Thermal-wave detection and thin-film thickness measurements with laser beam deflection

A new technique has been developed that employs highly focused laser beams for both generating and detecting thermal waves in the megahertz frequency regime. This technique includes a comprehensive 3-D depth-profiling theoretical model; it has been used to measure the thickness of both transparent and opaque thin films with high spatial resolution. Thickness sensitivities of ±2% over the 500–25,000-Å range have been obtained for Al and SiO2 films on Si substrates.