Plasma-enhanced atomic layer deposition of Ta and Ti for interconnect diffusion barriers

Abstract
Thin films of inert, refractory materials are used in semiconductor interconnect applications as diffusion barriers, seed, and adhesion layers. A typical example is the use of a thin, conformal Ta or Ti/TiN films on the walls of a dielectric trench or via which reduces or eliminates out-diffusion of the primary conductor, usually Cu, into the dielectric. Atomic layer deposition is a known technique which is intrinsically conformal and is appropriate for this application. Plasma enhancement of the process allows deposition at significantly lower temperatures than conventional chemical vapor deposition, which is a requirement for low-k dielectrics. Tantalum films deposited at 25–400 °C using ALD with a TaCl5 precursor and atomic hydrogen as the reactive species at up to a rate of 1.67 Ang/cycle are amorphous, conformal, and show moderate or controllable levels of impurities; primarily oxygen and a small level of Cl. Similar results have been observed for Ti using TiCl4 as a precursor. The process scales to manufacturing dimensions and applications and will facilitate the extension of interconnect technology beyond (below) 100 nm dimensions.

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