Direct observation of thermal energy transfer across the thin metal film on silicon substrates by a rear heating–front detection thermoreflectance technique

Abstract

The thermal energy transfer across molybdenum thin films on silicon substrates has been observed by a picosecond light pulse heating method under the rear heating–front detection (RF) configuration. A picosecond laser with 1550 nm wavelength is introduced as a heating laser. Since silicon is transparent and molybdenum is opaque to that wavelength, the surface of the molybdenum film on the silicon substrate side can be heated directly. Another picosecond pulse laser having a wavelength of 780 nm was incident on the front surface to observe the temperature history curve. Thin films were deposited on silicon and synthetic quartz substrates under the same batch process for present observation. The thermal diffusivities of the films are 3.8 × 10−5 m2 s−1, which were calculated from the one-dimensional heat diffusion equation considering the heat effusion from the films to the substrates. Those values were independent of the substrates. This report demonstrated that the light pulse thermoreflectance method under the RF-type configuration could be applied to a wide variety of thin films on silicon substrates that is familiar to electronics industry.