Semiconductor device and method for manufacturing semiconductor device

A semiconductor device comprising:

• a first conductive film;
• a first insulating film over the first conductive film;
• a first oxide semiconductor film over the first insulating film;
• a second oxide semiconductor film over the first oxide semiconductor film;
• a second conductive film and a third conductive film over the first insulating film;
• a third oxide semiconductor film over the second oxide semiconductor film;
• a second insulating film over the third oxide semiconductor film;
• and
• a fourth conductive film over the second insulating film,
• wherein each of the second conductive film and the third conductive film is in contact with a first side surface of the second oxide semiconductor film, and
• wherein, in a channel width direction, the fourth conductive film faces a second side surface of the second oxide semiconductor film.

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

• forming a first oxide semiconductor film over an insulating surface;
• forming a second oxide semiconductor film over the first oxide semiconductor film;
• forming a conductive film over the insulating surface and the second oxide semiconductor film;
• forming a first insulating film over the conductive film;
• performing a removing process on the conductive film and the first insulating film to expose the second oxide semiconductor film;
• etching the conductive film and the first insulating film which are subjected by the removing process to form a source electrode and a drain electrode which are in contact with side surfaces of the first oxide semiconductor film and the second oxide semiconductor film and form a second insulating film and a third insulating film over the source electrode and the drain electrode;
• forming a third oxide semiconductor film over the second oxide semiconductor film, the source electrode, and the drain electrode;
• forming a gate insulating film over the third oxide semiconductor film;
• and
• forming a gate electrode in contact with an upper surface of the gate insulating film and facing an upper surface and the side surface of the second oxide semiconductor film.