Patent ID: 6838334

Claim:
A method of forming a buried collar on a sidewall of a trench in a semiconductor substrate comprising: (a) providing said trench in said semiconductor substrate, said trench having a first dielectric layer formed on said sidewall in a upper region of said trench and a conductive material filling a lower region of said trench and a portion of said upper region of said trench, said conductive material covering a lower portion of said first dielectric layer; (b) removing said first dielectric layer not covered by said conductive material whereby a portion of said sidewall in said upper region is exposed; (c) forming a second dielectric layer on said exposed sidewall of said upper region and on a top surface of said conductive material; (d) removing an uppermost portion of said second dielectric layer from said sidewall in said upper region; (e) forming a third dielectric layer on said exposed sidewall of said upper region; and (f) increasing the thickness of said second dielectric layer to form said buried collar.