MORPHOLOGY OF HYDROGEN-TERMINATED SI(111) AND SI(100) SURFACES UPON ETCHING IN HF AND BUFFERED-HF SOLUTIONS

High resolution electron energy loss spectroscopy (EELS) and infrared absorption spectroscopy (IRAS) are used to characterize Si(111) and Si(100) surfaces after chemical etching in solutions of HF and buffered HF. Electron energy loss spectra confirm that the HF-etched silicon surfaces are completely terminated with hydrogen, and display essentially no loss features attributable to atomic or molecular impurities. IRAS and specular beam EELS measurements show that Si(111) surfaces become flatter as the pH of the etching solutions increases from 1 (concentrated HF) to 7.8 (ammonium fluoride solution). For high pH, the (111) surfaces are atomically flat and ideally H-terminated. In contrast the Si(100) surfaces remain rough for all pH. The surface morphology, however, depends critically on the pH and varies most for pH between 5 and 7. The EELS spectra are dominated by impact scattering and the loss features show no measurable dispersion except for the atomically smooth, ideally H-terminated Si(111) surface.