Session: 11-05-01: Thermophysical Properties: Characterization and Modeling Across Scales

Paper Number: 150683

150683 - Frequency Domain Thermoreflectance Measurements of Semiconductors With No Metal Transducer Layer 

Microelectronic devices often fail due to overheating, making accurate understanding of thermal properties critical to effective thermal design. Thermal property measurement techniques have advanced substantially in the recent decades, with pump-probe thermoreflectance techniques occupying a prominent position in understanding bulk thermal transport, thermal transport at interfaces, and microscale property variations. Typical implementations of thermoreflectance techniques use a metal transducer layer to drastically improve signal to noise ratio on non-metal materials. The transducer layer also substantially simplifies heat transfer analysis because of high absorption at pump wavelengths and high reflectivity at probe wavelengths. These measurements improvements come at some cost, however. The transducer layer can make analysis procedures more challenging due to an increased number of fit parameters such as the thermal boundary conductance between the transducer layer and sample of interest. In samples of lower thermal conductivity, heat may also spread preferentially in the transducer layer, decreasing sensitivity to the sample bulk properties of interest.

Despite the promise of transducerless measurements, modeling all physical effects present in the experiment is challenging. The effects of excited carriers must be taken into account in order to accurately predict the signals measured in thermoreflectance measurements. Previous work has shown some success in bulk semiconductors using time domain thermoreflectance and modeling both optical penetration of laser light and heating effects from excited carriers. Here we present experimental results using a frequency domain thermoreflectance setup on samples with no transducer layer. While our work here is still limited to bulk semiconductor materials, we demonstrate several advances to the state-of-the-art experiments and modeling. Models from the literature of optical absorption and heating due to excited carriers are used to analyze FDTR data collected at visible wavelengths on silicon and GaAs. We leverage those models to analyze data using UV wavelength lasers taken on intrinsic silicon, GaAs and SiC. Uncertainty in this fitting analysis is examined with particular attention to optical properties of the samples. Comparisons are made between measurements with and without transducer layers using the framework of sensitivity analysis. We additionally examine how doping in silicon will affect experimental data and subsequent data analysis. Using these new insights, we reexamine the outlook of thermoreflectance measurements on semiconductors for thermal property measurements and failure analysis.  

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Presenting Author: Wyatt Hodges Sandia National Laboratories

Presenting Author Biography: Wyatt Hodges received his PhD from University of California, Berkeley and is a Senior Member of Technical Staff at Sandia National Laboratories as well as an adjunct professor at University of New Mexico. His research focuses on thermal properties measurement methods for microelectronic materials.

Authors:

Wyatt Hodges Sandia National Laboratories
Amun Jarzembski Sandia National Laboratories
Anthony Mcdonald Sandia National Laboratories