Improving the accuracy of ellipsometers for multilayer film measurements using incident angle verification and retrieval

Ellipsometers have long been recognized as the best instrument for measuring the refractive index and thickness of thin films. Two aspects of ellipsometry have important implications. First, the refractive index and thickness of the thin film can be retrieved by using the proper layer model and by adopting an appropriate numerical-inversion technique. Secondly, the accuracy of the incident light beam angle is important in retrieving the correct answer. The main focus of this paper is to discuss the effects of the incident angle correction algorithm on the accuracy of the parameters retrieved, and then try to compensate for the inaccuracy resulting from the angle-varying mechanism of the ellipsometer. Detailed simulations have been performed to examine the accuracy of the optical indices and thin film thickness under various measurement conditions. From the simulation result, it has been shown that adopting the incident angle correction algorithm can be improve the accuracy of the ellipsometer. This leads us to believe that the accuracy of an ellipsometry system can be further improved if the incident angle correction algorithm is included in the data-retrieving algorithm.