Thermal Diffusivity Measurements of Metal Thin Films by Means of the Picosecond Thermoreflectance Technique

摘要

The National Metrology Institute of Japan (NMIJ)/AIST has been developing a picosecond thermoreflectance technique in order to measure thermophysical properties of submicrometer thin films. Ultra fast change of thin film temperature is observed by change in reflection intensity of probe picosecond pulses arriving at the surface with controlled delay time from the, heating picosecond pulse. The rear face heating / front face detection type (RF type) picosecond thermoreflectance method was developed by NMIJ/AIST for the first time in the world, in which a metal thin film is heated by a picosecond laser pulse through a transparent substrate and temperature change at the front surface is detected with the thermoreflectance method. This configuration is essentially same as the laser flash method, which is the standard measuring method of thermal diffusivity of bulk materials. Thermal diffusivity can be calculated from the heat diffusion time across the thin film and the film thickness with small uncertainty.