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Semiconductor device and manufacturing method for the same
| Details |
Inventors: Hayakawa, Masahiko;
Assignee: Semiconductor Energy Laboratory Co., Ltd. (Kanagawa-ken, JP)
Primary Examiner: Chang; Joni
Assistant Examiner: Coleman; William David
Attorney, Agent or Firm: Robinson; Eric J. Nixon Peabody LLP
A semiconductor device having an active layer comprising crystalline silicon, said active layer comprising a first layer comprising crystalline silicon formed on an insulating surface and a second layer comprising crystalline silicon formed on said first layer, wherein said first layer contains a metal element at a first concentration while said second layer is free from said metal element or contains said metal element at a second concentration which is lower than said first concentration. |
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DETAILED DESCRIPTION An object of the present invention is to form a thin film semiconductor layer having a very low content of elements such as nickel by employing heat crystallization in a low temperature process.
The present invention is characterized in that an amorphous silicon film is divided into two layers and a heat crystallization process is carried out twice to thereby easily obtain a crystalline silicon film having a very low content of elements such as nickel by a low temperature process.
In the present invention, since the most remarkable effect can be obtained when nickel is used, nickel will be used in the following description.
However, other usable elements include Pt, Cu, Ag, Au, In, Sn, Pd, P, As, and Sb.
Further, there can be used as well one or more elements selected from the VIII group elements and the IIIb, IVb and Vb group elements.
First, nickel which promotes the crystallization of an amorphous silicon film, is introduced into the amorphous silicon film constituting the first layer, and a heat treatment is carried out to crystallize the amorphous silicon film.
Then, an amorphous silicon film constituting the second layer is formed, and heat treatment is carried out to crystallize this amorphous silicon film.
In this way, a crystalline silicon film suitable for a thin film semiconductor layer is obtained.
For the introducing method for the nickel element promoting the crystallization, a layer containing nickel or a nickel compound can be formed in contact with the amorphous silicon film.
For forming the nickel-containing layer, a method in which a solution containing nickel is coated and then dried (for example, spin coating or dipping), a method in which a nickel or a nickel compound film is formed by sputtering, or a method in which gaseous organic nickel is used as a precursor material of a vapor phase deposition using heat, light and/or plasma as an energy source.
In all the methods, the thickness of the layer may be determined according to the amount of nickel needed
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MEMS 
