Microscopic Dynamics of Roughening in Copper Electroplating

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Electroplated copper is used in the fabrication of microelectronic devices. Because of its superior conductivity and scalability, it is likely to replace aluminum alloys for on-chip interconnects. The engineering design and control of plating processes rely on surface-active additives. This project is an experimental study of chemical and molecular surface processes, which determine the microscopic properties of the plated surface. Chloride ion and dissolved oxygen will be used as model additives in a first step toward generalizing the impact of surface processes on the organization of material on the sub-micron level during crystal growth. The central work of the project will be the quantitative measurement and analysis, by in-situ atomic-force microscopy, of the dynamic surface properties of homoepitaxial deposits on copper single crystals and on vapor-deposited seed layers during plating and at open circuit. The rates of change of key features will be used to evaluate surface processes, particularly nucleation, point of discharge, and surface diffusion, as they depend on deposition parameters and the presence of additive films. A rotating ring-disk electrode will be used to study the surface chemical regime and its relationship to the growth mechanisms. Exploratory work to determine the interactions of inorganic components with organic additives will be initiated.