1. An apparatus comprising: a substrate; a dielectric layer over the substrate; an interconnect structure within the dielectric layer; a bulk metal of the interconnect structure; and an amorphous noble metal barrier layer of the interconnect structure disposed between the bulk metal and the dielectric layer, the amorphous noble metal barrier layer including an alloy including mainly one or more noble metals selected from iridium, platinum, palladium, rhodium, osmium, gold, silver, rhenium, and nickel, together with one or more elements selected from carbon and boron, wherein the one or more elements selected from carbon and boron are at a sufficiently low level for interstitial solubility without alloying with the amorphous noble metal barrier layer, wherein the noble metal barrier layer has a thickness that is less than 50 Angstroms, and wherein a density of the noble metal barrier layer is greater than 16 g/cm 3 .