JP2534219B2 - Microwave discharge reactor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave discharge reaction apparatus, and more particularly to a microwave discharge reaction apparatus suitable for application to a dry etching apparatus, a plasma CVD apparatus, a sputtering apparatus, a surface reforming apparatus and the like. .

[0002]

2. Description of the Related Art Various microwave discharge reactors have been proposed as a microwave discharge reactor utilizing an electron cyclotron resonance phenomenon (ECR) which is an interaction between an electromagnetic wave in a microwave region and a magnetic field. These microwave discharge reaction devices generally employ a structure in which microwaves are introduced into a discharge chamber using a waveguide and an ECR is caused between the microwave and the magnetic field generated by the air-core coil.

As an example of applying a coaxial line with few size restrictions to the introduction of microwaves, for example, A. Yonesu et.al.
“Production of a large diameter uniform ECR plas
mawith a Lisitano coil. ”Jpn.J.Appl.Phys., 27 (198
9) There is a microwave discharge reactor shown in the literature such as L1746. This microwave reactor is a so-called Rigitano coil type, which uses a coaxial tube to introduce microwaves and uses a cylindrical electrode having a large number of slits as an antenna for microwave radiation to enable large-area processing. This is a device for that purpose. As a similar example, as disclosed in Japanese Patent Laid-Open No. 1-159379, it has been attempted to uniformly process a large area by using a flat plate electrode having a large number of slits as an antenna.

[0004]

In recent years, the size of a substrate to be processed used for manufacturing a semiconductor device has become larger and larger, and it is necessary to uniformly process a large substrate having a diameter of about 30 cm. Therefore, there is an urgent need to develop a discharge reactor suitable for processing a large area substrate. However, the various conventional ECR devices have the following unsolved problems, respectively.

The problems common to the apparatus utilizing the microwave introduced by the waveguide and the magnetic field produced by the air-core coil are:
Device design restrictions due to the size of the waveguide being determined by the frequency range used, anxiety about the reliability of the window for introducing microwaves, upsizing of the entire device due to the large air core coil, There were higher costs. Further, in order to efficiently generate plasma with this type of discharge reactor, there are restrictions on the dimensions of the discharge chamber depending on the microwave wavelength, and it is difficult to generate a magnetic field with good uniformity over the entire discharge chamber. Therefore, simply increasing the size of the discharge chamber of the microwave discharge reactor will make it non-uniform,
It was difficult to process a large area substrate with good uniformity.

Further, since the magnetic field by the air-core coil is also applied to some of the microwave discharge devices to which the above-mentioned coaxial line is applied, the uniformity of plasma is not uniform due to the same reason as the waveguide type device. It was enough. Further, no consideration has been given to the drawback that the coil is large.

Furthermore, the present inventors have combined a flat type electrode having a large number of slits and a permanent magnet with a flat type E.
A large-area plasma generation electrode called CR was previously proposed (Japanese Patent Application No. 2-400904). In this microwave discharge reaction device, a flat plate electrode having a slit having a predetermined shape such as a radiation type or a star type is provided, and microwaves are efficiently radiated into the discharge chamber, and at the same time, a magnetic field satisfying ECR conditions is generated. As a means for this, a plurality of cylindrical magnets are installed on a concentric circle. The magnetizing directions of these magnets were perpendicular to the electrodes, and the adjacent cylindrical permanent magnets were arranged so that their magnetizing directions were opposite to each other. The magnetic field strength at this time is set so as to satisfy the ECR condition near the surface of the flat plate electrode where plasma is generated. With this configuration, plasma can be generated only in a very narrow region near the surface of the flat plate electrode. did it.
Further, the magnetic circuit in the above microwave discharge reaction device, that is, the magnetic field by the permanent magnet is different from that by the air-core coil, and since the range of the magnetic field is limited only to the vicinity of the flat electrode, By installing it in a very weak place, it was possible to perform a surface treatment with good uniformity regardless of the shape of the magnetic field. As described above, it becomes possible to generate plasma with good uniformity over a large area by utilizing the combination of the flat electrode (slit antenna) and the magnetic circuit using the permanent magnet.

On the other hand, in the above flat type ECR apparatus, since the ECR condition is satisfied by the permanent magnet, only a very weak magnetic field exists on the substrate processing surface, and the plasma is made uniform by free diffusion. However, the plasma uniformity is essentially good, but the place where the plasma uniformity is good needs to be separated from the antenna for microwave radiation to some extent, and in order to obtain a high plasma density on the substrate processing surface, a large microwave is required. It was necessary to turn on the power.

An object of the present invention is to further improve the structure of the magnetic circuit of the previously proposed apparatus and to provide a planar microwave discharge reaction apparatus having higher practicality.

[0010]

A microwave discharge reactor according to the present invention comprises a vacuum container having a mechanism for maintaining a reduced pressure inside and a mechanism for introducing gas, and a microwave container for introducing microwaves into the vacuum container. A plasma generating mechanism for converting gas into plasma and a substrate holding mechanism facing the plasma generating mechanism at a predetermined interval are provided. The plasma generating mechanism is a coaxial device for introducing microwaves into the vacuum container. Type microwave transmission path, a flat plate electrode having at least one slit of a predetermined length and width for radiating microwaves, and a plurality of axially magnetized cylindrical permanent magnets adjacent to the flat plate electrode, It is composed of magnetic field generating means arranged concentrically so that the magnetizing directions of the matching magnets are opposite to each other, and makes the magnetic field strength of each of the plurality of cylindrical permanent magnets into a desired state. Configured to become.

In the above structure, preferably, the magnetic field strength of the inner cylindrical permanent magnet is weakened and the magnetic field strength of the outer cylindrical permanent magnet is strengthened.

In the above structure, preferably, the magnetic field strength of the inner cylindrical permanent magnet is increased and the magnetic field strength of the outer cylindrical permanent magnet is decreased.

In the above construction, preferably, the magnetic field strength of the central cylindrical permanent magnet is relatively weakened.

In each of the above-mentioned constitutions, preferably, the magnetic field strength is changed by changing the axial length of the cylindrical permanent magnet.

[0015]

In the microwave discharge reactor according to the present invention, the range of good plasma uniformity can be improved as compared with the conventional case by devising the structure of the magnetic circuit installed near the planar electrode for generating plasma. It can be controlled freely from a wide state to a narrow state. Further, in order to create a desired magnetic field for the shape of the separatrix, for example, the axial length is appropriately adjusted, and a plurality of cylindrical permanent magnets optimized according to the purpose are provided. Therefore, for example, the magnetic field in which the separatrix is expanded diffuses the plasma generated near the electrode with good uniformity while the distance from the electrode is short. Therefore, it became possible to install the substrate to be processed near the electrode while maintaining the uniformity of processing. The magnetic field having a narrowed separation in the vicinity of the electrodes can use high-density plasma for processing the substrate, and thus can perform surface processing at a high processing speed.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an internal structure of a microwave discharge reactor according to the present invention, FIG. 2 is a front view showing an example of a plate electrode, and FIG. 3 shows a distribution state of magnetic fields, that is, lines of magnetic force. It is a figure.

In FIG. 1, reference numeral 1 is a vacuum container. The shape of the vacuum container 1 is arbitrary, and an airtight substrate processing space is formed inside the vacuum container 1. A plasma generating mechanism 2 and a substrate holding mechanism 3 are installed inside the vacuum container 1. The substrate holding mechanism 3 is fixed to the vacuum container 1 using an insulator 4. The vacuum container 1 further includes a gas supply mechanism that introduces a gas used for plasma generation, and an exhaust mechanism that brings the inside of the vacuum container into a required reduced pressure state. Since the gas supply mechanism and the exhaust mechanism are generally well known, their illustration is omitted.

The main part of the plasma generating mechanism 2 is composed of a flat plate electrode 5, a magnetic circuit 6, and a back plate 7 for fixing the magnetic circuit 6. The plate electrode 5 has a function of forming an electric field in the vacuum container 1 and generating a plasma discharge by interaction with a magnetic field by the magnetic circuit 6, and is a plate material made of a conductive material such as metal. The magnetic circuit 6 is composed of, for example, three cylindrical (or ring-shaped) permanent magnets 8 magnetized in the axial direction. The three permanent magnets 8 have different diameters, are arranged in concentric circles around the microwave supply point (center point) of the plate electrode 5, and are fixed to the back plate 7.
The back plate 7 is a conductive plate material and is held at the ground potential.
Each permanent magnet 8 has an N or S polarity formed on the end surface of the cylinder. The polar arrangements of the three permanent magnets are set so that adjacent magnets are opposite to each other. For example, on the end surface of the permanent magnet 8 that contacts the back plate 7, the innermost permanent magnet with the smallest diameter has the polarity S, the permanent magnet with the middle diameter has the polarity N, and the outermost permanent magnet with the largest diameter has the polarity. It is arranged as S. According to this arrangement, lines of magnetic force are formed from the end faces of the permanent magnet existing at the intermediate position toward the respective end faces of the inner magnet and the outer permanent magnet. Therefore, on the surface of the flat plate-shaped electrode 5, a distribution of almost perpendicular magnetic force lines is formed in a space relatively close to the surface.

The axial length of each of the cylindrical permanent magnets 8 can be appropriately determined. In this embodiment, for example, the innermost and outermost permanent magnets have intermediate lengths. It is designed to be almost twice as long and longer than that. As is clear from the example shown in FIG. 1, the innermost and outermost permanent magnets are provided with two permanent magnets at intermediate positions with respect to the axial length, so that the axial length can be increased. Is doubled. Therefore, the magnetic field strength formed by the innermost and outermost permanent magnets is twice the magnetic field strength of the intermediate permanent magnets.

The thickness of each permanent magnet 8 and the interval between the permanent magnets are experimentally determined in accordance with the size of the microwave discharge reactor to be applied or in consideration of other conditions. A gap having a required size is provided between the plate electrode 5 and the back plate 7. This dimension is also determined experimentally. The gap cannot be made too large in order to generate a magnetic field having a constant strength on the surface of the flat plate electrode 7. On the contrary, if it is made too small, the microwave propagation is hindered. Therefore, it is usually set to about 1 to 10 mm.

FIG. 2 shows an example of the front shape of the plate electrode 5. Reference numeral 9 is a slit provided as an antenna for forming an electric field in the front space of the flat electrode 5. A plurality of slits 9 are formed. Although various shapes can be considered for the slit 9, the effect of improving the plasma uniformity according to the present invention does not depend on the shape of the slit. Since the slit shape mainly affects the utilization efficiency of microwave power, the slit shape will not be mentioned here. When microwave power is supplied to the center point 10 of the plate electrode 5 under the set conditions, a standing wave is formed on the slit 9. The electric field generated by the standing wave interacts with the magnetic field generated by the magnetic circuit 6 to create a condition in which plasma can be generated.

A means for supplying microwaves to the plasma generating mechanism 2 is a coaxial line (coaxial tube).
This coaxial line includes an outer conductor 11, an inner conductor 12, a coaxial window 13 for vacuum sealing, and a rectangular waveguide arranged outside the vacuum container 1 for guiding microwave power from a microwave power supply. 14 and a coaxial waveguide converter 15 that connects the rectangular waveguide 14 and the coaxial line. The outer conductor 11 is connected to the back plate 7, and the inner conductor 12 is connected to the plate electrode 5.

In order to perform the substrate processing by the above microwave discharge reaction apparatus, first, the inside of the vacuum container 1 is exhausted from the exhaust port 16 to a predetermined pressure by using an exhaust mechanism (not shown) (composed of a vacuum pump). After that, the gas used in the discharge reactor is introduced to a predetermined pressure by using a gas supply mechanism (not shown).

The substrate holding mechanism 3 includes a substrate holder 17,
For example, the substrate holder 17 is fixed to the vacuum container 1 by the fixed shaft 18.
Installed inside the. The fixed shaft 18 is attached to the upper wall of the vacuum container 1 via the insulator 4. The insulator 4 has a vacuum sealing function, and makes the substrate holding mechanism 3 have a floating potential. A mechanism for cooling or heating the substrate may be provided inside the substrate holder 17 and the fixed shaft 18. A bias voltage such as a direct current or a high frequency can be applied to the substrate holder 17 by using a power source (not shown) according to the content of the process performed in the vacuum container 1. The substrate 19 to be processed is placed on the substrate holder 17. Board 1
The processing surface 9 faces the front surface of the flat plate-shaped electrode 5 of the plasma generating mechanism 2. By supplying microwave power from the microwave power source to the flat plate-shaped electrode 5, the electric field generated by the standing wave on the slit 9 and the magnetic field generated by the magnetic circuit 6 interact with each other to generate plasma between the flat plate-shaped electrode 5 and the substrate holder 17. Are generated, and a predetermined discharge reaction can occur on the surface of the substrate 19. At this time, the intensity of the magnetic field formed by the magnetic circuit 6 is at a portion closer to the substrate 19 than the surface of the flat plate electrode 5 with respect to the frequency of the microwave supplied to the flat plate electrode 5 by electron cyclotron resonance ( If the condition of ECR) is satisfied, the plasma generation efficiency can be made extremely high. A mechanism for loading or unloading the substrate 19 is not shown.

The configuration shown in FIG. 1 is conceptual, and any structure having an equivalent action can be adopted depending on the specific coupling structure of the coaxial lines and the mounting structure of the magnetic circuit.

In the recent microwave discharge reactor used for semiconductor manufacturing, it is necessary to generate high-density and highly uniform plasma at a low gas pressure to carry out the surface treatment of the substrate to be treated. The microwave discharge reaction device of the present invention having the above configuration is suitable for such treatment. This is because the magnetic circuit 6 according to the present invention is suitable for generating a plasma with particularly excellent uniformity.

Here, the relationship between the configuration of the magnetic circuit and the plasma uniformity found by the study of the present inventors will be briefly described. The present inventors have studied the factors that determine the uniformity of plasma, and as a result, S.Iizuka et.al.
of large diameter uniform plasma for material proc
essing ”Proc. 9th.Symp.plasma Processing (1992) 32
As shown in 7., we have found that the plasma diffusion state is affected by a very weak magnetic field. For example, in the case where the axial lengths of the three cylindrical permanent magnets 8 are all the same in the magnetic circuit 6, the magnetic field distribution formed by this magnetic circuit is as follows:
Magnetic field lines formed by two cylindrical permanent magnets located outside (center and outermost permanent magnets) and magnetic field lines formed by two cylindrical permanent magnets located inside (center and innermost permanent magnets) The position of the boundary surface (called separatrix) that is formed between the two and the position of the minimum value of the plasma floating potential correspond to each other, and the uniformity of the plasma density is the inside of this floating potential minimum part. It turned out to be good. Based on this finding, it was concluded that it is effective to configure the magnetic circuit so that the boundary surface of the magnetic field lines, that is, the separatorix, spreads outward in order to increase the portion where the uniformity of the plasma density is good. In view of the above experimental results, the present invention proposes a planar ECR type microwave discharge reactor with good plasma uniformity by devising the structure of the magnetic circuit. One of the examples is the above-mentioned structure. Is proposed.

Next, a method of determining the structure of the magnetic circuit 6 will be described. According to the results of research conducted by the inventors, the most important factor that determines the uniformity of plasma is the shape of the boundary portion of the magnetic field lines, that is, the separatrix, as described above. If the magnetic circuit is designed so that the separation is directed to the outside as much as possible, it is possible to generate plasma with good uniformity in a wide range in a portion close to the electrode, that is, a portion having a high plasma density.

The magnetic circuit 6 described in the above embodiment is an example of optimum design. Here, for convenience of explanation, the cylindrical permanent magnets forming the magnetic circuit 6 are arranged in the first row, second row,
We will call it the third column. FIG. 3 shows the result of calculation of the magnetic force lines 20 generated by the magnetic circuit 6 shown in FIG. In FIG. 3, reference numeral 21 conceptually represents the plate electrode 5. According to the calculation result of the shape of the lines of magnetic force generated when the conventional three cylindrical permanent magnets having the same axial length are used, the separatorix is relatively large between the second and third rows of the magnetic circuit. It rises in a nearly vertical fashion and diverges outwards away from the electrodes. On the other hand, according to the magnetic circuit 6, as shown in FIG. 3, the separatrix 22 has a feature that it spreads widely toward the outside. Corresponding to the shape of the separatrix, the measurement result of the plasma characteristics shows that the portion with good uniformity is widely spread, and it is clear that the microwave discharge reactor has good characteristics.

Furthermore, the design of the magnetic circuit according to the invention can also be used to control the divergence of plasma. FIG. 4 shows a second embodiment of the magnetic circuit in which the axial length of the permanent magnets in the third row is doubled compared with the lengths in the first and second rows. FIG. 5 shows lines of magnetic force generated by the magnetic circuit 6 shown in FIG. In this example, the separatrix 22 has a tendency to be once held in the direction away from the plate electrode 5 and then spread, and it can be seen that the range of good plasma uniformity also corresponds to this.
Further, in this example, although the range of good plasma uniformity is narrow, the density on the central axis is larger than that in the above example, and it is shown that plasma loss is small because plasma divergence is suppressed. ing.

As is apparent from the above-mentioned embodiment, according to the present invention, it becomes possible to generate a plasma with good uniformity over a wider range than in the past. Calculation of magnetic field lines is one of the most effective methods for determining the configuration of a magnetic circuit. This calculation is
For example, it can be easily executed by the finite element method. It is clear from the experimental results of the present invention that the calculated results and the actual plasma density distribution are in good agreement, but in order to be convinced of the experimental results, a method such as Langmuir probe is effective. .

As described above, by devising the structure of the magnetic circuit, it becomes possible to widen the range of favorable plasma uniformity, and it is possible to easily achieve the treatment of a large area substrate and use it as a microwave discharge reactor. Thus, it is possible to obtain a result that is far superior to the conventional one. Further, by changing the configuration of the magnetic circuit according to the purpose of use, it is possible to perform high-speed processing in a narrower range, and the possibility of application as a surface processing apparatus is widened.

In each of the above-mentioned embodiments, the magnetic field strength of each permanent magnet is changed by changing the axial length of the cylindrical permanent magnet. However, the magnetic field strength is changed by changing the magnetization degree and material of the magnet. Can be changed.

[0035]

As is apparent from the above description, according to the present invention, a vacuum vessel which is a microwave discharge reaction chamber is provided with a flat plate-like electrode provided with a slit having a predetermined shape, and the slit for the electrode. In an electrode device including a magnetic circuit that generates a magnetic field in the same direction as the length direction of the magnetic circuit, the magnetic circuit is formed by concentrically arranging a plurality of cylindrical permanent magnets,
And since the magnetic field strength of each permanent magnet was changed appropriately as necessary, and the separatorix formed in the magnetic field was formed to have a desired shape, it is possible to expand the range of the uniformity of the plasma density, or according to the purpose. The range of plasma density uniformity can be reduced to increase density and improve processing speed. By increasing the plasma density, processing of large area substrates can be realized. Further, the microwave discharge reaction device can be manufactured in a small size at a low cost with a simple structure, and a highly practical device can be realized.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the internal structure of a microwave discharge reaction device according to the present invention.

FIG. 2 is a front view of a flat electrode.

FIG. 3 is a diagram showing a magnetic field line distribution state by the magnetic circuit of the first embodiment.

FIG. 4 is a cross-sectional view showing a second embodiment of the magnetic circuit.

FIG. 5 is a diagram showing a magnetic field line distribution state by the magnetic circuit of the second embodiment.

[Explanation of symbols]

 1 Vacuum Container 2 Plasma Generation Mechanism 3 Substrate Holding Mechanism 5 Flat Electrode 6 Magnetic Circuit 7 Back Plate 8 Permanent Magnet 9 Slit 11 Outer Conductor 12 Inner Conductor 14 Waveguide 15 Coaxial Waveguide Converter 16 Exhaust Port 17 Substrate Holder 19 Substrate 20 Magnetic field lines 22 Sepatrix

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Iizuka 6-5-10-Koriyama, Taichiro-ku, Sendai City, Miyagi Prefecture (72) Yukio Nakagawa 5-8-1 Yotsuya, Fuchu-shi, Tokyo NIDEC ANELVA CORPORATION (56) Reference JP-A-5-182785 (JP, A) JP-A-5-345990 (JP, A) JP-A-6-13198 (JP, A) JP-A-6-57457 (JP, A)

Claims (5)

(57) [Claims] 1. A vacuum container provided with a mechanism for maintaining a depressurized state inside and a mechanism for introducing gas, a plasma generation mechanism for introducing microwave into the vacuum container to convert the gas into plasma, and the plasma generation. In a microwave discharge reaction device comprising a mechanism and a substrate holding mechanism installed facing each other at a predetermined interval, the plasma generation mechanism, a coaxial transmission line for introducing the microwave into the vacuum container, A flat plate electrode having at least one slit having a predetermined length and width for radiating the microwave, and a plurality of cylindrical permanent magnets magnetized in the axial direction in the vicinity of the flat plate electrode are adjacent to each other. Magnetic field generating means arranged concentrically so that the magnetization directions are opposite to each other, and the magnetic field strengths of the plurality of cylindrical permanent magnets are made different. Microwave discharge reaction device comprising. 2. The microwave discharge reactor according to claim 1, wherein the magnetic field strength of the inner cylindrical permanent magnet is weakened and the magnetic field strength of the outer cylindrical permanent magnet is strengthened. Wave discharge reactor. 3. The microwave discharge reactor according to claim 1, wherein the magnetic field strength of the inner cylindrical permanent magnet is increased and the magnetic field strength of the outer cylindrical permanent magnet is decreased. Wave discharge reactor. 4. The microwave discharge reactor according to claim 1, wherein the magnetic field strength of the cylindrical permanent magnet in the center is relatively weakened. 5. The microwave discharge reactor according to any one of claims 1 to 4, wherein the magnetic field strength is changed by changing the axial length of the cylindrical permanent magnet. Characteristic microwave discharge reactor.