Correlating the Radiation Response of MOS Capacitors and Transistors

A new technique is presented for separating the threshold-voltage shift of an MOS transistor into shifts due to interface states and trapped-oxide charge. Using this technique, the radiation responses of MOS capacitors and transistors fabricated on the same wafer are compared. A good correlation is observed between p-substrate capacitors and n-channel transistors irradiated at 10 V, as well as between n-substrate capacitors and p-channel transistors irradiated at 0 V. These correlations were verified for samples having large variations in the amount of radiation-induced trapped holes and interface states. An excellent correlation is also observed between n-channel capacitors and n-substrate transistors irradiated under positive bias. The use of capacitors separately fabricated on control wafers for potential use in process development or monitoring is clearly demonstrated.