Microstructure Modulation in Copper Interconnects

Modulation of Cu interconnect microstructure in a low-k dielectric was achieved at an elevated anneal temperature of 250 °C. In contrast to the unpassivated conventional structure, a TaN metal passivation layer was deposited on the plated Cu overburden surface before annealing at the elevated temperature to prevent stress migration reliability degradation. As compared with the conventional structure annealed at 100 °C, the elevated annealing process enabled further Cu grain growth, which then resulted in an increased Cu grain size and improved electromigration resistance in the interconnects.