Emission microscopy

Photoemission microscopy, or light emission microscopy, 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. An infrared camera and a computer are used to accomplish this feature. Other failure analysis techniques are then performed to look for the physical anomaly responsible for the abnormal light emission.

Photoemission microscopy applications include but are not limited to the following :

• detection of previously unknown or undetectable electroluminescence;
• detection of avalanche luminescence from junction breakdowns, junction defects, currents due to saturated MOS transistors, and transistor hot electron effects;
• detection of dielectric electroluminescence from current flow through SiO2 and SiN.

Figure 1 shows the optical configuration of a versatile photon emission microscope. After removing the filter and beam splitter it can be used for just proving suspicious emissions. Alternatively, it can be used to overlay the radiation image and chip surface to better facilitate the localization of defects. This configuration can be expanded into a spectroscope by substituting beam splitter and filter by an appropriate dispersive element (basically also a filter). Spectral analysis of photon emissions promises to yield much more detailed information – because every defect has its own spectral signature. Most SWIR cameras  are already prepared for this task by offering a C-mount and mounting holes for a spectrometer.