Effects of biased cosputtering on resistivity and step coverage in tungsten silicide films

Abstract

Electrical resistivity and step coverage on thick oxide steps of various slopes were examined in tungsten silicide films sputter deposited by multilayering of W and Si utilizing magnetron targets. The desired composition was obtained by adjusting power levels to the targets and bias voltage. A broad minimum in electrical resistivity was obtained with bias voltage ranging from −40 to −80 V. Typical resistivity in films of 2500 Å thickness after annealing at 1000 °C was 52–66 μΩ cm when deposited on poly-Si substrates. The effect of bias was found to produce films with much lower levels of impurity such as N, O, C, and H and the sputtering gas Ar. Proper bias voltage (−50 V) was necessary to achieve good step coverage on thick oxide step with various slopes. Zero-bias sputtering provided minimum step coverage, while too high bias (−100 V) led to poor step coverage and formation of rounded corners and faceting.