PVD-TixSiyNz films formed by reactive RF-magnetron co-sputtering of Ti and Si in Ar/N2 are evaluated as a diffusion barrier between Cu and Si. A complete range of compositions are obtained by Ti targets inlaid with Si. Film composition is controlled by the target ratio of titanium to silicon and N2 partial pressure. Electrical results versus thermal history for films of∼6–18% Si as well as the composition and microstructure as determined by Rutherford back scattering (RBS), TEM and electron diffraction are reported. These films are an amorphous matrix with imbedded nanocrystals of titanium nitride as-deposited and undergo phase separation to yield titanium nitride and silicon nitride after a 1000°C anneal. As-deposited compositions which lie above the TiN-Si3N4 phase line yield crystals of TiN. Compositions below the TiN-Si3N4 phase line yield crystals of Ti2N. Bulk resistivity as-deposited (<400μΩ2-cm) is acceptable for use as a contact liner/berrier material and improves with annealing. Si pn-diodes metallized with 20nm Ti40Si15N45 and Cu show no significant increase in reverse leakage current at anneal temperatures below 700°C.