SRAM design to facilitate single fin cut in double sidewall image transfer process

Abstract

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.

What is claimed is: 
     
       1. A process for increasing active fin mask edge location tolerance associated with fabrication of an for forming an SRAM cell fin structure, the process comprising:
 forming a fin structure comprising plurality of fin pairs, wherein: 
 multiple fin pairs at of the plurality of fin pairs have a pitch of less than 40 nm,; 
 wherein individual fins in the multiple plurality of fin pairs are either active fins or inactive for the SRAM cell fin structure, fins;  
 wherein the inactive fins are included in fin pairs that are about two times the have a fin spacing between other that is about two times the fin spacing of fin pairs including that include only active fins,; and  
 wherein  the inactive fins are located between active regions of the SRAM cell fin structure; fins; and 
 
 removing the inactive fins fromcutting one or more of the inactive fins to form the SRAM cell 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. 
     
     
       7. The process of claim 1, wherein cutting one or more of the inactive fins comprises exposing the one or more of the inactive fins to an etchant through openings in a mask.  
     
     
       8. The process of claim 1, further comprising forming an isolation region in the location where the one or more of the inactive fins were cut.  
     
     
       9. The process of claim 1, wherein forming the plurality of fin pairs comprises forming sidewall spacers on a plurality of mandrels, each of the fins of the plurality of fin pairs corresponding to a sidewall spacer.  
     
     
       10. A fin cut process for forming an SRAM cell fin structure, the fin cut process comprising:
 forming a plurality of fin pairs, the plurality comprising multiple fin pairs having a fin pitch of less than 40 nm, a first fin pair of the plurality of fin pairs having a fin spacing that is about half the fin spacing of a second fin pair of the plurality of fin pairs; and   cutting a first fin of the second fin pair through an opening in a mask, wherein an edge of the mask opening extends parallel to and between the first fin and a second fin of the second fin pair, and cutting the first fin comprises etching the first fin through the opening.    
     
     
       11. The process of claim 10, wherein the fin pitch of the first fin pair is less than about 27 nm.  
     
     
       12. The process of claim 10, wherein the fin pitch of the first fin pair is about 24 nm.  
     
     
       13. The process of claim 10, wherein the fin spacing of the first fin pair is less than about 21 nm.  
     
     
       14. The process of claim 10, wherein the fin spacing of the first fin pair is about 18 nm.  
     
     
       15. The process of claim 10, wherein forming the plurality of fin pairs comprises:
 forming first sidewall spacers, wherein the forming causes the first sidewall spacers to merge in a region between at least two adjacent first mandrels; and   using the first sidewall spacers to form second mandrels, at least one of the second mandrels having a width corresponding to the width of the region between the at least two adjacent first mandrels; and   forming second sidewall spacers on the second mandrels.    
     
     
       16. The process of claim 10, wherein forming the plurality of fin pairs comprises forming sidewall spacers on a plurality of mandrels, each of the fins of the plurality of fin pairs corresponding to a sidewall spacer.  
     
     
       17. The process of claim 10, wherein the fin structure is formed using a self-aligned quadruple patterning (SAQP) process.  
     
     
       18. A process for forming an SRAM cell fin structure, the process comprising:
 forming a plurality of fin pairs, the plurality of fin pairs comprising:
 multiple fin pairs having a fin pitch of less than 40 nm; 
 a first fin pair having a first fin spacing less than about 21 nm; and 
 a second fin pair having a second fin spacing about twice the first fin spacing; and 
   cutting a fin of the second fin pair by exposing the fin to an etchant through an opening in a mask, wherein the mask is patterned to divide the second fin pair.    
     
     
       19. The process of claim 18, wherein the first fin spacing is about 18 nm.  
     
     
       20. The process of claim 18, wherein forming the plurality of fin pairs comprises:
 forming first sidewall spacers on at least two adjacent first mandrels, wherein the forming causes the sidewall spacers to merge in a region between the at least two adjacent first mandrels; and   using the first sidewall spacers to form second mandrels, at least one of the second mandrels having a width corresponding to the width of the region between the at least two adjacent first mandrels; and   forming second sidewall spacers on the second mandrels.    
     
     
       21. The process of claim 18, wherein forming the plurality of fin pairs comprises forming sidewall spacers on a plurality of mandrels, each of the fins of the plurality of fin pairs corresponding to a sidewall spacer.  
     
     
       22. The process of claim 18, wherein forming the fin structure comprises using a self-aligned quadruple patterning (SAQP) process.  
     
     
       23. A process for forming an SRAM cell fin structure comprising:
 forming first sidewall spacers on at least two adjacent first mandrels, wherein the forming causes the first sidewall spacers to merge in a region between the at least two adjacent first mandrels; and   using the first sidewall spacers to form second mandrels, at least one of the second mandrels having a first width and at least one of the second mandrels having a second width, the first width corresponding to a thickness of the first sidewall spacers, and the second width corresponding to the width of the region between the at least two adjacent first mandrels; and   forming second sidewall spacers on the second mandrels; and   using the second sidewall spacers to form a plurality of fin pairs, the plurality of fin pairs comprising at least two first fin pairs and a second fin pair, the at least two first fin pairs having a fin pitch of less than 40 nm and a first spacing corresponding to the first width, the second fin pair has a second spacing corresponding to the second width, and the second spacing is about two times the first spacing.    
     
     
       24. The process of claim 23, further comprising cutting one of the fins of the second fin pair to form the SRAM cell fin structure.  
     
     
       25. The process of claim 24, wherein the cutting comprises exposing the fin of the second fin pair to an etchant through an opening in a mask, wherein the mask is patterned to divide the second fin pair.  
     
     
       26. The process of claim 23, wherein the first spacing is less than or equal to 21 nm.  
     
     
       27. The process of claim 23, wherein the first spacing is about 18 nm.  
     
     
       28. A process for increasing active fin mask edge location tolerance associated with fabrication of an SRAM cell fin structure, the process comprising:
 forming a plurality of fin pairs using a self-aligned quadruple patterning (SAQP) process, the plurality comprising at least two first fin pairs and a second fin pair disposed between the two first fin pairs, wherein:
 the at least two first fin pairs comprise only active fins; 
 the second fin pair comprises an inactive fin; 
 the at least two first fin pairs have a pitch of less than 40 nm; and 
 a spacing between the fins of the second fin pair is about two times a spacing between fins of the first fin pair; and 
   cutting the inactive fin of the second fin pair.    
     
     
       29. The process of claim 28, wherein cutting the inactive fin comprises exposing the inactive fin to an etchant through an opening in a mask patterned to divide the second fin pair.  
     
     
       30. The process of claim 29, wherein cutting the inactive fin comprises a timed etch process.  
     
     
       31. The process of claim 30, wherein the inactive fin of the second fin pair is proximally located with respect to one of the first fin pairs.  
     
     
       32. The process of claim 30, wherein the inactive fin of the second fin pair is distally located with respect to one of the first fin pairs.  
     
     
       33. A process for forming an SRAM fin structure, the process comprising:
 forming first sidewall spacers on at least two first mandrels, wherein the first sidewall spacers merge in a region between the at least two first mandrels;   transferring a pattern defined by the first sidewall spacers to form a plurality of second mandrels;   forming second sidewall spacers on the plurality of second mandrels; and   transferring a pattern defined by the second sidewall spacers to form a plurality of fin pairs, the plurality of fin pairs comprising at least two first fin pairs having a pitch of less than 40 nanometers and a second fin pair disposed between the at least two first fin pairs, wherein a spacing between fins of the second fin pair is about two times a spacing between fins of first fin pairs.    
     
     
       34. The process of claim 33, wherein one of the fins in the second fin pair is an inactive fin, and the process further comprises cutting the inactive fin by exposing the inactive fin to an etchant through an opening in a fin cut mask.  
     
     
       35. The process of claim 1, wherein the fin structure is formed using a self-aligned quadruple patterning (SAQP) process.  
     
     
       36. The process of claim 1, wherein forming the plurality of fin pairs comprises:
 forming first sidewall spacers on at least two adjacent first mandrels, wherein the forming causes the first sidewall spacers to merge in a region between the at least two adjacent first mandrels;   using the first sidewall spacers to form second mandrels, at least one of the second mandrels having a width corresponding to the width of the region between the at least two adjacent first mandrels; and   forming second sidewall spacers on the second mandrels.