JPH0574713A - Manufacture of amorphous semiconductor thin film - Google Patents

Abstract

PURPOSE:To provide the manufacturing method for an amorphous semiconductor thin film having excellent productivity and no irregularity in the face direction of characteristics. CONSTITUTION:This semiconductor thin film is formed by alternately repeating a film forming process, wherein an amorphous semiconductor thin film is formed on a substrate 4 by introducing raw gas across an electrode couple (gas dissociation device) 1 opposing to the film-forming substrate 4 in a film-forming chamber 10, and a chemical annealing process in which the introduction of raw gas is shut out and atomlike hydrogen is grown by introducing hydrogen gas. Both film formation and chemical annealing can be conducted by merely switching gas by a gas dissociation device, and productivity can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an amorphous semiconductor thin film, and more particularly to a method for manufacturing an amorphous silicon thin film used in an amorphous silicon solar cell or the like.

[0002]

2. Description of the Related Art An amorphous silicon thin film has a problem called photodegradation in which the photoconductivity is lowered by irradiation with light. Japanese Patent Laid-Open No. 3-32019 discloses that an amorphous semiconductor thin film is formed in a film forming chamber. Then, it is disclosed that the amorphous semiconductor thin film is transferred to a reforming chamber, and the surface of the amorphous semiconductor thin film is exposed to an atomic hydrogen atmosphere in the reforming chamber to chemically anneal the surface.

Solid State Physics, Vol. 26, No.
1, 1991, pp. 43-49, a single chamber is equipped with a film forming apparatus for forming an amorphous semiconductor thin film and a microwave plasma apparatus for chemical annealing. It is disclosed that the amorphous semiconductor thin film having a predetermined thickness is obtained by alternately repeating the above steps in a single chamber.

[0004]

In the production of this type of amorphous semiconductor thin film, it is necessary to repeat film formation and chemical annealing a number of times. Since the one-chamber method does not require transfer time between chambers, the time required for formation can be significantly shortened and the productivity is excellent. However, in the latter method, a film forming apparatus for forming an amorphous semiconductor thin film and a microwave plasma apparatus for chemical annealing must be provided, and the film forming apparatus is naturally arranged facing the substrate. Since the microwave plasma device is provided, the microwave plasma device cannot but be provided laterally of the substrate. As a result, when manufacturing a large-area amorphous semiconductor thin film, the atomic hydrogen concentration may vary between the part of the thin film that is close to the microwave plasma device and the part of the thin film that is far from the microwave plasma device. There was a problem in the production of the amorphous semiconductor thin film. It is also conceivable to arrange a microwave plasma apparatus for chemical annealing and a film forming apparatus in parallel at a position facing the substrate, but in this case, positioning of both apparatuses becomes difficult and a large area is required. There is a possibility that the film formation may become non-uniform in the production of the amorphous semiconductor thin film.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing an amorphous semiconductor thin film which is excellent in productivity and has less variation in characteristics in the surface direction.

[0006]

According to the method for producing an amorphous semiconductor thin film of the present invention, a raw material gas is introduced into a gas dissociation device facing a film forming substrate in a film forming chamber to form the amorphous semiconductor thin film. Manufacture of an amorphous semiconductor thin film in which a film forming step of forming a film on a substrate and a chemical annealing step of blocking the introduction of the raw material gas and exposing the surface of the amorphous semiconductor thin film to atomic hydrogen are alternately performed. In the method, the chemical annealing step comprises
It is characterized in that hydrogen gas is introduced into the gas dissociation device used in the film forming step to generate the atomic hydrogen.

The gas dissociation device is a device that dissociates a gas to generate ions and active atoms, and is a plasma generation device such as an RF plasma device or a microwave plasma device.
A non-plasma device such as a catalytic coil can be employed.

[0008]

As described above, in the method for producing an amorphous semiconductor thin film of the present invention, the source gas and the hydrogen are added to the gas dissociation device which is arranged in the single film forming chamber so as to face the film forming substrate. Since film formation and chemical annealing can be performed simply by switching gas and gas alternately, it is possible to reduce the variation of chemical annealing characteristics in the surface direction and achieve high productivity, which is excellent in practical application. It is possible to exert the effect.

[0009]

(First Embodiment) An embodiment of the present invention will be described below. The manufacturing apparatus shown in FIG. 1 is an amorphous silicon film manufacturing apparatus, in which a film-forming substrate 4 is horizontally arranged at the bottom of a vacuum chamber 10 whose pressure is reduced by a vacuum pump (not shown). RF facing the substrate 4 above
(High frequency) plasma device (gas dissociation device in the present invention)
The upper electrode (gas outlet) 1 and the mesh electrode 3 are horizontally arranged.

The upper electrode 1 is a metal gas outlet having a gas introduction port 12 connected to a gas introduction pipe 11 on the upper surface and a mesh-shaped gas delivery net 13 on the lower surface,
The mesh electrode 3 is about 2c downward from the gas delivery net 13.
m away from the substrate 4 and about 1 cm above the substrate 4. Substrate 4 is a glass plate, about 40 cm x about 30 cm
And is horizontally mounted on the electric heating heater panel 5.

Using this manufacturing apparatus, an i-type amorphous silicon film was manufactured based on the timing chart of FIG. 2 and the manufacturing conditions of Table 1 below. The manufacturing process will be described below. (Film forming process) Period T in the timing chart of FIG.
The film forming process was carried out based on the film forming conditions shown in Table 1. As a result, SiH ₄ and H ₂ as source gases are turned into plasma by RF discharge, and an amorphous silicon film a-Si: H is formed on the substrate 4.

(Scavenging process) Next, the timing chart of FIG.
-Scavenging based on the scavenging conditions in Table 1 during period T2
The process is performed, and SiH in the vacuum chamber 10_FourRemove gas
It The important thing is to use high frequency power in this scavenging process.
Cut off and remain SiH_Four, H ₂During the scavenging process
It is not to be filmed. High frequency during scavenging process
Amorphous silicon film that is finally formed when electricity is applied
The characteristics and composition in the thickness direction of the
The lattice bond state of the fass silicon film deteriorates and
It has been experimentally determined that the deterioration of the light sensitivity of
I have revealed.

(Chemical anneal step) Next, a chemical anneal step was carried out based on the chemical anneal conditions shown in Table 1 during the period T3 in the timing chart of FIG. as a result,
The introduced H ₂ gas is turned into plasma by RF discharge,
Contacting the surface of the amorphous silicon film a-Si: H,
Atomic hydrogen is formed on this surface to penetrate into the vicinity of the surface of the amorphous silicon film a-Si: H, and stabilizes the lattice state of the network structure of the amorphous silicon film a-Si: H.

(Scavenging Step) Next, during the period T4 in the timing chart of FIG. 2, the scavenging step is carried out based on the scavenging conditions in Table 1 to remove the H ₂ gas in the vacuum chamber 10. The purpose of this scavenging step is the same as that of the scavenging step after film formation. The substrate temperature is set to 2 by the heater panel 5 through each process.
It was maintained at a predetermined temperature in the range of 00 ° C to 300 ° C. The cycle consisting of the above-mentioned four partial steps was repeated a predetermined number of times to obtain an amorphous silicon film having a required thickness.

The photodegradation characteristics of the amorphous silicon film thus formed are shown in FIG. For the light irradiation, a solar simulator was used, the spectrum at the time of light irradiation was AM1 (condition directly under the equator), the irradiation intensity was 200 mW / cm ^2, and the irradiation condition at the time of measuring photoconductivity was AM1, irradiation intensity 100 mW /
It was set to cm ² . Here, as a comparative example, an amorphous silicon film formed to have the same thickness only in the film forming step was adopted.

It can be seen from FIG. 3 that the amorphous silicon film of this example has excellent photodegradation characteristics due to the use of the chemical anneal as compared with the comparative example product which does not use it. (Embodiment 2) Another embodiment of the present invention will be described below. The manufacturing apparatus shown in FIG. 4 is a catalytic type amorphous silicon film manufacturing apparatus, and, as a substitute for the high frequency power source 6 and the mesh electrode 3, compared with the apparatus of FIG. A coil-shaped metal catalyst wire 8 which is electrically heated by a power source 20 for heating the catalyst is arranged immediately above.

Using this manufacturing apparatus, an i-type amorphous silicon film was manufactured on the basis of the timing chart of FIG. 5 and the manufacturing conditions of each step shown in Table 2 below. The manufacturing process will be described below. (Film forming process) Period T in the timing chart of FIG.
The film forming process was performed on the basis of the film forming conditions shown in Table 1. As a result, SiH ₄ and H ₂ as source gases are activated into atoms by the catalyst, and the amorphous silicon film a is formed on the substrate 4.
-Si: H is formed into a film. Here, as the metal catalyst wire 8, a tungsten wire heated to 1500 ° C. to 1600 ° C. is used, but a platinum wire or a molybdenum wire can also be used.

(Scavenging step) As in Example 1, the SiH ₄ gas in the vacuum chamber 10 is removed. (Chemical anneal step) Next, a chemical anneal step was carried out based on the chemical anneal conditions shown in Table 2 during the period T3 in the timing chart of FIG. As a result, the introduced H
_{2 The} gas is activated into atoms by a catalyst, contacts the surface of the amorphous silicon film a-Si: H, becomes atomic hydrogen on this surface, and penetrates into the vicinity of the surface of the amorphous silicon film a-Si: H. Film a-Si: H
Stabilizes the lattice state of the mesh structure of.

(Scavenging process) As in the first embodiment, H ₂ gas in the vacuum chamber 10 is removed. The substrate temperature was maintained at a predetermined temperature in the range of 200 ° C. to 300 ° C. by the heater panel 5 during each process. The cycle consisting of the above-mentioned four partial steps was repeated a predetermined number of times to obtain an amorphous silicon film having a required thickness.

It was found that the amorphous silicon film formed in this way also has substantially the same photodegradation characteristics as those of the first embodiment. As described above, in these examples,
Amorphous semiconductors that can be used for film formation and chemical annealing in the same gas dissociation device in the same tank by simply repeatedly switching the gas, with little variation in characteristics in the surface direction and excellent photodegradation characteristics. The thin film can be manufactured with high efficiency. Further, there is an advantage that the manufacturing apparatus has a simple structure and is highly reliable and economical.

[0021]

[Table 1]

[0022]

[Table 2]

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a manufacturing apparatus used in the manufacturing process of the first embodiment.

FIG. 2 is a timing chart of the first embodiment.

FIG. 3 is a characteristic diagram showing the photodegradation characteristics of the amorphous silicon film of the first embodiment.

FIG. 4 is a schematic sectional view of a manufacturing apparatus used in the manufacturing process of the second embodiment.

FIG. 5 is a timing chart of the second embodiment.

[Explanation of symbols]

 1 Upper electrode (gas dissociation device) 3 Lower electrode (gas dissociation device) 4 Substrate (deposition substrate) 10 Vacuum chamber (deposition chamber)

Claims (1)

[Claims] 1. A film forming step of introducing a source gas into a gas dissociation device facing a film forming substrate in a film forming chamber to form an amorphous semiconductor thin film on the substrate, and interrupting the introduction of the source gas. In the method for producing an amorphous semiconductor thin film, which comprises alternately performing a chemical annealing step of exposing the surface of the amorphous semiconductor thin film to atomic hydrogen, the chemical annealing step is used in the film forming step. A method for producing an amorphous semiconductor thin film, characterized in that hydrogen gas is introduced into the gas dissociator to generate the atomic hydrogen.