Development of Nanometer Resolution Focus Detector in Vacuum for Extreme Ultraviolet Microscope

摘要

We have developed a focus detection system for an extreme ultraviolet (EUV) mask inspection system with a high numerical aperture (NA) of 0.3. This system operates in a vacuum environment and needs a high resolution for focus detection, because the depth of focus (DOF) of optics with 0.3 NA becomes ± 100 nm or less. The focus detection system of the glancing-incidence type developed consists of a laser diode, a focusing lens, pinholes, and a dual-segmented photodiode. We achieved a focus sensor resolution of less than 20 nm. Furthermore, using our focus detection system, a vacuum pressure of 1 x 10~(-5) Pa was achieved.