Total dose effects on buried oxide breakdown

Trapped positive charge and other defects can affect breakdown voltage (V_br) and charge-to-breakdown (Q _br) in SIMOX (separation by implanted oxygen) buried oxides. Because total dose gamma radiation induces positive charge, lattice defects, and interface traps in SiO₂, experiments were performed to measure changes in V_br and Q _br with radiation dose. These experiments were performed on ion-implanted buried oxides of SOI (silicon-on-insulator) capacitors, and both single-implant (SI) and multiple-implant (MI) buried oxides were examined. Both types of buried oxide have preirradiation defects inherent to the implantation process, with MI having fewer defects. The goal was to find the response of oxide breakdown to irradiation for these two buried oxides. SI oxides are expected to have a higher density of defects, such as oxygen precipitates and silicon islands. High-frequency capacitance-voltage measurements showed a much greater difference between bottom and top threshold voltage shift in MI, indicating that radiation-induced positive charge was more widely distributed in SI, while in MI the charge was almost entirely concentrated at the top SiO₂ interface