US Patent 9991395 Semiconductor device and manufacturing method thereof

When an oxide semiconductor film is microfabricated, with the use of a hard mask, unevenness of a side surface of the oxide semiconductor film can be suppressed. Specifically, a semiconductor device comprises an oxide semiconductor film over an insulating surface; a first hard mask and a second hard mask over the oxide semiconductor film; a source electrode over the oxide semiconductor film and the first hard mask; a drain electrode over the oxide semiconductor film and the second hard mask; a gate insulating film over the source electrode and the drain electrode; and a gate electrode overlapping with the gate insulating film and the oxide semiconductor film, and the first and second hard masks have conductivity.