Patent ID: 7998801

Claim:
A method for manufacturing a thin film transistor, comprising the steps of: forming a gate insulating layer over a gate electrode over a substrate; forming a microcrystalline semiconductor layer over the gate insulating layer; forming an amorphous semiconductor layer over the microcrystalline semiconductor layer; forming a semiconductor layer including an impurity element which imparts one conductivity type, wherein the semiconductor layer forms a source and drain regions over the amorphous semiconductor layer; forming a source and drain electrodes by using a mask over the semiconductor layer; removing by first dry-etching, a part of the semiconductor layer, which is exposed from the source and drain electrodes, and partially a part of the amorphous semiconductor layer just below and in contact with the part of the semiconductor layer; removing by second dry-etching, partially a part of the amorphous semiconductor layer which is exposed by the first dry-etching; and performing plasma treatment on a surface of a part of the amorphous semiconductor layer that is exposed by the second dry-etching so that an altered layer is formed, wherein the surface of the part of the amorphous semiconductor layer that is exposed by the second dry-etching is exposed to a plasma containing OH free radicals in the plasma treatment.