Implications of radiation-induced dopant deactivation for npn bipolar junction transistors

Metal-oxide-silicon capacitors fabricated in a bipolar process were examined for densities of oxide trapped charge, interface traps and deactivated substrate acceptors following high-dose-rate irradiation at 100°C. Acceptor neutralization near the Si surface occurs most efficiently for small irradiation biases in depletion. The bias dependence is consistent with compensation and passivation mechanisms involving the drift of H⁺ ions in the oxide and Si layers and the availability of holes in the Si depletion region. The capacitor data were used to simulate the impact of acceptor neutralization on the current gain of an irradiated npn bipolar transistor. Neutralized accepters near the base surface enhance current gain degradation associated with radiation-induced oxide trapped charge and interface traps by increasing base recombination. The additional recombination results from the convergence of carrier concentrations in the base and increased sensitivity of the base to oxide trapped charge. The enhanced gain degradation is moderated by increased electron injection from the emitter. These results suggest that acceptor neutralization may complicate hardness assurance test methods for linear circuits, which are based on elevated temperature irradiations