Method for manufacturing oxide semiconductor device

A manufacturing method of a semiconductor device comprising steps of:

• forming a gate electrode layer over a substrate,
• forming a gate insulating layer over the gate electrode layer;
• introducing the substrate into a first treatment chamber in a reduced pressure state, after formation of the gate electrode layer and the gate insulating layer;
• forming, over the gate insulating layer, an oxide semiconductor layer by introducing into the first treatment chamber a sputtering gas, and using a target of a metal oxide placed inside the first treatment chamber while removing residual moisture from the first treatment chamber;
• forming, over the oxide semiconductor layer, a silicon oxide layer including defects by introducing the substrate into a second treatment chamber, introducing into the second treatment chamber a sputtering gas containing oxygen, and using a target including silicon placed inside the second treatment chamber, while removing residual moisture from the second treatment chamber;
• forming, over the silicon oxide layer, a silicon nitride layer by introducing the substrate into a third treatment chamber in a reduced pressure state, removing residual moisture from the third treatment chamber, introducing in the third treatment chamber a sputtering gas containing nitrogen, and using a target including silicon placed inside the third treatment chamber;
• and
• heating the substrate so as to diffuse towards, and trap into, the silicon oxide layer at least part of hydrogen or moisture included in the oxide semiconductor layer.