Samsung Advanced Institute of Technology

As the pitch size of a Cu line in back-end-of-line (BEOL) is decreased to sub-tens nm, many problems begin to emerge such as the exponetial increase of resistivity and the device failure due to the electromigration (EM). It has been shown that graphene is promising on both problems. However, the BEOL process requires the temperature as low as 400 ℃, and the graphene film grown at this temperature is far from ideal. It is questionable whether the defective graphene film can still offer performance benefits. In our study, we demonstrated the role of the defective graphene capping layer grown at the BEOL compatible temperature, which achieves both resistivity and reliability gains. The resistance of the Cu line is reduced by capping graphene. We proved that the resistivity gain by graphene capping is due to the improvement of the Cu surface, excluding other effects of the parallel resistivity and the grain boundary scattering, experimentally. Furthermore, the increased breakdown current and the 78 times higher EM lifetime indicate the improvement of reliability. We presented that the graphene edge？Cu bond can help suppressing the diffusion of Cu vacancy, improving EM lifetime. As a result, the graphene capping layer with the smaller domain, which have more edge contacts with Cu, showed better EM lifetime. Our work provides the insights into which graphene layer is required for the BEOL process and how to obtain it, depending on the purpose.