Patent ID: 8772778

Claim:
A semiconductor device comprising: a semiconductor film over an insulating surface; a gate insulating film over the semiconductor film; and a gate electrode comprising: a first conductive layer over the gate insulating film; and a second conductive layer over the first conductive layer; wherein the semiconductor film includes, a channel forming region, LDD regions in contact with the channel forming region, a source region and a drain region in contact with the LDD regions, wherein an end portion of the first conductive layer extends beyond an end portion of the second conductive layer, wherein the LDD regions overlap the first conductive layer with the gate insulating film interposed therebetween, wherein the second conductive layer has a tapered shape in an end portion of the second conductive layer in cross section, wherein the first conductive layer comprises at least a first element selected from the group consisting of Ta, W, Ti, Mo, Al, and Cu and the second conductive layer comprises at least a second element selected from the group consisting of Ta, W, Ti, Mo, Al, and Cu, and wherein the first element is different from the second element.