Influence of Bulk Doping and Halos on the TID Response of I/O and Core 150 nm nMOSFETs

Abstract

The total ionizing dose sensitivity of planar 150 nm CMOS technology is evaluated by measuring the DC responses of nMOSFETs at several irradiation steps up to 125 krad(SiO2). Different TID sensitivities are measured for transistors built with different channel dimensions and operating voltages (I/O and core). The experimental results evidence strong relations between TID sensitivity and the doping profiles in the channel. I/O transistors have the highest TID sensitivity due to their thicker gate oxide and lower bulk doping compared with core devices. In general, narrow-channel devices have the worst degradation with negative threshold voltage shifts, transconductance variations and increased subthreshold leakage currents, suggesting charge trapping in shallow trench isolation (STI). The enhanced TID tolerance of short-channel core devices is most likely related to the increased channel doping induced by the overlapping of halo implantations. Finally, transistors fabricated for low-leakage applications exhibit near insensitivity to TID due to higher bulk doping used during the fabrication to minimize the drain-to-source leakage current.