Producing method for thin film transistor with different crystallinities

A method of producing a thin film transistor, comprising:

• step (A) of providing a substrate, the substrate having formed on a surface thereof a gate electrode and a gate insulating layer covering the gate electrode;
• step (B) of forming a semiconductor film of amorphous silicon on the gate insulating layer;
• step (C) of forming an insulating film on the semiconductor film, and patterning the insulating film so as to form an insulating protection layer covering a first portion of the semiconductor film and not covering a second portion of the semiconductor film, when viewed from a normal direction of the substrate, the first portion overlapping the insulating protection layer and the gate electrode, and the second portion overlapping the gate electrode but not overlapping the insulating protection layer, the first portion including a region to become a channel region;
• step (D) of irradiating the first portion and the second portion of the semiconductor film with laser light from above the insulating protection layer under a same irradiation conditions to crystallize the first portion and the second portion of the semiconductor film so that, in a region overlapping the gate electrode as viewed from the normal direction of the substrate, the first portion of the semiconductor film has a crystallinity which is lower than a crystallinity of the second portion of the semiconductor film;
• and
• step (E) of forming a source electrode which is electrically connected to a part of the second portion of the semiconductor film and a drain electrode which is electrically connected to another part of the second portion of the semiconductor film.