There is considerable interest in the use of phase shift masks as a route to.extend the resolution, contrast, and depth-of-focus of lithographic tools beyond what is achievable with the normal chrome mask technology. In the attenuating phase shift mask, the chrome layer is replaced with a slightly transparent layer and the mask is etched so that light through the layer is 180-degrees out of phase with light through clear regions. Thus, optical interference occurs which has the effect of increasing contrast at edges and of improving depth-of-focus. In this article, experiments of thin film materials designed to provide both the desired 180-degrees phase shift and optical absorption in a single layer are described.