THERMAL-WAVE MEASUREMENT OF THIN-FILM THERMAL-DIFFUSIVITY WITH DIFFERENT LASER-BEAM CONFIGURATIONS

This work investigates and compares three laser-based ac heating metho ds for measuring thermal diffusivity of free-standing thin-film struct ures. These methods employ a modulated laser beam as the heating sourc e and a miniature thermocouple as the temperature sensor. Three laser beam configurations including uniform illumination, a line? and a poin t are utilized as the heating sources. Different models and systems ar e developed for these beam configurations. Samples studied include a G aAs/AlGaAs two-layer thin-film structure, a periodic GaAs/AlAs thin-fi lm structure, and a silicon film. Both the phase and amplitude signals of the ac temperature rise of samples are used to derive their therma l diffusivities. It is found that the uniform illumination method is m ore susceptible to error than the other two configurations due to two- dimensional effects. Both the line and the point source configurations yield satisfactory results. (C) 1996 American Institute of Physics.