Frieder H. Baumann

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.

Enhanced electromigration resistance through grain size modulation in copper interconnects

Grain size modulation in Cu interconnects was achieved at an elevated anneal temperature of 250 °C. As compared to the conventional annealing at 100 °C, the elevated process enabled further Cu grain growth, which then resulted in an increased grain size and improved electromigration resistance in the Cu interconnects. In order to prevent stress migration reliability degradation from the elevated annealing process, a TaN metal passivation layer was deposited on the Cu interconnect surface prior to the thermal annealing process, which suppressed void formation within the Cu features during the anneal process and reduced inelastic deformation within the interconnects after cooling down to room temperature.

Thermal stress control in Cu interconnects

Grain growth of Cu interconnects in a low k dielectric was achieved at an elevated anneal temperature of 250 °C without stress voiding related problems. For this, a TaN metal passivation layer was deposited on the plated Cu overburden surface prior to the thermal annealing process. As compared to the conventional structure annealed at 100 °C, the passivation layer enabled further Cu grain growth at the elevated temperature, which then resulted in an increased Cu grain size and improved electromigration resistance in the resulted Cu interconnects.

From Process Assumptions to Development to Manufacturing

A tool has been developed that can be used to characterize or validate a BEOL interconnect technology. It connects various process assumptions directly to electrical parameters including resistance. The resistance of narrow copper lines is becoming a challenging parameter, not only in terms of controlling its value but also understanding the underlying mechanisms. The resistance was measured for 45nm-node interconnects and compared to the theory of electron scattering. This work will demonstrate how valuable it is to directly link the electrical models to the physical on-wafer dimensions and in turn to the process assumptions. For example, one can generate a tolerance pareto for physical and or electrical parameters that immediately identifies those process sectors that have the largest contribution to the overall tolerance. It also can be used to easily generate resistance versus capacitance plots which provide a good BEOL performance gauge. Several examples for 45nm BEOL will be given to demonstrate the value of these tools.