Low capacitance and high reliability interconnect structures and methods of manufacture are disclosed. The method includes forming a copper based interconnect structure in an opening of a dielectric material. The method further includes forming a capping layer on the copper based interconnect structure. The method further includes oxidizing the capping layer and any residual material formed on a surface of the dielectric material. The method further includes forming a barrier layer on the capping layer by outdiffusing a material from the copper based interconnect structure to a surface of the capping layer. The method further includes removing the residual material, while the barrier layer on the surface of the capping layer protects the capping layer.