Research Summaries

Back Interfacial Creep in Thin Film Interconnect Structures in Micro-Systems

Fiscal Year 2007
Division Graduate School of Engineering & Applied Science
Department Mechanical & Aerospace Engineering
Investigator(s) Dutta, Indranath
Millsaps, Jr., Knox T.
Sponsor National Science Foundation (NSF)
Summary In many applications of multi-component micro-systems, large shear stresses exist at interfaces between dissimilar materials, and at least one of the materials adjacent to the interface is subjected to high homologous temperatures. This enables diffusionally accommodated sliding processes (interfacial creep) to operate at the interface, impacting the deformation behavior, dimensional stability, and reliability of the component. Furthermore, thin film interconnect structures in micro-systems often carry large electric current densities, which drive electromigration. As interconnect dimensions shrink, interfaces become the primary path for diffusion during electromigration, potentially leading to significant interactions between interfacial diffusive fluxes due to applied stress and electromigration. Thus, depending on the direction of applied current relative to the direction of the applied shear stress, electromigration--driven interfacial diffusion may either enhance or reduce interfacial sliding. With the emerging trend towards nano-scale miniaturization of multi-material assemblies in microelectronics, MEMS and functional nano-composites, and the commensurately explosive growth in interfacial area inside these assemblies, interfacial sliding is likely to become increasingly prominent, particularly since both thermomechanical and electrical loads are expected to increase in the future.
In this work, we propose a comprehensive experimental and analytical effort to obtain fundamental mechanistic insight into interfacial creep at thin film-substrate interfaces under thermomechanical, as well as thermomechanical-cum-electrical loads. The effort will combine creep testing with and without applied electrical current, detailed interfacial characterization, constitutive modeling and experimental/analytical investigations of microelectronic device structures.
The work will be of substantial fundamental importance since it will be the first-ever study of interfacial creep in thin film systems, and also the first-ever study to investigate the interaction between stress and electric current-driven diffusion in promoting/inhibiting interfacial sliding. Secondly, the work will be of great practical importance by generating kinetics data in a number of important engineering systems with applications in the micro-systems industry, and by developing a constitutive law which can be utilized for reliability predictions. Thirdly, the work will be of immense technological significance if interfacial sliding were ever to become performance-limiting in future micro-systems, since it will lay a framework for exploiting the interaction between stress and electric current to mitigate sliding through design considerations.
The broader impact of the work is related to its technological relevance to the entire micro/nano-systems industry by bringing to light a new phenomenon which may become performance limiting in a wide array of components in the future. Throughout the project, we will work closely with the industry to identify/address issues of emerging relevance. In addition to training graduate students and post-docs, we will hire summer high school student interns to work on the project through a local enrichment program, and hire high/middle school science teachers to work in our laboratory during summer and assist them in developing lesson modules relevant to the general area of this research.
Publications Publications, theses (not shown) and data repositories will be added to the portal record when information is available in FAIRS and brought back to the portal
Data Publications, theses (not shown) and data repositories will be added to the portal record when information is available in FAIRS and brought back to the portal