JP2780495B2 - Method for forming diamond film on Si substrate by CVD method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a diamond film on a Si substrate by a CVD method.

[0002]

2. Description of the Related Art Diamond is the hardest material among known materials, has the highest thermal conductivity, has high electrical insulation, is transparent, and is chemically stable. Applications to tools, wear-resistant parts, protective films for solar cells, heat sinks for semiconductor devices, and the like have been studied.

[0003] Conventionally, as a low-pressure synthesis method of diamond, a solid or liquid raw material is converted into a gas by a method such as evaporation or sublimation, and a PVD method (physical vapor deposition method) in which crystals are grown from the gas, and a compound containing carbon. There is a CVD method (chemical vapor deposition method) in which a gas is decomposed by heat or plasma to obtain a crystal.

[0004] That is, in the latter CVD method, a mixed gas of hydrocarbon and hydrogen is used as a raw material at atmospheric pressure or 1 ton.
Under reduced pressure of rr or more, heat, microwave or high frequency or the like is used to excite the raw material gas, and then guided on a substrate heated to 600 to 1000 ° C. to thermally decompose hydrocarbons, and by the action of activated hydrogen, This is to deposit carbon having a diamond structure on a substrate.

More specifically, for example, a hot filament CVD method in which a substrate is heated with a filament, a microwave plasma CVD method in which a source gas and hydrogen are decomposed using plasma.
And a photo-CVD method of irradiating an ultraviolet laser beam to a mixed raw material gas of hydrocarbon and hydrogen.

On the other hand, in the PVD method, a method using a glow discharge in a hydrocarbon gas and an ion beam is typical. For example, an ion beam for irradiating a substrate with an ion beam by evaporating carbon with an electron beam or the like is used. There are a beam sputtering method, an ion beam evaporation method of forming a film on a substrate by ionizing a source gas and atoms of the source, and extracting the ion by an electric field.

[0007]

The diamond film formed by the low-pressure vapor-phase synthesis method can be epitaxially grown on a diamond substrate. In addition, molybdenum, tungsten,
In addition to simple substances such as gold, copper, zirconium, and silicon, compounds such as cemented carbide, silica glass, and sapphire, there are ceramics such as silicon carbide, titanium carbide, boron nitride, and silicon nitride.

[0008] However, even on a silicon substrate having a crystal structure of a diamond structure, a technique for causing epitaxial growth has not been established at present. Moreover,
The above 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, an aggregate of diamond crystals having a grain size of about 1 to 10 μm is formed, so that only a film having a severe surface irregularity can be obtained.

That is, in the process of forming a diamond film, a large number of diamond nuclei are first generated on a Si substrate in the first stage, and then the nuclei grow into large crystal grains. Attachment starts to form a film. Thereafter, the film grows in a direction perpendicular to the Si substrate, and the film gradually becomes thicker. Due to such a growth process, the diamond film becomes a film in which polycrystals are gathered and surface roughness is severe.

By the way, the nucleation of diamond affected surface of the substrate, the substrate surface by performing the scratching treatment with diamond powder, from 10 ⁴ / cm ² in the Si substrate 10 ⁸ to 10 ⁹ / It is known that the number of nuclei increases to about cm ² .

That is, by rubbing with diamond powder of ^{2 to} 10 μm, the nucleation density is increased to a maximum of about 10 ⁹ / cm ² , and as the particles grow, they come into contact with each other and aggregate to form a film-like diamond. (Electronics, November 1987, p. 68).

In Japanese Patent Application Laid-Open No. 61-201698, diamond, nitride or the like having a substrate surface of 10 μm or less is used.
A smooth diamond film having a surface roughness of 0.4 μm or less is obtained by rubbing with an inorganic powder such as a carbide and making a scratch having a size of 1 μm or less.

Further, in Japanese Patent Application Laid-Open No. 60-86096, a sharp scratch is generated by rubbing a Si substrate with diamond powder having a size of 2 μm or less.
A diamond film made of fine crystal grains is obtained at a growth rate of μm / hr.

However, as described above, according to the conventional method in which the surface of the Si substrate is scratched prior to the vapor phase synthesis of the diamond film, the nucleation density of diamond is at most about one per 1,000 squared (10 ¹⁰ / cm 2). ^Two
In order to use the obtained diamond film as a semiconductor film or a wear film, it is necessary to improve the nucleation density and to smooth the surface irregularities.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems when a diamond film is formed on a Si substrate by a CVD method. An object of the present invention is to provide a method for forming a diamond film on a Si substrate by a CVD method capable of obtaining a smooth diamond film by reducing unevenness.

[0016]

The inventor of the present invention has found that, since it is effective to damage the substrate surface to increase the nucleation density of diamond, if a step is provided on the substrate surface, the diamond is formed at the step. The energy of nuclear generation decreases,
We focused on the fact that diamond nuclei are easily formed. Accordingly, the present inventors have conducted intensive studies on the density and depth of the steps on the substrate surface, which are the starting points of nucleation of diamond. As a result, the present inventors have found a method of setting the density of the steps on the substrate surface to a desired number, and have found an optimum range for the depth of the steps, thereby completing the present invention.

According to the method of forming a diamond film on a Si substrate by the CVD method of the present invention, a polycrystalline Si layer having a crystal grain size of 50 to 200 ° is formed on a Si substrate, and then a Si crystal plane anisotropic etching solution is applied. Then, a specific surface of the polycrystalline Si layer is etched to form etch pits having a depth of 10 to 50 °, and a distance between adjacent etch pits is set to 50 to 20.
The point is to form diamond nuclei on the polycrystalline Si layer after the angle is set to 0 °.

In the present invention, the polycrystalline Si on the Si substrate
To form a layer, a vacuum deposition method, a sputtering method,
A plasma CVD method or the like can be used. When forming a polycrystalline Si layer on a Si substrate, appropriately select a substrate temperature in the case of a vacuum deposition method, an argon pressure and a substrate temperature in the case of a sputtering method, a glow discharge condition and a silane gas concentration in the case of a plasma CVD method. As a result, the polycrystalline S
The crystal grain size of the i-layer can be adjusted.

The crystal grain size of the polycrystalline Si layer is 50 to 200 °
The reason is that if the crystal grain size is less than 50 °, etch pits of a desired depth cannot be formed by etching, and if it exceeds 200 °, etch pits of a desired density cannot be formed. It is. Further, it is preferable that the thickness of the polycrystalline Si layer be 1000 to 2000 °. If the thickness is less than 1000 °, the crystal grains do not grow sufficiently. If the thickness exceeds 2000 °, the Si layer is distorted and may be separated from the substrate.

As the anisotropic etching solution for Si, for example, an aqueous solution of ethylenediamine (NH ₂ (CH ₂ ) ₂ NH ₂ ) and pyrocatechol (C ₆ H ₄ (OH) ₂ ) can be used. This aqueous solution can etch only the (100) plane of the polycrystalline Si layer into a V-shape to a depth of 10 to 50 μm. The etching rate of the Si in each plane direction by this etchant was 50 μm / (100) plane.
h on the (110) plane, 30 μm / h, (1
(11) plane, 3 μm / h, and (11) of the polycrystalline Si layer
The 0) plane and the (111) plane are hardly etched.

As an illegal etching solution, an alkaline aqueous solution such as potassium hydroxide (KOH), hydrazine (N ₂ H ₄ ), or ammonia water (NH ₄ OH) may be used.
Alcohol such as isopropanol (CH ₃ COOHCH ₃ ) can be used as the buffer.

The reason why the depth of the etch pit formed in the polycrystalline Si layer is 10 to 50 ° is that if the depth is less than 10 °, diamond nuclei will not be generated. This is because the resulting diamond film has poor adhesion to the Si substrate.

The method of forming the diamond film after the substrate processing may be any of various methods such as a microwave CVD method, a laser CVD method, a high frequency plasma CVD method, a high frequency arc plasma CVD method, and an EACVD method, in addition to the thermal CVD method. Similar effects can be obtained.

[0024]

The operation of the present invention will be described with reference to the flow chart 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 formed, and the surface is subjected to RCA cleaning (a cleaning method for removing heavy metals, oils, and inorganics). Next, in step B, a polycrystalline Si layer 2 having a crystal grain size of 50 to 200 ° is formed on the surface of the Si substrate 1 by a thermal CVD method. Next, in Step C, an anisotropic etching solution that etches a specific crystal plane of the polycrystalline Si layer 2 is used to etch at a depth of 1
An etch pit 3 of 0 to 50 ° is formed.

Subsequently, when a diamond film is formed by the CVD method in step D, a large number of steps are formed between the etch pits 3 on the surface of the polycrystalline Si layer 2 formed on the Si substrate 1. The step portion serves as a starting point of diamond nucleation, and diamond nuclei 4 are generated at a nucleation density of about 3.3 × 10 ¹² / cm ² , and a smooth diamond film 5 is formed on the surface of the Si substrate 1 in step F. Is formed.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in comparison with a conventional example.
The effect of the present invention will be clarified. After the RCA cleaning of the Si substrate, a crystal grain size of 50 is formed on the surface of the Si substrate by a thermal CVD method.
A Å200 ° polycrystalline Si layer was deposited to a thickness of 2000 °. Next, an aqueous solution of ethylenediamine (NH ₂ (CH ₂ ) ₂ NH ₂ ) and pyrocatechol (C ₆ H ₄ (OH) ₂ ) was used as a Si anisotropic etching solution at an etching temperature of 10 ° C. for an etching time of 2 seconds. Then, when this polycrystalline Si layer was etched, fine V-shaped etch pits having a depth of 25 ° and a width of 50 to 200 ° were formed by selective etching of the (100) plane.

FIG. 4 shows the hot filament C used in this embodiment.
It is a schematic diagram of a VD device. The vacuum reaction chamber 10 is evacuated by an exhaust pump 16. A substrate holder 13 having a built-in heater 14 and a thermocouple 15 is installed in the center of the vacuum reaction chamber 16, and the substrate 1 is fixed. The Ta filament 1 faces the substrate 1 fixed to the substrate holder 13.
1 is provided, and a CH ₄ gas 8 and a H ₂ gas 9 are supplied toward the substrate 1 from a source gas supply pipe provided with a mass flow controller 6 and a valve 7.

After the Si substrate 1 in which fine V-shaped etch pits having a depth of 25 ° and a width of 50 to 200 ° are formed on the polycrystalline Si film formed on the surface is set on the substrate holder 13,
Electricity was supplied to the embedded heater 14 and the Ta filament 11, and the Ta filament 11 was maintained at 1800 ° C. or higher, and the substrate 1 was maintained at 900 ° C. by the thermocouple 15. Thereafter, 5 cc / min of CH ₄ gas, which is a source gas, and 500 c of H ₂ gas
c / min is adjusted to a predetermined flow rate by the mass flow controller 6, supplied to the vacuum reaction chamber 10 through the valve 7,
The gas was activated and decomposed by the Ta filament 11 to form a diamond nucleus and a diamond film on the substrate 1.

For comparison, the surface was set to 2 as a conventional example.
The same hot filament CVD as shown in FIG. 4 was applied to the Si substrate that had been scratched with 5 μm powdered diamond.
A diamond film was formed using an apparatus. When the nucleation density and the surface roughness of the obtained diamond films of the present invention and the conventional example were measured, the results shown in FIGS. 1 and 2 were obtained.

As apparent from FIG. 1, the nucleation density was 10 ¹⁰ / cm ² in the conventional example subjected to a scratching treatment with 25 μm powdered diamond, whereas the present invention example was the method of the present invention. Nucleation density is 3.3 × 10 ¹² / cm
² , which confirmed the effect of the present invention. Regarding the surface roughness, the conventional example had a surface roughness of 1500 to 3500 °, while the present invention example had a surface roughness of 600 to 1200 °. It became clear that a perfect diamond film could be obtained.

[0031]

According to the method for forming a diamond film on a Si substrate by the CVD method of the present invention, as described above, after forming a polycrystalline Si layer having a crystal grain size of 50 to 200 ° on a Si substrate, Using a crystal plane anisotropic etchant,
Etching a specific surface of the polycrystalline Si layer, 10 to 50
By forming an etch pit with a depth of Å, Si
The step of forming a large number of steps on the surface of the substrate, which is the starting point of the generation of diamond nuclei. The step of forming a diamond film on the surface-treated Si substrate by the CVD method significantly increases the nucleation density of diamond. And a diamond film having a smooth surface is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing diamond nucleus generation densities of a conventional example and an example of the present invention.

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

FIG. 3 is a process chart for explaining the method of the present invention.

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Si substrate 2 Polycrystalline Si layer 3 Etch pit of Si substrate 4 Diamond nucleus 5 Diamond film 8 CH ₄ gas 9 H ₂ gas 10 Vacuum reaction chamber 11 Ta filament 13 Substrate holder 14 Embedded heater 16 Exhaust pump

Claims (1)

(57) [Claims] After a polycrystalline Si layer having a crystal grain size of 50 to 200 ° is formed on a Si substrate, a specific surface of the polycrystalline Si layer is etched by using an anisotropic Si crystal plane etching solution. Forming an etch pit having a depth of 10 to 50 °, a distance between adjacent etch pits of 50 to 200 °, and then forming a diamond nucleus on the polycrystalline Si layer. A method for forming a diamond film on a substrate.