Microstructures of 50-nm Cu Interconnects along the Longitudinal Direction

Grain size distributions and average grain sizes in the longitudinal direction of the Cu interconnect in 50-, 70- and 80-nm-wide Cu interconnects were evaluated and compared with the resistivities of each interconnect. After annealing, the standard deviation of grain sizes for 50-nm Cu interconnect increased to 27.5, and the average grain size microstructure grew to larger than that of as-deposited 50-nm Cu interconnects. The value of standard deviation of grain sizes in the normal distribution histogram for a 50-nm wire was found to be much smaller than those for 70- and 80-nm Cu wires after annealing. This implies that adequate grain growth should not be expected in the very narrow Cu interconnects (less than 50-nm) of the future if they are made with the conventional annealing process.