On the Etching of Silicon by Oxidants in Ammonium Fluoride Solutions: A Mechanistic Study

A comparison is made between the mechanism of anodic photo‐oxidation and the etching by oxidants of n‐type silicon in fluoride solution under conditions where no oxide layer is formed on the surface. Both oxidation processes need holes for their initiation. In the first case, holes are generated by light absorption, and in the second case, by injection from the oxidants into the valence band. Hole injection from oxidants like , which can perform only one oxidation step per molecule, results in a doubling of the anodic current of Si oxidation. This occurs by injection of unpaired electrons from Si atoms on the surface into the conduction band, as is well known for the photocurrent doubling. Other oxidants, however, like and which can perform two or more oxidation steps per molecule, prevent this additional electron injection to some extent. A mechanism is proposed for the latter reactions.