Advancements in Mo/Si deposition techniques for high volume manufacturing of EUV mask blanks

State-of-the-art EUV photomask blanks are coated with an ion-beam-deposited multilayer of Mo/Si, specifically designed for high reflectivity at the 13.5 nm EUV wavelength. The process-of-record for these multilayers is secondary ion beam deposition, due to its exceptional performance in low defect density and ultra-smooth interfaces. As EUV transitions into high volume, the industry demands ever tighter specifications, particularly: more repeatable and uniform central wavelength (CWL); fewer and smaller defects; and higher throughput. We present several software and hardware advancements towards improving manufacturability of the Mo/Si multilayers. Specifically, we introduce refinements of endpoint algorithms and motion control enabling CWL control towards a projected demand for +/- 10 picometers. Furthermore, we demonstrate an enhanced target assembly for controlling the formation and evolution of target “nodules”. Nodules are a known source of defects in EUV mask blanks, as well as impacting throughput by shortening the mean-time-between-maintenance (MTBM). We also demonstrate broader target erosion and estimate the resulting improvement in MTBM. In addition, we present a next-generation ion source for further throughput improvement via higher deposition rates. We compare Mo and Si deposition rates with the existing and new ion sources, and project estimated throughput improvements by a factor of at least 2x, while maintaining the same ion energy.