Ellipsometric Study of Orientation‐Dependent Etching of Silicon in Aqueous KOH

Ellipsometric measurements (in conjunction with observations of reflectance and cell current and voltage) have been performed in for Si wafers, of various crystallographic orientations and dopant types, during growth of surface films under anodic and cathodic bias and during open‐circuit etch back. The optical effects have been modeled in terms of the formation and removal of thin films on the Si surface, with contributions, in some cases, from surface roughness. Changes in the thickness and stoichiometry of the surface phase during various treatments provide a basis for a model of the Si etching chemistry and for the orientation dependence of the etch rate.