Semiconductor device and method for manufacturing the same

A method for manufacturing a semiconductor device, comprising:

• forming a first insulating film over a substrate;
• forming a first oxide film, a second oxide film, and a first conductive film over the first insulating film;
• removing part of the second oxide film and part of the first conductive film selectively so as to form a first oxide, a first conductor, and a second conductor over the first oxide film;
• forming a third oxide film and a second insulating film over the first oxide film, the first oxide, the first conductor, and the second conductor;
• forming a third conductor over the second insulating film;
• performing dry etching treatment on the first oxide film, the third oxide film, and the second insulating film so as to form a second oxide, a third oxide, and a first insulator;
• performing etching treatment on the first insulating film so as to remove a vicinity of a surface of a region of the first insulating film, the region not overlapping with the second oxide;
• forming a third insulating film over the third conductor by a sputtering method so that at least part of the third insulating film is in contact with the first insulating film;
• and
• performing heat treatment.