Copper diffusion barrier films having low dielectric constants are suitable for a variety of copper/inter-metal dielectric integration schemes. Copper diffusion barrier films in accordance with the invention are composed of one or more layers of silicon carbide, at least one of the silicon carbide layers having a composition of at least 40% carbon (C), for example, between about 45 and 60% carbon (C). The films' high carbon-content layer will have a composition wherein the ratio of C to Si is greater than 2:1; or >3:1; or >4:1; or >5.1. The high carbon-content copper diffusion barrier films have a reduced effective k relative to conventional barrier materials.