REGRESSION CALIBRATION METHOD FOR ROTATING ELEMENT ELLIPSOMETERS

A new method for calibrating rotating element ellipsometers is described. This procedure is similar in concept to the residual calibration procedure developed by Aspnes (D. E. Aspnes, J. Opt. Soc. Am., 64 (1974) 812; D. E. Aspnes and A. A. Studna, Appl. Opt., 14 (1975) 220). However, instead of using a parabolic approximation to fit the calibration data, the calibration data are fitted to the exact expressions that model the response of the optical system, using an iterative regression algorithm. The regression calibration method offers many advantages: (1) accurate calibration can be obtained on nearly any sample; (2) highly accurate values of the ellipsometric parameters PSI and DELTA are also extracted from the regression analysis; (3) the quality of the regression fit can be used to quantify the accuracy of the optical system. The method may also be easily extended to account for non-ideal elements in the optical system, such as polarization-dependent sensitivity in the detector system.