Ultra-high-resolution low-voltage imaging of polymers

Abstract

We have been using an LVSEM with an immersion-type objective lens extensively for the examination of polymers at low (<2 keV) incident beam energies. Because of this instrument's field emission source, the incident probe can be demagnified down to subnanometer dimensions and still provide enough incident beam current to stimulate detectable image forming signals, esp. secondary electrons. Also, the incident beam penetration depth at low voltages is less than the SE escape depth (=200Å) for carbonaceous materials), so the sample/beam interaction volume is correspondingly smaller. The combination of these two factors suggest that the attainable resolution at low voltages for polymeric materials can be significantly higher than that which can be obtained via conventional SEM, all while the beam induced radiation damage is correspondingly reduced.Another reason that higher resolution can be obtained at low voltages is that, for all materials, a surface charge balance situation (wherein the incident beam current is equal to the summed SE and backscattered currents) exists for a particular incident beam energy, E2.