In the barrier metal layer 13 of the titanium nitride rich in titanium as compared with the stoichiometric ratio, the composition ratio x of nitrogen in the titanium nitride (TiNx) is preferably, for example, 0.1???0.95 for the following reason: When x is larger than 0.95, a reaction layer 6 of a compound principally including silicon and nitrogen is formed between the polysilicon film 12 and the