JPH0492894A - Vapor-phase synthesized diamond of high thermal conductivity - Google Patents

Abstract

PURPOSE:To obtain the title diamond by using either <12>C or <3>C in a reaction gas and by specifying the nitrogen concentration in said reaction gas. CONSTITUTION:Using as feedstock gas a methane gas with >=99.9% of the carbon atoms consisting of <12>C or <13>C and a nitrogen content of <=20ppm, a diamond thin film is synthesized through e.g. the microwave plasma CVD technique. This diamond thin film produced under such conditions will be >=99.9% in the purity of <12>C or <13>C and <= several ppm in nitrogen content. Because such a high-purity diamond film can be formed, the objective diamond with high thermal conductivity will be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a highly thermally conductive vapor-phase synthetic diamond used in a diamond heat sink that is effective in removing heat from high-power ICs, laser diodes, invat diodes, and the like.

[bl Conventional technology Diamond has the highest thermal conductivity of all materials at 22 W/cm-, and this property has already been used to stabilize the operation of high heat generating elements such as laser diodes and invat diodes. It has become an indispensable part. Diamond's high thermal conductivity is due to the phonon-based conduction mechanism, which has a high speed of transmission due to its strong crystal structure.

Until now, it was only possible to take advantage of these properties of diamond by creating single crystals using ultra-high pressure technology. In other words, sintered diamond requires the addition of a large amount of bonding material even with ultra-high pressure technology, making it impossible to achieve high thermal conductivity. As long as such a single crystal is used, its practical range is limited to an extremely narrow range due to size and cost limitations.

Problems to be Solved by the tc+ Invention Artificially synthesized diamonds can be manufactured to have a high thermal conductivity close to the above-described high thermal conductivity by controlling the nitrogen content to a certain amount or less. In order to further improve thermal conductivity, it is necessary to reduce the presence of atoms with different atomic weights present in the crystal lattice.

Natural carbon contains about 1% of 1sC, which is also known to cause phonon scattering as an impurity and cause a decrease in thermal conductivity.

Since the presence of other impurity atoms is also an important factor for the thermal conductivity of diamond, the content of these atoms must also be minimized.

Diamond vapor phase synthesis technology is attracting attention as a technology that will fundamentally change the way diamonds are used. While conventional ultra-high pressure technology could only produce diamond in the form of particles, vapor phase synthesis technology can produce diamond in the form of a film.

Further, it can be formed in a large area or in a shape other than a plane. The properties of vapor-phase synthetic diamonds that have been reported so far are as follows:
It is said to be the same as Type A diamond, which is a very pure diamond. However, the thermal conductivity is 16W.
/Cm- is reported to be below. This is caused by the fact that approximately 1% of lsC is usually mixed in, and that phases other than diamond are mixed in. Regarding the latter, it is possible to evaluate the presence of even trace amounts of graphite phase by Raman spectroscopy.

(Means for solving the problem) When producing diamond using vapor phase synthesis technology, the carbon in the reaction gas is either 12C or IsC. The purity must be 99.9% or higher.

In addition, it is necessary to limit the incorporation of nitrogen atoms as an element that can enter the lattice, or to limit the presence of foreign phases in order to obtain significantly higher thermal conductivity than conventional diamond, the nitrogen concentration in the reaction gas must be I came to think of limiting the The inventors confirmed this limit through experiments and found that the nitrogen content was 20 ppm or less.

It is preferable that the synthesized diamond has no graphite phase, but as shown in the existing application (Japanese Patent Application No. 1-51486), the graphite/diamond peak ratio is 0.0.
If it is 5 or less, high thermal conductivity can be obtained.

(e1 effect) The diamond film produced under the above conditions has l1IC
The purity of SSC is 99.9% or more, and the N content is several ppm or less. Since a diamond film of high purity can be formed in this way, diamond with high thermal conductivity can be obtained.

1IC and 110 are 12 from the viewpoint of phonon energy.
0 is considered preferable, but in both cases it was found to have significantly higher thermal conductivity than conventional pure diamond (type IIa).

The high thermal conductivity vapor-phase synthetic diamond described above has a thermal conductivity of 25 W/Cm- or more, and is suitable for high-output ICs,
It was found to be extremely effective in removing heat from laser diodes, invat diodes, etc.

(f) Examples Example 1 Using methane gas consisting of 99.95% "C" as a raw material,
A diamond film was formed using known microwave plasma CVD. At this time, the purity of methane and hydrogen is 9.
999% and 99.99999%. When the amount of nitrogen contained in the reaction gas was precisely measured by gas chromatography, the nitrogen content was 8 ppm.

A diamond film with a thickness of about 500 μm was produced by synthesis for 500 hours using a silicon wafer scratched with diamond abrasive as a substrate with a methane:hydrogen ratio of 1:100. After removing the substrate with acid, it was polished to a thickness of 300 μm.

The thermal conductivity of this film was measured and found to be 30 W/cm.

Example 2 A diamond film was produced in the same manner as in Example 1 using methane gas containing 120 as shown in Table 1. Table 1 shows the thermal conductivity of this film.

! Content rate (%) of 20 Thermal conductivity (W/cm4) 99
．． 5 16 99.8 18 99.9 25 99.92 29 99.95 30 99, 99 335Example 3 In the same manner as in Example 1, nitrogen as shown in Table 2 was extracted from methane gas containing 99.95% "C" carbon. A diamond film was prepared using a raw material gas containing a certain amount.The thermal conductivity of the obtained diamond is shown in Table 2.

Nitrogen content (s+pm) Thermal conductivity (W/cm-K
) Example 4 A diamond film was formed from methane gas containing 99.92% IBC by a known hot filament CVD method. In this case, the filament is made of tungsten.
Using 2 mmΦ, the filament temperature was 2080°C and the substrate temperature was maintained at 950°C. The nitrogen content in the reaction gas was 10 ppm. 6 at methane concentration 1.2%
A film of 450 μm was produced by synthesis for 00 hours, and after removing the substrate, the film was polished to a thickness of 300 μm. The thermal conductivity of this film was 25 W/Cm-.

(G1 Diamond with strictly limited impurity inclusion as described above can be produced using the vapor phase synthesis method. Plasma C
This can be done using known techniques such as VD, hot filament CVD, plasma jet method, and flame method. However, in the plug, fuget, and flame methods, synthesis in air is not appropriate because the nitrogen content cannot be controlled.

There is no problem with the raw material gas used in these gas phase synthesis techniques as long as it satisfies the scope of the claims, and carbon-containing gases such as methane, ethane, acetylene, alcohol, ketone, benzene, Co, and CCl2 have no effect as raw materials. There is no difference.

Furthermore, it is also effective to utilize the effects of the present invention to add general oxygen, water, or the like to the reaction gas as a means of forming a high-purity diamond film.

The following three methods can be considered to utilize such high thermal conductivity.

■Form polycrystalline diamond and remove it from the substrate for use.■Form and use polycrystalline diamond film on highly heat dissipating metals or ceramics.

■It is used by forming it on top of conventional single crystal diamond.

Claims (1)

[Claims] (1) When forming a diamond film using vapor phase synthesis technology, the reaction gas is carbon isotope ^1^2C or^1^8C, in which 99.9% or more of the carbon is carbon, and the nitrogen content is A highly thermally conductive vapor-phase synthetic diamond characterized by having a content of 20 ppm or less.