Micro-Raman Thermometry of Laser Heated Surfaces

Optically powered devices are typically irradiated by high intensity lasers and rely on the temperature excursion generated by the laser for operation. While numerical modeling can estimate the temperature profile of the irradiated devices, only direct measurements can determine the actual device temperatures. Available surface thermometry techniques, such as infrared imaging, scanning thermal microscopy and thermoreflectance are generally incompatible with an optical powering scheme, the micron-scale layer thicknesses of microsystem devices, or both. In this paper we discuss the use of micro-Raman thermometry to obtain the first spatially-resolved temperature measurements of various polycrystalline silicon (polysilicon) surfaces heated with an 808 nm continuous wave (CW) laser at a 60° angle of incidence. The micron-scale resolution of the micro-Raman technique permitted mapping of the surface temperature in the vicinity of the heating laser spot and throughout the device. In addition to discussing the requirements for accurate data collection, the implications of optical interference on the heated structures are also considered.