Patent ID: 7098100

Claim:
A method for preparing a trench capacitor, comprising steps of: forming at least one trench in a semiconductor substrate; forming a collar oxide layer on an upper inner surface of the trench; removing a predetermined portion of the collar oxide layer to form a first block and a second block, including: forming a first polysilicon layer on the semiconductor substrate; forming a photoresist layer on the first polysilicon layer, wherein the photoresist layer includes an opening exposing the second block; performing a dry etching process to remove a portion of the first polysilicon layer below the opening down to a first predetermined depth; and performing a wet etching process to remove a portion of the collar oxide layer below the opening down to a second predetermined depth so as to form the first block and the second block of the collar oxide layer, wherein the height of the first block is larger than the height of the second block, and forming an interface layer on a portion of the inner surface of the trench above the second block.