THIN-FILM MATERIALS FOR THE PREPARATION OF ATTENUATING PHASE-SHIFT MASKS

There is considerable interest in the use of phase shift masks as a ro ute to.extend the resolution, contrast, and depth-of-focus of lithogra phic tools beyond what is achievable with the normal chrome mask techn ology. In the attenuating phase shift mask, the chrome layer is replac ed with a slightly transparent layer and the mask is etched so that li ght through the layer is 180-degrees out of phase with light through c lear regions. Thus, optical interference occurs which has the effect o f increasing contrast at edges and of improving depth-of-focus. In thi s article, experiments of thin film materials designed to provide both the desired 180-degrees phase shift and optical absorption in a singl e layer are described.