Mo/Si multilayers deposited by low-pressure rotary magnet cathode sputtering for extreme ultraviolet lithography

摘要

We fabricated molybdenum (Mo)/silicon (Si) multilayers with a low-pressure rotary magnet cathode (RMC) sputtering system under several deposition conditions and investigated their properties. We obtained a high extreme ultraviolet (EUV) reflectivity of approximately 71% as measured in Mo/Si multilayers sputtered with low-pressure xenon (Xe) gas. We confirmed that the multilayers sputtered with Xe gas exhibited higher reflectivity than those sputtered with argon (Ar) gas, and that the multilayers sputtered at a lower pressure exhibited higher reflectivity than those sputtered at a higher pressure. From trans mission electron microscope (TEM) cross-sectional images of the high-reflectivity Mo/Si multilayers, we observed thinner interdiffusion layers between the Mo and Si layers than those in Mo/Si multilayers sputtered by ion-beam sputtering. We also obtained a low film stress of ―35 MPa in a doubly stacked Mo/Si multilayer where a 50-pair multilayer with a Γ ratio (the fractional thickness ratio of a Mo layer to the total thickness of a Mo layer and a Si layer) of 0.35 with compressive stress was stacked upon a 30-pair multilayer with a Γ ratio of 0.7 with tensile stress.