Selective deposition of tungsten by chemical vapour deposition from SiH 4 reduction of WF 6

Abstract

Tungsten films were deposited on tungsten-patterned wafers by the selective chemical vapour deposition (CVD) process from SiH 4-reduction of WF 6 in a cold-wall reduced pressure CVD reactor. The experimental conditions such as reactive gas flow ratio, temperature, total pressure etc. providing good selective deposition were investigated (in terms of voids and homogeneity of the coatings in each plug) and particularly the pretreatment of wafers by different sorts of plasma. The tungsten deposition rate and dependence of the selectivity loss on the SiO 2 film were checked using a scanning electron microscopy technique, vs. the different parameters. These results show the importance of the plasma pretreatment and of the first reactive gas introduced for the selectivity. A temperature window for optimum selectivity was established and an apparent activation energy was measured. From all these results, an interesting correlation could be made between the selectivity loss and the rate-controlling mechanism. Finally the flexibility of this process is demonstrated by the feasibility of selective tungsten deposition on aluminium-patterned wafers. The conditions for tungsten and for aluminium are very different; in particular, the electrical results obtained on aluminium show a high sensitivity to the pretreatment carried out before deposition.