JP2913796B2 - Vapor phase synthetic diamond - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a diamond having high thermal conductivity manufactured by a gas phase synthesis method.

[Conventional technology]

Diamond is the substance with the highest thermal conductivity among known substances, and high power is used for applications that take advantage of this property.
There are high performance heat sinks such as ICs and laser diodes.

Such diamond synthesis methods are roughly classified into an ultra-high pressure catalyst method and a gas phase synthesis method. The ultra-high pressure catalytic method is a method in which a carbon source and a metal solvent such as iron coexist to synthesize diamond under the conditions of ultra-high pressure and high temperature. There is a limit as a heat sink material that requires a size of a centimeter square. In addition, since the impurity element is inevitably mixed from the metal solvent and the like, the thermal conductivity is also limited, and about 22 W / cm · K, which is about the same as that of IIa type natural diamond, and more are obtained. Absent.

On the other hand, the vapor phase synthesis method (CVD method) is a method in which a raw material gas containing a carbon source and hydrogen is decomposed and activated, and diamond is deposited on a substrate in the form of a film or a plate. There is an advantage that the size can be increased as described above, and therefore the manufacturing cost is low. The gas phase synthesis method involves the decomposition and
Many methods are known due to the difference in activation means. Among them, the hot filament CVD method using a hot filament heated at a high temperature, and the plasma CVD method using microwave plasma or DC thermal plasma are typical methods. is there.

However, the thermal conductivity of diamonds produced by the conventional gas phase synthesis method is 16 W / cm · K or less, which is lower than that of natural diamond or diamond produced by the ultrahigh pressure catalytic method.

[Problems to be solved by the invention]

In view of such conventional circumstances, the present invention has a size and high thermal conductivity required for a heat sink material, preferably 25 W / cm.
The object is to provide a vapor-phase synthetic diamond having K or more.

[Means for solving the problem]

In order to achieve the above object, in the vapor-phase synthetic diamond of the present invention, 99.9% or more of the constituent carbon atoms are either 12 atomic weight carbon or 13 atomic weight carbon, and the diamond The peak intensity ratio of the non-diamond component with respect to is not more than 0.07, and the nitrogen atom content is not more than 5 ppm.

[Action]

Although heat conduction is explained by the propagation of phonons of lattice vibration, the presence of atoms having different atomic weights in the crystal causes scattering of phonons, leading to a decrease in thermal conductivity. According to the composition analysis of the vapor-phase synthetic diamond, nitrogen is mainly contained in the source gas as impurities.
Moreover, the carbon contained in the carbon source in the feed gas, since usually the carbon atom content 13 in addition to carbon atomic weight ^{12 (12 C) (13 C} ) is contained about 1.1% isotopically normal methane When is used as a carbon source, ¹³ C is taken into the diamond as it is, which is also one of the causes for lowering the thermal conductivity.

Therefore, in the present invention, as a result of examining the relationship with the thermal conductivity by changing the ratio of carbon isotopes and the content of nitrogen in diamond, the carbon constituting diamond is
^{It has been found that when} either ¹² C or ¹³ C is 99.9% or more and the nitrogen atom content is 5 ppm or less, diamond having a high thermal conductivity of 25 W / cm · K or more can be obtained.

The carbon source containing 99.9% or more of either ¹² C or ¹³ C is usually methane, ethane, acetylene, alcohol,
It is obtained by mass separation of carbon sources such as ketones and carbon monoxide.

The thermal conductivity of the vapor-phase synthetic diamond is also affected by non-diamond components such as graphite and amorphous carbon contained in the diamond. In order to improve the crystallinity of diamond and reduce non-diamond components, methods such as adding a small amount of oxygen or water to the raw material gas and selecting synthesis conditions such as substrate temperature should be effective. Is known.

In the present invention, the relationship between the content of the non-diamond component and the thermal conductivity in diamond is examined, and when the content of the non-diamond component is evaluated by Raman spectroscopy, the intensity ratio of the peak of the non-diamond component to diamond is determined. It has been found that if is less than 0.07, the thermal conductivity of diamond can be increased.

As a method for producing the diamond having high thermal conductivity of the present invention, a known gas-phase synthesis method can be used as long as a carbon source is selected and the contamination of nitrogen is limited, but a plasma jet method using a DC thermal plasma torch can be used. A method of synthesizing in the air, such as a burner method using an oxygen-acetylene flame or the like, is not suitable because it is difficult to control the amount of nitrogen.

〔Example〕

Example 1 By a known microwave plasma CVD method, carbon was 99.95.
% Of methane and hydrogen of ¹² C as source gas, diamond was deposited on a silicon wafer substrate (20 mm square) whose surface was damaged by # 5000 diamond abrasive grains. The content of nitrogen atoms in the raw material gas was 20 ppm as measured by gas chromatography. The ratio of methane to hydrogen in the source gas was 1: 100, and the pressure in the reaction chamber was 400 torr.
r, 50 at microwave power 400W and substrate temperature 950 ℃
Film formation was performed for 0 hour to obtain a diamond film having a thickness of about 500 μm on the entire surface of the substrate. After the film formation, the base material was dissolved with hydrofluoric acid to recover a diamond thin plate, and both surfaces were polished to a thickness of 300 μm.

When the composition of the obtained diamond was analyzed by a pyrolysis gas chromatograph-mass spectroscopy coupled analyzer, the content of ¹² C was 99.95% and the content of nitrogen atoms was 5 p.
pm. As a result of Raman spectroscopy, the peak intensity ratio of the non-diamond component to diamond was 0.03. The thermal conductivity of the diamond was 30 W / cm · K as measured by a method in which a temperature gradient under a steady heat flux was measured and compared with a known material.

Example 2 A diamond was synthesized in the same manner as in Example 1 except that the ratio of methane to hydrogen and the substrate temperature were variously changed.

When the obtained diamond was evaluated in the same manner as in Example 1, the content of ¹² C and nitrogen was the same as in Example 1, but the thermal conductivity and the ratio of non-diamond component / diamond peak intensity in Raman spectroscopy were measured. Table 1 shows the relationship.

Example 3 A diamond was synthesized in the same manner as in Example 1 except that the ¹² C content of carbon in methane was variously changed.

When the obtained diamond was evaluated in the same manner as in Example 1, the content of nitrogen and the peak intensity ratio of the non-diamond component / diamond in the Raman spectrum were the same as in Example 1. The content of ¹² C in diamond was the same as the content of ¹² C in carbon used in methane. Table 2 shows the relationship between the content of ¹² C in the diamond and the thermal conductivity of the diamond.

Example 4 A diamond was synthesized in the same manner as in Example 1 except that the content of ¹² C in carbon in methane was 99.9% and the nitrogen content in the raw material gas was changed as shown in Table 3 below.

When the obtained diamond was evaluated in the same manner as in Example 1, the content of ¹² C in the diamond was 99.9%, and the peak intensity ratio of the non-diamond component / diamond in the Raman spectrum was the same as that in Example 1. . Table 3 shows the relationship between the nitrogen atom content in the source gas and diamond and the thermal conductivity of diamond.

Example 5 By a known thermal filament CVD method, carbon was 99.92%.
Example 1 Using methane composed of ¹³ C and hydrogen as raw material gases
Diamond was deposited on a silicon wafer substrate (dimensions of 4 inch square) treated in the same manner as in Example 1. The content of nitrogen atoms in the raw material gas was measured by gas chromatography.
It was 50 ppm. The ratio of methane and hydrogen in the source gas is 1.
2: 100, the pressure in the reaction chamber was 40 torr, the temperature of a W filament having a diameter of 0.2 mm was 2080 ° C, and the temperature was 600
A diamond film having a thickness of about 450 μm was obtained over the entire surface of the substrate. After the film formation, the collected diamond was polished to a thickness of 300 μm.

When the obtained diamond was evaluated in the same manner as in Example 1, the content of ¹³ C in the diamond was 99.92% and the content of nitrogen atoms was 3 ppm. The peak intensity ratio of the non-diamond component / diamond in the Raman spectrum is
It was 0.03. The thermal conductivity of this diamond is 25W / cm
It was K.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, the vapor phase synthetic | combination diamond provided with the magnitude | size required as a heat sink material and a high thermal conductivity can be provided.

When using the vapor-phase synthetic diamond of the present invention as a heat sink, use it after removing the base material, use it by forming it on a metal or ceramics having high heat dissipation, or use it by forming it on a diamond single crystal. Can be considered.
In particular, high heat radiation can be realized with a thickness smaller than that of the conventional diamond, and in other cases, the thickness of the diamond can be saved more than before. Also, in any case from
By adjusting the thickness of the diamond, it is possible to secure the required heat dissipation.

Claims (1)

(57) [Claims] Claims 1. A diamond produced by a gas phase synthesis method from a source gas containing a carbon source and hydrogen, wherein 99.9% or more of carbon as a constituent element is either carbon having an atomic weight of 12 or carbon having an atomic weight of 13. The intensity ratio of the peak of the non-diamond component to diamond in the Raman spectrum is 0.07 or less, and the nitrogen atom content is 5 p.
Gas phase synthetic diamond characterized by being less than pm.