Porous silica frame for deep UV lithography

Several significant technical issues are associated with the current anodized aluminum photomask frame. These problems will become more acute as shorter wavelengths such as 193 nm and 157 nm become standard. For example, it is difficult to purge the pellicle space, and the non-porous nature of the aluminum frame can lead to pressure-induced film breakage. In addition, the thermal expansion behavior of aluminum does not match that of the silica substrate, which can lead to pattern distortion or bending of a hard pellicle film. Proposed solutions such as a perforated silica frame or a porous stainless steel frame may address some of these issues, but a complete solution has not been forthcoming. A porous silica frame technology based on sol-gel processing may eliminate concerns associated with the lack of porosity in the stainless steel frame, as well as thermal expansion mismatch problems. Several additional advantages may also be realized, including the removal of organic contaminants from inside the pellicle space, filtration of particulate contaminants, and stability under aggressive cleaning. This approach to a porous silica frame may help enable a cost-effective route to more rapid commercialization of shorter-wavelength microlithographic processes.