SPECTROSCOPIC ELLIPSOMETRY UNDER EXTERNAL EXCITATION

This contribution presents a new kind of spectroscopic ellipsometry un der modulated or pulsed external excitation when the sample physical p roperties (such as the refractive indices or thicknesses, eg. in a lay ered structure) can be changed by the absorption of the incident energ y. These photoinduced variations are detected through the ellipsometri c signals. The experimental procedure used is first to fix the azimuth of polarizer, next successively to set the azimuth of analyser at fou r positions with an interval of 45-degrees, then to measure the static signal and the photoinduced signal and finally to determine the ellip sometric parameters tan PSI and cos DELTA, and their variations d(tan PSI) and d(cos DELTA). So that the d(tan PSI) and d(cos DELTA) 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). Mini mum variations in the ellipsometric parameters d(tan PSI) and d(cos DE LTA) of the order of 10(-5) under modulated excitation, and 10(-6) und er pulsed excitation have been measured. This new technique has been a pplied to bulk and implanted semiconductors; dynamic indices and vario us heat diffusion processes can be observed from the stimulated spectr oscopic ellipsometry.