1. Field of the Invention
The present invention relates to a method for manufacturing crystal-system silicon, and also relates to a photoelectric conversion device having a semiconductor junction using the crystal-system silicon and a method for manufacturing the photoelectric conversion device.
2. Description of the Related Art
In response to global environmental issues in recent years, the market for photoelectric conversion devices such as residential photovoltaic systems has expanded. As photoelectric conversion devices, devices using a high conversion efficiency single crystalline or polycrystalline silicon wafer have been used in practice. The photoelectric conversion devices using single crystalline or polycrystalline silicon are manufactured by being cut out of large silicon ingots. However, it takes a long time to manufacture large silicon ingots, which means productivity is low, and since supply of raw materials of silicon itself is limited, the supply of silicon ingots is insufficient and cannot respond to the expansion of the market.
Photoelectric conversion devices using amorphous silicon have been developed, and it has been considered that reduction of cost is possible therewith. However, light deterioration is not overcome, and thus the photoelectric conversion devices using amorphous silicon do not spread. By a high-frequency plasma CVD method that is a method for manufacturing amorphous silicon, an amorphous silicon film can be formed to have a large area at low temperature, and conversion efficiency of a photoelectric conversion device in which amorphous silicon is made to be a photoelectric conversion layer can be 10% or more. However, light deterioration called Staebler-Wronski effect can not be overcome. Therefore, development of photoelectric conversion devices has been proceeding, in which microcrystalline silicon as crystal-system silicon capable of being manufactured by a plasma CVD method is made to be a photoelectric conversion layer (for example, refer to Reference 1: Japanese Published Patent Application No. 2000-277439).
As a crystal-system silicon film formed by a plasma CVD method and a photoelectric conversion device using the crystal-system silicon film, a semi-amorphous semiconductor film and a photoelectric conversion device using the semi-amorphous semiconductor film are reported (for example, refer to References 2 and 3: Japanese Examined Patent Application Publication No. H2-53941 and Japanese Examined Patent Application Publication No. S62-62073). The semi-amorphous semiconductor has a semi-amorphous or semi-crystalline structure, which is different from an amorphous semiconductor or a crystalline semiconductor by the inventors of the present invention.
In order to form a photoelectric conversion layer using microcrystalline silicon, a thickness of the layer needs to be 1 μm or more, preferably, about 10 μm; however, the deposition rate of a microcrystalline silicon film by a high-frequency plasma CVD method is, for example, 0.1 nm/sec. or less, which is impractical. In other words, use of microcrystalline silicon for a photoelectric conversion layer causes problems in that productivity is low and cost competitiveness is lower than that of a photoelectric conversion device using another kind of crystal-system silicon.