COMPARISON OF CL2 AND HCL ADSORPTION ON SI(100)-(2 X-1)

The chemisorption and reaction of Cl2 and HCl on Si(100)-(2 x 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 Cl2 and HCl dissociatively chemisorb on the dangling bonds of Si(100). At saturation coverage, following an exposure of the Si(100) surface to Cl2, the surface concentration of Cl is about one Cl atom per Si atom while HCI can produce a Cl coverage only about one-fourth of that achieved with Cl2. This is the first report of a self-site-blocking effect in adsorption on a semiconductor surface. HREELS spectra indicate that both Cl2 and HCI 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 Cl2 and HCI adsorption is oriented on the vertical plane containing the Si- Si dimer bond and is inclined from the surface normal by 25-degrees +/- 4-degrees. The etching products of Si(100) by Cl2 at elevated temperatures are SiCl2 at about 800 K and a small amount of SiCl4 at about 500 K. For HCI, the only observed etching product is SiCl2.