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

Abstract

Planar thin-film stacks comprising 750-nm Al-1%Cu/100-nm TiW/100-nm SiO/sub 2/ were subjected to a 25-ns excimer laser pulse (XeCl, 308 nm) at an optical fluence of 3.5 to 5.0 J/cm/sup 2/ at a substrate temperature of 250 degrees to 400 degrees C, and a number of the important film properties were measured. Resultant grain sizes ranged from 2 mu m to in excess of 300 mu m, 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 degrees C). Laser processing at the higher fluence condition (5.0 J/cm/sup 2/) produced large (>30%) increases in layer resistivity. Ultramicrohardness was found to range from 39 to 52 kg/mm/sup 2/ 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/cm/sup 2/, 400 degrees 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.<>