Juan Borja

On the dynamics of Cu ions injection into low-k nanoporous materials under oscillating applied fields

Cu injection into low-k dielectrics was studied using oscillating bipolar field experiments coupled with a mass transport model. Cu/SiCOH/Si structures were stressed using an oscillating square bipolar applied field at 200 °C. Breakdown was defined experimentally as the time it takes for the leakage current to exceed 1 × 10−5 A under given stress conditions. Time to failure was found to depend on field oscillating frequency and amplitude of the applied field. It was determined that ion solubility primarily affects the magnitude of lifetime enhancement, while mobility affects its onset in the frequency domain. Overtime, the local field generated by the accumulation of Cu ions during bias temperature stress resists the action of the oscillating field thus inhibiting the ability to sweep ions from cathode to anode through reversal of the applied field and thereby limits the observed lifetime enhancement. Predictions from the model match trends for experimental data involving transport of Cu ions into SiCOH.

Charge transport model to predict intrinsic reliability for dielectric materials

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. ...

Photocatalytic properties of porous titania grown by oblique angle deposition

High surface area nanorods of titanium dioxide were grown by oblique angle deposition on a transparent substrate to investigate their effectiveness as photocatalytic agents for the destruction of organic contaminants in air and water. Optical transmission measurements were made that allowed for an estimation of the porosity of the film (75%-78%). Comparing transmission measurements with those from a dense anatase film showed that the penetration depth for the light into the nanorod film was 2.5 times that in a dense, anatase film. The photocatalytic degradation of indigo carmine dye on the porous films was shown to depend on film thickness and annealing conditions. The effectiveness of the film was assessed by observing the change in absorbance of the dye at 610 nm over time and quantifying the film performance using a pseudo-first-order reaction rate model. Reaction rates increased as the film thickness increased from 600 nm to 1000 nm, but leveled out or decreased at thicknesses beyond 1500 nm. A transp...

Variable Ramp Rate Breakdown Experiments and the Role of Metal Injection in Low-

Varying the voltage ramp rate during conventional I-V testing allows one to distinguish between metals that react with the surface of a dielectric or barrier (Al), metals that react and can be injected into the dielectric or barrier (Cu), and metals that behave as inert electrodes (Au). By performing experiments over a wide range of ramp rates, one can distinguish between intrinsic breakdown driven by energetic electrons and holes and breakdown that is catalyzed by injected metal ions. The magnitude of the slopes of the I-V traces indicates whether breakdown is in trinsic or catalyzed by metal injection. A mass transfer model de scribing the drift of copper ions through the dielectric was able to reproduce the broad features of the experimental data. Predictions of the model, including that the slope of the I-V curve should be steeper for metal ion injection, that the breakdown field strengths for all metallizations should converge at very high ramp rates, and that d(ln(tfail))/dR ≈ -1, were confirmed experimentally. Breakdown was shown to be controlled by processes occurring at the anode and differences in the breakdown field strength for the different metals appear to be related to the formation of an interfacial oxide layer between the metal and dielectric.

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Time dependent dielectric failure has become a pivotal aspect of interconnect design as industry pursues integration of sub-22 nm process-technology nodes. Literature has provided key information about the role played by individual species such as electrons, holes, ions, and neutral impurity atoms. However, no mechanism has been shown to describe how such species interact and influence failure. Current leakage relaxation in low-k dielectrics was studied using bipolar field experiments to gain insight into how charge carrier flow becomes impeded by defects within the dielectric matrix. Leakage current decay was correlated to injection and trapping of electrons. We show that current relaxation upon inversion of the applied field can be described by the stretched exponential function. The kinetics of charge trapping events are consistent with a time-dependent reaction rate constant, k=k0⋅(t+1)β−1, where 0 < β < 1. Such dynamics have previously been observed in studies of charge trapping reactions in amorphou...

Dielectrics

Assessing the lifetime of low-k dielectric materials integrated with Cu remains an important issue for interconnect reliability as designs pursue dielectric thicknesses below 100 nm. We present electrical tests and a mass transport model to assess Cu-catalyzed dielectric failure when transient fields are applied. We show that beyond a certain frequency of oscillation, dielectric lifetime can be enhanced up to two orders of magnitude. The proposed transport model predicts the dynamics observed experimentally and reproduces trends observed as we change field frequency and amplitude.

Current leakage relaxation and charge trapping in ultra-porous low-k materials

Reliability and robustness of low-k materials for advanced interconnects has become one of the major challenges for the continuous down-scaling of silicon semiconductor devices. Metal catalyzed time dependent breakdown is a major force preventing integration of sub-32 nm process technology nodes. Here, the authors demonstrate that ions can behave as trapping points for charge carriers. A mechanism for describing trapping of charge carriers into mobile ions under bias and temperature stress is presented. Charge carrier confinement into ionic center was found to be dominated by ionic transport. After extended bias and temperature stress, the magnitude of charge trapping into ionic centers decreased. Simulations suggest that built-in fields could reduce the effect of externally applied fields in directing ionic drift, therefore inhibiting the trapping mechanism. This work depicts the dual role of ionic species when catalyzing dielectric failure (mobile defect and local field distortion).

Impact of Frequency From a Bipolar Applied Field on Dielectric Breakdown for Low-

Dielectric breakdown in a solid film is characterized as the irreversible loss of the material’s local dielectric insulation property. Failure originates when the dielectric is subjected to electrical stress beyond a critical point. In general, dielectric breakdown mechanisms in amorphous films can be categorized as either intrinsic or extrinsic in nature (He and Sun, High-k gate dielectrics for CMOS technology, 2012, p.166). Intrinsic failure corresponds to damage caused by the transport of electrons across the dielectric matrix, which eventually degrades the material and causes it to exceed its innate limit. Extrinsic failure corresponds to a breakdown accelerated by flaws stemming from the transport of foreign species across the dielectric film. Extrinsic failure occurs on a much faster timescale than intrinsic breakdown. Some of the most common causes of extrinsic failure are metal atoms, ions, and moisture. These foreign species are the result of manufacturing process steps and instabilities in metal/dielectric interfaces (He and Lu, MetalDielectric Interfaces in Gigascale Electronics Thermal and Electrical Stability, 2012, p.127). “It is not true that people stop pursuing dreams because they grow old, they grow old because they stop pursuing dreams.” —Gabriel Garcı́a Márquez 1.1 A Brief History of Dielectric Breakdown Whether in gases, liquids, or solids, dielectric breakdown is a field that continues to baffle the scientific community. The first significant studies of dielectric breakdown in crystalline solids date to the early 1930s. Zener (1934) explained dielectric breakdown in solids as a phenomenon caused by the direct excitation of electrons by an electric field. The magnitude of the applied electric field was found to considerably affect the onset of breakdown. Zener (1934) theorized that the rate by which electrons escape energy bands in the insulator is equal to P 1⁄4 qFa=h ð Þ exp π2mαφ=h qF j j , where F is the electric field, q is the elementary charge, α is the one-dimensional lattice period, m is the mass of the electron, φ

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A Multiple I-V Ramp Test is designed to stress low-k SiCOH-based dielectrics that have absorbed moisture. Two conduction regimes are found based on the total injected fluence into the dielectric films and the concentration of water in the dielectric. The dielectric under stress is either characterized by electron trapping, or the generation of traps and/or interface states. A mechanism for moisture-related breakdown is proposed that is consistent with results from previous works on water-diffused silicon dioxide films.

Materials

Summary form only given. The reliability of new ultra-porous low-k materials is often a fascinating and complex tale involving multiple concepts from material science, electrical and chemical engineering. Pursuing an understanding of reliability for novel low-k materials requires the dissection of fundamental mechanisms and phenomena altering the electrical and physical properties of the dielectric matrix. Failure mechanisms can be categorized into two main groups. Intrinsic failure arises from damage to the dielectric matrix due to the transport of charge carriers. Ion catalyzed failure results from the drift of ionic species originating from the metal/dielectric interface. Integration of sub-20nm process technology nodes can be radically advanced by resolving how major failure mechanisms coexist and collaborate to generate dielectric failures. Here, we present a set of dynamic applied field experiments designed to identify changes in the conduction and reliability of dielectric films as result of bias and temperature stress (BTS). It is shown that ionic species originating from the metal/dielectric interface can behave as trapping centers for charge carriers under BTS. Trapping of electrons into ionic centers could increase the scattering of charge carriers which leads to the additional formation of intrinsic defects across the dielectric matrix, thus accelerating intrinsic failure. A mechanism is proposed to describe how leakage current decay at the onset of BTS is related to charge carrier confinement into intrinsic and ionic defects. The kinetics of charge trapping events were found to be consistent with a time-dependent reaction rate constant, k = k0 · (t + 1)β-1 where 0<;β<;1. This formulation leads to a classic, stretched exponential decay rate that we are looking to use to help predict dielectric reliability.