Semiconductor device and manufacturing method thereof

A semiconductor device comprising:

• an oxide semiconductor film comprising a channel formation region;
• a first conductive film over and in contact with the oxide semiconductor film;
• a second conductive film over and in contact with the oxide semiconductor film;
• a first insulating film over and in contact with the first conductive film and a first region of the oxide semiconductor film;
• a second insulating film over and in contact with the second conductive film and a second region of the oxide semiconductor film;
• a third insulating film over and in contact with the channel formation region of the oxide semiconductor film, the first insulating film and the second insulating film;
• and
• a third conductive film overlapping with the channel formation region with the third insulating film provided therebetween,
• wherein resistance of the first region and the second region of the oxide semiconductor film is lower than resistance of the channel formation region, and
• wherein the channel formation region is between the first region and the second region.

A manufacturing method of a semiconductor device comprising the steps of:

• forming a first insulating film;
• forming an oxide semiconductor film over the first insulating film;
• forming a first conductive film and a second conductive film over and in contact with the oxide semiconductor film;
• forming a second insulating film over and in contact with the oxide semiconductor film, the first conductive film, and the second conductive film;
• processing the second insulating film so as to form a third insulating film over the first conductive film and a fourth insulating film over the second conductive film;
• forming a fifth insulating film over the oxide semiconductor film, the third insulating film, and the fourth insulating film;
• and
• forming a third conductive film over the fifth insulating film,
• wherein the third insulating film is in contact with a first region of the oxide semiconductor film and the fourth insulating film is in contact with a second region of the oxide semiconductor film,
• wherein the fifth insulating film is in contact with a third region of the oxide semiconductor film which is between the first region and the second region, and
• wherein the third conductive film overlaps with the third region of the oxide semiconductor film with the fifth insulating film provided therebetween.