Contrast optimization for 0.33NA EUV lithography

Abstract

0.33 NA EUV lithography is expected to be introduced into High Volume Manufacturing at k1 values of approximately 0.4...0.5. This is significantly larger than state of the art immersion lithography which can operate at k1 of 0.3. We investigated the impact of contrast enhancement on the imaging properties of Contact Holes and Lines and Spaces. Contrast was adjusted by changing the illumination properties pupil fill ratio and center incidence angle. We found a strong improvement of the local Critical Dimension control: line width variation for Lines and Spaces and hole to hole CD variations for arrays of contact holes. For all features we found a similar dependency on contrast. As the local Critical Dimension variations contribute significant to Edge Placement Error budgets, we foresee the implementation of contrast enhancements already at moderate k1 values around 0.4.