Back-glass cleaning: reducing repelliclization costs by focused action

With the optimization of sulfate-free cleaning the issue of haze under pellicle was almost eliminated. In consequence, current reasons for mask repelliclization needs are moving from pattern issues to more gross problems on back glass. Moreover, the longer life of photomasks allows a new problem to appear as growing defects on back glass, commonly ascribed to environmental conditions at user's site. The commonality of these problems is being independent on mask complexity and substrate. In order to avoid the criticalities of pellicle removal and cleaning treatment as well as the cost of necessary inspection after new pellicle application, the best solution is cleaning only the backside of the mask, provided that integrity of pellicle and pattern on front side are preserved In this article we present the results obtained by the use of the Mask cleaner DE050019 TM on several cases. The efficiency of the treatment was assessed in terms if removal capability on different kinds of contaminations, either from use or mask aging. Pattern inspections were conducted in order to assess ESD robustness. Ionic residues were checked by IC aimed to compare with standard cleanings. This methodology demonstrated to be capable of maintaining a Particle Removal Efficiency>97% on all kinds of contaminations, without any damage to pellicle or harm to patterns, still maintaining residual ions at the same level as after cleaning by standard tools.