STEP-FLOW MECHANISM VERSUS PIT CORROSION - SCANNING-TUNNELING MICROSCOPY OBSERVATIONS ON WET ETCHING OF SI(111) BY HF SOLUTIONS

Scanning-tunneling microscopy observation of atomic structures reveals strongly anisotropic rates for etching of Si(111) surfaces in weakly alkaline HF solutions and negligible etch rates for strongly acidic solutions, caused by increasingly more reactive di- and tri-hydride Si atoms at higher OH- concentrations. Here, slow nucleation of vacancies in monohydride-terminated (111) terraces is followed by rapid etching of newly exposed dihydride Si atoms. This results in a "step flow" etch mechanism where extended (111) terraces are eroded along the most stable [110BAR] steps with (111) microfacets.