Thermal Characterization of Pulse-Activated Microelectronic Devices by Thermoreflectance-Based Surface Temperature Scanning

This work reports on a system that can determine the thermal behavior of an activated complex microelectronic device by measuring its surface temperature field with a thermoreflectance-based system. The article describes the features of the experimental setup, provides details of the calibration process used to map the changes in the measured surface reflectivity to absolute temperature values, and explains the data acquisition procedure used to measure the transient temperature over a given active region. The measurement methodology requires two steps. First, the coefficient of thermal reflectance is determined for each of the surface materials to be scanned. Second, the changes in the surface reflectivity as a function of changes in temperature are measured at each point of interest with submicron spatial resolution and better than microsecond temporal resolution. The resulting reflectivity waveforms are combined to obtain a transient temperature field over the scanned area. The method is applied to determine the thermal behavior of actual MOSFET devices. First, the method is used to measured an activated MOSFET device and show that by scanning first and then switching the source and drain contacts, the two resulting steady state temperature scans are symmetrical. The method is then used to differentiate between the transient thermal behavior of identically activated devices that have been made on two different epitaxial layers, one with natural and the other with isotopically-pure silicon. The results show non-negligible differences in the resulting transient temperature signatures due to the use of different materials in the construction of the otherwise identical devices, with the isotopically-pure silicon device running cooler than the corresponding device made with natural silicon. This measured behavior provides confirmation of the authors’ previous measurement of a higher thermal conductivity for isotopically-pure silicon. The results are shown as quasi-steady temperature contour plots and snapshots of the temporal evolution of the surface temperature fields for both types of MOSFET devices.