The Effects of Nitride Passivation on the Total Dose Radiation Resistance of a Precision Operational Amplifier

This study investigated the effect of different processing steps on the total dose radiation resistance of a precision operational amplifier, the OP-108A. A unique bipolar process that uses a high temperature deposited silicon nitride as a surface passivation layer was modified to determine the role of the silicon nitride in circuit hardening. Process lots with and without nitride layers showed that the nitride layer is the dominant step in assuring radiation resistant circuits. Further experiments showed that the increase in epi inversion threshold voltage resulting from the nitride layer and its associated interface charges cannot be used to explain this hardening effect. The epi inversion voltage is the voltage that it takes to turn on a parasitic p-channel MOS device degrading circuit performance.