Off-axis electron holography with a dual-lens imaging system and its usefulness in 2-D potential mapping of semiconductor devices

Abstract

A variable magnification electron holography, applicable for two-dimensional (2-D) potential mapping of semiconductor devices, employing a dual-lens imaging system is described. Imaging operation consists of a virtual image formed by the objective lens (OL) and a real image formed in a fixed imaging plane by the objective minilens. Wide variations in field of view (100–900nm) and fringe spacing (0.7–6nm) were obtained using a fixed biprism voltage by varying the total magnification of the dual OL system. The dual-lens system allows fringe width and spacing relative to the object to be varied roughly independently from the fringe contrast, resulting in enhanced resolution and sensitivity. The achievable fringe width and spacing cover the targets needed for devices in the semiconductor technology road map from the 350 to 45nm node. Two-D potential maps for CMOS devices with 220 and 70nm gate lengths were obtained.