REGRESSION CALIBRATION METHOD FOR ROTATING ELEMENT ELLIPSOMETERS

A new method for calibrating rotating element ellipsometers is describ ed. This procedure is similar in concept to the residual calibration p rocedure 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). Howe ver, instead of using a parabolic approximation to fit the calibration data, the calibration data are fitted to the exact expressions that m odel 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) hig hly accurate values of the ellipsometric parameters PSI and DELTA are also extracted from the regression analysis; (3) the quality of the re gression fit can be used to quantify the accuracy of the optical syste m. The method may also be easily extended to account for non-ideal ele ments in the optical system, such as polarization-dependent sensitivit y in the detector system.