Method for forming oxide semiconductor film and method for manufacturing semiconductor device

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

• forming an oxide semiconductor film over a substrate having an insulating surface;
• forming a sacrifice film over the oxide semiconductor film;
• injecting oxygen ions into the oxide semiconductor film through the sacrifice film;
• removing the sacrifice film after injecting oxygen ions into the oxide semiconductor film;
• forming an island-shaped oxide semiconductor film by processing the oxide semiconductor film into which the oxygen ions are injected;
• forming a gate insulating film over the island-shaped oxide semiconductor film;
• forming a gate electrode over the gate insulating film so as to overlap with the island-shaped oxide semiconductor film with the gate insulating film positioned between the gate electrode and the island-shaped oxide semiconductor film;
• partly exposing the island-shaped oxide semiconductor film by processing the gate insulating film;
• and
• forming a source electrode and a drain electrode over the partly exposed island-shaped oxide semiconductor film,
• wherein the sacrifice film is formed using the same material as the oxide semiconductor film.