A detailed model for low-pressure CVD of tungsten

A computer modelling study has been made of low-pressure tungsten chemical vapour deposition from WF₆ and H₂ in a single-wafer reactor. A detailed description for the multiple reaction multi-species chemistry, based on the model developed by Arora and Pollard, has been combined with a multidimensional transport model for the conservation of mass, momentum, energy and chemical species. Some problems with the used chemistry model were encountered which yet need to be resolved, and further refinement of this model is necessary. Nevertheless, the predicted deposition rates at both very low and very high WF₆ concentrations, where more simple semi-empirical chemistry models loose their validity, are in fair agreement with experiments. Also, the model was used to study the influence of process conditions on the concentration distributions of tungsten subfluorides, which are believed to be responsible for selectivity loss. Thus, the potentials are demonstrated of combined transport and detailed chemistry modelling for the prediction of intermediates and the optimisation of selective processes.