Patent ID: 6867089

Claim:
A method of forming a bottle-shaped trench in a semiconductor substrate, suitable for formation of the capacitor of DRAM, comprising the steps of: (a) forming a hard mask having an opening on the semiconductor substrate; (b) etching the semiconductor substrate through the opening of the hard mask to create a trench, wherein the trench has a top portion and a bottom portion; (c) forming an nitride film on the surfaces of the trench and the hard mask; (d) filling a shield material in the bottom portion of the trench; (e) removing a part of the nitride film to leave the nitride film protected by the shield material and expose the surface of the semiconductor substrate at the top portion of the trench; (f) removing the shield material to expose the nitride film formed on the bottom portion of the trench; (g) forming a oxide film on the top portion of the trench; (h) removing the nitride film to expose the surface of the semiconductor substrate at the bottom portion of the trench; (i) forming a rugged polysilicon layer on the exposed surface of the semiconductor substrate at the bottom portion of the trench; (j) etching the rugged polysilicon layer and the semiconductor substrate through the bottom portion of the trench by a diluted ammonia solution as the etchant to form a bottle-shaped trench having a rugged surface; and (k) removing the oxide film.