JPH0477710B2 - - Google Patents

Description

[Detailed description of the invention]

[Summary] The present invention relates to a method for vapor phase synthesis of diamond, and an object of the present invention is to provide a method for vapor phase synthesis of diamond with a high film formation rate. A gas containing a carbon compound is supplied, and this gas is radicalized by direct current arc discharge between the electrodes to form a thermal plasma, which is ejected as a thermal plasma jet into a vacuum chamber, and this thermal plasma jet is then cooled. The structure is such that it collides with a substrate and is rapidly cooled to grow a diamond film on the substrate in a vapor phase. [Industrial Application Field] The present invention relates to a method for vapor phase synthesis of diamond. Diamond has a thermal conductivity of 2000 W/mK, which is four times that of copper, and it also has excellent hardness and insulation properties, making it an ideal material for heat sinks for semiconductor devices and circuit boards. It is. It also has excellent translucency over a wide wavelength range, making it an excellent optical material. Furthermore, diamond has a wide band gap of 5.45eV and is a semiconductor with high carrier mobility.
It is also attracting attention as a high-performance device such as high-temperature transistors and high-speed transistors. [Conventional technology] Conventionally, the thermal filament method (S.Matsumoto et al.
al., Japan.J.Appl.Phys.21 (1981) L183), microwave plasma CVD method (M.Kamo et al., J.
Gryst.Growth.62 (1983) 642), electron beam irradiation CVD
(A. Sawabe et al., Appl. Phys. Lett. 46 (1985)
There are chemical vapor deposition (CVD) methods such as 146). However, these manufacturing methods have a diamond deposition rate of several μm/h or less, and although they use inexpensive equipment and raw materials, they have poor productivity, resulting in high costs, and their practical application has been delayed. In addition, Kamo et al.'s high-frequency thermal plasma CVD method (Japan Society of Applied Physics Spring Conference
(March 1987) has a high film formation rate of 1 μm/min, but when the film thickness exceeds 30 μm, the surface becomes graphite, making it impossible to form a thick film. Thermal plasma generated by high frequency waves is
Due to the low flow rate, the substrate must be placed in contact with the thermal plasma. Therefore, the temperature of the substrate surface tends to increase, making it impossible to form a thick film. [Problems to be Solved by the Invention] An object of the present invention is to provide a vapor phase synthesis method that produces diamond having a sufficient film thickness and good film quality at a high film formation rate. [Means for solving the problem] The above problem is solved by using a nozzle that spouts gas containing hydrogen and gaseous carbon compounds as an anode, and a cathode located inside the nozzle close to the opening. A direct current arc discharge is used to radicalize this gas to form a thermal plasma, which is ejected as a thermal plasma jet into a vacuum chamber, collides with a cooled substrate, and quenches it, thereby growing a diamond film on the substrate in a vapor phase. ``Method for vapor phase synthesis of diamonds'' and ``A direct current arc discharge is generated between a nozzle that spouts hydrogen-containing gas as an anode and a cathode located inside the nozzle close to the opening.
This gas is converted into radicals and turned into thermal plasma, which is ejected into the vacuum chamber as a thermal plasma jet.
Diamond vapor phase synthesis is characterized by supplying a gas containing a carbon compound to this thermal plasma jet to radicalize it, colliding with a cooled substrate to rapidly cool it, and growing a diamond film on the substrate in vapor phase. This can be solved by a method. [Operation] Diamond synthesis by the CVD method involves decomposing and activating a gas mixture of carbon compounds such as methane, acetylene, alcohol, acetone, etc. and hydrogen, at a temperature suitable for the vapor phase growth of diamonds, i.e. 400~400°C. This method grows diamond on a substrate at 1500℃. In the synthesis of diamond, active species such as hydrogen atoms and methyl groups in the gas phase are said to play an important role.In order to increase the growth rate of diamond, it is necessary to increase the density of these active species. All you have to do is create a high-temperature plasma and supply it to the substrate surface. Plasma with a high degree of dissociation of gas molecules and extremely high activity includes ions, electrons,
A thermal plasma is known in which the temperature of each chemical species, such as neutral particles, is approximately equal and the temperature is over 5000K.
Figure 3 shows the temperature change of the equilibrium constant K = (P _H ) ² /P _H2 for the dissociation reaction H ₂ 2H of hydrogen molecules.At 5000K, almost all hydrogen molecules become hydrogen atoms. It can be seen that it is dissociated. However, if thermal plasma at this temperature is directly brought into contact with a substrate, it is difficult to synthesize diamond unless the temperature of the substrate is appropriately controlled depending on the intensity of the thermal plasma. FIG. 1 is an explanatory diagram of diamond synthesis by direct current arc discharge thermal plasma jet CVD method according to the present invention. While flowing a gas containing hydrogen 3 and carbon compound gas 4, a DC voltage is applied between an anode 1, which is a nozzle that spouts the gas, and a cathode 2, which is located inside the nozzle and close to the opening, When the arc 5 is discharged, this gas is rapidly heated between the narrow electrodes and becomes a thermal plasma of 10,000° C. or more near the nozzle 6.
At this time, the volume expands due to the rapid temperature rise,
The thermal plasma becomes a supersonic plasma jet 7 and is ejected from a nozzle 6 into a chamber 8 under reduced pressure. By colliding this plasma jet 7 with the efficiently cooled substrate 10 and rapidly cooling the plasma jet, active species such as short-lived hydrogen atoms react on the substrate before they disappear, forming diamonds. Synthesize membrane 1. Furthermore, the reaction on the substrate is affected by photoexcitation due to strong ultraviolet light generated during arc discharge and kinetic energy due to collisions of supersonic particles. In this way, the present invention allows a chemical reaction to occur with extremely high efficiency compared to the conventional method in which arc discharge is performed between the anode 1 and the cathode located outside the nozzle, so diamond can be synthesized at a high growth rate. I can do it. In the present invention, the raw material gas may be any carbon compound, but
Hydrocarbons, or hydrocarbons or halogenated carbons containing oxygen, nitrogen or halogen in the molecule are preferred. The stability of arc discharge can be improved by mixing an inert gas such as argon or helium in addition to the hydrogen of the discharge gas and the carbon compound of the source gas. In this case, although the film formation rate decreases, there is an advantage that the uniformity of the surface of the film increases. Furthermore, the effect of etching and removing non-diamond carbon can be enhanced by mixing a small amount of oxidizing gas such as oxygen, water, hydrogen peroxide, or carbon monoxide. The raw material gas 4 may be supplied between the electrodes together with the hydrogen of the discharge gas 3, or may be supplied into a thermal plasma jet 7 ejected from between the electrodes, as shown in FIG. However, in this case, it is necessary to uniformly supply the source gas into the thermal plasma jet. As the discharge gas, as shown in Fig. 3, hydrogen is used, which has a high ionization potential and is difficult to discharge, and the nozzle itself is the anode 1.
Since the cathode 2 is located inside the nozzle and close to the opening, the ejected thermal plasma becomes a high temperature jet. Therefore, the electrode material should preferably have high heat resistance. Tungsten to which rare earth element oxides such as lanthanum oxide, yttrium oxide, and cerium oxide are added is excellent as an electrode material. Furthermore, if contamination with impurities from the electrode is to be avoided, it is preferable to use a high-purity carbon electrode. Substrates subjected to intense thermal plasma jets require cooling to the appropriate temperature, as opposed to heating in conventional methods. [Example] Example 1 Both the anode 1 constituting the nozzle and the cathode 2 located inside the nozzle and close to the opening contain 2% by weight.
The plasma torch is made of tungsten doped with yttrium oxide and has a water-cooled structure, and is fixed to a manubrator (not shown) within the chamber 8, so that the direction of the nozzle 6 can be changed. The water-cooled substrate holder 9 can be moved up and down to change the distance between the nozzle and the substrate. A 5 mm square, 0.2 mm thick silicon wafer 10 is fixed to the substrate holder 9, and the inside of the chamber 8 is 2×
After exhausting to 10 ^-3 Torr, as shown in Fig. 1, H ₂ is discharged as discharge gas 3 at a pressure of 1 Kg/cm ² at a pressure of 20/cm 2.
min, CH ₄ as raw material gas 4 at a pressure of 1Kg/cm ²
It was flowed between the poles at a flow rate of 40 c.c./min, and the pressure inside the chamber 8 was maintained at 100 Torr. A current of 10 A was applied between the electrodes using a constant current arc power source, and was maintained for approximately 5 minutes until the voltage became constant. The voltage at this time is 72V
It was hot. The water-cooled substrate holder 9 was slowly moved closer to the nozzle 6, and the distance between the nozzle and the substrate was fixed at 5 mm, and diamond synthesis was carried out for one hour in this state. The synthesized diamond was then evaluated using scanning electron micrographs (SEM), X-ray diffraction, Raman spectroscopy, and hardness measurements. As shown in the SEM image of FIG. 4, it can be seen that regularly arranged diamond crystals are gathered on the surface of the diamond film. Also, in Figure 5
In the SEM, the center part shows a cross section of the diamond film, the bottom part shows a cross section of the silicon substrate, and the top part shows the surface of the diamond film. It can be seen that the surface of the diamond film is uniform and has few irregularities. Figure 6 shows the X-ray diffraction pattern of the diamond film, showing the diamond crystal planes 111, 220, 31.
1 appears very clearly, 331 and 4
00 is also accepted. FIG. 7 shows the Raman spectrum of the diamond film, and it can be seen that a peak unique to diamond is observed at a wave number of 1333 cm ^-1 , and that other carbonaceous and graphite peaks do not appear. In addition, for the Bitkers hardness Hv ₅₀₀ , the hardness of the sample was high and it was difficult to judge the indentation, but the hardness was 8000Kg/cm ²
That's all. From the above data, it can be seen that the synthesized diamond is a polycrystalline film of good quality. In addition, the film thickness was 80 μm, and a high-quality diamond film could be synthesized at a speed of 80 μm/h, more than 10 times faster than conventional methods. Furthermore, when synthesis was carried out for 10 hours under these conditions, the film thickness was approximately 1 mm at the center of the substrate, and even at the periphery.
It became 0.6mm. Furthermore, even when measured by X-ray and Raman spectroscopy, only diamond peaks were obtained, and the presence of graphite was not observed. Example 2 A Mo plate with a size of 10 x 10 x 0.2 mm was used as the substrate, and H ₂ gas was used as the discharge gas 3, as shown in Figure 2.
20/min, Ar gas 20/min, containing 2% acetone as raw material gas 4 to the plasma jet
Ar gas is supplied at 2/min, arc current is 20A, voltage is 60V, and the distance between nozzle and substrate is fixed at 10mm.
Synthesized time diamond. The film thickness was 60 μm, and the film quality was comparable to that of Example 1. Examples 3 to 8 The following table summarizes the diamond film formation speed when the reaction conditions are changed, such as by changing the gas supplied between the electrodes or by supplying gas into the thermal plasma jet generated between the electrodes. Change. The film quality of the diamond film obtained in each Example was comparable to that in Example 1.

【table】

〔Effect of the invention〕

According to the thermal plasma jet CVD method according to the present invention, an extremely high rate of 80 μm/h is achieved compared to conventional methods.
It was possible to grow high-quality diamonds at such a speed, and a major step forward was made toward the practical application of inexpensive diamonds by vapor phase synthesis. If diamonds synthesized using this method are used in semiconductor heat sinks and circuit boards,
Significant cost reductions and performance improvements are expected.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of one embodiment of the thermal plasma vapor phase synthesis method, FIG. 2 is an explanatory diagram of another embodiment of the thermal plasma vapor phase synthesis method, and FIG. 3 is an explanatory diagram of the dissociation reaction of hydrogen molecules. FIG. 4 is a photograph showing the crystal structure on the surface of the diamond film, FIG. 5 is a photograph showing the crystal structure in the cross section of the diamond film, and FIG. is a graph showing the X-ray diffraction results of the diamond film, and FIG. 7 is a graph showing the Raman spectrum of the diamond film. DESCRIPTION OF SYMBOLS 1... Anode, 2... Cathode, 3... Discharge gas, 4... Source gas, 5... Arc, 6... Nozzle, 7... Plasma jet, 8... Chamber, 9... Substrate holder, 10...
Substrate, 11...diamond film.

Claims (1)

[Claims] 1. A nozzle that spouts gas containing hydrogen and a gaseous carbon compound is used as an anode, and a direct current arc is discharged between the cathode located inside the nozzle and close to the opening, and this gas is It is converted into radicals and becomes a thermal plasma, which is ejected as a thermal plasma jet into a vacuum chamber, collides with a cooled substrate, and is rapidly cooled.
A diamond vapor phase synthesis method characterized by vapor phase growth of a diamond film on a substrate. 2. The method according to claim 1, wherein the gaseous carbon compound is a hydrocarbon or a hydrocarbon containing oxygen, nitrogen, or halogen in the molecule. 3 A gas containing hydrogen or a gaseous carbon compound is
The method according to claim 1, further comprising an inert gas and/or an oxidizing gas. 4. The method according to claim 1 or 2, wherein an inert gas and/or an oxidizing gas is supplied to the thermal plasma jet ejected from the anode nozzle. 5. The method according to claim 3 or 4, wherein the inert gas is argon or helium. 6. The method according to claim 3 or 4, wherein the oxidizing gas is oxygen, water, hydrogen peroxide or carbon monoxide. 7. The method according to any one of claims 1 to 6, wherein DC arc discharge is performed using a carbon electrode or a tungsten electrode containing a rare earth element oxide as an electrode. 8 A nozzle that spouts gas containing hydrogen is used as an anode, and a direct current arc is discharged between the cathode located inside the nozzle and close to the opening, and this gas is turned into radicals and turned into thermal plasma, which is then injected into the vacuum chamber. It is characterized by ejecting as a thermal plasma jet, supplying gas containing carbon compounds to this thermal plasma jet, turning it into radicals, colliding with a cooled substrate to rapidly cool it, and growing a diamond film on the substrate in a vapor phase. A method for vapor phase synthesis of diamond. 9. The method according to claim 8, wherein the gaseous carbon compound is a hydrocarbon or a hydrocarbon containing oxygen, nitrogen, or halogen in the molecule. 10. The method according to claim 8, wherein the gas containing hydrogen or a gaseous carbon compound further contains an inert gas and/or an oxidizing gas. 11. The method according to claim 8 or 9, wherein an inert gas and/or an oxidizing gas is supplied to the thermal plasma jet ejected from the anode nozzle. 12. The method according to claim 10 or 11, wherein the inert gas is argon or helium. 13. The method according to claim 10 or 11, wherein the oxidizing gas is oxygen, water, hydrogen peroxide, or carbon monoxide. 14. The method according to any one of claims 8 to 13, wherein DC arc discharge is performed using a carbon electrode or a tungsten electrode containing a rare earth element oxide as an electrode.