Thin film transistor, display device having thin film transistor, and method for manufacturing the same

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

• forming a conductive film over a substrate;
• forming a transistor comprising a gate electrode, a source electrode, and a drain electrode over the substrate;
• forming a first insulating film over the conductive film and the transistor;
• forming a second insulating film over the first insulating film;
• forming a first opening and a recessed portion in the second insulating film by using a multi-tone photomask, wherein the first opening exposes a first part of an upper surface of the first insulating film;
• forming a second opening which exposes an upper part of one of the source electrode and the drain electrode by etching the first part of the upper surface of the first insulating film;
• forming a third opening by widening the first opening, and a fourth opening by widening the recessed portion, wherein the fourth opening exposes a second part of the upper surface of the first insulating film over the conductive film;
• and
• forming an electrode over the second insulating film,
• wherein the electrode is electrically connected to the one of the source electrode and the drain electrode through the second opening and the third opening, and
• wherein the electrode overlaps with the conductive film and is in contact with the second part of the upper surface of the first insulating film in the fourth opening.