Mask 3D parameter optimization for improving imaging contrast of plasmonic lithography

Based on plasmonic lithography (PL) technology, and aiming at the special nano-optical effect of metal/dielectric multilayer composites and mask three-dimensional (M3D) effect, a method for optimizing mask parameters is proposed. As a common analytic formula, the optical transfer function method has been introduced to analyze the imaging process. In order to include the M3D effect, FDTD is used to quantitatively calculate the PL imaging results, and the aerial image (AI) intensity and the light intensity contrast of AI in the photoresist layer can be obtained. The simulation results suggest that the imaging resolution and light intensity contrast can be improved by optimizing the M3D parameters such as the sidewall angle, thickness, and material of the mask absorber. For the line space test pattern with critical dimension = 150 nm and pitch = 300 nm, the results indicate that the optimal sidewall angle is 40°, resulting in an increase in the light intensity contrast of 344%. The light intensity contrast with a mask thickness of 70 nm is improved by 11% when compared to a mask thickness of 60 nm. The use of Ta and opaque MoSi on glass as the mask absorber material improves the light intensity contrast to varying degrees compared to the Cr mask.