Total Dose Effects in Recessed Oxide Digital Bipolar Microcircuits

Total dose failure levels in digital bipolar microcircuits utilizing recessed oxides were measured at levels as low as 5 Krad(Si). Typical failure levels are in the 10-100 Krad(Si) range. Failure was found to be a strong function of irradiation bias and annealing time after irradiation. In addition, total dose "windows" below 100 Krad(Si) were observed. The radiation failure mechanism is predominantly inversion of p type silicon either at the bottom of the recessed field oxide, causing buried layer to buried layer channeling, or on the oxide sidewall causing collector to emitter leakage. In addition, a failure mode due to increased sidewall current was observed in a nonisolated form of integrated injection logic. Hardening approaches have been identified and investigated at several manufacturers. Device failure levels were found to vary by several orders of magnitude depending on process lot and layout revision.