Time-Resolved Thermoreflectance Imaging for Thermal Testing and Analysis Kazuaki Yazawa, Dustin Kendig Microsanj LLC., Santa Clara, CA USA kaz@microsanj.com, +1-408-256-1255 Ali Shakouri, Kazuaki Yazawa Purdue University, West Lafayette, IN USA Abstract High speed, time-resolved, thermoreflectance imaging is a novel way to locate defects or regions of potential failures in microelectronic devices. This paper reports on our thermoreflectance technique for dynamic imaging of circuit temperature distributions. This transient imaging method is based on a precise electrical lock-in technique with image processing similar to an old fashioned animation movie. An ordinal shutter speed camera is used in conjunction with an illumination LED that is pulsed for sampling the temperature distribution. This paper presents the method and gives a description of the system hardware. A theoretical comparison to lock-in thermography, which is based on infrared emission imaging, will be given. Limitations of thermoreflectance and the driving factors for spatial and time resolution will be discussed. Finally, we highlight and provide examples of near infrared (NIR) wavelength imaging, to enable both through- silicon thermal imaging and emission imaging in the same system. The combination of these two techniques is expected to enable hotspot temperatures and any anomalous emission sites to be correlated, hopefully leading to a better understanding of the nature of the defect. Introduction Detecting a time-dependent defect and identifying it as a potential failure or gaining an understanding of the failure mechanisms related to the defect is a challenge in failure analysis for today’s complex high-speed electronic devices. The scaling of device features results in a significant reduction in their time response and an increased sensitivity to transient events [1]. For example, a transient temperature change can result in a functional failure in a circuit with a tight design margin because of the timing perturbation caused by a small capacitance drift [2]. As device features shrink, the probability of detecting defects is also greatly reduced, thus leading to the development of statistics-based, large-area sampling methods [3]. Weaker signals and a lower probability of failure detection have made the understanding of the failures more difficult, but yet still very important. Some failures and defects can only be effectively isolated with the aide of thermal information that is obtained while the semiconductor devices are operating, or, at a minimum, while a bias is applied to the defective circuit. A “short circuit” defect caused, for example, by a whisker, or by a very minor local misalignment of circuit features can produce highly concentrated Joule heating, even with a very small amount of dissipated power. While some detection methods have been developed for these cases, they are effective only under limited conditions [5]. One major problem is the rapid diffusion of heat, which blurs the hotspot and makes localization difficult using DC/static techniques. Using a high speed transient imaging technique such as time- resolved thermoreflectance instead of static imaging enables weak heat signals to be captured and localized before the heat completely diffuses. This technique is capable of analyzing the small changes in temperature of the detailed features of a microelectronic device, while the device is driven under specific time-varying conditions such as a work load vector or a time varying bias. Besides providing better localization capability, time-resolved thermoreflectance is also useful for analyzing the time- dependence of hotspot locations. By acquiring a time sequence of images in accordance with a time-varying workload, unexpected transient hotspot locations can be identified. These hotspots could be an indication of a logic failure, a timing failure, or a circuit design anomaly. The thermoreflection concept itself has been known for some time, but its utilization for thermal analysis and defect detection has been limited. The current availability of turn-key systems, reduced complexity and cost, and innovations with CCD imaging and synchronization techniques has greatly enhanced the utility of this approach [4]. One recent innovation is the incorporation of photon emission imaging in a NIR thermoreflectance system. This combination enables comparisons to be made between hotpot and photon emission sites and makes it possible to analyze their correlations. Examples of backside imaging and the application of this combination will be shown. This paper will also provide the ISTFA 2013: Conference Proceedings from the 39th International Symposium for Testing and Failure Analysis November 3–7, 2013, San Jose, California, USA Copyright © 2013 ASM International® All rights reserved www.asminternational.org 194