JP6194850B2 - Thin film forming equipment - Google Patents

Description

  The present invention relates to a thin film forming apparatus for forming a thin film on a substrate by converting a raw material gas into plasma.

  In the semiconductor device manufacturing process, a plasma processing apparatus is used in a film forming process, an etching process, an ashing process, and the like because of high-precision process control. For example, a plasma chemical vapor deposition (CVD) apparatus is known as an apparatus used in a thin film forming process. In a plasma CVD apparatus, a raw material gas is turned into plasma by high-frequency power or the like in a film forming process, and a thin film is formed on a substrate by a chemical reaction.

  In addition, it is effective to perform plasma treatment as a pretreatment for the film formation treatment (see, for example, Patent Document 1). By this pretreatment, various effects such as removal of residual gas in the chamber and improvement of the passivation effect of the substrate can be obtained.

Japanese Patent Laid-Open No. 06-45255

  However, sufficient studies have not been made so far on the damage to the substrate by the pretreatment and the pretreatment conditions for obtaining an appropriate passivation effect. An object of this invention is to provide the thin film formation apparatus which can perform the pre-processing which the damage to a board | substrate is small and the high passivation effect is acquired.

According to one aspect of the present invention, (a) a chamber in which a sample holder on which a substrate to be processed is mounted is stored, and (a) a high frequency wave disposed in the chamber and facing the substrate mounted on the sample holder. (C) a gas supply mechanism for supplying either a pretreatment gas used in the pretreatment step or a reaction gas containing a raw material gas for a thin film formed on the substrate into the chamber; A high-frequency power source that supplies high-frequency pulsed power between the sample holder and the high-frequency electrode, excites plasma containing a pretreatment gas in a pretreatment step, and excites plasma containing a source gas in a film formation treatment step; A high-frequency pulse power is output from a high-frequency power source at a first duty ratio in the pre-processing step, and a second on-time ratio is longer than the first duty ratio in the film-forming processing step. The high-frequency pulse power to be output from the high-frequency power supply Yuti ratio, and a control unit for controlling the high frequency power source, the first duty ratio, without damaging the substrate in the pretreatment step, and a pretreatment gas There is provided a thin film forming apparatus which is set so as to obtain a passivation effect by combining hydrogen radicals in the contained plasma with unbonded hands of the substrate .

  ADVANTAGE OF THE INVENTION According to this invention, the thin film forming apparatus which can perform the pre-processing by which the damage given to a board | substrate is small and the high passivation effect is acquired can be provided.

It is a schematic diagram which shows the structure of the thin film forming apparatus which concerns on embodiment of this invention. It is a schematic diagram for demonstrating a pre-processing process. It is a table | surface which shows the result of having changed the pre-processing conditions and measuring carrier lifetime. It is a graph which shows the measurement result of carrier lifetime. It is a flowchart for demonstrating the thin film formation method using the thin film formation apparatus which concerns on embodiment of this invention. It is a schematic diagram which shows the example of the high frequency electrode of the thin film forming apparatus which concerns on embodiment of this invention. It is sectional drawing along the central axis of a through-hole for demonstrating the shape of the through-hole of the high frequency electrode shown in FIG.

  Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic. Further, the embodiment described below exemplifies an apparatus and a method for embodying the technical idea of the present invention, and the embodiment of the present invention has the following structure and arrangement of components. It is not something specific. The embodiment of the present invention can be variously modified within the scope of the claims.

  A thin film forming apparatus 10 according to the embodiment of the present invention shown in FIG. 1 is a thin film forming apparatus that forms a thin film on a substrate 100 to be processed. The substrate 100 is, for example, a silicon substrate used for a semiconductor device or a solar battery cell. The thin film forming apparatus 10 shown in FIG. 1 includes a chamber 11 in which a sample holder 12 on which a substrate 100 is mounted is stored, and a high-frequency electrode that is disposed inside the chamber 11 and faces the substrate 100 mounted on the sample holder 12. 13, a gas supply mechanism 15 for supplying either the pretreatment gas 121 used in the pretreatment process or the reaction gas 122 containing the raw material gas of the thin film formed on the substrate 100 to the inside of the chamber 11, A high-frequency power source 14 that excites plasma containing the pretreatment gas 121 in the processing step and excites plasma containing source gas in the film-forming processing step, and a controller 17 that controls the high-frequency power source 14 are provided.

  The high frequency power source 14 supplies high frequency pulse power between the sample holder 12 and the high frequency electrode 13 to excite plasma on the upper surface of the substrate 100. The control device 17 outputs the high-frequency pulse power from the high-frequency power source 14 at the first duty ratio in the pretreatment process, and at the second duty ratio having a longer on-time ratio than the first duty ratio in the film forming process. High frequency pulse power is output from the high frequency power supply 14.

  Here, the duty ratio of the high-frequency pulse power is the ratio of the pulse ON time to the OFF time. For example, the control device 17 can independently control the on-time of the high-frequency pulse power output from the high-frequency power source 14 in the range of 100 μsec to 1000 μsec and the off-time in the range of 10 μsec to 100 μsec.

  The thin film forming apparatus 10 further includes a gas exhaust mechanism 16 that exhausts the gas in the chamber 11 to the outside. The gas exhaust mechanism 16 is provided with a gas pressure regulating valve (not shown) to keep the pressure in the chamber 11 constant.

  The gas supply mechanism 15 supplies the pretreatment gas 121 or the reaction gas 122 supplied from the gas supply source 18 into the chamber 11. The gas supply source 18 includes a pretreatment gas source 181 that stores the pretreatment gas 121 and a reaction gas source 182 that stores the reaction gas 122. However, when the reaction gas source 182 includes a plurality of source gases, if any of those source gases can be used as the pretreatment gas 121, the gas supply source 18 does not include the pretreatment gas source 181. A structure having only the reactive gas source 182 may be used. The gas supply mechanism 15 is provided with a flow rate controller (not shown), and supplies a predetermined amount of pretreatment gas 121 or reaction gas 122 into the chamber 11.

  1 illustrates the case where the sample holder 12 is a boat-type sample holder on which the substrate 100 is mounted in the vertical direction. The sample holder 12 is used as an anode electrode. On the other hand, the high frequency electrode 13 functions as a cathode electrode. As shown in FIG. 1, the main surface of the high-frequency electrode 13 faces the substrate 100 mounted on the sample holder 12. As will be described later, the high-frequency electrode 13 is preferably a hollow cathode electrode in which a concave portion is formed on the main surface. High density plasma is stably generated in the chamber 11 by hollow cathode discharge using a hollow cathode electrode. As a result, the pretreatment gas 121 and the source gas are efficiently decomposed, and the pretreatment and film formation treatment for the substrate 100 can be performed in a short time.

  The sample holder 12 is disposed on the heater 19. The temperature of the substrate 100 mounted on the sample holder 12 can be set by the heater 19 so that the temperature of the substrate 100 becomes an optimum temperature in the film forming process or the like.

According to the thin film forming apparatus 10, a desired thin film can be formed on the substrate 100 by appropriately selecting a source gas. For example, a silicon semiconductor thin film, a silicon nitride thin film, a silicon oxide thin film, a silicon oxynitride thin film, a carbon thin film, or the like can be formed on the substrate 100. Specifically, a silicon nitride (SiN) film is formed on the substrate 100 using a mixed gas of ammonia (NH ₃ ) gas and monosilane (SiH ₄ ) gas. Alternatively, a silicon oxide (SiOx) film is formed on the substrate 100 using a mixed gas of monosilane (SiH ₄ ) gas and N ₂ O gas, or TEOS gas and oxygen gas.

  In the film forming process using the thin film forming apparatus 10, it is effective to perform a pre-process in order to enhance the passivation effect of the substrate 100 or to clean the surface of the substrate 100. That is, the surface of the substrate 100 before the film forming process is exposed to, for example, high-frequency plasma of ammonia. As a result, as shown in FIG. 2, hydrogen radicals in the high-frequency plasma are bonded to dangling bonds (dangling bonds) of the substrate 100. In general, in a polycrystalline silicon substrate used as a substrate for a crystalline silicon solar cell, a grain boundary of polycrystalline silicon becomes a defect. Carriers are supplemented by this defect, and the conversion efficiency of the solar cell is lowered. However, when hydrogen radicals are bonded to dangling bonds of the substrate 100, the capture of carriers due to defects is reduced, and the passivation effect is enhanced. As a result, the carrier lifetime in the substrate 100 is increased. Therefore, the conversion efficiency of the solar cell is improved by performing the above pretreatment before the step of forming the antireflection film or the passivation film of the solar cell.

  According to the study by the present inventors, the passivation effect is particularly high in the pretreatment using high-density plasma by hollow cathode discharge. For example, a sufficient passivation effect was obtained with a pretreatment of about 5 seconds.

  However, if the high-frequency power supplied from the high-frequency power source 14 is too large in the pretreatment, the substrate 100 is damaged. As a result, the carrier lifetime is reduced, and the performance of the device using the substrate 100 is lowered.

  By setting the pretreatment time short, damage to the substrate 100 can be reduced. However, when the pretreatment time is short, the plasma in the chamber 11 is not stable.

  On the other hand, if the power of the high-frequency power in the pretreatment is too small, it is not possible to sufficiently obtain the effect of generating high-density plasma by hollow cathode discharge. For this reason, in order to obtain an appropriate passivation effect, it is necessary to lengthen the pretreatment time to a certain level or more. However, the longer the time for the pretreatment process, the lower the production efficiency. Therefore, it is not sufficient to take measures to reduce the power of the high frequency power.

  In the film forming process, it is necessary to increase the power of the high frequency power as much as possible to shorten the film forming time and improve the production efficiency. That is, plasma discharges having different characteristics are required in the pretreatment process and the film forming process, and it is difficult to cope with this by simply changing the output of the high-frequency power source 14.

  On the other hand, the present inventors have repeatedly studied and found the optimum plasma discharge conditions for the pretreatment process as follows. FIG. 3 shows the result of measuring the carrier lifetime of the substrate 100 after the film formation process when the pretreatment conditions are changed. Conditions 1 to 4 shown in FIG. 3 are obtained by changing the power of the high-frequency pulse power output from the high-frequency power source 14 (hereinafter referred to as “high-frequency power”), the duty ratio of the high-frequency pulse power, and the preprocessing time. Yes. Here, the substrate 100 is an n-type silicon single crystal solar cell substrate, and the bulk lifetime before film formation is about 800 μm. In the film formation process, a silicon nitride (SiNx) film was formed on the substrate 100.

  The high-frequency electrode 13 used was a hollow cathode electrode shown in FIGS. Details of FIGS. 6 and 7 will be described later. A substrate plate extending in the vertical direction on which the substrate 100 of the sample holder 12 is mounted was a carbon plate having a rectangular main surface of 690 mm × 220 mm and a thickness of 2 mm. The high-frequency electrode 13 facing this was made of a carbon material having a rectangular main surface of 710 mm × 210 mm and a thickness of 5 mm. A high frequency pulse power of 250 kHz was supplied to the high frequency electrode 13 by the high frequency power source 14, and the sample holder 12 was heated to 450 ° C. by the heater 19.

  In the pretreatment, only ammonia gas was used as the pretreatment gas 121, the flow rate of ammonia gas was 3600 sccm, and the pressure in the chamber 11 was 95 Pa. The film forming conditions of the film forming process were the same in conditions 1 to 4, and a mixed gas of monosilane gas and ammonia gas was used as the source gas. The flow rate of silane gas was 2150 sccm, the flow rate of ammonia gas was 12,500 sccm, and the pressure in the chamber 11 was 95 Pa. In the film forming process, conditions of a high frequency power of 4500 W, an on time of 600 μsec, and an off time of 50 μsec were used.

  FIG. 3 shows a lifetime A immediately after the film forming process when the annealing process is not performed, a lifetime B when the annealing process is performed at 600 ° C., and a lifetime C when the annealing process is performed at 700 ° C. , And lifetime D when annealing at 800 ° C. was performed. The lifetime was measured using a μ-PCT method that measures the amount of carriers generated in a sample irradiated with a laser. FIG. 4 is a graph of lifetimes A to D under conditions 1 to 4.

  As shown in FIG. 3, the high frequency power of the high frequency pulse power under condition 1 was 6000 W, the on time of the high frequency pulse power was 600 μsec, the off time was 50 μsec, and the preprocessing time was 5 sec. Under condition 1, the lifetime A immediately after the film forming process is short, and the lifetime is about 440 μsec even if the annealing process is performed. This is because the substrate 100 is damaged by the plasma because the high frequency power in the pretreatment is high.

  In condition 2, the high-frequency power in the pretreatment is reduced to 3000 W compared to condition 1. For this reason, in condition 2, the lifetime A immediately after the film forming process is longer than that in condition 1, and the lifetime B when the annealing temperature is 600 ° C. is as long as 533 μsec. However, the lifetime C when the annealing temperature is 700 ° C. is lowered, and the lifetime D when the annealing temperature is 800 ° C. is significantly reduced to 5 μsec.

  In condition 3, the high frequency power is set to 3000 W, which is the same as that in condition 2, and the preprocessing time is set to 10 sec, which is longer than that in condition 2. By extending the processing time, the lifetimes B to C show a long value of 700 μsec or more even when the annealing temperature is 600 ° C. to 700 ° C., and the lifetime D is 125 μsec even when the annealing temperature is 800 ° C. Thus, Condition 3 has a longer lifetime than Conditions 1 and 2, and it is considered that a sufficient passivation effect is obtained.

  Condition 4 sets the high-frequency power to 5000 W lower than Condition 1 and higher than Conditions 2-3. Then, on-time 600 μsec and off-time 50 μsec of the high-frequency pulse power in the conditions 1 to 3, the on-time 300 μsec and off-time 50 μsec of the high-frequency pulse power in the condition 4 were set. That is, the on-time ratio is shorter than those in the conditions 1 to 3, and the duty ratio is reduced. As a result, the lifetimes B to C are equal to or greater than 700 μsec, which is equal to or greater than that of the condition 3, although the preprocessing time is 5 seconds shorter than that of the condition 3.

  As described above, according to the condition 4, damage to the substrate 100 can be suppressed and the lifetime can be increased by shortening the ratio of the on-time while shortening the pretreatment time with relatively high high-frequency power. This is because, since the duty ratio of the high-frequency pulse power is small, the cycle in which high-energy ions once disappear is short, and the time for high-energy ions to collide with the substrate 100 is short. As described above, by reducing the on-time ratio and reducing the duty ratio of the high-frequency pulse power, it is possible to realize pre-processing that can reduce damage to the substrate 100 and obtain a high passivation effect. The higher the high-frequency power, the shorter the pretreatment time and the higher the production efficiency. For this reason, the high frequency power of the condition 4 is larger than the high frequency power in the film forming process.

  On the other hand, in the film forming process, if the duty ratio of the high frequency pulse power is reduced, the film forming rate is lowered. As a result, the time required for the film forming process increases. For this reason, the duty ratio of the high frequency pulse power in the film forming process is set longer than the duty ratio in the pretreatment process. For example, as described above, the duty ratio in the pretreatment process is set to be 300 μsec on time and 50 μsec off time, and the duty ratio in the film forming process is 600 μsec on time and 50 μsec off time. Set to. Thereby, damage to the substrate 100 can be suppressed while suppressing a decrease in the film formation rate.

  Below, the example of the method of forming a thin film with the thin film forming apparatus 10 is demonstrated with reference to FIG.

In step S <b> 11, the substrate 100, which is a semiconductor silicon substrate targeted for film formation, is stored in the chamber 11. Next, in step S <b> 12, the pretreatment gas 121 is introduced into the chamber 11 by the gas supply mechanism 15. As the pretreatment gas 121, ammonia (NH ₃ ) gas, a mixed gas of ammonia and nitrogen (N ₂ ), hydrogen (H ₂ ) gas, or the like is used.

  In step S13, the inside of the chamber 11 is depressurized by the gas exhaust mechanism 16, and the pressure of the pretreatment gas 121 in the chamber 11 is set to a predetermined value.

  In step S 14, the high frequency power supply 14 is turned on, and high frequency pulse power is supplied between the sample holder 12 and the high frequency electrode 13. Thereby, the pretreatment gas 121 in the chamber 11 is turned into plasma, and the pretreatment before the film forming treatment step is started. That is, as illustrated in FIG. 2, hydrogen radicals in the plasma of the pretreatment gas 121 are bonded to dangling bonds (dangling bonds) of the substrate 100. At this time, the control device 17 outputs the high-frequency pulse power from the high-frequency power source 14 with the first duty ratio. The first duty ratio, the high-frequency pulse power, and the pretreatment process time are set so as not to damage the substrate 100 and to obtain the passivation effect of the substrate 100. For example, the first duty ratio is set so that the on-time is 300 μsec and the off-time is 50 μsec, the high-frequency pulse power is set to 5000 W, and the preprocessing step time is set to 5 sec.

  After pre-processing for a predetermined time, the high-frequency power source 14 is turned off in step S15, and the pre-processing step is ended. Thereafter, in step S16, the pretreatment gas 121 is exhausted by the gas exhaust mechanism 16, and the chamber 11 is evacuated.

  Next, in step S <b> 17, the reaction gas 122 is introduced into the chamber 11 by the gas supply mechanism 15. In step S18, the inside of the chamber 11 is depressurized by the gas exhaust mechanism 16, and the reaction gas 122 in the chamber 11 is adjusted to a predetermined gas pressure.

  Thereafter, in step S 19, the high frequency power supply 14 is turned on, and a predetermined high frequency pulse power is supplied between the sample holder 12 and the high frequency electrode 13. Thereby, the reaction gas 122 containing the source gas in the chamber 11 is turned into plasma. By exposing the substrate 100 to the formed plasma, excited species in the plasma are reacted on the surface of the substrate 100, and a thin film is formed on the surface of the substrate 100. At this time, the control device 17 outputs the high-frequency pulse power from the high-frequency power source 14 with the second duty ratio. The second duty ratio having a long on-time ratio is set to be larger than the first duty ratio so as to obtain a predetermined film formation rate.

  After the thin film is grown to a predetermined thickness, the high frequency power supply 14 is turned off in step S20, and the film forming process is terminated. Thereafter, in step S21, the reaction gas 122 is exhausted by the gas exhaust mechanism 16, and the chamber 11 is evacuated. Thus, a thin film is formed on the substrate 100.

For example, in the manufacture of a crystalline silicon solar cell, the substrate 100 is a substrate in which an n-type semiconductor layer having a surface diffusion concentration of 1 × 10 ¹⁸ to 1 × 10 ²² is formed on a p-type silicon substrate, or an n-type silicon substrate A substrate on which a p-type semiconductor layer having a surface diffusion concentration of 1 × 10 ¹⁸ to 1 × 10 ²² is formed can be used. Moreover, the thin film formed as an antireflection film of the solar cell is a silicon nitride (SiN) film having a refractive index of 1.8 to 3.0 and a film thickness of about 50 to 150 nm. In order to form a thin film made of a silicon nitride film on the substrate 100, monosilane, ammonia, or the like is used as a source gas, and nitrogen, hydrogen, argon (Ar), helium (He), or the like is used as a carrier gas. .

  By adopting a hollow cathode electrode as the high-frequency electrode 13, high-density plasma can be stably generated in the chamber 11. As a result, the pretreatment gas 121 and the source gas are efficiently decomposed, and the pretreatment and film formation treatment for the substrate 100 can be performed in a short time. By performing the pretreatment in a short time, damage to the substrate 100 can be reduced.

  For example, as shown in FIGS. 6 and 7, a high-frequency electrode 13 having a through hole 130 can be employed. The high-frequency electrode 13 is provided with openings in the first main surface 131 and the second main surface 132 facing the substrate 100, and a through-hole penetrating between the first main surface 131 and the second main surface 132. 130.

  In the high-frequency electrode 13 having an opening on the surface, plasma generation in the through hole 130 is a hollow cathode discharge, and in this hollow cathode discharge, electrons are confined in the through hole 130 and have kinetic energy. Thus, a high-density plasma region, which is a high-density electron space, is formed in the through hole 130.

  As shown in FIG. 6, the first main surface 131 and the second main surface 132 of the high-frequency electrode 13 are formed by forming a large number of through-holes 130 in which hollow cathode discharge is generated at a constant density on the surface of the high-frequency electrode 13. A uniform high electron density electric field can be easily formed. This is because the space in which high-density plasma is generated is the through-hole 130, and thus the plasma continuity is ensured between the first main surface 131 and the second main surface 132 of the high-frequency electrode 13. . In other words, the difference in plasma density between the first main surface 131 and the second main surface 132 is automatically corrected by the bipolar diffusion property of the plasma through the through hole 130. Therefore, the thin film forming apparatus 10 can generate a uniform high-density plasma region on both surfaces of the high-frequency electrode 13.

  In addition, as shown in FIG. 7, the opening part of the through-hole 130 is tapered. That is, the diameter d2 of the opening portion of the through hole 130 is larger than the diameter d1 of the through hole 130 in the central portion of the through hole 130, that is, inside the high frequency electrode 13. For example, the taper is provided so that the diameter d1 of the through hole 130 is 5 mm and the aperture d2 of the opening is 7 mm. Thereby, there exist the following effects.

  High-density plasma is also formed in the opening portion having the taper of the through hole 130. Therefore, according to the high-frequency electrode 13 having the funnel-shaped opening, the areas of the flat regions of the first main surface 131 and the second main surface 132 where the low-density plasma region is generated are narrow, and the high-density plasma region Can be widened. As a result, the plasma density is generally high on the surface of the high-frequency electrode 13, and the film quality of the film formed using the thin film forming apparatus 10 having the high-frequency electrode 13 is improved.

  As described above, in the thin film forming apparatus 10 according to the embodiment of the present invention, the duty ratio of the high frequency pulse power in the pretreatment process is set larger than that in the film formation process. As a result, pretreatment can be realized in which damage to the substrate 100 is small and a high passivation effect can be obtained. As a result, the carrier lifetime in the substrate 100 becomes longer, and for example, the conversion efficiency of the solar cell can be improved.

  In addition, by appropriately setting the duty ratio of the high-frequency pulse power in each of the pretreatment process and the film formation process, the time required for the pretreatment process can be shortened and a desired film formation rate can be secured. This suppresses a decrease in production efficiency without degrading the characteristics of the substrate 100.

(Other embodiments)
As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the above, an example in which the sample holder 12 is a boat type on which the substrate 100 is vertically mounted has been described. However, the present invention can be applied even if the sample holder 12 is another type. For example, in the case of a cart-type sample holder 12 in which the substrate 100 is mounted horizontally, the above pre-processing and film-forming processing are performed by the thin film forming apparatus 10 in which the high-frequency electrode 13 is extended in the horizontal direction and is opposed to the substrate 100. It can be performed.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 10 ... Thin film forming apparatus 11 ... Chamber 12 ... Sample holder 13 ... High frequency electrode 14 ... High frequency power supply 15 ... Gas supply mechanism 16 ... Gas exhaust mechanism 17 ... Control apparatus 18 ... Gas supply source 19 ... Heater 100 ... Substrate 121 ... Pretreatment gas 122 ... Process gas

Claims (4)

A chamber for storing a sample holder on which a substrate to be processed is mounted;
A high-frequency electrode disposed inside the chamber and facing the substrate mounted on the sample holder;
A gas supply mechanism for supplying either a pretreatment gas used in a pretreatment step or a reaction gas containing a raw material gas for a thin film formed on the substrate into the chamber;
A high frequency power source that supplies high frequency pulse power between the sample holder and the high frequency electrode, excites plasma containing the pretreatment gas in the pretreatment step, and excites plasma containing the source gas in the film formation treatment step When,
The high-frequency pulse power is output from the high-frequency power source at a first duty ratio in the pre-processing step, and the on-time ratio is longer than the first duty ratio in the film-forming step. A control device for controlling the high-frequency power supply so that high-frequency pulse power is output from the high-frequency power supply , wherein the first duty ratio does not damage the substrate in the pretreatment step, and A thin film forming apparatus, which is set so as to obtain a passivation effect by combining hydrogen radicals in the plasma containing a processing gas with dangling bonds of the substrate . The thin film forming apparatus according to claim 1, wherein the high-frequency pulse power in the film forming process is smaller than the high-frequency pulse power in the pretreatment process. Wherein the substrate and the opposite major surfaces of the high-frequency electrode, a thin film forming apparatus according to claim 1 or 2, characterized in that the opening of the through hole passing through the high-frequency electrode is provided. The thin film forming apparatus according to claim 3 , wherein the opening is tapered so that a diameter of the opening is larger than a diameter at an intermediate portion of the through hole.

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