Anodization of nanoscale Si layers in silicon-on-insulator structures

Anodization of silicon-on-insulator (SOI) layers is studied as a function of the SOI layer thickness in the range from 5 to 500 nm. It is found that thinning of the silicon film to less than 100 nm is accompanied by a sharp decrease in the anodization rate. For SOI films thinner than or on the order of magnitude of ∼10 nm, the limiting thickness of the oxidized silicon layer is 0.4 nm. It is shown that the main cause of a decrease in the anode current efficiency during oxidation of nanoscale Si layers is an increase in the resistance of the silicon active layer, which limits the hole current in the film plane and, hence, the number of silicon cations coming to the SiO₂/electrolyte interface for their subsequent oxidation.