Design and Fabrication of a 248-nm Near-Linearly Graded Transmittance Optical Film

Linearly graded transmittance films arc a key component of variable attenuators in lithography systems. In this work, the design and fabrication of a 218-nm near-linearly graded optical transmittance film were realized using electron beam evaporation technology. Through sensitivity calculation and optimization, a low-sensitivity nonregular film design was obtained using an anti-reflection film. High-precision film thickness monitoring method with UV light control-crystal control combination realized a film thickness control accuracy of 0. 3 % and an error tolerance of 0.5%. The transmittance film, which was deposited on a JGS1 fused silica substrate using Al2O3 and SiO2 as film materials, realized linear transmittance control from 10% to 97. 8% in an incidence angle range of 21 degrees-35 degrees under 218-nm S-polarized light, which meets the performance requirements of optical variable attenuators.