Abstract

Ellipsometers having rotating polarizers are commonly used in cases where data are to be collected automatically. Two different configurations are frequently utilized. One type involves one fixed and one rotating polarizer. With this arrangement, a dc signal and a signal at twice the rotation frequency of the polarizer are generated. The data reduction involves these signals and thus is adversely affected by fluctuations in the dc illumination level. The second configuration involves two fixed polarizers and a rotating polarizer. The second fixed polarizer introduces an additional signal at four times the frequency of the rotating polarizer. In this case, the ellipsometric data can be reduced using only the phases of the ac components, without being influenced by the fluctuations in signal amplitude. However, the mathematical form of the data reduction makes this method extremely sensitive to errors in the phases in certain circumstances. A single ellipsometer was used to evaluate both of these configurations. The only variable in the system was the presence or absence of the second fixed polarizer; the same optics, detector, and electronics were used for both systems. The results of the comparison for measurements of uncoated silicon and single-layer films on fused silica are presented.

© 1988 Optical Society of America