The invention is directed to a process for purifying tungsten hexafluoride to produce a pure material useful in applications such as the electronics industry in which the impurities level is required to be reduced as much as possible to avoid adverse effects. The steps are as follows:

a) evaporating tungsten hexafluoride from said non-volatile impurities dissolved in said liquid tungsten hexafluoride, b) condensing the evaporated tungsten hexafluoride, c) freezing the condensed tungsten hexafluoride to solid tungsten hexafluoride, d) evacuating volatile impurities from said solid tungsten hexafluoride, e) thawing said solid tungsten hexafluoride to liquid tungsten hexafluoride to release volatile impurities trapped in said solid tungsten hexafluoride to the gas phase, f) heating the thawed tungsten hexafluoride to a temperature above the boiling point of tungsten hexafluoride under pressure in a closed container whereby volatile impurities dissolved in the thawed tungsten hexafluoride are removed and collected above the thawed tungsten hexafluoride and heating the thawed tungsten hexafluoride, g) venting the volatile impurities collected above the thawed tungsten hexafluoride into an evacuated space. 

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A method of forming a composite tungsten film on a substrate is described. The composite tungsten film comprises sequentially deposited tungsten nucleation layers and tungsten bulk layers. Each of the tungsten nucleation layers and the tungsten bulk layers have a thickness less than about 300 Å. The tungsten nucleation layers and the tungsten bulk layers are formed one over the other until a desired thickness for the composite tungsten film is achieved. The resulting composite tungsten film exhibits good film morphology. The tungsten nucleation layers may be formed using a cyclical deposition process by alternately adsorbing a tungsten-containing precursor and a reducing gas on the substrate. The tungsten bulk layers may be formed using a chemical vapor deposition (CVD) process by thermally decomposing a tungsten-containing precursor.

A method of filling an opening in an insulating layer of an integrated circuit. First a tungsten-silicide layer is deposited over the opening. Next a tungsten layer is deposited onto the tungsten-silicide layer such that the opening is substantially filed with tungsten. The tungsten and tungsten-silicide layer are then chemically-mechanically polished back until the insulating layer is substantially revealed.