JP3085155B2 - Plasma processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to etching, ashing, and CVD of a large-diameter semiconductor element substrate, a large-sized liquid crystal display (LCD) glass substrate, and the like using plasma.
And the like.

[0002]

2. Description of the Related Art Reactive gas plasmas are widely used in LSI and LCD manufacturing processes. In particular, dry etching technology using plasma has been
And it is an indispensable basic technology for the LCD manufacturing process.

Generally, microwaves of 2.45 GHz and 13.56 GHz are used as excitation means for generating plasma.
MHz RF (high frequency) is used. The use of a microwave has advantages over a case of using an RF in that plasma can be obtained at a lower temperature and a higher density, and there is no problem of contamination from the electrode because an electrode is unnecessary.

However, since it is difficult to generate uniform plasma over a large area with a plasma processing apparatus using microwaves, it is difficult to uniformly process a large-diameter semiconductor substrate or an 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 over a large area (Japanese Patent Laid-Open No. Sho 62-5600). No., JP-A-62-99
481).

FIGS. 5 and 6 are a schematic plan view and a partial cross-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 is 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 is transmitted through the microwave introduction window 4 and supplied into the reaction chamber 2 to excite the reactive gas to generate plasma. The plasma treatment is performed on the surface of the sample S by this plasma.

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

The width of the tapered alignment portion 212 is
1, the width is linearly changed from the width W0 of 1 to the width W2 of the flat plate portion 213. The thickness of the tapered matching portion 212 is equal to the thickness T0 of the introduction portion 211 in the Z direction, which is the traveling direction of the microwave.
And linearly changes to the 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 device is performed as follows. In the introduction unit 211, the microwave propagating through the microwave waveguide 23 is introduced into the dielectric line 21, and the rectangular TM ₁₁
The mode microwave surface wave propagates. In tapered matching section 212, a microwave of the rectangular TM ₁₁ mode is expanded in the width direction. Microwaves spread was rectangular TM ₁₁ mode is introduced to the flat plate portion 213. By providing a tapered matching section 212, a microwave rectangular TM ₁₁ mode, without the higher order mode generating, large-area flat portion 2
13 to be propagated.

In the plasma processing apparatus having the dielectric line, since the microwave can be uniformly introduced and propagated into the large-area flat plate portion 213, the microwave introduction window 4 facing the flat plate portion 213 and the microwave conducting window 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 generation portion, and the high-order mode microwaves applied to the flat plate portion 213. It comprises a tapered matching section 212 for introducing microwaves without generation. Since the tapered matching portion 212 is not directly related to plasma generation, it is preferable that the taper matching portion 212 be shorter, since the size of the plasma processing apparatus can be reduced.

However, the tapered matching portion 212
Is simply shortened, the basic mode rectangle T
Microwave surface-wave of the M ₁₁ mode is attenuated, higher order modes are generated. Unlike the propagation of the fundamental mode microwave, which has a regular microwave electric field intensity distribution when the higher-order mode occurs, the microwave is a superposition of a plurality of modes, so that the electric field intensity distribution in the traveling direction of the microwave is improper. Become uniform. As a result, the distribution of the plasma generated by this electric field also becomes non-uniform. For this reason, there is a problem that the length of the tapered matching portion 212 cannot be simply shortened.

Further, the diameter of the semiconductor substrate is increased and LC is increased.
As the area of the glass substrate for D increases, the size of the flat plate portion 213 needs to be increased.
12 has to be made larger.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made in consideration of the above-described circumstances. It is an object of the present invention to provide a plasma processing apparatus capable of uniformly generating plasma over a large area by using a mode microwave.

[0016]

The electric field of the microwave propagating on the flat portion of the dielectric line leaks from the lower surface of the open dielectric line. The leaked electric field passes through the microwave introduction window and generates 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 near the microwave introduction window reflects the electric field intensity distribution. However, the generated plasma is uniformed by diffusion as the distance from the microwave introduction window increases, so that the generated plasma becomes uniform near the sample stage.

What makes the plasma non-uniform is the attenuation of the peak value of the electric field strength in the traveling direction of the microwave, which is caused by the generation of higher-order mode microwaves.

For this reason, the generation of high-order mode microwaves is suppressed by providing a tapered type matching portion, and the microwaves propagating in the flat plate portion of the dielectric line are converted into a single mode of uniform intensity level in the traveling direction. Microwaves are being used.

The generation of the high-order mode microwaves and the tapered matching section will be described. FIG. 10 is a schematic diagram illustrating 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 end position 212E of the tapered matching portion, a phase shift occurs at the center portion A and at the end portion B. When the phase shift θdif between the phase at the central portion A and the phase at the end portion B exceeds 3π / 4 (radian), microwaves in higher-order modes are easily generated.

The deviation θdif between the phase at the center A and the phase at the end 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 opening surface 212S to the end B, ∫ _A ds1
Denotes the integral 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 by a function of position, λ
g is a function of position.

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

The distance difference d is approximated by 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 substantially 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 waveguide 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 tapered matching portion is increased in proportion to the square. It is necessary to increase the length L.

[0025]

(Equation 1)

In order to reduce the phase shift θdif, the present inventor based on the above equation (1) requires that
It is noted 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 center A may be different (see FIG. 10). In order to change the propagation wavelength λg, the thickness of the dielectric at that position may be changed. That is, the propagation wavelength λg can be shortened by increasing the thickness, and the propagation wavelength λg can be reduced by decreasing the thickness.
Paid attention to the fact that it can be made long, and completed the present invention.

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 thick at the center and thin at the ends. By doing so, the propagation wavelength λg of the microwave propagating in the center of the tapered matching section 212 of the dielectric line 21 is made shorter than the propagation wavelength λg of the microwave propagating in the end. 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, the generation of higher-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 levels are made uniform in the traveling direction. A single mode microwave can be propagated without attenuation. As a result, the electric field intensity distribution becomes a uniform sinusoidal distribution with uniform intensity,
A uniform plasma can be generated near the sample stage in the reaction chamber.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of a plasma processing apparatus according to the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing one example of this plasma processing apparatus.

The microwave oscillator 26 is connected to the dielectric line 21 via the microwave waveguide 23. A fluororesin 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, there are provided a tuner 24 for matching microwaves and an isolator 25 for removing reflected microwaves.

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 from the microwave waveguide 23 into the dielectric line 21 at the introduction part 211, expanded in the width direction at the tapered matching part 212, and introduced into the flat plate part 213. In this way, the microwaves are uniformly propagated in the flat plate portion 213 without generation of higher-order modes.

The reaction vessel 1 is made of a metal such as aluminum (Al) into a hollow rectangular parallelepiped. A reaction chamber 2 is provided inside the reaction vessel 1. A microwave introduction port 3 is opened in the upper part of the reaction vessel 1, and the microwave introduction port 3 is connected between the microwave introduction window 4 and an 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 material having heat resistance and microwave permeability and low dielectric loss, such as quartz glass (SiO ₂ ) and alumina (Al ₂ O ₃ ).

In the reaction chamber 2, a sample table 7 on which the sample S is to be mounted is disposed 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 vessel 1,
By circulating a solvent at a predetermined temperature through the solvent passage 8, the reaction vessel 1 can be maintained at a predetermined temperature. A gate valve (not shown) for carrying the sample S into and out of the reaction chamber 2 is provided on the side wall of the reaction vessel 1.

A method for 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 reaction chamber 2 is evacuated to a required pressure by exhausting air from the exhaust port 6, a reaction gas is supplied from the gas introduction hole 5 to bring the reaction chamber 2 to a predetermined pressure.

A microwave is oscillated by a microwave oscillator 26, and is passed through a microwave waveguide 23 to a dielectric line 21.
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 is transmitted through the microwave introduction window 4 and 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 a dielectric line of the plasma processing apparatus of the present invention, and is a perspective view when the dielectric line is turned upside down. In the connection portion between the tapered matching portion 212 and the flat plate portion 213 of the dielectric line of this example, the center portion is flat with a thickness T2, the end portion is a thickness T1, and the thickness between the center portion and the end portion is It changes linearly. Of course, T2> T1. The thickness may be changed in a curved manner.
The width W1 of the central portion may be different from the width W0 of the introduction portion 211.

[0040]

【Example】

(Embodiment) Hereinafter, an embodiment of the plasma processing apparatus of the present invention will be described. The plasma processing apparatus of this embodiment is as shown in FIG. 1, and the dielectric line is as shown in FIG.

The dielectric line of this example 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
The thickness T1 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 portion is 300 mm, the width W1 of the central portion is 96 mm, and the thickness T.
2 is 27 mm, the thickness T1 of the end 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 is used.
_{For the 11} modes, the deviation θdif between the phase on the center line at the end position of the tapered matching section 212 and the phase from the waveguide opening surface at the end is π / 4.

The intensity of the electric field leaking from the open surface of the dielectric waveguide of this example was measured. The measurement was performed by scanning the loop antenna in the Z direction, which is the traveling direction of the microwave, with the end of the tapered matching section 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.
5 is a graph showing the distribution of Ex | ^{2 in} the Z direction. The electric field strength | Ex | ² was normalized by the maximum value. The electric field strength | Ex | ² is distributed sinusoidally in the Z direction, which is the direction in which microwaves travel, and there is not much attenuation in the Z direction. At this time, the microwave frequency is 2.45 GHz.
z, microwave power was 40 mW.

Next, the ion current density distribution was measured in a 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 inlet 3 of the reaction vessel has a width of 28.
0 mm and 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, and the pressure is 10 mTorr.
r, microwave power: 1 kW.

FIG. 4 is a graph showing the distribution of ion current density in the Z direction in the plasma generation region. The plasma generation region is a region from Z = 20 mm to Z = 340 mm. A substantially 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 apparatus 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 part 211 of the rectangular waveguide is 96 m.
m, thickness T0 is 27 mm. The length L1 of the tapered matching part 212 is 150 mm. The width W2 of the flat plate portion 213 is 300 m
m, thickness T1 is 20 mm, and length L2 is 350 mm. The thickness of the tapered matching portion 212 is constant in the width direction, and linearly decreases so as to become the thickness T1 of the flat plate portion 213 at the end in the Z direction, which is the traveling direction of the microwave.

[0050] At this time, with respect to the rectangular TM ₁₁ mode which is a fundamental mode of the microwave frequency 2.45 GHz, the waveguide opening of the phase and the end of the central line at the end position of the tapered matching section 212 Phase shift θdif is 3π / 4
Becomes

The intensity of the electric field 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 according to the present invention.
5 is a graph showing the distribution of Ex | ^{2 in} the Z direction. The electric field strength | Ex | ² was normalized by its maximum value. Electric field strength | Ex
| ² indicates an overall attenuation different from the attenuation due to the wavelength of the standing wave in the Z direction, which is the traveling direction of the microwave. At this time, the frequency of the microwave was 2.45 GHz, and the microwave power was 40 mW.

Next, the ion current density distribution was measured in a plasma processing apparatus equipped with this dielectric line. The measurement position was 60 mm from the microwave introduction window.
At this time, the microwave inlet 3 of the reaction vessel has a width of 280 m.
m and length were 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, and 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 was changed in the width direction, and the thickness of the tapered matching portion was changed from the waveguide opening surface at the end point B with respect to the phase of the center point A at the end position of the tapered matching portion. By reducing the phase shift θdif, the electric field intensity distribution was made a sinusoidal uniform distribution with uniform intensity, and the plasma could be generated uniformly.

[0057]

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

[Brief description of the drawings]

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

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

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

FIG. 4 is a graph showing the distribution of the ion current density in the Z direction of one 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 when a dielectric line of a conventional plasma processing apparatus is viewed upside down.

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

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

FIG. 10 is a schematic diagram showing a situation where 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 table 8 Solvent passage 9 O-ring 21 Dielectric line 22 Metal plate 23 Microwave waveguide 24 Tuner 25 Isolator 26 Microwave oscillator 211 Introduction section 212 Tapered matching section 213 Flat section

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05H 1/46 C23C 16/50 C23F 4/00 H01L 21/3065

Claims (1)

(57) [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 disposed to face the dielectric line. In a plasma processing apparatus provided with a metal reaction vessel in which a microwave introduction port is hermetically sealed by the microwave introduction window, a thickness in a width direction of a tapered matching portion of the dielectric line is increased at a center, A plasma processing apparatus characterized in that it is made thinner.