Encapsulating Ion-Solid Interactions in Metal-Oxide-Semiconductor (MOS) Devices

We report on a measurement of low energy ion irradiation effects on as-grown films of SiO2 on a Si substrate. Beams of normally incident Na⁺ ions with kinetic energies of 2 keV to 5 keV were focused onto ~ 1900 Å SiO2 films. Aluminum top metal contacts were subsequently deposited onto these targets such that irradiated regions and unexposed (pristine) regions of the target could be compared using capacitance-voltage (C-V) measurements of individual metal-oxide-semiconductor (MOS) devices. The C-V data reveal an energy-dependent shift in the flatband voltage ( VFB) that can be returned to its near-pristine value by a low temperature anneal. An increase in the density of interface states ( Dit) inferred from the C-V curves is found to have a superlinear dependence on the incident kinetic energy. These data are consistent with previously observed UV radiation effects on MOS oxides, where transferred energy leads to electron-hole pair production and the diffusion and trapping of holes throughout the oxide. Our measured trapped hole densities are compared with calculated densities, which are based on the incident ion dose and the predicted ion implantation range, to arrive at a fractional yield for hole survival and measurement within an encapsulated MOS device.