JPH04240189A - Formation of diamond film on si substrate by cvd method - Google Patents

Abstract

PURPOSE:To form a diamond film by CVD method which can increase nucleus generating density and form the film having a flat surface. CONSTITUTION:After a polycrystal Si layer of 50-200Angstrom crystal grain size is formed on the Si substrate, many difference parts in level which cause to start generation of diamond nucleus are formed on the surface of the Si substrate by etching specific surface of the polycrystal Si layer to form etch pits of 10-50Angstrom in depth using crystal face anisotropic etchant. The diamond film is formed on the surface of the Si substrate by CVD method. As many difference parts in level which cause to start generation of diamond nucleus are formed on the surface of the Si substrate by forming the etch pits, nucleus generating density of the diamond remarkably increases compared with the conventional example as shown by fig. and at the same time the diamond film having a flat surface is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a diamond film on a Si substrate by CVD.

0002

[Prior Art] Diamond is the hardest known substance, has the best thermal conductivity, high electrical insulation, good transparency, and is chemically stable. Applications to tools, wear-resistant parts, protective films for solar cells, heat sinks for semiconductor devices, etc. are being studied.

Conventional low-pressure synthesis methods for diamond include the PVD method (physical vapor deposition), in which a solid or liquid raw material is turned into a gas by evaporation, sublimation, etc., and crystals are grown from this gas, and the PVD method (physical vapor deposition), in which carbon-containing compounds are There is a CVD method (chemical vapor deposition method) in which crystals are obtained by decomposing gas using heat or plasma.

That is, in the latter CVD method, a mixed gas of hydrocarbon and hydrogen is used as a raw material, and
The raw material gas is excited using heat, microwaves, high frequencies, etc. under a reduced pressure of rr or more, and is guided onto a substrate heated to 600 to 1000°C to thermally decompose hydrocarbons and by the action of activated hydrogen, This method involves depositing diamond-structured carbon onto a substrate.

Specifically, examples include the hot filament CVD method in which a substrate is heated with a filament, the microwave plasma CVD method in which plasma is used to decompose a raw material gas and hydrogen, and the method in which ultraviolet laser light is applied to a mixed raw material gas of hydrocarbon and hydrogen. There is a photo-CVD method that irradiates.

On the other hand, typical PVD methods use glow discharge in hydrocarbon gas and ion beams. For example, carbon is evaporated with an electron beam and the substrate is irradiated with an ion beam. There are beam sputtering methods, and ion beam evaporation methods in which atoms of a source gas or source material are ionized and extracted by an electric field to form a film on a substrate.

[0007]

[Problems to be Solved by the Invention] Diamond films produced by the low-pressure vapor phase synthesis method can be epitaxially grown on diamond substrates, and the substrates on which diamond has been confirmed to form include molybdenum, tungsten, gold, and copper. , simple substances such as zirconium and silicon, cemented carbide,
In addition to compounds such as silica glass and sapphire, there are ceramics such as silicon carbide, titanium carbide, boron nitride, and silicon nitride.

However, at present, no technology has been established for epitaxial growth even on a silicon substrate having a diamond crystal structure. On top of that,
The above-mentioned hot filament CVD method, microwave plasma C
In a diamond film obtained by a CVD method such as a VD method or a photo-CVD method, aggregates of diamond crystals having a grain size of about 1 to 10 μm are formed, so that only a film with a severely uneven surface can be obtained.

That is, in the formation process of a diamond film, a large number of diamond nuclei are first generated on the Si substrate in the first step, and then the nuclei grow into large crystal grains, and then crystal grains and crystal grains are formed. The two begin to stick together and form a film. Thereafter, the film grows in a direction perpendicular to the Si substrate, and the film gradually becomes thicker. Because of this growth process, the diamond film becomes a film with a highly uneven surface, consisting of a collection of polycrystals.

By the way, diamond nucleation is affected by the surface of the substrate, and by scratching the surface of the substrate with a diamond powder, the number of nuclei can be reduced from 104/cm2 to about 108-109/cm2 on a Si substrate. It is known that the number of cases is increasing.

[0011] That is, by rubbing with a diamond powder of 2 to 10 μm, the nucleation density increases to a maximum of about 109/cm2, and as the particles grow, they come into contact with each other and aggregate to form a diamond film. It has been reported (Electronics, November 1988 issue, p. 68).

Furthermore, in Japanese Patent Application Laid-Open No. 61-201698, the surface of the substrate is coated with diamond, nitride, or
A smooth diamond film with a surface roughness of 0.4 μm or less is obtained by rubbing with an inorganic powder such as carbide and making scratches with a size of 1 μm or less.

Furthermore, in Japanese Patent Application Laid-Open No. 60-86096, a Si substrate is rubbed with diamond powder of 2 μm or less to generate sharp scratches, and then 3
A diamond film consisting of fine crystal grains was obtained at a growth rate of μm/hr.

However, as described above, in the conventional method of scratching the surface of the Si substrate prior to the vapor phase synthesis of the diamond film, the diamond nucleation density is at most about 1 per 1000 Å square (1010 nucleation/cm).
2), and in order to use the obtained diamond film as a semiconductor film or an abrasion film, it is necessary to improve the nucleation density and further smooth the surface irregularities.

The present invention has been made to solve the above-mentioned problems when forming a diamond film on a Si substrate by the CVD method. It is an object of the present invention to provide a method for forming a diamond film on a Si substrate by a CVD method, which reduces unevenness and provides a smooth diamond film.

[0016]

[Means for Solving the Problem] The inventor believes that scratching the surface of a substrate is effective in increasing the density of diamond nucleation, so if a step is provided on the surface of the substrate, diamond The energy for nuclear generation decreases,
We focused on the fact that diamond nuclei are easily generated. Therefore, we conducted extensive research into the density and depth of steps on the substrate surface, which are the starting point for diamond nucleation. As a result, the present invention was completed by finding a method for adjusting the density of the step portions on the surface of the substrate to a desired number, and also by finding an optimal range for the depth of the step portions.

In the method of forming a diamond film on a Si substrate by the CVD method of the present invention, a polycrystalline Si layer with a crystal grain size of 50 to 200 Å is formed on the Si substrate, and then an etching solution with anisotropic Si crystal plane is applied. etch a specific surface of the polycrystalline Si layer to form etch pits with a depth of 10 to 50 Å, and the distance between adjacent etch pits to 50 to 20 Å.
The gist is to form diamond nuclei on the polycrystalline Si layer after setting the thickness to 0 Å.

In the present invention, polycrystalline Si is deposited on a Si substrate.
To form the layer, vacuum evaporation method, sputtering method,
A plasma CVD method or the like can be used. When forming a polycrystalline Si layer on a Si substrate, appropriately select the substrate temperature for vacuum evaporation, the argon pressure and substrate temperature for sputtering, and the glow discharge conditions and silane gas concentration for plasma CVD. By this, polycrystalline S
The grain size of the i-layer can be adjusted.

[0019] The crystal grain size of the polycrystalline Si layer is set to 50 to 200 Å.
This is because if the crystal grain size is less than 50 Å, etch pits with the desired depth cannot be formed by etching, and if it exceeds 200 Å, etch pits with the desired density cannot be formed. It is. Further, the thickness of the polycrystalline Si layer is preferably 1000 to 2000 Å. This is because if the thickness is less than 1000 Å, crystal grains will not grow sufficiently, and if it exceeds 2000 Å, the Si layer may become strained and may peel off from the substrate.

As the anisotropic etching solution for Si, for example, an aqueous solution of ethylenediamine (NH2(CH2)2NH2) and pyrocatechol (C6H4(OH)2) can be used. This aqueous solution is in the polycrystalline Si layer (100
) surface can be etched in a V-shape to a depth of 10 to 50 μm. Note that this etching solution removes Si
The etching rate for each plane direction is 50 for the (100) plane.
μm/h, whereas on the (110) plane it is 30 μm/h.
, 3 μm/h for the (111) plane, and the (110) and (111) planes of the polycrystalline Si layer are hardly etched.

[0021] In addition, alkaline aqueous solutions such as potassium hydroxide (KOH), hydrazine (N2H4), and aqueous ammonia (NH4OH) are used as the heterogeneous etching solution, and isopropanol (CH3COOHCH3) is used as a buffer.
) can also be used.

The reason why the depth of the etch pit formed in the polycrystalline Si layer is set to 10 to 50 Å is because diamond nuclei will not be generated if the depth is less than 10 Å, and if the depth exceeds 50 Å, This is because the adhesion of the resulting diamond film to the Si substrate deteriorates.

[0023] As for the method of forming the diamond film after substrate processing, in addition to thermal CVD, various methods such as microwave CVD, laser CVD, high frequency plasma CVD, high frequency arc plasma CVD, and EACVD can be used. A similar effect can be obtained.

[0024]

[Operation] The operation of the present invention will be explained according to the process diagram of the present invention shown in FIG. First, in step A, a Si substrate 1 is used as a substrate on which a diamond film is to be formed, and its surface is subjected to RCA cleaning (a cleaning method for removing heavy metals, oils and fats, and inorganic substances). Next, in step B, a polycrystalline Si layer 2 having a crystal grain size of 50 to 200 Å is formed on the surface of the Si substrate 1 by thermal CVD. Next, in step C, an anisotropic etching solution is used to etch a specific crystal plane of the polycrystalline Si layer 2 to an etching depth of 1.
Etch pits 3 of 0 to 50 Å are formed.

Next, in step D, when a diamond film is formed by the CVD method, many step portions are formed on the surface of the polycrystalline Si layer 2 formed on the Si substrate 1 between it and the etch pits 3. This stepped portion becomes the starting point for diamond nucleus generation, and diamond nuclei 4 are generated at a nucleus generation density of about 3.3 x 1012/cm2, and a smooth diamond film 5 is formed on the surface of the Si substrate 1 in step F. be done.

[0026]

[Example] An example of the present invention will be explained in comparison with a conventional example,
The effects of the present invention will be clarified. After cleaning the Si substrate by RCA, a crystal grain size of 50 was deposited on the surface of the Si substrate by thermal CVD.
A ~200 Å polycrystalline Si layer was deposited to a thickness of 2000 Å. Next, using an aqueous solution of ethylenediamine (NH2(CH2)2NH2) and pyrocatechol (C6H4(OH)2) as an anisotropic etching solution for Si, this polycrystalline Si layer was etched at an etching temperature of 10°C for an etching time of 2 seconds. As a result of selective etching of the (100) plane, fine V-shaped etch pits with a depth of 25 Å and a width of 50 to 200 Å were formed.

FIG. 4 shows the hot filament C used in this example.
It is a schematic diagram of a VD device. The vacuum reaction chamber 10 is evacuated by an exhaust pump 16, and a substrate holder 13 containing an embedded heater 14 and a thermocouple 15 is installed in the center of the vacuum reaction chamber 16, and the substrate 1 is fixed thereto. A Ta filament 1 is placed opposite the substrate 1 fixed to the substrate holder 13.
1 is provided, and CH4 gas 8 and H2 gas 9 are further supplied toward the substrate 1 from a source gas supply pipe to which a mass flow controller 6 and a valve 7 are attached.

After setting the Si substrate 1 in which fine V-shaped etch pits are formed on the surface of the polycrystalline Si film to a depth of 25 Å and a width of 50 to 200 Å to a substrate holder 13,
Electricity was applied to the embedded heater 14 and the Ta filament 11, and the temperature of the Ta filament 11 was maintained at 1800° C. or higher, and the temperature of the substrate 1 was maintained at 900° C. using the thermocouple 15. After that, the raw material gas CH4 gas 5cc/min and H2 gas 500cc
c/min to a predetermined flow rate with a mass flow controller 6, and supplied to the vacuum reaction chamber 10 through a valve 7.
The gas was activated and decomposed using the Ta filament 11 to form diamond nuclei and a diamond film on the substrate 1.

For comparison, as a conventional example, the surface was
The same hot filament CVD method is also used for the Si substrate scratched with 5 μm powder diamond as shown in Figure 4.
A diamond film was formed using the apparatus. The nucleation density and surface roughness of the obtained diamond films of the present invention example and the conventional example were measured, and the results shown in FIGS. 1 and 2 were obtained.

As for the nucleus generation density, as is clear from FIG. 1, the conventional example in which the scratching process was performed with powdered diamond of 25 μm was 1010 nuclei/cm2, whereas the present invention example had Since a large number of step portions were formed by the treatment, the nucleation density was 3.3 x 1012/nuclei.
cm2, and the effect of the present invention was confirmed. Regarding the surface roughness, the conventional example had a surface roughness of 1500 to 3500 Å, while the present invention had a surface roughness of 600 to 1200 Å. It has become clear that a diamond film with excellent properties can be obtained.

[0031]

Effects of the Invention As explained above, in the method of forming a diamond film on a Si substrate by the CVD method of the present invention, after forming a polycrystalline Si layer with a crystal grain size of 50 to 200 Å on a Si substrate, Using a crystal plane anisotropic etching solution,
Etching a specific surface of the polycrystalline Si layer,
By forming etch pits with a depth of Å, Si
This process forms many steps on the surface of the substrate that serve as starting points for the generation of diamond nuclei, and the process of forming a diamond film on the surface-treated Si substrate using the CVD method significantly increases the density of diamond nucleus generation. At the same time, a diamond film with a smooth surface can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the diamond nucleation density of a conventional example and an example of the present invention.

FIG. 2 is a diagram showing the surface roughness of diamond films of a conventional example and an example of the present invention.

FIG. 3 is a process diagram illustrating the method of the present invention.

FIG. 4 is a schematic diagram of a hot filament CVD apparatus used in Examples.

[Explanation of symbols]

1 Si substrate
2 Polycrystalline Si layer 3 Etch pit of Si substrate 4 Diamond nucleus

Claims (1)

[Claims] 1. After forming a polycrystalline Si layer with a crystal grain size of 50 to 200 Å on a Si substrate, a specific surface of the polycrystalline Si layer is etched using a Si crystal plane anisotropic etching solution. , forming etch pits with a depth of 10 to 50 Å and setting the distance between adjacent etch pits to 50 to 200 Å, and then forming diamond nuclei on the polycrystalline Si layer. A method for forming a diamond film on a substrate.