Defect Inspection of Quartz-PSMs: Taking a Leap Forward

摘要

Defect inspection of Quartz-PSMs is challenging, as the optical contrast for defects within the quartz substrate is small. The performance of three phase contrast algorithms is studied with a variety of defect test masks. For alternating phase shift masks key parameters such as optimum focus offset, defect sensitivity for different feature sizes, as well as defect sensitivity with respect to defect printability criteria are studied. In the studied range for two of the algorithms the defect sensitivity is independent of the feature size, whereas the third algorithm exhibited a decrease in sensitivity with decreasing feature sizes. In focus runs performed on large feature sizes a single optimum focus offset is observed, whereas for small feature sizes a two-path inspection using a positive and negative focus offset is found necessary. With respect to defect printability all critical 180° defects were found. For the newest of the three algorithms good inspectability of chrome-less PSMs is achieved.