Method for modifying insulating film and method for manufacturing semiconductor device

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

• depositing an oxide semiconductor film;
• depositing a conductive film over the oxide semiconductor film;
• depositing a first insulating film over the conductive film;
• processing the first insulating film by an etching method to form a first insulating layer;
• processing the oxide semiconductor film and the conductive film into an island shape by using the first insulating layer as a mask to form a stack of an oxide semiconductor layer, a conductive layer, and the first insulating layer;
• forming a second insulating film over the first insulating layer;
• processing the second insulating film and the conductive layer to form a first conductor and a second conductor from the conductive layer and form an opening reaching the oxide semiconductor layer in the second insulating film and the first insulating layer;
• depositing an aluminum oxide film as a third insulating film by an ALD method to cover the opening;
• depositing a silicon oxide film as a fourth insulating film over the third insulating film by an ALD method at a deposition temperature higher than or equal to 200° C. and lower than or equal to 300° C.;
• and
• performing microwave treatment at a temperature range of higher than or equal to 200° C. and lower than or equal to 300° C.