Monitoring of SRAM gate patterns in KrF lithography by ellipsometry

This paper reports on the ellipsometric monitoring of SRAM gate patterns in KrF lithography. Results showed that ellipsometry is practical for monitoring repetitive patterns. A multivariable regression analysis was applied to predict gate lengths by using ellipsometric parameters. A good agreement (3σ=8.7 mn) between the measured width by CD-SEM and the predicted ones was achieved. Standard deviation of the predicted width (repeatability) was 0.5 nm. This suggests that ellipsometry is superior to CD-SEM in arriving at the average values