Thin film transistor, a method of manufacturing the same, and a display apparatus including the same

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

• forming a semiconductor layer over a substrate;
• sequentially forming a gate insulating material layer and a gate electrode material layer on the substrate to cover the semiconductor layer;
• forming a first photoresist pattern on the gate electrode material layer;
• forming a gate electrode by etching the gate electrode material layer using the first photoresist pattern as a mask;
• forming a second photoresist pattern covering both sidewalls and an upper surface of the gate electrode;
• and
• forming a gate insulating film by etching the gate insulating material layer using the second photoresist pattern as a mask, the gate insulating film including a first region and a second region having portions disposed at opposite sides of the first region, and a thickness of the first region is different than a thickness of the portions of the second region,
• wherein a portion of the first region and the portions of the second region do not overlap the gate electrode in a thickness direction of the substrate.