Layer-by-layer etching of Si(100)-2 x 1 with Br2: A scanning-tunneling-microscopy study.

Layer-by-layer etching of Si(100)-2×1 at 900 K with Br 2 has been studied with scanning tunneling microscopy. Preferential etching of S B (ragged) step edges dominates at low Br 2 exposures but etch pits that are one layer deep (vacancy islands) also appear on the terraces. The elongated shapes of the vacancy islands indicate that etching proceeds at a much faster rate along the dimer row direction than perpendicular to it. Chains and two-dimensional islands due to Si regrowth appear on the terraces. With increased exposure, the vacancy islands form networks on the terraces and become connected to step edges