Development of nm resolution focus detector in vacuum for EUVM

Since the numerical aperture of the optical system of the EUV microscope for mask inspection is as large as 0.3, the depth of focus becomes server within 100 nm. For this reason, the focus detection system which can operate in a vacuum environment and requires several 10 nm resolution is developed. Since this detector has to detect the sample position without contacting the surface of the sample, it employed the grazing incidence reflection system using laser light.