METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device with a suppressed increase in off current or a reduced negative shift of a threshold voltage.SOLUTION: The method comprises the steps of: forming a gate electrode over a substrate; forming a gate insulating layer over the gate electrode; forming an oxide semiconductor layer over the gate insulating layer; forming a titanium-containing layer over the oxide semiconductor layer; forming a conductive layer over the titanium-containing layer; selectively etching the conductive layer to form a source electrode and a drain electrode and to expose a part of the titanium-containing layer; and performing thermal treatment or plasma treatment in an oxygen-containing atmosphere in order to oxidize the exposed titanium-containing layer.