Patent ID: 7503975

Claim:
A method of manufacturing a semiconductor device comprising the steps of: forming a first amorphous semiconductor film comprising silicon and germanium on an insulating surface wherein a concentration of the germanium is within a range of 0.1 atom % to 10 atom %; forming a second amorphous semiconductor film comprising silicon on the first amorphous semiconductor film; providing a metal element in contact with the first amorphous semiconductor film or the second amorphous semiconductor film; crystallizing each of the first and second amorphous semiconductor films by heating to form a first crystalline semiconductor film and a second crystalline semiconductor film, respectively; forming a semiconductor film containing a rare gas element over the second crystalline semiconductor film; performing a heat treatment in a nitrogen atmosphere to remove or reduce the concentration of the metal element in the second crystalline semiconductor film, after forming the semiconductor film containing the rare gas element; and forming a gate insulating film on the second crystalline semiconductor film after crystallizing each of the first and second amorphous semiconductor films.