The properties of WNxCy films deposited by atomic layer deposition (ALD) using WF6, NH3, and triethyl boron were characterized as diffusion barriers for copper metallization. The films deposited at 313degreesC showed resistivity of about 350 muOhm cm with a density of 15.4 g/cm(3). The film composition measured by Rutherford backscattering spectrometry showed W, C, and N of approximately 48, 32, and 20 atom %, respectively. Transmission electron microscopy analyses showed that the as-deposited film was composed of a face-centered-cubic phase with a lattice parameter similar to both beta-WC1-x and beta-W2N with an equiaxed microstructure. The film kept its nanocrystalline microstructure until annealing at 700degreesC, although some amount of simple hexagonal alpha-WC was identified to be formed and the beta-W2N phase disappeared. As the annealing temperature increased to 800degreesC, relatively larger grains of body-centered-cubic W were newly formed with smaller grains of hexagonal-close-packed alpha-W2C or alpha-WC. All the phenomena are related to nitrogen release after annealing at 700 and 800degreesC. The results of diffusion barrier performance between Cu and Si analyzed by X-ray diffractometry showed that ALD-WNxCy film (12 nm) failed only after annealing at 700degreesC for 30 min by the formation of copper silicide, while the sputter-deposited Ta (12 nm) and ALD-TiN (20 nm) films failed at 650 and 600degreesC annealing, respectively. It is thought that the superior diffusion barrier performance of ALD-WNxCy film is the consequence of both the formation of equiaxed microstructure and the high-density nature of the film. (C) 2004 The Electrochemical Society.