Patent ID: 8748224

Claim:
A method for manufacturing a semiconductor device comprising the steps of: forming an oxide insulating film over a substrate, the oxide insulating film containing oxygen with a higher proportion than a proportion of oxygen in a stoichiometric composition; forming an oxide semiconductor film over the oxide insulating film; performing a heat treatment after forming the oxide semiconductor film; etching a part of the oxide semiconductor film to form an island-shaped oxide semiconductor film after performing the heat treatment; forming a pair of electrodes over the island-shaped oxide semiconductor film; forming a gate insulating film over the island-shaped oxide semiconductor film and the pair of electrodes; and forming a gate electrode overlapping with the island-shaped oxide semiconductor film with the gate insulating film therebetween, wherein, by the heat treatment, an amount of oxygen desorbed from the oxide insulating film is higher than or equal to 1.0×10 18 atoms/cm 3 .