Shadowing effect modeling and compensation for EUV lithography

Extreme ultraviolet (EUV) lithography is one of the leading technologies for 16nm and smaller node device patterning. One patterning issue intrinsic to EUV lithography is the shadowing effect due to oblique illumination at the mask and mask absorber thickness. This effect can cause CD errors up to a few nanometers, consequently needs to be accounted for in OPC modeling and compensated accordingly in mask synthesis. Because of the dependence on the reticle field coordinates, shadowing effect is very different from the traditional optical and resist effects. It poses challenges to modeling, compensation, and verification that were not encountered in tradition optical lithography mask synthesis. In this paper, we present a systematic approach for shadowing effect modeling and model-based shadowing compensation. Edge based shadowing effect calculation with reticle and scan information is presented. Model calibration and mask synthesis flows are described. Numerical experiments are performed to demonstrate the effectiveness of the approach.