Semiconductor device and manufacturing method thereof

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

• introducing a semiconductor material gas into a treatment chamber;
• forming a first semiconductor film in the treatment chamber over a gate insulating layer provided to cover a gate electrode;
• evacuating the semiconductor material gas from the treatment chamber;
• stopping the introduction of the semiconductor material gas into the treatment chamber and introducing a rare gas into the treatment chamber;
• performing plasma treatment on the first semiconductor film in the treatment chamber;
• forming a second semiconductor film over the plasma treated first semiconductor film;
• forming a third semiconductor film comprising a first impurity element imparting one conductivity type over the second semiconductor film;
• forming a semiconductor stack including the treated first semiconductor film, the second semiconductor film and the third semiconductor film;
• and
• forming a source electrode and a drain electrode in contact with the third semiconductor film,
• wherein formation of the first semiconductor film and the plasma treatment are performed without change in pressure and temperature of the treatment chamber.