since it has at least a ten fold lower solubility in copper next to form a copper conductor the method fills trench 20 as fig5 shows by depositing a 975 nanometer thick copper layer 24 on layer 22 and inside trench 20 in some embodiments another 10 nanometer thick adhesion layer is formed atop copper layer 24 to inhibit copper oxidation during later processing particularly during curing of subsequent polymeric layers to reduce copper oxidation one embodiment performs the adhesion material and the copper deposition at temperatures less than 450 u00b0 c another embodiment at temperatures between about 250 and 350 u00b0 c and another at around 300 u00b0 c in the 250 350 u00b0 c range a thin layer of cu 5 zr or beta tends to initially form at the interface of the copper and zirconium layers inhibiting diffusion of zirconium into the copper and preventing it from significantly increasing resistance of the copper a similar effect may be achieved by electroplating the copper and heat treating the zirconium and copper layers at 250 350 u00b0 c for one to two hours before curing the polymer inhibiting the diffusion of zirconium into the copper ultimately yields a copper conductor with a conductivity greater than 95 percent of iacs or international annealed copper standard the international annealed copper standard iacs is 1 7241 microhm centimeters at 20 c or 17 241 nanaohm meters thus the exemplary copper conductor has a conductivity greater than about 16 4 nanaohm meters however in other embodiments the conductor is in the range of 14 nanohm meters or greater afterwards excess copper and zirconium on the surface are then removed using a chemical mechanical polishing technique fig6 shows the resulting metal conductor 24.