JP2014075606A - Plasma cvd apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma CVD apparatus capable of performing uniform supply and exhaust of raw material gas even in a substrate with large area, and promptly removing higher-order silane generated in plasma space.SOLUTION: A plasma CVD apparatus comprises in a vacuum vessel: a grounded electrode serving as a substrate-holding member; and a first discharge electrode arranged in a position facing the grounded electrode. The plasma CVD apparatus comprises a structure, such that raw material gas is introduced into the vacuum vessel to generate plasma, and a thin film is formed on a surface of a substrate.

Description

  The present invention relates to a plasma CVD apparatus and a plasma CVD method. In particular, the present invention relates to a plasma CVD apparatus and a plasma CVD method for forming an amorphous silicon thin film used for silicon thin film solar cells, thin film transistors, and the like.

  As a technique for producing an amorphous silicon thin film used for a silicon-based thin film solar cell, a parallel plate type plasma CVD method using the apparatus shown in FIG. 7 is adopted. Such a conventional parallel plate type plasma CVD apparatus has a discharge electrode and a ground electrode that also serves as a substrate holding member disposed at a position facing the discharge electrode, and supplies a source gas to the surface of the discharge electrode. A plurality of small holes are provided to supply gas uniformly to the front space of the substrate, the inside of the vacuum vessel is held at a constant pressure by the exhaust system, high frequency power is applied to the discharge electrode to generate plasma, and amorphous silicon is formed on the substrate surface A thin film is formed.

  However, such a parallel plate type plasma CVD apparatus does not have a device for exhausting gas uniformly, and when a large-area substrate is used, unevenness of exhaust causes unevenness in the film quality and thickness of the amorphous silicon thin film.

Furthermore, it is known that the amorphous silicon thin film produced by the parallel plate type plasma CVD method increases the neutral dangling bonds (defects) in the film by light irradiation and causes photodegradation. Although this photodegradation has been found more than 30 years ago as the Starber-Wronski effect, it has not been resolved at present. Although the mechanism causing this photodegradation has not been clearly clarified, it is known that there is a correlation with the Si—H ₂ bond concentration in the film. Conversion efficiency of the solar cell is obtained in the case where the input energy due to the incident light normalized by 100 mW / cm ^2, the open circuit voltage Voc (V) × short circuit current density Jsc (A / cm ²⁾ × fill factor FF (%) . The curve FF is a value obtained by dividing [voltage × current] at the maximum output point in the voltage-current characteristics of the solar cell by [open circuit voltage Voc × short circuit current Isc]. Although the FF decreases due to photodegradation, it has been reported that in a film having a low Si—H ₂ bond concentration, the difference (ΔFF) between the FF before degradation and after degradation is small (Non-patent Document 1). Further, Non-Patent Document 2, before deterioration in _{Si-H 2} bond concentration 1.8% efficiency 9.00%, △ FF10.1%, and after deterioration efficiency 7.43% of an amorphous silicon film, _{Si-H 2} Amorphous silicon films having a pre-degradation efficiency of 8.79%, ΔFF of 3.9% and post-degradation efficiency of 8.09% at a bond concentration <0.9% have been reported. As described above, by using an amorphous silicon film in which the Si—H ₂ bond concentration is suppressed and ΔFF is small, a thin film solar cell with high post-degradation efficiency can be manufactured. As a cause of increasing the Si—H ₂ bond concentration, higher-order silane (Si _m H _{2m + 1} : m ≧ 4) generated during film formation is taken into the film. In order to prevent the high-order silane from being mixed into the film and form a high-quality film with little photodegradation, it is necessary to quickly remove the high-order silane from the plasma reaction region.

  As a technique for solving these problems, for example, there is an apparatus disclosed in Patent Document 1. This plasma CVD apparatus has a gas outlet having an inner diameter of 0.1 to 1.0 mm for discharging gas to the plasma space to the discharge electrode or the ground electrode, and an inner diameter for exhausting gas from the plasma space is less than the Debye length. It has a plurality of exhaust nozzles, has a gas chamber for supplying gas to the gas outlet inside the electrode, surrounds the side and back of the discharge electrode with a ground shield with a distance less than the Debye length, An exhaust chamber communicating with the exhaust nozzle is provided between the discharge electrode back surface. By disposing a gas ejection port and an exhaust nozzle on the entire surface of the electrode, uniform exhaust can be performed even on a large-area substrate. However, since the inner diameter of the exhaust nozzle for gas exhaust is less than the Debye length, plasma cannot be formed in the exhaust nozzle. In addition, the exhaust capacity is limited by the size of the exhaust nozzle being limited. Therefore, there is a problem that sufficient exhaust capacity for removing higher order silane cannot be realized.

  FIG. 6 shows an apparatus described in Patent Document 2. According to this apparatus, it is possible to remove higher order silane generated in the plasma from the plasma reaction region by the exhaust chamber communicating with the gas inlet. However, since an exhaust pipe for sending gas to the exhaust system is provided on the side surface of the electrode, there are problems that exhaust unevenness occurs and the exhaust capacity is limited when the size is increased.

  Further, there is an apparatus disclosed in Patent Document 3. In this apparatus, a porous high-frequency electrode, a porous ground electrode, and a substrate are arranged facing each other, a raw material gas is supplied from the substrate side, plasma is generated in the holes of the porous high-frequency electrode and the porous ground electrode, and the porous high-frequency electrode Is a device capable of creating a thermal gradient with the porous ground electrode by heating and removing large clusters such as higher order silane together with exhaust gas by thermophoresis. However, since the material gas is supplied from a ring-shaped gas supply pipe arranged around the substrate, there is a problem that uneven supply of air occurs when the substrate has a large area.

Japanese Examined Patent Publication No. 6-124906 JP 2000-12471 A International Publication WO2006 / 022179 Pamphlet

A. Matsuda et al., Solar Energy Materials & Solar Cells 78 (2003) 3-26 S. Shimizu et al., Journal of Non-Crystalline Solids 338-340 (2004) 47-50

  An object of the present invention is to enable uniform supply / exhaust of a source gas even on a large-area substrate, and to quickly remove higher order silanes generated in the plasma space. An object of the present invention is to provide a plasma CVD (Chemical Vapor Deposition) apparatus and a plasma CVD method capable of obtaining an amorphous silicon thin film.

In order to solve the above problems, the plasma CVD apparatus of the present invention has the following configuration. That is,
(1)
A vacuum vessel and an exhaust device connected to the vacuum vessel by an exhaust pipe; a ground electrode serving also as a substrate holding material in the vacuum vessel; and a first electrode disposed at a position opposite to the ground electrode In a plasma CVD apparatus having a discharge electrode, introducing a source gas into the vacuum vessel to form plasma, and forming a thin film on the substrate surface,
An air supply hole for introducing the plurality of source gases arranged in the first discharge electrode;
A plurality of plasma generating holes arranged in the first discharge electrode;
A second discharge electrode maintained at the same potential as the first discharge electrode,
The second discharge electrode is disposed so as to cover the side surface of the first discharge electrode, and has a space between the surface of the first discharge electrode opposite to the ground electrode and the second discharge electrode,
The space communicates with an exhaust pipe connection port in the vacuum vessel;
A plasma CVD apparatus in which the space and the plasma generation hole communicate with each other;
(2)
The plasma CVD apparatus according to (1), wherein a plurality of plasma generating holes arranged in the first discharge electrode have a diameter larger than a diameter of a supply hole for introducing the source gas arranged in the first discharge electrode.
(3)
A potential control plate is provided on the first discharge electrode side relative to the middle between the ground electrode and the first discharge electrode. The potential control plate has a plurality of through holes and is connected to a power source for keeping the potential constant. The plasma CVD apparatus according to (1) or (2),
(4)
Any one of (1) to (3), wherein a plurality of through holes provided in the potential control plate and a plurality of plasma generation holes arranged in the first discharge electrode are arranged to overlap each other in the direction of the ground electrode. A plasma CVD apparatus according to claim 1,
(5)
The vacuum vessel is held under reduced pressure, a substrate is placed on the ground electrode in the vacuum vessel, plasma is formed by applying high-frequency power to the first discharge electrode facing the ground electrode, and the source gas is evacuated to the vacuum In the plasma CVD method of introducing a thin film on the substrate introduced into a container,
The introduction of the source gas is performed from a plurality of air supply holes arranged in the first discharge electrode,
Forming plasma in a plurality of plasma generation holes that penetrate the first discharge electrode in the direction of the substrate and communicate with an exhaust pipe connection port for exhausting the vacuum vessel,
Maintained at the same potential as the first discharge electrode, a space is formed between the first discharge electrode and the surface opposite to the ground electrode at a position opposite to the ground electrode across the first discharge electrode. A plasma CVD method for removing exhaust gas in the vacuum vessel from an exhaust pipe connection port provided so as to communicate with the space in the second discharge electrode arranged to have,
It is.

According to the present invention, as described below, in a plasma CVD apparatus for forming an amorphous silicon thin film, high-quality amorphous silicon thin film that can quickly remove higher-order silane generated in the plasma space and has little photodegradation. Can be obtained. Moreover, when applied to a thin-film silicon solar cell, a film with very high power generation efficiency after degradation can be provided. Furthermore, uniform gas exhaust and uniform source gas supply / exhaust can be performed without limiting the exhaust capability of the apparatus due to the apparatus structure. Accordingly, it is possible to provide a plasma CVD apparatus and a thin film forming method capable of forming a thin film having a uniform film quality and film thickness even on a large area substrate.

It is the schematic which shows the structure of the plasma CVD apparatus by 1st embodiment concerning this invention. It is the schematic which shows the structure of the substrate side surface of the 1st discharge electrode of the plasma CVD apparatus by 1st Embodiment concerning this invention, and a 2nd discharge electrode. It is the schematic which shows the structure of another form of the space formed between the 1st electrode and 2nd electrode of the plasma CVD apparatus by 1st embodiment concerning this invention. It is the schematic which shows the internal structure of the 1st electrode of the plasma CVD apparatus by 1st embodiment concerning this invention. It is the schematic which shows the structure of the plasma CVD apparatus by 2nd embodiment concerning this invention. It is the schematic which shows the structure of the conventional plasma CVD apparatus. It is the schematic which shows the structure of the conventional parallel plate type plasma CVD apparatus.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
[First embodiment]
FIG. 1 is a schematic diagram showing the configuration of a plasma CVD apparatus according to the first embodiment of the present invention.
FIG. 2 is a schematic view showing the configuration of the substrate-side surfaces of the first discharge electrode 2 and the second discharge electrode 7 in the first embodiment of the present invention. The plasma CVD apparatus of the present invention includes a vacuum vessel 1 connected to an exhaust device (not shown), a first discharge electrode 2 provided in the vacuum vessel 1, and a ground electrode 3 that also serves as a holding member for the film formation substrate 4. And a second discharge electrode 7.

  The film formation substrate 4 only needs to be installed so as not to move on the ground electrode 3. For example, the ground electrode 3 is provided with a countersink, and the film formation substrate 4 is placed in the ground electrode 3. The film formation substrate 4 may be pressed against the ground electrode 3.

  The second discharge electrode 7 is arranged so as to cover the side surface of the first discharge electrode 2 and the surface on the exhaust pipe 8 side, and the exhaust space 13 is the side surface of the exhaust pipe 8 of the second discharge electrode 7 and the first discharge electrode 2. Formed between. As long as the pressure control in the vacuum vessel 1 is not hindered, there may be a gap between the side surface of the first discharge electrode 2 and the second discharge electrode 7 or contact as shown in FIG. . Further, the exhaust space 13 may have a shape with a tapered wall as shown in FIG. 3 in addition to the box shape as shown in FIG. The exhaust space 13 is connected to the exhaust pipe connection port 15, and the gas in the exhaust space 13 is sent to the exhaust pipe 8 through the exhaust pipe connection port 15.

  A high frequency power source 12 is connected to the first discharge electrode 2 and the second discharge electrode 7 via a matching box 11. The high-frequency power sources for the first discharge electrode 2 and the second discharge electrode 7 may not be the same as long as the two electrodes can be set to the same potential as a result. Since the first discharge electrode 2 and the second discharge electrode 7 are kept at the same potential, it is possible to suppress the generated plasma from moving to the position of the exhaust space 13 and causing abnormal discharge. The frequency of the high-frequency power source 12 can be arbitrarily selected, but is preferably 100 KHz to 100 MHz, more preferably 10 MHz to 60 MHz, from the viewpoint of plasma stability and film formation speed.

  When performing CVD, the source gas is introduced into the first discharge electrode 2 through the air supply pipe 10 by a mass flow controller (not shown). An air supply chamber 9 is formed inside the first discharge electrode 2. The supply chamber 9 has a connection groove structure as shown in FIG. 4, and the raw material gas introduced from the supply tube 10 spreads throughout the supply chamber 9 through the connection groove, and reaches the surface of the first discharge electrode 2. The film is introduced into the film formation space through the formed air supply holes 6. If the height of the air supply chamber 9, that is, the height of the connecting groove is too low, it is difficult for the source gas to spread uniformly throughout the air supply chamber 9, so that the height is preferably 5 mm or more. The diameter of the air supply hole 6 is the Debye length from the viewpoint of suppressing abnormal discharge in which plasma enters the air supply hole 6 (Equation 1).

The following is desirable. Here, ε ₀ is the vacuum dielectric constant, k is the Boltzmann constant, T is the temperature, _ne is the electron density, and e is the elementary electron content. Although the Debye length varies depending on the process conditions, the Debye length under the general conditions using the plasma CVD apparatus of this embodiment is about 0.5 to 2 mm. Considering the ease of electrode production, a diameter of 0.3 mm or more is preferable, and thus a preferable diameter of the air supply hole is 0.3 to 2 mm. The air supply holes 6 are preferably arranged uniformly on the surface of the discharge electrode, for example, as shown in FIG. 2 in order to supply air uniformly to the film formation region.

  On the surface of the first discharge electrode 2, a plasma generation hole 5 is provided together with an air supply hole 6. The plasma generation hole 5 penetrates the first discharge electrode 2 in the direction of the ground electrode 3 while avoiding the connection groove of the air supply chamber 9 formed inside the first discharge electrode 2, and communicates with the exhaust space 13. ing. The source gas introduced from the air supply hole 6 toward the substrate 4 is detoured between the first discharge electrode 2 and the substrate 4 and introduced into the plasma generation hole 5. At this time, high-frequency power is applied to the first discharge electrode 2 and the second discharge electrode 7 so that the source gas is turned into plasma in the plasma generation hole 5. By forming the plasma in a state in which the gas flow to the exhaust space is created, particles generated in the plasma are easily exhausted. For example, when plasma is formed using a source gas containing at least silicon, it is possible to suppress high-order silane film mixing in the plasma, so that an amorphous silicon thin film with little photodegradation can be formed.

The diameter of the plasma generation hole 5 needs to be at least larger than the Debye length in order to form plasma therein. For this reason, the diameter of the plasma generation hole 5 is larger than the diameter of the air supply hole 6. With respect to the plasma generation hole 5, it is important not to suppress the exhaust conductance of the electrode at the plasma generation hole 5 portion because particles having a larger gas flow rate in the hole are easier to remove particles. The average pressure in the plasma generation hole is P (Pa), the viscosity coefficient of the raw material gas is η (Pa · s), the viscosity coefficient of air is η ₀ (Pa · s), and the diameter of the plasma generation hole 5 is d (m). When the hole length is l (m) and the number of plasma generation holes is n (pieces), the exhaust conductance C (m ³ / s) of the first discharge electrode 2 is (Equation 2)

It becomes. From this, using the area S (m ² ) of the first discharge electrode 2, the exhaust conductance per unit area of the electrode is (Equation 3)

it is conceivable that. The average pressure P ₀ here is a value obtained by averaging the pressure in the vacuum vessel during the process, assuming that the pressure in the exhaust space 13 is ₀ Pa.

  The process pressure for forming an amorphous silicon thin film is about 5 to 100 Pa. The exhaust conductance per unit area in the present embodiment is preferably c ≧ 0.4, and if c <0.4, the exhaust capacity is suppressed at the electrode portion, and the particle removal effect tends to be reduced, which is not preferable. . From the viewpoint of removing particles by exhaust, a larger exhaust conductance is better. However, if the diameter of the plasma generation hole 5 is larger than 50 mm, the plasma is likely to be generated at a place other than the plasma generation hole 5 or the difference in plasma density between the central part and the end part of the plasma generation hole 5 becomes large. Film unevenness may occur. For this reason, in order to stably form plasma in the plasma generation hole 5, the diameter of the plasma generation hole 5 is preferably 50 mm or less, and more preferably 20 mm or less. Accordingly, the diameter d (m) of the plasma exhaust hole 5 is larger than that of the air supply hole 6 and (formula 4)

It is preferable that the size falls within the range.

  If the length of the plasma generation hole 5 is too short, the height of the air supply chamber 9 is limited and the uniformity of the air supply becomes insufficient. In addition, a part of the plasma formed in the plasma generation hole 5 is exhausted. There is a possibility that abnormal discharge will occur due to rising to the chamber 13. Therefore, the length of the plasma generation hole 5 is preferably not less than the diameter as a guide, but the relationship between the length of the plasma generation hole 5 and the size of the diameter is not uniquely determined.

  Further, from the viewpoint of gas exhaust and plasma uniformity, the positions of the plasma generation holes 5 are preferably evenly arranged on the surface of the first discharge electrode 2 as shown in FIG.

  In the exhaust space 13 formed in the upper part of the plasma generation hole 5, it is preferable that there is nothing other than the air supply pipe 10 as shown in FIG. There may be parts. In order to realize a large gas flow rate in the plasma generation hole 5 without suppressing the exhaust conductance at the electrode portion, the exhaust space 13 communicates with all the plasma generation holes 5 without being obstructed and is connected to the exhaust pipe. It is necessary to take a structure that is directly connected to the mouth 15. Furthermore, it is important that the shape of the space does not suppress the exhaust conductance as described above.

If the exhaust conductance of the exhaust pipe connection port 15 and the exhaust pipe 8 is less than the exhaust conductance of the plasma generation hole 5 described above, the gas flow rate in the plasma generation hole 5 is limited, which is not preferable. . When the electrode area S (m ² ) is determined, the exhaust conductance C of the plasma generation hole 5 portion is C = c × S when the exhaust conductance c (m / s) per unit area is used. On the other hand, if the exhaust conductance of the exhaust pipe 8 is C ′, the diameter D (m), the length L (m), the number N (pieces) of the exhaust pipe 16, and the above-described P (Pa), η (Pa · s), using η ₀ (Pa · s) (Formula 5)

It is expressed.

  Since it is desirable that the exhaust conductance C of the plasma generation hole 5 portion and the conductance C ′ of the exhaust pipe 8 satisfy C ′ ≧ C, the plasma CVD apparatus of the present embodiment has (Expression 6)

It is preferable to satisfy the above relationship. In addition, the diameter of the exhaust pipe connection port 15 is preferably equal to or larger than the diameter of the exhaust pipe 8 to which it is connected. Since the exhaust conductance is suppressed at the place where the exhaust resistance is the largest in the exhaust system, the above formula is the formula when all the exhaust pipes 8 have the same diameter and are connected to the pump without bending in the middle. It is. When the diameters of a plurality of connected exhaust pipes are different or have a bend in the middle, it is necessary to calculate the exhaust pipe conductance along the shape. In this case as well, it is the same that the combined conductance of the exhaust pipe 8 is preferably larger than the exhaust conductance of the plasma generation hole 5 portion.

[Second Embodiment]
The plasma CVD apparatus according to the second embodiment is obtained by adding a potential shield plate 14 to the plasma CVD apparatus according to the first embodiment, and there is no other change in the outline of the apparatus. FIG. 5 shows a schematic diagram of a plasma CVD apparatus according to the second embodiment.

  A potential control plate 14 is installed on the front surface of the first discharge electrode 2 in a state of being insulated from the first discharge electrode 2 and the second discharge electrode 7. The potential control plate 14 has a plurality of through holes. The potential control plate 14 is connected to ground or a DC variable power source. By maintaining the potential control plate 14 at the ground or negative potential, the effect of confining the plasma in the plasma generation hole 5 of the first discharge electrode 2 is strengthened and formed between the potential control plate 14 and the deposition target substrate 4. It becomes possible to weaken the plasma. The power source connected to the potential control plate 14 is not a problem as long as the potential can be applied to the potential control plate 14 as a result, and a DC offset potential by self-bias can be applied if the AC power source has a frequency of the kHz order or higher. In addition to the DC power supply, an AC power supply of about kHz or an RF power supply may be used.

  The potential control plate 14 may be positioned closer to the first discharge electrode than the middle between the first discharge electrode 2 and the ground electrode 3, but plasma is generated between the first discharge electrode 2 and the potential control plate 14. In order to suppress this, the distance between the potential control plate 14 and the first discharge electrode 2 is preferably 2 mm or less. Further, since the potential control plate 14 needs to be insulated from the first discharge electrode 2 and the second discharge electrode 7, the distance between the potential control plate 14 and the first discharge electrode 2 is preferably 0.5 mm or more. Further, for the purpose of not limiting the exhaust capability of the plasma generation hole 5, the through hole of the potential control plate 14 is formed so that the projected image on the first discharge electrode 2 overlaps the plasma generation hole 5 of the first discharge electrode 2. It is preferred that As a more preferable shape of the through hole, the through hole is arranged so that the central axis of the through hole of the potential control plate 14 is the same as the central axis of the plasma generating hole 5 of the first discharge electrode 2, and the diameter thereof is set to the plasma. It is to make it larger than the generation hole.

[Example 1]
The result of producing an amorphous silicon thin film using the plasma CVD apparatus according to the second embodiment of the present invention and evaluating its Si—H ₂ bond concentration will be described.
In the plasma CVD apparatus of this example, the electrode size was 185 mm × 185 mm, the diameter of the plasma generation hole 5 was 10 mm, the length was 30 mm, and the number of plasma generation holes was 85. From the viscosity coefficient of SiH _{4 and} the viscosity coefficient of air, η ₀ /η=1.58, and the average pressure was 15 Pa. The exhaust conductance per unit area of the plasma generation hole 5 portion in this embodiment is C = 26.5 m / s.

A specific method for producing an amorphous silicon thin film in this example is as follows. A high frequency power source of 60 MHz was connected to the discharge electrode of the plasma CVD apparatus in the second embodiment via a matching box. First, the inside of the plasma CVD apparatus was exhausted up to 1 × 10 ⁻⁴ Pa through an exhaust hole provided on the bottom surface of the vacuum vessel. Thereafter, switching to the exhaust from the plasma generation hole was performed, and SiH ₄ was introduced at a flow rate of 50 sccm from the air supply hole provided in the discharge electrode, and the pressure was adjusted to 30 Pa. Thereafter, an amorphous silicon thin film was formed on a single crystal silicon substrate placed on the ground electrode by applying 30 W of power to the discharge electrode to generate plasma.

The Si—H ₂ bond concentration in the film of the obtained amorphous silicon thin film was determined by FT-IR measurement. For FT-IR measurement, FT-720 manufactured by HORIBA was used, and the resolution was 4 cm ⁻¹ and the number of integrations was 16 times. The Si—H ₂ bond concentration was evaluated by the following procedure. From the peak near 2000 cm ⁻¹ , Gaussian function (Equation 7)

As a result, a peak at 2090 cm ⁻¹ was separated. Here, h is the peak height, σ is the peak width, and ω _p is the peak wave number.

  Next, the absorption coefficient (Equation 8)

, Bond hydrogen density from separated peak

Asked.
Here, Ts is the transmittance (%) of single crystal silicon, ΔT is the transmittance (%) of the amorphous silicon thin film minus the baseline, d is the film thickness (cm), ω is the wave number (cm ⁻¹ ), A Indicates a proportionality constant of 1.4 × 10 ²⁰ cm ⁻² . The Si atom number density approximated by ^{5.0 × 10 22 cm -3, Si} -H 2 bond concentration than N _H2

Was calculated.
As the measurement sample, an amorphous silicon thin film formed by the method of Example 1 on a 15 mm × 15 mm single crystal silicon substrate was used.

[Example 2]
An amorphous silicon thin film substrate was obtained in the same manner as in Example 1 except that the flow rate was set to 100 sccm.
From the obtained amorphous silicon thin film, the Si—H ₂ bond concentration was determined in the same manner as in Example 1.

[Comparative Example 1]
A high frequency power supply of 13.56 MHz was connected to the discharge electrode of the conventional parallel plate type plasma CVD apparatus shown in FIG. 7 through a matching box. The parallel plate electrode has an electrode size of 185 mm × 185 mm, and 256 air supply holes having a diameter of 0.5 mm are formed on the surface of the discharge electrode at a pitch of 8 mm. First, the inside of the plasma CVD apparatus was exhausted up to 1 × 10 ⁻⁴ Pa through an exhaust hole provided on the bottom surface of the vacuum vessel. Thereafter, SiH ₄ was introduced at a flow rate of 50 sccm from the air supply holes on the surface of the discharge electrode by a mass flow controller, and the pressure was adjusted to 30 Pa. Thereafter, an electric power of 30 W was applied to the discharge electrode to generate plasma, and an amorphous silicon thin film was formed on a single crystal silicon substrate placed on the ground electrode. No plasma generation hole is provided in the electrode, and plasma is formed between the discharge electrode and the ground electrode. Further, the gas is exhausted only from the bottom surface of the vacuum container, and the discharge electrode is not provided with an exhaust mechanism. Films other than those described above were formed under the same conditions as in Example 1.
From the obtained amorphous silicon thin film, the Si—H ₂ bond concentration was determined in the same manner as in Example 1.

Table 1 shows the Si—H ₂ bond concentrations obtained from Examples 1 and 2 and Comparative Example 1.

As shown in Example 1, a low Si—H ₂ bond concentration is obtained in the amorphous silicon film obtained by plasma CVD according to the present embodiment.
Moreover, as shown in Example 2, when the gas flow is increased, the flow velocity in the plasma generation hole is increased, and a lower Si—H ₂ bond concentration is obtained.

  In this way, when the plasma CVD apparatus according to the first and second embodiments is used and a silicon thin film is formed, there is less mixing of higher-order silane compared to the film formed by the conventional parallel plate type plasma CVD apparatus, A high quality film with reduced defects is obtained. In addition, by applying this high-quality amorphous silicon thin film substrate to a solar cell, it is possible to manufacture a thin film solar cell with little light degradation.

The present invention can be applied not only to the formation of a plasma CVD apparatus and an amorphous silicon thin film, but also to various thin film formations such as a microcrystalline silicon thin film, an etching apparatus and a plasma surface treatment apparatus. It is not limited.

DESCRIPTION OF SYMBOLS 1 Vacuum vessel 2 First discharge electrode 3 Ground electrode 4 Substrate 5 Plasma generation hole 6 Air supply hole 7 Second discharge electrode 8 Exhaust piping 9 Supply chamber 10 Supply tube 11 Matching box 12 High frequency power supply 13 Exhaust space 14 Potential control plate 15 Exhaust Piping connection port 16 Reaction vessel 17 Electrode part 18 Substrate 19 Substrate holder (ground electrode)
20 Gas exhaust hole 21 Gas intake hole

In order to solve the above problems, the plasma CVD apparatus of the present invention has the following configuration. That is,
(1)
A vacuum vessel and an exhaust device connected to the vacuum vessel by an exhaust pipe; a ground electrode serving also as a substrate holding material in the vacuum vessel; and a first electrode disposed at a position opposite to the ground electrode In a plasma CVD apparatus having a discharge electrode, introducing a source gas into the vacuum vessel to form plasma, and forming a thin film on the substrate surface,
An air supply hole for introducing the plurality of source gases arranged in the first discharge electrode;
A plurality of plasma generating holes arranged in the first discharge electrode;
An air supply chamber having a height of 5 mm or more formed in the first discharge electrode;
A second discharge electrode maintained at the same potential as the first discharge electrode,
The second discharge electrode is disposed so as to cover the side surface of the first discharge electrode, and has a space between the surface of the first discharge electrode opposite to the ground electrode and the second discharge electrode,
The space communicates with an exhaust pipe connection port in the vacuum vessel;
A plasma CVD apparatus in which the space and the plasma generation hole communicate with each other;
(2)
The plasma CVD apparatus according to (1), wherein a plurality of plasma generating holes arranged in the first discharge electrode have a diameter larger than a diameter of a supply hole for introducing the source gas arranged in the first discharge electrode.
(3)
A potential control plate is provided on the first discharge electrode side relative to the middle between the ground electrode and the first discharge electrode. The potential control plate has a plurality of through holes and is connected to a power source for keeping the potential constant. The plasma CVD apparatus according to (1) or (2),
(4)
The plasma CVD apparatus according to (3) , wherein a plurality of through holes provided in the potential control plate and a plurality of plasma generation holes arranged in the first discharge electrode are arranged to overlap each other in the direction of the ground electrode. ,
(5)
The vacuum vessel is held under reduced pressure, a substrate is placed on the ground electrode in the vacuum vessel, plasma is formed by applying high-frequency power to the first discharge electrode facing the ground electrode, and the source gas is evacuated to the vacuum In the plasma CVD method of introducing a thin film on the substrate introduced into a container,
The introduction of the source gas is performed from a plurality of air supply holes arranged in the first discharge electrode,
Forming plasma in a plurality of plasma generation holes that penetrate the first discharge electrode in the direction of the substrate and communicate with an exhaust pipe connection port for exhausting the vacuum vessel,
The ground electrode of the first discharge electrode is maintained at the same potential as the first discharge electrode having an air supply chamber having a height of 5 mm or more, and at a position opposite to the ground electrode across the first discharge electrode. A plasma CVD method for removing exhaust gas in the vacuum vessel from an exhaust pipe connection port provided so as to communicate with the space in a second discharge electrode disposed so as to have a space between the surface on the opposite side;
It is.

Claims (5)

A vacuum vessel and an exhaust device connected to the vacuum vessel by an exhaust pipe; a ground electrode serving also as a substrate holding material in the vacuum vessel; and a first electrode disposed at a position opposite to the ground electrode In a plasma CVD apparatus having a discharge electrode, introducing a source gas into the vacuum vessel to form plasma, and forming a thin film on the substrate surface,
An air supply hole for introducing the plurality of source gases arranged in the first discharge electrode;
A plurality of plasma generating holes arranged in the first discharge electrode;
A second discharge electrode maintained at the same potential as the first discharge electrode,
The second discharge electrode is disposed so as to cover the side surface of the first discharge electrode, and has a space between the surface of the first discharge electrode opposite to the ground electrode and the second discharge electrode,
The space communicates with an exhaust pipe connection port in the vacuum vessel;
A plasma CVD apparatus in which the space and the plasma generation hole communicate with each other. 2. The plasma CVD apparatus according to claim 1, wherein a plurality of plasma generating holes arranged in the first discharge electrode have a diameter larger than a diameter of air supply holes for introducing the source gas arranged in the first discharge electrode. A potential control plate is provided on the first discharge electrode side relative to the middle between the ground electrode and the first discharge electrode. The potential control plate has a plurality of through holes and is connected to a power source for keeping the potential constant. The plasma CVD apparatus according to claim 1 or 2. The plurality of through holes provided in the potential control plate and the plurality of plasma generation holes arranged in the first discharge electrode are arranged to overlap each other in the direction of the ground electrode. The plasma CVD apparatus as described. The vacuum vessel is held under reduced pressure, a substrate is placed on the ground electrode in the vacuum vessel, plasma is formed by applying high-frequency power to the first discharge electrode facing the ground electrode, and the source gas is evacuated to the vacuum In the plasma CVD method of introducing a thin film on the substrate introduced into a container,
The introduction of the source gas is performed from a plurality of air supply holes arranged in the first discharge electrode,
Forming plasma in a plurality of plasma generation holes that penetrate the first discharge electrode in the direction of the substrate and communicate with an exhaust pipe connection port for exhausting the vacuum vessel,
Maintained at the same potential as the first discharge electrode, a space is formed between the first discharge electrode and the surface opposite to the ground electrode at a position opposite to the ground electrode across the first discharge electrode. A plasma CVD method for removing exhaust gas in the vacuum vessel from an exhaust pipe connection port provided so as to communicate with the space in a second discharge electrode arranged to have.

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