Infrared ellipsometer for the study of surfaces, thin films, and superlattices

Abstract

An automatic infrared ellipsometer for the study of surface and interface phenomena has been constructed. The system is based on a Fourier transform spectrometer that we equipped with an ellipsometer unit. Polarizers and analyzers are of the ion-etched wire-grid type. Their rotation is governed by means of a computer-controlled stepping-motor system. A discussion of calibration procedures for the infrared range is given, and special attention is given to the problem of selecting the best measurement strategy. The polarization state of the reflected beam is determined by measuring the intensity at 72 regularly spaced polarizer/analyzer settings. It is found that the effects of interferometric polarization, beam wandering, and detector dichroism cannot be neglected. However, these error sources have been eliminated by analyzing the zeroth, second, and fourth harmonic components of the azimuthally recorded intensity. Both the multiplex advantage of Fourier transform spectroscopy and the phase sensitivity ofellipsometry are combined in this instrument. Measurements on superconducting films, superlattices, and doped GaAs films are reported.