Recombination coefficients for Cl on plasma-conditioned yttrium oxide chamber wall surfaces

Abstract

Studies of power-modulated chlorine inductively coupled plasmas (ICPs) bounded by yttria-coated chamber walls are presented. Time-resolved optical emissions from Cl and Xe actinometry trace gas were recorded over the 740–920 nm region as power at 13.56 MHz was modulated between high power and no power. The intensity ratio of Cl-to-Xe emission, proportional to Cl number density, nCl, followed the modulation in power, allowing Cl heterogeneous loss coefficients, γCl, to be obtained from a simple time-resolved, 0-dimensional model of the afterglow period that best matched computed relative changes in nCl at the beginning and end of the powered period, with γCl as the only adjustable parameter. This approach only requires a treatment of diffusion and avoids complications introduced by attempting simulations of the full modulation period. Cl recombination coefficients were determined on the mostly yttria surfaces for Cl2 ICPs (a) immediately after NF3 plasma cleaning (γCl = 0.20), (b) during long exposure to the Cl2 plasma with no substrate bias (γCl = 0.11), and (c) during Si etching with substrate bias (γCl = 0.055-0.070). For Cl2/5% O2 ICPs, these values are 0.28, 0.17, and 0.030, respectively. These results compare favorably to qualitative behavior reported previously for continuous Cl2 and Cl2/O2 ICPs in this yttria-coated chamber.