Structure Evolution During Volmer-Weber Growth of Metallic Films and Micro- and Nano-Structures

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

TECHNiCAL: Vapor-deposited metal films and structures generally evolve through the Volmer-Weber (VW) mechanism of crystal island nucleation, growth, and coalescence on substrate surfaces. Films formed via this mechanism do not stably wet their substrate, so film formation is a consequence of kinetic constraints that force the development of metastable or unstable films and particles. Consequently, kinetic processes dictate the course of all levels of structure evolution during film formation, and therefore define the final properties of the as-deposited structures. We plan to study to key aspects of structure evolution during VW growth: 1) pre-coalescence island evolution, and 2) post-coalescence surface structure evolution. In the latter case, we will include studies of evolution of surfaces of homoepitaxial films, to isolate effects of surface processes from effects associated with grain structures. In both regimes we will use in-situ stress measurements to probe both island-scale and atomic scale processes with both the measurement sensitivity and the temporal resolution required to characterize fast atomic-scale kinetic processes that operate during film formation conditions that are typical for engineering applications. We will also use in-situ electron diffraction to probe surface structure evolution, and ex-situ probe-based and electron-based microscopies to characterize morphology and crystallographic characteristics of quenched structures. We plan to investigate the effects of changes in deposition flux and substrate temperature on stress and structure evolution in both regimes. We will investigate effects of growth interruptions as well the temporal variations in the growth conditions (including island size focusing techniques). We also plan to investigate the effects of low-level surfactant coverage and of nano-scale lithographically defined substrate topography on the size, shape, spacing, orientation and ordering of island and surface features, and on the final properties of deposited structures. NON-TECHNICAL: Metallic thin films and nano-structures play critical roles in microelectronic, microelectromechanical, micromagnetic and microphotonic devices and systems, defining their performance and reliability. New envisioned applications also include metallic nano-particle arrays in new computing devices, energy harvesting, and biosensing applications. In all of these applications, stringent engineering control of the structure and properties is required. In all of the planned work, our goal will be to develop fundamental understandings that will have impact on engineering practices leading to improved control of metal films and nano-structures for applications. Two graduate research assistants will be directly supported by the program. In addition, the PI's research group of graduate and undergraduate students is now, and has historically been structured, to directly exploit new insights derived from NSF research in applications, especially in microelectronic and micromechanical devices and systems. Much of this research is directly supported by industry, and reported to industry. The research involves collaborations both inside and outside MIT, and results will be reported, as they have historically been, in both scientific and engineering venues. Research results and summaries are made available via the internet, and are included in MIT courses for undergraduate and graduate students, as well as professional engineers, the latter in the form of short courses at MIT and on-site in companies.