Total Ionizing Dose Effects on Strained ${\rm HfO}_{2}$-Based nMOSFETs

Abstract

Radiation-induced charge trapping and mobility degradation are measured on uniaxially stressed HfO 2 -based nMOSFETs. Controlled external mechanical stress is applied via a four-point bending jig while the samples are irradiated using 10-keV X-rays. Positive charge trapping is observed for unstressed devices, and for devices irradiated under both compressive and tensile stress. Reduced trapped charge is measured as the uniaxial stress level increases. These results suggest that the increased stress leads to a reconfiguration of defect microstructure, as compared to the unstressed devices. The reconfiguration consists of changes in bond lengths and angles and a corresponding change in trap energy levels, which can (1) reduce the probability that a defect can capture holes, (2) increase the probability for electron and trapped-hole recombination, and/or (3) increase the mobility of the transporting holes in the oxides of the devices that are irradiated under stress. These results show that increased mechanical stress in high-k dielectrics does not degrade their radiation hardness. We also observe that the post-irradiation channel mobility degrades less in uniaxially stressed devices than unstressed devices.Index Terms-Hafnium oxide (HfO 2 ), high-k, metal-oxidesemiconductor-field-effect-transistors (MOSFETs), radiation damage, strained-silicon, uniaxial, X-ray.

Reliability of HfSiON gate dielectric silicon MOS devices under [110] mechanical stress: Time dependent dielectric breakdown

“…16,29 This may result in improved PBTI via mechanical stress-induced increase in charge detrapping in thick ͑Ͼ7 nm͒ HfO 2 Si MOSFET. 31 An insignificant process-induced stress dependence of PBTI in thin ͑3 nm͒ high-k Si MOSFET has been already reported, resulting from negligible charge trapping in the thin high-k layer. 12,32 Thermal stress-induced subthreshold leakage, which can degrade the retention time of dynamic random access memory, 33 also results from Si-H bond breaking at high-k / Si interface.…”

“…23,[35][36][37][38] Two strain-related models can explain this discrepancy: ͑1͒ a decrease in charge trapping in relatively thick gate dielectric via strain-altered trap activation energy 23,35,36 and ͑2͒ straininduced Si band gap narrowing and an increase in impact ionization at the drain edge. 37,38 For both uniaxial tensile and compressive stresses, a decrease in a trapping of injected hot carriers in high-k likely results in an improved HCI, 25,31 while an increase in impact ionization may multiply the number of hot carriers, leading to a degradation of HCI. 39 In high-k integration, V Th instability has been one of the challenges.…”

“…16 As explained above, applied mechanical stress reduces electron and hole trap activation energies at the high-k / Si interface or high-k dielectric. 25,31 This results in ͑1͒ an increase in trap-assisted gate tunneling ͑or Poole-Frenkel emission͒ and ͑2͒ a decrease in charge trapping in high-k. 25,31 Therefore, V Th instability can be improved at the expense of an increased trap-assisted gate tunneling leakage under both uniaxial tensile and compressive stresses. Due to substantial reduction in gate leakage in high-k device, 29 this tradeoff will be beneficial for device performance.…”

The impact of device width on the variability of post-irradiation leakage currents in 90 and 65 nm CMOS technologies

“…In particular, it has been shown that in a symmetric layout, the stresses from adjacent STI edges (STI space) are added to the original STI stress [7,14]. For narrow devices where the STI spacing is smaller, there is more compressive stress, which results in variations in both doping concentration and amount of charge trapping [17,18]. In addition, random dopant fluctuations that result from variations in the implanted impurity concentration can also lead to variability in the as-processed device leakage [19][20][21][22].…”

Study of Neutron Irradiation Effects on SOI and Strained SOI MuGFETs Assessed by Low-Frequency Noise

“…While initially, no impact of 63 MeV proton (15) or 60 Co γ-irradiation (16) was reported, other studies indicate a relaxation of the processing-induced stress (17), which may lead to a reduction of the low-field mobility and of the device output current. On the contrary, it has also been shown that mechanically stressed transistors exhibit a better radiation performance under X-ray irradiation than unstressed devices (18), indicating that the impact of stress on the radiation performance strongly depends on the method of strain engineering employed. This certainly calls for further investigations.…”