Fluorescent Microthermal Imaging
As was previously mentioned, one of the most frequent problems in contemporary semiconductors and electronic devices is current leakage. A liquid crystal is one of the most popular methods for identifying current leakage since it is a quick and efficient way of isolating failure locations, but it has significant drawbacks that make it inapplicable in all circumstances. To identify a leakage site, liquid crystal relies on the heat produced by the leakage site to raise the temperature of the crystal to a “transition point,” where an analyst can visually observe a change in the crystal’s properties. As tiny flaws drain less power and hence produce less heat, a more subtle failure may never be able to heat the liquid crystal to its transition point. On the other hand, excessive leakage can generate enough heat to quickly elevate the device’s temperature to the point that it is hard to pinpoint the point of changeover. Fluorescent microthermal imaging can be added to the regular liquid crystal to address these drawbacks.
As a liquid crystal, fluorescent microthermal imaging (FMI) is powered by the heat produced by a leaky site. On the surface of a semiconductor die is painted a thin coating of a UV-fluorescent compound based on Europium. The component is then put under a light-emission microscope, which examines the light the fluorescent ink emits using a high-gain camera. The power supply to the device is controlled by the microscope, which toggles on and off numerous times per second. When the device is powered, the heat generated by the failure increases the quantity of light emitted by the ink. The system takes several pictures of the object, switching between photographs showing it powered on and off. The change in fluorescence owing to the heat created by the leakage can be precisely located and identified, isolating the failure spot by computationally subtracting the photos acquired with the power on from those taken with the power off.
Fluorescent microthermal imaging is sensitive to temperature change as opposed to the liquid crystal, which is sensitive to absolute temperature (the only temperature that produces relevant data is the transition point). When compared to a liquid crystal, FMI can detect significantly smaller levels of leakage current because the measurement is differential. FMI can also be used to isolate failures that generate high amounts of heat that are challenging to discover with liquid crystal due to the rapid heating of the device because it uses very short acquisition periods that prevent large amounts of heat diffusion.
Fluorescent microthermal imaging is a useful adjunct to liquid crystal for isolating current leakage, although it may require a more complicated setup. The more failures that can be isolated when FMI is used, the more likely it is that an analysis will be successful. Read more about failure analysis using fluorescent microthermal imaging.
