JP2697751B2 - Method of coating diamond film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a diamond film on a substrate to be processed, and more particularly to a method for coating a vapor-phase synthetic diamond film on a substrate to be processed with high adhesion. Diamond is an allotrope of carbon (C), showing a so-called diamond structure, and a Vickers hardness of 10,000 kg
/ mm ² and greater, and the thermal conductivity is remarkably excellent as compared with the 2000 W / mK and other materials, also speed of sound propagating bulk
It has features such as 18,000m / s, which is much faster than other materials.

[0002] Therefore, various uses are being studied by utilizing this property. For example, the use of high hardness for drill blades and cutting tools and for use as a wear-resistant coating are being studied.

Further, it is considered to be used as a component material of a heat-sink of a semiconductor device by utilizing its high thermal conductivity, and to utilize a high sound speed to make a diaphragm of a speaker or the like. Is being put to practical use.

[0004]

2. Description of the Related Art It is well known that a diamond film is synthesized by a high-pressure synthesis method or a low-pressure synthesis method. The high-pressure synthesis method is a method suitable for growing large single crystals, but it requires high temperature and high pressure, so that the equipment becomes large-scale, and the growth rate is extremely slow. Not suitable for formation.

On the other hand, there are various low pressure synthesis methods such as a hot filament method, a combustion flame method, a microwave plasma vapor phase growth method (abbreviated to microwave plasma CVD method), and a DC plasma jet CVD method. Also, a diamond film can be grown in the form of microcrystals on the substrate to be processed.

Here, the microwave plasma CVD method guides a microwave (μ wave) generated from a magnetron or the like to a plasma generation chamber by a waveguide, and decomposes a source gas made of a hydrocarbon such as methane (CH ₄ ). This is a method in which a plasma is formed and guided on a heated substrate to be processed, whereby carbon radicals are turned into diamond to grow microcrystals.

In the DC plasma jet CVD method, a mixed gas of hydrogen (H ₂ ) and a hydrocarbon, for example, CH ₄ is supplied to the reaction chamber from between the anode and the cathode, and the exhaust system is operated to operate the reaction chamber. When arc discharge is generated between the anode and cathode while maintaining a low vacuum, the mixed gas is decomposed into plasma, and the plasma jet containing carbon plasma collides with the substrate to be processed, growing a diamond film composed of microcrystals It is a way to make it.

As described above, a diamond film can be grown on a substrate to be processed by the plasma CVD method, but the plasma CVD method has a problem that the adhesion to the substrate to be processed is not good.

As a method of improving the adhesion of the diamond film grown on the substrate to be processed by the CVD method to the substrate, there are provided an intermediate layer such as a carbide layer, and the use of an anchor effect by making the underground uneven. A method has been tried.

That is, in the above-mentioned method, an intermediate layer made of carbide having a strong chemical affinity with diamond, such as tungsten carbide (WC) or molybdenum carbide (MoC), is provided to improve the adhesion. Has not been obtained.

In the conventional method, the conventional CVD method has a low nucleation density and a low film forming rate, so that the diamond film is grown to a thickness sufficient to fill the irregularities on the underlying surface and exhibit a sufficient anchor effect. It is difficult to do so and it has not been put to practical use.

[0012]

As mentioned above, the CVD
Although a diamond film can be grown on a substrate to be processed at a considerable growth rate by the method, the adhesion between the grown diamond film and the substrate is weak, and various improvement methods have been tried, but have been successful. Not in.

Accordingly, an object of the present invention is to improve the adhesion between the grown diamond film and the substrate when the diamond film is grown on the substrate by the plasma CVD method.

[0014]

According to the present invention, a porosity of 5 to 30% is formed on a substrate on which a diamond film is to be grown.
Is formed as an intermediate layer, and a diamond film is vapor-phase grown on the intermediate layer.

According to the present invention, a mixed powder of a low-melting-point material and a high-melting-point material is sprayed on a substrate to be processed, and the high-melting-point sprayed material is dispersed in the form of particles on the surface of the sprayed film, whereby irregularities are formed on the surface. Is provided, and a diamond film is vapor-phase grown thereon.

According to the present invention, there is provided a method for coating a diamond film, comprising blasting the surface of a substrate on which a diamond film is to be grown, and synthesizing a diamond film on the blasted surface. .

[0017]

According to the first aspect of the present invention, as shown in FIG.
A thin sprayed film 2 having fine irregularities is formed on the thin film, and a diamond film 3 is grown thereon by a CVD method.

Here, a flat film can be obtained by ordinary thermal spraying. However, the present invention uses a thermal sprayed film having a fine unevenness with a porosity of 5 to 30%. Are generated and grown to firmly bond the diamond film by the anchor effect.

Here, according to the results of the experiment, the porosity was 5%.
If the amount is less than 30%, the surface irregularities are too small to obtain a good anchoring effect, and if it exceeds 30%, the strength of the sprayed film itself is undesirably reduced.

Next, if the same material as that of the substrate 1 is used as the thermal spray material for forming the thermal spray film 2, the substrate 1 and the thermal spray film 2 are ideally well adhered to each other. In the case of a material such as nickel (Ni), cobalt (Co), and chromium (Cr) that forms a solid solution of carbon (C) so that diamond is difficult to grow, tungsten (W), molybdenum (Mo), etc. If a material is used, diamond can be grown with good adhesion. Examples of other thermal spray materials include Cu, Ti, Nb, Al ₂ O ₃ , and ZrO ₂ .

When a material having a thermal expansion coefficient greatly different from that of diamond is used as the substrate, the thermal stress can be reduced by forming the thermal spray layer using a material having an intermediate thermal expansion coefficient as a constituent material of the thermal spray layer. Can be. Further, in this case, if the sprayed film is constituted by a plurality of layers instead of a single layer, the influence of thermal stress can be further reduced. In order to enhance the anchor effect, it is necessary to increase the nucleation density of diamond on the surface of the sprayed film, and it is preferable that the surface of the sprayed film is scratched before the CVD growth of diamond.

As described above, in the second embodiment of the present invention, an uneven layer is formed on the substrate surface by thermal spraying, and a diamond film is grown thereon, so that the concave portion of the thermal sprayed intermediate layer is also formed. The diamond is nucleated and grown, and the diamond film is firmly bonded to the underlying substrate by the anchor effect. Specifically, the sprayed powder is made of a mixture of a material having a low melting point and a material having a high melting point. By making the melting point material powder exist in the sprayed film and on the surface in the form of particles, unevenness on the surface of the sprayed film is emphasized, and a high anchor effect is obtained.

FIG. 2 shows a cross-sectional structure of a diamond coating film according to the second embodiment of the present invention.
Denotes a base substrate, 5 denotes a sprayed film, 6 denotes high melting point sprayed material particles, 7 denotes a low melting point sprayed material, and 8 denotes a diamond film.

In the second embodiment of the present invention, the diamond film is firmly adhered to the base substrate by the anchor effect by the diamond entering into the concave portion on the surface of the sprayed film 5. What is important here is the internal structure and surface structure of the sprayed film. In general thermal spraying, sprayed powder melted at a high temperature of plasma collides with a substrate surface as droplets, where the droplets flatten and spread to form a film. The higher the flatness, the denser the film, and the higher the surface smoothness. If the flatness is low, the film becomes porous and the surface irregularities become large. Therefore, when trying to increase the unevenness of the sprayed film surface to enhance the anchor effect,
The film becomes porous, and the strength may be reduced.

The present invention has been made to solve such a problem and to form a sprayed film which is dense and has large surface irregularities. Specifically, the high-melting powder 6 and the low-melting powder 7 are simultaneously sprayed, and the high-melting material 6 is dispersed in the sprayed film of the low-melting material 7 in the form of particles. This is to obtain a state in which the melting point material particles 6 protrude from the surface and have large irregularities.

Further, if only the low-melting material or the high-melting material on the surface is removed by etching after the formation of the sprayed film, the unevenness on the surface is further increased, which is convenient.

The temperature of the thermal spraying material at the time of diamond synthesis (600
In principle, any material can be used as long as it is stable at a temperature of at least (° C), but metals (Fe, Ni, Co,
Cr, etc.) are not so preferred. Preferred thermal spraying materials are shown in the order of decreasing melting point, for example, Al, Cu, Si, Nb, Ti, Mo, W, Si.
O ₂ , Al ₂ O ₃ , ZrO ₂ , SiC, WC, Mo ₂ C and the like.

As shown in FIG. 3A, the sprayed powder does not have to be a mixture of the low melting point material powder 7 and the high melting point material powder 6, but rather, as shown in FIG. 3B. A powder made by dispersing a high melting point material powder 6 in a low melting point material 7;
As shown in (C) of FIG.
And the powder that is uniformly agglomerated into secondary particles,
It is preferable in terms of powder supply. Thermal spraying material has low melting point and high melting point.
Not only the types but also three or more materials having different melting points can be used. Further, the low-melting thermal spray material 7 is
When the same material is used, the adhesion between the substrate 4 and the sprayed film 5 is further enhanced, which is convenient for the object of the present invention.

By blasting the surface of the substrate 4 in the same manner as in normal thermal spraying, the adhesion between the substrate 4 and the thermal spray film 5 can be further improved.

A material whose substrate is unlikely to grow diamond (for example, Fe, Ni, Co, Cr, etc., which easily dissolves carbon)
In this case, if another material is selected as the thermal spraying material, diamond can be grown with good adhesion even on a substrate on which such diamond is difficult to be formed. Further, when the substrate is made of a material whose coefficient of thermal expansion is significantly different from that of diamond, thermal stress can be reduced by making the thermal spray layer have a coefficient of thermal expansion between diamond and the substrate material. The thermal spray layer is not limited to a single layer, and may have a multilayer structure having different compositions and materials.

It is important to increase the density of diamond nuclei generated on the surface of the sprayed film in order to enhance the anchor effect. Therefore, it is preferable that the surface of the sprayed film be scratched before diamond is formed.

As described above, in the third embodiment of the present invention, a diamond film is grown after blasting the substrate surface, so that the diamond film is firmly bonded to the substrate.

In the present invention, blast processing is usually
A powder mainly composed of diamond powder, nitride powder, carbide powder, carbonitride powder and a mixture thereof, particularly in a surface treatment method performed to enhance the adhesion between the sprayed film and the substrate as a pretreatment for thermal spraying, Abrasives such as silicon carbide (SiC) and tungsten carbide (WC) are blasted onto the surface of the substrate at high speed to form fine irregularities on the surface, and the adhesion between the sprayed film and the substrate is enhanced by the anchor effect. The present invention applies this blasting to diamond film coating,
The purpose is to obtain a high adhesion force by the anchor effect. In addition, the scratches and defects introduced into the substrate surface by the blasting process become sites for generating nuclei of diamond, so that the nucleation density of diamond is increased, and this also has the effect of improving the adhesion.

In order to enhance the anchor effect, it is important to generate diamond nuclei uniformly at a high density on the surface of the base material. Therefore, before forming the diamond film, a surface treatment for increasing the nucleation density is further performed. You can go.
In such a surface treatment, for example, a substrate can be immersed in a liquid in which diamond powder is dispersed and subjected to an ultrasonic treatment or the like, whereby fine scratches can be made on the substrate surface.

[0035]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples.

Example 1 In the present invention, a 20 mm square tungsten plate having a thickness of 5 mm was used as a substrate. Then, using tungsten having an average particle size of 50 μm, argon as a spray gas, and an output of 10 kW
Plasma spraying was performed under the conditions described above to form a sprayed film having a thickness of about 50 μm and a porosity of 20%.

Next, the substrate was immersed in alcohol in which diamond particles having an average particle size of 2 μm were dispersed, and ultrasonically applied for 15 minutes to damage the sprayed film on the substrate. Next, a DC plasma jet CVD device developed by the present inventors using this substrate (see Japanese Patent Application Laid-Open No. 64-33096).
Then, a diamond film having a thickness of 50 μm was formed on the surface of the sprayed film on the substrate by CVD growth.

When the adhesion strength of the diamond film was measured for this sample, the jig attached to the surface of the diamond film at about 100 kg / cm ² or more was peeled off, and a correct value could not be obtained.

On the other hand, a diamond film was directly formed on the tungsten plate by DC plasma jet CVD in the same manner as in Example 1 except that the sprayed film was not formed and the ultrasonic damage treatment was not performed. The adhesion of the obtained diamond film was 1.0 kg / cm ² or less, and it was found that the adhesion of the diamond film was greatly improved by the method of the present invention.

Example 2 In this example, 20 mm square and 5 mm thick Inconel (Ni-16Cr-8Fe) was used as a substrate. Then, using a molybdenum having an average particle size of 5 μm as a thermal spraying material and using argon as a thermal spraying gas, plasma spraying is performed under the condition of an output of 10 kW. Formed.

Thereafter, an ultrasonic scratching treatment was performed using diamond particles in the same manner as in Example 1, and the thickness of the surface was reduced.
A 50 μm diamond film was formed. When the adhesion strength of the diamond film was measured for this sample, 100 kg / cm
² or more. On the other hand, a diamond film could not be formed when an attempt was made to form a diamond film directly on Inconel in the same manner as in Example 2 except that the formation of the sprayed film and the ultrasonic damage treatment were not performed.

Example 3 A 20 mm square aluminum nitride (Al) having a thickness of 5 mm was used as a substrate.
N) was used. Next, a three-layer sprayed film composed of 50 μm of alumina, 30 μm of Cu, and 50 μm of Ti was formed on the substrate by plasma spraying. The porosity of the Ti film was 10%.

Thereafter, an ultrasonic scratching treatment was performed using diamond particles in the same manner as in Example 1, and the thickness of the surface was reduced.
When forming a diamond film of 50 [mu] m, was measured the adhesion strength of the diamond film on the sample, 100 kg / cm ²
That was all. On the other hand, in the same manner as in Example 3 except that the sprayed film was not formed and the ultrasonic damage treatment was not performed, the adhesion when the diamond film was formed directly on the AlN substrate was 1.0.
kg / cm ² or less.

Example 4 A 20 mm square, 5 mm thick Cu plate was used as a substrate, the surface of which was blasted using tungsten carbide (WC) particles, and a sprayed film having a thickness of about 50 μm was formed thereon by plasma spraying. Formed. As the thermal spray powder, as shown in FIG. 3 (B), a powder having an average particle size of 50 μm in which molybdenum (Mo) particles having an average particle size of 5 μm are dispersed in copper (Cu) is used.
50%. The thermal spraying conditions used argon as a thermal spray gas in the atmosphere, and the output was 10 kW. Next, using a Cu etching solution (aqueous nitric acid solution), only Cu on the
Etching was performed by μm so that Mo particles appeared on the surface to further increase the surface irregularities. This was immersed in alcohol in which diamond particles having an average particle diameter of 2 μm were dispersed, and ultrasonically applied at room temperature for 15 minutes to perform a scratching treatment. The obtained substrate was mounted on a DC plasma jet CVD device developed by the present inventors (see JP-A-64-33096), and the surface was coated with a diamond film having a thickness of about 100 μm. Diamond film coating conditions are 50 liters / min of hydrogen, methane 1
Liter / min, pressure 50 Torr, discharge output 6 kW, synthesis time 1
hr. When the adhesion strength of the diamond film was measured for the sample obtained above, the jig attached to the surface of the diamond film was peeled off at about 200 kg / cm ² or more, and a correct value could not be obtained.

On the other hand, a sample in which a diamond film was directly coated on a Cu plate in the same manner as in Example 4 except that the plasma sprayed film was not sprayed and the subsequent etching and ultrasonic scratching treatment were not performed, Was peeled off during lowering to room temperature, and the adhesion strength could not even be measured.

Example 5 A 20 mm square, 5 mm thick Inconel (Ni-16Cr-
8Fe), 80vol% of WC particles with an average particle size of 5μm as a thermal spraying material
And average particle diameter of 20vol% of Co particles with average particle diameter of 1μm
Using a 50 μm powder as shown in FIG. 3 (C) and forming a sprayed layer of 50 μm and etching the surface Co to form a diamond film of 100 μm in the same manner as in Example 4,
A diamond film having an adhesion of 200 kg / cm ² or more was obtained.

On the other hand, when a diamond film was directly formed on Inconel in the same manner as in Example 5 except that the plasma spraying and the subsequent etching and ultrasonic scratching treatment were not performed, no diamond could be formed.

Example 6 A 20 mm square, 5 mm thick molybdenum (Mo) plate was used as a base substrate, and its surface was blasted using silicon carbide (SiC) particles. The blast conditions were a particle size of 100 mesh, a blast pressure of 3 kg / cm ² , and a time of 10 minutes. The blasted substrate thus obtained is immersed in alcohol in which diamond particles having an average particle size of 2 μm are dispersed, and the blasted substrate is
Ultrasonic vibration was applied to further perform a scratching treatment. Next, the obtained substrate was mounted on a DC plasma jet CVD device (JP-A-64-33096) developed earlier by the present inventors.
The substrate surface was coated with a diamond film having a thickness of about 100 μm.

When the adhesion strength of the diamond film was measured for this sample, the jig attached to the surface of the diamond film was peeled off at about 200 kg / cm ² or more, and a correct value could not be obtained.

On the other hand, a molybdenum (Mo) plate was directly coated with a diamond film in the same manner as in Example 6, except that the blast treatment and the ultrasonic scratching treatment were not performed. After the film was formed, the sample was peeled off while the sample was cooled to room temperature, and it was not even possible to measure the adhesion strength.

[0051]

As is clear from the above description, according to the present invention, the adhesion strength between the substrate and the diamond film is 100%.
It is possible to obtain a diamond coating of kg / cm ² or more.For example, it is clear that a tool or a jig coated with diamond by applying the present invention can be expected to have a life several times to several tens times longer than that of a conventional tool. It is.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross-sectional structure of a diamond film to which the present invention is applied.

FIG. 2 is a schematic diagram showing a cross-sectional structure of a diamond film to which a second embodiment of the present invention is applied.

FIG. 3 is a drawing schematically showing a state of a sprayed powder used in a second embodiment of the present invention.

FIG. 4 is a schematic diagram showing a cross-sectional structure of a diamond film to which the third embodiment of the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Sprayed film 3 ... Diamond film 4 ... Substrate 5 ... Sprayed film 6 ... High melting point sprayed material (particles) 7 ... Low melting point sprayed material (particles) 8 ... Diamond film 9 ... Substrate 10 ... Blast processing surface 11 ... Diamond film

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 1-219043 (JP, A) JP-A 3-141193 (JP, A) JP-A 3-141195 (JP, A)

Claims (10)

(57) [Claims] A sprayed film having a porosity of 5 to 30% is formed as an intermediate layer on a substrate on which a diamond film is to be grown,
A method for coating a diamond film, wherein a diamond film is grown on the intermediate layer by vapor phase growth. 2. The method for coating a diamond film according to claim 1, wherein said sprayed film is subjected to a scratching treatment to grow a diamond film in a vapor phase. 3. The method for coating a diamond film according to claim 1, wherein said sprayed film has a multilayer structure. 4. A method for spraying a mixed powder of a low-melting material and a high-melting material on a substrate to be processed and dispersing the high-melting material on the surface of the sprayed film in a particle form, thereby providing irregularities on the surface.
A diamond film coating method, wherein a diamond film is vapor-phase grown thereon. 5. The method for coating a diamond film according to claim 1, wherein the surface of the substrate is blasted to increase the adhesion of the sprayed film before the formation of the sprayed film. 6. The method for coating a diamond film according to claim 4, wherein after forming the sprayed film, only the low melting point material or only the high melting point material on the surface is removed by etching to further increase the surface irregularities. 7. The method for coating a diamond film according to claim 4, wherein, after the formation of the sprayed film, the surface of the diamond film is scratched to increase the nucleation density of diamond, and then the diamond film is vapor-phase grown. 8. A method for coating a diamond film, comprising: blasting a surface of a substrate on which a diamond film is to be grown; and vapor-phase synthesizing the diamond film on the blasted surface. 9. The method for coating a diamond film according to claim 8, wherein the blast powder used for the blast treatment is a powder mainly composed of diamond, carbide, nitride, carbonitride, and a mixture thereof. 10. The method according to claim 8, wherein the substrate is immersed in a liquid in which diamond powder is dispersed, vibrated to give fine scratches on the surface of the substrate, and then the diamond is vapor-grown. 3. The method for coating a diamond film according to item 1.