Semiconductor device and manufacturing method thereof

A semiconductor device comprising:

• an oxide semiconductor film;
• a first film having conductivity and a second film having conductivity over the oxide semiconductor film;
• a first insulating film over the first film having conductivity;
• a second insulating film over the second film having conductivity
• a gate insulating film over the oxide semiconductor film, the first film having conductivity, the second film having conductivity, the first insulating film, and the second insulating film;
• and
• a gate electrode overlapping with the gate insulating film and the oxide semiconductor film,
• wherein an entire portion of each of the first film having conductivity and the second film having conductivity overlaps with the oxide semiconductor film.

A method for manufacturing a semiconductor device, comprising steps of:

• forming a first oxide semiconductor film over an insulating surface;
• forming a first film having conductivity over the first oxide semiconductor film;
• forming a first insulating film over the first film having conductivity;
• forming a first resist mask over the first insulating film;
• etching the first film having conductivity and the first insulating film using the first resist mask as a mask to form a second film having conductivity and a second insulating film;
• removing the first resist mask;
• etching the first oxide semiconductor film using the second film having conductivity and the second insulating film as a mask to form a second oxide semiconductor film;
• forming a second resist mask over the second insulating film;
• etching the second film having conductivity and the second insulating film using the second resist mask as a mask to form a pair of third films having conductivity and a pair of third insulating films;
• forming a gate insulating film over the second oxide semiconductor film and the pair of third insulating films;
• and
• forming a gate electrode over the gate insulating film to overlap with the second oxide semiconductor film.

A semiconductor device comprising:

• an oxide semiconductor film;
• a first film and a second film over the oxide semiconductor film, the first film and the second film each comprising tantalum and nitrogen;
• a first insulating film over the first film;
• a second insulating film over the second film;
• a gate insulating film over the oxide semiconductor film, the first film, the second film, the first insulating film, and the second insulating film;
• and
• a gate electrode overlapping with the gate insulating film and the oxide semiconductor film,
• wherein an entire portion of each of the first film and the second film overlaps with the oxide semiconductor film.

A semiconductor device comprising:

• an oxide semiconductor film;
• a first film having conductivity and a second film having conductivity over the oxide semiconductor film;
• a first insulating film over the first film having conductivity;
• a second insulating film over the second film having conductivity
• a gate insulating film over the oxide semiconductor film, the first film having conductivity, the second film having conductivity, the first insulating film, and the second insulating film;
• and
• a gate electrode overlapping with the gate insulating film and the oxide semiconductor film,
• wherein the first film having conductivity and the second film having conductivity each have a tapered shape at a side surface, and
• wherein an entire portion of each of the first film having conductivity and the second film having conductivity overlaps with the oxide semiconductor film.