Effects of Ti-containing underlayers on planarization and microstructure of magnetron sputtered Al-Cu thin films

The authors describe the effects of several Ti-containing underlayer materials on the microstructure and degree of planarization of Al-4% Cu thin films. Al-Cu films were deposited on SiO₂ either uncoated or precoated with an underlayer of Ti, Ti-W or Ti-N. Both batch and single-wafer sputtering systems were used. Planarization and microstructure were investigated by scanning-electron microscopy and cross-sectional transmission electron microscopy. In the batch system, Al₂Cu precipitates coexist in both the θ and θ´ phases in Al-Cu films deposited on SiO₂ substrates biased at -175 Vrf and -225 Vrf, and preheated to approximately 300°C. In the single-wafer system, substrates were held at temperatures ranging from 490°C to 520°C with a fixed substrate bias (-200 Vrf). In this temperature range, excellent planarization can be achieved, and θ´ precipitates are uniformly distributed throughout the thickness of the Al-Cu films