Reactive scattering study of etching dynamics: Cl 2 on GaAs(100)

Abstract

Pulsed supersonic molecular beam scattering has been used to study of the inelastic scattering, trapping desorption and reactive channels for the Cl 2+GaAs(100) thermal etching reactions. Temperature profiles of the reactive products GaCl, GaCl 3, AsCl 3, As 4 and As 2 are reported in the range 340 to 825 K. Angular and time-of-flight (TOF) distributions of inelastically scattered and trapped+desorbed Cl 2 are also reported. The translational inelasticity has been measured as a function of final scattering angle at two initial translational energies, 18 and 53.4 kJ mol −1. Angular distribution of all reaction products are described by a cos n ( θ) form with 1.1≤ n≤1.3. The TOF distributions of GaCl, GaCl 3 and AsCl 3 reveal prompt production but with measurable time delays (50 μs–5 ms). The As 4 and As 2 signals are effectively demodulated and correspond to delayed production on the surface with a time constant >1 s. The surface time profiles for GaCl and GaCl 3 are each well described by double-exponential decays for production desorption from the surface. The temperature dependence of the time constants for each product yield pairs of Arrhenius plots with common activation energies but different pre-exponential factors. It is argued that these do not correspond to two separate processes but reflect single product desorption with a coverage-dependent activation energy.