Laser-induced thermal size effects in micro-Raman thermal conductivity measurements

Thermal conductivity measurements of submicrometer structures are at the core of the efficient power design of semiconductor devices. Micro-Raman spectroscopy measures thermal conductivity in a fast, nondestructive, and non-contact manner. However, the focused laser heating in micro-Raman experiments may cause drastic thermal size effects. To date, the role of such effects in the accuracy and limitations of the measurement has not been addressed. Here, we present an advanced thermal model to capture the role of material properties, laser power, and film thickness in the thermal size effects, based on the three-dimensional (3D) gray phonon Boltzmann transport equation. Recalling that laser-induced thermal size effects can lead to unexpectedly high local temperatures, even damaging the measured materials, our advanced 3D model gains particular importance for the accurate measurements of directional thermal conductivities in submicrometer structures using future high-resolution optical pump-probe techniques.