JPS6265997A - Method and apparatus for synthesizing diamond - Google Patents

Abstract

PURPOSE:To easily synthesize perfect crystal diamond without contg. impurities by impressing a magnetic field to the plasma generated in a gaseous mixture composed of gaseous hydrogen and gaseous hydrocarbon so that cyclone resonance is generated in the electrons in the plasma. CONSTITUTION:The gaseous mixture composed of gaseous hydrogen and gaseous hydrocarbon such as methane or the gaseous mixture composed of gaseous hydrogen, inert gas and gaseous hydrocarbon is introduced from a gas introducing pipe 7 into a plasma chamber 6. Microwaves generated by a power unit 1 are then introduced via a waveguide 5 into the plasma chamber 6 to generate the plasma in the above-mentioned gaseous mixture. The magnetic field of at least the intensity at which the electrons in the plasma generate the cyclone resonance is impressed to the plasma by a magnetic coil 9 disposed on the outside. The ionization density of the hydrogen in the plasma is thereby improved and the reaction with the impurities is accelerated, by which the impurities are removed. The plasma accelerated by the magnetic field is conducted into a deposition chamber 10 to deposit the diamond contg. no impurities on the surface of a substrate 12 on a sample base 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for low-pressure synthesis of diamond in hydrogen plasma.

[Conventional technology]

The conventional method for synthesizing diamond was to process carbon powder such as graphite under extremely high temperature and high pressure, but in recent years, a method of synthesizing diamond at low pressure in plasma has been attracting attention as an alternative to the above method. . It has also been reported that diamond having a perfect crystal structure can be obtained by using hydrogen plasma in the plasma method described above (Japanese Patent Application Laid-open No. 135117/1983). In this hydrogen plasma method, diamond is synthesized by a gas phase reaction by supplying hydrogen gas continuously mixed with hydrocarbon gas at an appropriate concentration into hydrogen plasma.

[Problem that the invention seeks to solve]

The above hydrogen plasma method is advantageous in that perfectly crystalline diamond can be obtained relatively easily, but according to experiments conducted by the inventors, impurities such as graphitic carbon may precipitate along with perfectly crystalline diamond.

For example, at an atmospheric pressure of 20 Torr and a plasma temperature of approximately 700°C, hydrogen gas containing 2% concentration of methane (CH4) is continuously supplied into the hydrogen plasma for 4 hours, and the precipitates deposited on the substrate are Figure 6 shows the results of laser Raman spectrum analysis. According to the diagram, 1333C
The formation of diamond is confirmed by having a peak at I11-' (point χ in the figure), but at 1360 cm-
There are also peaks at ' and 1600 cm-' (point y in the figure,
2 points) Indicates the formation of amorphous carbon.

The present invention aims to solve these problems, and aims to provide a method for easily and reliably synthesizing impurity-free perfectly crystalline diamond using hydrogen plasma.

[Means for Solving the Problems] To achieve the above object, the present invention provides plasma generated in a mixed gas of hydrogen gas and hydrocarbon gas or in a mixed gas of hydrogen gas, inert gas, and hydrocarbon gas. In this method, a magnetic field strong enough to cause at least the electrons in the plasma to cause cyclone resonance is applied, and diamond is deposited on a substrate placed in the plasma.

[Effect]

According to the above means, among impurities such as diamond-like carbon generated from hydrocarbon gas in a plasma containing hydrogen gas and impurities such as graphitic carbon, only the impurities react with ionized hydrogen in the hydrogen plasma, resulting in the original carbonization. In order to return to hydrogen, applying a strong magnetic field that causes electron cycloton resonance to hydrogen plasma as in the present invention can improve the ionization density in the plasma and promote the reaction between impurities and ionized hydrogen. This allows impurities to be removed.

〔Effect of the invention〕

Therefore, according to the present invention, impurity-free diamond can be easily obtained.

〔Example〕

The present invention will be explained below based on embodiments shown in the drawings.

Fig. 1 is a schematic cross-sectional view showing the outline of the experimental apparatus used in the present invention, and Fig. 2 is a cross-sectional view explaining the details of the reactor section. 3 is an isolator that protects the magnetron from reflected power; 3 is a power monitor that displays the incident power supplied from the power unit 1 to the load and the reflected power that is returned without being consumed by the load; 4 is a power monitor that matches the microwave equipment; Microwaves are introduced into the plasma chamber 6 through a waveguide 5, which is a matching device that improves wave power consumption efficiency and transmits microwaves. A cooling water jacket section 6a for circulating cooling water is provided around the plasma chamber 6.

The plasma chamber 6 is configured to be supplied with a mixed gas of hydrocarbons and hydrogen from a gas introduction pipe 7 while at the same time maintaining the inside of the plasma chamber 6 in a reduced pressure state through an exhaust pipe 8a using an exhaust device 8 such as a vacuum pump.

Furthermore, a magnetic coil 9 (in the case of this embodiment, the microwave frequency is 2450 MHz, and the intensity of the central magnetic field is 875 MHz, which is the electron cyclotron resonance condition) is placed around the plasma chamber 6.
0e) to cause electrons in the plasma to undergo electron cyclotron motion and improve the ionization rate. Further, a quartz sample stage 11 insulated from the apparatus is provided in a deposition chamber 10 that partitions the lower part of the plasma chamber 6, and a substrate 12 such as a silicon wafer is placed thereon. The plasma in the plasma chamber 6 is accelerated by the intensity gradient of the diverging magnetic field created by the magnetic coil 9 while undergoing electron cyclotron motion, reaching the substrate 12 to form diamond particles or a diamond thin film.

In the apparatus constructed as described above, methane is
The inside of the plasma chamber is maintained at 50 Torr by a pressure reducing device while supplying hydrogen gas containing 0.1% from the gas introduction pipe 7 at a rate of 100 cc/min. Hydrogen plasma is then generated by introducing microwaves of 300MI (z or higher) using a plasma generator.Furthermore, a magnetic field is applied to this plasma at a microwave frequency of 2450MHz so that the strength of the central magnetic field is 8750e or higher, which is the electron cyclotron resonance condition. is applied.Electrons in the magnetic field move in a cyclotron around the lines of magnetic force due to the Lorentz force, and the rotation frequency f is f-Q, B/2πm. Here, q: electron charge, B: magnetic flux Density, m: Mass of the electron.When the frequency of circular motion caused by this magnetic field matches the frequency of the introduced microwave, the electron cyclotron resonance condition is established, the kinetic energy of the electron increases, and the kinetic energy of the electron increases. The ionization rate increases as the probability of collision increases.Therefore, microwave energy can be effectively used to decompose raw material gas
Another advantage is that it can be used to form a film on a substrate. Furthermore, if the intensity of the diverging magnetic field generated by the magnetic coil 9 has a gradient, the plasma can be accelerated toward the substrate. The results of Raman spectrum evaluation of the diamond synthesized as described above are shown in FIG. 5. Only the peak χ was observed, and no substances other than diamond were detected. This was also confirmed by electron beam analysis.

Furthermore, the growth rate was about 145 μm/hr or more, which is an order of magnitude faster than other conventional synthesis methods, and the temperature near the substrate was about 550° C., allowing stable synthesis to be maintained without temperature control.

Table 1 shows an example of the experimental results obtained by changing the methane concentration, the output of the microwave for plasma generation, the substrate temperature, the gas pressure in the plasma chamber, the material of the support, etc. In the present invention using electron cyclotron resonance (hereinafter referred to as ECR),
Only diamond is obtained, and compared to synthesis by conventional microwave plasma CVD, the substrate temperature is about 400''C lower at the same microwave output, and the growth temperature is more than twice as high.

In addition, no graphite contamination was observed even when the methane concentration was increased.
Diamond synthesis conditions can be greatly expanded. In addition, if the microwave output is increased, diamond of good quality such as crystallinity can be obtained, but at the same time, the sample and support stand are heated by the microwave, and the reverse transition temperature from diamond to graphite (
The contradictory conditions of exceeding 1300℃)
The best conditions can be selected without taking measures such as cooling the board or installing microwave absorbers. Furthermore, according to the present invention, it becomes possible to synthesize a single substrate material, which was conventionally limited due to an increase in substrate temperature, onto a material with a low heat resistance temperature.

Below is a blank space.Next, the present invention provides a third
It may be modified as shown in the figure. In other words, 100
Plasma can be further accelerated and reach the substrate 12 by installing a mesh-like reticular electrode 13 and applying a voltage of 200 to 1200 V as an ion extraction power source. Also,
As shown in FIG. 4, a second gas introduction pipe 14 having several gas introduction holes 14a directed toward the inside of a ring-shaped metal pipe is installed above the substrate 12 as shown in FIG. By supplying hydrogen from the gas introduction pipe 7 and methane from the second gas introduction pipe lower 4, the decomposed methane can be uniformly supplied to the substrate 12 without contaminating the plasma chamber 6.

Further, the hydrocarbon gas used in the present invention is not limited to methane, and any hydrocarbon that can be excited and dissociated in microwave or ECR plasma may be used. Examples include ethane, propane, acetylene, and benzene. Argon, helium, etc. can be used as the inert gas. The frequency of the microwave and the strength of the magnetic field of the magnetic coil are not limited to the above-mentioned resonance condition, but may be such that the magnetic field has an intensity higher than the resonance condition.

The volume ratio of hydrocarbon gas (C) and hydrogen gas (H) is C/
The range of H=1 to 0.001 is preferable, and the inert gas (A
) also when mixed with C/ (H + A) = 1 to 0.001
If you mix them together, you can synthesize diamonds. It is preferable that A accounts for 50% or less of H. The higher the output of the microwave oscillator, the better the diamond quality.
300-2kw is preferable.

The material of the substrate is not limited to silicon wafer, but also tungsten,
Metals such as molybdenum and niobium, quartz, glass, etc. may be used, and those subjected to surface treatment as necessary may also be used.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram illustrating the structure of the apparatus used in the diamond synthesis method of the present invention, Fig. 2 is a sectional view illustrating the structure of the reaction chamber, and Fig. 3 shows the structure of another embodiment of the apparatus. 4 is a front view illustrating the shape of the second gas supply port in FIG. 3, and FIGS. 5 and 6 are diamonds formed by the method of the present invention and the conventional hydrogen plasma method. FIG. 2 is a characteristic diagram showing the results of laser Raman spectrum analysis of . 6... Plasma chamber, 7... Gas introduction tube, 8... Vacuum pump, 9... Magnetic coil, 12... Substrate.

Claims (2)

[Claims] (1) Applying a magnetic field strong enough to cause at least the electrons in the plasma to cause cyclone resonance to a plasma generated in a mixed gas of hydrogen gas and hydrocarbon gas or a mixed gas of hydrogen gas, inert gas, and hydrocarbon gas. and depositing diamond on a substrate placed in the plasma. (2) A plasma chamber that generates plasma, a plasma generator that generates plasma by introducing microwaves into the plasma chamber, an introduction pipe that supplies raw material gas to the plasma chamber, and a a substrate for depositing generated diamond; a decompression device for keeping the inside of the plasma chamber in a reduced pressure state; and a magnetic coil for causing cycloton resonance in electrons in the plasma, provided at the outer periphery of the plasma chamber. A diamond synthesis device featuring: