Semiconductor device and manufacturing method thereof

A semiconductor device comprising:

• a gate electrode;
• an oxide semiconductor film over the gate electrode;
• an insulating film over and in contact with a channel formation region of the oxide semiconductor film, the insulating film comprising silicon oxide;
• a first layer over and in contact with the oxide semiconductor film;
• a second layer over and in contact with the oxide semiconductor film;
• a source electrode over and in contact with the first layer, the source electrode being electrically connected to the oxide semiconductor film;
• and
• a drain electrode over and in contact with the second layer, the drain electrode being electrically connected to the oxide semiconductor film,
• wherein the oxide semiconductor film comprises indium, gallium, and zinc,
• wherein the insulating film does not contact the source electrode or the drain electrode,
• wherein the source electrode or the drain electrode comprises a first conductive layer and a second conductive layer over the first conductive layer, and
• wherein, in a cross sectional view in a channel length direction, the first layer or the second layer comprises a first region which is overlapped by the second conductive layer and a second region which extends beyond an end portion of the second conductive layer in the channel length direction.

A semiconductor device comprising:

• a gate electrode;
• an oxide semiconductor film over the gate electrode;
• an insulating film over and in contact with a channel formation region of the oxide semiconductor film, the insulating film comprising silicon oxide;
• a first layer over and in contact with the oxide semiconductor film;
• a second layer over and in contact with the oxide semiconductor film;
• a source electrode over and in contact with the first layer, the source electrode being electrically connected to the oxide semiconductor film;
• and
• a drain electrode over and in contact with the second layer, the drain electrode being electrically connected to the oxide semiconductor film,
• wherein the oxide semiconductor film comprises indium, gallium, and zinc,
• wherein the oxide semiconductor film comprises a first region overlapped by the source electrode or the drain electrode and a second region in contact with the insulating film,
• wherein a thickness of the first region of the oxide semiconductor film is smaller than a thickness of the second region of the oxide semiconductor film,
• wherein the insulating film does not contact the source electrode or the drain electrode,
• wherein the source electrode or the drain electrode comprises a first conductive layer and a second conductive layer over the first conductive layer, and
• wherein, in a cross sectional view in a channel length direction, the first layer or the second layer comprises a first region which is overlapped by the second conductive layer and a second region which extends beyond an end portion of the second conductive layer in the channel length direction.