JPH0785437B2 - Plasma generation source by microwave excitation - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plasma generation source using microwave-excited electron cyclotron resonance, which is used as a generation source of plasma ions radicals.

[Conventional technology]

Etching, film formation, and ion implantation technology using activated particles such as plasma and ions are widely used as fine and high-definition manufacturing technology for semiconductor LSIs. Various types of discharge have been studied as a plasma generation source for generating plasma. Among them, plasma discharge using electron cyclotron resonance by microwave excitation (ECR discharge)
Is capable of discharging at a low pressure (1 × 10 ^-5 Torr or less), the ions are aligned in the same direction, a high-density plasma can be generated, and since it is an electrodeless discharge, it has a long life and can use active gas. It is attracting attention because it has excellent characteristics.

FIG. 2 shows the basic configuration of a conventional plasma generation source using ECR discharge. 1 is a plasma generation chamber, 2 is a microwave introduction window, 3 is a waveguide, 4 is a magnetic coil, 5 is a gas introduction port,
Reference numeral 6 is a plasma limiter, and 7 is an extracted plasma flow. Gas is introduced into the plasma generation chamber 1 through the gas inlet 5.
A microwave (for example, 2.45 GHz) is introduced from the waveguide 3 (a microwave oscillation source, an isolator, a matching device, and a microwave power meter are omitted in the figure), and a magnetic coil 4
Therefore, when a DC magnetic field (875 Gauss) under the electron cyclotron resonance (ECR) condition is ignited in a direction perpendicular to the microwave electric field, these interactions cause the plasma generation chamber 1
The gas introduced into the plasma becomes plasma.

In the configuration of the plasma generation source that introduces microwaves into the plasma generation chamber through the microwave introduction window 2 as described above, the cavity of the plasma generation chamber 1 is configured to propagate microwaves. This is because it is necessary to excite the electrons in the cavity chamber with microwaves in order to generate plasma, and for that purpose, it is premised that the microwaves propagate into the cavity chambers.

As described above, the inner diameter of the conventional plasma generation chamber had a size required to propagate the microwave without loss.
For example, when a cylindrical or rectangular waveguide is used in the plasma generation chamber, the wavelength (cutoff wavelength) λ _c of the microwave corresponding to the cutoff frequency at which the microwave does not propagate is expressed by the following equation.

λ _c = 2a (TE ₁₀ mode of rectangular waveguide, a is the length of one side)
…… (1) λ _c = 2πr / 1.84 (TE ₁₁ mode of cylindrical waveguide, r is radius) …… (2) Therefore, cylindrical waveguide with inner diameter of 7.15 cm or more for microwave of 2.45 GHz A tube or a rectangular waveguide having 6.1 cm or more on one side (hereinafter, such a diameter and the size of one side is referred to as a diameter dimension) (the length of the other side is not limited) is the minimum. It is necessary, and in actuality, 1.6 times or more of this value was required in consideration of the propagation loss of microwaves.
That is, the inner diameter of about 11 cm or more is required for the plasma generation chamber using the cylindrical waveguide.

This also applies to the waveguide 3 for introducing microwaves, and if a rectangular waveguide is used to propagate microwaves without loss, one side has a value of 1.
It was necessary to use a waveguide having a dimension more than 6 times (for example, a rectangular waveguide of 10.9 × 5.46 cm, 9.6 × 2.7 cm is standardized).

Further, the plasma generation chamber usually has a resonance mode configuration in order to increase the electric field strength and efficiently absorb microwaves in the plasma. In general, the guide wavelength λ _n in the waveguide
Is It is represented by. Here, λ _c is the cutoff wavelength represented by the formulas (1) and (2), and λ is the wavelength of the microwave used. Therefore, the cavity of the plasma generation chamber becomes smaller and λ
As / λ _c approaches 1, the in-tube wavelength becomes longer. The resonance length of the basic resonance mode (lowest order mode) is
Since the wavelength is half the wavelength in the tube, if the cavity is made thin, the plasma generation chamber of the resonance mode configuration becomes elongated. As a result, the magnetic circuit that obtains the desired distribution becomes complicated, the number of collisions between plasma and the tube wall increases, and the plasma density decreases,
It is predicted that high efficiency plasma generation will be difficult due to contamination due to spattering.

Now, as a guide, when the condition that the axial length of the cavity is smaller than the inner diameter D is calculated by configuring the plasma generation chamber in the basic resonance mode, (However, A is 2 for a rectangular waveguide and π / 1.84 for a cylindrical waveguide.) Here, D ₀ is the inner diameter of the waveguide whose cutoff wavelength is the wavelength of the microwave used. Therefore, from the above viewpoint, a waveguide having an inner diameter of at least 1.3 to 1.4 times D ₀ is required. Conventionally, the plasma generation chamber of ECR plasma CVD equipment and ECR ion shower etching equipment usually has a diameter
It consisted of a 20 cm TE ₁₁₃ resonant mode configuration cavity (for example, the Japanese Journal of Applied Phisic).
s) Vol. 22, No. 4, (1983) L210-212).

[Problems to be solved by the invention]

As described above, in the configuration in which the microwave is introduced by directly connecting the rectangular waveguide to the plasma generation chamber formed of the conventional cylindrical cavity,
It is determined according to the frequency of the microwave to be used in consideration of various conditions. The size of the plasma was smaller than 1.6 times the minimum size required to propagate the microwave, and a smaller plasma generation source was not realized. Also,
Actually, the size of the wafer to be used has been increasing to 6 to 8 inches as a conventionally used apparatus for manufacturing LSI, so that there is no particular demand for downsizing.

However, the plasma generation source by microwave excitation is more likely to be used in various fields in the future, and there is a demand for a small ion source having a small outer shape. However, including the possibility of reducing the diameter of the plasma generation chamber, the size of the microwave introduction waveguide that introduces microwaves into the plasma generation chamber, and the size of the microwave coupling opening that couples microwaves with plasma. For example, no study has been made to reduce the size of the plasma generation source.

[Means for solving problems]

According to the present invention, as a means for reducing the size of a plasma generation source by microwave excitation, the inside wavelength of the microwave in the plasma generation chamber when the plasma generation chamber is a waveguide is λ
_{where n is} the axial length of the plasma generation chamber, the plasma generation chamber is a cavity having an axial length that satisfies L <λ _n / 2, the waveguide is on the microwave coupling opening side, and the cutoff wavelength is dielectric. Converted to the state that the body is not filled,
It has 1.2 times the size.

[Action]

In this way, even with a size that is 1 to 1.2 times the wavelength of the microwave, the microwave is propagated to the plasma generation chamber even if only slightly, and plasma is generated. Moreover, when the plasma is generated, that portion becomes equivalent to being filled with a dielectric (plasma) having a high dielectric constant, and the plasma is constantly generated.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 8 is a microwave introduction waveguide for introducing microwaves into the plasma generation chamber, 9 is a microwave introduction window, 10 is a microwave coupling opening for coupling the microwaves with the plasma generation chamber, 11 Is a plasma generation chamber, 12 is a cooling water inlet (the cooling water outlet is omitted in this figure), 13 is a gas inlet, 14 is a magnetic coil, 15 is a plasma limiter, and 16 is a plasma flow. . Although the microwave matching section, the microwave power type, or the microwave circuit portion such as the microwave oscillation source and the isolator is not shown in the drawing, it is needless to say that they are used as necessary.

Here, as the waveguide 8 for introducing microwaves, three types of rectangular waveguides having a side length of 7 cm and the other side lengths of 2.7 cm, 2 cm, and 1 cm were used. As described above, such a waveguide having such a small diameter is not generally used, and in this embodiment, the waveguide 8 is a commercially available waveguide 17 (for example, 9.6 × 2.7 cm).
The rectangular waveguide 18) is used to connect with the tapered waveguide 18. This is because the cost of manufacturing the waveguide itself is high if the waveguide 8 alone is used, and
In accordance with that, it is necessary to specially make the above-mentioned various microwave circuit parts, and further, since the microwave is repeatedly reflected and propagated on the inner wall of the waveguide, the attenuation is large, and high power is supplied to the plasma generation chamber. This is because it is not always easy to bring in the density, and there is a possibility that the waveguide absorbs microwaves and is overheated. That is, it propagates in a commercially available waveguide of a larger diameter dimension (thus, a commercially available microwave circuit component can be used between them), and the diameter dimension is reduced by a tapered waveguide at the microwave coupling opening side. In this way, the cost of the waveguide and other microwave circuit components can be kept low, and the microwave power density can be easily increased.

In this embodiment, due to the arrangement of the magnetic coil 14, the cooling water inlet 12 and the gas inlet 13, the waveguide 8 having no taper is interposed, and then the commercially available waveguide 18 is provided by the tapered waveguide 18. tube
Although it is connected to 17, the microwave propagated by the commercially available waveguide 17 is directly used for the plasma generation chamber via the tapered waveguide 18 without using the waveguide 8 as is clear from the above description. It goes without saying that it may be introduced into.

As the plasma generation chamber 11, three types of cylindrical waveguides having inner diameters of 9 cm, 8 cm, and 7 cmφ were used. Microwave introduction window 9
A quartz window of 8 cmφ was used as The microwave introduction window 9 needs to be not only introduced into the plasma generation chamber but also must be vacuum-sealed so that the plasma generation chamber 11 can be evacuated to a vacuum. Therefore, the size of the microwave coupling opening 10 is, of course, smaller than the inner diameter of the plasma generation chamber 11, but is smaller than the microwave introduction window 9 by 2 cm or more because of the O-ring press for vacuum sealing. Is desirable. The size of this opening 10 is 6 cm, 4.5 cm, 3c, which is the size that blocks the propagation of microwaves at 2.45 GHz.
Three types of mφ were examined. Even if the largest plasma generation chamber of 9 cm is used, the external size of the plasma generation source including the magnetic circuit is 17 to 16 cm or less, and the size that can be easily installed at any place of the device through the flange. It was by weight. Furthermore, if a coaxial waveguide converter that excites microwaves in a waveguide via a coaxial cable is used, its usage becomes simpler.

In such a configuration, microwaves of 2.45 GHz are introduced from the microwave introduction waveguide 8, gas is introduced into the plasma generation chamber 11 through the gas introduction port 13, and the ECR condition is satisfied inside the plasma generation chamber 11. A plasma was generated by applying a magnetic field of 875 Gauss or more. As described above, the microwave guiding waveguide 8 has a side of 10.9 cm and 9.6 cm.
7c, which is much smaller than the cutoff wavelength (comparable to the standard product and used for conventional plasma generation sources)
A rectangular waveguide of m was used, but there was no problem during heating even for long-term use. Also, the diameter of the circular waveguide corresponding to the cutoff frequency of microwaves for 2.45 GHz is
Although it was 7.15 cm, the microwave coupling opening 10 having an inner diameter smaller than that (thickness up to 3 cmφ was examined) was used, but no difference was observed in the characteristics of the plasma generation source.

Thus, it was found that a high-performance plasma generation source can be realized even if each component is made small.
It is considered that once the plasma is generated, the permittivity of that portion becomes the permittivity of the plasma and microwaves are easily introduced. In particular, it has been found that the microwave coupling opening 10 may be sized to block microwaves. That is, the plasma generation chamber 11 and the waveguide 8 must be larger than the size of the microwave coupling opening 10 inevitably, which is necessary in the present invention to propagate the microwave used. The miniaturization to the minimum size is also premised on that the microwave coupling opening 10 may be smaller than that. From the above-described mechanism of plasma generation, generally, the magnetic field in the vicinity of the microwave coupling opening 10 is set to a magnetic field that satisfies the ECR condition in which plasma discharge can be easily started, and after the plasma is generated, high It is desirable to adjust the magnetic field distribution to generate the density plasma.

The microwave generation source of this embodiment has the following features.

(A) Since the microwave introduction waveguide 8 for introducing microwaves and further the plasma generation chamber 11 are downsized, the power density becomes higher with respect to the same microwave power, and low microwave power is obtained. A high density plasma is obtained.
For example, if electric power is transmitted by a coaxial cable, it is difficult to achieve power of 200 W or more, and in such a case, it is particularly effective.

(B) Since the cavity of the plasma generation chamber 11 is small, it is possible to make the radial direction of plasma the same condition, and it is easy to obtain uniform plasma in the radial direction.

(C) In the plasma generation chamber, high-density plasma can be obtained without the resonance mode configuration. In this experiment, the ion source is configured by making the axial length and the inner diameter of the plasma generation chamber 11 substantially equal. That is, the axial length is smaller than 1/2 of the in-tube wavelength with respect to the plasma generation chamber having the inner diameter of 7 cm, 8 cm, and 9 cm, and the axial length is shorter than that in the resonance mode configuration. In this way, good results can be obtained with a compact and non-resonant mode configuration.If the plasma generation chamber is made smaller, the wavelength inside the tube becomes longer, so that the strong electric field region of the microwave expands, and the microwave in that region is expanded. It is considered that this is because the absorption efficiency (conversion efficiency) to plasma increases. Therefore, the first 1 / th of the microwave introduced into the plasma generation chamber
Microwaves are highly efficiently absorbed by the plasma between the two wavelengths, so that high-density plasma is generated in the plasma chamber having a short axial length.

With such a configuration, specifically, downsizing can be realized to the extent shown below (when the microwave used is 2.45 GHz).

Size of plasma generation chamber: Assuming that a cylindrical waveguide is used, theoretically, it is possible to reach up to about 7.2 cmφ, but it was experimentally confirmed that 7 cmφ is also acceptable. Therefore, even if gas introduction and water cooling are taken into consideration, the outer shape of the plasma generation chamber can be reduced to 9 cm or less.

Size of the microwave introducing waveguide on the microwave coupling opening side: In principle, the cutoff wavelength can be up to about 6.1 × 0.5 cm, which is almost equal to the microwave wavelength,
External shape considering the wall thickness of the waveguide and the flange for screwing
It can be up to 8 cm. Even if a 7 × 1 cm rectangular waveguide is used, the outer shape can be made 9 cm or less.

Size of microwave introduction window: This window must be larger than the opening of the microwave introduction waveguide in order to introduce the microwave into the plasma generation chamber without reflecting or absorbing it. Moreover, considering the size of the holding portion of the window and the passage of the gas introduction pipe, it is desirable that the window be smaller than the inner diameter of the plasma generation chamber. Therefore, the size of the microwave introduction window is about 7 cm due to these two restrictions.

Microwave coupling opening size: It is desirable that the size is about 2 cm smaller than the microwave introduction window because the plasma generation chamber is vacuum-sealed. Therefore, it may be set to 5 cm or less, but as a result of experiments, it has been confirmed that it may be set to 3 cm, and this is not a big limitation as described above.

Based on the above, the outer diameter is 9 cmφ (the outer diameter is 8
cmφ ... For example, the removal of cooling water, the use of a 6.1 cm microwave introduction waveguide) can realize a plasma generation source,
Even including the magnetic coil, a plasma generation source with an outer diameter of 14 (~ 13) cmφ can be constructed.

In the above description, the case where the microwave introducing waveguide 8 and the microwave coupling opening 10 are not filled is described, but it goes without saying that these portions may be filled with a dielectric. Yes. When the permittivity of the dielectric material filled in the waveguide is ε, the size of the waveguide can be reduced in inverse proportion to the 1/2 power of the permittivity ε for microwaves of the same frequency. For example, filling a dielectric with a dielectric constant of 4 is equivalent to a waveguide that is half the size. Dielectric materials that can be used include quartz (dielectric constant 4), BN (4), forthulite (6.2), steatite (6), alumina (9). In addition, in using this filler, quartz is used for the part that requires non-degassing and heat resistance against contact with plasma, and that requires airtightness and flatness for vacuum sealing. It is desirable to use alumina or the like. When the dielectric is used as described above, the above-mentioned condition is eliminated under a large constraint condition, but the structure is only complicated, and the size of the plasma generation source cannot be substantially reduced.

In the above, the case where it is mainly used as a plasma / radical generation source has been described. However, the plasma generation source of the present invention is a high-density / high-current ion source if an ion extraction electrode system having a three-electrode structure with an acceleration-deceleration structure is used. Is effective as. Further, if a single-electrode / single-leaf mesh electrode is used, it is also effective as a generation source of low energy ions.

〔The invention's effect〕

According to the present invention, when the plasma generation chamber is a waveguide, the microwave wavelength in the plasma generation chamber is λ _n , the axial length of the plasma generation chamber is L, and the plasma generation chamber has L <λ _n / Consisting of a cavity with an axial length that satisfies 2,
The waveguide is on the side of the microwave coupling opening, and its cutoff wavelength is converted to a state in which the dielectric is not filled, and is 1 of the microwave wavelength.
By making the size 1.2 times larger, the plasma generation source can be made smaller. For the same microwave power, the smaller the size, the higher the power density and the longer the wavelength inside the plasma generation chamber, so the microwave is converted to plasma with high efficiency, and the low power consumption and high density plasma Can be generated.

Since it can be used as a source of small plasma, ions, and radicals in this way, it accelerates the surface reaction with a complex device added to the MBE device, MOCVD device, plasma application device, etc.
By increasing the efficiency of doping, the etching and film forming technology can be highly controlled. Also, by installing an accelerating-decelerating ion extraction electrode, it can be used as a small high-current ion source and is promising as an ion source for an ion implantation device, and low energy can be obtained by using a single-electrode / single-leaf mesh electrode. It is also effective as a source of ions.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional example. 8 ... Waveguide for microwave introduction, 10 ... Microwave coupling opening, 11 ... Plasma generation chamber, 13 ... Gas inlet, 14
…… Magnetic coil, 18 …… Tapered waveguide.

Claims (3)

[Claims] 1. A plasma generating chamber for generating plasma,
In a plasma generation source by microwave excitation provided with a waveguide for introducing microwaves into the plasma generation chamber through a microwave coupling opening, the plasma generation chamber when the plasma generation chamber is a waveguide wherein the guide wavelength of the microwave lambda _n, the axial length of the plasma generating chamber as L in, consists cavity having an axial length of the plasma generating chamber satisfies L <λ _n / 2,
The microwave is characterized in that the waveguide has a dimension such that the cutoff wavelength is 1 to 1.2 times the wavelength of the microwave when converted into a state in which the dielectric is not filled on the microwave coupling opening side. Plasma generation source by excitation. 2. The first waveguide having a diameter larger than the diameter of the microwave coupling opening, and the first waveguide.
2. A plasma generation source by microwave excitation according to claim 1, further comprising a tapered waveguide connected to the waveguide of FIG. 3. The microwave coupling opening has a dimension such that its cutoff wavelength is a wavelength smaller than the wavelength of the microwave when converted into a state in which the cutoff wavelength is not filled with a dielectric material. A plasma generation source by microwave excitation according to item 1 or 2.