Thermal stability of the C/Cu bilayer structure is studied up to 800 °C. Using electron-beam-evaporated Cu and amorphous C (700 Å) films on SiO2-coated Si substrates, no out-diffusion or oxidation of Cu is observed up to a heating of 72 h at 700 °C, or 6 h at 750 °C in a N 2-H2 ambient. Reaction between Cu and the SiO2 layer is, however, observed under such conditions. Concerns such as adhesion are addressed by peeling the films at different stages of heat treatment and analyzing the surfaces exposed. Application of the carbon barrier to the reaction between Cu and other materials is studied using the Au/C/Cu structure. An enhanced out-diffusion of Cu through C is observed due to the presence of Au, which acts as a receiving layer for Cu. The out-diffused flux of Cu is enhanced by many orders of magnitude. The resulted dilution of the Au layer, however, is much less than that using Ni as a barrier in the Au/Ni/Cu structure. The mechanisms involved are discussed by considering the structural, chemical, and mechanical effects. Both the advantage and concerns using carbon as a barrier are also discussed.