Ion beam deposition for larger form-factor EUV mask blanks

EUV photomask blanks are coated with an ion-beam-deposited (IBD) multilayer mirror of Mo/Si,. IBD is further a candidate for pellicle processes, due to its low defect density and uniform coating. The within-mask uniformity requirement is currently +/- 0.015nm in Central Wavelength (CWL) across the 6” x 6” area., requiring film uniformity of ~ 0.1%. To avoid stitching under high-NA anamorphic projection, larger form-factor masks and pellicles are being considered. Proposals include 300mm round or 12” x 6” rectangular blanks. We present simulations and data for the uniformity performance of the Veeco ion beam deposition tool over the double-sized active area, namely a rectangle of 104 mm x 264 mm. We demonstrate that the non-uniformity of today’s processes-of-record could result in 3.3x higher nonuniformity over the extended area, implying a CWL uniformity of +/- 0.05 nm. We then demonstrate process and hardware modifications to enable CWL uniformity recovery to better than +/- 0.015 nm.