Effects of component imperfections on ellipsometer calibration

The accuracy of determination of film properties from ellipsometer measurements is determined by the accuracy with which ψ and Δ can be measured. This paper examines the effects of off-diagonal elements in the Jones matrices on calibration measurements in P -A, P -C -A, and P -S -A configurations. Based on these results, specific calibration procedures for determining instrument constants are given that will minimize the effects of off-diagonal elements. In particular, the method of McCrackin et al. for determining the polarizer–prism offset is found to be influenced by off-diagonal elements, and a simpler method based on extinction readings is presented. The advantages of using a sample with ρ˜=±j during P -S -A calibration measurements and a subsequent P -C -S -A check are pointed out. Polarizer–prism beam deviation in combination with photomultiplier sensitivity variations has been found to be a source of error. However, a specific procedure for determining the relative phase retardation δ′ of the compensator in the P -C -A configuration is described, which eliminates beam-deviation effects.