Mask cleaning has been a significant challenge. Advanced PhotoMasks have proven to be even more difficult. The experimental work on 157nm systems uncovered an issue of particle growth under the pellicle. Since the mask blank had a different composition from existing production mask blanks, there was not a concern about current production impact. Investigations were started after a few incidents occurred on 193nm masks. The investigations demonstrated that the masks have a consistent family of contaminants that are on all chrome absorber masks. The initial work provided clues to the nature of the particle growth and some indication of the potential sources. The issues seemed to evolve from the total system and not a single contaminant source. Currently, hard defects due to particle growth under the pellicle occur industry wide. This paper will provide the methodology employed for a recent cleaning evaluation and identify some of the culprits that cause particle growth. The issue has grown to a major problem and needs to be quickly addressed.