JPS63190635A - Treating device for microwave plasma - Google Patents

Abstract

PURPOSE:To form uniform plasma by fitting a dielectric plate consisting of a dielectric which is large in relative dielectric constant and small in dielectric loss to the inner wall of the terminal part of a waveguide or the terminal part and the inner wall of the part adjacent to the terminal part. CONSTITUTION:Output electric power of a microwave oscillator 1 is led to a reaction vessel 3 made of quartz via a waveguide 2. Specified kind of gas is introduced into the reaction vessel 3 via a gas feed pipe 6 and discharged at constant flow rate through an exhaust pipe 7. Thereby the inside of the reaction vessel 3 is maintained at constant pressure and the introduced gas is made to plasma by means of microwave electric power and etching processing or depositing treatment of a thin film is performed on the surface of a sample 4 placed on a sample base 5. The cross-section of the waveguide 2 is a rectangular shape or a circular shape and its end is housed in the reaction vessel 3 and enlarged into a tapered shape to reduce the reflection of microwave electric power.

Description

[Detailed description of the invention] a. Industrial application field The present invention relates to a microwave plasma processing apparatus.

A plasma processing apparatus is an apparatus that converts a certain gas into plasma and etches a sample or deposits a thin film on the surface of the sample using the reaction product.

In recent years, methods using microwaves as a means of turning gas into plasma have come into widespread use.

The advantages of using microwaves are that plasma density can be increased more efficiently than other methods, that the pressure range that can be turned into plasma is wide, that it is possible to heat the sample as necessary, and that there is no need for electrodes to generate electric discharge. Since there are no substances in the reaction vessel, contamination of the sample surface can be reduced.

b. Prior Art FIG. 4 is a conceptual elevational view of a microwave plasma processing apparatus according to the prior art.

The output power of the microwave oscillator 1a is guided to a quartz reaction vessel 3a via a waveguide 2a. A specific type of gas is introduced into the reaction vessel 3a from the gas supply pipe 6a, and is exhausted at a constant flow rate from the exhaust pipe 7a. As a result, reaction vessel 3
The inside of a is maintained at a constant pressure. The introduced gas is turned into plasma by microwave power, and the surface of the sample 4a placed on the test plate 5a is etched.

Or perform a thin film deposition process.

The waveguide 2a has a rectangular or circular cross section, and its end is tapered to accommodate the reaction vessel 3a and to reduce reflection of microwave power.

C1 Problems to be Solved by the Invention When the waveguide is, for example, a rectangular waveguide with a uniform dielectric constant ε distributed as shown in FIG. The electric field is maximum at the bisecting plane of the waveguide. Note that the y component Ey of the electric field is illustrated. The microwave energy density P is the central part of the waveguide (
It is maximum at the bisector of the long side of the rectangle). This means that the microwave power is concentratedly irradiated onto the gas in the reaction vessel within the bisecting plane of the waveguide.

Generally, as the pressure in the reaction vessel increases, the mean free path of ionized electrons, etc. in the plasma becomes shorter, especially when the gas pressure is about 1 torr or higher. Therefore, by locally irradiating microwaves, the plasma is further reduced. That is, there are problems in that it is not possible to uniformly process the surface of the sample 4a, and the sample 4a is likely to be locally heated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a microwave plasma processing apparatus that can uniformly irradiate gas in a reaction vessel with microwaves to form uniform plasma.

Means for solving the d0 problem The above problem consists of a microwave oscillation circuit, a waveguide for propagating microwaves, a reaction vessel housed at the end of the waveguide, and a gas sent to the reaction vessel. It is equipped with a gas supply pipe, a gas exhaust pipe for discharging gas from the reaction vessel, and a sample stage for placing the sample in the reaction vessel.The gas in the reaction vessel is irradiated with microwaves to excite the gas and generate plasma. In a microwave plasma processing apparatus that generates plasma and performs plasma treatment on a sample with the plasma, a dielectric material having a large relative dielectric constant is used on the inner wall of the terminal end of the waveguide, or on the inner wall of the terminal end and a portion adjacent to the terminal end. The problem was solved by a microwave plasma processing apparatus that is equipped with a dielectric plate made of a dielectric material with low loss.

e. Microwaves propagating inside a waveguide whose inner wall is metal (hereinafter referred to as a metal waveguide) are traveling waves in the direction of microwave propagation, and constant in a plane perpendicular to the direction of propagation. There is a wave. When a microwave consists of a single mode, the spatial distribution of the microwave Boing vector becomes a distribution function specific to that mode.

For example, E. In the microwave mode, the waveguide's 2
The energy distribution is maximum near the equiparting surface.

In the microwave plasma processing apparatus according to the present invention,
Near the end of the waveguide, the metal on the inner wall parallel to the microwave electric field component is covered with a dielectric.

Since the phase velocity of light inside a dielectric and the phase velocity of light in a vacuum are different, the boundary conditions of microwaves in this vicinity are different from those of a metal waveguide.

That is, the microwave in this vicinity cannot be expressed as a single mode for the metal waveguide, but becomes a complex mode microwave that is a combination of a plurality of eigenmodes of the metal waveguide.

-a Since the energy distribution of high-order mode microwaves is more uniform compared to that of low-order modes, the energy distribution of complex-mode microwaves including high-order modes is a single mode consisting only of low-order modes. The energy distribution is more uniform than with microwaves.

Therefore, the energy distribution of the plasma excited by the microwave becomes uniform.

f. Example FIG. 1 is a conceptual sectional view of a microwave plasma processing apparatus according to the present invention.

The output power of the microwave oscillator 1 is guided to a quartz reaction vessel 3 via a waveguide 2. A gas supply pipe 6 is provided in the reaction vessel 3.
A specific type of gas is introduced from the exhaust pipe 7 and exhausted at a constant flow rate from the exhaust pipe 7. As a result, the inside of the reaction vessel 3 is maintained at a constant pressure. The introduced gas is turned into plasma by microwave power, and the surface of the sample 40 placed on the sample stage 5 is etched.

Or perform a thin film deposition process.

The waveguide 2 has a rectangular or circular cross section,
Its end is tapered to accommodate the reaction vessel 3 and to reduce reflection of microwave power.

Termination part 2A of waveguide 2, or termination part 2A and termination part 2A
A dielectric plate made of alumina ceramics is attached to the inner wall of the portion 2B adjacent to the microwave electric field component parallel to the microwave electric field component. Note that the dielectric plate is not limited to alumina ceramics, and a dielectric plate made of other materials having a large dielectric constant and a small dielectric loss can also be used.

FIG. 2 is a conceptual distribution diagram of the dielectric constant in the BB cross section of FIG.

Since the dielectric constant ε is large at the boundary of the waveguide, the phase velocity of the electromagnetic wave at the boundary of the waveguide is different from that at the center of the waveguide. Therefore, in order to satisfy the boundary condition 2 between the dielectric material and the metal inner wall and the boundary condition between the dielectric material and the vacuum, microwaves with different phases or microwaves in a higher order mode are generated. That is, in a plane perpendicular to the microwave propagation direction, the microwave is no longer a standing wave, but becomes a superposition of microwaves of various phases and microwaves of higher order modes. For example, the y component E of the electric field has a distribution that is relatively uniform inside the waveguide and zero at the boundary between the dielectric and the metal, as shown in FIG. As a result, the energy distribution inside the waveguide becomes more uniform than when no dielectric plate is attached. Note that the distribution of E is as follows for each cross section:
and temporally variable.

Note that in order to reduce the energy loss in the dielectric plate 8 for microwaves, the dielectric material has a dielectric loss ta.
A substance with a small n δ is preferred.

As a result of actual use, the positions for dielectric mounting are the part that accommodates the reaction chamber 3 and the expanded part of the waveguide approximately one wavelength before the reaction chamber 3, that is, the end part 28 of the waveguide and the end part 28 of the waveguide. It has been found that a more uniform plasma than in the prior art can be obtained by attaching a dielectric plate to the inner wall parallel to the microwave electric field component of the portion 2B adjacent to the . The thickness of the dielectric was approximately 1/10 of the wavelength within the dielectric.

Note that even when a dielectric plate was attached only to the portion 2A housing the reaction chamber 3, a fairly uniform plasma was obtained.

Even if the dielectric plate 8 is attached from a position one wavelength or more before the reaction chamber 3, the effect remains the same except that the power loss increases.

g. Effect Microwave irradiation allows sample 4 to be removed independently of plasma.
．． The sample stage is heated, but at this time, only the central part of the sample 4° sample stage 5 is heated uniformly without being locally heated. Therefore, in the present invention, in combination with uniform plasma generation over a wide gas pressure range, more uniform reaction on a sample and formation of a thin film are possible than in the prior art.

[Brief explanation of the drawing]

FIG. 1 is a conceptual sectional view of a microwave plasma processing apparatus according to the present invention, FIG. 2 is a conceptual distribution diagram of the dielectric constant ε in the AA cross section of FIG. - A conceptual distribution diagram of the electric field in the A cross section, FIG. 4 is a conceptual cross-sectional diagram of a microwave plasma processing apparatus according to the prior art, and FIG.
Conceptual distribution diagram of permittivity ε in the BB cross section of the figure, No. 6
The figure is a conceptual distribution diagram of the electric field in the BB cross section of FIG. 4. 1...Microwave oscillation circuit, 212□, 23...
Waveguide, 3... Reaction container, 4... Sample, 5... Sample stage, 6... Gas supply pipe, 7... Exhaust pipe, 8... Dielectric plate.

Claims (1)

[Scope of Claims] A microwave oscillation circuit, a waveguide for propagating microwaves, a reaction vessel housed in the terminal end of the waveguide, a gas supply pipe for feeding gas to the reaction vessel, and a gas supply pipe for supplying gas from the reaction vessel to the reaction vessel. Equipped with a gas exhaust pipe for discharging gas and a sample stage for placing a sample in a reaction vessel, the gas in the reaction vessel is irradiated with microwaves to excite the gas and generate plasma, and the plasma is applied to the sample. In a microwave plasma processing apparatus that performs plasma processing, a dielectric material made of a dielectric material with a large relative dielectric constant and a small dielectric loss is provided on the inner wall of the terminal end of the waveguide, or on the inner wall of the terminal end and a portion adjacent to the terminal end. A microwave plasma processing apparatus characterized in that a body plate is attached.