UHV-TED study of clean Si(100) surface structures

Abstract

Detailed information about the structure of silicon surfaces is very important prior to deposition of metal contacts. Though transmission electron diffraction is sensitive to the atomic structures of both the surface and the bulk, under appropriate conditions, information on the structure of the surface can be obtained from a careful analysis of the diffraction spot intensities.Since Si(100) surface is highly reactive (sticking coefficient for water = 1), preparation and observation of clean surfaces necessitates ultra-high vacuum (UHV) conditions. A thin sample of Si(100) (B doped to 1 ohm-cm) was prepared for observation inside a Hitachi UHV-H9000 300keV electron microscope (stable operation pressure ∼9xl0-11 Torr). It was mechanically polished, dimpled and ion-milled before being transferred into a UHV surface science chamber attached to the microscope. In situ sample preparation carried out inside this chamber involved a combination of sputtering using 2-4 keV argon ions (to clean the surface) and electron-gun annealing cycles (to order the surface).