JP3138222B2 - Method for producing free-standing 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 producing a diamond free-standing film synthesized by a vapor phase synthesis method.

[0002]

2. Description of the Related Art Conventionally, various methods have been proposed for forming a free-standing diamond film by a vapor phase synthesis method. In order to increase the adhesion strength between the diamond coating layer and the substrate, a method using a chemical reaction by etching with acid or the like, or a method of forming fine irregularities on the surface of the substrate by physically processing with abrasive grains etc. are proposed. (Japanese Patent Laid-Open No. 7-3)
15989).

[0003] A diamond free-standing film formed by a vapor phase synthesis method generates a tensile stress due to a growth defect or intrinsic strain.
Therefore, the free-standing film is warped. Therefore, as a method for producing a flat free-standing film, a diamond convex type film synthesized under the condition that the growth surface side is convex when the substrate is removed and a diamond convex type film synthesized under the condition that the growth surface side is concave when the substrate is removed are synthesized. A method has been proposed in which a diamond free-standing film is formed by a vapor phase synthesis method and then the substrate is removed to produce a free-standing diamond film (Japanese Patent Laid-Open No. Hei 7-21579).
6). The self-supporting diamond film has applications such as a heat sink for various semiconductor devices and a wear-resistant member.
Here, the self-supporting film refers to a film that can maintain the film shape by itself, and does not include a film that adheres to a substrate made of another material and maintains the film shape.

[0004]

When a self-standing diamond film is formed by a vapor phase synthesis method, it is necessary to polish the deposition surface side of the diamond coating layer, and high-speed polishing is required. When the adhesion between the diamond coating layer and the substrate is low, the adhesion strength between the diamond coating layer and the substrate becomes a problem.

On the other hand, in the case of manufacturing a free-standing diamond film, the free-standing film is warped. Therefore, when trying to obtain a flat free-standing diamond film, a more efficient method for reducing such warpage is required. It is becoming.

When a self-supporting diamond film is to be obtained by a vapor phase synthesis method, a diamond film is usually formed on a substrate. Therefore, when a self-supporting diamond film is to be obtained, it is necessary to remove the substrate. There was a problem that it took days to remove.

In the case where a free-standing diamond film is to be formed by two-step film formation, it is necessary to polish the surface of the second diamond coating layer which is in close contact with the first diamond coating layer (hereinafter referred to as "back surface"). The second layer was very hard and difficult to polish. It is a technical object of the present invention to solve the above problems.

[0008]

Means for Solving the Problems The method for producing a free-standing diamond film by a vapor phase synthesis method according to the present invention comprises: (a) a first step of forming fine irregularities on a substrate; A second step of forming a diamond first coating layer on the surface by a vapor phase synthesis method and coating the surface of the substrate with the coating layer; and (c) diamond formed of diamond having a higher crystal density than the first coating layer. The first layer is coated with the second layer.
A third step of coating the surface of the coating layer, (d) a fourth step of polishing the deposition surface side of the second coating layer, (e) a fifth step of removing the substrate, and (f) the first step. The method is characterized by comprising a sixth step of removing the first coating layer by polishing the side of the layer that is in close contact with the substrate surface, and flattening the back surface of the second coating layer.

In the second step, methane 5-10
vol.%, 90 to 95% by volume of hydrogen, and 0.1 to 3% by volume of methane and 97 to 99.% of hydrogen in the third step.
It is also desirable to form the diamond coating layer by a gas phase synthesis method in which a mixed gas of 9 vol% is reacted.

Further, in the fifth step, the substrate is made of Co.
It is also preferable to use a binderless cemented carbide having a content of less than 1% as a substrate.
It is also preferable to use a cemented carbide having an o content of 1 to 5% as a substrate.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the production of a free-standing diamond film, a binder-less cemented carbide having a Co content of less than 1% by weight or a cemented carbide containing 1 to 5% by weight of Co is used for a substrate. . Although the thermal conductivity decreases due to the inclusion of Co, it is considered to have a high value when used as a heat sink. In addition, when producing a free-standing diamond film, it is necessary to remove the substrate. In this case, when a substrate containing Co is used, the substrate is peeled off very quickly when the substrate is removed, so that the number of production days can be reduced.

Fine irregularities are formed on the electric discharge machining surface of the substrate by using a laser or the like. Further, wire discharge may be used. The formation of these fine irregularities has the effect of improving the adhesion between the substrate and the diamond coating layer. Also, when trying to obtain a flat self-supporting film, it is necessary to polish the surface of the diamond coating layer, so that the adhesion strength between the diamond coating layer and the substrate is improved,
It has the feature that high-speed polishing is possible. The shape of the fine unevenness may be a known shape. For example, when a fine slit is formed using a laser, a well shape or a waveform may be used.

Further, by using the above-mentioned substrate,
When the diamond free-standing film is formed, there is a problem that such a film is warped. However, the formation of fine irregularities disperses the stress and can stop the warpage mechanically. Therefore, it becomes easy to manufacture a flat free-standing film.

Next, 5 to 10 vol% of hydrogen and 90 to 90 vol.
A diamond-coated first layer is formed using a gas having a high methane concentration of 95 vol%. The formation of the film having a high methane concentration has an advantage that the fine irregularities of the substrate can be covered in a short time with a large number of nuclei generated.

The high methane concentration film is soft because of its low crystal density. Therefore, when a diamond free-standing film is to be obtained, it has a feature that it is soft and easy to remove when polishing the back surface.

Further, on the surface of the high methane concentration film, a methane concentration of 0.1 to 3 vol%, hydrogen of 97 to 99.9%
To form a second diamond coating layer.
The method for forming the second diamond coating layer is the same as the method for forming a film having a high methane concentration, except that the methane concentration is 0.1 to 3 vol%.

The deposition surface side is polished while the surface of the diamond second coating layer remains adhered to the substrate. The polishing is performed using a known method.

In the next step, the substrate is removed to form a self-supporting diamond film. As the removing method, the substrate was separated by a method of corroding using a mixed acid of HF + HNO3. When Co was contained, it was confirmed that the film was peeled earlier than before.

Finally, the first diamond coating layer is removed,
Polish the back surface. Although the thermal conduction of diamond is due to lattice vibration, there is a disadvantage that the thermal conductivity is reduced due to many grain boundaries and many impurities (such as non-diamond carbon) on the nucleus generating surface side. Therefore, there is an advantage that a decrease in thermal conductivity can be prevented by polishing the back surface.

In the present invention, a free-standing diamond film having a high thermal conductivity can be obtained by using a binderless superhard body having a Co content of less than 1% by weight. On the other hand, in the present invention, the use of a cemented carbide containing 1 to 5% by weight of Co for the substrate slightly reduces the thermal conductivity, but
While it is considered that the film has sufficient performance for use as a heat sink, the peeling time of the substrate can be shortened when the diamond free-standing film is formed. Therefore, manufacturing efficiency is increased.

By forming fine irregularities on the surface of the substrate, the adhesion between the substrate and the diamond coating layer is enhanced, and the coating layer and the substrate are polished at a high speed to flatten the diamond coating layer. The adhesion strength is improved.

By forming a high methane film on the diamond first coating layer, nuclei are generated and the fine irregularities can be covered with the diamond coating film in a short time. Also,
After the self-supporting film is formed, the first coating layer is soft and easy to remove when polishing, and the self-supporting film is easily formed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to FIG. (Example 1) (Preparation of a substrate) As a material of a substrate, a material that can withstand a vapor phase synthesis method of a diamond film, such as a cemented carbide or a ceramic, can be used. In the present invention, a binderless (hardener-free) superhard base material containing WC as a main component is used, and a Co content of less than 1% by weight is used. The preparation method is as follows: WC powder and Co powder are mixed as raw material powders, these raw material powders are blended so as to have the above-mentioned composition after sintering, wet-mixed, dried, and then subjected to a discharge sintering process to obtain black smoke. Put the powder in the mold 60
Sintering was performed at a temperature of 1530 ° C. for 6 to 10 minutes while applying a pressure of 0 kgf / cm ² to produce the sintered body.

(Formation of Fine Irregularities-First Step) Fine irregularities are formed on the electric discharge machined surface of the substrate. In the present invention, a fine slit was formed. In such a case, the width is preferably about 50 μm, the depth is about 10 μm, and the interval is preferably about 200 μm using a laser. The type of the laser may be a known type, such as a YAG laser.

(Formation of Diamond First Coating Layer-Second Step) A free-standing diamond film was formed by a microwave plasma CVD method using the above-mentioned substrate by a gas phase synthesis method under the following conditions. Substrate temperature 700 ° C. Pressure 70 torr Microwave 1200 W The raw material gas is methane 10 vol%, hydrogen 90 vol
1% mixed gas was used. The growth rate of the diamond film was 2 μm / hr. Under the above conditions, a diamond film having a high methane concentration of 50 μm was formed.

(Diamond Second Coating Layer-Third Step) Next, the basic temperature was set to 910 ° C. and the raw material gas was 1 vol.
1% and 99 vol% of hydrogen. The growth rate of the diamond film was 2 μm / hr. Under the above conditions, a 300 μm diamond film was formed.

(Polishing of Deposited Surface—Fourth Step) The deposited surface side of the second diamond coated layer was polished with the diamond coating layer adhered to the substrate.

(Removal of Substrate—Fifth Step) Next, the substrate is removed. As a removing method, a mixed acid of hydrofluoric acid (HF) and nitric acid (HNO3) is used. Conventionally, when using a binderless cemented carbide substrate that does not contain Co, a peeling time of about 7 days is required. On the other hand, when Co is contained, peeling is performed in 2 to 3 days. Was done.

(Surface Polishing—Sixth Step) After removing the diamond first coating layer under the same conditions as those for polishing the deposition surface, the back surface of the diamond second coating layer is also polished. In addition, a comparison was made between when the back surface was polished and when it was not polished. The result is shown in FIG. As shown in FIG. 2, the one subjected to double-side polishing had excellent thermal conductivity.

(Measurement of Thermal Conductivity) The thermal conductivity was measured by the following method. Photo-current method thermal constant measuring device (PIT-
R2 type vacuum Riko Co., Ltd.) was used to measure the thermal diffusivity of a diamond free-standing film prepared using a cemented carbide substrate sample having a Co content of less than 1% by weight, and the thermal conductivity was determined. . Table 1 summarizes the results of Example 1 described above.

(Examples 2 to 13) As a material for the substrate, Co was used.
A sample was prepared under the same conditions as in Example 1 except that a cemented carbide substrate having a different content was prepared and used as a substrate, and the thermal conductivity was measured under the same conditions as in Example 1. Table 1 shows the results. In the method for producing a free-standing diamond film obtained by the method of the present invention, the thermal conductivity shows a value superior to that of the comparative example.

[0032]

[0033]

According to the present invention, the use of binderless carbide makes it possible to easily produce a free-standing diamond film having high thermal conductivity.

In the present invention, the use of a cemented carbide containing 1 to 5% by weight of Co as the base material shows a slight decrease in the thermal conductivity of the free-standing diamond film, but shows a high value for a heat sink. In addition, the separation time between the diamond coating layer and the substrate can be shortened, and the production efficiency can be improved.

By forming fine irregularities using a laser or the like, the adhesion between the substrate and the diamond coating layer is enhanced, and when the deposition surface of the second diamond coating layer is polished, the adhesion strength between the diamond coating layer and the substrate is increased. Because of its excellent properties, polishing becomes easy.

By forming a high-concentration methane film on the diamond first coating layer, it is possible to coat the fine irregularities in a short time, and when removing the first coating layer by polishing, the high-concentration methane film is formed. The presence of the film facilitates removal because such a film is soft.

[Brief description of the drawings]

FIG. 1 is a process chart showing a manufacturing method of the present invention.

FIG. 2 is a graph showing a change in thermal conductivity when the methane concentration is changed.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-81299 (JP, A) JP-A-7-215796 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C30B 29/04 C23C 16/27

Claims (4)

(57) [Claims] 1. A method for producing a diamond free-standing film by a vapor phase synthesis method, comprising: (a) a first method for forming fine irregularities on a substrate;
(B) a second step of forming a diamond first coating layer on the surface of the substrate having the fine irregularities by a gas phase synthesis method and coating the surface of the substrate with the coating layer; A third step of coating the surface of the first coating layer with a second diamond coating layer made of diamond having a crystal density higher than that of one layer; and (d) polishing a deposition surface side of the second coating layer. (E) a fifth step of removing the substrate, and (f) removing the coating first layer by polishing the side of the first layer that is in contact with the substrate surface, thereby removing the coating second layer.
A method for producing a free-standing diamond film, comprising a sixth step of flattening the back surface of the layer. 2. In the second step, 5 to 10 vol.
%, Hydrogen of 90 to 95 vol%, and methane of 0.1 to 3 vol% and hydrogen of 97 to 99.9 vol in the third step.
The method for producing a free-standing diamond film according to claim 1, wherein the diamond coating layer is formed by a gas phase synthesis method in which a mixed gas of 1% is reacted. 3. The method for producing a self-supporting diamond film according to claim 1, wherein in the fifth step, a binderless carbide having a Co content of less than 1% is used as the substrate. 4. The method for producing a free-standing diamond film according to claim 1, wherein in the fifth step, the substrate is a cemented carbide having a Co content of 1 to 5%. .