An XPS study of the SF6 reactive ion beam etching of silicon at low temperatures

The surface chemistry of silicon bombarded at low temperature with a beam e xtracted from a SF6 microwave plasma has been studied using quasi in situ X -ray photoemission spectroscopy. At 123 K and when no ions strike the surfa ce, strong adsorption of neutral SFx species generated in the plasma is obs erved. In these conditions, physisorbed SF3 and SF4 species are detected bu t the presence of SF6 molecules is not observed. Increasing the ion energy to 360 eV and the ion current density to 650 mu A cm(-2) allows to desorb t he adsorbed species and to maintain the adsorbed layer well below 75 Angstr om. At room temperature, the presence of chemisorbed sulfur, chemisorbed SF 3 radicals and physisorbed SF4 species is observed for 60 eV and 5 mu A cm( -2) ion bombardment conditions. Physisorbed SF species and chemisorbed sulf ur are detected after ion bombardment at 360 eV and 650 CIA cm(-2). During these different experiments, the presence of Fe and Cr due to the contamina tion of the beam is also observed. Results of this XPS analysis are correla ted with etch rates measurements presented in a previous work. The role of ion-stimulated desorption and ion-induced reaction mechanisms on the silico n surface chemistry is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.