Patent ID: 7705358

Claim:
A semiconductor device comprising: an island-shaped semiconductor film, said island-shaped semiconductor film comprising: a channel-formation region; a high-concentration impurity region including a silicide layer; a first low-concentration impurity region between the channel-formation region and the high-concentration impurity region; and a second low-concentration impurity region between the first low-concentration impurity region and the high-concentration impurity region; a gate insulating film over the channel-formation region, the first low-concentration impurity region and the second low-concentration impurity region; a first gate electrode overlapping with the channel-formation region and the first low-concentration impurity region with the gate insulating film interposed therebetween; a second gate electrode on the first gate electrode, said second gate electrode overlapping with the channel-formation region with the gate insulating film and the first gate electrode interposed therebetween; and a sidewall formed on side surfaces of the first gate electrode and the second gate electrode, wherein a thickness of the gate insulating film is smaller in a region over the second low-concentration impurity region than in a region over the channel formation region and the first low-concentration impurity region, and wherein an impurity concentration of the second low-concentration impurity region is higher in a lower portion of the second low-concentration impurity region than in an upper portion of the second low-concentration impurity region.