INVESTIGATION OF THE KINETIC MECHANISM OF THE AR+-ION-ENHANCED CL2/GAAS(110) ETCH RATE PHENOMENON - DEPENDENCE ON THE REACTANT FLUX RATIO

The effect of 1 keV Ar+-ion bombardment on the reaction of a high-intensity pulsed Cl2 supersonic beam with GaAs{110} at room temperature has been investigated by measuring time-of-flight wave forms of the unreacted Cl2 scattered from the surface as a function of the incident Ar+/Cl2 flux ratio and the kinetic energy of the Cl2 beam. Measurements made with a high-kinetic-energy Cl2 beam (E(i) = 0.48 eV) show that ion bombardment enhances the dissociative chemisorption of Cl2 Species trapped at the surface in a weakly adsorbed precursor state and has a negligible affect on Cl2 Species that enter the direct-inelastic scattering channel. Quantitative analysis of the room-temperature etch rate, determined using a low-energy Cl2 beam (E(i) = 0.14 eV), indicates a strong dependence on the incident Ar+/Cl2 flux ratio. Typical values range between 0.02 and 0.10-mu-m/min. These etch rates are approximately 100 times larger than the Ar+-ion sputter desorption rate expected for the ion flux used in these measurements. Under high Cl2 flux conditions the kinetics of the ion-assisted etch reaction exhibits a first-order dependence on Ar+ flux. Postetch surface stoichiometric measurements indicate a correlation of an increasingly As-rich surface layer with an increasing etch rate. An As-rich surface layer indicates that the relative Ga to As product desorption rate is larger under the condition of stoichiometric ion-assisted etching. It is proposed that the ion-enhanced etch rate phenomenon results from the fact that ion bombardment opens a momentum desorption channel facilitating the nonthermal preferential desorption of a thermal rate-limiting Ga-intermediate species. In addition, ion bombardment creates Cl2 dissociation sites by both a physical and a chemical mechanism which leads to an increase in the concentration of reactive surface intermediate species.