JPH1154433A - Method for forming silicon film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily form a silicon film comprising large crystal particles on a substrate, by forming metal particles on the substrate, depositing amorphous silicon on the substrate, and heating the substrate for crystallizing the amorphous silicon. SOLUTION: Metal particles 2 are formed on a substrate 1. In order for forming the metal particles 2 on the substrate 1, a metal film may be formed near a room temperature and then heated and aggregated for the metal particles 2, the metal film may be formed up a room temperature for patterning with photolithography, the substrate 1 may be heated to supply metal for forming, or metal powder may be sprinkled. After that, an amorphous silicon 3 is formed on the substrate 1. Then, the substrate 1 is heated, the amorphous silicon 3 is reacted with the metal particles 2 for depositing a silicon crystal 4, the silicon crystal 4 is grown with it as nucleus, so that a silicon polycrystal thin film 4A is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a desired silicon crystal film on a substrate, which is suitable for application to solar cells and the like.

[0002]

2. Description of the Related Art Due to the recent increase in energy demand and the decrease in reserves of fossil energy such as petroleum and coal, the importance of solar cells for effectively utilizing solar energy, which has not been sufficiently utilized in the past, is increasing. . At present, a solar cell mainly employs a substrate obtained by cutting a silicon ingot with a thickness of several hundred microns and having a pn junction and an electrode formed thereon.
Since a large amount of silicon is used in this method, shortage of silicon is expected when solar cells are mass-produced.

As a method for solving this problem, for example, T. Matsuyama et al., Japanese Journal of Applied Physi
cs) As described in Vol. 32 (1993), pp. 3720-3728, there is a method in which a polycrystalline silicon film is formed on a substrate such as glass, and a pn junction and an electrode are formed thereon to form a solar cell. In this method, a small amount of silicon raw material is used, and there is no fear that the silicon raw material will be insufficient even when a large number of solar cells are manufactured.

[0004]

However, when a polycrystalline silicon film is formed on a substrate such as glass, the size of the silicon crystal is as small as several microns or less. There is a problem that the conversion efficiency of the battery is not improved.

[0005] The present invention has been proposed in view of the above points. It is an object of the present invention to form a silicon film having large crystal grains on a substrate easily, and to use it for a solar cell. Another object of the present invention is to provide a method for forming a silicon film that can be expected to improve conversion efficiency.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a step of forming metal particles 2 on a substrate 1, a step of depositing amorphous silicon 3 on the substrate 1, and a step of heating the substrate 1 to form the amorphous silicon 3. The above object is attained by constituting the silicon crystal 4 by crystallizing 3.

Further, a step of forming metal particles 2 on a substrate 1 and a step of forming silicon particles 3 while heating the substrate 1 in a vacuum.
And the step of forming the silicon crystal 4 to achieve the above object.

Further, a step of depositing amorphous silicon 3 on the substrate 1, a step of forming metal particles 2 on the amorphous silicon 3, and a step of heating the substrate 1 to crystallize the amorphous silicon 3 4
The above object is attained by comprising in the process of forming.

[0009]

1A to 1D show a method for forming a silicon film according to a first embodiment of the present invention.

In these figures, reference numeral 1 denotes a substrate, which is preferably made of, for example, glass or a metal plate such as stainless steel subjected to insulation treatment.
Any substrate may be used as long as it does not adversely affect the silicon crystal 4 formed on the substrate 1. Reference numeral 2 denotes metal particles formed on the substrate 1. As the metal particles 2, when mixed into the silicon crystal 4, any metal particles that do not deteriorate the electrical and optical properties of the crystal may be used.
Sn, Al, Ge, or the like can be used. Also, 3
Is an amorphous silicon formed on the substrate 1 and 4A is a polycrystalline silicon thin film made of the grown silicon crystal 4.

In the first embodiment, metal particles 2 are formed on a substrate 1, an amorphous silicon film is deposited on the substrate 1, and the amorphous silicon film is heated to form an amorphous silicon film 3.
Is crystallized. The metal particles 2 on the substrate 1 are spatially dispersed, and react with the amorphous silicon 3 by heating to deposit a silicon crystal 4. Therefore, the crystallization speed is higher in the place where the metal particles 2 are present than in the portion of the amorphous silicon alone, and the silicon crystal 4 can grow in a size uniquely determined by the interval between the metal particles. doing.

Next, a method for forming the silicon crystal 4 will be specifically described.

First, as shown in FIG. 1A, first, metal particles 2 are formed on a substrate 1. Metal particles 2 on substrate 1
Can be formed by forming a metal film near room temperature and then heating and aggregating the metal film to form metal particles 2, or by forming a metal film at room temperature and then patterning using photolithography. 1 may be formed by heating and supplying a metal, a metal powder may be sprayed, or another method may be used as long as a desired density and size are obtained.

Next, as shown in FIG. 1B, an amorphous silicon 3 is formed on the substrate 1. The amorphous silicon 3 may be formed by any method including plasma CVD as long as it is amorphous silicon suitable for solid phase growth.

Next, as shown in FIG. 1C, the substrate 1 is heated to cause the amorphous silicon 3 to react with the metal particles 2 to deposit a silicon crystal 4, and the silicon crystal 4 is grown using the nucleus as a nucleus. Then, as shown in FIG. 1D, a silicon polycrystalline thin film 4A is formed.

That is, in the first embodiment, a stainless steel plate having SiO ₂ adhered thereto is used for the substrate 1,
While being heated at a high temperature, Sn was deposited in a thickness of 5 nm. At this time, Sn is aggregated, and Sn particles having an average particle interval of about 10 microns are formed as the metal particles 2. Silicon was supplied onto the substrate 1 at 150 degrees by using plasma CVD. Thus, a substrate 1 having an amorphous silicon layer on the substrate 1 in which the Sn particles were dispersed was obtained. When this substrate 1 was held at 500 degrees for 8 hours, as shown in FIG.
I got

FIGS. 2A to 2C show a second embodiment of the present invention. In this embodiment, metal particles 2 are formed on a substrate 1 and silicon is supplied while heating the substrate 1 in a vacuum. The metal particles 2 on the substrate 1 are dispersed and react with silicon by supplying a silicon raw material to form a eutectic of silicon and metal. Therefore, crystallization occurs preferentially in a place where the metal particles 2 are present as compared with a part where the metal particles 2 are not present, and the crystal is grown to a size uniquely determined by an interval between the metal particles 2. Has features.

That is, first, the metal particles 2 are formed on the substrate 1 by the method described with reference to FIG.
(A)). Next, while heating the substrate 1 in a vacuum, silicon is supplied as indicated by an arrow 5 (FIG. 2B). The method of supplying silicon may be any method including plasma CVD, thermal CVD, and sputtering. The supplied silicon reacts with the metal particles 2 to cause crystallization preferentially. Thereby, a silicon crystal 4 corresponding to the dispersion of the metal particles 2 is obtained (FIG. 2B). And finally, as shown in FIG. 2C, a silicon polycrystalline thin film 4A can be obtained.

In Example 2, a glass substrate was used as the substrate 1. 10 nm of Al is added to this glass substrate at room temperature.
Was sputtered. The substrate 1 was heated to 700 degrees. During this heating, Al was agglomerated into particles with an average interval of 20 microns. Next, silicon was supplied to the substrate 1 by using sputtering. Thus, a polycrystalline silicon thin film 4A having an average particle diameter of 20 microns was obtained.

FIGS. 3A to 3D show a third embodiment of the present invention. In this embodiment, an amorphous silicon film is deposited on a substrate 1, metal particles 2 are formed on the substrate 1, and this is heated to crystallize the amorphous silicon 3. The metal particles 2 are dispersed and react with the amorphous silicon 3 by heating to form a melt of silicon and metal, thereby depositing a silicon crystal 4. Therefore, the crystallization speed is higher in the place where the metal particles 2 are present than in the portion of the amorphous silicon alone, and the crystal can grow in a size uniquely determined by the interval between the metal particles 2. I have.

That is, first, a layer of amorphous silicon 3 is formed on the substrate 1. Next, metal particles 2 are formed by dispersing metal powder or the like. Next, this is heated to cause the amorphous silicon 3 and the metal particles 2 to react with each other to precipitate a silicon crystal 4 and to grow the silicon crystal 4 using the nucleus as a nucleus. The amorphous silicon 3 reacts with the metal particles 2 to preferentially crystallize. Thereby, large silicon crystal grains corresponding to the dispersion of the metal particles 2 can be obtained.

In the third embodiment, a glass substrate is used as the substrate 1 as in the second embodiment. Then, an amorphous silicon film was formed on the glass substrate at 150 degrees by using plasma CVD. On this, In powder having a particle size of 3 μm or less was dispersed at a rate of 500 particles / square mm. When this was held at 500 degrees for 8 hours, a silicon polycrystalline thin film 4A having an average particle size of 40 microns was obtained.

In each of Examples 1 to 3, the temperature at which the metal particles 2 react with silicon after deposition is preferably equal to or higher than the temperature at which the metal is melted or the temperature at which the alloy of metal and silicon is melted. However, when the temperature exceeds 500 ° C., since crystallization of silicon alone is started in a place other than the place where a metal and silicon are reacted to form a silicon crystal, it is desirable to keep the temperature below about 500 ° C.

In the embodiment shown in FIGS. 1 and 2, the distance between the metal particles 2 is determined by the wettability with the substrate 1. Since this interval is determined by variously selecting the combination of the type of metal, the temperature of the substrate 1, the type of the substrate 1, for example, SiO ₂ , silicon nitride, glass, and the like, a desired value can be selected. For solar cells, it is desirable that the spacing be greater than the desired silicon film thickness. Needless to say, in the embodiment of FIG. 3 as well, for solar cells, it is desirable to set the interval larger than the desired silicon film thickness.

In each of the embodiments shown in FIGS. 1 to 3, when a layer mainly composed of a metal remains and this layer is not necessary for fabricating the device, it is needless to say that the layer may be removed by etching. is there.

[0026]

As described above, according to the present invention, the dispersed metal particles 2 are used, and the metal particles 2 are reacted with the amorphous silicon 3 to precipitate the silicon crystal 4. The crystallization speed is higher in the portion where the metal particles 2 are present than in a single portion, and the silicon polycrystalline thin film composed of large-sized silicon crystals 4 having a size uniquely determined by the interval between the metal particles 2 4
A can be formed, and a solar cell using a silicon film having such large crystal grains can be expected to improve conversion efficiency, and a thin film transistor (so-called TFT)
It is also effective for such things.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the present invention, in which (a) to (d)
Indicates a process leading to the formation of a polycrystalline silicon thin film.

FIG. 2 shows a second embodiment of the present invention, in which (a) to (c).
Indicates a process leading to the formation of a polycrystalline silicon thin film.

FIG. 3 shows a third embodiment of the present invention, in which (a) to (d)
Indicates a process leading to the formation of a polycrystalline silicon thin film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Metal particle 3 Amorphous silicon 4 Silicon crystal 4A Silicon polycrystalline thin film 5 Supply of silicon

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeshi Kawakami Nippon Telegraph and Telephone Co., Ltd. 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo

Claims (3)

[Claims] 1. A step of forming metal particles (2) on a substrate (1), a step of depositing amorphous silicon (3) on said substrate (1), and heating said substrate (1) A step of crystallizing amorphous silicon (3) to form a silicon crystal (4). 2. A step of forming metal particles (2) on a substrate (1), and supplying silicon (3) while heating the substrate (1) in a vacuum to form a silicon crystal (4). A method of forming a silicon film. 3. A step of depositing amorphous silicon (3) on a substrate (1), a step of forming metal particles (2) on the amorphous silicon (3), and heating the substrate (1). Crystallizing the amorphous silicon (3) to form a silicon crystal (4).