<title>Optimized secondary electron collection in in-lens-type objective lens</title>

Abstract

Secondary Electron (SE) trajectories were numerically simulated for an ultra-high resolution Hitachi S-900 SEM with an in-lens type objective lens in order to optimize the SE detector position. The trajectories of SEs emitted from the sample were computed as follows. The electrostatic field of SE detector was calculated by a 2D rectangular finite element method (FEM). On the other hand, the magnetic field of the objective lens was calculated by a 2D axially symmetrical FEM. SE trajectories were then 3D simulated by Runge-Kutta method. The SE detector angle relative to the electron optical axis was changed from 45 degree(s) to 60 degree(s) and the SE trajectories were calculated for a various SE positions on the sample at 1 kV to 30 kV accelerating voltage. As a result, the position of the SE detector was optimized so that it gave no variation of brightness even in a low magnification of 250.