Patent ID: 7618881

Claim:
A method for manufacturing a thin-film transistor, comprising the steps of: forming a non-single-crystal semiconductor thin film on an insulating substrate; forming a gate insulating film on the non-single-crystal semiconductor thin film; forming a gate electrode including a lower gate electrode and an upper gate electrode on the gate insulating film, the lower gate electrode having a portion that is not covered by the upper gate electrode; forming a heavily doped region and a lightly doped region in the non-single-crystal semiconductor thin film concurrently by introducing an impurity into the non-single-crystal semiconductor thin film through the gate electrode and the gate insulating film; and etching away an exposed portion of the lower gate electrode by using the upper gate electrode as a mask, wherein the step of forming a gate electrode comprises the steps of: forming a conductive film including a plurality of layers on the gate insulating film; and forming the gate electrode by selectively etching the conductive film, wherein the step of forming a gate electrode comprises the steps of: forming a conductive film including a plurality of layers on the gate insulating film; selectively forming a photoresist film on a top layer of the conductive film; and forming the upper gate electrode by applying isotropic etching to the conductive film by using the photoresist film as a mask and forming the lower gate electrode by applying anisotropic etching to the conductive film by using the photoresist film as a mask.