AUTOMATIC ROTATING ELEMENT ELLIPSOMETERS - CALIBRATION, OPERATION, AND REAL-TIME APPLICATIONS

In a typical reflection ellipsometry experiment, one characterizes the polarization state change that a polarized light beam undergoes upon reflection from a specular surface. This measurement provides ρ≡r p/rs, where rp and rs are the complex amplitude reflection coefficients of the surface for p- and s-polarized waves. Nearly 15 years have passed since the development of automatic ellipsometers along with the detailed calibration, error analysis, and data reduction procedures to be used with them. More specifically, these powerful instruments permit (1) determination of bulk dielectric functions and nondestructive depth profiling of static multilayered materials through measurements as a function of photon energy and (2) characterization of dynamic surfaces in adverse environments through measurements as a function of time at fixed photon energy. In the 15 intervening years, the major research thrusts in ellipsometry have been the exploitation of these instruments in materials and process characterization in diverse areas of materials science and electrochemistry. One of the simplest and most popular automatic ellipsometers is a photometric instrument in which one or more of the optical elements (polarizer, compensator, and/or analyzer) is designed to rotate continuously. In this article, the major developments in rotating element ellipsometry are reviewed since the first report of an automatic rotating analyzer instrument by Cahan and Spanier in 1969. The topics covered include rotating element configurations, calibration, characterization of errors and imperfections, absolute accuracy, data reduction, precision, and a review of the real-time applications accessible to these instruments. The sections on calibration, errors, and data reduction include new material and are written from a practical standpoint to assist in instrumentation setup and troubleshooting. The development and improvement of next-generation rotating element instruments that employ optical multichannel detectors to collect spectroscopic data on dynamic surfaces with time resolution as short as 5 ms now defines the forefront of research in this field.