SRAM design to facilitate single fin cut in double sidewall image transfer process
View Patent ↗A double sidewall image transfer process for forming FinFET structures having a fin pitch of less than 40 nm generates paired fins with a spacing determined by the width of a sidewall spacer that forms a second mandrel. Here, the fin pairs are created at two different spacings without requiring the minimum space for the standard sidewall structure. An enlarged space between paired fins is created by placing two first mandrel shapes close enough so as to overlap or merge two sidewall spacer shapes so as to form a wider second mandrel upon further processing. The fin pair created from the wider second mandrel is spaced at about 2 times the fin pair created from the narrower second mandrel. For some circuits, such as an SRAM bitcell, the wider second mandrel can be utilized to form an inactive fin not utilized in the circuit structure, which can be removed. In some embodiments, all dummy inactive fins are eliminated for a simpler process.
1. A process for increasing active fin mask edge location tolerance associated with fabrication of an SRAM cell fin structure, the process comprising:
forming a fin structure comprising multiple fin pairs at a pitch of less than 40 nm, wherein individual fins in the multiple fin pairs are either active or inactive for the SRAM cell fin structure, wherein the inactive fins are included in fin pairs that are about two times the spacing between other fin pairs including active fins, wherein the inactive fins are located between active regions of the SRAM cell fin structure; and
removing the inactive fins from the fin structure.
2. The process of claim 1 , wherein removing the at least one inactive fin from the fin structure comprises patterning a photoresist layer to form openings exposing the at least one inactive fin within the fin pair having about two times the spacing relative to other fin pairs; and etching to remove the at least one inactive fin from the fin structure.
3. The process of claim 1 , wherein etching to remove the at least one inactive fin comprises a timed etching process.
4. The process of claim 3 , wherein the inactive fin in the fin pair having about two times the spacing relative to other fin pairs is proximally located to the other fin pairs with the minimal spacing.
5. The process of claim 3 , wherein the inactive fin in the fin pair having about two times the spacing relative to other fin pairs is distally located to the other fin pairs with the minimal spacing.
6. The process of claim 3 , wherein etching removes all of the inactive fins included in the fin pairs that are about two times the spacing between other fin pairs.