Initial resolution measurements of an improved magnetic–electrostatic detector objective lens for LVSEM

In this paper we present some initial resolution measurements of an improved magnetic–electrostatic detector objective lens for a low-voltage scanning electron microscope. The electron optical design of the lens was already proposed by the authors [G. Knell, E. Plies, Nucl. Instr. & Meth. A 427 (1999) 99]. The magnetic circuit of this lens has a radially arranged pole-piece gap. Thus, the specimen is immersed in a strong magnetic field of 106 mT (working distance: 1 mm, primary electron energy: 200 eV). The electrostatic field strength of our optimized lens variant amounts to a moderate value of 100 V/mm for a working distance of 1 mm. At a final beam energy of 1 keV a resolution of 3 nm, at 260 eV a resolution of 5 nm was obtained.