JPH0512311B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an improved method for synthesizing diamond by plasma CVD.

(Conventional technology and problems to be solved) A method for synthesizing diamond in a thermodynamically metastable region uses plasma generated by electrical discharge.
The CVD method is now a well-known method.

There are two methods for this: one uses low-temperature plasma due to glow discharge, and the other uses high-temperature or thermal plasma due to stronger discharge.

However, in the former method, the growth rate of diamond is usually slow at 0.1 to several μm/hr, while in the latter method, the growth rate is more than 100 times faster than the former, but the gas temperature is usually high, at 2000 to 3000 K or more. Therefore, in order to grow diamond, it was necessary to cool the gas or substrate temperature by some method.

The present inventors have proposed two methods for this cooling: (1) cooling of the gas phase, substrate, or substrate holder using gas or refrigerant (Japanese Patent Application Laid-open No. 158195/1983), (2) rapid cooling method using adiabatic expansion of gas (Special (Gan No. 61-252391) was developed.

However, in method (1), spatially uniform cooling and its control are difficult, while in method (2), a large capacity exhaust system is required and the growth rate is also slightly reduced. It was hot.

The present invention solves the above-mentioned drawbacks of the prior art, and provides a method that can effectively cool the gas or substrate temperature when synthesizing diamond by plasma CVD, and can synthesize diamond without reducing the growth rate. The purpose is to provide

(Means for Solving the Problems) As a result of intensive research into measures that can eliminate the above-mentioned drawbacks in diamond synthesis using plasma CVD, the present inventors found that by using amplitude-modulated electric power for discharge, gas temperature and The present invention was completed by discovering that diamond synthesis can be performed at a high growth rate while preventing an excessive rise in substrate temperature.

That is, the gist of the present invention is a method for synthesizing diamond by plasma CVD, which is characterized in that the plasma is generated by amplitude-modulated electric power.

The present invention will be explained in detail below.

(Operation) As described above, the present invention, in short, generates plasma by applying amplitude-modulated electric power to a single gas or a mixture of gases selected from hydrocarbon gas, hydrogen gas, oxygen gas, and inert gas. is generated, and diamond is precipitated from the gas obtained by decomposing, evaporating, and dissociating organic compounds, carbon oxides, or carbon materials in the plasma.

Therefore, conditions other than using amplitude-modulated power are not particularly limited.

Those conditions will be explained below.

The discharge used in the present invention may be a glow discharge, an arc discharge, or a discharge in the glow-arc transition region. The power source used for the discharge may be direct current, low-frequency alternating current, high frequency, or microwave, or may be a combination of these, and either an electroded or electrodeless discharge method may be used.

The frequency of these power modulations depends on the original frequency (carrier frequency), the frequency characteristics of the transmission system/discharge applicator, etc., but a range of about 10 Hz to (original frequency) x 1/20 is used. for example,
For a high frequency of 13.56MHz, it is 10Hz to 500kHz.
However, if burst oscillation or the like is used, the wave number of the modulated wave can be controlled in units of wave numbers, and if modulated by an arbitrary waveform oscillator, the modulation frequency can be varied during oscillation. Direct current power can be modulated in the same way, and approximately 10Hz to 500kHz can be used.

The modulation waveform may be of any shape, such as a sine wave, a triangular wave, or a rectangular wave, but a rectangular wave is most effective. It is also possible to apply a bias to these waveforms so that, for example, a certain amount of output can be produced when square wave modulation is turned off. In pulse modulation, the duty can be changed.

Applying these modulated powers to the discharge, i.e. strong power and weak power or power O
By repeatedly applying these steps, it is possible to obtain a faster growth rate with less average power without excessively increasing the gas temperature and substrate temperature.

The reason for this effect is not clear, but
It is presumed that this is because even if the average power is low, a strong electric field is instantaneously applied, which effectively ionizes and dissociates the gas, but because the average power is low, the rise in gas temperature is reduced.

The discharge power varies depending on these modulation waveforms, the size of other reactors or electrodes in the duty unit, gas flow rate, gas pressure, etc., but it can be used when the temperature of the substrate or the gas phase temperature of the growth space is in the range of 350 to 1400°C. chosen to be.

Any carbon source may be used as long as it decomposes in plasma to generate ion species and radical species. For example, saturated or unsaturated aliphatic or aromatic hydrocarbons such as methane, ethane, propane, ethylene, benzene, and cyclohexane; organic compounds containing oxygen such as alcohols, acetone, and aldehydes; organic compounds containing nitrogen such as amines and amides; , organic compounds containing halogens such as methyl chloride and chloroform, organic compounds containing sulfur such as thiophene, organic compounds containing phosphorus such as phosphine, polymeric compounds such as polyethylene, carbon monoxide, carbon dioxide, etc. Furthermore, solid graphite material can also be used by being introduced into the plasma.

The plasma gas pressure can be used in a range of 10 ^-4 to 5×10 ² atm. If the pressure is too low, the rate of diamond precipitation will be slow, and if the pressure is too high, handling of the container will be troublesome and the equipment will be expensive, so the pressure is preferably 10 ^-3 to 10 atm.

As the substrate, any of metals such as molybdenum and stainless steel, semiconductors such as silicon, ceramics such as alumina, or single crystal diamond can be used. The substrate temperature can be raised to the above 350 to 1400℃ using only plasma heating, but
If necessary, the temperature can be adjusted by heating with a heater or cooling with a refrigerant.

Next, an example of an apparatus used to carry out the present invention will be explained with reference to the drawings.

Figure 1 shows a reaction apparatus using a DC plasma jet, where 1 is a DC plasma torch, 2 is a DC power source, 3 is a substrate, 3' is a substrate holder, 4 is a reaction chamber, and 5 is an exhaust device. , 6 is a gas supply device, and 7 and 7' are gas flow rate adjustment valves. The operating procedure is as follows: First, the reaction chamber 4 is evacuated using the exhaust device 5, and then plasma generating gas is supplied through the gas flow rate adjustment valve 7. After setting the pressure to a predetermined value, pulsed power is supplied from the DC power source 2 between the electrodes of the plasma torch 1 to generate plasma. Subsequently, diamond is deposited on the substrate by supplying a carbon source into the plasma from the valve 7'.

Figure 2 shows a reaction device for parallel plate DC discharge or high frequency discharge, where 8 is a DC or high frequency power supply, 9 and 9' are flat plate electrodes, and other members are the same as in Figure 1. . The operating procedure is to first evacuate the reaction chamber 4 using the exhaust device 5, then flow the diluent gas and reaction gas through the gas flow rate adjustment valve 7, apply direct current or high frequency between the electrodes 9 and 9', and generate plasma. Then, diamond is deposited on the substrate placed on the electrode 9'.

Figure 3 shows the reaction apparatus for work coil type high frequency discharge, where 4' is a quartz reaction chamber, 7,
7', 7'' are gas flow rate adjustment valves, 10 is a high frequency power source, 11 is a work coil, and other members are the same as those shown in FIG. After evacuating the
Sheath gas is flowed through valve 7'' and plasma gas is flowed through valve 7', high frequency power is supplied to work coil 11 to generate plasma, and carrier and raw material gas are flowed through valve 7 to deposit diamond on the substrate. Reaction. When the chamber pressure is low, a mixed gas of dilution gas and reaction gas may be flowed through valve 7 or 7'.

Figure 4 shows an outline of a device using microwave discharge, in which 12 is a microwave power source, 13 is a waveguide, 1 is a plunger, and other members are the first
~Same as Figure 3. The operation procedure is as follows: First, the reaction chamber 4' is evacuated, the sheath gas is supplied from the valve 7', the dilution gas and the reaction gas are supplied from the valve 7, and then microwaves are supplied from the power supply 12 through the waveguide 13, and the plunger 14 By adjusting the temperature, plasma is generated in the reaction chamber and diamond is deposited. When the reaction chamber pressure is low, it is not necessary to flow the sheath gas through the valve 7'.

(Example) Next, examples of the present invention will be shown.

Example 1 Using the apparatus shown in Figure 1, a reaction chamber was prepared.
After exhausting to 0.1 Torr or less, argon was flowed at 20/min and hydrogen was flowed at 10/min from valve 7, and methane was flowed at 0.75/min from valve 7' as a carbon source.
Discharge was performed for 10 minutes at 200 Torr with a power output of 12 KW, a repetition frequency of 100 Hz, and a duty of 30%.
However, the output during peak off was 2KW. As a result, a diamond film with a thickness of 40 μm at the center was obtained on a molybdenum substrate. On the other hand, the output without modulation
At 5KW, discharge could not be maintained with the same gas flow rate.

Example 2 Hydrogen 0.96/
min and while flowing methane 0.04/min, the pressure
A diamond film with a thickness of 15 μm was obtained on the molybdenum substrate placed on the anode by performing direct current discharge of 6 KW at peak, 20% duty, and 500 pps between the electrodes at 200 Torr for 1 hour. The precipitation rate is
It is 15μm/hr. On the other hand, with continuous DC discharge of 1.2 KW, the deposition rate was 9 μm/hr.

Example 3 Using the apparatus shown in Figure 2, 195 ml of hydrogen/
By using a high frequency of 13.56 MHz at a gas pressure of 1 Torr with square wave modulation of a peak output of 5 KW, a repetition frequency of 20 KHz, and a duty of 20% while flowing a mixed gas of 5 ml/min of methane and 5 ml/min of methane, plasma is generated. After 3 hours, a diamond film with a thickness of about 1 μm was obtained on the silicon substrate. The deposition rate is approximately 0.3 μm/hr. Meanwhile, 1KW without modulation
In the case of an output of , the deposition rate was 0.1 μm/hr.

Example 4 Using the apparatus shown in Figure 3, argon 15/min + hydrogen 6/min from valve 7'', valve 7'
Argon 1/min and methane 2/min + methane 0.8/min were flowed from valve 7 at a pressure of 1 atm, a high frequency of 15 MHz, and an output of 15 KW was modulated with a rectangular frequency of 500 Hz and a duty of 30%. A diamond film with a thickness of 10 μm was obtained on a molybdenum substrate in 10 minutes by performing electric discharge. The substrate temperature was approximately 1100°C. On the other hand, in the case of 15KW without modulation, the substrate temperature was approximately 1600°C, and the precipitates were mostly graphite. Moreover, in the case of 4.5KW, the plasma disappeared in the above gas flow.

Example 5 Using the apparatus shown in Fig. 3, 200 ml/min of hydrogen and 0.015 g/min of alcohol vapor were flowed from valve 7' at an output of 30 Torr, a frequency of 15 MHz, and an output of 3 KW.
A diamond film with a thickness of 1.5 μm was obtained on a silicon substrate in 3 hours by performing a discharge using a high frequency power modulated with a 10 KHz square wave and a duty of 20%. The deposition rate is 0.5 μm/hr. On the other hand, without modulation
In the case of 600W output, the deposition rate was 0.2 μm/hr.

Example 6 Using the apparatus shown in Fig. 4, a mixed gas of hydrogen 10/min and argon 10/min was supplied from valve 7'.
Methane 0.7/min and argon 1 from valve 7
Flow a mixed gas of /min at a pressure of 1 atm.
A diamond film with a thickness of 6 μm was obtained on a molybdenum substrate in 20 minutes by discharging a 2.45 GHz, 5 KW microwave with power modulated by a 3 KHz, 30% duty square wave. On the other hand, the discharge could not be maintained with unmodulated 1.5KW discharge.

Example 7 Using the device shown in Figure 4, hydrogen was supplied from valve 7.
190ml/min, helium 6ml/min and methane 4
Flow a mixed gas of ml/min at a pressure of 50 Torr.
A diamond deposition rate of 1.3 μm/hr was obtained by modulating and discharging a 2.45 GHz, 3 KW microwave with a 1 MHz, 10% duty square wave. On the other hand, for 300W continuous wave without modulation, 0.6μ
The precipitation rate was m/hr.

(Effects of the Invention) As described in detail above, according to the present invention, a faster diamond precipitation rate can be obtained with less average discharge power. Furthermore, diamond synthesis can be performed by reducing the rise in gas temperature even with discharge at high gas pressure. Furthermore, excellent effects such as easy control of gas or substrate temperature and no need for a large-capacity exhaust device as in the prior art can be obtained.

[Brief explanation of the drawing]

Figures 1 to 4 are schematic diagrams showing an example of the apparatus used to carry out the present invention. Figure 1 is for a DC plasma jet type, and Figure 2 is for a parallel plate type DC discharge and high frequency discharge. FIG. 3 shows the case of work coil type high frequency discharge, and FIG. 4 shows the case of microwave discharge. 1...DC plasma torch, 2...DC power supply,
3...Substrate, 3'...Substrate holder, 4,4'...
reaction chamber, 5...exhaust device, 6...gas supply device,
7, 7', 7''...Gas flow rate adjustment valve, 8...DC power supply or high frequency power supply, 9,9'...Discharge electrode, 10...High frequency power supply, 11...Work coil, 12...Microwave power supply , 13... waveguide,
14...Plunger.

Claims (1)

[Claims] 1. A method for synthesizing diamond by plasma CVD, characterized in that the plasma is generated by amplitude-modulated electric power.