Patent ID: 6861375

Claim:
A method of fabricating a semiconductor device, the method comprising the steps of: (a) forming a silicon oxynitride film on a silicon substrate; (b) performing a heat treatment while keeping a surface of the silicon oxynitride film in contact with a gas containing nitrogen and oxygen to introduce at least nitrogen into the silicon oxynitride film; (c) after step (b), forming a semiconductor film containing an impurity of first conductivity type on the silicon oxynitride film; (d) after step (c), forming a protecting film for the gate on the semiconductor film; (e) after step (d), forming a protecting layer on the gate composed of the protecting film for the gate and a gate electrode composed of the semiconductor film by patterning the protecting film for the gate and the semiconductor film; (f) forming a first side wall with a L-shape cross sectional view on the sides of the gate electrode and the protecting layer on the gate, and a second side wall that spreads over the side and the base of the first side wall; (g) after step (f), forming a gate insulating film composed of the silicon oxynitride film by patterning the silicon oxynitride film, wherein the gate insulating film has a nitrogen concentration peak formed at around the center portion of the silicon oxynitride film.