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Effect of pressure differentials on pelliclized photomasks

Maintaining the integrity of a pelliclized photomask during air shipments can be very challenging. Changes in air pressure in the cargo area or cabin of an airplane can cause the volume of air under the pellicle membrane to expand or contract. Pellicle membranes can be damaged or even break under too much stress. Some evidence has suggested that particles may develop in the critical area in the pellicle cavity during shipment. Pellicle suppliers have developed several different methods for equalizing pressure differentials between the pellicle cavity and the surrounding environment. This paper surveys and characterizes the different methods used to relieve pressure differentials on pelliclized photomasks. The effect of membrane expansion on membrane quality and defect formation is also studied.