Merits of Batch ALD

In this presentation, we provide an overview of the merits and applications of batch ALD in a vertical furnace. In addition, a number of common perceptions related to cycle time, films specs and batch processing in industry will be examined more closely.Batch ALD offers a significant cost-per-wafer reduction compared to clustered single-wafer tools for a range of existing and emerging materials and applications. We present results on cycle time reduction to 20 s and below for ALD Al2O3 and TiN processes without significantly impacting uniformity, resistivity and step coverage. How purge and precursor flows influence the deposition process will be shown by combining experiment and simulation. The influence of deposition temperature and growth inhibition will be covered by presenting a thermal process for the deposition of AlN. A throughput of >50 wafers per hour was achieved for 10 nm films. For Si solar cells, the throughput and costs requirements are the most stringent. We will show that a platform of 4 reactors with automated handling for square solar wafers can reach 4800 wafers/hour (5 nm Al2O3) with remarkably low TMA consumption.With the workhorse materials being TiN and Al2O3 and applications as diverse as metal gates in logic, trench capacitor electrodes, capacitor dielectrics, barrier layers and passivation films, batch ALD has firmly established itself at device manufacturers and foundry sites. Prospects for emerging markets such as MEMS, solar and LED will be discussed.

Bismuth telluride (Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) and its alloys are the most commonly used materials for thermoelectric devices. In this paper, the fluxless bonding process was developed to bond Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> chips to alumina substrates for high temperature applications. The silver-indium (Ag-In) system was chosen for the process development. To work with this system, the Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> chips were coated with 100 nm titanium (Ti) and 100 nm gold (Au) as barrier layer and plated with 10 μm Ag layer. The Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> samples were annealed at 250 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C for 200 h. No interdiffusion between Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and Ag was detected. The Ti/Au barrier layer was not affected either. It showed exceptional step coverage on the rough Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> surface even after the annealing process. To prepare for bonding, alumina substrates with 40 nm TiW and 2.5 μm Au were plated with 60 μm Ag, followed by 5 μm In and thin Ag cap layer for oxidation prevention. The Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> chips were bonded to alumina substrates at 180 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. No flux was used. The resulting void-free joint consists of five regions: Ag, (Ag), Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> In, (Ag) and Ag. (Ag) is Ag-rich solid solution. The joint has a melting temperature higher than 660 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. Due to the thick ductile Ag layer on alumina, the Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> chip did not break after bonding despite its significant coefficient of thermal expansion mismatch with alumina.

Determining the electric-field strength in a passive film via photo-induced electric fields

Dramatically reducing cycle times through flash development

Copper-based alloys are widely used in the consumer electronics industry for components such as connector contacts, shielding gaskets, and terminals. Nickel silver is a general term for alloys that contain copper, nickel, and zinc. Nickel silver first became popular as a base metal for silver-plated cutlery and other silverware, notably electro-plated nickel silver, jewelery and coins. In this article, the electrochemical stability of Cu–10Ni–10Zn alloy was compared with that of pure copper and two of copper ternary alloys, namely Cu–10Al–10Zn and Cu–10Al–10Ni in synthetic sweat solution, Hank’s solution and in Ringer physiological solution. Corrosion behavior of the different electrodes was investigated using cyclic voltammetry, potentiodynamic polarization, and impedance spectroscopy techniques. The CVs showed peaks concerning the redox reactions for copper. These peaks were assigned to the formation and reduction of copper species. Furthermore, they showed that the copper oxidation was suppressed to a large extent by the presence of Ni and zinc in the alloy composition than the presence of Al and Zn or the presence of Al and Ni elements. Also, the results showed that the Cu–10Ni–10Zn alloy exhibited good corrosion resistance due to the formation of a protective passive film. The electrochemical impedance spectroscopy results indicated that either a duplex film with an inner barrier layer and an outer porous layer or a single passive layer was formed on the surface. The formation of such passive film was discussed, and the different alloy surfaces examined by scanning electron microscopy and subjected to EDAX analysis. The surface analysis has shown the participation of the different alloying elements in the passive film according to the alloy constituents. Addition of Ni decreases the rate of corrosion of the Cu, and the Cu–10Ni–10Zn was found to be the most corrosion-resistant alloy.

The stability of the barrier layers of bilayer passive films that form on metal and alloy surfaces, when in contact with oxidizing aqueous environments, is explored within the framework of the Point Defect Model (PDM) using phase-space analysis (PSA), in which the rate of growth of the barrier layer into the metal, (dL{sup +}/dt), and the barrier layer dissolution rate, (dL{sup -}/dt), are plotted simultaneously against the barrier layer thickness. A point of intersection of dL{sup -}/dt with dL{sup +}/dt indicates the existence of a metastable barrier layer with a steady state thickness greater than zero. If dL{sup -}/dt > (dL{sup +}/dt){sub L=0}, where the latter quantity is the barrier layer growth rate at zero barrier layer thickness, the barrier layer cannot exist, even as a metastable phase, as the resulting thickness would be negative. Under these conditions, the surface is depassivated and the metal may corrode at a rapid rate. Depassivation may result from a change in the oxidation state of the cation upon dissolution of the barrier layer, such that the dissolution rate becomes highly potential dependent (as in the case of transpassive dissolution of chromium-containing alloys, for example, in which the reaction Cr{sub 2}O{sub 3} + 5H{sub 2}O {yields} 2CrO{sub 4}{sup 2-} + 10H {sup +} + 6e{sup -} results in the destruction of the film), or by the action of some solution-phase species (e.g., H{sup +}, Cl{sup -}) that enhances the dissolution rate to the extent that dL{sup -}/dt > (dL{sup +}/dt){sub L=0}. The boundaries for depassivation may be plotted in potential-pH space to develop Kinetic Stability Diagrams (KSDs) as alternatives to the classical Pourbaix diagrams for describing the conditions under which metals or alloys exist in contact with an aqueous environment. The advantage of KSDs is that they provide kinetic descriptions of the state of a metal or alloy that is in much closer concert with the kinetic phenomenon of passivity and depassivation than are equilibrium thermodynamic diagrams. Thus, KSDs more accurately account for the limits of passivity in highly acidic systems, where acid depassivation occurs, and at high potentials, where transition to the transpassive state may occur in some systems. In any event, phase space analysis of the PDM permits specification of the conditions over which reactive metals will remain passive in contact with aqueous systems and hence of the conditions that must be met for the existence of our metals-based civilization.

Surface cleaning of patterned wafers by batch processing has become a challenge as semiconductor fabrication moves deeper into submicron technology nodes and utilizes larger wafer sizes. Many fabrication plants (fabs) have already employed single wafer cleaning tools. A key challenge in the application of single-wafer processing tools, compared to conventional multi-wafer batch tools, is their lower throughput. Typical surface cleaning consists of exposure to a chemistry intended to remove contaminants, followed by rinsing with ultrapure water, followed by drying. To help reduce cycle time and to minimize resource consumption during rinse processes while producing a highly clean surface, a novel in situ metrology has been developed for the detection of trace residual impurities in fine structures of patterned wafers during surface preparation processes. This technology includes both hardware for in situ measurement of impurities and software for process data analysis. The technology can be used for on-line control in existing processes as well as for development and testing of new recipes and processes. In this paper, the effects of the key rinse process parameters such as water flow rate, wafer spin rate, and water temperatures are studied. Successful incorporation of this metrology into surface preparation steps will eliminate dependence on costlier and more time-consuming external analysis techniques.

Detailed potential/pH stability diagrams for the lithium‐water system at 25°C have been derived as part of a program to describe the electrochemistry of the lithium anode in aqueous alkaline environments. The diagrams include lithium hydride as a stable solid phase at sufficiently negative potentials, and it is postulated that the passive film on Li in contact with concentrated alkaline solutions, under open‐circuit conditions, comprises a LiH barrier layer covered with a hydrated LiOH outer layer. The postulated existence of as a barrier layer, under open‐circuit conditions, is inconsistent with the thermodynamic data for metallic lithium in contact with concentrated LiOH and LiOH + KOH solutions. © 1999 The Electrochemical Society. All rights reserved.

The growth kinetics of the surface film formed upon the multi-principal element alloy AlTiVCr under anodic polarisation in 0.6 M NaCl was investigated using atomic emission spectroelectrochemistry (AESEC). The AESEC charge balance analysis revealed that thickness of the barrier layer of the passive film upon the alloy: (1) increases linearly with the increase in anodic potential during potentiodynamic polarisation, and (2) increases logarithmically with exposure time during potentiostatic polarisation. This is consistent with the assumptions of the point defect model, despite the film being a multi-oxide film with transpassive dissolution of V and Cr. The X-ray photoelectron spectroscopy (XPS) analysis suggested that the growth of the film was predominantly due to TiO2 during anodic polarisation. The electric field was found to decrease with enrichment of TiO2 in the barrier layer. The Mott-Schottky analysis revealed that the diffusivity of oxygen vacancies increased with the increase in fraction of TiO2 in the film, which subsequently led to the increase in the growth rate of the barrier layer during transpassive dissolution. The present work is a discrete effort towards understanding the growth behaviour of the passive film experiencing complex and competing interfacial electrochemical processes, upon a multi-principal element alloy.

Damascene approaches are widely used for creating microelectronic interconnects. Successful implementation of the process is reliant upon the deposition of a refractory metal or metal nitride liner coating. It functions as a diffusion barrier layer to suppress transport of subsequently deposited interconnect metals into the surrounding dielectric. The development of vapor-phase processes for the deposition of uniform thickness liner layers has been problematic. Flux collimation and energetic deposition approaches have been attempted with mixed results as the feature size is decreased. Here, a modified kinetic Monte Carlo (KMC) method has been used to explore the physical vapor deposition of liner coatings. To incorporate the many effects associated with energetic metal fluxes, the results of molecular dynamics calculations of incident atom reflection, resputtering, surface biased diffusion, and athermal relaxations have been introduced into the KMC algorithm. The method has been applied to investigate the effects of the incidence flux’s angular distribution and kinetic energy upon the liner coating coverage. It has been found that trench step coverage uniformity increases with increasing atom kinetic energy above a threshold energy value of 20 eV. Atom resputtering/reflection are found to be the most important mechanisms responsible for improvements in the step coverage. Sputtering of already deposited material is found to be the most important mechanism for transporting the flux to the most difficult to coat lower sidewall region of a trench. Energetic deposition processes that activate these mechanisms are therefore preferred. The simulations reveal the existence of an optimal incident angular distribution to maximize coverage uniformity. For a flux with a kinetic energy of 70 eV, a cosine angular distribution within the collimation angle of ±15°–25° provided the best balance of direct and resputtered/reflected fluxes to maximize coating uniformity.

Passivity breakdown is the precursor to most forms of localized corrosion, including pitting, stress corrosion cracking, corrosion fatigue, and crevice corrosion, and also results in the phenomenon of depassivation, including electrochemical polishing and trans-passive dissolution, corresponding to passivity breakdown over macroscopic dimensions. In this OLIN Palladium Medal address, I will review my work in this area in terms of developing the Point Defect Model (PDM) for passivity and passivity breakdown and will identify principal challenges, as I see them. Starting with the rate equation for barrier layer growth, as predicted by the PDM, and by using phase-space analysis, I derive the condition that must be met for passivity to exist; the rate of growth of the barrier layer at the metal/barrier layer interface, due to the generation of oxygen vacancies at zero barrier layer thickness, must exceed the dissolution rate of the barrier layer. If this condition is met, the barrier layer may exist as a meta-stable phase and passivate the surface. In this regard, it is important to note that passivity is a kinetic state, not a equilibrium thermodynamic phenomenon, as has been so often assumed in the past. This fact has been used to resolve Faraday’s famous paradox arising from his iron-in-nitric acid experiments of 1833. Violation of this condition implies that the barrier layer cannot exist on the surface, even as a meta-stable phase and, hence, that the surface depassivates (loss of the barrier layer). If depassivation occurs over a macroscopic area, this phenomenon accounts for acid depassivation, transpassive dissolution, resistive depassivation, and electrochemical polishing. However, if depassivation occurs on a microscopic area, localized corrosion phenomena, including pitting, stress corrosion cracking, corrosion fatigue, and crevice corrosion occur, resulting in rapid penetration of a cavity into the metal. This unified theory of corrosion (UTC) accounts for all known forms of corrosion, except for hydrogen embrittlement, which lies outside of the realm of the PDM. After having established the basis of the UTC, I will then proceed to discuss the mechanism by which both general and localized depassivation occurs, which has been identified as being due to cation vacancy condensation at the m/bl interface, such that the barrier layer separates from the metal and film growth into the metal via oxygen vacancy generation cannot occur. This condition assures the depassivation inequality stated above, because the rate of growth of the barrier layer into the metal is reduced to zero and because all oxides exhibit a finite dissolution rate. The lecture will then proceed to show how the UTC predicts the critical breakdown voltage and induction time for a single breakdown site, as a function of the chloride activity, pH, and potential. It will then be shown that, by postulating that the breakdown sites are normally distributed with respect to the cation vacancy diffusivity, it is possible to derive the distribution functions for the breakdown voltage and the induction time for a large population of potential breakdown sites on the surface and to identify the critical characteristic of a breakdown site (high cation vacancy diffusivity). From there, I will demonstrate a variety of phenomena, including photo-inhibition of passivity breakdown, the impact of other halides (F-, Br-, I-), anion inhibition via competitive absorption into surface oxygen vacancies, the role of the precipitated outer layer, and the predicted impact of alloying elements on passivity breakdown. Where possible and appropriate, these predictions will be compared with experiment. As expected the PDM contains many model parameters that are poorly-known. However, values for all of the parameters may be obtained by optimizing the expressions for the impedance of the barrier layer as a function of frequency and film formation potential, as derived from the PDM, on experimental electrochemical impedance spectroscopic (EIS) data and optimization of the expressions for passivity breakdown (potential and induction time) on the corresponding experimental data. Finally, I will demonstrate how the PDM has led to the development of a deterministic protocol, Damage Function Analysis (DFA), for predicting the evolution of localized corrosion damage on metal and alloy surfaces, as a system evolves along a pre-determined corrosion evolutionary path, which is defined as the path taken by the system in terms of those properties of the system (temperature, potential, pH, [Cl-], etc) that have a significant impact of the damage accumulation rate. Time permitting, I will demonstrate how DFA may be used to predict the evolution of general and localized corrosion damage in practical systems.

A Three-Layered Approach to Radiation Therapy Software Recall Analysis

In this paper, the electrochemical behavior of the third-generation Al-Li alloy 2098 was investigated with a fundamental approach, where experimental results were theoretically analyzed in terms of the Point Defect Model (PDM). For this purpose, the AA2098-T851 was tested in NaHCO3 solution under a CO2 atmosphere to investigate the kinetics of formation and breakdown of the protective passive film. Experiments were performed at potentials where both metal dissolution and the hydrogen evolution reaction (HER) occur. Electrochemical impedance spectroscopy (EIS) was conducted at potentials obtained by stepping the potential in the anodic direction with the impedance being measured after holding the potential constant after each step for a sufficient time for steady-state to be achieved. The data were interpreted in terms of the Mixed Potential Model (MPM) that describes the passive dissolution of the metal as described by the PDM and uses the Butler-Volmer (B-V) equations to describe the kinetics of the cathodic reaction of hydrogen evolution. Optimization of the MPM on the EIS data showed that the principal point defects in the barrier layer are Al interstitials. Therefore, the diffusivity of these point defects plays a major role in the formation of the passive layer, particularly the outer layer. The barrier layer is formed exclusively via the generation of oxygen vacancies at the metal/barrier layer interface. On the other hand, the passive current density is dominated by the migration of metal interstitials and the hydrolysis of the metal interstitials ejected from the barrier layer at the barrier layer/solution interface. This leads to the formation of the non-defective outer layer. Furthermore, the cathodic Tafel constant (Pc) was obtained by considering quantum mechanical tunneling of the charge carriers produced by HER across the barrier layer on the metal surface, which revealed that the cathodic partial reaction was consistent with the slow discharge of water for the HER.

NASA's Aeronautics Research Mission Directorate recently restructured its Vehicle Systems Program, refocusing it towards understanding the fundamental physics that govern flight in all speed regimes. Now called the Fundamental Aeronautics Program, it is comprised of four new projects, Subsonic Fixed Wing, Subsonic Rotary Wing, Supersonics, and Hypersonics. The Aeronautics Research Mission Directorate has charged the Hypersonics Project with having a basic understanding of all systems that travel at hypersonic speeds within the Earth's and other planets atmospheres. This includes both powered and unpowered systems, such as re-entry vehicles and vehicles powered by rocket or airbreathing propulsion that cruise in and accelerate through the atmosphere. The primary objective of the Hypersonics Project is to develop physics-based predictive tools that enable the design, analysis and optimization of such systems. The Hypersonics Project charges the systems analysis discipline team with providing it the decision-making information it needs to properly guide research and technology development. Credible, rapid, and robust multi-disciplinary system analysis processes and design tools are required in order to generate this information. To this end, the principal challenges for the systems analysis team are the introduction of high fidelity physics into the analysis process and integration into a design environment, quantification of design uncertainty through the use of probabilistic methods, reduction in design cycle time, and the development and implementation of robust processes and tools enabling a wide design space and associated technology assessment capability. This paper will discuss the roles and responsibilities of the systems analysis discipline team within the Hypersonics Project as well as the tools, methods, processes, and approach that the team will undertake in order to perform its project designated functions.

The stress variations during polarization of iron thin film electrode in pH 8.4 borate buffer solution have been measured by a cantilever bending method to investigate the correlation between stress evolution and electrochemical reaction of the iron electrode. The stress variations toward compressive direction during active dissolution of iron result from the relaxation of the residual tensile stress due to the decrease in thickness of the iron electrode. The stress variations toward tensile direction in the pre-passive region are brought by the anodic deposition of ferrous ions once dissolved into solution. The successive potential steps for each interval of 1 h in the passive region between 0.20 and 0.90 V induce the stress variations toward compressive direction at potentials more positive than 0.30 V in connection with the growth of the inner (barrier) layer in the passive film. The electrostriction stress in the inner layer of the passive film formed on iron at 0.90 V has been estimated from the stress relaxation in the cathodic potential sweep after 1-h passivation at 0.90 V. In addition, the stress variations toward compressive direction during cathodic reduction of the passive film are attributed to the volume expansion due to the formation of iron (II) hydroxide at the intermediate step of the cathodic reduction at pH 8.4. Furthermore, the rapid stress variations toward compressive direction during hydrogen evolution at potentials more negative than 0.52 V are caused by the volume expansion in near the surface region of the iron thin film electrode due to hydrogen adsorption or absorption.