JPH08239752A - Thin film of boron-containing aluminum nitride and its production - Google Patents

Abstract

PURPOSE: To easily produce a thin film of boron-containing aluminum nitride having high hardness and excellent in crystal-linity by forming a thin aluminum nitride single crystal film as an intermediate layer on a single crystal substrate and further forming a thin film of boron-containing aluminum nitride single crystal on the intermediate layer. CONSTITUTION: A thin film 2 of aluminum nitride single crystal is formed as an intermediate layer on a single crystal substrate 1 (diamond, sapphire, etc.) to about 1mm-1μm thickness. On this intermediate layer, a thin film 3 of boron- containing aluminum nitride single crystal is formed. At this time, this thin single crystal film 3 has a composition represented by Bx Al1-x Ny (where 0.001<=x<=0.3 and 0.85<=y<=1.05 are satisfied) and also has a wurtzitic crystalline structure. By this method, the thin film 3 of boron-containing aluminum nitride single crystal, having wide band gap and high sonic velocity and easy control of valence electron, can be obtained.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Boron-containing aluminum nitride thin films used for tools, wear resistant parts, surface acoustic wave devices, light emitting devices, high thermal conductive heat sinks, etc.

[0002]

2. Description of the Related Art Nitride having a high hardness such as boron nitride and aluminum nitride does not exist in nature, and attempts have been made to synthesize powders and thin films. Aluminum nitride has a wurtzite type crystal structure, high hardness, fast sound velocity, and wide band gap, and powder, its sintered body, and a thin film are manufactured. Since large single crystals cannot be manufactured, practical thin films or thin films with orientation have been put into practical use or development research as tools, high frequency surface acoustic wave filters, short wavelength light emitting devices and the like.

Boron nitride has a low-pressure phase typified by a hexagonal type in which nitrogen and boron are bonded in an sp2 hybrid orbital, and a cubic or wurtzite type crystal structure in which nitrogen and boron are bonded in an sp3 hybrid orbital. The high-pressure phase boron nitride has a high-pressure phase, but fine particles of high-pressure phase boron nitride have heretofore been synthesized only by a static high-pressure method or an implosion method. Many attempts have been made to synthesize such a thin film of high-pressure phase boron nitride without using a high-pressure generator, but a high-pressure phase boron nitride film with high crystallinity required for semiconductors and high-frequency filters has been developed. Not obtained.

Japanese Laid-Open Patent Publication No. 1-232695 uses an AC pulse having different phases and an AC pulse having different amplitudes in the forward and reverse directions by using a composite thin film made of AlN and BN as a dielectric layer of a thin film EL element. It describes a thin film element that has stable B / V characteristics for a long time even when driven by. However, there is no description about what kind of crystal structure the composite has.

[0005]

In order to solve the above-mentioned problems, the present invention has a higher hardness, a wider bandgap, and a higher sound velocity than aluminum nitride, is easy to control valence electrons, and has good crystallinity. It is intended to provide a boron-containing aluminum nitride single crystal thin film.

The inventors have found that an aluminum nitride thin film containing boron (boron-containing aluminum nitride (BAlN) single crystal thin film) has the same crystal structure as wurtzite type boron nitride and wurtzite type aluminum nitride, AlN) is superior in hardness, speed of sound, band gap, etc., and it is possible to easily synthesize a thin film with higher quality crystallinity than wurtzite type boron nitride. I got a conclusion.

[0007]

[Means for Solving the Problems] Boron, aluminum,
Consisting of nitrogen, B _x Al _1-x N _y (0.001 ≤ x ≤ 0.7, 0.85 ≤ y ≤
1.05), and a ternary thin film having a wurtzite crystal structure, if it is formed so as to maintain its crystallinity at a high quality, it has higher hardness, faster sound velocity, and wider band gap than the aluminum nitride thin film. It has a high functionality, has a narrower half-width of the rocking curve of X-ray diffraction than the high-pressure phase boron nitride thin film, and provides a high-quality crystalline thin film with excellent crystallinity and crystal orientation. is there.

At this time, in particular, an aluminum nitride single crystal thin film is formed as an intermediate layer on the single crystal substrate, and a boron-containing aluminum nitride (BAlN) single crystal thin film is grown on this aluminum nitride to directly deposit the single crystal substrate. BAlN
It becomes possible to grow a single crystal to a B / Al composition ratio (x ≦ 0.3) higher than that for growing a thin film. When x> 0.3, the lattice mismatch between the underlayer and the thin film becomes large, making it difficult to form a single crystal thin film.

Further, B / Al is used as an intermediate layer on the single crystal substrate.
A BAlN single crystal gradient composition layer in which the composition ratio is continuously or stepwise increased, or an aluminum nitride single crystal layer as the first intermediate layer and a B / Al composition ratio as the second intermediate layer on the aluminum nitride single crystal layer continuously or Gradually increased BAlN single crystal gradient composition layer B _α Al ₁ - _α N _β (0.0001 ≦ α ≦ X, 0.85 ≦ β ≦ 1.05)
By growing BAlN on these using B _x
In the composition range of Al _1-x N _y (0.001 ≦ x ≦ 0.7, 0.85 ≦ y ≦ 1.05), a single crystal thin film can be formed.

To form such a BAlN single crystal thin film, a material selected from aluminum, boron, aluminum nitride, boron nitride and aluminum-boron alloy is used as a target in a gas atmosphere containing at least nitrogen or ammonia. A BAlN single crystal thin film is formed by the sputtering method, or at least a halide or hydride containing boron and aluminum or an organometallic compound, a metal alkoxide is diluted with hydrogen or an inert gas and supplied as a raw material, and then the plasma CVD method is used. Method for forming BAlN single crystal thin film, MOCVD method, M
We have found that the BE method is preferable.

By the above manufacturing method, B is formed on a single crystal of diamond, Si, Al ₂ O _3, SiC or MgO.
When an AlN thin film is formed under appropriate conditions, B
An AlN thin film can be obtained. B thus obtained
The AlN single crystal thin film can be used as deposited on the substrate or after removing the substrate if necessary.

[0012]

[Action]

<Film forming method (process, raw material)> In order to incorporate nitrogen into the crystal during synthesis such as aluminum nitride and boron nitride, nitrogen is extremely stable in the form of molecular nitrogen (N ₂ ). It is necessary that the atmosphere is highly active, that is, the partial pressure of nitrogen is high or the nitrogen is in a state of high activity of atoms and ions. Sputtering method, plasma CVD method, ion beam evaporation method, laser ablation method, MBE method, MOCVD
The method is preferred.

<Composition range> The composition of each element in the film is BAlN
The useful range of the functionality and crystallinity of the membrane is determined. In the composition represented by B _x Al _1-x N _y as a general tendency, when the value x that determines the ratio of B to Al in the range of 0 to 0.2, the crystallinity is the same as that of the AlN thin film, and the crystallinity is very high. BAlN
A film is obtained. However, when x is less than 0.001, its functional properties are not different from those of AlN, so it is not useful as a BAlN film. When x exceeds 0.2, the crystallinity of the synthesized BAlN film decreases, and when x exceeds 0.7, its crystallinity is significantly lost.
The function as the lN film cannot be exerted.

However, by forming an AlN single crystal thin film as an intermediate layer on a single crystal substrate and growing a BAlN single crystal thin film on this AlN, a BAlN single crystal thin film can be obtained up to a composition of x = 0.3. . Further, as an intermediate layer, a BAlN single crystal gradient composition layer in which the B / Al composition ratio is continuously or stepwise increased, or an aluminum nitride single crystal layer as the first intermediate layer and an intermediate layer B as the second intermediate layer thereon. _α Al ₁ - _α N _β
(0.0001 ≤ α ≤ X, 0.85 ≤ β ≤ 1.05) using a single crystal gradient composition layer, by growing a BAlN single crystal thin film on them, B _x Al _1-x N _y (0.001 ≤ x ≤ 0.7, 0.85 ≦ y ≦ 1.05)
In this composition range, it becomes possible to form a single crystal thin film. It is considered that the crystallinity of the BAlN film is the best and the defects are few when the value y that determines the nitrogen content is equal to 1, but in the study of the inventors, when the value of y is 0.85 to 1.05, the BAlN film functions. It was found that the crystallinity was so high that it could be expressed. The single crystal thin film described in the present application means that the crystal orientation of the thin film on the substrate is not only the plane orientation parallel to the substrate but also the orientation in the plane parallel to the substrate in one direction epitaxially. Even when a crystal grain boundary exists in a thin film due to growth or the like, it is included in a single crystal thin film if the crystal orientations of the respective crystal grains are all aligned in one direction.

<Single-Crystal Substrate> As a base material for forming a BAlN film, any material can be used as long as it can withstand a temperature of 700 ° C. or higher required for film formation. Poor materials are preferred, Mo, W, Ni, Ta, Nb for metals, diamond, Si, Ge, AlN, SiC, GaN, BP, I for semiconductors.
For nN and other compounds, Al ₂ O ₃ , SiO ₂ , MgO, BeO, ZnO and the like are preferable.

To form a single crystal BAlN thin film, BAlN
The material must be chosen so that the film grows according to the orientation of the substrate, and the substrate material must be single crystal. Such substrate materials include diamond, Si, Al
₂ O ₃ , SiO ₂ , SiC, MgO and the like. When a single crystal is used as the substrate, the crystal plane of the substrate on which the thin film is formed is preferably 3 or 6 times because the crystal planes having symmetry are oriented to the C plane, which tends to improve the crystallinity of the BAlN film. Such crystal faces include (111) face of diamond, Si, cubic SiC, α-Al ₂ O ₃ , C face <(0001) face> of MgO (111) face of hexagonal SiC. In some cases, the crystallinity of the BAlN single crystal thin film can be improved by inserting an intermediate layer between the substrate material and the BAlN single crystal thin film.

<Intermediate Layer> As an intermediate layer, AlN, SiC, BP,
When one or more kinds of single-crystal thin films of GaN, ZnO, etc. are formed on a base material and then BAlN is formed, the crystallinity may be better than that directly formed on the base material. BA especially on Si single crystal
When forming lN, these five materials are Si and BAlN.
Since it has an intermediate lattice constant of 1, the defects and strains in the BAlN single crystal thin film can be reduced by forming the intermediate layer on Si, and a higher quality BAlN single crystal thin film can be obtained. Substrates other than Si are often effective. As the intermediate layer, AlN shown in FIG. 1 is the most preferable, SiC is the next most preferable, and BP, GaN, and ZnO are less effective than these. The suitable thickness of the intermediate layer is 1 nm or more and 1 μm or less.
If it is thinner than this, it is the same as when there is no intermediate layer, and if it is thicker, distortion and defects occur in the intermediate layer itself, which rather reduces the crystallinity of the BAlN single crystal thin film. Also, as shown in FIG.
A boron-containing aluminum nitride single crystal gradient composition can be formed instead of AlN, and a boron-containing aluminum nitride single crystal thin film can be formed thereon.

Particularly, when a BAlN single crystal thin film is grown on an AlN single crystal film formed as an intermediate layer on a single crystal substrate, good crystallinity is maintained even in a high boron content composition, and the single crystal film is maintained. Can be obtained. In this case, the composition range in which the BAlN single crystal thin film is obtained is x ≦ 0.3, and a BAlN single crystal can be obtained up to a higher B composition than in the case where the AlN single crystal intermediate layer is not used. Further, as an intermediate layer, a BAlN single crystal graded composition layer in which the B / Al composition ratio is continuously or stepwise increased, or, as shown in FIG. 3, an aluminum nitride single crystal layer as an intermediate layer first layer and an intermediate layer on this layer. As a second layer, a BAlN single crystal gradient composition layer in which the B / Al composition ratio is continuously or stepwise increased is used, and BAlN is grown on these layers to obtain B _x Al _1-x N _y (0.001 A single crystal thin film can be formed in the composition range of ≦ x ≦ 0.7, 0.85 ≦ y ≦ 1.05). For the BAlN single crystal gradient composition layer, both a B / Al composition ratio with a continuous increase and a B / Al ratio with a stepwise increase in a laminated structure can be used.

As a method of forming these intermediate layers,
A known method such as a sputtering method, an MBE method, a MOCVD method or a plasma CVD method can be selected and used. In the case of the MBE method, the BAlN single crystal gradient composition layer can be formed by preparing two vapor deposition sources for B and Al and continuously or stepwise changing the vapor deposition rate of each. plasma
In a CVD method such as CVD or MOCVD, the flow rate ratio of the gas serving as the B source and the Al source may be changed.

<Control of Valence Electron> A BAlN film having n-type conductivity can be obtained by doping an element such as Si, C, S or Se during film formation or by a method such as ion implantation. Similarly, a p-type BAlN single crystal thin film can be obtained by doping an element such as Be, Mg, Zn, or Ca. These elements can be doped using a simple substance of each element, an oxide, a halide, a hydride, or an organometallic compound as a raw material during the formation of the BAlN film. The ion implantation method is not preferable because it is difficult to recover crystal defects after the implantation.

[0021]

【Example】

Example 1 A single crystal Si (111) substrate was used to synthesize an aluminum nitride intermediate layer and a boron-containing aluminum nitride thin film on the intermediate layer by a sputtering method. The board is 10 mm
The square single crystal Si (111) was used after being immersed in hydrofluoric acid diluted with pure water to 5% and washed with acetone. As a target for sputtering, aluminum was used for forming an AlN intermediate layer, and metallic aluminum was used for forming BAlN in vacuum nitrogen, and 30% by weight of cubic boron nitride powder was dispersed and solidified.

A substrate and a target were set in a normal high frequency magnetron sputtering apparatus, and a gas in which an equal amount of Ar / N ₂ was mixed was introduced to adjust the total pressure to 0.005 Torr. Substrate is heated to 1150 ℃, high frequency (13.56MHz) output 40
At 0W, sputter an aluminum target for 10 minutes,
After forming the intermediate layer, a BAlN forming target was sputtered for 1 hour under the same conditions to obtain a thin film having a thickness of about 0.7 μm.

Composition analysis of this thin film by secondary ion mass spectrometry revealed that the composition of the intermediate layer was AlN _0.98 and the composition above the intermediate layer was B _0.25 Al _0.75 N _0.97. did. When observed by the X-ray diffraction method, only the diffraction line from the C plane was observed, and it was expected that the film was a wurtzite highly oriented film or a single crystal film. The full width at half maximum of the rocking curve of X-ray diffraction was 1.5 degrees, indicating high quality and highly oriented crystals.
Further high-speed backscattered electron diffraction observation revealed that this film was a wurtzite type single crystal thin film. Furthermore, the film thickness of only the intermediate layer formed under the same conditions was about 0.1 μm, and when evaluated by high-speed reflection electron diffraction, a diffraction pattern showing a wurtzite crystal structure was observed, and the electron beam It was confirmed that the film was a single crystal thin film because different patterns were observed in accordance with the change of the incident direction.

Example 2 As a substrate, a 3.5 mm square surface of an ultrahigh pressure synthetic diamond single crystal having a flat surface was polished (11
Using the 1) surface, after cleaning with an organic solvent and subsequent cleaning with a 10% hydrogen chloride aqueous solution, surface hydrogen termination treatment was performed. Surface hydrogen termination is microwave plasma CVD
Using the device, supply only hydrogen gas into the device, pressure 100T
It was performed for 10 minutes at orr and microwave power of 400W.

Using an MBE device on this diamond single crystal substrate, BAlN was formed on the aluminum nitride intermediate layer and the intermediate layer.
A thin film was synthesized. Al source and B source respectively
Was used as a raw material and was supplied by electron beam evaporation from separate evaporation sources. As the nitrogen source, N ₂ gas was used as the raw material and was supplied by the ECR ion source. Substrate temperature 900 degrees, microwave power of ECR ion source 50W, ion current density 25μA near the substrate, AlN intermediate layer was grown from Al evaporation source at 0.025nm / s deposition rate for 38 minutes, then Al deposition rate 0.02 nm / s, B deposition rate 0.005 nm / s
The BAlN film was grown for 150 minutes. Total film thickness is about 0.25
It was μm.

Composition analysis of this thin film by secondary ion mass spectrometry revealed that the composition of the intermediate layer portion was AlN _0.99 and the composition of the upper portion of the intermediate layer was B _0.2 Al _0.8 N _0.99 . . When observed by the X-ray diffraction method, only the diffraction line from the C plane was observed, and it was expected that the film was a wurtzite highly oriented film or a single crystal film. The full width at half maximum of the rocking curve of X-ray diffraction was 1.3 degrees, indicating high quality and highly oriented crystals. Further high-speed backscattered electron diffraction observation revealed that this film was a wurtzite type single crystal thin film. Furthermore, the film thickness of the case where only the intermediate layer is formed under the same conditions is about 0.
It is 05 μm, and when evaluated by high-speed backscattered electron diffraction,
A diffraction pattern showing a wurtzite crystal structure was observed, and different patterns were observed corresponding to changes in the incident direction of the electron beam, confirming that the film was a single crystal thin film.

Example 3 A BAlN thin film was synthesized on a single-crystal hexagonal SiC (0001) using an MBE apparatus to form a BAlN gradient composition layer as an intermediate layer. Before being introduced into the MBE device, the SiC substrate was washed with an organic solvent, the oxide film was removed with 10% hydrofluoric acid, and then washed in pure water. As Al source and B source,
Each of Al and B was used as a raw material and supplied by electron beam evaporation from different evaporation sources. EC using N ₂ gas as a nitrogen source
Supplied by an R ion source. Substrate temperature 900 degrees, microwave power of ECR ion source 50W, ion current density near the substrate 25
At μA, Al deposition rate from 0.025 nm / s to 0.015 nm / s, B
The deposition rate was changed from 0 to 0.01 nm / s continuously over 75 minutes at the same time to form a BAlN gradient composition layer, and the Al deposition rate was set to 0.
015nm / s, B deposition rate is fixed at 0.01nm / s and BAlN for 150 minutes
The film was grown. The total film thickness was about 0.3 μm.

Composition analysis of this thin film by secondary ion mass spectrometry revealed that the composition of the intermediate layer was AlN _0.99 to B _0.3 Al _0.7 N.
_The B / Al ratio changes continuously up to _0.99, and the uppermost layer of BAlN
It was found that B _0.3 Al _0.7 N _0.99 was constant in the layer. When observed by X-ray diffractometry, only diffraction lines from the C plane were observed, and it was expected that the wurtzite-type highly oriented film or single crystal thin film was obtained. The full width at half maximum of the rocking curve of X-ray diffraction was 1.3 degrees, indicating high quality and highly oriented crystals. Further high-speed backscattered electron diffraction observation revealed that this film was a wurtzite type single crystal thin film. Furthermore, the film thickness of the case where only the intermediate layer is formed under the same conditions is about 0.
It was 1 μm, and when evaluated by high-speed reflection electron diffraction, a diffraction pattern showing a wurtzite crystal structure was observed, and different patterns were observed corresponding to changes in the incident direction of the electron beam. It was confirmed to be a crystalline thin film.

Example 4 Using the C-plane of sapphire single crystal as a substrate, cleaning with an organic solvent and subsequent cleaning 10
% Aqueous solution of hydrogen chloride was used for washing. MB on this board
Using the E equipment, after forming aluminum nitride as the first intermediate layer and a BAlN gradient composition layer as the second intermediate layer, BAlN is formed.
A thin film was synthesized. Al source and B source respectively
Was supplied as a raw material by electron beam evaporation from separate evaporation sources. As the nitrogen source, N ₂ gas was used as the raw material and was supplied by the ECR ion source. Substrate temperature 900 degrees, ECR ion source microwave power 50W, N ₂ gas as raw material, ion current density near substrate 2
At 5μA, A for 38 minutes at a deposition rate of 0.025nm / s from an Al evaporation source.
After growing lN intermediate layer, Al deposition rate from 0.025nm / s
A BAlN gradient composition layer was formed by simultaneously changing the B deposition rate from 0 to 0.01 nm / s over 75 minutes to 0.015 nm / s, and the Al deposition rate was 0.015 nm / s and the B deposition rate was 0.01 nm / s. Fixed to 150
The BAlN film was grown for a minute. Total film thickness is about 0.35 μm
Met.

Composition analysis of this thin film by secondary ion mass spectrometry revealed that the composition of the first layer of the intermediate layer was AlN _0.99 and the composition of the second layer of the intermediate layer was AlN _0.99 to B _0.3 Al _0.7 N _0.99 B / The Al ratio is continuously changing, and B _0.3 Al in the uppermost BAlN layer.
It was found to be constant at _0.7 N _0.99 . When observed by the X-ray diffraction method, only the diffraction line from the C plane was observed, and it was expected that the film was a wurtzite highly oriented film or a single crystal film. The full width at half maximum of the rocking curve of X-ray diffraction was 1.3 degrees, indicating high quality and highly oriented crystals. Further high-speed backscattered electron diffraction observation revealed that this film was a wurtzite type single crystal thin film. Furthermore, the film thicknesses of the intermediate layer 1st layer only and the intermediate layer 2nd layer formed under the same conditions were about 0.05 μm and about 0.15 μm, respectively. A diffraction pattern showing that it had a mineral crystal structure was observed, and different patterns were observed corresponding to changes in the incident direction of the electron beam, confirming that it was a single crystal thin film.

Example 5 Single crystal Si (111) was used as a substrate and washed in the same manner as in Example 1 before film formation.
Microwave plasma C used for diamond synthesis
The substrate was placed in a VD device (Japanese Patent Laid-Open No. 59-3098), and a mixed gas of aluminum chloride (AlCl ₃ ) 5%, hydrogen 45% and ammonia 50% was introduced to adjust the total pressure to 5 Torr. . The substrate was heated to 1150 ° C. while generating plasma with microwave (2.45 GHz) output of 800 W, and growth was performed for 10 minutes. Then, gas was diborane (B ₂ H ₆ ) 2.5%, aluminum chloride 2.5.
%, Hydrogen 45%, ammonia 50%, and the growth was continued for 2 hours without changing other film forming conditions. The total film thickness was 2.5 μm.

Composition analysis of this thin film by secondary ion mass spectrometry revealed that the composition of the intermediate layer was AlN _0.99 and the composition above the intermediate layer was B _0.25 Al _0.75 N _0.99 . . When observed by the X-ray diffraction method, only the diffraction line from the C plane was observed, and it was expected that the film was a wurtzite highly oriented film or a single crystal film. The full width at half maximum of the rocking curve of X-ray diffraction was 1.5 degrees, indicating high quality and highly oriented crystals. Further, when evaluated by high-speed electron beam diffraction, a diffraction pattern showing a wurtzite crystal structure was observed, and different patterns were observed corresponding to changes in the incident direction of the electron beam, indicating that it is a single crystal thin film. It was confirmed. Furthermore, the film thickness of the intermediate layer formed under the same conditions is approximately
It was 0.1 μm, and when evaluated by high-speed backscattered electron diffraction, a diffraction pattern showing a wurtzite crystal structure was observed, and a different pattern was observed corresponding to the change in the incident direction of the electron beam. It was confirmed to be a single crystal thin film.

Example 6 After cleaning the substrate in the same manner as in Example 4, using the C plane of sapphire single crystal as the substrate,
Place the substrate on the graphite susceptor in the reaction chamber and
A BAlN gradient composition layer was formed as an intermediate layer by the CVD method, and then a BAlN film was synthesized. Trimethyl aluminum (TMA) was bubbled with hydrogen gas as an aluminum source and introduced into the reaction chamber. As the boron source, diborane (B ₂ H ₆ ) diluted with hydrogen at a concentration of 1% was used. Ammonia was used as the nitrogen source. Hydrogen was used as the carrier gas. Ammonia flow rate 31 / min, carrier hydrogen gas flow rate 100c
The TMA is fixed at 10 cm and the hydrogen bubbling gas flow rate from 10 ccm
After continuously changing B ₂ H ₆ from 0 to 5 ccm for 10 minutes up to 5 ccm and growing a BAlN gradient composition layer, TM
A is fixed at a hydrogen publing gas flow rate of 5 ccm and B ₂ H ₆ is fixed at 5 ccm.
AlN was grown for 2 hours. The pressure in the reaction chamber was kept constant at 5 Torr during both the growth of the graded composition layer and the growth of BAlN, and the susceptor was heated by high-frequency heating so that the growth substrate temperature became 1200 ° C. The total film thickness was 5.5 μm.

Composition analysis of this thin film by secondary ion mass spectrometry revealed that the composition of the intermediate layer was AlN _0.99 to B _0.3 Al _0.7 N.
_The B / Al ratio changes continuously up to _0.99, and the uppermost layer of BAlN
It was found that B _0.3 Al _0.7 N _0.9 was constant in the layer. When observed by the X-ray diffraction method, only the diffraction line from the C plane was observed, and it was expected that the film was a wurtzite highly oriented film or a single crystal film. The full width at half maximum of the rocking curve of X-ray diffraction was 1.5 degrees, indicating high quality and highly oriented crystals. Further, when evaluated by high-speed reflection electron diffraction observation, a diffraction pattern showing a wurtzite crystal structure was observed, and a different pattern was observed corresponding to the change in the incident direction of the electron beam. Was confirmed. further,
The thickness is about 0.5 μm when only the intermediate layer is formed under the same conditions.
When evaluated by high speed reflection electron diffraction, it was found to be a wurtzite type single crystal film.

Example 7 Single crystal Si (111) as a substrate
After cleaning the substrate in the same manner as in Example 1, the same microwave plasma apparatus as in Example 5 was used to form a BAlN gradient composition layer as an intermediate layer and then synthesize a BAlN film. Trimethyl aluminum (T
(MA) was bubbled with hydrogen gas and introduced into the reaction chamber. Boron chloride with a hydrogen concentration of 0.5% as the boron source
(BCl ₃ ) was used. Ammonia was used as the nitrogen source. Hydrogen was used as the carrier gas. Ammonia flow rate
31 / min, constant with carrier hydrogen gas flow rate of 100 ccm, TMA
Hydrogen bubbling gas flow rate from 10ccm to 5ccm, BCl ₃ 0
From 5 to 5 cm, change continuously over 10 minutes,
After the BAlN gradient composition layer was grown, TMA was fixed at a hydrogen bubbling gas flow rate of 5 ccm and BCl ₃ was fixed at 5 ccm, and BAlN was grown for 2 hours. During the growth of the graded composition layer and the growth of BAlN, the pressure in the reaction chamber was 5 Torr, the microwave (2.45 GHz) output was 800 W, and the substrate temperature was 1150 ° C. The total film thickness was 2.5 μm.

Composition analysis of this thin film by secondary ion mass spectrometry revealed that the composition of the intermediate layer was AlN _0.99 to B _0.28 Al _0.72 N.
_The B / Al ratio changes continuously up to _0.99, and the uppermost layer of BAlN
It was found that the layer had a constant B _0.28 Al _0.72 N _0.99 . When observed by the X-ray diffraction method, only the diffraction line from the C plane was observed, and it was expected that the film was a wurtzite highly oriented film or a single crystal film. The full width at half maximum of the rocking curve of X-ray diffraction was 1.5 degrees, indicating high quality and highly oriented crystals. Further, when evaluated by high-speed reflection electron diffraction observation, a diffraction pattern showing a wurtzite crystal structure was observed, and a different pattern was observed corresponding to the change in the incident direction of the electron beam. Was confirmed. Furthermore, the film thickness of the case where only the intermediate layer is formed under the same conditions is about 0.
It was 1 μm, and when evaluated by high-speed backscattered electron diffraction, it was found to be a wurtzite type single crystal film.

[0037]

According to the present invention, it is possible to easily obtain a boron-containing aluminum nitride thin film having a higher hardness, a wider bandgap, a larger sonic velocity than aluminum nitride, easy valence electron control, and good crystallinity.

[Brief description of drawings]

FIG. 1 is an example of Examples 1, 2 and 5 in which an aluminum nitride single crystal thin film is formed on a single crystal substrate, and a boron-containing aluminum nitride single crystal thin film is further formed thereon.

FIG. 2 Examples 3, 6, 7 in which a boron-containing aluminum nitride single crystal gradient composition layer was formed on a single crystal substrate, and a boron-containing aluminum nitride single crystal thin film was further formed thereon.
Example.

FIG. 3 shows an aluminum nitride single crystal layer formed as an intermediate first layer on a single crystal substrate, a boron-containing aluminum nitride single crystal gradient composition layer formed as an intermediate second layer thereon, and further thereon. An example of Example 4 in which a boron-containing aluminum nitride single crystal thin film was formed.

[Explanation of symbols]

 1: Single crystal substrate 2: Aluminum nitride single crystal thin film 3: Boron-containing aluminum nitride single crystal thin film 4: Single crystal substrate 5: Boron-containing aluminum nitride single crystal gradient composition layer 6: Boron-containing aluminum nitride single crystal thin film 7: Single crystal Substrate 8: Aluminum nitride single crystal layer 9: Boron-containing aluminum nitride single crystal gradient composition layer 10: Boron-containing aluminum nitride single crystal thin film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 21/203 H01L 21/203 Z 21/205 21/205 // B23B 27/14 B23B 27/14 A

Claims (11)

[Claims] 1. An aluminum nitride single crystal thin film (2) is formed as an intermediate layer on a single crystal substrate (1), and a boron-containing aluminum nitride single crystal thin film (3) is formed on the aluminum nitride single crystal thin film. A boron-containing aluminum nitride single crystal thin film having a structure. 2. A boron-containing aluminum nitride single crystal thin film having a composition of B _x Al _1-x N _y (0.001 ≦ x ≦ 0.3, 0.85 ≦ y ≦ 1.05) and a wurtzite crystal structure. The boron-containing aluminum nitride single crystal thin film according to claim 1. 3. B / Al as an intermediate layer on a single crystal substrate (4)
A boron-containing aluminum nitride single crystal gradient composition layer (5) having a composition ratio continuously or stepwise increased is formed,
A boron-containing aluminum nitride single crystal thin film (6) having a B / Al composition ratio equal to or higher than that of the uppermost composition of the boron-containing aluminum nitride single crystal gradient composition layer is formed on the boron-containing aluminum nitride single crystal gradient composition layer. A boron-containing aluminum nitride single crystal thin film having a formed structure. 4. An aluminum nitride single crystal layer (8) is formed as a first intermediate layer on a single crystal substrate (7), and a B / Al composition ratio is formed as a second intermediate layer on the aluminum nitride single crystal layer. Is continuously or stepwise increased to form a boron-containing aluminum nitride single crystal gradient composition layer (9), and the boron-containing aluminum nitride single crystal gradient composition layer is provided on the boron-containing aluminum nitride single crystal gradient composition layer. 1. A boron-containing aluminum nitride single crystal thin film having a structure in which a boron-containing aluminum nitride single crystal thin film (10) having a B / Al composition ratio equal to or higher than that of the above is formed. 5. A boron-containing aluminum nitride single crystal gradient composition layer is B _α Al _{1 -α} N β (0.0001 ≦ α ≦ x, 0.85 ≦ β ≦ 1.0
5) B increased continuously or stepwise within the composition range
/ Al composition ratio and wurtzite crystal structure, the boron-containing aluminum nitride single crystal thin film formed on the boron-containing aluminum nitride single crystal gradient composition layer is B _x Al _1-x N _y (0.0
The boron-containing aluminum nitride single crystal thin film according to claim 3 or 4, wherein the composition is 01≤x≤0.7, 0.85≤y≤1.05) and has a wurtzite type crystal structure. 6. A diamond, Si, sapphire, hexagonal SiC, cubic SiC, MgO is used as a single crystal substrate, claim 1, claim 2, claim 3, claim 4, characterized in that.
The boron-containing aluminum nitride single crystal thin film according to claim 5. 7. A MOCVD method for forming an aluminum nitride single crystal thin film and a boron-containing aluminum nitride single crystal thin film.
Method, sputtering method, MBE method, or plasma CVD method is used, claim 1, claim 2, claim 3,
A method for producing a boron-containing aluminum nitride single crystal thin film according to claim 4, claim 5, or claim 6. 8. A target material selected from aluminum, boron, aluminum nitride, boron nitride, and an aluminum-boron alloy is used in a gas atmosphere containing nitrogen or ammonia in a B _x Al _1-x N by sputtering method.
_A method for producing a boron-containing aluminum nitride single crystal thin film, which comprises forming a boron-containing aluminum nitride single crystal thin film of _y (0.0001 ≤ x ≤ 0.7, 0.85 ≤ y ≤ 1.05) on a substrate. 9. An aluminum-containing organic metal compound as an aluminum source, and a boron source as a raw material by diluting a boron-containing halide or hydride or an organometallic compound or metal alkoxide with hydrogen or a noble gas, respectively. Supply, nitrogen or ammonia gas as a nitrogen source, and B _x Al _1-x N _y by MOCVD method
A method for producing a boron-containing aluminum nitride single crystal thin film, comprising forming a boron-containing aluminum nitride single crystal thin film (0.0001 ≦ x ≦ 0.7, 0.85 ≦ y ≦ 1.05) on a substrate. 10. A boron or aluminum source, a halide or hydride containing boron and aluminum respectively, or an organometallic compound or a metal alkoxide, is diluted with hydrogen or a rare gas and supplied as a raw material, and nitrogen or ammonia is used as a nitrogen source. Supply gas,
B _x Al _1-x N _y (0.0001 ≦ x ≦ 0.7, 0.
A method for producing a boron-containing aluminum nitride single crystal thin film, which comprises forming a boron-containing aluminum nitride single crystal thin film of 85 ≦ y ≦ 1.05) on a substrate. 11. A material selected from aluminum, boron, aluminum nitride, boron nitride, and an aluminum-boron alloy as an aluminum source and a boron source is supplied by using an electron beam evaporation source or a K cell (Knudsen cell), N ₂ or NH ₃ as a nitrogen source is used as a raw material and is supplied by using an RF ion source or an ECR ion source, and B _x Al _1-x N _y (0.0001 ≦ x ≦ 0.7, 0.85 ≦ y ≦ 1.05) of the MBE method is supplied. A method for producing a boron-containing aluminum nitride single crystal thin film, which comprises forming a boron-containing aluminum nitride single crystal thin film on a substrate.