Charge transport model to predict intrinsic reliability for dielectric materials

Abstract

Several lifetime models, mostly empirical in nature, are used to predict reliability for low-k dielectrics used in integrated circuits. There is a dispute over which model provides the most accurate prediction for device lifetime at operating conditions. As a result, there is a need to transition from the use of these largely empirical models to one built entirely on theory. Therefore, a charge transport model was developed to predict the device lifetime of low-k interconnect systems. The model is based on electron transport and donor-type defect formation. Breakdown occurs when a critical defect concentration accumulates, resulting in electron tunneling and the emptying of positively charged traps. The enhanced local electric field lowers the barrier for electron injection into the dielectric, causing a positive feedforward failure. The charge transport model is able to replicate experimental I-V and I-t curves, capturing the current decay at early stress times and the rapid current increase at failure. The model is based on field-driven and current-driven failure mechanisms and uses a minimal number of parameters. All the parameters have some theoretical basis or have been measured experimentally and are not directly used to fit the slope of the time-to-failure versus applied field curve. Despite this simplicity, the model is able to accurately predict device lifetime for three different sources of experimental data. The simulation's predictions at low fields and very long lifetimes show that the use of a single empirical model can lead to inaccuracies in device reliability.

On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

“…These observations confirmed that the increased electron mobility after stressing is not due to the trap-filling effect but due to some permanent changes in the material. This may be interpreted in analogy to the progressive degradation in gate dielectrics that continuous trap creation and enhanced trap-assisted tunneling cause an increase in the leakage current close to breakdown 45 . In the case of a polymer, the injected charges can induce exciton formation, catalyze bond cleavage, generate free radicals and encourage oxidations as they diffuse throughout the material 46 , which is likely to create more deep traps along its path so that direct tunneling between deep traps becomes more favorable and thus may explain the increase in the apparent charge mobility.…”

Atomic bonding and electrical potential at metal/oxide interfaces, a first principle study

“…The Al-O bond is also more polar than the Si-O bond. Then, according to the field accelerated defect creation model, the Al-O bond is supposed to be more sensitive to electric fields 2,[11][12][13] . However, the interfacial oxygen atom binding energy is reduced by only ~30 meV, by applying a 0.3 V/Å electric field, which corresponds to a ~6.4 MV/cm oxide field.…”

“…All these models correlate the time dependence of the breakdown to the dynamics of point defect generation in thin oxides [1][2][3] . Both potential-based and current-based breakdown models assume that the applied electric field, or the flow of tunneling and thermally injected electron in the oxide barrier, is responsible for the creation of point defects 11,12 . It is further assumed that such defects act as charged traps that locally enhance the oxide electric field.…”

“…While being successful at reproducing the time to breakdown trends as a function of the applied electric magnitude, adjusted parameters are most often used to describe the bond breaking dynamics. In experiments, impurities present in the oxide or diffusing from the electrodes can trigger extrinsic breakdown, and the precise nature of the involved point defects is rarely assessed 11,12 . The point defect characteristics can however be deduced from measurements, where it has been concluded that involved defects in SiCOH low-k dielectrics must be positively charged and able to trap electrons.…”

Hydrogen release at metal-oxide interfaces: A first principle study of hydrogenated Al/SiO 2 interfaces

“…Silica constitutes the basis of low-k materials that have been used extensively for the metal-oxide interconnect structure of integrated circuits (IC) to minimize signal delays [1,2]. Dielectric breakdown triggered by the oxide degradation [3][4][5][6][7][8][9] is one of the major failure mechanisms for these devices. Three primary defect generation models have been built to describe the dielectric breakdown: (i) electron impact ionization [10], (ii) Anode Hole Injection (AHI) [11], and (iii) Anode Hydrogen Release (AHR) [12][13][14].…”