STRUCTURE OF SELECTIVE LOW PRESSURE CHEMICALLY VAPOR DEPOSITED FILMS OF TUNGSTEN.

Tungsten (W) films have been selectively deposited (i. e. , deposited on Si and TaSi//2 to the exclusion of SiO//2) by low pressure chemical vapor deposition via the reduction of WF//6 by either Si of H//2. Films formed by H//2 reduction can be unlimited in thickness. However, those formed by Si reduction are self-limited in thickness to about 150Angstrom due to the inability of WF//6 to further react with the underlying Si once such a W film is formed. Selective W films greater than about 400Angstrom thick are found to be excellent diffusion barriers between Al and Si up to an annealing temperature of 450 degree C. Their selective nature makes additional patterning and etching steps unnecessary. A mechanism of selectivity, based on the effects of glass chemistry and microstructure on their WF//6 etching rates, has been proposed. The effects of deposition parameters such as temperature and WF//6 and H//2 flow rates on the properties of the W films have been investigated.