We report on the development and first experimental results of a “at wavelength” full-field imaging technique for defect inspection of multilayer mask blanks for extreme ultraviolet (EUV) lithography. According to the International Semiconductor Roadmap by Sematech, less than 5×10−3 defects per cm2 should be present on such multilayer mask blank to enable mass production of microelectronics using EUV lithography, thus fast high-resolution methods for mask defect inspection and localization are needed. Our approach uses a photoemission electron microscope in a normal incidence illumination mode at 13 nm to image the photoelectron emission induced by the EUV wave field on the multilayer mask blank surface. We show that by these means, buried defects in the multilayer stack can be probed down to a lateral size of 50 nm.
A new method for the actinic at-wavelength inspection of defects inside and ontop of Extreme Ultraviolet Lithography (EUVL) multilayer-coated mask blanks is presented. The experimental technique is based on PhotoElectron Emission Microscopy (PEEM) supported by the generation of a standing wave field inside and above the multilayer mask blank when illuminated near the resonance Bragg wavelength at around 13.5 nm wavelength. Experimental results on programmed defect samples based on e-beam lithographic structures or PSL equivalent silica balls overcoated with an EUV multilayer show that buried defects scaling down to 50 nm in lateral size are detectable with further scalability down to 30 nm and smaller due to the PEEM´s instrumental performance. Furthermore, phase structures as shallow as 6 nm in height on a programmed phase grating sample has been detected by this technique. The visibility of the phase defect structures has been shown to be strongly dependent on and controlled by the phase of the standing wave field at the mask blank surface and thus can be optimized by tuning the illumination wavelength between 12.5 nm and 13.8 nm.
A new method for the actinic inspection of defects inside and on top of extreme ultraviolet (EUV) lithography multilayer-coated mask blanks is presented. The experimental technique is based on photoemission electron microscopy supported by the generation of a standing wave field inside and above the multilayer mask blank when illuminated near the resonance Bragg wavelength at around 13.5nm. Experimental results on programed defect samples based on electron beam lithographic structures or silica balls overcoated with an EUV multilayer show that buried defects with a lateral size down to 50nm are detectable. Furthermore, phase structures as shallow as 6nm in height on a programed phase grating sample have been detected by this technique. The contrast of the phase defect structures has shown to be strongly dependent on and controlled by the phase of the standing wave field at the mask blank surface, and thus can be optimized by tuning the inspection wavelength.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.