New Directions in LCVD Metallisation
Emphasis was placed on processes important in the laser deposition, both pyrolytic and photolytic, of tungsten, aluminium and gold. Whilst it may be difficult to generalise about specific metallisation processes, these elements are examples of refractory metals, main group and noble metals respectively. Specifically, factors controlling film purity and morphology were addressed. These two factors are related and limiting features in the technological adoption of LCVD processes. In particular, impurity levels are high and the morphology is poor when W(CO)6. is used as the precursor. Despite the great deal of attention paid to fundamental work on thephotolysis of this molecule, present knowledge about the mechanism of carbon incorporation is sufficient to warrant optimism that high purity W can be produced from W(CO)2. This is certainly true when large deposition rates are required and fragments W(CO)x and CO may be incorporated into the growing film. Knowledge of the effects that such impurities have on the crystallinity, morphology and physical properties eg. porosity are not well understood. The thermal decomposition of WF6 in the presence of H2 as a means of thermal deposition is attractive. Such processes are similar to the selective area reduction of WF6 over a silicon surface under a H2 ambient. Using SiH4, as the reducing agent appears to be a promising route to high purity W and could be broadened to include substrate material other than silicon. There is a need to investigate other gaseous reducing agents to eliminate the hazards associated with WF6/SiH4 mixtures.