Smooth Critical Dimension Compensation Across Photomask Transmittance Discontinuities Enabled by Selective and Direct Laser Patterning Inside Mask

Abstract

A selective laser patterning technique applied inside photomasks as a practical method to mitigate critical-dimension non-uniformity caused by overexposure in large-area lithography systems with segmented illumination was investigated. The geometric characteristics of laser-induced voids were analyzed depending on various laser patterning conditions, and the resulting critical-dimension behavior was evaluated across regions with various transmittance levels, including sharply discontinuous transmittance boundaries. The results show that the void size and morphology can be tuned by adjusting the laser pulse energy, although excessive pulse energy leads to mask fracture, from which we derived appropriate processing windows. Furthermore, photomask transmittance was controllable over a wide range (20-92%) by varying laser parameters, void density, pattern arrangement, and the number of patterned layers. This enabled critical-dimension compensation with nanometer- to tens-of-nanometer-level precision. To examine critical-dimension behavior under abrupt transmittance transitions analogous to overexposure zones, 80% and 50% transmittance regions were placed adjacently. Despite the 30% transmittance difference, critical-dimension variation remained smooth, confirming that sharp transmittance changes do not induce abrupt critical-dimension shifts. Overall, our findings experimentally demonstrate that selective and direct laser patterning inside photomasks is a practical and effective critical-dimension compensation approach for large-area lithography employing segmented illumination systems.