Abstract
Attenuated phase shifting masks (Att PSMs) use a slightly transmissive absorber with a π (180°) phase shift. Unlike many other phase-shifting masks, they can be used for any arbitrary mask pattern. In this paper, the exposure-defocus (E-D) window methodology is used to characterize Att PSMs; figures of merit for depth of focus (FDOFs) are obtained for single layer resists, single layer resists with antireflection coatings, and multilayer resists. A small positive mask bias improves resolution and allows shorter exposures. Compared with rim phase-shifting masks, Att PSMs show note-worthy improvements, especially for hole and line openings. They have greater depth of focus, require shorter exposures, and use less mask area.