Spectroscopic ellipsometry under external excitation

This contribution presents a new kind of spectroscopic ellipsometry under modulated or pulsed external excitation when the sample physical properties (such as the refractive indices or thicknesses, e.g. in a layered structure) can be changed by the absorption of the incident energy. These photoinduced variations are detected through the ellipsometric signals. The experimental procedure used is first to fix the azimuth of polarizer, next successively to set the azimuth of analyser at four positions with an interval of 45°, then to measure the static signal and the photoinduced signal and finally to determine the ellipsometric parameters tan ψ and cos Δ, and their variations d(tan ψ) and d(cos Δ). So that the d(tan ψ) and d(cos Δ) can be recorded as a function of time or frequency, the time resolution is as fast as a few nanoseconds (limited by our laser pulse duration). Minimum variations in the ellipsometric parameters d(tan ψ) and d(cos Δ) of the order of 10−5 under modulated excitation, and 10−6 under pulsed excitation have been measured. This new technique has been applied to bulk and implanted semiconductors; dynamic indices and various heat diffusion processes can be observed from the stimulated spectroscopic ellipsometry.