Publications

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An analytical capability is being developed that can be used to predict the effect of corrosion on the performance of electrical circuits and systems. The availability of this ''toolset'' will dramatically improve our ability to influence device and circuit design, address and remediate field occurrences, and determine real limits for circuit service life. In pursuit of this objective, we have defined and adopted an iterative, statistical-based, top-down approach that will permit very formidable and real obstacles related to both the development and use of the toolset to be resolved as effectively as possible. An important component of this approach is the direct incorporation of expert opinion. Some of the complicating factors to be addressed involve the code/model complexity, the existence of large number of possible degradation processes, and an incompatibility between the length scales associated with device dimensions and the corrosion processes. Two of the key aspects of the desired predictive toolset are (1) a direct linkage of an electrical-system performance model with mechanistic-based, deterministic corrosion models, and (2) the explicit incorporation of a computational framework to quantify the effects of non-deterministic parameters (uncertainty). The selected approach and key elements of the toolset are first described in this paper. These descriptions are followed by some examples of how this toolset development process is being implemented.

A physics-based understanding of material aging mechanisms helps to increase reliability when predicting the lifetime of mechanical and electrical components. This report examines in detail the mechanisms of atmospheric copper sulfidation and evaluates new methods of parallel experimentation for high-throughput corrosion analysis. Often our knowledge of aging mechanisms is limited because coupled chemical reactions and physical processes are involved that depend on complex interactions with the environment and component functionality. Atmospheric corrosion is one of the most complex aging phenomena and it has profound consequences for the nation's economy and safety. Therefore, copper sulfidation was used as a test-case to examine the utility of parallel experimentation. Through the use of parallel and conventional experimentation, we measured: (1) the sulfidation rate as a function of humidity, light, temperature and O{sub 2} concentration; (2) the primary moving species in solid state transport; (3) the diffusivity of Cu vacancies through Cu{sub 2}S; (4) the sulfidation activation energies as a function of relative humidity (RH); (5) the sulfidation induction times at low humidities; and (6) the effect of light on the sulfidation rate. Also, the importance of various sulfidation mechanisms was determined as a function of RH and sulfide thickness. Different models for sulfidation-reactor geometries and the sulfidation reaction process are presented.

Ion-beam irradiation and ion implantation were used to evaluate the influence of point defects and alloying elements on the sulfidation rate of copper films in atmospheric environments containing H2S. Low-energy ions from an oxygen plasma were used to grow thin metal oxide passivation layers on Cu films that were subsequently irradiated and exposed to sulfidizing environments (50-600 ppb H2S in air with 0.5-85% relative humidity). The type of oxide proved to be important in that a CuO layer essentially prevented sulfidation whereas a Cu2O layer permitted sulfidation. For the native copper oxide (Cu2O), density-functional theory modeling of Cu divacancy binding energies suggested that alloying with In or Al would cause vacancy trapping and possibly slow the rate of sulfidation. This finding was then experimentally verified for an In-implanted Cu film. A series of marker experiments using unalloyed Cu showed that sulfidation proceeds by solid-state transport of Cu from the substrate through the Cu2S product layer. © 2001 Elsevier Science B.V.

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