JPS6360530A - Microwave plasma processor - Google Patents

Abstract

PURPOSE:To uniformly form a plasma by composing a waveguide of a first section of a tube connected to the output terminal of a microwave oscillator and a third section of a plurality of tubes connected to the second section of a tapered part and having a section through which a microwave of wavelength passing the first section can pass. CONSTITUTION:A microwave is applied through a waveguide to a reaction vessel 3. The waveguide is composed of a first section 21 connected to a microwave oscillator 1, and a tapered part of a frustum of quadrangular prism shape connected to the first section, and the part near the vessel 3 of the tapered part is divided by a metal dividing plate 8 passing the bisector of the long side of the rectangle of the section into to waveguides 91, 92. The microwave passing the first section passes the section of the third section, and the microwave is propagated through the waveguides for forming the third section. The pointing vector distribution in the waveguides of the third section is not uniform, but is formed of a plurality of tubes. Thus, the pointing vector distribution is considerably uniformized as the whole third section, and even if the mean free stroke of the ionized electrons in the plasma is short, relatively uniform plasma can be formed.

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. 3 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 sample stage 5a is etched.

Or perform a thin film deposition process.

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

C8 Problems to be Solved by the Invention When the waveguide is, for example, a rectangular four-wave tube and excited in the TE+o mode as shown in FIG. 4, the solid lines in FIG. ), the Bointing vector, that is, the microwave energy density P, is determined at the center of the waveguide (the bisector of the long side of the rectangle), as shown in Figure 5.
becomes maximum. 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. As a result, when microwaves are irradiated only locally, the plasma shrinks. That is, there are problems in that the surface of the sample 4a cannot be uniformly treated, and the sample 4a is likely to be locally heated.

The present invention provides a microwave plasma processing apparatus that is capable of uniformly irradiating microwaves onto gas in a reaction vessel to form uniform plasma in order to generate uniform plasma. The purpose is to provide.

d. Means for solving the problem The above problem consists of a microwave oscillation circuit, a waveguide for propagating microwaves, a reaction vessel through which microwaves are transmitted,
It is equipped with a gas supply pipe that sends gas to the reaction container, a gas exhaust pipe that discharges gas from the reaction container, and a sample stage that places a sample in the reaction container. In a microwave plasma processing apparatus that excites plasma to generate plasma and performs plasma treatment on a sample with the plasma, the waveguide is a first portion consisting of a tube connected to an output end of a microwave oscillation circuit. , a second part consisting of a tapered part connected to the end of the first part and expanding the cross-sectional area of the waveguide; and a second part connected to the second part and having a wavelength that can pass through the first part. The problem has been solved by a microwave plasma processing device characterized in that it consists of a third section consisting of a plurality of tubes with cross-sectional dimensions that allow microwaves to pass through.

e. Operation The microwave generated by the microwave oscillation circuit propagates in the waveguide. At this time, the microwave inside the waveguide has an electric field E and a magnetic field H corresponding to each mode.

But the electric field E! : The Poynting vector defined by the vector product of the magnetic field H is not uniform within the tube. For example, the first part of the waveguide is a rectangular waveguide TE. When mode waves are used, the Poynting vector is maximum within the bisecting plane of the long side.

Since the second portion of the waveguide is a tapered portion with increasing cross-sectional area, the microwaves passing through the first portion can pass through the second portion.

The cross-section of the third section, consisting of a plurality of tubes connected to the second section, has dimensions that allow the microwaves directed to the first section to pass through, so that each conductor forming the third section Microwaves propagate inside a wave tube.

Although the distribution of Bointing vectors within each tube of the third portion is not uniform, since the third portion is formed by a plurality of tubes, the distribution of Bointing vectors is fairly uniform for the third portion as a whole. be changed.

Therefore, the gas in the reaction vessel is irradiated with relatively similar microwaves. As a result, even if the mean free path of ionized electrons in the plasma is short, a relatively -like plasma can be formed.

f. Embodiment FIG. 1 is a conceptual elevational view of a preferred embodiment of the microwave plasma processing apparatus according to the present invention.

Microwaves of 2.45 GH2 generated by the microwave oscillator 1 reach the reaction vessel 3 via a waveguide. The waveguide consists of a first part 2 of the waveguide consisting of a single tube connected to a microwave oscillator 1. and the first part 2. head 4 connected to
It consists of a pyramid-shaped tapered part. The part of the tapered part of the truncated pyramid shape near the reaction vessel 3 is connected to two waveguides 9 by a metal dividing plate 8 that passes through the bisector of the long side of the rectangle in its cross section.
．． ．． 9. It is divided into. That is, in this embodiment, the second portion 2□ of the waveguide is a portion of the tapered portion of the truncated four-pyramid shape where the dividing plate is not provided, and the third portion 2□ of the waveguide is the portion where the dividing plate is not provided. is the part 9 divided by the dividing plate
□Corresponds to 9t.

When the length of the long side of the cross section of the first portion 21 is al+ and the wavelength of the microwave is λ, the condition for the microwave to pass through the waveguide is a,>λ/2. This microwave is the third
The sufficient condition for passing through the third part 23 is
The length a of the long side of the cross section of the third portion 23 at the boundary between the second portion 2□ and the second portion 2□ satisfies a,>λ/2. At this time, the microwave energy is transferred to the third part 2□
Two waveguides 9. It is divided into +9z and guided to the quartz reaction vessel 3. A specific gas is introduced into the reaction vessel 3 from a gas supply pipe 6 and exhausted from an exhaust pipe 7 at a constant flow rate. As a result, the inside of the reaction vessel 3 is maintained at a constant pressure. The introduced gas is uniformly turned into plasma by the averaged microwave power, and the surface of the sample 40 placed on the sample stage 5 is uniformly etched or thin film deposited.

Note that the waveguides 21, 2□, 2. As for the material of the dividing plate 8, copper and aluminum are excellent in terms of loss, and stainless steel is preferable when emphasis is placed on heat resistance.

Note that even if the long side of the rectangular cross section at the boundary between the second part 2 and the third part of the waveguide is not divided, and the short side of the rectangle is divided into two, each part will operate in an independent mode. Therefore, it is possible to average the microwave energy. In this case, although there is a change in impedance, no microwave interruption occurs.

FIG. 2 is a conceptual perspective view of a waveguide portion of another preferred embodiment of the microwave plasma processing apparatus according to the present invention.

A truncated pyramid-shaped taper is connected to the end of the first portion of the waveguide connected to the microwave oscillator. The side closer to the reaction container (not shown) is divided into four by metal dividing plates 88, 8□ which divide the long and short sides of the cross section into two, respectively. In this example, the second waveguide
and the third part are included in the truncated four-sided pyramid, and the first part 2. The part adjacent to 2. is the second part 28, and the part divided into four parts is the third part 2. It is.

Third part 2. When a microwave close to TE+o mode (TB, since the waveguide is a truncated pyramid with no mode) propagates through each waveguide, the intensity of the Bointing vector at the center of each waveguide is is the maximum.

However, since the energy of the microwave propagating through the first portion is divided into four parts, the energy of the microwave is more averaged and irradiated to the gas in the reaction vessel (not shown). The reaction vessel is accommodated in the cavity 10 adjacent to the third part 23.

Averaging of microwave energy is TE. This does not only happen for modes, but also for other modes. For this purpose, it is preferable to provide a dividing plate at a position where the Bointing vector is maximum for the mode before being divided.

Note that the waveguide 2 in FIG. ．． 22,2.0 conceptual perspective view is obtained by removing the metal division Fi8□ from FIG.

At this time, the metal dividing plate 8 in FIG. 1 corresponds to the metal dividing plate 81 in FIG. 2.

In the embodiments of FIGS. 1 and 2, both the second and third portions of the waveguide are provided in the tapered portion of the truncated pyramid shape, but the third portion is It is not necessary to have a Taber structure, and it is also possible to make only the second part a Taber structure, the third part a waveguide with a rectangular parallelepiped structure, and divide the inside into a plurality of waveguides with a dividing plate.

Furthermore, it is also possible that the first part of the waveguide has a cylindrical structure and the second and third parts have a frustoconical structure.

It is also possible to make only the second part a truncated conical structure and the third part a cylindrical structure, and to divide the inside thereof into a plurality of waveguides by a dividing plate.

The length of the third portion is preferably equal to or longer than the A wavelength of the microwave used, in order to average the microwave energy density.

g. Effect It is possible to average the energy density of microwaves and generate uniform plasma.

[Brief explanation of drawings]

FIG. 1 is a conceptual elevational view of a preferred embodiment of a microwave plasma processing apparatus according to the present invention, and FIG. 2 is a conceptual elevational view of another preferred embodiment of a microwave plasma processing apparatus according to the present invention. FIG. 3 is a conceptual elevational view of an example of a microwave plasma processing apparatus according to the prior art, and FIG. 4 is Tll! ,,
A conceptual distribution diagram of the electric field and magnetic field of the mode, Fig. 5 is the TE of Fig. 4. This is the Boingting vector density distribution of the microwave mode. 1... Microwave oscillation circuit, 2+, 2z, 2s... Waveguide, 3... Reaction container, 4... Sample, 5... Sample stage, 8... Dividing plate, 9. 9z... Waveguide, 10... Vacant room. Patent applicant Denki Kogyo Co., Ltd. - 51 U (and 2 others)

Claims (5)

[Claims] (1) A microwave oscillation circuit, a waveguide for propagating microwaves, a reaction vessel through which the microwaves pass, a gas supply pipe for sending gas to the reaction vessel, and a gas exhaust pipe for discharging gas from the reaction vessel. Microwave plasma processing, which includes a sample stage on which a sample is placed in a reaction vessel, irradiates the gas in the reaction vessel with microwaves to excite the gas, generates plasma, and performs plasma treatment on the sample with the plasma. In the apparatus, the waveguide includes a first part consisting of a tube connected to an output end of a microwave oscillation circuit, and a tapered part connected to a terminal end of the first part and expanding the cross-sectional area of the waveguide. and a third section connected to the second section and consisting of a plurality of tubes having cross-sectional dimensions that allow microwaves of a wavelength that can pass through the first section. Features of microwave plasma processing equipment. (2) Claims characterized in that the first portion is a rectangular waveguide, and the second portion and the third portion are included in a tapered portion having a truncated pyramid shape. The microwave plasma processing apparatus according to item 1. (3) The microwave plasma processing apparatus according to claim 1, wherein the third portion consists of two waveguides. (4) The microwave plasma processing apparatus according to claim 1, wherein the third portion comprises four waveguides. (5) The first part is a circular waveguide, and the second part and the third part are included in a truncated conical tapered part. The microwave plasma processing apparatus according to item 1.