Self-regulating charge control for ultra high resolution scanning electron microscopy

We present a low vacuum tool for ultra high resolution scanning electron microscopy of insulators and floating conductors. Charging is stabilized by ionized gas molecules generated using an environmental secondary electron detector designed to operate within the magnetic field on an immersion objective lens. The charge stabilization mechanism yields consistent charge control that is transparent to the operator, and independent of the tasks performed during imaging. This is illustrated by series of artifact-free, high resolution images of an insulating test sample acquired as a function of magnification and scan speed, at a number of accelerating voltages. The low vacuum method is compared to the high vacuum technique of adjusting the electron beam landing energy so as to minimize charging artifacts (i.e., the "total yield" method). The low vacuum approach is less sensitive to changes in beam current density (determined by the beam current, magnification, scan speed and beam diameter) and yields higher ultimate image resolution. The resolution improvement results from effective suppression of both charge-induced defocusing of the electron beam and distortion of the scan pattern.