Beyond EUV binary and phase shift masks simulation

Beyond Extreme Ultraviolet (BEUV) lithography is expected to be used for high volume manufacturing of 1 nm node process at 6.7 nm wavelength. In this report, we simulate the optical design of BEUV photomask coatings, including BEUV multilayer mirrors, capping layers, and absorbers to use the shorter wavelength from 13.5 nm as the current EUV lithography to 6.7 nm. The simulation illustrates the expected materials of each layer, in terms of reflectivity, effective reflection plane, and phase shift. We estimate the requirements of BEUV mask design with multilayer and absorber thickness dependence as binary and phase shift masks in order to minimize the mask 3D effect. The result suggests that the phase shift mask is suitable to achieve the superior optical resolution and requires the architecture with the shallower depth of the effective reflection plane compared to EUV. This work has demonstrated the optimal mask conditions as the first generation of BEUV photomasks.