ELLIPSOMETRIC APPROACH FOR EVALUATION OF OPTICAL-PARAMETERS IN THIN MULTILAYER STRUCTURES

An ellipsometric approach has been proposed for the determination of t he optical parameters of a transition layer existing between a substra te and a grown film. In the approach the functions tan psi cos DELTA a nd tan psi sin DELTA vs. top layer thickness are approximated by the a ppropriate polynomials. The absolute terms of the polynomials are conn ected with the ellipsometric angles psi' and DELTA' related to the sub strate-transition layer system. For finding the tan psi cos DELTA and tan psi sin DELTA vs. top layer thickness dependences it is necessary either to etch gradually the top layer and to make ellipsometric measu rements after each etching step or to trace ellipsometrically the grow th process of the film in situ. Since the approximation does not requi re the complete removal of the top layer, the proposed approach is ver y useful for obtaining the optical parameters of a thin intermediate f ilm in a double-layer-substrate structure when complete removal of the top layer is impossible without damaging the layer underneath. The er ror introduced by the approximation is approximately 0.016-degrees, wh ich is within the range of the standard ellipsometric accuracy for psi and DELTA.