Methods to Enhance Infrared Imaging for Defect Localization Using Lock-in Thermography

Abstract In this paper, we demonstrate three approaches to enhance the topographical contrast of infrared images obtained from lockin thermography (LIT). Infrared imaging, particularly LIT, is one of the extensively used techniques for failure analysis (FA) in the semiconductor industry. However, low-contrast topography images are obtained at room temperature from conventional LIT due to poor emissivity contrast in the devices and the limitation on the performance of the infrared camera. The gray-scale topographical contrast is improved by 85% when the device under test is heated from room temperature to 75°C, using a printed circuit board heater. Furthermore, a heat-assisted LIT approach is proposed and demonstrated at the die level on an electrically leaky silicon interposer sample. The topographical contrast and the signal intensity of the hotspot obtained are enhanced when compared to the classical LIT, which is performed at room temperature. Further, the dual LIT approach is developed to reduce the thermal budget of the heat-assisted approach. The hotspot amplitude and improved topography image are obtained from two consecutive lock-in measurements. In addition, the topography image from this technique is obtained by averaging several hundred frames from the camera for a period of ten minutes, which results in an image that is less susceptible to input noise levels. To increase the throughput of the FA process, quadrature lock-in thermography, a dual-purpose measurement technique is shown. A high-contrast topography image and the hotspot location are obtained from the same lock-in thermogram by performing trigonometric conditioning. The throughput from this approach is the same as the classical LIT technique.