Patent ID: 6875669

Claim:
A method of controlling the top width of a deep trench, comprising the steps of: providing a substrate having a trench therein; forming a first conductive layer filling a portion of the trench; forming a α-silicon layer on the sidewall of the trench and the first conductive layer, wherein the α-silicon is thicker at the top of the trench than elsewhere; oxidizing the α-silicon layer to form a silicon oxide layer; forming a dielectric layer on the silicon oxide layer, and anisotropically etching the dielectric layer and the silicon oxide layer to form a collar dielectric layer on the sidewalls of the trench; forming a second conductive layer to fill the trench, wherein the upper surface of the second conductive layer is lower than the opening of the trench; and recessing the collar dielectric layer below the second conductive layer such that the substrate surface at the sidewall of the trench is exposed.