Patent ID: 6992021

Claim:
A method of forming a silicon nitride layer for a bottle-shaped trench process, comprising: providing a silicon substrate; forming a trench in the silicon substrate; conformally depositing a dielectric layer in the trench; selectively etching the dielectric layer, exposing an upper region in the trench and sidewalls thereof, leaving a lower region in the trench covered by the remaining dielectric layer; performing an ion implant process, implanting nitrogen atoms into the silicon substrate adjacent to the sidewalls; performing a thermal nitridation process, forming a silicon nitride layer on the surface of the sidewalls, wherein the silicon nitride layer includes the silicon nitride formed on the silicon surface by reaction of the silicon surface with the nitrogen atoms therein; removing the remaining dielectric layer from the lower region of the trench; and using the silicon nitride layer as an etching mask, etching the silicon substrate in the lower region, forming an expanded region therein, and forming a bottle-shaped trench consisting of the trench portion in the upper region and the expanded region in the lower portion.