Manufacturing method which prevents abnormal gate oxidation

1. A method for manufacturing a gate electrode structure, comprising:

forming an insulating film on a surface of a semiconductor substrate;

forming an impurity diffused polysilicon film on the insulating film;

forming an impurity diffusion preventing film on the impurity diffused polysilicon film;

forming a refractory metal silicide film on the impurity diffusion preventing film;

forming a first nitride film on the refractory metal silicide film;

patterning the first nitride film, the refractory metal silicide film and the impurity diffusion preventing film on a first gate electrode;

forming a first spacer constituted by a second nitride film on side surfaces of the first gate electrode;

performing anisotropic etching on the impurity diffused polysilicon film with the first nitride film and the second nitride film as a mask; and

performing an oxidation process.

2. The method for manufacturing a gate electrode structure according to claim 1 , wherein a silicon-based film is formed after said forming an insulating film, and said forming an impurity diffused polysilicon film is then carried out.

3. The method for manufacturing a gate electrode structure according to claim 1 , wherein the impurity diffusion preventing film is a nitride film.