A metrological generalized ellipsometer for traceable measurements

A traceable ellipsometer is described that uses two photoelastic modulator-polarizer pairs operating at different frequencies. The ellipsometer is capable of measuring all 16 elements of the sample Mueller matrix with four measurements made at different azimuth orientations of the photoelastic modulator-polarizer pairs. The time-dependent intensity of the light beam is extremely complicated but can be found using a Fourierbased software lock-in amplifier, if the relative phases of the phase modulators are known from reference measurements. We demonstrate a new experimental data acquisition setup that simultaneously digitizes signal and reference signals together with a new set of phase equation relating the signals that makes it possible to find the intensities without a prior knowledge of the relative modulator phases. Ellipsometry is a non-imaging technique that finds the dimensions and optical parameters by optimizing them in a mathematical forward-scattering model. The dimensions are obtained from a best-fit procedure between the measured and the calculated ellipsometric parameters. In this paper we present a method of least squares that takes estimates and uncertainties for all measured parameters (ellipsometric parameters, angle of incidence, azimuth angle, wavelength) and model parameters with specified constraints as input values. The output of the method consists of adjusted measured and modeled parameters that satisfy the imposed constraints together with the uncertainties of these parameters. The advanced data acquisition and analyzing methods facilitate both the establishment of the traceability and the reduction of measurement uncertainty.