Method for forming an isolated film on a semiconductor device

Claim 3

In the method for forming an isolated film on a semiconductor device according to claim 1, the steps of: forming a pad oxide film and a nitride film on the substrate in that order; forming a mask window using a photoetching process, for depositing a polysilicon layer and for implanting field ions in the polysilicon layer; forming an insulated layer over the mask region for leveling the surface and then etching back the insulated layer to level the surface; etching said polysilicon layer and said substrate using a self-alignment method to form a deep cylindrical groove within said substrate; forming a CVD oxide film into said groove and over the polysilicon layer and etching it back by using a dry etching method to expose said polysilicon layer; and oxidizing said polysilicon layer to remove said nitride film.