plasmochemical etching, a mask of 1.3 µm thick FP91-20-1 photoresist hardened at 120oC during 20 minutes was used. A diode type plant was used. The discharge power was between 200 and 350 Wt, discharge frequency was 105 KHz. Temperature inside the reaction chamber was varied from 20oC to 90oC, etching time – from 10 to 35 minutes. Mixtures of CCL2F2+Ar, CCL2F2+He, and CCL2F2+O2 of various percentages were used as reagent gases. The pressure in the processing chamber during samples etching varied from 0.2 to 0.85 mBar. The samples surface texture after etching depends upon the etchant, the process conditions, and the preliminary surface treatment. Prior to etching, the samples were treated with Ar and He ions. Loose texture surface was observed on the samples; such texture had been formed probably by precipitation of products of reaction on the sample surface. Water vapor and oxygen may be absorbed on the reactor surface and slow down etching till they completely react with the working gas. The period of etching slow down may be decreased by eliminating of the said factors with the help of a "loading lock". For this purpose, another construction of the plant was chosen that applied the reactive-ion technology of film etching with the loading lock. Use of such plant made it possible to combine glow discharge plasma and the chemical medium providing etching. The medium consists of charged particles, radicals and neutral particles participating in chemical reactions on the film surface. Volatile products are formed in the medium. Positive ions being accelerated in the interelectrode

problem, we have searched for other methods of etching.

space bombard the surface of plates thus finishing material removing.

The following conditions of the process of fianite film etching were examined: Working pressure in the reactor 0.03-0.08 mBar

Adding of O2 to chloride bearing plasma increases concentration of Cl and suppresses polymer film forming on the sample surface. Adding of inert gases stabilizes plasma. Stabilization may be achieved due to thermal properties of the discharge gas used,

Unfortunately, in this method the rate of film etching was found to be low; besides, the problem of mask selection occurred. That is why, the studied technologies of plasmachemical and reactive-ion etching for fianite films are rather inefficient. But they may

Of cause, capabilities of the investigated technologies may be expanded by use of more active reagents, such as CCl4BC3*.* But, such reagents are referred to extremely hazardous

Discharge power 320-800 Wt Discharge frequency 13.56 MHz Etching time 10-45 minutes

**4.3.2 Plasmachemical etching** 

especially in case of helium adding.

be used for gold contacts etching.

substances. Any work with such substances requires availability of specific production or laboratory premises, equipping of which is allowed only in specific industrial areas and causes additional labour and financial costs. That is why further researches were devoted to fianite film etching using ion-beam method.

#### **4.3.3 Ion-beam etching**

This method is based on material scattering under ion bombardment. The sample (fianitesemiconductor structure) was fixed on a holder. The holder was cooled to avoid overheating. Ions were generated in a direct current discharge in a separate "ion" gun, were focused and accelerated towards the samples treated.

A fianite film of 1000 Å was etched through a photoresist mask with the help of ion-beam etching during 35 minutes.

## **4.4 Characterization of the fianite films**

The fianite films were studied by means of scanning electron microscopy, ellipsometry and CV-parameters measurement techniques. The films parameters were found as follows:


#### **4.4.1 The capacity-voltage characteristic measurements of fianite-on-silicon" structures**

The capacity-voltage (CV) characteristics of the structures supplied with fianite films deposited on *p*-Si and *n*-Si substrates were measured.

Capacity measurements provide evaluation of dielectric properties of the films under the study: dielectric constant *ε* and dielectric loss *tgδ.* The application of multifrequency device allows determination of frequency dependencies of dielectric constant and high-frequency loss in dielectric films. Since the dielectric film is deposited on semiconductor a MIS structure (metal-insulator-semiconductor) is formed, so the CV-measurement provides additional information concerning the semiconductor and the dielectric-semiconductor interface, namely, type of the semiconductor conductivity (n- or p) and concentration of the dopant, flat band barrier voltage Vfb, density of boundary states and a charge induced in the dielectric.

The device used for CV- measurements allowed determining of capacity and high-frequency conductivity of the structures, as well as its dependency on the applied voltage. The measurements were carried out at 500 KHz and 1 MHz frequencies. Direct potential bias range was ±40 V. Thermally sputtered Al of 1 mm surface diameter was used as the contacts. The results obtained are shown in Fig. 20.

"Al-fianite-Si" MIS structure parameters: flat band barrier voltage – 4 V for 180 nm film and 1.5 V for 20 nm film; density of boundary state charge~ +1012 см-2.

Fianite in Photonics 161

of conventional SiO2 by increasing of integration level. That requires a change of SiO2 over dielectrics with higher dielectric constant (high-k materials) [33-35,51]. The resent studies have limited possible alternatives to fianite, HfO2, ZrO2 and its silicates. For example, ZrO2 has high dielectric constant value, good dielectric properties (5.8 eV energy gap width) and rather good crystallochemical matching with Si [56] (see Fig. 5). Intel Corp. – one of the leaders of the world electronics, has demonstrated that the change of SiO2 over HfO2 as a gate dielectric in 45 nm technological process allows decreasing leakage currents (which became a serious problem for transistors) by more than two orders of magnitude [57].

Comparison of fianite and SiO2 films [34] with electrical equivalent oxide thickness of about 1.46 nm has shown that the leakage current for fianite was four orders of magnitude lower

The hysteresis and interface state density in this film was measured to be less than 10 mV and 2.0 x 1011eV-1cm-2. It demonstrated that crystalline oxide on semiconductor could be

It is worth to note that quality of the synthesized fianite, as well of the interfaces [85], is very important for integration of such a dielectric to the CMOS technology currently in use.

Synthesizing of fianite-on-silicon structures of high quality featuring with sharp interfaces is

First, silicon surface readily undergoes to transformation into SiO2 amorphous layer due to either interaction with oxygen-containing fianite film, or oxidative atmosphere usually used at the fianite growth. In practice, it is very difficult to avoid formation of this layer at the fianite deposition or subsequent high-thermal treatment. Therefore, a development of

Second, oxygen from the fianite layer readily diffuses to a silicon substrate or reacts with silicon surface resulting in SiO2 formation having low dielectric constant value. At the development of the gate dielectric technology these issues are of peculiar importance

One of the routes to solve this problem is in application of low-temperature growth and annealing regimes, as those, which were used in the series of experiments described below, Type of a substrate and the annealing media were also varied. Conditions of the synthesis of the fianite/Si structures are given in Tab. 4. XRD technique has shown that fianite layers

С, 10 min

annealing

z 2 room vacuum ~20 Si <B> z 3 room oxygen ~20 Si <B> z 4 room oxygen ~20 Si <Sb> z 5 600 oxygen ~20 Si <B>

Film thickness, nm Substrate

~20 Si <B>

obtained by laser deposition at room temperature were of amorphous structure.

associated with significant difficulties because of a number of principal problems.

than that of conventional SiO2 gate oxides.

special technological tools is necessary.

used for future generation of semiconductor-based devices.

because thickness of the last layer is about some nanometers.

Sample T of growth, С Annealing, 600

z 1 room without

Table 4. Parameters of growth and annealing of the fianite-on-Si films

Fig. 20. CV- characteristics of fianite-on- *p*-Si sample

#### **4.4.2 Investigation of ZrO2 films on Si and Ge substrates by means of scanning electron microscopy**

The ZrO2 films were studied using scanning electron microscopy. All of the films studied were porous-free. Since square of the samples studied was 5-6 см2, it is possible to consider the porosity value at least not exceeding 0.15-0.2 см-2. For comparison, it is worth to mention that porosity of SiO2 films is 4-8 см-2 . Therefore, it is possible to consider ZrO2 films as the protective layer for Ge devices actually superior SiO2 films because its porosity decreased in 1.5-2 orders of magnitude.

The study of morphology of the films deposited by magnetron sputtering technique at high magnification has shown its satisfactory homogeneity. Some regions of the surface featured by a relief composed by quasi-spherical hills of 500-600 nm in diameter and exhibiting lateral periodicity. Analytical study of the films has shown an absence of inclusions of impurities.

An attempt to study mechanism of formation of the films with the purpose to optimize conditions of magnetron sputtering was done using electron microscopy (JSM JEOL 5910 LV). The particles were identified by means of electron probe. The film was removed by polishing using diamond paste with 2.5-4µm particle size. This abrasive size was chosen to minimize decreasing particle size of the film constituents at the polishing. The obtained material was flushed by ethanol (9-12 purity grades "for microelectronics") and the suspension was put in plastic syringes (1 ml). In order to disintegrate aggregates ultrasonic (US) treatment was carried out. The US dispersion was conducted using «Sapphire 3M-1.3» US device with 35 GHz operational frequency. The syringes were inserted to the device chamber filled with water. The chamber was thermostated at 27оС. Followed by 3 min of the US treatment the suspension was aspirated onto conductive (graphitized) ribbon for subsequent microscopy study. The study has shown that the largest constituents of the zirconia film were quasi-spherical particles of 50-100 nm size that explained X-ray amorphous nature of the film. It is possible to suggest that formation of larger elements of the relief occurred by enlargement of such particles. The reasons of local enlargement (formation of spherical hills) can be gradients of temperature and mass-transfer, as well as occurrence of impurities. The observations allowed refining the refine conditions of the sputtering of ZrO2 and fianite films in order to minimize surface roughness.

#### **4.5 Fianite as a gate dielectric**

Recently, a sharp surge of interest in the use of fianite as a gate dielectric in CMOS technology has been observed. It is associated with an increase of leakage current at the use

**Capacity, pF**

Fig. 20. CV- characteristics of fianite-on- *p*-Si sample

**electron microscopy** 

1.5-2 orders of magnitude.

**4.5 Fianite as a gate dielectric** 







**4.4.2 Investigation of ZrO2 films on Si and Ge substrates by means of scanning** 




The ZrO2 films were studied using scanning electron microscopy. All of the films studied were porous-free. Since square of the samples studied was 5-6 см2, it is possible to consider the porosity value at least not exceeding 0.15-0.2 см-2. For comparison, it is worth to mention that porosity of SiO2 films is 4-8 см-2 . Therefore, it is possible to consider ZrO2 films as the protective layer for Ge devices actually superior SiO2 films because its porosity decreased in

The study of morphology of the films deposited by magnetron sputtering technique at high magnification has shown its satisfactory homogeneity. Some regions of the surface featured by a relief composed by quasi-spherical hills of 500-600 nm in diameter and exhibiting lateral periodicity. Analytical study of the films has shown an absence of inclusions of impurities.

An attempt to study mechanism of formation of the films with the purpose to optimize conditions of magnetron sputtering was done using electron microscopy (JSM JEOL 5910 LV). The particles were identified by means of electron probe. The film was removed by polishing using diamond paste with 2.5-4µm particle size. This abrasive size was chosen to minimize decreasing particle size of the film constituents at the polishing. The obtained material was flushed by ethanol (9-12 purity grades "for microelectronics") and the suspension was put in plastic syringes (1 ml). In order to disintegrate aggregates ultrasonic (US) treatment was carried out. The US dispersion was conducted using «Sapphire 3M-1.3» US device with 35 GHz operational frequency. The syringes were inserted to the device chamber filled with water. The chamber was thermostated at 27оС. Followed by 3 min of the US treatment the suspension was aspirated onto conductive (graphitized) ribbon for subsequent microscopy study. The study has shown that the largest constituents of the zirconia film were quasi-spherical particles of 50-100 nm size that explained X-ray amorphous nature of the film. It is possible to suggest that formation of larger elements of the relief occurred by enlargement of such particles. The reasons of local enlargement (formation of spherical hills) can be gradients of temperature and mass-transfer, as well as occurrence of impurities. The observations allowed refining the refine conditions of the

sputtering of ZrO2 and fianite films in order to minimize surface roughness.

Recently, a sharp surge of interest in the use of fianite as a gate dielectric in CMOS technology has been observed. It is associated with an increase of leakage current at the use


**Potential bias, V**

0

1

2

3

4

5

6

7

8

9

10

of conventional SiO2 by increasing of integration level. That requires a change of SiO2 over dielectrics with higher dielectric constant (high-k materials) [33-35,51]. The resent studies have limited possible alternatives to fianite, HfO2, ZrO2 and its silicates. For example, ZrO2 has high dielectric constant value, good dielectric properties (5.8 eV energy gap width) and rather good crystallochemical matching with Si [56] (see Fig. 5). Intel Corp. – one of the leaders of the world electronics, has demonstrated that the change of SiO2 over HfO2 as a gate dielectric in 45 nm technological process allows decreasing leakage currents (which became a serious problem for transistors) by more than two orders of magnitude [57].

Comparison of fianite and SiO2 films [34] with electrical equivalent oxide thickness of about 1.46 nm has shown that the leakage current for fianite was four orders of magnitude lower than that of conventional SiO2 gate oxides.

The hysteresis and interface state density in this film was measured to be less than 10 mV and 2.0 x 1011eV-1cm-2. It demonstrated that crystalline oxide on semiconductor could be used for future generation of semiconductor-based devices.

It is worth to note that quality of the synthesized fianite, as well of the interfaces [85], is very important for integration of such a dielectric to the CMOS technology currently in use.

Synthesizing of fianite-on-silicon structures of high quality featuring with sharp interfaces is associated with significant difficulties because of a number of principal problems.

First, silicon surface readily undergoes to transformation into SiO2 amorphous layer due to either interaction with oxygen-containing fianite film, or oxidative atmosphere usually used at the fianite growth. In practice, it is very difficult to avoid formation of this layer at the fianite deposition or subsequent high-thermal treatment. Therefore, a development of special technological tools is necessary.

Second, oxygen from the fianite layer readily diffuses to a silicon substrate or reacts with silicon surface resulting in SiO2 formation having low dielectric constant value. At the development of the gate dielectric technology these issues are of peculiar importance because thickness of the last layer is about some nanometers.

One of the routes to solve this problem is in application of low-temperature growth and annealing regimes, as those, which were used in the series of experiments described below, Type of a substrate and the annealing media were also varied. Conditions of the synthesis of the fianite/Si structures are given in Tab. 4. XRD technique has shown that fianite layers obtained by laser deposition at room temperature were of amorphous structure.


Table 4. Parameters of growth and annealing of the fianite-on-Si films

Fianite in Photonics 163

In case of low magnetron power, plasma is unstable ("blinking plasma"); in case of larger values of discharge power, the growth rate increases, but irregularity of substrate surface layers and growing film coarse-graining are possible. Fianite sputtering requires higher power than in case of ZrO2; provided that the growth rate is twice as much than in case

The developed technique of magnetron sputtering made it possible to vary the fianite film thickness between 600 and 2000 Å. Ge and Si plates with fianite film thereon were made using this technology. Ge samples with fianite film were used to try out further operations

Inorganic dielectric coatings are usually used for passivating and protection of p-n transition surface, as shielding and thermal compensation layer at ion implanting and for interference antireflecting protection. Passivation of the surface is the most important issue for manufacturing ot germanium photodiodes because natural GeO and GeO2 oxides are unstable and, so, can not be considered as the only passivating coatings. It is one feature distinguishing Ge and Si devices (the latter have stable and effective coating of its own SiO2 oxide). This oxide film deposited from a gas phase is of the most frequent use for photodiodes with p+ - n-structure. It has positive charge and by attracting electrons to the surface prevents growth of p-channels thus decreasing probability of generation in the layer. It is worth to note that for improved reliability and stability of characteristics of photodiodes it is necessary to maintain surface state density at 1011 cm-2 eV-1 level. However, this passivating technique is far from ideal because high porosity of SiO2 films that decreases

In order to improve dielectric properties of the protective coating fianite films deposited by magnetron sputtering were used. The opportunity of its application for maintaining highquality practically porous-free protective coating has been confirmed earlier by the

It has been demonstrated that the use of the fianite protective layer in Ge-structures instead of SiO2 eliminated pulse noise and thus considerably improved photoelectric and performance characteristics of these devices. It has been established that the improvement was related to more uniform nature of the fianite films, in particular, absence of pores, in

**4.6.3 Some properties of the device structures supplied with zirconium dioxide films** Photoelectric characteristics and noise of germanium photodiodes supplied with ZrO2 and SiO2 films described above have been investigated. Monochromatic sensitivity of these photodiodes is typical for germanium devices and equals to 0.5-0.6 A/W (at 1.06 and 1.55 µm wavelengths). The change SiO2 over ZrO2 resulted in somewhat decrease of a dark current (on average for 10%). Main improvement of the photodiodes quality achieved due to the application of ZrO2 films revealed at the noise studies. Under the voltage exceeding operational one (that corresponds to accelerated reliability testing conditions) the check samples with SiO2 films have shown pulse noise of telegraphic type in the oscillogram, which can be associated with processes of energizing- deenergizing of the surface

comparison with SiO2 films, which containing defects in form of pores.

of device structures making: photolithography and etching.

humidity resistance and reliability of the devices.

**4.6.2 Protective and stabilizing properties of fianite films on Ge** 

of ZrO2.

experiments.

Subsequent post-growth recrystallization annealing resulted in arising of a polycrystalline phase in the layer. At the same time, the layers sustained mirror-flat and uniform. Profile of the surface of z4 sample (Table 4) obtained using Talysurf interference microscope is shown in Fig. 22 a. Roughness of this ZrO2 surface was estimated as Sq = 0.852 nm that is not practically differ from roughness of the Si substrate used for the fianite growth (Sq = 0.7877 nm).

Preliminary studies of gate properties of thin (10–15 nm) fianite films obtained by laser deposition on Si substrates have been carried out. The studies conducted on the test structures with deposited Al contacts have shown that thin fianite films featured with low values of loss currents, minimum values being 10-12 А/cm2 at 1V voltage (Fig. 21 b, samples z 3 and z 4).

Fig. 21. Surface roughness of fianite film on Si substrate, sample Z4 (a) and leakage current of Al/fianite/Si structure (b), samples z 1 – z 5 were prepared under different conditions.

#### **4.6 Fianite and ZrO2 as protective and stabilizing layers on Ge and Si substrates and multilayer structures**

#### **4.6.1 Deposition modes**

For magnetron deposition of fianite and zirconium dioxide films, 2 types of vacuum evaporation Leybold Heraeus units were used with different target dimensions: 70 mm in diameter for fianite and 203 mm – for ZrO2 (table 5).

HF magnetron and direct voltage sputtering techniques were tested. The latter technique did not provide sufficient film growth rate, that is why magnetron HF sputtering (13.56 MHz) was chosen. The optimal modes of fianite and ZrO2 sputtering are also shown in table 5.


Table 5. Optimal Modes of Fianite and ZrO2 Sputtering

Subsequent post-growth recrystallization annealing resulted in arising of a polycrystalline phase in the layer. At the same time, the layers sustained mirror-flat and uniform. Profile of the surface of z4 sample (Table 4) obtained using Talysurf interference microscope is shown in Fig. 22 a. Roughness of this ZrO2 surface was estimated as Sq = 0.852 nm that is not practically differ from roughness of the Si substrate used for the fianite growth

Preliminary studies of gate properties of thin (10–15 nm) fianite films obtained by laser deposition on Si substrates have been carried out. The studies conducted on the test structures with deposited Al contacts have shown that thin fianite films featured with low values of loss currents, minimum values being 10-12 А/cm2 at 1V voltage (Fig. 21 b, samples

a b

diameter for fianite and 203 mm – for ZrO2 (table 5).

Table 5. Optimal Modes of Fianite and ZrO2 Sputtering

Fig. 21. Surface roughness of fianite film on Si substrate, sample Z4 (a) and leakage current of Al/fianite/Si structure (b), samples z 1 – z 5 were prepared under different conditions.

**4.6 Fianite and ZrO2 as protective and stabilizing layers on Ge and Si substrates and** 

For magnetron deposition of fianite and zirconium dioxide films, 2 types of vacuum evaporation Leybold Heraeus units were used with different target dimensions: 70 mm in

HF magnetron and direct voltage sputtering techniques were tested. The latter technique did not provide sufficient film growth rate, that is why magnetron HF sputtering (13.56 MHz) was chosen. The optimal modes of fianite and ZrO2 sputtering are also shown

Target Material Fianite ZrO2 Plant Z Z-400 Z-550 Target diameter 70 mm 203 mm Argon pressure 5\*10-3 mBar 5\*10-3 mBar Power ~ 500 Wt ~ 400 Wt Film growth rate 100 Å/min ~ 50 Å/min

I, A

z 5 z 2

0123

V , Â

z 3 z 4

z 1

(Sq = 0.7877 nm).

z 3 and z 4).

**multilayer structures 4.6.1 Deposition modes** 

in table 5.

In case of low magnetron power, plasma is unstable ("blinking plasma"); in case of larger values of discharge power, the growth rate increases, but irregularity of substrate surface layers and growing film coarse-graining are possible. Fianite sputtering requires higher power than in case of ZrO2; provided that the growth rate is twice as much than in case of ZrO2.

The developed technique of magnetron sputtering made it possible to vary the fianite film thickness between 600 and 2000 Å. Ge and Si plates with fianite film thereon were made using this technology. Ge samples with fianite film were used to try out further operations of device structures making: photolithography and etching.
