Process Investigations of Total-Dose Hard, Type-108 OP Amps

Analyses and process investigations of a 108 op amp fabrication sequence have been conducted. The analysis was initiated with a total dose characterization of 108 op amps that indicated that total-dose sensitive commercial devices could be radiation hardened by modifying their standard processing. Subsequent failure analysis identified the critical op amp failure modes as primarily the result of superbetagain loss and leakage increase. A process-flow analysis with MOS capacitors on the selected baseline fabrication sequence was followed by a study of specific processing steps on the radiation performance of 108 op amps. Amplifiers, transistor test devices and MOS capacitors were evaluated. Emphasis was placed on processing steps near the end of the process sequence. Using the defined process it was possible to fabricate 108 devices with minimal degradation at 106 rads(Si). Some relaxation of initial 108A performance is required for the hard devices.