The focus of this thesis is the fabrication and characterisation of ultra-thin self-forming Cu diffusion barrier layers for future interconnect technologies. These barrier layers form by the chemical interaction of an expelled metal from a copper alloy with the surface of a dielectric material to form a stable chemical species suitable for integration into future interconnect fabrication strategies. Studies of both manganese and aluminium as the alloying elements were undertaken and the characterisation techniques included x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) and secondary ion mass spectroscopy (SIMS). Electrical characterisation measurements used to establish the effectiveness of the barrier layers at preventing copper diffusion were performed on fabricated metal-oxide-semiconductor (MOS) structures. A novel approach involving interface chemistry studies and MOS device fabrication on the same dielectric substrate was successfully demonstrated. Barrier formation on a range of prototype low-k dielectric materials with different carbon concentrations and porosities were undertaken and surface chemical modifications prior to barrier layer formation were also investigated. The results show that both Mn and Al are effective at preventing copper diffusion into SiO2, but the inherent porous structure of low-k dielectrics present significant challenges to barrier layer formation, particularly at the dimensional range required for future technology nodes.