Electron-beam enhanced growth of CVD-deposited silicon on alumina

Abstract

Silicon was deposited onto polycrystalline alumina and single crystal sapphire substrates by low-pressure chemical vapor decomposition (CVD) of silane. The experiments were conducted in a custom UHV specimen/reaction chamber of a transmission electron microscope and recorded in-situ using an image intensifier-TV chain. Sapphire substrate areas were obtained by in-situ electron beam flash-heating of electron-transparent alumina films prepared by anodic oxidation of aluminum foil. Silicon was observed to grow epitaxially on those sapphire substrate areas that were impinged by the electron beam during the CVD process, while in all other recrystallized substrate areas no silicon was deposited. Silicon also deposited the original amorphous/polycrystalline alumina areas that had not been heated by or exposed to the electron beam. On the other hand, no deposit was noted in alumina areas heated by the electron beam to over 1000°C but below the sapphire recrystallization temperature. We speculate that, once the substrate surface is clean, no silicon will deposit, independent of the state of crystallinity; only where the electron beam locally stimulates the decomposition of silane, deposition of silicon on the alumina substrate is observed.