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Effects of additional thermal budget associated with a three-dimensional (3D) fabrication sequence are evaluated for the total-ionizing dose radiation response of fully depleted silicon-on-insulator (FD-SOI) MOSFETs. Current-voltage and low-frequency (1/ ${f}$ ) noise measurements are compared for (1) conventional planar FD-SOI MOSFETs, and (2) MOSFETs formed in the bottom layer of the 3D process and subjected to the process steps associated with formation of a second active layer. Similar radiation-induced voltage shifts and increases of 1/ ${f}$ noise are observed after irradiation for both types of structures. These similar changes in response show that the additional thermal processing involved with 3D fabrication has little effect on border-trap densities and radiation-induced charge trapping in gate and/or buried oxides of MOSFETs formed in the bottom layer of the 3D process.

There have been no studies to date estimating the quantitative relation between the increase of interface traps and SiH groups in silicon dioxide films for the effects of total ionizing dose including enhanced low-dose-rate sensitivity (ELDRS). In this study, SiH groups densities in silicon dioxide films are measured and compared with interface trap densities developed at different dose rates to evaluate the impacts of direct proton release mechanism on ELDRS by X-ray photoelectron spectroscopy (XPS) analysis with the combined use of gamma-ray and electron-beam irradiation. The measurement results in this study clearly show that ELDRS depends linearly on SiH groups densities. The linear relationship demonstrates ELDRS is caused by the direct proton release mechanism. The order of magnitude of ELDRS we observed is almost the same as the experimental results reported previously. We emphasize that our results provide the first experimental evidence that the direct proton release mechanism is a critical mechanism affecting ELDRS in addition to the space charge model and H 2 cracking.