AbstractHot‐spot detection, a thermographic technique with liquid crystals, marks hot regions on a surface. The use of this highly sensitive method in failure analysis of integrated devices allows the detection of points on a chip where electrical power is converted into heat. Points such as these are often indicative of a fault, e.g. a leakage path or an increase in transfer resistance. The technique is based on the birefringence of a liquid crystal (LC) in the anisotropic state below the clearing temperature(Tc). Above this temperature, in the isotropic state, the effect disappears. The device under test, covered with the LC, is observed below the clearing point in polarized light with a crossed polarizer and analyser. Owing to the optical rotation of the anisotropic LC the image is bright. At hot spots the LC changes to the isotropic state and a dark spot is produced. A decisive factor for the thermal resolution of the technique is the precise temperature adjustment of the tested device. With lateral resolution of some tenths of a μ‐m it is still possible to detect current paths with dissipation of 50 to 500μW. The sensitivity can be increased further. Square‐wave pulses of selectable voltage, frequency and duty cycle are used to drive the test item. Four examples from failure analysis demonstrate the possibilities of using hot‐spot thermography, the main features of which are speed, uncomplicated handling and depth of in
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