Patent ID: 8598586

Claim:
A semiconductor device having a thin film transistor, the thin film transistor comprising: a gate electrode; a gate insulating layer over the gate electrode; a microcrystalline semiconductor region over and in contact with the gate insulating layer; a pair of amorphous semiconductor regions over and in contact with part of the microcrystalline semiconductor region; a pair of impurity semiconductor layers over the pair of amorphous semiconductor regions; and a pair of wirings over and in contact with the pair of impurity semiconductor layers, wherein the microcrystalline semiconductor region includes a first region which is not covered with the pair of amorphous semiconductor regions and a second region which is in contact with the pair of amorphous semiconductor regions, wherein an upper surface of the second region has a projection and a depression and flatness of the first region is higher than flatness of the second region, and wherein a thickness d 1 of the first region is smaller than a thickness d 2 of the second region and the thickness d 1 is greater than or equal to 30 nm, where d 2 is a distance between an upper surface of the gate insulating layer and a tip of the projection.