Mo/Si multilayer improvements for EUV photomask performance

Optical calculation and experimental data are presented for the impact of reflectivity of the Mo/Si multilayers for EUV photomasks deposited by secondary Ion Beam Deposition (IBD). Simulations of Mo/Si multilayer stacks in which the bottom-most 30 bilayers remain intermixed, and up to ten top bilayers are not intermixed at all or less intermixed is revealed to have the benefit of approximately 2.5% of reflectivity improvement while the simulation of 40-bilayer stack which has a typical intermixed layers of 1.1nm at the interface on top of the Silicon and 0.5nm at the interface on top of the Molybdenum indicate a maximum reflectivity of 68.5%. The multiple beam voltage deposited multilayers with lower beam voltage for top bilayers and with higher beam voltage for bottom bilayers are demonstrated and discussed using XRR measurement and TEM observation.