JPH0637086A - Plasma processing method and apparatus - Google Patents

Abstract

(57) [Summary] [Structure] In a plasma processing apparatus for processing a sample by generating a plasma in an airtight container 4 by a microwave generator 1 and a microwave introducing means 2, a TE 12 having a circular waveguide or a similar one. In the portion of the microwave introducing means 2 having a tube diameter through which the above modes can be passed or in the airtight container 4, a mode filter having different microwave passing rates for at least two modes is provided. [Effect] The mode of the microwave electromagnetic field passing through the portion having a large tube diameter is fixed, the mode jump phenomenon is less likely to occur, and more stable plasma processing becomes possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing method and apparatus, and more particularly to a plasma processing method and apparatus suitable for film formation and etching processing using microwaves.

[0002]

2. Description of the Related Art The demand for microfabrication of a large-area sample is increasing more and more due to the higher integration of semiconductor elements and the larger diameter of the sample. The plasma treatment using microwaves has an advantage that it can generate high-density plasma under a low gas pressure and enables anisotropic treatment with excellent directivity such as ion flow, and thus is applicable to manufacturing of semiconductor integrated circuits. It is being advanced.

FIG. 13 shows a conventional plasma processing apparatus using microwaves. 1 is a microwave generator, 2 is microwave introduction means, 3 is a quartz bell jar, 4 is a metal container, 5 is gas introduction means, 6 is a valve, 7 is exhaust means, 8 is a solenoid coil, 9 is a sample, 10 is A sample stand, 11 is a ground electrode, and 12 is an AC generator. Microwave introduction means 2
In this case consists of a rectangular waveguide 2a, a rectangular-to-circular conversion waveguide 2b, circular waveguides 2c and 2d.

A processing chamber is constituted by the metal container 4 and the quartz bell jar 3 which is hermetically provided at the upper opening of the metal container 4. A predetermined flow rate of the processing gas is introduced into the processing chamber by the gas introduction unit 5, the valve 6 and the exhaust unit 7, and the processing chamber is evacuated to a predetermined pressure under reduced pressure. In this case, the microwave generated by the microwave generator 1 is guided into the processing chamber through the quartz bell jar 3 by the microwave introducing means 2 which is a waveguide. Due to the interaction between the microwave and the magnetic field formed by the solenoid coil 8, the gas in the processing chamber is efficiently turned into plasma. The ions in the plasma are attracted by the AC voltage applied between the sample stage 10 and the ground electrode 11 by the AC generator 12 and are incident on the processed surface of the sample 9 with good directionality.

A device using a microwave of this type for processing a large-diameter sample is disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No.
-44720, JP-A-1-205534, etc. are mentioned.

[0006]

In the above-mentioned conventional device, a rectangular waveguide having a small cross-sectional area is usually used at the output part of the microwave generator. For example, 109 mm × 55.
A BRJ-2 type rectangular waveguide having a mm cross section is used. On the other hand, along with the increase in sample diameter,
The diameter of the circular waveguide surrounding the quartz bell jar is gradually increasing, and the inside diameter of the processing chamber where the sample is placed is as large as about 250 mm or more. As described above, as the inner diameter of the processing chamber increases, it has become more common that plasma excited by microwaves becomes unstable. That is, even if a desired microwave electromagnetic field mode is generated in a waveguide with a small cross-sectional area, if the desired electromagnetic field mode is generated in the waveguide with a large cross-sectional area, the sample surface in the processing chamber, or the plasma generation part, the desired cross-sectional area is It is difficult to generate a stable plasma because a high-order mode other than the mode and a microwave of another mode are generated, and a mode jump phenomenon or the like occurs in relation to the formed plasma.

Table 1 shows the diameter (D) of the circular waveguide and the cutoff wavelength (input
The relationship with c) and the diameter of the circular waveguide that serves as the cutoff of the microwave for each mode at the frequency f = 2.45 GHz are shown. When the frequency f = 2.45 GHz, modes TE11 to TM41 can exist as shown in Table 1 for a circular waveguide having a diameter of 300 mm. However, as the order increases, the proportion of existing modes decreases, and the proportion of existing modes also changes depending on the symmetry of the electromagnetic field of the excited mode.

[0008]

[Table 1]

FIG. 12 (b) shows the mode content in the output when the TE11 mode is input to the tapered waveguide as shown in FIG. 12 (a) with respect to the taper angle θ. It was made clear by the inventors. As the taper angle θ increases, TM11 mode and T
The content rate of E12 mode is increasing. FIG. 12 shows an ideal case, but in an actual device, the content of modes other than the TE11 mode is further increased due to fluctuations in plasma as a load, unevenness of the waveguide, and the like. When the TE11 mode is input, the most mixed modes in the output are the TM11 mode and the TE12 mode, and when excited in the TE01 mode which is one of the other basic modes, the mixed modes are: It was confirmed that TE21 mode and TM21 mode were the most.

An object of the present invention is to provide a plasma processing method and apparatus using microwaves which can generate stable plasma even if the diameter of the processing chamber is increased.

[0011]

SUMMARY OF THE INVENTION In a plasma processing apparatus using microwaves, the above object is to provide microwaves for at least two modes in a circular propagation space having a large diameter in which microwaves of a plurality of modes can exist. A device provided with a mode filter having different transmission rates, and a method of changing the transmission rate of microwaves for at least two modes in a circular propagation space having a large diameter in which microwaves of multiple modes can exist. Is achieved by

[0012]

In a circular propagation space having a large diameter in which multiple modes of microwaves can exist, the microwave electromagnetic field that passes through a portion with a large pipe diameter is obtained by changing the microwave transmission rate for at least two modes. Since the mode is fixed, the jump phenomenon of the mode is less likely to occur, and stable plasma generation is possible.

[0013]

EXAMPLE As confirmed by the tapered waveguide of FIG. 12, when the TE11 mode is input, the TM11 mode and the TE12 mode are the most mixed modes in the output, and these two modes are mixed. It has been confirmed by the present inventors that the stability of the plasma is greatly improved if it is blocked. In addition, TE01 which is one of the other basic modes
When excited by the mode, the mixed mode is TE2
It was similarly confirmed that the 1st mode and the TM21 mode were the most, and that the stability of the plasma was improved by preventing the mixing of these two modes.

As shown in Table 1, the frequency f = 2.45G
The tube diameter through which the TE12 mode of the circular waveguide can pass at 20 Hz is 207.9 mm or more. Other basic modes TM
01, TM11 and other low-order modes TE21, TE31, etc. are mainly used, the TE12 of the circular waveguide is also used.
Alternatively, it was confirmed that the stability of plasma is improved in the same manner as in the TE11 and TE01 modes by installing a mode filter that blocks passage of these modes in a portion through which similar modes can pass.

As a place to install the mode filter, it is effective to install the mode filter in a portion having a large pipe diameter, but there is a drawback that the structure of the filter becomes large. However, in order to effectively produce the filter effect, TE
It is necessary to install in the part of the pipe diameter through which 12 modes can pass. Further, it is effective to install the mode filter in a part of the microwave introducing means, but if the effect is insufficient, install it either in the processing chamber or by installing it separately. Can be increased. When a mode filter is installed in the processing chamber, gas molecules and ions directly collide with the mode filter.Therefore, use a metal whose surface is covered with an insulator to prevent impurities from entering the sample. It is preferable to have it. Also,
Even if the cross section of the waveguide is oval or polygonal other than circular,
The same applies as long as a mode similar to the circular waveguide can be passed.

An embodiment of the plasma processing apparatus of the present invention will be described below with reference to FIGS. 1 and 2. In FIG. 1, the same reference numerals as those in FIG. 13 indicate the same members, and the description thereof will be omitted. 13 is different from FIG. 13 in that the mode filter 13 is arranged in the circular waveguide 2d in front of the quartz bell jar 3 with respect to the traveling direction of the microwave, that is, above the quartz bell jar 3 in the drawing. It is a point provided. Mode filter 1
3 is a conductive metal plate such as aluminum. In this case, as shown in FIG. 2B, a mode filter constituted by disposing a plurality of arc-shaped metal plates having different curvatures in a metal cylinder. 13a. Further, the metal cylinder and the metal plate have the longitudinal direction in a direction substantially parallel to the magnetic field generated by the solenoid coil 8.

When the mode filter 13a is used, only an electric field substantially perpendicular to each arcuate metal plate, that is, an electric field as shown in FIG. 2A can be passed, and the electric field is passed through the mode filter 13a. The possible microwave mode is then the TE11 mode. In other words, the mode filter 13a is provided with the respective metal plates so as to be perpendicular to the electric field of the TE11 mode. By doing so, there is little influence on the desired mode, and the effect of preventing the mixing in other modes is obtained. The length of the mode filter is preferably an integral multiple of 1/4 of the guide wavelength, but can be achieved by installing a plurality of short filters in multiple stages. By the way, in this case,
Even if the mode filter 13 was installed in the circular waveguide 2c having a diameter of 110 mm, there was almost no effect of plasma stabilization, but the mode filter 13 was installed in the circular waveguide 2d having a diameter of 300 mm. As a result, plasma was stabilized.

As described above, according to this embodiment, only the TE11 mode microwave is provided in the circular waveguide surrounding the quartz bell jar just before the quartz bell jar forming the processing chamber, that is, in front of the traveling direction of the microwave. By providing a mode filter capable of passing the microwaves of other modes, the microwaves of the TE11 mode can be introduced into the processing chamber by blocking the passage of microwaves of other modes. The mode of the wave electromagnetic field is fixed, the jump phenomenon of the mode is less likely to occur, and stable plasma can be generated.

The mode filter in this embodiment is a TE filter.
Although it corresponds to the 11 mode, when passing a mode other than the TE11 mode as the desired mode,
For example, a mode filter as shown in FIGS. 3 to 7 may be used.

The mode filter 13b shown in FIG. 3B in which a plurality of metal cylinders having different diameters are concentrically arranged is shown in FIG.
This corresponds to the TM01 mode in which the lines of electric force are as shown in (a). The mode filter 13c formed of a plurality of metal plates radially arranged in the metal cylinder shown in FIG. 4B corresponds to the TE01 mode having electric lines of force as shown in FIG. 4A. The mode filter 13d in which the inside of the metal cylinder shown in FIG. 5 (b) is divided into four equal parts by metal plates and arcuate metal plates are arranged inwardly is shown in FIG. 5 (a). It corresponds to the TE21 mode. The mode filter 13e shown in FIG. 6B in which the inside of the metal cylinder is bisected by a metal plate and a metal cylinder having a small diameter is arranged in each is shown in FIG.
It corresponds to the TM11 mode in which the lines of electric force are as shown in (a). The mode filter 13f shown in FIG. 7B, which is composed of a plurality of metal plates arranged concentrically with two metal cylinders having different diameters and radially arranged between the two metal cylinders, is shown in FIG. It corresponds to the TE12 mode in which the lines of electric force are as shown in.

Next, another embodiment of the plasma processing apparatus of the present invention will be described with reference to FIG. 8, the same reference numerals as those in FIG. 13 indicate the same members, and the description thereof will be omitted. 13 is different from FIG. 13 in that the metal container 4a also serves as a circular waveguide and constitutes a processing chamber, and that the microwave introducing means 2 is provided in the upper opening of the metal container 4a via the quartz plate 14. And the microwave introducing means 2 is constituted by the rectangular waveguide 2e, the rectangular-circular conversion waveguide 2f and the circular tapered waveguide 2g, and the mode filter 17 is provided at the maximum inner diameter portion of the circular tapered waveguide 2g. Is provided and the mode filter 18 is provided in the metal container 4a. The inner wall surface of the metal container 4a, which serves as the discharge part, is covered with an insulator 4b to prevent impurities and the like from entering the sample.

In this case, the pipe diameters of the portions where the mode filters 17 and 18 are installed are, for example, 250 mm and 300 mm, respectively. In this case, the mode filters 17 and 18 have the TE11 mode shown in FIG. 9 is a modification of the mode pass filter corresponding to
The one shown in is used. For the sake of explanation, the mode pass filter 17 is used in FIG. Mode pass filter 17
Divides a metal cylinder 20 having a length L and an inner diameter of 2R into two semi-cylinders by a partition plate 21 passing through the center, and further dividing each semi-cylinder into arc-shaped partition plates 22a and 22.
b is provided. The distance d ₁ between the center of the metal cylinder 20 and the partition plates 22a and 22b is set at a position satisfying the relationship of 0.4 ≤ d ₁ / R ≤ 0.6.
The pass rate of modes other than the mode can be reduced. As shown in FIG. 10, when the partition plate 21 is provided with an axial slit at a position d ₂ from the center of the metal cylinder 20, TE1 is formed.
The pass rate in modes other than 1 is further reduced. As d ₂ , the relationship of 0.3 ≦ d ₂ / R ≦ 0.4 is satisfied, and the width t ₁ of the axial slit is t ₁ / t ₀ ≦ 2 with respect to the thickness t ₀ of the partition plate 21. The effect is remarkable when the condition is satisfied. The width t ₁ of the axial slits and the slit interval t ₂ may be t ₁ ≈t ₂ .

The mode pass filter 1 shown in FIG.
As a modification of 7, a metal cylinder 20 having an inner diameter of 2R is divided into two semi-cylinders by a partition plate 21 passing through the center, and each semi-cylinder is bent into a trapezoidal shape, or three flat plates as shown in FIG. A plurality of partition plates 23a, 24a and 23b, 24b formed by connecting the above may be provided. Ideally, this partition plate should be completely perpendicular to the microwave electric field when there is no partition plate, but due to manufacturability, even a slight deviation does not pose a practical problem. The distance d ₃ between the center of the metal cylinder 20 and the partition plates 23a, 23b and the center of the metal cylinder 20 and the partition plates 24a, 2b
The distance d ₄ with respect to 4b is set to a position satisfying the relation of 0.35 ≤ d ₃ / R <d ₄ / R ≤ 0.65.
The pass rate of modes other than the mode can be reduced. Although four partition plates 22 are shown in FIG.
In the case of more than one, the same effect is obtained if four of them satisfy the above formula.

According to this embodiment, it is possible to block the passage of microwaves of other modes and introduce only the microwaves of a desired mode as in the case of the first embodiment, so that stable plasma is generated. There is an effect that can be. In addition, since the mode filters can be arranged in front of and behind the processing chamber to control the mode in two steps, there is an effect that more stable plasma can be generated.

In addition to the mode filter described in the present embodiment, it goes without saying that the mode filters 13a to 13f described in the above embodiments may be used according to the desired mode.

[0026]

EFFECTS OF THE INVENTION In a circular propagation space having a large diameter in which microwaves of a plurality of modes can exist, microwaves passing through a portion having a large pipe diameter are changed by changing the microwave passage rate for at least two modes. Since the mode of the electromagnetic field is fixed, the jump phenomenon of the mode is less likely to occur,
There is an effect that stable plasma can be generated. This allows stable plasma processing of large-diameter samples.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an example of a mode filter used in the present invention.

FIG. 3 is a diagram showing an example of a mode filter used in the present invention.

FIG. 4 is a diagram showing an example of a mode filter used in the present invention.

FIG. 5 is a diagram showing an example of a mode filter used in the present invention.

FIG. 6 is a diagram showing an example of a mode filter used in the present invention.

FIG. 7 is a diagram showing an example of a mode filter used in the present invention.

FIG. 8 is a vertical sectional view showing another embodiment of the plasma processing apparatus of the present invention.

FIG. 9 is a diagram showing an example of a mode filter used in the present invention.

FIG. 10 is a diagram showing details of a slit portion of FIG.

FIG. 11 is a diagram showing an example of a mode filter used in the present invention.

FIG. 12 is a diagram showing a shape of a tapered waveguide and a mode content rate of microwaves in the tapered waveguide.

FIG. 13 is a vertical sectional view showing an example of a conventional plasma processing apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Microwave generator, 2 ... Microwave introduction means, 2d ... Circular waveguide, 3 ... Quartz bell jar,
4, 4a ... Metal container, 5 ... Gas introduction means, 6 ...
..Valves, 7 ... Exhaust means, 8 ... Solenoid coils, 9 ... Samples, 10 ... Sample stands, 11 ... Ground electrodes, 12 ... AC generators, 13 ... Mode filter, 14 ... Quartz plate.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H01P 1/16 H05H 1/18 9014-2G

Claims (9)

[Claims] 1. A plasma processing method using microwaves, characterized in that a microwave transmission rate is changed for at least two modes in a circular propagation space having a large diameter in which microwaves of a plurality of modes can exist. And a plasma processing method. 2. In a plasma processing apparatus using microwaves, a mode filter having different microwave passage rates for at least two modes is provided in a circular propagation space having a large diameter in which microwaves of a plurality of modes can exist. A plasma processing apparatus comprising: 3. The plasma processing apparatus according to claim 2, wherein the mode filter is configured by disposing a plurality of arc-shaped metal plates having different curvatures in a metal cylinder. 4. The plasma processing apparatus according to claim 2, wherein the mode filter is configured by concentrically disposing a plurality of metal cylinders having different diameters. 5. The plasma processing apparatus according to claim 2, wherein the mode filter is configured by radially disposing a plurality of metal plates in a metal cylinder. 6. The plasma processing apparatus according to claim 2, wherein said mode filter is configured such that the inside of the metal cylinder is divided into four equal parts by metal plates and arc-shaped metal plates are respectively arranged inward. 7. The plasma processing apparatus according to claim 2, wherein the mode filter is configured such that the inside of the metal cylinder is bisected by a metal plate and a metal cylinder having a small diameter is arranged in each of the two parts. 8. The plasma processing according to claim 2, wherein the mode filter is configured by concentrically disposing two metal cylinders having different diameters and radially disposing a plurality of metal plates between the two metal cylinders. apparatus. 9. An airtight container having a sample table in which a sample can be placed, gas introducing means for introducing gas into the airtight container, exhaust means for decompressing and exhausting the airtight container, and microwave generation. A microwave generator and microwave introducing means for transmitting microwave power from the microwave generator into the airtight container, and a part of the microwave introducing means or a circular waveguide in the airtight container. Tube TE12
Alternatively, the plasma processing apparatus is characterized in that a tube diameter through which a mode similar to it can pass is provided, and a mode filter through which a microwave of a desired mode can pass is provided in a part of the microwave introducing means or in the airtight container.