Electromigration Lifetimes of Single Crystal Aluminum Lines with Different Crystallographic Orientations

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Abstract
Near-bamboo interconnects are susceptible to failure either at polygranular clusters or within bamboo grains (transgranular failure). Polygranular failure mechanisms are often dominant in lines with near-bamboo structures at test conditions, but at service conditions, transgranular failure mechanisms are expected to dominate. In order to study the temperature and current density dependence as well as the crystallographic dependence of these transgranular failure mechanisms, it is necessary to isolate them from other mechanisms. To do this, we have studied single crystal Al lines on oxidized silicon.We have tested lifetimes of passivated and unpassivated Al single crystal lines with various textures. In both passivated and unpassivated lines, the median time to failure, t50, was found to be texture-dependent, with t50(l11) > t50(133) > t50(110), and with t50(111) ∼ 10×t50(110). The activation energy for failure for both passivated and unpassivated (110) single crystal lines was about 1 eV. This value differs from that of aluminum bulk diffusion (1.4 eV), suggesting that interface diffusion is the dominant diffusion mechanism in these lines, and perhaps in bamboo regions of near-bamboo lines as well.