Provided is a method for creating a mask blank that includes a capping layer and a shifter layer. The capping layer is optically compatible and process compatible with the shifter layer. The method may include providing a cleaned and polished mask substrate to a deposition tool and depositing, within the deposition tool, a shifter layer over a cleaned and polished mask substrate. The shifter layer may include each material of a set of materials in a first proportion. The method may also include depositing an additional layer over the shifter layer, the additional layer providing a capping layer over the shifter layer. The capping layer includes the materials in a second proportion unequal to the first proportion. The capping layer includes molybdenum, silicon, and nitride in a proportion that aids in detection by a residual gas analyzer. Also provided is also a mask blank structure incorporating the compatible capping layer.