A pellicle consists of a thin transparent membrane (made of fluoropolymer, nitrocellulose orsimilar material) stretched over an aluminum frame of a specified height. The pellicle is placedon the chrome side of a UT1X reticle over the row of fields. The purpose of a pellicle is to protect the critical area of the reticle from contamination and to keep any particles on the pellicle surfaceout of the focal plane of the stepper.