As the name implies, a barrier metal must have high electrical conductivity in order to maintain a good electronic contact, while maintaining a low enough copper diffusivity to sufficiently chemically isolate these copper conductor films from underlying device silicon. The thickness of the barrier films is also quite important; with too thin a barrier layer, the inner copper may contact and poison the very devices that they supply with energy and information; with barrier layers too thick, these wrapped stacks of two barrier metal films and an inner copper conductor can have a greater total resistance than the traditional aluminum interconnections would have, eliminating any benefit derived from the new metallization technology.
Some materials that have been used as barrier metals include cobalt, ruthenium, tantalum, tantalum nitride, indium oxide, and titanium nitride (the last three being conductive ceramics, but "metals" in this context).
See also diffusion barrier.
US Patent Issued to Sharp Laboratories of America on Sept. 11 for "Multilayered Barrier Metal Thin-Films" (Washington, Oregon Inventors)
Sep 16, 2012; ALEXANDRIA, Va., Sept. 16 -- United States Patent no. 8,264,081, issued on Sept. 11, was assigned to Sharp Laboratories of...