COMPARISON OF BACKSCATTERED ELECTRON AND OPTICAL IMAGES FOR SUBMICRON DEFECT DETECTION.

A rapid and automated inspection system is a necessity for the detection of defects in x-ray and optical lithography masks. Monte Carlo techniques and optical simulation are used to examine the relative qualities of backscattered electron signals and transmitted optical images for use in a mask inspection system. The backscattered electron signals from one and two dimensional submicron structures are examined for different take-off angle ranges and beam sizes and compared to the corresponding optical images for different wavelengths and numerical apertures. It is shown that signal quality in electron-beam inspection systems can improve as defect size decreases while the optical images tend to degrade. An examination of shot noise signal-noise ratio characteristics shows that shot noise alone should not be a fundamental limit in a well designed inspection system.