Oxide Breakdown Mechanism Research Articles

On the "intrinsic" breakdown of thick gate oxide.

The thick gate oxide breakdown mechanism has become an important topic again due to the rising demand for power electronics. The failure of the percolation model in explaining the observed Weibull shape factor, β, seriously hampers the establishment of thick gate oxide breakdown models and the ability to project reliability from measurement data. In this work, lifetime shortening by oxide defects are simulated to produce degraded breakdown distributions that match experimentally observed βs. The result shows that even a low density of defects with the right energy is enough to greatly degrade β for thick oxides. Strong area scaling for thin oxides counters this sensitivity to defects effectively and explains why the percolation model is successful in thin oxides but not in thick oxides. Only defects with the appropriate energy can degrade the breakdown distribution. The required energy is consistent with oxygen vacancy defect after capturing a hole and the concentration required is consistent with very high-quality oxide. This explains the consistent low β values for thick oxides universally reported in the literature.

Electric-induced oxide breakdown of a charge-coupled device under femtosecond laser irradiation

A femtosecond laser provides an ideal source to investigate the laser-induced damage of a charge-coupled device (CCD) owing to its thermal-free and localized damage properties. For conventional damage mechanisms in the nanosecond laser regime, a leakage current and degradation of a point spread function or modulation transfer function of the CCD are caused by the thermal damages to the oxide and adjacent electrodes. However, the damage mechanisms are quite different for a femtosecond laser. In this paper, an area CCD was subjected to Ti: sapphire laser irradiation at 800 nm by 100 fs single pulses. Electric-induced oxide breakdown is considered to be the primary mechanism to cause a leakage current, and the injured oxide is between the gate and source in the metal-oxide semiconductor field-effect transistor (MOSFET) structure for one CCD pixel. Optical microscopy and scanning electron microscopy are used to investigate the damaged areas and the results show that the electrodes and the oxide underneath are not directly affected by the femtosecond laser, which helps to get rid of the conventional damage mechanisms. For the primary damage mechanism, direct damage by hot carriers, anode hole injection, and an enlarged electric field in the insulating layer are three possible ways to cause oxide breakdown. The leakage current is proved by the decrease of the resistance of electrodes to the substrate. The output saturated images and the dynamics of an area CCD indicate that the leakage current is from an electrode to a light sensing area (or gate to source for a MOSFET), which proves the oxide breakdown mechanism.

Programming Void Populations in the Passive Oxide of Aluminum in an Attempt to Correlate Evolving Nanostructure with Passivity Loss

Galvanostatic polarization in aqueous chloride media is shown to be a viable method for controlling the characteristics of a void and pore population within the passive oxide on aluminum thin films. Current density and anion type are demonstrated to be effective control parameters of nanoscale feature density and size. The use of the borate anion with chloride regulates the void formation and points to a mechanism where competitive anion adsorption at the barrier layer dictates the fraction of current density that is channeled into void formation versus oxide growth. Preliminary results are presented for microcapillary-based measurements of pit initiation in the presence of a pre-programmed void population. These results show the presence of an induction time with pre-existing voids. These findings suggest that where voids may play a role in pit initiation, other factors may be necessary in a more concerted mechanism of oxide breakdown and pit initiation.

On the role of holes in oxide breakdown mechanism in inverted nMOSFETs

Using constant voltage stresses carried out in the inversion regime on nMOS transistors, poly-Si gated to poly-SiGe gated devices are compared. It is shown that charge (and time) to breakdown is significantly increased by the use of silicon–germanium alloy as a gate material. The result is discussed from the anode hole injection and the hydrogen release mechanisms point of view by estimating the expected modifications of each defect generation probability. It is concluded that even in the absence of (minority/majority) hole carrier density at the anode/oxide interface, the hole distribution is likely to impact the breakdown mechanisms.

Effect of physical stress on the degradation of thin SiO/sub 2/ films under electrical stress

In this work, we demonstrate that for ultrathin MOS gate oxides, the reliability is closely related to the SiO/sub 2//Si interfacial physical stress for constant current gate injection (V/sub g//sup -/) in the Fowler-Nordheim tunneling regime. A physical stress-enhanced bond-breaking model is proposed to explain this. The oxide breakdown mechanism is very closely related to the Si-Si bond formation from the breakage of Si-O-Si bond, and that is influenced by the physical stress in the film. The interfacial stress is generated due to the volume expansion from Si to SiO/sub 2/ during the thermal oxidation, and it is a strong function of growth conditions, such as temperature, growth rate, and growth ambient. Higher temperatures, lower oxidation rates, and higher steam concentrations allow faster stress relaxation through viscous flow. Reduced disorder at the interface results in better reliability. Fourier transform infrared spectroscopy (FTIR) technique has been used to characterize stress in thin oxide films grown by both furnace and rapid thermal process (RTP). In conjunction with the Gibbs free energy theory, this model successfully predicts the trends of time-to-breakdown (t/sub bd/) as a function of oxide thickness and growth conditions. The trends of predicted t/sub bd/ values agree well with the experimental data from the electrical measurement.

Mechanism of time-dependent oxide breakdown in thin thermally grown SiO2 films

In the thermally grown silicon dioxide (SiO2) films, thermochemical-breakdown and hole-induced-breakdown models are theoretically formulated to explain the external electric-field dependence of time-dependent dielectric breakdown (TDDB) phenomenon. Long-term TDDB test results proved to support the thermochemical-breakdown model. The time-dependent oxide breakdown mechanism is further studied on the basis of quantum physical chemistry. The structural transformations of a-SiO2 up to breakdown are simulated by a semiempirical molecular orbital calculation method (PM3 method) using Si5O16H12 clusters. The structural transformations can be classified into: (a) amorphous-like SiO2 (a-SiO2), (b) hole-trapped SiO2 (hole trap), and (c) electrically broken down SiO2 (breakdown) structures. The atom configuration shows a shortened length between the nearest oxygen atoms due to hole trapping. This leads to time-dependent oxide breakdown, and the breakdown structure consists of a pair of oxygen-excess (Si–O–O–Si) and oxygen-vacancy (Si–Si) defects. The heat of formation and frontier orbital energies of structural transformations account well for the physical aspects of the TDDB phenomenon.

Roles of Primary Hot Hole and FN Electron Fluences in Gate Oxide Breakdown

ABSTRACTIn this work, we report the link between the primary hot hole and Fowler Nordheim (FN) electron injections in oxide breakdown mechanism. A simple breakdown model is established. The experimental method is carefully designed to measure the primary hot hole fluence and FN electron fluence separately and accurately. The calculation based on our model is in very good agreement with our experiments. Oxide breakdown is stimulated by a combined effect when the sum of the trap density Dpri activated by primary hot hole injection and the trap density Dn activated by FN electron injection reaches a critical value Dcri. The hole is two orders of magnitude more effective than FN electron in causing breakdown. Since primary hot hole injection may occurs under many realistic device operation in the circuit, existing oxide lifetime projected from conventional TDDB measurement by only applying FN stress is overestimated in many cases. The model demonstrated in this work lays the groundwork in approaching a more appropriate way for predicting the oxide reliability and lifetime.

Modeling manufacturing yield and reliability

In this paper, we introduce the concept of reliability defect, present the time-dependent defect growth model during operations based on a defect-related gate oxide breakdown mechanism, and build the yield-reliability relation model. Discussions presented here can also be applicable to other device failures when different physics-of-failure mechanisms are found. Through the relation model, it is possible to find a minimum level of latent defect screening to assure the required level of reliability and predict reliability for new products when it is combined with a yield prediction model.

Pitting Corrosion of Titanium

The breakdown of native and anodically grown oxide films on Ti electrodes is investigated by scanning electrochemical microscopy (SECM), video microscopy, transmission electron microscopy, and voltammetry. SECM is used to demonstrate that the oxidation of Br− on Ti occurs at microscopic surface sites (10 to 50 μm diam, 30 sites/cm2) that are randomly positioned across the oxide surface. After determining the position of the active sites for Br− oxidation, breakdown of the oxide is initiated by increasing the electrode potential to more positive values. Direct correspondence is observed between the location of the electroactive sites and corrosion pits, indicating that oxide breakdown is associated with a localized site of high electrical conductivity. The potential at which pitting is observed in voltammetric experiments is found to be proportional to the average oxide thickness, for values ranging between 20 and 100 Å, indicating that breakdown is determined either by the magnitude of the electric field within the oxide or by the interfacial potential at the oxide/Br−solution interface. Pitting occurs at significantly lower potentials in Br− solutions than in Cl− solutions, suggesting a strong chemical interaction between the surface and Br−. A mechanism of oxide breakdown is proposed that is based on the potential‐dependent chemical dissolution of the oxide at microscopic surface sites.

Electrcn Trapping/Detrapping in Thin SiO2 Under High Fields

ABSTRACTA constant alternating current stressing technique is employed to study the electron trapping and detrapping cha~acteristics within a layer of thin silicon dioxide (˜.100 Å). A two-charge centroid model is proposed to explain the trapping/detrapping phenomena under high electric fields. The oxide breakdown mechanism induced by the local field of trapped electrons is also discussed.