Atomic layer deposited nanocrystalline tungsten carbides thin films as a metal gate and diffusion barrier for Cu metallization

Abstract

Tungsten carbides (WCx) thin films were deposited on thermally grown SiO2 substrates by atomic layer deposition (ALD) using a fluorine- and nitrogen-free W metallorganic precursor, tungsten tris(3-hexyne) carbonyl [W(CO)(CH3CH2C CCH2CH3)(3)], and N-2+H-2 plasma as the reactant at deposition temperatures between 150 and 350 degrees C. The present ALD-WCx system showed an ALD temperature window between 200 and 250 degrees C, where the growth rate was independent of the deposition temperature. Typical ALD characteristics, such as self-limited film growth and a linear dependency of the film grown on the number of ALD cycles, were observed, with a growth rate of 0.052 nm/cycle at a deposition temperature of 250 degrees C. The ALD-WCx films formed a nanocrystalline structure with grains, similar to 2 nm in size, which consisted of hexagonal W2C, WC, and nonstoichiometric cubic beta-WC1-x phase. Under typical deposition conditions at 250 degrees C, an ALD-WCx film with a resistivity of similar to 510 mu Omega cm was deposited and the resistivity of the ALD-WCx film could be reduced even further to similar to 285 mu Omega cm by further optimizing the reactant pulsing conditions, such as the plasma power. The step coverage of ALD-WCx film was similar to 80% on very small sized and dual trenched structures (bottom width of 15 nm and aspect ratio of similar to 6.3). From ultraviolet photoelectron spectroscopy, the work function of the ALD-WCx film was determined to be 4.63 eV. Finally, the ultrathin (similar to 5 nm) ALD-WCx film blocked the diffusion of Cu, even up to 600 degrees C, which makes it a promising a diffusion barrier material for Cu interconnects. (C) 2016 American Vacuum Society.