Thin SiO2 layers on Si(111) with ultralow atomic step density

The morphologies of the oxide surface and of the ${\mathrm{Si–SiO}}_2$ interface that form on special Si(111) substrates have been studied by atomic force microscopy (AFM). The substrates are totally free of atomic steps or have very low step density. Step-free regions are formed on patterned Si(111) by thermal processing. AFM scans of the same areas prior to oxidation, after oxidation, and after chemical removal of the oxide allow the relative roughnesses to be compared. The step structure of the Si(111) substrate is translated to the oxide surface even for ${\mathrm{SiO}}_2$ layers in the 10 nm range. The lack of significant displacement of the atomic steps at the ${\mathrm{Si–SiO}}_2$ interface indicates that the oxide grows by a layer-by-layer mechanism.