Semiconductor device having insulated gate field effect transistors and method of fabricating the same

A method of fabricating a semiconductor device, comprising:

• forming an N well layer and a P well layer in a surface region of a semiconductor substrate;
• forming a first gate insulating film on the N well layer and the P well layer;
• forming a first hafnium layer on the first gate insulating layer;
• etching the first gate insulating film and the first hafnium layer formed on the P well layer selectively;
• forming a second gate insulating film on the exposed P well layer;
• depositing a hafnium layer on the second gate insulating film and the first hafnium layer to form a second hafnium layer on the second gate insulating film so that a surface density of the first hafnium layer is higher than a surface density of the second hafnium layer;
• depositing a gate electrode material on the first and the second hafnium layers;
• and
• etching the gate electrode material, the first hafnium layer and the first gate insulating film which are formed on the N well layer so as to pattern the first gate insulating film, the first hafnium layer and a first gate electrode which are stacked on the N well layer, and etching the gate electrode material, the second hafnium layer and the second gate insulating film which are stacked on the P well layer so as to pattern the second gate insulating film, the second hafnium layer and a second gate electrode which are stacked on the P well layer.