Effects of surfaces on H-atom concentration in pulsed and continuous discharges

Abstract

We report on the effect of Si and GaAs substrate materials on the hydrogen atom ground-state concentration profiles in 10 MHz pulsed and continuous rf discharges. We measure absolute hydrogen atom concentrations in the discharge via two-photon absorption laser-induced fluorescence. The spatial profiles of the H atoms in an unloaded plasma reactor show a concentration on the order of 1014 atoms/cm3 at the center of the discharge, a concentration relatively constant until it sharply decreases at a 3–4 mm distance away from the electrode surfaces. However, when the discharge is loaded with semiconducting materials, the H-atom concentration drastically increases at the region adjacent to the semiconducting surfaces. The evolution of these profiles obtained in a pulsed discharge suggests that the H atoms are produced in localized regions in the discharge, and they diffuse towards the center and the confining surfaces. We discuss the validity of a diffusion model which treats the metallic surfaces as sinks, and the Si and GaAs surfaces as nearly perfect reflectors.