Thin film transistor, method for manufacturing thin film transistor, and organic EL display device

A method for manufacturing a thin film transistor, the method comprising:

• forming a gate electrode;
• forming a gate insulating layer above the gate electrode;
• forming an oxide semiconductor layer including fluorine above the gate insulating layer;
• and
• forming a source electrode and a drain electrode above the oxide semiconductor layer to be electrically connected to the oxide semiconductor layer,
• wherein metallic elements included in the oxide semiconductor layer include at least indium,
• fluorine is included in a region which is an internal region in the oxide semiconductor layer and is close to the gate insulating layer, and
• a fluorine concentration of the region close to the gate insulating layer in the oxide semiconductor layer is higher than a fluorine concentration of a contact region for the source electrode or the drain electrode in the oxide semiconductor layer.