Accurate measurement of atomic chlorine radical density in process plasma with spatially resolvable optical emission spectrometer

We measure the density of atomic chlorine radicals in inductive coupled plasma (ICP) with an optical emission spectrometer (OES). Our results revealed a transition point in the dissociation rate of molecular chlorine with respect to radio frequency (RF) power; above the transition point, the signal interference in the measurement of atomic chlorine radical density by dissociated molecular chlorine becomes negligibly small. Based on the dissociation rate of the molecular chlorine, we determine appropriate conditions for accurate measurement of atomic chlorine radical density with an uncertainty of less than 2.4%. By applying argon-based optical actinometry, we measure the distribution of atomic chlorine radical density on a 12-inch wafer to predict the chrome ICP etch process used to fabricate lithographic photomasks in the semiconductor industry. We also find that the distribution of atomic chlorine radical density is in good agreement with the etch rate of the chrome thin film.