Porous silica pellicle frame

Two main issues with current pellicle frames are: (1) thermal expansion mismatch between the anodized aluminum frame and the photomask, and (2) the lack of porosity for purging and contamination control. Both issues can be addressed by using a sol-gel-derived porous silica frame. The silica frame has essentially the same thermal expansion coefficient as the fused silica photomask substrate. The porous nature of the silica frame provides contamination control by N-2 purging and scavenging capability. The porosity characteristics and mechanical properties of the frame material were determined. Porous silica frame was successfully mounted onto quartz plate by a commercial process, suggesting the suitability of using porous silica as pellicle frame material. The sol-gel derived porous silica represents the first proof-of-concept for an alternative frame material with a potentially significant impact on the photomask industry.