Halogen etching of Si via atomic-scale processes

Abstract

Scanning tunneling microscopy (STM) studies of spontaneous halogen etching of Si(1 0 0)-2×1 and Si(1 1 1) in the range 700–1100 K are reviewed. Although the morphology depends on temperature, the steady-state removal of Si by chlorine, bromine and iodine is dominated by layer-by-layer etching that produces bounded surface roughness. For Si(1 0 0), the etch pits, step profiles, and Si regrowth structures on the exposed surfaces exhibit temperature-dependent characteristic patterns. Healing of this etched surface begins at ∼1000 K, and there is complete halogen desorption and restoration of the pre-etch morphology by ∼1100 K. Since reaction pathways involve atomic level interactions, it is possible to use the data obtained with STM to extract information about the atomic-scale processes involved during etching. Thermally activated reactions of adsorbed F show that dimer vacancies (DVs) are produced in the top layer but, more significantly, there is multilayer pitting that accounts for a surface roughening which is unique to F. For Si(1 1 1)-7×7 etching in the range 700⩽ T⩽900 K involves Si removal from adatom sites and conversion to a 1×1 periodicity that is stabilized by the halogen. In this temperature range, bilayer step flow etching dominates and regrowth structures derived from six-membered Si rings terminated by Br appear near the bilayer steps. Step flow continues at 1000 K but terrace pitting is also activated. This produces triangular bilayer pits bounded by 〈1 1 ̄ 0〉 edges. At 1100 K, etching produces disordered vacancy clusters in the adatom layer. The presence of small ordered domains amidst randomly distributed adatoms is attributed to facile local removal.