Carbon as a barrier for the outdiffusion of Cu

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 Å 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 SiO2 layer 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.