JP2001313272A - Plasma cvd method and apparatus used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems of a difficulty in a rapid film formation or an increase in an area, a large plasma damage in a conventional plasma CVD method, and difficulty in a temperature control of a substrate or obtaining a film of a high quality with a low defect density in a conventional catalytic CVD method. SOLUTION: A plasma CVD method comprises the steps of plasma activating a raw material gas introduced into a chamber, and depositing a component in the gas on a substrate to be coated. The method further comprises the steps of arranging a heat catalyst made of a tungsten or a tantalum at an upstream side from the plasma generating area at a route of the gas, and depositing the component in the gas on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plasma CVD method and an apparatus used therefor, and more particularly to a plasma CVD method for manufacturing a thin film polycrystalline Si device such as a solar cell or a field effect transistor and an apparatus used therefor.

[0002]

2. Description of the Related Art In order to manufacture a thin-film polycrystalline Si device typified by a thin-film polycrystalline Si solar cell at low cost, a polycrystalline Si film is formed on a low-cost substrate such as a glass substrate.
There is a need for a technique for forming a film at a high speed at a relatively low temperature of about 00 ° C. or less. Conventionally, as a film forming method, a plasma CVD method and a catalytic CVD method have been mainly researched and developed.

FIG. 3 shows a conventional plasma CVD apparatus.
3, 11 is a chamber, 12 is a shower electrode, 13
Is a substrate heating heater, 14 is a raw material gas introduction pipe, 15 is a substrate, 16 is a vacuum pump, and 17 is a high frequency generation source. In the plasma CVD method using such an apparatus, a high-frequency power supply 17 of 13.5 MHz has been often used as a plasma generation source. However, in this frequency band, a polycrystalline Si film for a solar cell is formed. Must be diluted with a large amount of hydrogen, and high-speed film formation could not be expected under these conditions.

[0004] If the high frequency power is increased, the film forming speed can be increased. However, plasma damage of the film increases with the increase in power, and it is difficult to form a high quality polycrystalline Si film having a low defect density. Was.

On the other hand, in recent years, a high-quality thin-film polycrystalline silicon with less plasma damage has been recently used by using a high-frequency power supply in a VHF band such as 40 MHz or 100 MHz.
It has been found that films can be formed at a relatively high speed, and application technology development for thin-film polycrystalline Si solar cells has become active (J. Meier et al, Technical digest of 11th PVSEC).
(1999) p.221, O. Vetterl et al, Technical digest o
f 11th PVSEC (1999) p.233).

However, as the frequency of the high-frequency power supply increases, there is a problem that it is difficult to increase the area, and there is still a problem in using it as a solar cell film forming technique that requires a large area film forming.

FIG. 4 shows a conventional catalytic CVD apparatus. In FIG. 4, 11 is a chamber, 13 is a substrate heater, 14 is a raw material gas introduction pipe, 15 is a substrate, 16 is a vacuum pump, and 18 is a thermal catalyst. Catalytic CVD using such an apparatus (= Cat-CVD; hot wire C)
In the VD method (HW-CVD method, the same principle), the activation of the source gas 14 is performed by the thermal catalyst 18 such as tungsten, so that plasma damage which is a problem in the plasma CVD method does not exist in principle. In addition, since the activation efficiency of the raw material gas 14 by the thermal catalyst 18 is high, high-speed film formation can be performed relatively easily, and there is no principle limitation on the enlargement of the area. Is attracting attention as a thin film polycrystalline Si film forming technology for solar cells (H. M.
atsumura, Jpn. J. Appl. Phys. 37 (1998) 3175-3187, R.
EI Schropp et al, Technicaldigest of 11th PVSE
C (1999) p.929-930).

However, under the present circumstances, a chemical reaction (silicide formation) between the Si-based source gas 14 such as SiH ₄ or Si ₂ H _{6 as} a source gas when forming the Si film and the thermal catalyst 18 is prevented. Therefore, it is necessary to set the temperature of the thermal catalyst body 18 to about 1600 ° C. or more, and accordingly, the residual gas pressure increases,
There is a problem that impurities are likely to be mixed into the polycrystalline Si film due to evaporation of impurity components in the thermal catalyst 18 or reaction vaporization with an atmospheric gas.

Further, there is another problem that the temperature of the substrate 15 rises during the film formation due to the heat radiation from the thermal catalyst 18 and it is difficult to control the temperature of the substrate 15.

Furthermore, in this method, although the thermal kinetic energy of the film-forming species is large and a polycrystalline Si film having a high crystallization rate can be formed at a high speed even at a relatively low temperature, the electron temperature of the film-forming species is limited to the plasma temperature. Since it is lower than that in the CVD method, there is also a problem that a bonding reaction between a film forming species and a film forming surface atom is weak, and it is difficult to obtain a high quality film having a low defect density.

The present invention has been devised in view of the problems of the prior art described above, and it is difficult to perform high-speed film formation, to cause large plasma damage, or to increase the area. The conventional catalyst C, which solves the problems of the plasma CVD method and has difficulty in controlling the temperature of the substrate and in obtaining a high-quality film having a low defect density.
An object of the present invention is to provide a plasma CVD method which solves the problems of the VD method and an apparatus used for the same.

[0012]

In order to achieve the above object, in the plasma CVD method according to the first aspect, the source gas introduced into the chamber is activated by plasma to remove the components in the source gas. Plasma C deposited on the destination substrate
In the VD method, a thermal catalyst made of tungsten or tantalum is disposed upstream of the plasma generation region in a path of the source gas, and components in the source gas are deposited on the substrate.

In the above-mentioned plasma CVD method, it is preferable that a plurality of feed paths for the source gas be provided in the chamber, and a different thermal catalyst be provided for each feed path of the source gas.

In the above-mentioned plasma CVD method, it is preferable that a hydrogen gas introduction path is provided in the chamber as an introduction path of the source gas, and the thermal catalyst is provided only in the hydrogen gas introduction path.

According to a fourth aspect of the present invention, in the plasma CVD apparatus, the raw material gas introduced into the chamber is activated by plasma to deposit components in the raw material gas on the adherend plate. A thermal catalyst made of tungsten or tantalum is disposed upstream of the plasma generation region in the path of the source gas.

In the above-mentioned plasma CVD apparatus, it is preferable that a shower electrode having an ejection hole for the source gas is provided in the chamber, and the plurality of source gases are mixed downstream of the shower electrode.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a plasma C according to claim 1 will be described.
An embodiment of the VD method and the plasma CVD apparatus according to claim 4 will be described. FIG. 1 shows a plasma CVD according to claim 1.
FIG. 1 is a view showing a plasma CVD apparatus used in the method, wherein 1 is a chamber, 2 is a shower electrode, 3 is a substrate heater,
Is a source gas introduction pipe, 6 is a vacuum pump, 7 is a high frequency generator, and 8 is a thermal catalyst.

The basic structure of the apparatus is the same as that of a conventional parallel plate type (capacitive type) plasma CVD apparatus. A raw material gas pipe 4 and a high-frequency power source 7 are connected to a shower electrode 2, and a vacuum system is provided for an exhaust system. The pump 6 has a substrate heating heater 3 installed on a substrate holder (not shown).

The raw material gas introduced from the raw material gas introduction pipe 4 includes SiH ₄ and Si ₂ H ₆ as the Si-based gas, H ₂ and Cl ₂ as the diluent gas as the non-Si-based gas, B ₂ H ₆ or the like is used as a p-type doping gas, and PH ₃ or the like is used as an n-type doping gas.

It is desirable to install a dry vacuum pump 6 such as a turbo molecular pump in the vacuum pump 6 of the exhaust system in order to prevent impurities from entering the film from the exhaust system.
Ultimate vacuum of at least 1 × 10 ^{- 3} Pa or less and then, 1 ×
It is more preferable that the pressure be 10 ⁻⁴ Pa or less. The pressure during film formation is in the range of about 10 to 1000 Pa.

The frequency of the high-frequency power source 7 is desirably 13.5 MHz in the past when forming a large area film having a size of about a square meter or more. Even if a high frequency power supply 7 in the VHF band of about 100 MHz or more is used, film formation can be performed without any problem.

The thermal catalyst 8 is made of a material having a high melting point such as tungsten or tantalum, and is heated to a high temperature by flowing a direct current. The temperature of the thermal catalyst 8 is set to about 1600 ° C. or higher to avoid a low-temperature reaction with the Si-based source gas. The shape of the thermal catalyst 8 may be linear or planar.

The substrate temperature was set at 10 by the substrate heater 3.
The temperature condition is about 0 to 400 ° C., preferably 200 to 400 ° C.
It is about 300 ° C. In the present apparatus, since the thermal catalyst 8 is installed at a position away from the film formation region with the shower electrode 2 interposed therebetween, heat radiation to the film formation surface is suppressed low, and the substrate temperature can be easily controlled. Can be.

Further, in the present apparatus, the activation of the source gas can be efficiently performed by the thermal catalyst 8, so that high-speed film formation can be performed even when the high-frequency power is set to a relatively low power in order to reduce plasma damage. It becomes possible.

Further, in this apparatus, the plasma CVD
Because of the combination of the CVD method and the catalytic CVD method, it is possible to form a polycrystalline Si film having a higher quality and a higher crystallization rate at a high speed even at a relatively low temperature by utilizing the respective features.

That is, the high-frequency power generating the plasma is mainly absorbed by the electrons of the film-forming species, raises the electron temperature, and promotes the bonding reaction between the film-forming species and atoms on the film-forming surface.
Since the density of dangling bonds (unpaired electrons), which is a cause of defects in the film, can be reduced, a high-quality polycrystalline Si film can be obtained even at a relatively low temperature. On the other hand, the thermal catalyst 8 increases the thermal kinetic energy of the film-forming species and promotes migration on the film-forming surface of the film-forming species, so that a polycrystalline Si film having a high crystallization rate even at a relatively low temperature is obtained. be able to.

If the distance between the substrate 5 and the shower electrode 2 is made variable, the degree of freedom in film forming conditions can be further increased. Plasma can be generated at a film pressure, and a higher-speed film can be formed with lower plasma damage.

FIG. 2 shows that the source gas introduction path 4 is divided into a non-Si-based gas 4a and a Si-based gas 4b,
An apparatus configuration in the case where the apparatus is installed only in the introduction path of the i-system gas 4a is shown. In addition, in order to avoid film formation in the gas introduction path 4 and to perform film formation more efficiently, the non-Si-based gas 4a and the Si-based gas 4b must be mixed after exiting the shower electrode 2. Is desirable.

In the present apparatus configuration, only the non-Si-based gas 4a is activated by the thermal catalyst 8, and the contact between the Si-based gas 4b and the thermal catalyst 8 is avoided.
The temperature can be set to about 600 ° C. or less, and unnecessary rise of the residual gas pressure, evaporation of impurity components in the thermal catalyst 8, reaction vaporization with an atmospheric gas, and the like can be avoided, and impurities are mixed into the polycrystalline Si film. Can be reduced.

In FIG. 2, the gas introduction path 4 is divided into a Si-based 4a and a non-Si-based
Although the case where the thermal catalyst 8 is installed only at the position a is shown, if the thermal catalyst 8 is independently installed (or not installed) in each of the plurality of gas paths 4 to be introduced, the degree of freedom in setting the film forming conditions is further increased. Because it can be enlarged, higher quality film formation can be expected.

In this embodiment, a parallel plate type plasma CVD apparatus has been described as an example. However, the present invention can be applied to other types such as an ECR type remote plasma CVD apparatus in the same manner. Needless to say.

[0032]

As described above, according to the plasma CVD method according to the first aspect, the thermal catalyst made of tungsten or tantalum is disposed upstream of the plasma generation region in the path of the source gas. Since the components contained therein are deposited on the substrate to be deposited, the activation of the source gas can be performed efficiently, and a high-quality thin film polycrystalline Si film with low plasma damage and a high crystallization rate can be formed at a relatively low temperature. It can be formed under high speed. Thus, a low-cost and highly efficient thin-film polycrystalline Si solar cell can be manufactured.

According to the plasma CVD apparatus of the fourth aspect, since the thermal catalyst made of tungsten or tantalum is disposed on the upstream side of the plasma generation region in the path of the source gas, the activity of the source gas can be reduced. Therefore, a high-quality thin-film polycrystalline Si film with a low degree of plasma damage and a high crystallization rate can be formed at a relatively low temperature and at a high speed. Thus, a low-cost and highly efficient thin-film polycrystalline Si solar cell can be manufactured.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of an apparatus used for a plasma CVD method according to claim 1;

FIG. 2 is a view showing another embodiment of the apparatus used for the plasma CVD method according to claim 1;

FIG. 3 is a diagram showing a conventional plasma CVD apparatus.

FIG. 4 is a view showing a conventional thermal catalyst CVD apparatus.

[Explanation of symbols]

1: chamber, 2: shower electrode, 3: substrate heater, 4: source gas introduction pipe, 6: vacuum pump, 7: high frequency generator, 8: thermal catalyst

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K030 AA06 AA17 BA29 BB03 EA01 FA03 FA14 KA17 KA25 KA30 LA16 4M104 BB01 DD44 DD45 HH20 5F051 AA03 AA16 BA12 BA14 CB12 CB29

Claims (5)

[Claims] In a plasma CVD method in which a source gas introduced into a chamber is activated by plasma to deposit a component in the source gas on a substrate to be deposited, a plasma generation region in a path of the source gas is used. A plasma CVD method, further comprising arranging a thermal catalyst made of tungsten or tantalum on the upstream side and depositing the components in the source gas on the substrate. 2. The plasma CVD method according to claim 1, wherein a plurality of feed paths for the source gas are provided in the chamber, and different thermal catalysts are provided for each of the feed paths for the source gas. 3. The method according to claim 1, wherein a hydrogen gas introduction path is provided in the chamber as the source gas introduction path, and the thermal catalyst is disposed only in the hydrogen gas introduction path. Plasma CVD method. 4. A plasma CVD apparatus in which a source gas introduced into a chamber is activated by plasma to deposit a component in the source gas on an adherend plate. A plasma CVD apparatus characterized in that a thermal catalyst made of tungsten or tantalum is disposed on the upstream side. 5. The apparatus according to claim 4, wherein a shower electrode having a discharge hole for the source gas is provided in the chamber, and the plurality of source gases are mixed downstream of the shower electrode. Plasma CVD equipment.