Cleaning of photomasks prior to pelliclizatlon Is the most demanding of all mask cleaning operations. A single particle found under a pellicle can lead to costly and time consuming repelliclization. Improved stepper resolution and automatic post pellicle inspection systems are making the requirement even more difficult to meet. Careful anal ysi s of parti culate sou rces an d clean i n g p rocesses b y Solid State Equipment Corporation have lead to the evolution of the SSEC Model 156SC which has proven to be effective as a sub micron prepellicle mask cleaner. It uses a combination of brush surfactant high pressure water static control fluid and rapid drying to achieve superior cleaning results. In an effort to meet their cleaning requirements In a cost effective manner DuPont Photomasks has installed this system in their San Jose Facility. The system design and the evaluation techniques are described. Some experimental data is presented.