Scanning electron beam method for examining surfaces in a short focal length magnetic lens

Abstract

A new scanning electron microscope method for examining the surface of bulk samples is described that uses a short focal length (1 mm), low aberration, magnetic electron lens. The minimum beam size produced by the lens is 2-3 times smaller than the minimum beam size in a conventional secondary electron scanning electron microscope. The new method, in which backscattered electrons are detected with silicon diodes located inside the pole-piece gap of the lens, allows large area samples such as silicon integrated circuit wafers to be examined, despite the constricted sample region of the lens. The new method also makes it possible to use this type of short focal length lens for electron beam lithography, because it allows alignment marks on the wafers to be detected while the wafers are immersed in the lens. A 1 mm focal length lens produces a beam current density that is more than 20 times higher than that produced by the longer focal length lenses used in conventional electron beam lithography systems.