Estimating and controlling atomic chlorine concentration via actinometry

Actinometry has been used as the basis of a successful sensor for controlling fluorine concentration in fluorocarbon plasmas commonly employed in etching. An analogous sensor would be useful for chlorine plasmas as well. One problem with actinometry in [Cl.sub.2] plasmas is that excitation can occur by electron impact dissociation and by dissociative attachment, leading to potential ambiguity between the intensity of observed chlorine emission in a plasma and the actual concentration of chlorine. On the basis of a simple model, this paper analyzes the consequences of the dissociative excitation pathway on the accuracy of the estimation and control of chlorine concentration via actinometry. When the contribution of the dissociative excitation pathway is known, it is shown that asymptotic observer theory can be used to improve the accuracy of the estimation of chlorine concentration.