Micromachined single-crystal silicon electron lenses

Abstract

We report on the design, simulation, and fabrication of micromachined single-crystal silicon electrostatic lenses and lens arrays. The lenses consist of two or three high-aspect-ratio silicon tubes, which are fabricated from a single silicon substrate using a self-aligned process. The tubes are isolated from each other and the substrate by long (>20 μm) thermal silicon oxide spacers. Single microlenses, multipole lens elements, and microlens arrays have been fabricated with tube diameters ranging from 5 to 50 μm and lengths from 5 to 240 μm. After a brief review of scaling considerations for electron microsource and microlenses, a detailed description of the fabrication process is presented. This process is also applicable to a wide variety of other multiple level (array) structures. The electron-optical properties of the microlenses are discussed. Numerical simulation results are used to predict the spherical and chromatic aberration coefficients and to investigate the effects of mechanical tolerances (misalignment, tilt, ellipticity).