| 摘要 |
There is provided a semiconductor device in which a semiconductor layer and a gate electrode are formed with a gate insulating layer between then and in which a region of the semiconductor layer opposite to the gate electrode is used as a channel region. On the semiconductor layer, an insulating protection film and an amorphous semiconductor layer are successively formed. The protection film covers at least the channel region of the amorphous semiconductor layer, and annealing is applied to the amorphous semiconductor layer, thereby converting the amorphous semiconductor layer into the polycrystal semiconductor layer. A portion to be the channel region of the amorphous semiconductor layer is covered by the protection film. Therefore, even when exposed to the atmosphere due to annealing, surface contamination can be prevented and a semiconductor device having satisfactory characteristics can be obtained. A thickness d of the protection film is set to be nearly " lambda /4n" for a wavelength lambda of laser beam and a refractive index n of materials for the protection film. If there is unevenness of the thickness of the amorphous semiconductor layer to be formed, the protection film will be formed, with its thickness being optimum for a region which the amorphous semiconductor layer is formed thickest. On the other hand, if there is unevenness of the thickness of a gate insulating layer, the protection film will be formed, with its thickness being optimum for a region which the gate insulating layer is formed thinnest.
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