F-2, H2O, and O-2 etching rates of diamond and the effects of F-2, HF and H2O on the molecular O-2 etching of (110) diamond

Oxidation kinetics of natural (110) diamond by oxygen and water were investigated using in situ Fizeau interferometry. Apparent activation energies of 53 and 26 kcal mol(-1) were obtained for the etching of (110) type Ia diamond by O-2 and H2O respectively. The etch rate was found to follow second-order kinetics with respect to O-2 pressure in the pressure range 0.04-10 Torr. For water over the vapour pressure range 0.1-2 Torr, the reaction has a reaction order near unity. The diamond (110) surface was impervious to etching by molecular fluorine at all temperatures up to 1300 degrees C. Fluorine, hydrogen fluoride and water were found to inhibit the molecular oxygen etching of diamond. Below 900 degrees C, oxidation is inhibited by the addition of F-2 and HF presumably by blocking reactive sites on the diamond surface through formation of C-F bonds. Above 900 degrees C, the fluorine is thought to desorb from the diamond (110) surface, rendering the surface susceptible to further oxidation. Addition of water below 800 degrees C was found to retard etching by molecular oxygen. This is attributed to the formation of C-OH bonds, analogous to C-F.