Abstract: A high-sensitivity holographic and interferometric metrology developed at the Center for X-ray Lithography (CXrL) has been employed to investigate in-plane distortions (IPD) produced in x- ray mask materials. This metrology has been applied to characterize damage to x-ray mask materials exposed to synchrotron radiation. X-ray mask damage and accelerated mask damage studies on silicon nitride and silicon carbide were conducted on the Aladdin ES-1 and ES-2 beamline exposure stations, respectively. Accumulated in-plane distortions due to x-ray irradiation were extracted from the incremental interferometric phase maps to yield IPD vs. dose curves for silicon nitride mask blanks. Silicon carbide mask blanks were subjected to accelerated mask damage in the high flux 2 mm $MUL 2 mm beam of the ES-2 exposure station. An accelerated damage study of silicon carbide has shown no in-plane distortion for an accumulated dose of 800 kJ/cm$+2$/ with a measurement sensitivity of less than 5 nm. !5
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