In-situ measurement of depletion zones in power devices

Methods for evaluation of junction in power semiconductor devices are discussed. An Insulated Gate Bipolar Transistor (IGBT) chip was selected for the experiment. Samples were alternatively mechanically polished, cleaved, or in a third case, sectioned with an experimental FIB (Focused Ion Beam) section. From here, sensitive Electron Beam Induced Current (EBIC) measurements were undertaken and results were compared. There was little difference in the ability to detect depletion zones between the techniques, indicating that Ga+ contamination or amorphization from the FIB did not prevent the collection of useful data from the p/n junctions. During the course of experimentation, it was determined that the pixel dwell time during electron beam stimulation had a strong effect on removing artifacts and increasing the contrast of the result. In the optimized analysis, the EBIC work crisply imaged the depletion zones of not only the P body / N- drift regions, but also the N+ / body regions in the same image. Additional observations were made to compare the different physical extents of the implant regions by Passive Voltage Contrast (PVC) versus the depletion zones from the EBIC results.