Comparison of MOS capacitor and transistor postirradiation response

The postirradiation response of MOS capacitors and transistors fabricated on the same chip is examined as a function of dose and anneal bias. A variety of analysis techniques are used to evaluate the postirradiation response of these structures, including low- and high-frequency capacitance-voltage techniques, subthreshold current-voltage techniques, and charge pumping. Although there are changes in the postirradiation energy spectrum of ΔD_it, no clear evidence of defect transformation is observed on transistors or capacitors under any conditions examined. Postirradiation response at 80°C is found to be similar in the two structures for low levels of damage (100 krad). For both structures, interface-trap densities continue to grow following irradiation under these conditions. In contrast, the postirradiation response of capacitors and transistors can differ qualitatively at higher levels of damage (1 Mrad), with the number of interface traps increasing postirradiation at 80°C for transistors and postannealing for capacitors. These results indicate that capacitor structures may not be suitable for hardness assurance studies that involve elevated temperature irradiations or postirradiation anneals