Pattern size dependence of grain growth in Cu interconnects

Fine Cu interconnects possess small grains that increase the electrical resistivity of the interconnects. We have performed an extensive transmission electron microscopy study of the grain growth in lines of different sizes, using a recently developed automated indexing method. Different annealing processes were conducted, some with the presence of a top layer that possesses very large grains. Quantification (by crystallographic indexation and mapping) of grain growth in lines as narrow as 80 nm was achieved. We found that grain growth is clearly impeded by geometrical constraints.