Semiconductor device and method of fabricating the same

A semiconductor device comprising:

• a gate insulating film selectively formed on a predetermined region of a semiconductor substrate;
• a gate electrode comprising a first film formed on said gate insulating film and containing a predetermined semiconductor material and germanium, and a second film formed on said first film, containing the semiconductor material, and having a germanium concentration lower than that of said first film;
• and
• a source region and drain region formed in a surface portion of said semiconductor substrate on two sides of a channel region positioned below said gate electrode.

A semiconductor device fabrication method comprising:

• forming a first-conductivity-type semiconductor region and second-conductivity-type semiconductor region in a surface portion of a semiconductor substrate;
• forming a gate insulating film on the semiconductor substrate;
• forming a film containing a predetermined semiconductor material and germanium on the gate insulating film;
• oxidizing the film to form a first film having a germanium concentration higher than that of the film and a film thickness smaller than that of the film on the gate insulating film, and form an oxide film on the first film;
• removing the oxide film;
• forming a mask pattern having a pattern corresponding to the second-conductivity-type semiconductor region, and etching the first film by using the mask pattern, thereby removing the first film formed on the first-conductivity-type semiconductor region via the gate insulating film;
• removing the mask pattern, and forming a second film containing the semiconductor material and having a germanium concentration lower than that of the first film, on the gate insulating film formed on the first-conductivity-type semiconductor region, and on the first film formed on the second-conductivity-type semiconductor region;
• forming a first gate electrode by etching the second and first films formed on the second-conductivity-type semiconductor region, and forming a second gate electrode by etching the second film formed on the first-conductivity-type semiconductor region;
• and
• forming a first source region and first drain region by ion-implanting a first-conductivity-type impurity in the second-conductivity-type semiconductor region by using the first gate electrode as a mask, and forming a second source region and second drain region by ion-implanting a second-conductivity-type impurity in the first-conductivity-type semiconductor region by using the second gate electrode as a mask.