Time-dependent Dielectric Breakdown Mechanism Research Articles

The TDDB Characteristics of Ultra-Thin Gate Oxide MOS Capacitors under Constant Voltage Stress and Substrate Hot-Carrier Injection

The breakdown characteristics of ultra-thin gate oxide MOS capacitors fabricated in 65 nm CMOS technology under constant voltage stress and substrate hot-carrier injection are investigated. Compared to normal thick gate oxide, the degradation mechanism of time-dependent dielectric breakdown (TDDB) of ultra-thin gate oxide is found to be different. It is found that the gate current (Ig) of ultra-thin gate oxide MOS capacitor is more likely to be induced not only by Fowler-Nordheim (F-N) tunneling electrons, but also by electrons surmounting barrier and penetrating electrons in the condition of constant voltage stress. Moreover it is shown that the time to breakdown (tbd) under substrate hot-carrier injection is far less than that under constant voltage stress when the failure criterion is defined as a hard breakdown according to the experimental results. The TDDB mechanism of ultra-thin gate oxide will be detailed. The differences in TDDB characteristics of MOS capacitors induced by constant voltage stress and substrate hot-carrier injection will be also discussed.

Modeling of TDDB in advanced Cu interconnect systems under BTS conditions

Due to the shrinking of the device size in integrated circuits together with the use of novel, less stable low-k back-end-of-line dielectrics more attention has to be paid to the time dependent dielectric breakdown (TDDB) effect. In this work the TDDB mechanisms are investigated and modeled based on constant-voltage bias-temperature stress (BTS) experiments from the 90nm and 45nm technology nodes. The modeling of the I-t dependencies is based on the numerical model of Haase in which it is assumed that the degradation of the dielectric is caused just by the electronic leakage current itself. By two simple modifications of the model and an adjustment of several model parameters it was possible to achieve a very good agreement between the model and the experiment for single constant-voltage BTS dependencies. For two different experimental data sets from the 45nm technology node the TDDB behavior in dependence on the bias voltage and temperature is analyzed and compared with the results of the modified Haase model and the Poole-Frenkel lifetime model.

(Invited) A Study of Dielectric Breakdown Mechanisms in MG/HK MISFETs: From the Viewpoint of TDDB Statistics

The Time Dependent Dielectric Breakdown mechanisms of n/p-FETs having high-k gate dielectrics have been studied through the Weibull distribution. From the thickness dependence of Weibull beta, it is found that the breakdown in n-FETs and p-FETs is mostly determined by the breakdown of high-k layer and interfacial layer (I.L.), respectively. Furthermore, Weibull beta in p-FETs is found to be independent of the injected carrier ratio (Jhole/Jelectron) while those in n-FETs strongly depend on this ratio. Improvement of Weibull beta through the control of the injected carrier ratio together with metal gate application leads to extremely longer lifetime in n-FETs. Improvement of average Tbd through the control of hydrogen concentration in high-k leads to longer life time also in p-FETs.

Phenomenological classification of stress-induced leakage current and time-dependent dielectric breakdown mechanism

The time-dependent dielectric breakdown (TDDB) of Cu damascene interconnects was investigated, noting the time variations in stress-induced leakage current. Copper interconnects normally have symmetric current-voltage curves, which suggests that defects are distributed symmetrically between two Cu lines. Although the impact damage model satisfies this requirement, as does the thermochemical E-model, the Cu diffusion model does not. Without the barrier metal, Cu+ ions rapidly penetrate the dielectric film and form unstable conduction filaments. The leakage current fluctuates greatly due to the rapid Cu movement in the last stage of bias temperature stressing. These current fluctuations also appear in the triangular voltage sweep so that a spurious peak emerges, which is unrelated to the ionic displacement current. The extrinsic TDDB has a small field acceleration parameter (0.5 cm/MV); however, it switches to a large one (4.5 cm/MV) at electrical fields that are higher than 2 MV/cm. Another type of degradation is the thermal reaction between Cu and low-k. High-temperature annealing (>200 °C) generates shallow-energy-level defects in the SiO forbidden-energy gap. The shallow-energy-level defects have less impact on the TDDB lifetime although they cause a large Poole–Frenkel type current.

Accurate TDDB Lifetime Prediction of High-k Stacked Gate Dielectrics with Regarding High Density Initial Traps

Essentials required for the accurate TDDB lifetime (TBD) prediction of high-k stacked gate dielectrics are discussed. For this purpose, thorough understanding of the time dependent dielectric breakdown (TDDB) mechanism is indispensable, along with clarifying its stress gate voltage (VG) dependence. As for the TDDB mechanism, we propose the Generated Subordinate Carrier Injection (GSCI) model, which presumes that the degradation is dominated by the injected subordinate carriers (IDC). Because of the coexistence of the current component which does not contribute to the breakdown such as the trap-assisted current, the decomposition of the subordinate carrier current to each component is needed. On the other hand, to obtain the stress VGdependence of TBD, we point out the universal relationship between the voltage acceleration factor of TBD and the stress VG. It is demonstrated that the accurate lifetime prediction can be realized on the basis of the GSCI model combined with this universality.

Charge to breakdown mechanism of thin ONO films

Effects of charge trapping in the thin ONO (oxide silicon nitride oxide) film caused by the voltage stress on the time-dependent dielectric breakdown (TDDB) mechanism are studied. The purpose is to report the TDDB data of the films after various treatments of charge injection and thermal annealing together with analysis of the experimental data to enhance the understanding of the dielectric breakdown mechanisms of the ONO film. It is observed that the trapped charges injected from one electrode have very little effect on the TDDB mechanism during stress to the other electrode. This suggests that the position of trapped charges may be quite different for the two injecting electrodes and that breakdown mechanisms may be initiated from the different charge positions and sources. >