Patent ID: 8349671

Claim:
A method for manufacturing a thin film transistor, comprising the steps of: forming a gate insulating layer over a gate electrode layer; forming a semiconductor layer over the gate insulating layer; forming an impurity semiconductor layer over the semiconductor layer; forming an island-shaped semiconductor layer comprising the semiconductor layer and the impurity semiconductor layer by using a first resist mask, the island-shaped semiconductor layer overlapping at least a part of the gate electrode layer; forming a conductive layer over the gate insulating layer and the island-shaped semiconductor layer; etching the conductive layer to form source and drain electrode layers by using a second resist mask over the conductive layer; etching the impurity semiconductor layer of the island-shaped semiconductor layer, to expose a part of the semiconductor layer so that a back channel portion in the thin film transistor is formed; removing the second resist mask after etching the impurity semiconductor layer of the island-shaped semiconductor layer; and etching a part of the back channel portion, after removing the second resist mask.