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

Pulsed supersonic molecular beam scattering has been used to study of the i nelastic scattering, trapping desorption and reactive channels for the Cl-2 + GaAs(100) thermal etching reactions. Temperature profiles of the reactiv e products GaCl, GaCl3, AsCl3, As-4 and As-2 are reported in the rang 340 t o 825 K. Angular and time-of-flight (TOF) distributions of inelastically sc attered and trapped + desorbed Cl-2 are also reported. The translational in elasticity has been measured as a function of final scattering angle at two initial translational energies, 18 and 53.4 kJ mol(-1). Angular distributi on of all reaction products are described by a cos(n)(theta) form with 1.1 less than or equal to n less than or equal to 1.3. The TOF distributions of GaCl, GaCl3 and AsCl3 reveal prompt production but with measurable time de lays (50 mu s-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 GaCl3 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 o f Arrhenius plots with common activation energies but different pre-exponen tial factors. It is argued that these do not correspond to two separate pro cesses but reflect single product desorption with a coverage-dependent acti vation energy. (C) 1998 Elsevier Science B.V. All rights reserved.