Comparison of Cl 2 and HCl adsorption on Si(100)−(2 × 1)

Abstract

The chemisorption and reaction of Cl 2 and HCl on Si(100)−(2 × 1) have been studied using Auger electron spectroscopy, high resolution electron energy loss spectroscopy (HREELS), digital electron-stimulated desorption ion angular distribution (ESDIAD), and temperature programmed desorption. At 100 K, both Cl 2 and HCl dissociatively chemisorb on the dangling bonds of Si(100). At saturation coverage, following an exposure of the Si(100) surface to Cl 2, the surface concentration of Cl is about one Cl atom per Si atom while HCl can produce a Cl coverage only about one-fourth of that achieved with Cl 2. This is the first report of a self-site-blocking effect in adsorption on a semiconductor surface. HREELS spectra indicate that both Cl 2 and HCl adsorption at 100 K give a monochloride surface species with an Si-Cl stretching frequency of about 550–600 cm −1. Digital ESDIAD measurements reveal that the Si-Cl bond angle for the monochloride from both Cl 2 and HCl adsorption is oriented on the vertical plane containing the Si-Si dimer bond and is inclined from the surface normal by 25° ± 4°. The etching products of Si(100) by Cl 2 at elevated temperatures are SiCl 2 at about 800 K and a small amount of SiCl 4 at about 500 K. For HCl, the only observed etching product is SiCl 2.