CHEMICAL VAPOR-DEPOSITION OF TUNGSTEN BY H2 REDUCTION OF WCL6

Tungsten chemical vapour deposition in a cold wall reactor using WCl6 as tungsten source has been investigated. Film growth on silicon substrates by H-2 reduction of WCl6 has been studied at atmospheric pressure and at a pressure of 40 Torr in the temperature range 480 to 670-degrees-C. Deposition at atmospheric pressure is limited by transport of reactants to the growth surface, resulting in non-uniform films with rough surfaces. At 40 Torr smooth films are obtained and growth rates are 10 to 110 nm/min. Resistivities are 8 to 17-mu-OMEGA.cm in the film thickness range of 100 to 800 nm. These values are comparable to those obtained in the WF6/H2 process. However, reproducibility of the process is poor. Tungsten can also be deposited on Mo, TiN and W surfaces from WCl6/H2 gas mixtures. In absence of hydrogen tungsten films are etched by WCl6. Thermodynamic calculations predict the formation of tungsten subchlorides in this reaction.