HIGH BIAS SPUTTERING FOR LARGE-AREA SELECTIVE DEPOSITION

Bias sputtering is a widely used technique for improving the quality of sputter-deposited thin films. Normally a 50-100 V negative bias voltage is used. Higher bias voltages have been used to produce planarization of patterned substrates during sputter metallization. At even higher substrate bias values the resputtering rate becomes comparable with the deposition rate. In this mode of operation all deposited material may be resputtered. At steady state, however, a certain concentration of the deposited film material will be built up at the substrate surface. A film-bulk concentration depth profile will thus be established which enables the resputtering rate to balance the deposition rate exactly. This will define a partial sputtering yield value of the resputtered film material which is found both theoretically and experimentally to depend strongly on the substrate material. Because of this substrate dependence it is possible to bias sputter deposit thin films selectively onto patterned substrates. By this simple and inert technique we have selectively deposited aluminum onto silicon oxide windows interconnecting two metal layers on an integrated circuit.