The present invention has provided on a back channel side of the TFT a
blocking layer that is formed by laminating a 50 nm to 100 nm thick
silicon oxynitride film (A) and a 30 nm to 70 nm thick silicon oxynitride
film (B). By forming a lamination structure of such silicon oxynitride
films, not only can be the contaminations caused by impurities such as
alkali metallic elements from the substrate prevented, but the
fluctuations in the electrical characteristics of the TFT can be reduced.
