Surface loss rates of H and Cl radicals in an inductively coupled plasma etcher derived from time-resolved electron density and optical emission measurements

A study is undertaken of the loss kinetics of H and Cl atoms in an inductively coupled plasma (ICP) reactor used for the etching of III-V semiconductor materials. A time-resolved optical emission spectroscopy technique, also referred to as pulsed induced fluorescence (PIF), has been combined with time-resolved microwave hairpin probe measurements of the electron density in a pulsed Cl(2)/H(2)-based discharge for this purpose. The surface loss rate of H, k(w)(H), was measured in H(2) plasma and was found to lie in the 125-500 s(-1) range (gamma(H) surface recombination coefficient of (0.006-0.023), depending on the reactor walls conditioning. The PIF technique was then evaluated for the derivation of k(w)(Cl), and gamma(Cl) in Cl(2)-based plasmas. In contrast to H(2) plasma, significant variations in the electron density may occur over the millisecond time scale corresponding to Cl(2) dissociation at the rising edge of the plasma pulse. By comparing the temporal evolution of the electron density and the Ar-line intensity curves with 10% of Ar added in the discharge, the authors show that a time-resolved actinometry procedure using Ar as an actinometer is valid at low to moderate ICP powers to estimate the Cl loss rate. They measured a Cl loss rate of similar to 125-200 s(-1) (0.03 <= gamma(Cl) <= 0.06) at 150 W ICP power for a reactor state close to etching conditions. The Cl surface loss rate was also estimated for high ICP power (800 W) following the same procedure, giving a value of similar to 130-150 s(-1) (gamma(Cl) similar to 0.04), which is close to that measured at 150 W ICP power. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3330766]