Barrier Metal

A barrier metal is a material used in integrated circuits to chemically isolate semiconductors from soft metal interconnects, while maintaining an electrical connection between them. For instance, a layer of barrier metal must surround every copper interconnection in modern copper-based chips, to prevent diffusion of copper into surrounding materials.
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a metal layer designed to stop other layers from interacting. The most common barrier metals is titanium nitride, TiN, titanium tungsten, TiW was widely used at one time, chromium, Cr, has seen some use, tantalum, Ta, and tantalum nitride, TaN, are seeing increased use with copper metalization processes and tungsten nitride ,WN, is a relatively new barrier metal.