In a copper-SiO2 dielectric multilevel interconnection scheme a diffusion barrier is needed between the metal and the dielectric to prevent the diffusion of Cu into SiO2 when subjected to thermal treatments and high electric bias. Ultra thin layers (50–100Å) of Al and Ti are being investigated for use as the required diffusion barrier as well as an adhesion promoter between Cu and SiO2 The results of our investigations, using C-V, resistance, and XPS measurements, will be presented and discussed. It will be shown that both Al and Ti reduce the SiO2 surface leading to a metal, oxygen, and Si bonded layer which acts as diffusion barrier under applied electrical bias of 1.5 MV/cm at temperatures as high as 250–300°C. Upper layers of Al and Ti are consumed by reaction with Cu. Such reactions increase the electrical resistivity and corrosion resistance of Cu (especially with Al). The results and the applicability of such barriers in practical cases will be presented and discussed.