→ yellowfishie:看來很神奇，但是還是受限於 variation 吧 :) 08/14 09:58
Intermediate pattern accumulation
A "brute force" approach, intermediate pattern accumulation involves a
sequence of (at least) two separate exposures and etchings of independent
patterns into the same layer. For each exposure, a different photoresist
coating is required. When the sequence is completed, the pattern is a
composite of the previously etched subpatterns. By interleaving the
subpatterns, the pattern density can theoretically be increased indefinitely,
the half-pitch being inversely proportional to the number of subpatterns
used. For example, a 25 nm half-pitch pattern can be generated from
interleaving two 50 nm half-pitch patterns, three 75 nm half-pitch patterns,
or four 100 nm half-pitch patterns. The feature size reduction will most
likely require the assistance of techniques such as chemical shrinks, thermal
reflow, or shrink assist films. This composite pattern can then be
transferred down into the final layer.
A possible application would be, for example, dividing the contact layer into
two separate groups: gate contacts and source/drain contacts, each defining
its own mask. IMEC recently used an approach like this to demonstrate a 45 nm
node 6-transistor SRAM cell using dry lithography [2].
As with the heterogeneous approach, any discrepancy among the different
interleaved patterns would be a source of feature-to-feature variation.
http://en.wikipedia.org/wiki/Multiple_patterning
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