Corrosion of Narrow Copper Damascene Interconnects

The influences of Cu line width and pattern density are considered as the physical factors affecting corrosion of Cu damascene interconnects. The Cu etch rate data reveals a line width dependency, for both isolated and semidense Cu lines, by showing higher etch rates for decreasing line width ( 0.2 μ m < width < 1.0 μ m ) in an inorganic acid-based model chemical mechanical planarization (CMP) solution. This is related to the Cu grain boundaries, which are shown to be higher in number in the narrow lines and are preferential sites for chemical attack. The absence of such a line width dependency in an organic acid-based solution signifies the importance of the interactions between Cu and CMP slurry chemicals. The Cu grain size and grain boundary volume, both as a function of line width and pattern density, are shown to be a function of the Cu electroplating bath chemistry and the plating recipe, as revealed by the microstructural data. Consequently, the lines with smaller grains are etched faster in an inorganic acid solution but not in an organic one. Therefore, by enhancing grain growth in narrow trenches and by tailoring the Cu-slurry interactions, narrow trench corrosion during CMP need not be such a challenge in future processing technologies.