Patent ID: 8241991

Claim:
A method for forming an interconnect structure with airgaps, comprising: forming photoresist patterns at a pitch of 2X on a hard mask, each photoresist pattern having a width of X; etching the hard mask between adjacent photoresist patterns, each etched portion having a width of (X−2Y); etching the hard mask underneath each photoresist pattern, each etched portion having a width of (X−2Y), thereby forming hard mask patterns at a pitch of X, each hard mask pattern having a width of 2Y; etching a layer underneath the hard mask patterns, thereby providing a structure having trenches formed on a substrate; depositing a spacer oxide layer on sidewalls of each trench as sidewall spacers so that the sidewall spacers-provided trenches each have a width of X/2 and are distanced at an interval of X/2; filling the trenches having the sidewall spacers with copper, thereby forming copper patterns at a pitch of X; removing the sidewall spacers to form an airgap structure; and encapsulating the airgap structure, wherein airgaps are formed between the copper patterns, where the copper patterns each have a width of X/2 and are distanced at an interval of X/2, and the airgaps each have a width of (X/2−2Y)/2 or less, wherein X and Y are selected to achieve a targeted dielectric constant of the encapsulated airgap structure between the copper patterns.