Scattering of Cl 2 beams from Si(100) for kinetic energies up to 2.6 eV: implications for sticking coefficients and reaction product formation

Abstract

Scattering of pulsed hyperthermal beams of Cl 2 by a Si(100) surface is studied at 300 K and 45° incidence. The beams are produced by laser vaporization of cryogenic Cl 2 films and contain ≤ 14% Cl. The beams have a broad range of translational kinetic energies up to 6 eV; with velocity selection, beams with a narrow kinetic energy distribution and energies up to 2.6 eV are also used. The scattered flux from Si is quantified by comparing to scattering by quartz, after the angular differences are taken into account. The angular distributions of the scattered species from Si(100) show a cos 3θ isotropic scattering contribution, as well as a narrow Gaussian distribution about the specular angle, with little alteration of the kinetic energy in the scattering process. From quartz, the angular distribution is isotropic and the kinetic energy of the scattered species is considerably broadened to lower energy. The amount of Cl 2 flux scattered by the silicon surface decreases with increasing kinetic energy of the incident beam, but increases with increasing coverage of chlorine on the surface. From the scattered fluxes, the upper limit for the initial sticking coefficient, S 0, ranges from 24 ± 7% for a beam with 〈 E〉 = 0.5 eV to 83 ± 3% for a beam with 〈 E〉 = 2.6 eV. Comparison of the scattering results with Auger measurements of the surface chlorination supports previous studies which show an onset for etching product formation when the mean translational kinetic energies are near or above 2 eV.