A method for fabricating a semiconductor device, includes forming a
silicon nitride film on a base body, forming a silicon film on said
silicon nitride film, forming at least one groove extending from said
silicon film to inside of said base body, forming by high-density
plasma-enhanced chemical vapor deposition a silicon-containing dielectric
film in said groove and on said silicon film in such a way that a
silicon-rich layer is formed at a height position spaced apart from said
base body within said groove, said silicon-rich layer being higher in
silicon content than remaining silicon-containing dielectric film,
removing by etching a portion of said silicon-containing dielectric film
above said silicon film and a portion of said remaining
silicon-containing dielectric film above said silicon-rich layer, if any,
and after having removed said silicon-containing dielectric film,
removing by etching said silicon-rich layer and said silicon film.