18 September 1995 Optical characterization of power devices
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For the realization of high breakdown voltages, power devices require a thick silicon layer with high resistivity. Therefore, the density of detrimental defects in the electrically active device regions must be extremely low to obtain low leakage currents, low on-state voltages and good stability of the electrical data. Contamination analyses have shown that considerable diffusion of heavy metals into Si wafers can occur due to improper processing. In order to assess the influence of heavy metals on carrier lifetime in power devices, optical analyses of the carrier lifetime and its lateral distribution were performed by the Elymat, the microwave photoconductive decay and the surface photovoltage method. Furthermore, we applied a method based on collector current decay. Contaminations acting as donors were ivnestigated by laser-induced free charge carriers resulting in a lateral voltage drop in the case of lateral doping inhomogeneities. Vertical carrier and temperature profiles have been analyzed by the internal laser deflection method. Comparing the results of all these measurements with the influence on the electrical data, it is found that the electrical data of power devices are very sensitive to contamination.
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H.-J. Schulze, H.-J. Schulze, G. Deboy, G. Deboy, "Optical characterization of power devices", Proc. SPIE 2638, Optical Characterization Techniques for High-Performance Microelectronic Device Manufacturing II, (18 September 1995); doi: 10.1117/12.221201; https://doi.org/10.1117/12.221201

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