JP2975942B2 - Preparation of amorphous silicon based thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly stable amorphous silicon-based thin film (hereinafter referred to as an a-Si based thin film) which is applied to a solar cell, a photoelectric conversion device or the like to provide a more excellent light deterioration suppressing performance. ) Is efficiently produced.

[0002]

2. Description of the Related Art Conventionally, as a method of forming an amorphous silicon-based film, a plasma CVD method, a photo-CVD method, or the like has been used. Photodeterioration is manifested by the so-called Stibler-Lonski effect, in which the rate is reduced to about 1/10, and even today, the above-mentioned film having sufficient photodeterioration suppression performance is hard to obtain and has not yet been satisfied.

[0003] Further, a pin type a-Si
Even in a solar cell, a new defect is generated by recombination of photogenerated carriers by light irradiation, and the initial characteristics (photoelectric conversion efficiency) are greatly reduced. As means for suppressing the light degradation, for example, Attempts have been made to make the i-layer thinner, to form the i-layer at a high temperature, to form a film with less impurities such as O ₂ and N ₂ , or to use a source gas for forming a fluorine-based thin film. However, there is a problem that none of the methods is effective, and there is a problem in that the film formation technique or the operation is complicated, and the countermeasure also leads to an increase in the cost of the apparatus.

[0004] For example, Japanese Patent Application Laid-Open No. 59-542 discloses a technique for preventing deterioration of photoelectric conversion efficiency due to light irradiation.
No. 74 discloses a photovoltaic device which is intended to be obtained by including a small amount of a group V element (for example, about 0.5 to 3% of nitrogen) in an amorphous silicon-based semiconductor layer. And JP-A-63-84079 discloses that the ratio of silicon atoms bonded to two hydrogen atoms is about 1%.
The following photovoltaic device is described in which a hydrogenated amorphous semiconductor is mainly used as a photoactive layer that performs a photoelectric conversion operation. JP-A-2-219284 discloses a photovoltaic device in which the flow rate ratio of helium gas to monosilane gas is 0.1. There is known a method of manufacturing an amorphous solar cell using a mixed gas of helium gas and monosilane gas as described above as a source gas.

On the other hand, as an example of the CVD method using xenon gas, for example, Japanese Patent Application Laid-Open No. 294866/1990 discloses that in a plasma CVD method, a Xe gas, especially an Xe gas, is added to a raw material gas for forming an amorphous silicon film. By using the amount of 2 Vol.% Or less with respect to the source gas, it is possible to promote the decomposition and activation of the source gas and to improve the film formation rate without deteriorating the film characteristics. A method for forming an amorphous silicon film is described.
Further, Japanese Patent Publication No. 1-36522 describes a method for producing an amorphous silicon film using an inert gas such as xenon as a photosensitizer added to a silane-containing gas mixture in a photo-CVD method. is there.

[0006]

SUMMARY OF THE INVENTION Problems to be Solved by the Invention
The means described in JP-A-54274, JP-A-63-84079 and JP-A-2-219284 do not sufficiently reduce the photoelectric conversion efficiency due to light irradiation. It's still hard to say. On the other hand, for an amorphous silicon film formed by the method described in JP-A-1-294866,
Even if it is possible to improve the film formation rate by adding Xe gas of 2 Vol% or less, there is no description that the film has the light deterioration suppressing performance in the range, and the improvement can be achieved. This is not necessarily the case, and the method described in Japanese Patent Publication No. 1-36522 is intended to increase the sensitivity of the reactants to photon absorption, and to reduce water and mobility. Although it is intended to increase the reliability of solid-state devices by preventing corrosion and device deterioration due to the adverse effect of environmental pollution caused by both ions, it does not mention at all that it has light deterioration suppression performance, either. It is hard to say that improvement can be achieved.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional drawbacks, and has specified xenon (Xe) gas and hydrogen gas as raw material gases for forming an amorphous silicon-based film. By using a mixture gas mixed in a sufficient amount and forming a film on a substrate by a conventional plasma CVD method without major modification or expansion, xenon gas and hydrogen gas, especially It is an object of the present invention to provide a method for producing an amorphous silicon-based thin film which sufficiently suppresses photodegradation by a function and effect considered to be physical.

That is, the present invention provides a method for forming an amorphous silicon-based film on a substrate by a plasma CVD method using a mixed gas containing a source gas for forming an amorphous silicon-based film and a xenon gas. An object of the present invention is to provide a method for producing an amorphous silicon-based thin film, characterized by using a mixture gas to which 0.05 to 1 times xenon gas and 5 to 30 times hydrogen gas are added in a volume ratio to a gas.

Here, a mixture gas is used in which xenon gas and hydrogen gas are added in a volume ratio of 0.05 to 1 times and hydrogen gas in a volume ratio of 5 to 30 times with respect to the raw material gas for forming the amorphous silicon film. The reason is that if the mixture gas is a mixture of xenon gas less than 0.05 times and hydrogen gas less than 5 times the film forming source gas, the effect of suppressing light deterioration cannot be sufficiently obtained. If the amount of xenon gas is more than 1 times, the dark conductivity is high and it is difficult to obtain a high-quality film, and the more the amount of xenon gas is used, the higher the manufacturing cost becomes. When, for example, about 50 times, the peeling phenomenon of the film occurs, the power density at the time of film formation is increased while the suppression of photodeterioration is ensured, and the film quality is also low in dark conductivity. This is because it is possible to improve such a thing. It is preferable to use a mixed gas obtained by mixing about 0.1 to 0.9 times xenon gas and about 5.5 to 25 times hydrogen gas.

The raw material gas for forming an amorphous silicon-based film includes, for example, silane (SiH ₄ ), disilane (Si ₂ H ₆ ), a mixed gas of germane (GeH ₄ ) and silane or disilane, and methane (CH ₄ ). And a mixture gas of silane and disilane, etc., and a general raw material for forming an amorphous silicon-based film, particularly those used in a plasma CVD method can be used.

The amorphous silicon-based thin film includes amorphous silicon thin films and various amorphous silicon-based alloy thin films such as amorphous silicon germanium (a-SiGe) and amorphous silicon carbon (a-SiC). It is a generic term.

Furthermore, the reason why the plasma CVD method is used is that the plasma CVD method is used to obtain the effect of the xenon and the hydrogen gas, and other amorphous silicon-based thin films are used. It is needless to say that the above-mentioned effects can be obtained by applying and applying the film forming method. The substrate is made of glass, aluminum, stainless steel or the like, and is not particularly limited.

[0013]

As described above, the method for producing an amorphous silicon-based thin film according to the present invention uses a xenon gas of 0.05 to 1 times and a xenon gas of 5 to 30 times specified by volume ratio to the raw material gas for forming an amorphous silicon based film. Hydrogen gas is added to each other to use a mixture gas, so that the thin film having excellent light degradation suppressing performance can be formed, and the production cost can be efficiently reduced.
The effect of xenon mixing when preparing an amorphous silicon-based thin film in Method D is that the energy of the long-lived excited species of Xe is 9.45 eV, so that SiH ₃
Can be expected, so-called good film quality can be expected, and it is possible to prevent generation of SiH ₂ which induces bad film quality, and that a heavy substance called Xe (m = 131) exists on the film growth surface. The existence of a certain amount of scattered spots suppresses the radical motion on the surface of the film-forming radical SiH ₃ , thereby preventing crystallization and, furthermore, being able to incorporate voids in which hydrogen atoms are gathered into the network. Inferred and confirmed, the hydrogen gas specified in addition to this is to appropriately improve the film quality, and these effects are the above-mentioned specific numerical value, that is, the raw material gas for forming the a-Si film. By volume ratio, from 0.05 to
It has been found that the use of an additive mixture gas of 1 times Xe gas and 5 to 30 times H ₂ gas is effective for securing the light degradation suppressing performance and reducing the manufacturing cost. Thus, the amorphous silicon-based thin film formed by the method of the present invention becomes more efficient, inexpensive, and has a sufficiently long-term light degradation suppressing performance, and employs an amorphous silicon-based thin film including a solar cell. It is useful in a wide range of fields such as various electronic articles.

[0014]

An embodiment of the present invention will be described below. However, the present invention is not limited to such an embodiment.

Examples 1 to 8 In forming an amorphous silicon-based thin film on a glass substrate by using the manufacturing method of the present invention, a parallel plate type plasma CV was used.
D apparatus was used. That is, the plasma CVD apparatus comprises a reaction vessel which can be decompressed to be a vacuum chamber, a flat discharge electrode concentric with the vessel and arranged vertically in parallel, and a high frequency power supply connected to the upper side of the electrode. And the glass substrate is placed in the lower electrode on which the glass substrate is placed.
A heater for heating to about 00 ° C., a source gas supply source for forming an amorphous silicon-based film such as SiH ₄ , Si ₂ H ₆ , and GeH ₄ , a xenon gas supply source, and a hydrogen gas supply source are supplied as described above. An introduction pipe for introducing the mixture gas mixed at a volume ratio into the reaction vessel, and an exhaust port connected to an exhaust pump for maintaining the pressure of the supply gas at a predetermined value after exhausting the reaction vessel to a high vacuum once. It consists of:

In the above plasma CVD apparatus,
After mounting the glass substrate on the head side electrode, close the reaction vessel
Then, the container is evacuated and a high vacuum (for example, 1 × 10^-6~ 1
× 10 ^-8(About Torr).
The glass substrate is heated to about 200 to 300 ° C by the heater
For example, heating to a predetermined temperature of about 250 ° C.), and then
For example, as in Example 1, amorphous silicon-based film
SiH from raw material supply source_Four5 SCCM gas, xenon gas supply
5 SCCM of Xe gas from supply source, hydrogen gas from hydrogen gas supply source
Mixing by controlling the flow rate by 25 SCCM
Substance gas is introduced into the reaction vessel from the introduction pipe, and the
While maintaining the gas pressure at about 100 mTorr,
0.03-0.5w / cm depending on source^TwoPower to the discharge electrode
By providing, the film thickness on the surface of the glass substrate is about
Amorphous silicon of about 5000-6000６
A thin film is formed.

With respect to the amorphous silicon thin film obtained as described above, for example, regarding photoconductivity,
Measured and evaluated by an automatic conductivity measurement system manufactured by Spannics, and simulated sunlight (AM-1,
(100 mW / cm ² , irradiation with a solar simulator light), the photoconductivity was measured after light irradiation for about 167 hours or so, and evaluated by comparing with the photoconductivity before light irradiation.

Table 1 shows the film forming conditions and the results. Note that -lnσ _P / lnt in the table shows the change in the photoconductivity σ _P due to t during light irradiation in each logarithmic ratio (slope). For example, the above-mentioned ratio of the a-Si thin film obtained under the i-layer film forming conditions of the conventional solar cell (for example, when only SiH ₄ gas is used) exceeds about 0.3. It showed a large value.

As is clear from Table 1, the initial values of the photoconductivity (σ _P ) are 10 ⁻⁵ / Ω · cm and 10 ⁻⁴ / Ω ·
cm, and the difference between σ _P and σ _d (initial photoconductivity) is about 10 ^−6, that is, about 6 digits, and shows the degree of suppression of photodeterioration-lnσ _P / lnt. Thus, an amorphous silicon-based thin film which is excellent and the photodeterioration rate is remarkably reduced and suppressed is obtained.

[0020]

[Table 1]

Comparative Examples 1 to 8 The same apparatus and the same measurement and evaluation were carried out under the same film forming conditions as shown in Table 2, and the results are shown in Table 2.

As is apparent from Table 2, the difference between the production method and the composition of the present invention or the one out of the specified numerical range has a difference between σ _P and σ _d of about 10 ^-6, that is, a ratio of about 6 digits. Some show the degree of suppression of photodeterioration-ln σ _P / Int exceeds 0.3, and even those with suppression of photodeterioration have σ _P and σ
The gap with _d is about 4 digits, and furthermore, it shows good film peeling, and shows the suppression of light deterioration.
It is not a better practical amorphous silicon-based thin film.

[0023]

[Table 2]

[0024]

According to the present invention, in a plasma CVD method, xenon gas and hydrogen gas are supplied and mixed at a specified volume ratio to a film forming raw material gas to form an amorphous silicon-based thin film. Therefore, it is possible to efficiently form an amorphous silicon-based thin film having substantially no photodegradation, and for example, it is possible to suppress photodegradation, which is one of the biggest problems in amorphous silicon solar cells, and An object of the present invention is to provide a method for producing a useful amorphous silicon-based thin film that can contribute to its spread by practical use.

──────────────────────────────────────────────────の Continuing from the front page (72) Koji Fujita, Inventor 1510 Oguchi-cho, Matsusaka-shi, Mie Inside the Technical Center, Central Glass Co., Ltd. (72) Inventor Kunishi Mashima 1510, Oguchi-cho, Matsusaka, Mie, Japan Examiner in the Technical Center of the Company Ken Haseyama (56) References JP-A-4-348083 (JP, A) JP-A-4-206630 (JP, A) JP-A-62-100744 (JP, A) JP-A Sho57 -99725 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/205 H01L 31/04

Claims (1)

(57) [Claims] In a method for forming an amorphous silicon-based film on a substrate by a plasma CVD method using a mixture gas containing a source gas for forming an amorphous silicon-based film and a xenon gas, the volume of the source gas for forming a film is reduced. Xenon gas of 0.05 to 1 times and 5 to 3 times
A method for producing an amorphous silicon-based thin film, comprising using a mixture gas to which 0 times hydrogen gas is added.