Optical Scanning Techniques for Semiconductor Device Screening and Identification of Surface and Junction Phenomena

The electrical response of semiconductor devices to light can be used to study various device phenomena and to identify the causes of anomalous device behavior. To implement such a study, a flying spot scanner has been constructed. This instrument deflects a light beam into a raster pattern and focuses it on the device under test. The light source is a helium-neon laser. Sinusoidal sweeps are used for simplicity. The electrical output from the device is amplified and intensity modulates the electron beam of a cathode-ray tube. By synchronizing the CRT beam deflection with the light spot on the sample, an image of the device electrical output is traced on the CRT. The resolution is about 5 ¿ (0.0002"), referred to the surface under study. Interpretation of the image yields the desired device information. The system is constructed from equipment ordinarily available in an experimental laboratory. The scanner has been used principally for tests on photodevices, but results show that it should also be very useful for nondestructive testing of transistors and integrated circuits. Device phenomena, which have been identified and studied, include localized surface and junction breakdown, channeling, and uniformity of avalanche multiplication in silicon avalanche photodiodes. The information obtained has allowed us to prepare improved devices by relating these observations to device fabrication steps. Both discrete devices and their arrays on a single wafer have been analyzed.