Patent ID: 7335540

Claim:
A method of forming a low temperature polysilicon thin film transistor, comprising: forming an amorphous silicon layer over a substrate; performing a plasma treatment to the amorphous silicon layer, wherein the plasma treatment is selected from nitrous oxide (N 2 O) plasma, ammonia (NH 3 ) plasma or hydrogen (H 2 ) plasma, and there is no film layer formed on the surface of the amorphous silicon layer after the plasma treatment is performed; transforming the amorphous silicon layer into a polysilicon layer; patterning the polysilicon layer to form a plurality of island polysilicon layers; forming a channel region and a doped source/drain region on each side of the channel region in each island polysilicon layer; and forming a gate over each channel region, wherein the channel region composed of polysilicon has an adjusted threshold voltage determined by the plasma treatment.