W deposition by GeH4 reduction of WF6 is a promising alternative for W deposition from H2/WF6 and SiH4/WF6. The structure and composition of W layers deposited from WF6 and GeH4, are determined mainly by the deposition temperature. At temperatures between 300 and 400°C, W layers with the A15 bcc 13-W crystal structure are formed. These 0-w layers contain a substantial amount of homogeneously distributed Ge, roughly between 10 and 15 atomic percent (a/o). At higher temperatures, films are formed which consist of a mixture of p-w and a-W. At temperatures greater than 500°C, the layers consist exclusively of a-W, and the Ge concentration is less than 1 a/o. The amount of p-w in the film correlates with the resistivity and the amount of incorporated Ge. The incorporated Ge may promote the formation of the 0-w phase. Other process parameters, such as the total pressure and the GeH4/WF6 ratio, have a minor effect on the structure and composition of the films. The P-W deposited at —375°C —375°C is well suited for use as contact material to active Si areas of ULSI circuits. The contact resistivity of the -W layers to 2 x 2 um2 n+ Si and p+ Si contacts is as low as the contact resistivity of annealed Al(Si 1 %)/Si reference samples. The contact resistivity to the p+ diffusions was slightly higher than to the n+ diffusions. No leakage current was observed, indicating that no harmful attack of the active Si areas occurred during the deposition of 0-W. High resolution SEM pictures confirmed the absence of any significant Si consumption, encroachment, or tunnels at the Si interface. The p-w layers are stable and transform to a-W only at temperatures greater than 600°C during 30-min anneals. After transformation to a-W, silicidation to WSi2 occurs. The 13-W is an effective diffusion barrier between Al and Si. During 30-min anneals at 500°C, a p-w film as thin as 60 nm prevented all Al/Si interdiffusion. A nm thick 13-W film prevented Al/Si interdiffusion to at least 540°C. Finally, a deposition sequence consisting of the GeH4 reduction of WF6 followed by SiH4 or H2 reduction’ of WF6, combines the excellent interface properties of the GeH4/WF6 process with the higher growth rate and better selectivity of the H2/WF6 or SiH4/WF6 process.