Layer-by-layer etching of Si(100)-2×1 withBr2: A scanning-tunneling-microscopy study

Layer-by-layer etching of Si(100)-2×1 at 900 K with ${\mathrm{Br}}_2$ has been studied with scanning tunneling microscopy. Preferential etching of ${\mathit{S}}_{\mathit{B}}$ (ragged) step edges dominates at low ${\mathrm{Br}}_2$ 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. Studies of Si(100) after extended Br etching reveal global morphologies that are steady state and expose no more than three layers on a given terrace. Hence, the surface roughness is bounded.