Methods for evaluating lithographic performance of exposure tools for the 45nm node: ECD and scatterometry

This paper compares two metrology methodologies, ECD (Electrical CD) and SCD (Spectroscopic CD), for the 450nm-node-like gate level. Measurements were taken on both metrology tools, for different features, and the data was processed to reflect the exposure tool's fingerprint within the exposure field. ACLV (cross chip line-width variation) and through-focus measurements were also collected. There is a DC bias between the ECD and SCD. The cross slit and cross scan average plots are very similar between the two methods. The correlation between ECD and SCD gave R-2 of 0.95 and 0.92 for 220nm and 480nm pitches respectively. Results showed that SCD is a viable candidate to replace ECD for characterizing the exposure system for the 45nm node. Data also showed that there are fundamental differences between the two methods that cannot be attributed to random errors. These differences account for less than I nm at 3 sigma.