A pellicle is a thin, transparent membrane that covers a photomask during the production flow. The pellicle is a dust cover, as it prevents particles and contaminates from falling on the mask. It also must be transparent enough to allow light to transmit from the lithography scanner to the mask.
Pellicles are an important part of the IC-manufacturing supply chain. Today’s optical photomasks consist of an opaque layer of chrome on a glass substrate. In the production flow, a scanner tends to generate unwanted particles and contaminates. So for decades, the industry has used a pellicle on the mask. The pellicle for an optical mask is based on a thin polymer material.
EUV pellicles are required to put EUV lithography into mass production, at least for logic chips. If a particle lands on an EUV mask, the scanner would likely print an unwanted defect on a wafer.
In theory, the pellicle will dissipate heat when EUV light hits the pellicle, which can rise to anywhere between 600 and 1,000 degrees Celsius. But at those temperatures, there are also fears that the EUV pellicle could deteriorate during processing, causing damage to the EUV mask and scanner.