Optical lithography applied to 20-nm CMOS Logic and SRAM
2011
Achieving 20nm designs with 193nm lithography is difficult even with immersion technology. At 20nm, the metal-1
pitch will be ~64nm, which is well below the 80nm limit for single exposure. In this work we extend on our earlier
results [1-4] to show simulation-based patterning of both SRAMs and logic cells. This is consistent with the emerging
industry consensus that regular designs and multiple exposure techniques will extend 193nm immersion as far down
as 7nm [5].
The approach relies on 1D Gridded Design Rules with Lines/Cuts (1D GDR LC) selective double patterning. Due to
the highly regular patterns of 1D GDR LC we are able to determine a sharp lithographic optimum as a result of
numerical co-optimization of key layout parameters and lithography settings such as scanner illumination, etc.
including realistic scanner capability.
Critical layers (holes/cuts in 1D GDR LC) consist of a number of identical hole/cut patterns with varying density. We
propose a novel algorithm for full-chip proximity correction of such critical layers. The algorithm consists of 1) a
source-mask optimization step (SMO) to choose optimal scanner settings for a class of designs using standard cells,
followed by 2) a final correction step applied to the entire layout to determine individual sizing for each cut to componsate
for its optical/process environment. This procedure converges rapidly in our test cases producing close to
0nm CD error for each cut. Several test designs including one with approximately 100k transistors using ~20 cells
from a standard cell library including both SRAM and logic cells were used, with good convergence obtained in all
cases.
Out procedure is a combination of an SMO step followed by cuts-OPC, the equivalent to OPC applied to cuts of 1D
GDR LC designs. The procedure scales linearly with layout area and can be efficiently applied to full-chip designs.
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