Investigations of ultra thin aluminum as an adhesion promoter and electrically stable diffusion barrier for copper metallization on SiO(2)

This study explores some basic aspects of copper metallization for integrated circuits. Interconnect technology is now becoming a major aspect of IC production, accounting for significant cost of manufacturing and beginning to dominate circuit speed. In order to decrease the delay due to the interconnects, either lower dielectric constant interlevel insulators or lower resistivity metals like copper must be used.; Unfortunately copper can easily diffuse through many IC materials, and seriously degrade the operation of silicon devices. Also, the reliability of any new interconnect scheme must be evaluated. This report addresses the use of copper on SiO{dollar}sb2{dollar} using thin aluminum films as a diffusion barrier/adhesion promoter. In particular, sheet resistance, film stress, adhesion and diffusion barrier properties were studied.; The results show that 50 to 100 A0. of aluminum deposited on SiO{dollar}sb2{dollar} forms a passivating layer of Al{dollar}sb2{dollar}O{dollar}sb3{dollar} at the metal-oxide interface. This layer, and perhaps in conjunction with metallic aluminum, promotes adhesion and limits copper diffusion into the dielectric. Adhesion of copper to SiO{dollar}sb2{dollar} with the aluminum layer is more typical of aluminum than copper. Bias temperature aging of MOS capacitors showed no shift in flat band voltage using a 100 A barrier layer, indicating there is no build up of copper ion charge in the oxide.; Stress measurements of metal films deposited on oxidized silicon substrates show that the copper with the barrier layer has significantly higher stress than both pure copper and aluminum, while the stress was only about 10% higher than in aluminum alloyed with about 0.5 at.% copper. Greater additions of aluminum to the copper metallization reduces the thermal stress toward that of the aluminum alloy. The higher aluminum content would also limit plastic flow, leading to a much broader stress response, and thus higher room temperature stress.; Sheet resistance as a function of annealing temperature and time shows an initial grain boundary controlled diffusion of aluminum into the copper. This process has an activation energy near 0.9 eV. The amount of aluminum dissolved in the copper appears to be limited by surface accumulation, possibly due to the formation of Al{dollar}sb2{dollar}O{dollar}sb3{dollar}. The surface process may have a limited temperature response, thus it dominates at lower temperatures leading to a lower final metal resistivity.; 5000 A of copper used in conjunction with a 50 A aluminum diffusion barrier/adhesion promoter shows no adverse effect on resistivity. This film system has only marginally higher stress than an aluminum-copper alloy metallization, while it also may prevent copper from diffusing into underlying SiO{dollar}sb2{dollar}. These results indicate that this method for copper metallization on SiO{dollar}sb2{dollar} warrants further study as an IC interconnect scheme.