Improvement in off-State Leakage Current of n-Channel SOS MOSFETs by Hydrogen Annealing of the SOS Film

The off-state source-to-drain leakage current and punchthrough voltage are the quantities that frequently limit the performance of short-channel floating-body silicon-on-sapphire (SOS) n-channel MOSFETs. In this paper, we demonstrate that the high-temperature hydrogen annealing of the SOS film prior to the device fabrication leads to marked improvement in these two parameters. The effect is attributed to the impact of hydrogen on the out-diffused thin alumina layer formed at the silicon-sapphire interface during the anneal. The thin alumina layer acting as a p-type dopant source at the back interface eliminates the back surface depletion of SOS n-MOSFETs. It also acts as a recombination center to eliminate the floating-body effect of floating-body n-MOSFETs. This technique provides a practical and reliable process to build short-channel floating-body SOS n-MOSFETs with off-state leakage as low as the junction leakage and punchthrough voltage as high as 6 V or higher at the gate length of 0.5 μm without any degradation on the inversion layer carrier mobility or increase in the junction leakage current.