Polarization contact: mask engineering

摘要

Test structures for measuring polarization effects in the illumination, high-NA imaging, and resist coupling are introduced. Specifically, polarization bars are used to transform the mask into a precision instrument capable of monitoring polarization imbalances in the illumination system and to enable studies of both high-NA and polarization dependent resist coupling effects. Critical issues dealing with mask fabrication are addressed. Bar and gap tolerances are investigated to understand uniformity effects on polarization. While the total relative open areas between two polarization bar regions should be kept to within 1 % of each other for good polarization uniformity, polarization bars are quite robust to average mask writing errors when the gap widths are kept small (<50nm). Major improvements in the polarization ratio of chrome masks are possible by using materials with a real part of the refractive index near 2.