An intensity-monitoring technique for measuring ellipsometric transients

Abstract

Intensity-monitoring techniques make possible the measurement of rapid changes in the ellipsometHc parameters. Methods used hitherto have been suitable for measuring slight changes only and require prior knowledge of the A and ~ values for the initial surface. It is shown that larger changes can also be measured and that the values of A and ~ for the initial surface need not be known beforehand. To illustrate the method measurements are made relating to the anodising of a hanging mercury drop electrode in 1 mol dm -3 NaOH; under these conditions a thick oxide layer is known to be formed.(1) INTRODUCTION Ellipsometry is a widely used technique for in situ studies of film formation and growth on mirror-like substrates. Manual-nulling ellipsometry, however, is much too slow to permit a kinetic study of dynamic surface processes. Different types of automatic ellipsometers have been built to overcome this problem [ 1,2]. Various efforts have also been made to obtain transient measurements with simple instrumentation in the form of intensity-monitoring techniques.In the first attempts [3--5] light intensity changes were recorded by means of an ellipsometer whose components were adjusted to an extinction-setting under film-free conditions. Later [6--8] sensitivity was increased by recording transients with off-null settings of the ellipsometer components. Quantitative methods of measurement were also described [9--11].Horkans et al. [12,13] and Barrett and Parsons [14] realized that the reflectivity of the surface also contributes to the intensity expression; this factor was not taken into account in the earlier treatments.Horkans et al. [12,13] derived an expression of the formwhere I is the measured intensity, R is the reflectivity of the surface and A and are the ellipsometric parameters, a and fl_are co_mplex functions of A, 4, A and P. a and ~ can be calculated once the A and ~ of the unperturbed surface are known. Thus, if three separate measurements are performed with the same polarizer setting P and three different analyser settings A, a system of three equa-