JPH05117086A - Production of diamond thin film and diamond substrate - Google Patents

Abstract

PURPOSE:To enable the mass-production and cost-reduction in the formation of a diamond thin film by vapor-phase deposition process by forming a diamond film on a substrate obtained by synthesizing BN or a boron phosphide nitride expressed by a specific formula on BP. CONSTITUTION:A thick BP film is formed on an Si substrate by thermal CVD process, etc., and the Si layer is removed by immersing in fluoronitric acid to obtain a single crystal BP thick film. A boron phosphide nitride film having a gradient composition structure expressed by formula BPxN1-x is formed by an ion plating apparatus using B as a solid raw material and PH3 and N2 as the raw material gas while slowly increasing the content of N2. A diamond film is grown on the obtained film by hot filament CVD process to obtain a diamond substrate having a diamond/BPxN1-x/BP structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a transistor and a sensor.
The present invention relates to a diamond substrate that can be used as a high hardness coating used for various semiconductor devices such as, an insulating film, and a cemented carbide tool.

[0002]

2. Description of the Related Art Attempts to synthesize diamond have been made for a long time, and in the 1950s, diamond was successfully synthesized by a high pressure synthesis method. On the other hand, the synthesis of diamond from the gas phase has been actively carried out due to the requirement to synthesize a diamond thin film. The microwave plasma CVD method, high frequency plasma CVD method, hot filament CVD method, ECR plasma CVD method, arc discharge Plasma jet CVD
There are reports of successful synthesis by various methods such as the method, combustion flame method and others. Needless to say, diamond has the highest hardness on earth as of 1991. In addition to its high hardness, diamond has many excellent properties. For example, since it has a very wide band gap and can be made into a p-type semiconductor by doping various impurities such as B, it can be used as a transistor or sensor operating at high temperature, or a short wavelength light emitting element. The use as various electronic devices is considered. Moreover, due to its high thermal conductivity, it is expected to be used as a heat sink.

[0003]

When used as an electronic device as described above, a high-purity large-area thin film single crystal is desired. However, for example, the diamond currently obtained by high-pressure synthesis is only a plate-like or granular crystal having a size of only a few millimeters. Further, the high-pressure synthesis method requires a very expensive high-pressure generator, and thus has a big problem that the unit price of a single crystal becomes extremely expensive. On the other hand, many methods of synthesizing diamond from the vapor phase have been tried as described above. The single crystal diamond thin film is obtained only when a diamond single crystal obtained by a high pressure synthesis method or a zinc blende type boron nitride single crystal (hereinafter abbreviated as c-BN) is used as a substrate. However, it is difficult to obtain a large area substrate because the substrate itself is made by the high pressure synthesis method. In addition to diamond and c-BN, Si or the like is often used as a substrate, but only a polycrystalline thin film can be obtained on a substrate such as Si, and the surface of diamond is highly uneven. From the above, it is an object of the present invention to provide a large amount of high-purity, large-area smooth diamond substrates or single crystal diamond substrates at low cost.

[0004]

According to the present invention,
(1) C-BN or boron-phosphorus-nitrogen ternary cubic single crystal compound (hereinafter B) on boron phosphide (hereinafter abbreviated as BP)
(Also referred to as P _x N _1-x ) and used as a substrate for growing a diamond thin film, (2) a structure in which BP is gradually changed in the thickness direction from BP to c-BN, or BP
using a substrate having a structure changed to _x N _1-x ,
(3) When synthesizing c-BN or BP _x N _1-x on BP, the boron surface of BP is used, and c-B synthesized on it is used.
Provided is a method for producing a diamond thin film, which is characterized by using N or BP _x N _1-x as a substrate.

Furthermore, (4) a structure having a c-BN layer on the BP and further having a diamond layer on the c-BN layer (FIG. 6).
(5), and (5) there is a BP _x N _1-x layer having a cubic crystal structure of three elements of B-P-N on BP, and a structure having a diamond layer on it (see FIG. 7). Show),
(6) A structure having a layer in which the composition gradually changes from BP to c-BN in the thickness direction on the BP and finally becomes c-BN, and further has a diamond layer thereon (see FIG. 8). Show),
(7) Gradually nitriding on BP in the thickness direction to obtain BP _x N
There is also provided a diamond substrate, each characterized by a structure having a _1-x layer and further having a diamond layer thereon (shown in FIG. 9). 6 to 9 show the structure of the diamond substrate of the present invention, and the ratio x of P in the mixed crystal BP _x N _1-x is shown on the right side thereof. X = 0 for BN, x = 1 for BP
In the middle, the value of x changes in various ways.

The steps will be described below in order. First, the BP itself. Compared with diamond and c-BN which are conventionally used as a substrate for obtaining a single crystal diamond by a high pressure synthesis method, BP has a feature that it can be easily synthesized and an area can be increased. The BP substrate used in the present invention may be manufactured by a known technique such as a flux method or a thermal CVD method. BP is nothing
It may be one that is not pinged or one that is doped with Si or the like. It may also be one that can act as an active layer of a p-type or n-type semiconductor by slightly supplying B or P excessively. Alternatively, it may be synthesized on a substrate such as Si, SiC or Al ₂ O ₃ by a known technique such as a thermal CVD method. In this case, BP remains on the substrate such as Si, SiC or Al ₂ O _3. Alternatively, it may be a self-standing film of BP obtained by removing these substrates. Note that SiC has a lattice constant of 0.4360 nm.
Since the lattice constant is close to that of BP, the crystallinity of the BP layer formed thereon is better than that when Si or Al ₂ O ₃ is used as the substrate. As a result, c-BN and BP on this BP
It is possible to obtain _x N _1-x , and diamond with good crystallinity as well. However, it is desirable that it is a single crystal BP.

C-BN is synthesized on this BP layer. This is known CVD such as ECR plasma CVD or RF plasma CVD, or IVD (Ion Vapor Deposition).
Method) or ion plating method. Although c-BN may be immediately synthesized on the BP substrate (Fig. 6), BP has a lattice constant of 0.4.
At 539 nm, c-BN is 0.3615 nm. The difference in lattice constant between these is not small. Therefore BP and c-B
Since a large internal stress exists at the interface with N, peeling or the like is likely to occur. However, both BP and c-BN are zinc blende type crystals. Therefore, the P position of BP is gradually and continuously or stepwise switched to N, so that the P structure of the BP is gradually replaced with N in the thickness direction even though it is a cubic system. A membrane can be made (Figs. 7-9). In this way, P of BP is gradually replaced with N, and diamond is finally synthesized on the substrate that has become P-free c-BN (Fig. 8), thereby obtaining a smooth diamond thin film with better crystallinity. Can be synthesized. In addition, when forming a BP-N ternary cubic crystal BP _x N _1-x on the BP substrate or gradually replacing P with N, some P is finally contained. In this state, BP _x N _1-x may be left as it is, and diamond may be synthesized thereon (FIG. 9). Also in this case, it is possible to obtain a diamond thin film having good crystallinity.

When c-BN or BP _x N _1-x is formed on the BP substrate or the composition is graded, B
These may be deposited on the P substrate, or P or a part of P may be replaced with N in the vicinity of the surface of the BP substrate. In this case, as a method of substituting P or a part of P with N, (1) in a state where the BP substrate is heated, a gas containing N (eg, N ₂ , NH ₃ etc.) is ionized and accelerated to B
Method of irradiating P substrate, (2) Method of exposing to plasma of gas containing N, (3) Method of heat treatment in gas containing N,
Etc. are possible. C-BN or B on the above BP
In the case of synthesizing P _x N _1-x (including c-BN and BP _x N _1-x obtained by gradually substituting P of BP with N), it is particularly synthesized on the boron surface of BP. It is preferable to do. c
-C-B especially when synthesizing diamond on BN
A good crystal diamond can be obtained on the boron surface of N. c-
In order for BN or BP _x N _{1-x to} have a boron surface which is preferable for synthesizing a single crystal diamond on the outermost surface, c-BN or BP _x N _1-x should be synthesized on the underlying BP, especially on the boron surface. Is preferred.

[0009]

FUNCTION Diamond is a cubic crystal and its lattice constant is 0.3543 nm. Si, which has been conventionally used as a substrate for synthesizing diamond thin films, has the same crystal structure as diamond, but has a lattice constant of 0.5430n.
It is as large as m. Due to this large difference in lattice constant, it is difficult to epitaxially grow diamond on a Si substrate. Table 1 shows the lattice constant of each substance. Of these, the one with the closest lattice constant to diamond is cB
N. On the other hand, there are several reports that single crystal diamond has actually grown on c-BN. However, as described above, it is difficult to synthesize c-BN, and a good-quality c-BN single crystal is very small (about several mm) by the high-pressure synthesis method and extremely expensive. Therefore, the inventors have synthesized a large area c-BN crystal or BP _x N _1-x on a BP capable of forming a large single crystal thin film, and have prepared this c-BN or BP.
By synthesizing diamond on the _x N _1-x crystal, it has succeeded in epitaxially growing a large area smooth diamond or a single crystal diamond having a uniform crystal orientation on the crystal, resulting in the present invention. ..

[0010]

[Table 1]

BP is a crystal having a zinc blende type structure having a lattice constant of 0.4539 nm and is known to grow epitaxially on Si or SiC. On the other hand, c-BN has a lattice constant of 0.3615 nm, which is somewhat smaller than that of BP, but has the same zinc blende type crystal structure as BP. Generally, when boron nitride is prepared by the above-mentioned known synthesis method, hexagonal boron nitride (hereinafter abbreviated as h-BN) or amorphous boron nitride (hereinafter a-B).
Only a film containing N) is obtained. However, this is because they are synthesized on Si, which is a material having greatly different lattice constants. BP has a lattice constant closer to that of c-BN than that of Si. Therefore, c-BN with good crystallinity on BP
The inventors believe that a single-phase membrane could be synthesized.

Also, a part of P of BP is gradually N
By replacing with c-BN with better crystallinity
Can be synthesized. Therefore, by growing diamond using this substrate, smooth or uniform single crystal diamond can be obtained. When a thin film having a structure in which a part of P of BP is gradually replaced with N in the thickness direction is formed, the outermost surface does not necessarily have to be c-BN. Ie B and P
A ternary crystal of N and N may be used. The present inventors believe that a single crystal diamond having a smooth or uniform orientation grows because it becomes smaller than the original lattice constant of BP by substituting a part of P with N, and approaches the lattice constant of diamond. ing. In the present invention, the smooth diamond layer has a surface roughness of Rmax of 5 which is measured by a surface roughness meter.
% Or less. Such a smooth diamond layer has a single crystal, a single crystal containing twins, or a grain size of several μm.
It is considered to be composed of the above polycrystals. Of these, single crystals, particularly single crystals with few twins, are preferred. Here, the diamond layer may be a non-doped layer, but may also be used as an active layer of a semiconductor device as a p-type or n-type semiconductor by doping various impurity elements such as B. The thickness of the diamond layer formed in the present invention is preferably 10 μm or less. This is c- on the outermost surface of the substrate
This is because the substrate warps due to the difference in thermal expansion coefficient between BN and BP _x N _1-x . However, when diamond is used as a self-supporting film by removing BP of the substrate after film formation, the thickness may be 10 μm or more.

[0013]

EXAMPLES Examples 1, 2, and 3 of the present invention will be described below.
For comparison, the same method is used for synthesizing diamond using a silicon substrate or an alumina substrate. Conventional examples are also comparative examples 1.1, 1.2; 2.1, 2.2; 3.1, 3.2.
As described below. The substrate of Example 1 is a, Comparative Example 1.1,
Substrates 1.2 are designated as b and c. These schematic configurations are shown in FIG.
~ 12. The substrates of Example 2 are d, e and f, the substrates of Comparative Examples 2.1 and 2.2 are g and h, and the schematic configurations are shown in FIGS. The substrate of Example 3 is i, j, k, l, m, and the substrates of Comparative Examples 3.1 and 3.2 are n and o.
18 shows a schematic configuration. Further, Table 5 summarizes the method of forming each thin film in Examples 1 to 3.

1. Example 1 and Comparative Example 1.1, Comparative Example 1.
2-Microwave Plasma CVD Method Using the microwave plasma CVD apparatus (FIG. 1), diamond was synthesized on the substrate and the present invention and the conventional example were compared. Example 1 Substrate a FIG. 10 First, a BP having a thickness of 0.2 mm was synthesized on a (111) plane of Si having a size of 10 mm × 20 mm by a known thermal CVD method. When this was observed by a high-speed reflection electron diffraction method (hereinafter also abbreviated as RHEED method), it was confirmed that the single crystal had a (111) plane. Then, the Si layer was removed by immersing the same substrate in hydrofluoric nitric acid to obtain a single crystal BP free-standing film. Then, a BN film was synthesized on this BP substrate by a magnetic field microwave plasma CVD apparatus (FIG. 2). The apparatus shown in FIG. 2 is also called an ECR plasma CVD apparatus. In the microwave generator 20, for example, 2.45 GHz
Microwave 21 is generated. This propagates through the waveguide 22 and enters the vacuum chamber-24 through the dielectric window 23. A substrate 26 is supported inside this by a substrate holder 25. A coil 27 that gives a magnetic field for electron resonance is provided on the outer circumference of the vacuum chamber 24. The strength of the resonance magnetic field is 875
Gauss. The raw material gas is introduced from the gas introduction section.
This is excited by the energy of electrons generated by the resonance of the microwave and the magnetic field, and becomes plasma 28. Board 2
An appropriate bias can be applied to 6 by a power supply 29. Due to the energy of plasma, a gas phase reaction occurs even at a relatively low temperature. Then, the reaction product is deposited on the substrate 26. The exhaust gas is discharged from the exhaust port 30.

After placing the BP substrate in the vacuum chamber, BN was grown to 100 nm on the BP substrate by the magnetic field microwave plasma CVD method under the following conditions. BN growth: Source gas B ₂ H ₆ , N ₂ , Ar flow rate B ₂ H ₆ 1.5 sccm N ₂ 1.5 sccm Ar 13.5 sccm pressure 5.3 × 10 ^-2 Pa microwave frequency 2.45 GHz Microwave power 300 W Magnetic field by coil 875 G Substrate temperature 520 K Substrate bias -80 V BN film thickness 100 nm Crystalline state of the BN layer of the obtained BN / BP substrate was RHEE.
As a result of observation by the D method, diffraction corresponding to h-BN or a-BN was not seen, but only diffraction corresponding to c-BN was seen. In addition, only the absorption corresponding to c-BN was observed by infrared absorption spectroscopy.

Subsequently, this c-BN / BP substrate was placed in the vacuum chamber of the apparatus shown in FIG. 1 and diamond was grown on it. The apparatus of FIG. 1 is a microwave plasma CVD
It is a device. The microwave generator 11 supplies the microwave 12
Occurs. This reaches the quartz tube 14 which is the reaction space through the waveguide 13. A substrate holder 15 is provided inside the quartz tube 14 to support a substrate 16. The raw material gas is introduced from the gas introduction part 17 above the quartz tube 14. The gas is excited by the action of microwaves and becomes plasma 18. A gas phase reaction occurs in the plasma, and reaction products are deposited on the substrate. Exhaust gas is discharged from the exhaust port 19 connected to the exhaust system.

1 μm of diamond was grown on the c-BN substrate by the microwave plasma CVD method under the following conditions. Diamond growth: Source gas CH ₄ , H ₂ (simultaneously introduced) Flow rate CH ₄ 2 sccm H ₂ 200 sccm Pressure 1 × 10 ⁴ Pa Microwave frequency 2.45 GHz Microwave power 200 W Growth time 1.5 hours Substrate temperature 1130 K diamond film thickness 1 μm First, it was confirmed by Raman spectroscopy that the film obtained was diamond. As a result of observing the crystal state of the obtained diamond layer by the RHEED method, a diffraction pattern corresponding to the (111) plane was obtained. Further, when the surface roughness was examined by a surface roughness meter, it was R _max = 30 nm.

[Comparative Example 1.1] Substrate b FIG. 11 For comparison, an attempt was made to form a diamond layer on a single crystal Si substrate having a plane orientation (111) by a microwave plasma CVD apparatus under the same conditions as in Example 1 above. It was However, the mirror surface Si
Almost no diamond was formed on the upper part, and only very few diamond particles having a non-uniform crystal orientation were observed.

[Comparative Example 1.2] Substrate c FIG. 12 Further, a single crystal Si substrate having a plane orientation (111) which was scratched with diamond abrasive grains of 20 to 40 μm was also treated by the microwave plasma CVD apparatus in the above Example. An attempt was made to form a diamond layer under the same conditions as in 1. In this case, the film thickness is 1
A μm diamond layer was obtained. RHEE
The crystal state of the layer obtained by the D method was observed, and only a spotty ring pattern corresponding to diamond was obtained, and it was confirmed that this diamond layer was a polycrystal having a non-uniform crystal orientation. The surface roughness is R _max = 400.
It was nm. Table 2 shows Example 1 and Comparative Examples 1.1 and 1.2.
The process and the structure of the substrate are outlined.

[0020]

[Table 2]

2. Example 2 and Comparative Example 2.1, Comparative Example 2.2-Hot Filament CVD-Diamond was synthesized on a substrate using a hot filament CVD apparatus (FIG. 3) to compare the present invention with a conventional method. Example 2 Substrates d, e, f FIG. 13 2 mm × 2 mm × synthesized by the flux method as a substrate
A single crystal BP having a plane orientation (100) of 1 mm was used. This was washed with various acids and organic solvents. Then this B
BP on the P substrate with an ion plating device (Fig. 4)
A -N graded composition structure film was synthesized. Ion plate in Fig. 4
The towing device will be described first. The vacuum container 37 is a container that has an exhaust port 38 and a gas introduction port 39 and can be evacuated. An ionization electrode 40 and a filament 49 are provided in the middle part. The ion electrode is connected to the DC power supply 41. The substrate 42 is attached to the upper electrode above.
There is a heater 43 on the back surface to heat the substrate 42 to an arbitrary temperature. A high frequency power supply 44 is connected to the upper electrode. In the lower part there is a water-cooled crucible 45 in which there is metallic boron 46.
Is housed. An electron beam is emitted from the electron gun 47, is bent by a magnetic field, and collides with metallic boron. Kinetic energy
To heat the boron into steam. The vapor rises upward and is excited by the plasma of the gas, and part of it becomes ions.
The dust reaches the vicinity of the substrate as neutral vapor. The source gas is separately introduced from the gas inlet 39, which becomes plasma by the high frequency power between the ionization electrode and the upper electrode. The plasma hits the substrate and activates the surface. Boron reacts with the gas to deposit the boride on the substrate.

A BP substrate was attached to the upper electrode of this ion plating apparatus. 1x1 in the vacuum chamber
After the gas is exhausted to 0 ^-4 Pa or less, the raw material gas is introduced to start the evaporation of boron and the graded structure BP
_{A x} N _1-x film was grown. Growth of BP _x N _{1 -x} : Raw material solid boron Raw material gas Ar, PH ₃ , N ₂ raw material gas partial pressure Ar 2.5 × 10 ⁻¹ Pa PH ₃ (initial) 2.0 × 10 ⁻¹ Pa (decrease) N ₂ Gradual increase Ionization electrode bias 60 V Substrate RF bias 100 W Substrate temperature (heated by heater) 570 K In this method, BP _x N _1- x with different x 3
The types of substrates d, e, and f were created.

The elemental analysis of the surface of the obtained BN or B-P-N layer was conducted by X-ray photoelectron spectroscopy. The results are: (1) B: P: N = 10.0: 0.2: 9.5 for substrate d, and (2) B: P: N = 10.0: 2.0: 7.8 for substrate e. (3) In the substrate f, B: P: N = 10.0: 5.0: 4.9. As a result of observing the crystalline state of these films by the RHEED method, in the case of the substrate d, the diffraction corresponding to c-BN, and in the case of the substrates e and f, the cubic system having a larger lattice constant than c-BN Only diffractions belonging to

Subsequently, the substrates d, e, and f were placed in the vacuum chamber of the apparatus shown in FIG. The apparatus of FIG. 3 is a hot filament CVD apparatus. A tungsten filament 32 is provided inside the vacuum chamber 31. A substrate holder-34 for holding the substrate 33 is installed opposite to this. The raw material gas is introduced from the upper gas introduction part 35. When the filament is energized, heat is generated and radiant heat is generated. This heat excites the raw material gas to cause a gas phase reaction. Since the product is deposited on the substrate 33, thin film formation is possible. The exhaust gas is discharged from the exhaust port 36.

The substrates d to f have a structure of BP _x N _1-x / BP, and diamond was grown on the BP _x N _1-x surface by the hot filament CVD method under the following conditions. Diamond growth: Raw material gas CH ₄ , H ₂ raw material gas flow rate CH ₄ 4 sccm H ₂ 200 sccm pressure 4 × 10 ³ Pa filament temperature 2273 K substrate surface temperature 1100 K filament substrate distance 10 mm growth time 2 hours diamond film thickness 2 The obtained product has a structure of diamond / BP _x N _1-x / BN. RHEED the crystalline state of the diamond layer
When observed by the method, diffraction corresponding to diamond was seen from the diamond thin film formed on any of the substrates d, e, and f. As a result of the analysis, it was found that these diamond layers are oriented polycrystalline diamonds composed of some large crystals including twins. The surface roughness was R _max = 75 nm.

[Comparative Example 2.1] Substrate g FIG. 14 For comparison, an attempt was made to form a diamond layer on a single crystal Si mirror-finished substrate having a plane orientation (100) by the hot filament CVD method under the same conditions as in Example 2 above. It was However, it was not possible to obtain a thin film because only a part of the diamond particles having a non-uniform crystal orientation were observed.

[Comparative Example 2.2] Substrate h FIG. 15 Further, the plane orientation (1
A diamond layer was also tried to be formed on the single crystal Si substrate of (00) by the hot filament CVD method under the same conditions as in Example 2 above. In this case, a diamond layer having a film thickness of 1 μm was obtained. Also for this, the crystal state of the layer obtained by the RHEED method was observed, and only a spotty ring pattern corresponding to diamond was obtained, and it was confirmed that this diamond layer was a polycrystal with a non-uniform crystal orientation. did. The surface roughness of the thin film was R _max = 300 nm. Table 3 outlines the steps and substrate structures of Example 2 and Comparative Examples 2.1 and 2.2.

[0028]

[Table 3]

3. Example 3, Comparative Example 3.1, Comparative Example 3.
2-ECR Plasma CVD Method-The present invention and the conventional method were compared by growing diamond on a substrate using a magnetic field microwave plasma CVD apparatus (FIG. 2: ECR plasma CVD apparatus). [Example 3] Substrates i, j, k, l, and m; Fig. 16 and Fig. 17 As the substrate, 1 was synthesized by the thermal CVD method as in Example 1.
A single crystal BP substrate having a plane orientation (111) of 0 mm × 20 mm × 0.2 mm was used. However, this time, the Si used for synthesizing BP was not removed, and the BP / Si two-layer structure in which BP was present on Si was used for the substrate as it was. This was washed with hydrofluoric acid and an organic solvent such as isopropyl alcohol and acetone. It was confirmed that the surface of this substrate was a boron surface by etching the surface of this substrate.

Subsequently, a substrate was synthesized on this substrate by using the RF plasma CVD apparatus (FIG. 5) by the following two kinds of methods. In the apparatus shown in FIG. 5, the vacuum chamber 51
Is a container whose inside can be evacuated. Above the substrate is a substrate holder 53 to which the substrate 52 is attached. This also serves as the upper electrode. A hollow lower electrode 54 is installed below. A large number of gas outlets 55 are formed on the upper surface of the lower electrode 54. The gas introduced from the lower gas inlet 56 enters the internal space from the outlet 55. The lower electrode 54 can be supplied with high frequency power by a high frequency power source oscillator 57. The supply holder 53 as the upper electrode has a heater 58 so that the substrate can be heated to a desired temperature.
A bias can be applied to the upper electrode by a DC power supply.

(I) -nitriding of BP surface-substrates i, j;
FIG. 16 shows a method of forming a B-P-N gradient composition structure layer by reacting BP with NH ₃ to nitride the surface of the BP. BP / on the substrate holder in the vacuum chamber
After the Si substrate was attached, a BP _x N _1-x layer was formed under the following conditions: BP _x N _1-x layer formation: Source gas NH ₃ , N ₂ gas flow rate NH ₃ 5 sccm N ₂ 95 sccm Pressure (60 Torr ) 8 × 10 ³ Pa RF power between electrodes 200 W Substrate temperature 1000 K Since plasma contains nitrogen components, P in BP
Are replaced by N over time. If it is treated for a long time, the ratio of P decreases and the ratio of nitrogen increases. By reacting for various times in this state, 1. B: P: N = 10.0: 0.0: 9.9 ... Substrate i 2. B: P: N = 10.0: 4.9: 4.9 ... A phase having a substrate j was synthesized. The above elemental analysis is X
It was performed by line photoelectron spectroscopy. When these films were observed by the RHEED method, in the case of the substrate i, diffraction corresponding to the (111) plane of c-BN was observed, and
In the case of, only the diffraction corresponding to the cubic (111) plane having a lattice constant larger than that of c-BN was obtained. Further, it was confirmed by the Rutherford backscattering method that the surface of the BPN crystal film formed on the surfaces of the substrates i and j was a boron surface.

(II) -Changing the composition of raw material gas-
Substrates k, l, m; FIG. 17 Another method is to deposit a B-P-N gradient composition structure film on the BP surface while changing the P / N component of the raw material. After placing the substrate in the vacuum chamber of the apparatus of FIG. 5, BP _x N _1-x was grown on the BP / Si substrate as follows. BP _x N _1-x growth: Raw material gas Ar, H ₂ , B ₂ H ₆ , PH ₃ , NH ₃ gas flow rate B ₂ H ₆ 0.1 sccm, PH ₃ (initial) 0.5 sccm, H ₂ 100 sccm Ar 100 sccm (The above gases are introduced at the same time) NH ₃ Gradually increase Pressure (80 Torr) 1.1 × 10 ⁴ Pa RF power between electrodes 300 W Substrate temperature 870 K Substrate RF bias -100 V Used for film formation in this case Among the above gases, PH ₃ gas was gradually replaced with NH ₃ gas. Film formation was performed up to various gas ratios to prepare three types of substrates k, l, and m.

The surface of the obtained BN or B-P-N layer was subjected to elemental analysis by X-ray photoelectron spectroscopy as in Example 2. As a result, 1. For substrate k, B: P: N = 10.0: 0.1: 9.7 2. For substrate l, B: P: N = 10.0: 7.8: 2.1 3. In the substrate m, B: P: N = 10.0: 4.8: 5.0. As a result of observing the crystalline state of these films by the RHEED method, in the case of the substrate k, (111) of c-BN was obtained.
The diffraction corresponding to the plane is also c- in the case of substrates l and m.
Only the diffraction belonging to the cubic (111) plane having a lattice constant larger than that of BN was obtained. It was also confirmed that the surface of the B-P-N film obtained by the Rutherford backscattering method was a boron surface.

Subsequently, these substrates were attached to a magnetic field microwave plasma CVD apparatus (ECR plasma CVD apparatus) shown in FIG.
It was installed in a vacuum chamber of No. 1 and diamond was grown under the following conditions. Diamond growth: Source gas CH ₄ , H ₂ gas flow rate CH ₄ 4 sccm H ₂ 200 sccm pressure 10 Pa microwave frequency 2.45 GHz microwave power 500 W magnetic field 875 G growth time 30 minutes Diamond growth for 30 minutes under these conditions Let's do diamond /
Was obtained _{BP x N 1-x / BP} / Si structure. As a result of observing the obtained diamond with a scanning electron microscope, it was found that diamond particles having a uniform crystal orientation were formed on all the substrates. Table 6 shows the nucleation density of diamond particles on each substrate. It can be seen that a large number of diamond particles are nucleated.

[0035]

[Table 6]

Comparative Example 3.1 Substrate n FIG. 18 For comparison, a single crystal Al ₂ O ₃ mirror substrate having a plane orientation of (0001) was prepared by a magnetic field microwave plasma CVD method under the same conditions as in Example 3 above. Tried to form diamond.
Similar to the film formation on the mirror-finished Si substrate in Comparative Example 1.1 (substrate b) and Comparative Example 2.1 (substrate g), a very small part (nucleus generation density 2.1 × 10 ⁵ cm ⁻² ) crystals It was not possible to obtain a thin film because only diamond particles with non-uniform orientation were observed.

[Comparative Example 3.2] Substrate o FIG. 19 Plane orientation (000
An attempt was made to form a diamond layer on the single crystal Al ₂ O ₃ substrate of 1) by the magnetic field microwave plasma CVD method under the same conditions as in Example 3 above. In this case, diamond particles having a nucleus generation density of 1.6 × 10 ⁸ cm ⁻² and having non-uniform crystal orientations were obtained. In Table 4, Example 3 (substrates i, j,
The processes of k, l, m) and Comparative Examples 3.1 (substrate n) and 3.2 (substrate o) and the structure of the substrate are schematically shown.

[0038]

[Table 4]

Table 5 shows a method of forming each thin film in Examples 1 to 3.

[0040]

[Table 5]

[0041]

According to the present invention, a large area smooth diamond substrate or single crystal diamond substrate useful for semiconductor applications, cemented carbide tools applications, etc. can be manufactured in large quantities and at low cost.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a microwave plasma CVD apparatus used in the present invention.

FIG. 2 is a magnetic field microwave plasma CV used in the present invention.
FIG.

FIG. 3 is a schematic sectional view of a hot filament CVD apparatus used in the present invention.

FIG. 4 is a schematic cross-sectional view of an ion plating device used in the present invention.

FIG. 5 is a schematic sectional view of an RF plasma CVD apparatus used in the present invention.

FIG. 6 is a schematic cross-sectional view of a diamond substrate of the present invention having a diamond / c-BN / BP structure and a diagram showing the P ratio in each layer.

FIG. 7 is a schematic cross-sectional view of a diamond substrate of the present invention having a diamond / BP _x N _1-x / BP structure and having a constant x in the intermediate layer, and a diagram showing the P ratio in each layer.

FIG. 8 is a schematic cross-sectional view of a diamond substrate of the present invention having a diamond / BP _x N _1-x / BP structure in which x changes from 1 to 0 in an intermediate layer and a P ratio in each layer. Fig.

FIG. 9 is a schematic cross-sectional view of a diamond substrate of the present invention having a diamond / BP _x N _1-x / BP structure in which x varies from 1 to more than 0 in an intermediate layer and P in each layer. The figure which shows a ratio.

10 is a cross-sectional view of a substrate having a diamond / c-BN / BP structure according to Example 1 of the present invention and a diagram showing P ratios in respective layers. FIG.

FIG. 11 is a cross-sectional view of Comparative Example 1.1 in which diamond is formed on a mirror-like silicon substrate.

FIG. 12 is a sectional view of Comparative Example 1.2 in which diamond is formed on a scratched silicon substrate.

FIG. 13 is a sectional view of a substrate according to Example 2 of the present invention having a diamond / BP _x N _1-x / BP structure and P in each layer.
The figure which shows a ratio.

FIG. 14 is a cross-sectional view of Comparative Example 2.1 in which diamond is formed on a mirror-like silicon substrate.

FIG. 15 is a cross-sectional view of Comparative Example 2.2 in which diamond is formed on a scratched silicon substrate.

FIG. 16 is a cross section of a substrate of Example 3 having a diamond / BP _x N _1-x / BP structure and adapted to change x from 1 to near 0 by nitriding BP with NH _{3 in an} intermediate layer. The figure and the figure which shows the P ratio in each layer.

FIG. 17 shows that of Example 3 having a diamond / BP _x N _1-x / BP structure and changing x from 1 to near 0 by changing the gas composition from PH ₃ to NH _{3 in the} intermediate layer. FIG. 3 is a cross-sectional view of a substrate and a diagram showing P ratio in each layer.

FIG. 18 is a sectional view of comparative example 3.1 in which diamond is formed on a mirror-like alumina substrate.

FIG. 19 is a cross-sectional view of Comparative Example 3.2 in which diamond is formed on a scratched alumina substrate.

[Explanation of symbols]

 11 Microwave generator 12 Microwave 13 Waveguide 14 Quartz tube 15 Substrate holder 16 Substrate 17 Gas introduction part 18 Plasma 19 Exhaust port 20 Microwave generator 21 Microwave 22 Waveguide 23 Dielectric window 24 Vacuum chamber-25 Substrate holder-26 Substrate 27 Coil 28 Plasma 29 Power source 30 Exhaust port 31 Vacuum chamber-32 Filament 33 Substrate 34 Substrate holder-35 Gas introduction part 36 Exhaust port 37 Vacuum container 38 Exhaust port 39 Gas introduction port 40 Ionization electrode 41 DC power source 42 Substrate 43 Heater 44 High Frequency Power Supply 45 Water Cooling Crucible 46 Metal Boron 47 Electron Gun 48 Shutter 49 Filament 51 Vacuum Chamber 52 Substrate 53 Substrate Holder 54 Lower Electrode 55 Blowout 56 Gas Inlet 57 High Frequency Power Source Oscillator 58 Heat 59 DC power supply 60 plasma

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 21/205 7454-4M

Claims (10)

[Claims] 1. A method for producing a diamond thin film, which comprises forming a diamond thin film by a vapor phase epitaxy method on a substrate obtained by synthesizing boron nitride or boron phosphide nitride on boron phosphide. 2. A substrate having a structure in which the ratio of nitrogen is gradually increased on boron phosphide in the thickness direction thereof from boron phosphide to boron phosphide nitride or from phosphide boron to boron nitride. A method for producing a diamond thin film, which comprises forming a diamond thin film on the top by vapor phase epitaxy. 3. A diamond thin film according to claim 1, wherein diamond is grown on boron nitride formed on boron phosphide or on a boron surface of boron phosphide nitride. Production method. 4. Boron phosphide is grown on a silicon single crystal, boron nitride or boron phosphide nitride is synthesized on this boron phosphide, and a diamond thin film is formed on this substrate by vapor phase epitaxy. A method for producing a diamond thin film, which comprises: 5. Boron phosphide is grown on a silicon single crystal and gradually changed in the thickness direction so that the nitrogen ratio increases from boron phosphide to boron phosphide nitride or from phosphide boron to boron nitride. A method for producing a diamond thin film, which comprises synthesizing boron phosphide nitride to be formed on the boron phosphide and forming a diamond thin film on the substrate by vapor phase epitaxy. 6. Boron phosphide is grown on a silicon single crystal, the silicon substrate is removed, and the nitrogen ratio is gradually changed from boron phosphide to boron phosphide nitride or from boron phosphide to boron nitride in the thickness direction. A method for producing a diamond thin film, which comprises synthesizing boron phosphide nitride that changes so as to increase the amount on the boron phosphide, and forming a diamond thin film on the boron phosphide nitride by vapor phase epitaxy. 7. A diamond substrate having boron phosphide, a boron nitride layer or a boron phosphide nitride layer grown on the boron phosphide, and a diamond layer further grown thereon. .. 8. Boron phosphide and the nitrogen ratio grown on said boron phosphide such that the nitrogen ratio gradually increases in the thickness direction from boron phosphide to boron phosphide nitride or from boron phosphide to boron nitride. A changing diamond substrate having a layer of boron phosphide nitride changing to, and a diamond layer grown thereon. 9. A silicon substrate, boron phosphide grown on the silicon substrate, and boron phosphide grown on the silicon phosphide gradually changing in thickness direction from boron phosphide to boron phosphide nitride or A diamond substrate comprising: a boron phosphide nitride that changes so that the nitrogen ratio increases from boron phosphide to boron nitride; and a diamond layer further grown thereon. 10. A silicon substrate, boron phosphide grown on the silicon substrate, a boron nitride layer or a boron phosphide nitride layer grown on the boron phosphide, and further grown thereon. And a diamond layer.