Multiple Patterning - 2D Layout Considerations

2D Layout Considerations

For 2D patterns the density increase is very dependent on the nature of the pattern. For instance, contact arrays have optimal packing density as rectangular arrays for double patterning but as hexagonal close packed arrays for triple patterning – achieving a close to 2 and 3 times area improvement respectively. For 2D layouts double patterning compliance errors occur when there are odd cycles of minimum spaces. This can be resolved by relaxing one of these spaces to a distance where both features can be patterned in the same imaging step. Triple patterning is compliant with odd cycles but in turn is non-compliant for two facing pairs of line-ends where the corner to corner space is below the single patterning distance. This in turn is compliant under quadruple patterning. The improvement in density with the use of multiple patterning schemes is thus highly dependent on the pattern. Often simple redesigns or relaxation of dimensions in one direction can avoid the expense of going to more complex and expensive multiple patterning processes.

Synopsys has begun consideration of triple patterning decomposition of layers which are less easy to split into two patterns, such as contact layers. While only increasing the number of processing steps by 50% (compared to 100% for the insertion of double patterning), triple patterning would enable 16 nm node patterning on a 45 nm node lithography tool. Likewise, quadruple patterning would enable 11 nm node patterning on the same 45 nm node lithography tool, with only 33% additional steps over triple patterning.