The effectiveness of carbon as a barrier for the outdiffusion of Cu is studied using C/Cu/substrate and Au/C/Cu/substrate structures. For the C/Cu structure deposited on SiO2‐coated Si with a 700 A˚ C layer, heating to 700 °C for 72 h and 750 °C for 6 h shows no outdiffusion of Cu to the carbon surface in N2‐H2.Only reaction between Cu and the SiO2layer underneath is observed. Application of the carbon barrier between Cu and Au in the Au/C/Cu/substrate structure shows that the dilution of the Au layer due to the Cu outdiffusion is similar to but less than that of the Au/Ni/Cu/substrate structure using Ni as a barrier. The stability of the Au/C/Cu/substrate structure is enhanced relative to that of the Au/Ni/Cu/substrate one by more than 150 °C. Both the advantage and concerns using carbon as barriers for the interconnect and contact metallurgies are discussed.