Abstract: Diffusion barrier layer is required during copper metallization in IC processing to prevent Cu from diffusion into the contacting silicon material and reacting to form copper silicide, which consumes Cu and deteriorates electrical conduction. With decreasing feature sizes of IC devices, such as those smaller than 90 nano-meter (nm), the thickness of diffusion barrier layer must be thinner than 10 nm. For example, a thickness of 2 nm will be called for at the feature size 27 nm. Disclosed in the present invention is ultra-thin barrier materials and structures based on tantalum silicon carbide, and its composite with another metallic layer Ru film. The retarding temperature, by which no evidence of copper diffusion can be identified, is 600˜850° C. depending on thickness, composition and film structure, at a thickness 1.6˜5 nm.