why double patterning is not used for all layers

[Amy25]

hi All,

Why double pattering technique is not required for all metals layers in lower technologies??

 

[erikl]

Double patterning only needs to be used for the first few patterns (say: diff, poly, contact, M1, via12, M2) which define very small structures and need high accuracy. The higher metal layers mostly have wider dimensions and spacing, so need less definition accuracy, hence single patterning is sufficient.

Double patterning needs at least a second UV exposure, and in some cases one more mask, which is expensive and detrimental to yield.