The interaction of Sb₄ molecular beams with Si(100) surfaces: Modulated-beam mass spectrometry and thermally stimulated desorption studies

Abstract

Modulated-beam mass spectrometry and thermally-stimulated desorption measurements were used to show that Sb4 is dissociatively chemisorbed on clean Si(100) at all temperatures investigated, from 100 to 1025°C. For Si substrate temperatures Ts less than 600°C, desorption was only observed from precursor states corresponding to Sb4 molecules adsorbed on top of a dissociatively chemisorbed Sb layer. The Sb4 sticking probability s was nearly unity and independent of θSb for θSb ≲ 0.7 monolayers (ML) but decreased rapidly with increasing θSb above 0.7 ML to reach s = 0 at a saturation coverage of θSb = 1.0 ML (referenced to the surface site density of unreconstructed Si(100), 6.8 × 1014 cm-2). Above 600°C, the desorbing Sb4 flux decreased rapidly as the saturation coverage decreased and an increasing fraction of the impinging Sb4 flux was desorbed from dissociatively chemisorbed states as Sb monomers. Sb1 was the only desorbing species detected at Ts ≳ 800°C. The activation energy for Sb1 desorption was 2.40 ± 0.1 eV for θSb ≲ 0.5 ML and 2.33 ± 0.1 eV for θSb ≳ 0.5 ML as determined by thermally stimulated desorption, surface lifetime, and saturation coverage measurements. A simple model for Sb4/Si(100) interactions involving a mobile Sb4 precursor state and repulsive lateral interactions between chemisorbed Sb adatoms was used to calculate desorption rate kinetics and found to provide excellent agreement with the measured data. © 1986.