Semiconductor device and method for fabricating the same

A method for fabricating a semiconductor device, the method comprising the steps of:

• (a) forming a gate insulating film, a silicon film and a protective film in this order over a semiconductor substrate divided into a first region and a second region;
• (b) patterning at least the protective film and the silicon film, thereby forming a first gate-electrode formation film including a first protective film and a first gate silicon film formed out of the protective film and the silicon film, respectively, in the first region, and also forming a second gate-electrode formation film including a second protective film and a second gate silicon film formed out of the protective film and the silicon film, respectively, in the second region, the second gate-electrode formation film having a gate length larger than that of the first gate-electrode formation film;
• (c) forming sidewalls of an insulating film on side faces of the first gate-electrode formation film and the second gate-electrode formation film;
• (d) forming an impurity layer in the first region and the second region of the semiconductor substrate using, as masks, the first gate-electrode formation film and the second gate-electrode formation film provided with the sidewalls;
• (e) removing the first protective film and the second protective film after the step (d), thereby exposing the first gate silicon film and the second gate silicon film;
• (f) reducing the thickness of at least a middle portion in a gate length direction of the second gate silicon film so that the thickness is smaller than the thickness of the first gate silicon film, after the step (e);
• and
• (g) forming a metal film on the first gate silicon film and the second gate silicon film and then performing heat treatment on the metal film after the step (f), thereby fully siliciding the first gate silicon film and the second gate silicon film.