High Precision Scanning Ellipsometer

We describe the design, construction, alignment, and calibration of a photometric ellipsometer of the rotating-analyzer type. Data are obtained by digital sampling of the transmitted flux with an analog-to-digital converter, followed by Fourier transforming of the accumulated data with a dedicated minicomputer. With an operating mechanical rotation frequency of 74 Hz, a data acquisition cycle requires less than 7 msec. The intrinsic precision attainable is high because precision is limited only by shot noise or intrinsic source instabilities, even when relatively weak continuum lamps are used as light sources. Precision may be improved by accumulating the data for consecutive cycles at a fixed wavelength. The system allows complex reflectance ratios to be determined as continuous functions of wavelength from the near infrared to the near ultraviolet spectral range. Data reduction programs can be modified to calculate complex refractive index or dielectric function spectra, or film thicknesses and refractive indices, as well as the usual ellipsometric parameters tanpsi, cosDelta.