Exposure tool settings and OPC strategies for EUV Lithography at the 16nm node

摘要

The EUV exposure tool settings and OPC strategies to be used for the 16 nm logic node are discussed. Imaging simulation was done for various types of CD through pitch patterns to investigate the tradeoff between NA, illumination settings, and resist diffusion blur. EUV optics still provides very good optical resolution at 56 nm min pitch, but resist diffusion degrades imaging contrast significantly. The CD variations due to resist blur are relatively larger for EUV lithography than they are for 193 nm lithography, because of the high quality of the EUV lithography images. EUV shadowing effect and flare effect contribute additional CD variations, which need to be corrected and controlled. Nonetheless, a resist blur of about 15 nm FWHM or better provides adequate imaging performance even with current EUV optical settings of 0.25 NA and conventional illumination for 28 nm half-pitch applications. Experimental results show that state-of-art EUV resists have resist blur values close to this requirement, although their current performance is limited by resist material properties and processing conditions.