Photoemission Microscopy; Light Emission Microscopy (LEM)

Photoemission Microscopy

Photoemission microscopy, or light emission microscopy (LEM), is a relatively new failure analysis technique for detecting photonic radiation from a defect site, primarily due to carrier recombination mechanisms. Such defect sites emit light during device operation which would otherwise be absent in a normal device. Such photoemissions, being very low-level, are not visible to the naked eye.

Photoemission microscopy uses a powerful image intensification technology to amplify the light emitted by photo-emitting defect sites. The resulting radiation image is then overlaid with its corresponding die surface image, such that the emission spot coincides with the precise location of the defect. A CCD camera and a computer are used to accomplish this feat. Other FA techniques are then performed to look for the physical anomaly responsible for the abnormal light emission.

Fig. 1. Example of a Light Emission Microscope

Photoemission microscopy applications include but are not limited to the following : 1) detection of previously unknown or undetectable electroluminescence; 2) detection of avalanche luminescence from junction breakdowns, junction defects, currents due to saturated MOS transistors, and transistor hot electron effects; 3) detection of dielectric electroluminescence from current flow through SiO2 and SiN.

Fig. 2. Examples of light emission images

Caution must be exercised when performing light emission microscopy because not all abnormal light emissions emanate from the actual defect site itself. Some defect sites can drive a good transistor to saturation, making it emit light that can easily be misinterpreted as anomalous by a novice analyst. LEM results should always be complemented by results from other FA techniques such as high power inspection and microprobing to prevent inaccurate FA conclusions.

Microprobing; FA Lab Equipment; Basic FA Flows; Package Failures; Die Failures

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