Display device and manufacturing method thereof

A manufacturing method of a display device, the method comprising:

• forming a first conductive layer on a substrate;
• forming a first insulating layer and a semiconductor layer on the first conductive layer;
• forming a first mask pattern including a first portion and a second portion having different thicknesses, and having a first opening, on the semiconductor layer;
• patterning the first insulating layer and the semiconductor layer by utilizing the first mask pattern as a mask to form a second opening of the first insulating layer;
• removing the second portion of the first mask pattern to form a second mask pattern including a part of the first portion and having a thickness less than the thickness of the first portion;
• patterning the semiconductor layer by utilizing the second mask pattern as a mask to form a semiconductor pattern;
• forming a second insulating layer and a second conductive layer on the semiconductor pattern;
• forming a third insulating layer on the second conductive layer;
• and
• forming a third mask pattern on the third insulating layer and patterning the third insulating layer by utilizing the third mask pattern as a mask to form a third opening overlapping the second opening.