JPS6353123B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an amorphous silicon film used in various electronic devices such as solar-electrical energy converters.

Conventionally, semiconductor materials used in electronic devices such as solar-electrical energy converters have been made using the Czyochralski method, the floating zone method, or silicon single crystals produced by pulling into a ribbon shape. However, such single crystals have not been widely used as a general power supply method due to their manufacturing costs. As a way to reduce manufacturing costs,
In recent years, amorphous silicon (hereinafter referred to as amorphous silicon, a-Si) film is deposited on a substrate by decomposing monosilane (SiH ₄ ) gas or the like in a glow discharge. A so-called plasma CVD method has been proposed in US Pat. No. 4,064,521 and other publications. According to this manufacturing method, a
- There are relatively few localized levels existing in the forbidden band of Si, and valence electron control is possible to some extent by doping with substitutional impurities, making it possible to use electronic devices such as solar-electrical energy converters (hereinafter referred to as solar cells). can be created, and the manufacturing cost is somewhat reduced.

However, this plasma CVD method had the following drawbacks. In order to reduce the localized levels existing in the forbidden band of a-Si and to keep the crystallinity of the a-Si film sufficiently low to enable control of valence electrons, the substrate temperature is kept at 400°C at most. ℃, preferably below 300℃. However, it is known that the adhesion strength between the substrate and the deposited film mainly depends on the temperature of the substrate when the film is deposited, so the a-Si film created by the Plasma CVD method has problems in adhesion to the substrate. , it lacked practicality. In other words, the a-Si film peeled off during heat cycles or in a high humidity atmosphere, resulting in a lack of reliability.

Furthermore, monosilane (SiH ₄ ) gas, which is a raw material gas, takes time to produce and is very expensive. Moreover, in the plasma CVD method, the yield of raw material gas is at most 10
%, usually about 5%, and the remaining gas has no choice but to be exhausted, making it more expensive.

In addition, SiH ₄ gas reacts explosively with oxygen in the air to create SiO ₂ , which requires a huge amount of cost for safety measures, and at the same time, it reacts with oxygen remaining in the reaction vessel and deposits a- In many cases, the Si film has poor characteristics.

In addition, a-Si produced by plasma CVD method
The drawback that a considerable amount of dangling bonds are still formed in the film and the resulting high density of localized levels makes it difficult to control the electrical conductivity by doping, especially in the low conductivity range, has not been fully resolved. Currently, even in a-Si solar cells, for example, sufficiently high light-to-electrical energy conversion efficiency has not been achieved.

Therefore, the inventor conducted various studies to solve the above-mentioned drawbacks, and as a result, silicon was heated and evaporated in a vacuum container, and a-
It was thought that the above drawbacks could be overcome if an a-Si film was formed by a so-called ion plating method of depositing a Si film.

Among the many thin film production techniques, the ion plating method has overwhelmingly superior adhesive strength between the substrate and the film.
In addition, the film deposition rate is sufficiently fast that plasma CVD
It is convenient because it is known to be equal to or better than the law. In addition, polycrystalline silicon can be used as a raw material, and its purity can be relatively low because it forms an amorphous film, and the yield is also low.
Significant improvement compared to CVD method. Furthermore, according to the SiH ₄ glow discharge decomposition method, the film created is an amorphous alloy of silicon and hydrogen, and in order to lower the localized level density even further, it is necessary to create an amorphous alloy of silicon and other elements. It is said that it is necessary to create quality. However, the plasma CVD method requires the raw material to be in a gaseous state.
Difficult to form alloys with elements that are difficult to form into a gas state. However, according to the ion plating method, if it is possible to add gaseous elements, it is also possible to add other elements by alloying silicon, which is an evaporation source, with other elements.

Therefore, one object of the present invention is to provide a method for manufacturing an a-Si film that has excellent adhesive strength to a substrate. Another object of the present invention is to provide an inexpensive method for manufacturing an a-Si film. One object of the present invention is to
The object of the present invention is to provide a method for manufacturing an a-Si film that facilitates the addition of other elements and has a low localized level density. Examples will be described in detail below.

FIG. 1 is a block diagram showing an overview of an embodiment of the apparatus used for manufacturing the a-Si film of the present invention.
is a vacuum container, 2 is a substrate mounting stand, 3 is a substrate, 4 is an evaporation source, 5 is a heater for heating the substrate, 6 is a power source that keeps the substrate at a negative potential with respect to the evaporation source, 7 is between the evaporation source and the substrate Auxiliary electrodes provided, 8 a DC and/or AC power source for the auxiliary electrode 7, 9 an exhaust gas port,
10 is a gas supply pipe.

The operation of this manufacturing apparatus will be explained. First, we will describe the creation of an i-type a-Si film that is not doped with substitutional impurities. After starting the exhaust pump (not shown) connected to the exhaust gas port 9 and reducing the pressure inside the vacuum container 1 to approximately 10 ^-7 Torr, the substrate 3 installed on the substrate mounting stand 2 is heated by the heater 5. Approximately 250℃
Heat to. Next, hydrogen gas, for example, is supplied into the vacuum vessel 1 through the gas supply pipe 10, and the pressure within the vacuum vessel 1 is set to 10 ^-1 to ^{10 -6} Torr. Then, the silicon evaporation source 4 is heated and evaporated by resistance heating or electron beam, and ionization is promoted along with hydrogen by an auxiliary electrode having a DC and/or AC potential.
A substrate 2 maintained at a negative potential with respect to an evaporation source 4 is deposited. The film deposited at this time becomes an amorphous film of an alloy of silicon and hydrogen, and becomes a film that can control valence electrons with few localized levels.

In the above operation description, before supplying hydrogen gas, a gas such as argon is supplied from the gas supply pipe 10 to bring the pressure inside the vacuum vessel 1 to 10 ^-1 to 10 ^-4 Torr, and a voltage is applied by the power supply 5. It is also possible to cause glow discharge and to purify the surface of the substrate 3 by ion bombardment. In addition, the ion plating method creates a plasma state and uses ionization of atmospheric gases such as vaporized silicon and hydrogen, so the partial pressure of gases such as hydrogen in the atmosphere is reduced.
Above 10 ^-1 Torr and below 10 ^-6 Torr, it is difficult to stabilize the plasma, which is not preferable.

As a method for heating the evaporation source, resistance heating or electron beam heating is preferable, and electron beam heating is particularly preferable from the viewpoint of ionization efficiency and prevention of contamination of the evaporation source.

The ion plating method may be a method in which the above-mentioned auxiliary electrode 7 is arranged to increase ionization efficiency, or a normal DC bipolar method, and a so-called ion plating method in which a film is deposited on a substrate kept at a negative potential with respect to the evaporation source. The Teing method is sufficient.

The above operation description describes the creation of an amorphous silicon-hydrogen alloy film by ion plating in a hydrogen atmosphere. For example, in order to obtain an amorphous film of silicon, fluorine-hydrogen alloy, This is possible by ion plating in a gas atmosphere containing fluorine such as carbon tetrafluoride (CF ₄ ). Furthermore, an a-Si film to which other elements are added can be obtained by ion plating in a gas atmosphere containing the element or by using an alloy of the element and silicon as the evaporation source.

Next, the creation of an n-type a-Si film will be described. It is created in the same manner as the i-type a-Si film described above, but
The difference is that a gas mixture of hydrogen and a compound of a group V element such as phosphine (PH ₃ ) or arsine (AsH ₃ ), which is a doping gas, and hydrogen or a halogen element is supplied into the vacuum vessel 1 from the gas supply pipe 10. Then, the pressure inside the vacuum vessel 1 is set to 10 ^-1 ~
10 ^-6 Torr. The ratio of doping gas to hydrogen at this time varies depending on the production conditions and the required doping amount, but is usually 2 ppm to 10%.
is within the range of It is also clear that instead of using a doping gas, the evaporation source may be silicon doped with a group V element such as P or As.

Next, the creation of a P-type a-Si film will be described. It is created in the same manner as the i-type a-Si film described above, but
The difference is that a gas mixture of hydrogen and a compound of a group element such as diborane (B ₂ H ₆ ), which is a doping gas, and hydrogen or a halogen element is supplied into the vacuum vessel 1 from the gas supply pipe 10. The aim is to reduce the internal pressure to 10 ^-1 to ^{10 -6} Torr. The ratio of doping gas to hydrogen at this time varies depending on the production conditions and the required doping amount, but usually
It ranges from 2ppm to 10%.

It is also clear that instead of using a doping gas, the evaporation source could be silicon doped with a group element such as B.

Next, an example of a specific electronic device manufactured by the manufacturing method of the present invention will be described. FIG. 2 is a cross-sectional view showing an example of the structure of an a-Si solar cell produced by the manufacturing method of the present invention, in which 11 is a stainless steel substrate;
2, 13, and 14 are n-type, i-type, and p-type a-
A Si layer, 15 a transparent conductive film, and 16 sunlight. In such a structure, the area of the light receiving surface is
2.25cm ² , the thickness of the stainless steel substrate 11 is 0.6mm,
The n-type, i-type, and p-type a-Si layers 12, 13, and 14 are created by the method described above, and the thickness of the n-type a-Si layer 12 is approximately 500 Å, and the thickness of the i-type a-Si layer 13 is approximately 500 Å. is about
5000 Å, the thickness of the p-type a-Si layer 14 is 100 to 300 Å
Å, the transparent conductive layer is created by a known electron beam evaporation method, sputtering method, etc., and its thickness is approximately
It is 1000Å.

A solar cell with the structure shown in Figure 2 was published in the U.S. patent.
Plasma as disclosed in specification No. 4064521
The characteristics were compared between the case where it was made by the CVD method and the case where it was made by the manufacturing method according to the present invention.

First, in the heat cycle test, the temperature was held at -20℃ and 80℃ for 2 hours each, and the temperature was raised and lowered for 1 hour each.
Solar cell a made by plasma CVD method in 20 times
In contrast to 70% of the cases in which the Si film peeled off, in the case of the cases produced by the manufacturing method of the present invention, no peeling of the a-Si film from the substrate occurred.

High temperature and high humidity environment test (temperature: 60℃, relative humidity: 95
% (held for 100 hours) using the plasma CVD method, 80% of the solar cells had a-Si film peeled off. The film did not peel off at all.

In addition, the solar cell's sunlight-electrical energy conversion efficiency is 80mW/ ^cm2 when irradiated with sunlight, the plasma
The percentage of products produced by the CVD method was 2%, and the percentage of products produced by the production method according to the present invention was 2.1%.

Although this value is industrially sufficient, according to the production method of the present invention, since various additive elements can be added, the localized levels can be reduced and the energy conversion efficiency can be increased.

Although the above description has been made regarding the case where the substrate is made of stainless steel, the same effect can be obtained even if the substrate is made of other metals, conductors, or insulators such as glass or ceramics.

Furthermore, although the above explanation was given regarding solar cells,
Needless to say, similar effects can be obtained not only in solar cells but also in any electronic device using an a-Si film.

As explained in detail above, according to the manufacturing method of the present invention, the adhesive strength between the a-Si film and the substrate becomes extremely strong, and electronic devices such as solar cells using the a-Si film are extremely reliable. Become something. In addition, according to the manufacturing method of the present invention, polycrystalline silicon of relatively low purity is used as a raw material, and the yield is also very good, so an a-Si film that can control valence electrons can be manufactured at a low cost, and it can be used with various elements. An amorphous film of silicon alloy can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an overview of an embodiment of the apparatus used for manufacturing the a-Si film of the present invention.
FIG. 2 is a sectional view showing an example of the structure of an a-Si solar cell produced by the manufacturing method of the present invention.

Claims (1)

[Claims] 1. In a vacuum container in which an auxiliary electrode with a DC potential is placed between the evaporation source and the substrate, a hydrogen atmosphere of 10 ^-1 to
An amorphous silicon film is deposited on a substrate kept at a negative potential with respect to the silicon evaporation source by thermally evaporating silicon or a silicon alloy at 10 ^-6 Torr and ionizing it using an auxiliary electrode. A manufacturing method for quality silicon film. 2. The method for producing an amorphous silicon film according to claim 1, which comprises introducing a gas selected from the group consisting of PH ₃ , AsH ₃ and B ₂ H ₆ into the vacuum container.