Thermal measurements of active semiconductor micro-structures acquired through the substrate using near IR thermoreflectance

Modem, high-density integrated circuits (IC) typically use a flip chip bonding technique to increase performance on a greater number of interconnects. In doing so, the active devices of the IC are hidden under the exposed substrate, which precludes the use of typical surface thermal characterization techniques. A near infrared thermoreflectance method is described such that the temperature of active semiconductor devices can be measured through the substrate. Experimental results were obtained through a 200 mum thick silicon substrate. Temperature resolution of 0.1 K and spatial resolution of 5 mum has been achieved. The Fabry-Perot effect, due to multiple reflections between the device and the back of the substrate, has been experimentally and theoretically analyzed. Techniques to enhance the spatial resolution will be discussed. (C) 2004 Elsevier Ltd. All rights reserved.