ELSEVIER Surface Science 356 (1996) 75-91 surface science The adsorption and bonding of chlorine at silicon (100) investigated using ESD/ESDIAD with C1÷ and C1- ions Q. Guo, D. Sterratt, E.M. Williams ,,1 IRC in Surface Science, The University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK Received 26 July 1995; accepted for publication 13 December 1995 Abstract The adsorption of chlorine on Si(100) 2 × 1 surface has been studied using electron stimulated desorption (ESD) and electron stimulated desorption ion angular distribution (ESDIAD) in conjunction with AES and gas uptake techniques. ESDIAD and ESD measurements were performed on negative as well as positive atomic chlorine species, and the responses with the different polarity of charged species are not seen as complementary. Gas uptake at the surface proceeds initially with a high sticking probability with the atomic chlorine resulting from dissociation not being limited to single dimer sites. ESDIAD studies with positive CI ÷ ions reveal normal and off-normal beams associated with symmetric and asymmetric dimers, with relative contributions depending on surface coverage and temperature. Transformations between bonding configurations seen in positive ion ESDIAD are linked with lateral interactions in the adsorbate layer, and their influence is also evident in the forms of the ion yields of both polarity of species with changing coverage. Negative chlorine ions exhibit a predominance of emission around the surface normal, and are produced via a dipolar dissociation process. Missing atom defect sites with an associated high electron density are postulated as playing a central role in their production. The desorption of positive chlorine ions follows mainly from a two-hole, one-electron (2hle) repulsive state initiated by the ionisation of the C1 3s level. Keywords: Angle resolved DIET; Chemisorption; Chlorine; Electron stimulated desorption (ESD); Low index single crystal surfaces; Silicon; Solid-gas interfaces 1. Introduction The study of the interaction between chlorine and silicon surfaces is an important subject in regard to the operation of dry etching processes in VLSI technology [ 1] and is currently the focus of much scientific interest. The application of surface science techniques has undoubtedly enhanced the understanding of many fundamental processes * Corresponding author. Fax: +44 151 708 0662; e-mail: emw@ssci.liv.ac.uk 1 Also at Department of Electrical Engineering and Electronics, The University of Liverpool. relating to the geometric and electronic structure of the chlorine-silicon interface [2-14]. Compared with ESDIAD (electron stimulated desorption ion angular distribution) of F ÷ ions from Si(100), where only off-normal emission associated with tilted Si-F bonds is observed [ 11,15], the findings of ESDIAD with C1÷ ions are more complicated with both normal and off-normal emission having been reported [11,12,14]. This is also reflected in X-ray adsorption spectroscopy (XAS) 1-9] and angle resolved photoemission results [3] where normal as well as off-normal Si-C1 bond directions have been proposed. As will be demonstrated in the present paper, the conditions of chlorine cover- 0039-6028/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved PH S0039-6028(96)00011-8