Characterization of Tungsten Deposited by Geh4 Reduction of Wf6, and its Application as Contact Material to Si

C.A. van der Jeugd, G.J. Leusink, T.G.M. Oosterlaken, P.F.A. Alkemade, L.K. Nanver, E.J.G. Goudena, G.C.A.M. Janssen, S. Radelaar

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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.

Original languageEnglish
Pages (from-to)3615-3623
Number of pages9
JournalJournal of the Electrochemical Society
Issue number12
Publication statusPublished - 1 Jan 1992
Externally publishedYes


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