A pellicle is a thin membrane stretched over an aluminum frame and glued to the photomask to protect it from contaminants, such as particles. Even if particles sit on the membrane, they are not printed on the wafer because they are out of focus during the exposure from the lithography process.

• To improve the yield rate of IC chips
• To extend the cleaning period of the photomask
• To protect the photomasks from contamination
• To extend the lifetime of the photomask
• To isolate sources of contamination