REACTIONS OF CHLORINE WITH SI(100) AND SI(111) - ADSORPTION AND DESORPTION-KINETICS

Adsorption of atomic and molecular chlorine on the Si(100) and Si(111) surfaces, and the desorption kinetics of the formed chlorosilicon species have been investigated. The saturation coverage after Cl2 exposure is 1.0 +/- 0.1 ML on Si(100) and 1.4 +/- 0.1 ML on Si(111), while in atomic chlorine exposure the uptake slows down considerably above almost-equal-to 1.5 ML on both surfaces. The desorption kinetics of the major chiorosilicon products, SiCl2 and SiCl4, is first order in chlorine coverage under 850 K. Above 900 K the SiCl2 desorption kinetics is different on Si(111) and Si(100). Desorption of SiCl2 above 900 K from Si(111) is second order in chlorine coverage. From the Si(100) surface above 900 K the SiCl2 desorption rate is first order at 0.1 ML < theta(Cl) < 0.4 ML, increases steeply at almost-equal-to 0.5 ML and becomes zero order and negative order in chlorine coverage as the saturation coverage (1.0 ML) is approached. The second order kinetic parameters extracted for SiCl2 desorption from Si(111) above 950 K at theta(Cl) almost-equal-to 0.3 ML are nu(d) = 2000 cm2/s and E(d) = 83 kcal/mol. When empty surface sites are available, desorption of SiCl(n) (n > 1) is accompanied by dissociation of some of the SiCl(n) on the surface to form SiCl(ads).