Self-aligned-double-level metal process for massively arrayed electron-beam lithography systems

Arrays of field emission micro-cathodes are the basis for massively arrayed electron beam lithography systems. We report on the fabrication of single crystal silicon field emitter arrays that have self-aligned extraction and focusing electrodes. By exposing a `capped' silicon pedestal to a lateral high temperature thermal oxidation, tips of uniform height and profile are formed, with radii of curvature typically less than 20 nm. The field emitters, the first level metal electrodes, and the second level metal electrodes are defined in the same optical lithography step and the first and second level metals are deposited during the same electron beam evaporation. In this fashion, both the extraction and focusing electrodes are formed simultaneously and are self-aligned to the field emitter. Sub- micron first level metal apertures and three micron second level metal apertures have been demonstrated using this process. The diameter of the second level metal electrode is determined by the optical lithography step. It is therefore possible to reduce the second level metal aperture by as much as 1.5 microns before necessitating the use of electron beam lithography. This process is suitable for fabricating self-aligned, second level quadrapole and octapole focusing electrodes.