Lock on! Low-cost optical technologies home in on defect sites in microcircuits

Abstract

We demonstrate failure analysis of integrated circuits (IC) at optical resolution (~ 1 μm) using an optical feedback laser diode confocal microscope. By acquiring the reflectance image and simultaneously measuring the optical-beam-induced current (OBIC) at each point on the sample, it is possible to discriminate the semiconductor from the metallic sites in integrated circuits. This aids in properly localizing defects on the sample and yield hints as to the possible cause of the defect. This is extended to generate differential thermal maps of semiconductor edifices in IC. An inexpensive optical feedback laser-scanning microscope detects changes in the OBIC signal that are produced in the active layer in response to variations in the IC package temperature. The OBIC yield of a semiconductor normally increases with temperature. A differential thermal map derived from the OBIC output variations, shows locations of high thermal activity in the active layer including anomalous regions where the OBIC outputs decrease with increasing temperature. Anomalous regions are loci of accumulating semiconductor electrical resistance that are highly susceptible to device failure. They provide the best jump-off points for efficient and accurate IC fault analysis procedure.
Aside from absorption, reflectance can also yield thermal information about the IC. We demonstrate a versatile and cost-effective spectral microscopy technique for generating spectral reflectance maps that distinguish subtle differences in performance among various semiconductor components in the active layer of an IC sample. The technique utilizes a grating prism pair (GRISM) system to disperse reflected light into its spectral components. The spectral characteristics of specific structures are established by line-scanning the IC across the GRISM slit to form a pair of spectral images under biased and unbiased conditions. Thermal maps are generated from the image pair to reveal regions of rapid heat accumulation. They allow a rapid assessment of the thermal integrity of the IC architecture including the identification of possible failure sites. The benefit of spectral selectivity is demonstrated further by determining the reflectance properties of a biased light emitting diode in the presence of a strong electroluminescence background. Spectral unmixing is employed to remove the background and isolate the thermal maps. Unmixing facilitates the difficult task of thermography in biased light emitting devices.
Finally we demonstrate the feasibility of imaging IC defects remotely by controlling an Olympus BX-61 motorized microscope through a web interface via internet, and through a mobile phone using SMS and GPRS. Captured images can be viewed via the web interface, sent through MMS or live-video streaming. Remote imaging and control of the microscope can enhance collaborations between researchers without the need to be physically present on the experimental site.