Patent ID: 7666792

Claim:
A method for fabricating a deep trench in a substrate, comprising the steps of: providing a substrate having thereon a pad layer and a first sacrificing layer on the pad layer, wherein the first sacrificing layer has at least one first opening; forming a lining layer on interior surface of the at least one first opening and on the first sacrificing layer; filling the at least one first opening with a second sacrificing layer, wherein a top surface of the second sacrificing layer and the lining layer form a recessed area; forming a first insulating layer within the recessed area, wherein the first insulating layer and the lining layer enclose the second sacrificing layer; selectively etching away a portion of the lining layer, thereby exposing the first sacrificing layer; completely removing the first sacrificing layer, thereby forming a second opening; filling the second opening with a second insulating layer; removing the first insulating layer to expose the second sacrificing layer; completely removing the second sacrificing layer, thereby forming a thick hard mask on the substrate; and etching the substrate to form a deep trench.