Semiconductor device, method for manufacturing same, and display device including same

A method for manufacturing a semiconductor device including a semiconductor layer formed of an oxide semiconductor on an insulating substrate, a gate insulating film having tapering side surfaces and formed on the semiconductor layer, a gate electrode having tapering side surfaces and formed on the gate insulating film, a source region and a drain region being low-resistance regions formed in the semiconductor layer on opposite sides with respect to the gate electrode, a silicon nitride film formed on the source region and the drain region of the semiconductor layer, and a source electrode layer and a drain electrode layer respectively in ohmic contact with the source region and the drain region, the method comprising the steps of:

• determining a first length of a portion of the low-resistance region on the basis of a condition for thermal treatment performed after the formation of the silicon nitride film, the first length ranging from a position corresponding to an end of the gate insulating film to a channel region below the gate electrode;
• selecting from among a plurality of predetermined processing conditions a processing condition for forming the gate electrode and the gate insulating film by etching such that the first length is substantially equal to a second length from the first position to a second position on the semiconductor layer corresponding to an end of the gate electrode;
• forming the semiconductor layer on the insulating substrate;
• sequentially forming the gate insulating film and a metal film serving as the gate electrode on the semiconductor layer;
• forming a resist pattern on the metal film;
• forming the gate electrode and the gate insulating film by etching the metal film and the gate insulating film using the resist pattern as a mask under the selected processing condition;
• forming the silicon nitride film on the source region and the drain region;
• and
• performing thermal treatment such that hydrogen contained in the silicon nitride film spreads into the semiconductor layer.