Abstract
IEEE Transactions on Nuclear Science 2018, 65, 164-174
Influence of LDD spacers and H+ transport on the total-ionizing-dose response of 65 nm MOSFETs irradiated to ultrahigh doses
Faccio F, Borghello G, Lerario E, Fleetwood DM, Schrimpf RD, Gong H, Zhang X, Wang P, Michelis S, Gerardin S, Paccagnella A, Bonaldo S
The degradation induced by ultrahigh total ionizing dose in 65-nm MOS transistors is strongly gate-length dependent. The current drive decreases during irradiation, and the threshold voltage often shifts significantly during irradiation and/or high-temperature annealing, depending on transistor polarity, applied field, and irradiation/annealing temperature. Ionization in the spacer oxide and overlying silicon nitride layers above the lightly doped drain extensions leads to charge buildup as well as the ionization and/or release of hydrogen. Charge trapped in the spacer oxide or at its interface modifies the parasitic series resistance, reducing the drive current. The released hydrogen transports as H + with an activation energy of ~0.92 eV. If the direction of the electric field is suitable, the H + can reach the gate oxide interface and depassivate Si-H bonds, leading to threshold voltage shifts. Newly created interface traps are most prominent near the source or drain. The resulting transistor responses and defect-energy distributions often vary strongly in space and energy as a result, as demonstrated through current-voltage, charge-pumping, and low-frequency noise measurements.