High-resolution, low-voltage SEM for true surface imaging and analysis

Abstract

A novel design concept for the electron optical column has been implemented in the realization of a new ultra-high performance SEM. A compound magnetic/ electrostatic objective lens is at the heart of the high-performance column: the imaging aberrations of this new lens type decrease with decreasing beam energy. Any beam cross-over between the electron source (Schottky FE-gun) and the sample has been eliminated in order to avoid broadening of the beam energy spread (Boersch effect). A high beam energy is maintained throughout the column regardless of the electron probe energy selected by the operator. This protects the beam against the effect of stray fields and minimizes any loss of beam brigthness due to stochastic electron-electron interactions. The new SEM achieves outstanding resolution, particularly at the low beam energies (3 nm achievable at E_PE = 1 keV). The secondary electrons emitted by the sample are detected with very high efficiency by an internal annular detector situated above the final lens. Due to the low imaging aberration level, a high current can easily be focused in a very small probe, thus making the new SEM ideally suited for high-resolution, quantitative X-ray analysis.