KINETIC-MODEL OF THE CHEMICAL ETCHING OF SI(111) SURFACES BY BUFFERED HF SOLUTIONS

Etching of Si(111) surfaces in HF solutions has been studied as a function of the solution pH with infrared absorption spectroscopy. The etching process results in complete H-termination of the silicon surfaces, in particular of terraces, steps and other structural defects. Polarized infrared absorption spectra of the Si-H stretching vibrations (i.e. in the region 2060-2150 cm-1) are recorded on both flat and stepped Si(111) surfaces to deduce the surface morphology as the pH of the etching solutions is varied from 2 to 8. Thus, the etching process can be characterized and modeled. A kinetic model is presented, based on different etching rates for each individual surface species. The differences are attributed to the influence of steric hindrance on the reaction rates. The strong increase of the total etching rate with the pH suggests that the initial oxidation of surface Si atoms is the rate limiting step in the etching of silicon rather than the reaction with (solvated) F- atoms.