Izumi Hirano

Thermochemical understanding of dielectric breakdown in HfSiON with current acceleration

Based on experimental results, the lifetime projection of breakdown and its mechanisms in HfSiON dielectrics were discussed. In HfSiON dielectrics, the total hole fluence to breakdown (Qp) was not found to be a dominant factor. We propose that the thermochemical breakdown along with the acceleration by injected carriers is the primary degradation mechanism in HfSiON dielectrics, especially at high temperature.

Effects of nitrogen concentration and post-treatment on reliability of HfSiON gate dielectrics in inversion states

We have studied the effects of nitrogen concentration ([N]=N/(Hf+Si+O+N)) in HfSiON films and post-nitridation annealing (PNA) conditions on the reliability of metal oxide semiconductor field effect transistors (MOSFETs) with HfSiON gate dielectrics in inversion states with constant voltage stress. In nMOS case, higher [N] and lower PNA temperatures are effective to reduce stress induced leakage current (SILC). SILC is related to crystallinity in HfSiON films. On the other hand, only small SILCs were observed in pMOSs, and the currents were independent of [N] and PNA temperatures without regard to crystallinity in the HfSiON films. Differences in SILC behavior between nMOS and pMOS are related to the electron transport mechanism. It is thought that SILC was generated by increasing positive oxygen vacancies whose energy level is near the conduction band edge of HfSiON. Since electrons in pMOS move through the deep trap level, their transit is independent of positive oxygen vacancies. For highly reliable HfSiON gate films, it is important to form homogeneous and amorphous HfSiON films.

Impact of metal gate electrode on Weibull distribution of TDDB in HfSiON gate dielectrics

The slope parameter of Weibull plot of Tbd, β, strongly depends on gate electrode material for metalgate/HfSiON gate stacks in n-FETs. Furthermore β of Tbd under bipolar stress is larger than that under DC stress. From these results, it is found that the balance of injected carriers is strongly related to β in terms of the origin of large β for metal-gate/high-k.

Breakdown Voltage Prediction of Ultra-Thin Gate Insulator in Electrostatic Discharge (ESD) Based on Anode Hole Injection Model

A prediction model for the breakdown voltage of ultra-thin gate insulator in electrostatic discharge (ESD) is proposed. The time-dependent-dielectric-breakdown characteristics under DC stress successfully predicts ESD oriented dielectric breakdown on the basis of the modified anode hole injection model. The proposed model redistributes experimental breakdown voltages and number of pulses to breakdown in extensive gate voltages and gate insulator thicknesses. In conclusion, the present model is quite effective for the prediction of ESD reliability in highly scaled ULSI devices

Significant role of cold carriers for dielectric breakdown in HfSiON

Dielectric breakdown mechanisms in HfSiON were thoroughly investigated by utilizing the substrate hot carrier injection. It was found that the total hole fluence (Q/sub p/) dose not dominate the breakdown in HfSiON. Furthermore, it was experimentally clarified that the injected electrons into HfSiON have the significant role for the breakdown, irrespective of their potential energy. This result strongly suggests that the roles of injected cold electrons in HfSiON are remarkably different from those in SiO/sub 2/ and SiON.

Method of Decoupling the Bias Temperature Instability Component from Hot Carrier Degradation in Ultrathin High-k Metal–Oxide–Semiconductor Field-Effect Transistors

Hot-carrier (HC) degradation becomes more critical as the channel length is reduced. Furthermore, both positive and negative bias temperature instabilities (PBTI and NBTI, respectively) are significant in high-k devices. Under HC stress, BTI caused by the vertical electric field is unavoidable. The decoupling of the BTI component from HC degradation is necessary to predict device lifetime more accurately. In this study, a new decoupling method of HC degradation is proposed. By using the relation between ΔVth and Jg, the BTI component can be decoupled from the degradation under Vg=Vd stress. The application of our method to HfSiON metal–oxide–semiconductor field-effect transistors (MOSFETs) is demonstrated. The channel length dependence of each component shows the improvement resulting from the decoupling method. Furthermore, the activation energy of the NBTI component in HC degradation coincides with that of NBTI.

Influence of Traps and Carriers on Reliability in HfSiON/

The influence of traps and current on the degradation in HfSiON has been studied. Different characteristics of activation energy for TDDB between thick and thin HfSiON, where the Poole Frenkel (PF) and tunnel currents mainly flow, respectively, were observed in the same temperature range. It was indicated that the current could promote the breakdown in HfSiON. Furthermore, we investigated the correlation between pre-existing traps and trap generation in HfSiON/SiO2 stacks with fluorine incorporation. It was found that the nature of generated traps correspond to that of pre-existing traps. From these results, it was considered that the interaction between traps and carriers causes the degradation in HfSiON.

\hbox{SiO}_{2}

Time Dependent Dielectric Breakdown (TDDB) in p-FETs with HfSiON/SiO2 gate stacks under negative bias stress has been studied. It is shown that the shape parameter of Weibull distribution of Tbd, β, is very small value independent of gate electrode materials. This small β seems to arise from the interface layer (I.L.) breakdown. Further experimental result reveals the existence of additional interface layer degradation mechanisms due to hydrogen in HfSiON. The reduction of hydrogen amount in high-k dielectrics leads to the longer-term reliability in metal-gate /high-k gate stacks.

Stacks

We have investigated the impact of polarity of gate bias and Hf concentration on HfSiON/SiO2 gate dielectric breakdown (DB) with time-zero DB (TZDB) and time-dependent DB (TDDB). At TZDB, the gate leakage currents at breakdown (BD) under negative bias are much smaller than those with positive bias without regard to accumulation or inversion states. Since the electric fields at BD are not all the same, the BD mechanism cannot be explained with a simple thermochemical model for all types of stress for HfSiON gate dielectric. With TDDB, the electric-field acceleration constant is dependent on the Hf concentration. Calculated active dipole moments in HfSiON have been shown to be similar to theoretical values for nMOS but not pMOS. Thermochemic BD of HfSiON, itself (not interface SiO2), is adequate to describe nMOS in the inversion state. On the other hand, the BD of pMOS in the inversion state is affected by the carrier currents and not the electric fields as the TZDB. The BD mechanisms are strongly dependent on both the polarity of the gate bias and the Hf concentration.

Novel TDDB mechanism for p-FET accelerated by hydrogen from HfSiON film

We have investigated the impact of polarity and Hf concentration on HfSiON/SiO2 gate dielectrics breakdown with TZDB and TDDB. In TZDB, gate leakage currents at breakdown in negative bias are much smaller than those in positive bias without regard to accumulation or inversion states. Since electric fields at breakdown are not all the same, the breakdown mechanism cannot be explained with a simple thermochemical model. In TDDB, thermochemical breakdown of HfSiON itself is adequate for nMOS in inversion. On the other hand, breakdown of pMOS in inversion is affected by the carrier currents. The breakdown mechanisms are strongly dependent on the polarity and Hf concentration