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

Pulsed supersonic molecular beam scattering has been used to study the inel astic scattering, trapping+desorption and reactive channels for the HCl + G aAs(100) thermal etching reactions. Temperature profiles of the reaction pr oducts GaCl, As-2 and Ga are reported in the range 600 to 883 K. Angular an d time-of-flight (TOF) distributions of inelastically scattered and trapped + desorbed HCl are also reported. Angular distribution of all reaction pro ducts are described by a cos(n) (theta) form with 0.95 less than or equal t o n less than or equal to 1.4. The TOF distribution of GaCl reveals rapid p roduction but with measurable time delay (50 mu s-10 ms). The As-2 signals are effectively demodulated and correspond to delayed production on the sur face with a time constant > 1 s. A kinetic model initially proposed by Bent and colleagues (C. Su, Z. Dai, W. Luo, D. Sun, M. F. Vernon and B. E. Bent , Surf. Sci., 1994, 312, 181) is extended and provides excellent fits to th e temperature profiles and the surface residence times for GaCl and As-2.