JPH06140652A - Laminated silicon element - Google Patents

Abstract

PURPOSE:To provided a laminated silicon element whose electrical resistance can be reduced and whose silicon film is hardly peeled off. CONSTITUTION:A laminated silicon element 20 is composed of a sheet-type carbon fiber woven cloth 21 which does not have small holes over its whole area, an SiC intermediate film 22 which is formed over the whole surface of the woven cloth 21 and a polycrystalline silicon film 23 which is formed over the whole surface of the film 22. As the woven cloth 21 does not have small holes over its whole area, an electrical resistance can be reduced and, further, the film stress of the polycrystalline silicon film 23 can be reduced by the effect of the intermediate film 22. Moreover, an ohmic junction between the woven cloth 21 and the polycrystalline silicon film 23 can be formed by the effect of the intermediate film 22. Therefore, if the laminated silicon element 20 is applied to a solar cell, etc., its photoelectric conversion efficiency can be improved and, further, as the silicon film is hardly peeled off, its physical strength can be also improved and an ohmic junction between the silicon layer and an rear electrode can be also formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon-based base material and a polycrystalline silicon film formed on the base material, the main part of which is composed of, for example, a silicon layer forming a part of a solar cell. The present invention relates to a silicon laminated body that can be integrally applied as a back electrode member, and particularly to an improvement of a silicon laminated body that can reduce its electric resistance.

[0002]

2. Description of the Related Art As a silicon laminate of this type to which a carbon-based material is applied, for example, one described in JP-A-55-73450 is known.

That is, in this silicon laminate, a carbon fiber woven cloth having a net-like structure having a series of holes is dipped in the melted silicon contained in the melting tank, and the melted silicon is filled in the holes and on the surface. In addition, a structure is known in which the melt is crystallized while being coated, and the melt is crystallized. For example, it is integrally applied as a silicon layer and a back electrode member of the solar cell shown in FIG. There is.

In FIG. 3, a is a p-type silicon layer and b is n.
A type silicon layer, c is an antireflection layer such as ITO, d is a comb-shaped electrode, e is an ohmic contact layer, and f is a backside electrode.

By the way, in this silicon laminate, a carbon fiber woven cloth having a net-like structure provided with a series of holes for holding and crystallizing the molten silicon is applied. Since the electric resistance increases as much as the holes are provided, there is a drawback that it is difficult to improve the photoelectric conversion efficiency of the solar cell incorporating the silicon laminated body.

Therefore, in the past, the thermal CV is usually used.
A method for producing a silicon laminated body by directly forming a polycrystalline silicon film on a sheet-shaped carbon-based substrate surface by a film forming means such as D method or plasma CVD method, and incorporating the silicon laminated body into the solar cell or the like. Is taken.

[0007]

However, the latter silicon laminated body manufactured by applying the above-mentioned film forming means also has the following problems.

That is, when a polycrystalline silicon film is formed on a sheet-like carbon-based substrate surface by means of a thermal CVD method or the like, due to the difference in thermal expansion coefficient between the carbon-based substrate and silicon. The formed polycrystalline silicon film has a drawback that stress is likely to occur.

Therefore, unless the film thickness of the polycrystalline silicon film is set to a certain level, defects and cracks are likely to occur in the film, and the film stress causes a large amount of the film from the substrate. There is a problem that the crystalline silicon film is easily peeled off.

The present invention has been made by paying attention to such a problem, and its problem is that a main part is composed of a carbon-based base material and a polycrystalline silicon film to reduce the electric resistance thereof. At the same time, it is to provide a silicon laminate in which the silicon film is not easily peeled off.

[0011]

That is, in the invention according to claim 1, the silicon laminated body comprises a sheet-like carbon-based base material and silicon carbide formed over the entire surface of the carbon-based base material. And a polycrystalline silicon film formed on the intermediate film.

In the above technical means, the carbon-based substrate means a sheet-shaped substrate which contains carbon as a main component and does not have small holes over the entire area thereof. , For example, a graphite plate or sheet-like carbon-carbon composite material whose surface and internal structure are in a dense state (for example, one whose main part is composed of carbon fiber and a carbonized resin component), and A carbon fiber woven cloth or the like having a dense surface and inner structure can be applied.

The sheet-like carbonaceous substrate applied to the present invention does not have small holes all over its area, so that the electric resistance can be reduced, and the substrate and the polycrystalline silicon film are combined. Since an intermediate film of silicon carbide having an intermediate property between carbon and silicon chemically and physically is interposed between them, it is possible to improve the chemical affinity and reduce the film stress after the polycrystalline silicon film is formed. Furthermore, it becomes possible to form an ohmic contact between the polycrystalline silicon film and the carbon-based substrate.

Therefore, when the silicon laminate according to the present invention is applied to a solar cell or the like, its electrical resistance is small, so that the photoelectric conversion efficiency and the like can be improved, and even if the film thickness is set thin The polycrystalline silicon film thus formed has no defects or cracks and is less likely to be peeled off from the carbon-based base material, so that its physical resistance is improved, and ohmic contact between the silicon layer and the back electrode is also formed. It has the advantage of being possible.

The application target of such a silicon laminate is not limited to the above-mentioned solar cell, but may be, for example, an optical sensor.

[0016]

According to the invention of claim 1, a sheet-shaped carbon-based substrate, an intermediate film made of silicon carbide formed over the entire surface of the carbon-based substrate, and a film formed on this intermediate film. And a polycrystalline silicon film formed into a silicon laminate, and the sheet-shaped carbon-based substrate does not have small holes over the entire area, so that the electrical resistance can be reduced and the carbon-based substrate can be formed. Since an intermediate film of silicon carbide, which is chemically and physically intermediate between carbon and silicon, is interposed between the material and the polycrystalline silicon film, the chemical affinity is improved and the polycrystalline silicon film is made. It is possible to reduce the film stress immediately after the film and form an ohmic contact between the carbon-based substrate and the polycrystalline silicon film.

[0017]

EXAMPLES Examples of the present invention will be described in detail below.

First, the silicon laminate 2 according to this embodiment.
As shown in FIG. 1, reference numeral 0 denotes a sheet-like carbon fiber woven fabric 21 having no small holes throughout the entire region, and an intermediate film made of silicon carbide formed over the entire surface of the carbon fiber woven fabric 21. 22 and a polycrystalline silicon film 23 formed on the intermediate film 22 constitute a main part thereof.

The carbon fiber woven cloth 21 has carbon fiber cloth (trade name: CFS) manufactured by Arisawa Manufacturing Co., Ltd. whose characteristics are shown in Table 1 below.
1140) has been applied.

[0020]

[Table 1] The silicon stack 20 is manufactured by the method described below. That is, as shown in FIG. 2, a high temperature plasma generating part 1 capable of forming arc plasma and induction plasma, and a reaction chamber 3 provided adjacent to the high temperature plasma generating part 1 and having a substrate holder 7 therein, The carbon fiber woven fabric 21 is arranged in the apparatus constituting the part, and the inside of the reaction chamber 3 is -10 ⁻³ Torr.
After evacuating the air and the like in the reaction chamber 3 until the plasma chamber is ignited, the carbon fiber woven cloth 21 is horizontally attached to the base material holder 7 prior to ignition in order to prevent rapid heating and local overheating after plasma ignition. A moving mechanism (not shown) for moving to (1) was operated.

Next, argon gas and hydrogen gas were introduced into the plasma generating part 1 and plasma ignition was performed. As the power source, direct current was first applied and then high frequency was applied.
The shape of the high temperature plasma flame varied considerably depending on the flow rates of argon gas and hydrogen gas, but a stable state could be obtained relatively easily. In addition, a pressure control valve is attached to the inlets of argon gas and hydrogen gas and the inlet of silicon raw material, and an exhaust system 4 is provided downstream of the reaction chamber 3 in this apparatus. The pressure in the reaction chamber 3 is maintained at ˜550 Torr.

The carbon fiber woven fabric 21
Is heated by the high temperature plasma and the heating means 8 provided in the substrate holder 7 and the surface temperature is monitored to be sufficiently elevated by using a radiation thermometer.
When the temperature reached 500 ° C., a fixed amount of silicon particles 6 were introduced from the inlet of the silicon raw material to melt the silicon particles 6 in high temperature plasma, and the melt was supplied onto the carbon fiber woven fabric 21. The silicon component and the carbon component of the woven fabric 21 are heated and reacted to produce silicon carbide (Si
An intermediate film 22 made of C) was formed.

Next, the output of the heating means 8 is lowered to lower the temperature of the carbon fiber woven cloth 21 to a temperature just below the melting point of silicon (1400 ° C.), and silicon particles are deposited on the intermediate film 22 under this temperature condition. The melt of 6 was formed into a film.

Then, this film forming treatment is performed for 2 to 3 minutes,
Further, even after the supply of the silicon particles 6 is stopped, a high frequency is applied to continue the high temperature plasma of argon to control the cooling for about 5 to 10 minutes to form a polycrystalline silicon film 23 with a film thickness of about 1 mm to form the above silicon laminated body. 20 was produced.

The moving mechanism provided on the base material holder 7 is continuously operated before the formation of the intermediate film 22 and during the cooling control of the silicon film.
The heat input to the surface is made uniform.

(Film forming strip
Conditions) Pressure in reaction chamber ~ 550 Torr DC plasma input power 5KW RF plasma input power 30KW Argon gas flow rate 60-80 liters / min Hydrogen gas flow rate 2-4 liters /
min Particle size of silicon particles 75 to 150 μm Supply amount of silicon particles 1 g / min Distance between high temperature plasma generation part and woven fabric 10 to 20 cm TEM observation was conducted on the polycrystalline silicon film 23 thus obtained, and the film was found. It was confirmed that the crystal grain size reached about 100 μm at a thickness of about 1 mm, and that the film characteristics were also uniform.

[0027]

According to the invention of claim 1, since the sheet-shaped carbon-based substrate does not have small holes over its entire area, the electric resistance can be reduced, and the carbon-based substrate and the carbon-based substrate can be mixed with each other. Since an intermediate film of silicon carbide, which is chemically and physically intermediate between carbon and silicon, is interposed between the crystalline silicon film and the crystalline silicon film, the chemical affinity is improved and the film immediately after the polycrystalline silicon film is formed. It is possible to reduce the film stress and form an ohmic contact between the carbon-based substrate and the polycrystalline silicon film.

Therefore, there is an effect that it is possible to provide a silicon laminate having a low electric resistance and in which the polycrystalline silicon film is hard to be peeled off.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a silicon stack according to an example.

FIG. 2 is a structural conceptual diagram of an apparatus applied to the manufacturing method of the embodiment.

FIG. 3 is a schematic sectional view of a conventional solar cell.

[Explanation of symbols]

 20 Silicon Laminate 21 Carbon Fiber Woven 22 Intermediate Film (SiC) 23 Polycrystalline Silicon Film

Claims (1)

[Claims] 1. A sheet-shaped carbon-based substrate, an intermediate film made of silicon carbide formed over the entire surface of the carbon-based substrate, and a polycrystalline silicon film formed on the intermediate film. A silicon laminated body characterized by being constituted.