JP2005039051A - Coaxial cable for high frequency power supply, plasma surface treatment apparatus comprising the same, and a plasma surface treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface treatment apparatus and a surface treatment method capable of uniformly generating a plasma in a VHF band (30 MHz to 300 MHz) between a pair of electrodes in a vacuum vessel with high reproducibility, so as to apply a uniform plasma surface treatment even to a large-area substrate of a 1m × 1m class. <P>SOLUTION: A coaxial cable is disclosed with a structure that the impedance of the outer surface of the outer conductor viewed from one end of the coaxial cable toward the other end is made infinite. The coaxial cable 19 for high frequency power supply is used to supply the output of a high frequency power supply 15 to a pair of the electrodes 2, 4, in the surface treatment apparatus and method for treating the surface of the substrate 13 located to one of a pair of the electrodes 2, 4 in the vacuum vessel 1 by utilizing the plasma. The plasma surface treatment apparatus and the plasma surface treatment method employ the coaxial cable. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface treatment apparatus and a surface treatment method for performing a predetermined treatment on a surface of a substrate using plasma. The present invention particularly relates to a surface treatment apparatus and a surface treatment method using reactive plasma that generates plasma by glow discharge of a discharge gas generated by high-frequency power having a frequency of 30 MHz to 300 MHz.

  Various kinds of processing are performed on the surface of the substrate using reactive plasma, and various electronic devices are manufactured. LSI (Large Scale Integrated Circuit), LCD (Liquid Crystal Display), Amorphous Si Solar Cell, Thin Film Polycrystalline Si System Already put into practical use in the fields of solar cells, photoconductors for copying machines, and various information recording devices. In addition, practical application is also progressing in the field of manufacturing ultra-hard films such as diamond thin films and cubic boron nitride (C-BN).

  The above technical fields cover various fields such as thin film formation, etching, surface modification, and coating, all of which utilize the chemical and physical action of reactive plasma. The apparatus and method relating to the generation of the reactive plasma are roughly classified into two typical techniques.

  The first typical technique is described in, for example, Patent Documents 1 and 2 and Non-Patent Documents 1 and 2, and two parallel plate electrodes composed of a non-ground electrode and a ground electrode are paired for plasma generation. It is characterized by using. The second representative technique is described in, for example, Patent Documents 3 and 4, and is characterized by using a pair of a ladder electrode and a flat plate electrode for plasma generation.

  The features of the technique described in the above document are roughly as follows. In the technique of Patent Document 1, the distance between two longest points of any two points on the periphery of the surface facing the space where the plasma is generated is a quarter of the wavelength of the high-frequency power. And a plurality of power supply points are set at equal positions. In the technique of Patent Document 2, the position of the power supply point of the non-ground electrode is set on the side surface of the boundary between the first surface that is in contact with the space where plasma is generated and the second surface that is the back side of the first surface. It is characterized by being located. The technique of Patent Document 3 is characterized in that the shape of the non-grounded electrode is a ladder type (ladder type). In the technique of Patent Document 4, by changing temporally the phase difference between the voltage of power supplied to one certain feeding point on the electrode and the voltage of the power supplied to at least one other feeding point, It is characterized in that the electric field distribution between the pair of electrodes is averaged, and as a result, the spatial distribution of the plasma intensity is made uniform. The technology of Non-Patent Document 1 is characterized in that an H-shaped feeding band is installed on the back side of the surface of the non-grounded electrode that contacts the plasma, and a plurality of feeding points are installed on the H-shaped feeding band. Yes. The technology of Non-Patent Document 2 is that a reactance circuit is installed on the opposite side of the feeding point of the non-grounded electrode, that is, at the end of the electrode located in the direction of power propagation, and It is characterized by controlling the position of the antinode of the standing wave generated in the.

As described above, there are several types of conventional technologies. As a typical example of a large area plasma technology using a VHF band (30 MHz to 300 MHz), which is attracting attention as a method for generating high-density plasma, The plasma surface treatment apparatus and method described in Documents 1 and 4 will be described with reference to FIGS.

(Conventional example 1)
First, an apparatus and method described in Patent Document 1 will be described with reference to FIGS. 8 and 9 as a conventional first representative technique. FIG. 8 is a configuration diagram of a plasma surface treatment apparatus according to a first conventional representative technique, and FIG. 9 is a diagram showing a structure of a connection portion between an electrode and a power supply coaxial cable according to a first conventional representative technique. FIG. As shown in FIG. 8, the first typical example of the prior art includes a vacuum vessel 101, a ground electrode 104 on which a substrate 113 is installed, a non-ground electrode 102 disposed facing the ground electrode 104, and a high-frequency signal applied to these electrodes. A power supply system for supplying electric power, a discharge gas supply system, and an exhaust system are provided.

  The ground electrode 104 incorporates a substrate heater 103 and sets the temperature of the substrate 113 to a predetermined value. The non-ground electrode 104 is specifically a rectangular plate (area of about 500 mm × 500 mm to about 1,000 mm × 1,000 mm), and the material is stainless steel.

  On the other hand, the non-grounded electrode 102 is attached to the upper portion of the vacuum vessel 101 via an insulator 106. The inside of the non-grounded electrode 102 is hollow, and a large number of gas ejection holes 102b having a diameter of about 0.5 mm are arranged at a hole interval of 10 to 15 mm on a surface 102a in contact with a space 192 where plasma is generated.

  On the upper surface of the non-ground electrode 102, an opening 102c for the discharge gas is disposed. The opening 102c is connected to a discharge gas introduction tube 109 via a connecting member 194 (material is ceramic), and silane gas (SiH4), for example, is supplied via a valve 193 from a material gas supply source (not shown). The gas in the vacuum vessel 101 is discharged from the vacuum pump 112 through the exhaust pipe 111. The substrate 113 is installed on the ground electrode 104 with the gate valve 195 opened, and is heated to a predetermined temperature by the substrate heater 103 and the substrate heater power source 191.

  At the power supply points 114a and 114b of the non-grounded electrode 102, an output of a high-frequency power source 115 that generates predetermined high-frequency power includes a power distributor 190 that distributes the output into a plurality of parts, and first and second matching units. 117a and 117b, and first, second, third and fourth coaxial cables 116a, 116b, 116c and 116d. FIG. 9 shows the structure of the connection portion between the electrode 102 and the power supply coaxial cable. In FIG. 9, the core wire 123 of the coaxial cable 116 d is connected to the power supply point 114 b and the vicinity thereof is insulated by the insulating ring 121. The end portion of the outer conductor of the coaxial cable 116d is connected to the vacuum vessel 101 through the ground conductor 196. Note that reference numerals 102 and 106 in FIG. 9 are a non-grounded electrode and an insulator, respectively.

  When generating plasma, the output of the high-frequency power supply 115 is set to a predetermined value, and the first and second matching units 117a are viewed while watching a traveling wave / reflected wave detector (monitor) attached to a high-frequency power supply (not shown). 117b are sequentially adjusted to set a state in which the reflected wave is approximately 1 to 10%. As a result, about 90 to 99% of the output of the high-frequency power source is supplied downstream from the matching units 117a and 117b.

  Next, the case where an amorphous Si (a-Si) film, for example, is formed using the apparatus shown in FIGS. 8 and 9 will be described. The gate valve 195 is opened, the substrate 113 is placed on the ground electrode 104, and the gate valve 195 is returned to the closed state. The vacuum pump 112 is driven to exhaust the pressure in the vacuum vessel 101 to about 1E-7 Torr (1.33E-5 Pa). The temperature of the substrate 113 is set to a predetermined temperature using the substrate heater 103 and the substrate heater power source 191. A predetermined amount of, for example, silane gas is supplied through the discharge gas introduction tube 109 to keep the inside of the vacuum vessel 101 at 0.05 to 0.5 Torr (6.65 to 66.5 Pa), and a pair of electrodes using the power supply system. Power is supplied to 102 and 104. Thereby, glow discharge plasma is generated between the non-ground electrode 102 and the ground electrode 104. When the silane gas is turned into plasma, radicals such as SiH 3, SiH 2, and SiH existing therein are diffused by a diffusion phenomenon, and are adsorbed and deposited on the surface of the substrate 113. As a result, an amorphous Si film is formed.

  In addition, by adjusting the mixing ratio of discharge gas, for example, the flow ratio of SiH4 and H2, the pressure, the substrate temperature, and the plasma generation power as the film forming conditions, not only a-Si but also microcrystalline Si and polycrystalline It is known that Si films can be produced.

  Further, it is known that etching treatment of the substrate surface can be performed by using an etching gas such as SF6, SiCl4, CF4, and NF3 as the discharge gas.

(Conventional example 2)
Next, as a second conventional representative technique, a conventional technique described in Patent Document 4 will be described with reference to FIGS. FIG. 10 is a conceptual diagram of a conventional surface treatment apparatus according to the second technique, FIG. 11 is a block diagram of a power feeding system related to the apparatus shown in FIG. 10, and FIG. 12 is an electrode and power supply related to the apparatus shown in FIG. FIG. 13 is an explanatory diagram of a voltage wave related to a conventional second representative technique, and FIG. 14 is a diagram of a combined voltage of a voltage related to the second representative technique. It is explanatory drawing. As shown in FIGS. 10 and 11, the conventional plasma surface processing apparatus of the second representative technique includes a vacuum vessel 201, a ground electrode 204 on which a substrate 213 is installed, and a ladder that is disposed facing the ground electrode 204. A non-grounded electrode 202 having a mold structure (referred to as a ladder electrode) and a power supply system for supplying high-frequency power between these electrodes, a discharge gas supply system, and an exhaust system are provided.

  A vacuum pump 212 is connected to the vacuum vessel 201 via an exhaust pipe 211 that exhausts a gas such as a reaction gas in the vacuum vessel 201. An earth shield 208 is disposed. The earth shield 208 is used in combination with the exhaust pipe 211 to discharge the reaction gas and other products introduced from the reaction gas introduction pipes 209 a and 209 b through the exhaust pipe 211. When the vacuum pump 212 is operated, it is evacuated to a pressure of about 1E-6 Torr (1.33E-4 Pa). When, for example, silane gas is supplied as a reaction gas from the reaction gas introduction pipes 209a and 209b, the silane gas uniformly flows between the ladder electrode 202 and the ground electrode 204 from a large number of gas ejection holes (not shown).

  The substrate 213 is held by the ground electrode 204 and heated to a predetermined temperature by a built-in heater 203 (not shown). For the substrate, glass having a size of about 460 mm × 460 mm and a thickness of about 1 mm is used. The ladder electrode 202 is manufactured by assembling a round bar member having a size of, for example, an outer dimension of about 520 mm × 520 mm and a diameter of about 6 mm in a ladder shape at equal pitch intervals. As shown in FIGS. 11 and 12, the electrode 202 is connected to coaxial cables 216a, 216b, 216c and 216d at four feeding points 214a to 214d.

  As shown in FIGS. 10 and 11, the power feeding system includes a high-frequency transmitter 232, a signal distributor 233, a phase shifter (phase shifter) 234, a pair of power amplifiers 236a and 236b, a pair of matching units 217a and 217b, and a pair. Power distributors 240a and 240b, a computer 235, and the like. The phase of one voltage of the two outputs of the signal distributor 233 is temporally changed within a range of ± 180 degrees by a phase shifter 234 driven and controlled by the computer 235. The signal having the phase change is amplified by the second power amplifier 236b and supplied to the feed points 214c and 214d via the second matching unit 217b and the second power distributor 240b. The other output is supplied to the feed points 214a and 214b via the first power amplifier 236a, the first matching unit 217a, and the first power distributor 240a.

  FIG. 12 shows the structure of the connecting portion between the ladder electrode 202 and the power supply coaxial cable. In FIG. 12, a core wire (internal conductor) 223 of a coaxial cable 216a installed through the earth shield 208 is connected to the feeding point 214a. The core wire 223 is surrounded by an insulating ring 237 for preventing discharge. The outer conductor of the coaxial cable is connected to the earth shield 208 by a mounting ring 239, and its end is shaped by a coupling 241.

  In the case of generating plasma, the first and second matching units 217a and 217b are sequentially adjusted while watching the traveling wave / reflected wave detectors (monitors) (not shown) attached to the power amplifiers 236a and 236b, and the reflected waves Is set to about 1 to 10%. As a result, the output of the power amplifiers 236a and 236b is supplied approximately 90 to 99% from the matching units 217a and 217b to the downstream side, respectively.

  Next, a case where a microcrystalline Si film is manufactured using the apparatus shown in FIGS. 10 and 11 will be described. A substrate 213, for example, glass having a size of 460 mm × 460 mm is placed on the ground electrode 204 from a gate valve (not shown), and the gate valve is closed. Subsequently, as in Conventional Example 1, the vacuum pump 212 is driven to evacuate to a predetermined degree of vacuum. The temperature of the substrate 213 is set to 200 ° C., and the pressure is set to 0.15 Torr (20 Pa) while supplying silane gas at 500 sccm and hydrogen gas at 3,500 sccm.

  Then, the frequency of the high frequency oscillator 232 is set to 60 MHz, for example. The phase shifter 234 modulates the phase of one output signal (sine wave) of the signal distributor 233 temporally into a triangular wave. In this case, the electric field between the ladder electrode 202 and the ground electrode 204 changes correspondingly because the phase difference of the voltage of the power supplied to the feeding points 214a, 214b and 214c, 214d changes with time. This is shown as a voltage wave in FIG.

In FIG. 13, the position of the ladder electrode 202 in the length direction is x, the voltage wave propagating in the right direction (the positive direction of x) is W1 (x, t), and the voltage wave propagating in the left direction (the negative direction of x). Is W2 (x, t), it is expressed as follows.
W1 (x, t) = V0 · sin (ωt + 2π / λ). . . . . (1)
W2 (x, t) = V0 · sin {ωt−2π (x−L0) / λ + Δθ}. . . (2)
However, V0 is the amplitude of the voltage, ω is the angular frequency of the voltage, λ is the wavelength of the voltage, t is the time, L0 is the length in the propagation direction of the ladder electrode 202, and Δθ is the phase difference. The voltage composite wave W (x, t) is expressed by the following equation.
W (x, t) = W1 (x, t) + W2 (x, t) = 2 · V0cos {2π (x−L0 / 2) / λ−Δθ / 2} · sin {ωt + (2πL0 / λ + Δθ / 2} ... (3)

  FIG. 14 conceptually shows the combined wave W (x, t) that can be expressed by the above equation (3). In the case of Δθ = 0, the intensity of the generated plasma is strong at the center portion (x = L0 / 2) of the ladder electrode and weak at both ends. The strong plasma portion is the right end portion of the ladder electrode when Δθ> 0, and the left end portion when Δθ <0. That is, by using the phase shifter 234, Δθ in the equation (3) is changed in a triangular wave shape over time between −180 degrees and +180 degrees, so that plasma with uniform intensity on a time average can be obtained. Generated. As a result, the nonuniformity of the plasma intensity is averaged over time, so that a microcrystalline Si film having a uniform film thickness distribution can be obtained.

JP-A-8-325759 (page 3-9, Fig. 1-4) Japanese Patent Laid-Open No. 2002-12977 (page 5-13, FIG. 1-6) JP-A-4-236811 (page 2-4, Fig. 1-4) Japanese Patent Laid-Open No. 2001-257098 (page 3-8, Fig. 1-3)

L. Sansonnens, A. Pletzer, D. Magni, AA Howling, Ch. Hollenstein and JPMSchmitt ,: A voltage uniformity study in large-area reactors for RF plasma deposition, Plasma Source Sci. Technol. 6 (1997), p. 170-178. J. Kuske, U. Stephan, O. Steinke and S. Rohleck: Power feeding in large area PECVD of amorphous silicon, Mat. Res. Soc. Symp. Proc. Vol. 377 (1995), p.27-32.

  The above-mentioned plasma surface treatment technology, that is, the plasma surface treatment apparatus and the plasma surface treatment method, reduce the product cost and increase the area of the product due to the improvement in productivity in any of the industrial fields such as LCD, LSI, electronic copying machine and solar cell. The need for large area, uniformization, and high-speed processing is increasing year by year for improving performance (specifications) such as wall-mounted TV.

  Recently, in order to meet the above needs, not only in industry but also in academic societies, especially in plasma CVD (chemical vapor deposition) technology and plasma etching technology, the VHF band (characterized by high density plasma and low electron temperature ( Research and development on plasma CVD using a power source of 30 MHz to 300 MHz) and a high-speed film formation and a large area and high-speed plasma etching have become active. However, the following problems still exist in the prior art.

  (1) The first problem is to increase the area of plasma surface treatment (improvement of productivity and improvement of performance). As an apparatus and method for plasma surface treatment, several types of techniques described above are used. For example, when an a-Si film is manufactured by the conventional VHF plasma technology, assuming that reproducibility is ensured, a film thickness distribution of about ± 10% to 15% and a thickness of about 100 cm × 100 cm are obtained when the substrate area is about 50 cm × 50 cm. Is a film thickness distribution of about ± 15 to 20%.

  In general, in the LCD field, the film thickness distribution ensures reproducibility of about ± 5%, and in the solar cell field, the film thickness distribution ensures reproducibility of about ± 10%. It has become. Therefore, there is a problem that the prior art cannot be practically used for manufacturing a product with a large area of 1 mx 1 m class, which is expected as a plasma application in a power supply frequency of VHF region (30 MHz to 300 MHz).

  (2) The second problem is speeding up the surface treatment (improving productivity). The premise is that it is effective to increase the power generation frequency of plasma generation to the VHF band of 30 MHz to 300 MHz in order to speed up the plasma surface treatment technology on the premise of ensuring product quality. It has become. However, when the power supply frequency is increased to the VHF band, there arises a problem that the film thickness distribution is remarkably deteriorated.

  The reason can be considered as follows. As pointed out in Patent Documents 1, 2, 4 and Non-Patent Documents 1, 2, when the high frequency of the power supply becomes the VHF band, the wavelength of the radio wave, the propagation path of the power supply system, and the propagation path on the electrode It is considered that the spatial uniformity of the plasma density cannot be ensured because the lengths are substantially equal and a wave interference phenomenon (the wave traveling wave and the reflected wave interfere) occurs. Another reason is considered to be due to an increase in impedance in the power propagation path due to the skin effect, which is a phenomenon peculiar to VHF, and its non-uniformity.

  The present inventor has recently proposed an electric power supply system shown below as an essential cause regarding the difficulty of large area, uniformization, and high speed processing by the conventional VHF plasma. I found that structural problems were involved.

  Specifically, in FIG. 9 and FIG. 12 in the prior art, the connection part between the coaxial cable and the electrode of the constituent member of the output circuit of the power feeding system has a shape in which lines having different structures are connected. That is, the coaxial cable is a transmission system in which the inner conductor (core wire) and the inner surface of the outer conductor are used as the forward path and the return path, but the structure of the electrode serving as a load is a structure corresponding to two parallel lines unlike the coaxial cable. It is. As a result, a leakage current is generated at the connection point. This phenomenon becomes a problem when the power supply frequency is in the VHF band. This is shown in FIG. In FIG. 6, inside the coaxial cable, a current I having the same amplitude and a phase different by 180 degrees flows through the inner surface of the core wire and the outer conductor, but currents I1 and I2 different from the above-mentioned I from the end of the coaxial cable. And I3 are flowing out. The difference in current between the inside and the end of the coaxial cable is the current represented by I3, which is a problem phenomenon. Here, I3 is called a leakage current. FIG. 6 conceptually shows a certain moment of high-frequency power current at the junction between the end of the coaxial cable and the pair of electrodes. Changes over time.

  When the location and concept of the leakage current shown in FIG. 6 are specifically considered by the theory of the transmission circuit, it is as follows. In FIG. 6, the current flowing inside the coaxial cable core wire and the outer conductor is I, the current flowing through the connection line between the power supply location of the pair of electrodes and the coaxial cable is I1, I2, and the outside of the outer conductor of the coaxial cable. Is represented by I3 (referred to herein as leakage current). The impedance of the pair of electrodes viewed from the end of the coaxial cable is considered to be separable into an unbalanced impedance and a balanced impedance, and each is represented by Za and Zb. Further, the connection between the coaxial cable and the electrode in FIG. 6 is connected to the unbalanced transmission system model (transmission path in which the potentials of both lines are equal and the ground is the return path) and the balanced transmission system model (the current amplitude of the forward path and the return path is equal). , Each model is expressed as shown in FIGS. 7A and 7B. 7A and 7B are represented by symbols illustrated in FIGS. 7A and 7B, respectively.

According to the theory of the transmission circuit, in FIGS. 6 and 7, the currents I1, I2 and the leakage current I3 flowing through the connection line are expressed by the following equations.
I1 = Ia / 2-Ib. . . . . (4)
I2 = Ia / 2 + Ib. . . . . (5)
I2 + I3 = −I. . . . . . . . . (6)
I3 = −Ia. . . . . . . . . (7)
The impedance of the unbalanced transmission system has the following relationship.
Va / Ia = Z3 + Za. . . . (8)
However, Z3 is the impedance which looked at the right side from the outer end part of the outer conductor of a coaxial cable in Fig.7 (a). In addition, the impedance of the balanced transmission system has the following relationship.
Vb / Ib = Zb. . . . . . (9)
In addition, there is the following relationship regarding the voltage and current ratio of the unbalanced transmission system and the balanced transmission system.
Va / Vb = -1 / 2. . . . (10)
Ia / Ib = −Zb / {2 (Za + Z3)}. . . . (11)

  In the right side of the above equation (11), generally, the unbalanced impedance Za is not an infinite value, so the current Ia does not become zero unless the impedance Z3 is an infinite value. That is, a leakage current I3 is generated.

  None of the conventional types of plasma surface treatment apparatuses are manufactured so that the impedance Z3 has an infinite value. Therefore, the conventional technique has a problem that the leakage current I3 is generated. That is, there is a phenomenon in which leakage current occurs due to the ground, that is, the structure inside the vacuum vessel, at the connection between the coaxial cable shown in FIGS. 9 and 12 and the power supply location of the pair of electrodes.

  This leakage current is a cause of a non-uniform electric field in the vicinity of the power supply location and causes abnormal discharge. This abnormal discharge is a very serious problem because it is an obstacle to uniform plasma generation.

  Further, since the leakage current is a phenomenon in which a structure inside the vacuum vessel is interposed, it is strongly influenced by individual characteristics of the structure. Therefore, the adjustment work for generating plasma in the prior art requires a great deal of labor and time for selecting optimum conditions for grounding the coaxial cable and evaluating reproducibility. In a production apparatus or the like, since the grounding condition of the apparatus changes every time the apparatus is maintained, it may be difficult to manufacture a product with reproducibility.

  As described in detail above, in the prior art, it is still difficult to apply VHF plasma CVD and plasma etching to a large area substrate required for mass productivity improvement and cost reduction, for example, a large area substrate of size 1 mx 1 m class, It seems impossible. Under such circumstances, researches are active in related academic societies such as the Japan Society of Applied Physics and the Institute of Electrical Engineers of Japan, but the success of the surface treatment method using VHF plasma and its apparatus for 1mx1m class large area substrates has been announced. It has not been.

  Therefore, the present invention has been made to solve the above problems, and has been considered difficult in the prior art, for example, using a frequency in the VHF band (30 MHz to 300 MHz) even for a large area substrate of 1 mx 1 m class. An object of the present invention is to provide a plasma surface treatment apparatus and a plasma surface treatment method excellent in high speed and uniformity.

  In order to achieve the above object, according to the first aspect of the present invention, a vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, and a substrate are set. A pair of electrodes composed of a first electrode and a second electrode disposed opposite to the first electrode, and a power supply system for supplying high-frequency power of a high-frequency power output to the pair of electrodes are generated. A coaxial cable for high-frequency power supply used in a plasma surface treatment apparatus that treats the surface of a substrate using plasma, the coaxial cable on the outer conductor outer surface at the end of the pair of electrodes of the coaxial cable The impedance viewed from the other end of the electrode is a value 100 times or more larger than the impedance between the pair of electrodes.

  Similarly, in order to achieve the above object, the invention according to claim 2 of the present application is that a vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, and a substrate are set. A pair of electrodes composed of a first electrode and a second electrode disposed opposite to the first electrode, and a power supply system for supplying high-frequency power of a high-frequency power output to the pair of electrodes, A coaxial cable for high-frequency power supply used in a plasma surface treatment apparatus that treats the surface of a substrate using generated plasma, wherein the coaxial cable and an external conductor are used as an input portion and the coaxial cable At the other end of the cable, the length is a quarter of the wavelength λ of the high frequency power output considering the wavelength shortening rate, that is, λ / 4, and one end face of the cylindrical conductor is opened, Connect the other end to the outer conductor of the coaxial cable And an insulating ring is installed between the cylindrical conductor and the coaxial cable, and the open end face of the cylindrical conductor and the end face of the coaxial cable are installed on the same plane, and The coaxial cable has a configuration in which a core wire at the other end and an outer conductor are used as an output portion.

  In the above-mentioned claim 2 (the same applies to other claims), the wavelength λ in consideration of the wavelength shortening rate is the wavelength of the radio wave when propagating inside the coaxial cable, and is the wavelength shortening rate, for example, the dielectric of the coaxial cable. When the body is polyethylene, it means 0.67 or 0.34 when alumina, and the product of the wavelength of the radio wave corresponding to the output frequency of the high frequency power source when propagating in vacuum.

  Similarly, in order to achieve the above object, the invention according to claim 3 of the present application is a set of a vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, and a substrate. A pair of electrodes composed of a first electrode and a second electrode disposed opposite to the first electrode, and a power supply system for supplying high-frequency power of a high-frequency power output to the pair of electrodes, A coaxial cable for high-frequency power supply used in a plasma surface treatment apparatus that treats the surface of a substrate using generated plasma, wherein the coaxial cable and an external conductor are used as an input portion and the coaxial cable The other end of the cable is covered with a tube-shaped conductor open at both ends and a cylindrical conductor with one end open, and the outer surface of the tube-shaped conductor and the inner surface of the cylindrical conductor are in close contact with each other. The other end face of the type conductor is outside the coaxial cable. The distance between one end face of the tubular conductor and the closed end face of the cylindrical conductor is a quarter of the wavelength λ of the high-frequency power output considering the wavelength shortening rate. 1 or λ / 4, and an insulating ring is installed between the tubular conductor and the outer conductor of the coaxial cable, and one end face of the tubular conductor and the end face of the coaxial cable are on the same plane. And having a configuration in which the core wire and the outer conductor at the other end of the coaxial cable are used as the output section.

  Similarly, in order to achieve the above object, the invention according to claim 4 of the present application is that a vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, and a substrate are set. A pair of electrodes composed of a first electrode and a second electrode disposed opposite to the first electrode, and a high-frequency power supply coaxial cable for supplying high-frequency power of a high-frequency power output to the pair of electrodes A high-frequency power supply coaxial cable according to any one of claims 1 to 3, wherein the high-frequency power supply coaxial cable is a plasma surface treatment apparatus that treats the surface of the substrate using the generated plasma. It is comprised by the coaxial cable for electric power supply, It is characterized by the above-mentioned.

  Similarly, in order to achieve the above object, the invention according to claim 5 of the present application is a set of a vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, and a substrate. A pair of electrodes composed of a first electrode and a second electrode disposed opposite to the first electrode, and a high-frequency power supply coaxial cable for supplying high-frequency power of a high-frequency power output to the pair of electrodes A high-frequency power supply coaxial cable according to any one of claims 1 to 3, wherein the high-frequency power supply coaxial cable is a plasma surface treatment method for treating a surface of a substrate using generated plasma. It is constituted by a coaxial cable for power supply, and plasma surface treatment is performed.

  According to the coaxial cable for high-frequency power supply of claim 1, the vacuum vessel provided with the exhaust system, the discharge gas supply system for supplying the discharge gas into the vacuum vessel, and the first electrode on which the substrate is set And a pair of electrodes composed of a second electrode disposed opposite to the first electrode, and a power supply system configured by a coaxial cable for high-frequency power supply that supplies high-frequency power of a high-frequency power output to the pair of electrodes. A plasma surface treatment apparatus for treating a surface of a substrate using generated plasma, wherein the other end portion of the coaxial cable on the outer conductor outer surface of the pair of electrode ends of the coaxial cable is provided. Since the impedance viewed from the direction is at least 100 times greater than the impedance between the pair of electrodes, leakage current at the power supply unit to the pair of electrodes can be suppressed, and the pair of electrodes Since the plasma uniformity can be improved, the spatial distribution of the high-density plasma using the power source in the VHF band (30 MHz to 300 MHz), which has been regarded as difficult in the past, can be made uniform. It is possible to improve the film speed and the etching speed and improve the uniformity with good reproducibility. This effect is remarkably large not only in the LSI, LCD, and photoconductor photoconductor industries, but also in the contribution relating to productivity improvement in the solar cell industry.

  According to the coaxial cable for high-frequency power supply of claim 2, the vacuum vessel provided with the exhaust system, the discharge gas supply system for supplying the discharge gas into the vacuum vessel, and the first electrode on which the substrate is set And a pair of electrodes composed of a second electrode disposed opposite to the first electrode, and a power supply system configured by a coaxial cable for high-frequency power supply that supplies high-frequency power of a high-frequency power output to the pair of electrodes. In the plasma surface treatment apparatus for treating the surface of the substrate using the generated plasma, the core wire and the outer conductor of one end of the coaxial cable as an input unit, the other end of the coaxial cable, Cover the cylindrical conductor whose length is a quarter of the wavelength λ of the high-frequency power supply output considering the wavelength shortening rate, that is, λ / 4, and open one end face of the cylindrical conductor, and the other end face The external conductor of the coaxial cable And an insulating ring is installed between the cylindrical conductor and the coaxial cable, and the open end face of the cylindrical conductor and the end face of the coaxial cable are installed on the same plane, and Since the configuration is such that the core wire and the outer conductor at the other end of the coaxial cable serve as the output section, leakage current at the power supply section to the pair of electrodes can be suppressed, and the plasma between the pair of electrodes can be suppressed. Since the uniformity can be improved, the spatial distribution of the high-density plasma using the power supply in the VHF band (30 MHz to 300 MHz), which has been regarded as difficult in the past, can be made uniform, and the uniform surface treatment for the substrate, that is, the film forming speed and etching. The speed and uniformity can be improved with good reproducibility. This effect is remarkably large not only in the LSI, LCD, and photoconductor photoconductor industries, but also in the contribution relating to productivity improvement in the solar cell industry.

  According to the coaxial cable for high-frequency power supply of claim 3, the vacuum vessel provided with the exhaust system, the discharge gas supply system for supplying the discharge gas into the vacuum vessel, and the first electrode on which the substrate is set And a pair of electrodes composed of a second electrode disposed opposite to the first electrode, and a power supply system configured by a coaxial cable for high-frequency power supply that supplies high-frequency power of a high-frequency power output to the pair of electrodes. In the plasma surface treatment apparatus for treating the surface of the substrate using the generated plasma, the core wire and the outer conductor of one end of the coaxial cable as an input unit, the other end of the coaxial cable, A tubular conductor open at both ends and a cylindrical conductor open at one end are covered, the outer surface of the tubular conductor and the inner surface of the cylindrical conductor are in close contact, and the other end surface of the cylindrical conductor is Closely connected to the outer conductor of the coaxial cable And the distance between one end face of the tubular conductor and the closed end face of the cylindrical conductor is a quarter of the wavelength λ of the high-frequency power output considering the shortening rate, that is, λ / 4 and an insulating ring is installed between the outer conductor of the tubular conductor and the coaxial cable, and one end face of the tubular conductor and the end face of the coaxial cable are installed on the same plane, And since it is the structure which makes the core wire and outer conductor of the other end part of this coaxial cable an output part, the leakage current in the power supply part to the pair of electrodes can be suppressed, and the plasma between the pair of electrodes Therefore, the spatial distribution of high-density plasma using a power supply in the VHF band (30 MHz to 300 MHz), which has been regarded as difficult in the past, can be made uniform. Improved etching speed and uniformity But it is possible with good reproducibility. This effect is remarkably large not only in the LSI, LCD, and photoconductor photoconductor industries, but also in the contribution relating to productivity improvement in the solar cell industry.

  According to the plasma surface treatment apparatus of claim 4, a vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, a first electrode on which a substrate is set, and the A pair of electrodes composed of a second electrode disposed opposite to the first electrode, and a power supply system configured by a coaxial cable for high-frequency power supply that supplies high-frequency power of a high-frequency power output to the pair of electrodes. 4. A plasma surface treatment apparatus for treating a surface of a substrate using generated plasma, wherein the coaxial cable for high-frequency power supply is configured by the coaxial cable for high-frequency power supply according to any one of claims 1 to 3. Therefore, the leakage current in the power supply unit to the pair of electrodes can be suppressed, and the uniformity of the plasma between the pair of electrodes can be improved. Uniformity of spatial distribution of a high-density plasma using the power of Z～300MHz) becomes possible, uniform surface treatment to the substrate, i.e. improvement and improving uniformity of the film deposition rate and the etch rate can be reproducibly. This effect is remarkably large not only in the LSI, LCD, and photoconductor photoconductor industries, but also in the contribution relating to productivity improvement in the solar cell industry.

  According to the plasma surface treatment method of claim 5, a vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, a first electrode on which a substrate is set, and the A pair of electrodes composed of a second electrode disposed opposite to the first electrode, and a power supply system configured by a coaxial cable for high-frequency power supply that supplies high-frequency power of a high-frequency power output to the pair of electrodes. A plasma surface treatment method for treating a surface of a substrate using generated plasma, wherein the coaxial cable for high-frequency power supply is configured by the coaxial cable for high-frequency power supply according to any one of claims 1 to 3. Since the plasma surface treatment is performed, the leakage current at the power supply unit to the pair of electrodes can be suppressed, and the uniformity of the plasma between the pair of electrodes can be improved. The spatial distribution of high-density plasma using a power source in the VHF band (30 MHz to 300 MHz) can be made uniform, and uniform surface treatment on the substrate, that is, the film forming speed and the etching speed can be improved and the uniformity can be improved with good reproducibility. It is. This effect is remarkably large not only in the LSI, LCD, and photoconductor photoconductor industries, but also in the contribution relating to productivity improvement in the solar cell industry.

  Among the problems still existing in the prior art, the present inventor has paid attention to the problem related to the leakage current generated at the connection portion between the pair of electrodes and the coaxial cable for supplying the output of the high frequency power supply, and has earnestly As a result of various studies, the inventors have succeeded in creating a solution and a solution. The idea utilizes the relationship of the above equation (11), and the impedance (Z3) of the outer surface of the outer conductor viewed from one end of the coaxial cable toward the other end is made infinite. By taking measures, the leakage current that becomes a problem can be drastically suppressed.

  The basic concept of the present invention is that the ratio of the current Ia in the unbalanced system model in FIG. 6 and FIG. 7 to the current Ib in the balanced model is infinitely small, that is, at least one-hundred or less, that is, Ia / Ib < In order to suppress to 1/100, the impedance of the other end of the coaxial cable viewed from the outer surface of the outer conductor at the end of the pair of electrodes of the coaxial cable from the relationship of the equation (11) Z3 is an infinitely large value, at least about 100 times greater than the equilibrium impedance Zb between the pair of electrodes. If the current Ia in the unbalanced model is suppressed to 1% or less of the current Ib in the balanced model, the plasma phenomenon between the pair of electrodes can reduce the influence of Ia by 1% or less. This is because it is considered that the current can be controlled depending on the current Ib. As specific examples of means and methods for realizing the basic concept, two examples will be described below.

  A coaxial cable for supplying high-frequency power according to an embodiment of the present invention, a plasma surface treatment apparatus and a plasma surface treatment method constituted by the coaxial cable will be described below with reference to the drawings. In the following description, as an example of a plasma surface treatment apparatus and a plasma surface treatment method, an apparatus and method for producing an a-Si thin film necessary for producing a solar cell are described. However, the present invention is not limited to the devices and methods of the following specific examples.

  A coaxial cable for supplying high-frequency power according to Example 1, a plasma surface treatment apparatus (plasma CVD apparatus) and a plasma surface treatment method (plasma CVD method) constituted by the coaxial cable will be described below with reference to FIGS. explain. FIG. 1 is a schematic view showing the entire plasma surface treatment apparatus according to the first embodiment, FIG. 2 is a block diagram of the plasma surface treatment apparatus of FIG. 1, and FIG. 3 is a diagram of a coaxial cable for high-frequency power supply according to the first embodiment. FIG. 4 is an explanatory view showing the configuration of a specific example of FIG. 1, and FIG. 4 is an explanatory view showing a connection portion between a first specific example of a coaxial cable for high-frequency power supply and a pair of electrodes in the plasma surface treatment apparatus of FIG. .

  First, the configuration of the apparatus will be described. 1 and 2, reference numeral 1 denotes a vacuum vessel. The vacuum vessel 1 is provided with a pair of electrodes for converting a discharge gas, which will be described later, into plasma, that is, a first non-grounded electrode 2 and a second non-grounded electrode 4 incorporating a substrate heater 3 (not shown). The second non-grounded electrode 4 is fixed to the vacuum vessel 1 with insulating support members 5a and 5b. The first non-grounded electrode 2 is fixed to the vacuum vessel 1 via an insulator 6 (not shown). A large number of small holes 7 having a diameter of about 2 mm to 10 mm are arranged in the first non-grounded electrode 2 with an aperture ratio of 40% to 60%. The small holes are provided in order to allow discharge gas described later to flow uniformly between the pair of electrodes 2 and 4. It is also expected as a means for generating hollow cathode discharge that is effective in generating high-density plasma. An earth shield 8 is disposed around the first non-grounded electrode 2. The earth shield 8 suppresses discharge at unnecessary portions, and discharge gas such as SiH 4 supplied from the discharge gas supply pipes 9a and 9b is disposed in the rectifying hole 10 and the non-ground electrode 2 in large numbers. The small hole 7 has a function of supplying uniformly between the pair of electrodes 2 and 4. The earth shield 8 is used in combination with the exhaust pipe 11 and a vacuum pump 12 (not shown), and thus has a function of discharging the used discharge gas that has been converted into plasma in the plasma generation space.

  The pressure in the vacuum vessel 1 is monitored by a pressure gauge (not shown), and is automatically adjusted and set to a predetermined value by a pressure adjustment valve (not shown). In the case of the present embodiment, when the discharge gas has a flow rate of about 500 sccm to 1,500 sccm, the pressure can be adjusted to about 0.01 Torr to 10 Torr (1.33 Pa to 1,330 Pa). The vacuum ultimate pressure of the vacuum vessel 1 is about 2 to 3E-7 Torr (2.66 to 3.99E-5 Pa).

  Reference numeral 13 denotes a substrate, which is placed on the second non-grounded electrode 4 by opening and closing a gate valve 39 (not shown). Then, it is heated to a predetermined temperature by a substrate heater 3 (not shown).

  1 and 2, reference numeral 15 denotes a high frequency power source, which generates power having a frequency of 30 MHz to 300 MHz (VHF band). The power is insulated by a first coaxial cable 16a, a matching unit 17, a second coaxial cable 16b, a current introduction terminal 18, a high-frequency power supply coaxial cable 19 and insulating rings 21a and 21b (not shown). The power is supplied to the feeding points 14 a and 14 b of the pair of electrodes 2 and 4 via the second feeding lines 23 and 29.

  As an example of the specific structure of the coaxial cable having the function that the impedance Z3 is infinite, a first specific example 32 of the coaxial cable for supplying high-frequency power is shown in FIG. The apparatus shown in FIG. 3 has a core wire 60 and an outer conductor 61 at one end of a coaxial cable 16c composed of a core wire 23a, an outer conductor 24 and a dielectric 25 as an input portion, and the other end of the coaxial cable, The end portion on the side connected to the pair of electrodes 2 and 4 has a structure in which a cylindrical conductor 26 is covered, and the core wire 23a and the external conductor 24 at the other end portion are used as an output portion. The cylindrical conductor 26 has a cylindrical shape, one end face is opened, and the other end face 27 is in close contact with and connected to the external conductor 24. The length is a quarter of the wavelength λ in consideration of the wavelength shortening rate of the output power of the high frequency power supply 15, that is, λ / 4. For example, the value is 0.34 × 5 m because the wavelength of the radio wave being propagated in a vacuum is 5 m when a coaxial cable with an alumina dielectric is used (wavelength reduction rate: 0.34) and the power frequency is 60 MHz. /4=0.425 m. The wavelength λ in consideration of the wavelength shortening rate is the wavelength of the radio wave when propagating inside the coaxial cable. The wavelength shortening rate, for example, 0.67 when the dielectric of the coaxial cable is polyethylene, or alumina 0.34, which is the product of the wavelengths of radio waves corresponding to the output frequency of the high frequency power source when propagating in a vacuum. The distance between the cylindrical conductor 26 and the outer conductor 24 is about 2 mm to 60 mm. Note that the value of this interval is preferably constant for the entire inner surface of the cylindrical conductor 26. Insulating rings 28a and 28b are arranged between the cylindrical conductor 26 and the outer conductor 24, and the distance between them is kept constant. As shown in FIG. 3, a second feed line 29 is connected to the end of the external conductor 24, and the power to the feed points 14a and 14b is combined with the first feed line 23 connected to the core line 23a. Used for supply. The open end face of the cylindrical conductor and the end face of the coaxial cable are set to be on the same plane.

  In FIG. 3, when a leakage current tries to flow from the point 30a on the end face of the outer conductor 24 to the point 31 on the other end face via the point 30b on one end face of the cylindrical conductor 26, Since the length from the point 30a to the point 30b is a quarter of the wavelength λ considering the wavelength shortening rate, that is, λ / 4, the impedance between the point 30a and the point 31 is infinite. The wavelength λ in consideration of the wavelength shortening rate is the wavelength of the radio wave when propagating inside the coaxial cable. The wavelength shortening rate, for example, 0.67 when the dielectric of the coaxial cable is polyethylene, or alumina 0.34, which is the product of the wavelengths of radio waves corresponding to the output frequency of the high frequency power source when propagating in a vacuum. As a result, the leakage current I3 (that is, Ia) becomes zero when Z3 is infinite, according to the relationship of the equation (11). That is, no leakage current is generated from the end face of the outer conductor 24.

  A case will be described in which the first specific example 32 of the coaxial cable for high-frequency power supply shown in FIG. 3 is used as one configuration of the surface treatment apparatus according to the first embodiment shown in FIGS. 1 and 2. FIG. 4 shows a wiring situation in which the pair of electrodes 2 and 4 shown in FIGS. 1 and 2 and the first specific example 32 of the coaxial cable for supplying high-frequency power are connected. The first coaxial cable for high-frequency power supply is connected to a feeding point 14a located in the small hole 7 portion of the inner surface of the non-grounded electrode 2 in contact with the plasma generation space (here, the surface on the opposite electrode side of the electrode is referred to as the inner surface). The core wire 23 of the coaxial cable of the specific example 32 is connected. Further, the lead wire 29 of the first specific example 32 of the coaxial cable for high-frequency power supply is connected to the feeding point 14 b on the inner surface of the ground electrode 4. The core wire 23 and the lead wire 29 are provided with insulating rings 21a and 21b made of, for example, alumina (not shown) to suppress abnormal discharge.

  Next, a method of forming a-Si for an a-Si solar cell using the above-described configuration, that is, the plasma surface treatment apparatus shown in FIGS. 1 to 4, in advance, the substrate 13 is placed on the second non-grounded electrode 4 and the vacuum pump 12 is operated to remove the impurity gas and the like in the vacuum vessel 1, and then the discharge gas supply tube 9a. 9b, while supplying SiH4 gas at 500 sccm and a pressure of 0.5 Torr (66.5 Pa), for example, high-frequency power, for example, power at a frequency of 60 MHz, is supplied to the pair of electrodes 2 and 4. The substrate temperature is kept in the range of 80 to 350 ° C., for example, 180 ° C.

  That is, the output of the high frequency power supply 15 is, for example, a frequency of 60 MHz, and the output of 500 W is the first coaxial cable 16a, the matching unit 17, the second coaxial cable 16b, the current introduction terminal 18, and the first high frequency power supply coaxial cable 19. The power is supplied to the feeding points 14a and 14b via the specific example 32 and the first and second feeding lines 23 and 29 insulated by the insulating rings 21a and 21b, respectively. In this case, by adjusting the matching unit 17, the reflected wave of the supplied power can be prevented from returning to the upstream side of the matching unit 17. As a result, plasma of SiH 4 gas is generated.

  Here, the power supplied to the feeding points 14a and 14b is controlled by the leakage current prevention function of the first specific example 32 of the coaxial cable 19 for high-frequency power supply, and the first and The two power supply lines 23 and 29 can supply the pair of electrodes 2 and 4. Accordingly, abnormal discharge such as local discharge does not occur in the vicinity of the feeding points 14a and 14b. The insulating effect of the insulating rings 21a and 21b around the first and second feeder lines 23 and 29 also suppresses abnormal discharge between them. In addition, in the prior art, since the generation method of the leakage current is related to the ground structure and wiring conditions around the pair of electrodes 2 and 4, it is difficult to generate plasma with good reproducibility. Since no current is generated, plasma with good reproducibility can be generated.

  In the above process, when SiH 4 gas is turned into plasma, radicals such as SiH 3, SiH 2, and SiH existing in the plasma are diffused by a diffusion phenomenon and adsorbed on the surface of the substrate 13, thereby depositing an a-Si film. To do. It is a known technique that microcrystalline Si or thin-film polycrystalline Si can be formed by optimizing the flow rate ratio, pressure, and power of SiH4 and H2 in the film forming conditions.

  Specific conditions in the case of film formation by the above procedure will be described below. Forming a-Si having a film forming speed of 1 nm / s and a film thickness distribution of ± 10% on a glass substrate 13 having a size of about 1200 mm × 300 mm (thickness 4 mm) is performed.

The film forming conditions are as follows.
(Film forming conditions)
・ Discharge gas: SiH4
・ Flow rate: 500sccm
・ Pressure: 0.5 Torr (66.5 Pa)
・ Power supply frequency: 60 MHz
・ Power: 500W
-Temperature of substrate 13: 180 ° C

  When plasma is generated under the film forming conditions, since the generation of leakage current at the connecting portion between the power supply system and the pair of electrodes 2 and 4 is suppressed by the high-frequency power supply coaxial cable, the density of the generated plasma The spatial distribution is uniform with good reproducibility compared to the conventional case. As a result, the film thickness distribution of the a-Si film to be formed becomes uniform with good reproducibility compared to the conventional case. Numerically, film formation becomes possible when the a-Si film thickness distribution is within ± 10.

  In this embodiment, since the power supply point is set to one point (a pair) for each of the pair of electrodes 2 and 4, the substrate size is limited to about 1200 mm × 300 mm. However, if the number of power supply points is increased, the width of the size is increased. It is natural that it can be expanded.

  Further, in the manufacture of a-Si solar cells, thin film transistors, and photosensitive drums, there is no problem in performance as long as the film thickness distribution is within ± 10%. According to the above embodiment, it is possible to obtain a significantly better film thickness distribution as compared with the conventional apparatus and method even when a power supply frequency of 60 MHz is used. This means that the industrial value related to productivity improvement and cost reduction in the manufacturing field of a-Si solar cells, thin film transistors, and photosensitive drums is remarkably large.

  FIG. 1, FIG. 2, FIG. 4 shows a coaxial cable for high-frequency power supply of Example 2 of the present invention, a plasma surface treatment apparatus (plasma CVD apparatus) and a plasma surface treatment method (plasma CVD method) constituted by the coaxial cable. This will be described with reference to FIG. FIG. 5 is an explanatory diagram illustrating a configuration of a second specific example 40 of the coaxial cable for high-frequency power supply according to the second embodiment.

  First, the configuration of the apparatus will be described. However, the same members as those in FIGS. The configuration of the apparatus of the second embodiment is the same as that of the first embodiment, that is, the first specific example 32 of the high-frequency power supply coaxial cable used as the high-frequency power supply coaxial cable 19 in FIGS. Instead of this, the second specific example 40 of the coaxial cable for supplying high-frequency power shown in FIG. 5 is used, and all other device components are the same. Therefore, the components of the apparatus other than the second specific example 40 of the coaxial cable for supplying high-frequency power will be described with reference to FIGS. 1, 2, and 4, and description thereof will be omitted here.

  In FIG. 5, the core wire 60 and the outer conductor 61 at one end of the coaxial cable 16c constituted by the core wire 23a, the outer conductor 24, and the dielectric 25 are used as input portions, and the other end portion of the coaxial cable, that is, the pair of pairs The end connected to the electrodes 2 and 4 has a structure in which both ends of the tubular conductor 26a and the cylindrical conductor 26b are covered, and the core wire 23a and the outer conductor 24 at the ends are output. Part. As shown in FIG. 5, the tubular conductor 26a and the cylindrical conductor 26b are in a relationship between an inner cylinder and an outer cylinder, and the outer surface of the tubular conductor 26a and the inner surface of the cylindrical conductor 26b are electrically connected. Is short-circuited. The distance between the overlapped portions in the relationship between the inner cylinder and the outer cylinder is adjusted using mounting bolts 42a, 42b and 41a, 41b, which will be described later. The distance between one end face 31 of the tubular conductor 26a and the end face 27 of the cylindrical conductor 26b is a quarter of the wavelength λ taking into account the wavelength shortening rate of the output power of the high frequency power supply 15 (ie, λ / 4). For example, the value is 0.34 × 5 m because the wavelength of the radio wave being propagated in a vacuum is 5 m when a coaxial cable with an alumina dielectric is used (wavelength reduction rate: 0.34) and the power frequency is 60 MHz. /4=0.425 m. The distance between the inner surface of the tubular conductor 26a and the outer conductor 24 is about 2 mm to 60 mm. Note that the value of this interval is preferably constant for the entire inner surface of the cylindrical conductor 26. Insulating rings 28a and 28b are arranged between the tubular conductor 26a and the outer conductor 24, and the distance between them is kept constant. The open end face of the cylindrical conductor and the end face of the coaxial cable are set to be on the same plane. As shown in FIG. 5, a second feed line 29 is connected to the end of the outer conductor 24, and the power to the feed points 14a and 14b is combined with the first feed line 23 connected to the core line 23a. Used for supply.

  In FIG. 5, a leakage current tends to flow from the point 30a on the end face of the outer conductor 24 to the point 31 on the end face of the tubular conductor 26a via the point 30b on the end face of the cylindrical conductor 26b. In this case, since the length from the point 30a to the point 30b is a quarter of the wavelength λ considering the wavelength reduction rate, that is, λ / 4, the impedance between the point 30a and the point 31 is infinite. That is, Z3 in the equation (11) is infinite. As a result, the leakage current I3, that is, Ia is zero according to the relationship of the equation (11). This means that no leakage current occurs.

  Next, a case where the second specific example 40 of the coaxial cable for supplying high-frequency power shown in FIG. 5 is used as one configuration of the surface treatment apparatus shown in FIGS. 1 and 2 will be described. FIG. 4 shows a wiring situation in which the pair of electrodes 2 and 4 shown in FIGS. 1 and 2 and the first embodiment 32 of the coaxial cable for high-frequency power supply are connected. The second specific example 40 of the coaxial cable is used. The coaxial cable for supplying high-frequency power to a feeding point 14a located in the small hole 7 portion of the inner surface of the first non-grounded electrode 2 in contact with the plasma generation space (here, the surface on the opposite electrode side of the electrode is referred to as the inner surface) The core wire 23 of the coaxial cable of the second embodiment 40 is connected. The lead wire 29 of the second embodiment 40 of the coaxial cable for high-frequency power supply is connected to the feeding point 14b on the inner surface of the second non-grounded electrode 4. The core wire 23 and the lead wire 29 are provided with insulating rings 21a and 21b made of, for example, alumina (not shown) to suppress abnormal discharge.

  A method for forming a-Si for an a-Si solar cell using the surface treatment apparatus having the above-described configuration will be described. 1, 2, 4, and 5, after the substrate 13 is previously placed on the second non-grounded electrode 4, the vacuum pump 12 is operated, and the impurity gas in the vacuum vessel 1 is removed. While supplying SiH4 gas from the discharge gas supply tubes 9a and 9b at, for example, 500 sccm and a pressure of 0.5 Torr (66.5 Pa), high-frequency power, for example, power at a frequency of 70 MHz, is supplied to the pair of electrodes 2 and 4. The substrate temperature is kept in the range of 80 to 350 ° C., for example, 180 ° C.

  That is, the output of the high frequency power supply 15 is, for example, a frequency of 70 MHz, and the output 500 W is the second coaxial cable 16a, the matching unit 17, the second coaxial cable 16b, the current introduction terminal 18, and the second high frequency power supply coaxial cable 19. The power is supplied to the feed points 14a and 14b via the specific example 40 and the first and second feed lines 23 and 29 insulated by the insulating rings 21a and 21b, respectively. In this case, by adjusting the matching unit 17, the reflected wave of the supplied power can be prevented from returning to the upstream side of the matching unit 17. Temporarily, the adjustment of the length of the second specific example 40 of the coaxial cable for supplying high-frequency power does not match the frequency of 70 MHz, so that the current between the coaxial cable 19 and the pair of electrodes 2 and 4 is not adjusted. If leakage has occurred, the generation of plasma is temporarily interrupted, and the length of the second specific example 40 of the coaxial cable for high-frequency power supply is adjusted to generate plasma again and reflect the power. Can be confirmed.

  In the second specific example 40 of the high-frequency power supply coaxial cable, when the frequency of the high-frequency power supply 15 is slightly changed, the length of the second specific example 40 of the coaxial cable is corresponding to the frequency. There is an advantage that it can respond by adjusting.

  Here, the power supplied to the feeding points 14a and 14b is obtained by maximizing the effect of suppressing the leakage current by adjusting the length of the second specific example 40 of the coaxial cable 19 for high-frequency power supply. The loss can be minimized and the first and second feeders 23 and 29 can supply the pair of electrodes 2 and 4. Accordingly, abnormal discharge such as local discharge does not occur in the vicinity of the feeding points 14a and 14b. In addition, the insulating effect of the insulating rings 21a and 21b around the first and second power supply lines 23 and 29 is also added to suppress abnormal discharge between them.

  When the SiH 4 gas is turned into plasma, radicals such as SiH 3, SiH 2, and SiH existing in the plasma diffuse due to a diffusion phenomenon and are adsorbed on the surface of the substrate 13, thereby depositing an a-Si film. It is a known technique that microcrystalline Si or thin-film polycrystalline Si can be formed by optimizing the flow rate ratio, pressure, and power of SiH4 and H2 in the film forming conditions.

  Specific conditions in the case of film formation by the above procedure will be described below. Forming a-Si having a film forming speed of 1 nm / s and a film thickness distribution of ± 10% on a glass substrate 13 having a size of about 1200 mm × 300 mm (thickness 4 mm) is performed.

The film forming conditions are as follows.
(Film forming conditions)
・ Discharge gas: SiH4
・ Flow rate: 500sccm
・ Pressure: 0.5 Torr (66.5 Pa)
・ Power supply frequency: 70 MHz
・ Power: 500W
-Temperature of substrate 13: 180 ° C

  When plasma is generated under the above film forming conditions, generation of leakage current at the connecting portion between the power supply system and the pair of electrodes is suppressed by the high frequency power supply coaxial cable as in the first embodiment. The spatial distribution of the plasma density is uniform with good reproducibility compared to the conventional case. As a result, the film thickness distribution of the a-Si film to be formed becomes uniform with good reproducibility compared to the conventional case. Numerically, film formation becomes possible when the a-Si film thickness distribution is within ± 10.

  However, in the second embodiment, the function of the coaxial cable for supplying the high frequency power of the apparatus constituent member is different from that in the first embodiment, and the corresponding wavelength has a slight adjustment function, so the frequency of the high frequency power supply 15 is slightly changed. Even if it is, the advantage is that it can be handled by adjusting the length without installing a new coaxial cable for supplying high-frequency power.

  In the second embodiment, since the power supply point is set to one point (a pair) for each of the pair of electrodes 2 and 4, the substrate size is limited to about 1200 mm × 300 mm. However, if the number of power supply points is increased, the width of the size is increased. Of course, it is expandable.

  Further, in the manufacture of a-Si solar cells, thin film transistors, and photosensitive drums, there is no problem in performance as long as the film thickness distribution is within ± 10%. According to the above embodiment, even if a power supply frequency of 70 MHz is used, it is possible to obtain a significantly better film thickness distribution as compared with the conventional apparatus and method. This means that the industrial value related to productivity improvement and cost reduction in the manufacturing field of a-Si solar cells, thin film transistors, and photosensitive drums is remarkably large.

1 is a schematic view showing an entire plasma surface treatment apparatus according to Embodiment 1. FIG. 1 is a block diagram of the plasma surface treatment apparatus of FIG. FIG. 3 is an explanatory diagram illustrating a configuration of a first specific example of a coaxial cable 19 for supplying high-frequency power according to the first embodiment. 1 is an explanatory diagram showing a connection portion between a first specific example of a coaxial cable for high-frequency power supply and a pair of electrodes in the plasma surface treatment apparatus of FIG. 1 according to Embodiment 1. FIG. Explanatory drawing which shows the structure of the 2nd specific example of the coaxial cable for high frequency electric power supply concerning Example 2. FIG. Explanatory drawing which shows the location and concept of the leakage current which are problems of the prior art. Explanatory drawing which shows the leakage current of FIG. 6 illustration as a model of a transmission circuit theory. The block diagram of the plasma surface treatment apparatus concerning the conventional 1st typical technique. Explanatory drawing which shows the structure of the connection part of the electrode concerning the apparatus shown in FIG. 8, and the coaxial cable for electric power supply. The conceptual diagram of the plasma surface treatment apparatus concerning the conventional 2nd typical technique. FIG. 11 is a block diagram of a power feeding system related to the apparatus shown in FIG. 10. Explanatory drawing which shows the structure of the connection part of the electrode concerning the apparatus shown in FIG. 10, and the coaxial cable for electric power supply. Explanatory drawing which shows the voltage wave concerning the conventional 2nd typical technique. Explanatory drawing which shows the synthetic wave of the voltage concerning the conventional 2nd typical technique.

Explanation of symbols

1. . . Vacuum vessel,
2. . . A first ungrounded electrode,
4). . . A second ungrounded electrode,
5a, 5b. . . Insulation support,
7. . . Small holes,
8). . . Earth shield,
9a, 9b. . . Discharge gas supply pipe,
10. . . Rectifying hole,
11. . . Exhaust pipe,
13. . . substrate,
14a, 14b. . . Feeding point,
15. . . High frequency power supply,
16a, 16b. . . First and second coaxial cables,
17. . . Matcher,
18. . . Current introduction terminal,
19. . . Coaxial cable for high frequency power supply,
23. . . A first feeder line,
23a. . . Core wire,
24. . . Outer conductor,
25. . . Dielectric,
26. . . Cylindrical conductor,
26a. . . Tubular conductor,
26b. . . Cylindrical conductor,
27. . . End face,
28a, 28b. . . Insulation ring,
29. . . A second feeder,
32. . . A first specific example of a coaxial cable for high-frequency power supply;
40. . . A second specific example of a coaxial cable for high-frequency power supply;
41a, 41b42a, 42b. . . Mounting bolt.

Claims (5)

A vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, a first electrode on which a substrate is set, and a second electrode disposed opposite to the first electrode A plasma surface treatment apparatus that includes a pair of electrodes and a power supply system that supplies high-frequency power of high-frequency power output to the pair of electrodes, and that processes the surface of the substrate using the generated plasma. A coaxial cable for supplying high-frequency power, wherein an impedance of the outer surface of the outer conductor at the end of the pair of electrodes on the side of the pair of coaxial cables viewed from the other end of the coaxial cable is between the pair of electrodes. A coaxial cable for supplying high-frequency power, characterized in that the value is 100 times greater than the impedance of the cable. A vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, a first electrode on which a substrate is set, and a second electrode disposed opposite to the first electrode A plasma surface treatment apparatus that includes a pair of electrodes and a power supply system that supplies high-frequency power of high-frequency power output to the pair of electrodes, and that processes the surface of the substrate using the generated plasma. A high-frequency power supply coaxial cable, wherein the coaxial cable has a core wire at one end and an outer conductor as an input section, and the other end of the coaxial cable has a length considering the wavelength reduction rate. Cover one-fourth of the wavelength λ of the output, that is, λ / 4, and open one end face of the cylindrical conductor, and close the other end face to the outer conductor of the coaxial cable, And the cylindrical conductor and the coaxial cable An insulating ring is installed between the cables, the open end face of the cylindrical conductor and the end face of the coaxial cable are placed on the same plane, and the core wire and the outer conductor at the other end of the coaxial cable A coaxial cable for supplying high-frequency power, characterized in that it has a configuration in which an output portion is used. A vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, a first electrode on which a substrate is set, and a second electrode disposed opposite to the first electrode A plasma surface treatment apparatus that includes a pair of electrodes and a power supply system that supplies high-frequency power of high-frequency power output to the pair of electrodes, and that processes the surface of the substrate using the generated plasma. A coaxial cable for supplying high-frequency power, wherein a core wire and an outer conductor at one end of the coaxial cable are used as an input portion, and a tubular conductor open at both ends and one end face are provided at the other end of the coaxial cable. Covering the open cylindrical conductor, the outer surface of the tubular conductor and the inner surface of the cylindrical conductor are in close contact, the other end surface of the cylindrical conductor is in close contact with the outer conductor of the coaxial cable, and One end face of the tubular conductor and the cylindrical conductor The distance from the closed end face of the body is a quarter of the wavelength λ of the high-frequency power output considering the wavelength shortening rate, that is, λ / 4, and the outer conductor of the tubular conductor and the coaxial cable An insulating ring is installed in between, and one end face of the tubular conductor and the end face of the coaxial cable are placed on the same plane, and the core wire and the outer conductor of the other end of the coaxial cable are output. A coaxial cable for supplying high-frequency power, characterized by having a configuration of being a part. A vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, a first electrode on which a substrate is set, and a second electrode disposed opposite to the first electrode A pair of electrodes composed of electrodes, and a power supply system configured by a coaxial cable for supplying high-frequency power of high-frequency power output to the pair of electrodes, and the surface of the substrate is formed using the generated plasma. 4. A plasma surface treatment apparatus for processing, wherein the high-frequency power supply coaxial cable comprises the high-frequency power supply coaxial cable according to any one of claims 1 to 3. A vacuum vessel provided with an exhaust system, a discharge gas supply system for supplying a discharge gas into the vacuum vessel, a first electrode on which a substrate is set, and a second electrode disposed opposite to the first electrode A pair of electrodes composed of electrodes, and a power supply system configured by a coaxial cable for supplying high-frequency power of high-frequency power output to the pair of electrodes, and the surface of the substrate is formed using the generated plasma. In the plasma surface treatment method to be processed, the high-frequency power supply coaxial cable is configured by the high-frequency power supply coaxial cable according to any one of claims 1 to 3, and plasma surface treatment is performed. Surface treatment method.

Images