Method for manufacturing semiconductor device

摘要

An object is to provide a thin film transistor including an oxide semiconductor layer, in which the contact resistance between the oxide semiconductor layer and source and drain electrode layers is reduced and whose electric characteristics are stabilized. Another object is to provide a method for manufacturing the thin film transistor. The thin film transistor including an oxide semiconductor layer is formed in such a manner that buffer layers whose conductivity is higher than that of the oxide semiconductor layer are formed and the oxide semiconductor layer and the source and drain electrode layers are electrically connected to each other through the buffer layers. In addition, the buffer layers whose conductivity is higher than that of the oxide semiconductor layer are subjected to reverse sputtering treatment and heat treatment in a nitrogen atmosphere.