In order to meet the needs of multiple customers with varying design specifications, merchant photomask suppliers need to provide photomasks for a wide range of design patterns. Some masks require etching less than 1% of the total mask film, while others require etching over 80% of the mask. Etching masks with these extremes in pattern loads can often require upgrading existing tool sets, particularly as the mask specifications become tighter. One alternative to upgrading tools is to develop new load-specific processes on existing lower-end tools, which requires a substantial amount of development work. Dry etching MoSi Embedded Attenuating Phase Shift Material using sulfur hexafluoride and helium under all etch loads presents challenges in the Unaxis Generation II mask etch platform. Etch processes developed for low load masks cannot always be used for high load masks due to problems in maintaining a stable process with good performance. In order to improve the etch performance for high MoSi loads (> 70% clear), a Gen II specific hardware design which can adversely affect uniformity at high loads was identified and eliminated as a dominant source of non-uniformity. A DOE studying total gas flow, He/SF6 ratio, pressure, ICP, and RIE power was then used to identify a stable process window for high MoSi loads. Another DOE studying the effects of pressure, ICP power, and RIE power on process uniformity was then carried out within the stable process window. Process conditions were identified which produced highly loaded 248nm and 193nm EAPSM masks with phase uniformity below 3°. Sidewall profiles were vertical for 193nm MoSi films but were slightly tapered for 248nm MoSi films, both with less than 5nm of CD bias.