Estimating and controlling atomic chlorine concentration via actinometry

Actinometry has been used as the basis of a successful sensor for controlli ng fluorine concentration in fluorocarbon plasmas commonly employed in etch ing. An analogous sensor would be useful for chlorine plasmas as well. One problem with actinometry in Cl-2 plasmas is that excitation can occur by el ectron impact dissociation and by dissociative attachment, leading to poten tial ambiguity between the intensity of observed chlorine emission in a pla sma and the actual concentration of chlorine. On the basis of a simple mode l, this paper analyzes the consequences of the dissociative excitation path way on the accuracy of the estimation and control of chlorine concentration via actinometry. When the contribution of the dissociative excitation path way is known, it is shown that asymptotic observer theory can be used to im prove the accuracy of the estimation of chlorine concentration.