JPH0785438B2 - 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]

As a fine and high-definition manufacturing technology for semiconductor LSIs, etching using an activated particle such as plasma and ions, film formation, and ion implantation technology are widely used. 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) has a low pressure (1 × 10 ⁻ Discharge is possible at ⁵ Torr or less), the direction of ions is aligned, high-density plasma can be generated, and the life is long because of electrodeless discharge.
It has attracted attention because it has excellent characteristics such as the ability to use active gas.

FIG. 3 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 applied in the direction perpendicular to the microwave electric field, the interaction between them causes 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 microwave wavelength (cutoff wavelength) λ _C corresponding to the cutoff frequency at which the microwave does not propagate is expressed by the following equations.

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 2.45 GHz microwave 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, in consideration of the propagation loss of microwaves and the like, a waveguide of 1.6 times or more of this value is usually used. That is, most of the plasma generation chambers having a cylindrical waveguide have an inner diameter of about 11 cm or more. Conventionally, the plasma generation chamber of ECR plasma CVD equipment and ECR ion shower etching equipment usually has a diameter of 20 cm.
It consisted of cavities (for example, Japanese Journal of Applied Physics (Japanese Journ
al of Applied Phisics) Volume 22, Issue 4 (1983) L210 ~ 21
2).

[Problems to be solved by the invention]

As described above, in the configuration in which the microwave is introduced by directly connecting the waveguide such as the rectangular waveguide and the cylindrical waveguide to the plasma generation chamber having the conventional cylindrical cavity, various conditions are taken into consideration and used. The diameter dimension of 1.6 times or more of the minimum dimension required for propagating the microwave, which is determined by the frequency of the microwave, is used, and a smaller plasma generation source has not been studied. In particular, it is difficult to generate plasma in a plasma generation chamber where microwaves do not propagate because microwaves do not propagate, and the inner diameter of the plasma generation chamber must be at least the minimum required to propagate microwaves. Was being considered. Therefore, the inner diameter limit of the plasma generation source was thought to require a dimension larger than that of microwave propagation in principle, so it is necessary to introduce the microwave into the cavity having a small dimension of the non-propagation mode by the waveguide. There is no study example of such a plasma generation source, and a plasma generation source with such a small cavity has not been realized. Further, in actuality, as a conventionally used apparatus for LSI manufacture, the size of a wafer used is as large as 6 to 8 inches, 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.

As a configuration other than the type that introduces microwaves with a waveguide, there is an example in which the antenna is directly inserted into the plasma generation chamber to make it small, but this type has a problem when the antenna is worn out by a spatter. It was

[Means for solving problems]

The present invention breaks the conventional wisdom and makes the inner dimension of the plasma generation chamber smaller than the diameter dimension having the transmission mode of the pass band for the introduced microwave when the plasma generation chamber is a waveguide. Is.

[Action]

The microwave guided by the waveguide propagates to the microwave introduction opening, and a part of the microwave slightly leaks to the plasma generation chamber, so that plasma is generated. Moreover, when plasma is generated, that portion is equivalent to being filled with a dielectric material (plasma) having a high dielectric constant, and microwaves propagate inside the plasma generation chamber, so that plasma is constantly generated. To be done.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention. 8 is a connection port of a coaxial cable, 9 is a coaxial waveguide converter, 10 is a tapered waveguide, 11 is a waveguide, 12 is a dielectric, 13 is a cavity for plasma generation, 14 is a magnetic coil, 15 is A gas inlet, 16 is a microwave inlet, 17 is a plasma limiter, and 18 is a plasma flow. The plasma generating cavity 13 is a cavity having a small internal dimension corresponding to a non-guided mode that does not transmit microwaves when plasma is not generated. That is, for a microwave of 2.45 GHz, the inner diameter is 7.2 cm or less in the case of a cylindrical cavity, and the long side is 6.1 cm or less in the case of a rectangular cavity. In this figure, an example in which microwaves are introduced by a coaxial cable is shown. That is, the microwave is introduced into this system by the coaxial cable through the connection port 8 of the coaxial cable. The microwave introduced by the coaxial cable becomes a waveguide mode by the coaxial waveguide converter 9. It is usually matched to a rectangular waveguide. The microwave excited in this waveguide is guided to the plasma generation cavity 13 via the rectangular tapered waveguide 10 and the cylindrical waveguide 11.

When the plasma generating cavity 13 has a size capable of propagating microwaves, there is no major problem in the configuration of the waveguide 11. However, when the size is reduced by using the plasma generation cavity 13 having a size that does not allow microwaves to propagate as in the present invention, the plasma generation cavity 13 is correspondingly reduced.
It is necessary to reduce the size of the entire microwave waveguide so that the overall size can be reduced. In general, the size of one side of a rectangular waveguide corresponding to the cutoff frequency of microwave is 2.16 GHz is 6.1 cm, but as mentioned earlier, considering propagation loss etc., about 1.6 times this value is It is used, and a waveguide of 10.9 cm or 9.6 cm for 2.45 GHz microwave is commercially available as a standard product. Therefore, when microwaves are introduced into the small-sized plasma generating cavity 13 of the present invention by a waveguide having a size matched thereto, it is usually (commercially available)
This is difficult to achieve with the waveguide of. Furthermore, even if the waveguide is made small and the microwave is introduced into the cavity portion 13 for plasma generation having a non-waveguide mode size by the waveguide, the size of the waveguide of the waveguide mode is too large. It was difficult to realize a compact plasma generation source.

Therefore, in order to solve this problem, in the present embodiment, the waveguide 11 that is made compact by filling the dielectric is used to guide the microwave to the cavity 13 for plasma generation. 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, when a dielectric material having a dielectric constant of 4 is filled, a cylindrical waveguide having a diameter of 3.6 to 5.5 cm or a rectangular waveguide having a long side of 5 to 3 cm can be used. Furthermore, if a dielectric material having a dielectric constant of 9 is used, the inner diameter of the cylindrical waveguide can be reduced to 2.4 cm, and the long side of the rectangular waveguide can be reduced to 2.1 cm. Therefore, if a waveguide of this size is used as the waveguide 11, the cavity 13 for plasma generation having an outer shape of 5 cm or less can be realized. Although FIG. 1 shows an example in which a cylindrical waveguide is used as the waveguide 11, it is obvious that a rectangular waveguide can be similarly configured. Dielectric materials that can be used for this purpose include quartz (dielectric constant 4), BN (4), forthulite (6.2), steatite (6), alumina (9). In addition, when using these fillers, quartz is used for the parts that require non-degassing and heat resistance against contact with plasma, and that require airtightness and flatness for vacuum sealing. The dielectric can be divided into several parts, such as alumina, and other parts using a cheaper material. Furthermore, it is effective to use a dielectric material having a high dielectric constant in order to introduce microwaves into a plasma having a high plasma density. Further, the tapered waveguide 10 is also filled with a dielectric material so that it can be used as a standard rectangular waveguide (the coaxial waveguide converter 9 in this case) and a special type with such a reduced size. The microwave can be propagated by matching with the waveguide 11. At this time, the shape of this tapered waveguide on the special waveguide side does not have to match the shape of the special waveguide 11.
For example, a rectangular waveguide can be used as the tapered waveguide 10 for connection with a special small cylindrical waveguide 11. However,
It is desirable that the inner dimension of the rectangular tapered waveguide is smaller than the inner dimension of the waveguide 11 in terms of microwave matching. At this time, it is obvious that a combination of several tapered waveguides or linear waveguides may be used if necessary. For example, the rectangular waveguide of the coaxial waveguide converter 9 has a rectangular shape.
After connecting the cylindrical waveguide converter and converting it to a cylindrical waveguide,
It can be configured to convert to a smaller size with a cylindrical tapered waveguide to match the size of the smaller size waveguide 11. In any case, the internal dimension of the waveguide 11 is thus changed so that the microwave does not propagate when the dielectric is not inserted on the microwave introduction opening side. The waveguide 11 can be downsized and the microwave power density can be increased by reducing the size corresponding to the above. That is, high density plasma can be generated with low power microwave power.

In such a configuration, the microwave introduced through the coaxial cable connection port 8 is propagated to the microwave introduction opening 16 of the plasma generation cavity 13, and a part of the microwave is generated in the plasma generation cavity. There is a slight leak to 13. In this state, gas is introduced from the gas inlet 15 into the plasma generation cavity 13, and the EC is introduced into the plasma generation cavity 13.
When a magnetic field of 875 Gauss or more that satisfies the R condition is applied, plasma is generated. In particular, when plasma is generated, the plasma generation cavity 13 is equivalent to being charged with a dielectric (plasma) having a high dielectric constant, and microwaves propagate to the plasma generation cavity. And a steady plasma is generated. For this reason, in actuality, a magnetic field that satisfies the ECR condition that makes it easy to start plasma discharge is applied near the microwave introduction opening 16 to start plasma generation immediately, and the microwave is steadily set in the plasma. The magnetic field distribution is set optimally for the high density plasma generation after the introduction of the magnetic field.

With such a small size, since the power density for the same microwave power increases, it is possible to generate plasma with low power and high density. Furthermore, when the refractive index is the same, the in-tube wavelength of the microwave propagating in the plasma becomes longer as the inner diameter of the plasma generation chamber becomes smaller, so that the region where the microwave is absorbed by the plasma expands and the plasma is more efficiently generated. Can be generated.

Although a method of introducing microwaves using a coaxial cable has been shown, a system in which a waveguide is connected to the magnetron of the microwave oscillation source may be used if a higher microwave power is required. . Further, although FIG. 1 does not show microwave circuit components such as a microwave matching box and a microwave power meter (microwave oscillating source, isolator), they can be used as necessary.

Fig. 2 shows a cavity for plasma generation with an inner diameter of 4.5 cmφ.
An example of characteristics when microwaves are introduced into the cavity for plasma generation through the microwave introduction opening of cmφ is shown. The ion current is measured by extracting ions with a single-leaf mesh electrode, and an ion current similar to that of a larger-shaped ion source configuration is obtained. Further, the distribution of the plasma density with respect to the axial length of the cavity for plasma generation becomes smaller as the axial length becomes larger than the inner diameter of the cavity. Therefore, the size of the cavity for plasma generation is preferably such that the axial length is equal to or smaller than the inner diameter.

As described above, the case where the plasma generation source is mainly used as the generation source of plasma radicals is described.
If a single-electrode / single-leaf mesh electrode is used, it is also effective as a source of low-energy ions. Furthermore, it is particularly effective as a high-density, high-current ion source if an ion extraction electrode system having a three-electrode structure of acceleration-deceleration structure is used.

〔The invention's effect〕

According to the present invention, regardless of the conventional concept of constructing a plasma generation chamber in a guided mode configuration, a plasma generation chamber having a small cavity in which the frequency of the introduced microwave becomes the cutoff frequency is used, By realizing plasma generation in the wave mode, a compact plasma generation source can be constructed. Further, the smaller the size, the higher the microwave power density becomes with respect to the same microwave power, and the longer the wavelength inside the tube. Therefore, there is an advantage that a higher density plasma can be generated with respect to the same microwave power. .

Since it can be used as a small-sized and high-density source of plasma, ions, and radicals, it can be used in MBE equipment, MOCVD equipment,
A composite device combined with a plasma application device enables higher control of etching and film forming technology by promoting surface reactions and increasing the efficiency of doping. 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 apparatus, and by using a single electrode / single leaf mesh electrode, It is also effective as a source of energetic ions.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing its characteristic example, and FIG. 3 is a block diagram showing a conventional example. 10 ... Tapered waveguide, 11 ... Waveguide, 13 ... Plasma generation cavity, 14 ... Magnetic coil, 15 ... Gas inlet, 16
…… Microwave introduction opening.

Claims (4)

[Claims] 1. A plasma generation chamber comprising a cavity portion for generating plasma and a conductor wall including the cavity portion and having a microwave introduction opening and excluding the microwave introduction opening, and a plasma generation chamber connected to the microwave introduction opening. Has a waveguide for introducing microwaves into the plasma generation chamber and a magnetic field generator for generating a magnetic field inside the plasma generation chamber, and introduces the microwaves into the plasma generation chamber through the waveguide. A microwave electric field is generated in the plasma generation chamber, and a magnetic field satisfying an electron cyclotron resonance condition determined by the frequency of the microwave in at least a part of the plasma generation chamber is generated in the plasma generation chamber by the magnetic field generator. In this state, a gas to be turned into a plasma is introduced, and an electron cyclo by the microwave electric field and the magnetic field is introduced. In a plasma generation source by microwave excitation for generating plasma by Ron resonance absorption, the internal dimension of the plasma generation chamber is such that when the plasma generation chamber is a waveguide, transmission of a pass band for the introduced microwaves. A plasma generation source by microwave excitation characterized by being smaller than a dimension having a mode. 2. A waveguide according to claim 1, wherein an inner dimension of the waveguide is reduced to a dimension at which a microwave does not propagate when a dielectric is not inserted, on the microwave introduction opening side. A plasma generation source by microwave excitation according to item 1. 3. The waveguide is configured so as to be in a transmission mode in a pass band with respect to the introduced microwaves up to a microwave introduction opening provided in the plasma generation chamber. The plasma generation source by microwave excitation according to claim 1, wherein the waveguide and the plasma generation chamber are connected so that a part thereof slightly leaks into the plasma generation chamber. 4. The waveguide transmits the introduction microwave when the dielectric is inserted and immediately before the microwave introduction opening provided in the plasma generation chamber, and transmits the introduction microwave when the dielectric is not inserted. The microwave-excited plasma generation source according to claim 1, wherein the plasma generation source has a small internal dimension that does not occur.