JPH0558783A - Diamond substrate and its production - Google Patents

Abstract

PURPOSE:To produce a diamond substrate having novel constitution and usable for various semiconductor devices such as a transistor and a sensor or as an insulating film or a high hardness coating film used for a superhard tool. CONSTITUTION:A diamond layer is grown on a boron phosphide substrate to produce the objective diamond substrate. By this method, high purity smooth diamond substrates or single crystal diamond substrates having a large area can be provided in large quantities at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond substrate which can be used as a high hardness coating used for various semiconductor devices such as transistors and sensors, insulating films, cemented carbide tools and the like.

[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, in order to synthesize a diamond thin film, diamond synthesis from a gas phase is also actively performed, and microwave plasma CVD method, high frequency plasma CVD method, thermal CVD method, hot filament C
There have been reports of successful synthesis by various methods such as VD method, ECR plasma CVD method, arc discharge plasma jet CVD method, combustion flame method and the like. Needless to say, diamond is 199
As of 1 year, it is the substance with the highest hardness on earth. In addition to its high hardness, diamond has many excellent properties. For example, since it has a very wide bandgap and can be made into a p-type semiconductor by doping various impurities such as B (boron), it can be used in transistors and sensors operating at high temperatures, short wavelength light emitting elements, etc. Applications as various electronic devices are considered. Moreover, due to its high thermal conductivity, it is expected to be used as a heat sink.

[0003]

When diamond is used as an electronic device as described above, a high-purity large-area thin film single crystal is desired. However, currently, for example, diamond obtained by high-pressure synthesis is only a plate-like or granular crystal with a size of only a few millimeters. Further, since the high-pressure synthesis method requires a very expensive high-pressure generator, there is 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 or a zinc blende type boron nitride single crystal (hereinafter abbreviated as cBN) obtained by a high pressure synthesis method is used as a substrate. However, it is difficult to obtain a large area substrate because the substrate itself is manufactured by the high pressure synthesis method. Si is often used as a substrate other than diamond and cBN, but only a polycrystalline thin film is obtained on the Si substrate. From the above, it is an object of the present invention to provide a high-purity, large-area smooth diamond substrate or a single-crystal diamond substrate in large quantities and at low cost.

[0004]

As a means for solving the above problems, the present invention is characterized by growing a diamond layer on a boron substrate and a diamond substrate having a diamond layer on the boron phosphide substrate. The present invention provides a method for manufacturing a diamond substrate.

Conventional substrate for obtaining single crystal diamond
Which was used as
Compared to cBN, boron phosphide (hereinafter also referred to as BP) is more synthetic.
It is easy and can be made large in area.
The BP substrate used in the present invention is a flux method or a thermal CVD method.
It may be manufactured by a known technique such as. In the present invention
The BP used may be undoped
It may be doped with Si or the like. Also
By supplying a slight excess of B or P
Each capable of acting as an active layer of p-type or n-type semiconductor
But it's okay. Further, the BP of the present invention is a known material such as a thermal CVD method.
Si or Al depending on the technology₂O ₃Synthesized on a substrate such as
It is also possible to remove these substrates.
It may be a self-supporting film of BP obtained by. Anyway
Also, the BP of the present invention is preferably a single crystal BP. Book
Diamond formed on this BP substrate in the invention
The layer is formed by various known CVD methods or PVD methods as described above.
Can be formed. B, which is a p-type semiconductor
Do not go to P and form n-type diamond on it
If so, a semiconductor element having a pn junction can be formed. Also B
Removing BP after forming diamond on P
It is also possible to obtain a smooth diamond free-standing film by
It

[0006]

FUNCTION Diamond is a cubic crystal and its lattice constant is 0.3543 nm. Si, which has been conventionally used as a substrate for diamond thin film synthesis, has the same crystal structure as diamond, but has a lattice constant of 0.5430.
nm is large. Due to this large difference in lattice constant, S
It is difficult to epitaxially grow diamond on an i substrate.

Therefore, the present inventors have succeeded in epitaxially growing single crystal diamond on BP by using BP, which has a lattice constant closer to that of diamond than Si, as a substrate, and arrived at the present invention. BP has a zinc blende type structure with a lattice constant of 0.4539 nm.
The difference in lattice constant from diamond is relatively large, but S
It is considered that diamond is epitaxially grown on the BP substrate because it is closer to i and has a structure similar to that of diamond.

The smooth diamond layer in the present invention has a surface roughness Rma measured by a surface roughness meter.
x is about 5% or less of the film thickness. It is considered that such a smooth diamond layer is composed of a single crystal, a single crystal including a twin crystal, or a polycrystal having a grain size of several μm or more. Of these, single crystals, particularly single crystals with few twins, are preferred.

The diamond layer of the present invention may be a non-doped layer, or may be an active layer of a semiconductor device as a p-type or n-type semiconductor by doping with various impurity elements such as B. The thickness of the diamond layer formed in the present invention is preferably 10 μm or less. 1
This is to avoid warping of the substrate due to the difference in thermal expansion coefficient from BP used as the substrate when the thickness exceeds 0 μm. 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.

[0010]

【Example】Example 1 and Comparative Examples 1.1 and 1.2 Using the microwave plasma CVD apparatus shown in FIG.
The invention and the conventional method were compared. First of all, the size of 10mm x 20mm
On the (111) surface of the Si of the grain, a known thermal CVD method is used.
As a raw material gas, H₂PH of dilution₃(5%): 30
0 sccm, H ₂Diluted B₂H₆(1%): 20 scc
m, H₂: React at 950 ° C. using 2500 sccm
A BP having a thickness of 0.2 mm was synthesized under the condition that
The obtained BP was subjected to a high-speed reflection electron diffraction method (hereinafter referred to as RHEED
Observation of the (111) plane
It was confirmed to be crystalline. Then, the substrate is
By immersing in acid and removing the Si layer, the single crystal BP
A standing film was obtained. After installing this in the vacuum chamber, C
H_FourGas 2 sccm and H₂Gas 200sccm true
Simultaneously introducing into the empty chamber,
1 x 10 ^FourIt was adjusted to Pa. In this state
From the 2.45 GHz microwave generator through the waveguide
To supply 200w microwave into the chamber.
Thus, plasma was formed on the substrate in the chamber. This
At that time, the substrate temperature was 1130K. Film thickness in this state
A 1 μm diamond layer was formed (deposition time 3:00
while). The crystalline state of the obtained diamond layer is RHEE
As a result of observation by the D method, twins are included in the film
The diffraction corresponding to the diamond single crystal was observed. Solution
As a result of the deposition, the diamond layer was a single crystal die containing twins.
It was found that it was the (111) plane of Yamond (Example
1).

For comparison, an attempt was made to form a diamond layer on a single crystal Si substrate having a plane orientation (111) under the same conditions as in Example 1 above. Only diamond particles were observed in the area. That is, a single crystal thin film could not be obtained (Comparative Example 1.1).

Further, a diamond layer was tried to be formed on a single crystal Si substrate having a plane orientation (111) which was scratched with diamond abrasive grains of 20 to 40 μm under the same conditions as in Example 1 above. A diamond layer having a film thickness of 1 μm was obtained (film formation time 3 hours). Also for this, the crystal state of the obtained layer was observed by the RHEED method, but again only a spotty ring pattern corresponding to diamond was obtained, and it was confirmed that this diamond layer was polycrystalline (Comparative Example 1. 2).

Example 2, Comparative Example 2.1 , Comparative Example 2
2 The present invention and the conventional method were compared using the hot filament CVD apparatus shown in FIG. As a substrate, follow the flux method,
Using commercially available BP powder and Cu ₃ P as raw materials, 1300 ° C., 1
It was recrystallized at 8 atm, crushed, and the BP-rich part was placed under another crucible.
A single crystal BP having a plane orientation (100) of 2 mm × 2 mm × 1 mm synthesized by holding it at 18 atm for 20 hours and then gradually cooling it was used. After washing the obtained BP with various acids and organic solvents, the substrate was placed in a vacuum chamber. 2273K Tungsten filament installed facing the substrate in the vacuum chamber
While being heated to ₄ sccm, ₄ sccm of CH ₄ gas and 100 sccm of H ₂ gas were simultaneously supplied into the vacuum chamber so that the inside of the chamber was adjusted to 4 × 10 ³ Pa.
The distance between the substrate and the filament was 10 mm, and the temperature of the substrate surface was about 1100K. In this state, a diamond layer having a film thickness of 2 μm was formed (film formation time 2 hours). The crystal state of the obtained diamond layer is RHEED
When observed by the method, diffraction corresponding to the diamond single crystal was observed. As a result of the analysis, it was found that the diamond layer was the (100) plane of single crystal diamond containing twins (Example 2).

For comparison, an attempt was made to form a diamond layer on a single crystal Si mirror-faced substrate having a plane orientation (100) under the same conditions as in Example 2, but only a very small part of diamond particles were observed. No thin film could be obtained (Comparative Example 2.1).

Further, a diamond layer was tried to be formed on a single crystal Si substrate having a plane orientation (100) which was scratched with diamond abrasive grains under the same conditions as in Example 2 above. In this case, the film thickness was 1 μm. Obtained a diamond layer (deposition time 1
time). Also for this, the crystal state of the obtained layer was observed by the RHEED method, but again only a spotty ring pattern corresponding to diamond was obtained, and it was confirmed that this diamond layer was polycrystalline (Comparative Example 2).
・ 2).

Example 3 and Comparative Example 3.1 , Comparative Example 3
2 The present invention and the conventional method were compared using the magnetic field microwave plasma CVD apparatus shown in FIG. Example 1 as a substrate
10 mm × 20 mm × synthesized by thermal CVD method
A single crystal BP substrate having a plane orientation (111) of 0.2 mm was used. However, in this example, Si used for synthesizing BP was used.
Was not removed and used as a substrate with a two-layer structure in which BP was present on Si. This was washed with hydrofluoric acid and an organic solvent such as isopropyl alcohol and acetone.
After this substrate was placed in a vacuum chamber, CH ₄ gas 4 sccm and H ₂ gas 200 sccm were simultaneously introduced into the vacuum chamber so that the inside of the chamber was adjusted to 10 Pa. In this state, by supplying a microwave of 500w into the chamber from the 2.45 GHz microwave generator through the waveguide and simultaneously applying a magnetic field of 875 G, plasma was formed in the chamber under a magnetic field. .. The substrate temperature at this time was kept at 1000 K by an external heater. In this state, a diamond layer having a film thickness of 5 μm was formed (film formation time 10 hours). When the crystal state of the obtained diamond layer was observed by the RHEED method, diffraction corresponding to the diamond single crystal was observed, and as a result of analysis, the diamond layer was the (111) plane of single crystal diamond containing twins. It was found (Example 3).

For comparison, a surface was prepared under the same conditions as in Example 3 above.
Orientation (0001) single crystal Al₂O ₃Die on the mirror substrate
An attempt was made to form a yamond layer, but Comparative Examples 1.1 and Comparative
Similar to the film formation on the mirror-finished Si substrate in Example 2.1, extremely partial
A thin film can be obtained only by observing diamond particles.
Was not possible (Comparative Example 3.1).

Further, a diamond layer was tried to be formed on a single crystal Al ₂ O ₃ substrate having a plane orientation (0001) which was scratched with diamond abrasive grains under the same conditions as in Example 3 above. A diamond layer having a thickness of 5 μm was obtained (film forming time: 10 hours). The crystal state of this diamond film was also observed by the RHEED method. However, only a spotty ring pattern corresponding to diamond was obtained, and it was confirmed that this diamond layer was polycrystalline (Comparative Example 3.2).

[0019]

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 explanatory view showing a case of using a microwave plasma CVD method in an embodiment of the present invention.

FIG. 2 is a schematic explanatory view showing a case of a hot filament CVD method in another embodiment of the present invention.

FIG. 3 is a schematic explanatory view showing a case of using a magnetic field microwave plasma CVD method in still another embodiment of the present invention.

Claims (2)

[Claims] 1. A diamond substrate having a diamond layer on a boron phosphide substrate. 2. A method for manufacturing a diamond substrate, which comprises growing a diamond layer on a boron phosphide layer.