Thin film transistor substrate, display device having the same and method of manufacturing the same

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

• sequentially forming a semiconductor layer, a first insulation layer and a second insulation layer, on a base substrate;
• forming a first photoresist pattern on the second insulation layer and having a first thickness portion, and a second thickness portion thinner than the first thickness portion;
• removing exposed portions of the second insulation layer, the first insulation layer and the semiconductor layer using the first photoresist pattern as a mask, to form an intermediate insulation pattern, a first insulation pattern and a semiconductor pattern from the second insulation layer, the first insulation layer and the semiconductor layer, respectively;
• reducing an entirety of the first photoresist pattern by a thickness of the second thickness portion, to form a second photoresist pattern having a third thickness and expose a portion of the intermediate insulation pattern;
• removing the exposed portion of the intermediate insulation pattern using the second photoresist pattern as a mask, to form a second insulation pattern from the intermediate insulation pattern;
• and
• forming a gate electrode on and overlapping both the first insulation pattern and the second insulation pattern.