Manufacturing method of thin film transistor and manufacturing method of display device

A manufacturing method of a thin film transistor, comprising the steps of:

• forming a first conductive film;
• forming an insulating film over the first conductive film;
• forming a semiconductor film over the insulating film;
• forming an impurity semiconductor film over the insulating film;
• forming a second conductive film over the impurity semiconductor film;
• forming a first resist mask including a recessed portion, over the second conductive film;
• first etching the insulating film, the semiconductor film, the impurity semiconductor film, and the second conductive film using the first resist mask to expose at least a surface of the first conductive film;
• second etching a portion of the first conductive film to form a gate electrode layer in such a manner that a width of the gate electrode is narrower than a width of the insulating film;
• forming a second resist mask by making the first resist mask recede to expose a part of the second conductive film overlapping with the recessed portion of the first resist mask;
• and
• third etching the second conductive film, the impurity semiconductor film, and a part of the semiconductor film using the second resist mask to form a source and drain electrode layer, a source and drain region layer, and a semiconductor layer.

A thin film transistor comprising:

• a gate electrode on an insulating surface;
• an insulating film over the gate electrode;
• a semiconductor layer over the insulating film;
• an impurity semiconductor layer over the semiconductor layer;
• and
• a conductive film over the impurity semiconductor layer,
• wherein a cavity is formed adjacent to the gate electrode and between the insulating film and the insulating surface.