The ability to fabricate defect-free reflective Mo-Si multilayer (ML) blanks is a well-recognized challenge in enabling extreme ultraviolet (EUV) lithography for semiconductor manufacturing. Both the specification and reduction of defects necessitate the understanding of their printability and how they are generated and grow during ML deposition. A ML phase defect can be depicted by its topographical profile on the surface as either a bump or pit, which is then characterized by height or depth and width. These phase defects are complex in nature and their impact to resist printing. The authors developed an effective way to study phase defects with programmed defect mask (PDM) as "model" test vehicle. The defects are produced with tuned ML deposition process and placed in varying proximity to absorber patterns on the mask. This article describes the recent study of ML phase defect printability from exposures of a ML PDM on the EUV microexposure tool with annular, monopole, and dipole illuminations. (c) 2007 American Vacuum Society.