Display device and manufacturing method of the same

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

• forming a semiconductor layer over an upper surface of a substrate;
• forming an insulation film over an upper surface of the semiconductor layer;
• using a mask which covers a first region of the insulation film and exposes a second region of the insulation film, and performing an implantation of impurities into the semiconductor layer in the second region of the insulation film through the insulation film;
• removing the mask after the step of performing the implantation of the impurities into the semiconductor layer;
• and
• after the step of removing the mask, etching a surface of the insulation film in the first region and the second region to an extent that the insulation film in the second region remains, whereby a film thickness of the insulation film in the second region is set smaller than a film thickness of the insulation film in the first region.