Annealing of MOS Capacitors with Implications for Test Procedures to Determine Radiation Hardness

The short- and long-term anneal of radiation-induced flatband voltage shift in both Al- and Si-gate MOS capacitors following pulsed e-beam irradiation is examined. The short-term anneal was measured and found to be similar for both Al- and Si-gate capacitors. Experiments were performed to investigate the dependence of the long-term anneal on oxide thickness, temperature, and bias. The Al-gate capacitors exhibited a low interface-state buildup following irradiation and had a long-term annealing curve with a simple ln(t) dependence, while the Sigate capacitors studied had a more complicated annealing curve due to the buildup of a larger number of interface states and lateral nonuniformities (LNUs). Thinning the gate oxide was found to dramatically reduce the effects of interface states and LNUs on the long-term anneal. In capacitors where the effects of interface states and LNUs are small the long term annealing was found to be only weakly temperature dependent over the range -60 to 100°C, and removal of bias following irradiation had little effect. On the other hand, the long-term annealing of capacitors with a significant buildup of radiation-induced interface states and LNUs exhibited a strong temperature and post-radiation bias dependence. Some implications of the experimental results for the proper design of test procedures for determining radiation susceptibility are discussed.