Excimer laser processing of Al-1%Cu/TiW interconnect layers

Planar thin-film stacks comprising 750-nm Al-1%Cu/100-nm TiW/100-nm SiO₂ were subjected to a 25-ns excimer laser pulse (XeCl, 308 nm) at an optical fluence of 3.5 to 5.0 J/cm² at a substrate temperature of 250° to 400°C, and a number of the important film properties were measured. Resultant grain sizes ranged from 2 μm to in excess of 300 μm, the largest grains corresponding to the highest fluence/temperature condition. The melting of the Al-Cu films was found to eliminate hillock growth completely during subsequent furnace annealing (450°C). Laser processing at the higher fluence condition (5.0 J/cm²) produced large (>30%) increases in layer resistivity. Ultramicrohardness was found to range from 39 to 52 kg/mm² for the treated films. Accelerated stress testing revealed no significant difference in open-circuit electromigration resistance between the as-deposited and the majority of the laser-processed Al-Cu films. However, one particular group of laser-melted samples (3.5 J/cm², 400°C) demonstrated lifetimes at least 10 times greater than those of the other sample groups. Specular reflectivity, impurity distribution, and layer morphology were also examined