Patent ID: 7915133

Claim:
A method of forming a trench capacitor, comprising: providing a substrate; forming a borophosphosilicate glass layer on the substrate; forming a negative-type photoresist layer on the borophosphosilicate glass layer; providing a first photomask having a first feature pattern defining the outer wall; exposing the negative-type photoresist layer with the first photomask; providing a second photomask having a second feature pattern defining the inner wall; exposing the negative-type photoresist layer with the second photomask; and developing the negative-type photoresist layer to form a patterned photoresist layer, the patterned photoresist layer defining a ring pattern; and removing a portion of the borophosphosilicate glass layer by using the patterned photoresist layer as a mask to transfer the ring pattern to the borophosphosilicate glass layer; removing a portion of the substrate by using the ring-patterned borophosphosilicate glass layer as a mask to form a ring-type trench in the substrate, the ring-type trench having an inner wall and an outer wall; and forming a capacitor structure on the inner wall and the outer wall of the ring-type trench.