COMPOSITIONAL CHANGES DURING MAGNETRON SPUTTERING OF ALLOYS

The transport of atoms sputtered from an alloy target has been examined by monitoring the composition of the resultant films as a function of various discharge and experimental parameters. Films were deposited by magnetron sputtering on both the sample plane as well as on the central and edge regions of the magnetron cathode and on side areas. To examine the effect of atom mass, cathodes were used of TiW and AlCu, in which one of the alloy components is 2-4 times the mass of the other. The transport was found to be characterized by three regimes. At low pressure, the transport was ballistic, and the sputtered atoms had virtually no collisions with gas atoms during transport. At high pressures, the transport was diffusive and was characterized by simple gas phase diffusion. In intermediate pressures, the lighter sputtered species tended to suffer more momentum- and direction-changing collisions than the heavier atoms. In this regime, the backscattered films were enriched in the lighter species, and the films deposited on the substrate were enriched in the heavier species. In addition, a dependence on the discharge power was observed, which is consistent with changes in the local gas density near the cathode due to heating by the sputtered atoms.