Abstract: A photomask assembly is disclosed having a photomask substrate and a composite pellicle frame that includes both a metallic frame component and a scavenger component. The metallic frame component has a cross-sectional thickness of at least 100 micrometers in all directions, and the volume percentage of the scavenger component relative to the overall volume of the composite frame is in the range of 0.1 to 95%. The scavenger component has a gas permeability to oxygen or nitrogen greater than about 10 ml·mm/cm2·min·MPa, an average pore size between 0.001 and 10 micrometers, and a pore surface area greater than 10 m2/g. This configuration enables the pellicle frame to have sufficient strength to withstand stresses encountered during normal use, yet also to have the capability of scavenging impurity molecules from the space adjacent to the photomask substrate.