Patent ID: 7888268

Claim:
A method of manufacturing a semiconductor device comprising: forming a first insulating film over a semiconductor substrate; forming a first silicon film over the first insulating film; forming a second silicon film over the first silicon film; forming a mask layer in a predetermined pattern over the second silicon film; first etching the second silicon film in a depth such that the first silicon film is not exposed, in a first condition while using the mask layer as an etching mask; second etching a remaining portion of the second silicon film and the first silicon film in a depth such that the first insulating film is not exposed, in a second condition which gives a higher vertical etching component ratio than the first condition; and third etching a remaining portion of the first silicon film in a third condition of which a ratio of an etching rate for the first silicon film to an etching rate for the first insulating film is larger than that of the second condition, wherein an impurity concentration of a first conductivity type in the first silicon film is higher than an impurity concentration of the first conductivity type in the second silicon film.