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 Cl₂ / H₂ -based discharge for this purpose. The surface loss rate of H, k_w^H, was measured in H₂ plasma and was found to lie in the 125-500 s-1 range (γH 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 γCl in Cl₂ -based plasmas. In contrast to H₂ plasma, significant variations in the electron density may occur over the millisecond time scale corresponding to Cl₂ 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 ∼125-200 s ^-1 (0.03≤ γCl ≤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 ∼130-150 s^-1 (γCl ∼0.04), which is close to that measured at 150 W ICP power.