Semiconductor device, manufacturing method thereof, display device, and display module

A semiconductor device comprising:

• a gate electrode;
• a first insulating film over the gate electrode;
• an oxide semiconductor film over the first insulating film;
• a source electrode electrically connected to the oxide semiconductor film;
• a drain electrode electrically connected to the oxide semiconductor film;
• a second insulating film over the oxide semiconductor film, the source electrode, and the drain electrode;
• and
• a third insulating film over the second insulating film,
• wherein the second insulating film includes a region including a halogen element, and
• wherein the halogen element is distributed in the region at a higher concentration toward a surface of the second insulating film.

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

• forming a gate electrode over a substrate;
• forming a first insulating film over the gate electrode;
• forming an oxide semiconductor film over the first insulating film;
• forming a source electrode and a drain electrode over the oxide semiconductor film;
• forming a second insulating film over the oxide semiconductor film, the source electrode, and the drain electrode;
• adding a halogen element to the second insulating film;
• forming a protective film over the second insulating film;
• adding oxygen to the second insulating film through the protective film;
• and
• removing the protective film.