Charge generation, transport, and recombination processes in UNIBOND® silicon-on-insulator wafers are studied via an optical second-harmonic generation (SHG) technique. The electric fields at the interfaces vary with time due to charge trapping. The presence of a thin native oxide layer on the top Si film contributes significantly to the SH intensity due to the strong time-dependent electric field generated by electrons transported to the surface. For the thick buried oxide, the electric field is primarily due to carrier trapping at the interface, and it varies with time weakly. The SHG signals depend strongly on the externally applied electric field, which can differentiate the contribution of each interface to the total SH signal.
We present an investigation of the observed variations in the total dose tolerance of the emitter-base spacer and shallow trench isolation oxides in a commercial 200 GHz SiGe HBT technology. Proton, gamma, and X-ray irradiations at varying dose rates are found to produce drastically different degradation signatures at the various oxide interfaces. Extraction and analysis of the radiation-induced excess base current, as well as low-frequency noise, are used to probe the underlying physical mechanisms. Two-dimensional calibrated device simulations are employed to correlate the observed results to the spatial distributions of carrier recombination in forward-and inverse-mode operation for both pre-and post-irradiation levels. Possible explanations of our observations are offered and the implications for hardness assurance testing are discussed.
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