Quantification of Cu Segregation to Grain Boundaries in an Al - 4 Wt.% Cu Thin Film Using High Resolution X-Ray Mapping

Extract

A typical microprocessor chip has several million devices patterned into it and, as fabrication techniques improve, device dimensions continue to shrink. This miniaturization results in a corresponding decrease in the dimensions of the interconnects between devices, causing an increased susceptibility to failure by current-induced mass transport, or electromigration (EM). It is well known that the addition of a small amount of Cu to Al interconnects increases their median time to failure profoundly. Since EM in these films occurs almost exclusively at grain boundaries, the simplest explanation for the role of Cu is that it segregates to the grain boundaries and reduces their diffusivity. Analytical electron microscopy studies have shown that Cu segregates to grain boundaries in Al under the proper conditions, and its concentration was measured using X-ray energy dispersive spectroscopy (EDS), but only a small number of boundaries were measured.In order to determine whether the distribution of Cu affects the resistance of a material to EM damage, it is first necessary to characterize the Cu content of the material as a whole, which requires the analysis of large numbers of boundaries rather than just a few.