Thin film transistor, method for manufacturing same and semiconductor device comprising said thin film transistor

A method for manufacturing a thin film transistor in which a gate electrode, a gate insulating film, and an oxide semiconductor film are laminated on a substrate,

• a source region and a drain region are formed on both outer sides of the oxide semiconductor film in a width direction,
• a channel region is formed in a region between the source region and the drain region,
• a source electrode is connected to the source region, and
• a drain electrode is connected to the drain region, the method comprising:
• forming a gate insulating film containing fluorine as the gate insulating film, wherein a content of fluorine in the gate insulating film is 1 to 25 at %;
• and
• forming the source region and the drain region on the oxide semiconductor film so that a ratio (W/L) of a width W to a length L of the channel region is less than 8, wherein the thin film transistor has a field effect mobility of greater than 20 cm2/Vs.