Resolution improvement of low-voltage scanning electron microscope by bright and monochromatic electron gun using negative electron affinity photocathode

Abstract

The scanning electron microscope (SEM) is a powerful tool for analyzing the surface of various specimens. SEM observation at low voltage, which is typically lower than the 1 kV range, is very effective for obtaining surface information of specimens. However, at the low voltage range, resolution is restricted by the brightness and energy spread of electron sources. Therefore, to improve the resolution, a bright and monochromatic electron source is indispensable. In this work, we focused on an electron gun with a negative electron affinity photocathode using p-type GaAs and Cs–O adsorbates. The resolution of a prototype SEM was improved by approximately 16% compared with a SEM using a conventional Schottky emission (SE)-type emitter at the acceleration voltage of 1 kV. In addition, results showed that the measured brightness was as high as an SE-type emitter (∼107 A/m2/sr/V) and the estimated energy spread was less than 0.2 eV, which was narrower than that of a cold field emission-type emitter.

Secondary electron emission and photoemission from a negative electron affinity semiconductor with large mean escape depth of excited electrons

“…[3][4][5][6] Therefore, NEASs are an important topic. [7][8][9][10][11] A NEAS with high E pom (> 20.0 keV) and large λ (> 1.0 × 10 4 Å) is called a NEAS with large λ (NEASLD), where λ is mean escape depth of secondary electrons and E pom is the incident energy of primary electrons E po corresponding to δ m . A NEASLD has several outstanding SEE parameters, such as a large δ m (≥ 100).…”