Experimental and thermodynamical investigation of selective low pressure chemical vapour deposition of tungsten using WCl 6 as tungsten source

Abstract

Selective low pressure chemical vapour deposition of tungsten using WCl 6 as the tungsten source was investigated both experimentally and thermodynamically. The process was found to be very sensitive to the thickness of the native oxide, thus making it difficult to obtain good reproducibility. The selectivity of the chloride process was good for both Ar-WCl 6 and H 2-WCl 6 reaction gas mixtures. Tungsten layers thicker than 2000 Å were occasionally deposited from the Ar-WCl 6 reaction gas mixture. This is explained by the porosity of the coatings, allowing for WCl 6 diffusion through the tungsten layer and permitting continued tungsten growth. Channel-like growth of tungsten into the silicon windows of patterned Si/SiO 2 was also observed when the Ar-WCl 6 gas mixture was employed. It is suggested that oxygen-containing species from the simultaneous etching of SiO 2 may promote the formation of channels.