Low temperature chemical vapor deposition of tungsten carbide for copper diffusion barriers

Tungsten carbide films were grown by chemical vapor deposition using W(CO)( 6) and C2H4 between 250 and 450 degreesC. Pyrolysis studies indicate W(CO), thermally decomposes over the 150-200 degreesC temperature range with or w ithout ethylene. Carbon incorporation increased from 13 to similar to 33% w hen C2H4 was co-fed with W(CO)(6). The W/C carbon ratio, as established by X-ray photoelectron spectroscopy (XPS), remained approximately 2:1 regardle ss of the C2H4 to W(CO)(6) flow ratio for temperatures between 250 degrees and 450 degreesC. Films (50 nm thick) grown at 290 degreesC have a resistiv ity of 250 mu Omega -cm. Above 500 degreesC, the W/C ratio decreased to sim ilar to1:1.25 and the resistivity increased to 535 mu Omega -cm. The tungst en and carbon are present in the tungsten carbide chemical state. X-Ray dif fraction, XPS, selected area electron diffraction and transmission electron microscopy analysis reveal the films are a mixture of 5-6 nm W2C crystalli tes in an amorphous matrix, whose stoichiometry is similar to2:1 W/C. Coppe r was not found to diffuse through 7-nm-thick tungsten carbide films in Cu/ WC/SiO2 stacks that were annealed at 400 degreesC for 8-9 h. (C) 2001 Elsev ier Science B.V. All rights reserved.