A study of defect measurement techniques and corresponding effects on the lithographic process window for a 193-nm EPSM photomask

Photomasks with small dense features and high mask error enhancement factor (MEEF) lithography processes require stringent reticle quality control. The ability to quickly and accurately measure reticle defects on a high-resolution inspection system and to simulate their impact on wafer printing are key components in ensuring photomask quality. This paper discusses the correlation of measurements made with UV and DUV-based inspection systems; simulation performed with a 193nm aerial image review tool and aerial image simulation software. Ease-of-use is discussed for each technique. Data accuracy is compared to measurements performed by a Scanning Electron Microscope (SEM) on mask and wafer. Tests show that the inspection system can quickly and accurately determine sizes of most defects. The study also indicates that the simulation techniques can accurately tract the lithographic results, and can be used to reduce or eliminate the use of test wafers and expensive lithography and wafer metrology time. The outcome of this study leads to better defect dispositioning by providing techniques to determine the size and printability of reticle defects.