Display device and method of manufacturing the same

1. A method of manufacturing a display device having a thin film transistor formed on a substrate including a display portion, wherein the thin film transistor is manufactured by the following steps of:

forming a gate insulating film so as to cover at least a gate electrode;

forming on top of the gate insulating film at least a polycrystalline semiconductor film, an amorphous semiconductor film, a heavily doped amorphous semiconductor film, and a metal film in sequence,

forming on the metal film a patterned photoresist;

etching only the metal film by using the patterned photoresist film as a mask to form a drain electrode and a source electrode of the thin film transistor;

forming a photoresist film on at least a channel region between the drain electrode and the source electrode;

etching the heavily doped amorphous semiconductor film, the amorphous semiconductor film, and the polycrystalline semiconductor film in sequence by using the photoresist film and the metal film as a mask;

removing the photoresist film; and

etching the heavily doped amorphous semiconductor film by using the drain electrode and the source electrode as a mask to such an extent that the amorphous semiconductor film thereunder is exposed.

2. A method of manufacturing a display device according to claim 1 , wherein the photoresist film is removed by ashing.