JPH0969398A - Plasma processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma processing device, which can evenly generate the plasma over a larger area, by forming the microwave, which is transmitted in a flat plate part of a dielectric line, into the single mode microwave, of which intensity level in the traveling direction is evened, without unnecessarily enlarging a device. SOLUTION: This plasma processing device is provided with a dielectric line 21 having a taper-shaped matching part 212, a microwave guide window 4 arranged opposite to the dielectric line 21, and a reaction container 1 made of metal, of which microwave guide port 3 is air-tightly sealed by the microwave guide window 4. Cross directional thickness of the taper-shaped matching part 212 of the dielectric line 21 is formed thick at a central part and thin at each end.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-diameter semiconductor device substrate, a glass substrate for a large-sized liquid crystal display (LCD), etc. by utilizing plasma for etching, ashing, and CVD.
The present invention relates to a plasma processing apparatus that performs processing such as the above.

[0002]

Reactive gas plasmas are widely used in LSI and LCD manufacturing processes. In particular, dry etching technology using plasma is
And it has become an essential basic technology for LCD manufacturing process.

Generally, as an excitation means for generating plasma, a microwave of 2.45 GHz and 13.56 are used.
RF (high frequency) of MHz is used. Compared with the case of using RF, high density plasma can be obtained when microwave is used, and there is an advantage that there is no problem of contamination from the electrode because no electrode is required.

However, since it is difficult to generate uniform plasma in a large area in a plasma processing apparatus using microwaves, it is difficult to uniformly process a large-diameter semiconductor substrate or LCD glass substrate. is there.

In this regard, the present applicant has proposed a method using a dielectric line as a plasma processing apparatus capable of uniformly generating microwave plasma in a large area (Japanese Patent Laid-Open No. 62-5600). JP-A-62-99
481).

FIG. 5 and FIG. 6 are a schematic plan view and a partial sectional view of a plasma processing apparatus having a dielectric line proposed in the above publication.

In the plasma processing apparatus shown in these figures,
The microwave is oscillated by the microwave oscillator 26 and introduced into the dielectric line 21 via the microwave waveguide 23.
An electric field is formed in the lower hollow layer 20 by the microwave propagating through the dielectric line 21. This electric field passes through the microwave introduction window 4 and is supplied into the reaction chamber 2 to excite the reactive gas and generate plasma. The plasma treatment is performed on the surface of the sample S by this plasma.

FIG. 7 is a perspective view of the dielectric line when it is turned upside down. The dielectric line 21 is fixed to the metal plate 22. The dielectric line 21 includes an introduction part 211 and a taper type matching part 2.
12 and the flat plate portion 213. The introduction part 211 is inserted into the microwave waveguide 23.

The width of the tapered matching portion 212 is equal to that of the introduction portion 21.
The width W0 of 1 is linearly changed to the width W2 of the flat plate portion 213. The thickness of the tapered matching portion 212 is the thickness T0 of the introduction portion 211 in the Z direction, which is the traveling direction of microwaves.
To a thickness T1 of the flat plate portion 213, and the thickness is constant in the width direction.

From the microwave waveguide 23 to the dielectric line 21
The introduction of microwaves into the cell is performed as follows. In the introduction part 211, the microwave propagating through the microwave waveguide 23 is introduced into the dielectric line 21, and the rectangle TM ₁₁
Mode microwave surface waves propagate. In the tapered matching section 212, the rectangular TM ₁₁ mode microwave is spread in the width direction. The expanded rectangular TM ₁₁ mode microwaves are introduced into the flat plate portion 213. By providing the taper-type matching portion 212, the rectangular TM ₁₁ mode microwave is generated without generating a higher-order mode, and the flat plate portion 2 having a large area is formed.
13 and can be propagated.

In the plasma processing apparatus having this dielectric line, since the microwave can be uniformly introduced and propagated in the flat plate portion 213 having a large area, the microwave introduction window 4 and the microwave guiding window facing the flat plate portion 213 can be introduced. If the inlet 3 is expanded, a large area microwave plasma can be generated in the reaction chamber 2.

[0012]

As described above, the dielectric line 21 includes the introduction portion 211, the flat plate portion 213 for supplying an electric field to the plasma generating portion, and the flat plate portion 213 of the microwave of the higher mode. It is composed of a tapered matching part 212 that introduces microwaves without generation. Since the tapered matching portion 212 is not directly related to plasma generation, the shorter it is, the smaller the size of the plasma processing apparatus can be, which is preferable.

However, this taper type matching portion 212
If the length of is simply shortened, the rectangle T, which is the basic mode,
The surface wave of the M ₁₁ mode microwave is attenuated to generate a higher order mode. When a higher-order mode occurs, unlike the fundamental mode microwave propagation, which has a regular microwave field intensity distribution, microwaves are a superposition of multiple modes, so the field intensity distribution in the microwave traveling direction is not Be uniform. As a result, the distribution of plasma generated by this electric field also becomes non-uniform. Therefore, there is a problem that the length of the tapered matching portion 212 cannot be simply shortened.

Further, the semiconductor substrate has a large diameter and LC
It is necessary to increase the size of the flat plate portion 213 as the area of the D glass substrate is increased.
The problem has arisen that 12 also needs to be larger.

The present invention has been made in view of the above problems, and a microwave propagating through a flat plate portion of a dielectric line has a uniform intensity level in the traveling direction without increasing the size of the device unnecessarily. An object of the present invention is to provide a plasma processing apparatus capable of uniformly generating plasma in a large area by using a mode microwave.

[0016]

The electric field of the microwave propagating through the flat plate portion of the dielectric line leaks from the open bottom face of the dielectric line. The leaked electric field passes through the microwave introduction window to generate plasma in the reaction chamber. Since the microwave propagating through the dielectric line is a standing wave and exhibits a sinusoidal electric field intensity distribution, the plasma distribution in the vicinity of the microwave introduction window reflects this electric field intensity distribution. However, since the generated plasma is made uniform by diffusion as it moves away from the microwave introduction window, it becomes uniform plasma near the sample stage.

What makes the plasma non-uniform is the attenuation of the peak value of the electric field strength in the direction of microwave propagation, which is due to the generation of microwaves of higher modes.

For this reason, the tapered matching portion is provided to suppress the generation of microwaves of higher modes, and the microwaves propagating through the flat plate portion of the dielectric line are of a single mode whose intensity level is uniform in the traveling direction. The microwave is being used.

The taper type matching section and generation of microwaves of higher modes will be described. FIG. 10 is a schematic diagram showing a situation in which a microwave propagates through a dielectric line. The broken line indicates the wavefront of the microwave.

Considering the phase of the microwave introduced from the waveguide opening surface 212S at the terminal position 212E of the tapered matching portion, the phase at the central portion A and the phase at the end portion B are deviated. When the phase shift θdif at the central portion A and the phase at the end portion B exceeds 3π / 4 (radian), microwaves of higher order modes are likely to be generated.

The phase shift θdif between the phase at the central portion A and the phase at the end portion B is expressed by the following equation (1). Where λg
Is the propagation wavelength of the microwave in the dielectric, ∫ _B ds2 is the integral from the waveguide aperture 212S to the end B, ∫ _A ds1
Means the integration from the waveguide opening surface 212S to the central portion A. λg is a function of the cross-sectional shape of the dielectric line,
It can be approximated by a function of thickness, and if the thickness is expressed as a function of position, λ
g is a function of position.

When λg is approximated by the average value (λg) av in the taper matching portion, the phase shift θdif between the phase at the central portion A and the phase at the end portion B is expressed by the equation (1) '.
d is the difference between the distance from the waveguide opening surface 212S to the central portion A and the distance to the end portion B.

The distance difference d is approximated by the equation (2). W is the width of the flat plate portion 213 of the dielectric line, that is, the width at the end position 212E of the tapered matching portion 212, W0 is the width at the waveguide opening surface 212S, and L is the length of the tapered matching portion. The distance difference d is approximately proportional to the square of the width W of the flat plate portion 213 of the dielectric line, and substantially inversely proportional to the length L of the tapered matching portion 212. Further, from the equation (2), the length L of the tapered matching portion is substantially proportional to the square of the width W of the dielectric line.

Therefore, when the width W of the flat plate portion 213 of the dielectric line is increased in accordance with the increase in the diameter of the semiconductor substrate and the increase in the area of the glass substrate for LCD, the taper type matching portion is proportional to the square thereof. It is necessary to increase the length L.

[0025]

[Equation 1]

The inventor of the present invention, in order to reduce the phase shift θdif, based on the equation (1), the waveguide opening surface 21
We paid attention to the fact that the propagation wavelength λg on the path from 2S to the end B and the propagation wavelength λg on the path from the waveguide opening surface 212S to the central portion A may be different (see FIG. 10). To change the propagation wavelength λg, the thickness of the dielectric material at that position can be changed. That is, the thicker the propagation wavelength λg, the shorter the propagation wavelength λg.
The present invention has been completed, focusing on the fact that can be made longer.

According to the plasma processing apparatus of the present invention, the thickness of the tapered matching portion 212 of the dielectric line 21 in the width direction is thicker at the center and thinner at the ends. By doing so, the propagation wavelength λg of the microwave propagating in the central portion of the tapered matching portion 212 of the dielectric line 21 is made shorter than the propagation wavelength λg of the microwave propagating in the end portion. As a result, the phases at the points A and B can be aligned and the phase shift θdif can be suppressed.

By doing so, generation of high-order mode microwaves in the tapered matching portion 212 is suppressed without lengthening the tapered matching portion 212 of the dielectric line 21, and the intensity level is aligned in the traveling direction. Single mode microwaves can be propagated without attenuation. As a result, the electric field strength distribution becomes a sinusoidal uniform distribution with uniform strength,
A uniform plasma can be generated near the sample table in the reaction chamber.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the plasma processing apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view schematically showing an example of this plasma processing apparatus.

The microwave oscillator 26 is connected to the dielectric line 21 via the microwave waveguide 23. A fluorine resin such as Teflon (registered trademark) is used for the dielectric line 21. Aluminum or the like is used for the metal plate 22.

In the middle of the microwave waveguide 23, a tuner 24 for matching the microwaves and an isolator 25 for removing the reflected waves of the microwaves are provided.

The microwave oscillated by the microwave oscillator 26 is transmitted through the microwave waveguide 23 to the dielectric line 21.
Will be introduced. As described above, the microwave is introduced into the dielectric line 21 from the microwave waveguide 23 by the introduction part 211, expanded in the width direction by the tapered matching part 212, and introduced into the flat plate part 213. In this way, in the flat plate portion 213, the microwaves are uniformly propagated without the generation of higher-order modes.

The reaction container 1 is made of a metal such as aluminum (Al) in a hollow rectangular parallelepiped. A reaction chamber 2 is provided inside the reaction container 1. A microwave introduction port 3 is opened in the upper part of the reaction vessel 1, and the microwave introduction port 3 is O between the microwave introduction window 4 and the upper wall of the reaction vessel 1.
The ring 9 is sandwiched and hermetically sealed. The microwave introduction window 4 is formed of a dielectric having heat resistance and microwave transparency and having a small dielectric loss, for example, quartz glass (SiO ₂ ), alumina (Al ₂ O ₃ ), or the like.

In the reaction chamber 2, a sample table 7 on which the sample S is placed is arranged at a position facing the microwave introduction window 4. A gas introduction hole 5 for introducing a reaction gas and an exhaust port 6 connected to an exhaust device (not shown) are provided. A solvent passage 8 is formed on the peripheral wall of the reaction container 1,
By circulating the solvent having a predetermined temperature in the solvent passage 8, the reaction container 1 can be maintained at a predetermined temperature. A gate valve (not shown) that carries the sample S into and out of the reaction chamber 2 is provided on the side wall of the reaction container 1.

A method of performing plasma processing on the surface of the sample S placed on the sample table using this plasma processing apparatus will be described.

After the gas is exhausted from the exhaust port 6 to exhaust the reaction chamber 2 to a required pressure, the reaction gas is supplied from the gas introduction hole 5 to bring the reaction chamber 2 to a predetermined pressure.

The microwave is oscillated by the microwave oscillator 26, and the dielectric waveguide 21 is passed through the microwave waveguide 23.
To be introduced. An electric field is formed in the lower hollow layer 20 by the microwave propagating through the dielectric line 21. This electric field passes through the microwave introduction window 4 and is supplied to the reaction chamber 2,
A plasma is generated. The plasma treatment is performed on the surface of the sample S by this plasma.

FIG. 2 is an example of the dielectric line of the plasma processing apparatus of the present invention, and is a perspective view of the dielectric line when it is turned upside down. The connecting portion of the tapered matching portion 212 of the dielectric line of this example with the flat plate portion 213 is flat with a thickness T2 at the central portion, has a thickness T1 at the end portion, and has a thickness between the central portion and the end portion. It is changing linearly. Of course, T2> T1. The method of changing the thickness may be curved.
The width W1 of the central portion may be different from the width W0 of the introduction portion 211.

[0040]

【Example】

(Embodiment) An embodiment of the plasma processing apparatus of the present invention will be described below. The plasma processing apparatus of this embodiment is that shown in FIG. 1, and its dielectric line is that shown in FIG.

The dielectric line of this embodiment was made of Teflon (relative permittivity ε = 2.1). The dimensions are as follows. The width W0 of the introduction part 211 connected to the rectangular waveguide is 9
6 mm, thickness T0 is 27 mm. The width W1 of the central portion at the end of the tapered matching portion 212 is 96 mm, and the thickness T2 is 2
7 mm, the thickness T1 of the end portion at the end of the tapered matching portion 212 is 15 mm, and the length L1 is 150 mm. The width W2 of the flat plate portion is 300 mm, the width W1 of the central portion is 96 mm, and the thickness T
2 is 27 mm, the end thickness T1 is 15 mm, and the length L2 is 380 mm.

At this time, a rectangular TM which is a fundamental mode of a surface wave generated by a microwave having a frequency of 2.45 GHz.
_With respect to the ₁₁ mode, the phase shift θdif between the phase on the center line at the end position of the tapered matching portion 212 and the phase at the end portion from the waveguide opening surface is π / 4.

The electric field intensity leaking from the open surface of the dielectric line of this example was measured. The measurement was performed by scanning the loop antenna in the Z direction, which is the traveling direction of microwaves, with the end of the tapered matching portion 212 of the dielectric line as the zero point. The measurement position was 25 mm from the dielectric surface. The measurement range was 330 mm in the Z direction.

FIG. 3 shows the electric field strength of the dielectric line of the present invention.
7 is a graph showing the distribution of Ex | ^{2 in} the Z direction. The electric field strength | Ex | ² was standardized by its maximum value. The electric field strength | Ex | ² was distributed sinusoidally in the Z direction, which is the microwave traveling direction, and there was little attenuation in the Z direction. The microwave frequency at this time is 2.45 GHz.
z, microwave power was 40 mW.

Next, the ion current density distribution was measured in the plasma processing apparatus equipped with this dielectric line. The measurement position was 60 mm from the microwave introduction window 4. At this time, the microwave introducing port 3 of the reaction container has a width of 28
The length was 0 mm and the length was 320 mm. The microwave introduction window 4 was a quartz plate having a width of 360 mm × 380 mm and a thickness of 20 mm.

The conditions for plasma generation are as follows.
The reaction gas is Ar: 30 sccm, the pressure is 10 mTorr.
r, microwave power: 1 kW.

FIG. 4 is a graph showing the distribution of the ion current density in the plasma generation region in the Z direction. The plasma generation region is a region from Z = 20 mm to Z = 340 mm. An almost uniform ion current density distribution was obtained in this region.

(Comparative Example) The electric field intensity distribution and the ion current distribution were measured for the conventional devices shown in FIGS. 5, 6 and 7.

The dimensions of the dielectric line of this embodiment are as follows. The width W0 of the introduction portion 211 of the rectangular waveguide is 96 m.
m, thickness T0 is 27 mm. The length L1 of the tapered matching portion 212 is 150 mm. The width W2 of the flat plate portion 213 is 300 m
m, the thickness T1 is 20 mm, and the length L2 is 350 mm. The thickness of the tapered matching portion 212 is constant in the width direction, and in the Z direction that is the traveling direction of microwaves, it linearly decreases to the thickness T1 of the flat plate portion 213 at the terminal end portion.

At this time, with respect to the rectangular TM ₁₁ mode which is the fundamental mode of the microwave having the frequency of 2.45 GHz, the phase on the center line at the end position of the tapered matching portion 212 and the waveguide opening surface at the end portion. Phase shift from θdif is 3π / 4
Becomes

The electric field intensity leaking from the open surface of the dielectric line of this comparative example was measured. The measuring method and the measuring position are the same as in the previous embodiment.

FIG. 8 shows the electric field strength of the dielectric line of the present invention.
7 is a graph showing the distribution of Ex | ^{2 in} the Z direction. The electric field strength | Ex | ² was standardized by its maximum value. Electric field strength | Ex
| ² showed an overall attenuation different from the attenuation due to the wavelength of the standing wave with respect to the Z direction is a microwave travel direction. At this time, the microwave frequency was 2.45 GHz and the microwave power was 40 mW.

Next, the ion current density distribution was measured in the plasma processing apparatus equipped with this dielectric line. The measurement position was 60 mm from the microwave introduction window.
At this time, the microwave introducing port 3 of the reaction container has a width of 280 m.
m and the length was 320 mm. The microwave introduction window 4 was a quartz plate having a width of 360 mm × 380 mm and a thickness of 20 mm.

The conditions for plasma generation are as follows.
The reaction gas is Ar: 30 sccm, the pressure is 10 mTorr.
r, microwave power: 1 kW.

FIG. 9 is a graph showing the distribution of ion current density in the plasma generation region in the Z direction. The plasma generation region is a region from Z = 20 mm to Z = 340 mm. There was a tendency for the ion current density distribution to decay.

From the above results, the thickness of the tapered matching portion of the dielectric line is changed in the width direction, and the thickness is changed from the waveguide opening surface at the end point B to the phase of the center point A at the end position of the tapered matching portion. By reducing the phase shift θdif of, the electric field intensity distribution was made to be a sinusoidal uniform distribution with uniform intensity, and plasma could be generated uniformly.

[0057]

As described above in detail, in the plasma processing apparatus of the present invention, the electric field of the microwave propagating through the dielectric line is made into a single-mode electric field having a uniform intensity level to uniformly generate plasma. it can. Thus, a large-diameter semiconductor substrate and a glass substrate for LCD can be uniformly plasma-processed.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an example of a plasma processing apparatus of the present invention.

FIG. 2 is a perspective view of an example of the plasma processing apparatus of the present invention when the dielectric line is turned upside down.

FIG. 3 is a graph showing the distribution in the Z direction of the electric field strength | Ex | ² of an example of a dielectric line of the plasma processing apparatus of the present invention.

FIG. 4 is a graph showing the distribution of ion current density in the Z direction in an example of the plasma processing apparatus of the present invention.

FIG. 5 is a plan view schematically showing a conventional plasma processing apparatus.

FIG. 6 is a cross-sectional view schematically showing a conventional plasma processing apparatus.

FIG. 7 is a perspective view of the conventional plasma processing apparatus when the dielectric line is turned upside down.

FIG. 8: Electric field strength | Ex | ^{2 of a} conventional plasma processing apparatus
5 is a graph showing the distribution in the Z direction.

FIG. 9: Z of ion current density of a conventional plasma processing apparatus
It is a graph which shows distribution of directions.

FIG. 10 is a schematic diagram showing a situation in which a microwave propagates through a dielectric line.

[Explanation of symbols]

 S sample 1 reaction vessel 2 reaction chamber 3 microwave introduction port 4 microwave introduction window 5 gas introduction hole 6 exhaust port 7 sample stage 8 solvent passage 9 O-ring 21 dielectric line 22 metal plate 23 microwave waveguide 24 tuner 25 Isolator 26 Microwave oscillator 211 Introduction part 212 Tapered matching part 213 Flat plate part

Claims (1)

[Claims] 1. A microwave oscillator, a microwave waveguide, a dielectric line having a tapered matching portion connected to the microwave waveguide, and a microwave introduction window arranged to face the dielectric line. In the plasma processing apparatus provided with a metal reaction container in which the microwave introduction port is hermetically sealed by the microwave introduction window, the thickness in the width direction of the tapered matching part of the dielectric line is increased in the center, Plasma processing equipment characterized by being thinned by.