Pattern formation and shadow instability in collimated energetic molecular beam growth of silicon

Abstract

Epitaxial silicon thin films were deposited on Si(100) substrates at variable angles of incidence using well-collimated supersonic molecular beams of disilane, Si2H6. The resulting thin-film surface topology has been examined using atomic force microscopy. Rough surface morphology is observed as the beam angle of incidence is increased above ∼60°. Thin films deposited at substrate temperatures ⩽600 °C exhibit anisotropic features, which are elongated in a direction perpendicular to the incident beam. Increasing the substrate temperature leads to films with increased root-mean-square roughness and larger characteristic features, maintaining a nearly constant feature aspect ratio. Analysis indicates that the film feature size is controlled by a competition between roughening driven by the shadow instability and smoothening driven by surface mass transport.