JPH0660411B2 - Optical plasma vapor phase synthesis method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A method and an apparatus for high-speed vapor phase synthesis of diamond, boron nitride, etc., for the purpose of increasing the deposition rate of diamond or boron nitride. The thermal plasma generated by the optical arc discharge by the beam is used as a plasma jet,
The target substance is ejected from a nozzle at the tip of the torch and rapidly cooled by cooling the substrate, preferably by blowing a cooling gas to bring it into contact with the substrate to be processed, so that a target substance is grown on the substrate to be processed at high speed.

[Industrial application field]

The present invention relates to a method and an apparatus for high speed vapor phase synthesis of substances such as diamond and boron nitride which cannot be synthesized by a conventional method. For example, a diamond film has a thermal conductivity of 2000
It is equivalent to W / mK, which is four times that of copper, and has excellent hardness and insulation, making it an ideal material for heat sinks and circuit board materials for semiconductors. Further, it has excellent translucency in a wide wavelength range and is excellent as an optical material. Further, diamond has a wide bandgap of 5.4 eV and is also a semiconductor having high carrier mobility, and is attracting attention as a structural device such as a high temperature transistor and a high speed transistor.

[Conventional technology]

Conventionally, the hot filament method (S. Matsumoto et al .: Jpn.J.App.
l.Phys.21 (1981) L183), microwave plasma CVD method (M.Kamo et al.:J.Cryst. Growth 62 (1983) 642), electron beam irradiation CVD method (A.Sawabe et al.:Appl) .Phys.Lett.4
6 (1985) 146) and other CVD methods are known.

[Problems to be Solved by the Invention]

Since the diamond film formed by vapor phase synthesis has excellent thermal conductivity, hardness, insulation, translucency, and corrosion resistance,
It is expected to be used as a substrate for high-density mounting of semiconductor elements, a high-hardness coating film for various tools, an optical component, etc. However, the film formation rate is as slow as 1 μm / h or less by any of the above-mentioned manufacturing methods. It was a problem in terms of cost and productivity.

Therefore, an object of the present invention is to solve the above problems and provide a vapor phase synthesis method of diamond having a high film formation rate.

[Means for Solving the Problems]

The present invention, in order to solve the above problems, thermal plasma generated by optical arc discharge by a focused high-power laser beam as a plasma jet, jetted from a nozzle at the tip of the torch, and rapidly cooled to the substrate to be processed. An optical plasma vapor phase synthesis method for bringing a target substance into contact with a substrate to be processed to grow at high speed, and a device for carrying out this method, a means for condensing a high-power laser beam, and a method for collecting the laser beam. A means for supplying a discharge gas to a position to be illuminated, a means for directing a thermal plasma generated by a light arc discharge of the discharge gas irradiated with the laser beam to a substrate to be processed, and a substrate to be processed capable of cooling the substrate to be processed. An optical plasma vapor phase synthesizer comprising a substrate holder for holding a substrate,
I will provide a.

In the photoplasma jet CVD method, for example, in order to vapor-phase synthesize diamond at a high rate, active species such as hydrogen atoms and hydrocarbon radicals must be supplied onto the substrate at a high density. Such high radical concentration can be obtained by generating thermal plasma, but thermal plasma cannot be directly supplied onto the substrate because its temperature is as high as 5000 ° C. or higher. Therefore, the invention was invented under the idea of quenching the thermal plasma and freezing the high gas dissociation rate at high temperature as it is, and supplying non-equilibrium plasma having a high radical concentration even at low temperature onto the substrate.

In this method, thermal plasma generated by optical arc discharge is struck as a plasma jet on a water-cooled substrate to rapidly cool the thermal plasma and rapidly synthesize diamond. With this method, an extremely high film forming rate of 10 μm / h or more has been obtained. However, in this method, the substrate has to be sufficiently cooled in order to enhance the quenching effect of the thermal plasma, and therefore the substrate is strongly restricted. That is, the substrate had a high thermal conductivity and only a thin substrate could be used. Therefore, we solved the above problems,
In order to be able to grow a diamond film on any underlayer at a high speed, the present invention similarly uses a thermal plasma generated by an optical arc discharge by a focused high-power laser beam as a plasma. As a jet, it is ejected from a nozzle at the tip of the torch, a cooling gas is blown to this plasma jet, the thermal plasma is rapidly cooled, active non-equilibrium plasma with a high concentration of radicals is generated, and the substrate to be processed is attached to this non-equilibrium plasma. An optical plasma vapor phase synthesis method characterized by bringing a target substance into contact with the substrate to be grown at a high speed, and an apparatus for carrying out this method, a means for condensing a high-power laser beam, , A means for supplying a discharge gas to a position where the laser beam is focused, and a discharge arc generated by the discharge gas being irradiated with the laser beam Means for directing the thermal plasma to the substrate to be processed that provides an optical plasma vapor synthesis apparatus, characterized by comprising means for blowing a cooling gas into the thermal plasma toward the substrate to be processed.

[Operation and Example]

As shown in FIG. 1, a high-power laser 1, for example, CO ₂
The laser beam A from the laser is focused on the tip of the focusing cone 3 by the focusing lens 2 to obtain an extremely high light intensity.

The raw material gas is introduced at atmospheric pressure or higher pressure,
It is heated by the laser beam focused at the tip of the cone 3 and becomes a high temperature thermal plasma with high chemical activity due to the light arc discharge. At this time, a rapid thermal expansion occurs,
It becomes a plasma jet B and is ejected from the nozzle 6. In the case of diamond synthesis, the source gas is CV
It is used for diamond synthesis by method D. For _example, using a H 2 -1% CH _4. In the case of synthesizing cubic boron nitride (CBN), H ₂ -0.5% B ₂ H ₆ -1%
Use NH ₄ .

According to the present invention, plasma having a higher activity than that of the conventional method is obtained as the plasma jet B. This plasma jet B
Is sprayed on the water-cooled substrate 7, the effect of rapidly cooling the thermal plasma is exerted, and diamond, CBN, etc. can be synthesized at a much higher rate than in conventional CVD.

In this method, in order to increase the stability of the plasma,
A rare gas such as He or Ar may be added to the raw material gas. However, the film forming rate is somewhat reduced by mixing the rare gas.

Note that FIG. 1 is a schematic diagram showing the principle of the photoplasma CVD method of the present invention. In the figure, 1 is a laser generator, 2 is a condenser lens, 3 is a condenser cone, 4 is a gas introduction tube, 5 is a nozzle, 6 and 9 are cooling tubes, 7 is a substrate, 8 is a substrate holder, 1
Reference numeral 0 is a vacuum chamber, and 11 is an exhaust pipe.

FIG. 2 is a schematic diagram showing the principle of optical plasma vapor phase synthesis in which a cooling gas is blown onto the thermal plasma to cool it. In the figure,
21 is a high-power laser, 22 is a laser beam, 23 is a condenser lens, 24 is discharge gas, 25 is nozzle cooling water, 2
6 is a water-cooled torch nozzle, 27 is a plasma jet, 28
Is a cooling gas, 29 is a cooling gas ejection port, 30 is a cone, 3
Reference numeral 1 is a non-equilibrium plasma, 32 is a substrate, 33 is a diamond film, and 34 is an arc.

Explaining again with the example of diamond synthesis, the discharge gas 24 composed of hydrogen gas and carbonized compound gas is supplied to the condensing cone 30.
When the laser beam 22 focused inside is applied and a light arc discharge is generated in the vicinity of the torch nozzle, the discharge gas is rapidly heated to a thermal plasma of 10,000 ° C. or higher. At this time, the thermal plasma becomes a supersonic plasma jet 27 due to the volume expansion due to the rapid temperature rise, and is ejected from the nozzle 26. Hydrogen gas is vigorously blown onto the plasma jet as the cooling gas 28 to forcefully mix the plasma jet, whereby the thermal plasma is rapidly cooled and the non-equilibrium plasma 31 is generated. When the substrate 27 is placed in this non-equilibrium plasma, the diamond film 33 grows on its surface.

This method is characterized by using a method of blowing a gas to a plasma jet (gas cooling method) instead of cooling the substrate as a means for rapidly cooling the thermal plasma. In this method, the plasma is instantaneously cooled by forcibly mixing the plasma jet and a gas at about room temperature, so that the plasma can be generated in a non-equilibrium state irrespective of the substrate. Therefore, it is possible to synthesize diamond, CBN, etc. on the surface at high speed simply by adjusting and holding the object to be treated in this non-equilibrium plasma so that it has a temperature at which diamond, CBN, etc. can be produced. it can.

As described above, in this method, the thermal plasma can be rapidly cooled irrespective of the substrate, as compared with the optical plasma jet CVD method for cooling the substrate described above, so that there is no restriction on the substrate and diamond can be deposited at high speed on any substrate. There is an advantage that can be grown.

In this method, the raw material gas may be the same as in the above-mentioned optical plasma CVD method, but the raw material gas may be introduced not as the discharge gas but as the cooling gas.

An inert gas such as Ar or He may be mixed with the discharge gas or the cooling gas. In this case, the stability of plasma is improved, but the film forming rate is decreased.

In addition, in order to enhance the etching effect of undesired carbon such as amorphous carbon in the discharge gas or the cooling gas, O ₂ , H ₂ O, H ₂ O ₂ , CO
You may mix a small amount of oxidizing gas such as.

FIG. 3 is a schematic diagram of a gas-phase synthesis apparatus using a gas-cooled optical plasma jet CVD method of cooling thermal plasma using a cooling gas, 43 is a plasma torch, 44 is a discharge gas supply pipe, 45 is a laser, 46 Is a torch cooling water pipe, 47 is a substrate holder, 48 is a substrate, 48 is a vacuum chamber, 50 is an exhaust system, 51 is a laser beam, 52 is a flow meter, 53 is a gas cylinder, 54 is a cooling gas jet port, and 55 is a substrate. It is a manipulator. In Examples 2 and 3 below, a flow type CO ₂ laser having an emission frequency of 10.6 μm, an output of 20 kW and a beam diameter of 80 mm was used as a light source, and a condenser lens having an aperture of 80 mm and f1.5 was used. Since the position and orientation of the substrate holder can be controlled by the manipulator, the target substance can be uniformly grown even on a large-area substrate or an object to be processed having a complicated surface shape. Although not shown in this schematic diagram, a heater for heating the substrate and a water cooling mechanism may be attached to control the temperature of the substrate.

Example 1 A plasma beam A generated by using a flow type CO ₂ laser 1 having an oscillation wavelength of 10.6 μm, an output of 20 kW and a beam diameter of 80 mm was used, as shown in FIG. From the gas condensing cone 3 into the condensing cone 3, and the raw material gas is introduced from the gas introducing pipe 4 into the condensing cone 3 at a flow rate of H ₂ 5 / min and CH ₂ 0.2 / min. It was ejected from a 3 mm nozzle 5. The nozzle 5 is opened in the vacuum chamber 10 having a pressure of 200 Torr, and is 20 mm apart from the nozzle 5 by 30 mm and has a thickness of 0.
Thermal plasma was sprayed onto the 5 mm substrate 7. The nozzle 5 and the substrate holder 8 have cooling water pipes 6 and 9 respectively.
Then, the temperature of the substrate was adjusted to 900 ° C. to quench the thermal plasma. 20 minutes after 30 minutes
A μm colorless transparent film was produced. In this film, a peak of only diamond was detected by X-ray diffraction, and some broad peaks due to amorphous carbon were detected by Raman spectroscopy in addition to the peak of diamond.

Example 2 Using the apparatus shown in FIGS. 2 and 3, 5 × 5 as a substrate
2 × 10 ^-3 inside the chamber using Si wafer of 0.2 mm
After evacuated to Torr, pressure 10 / min of hydrogen as a discharge gas 1kg / cm ^2, 80ml methane at a pressure of 1 kg / cm ²
/ Min Hydrogen as a cooling gas 10 at a pressure of 1 kg / cm ²
/ Min and the pressure in the chamber was maintained at 200 Torr.
The cooling gas was ejected toward the plasma jet from four ejection ports installed 3 mm below the torch nozzle. A laser beam having an output of 10 kW was irradiated from a laser oscillator to cause a light arc discharge and generate a plasma jet.
Next, the substrate was slowly moved closer to the torch, the nozzle-substrate distance was fixed at 5 mm, and film formation was performed for 10 minutes in this state.

The synthesized diamond film was a dense polycrystalline body having a clear automorphic shape with a thickness of about 15 μm. In X-ray diffraction, only sharp peaks of cubic diamond were detected. In the Raman spectrum, only the diamond peak at 1333 cm ^-1 was detected, and no peak due to graphite or amorphous carbon was detected. The Vickers hardness was about 10,000 kg / cm ² under a load of 500 g, which was the same value as natural diamond.

From the above results, it can be seen that the synthesized diamond is a good quality polycrystalline film. The film forming speed is 100 μm
It can be seen that / h is reached.

Example 3 Hydrogen as a discharge gas at a pressure of 1 kg / cm ² was 10 / min.
, B ₂ H ₆ at a pressure of 1 kg / cm ² at 50 ml / min, hydrogen as a cooling gas at a pressure of 1 kg / cm ² at 10 / min, NH ₃ at 1 k
Flow at 90 ml / min at a pressure of g / cm ² , other conditions being Example 2
When BN was synthesized in the same manner as in, wurtzite BN
A film of c-BN containing (w-BN) and having a thickness of about 10 μm was formed. X-ray diffraction of this film shows hexagonal structure of graphite structure
No BN (h-BN) was detected.

〔The invention's effect〕

According to the vapor phase synthesis method using the photoplasma jet of the present invention, a thin film such as diamond or CBN that cannot be synthesized by a normal CVD method can be formed at high speed and continuously, and cost and productivity can be improved. .

Further, by using the gas-cooled optical plasma jet CVD method and apparatus of the present invention, it is possible to form a material that is difficult to synthesize by a vapor phase method such as diamond or c-BN at an extremely high film-forming rate without cooling the substrate. Therefore, the range of application of these substances can be greatly expanded.

[Brief description of drawings]

FIG. 1 is an explanatory view of an optical plasma jet vapor phase synthesis apparatus for carrying out the method of the present invention, and FIG. 2 is a gas cooling plasma CVD.
FIG. 3 is a diagram explaining the principle of the gas cooling plasma CVD.
It is a schematic diagram of an apparatus. A ... laser beam, B ... plasma jet, 1 ... laser, 2 ... focusing lens, 3 ... focusing cone, 4 ... gas introducing tube, 5 ... nozzle, 6, 9 ... cooling water tube , 7 ... Substrate, 8 ... Substrate holder, 10 ... Vacuum chamber, 11 ... Exhaust pipe, 21 ... Laser, 22 ... Laser beam, 23 ... Condensing lens, 24 ... Discharge gas, 25 ... … Nozzle cooling water, 26 …… Water cooling torch nozzle, 27 …… Plasma jet, 28 …… Cooling gas, 29 …… Cooling gas jet nozzle, 30 …… Condensing cone, 31 …… Non-equilibrium plasma, 32 …… Processing target Substrate, 33 ... Growth film, 43 ... Plasma torch, 44 ... Discharge gas supply pipe, 45 ... Laser, 46 ... Torch cooling water pipe, 47 ... Substrate holder, 48 ... Substrate, 49 ... Vacuum chamber, 50 ...... Exhaust system, 52 …… Flowmeter, 53 …… Gas cylinder, 54 …… Cooling gas jet, 55 …… Substrate manipulator.

Claims (4)

[Claims] 1. A thermal plasma generated by an optical arc discharge by a focused high-power laser beam is ejected from a nozzle at the tip of a torch as a plasma jet, and is rapidly cooled to contact the substrate to be treated. Photo-plasma vapor-phase synthesis method for growing target material at high speed. 2. A thermal plasma generated by a light arc discharge by a focused high-power laser beam is used as a plasma jet and is ejected from a nozzle at the tip of the torch, and a cooling gas is blown to the plasma jet to quench the thermal plasma. Plasma to generate an active non-equilibrium plasma having a high concentration of radicals, contact the substrate to be processed with the non-equilibrium plasma, and grow a target substance on the substrate to be processed at high speed. Method. 3. A means for focusing a high-power laser beam,
A means for supplying a discharge gas to a position where the laser beam is focused; a means for directing a thermal plasma generated by the light arc arc discharge of the discharge gas to the processed substrate; An optical plasma vapor phase synthesizing apparatus comprising: a substrate holder for holding a cooled substrate to be processed. 4. A means for collecting a high-power laser beam,
A means for supplying a discharge gas to a position where the laser beam is focused; a means for directing thermal plasma generated by the arc arc of the discharge gas irradiated with the laser beam to the substrate to be processed; And a means for spraying a cooling gas onto the thermal plasma directed to the optical plasma vapor phase synthesis apparatus.