Abstract: A cap or barrier layer that can prevent the migration of impurities in low dielectric constant material, thereby preventing the impurities from attacking conductive elements in subsequent levels of a multi-level integrated circuit structure. The integrated circuit by may be fabricated by disposing the diffusion-preventing barrier layer between a first dielectric layer and the conductive layer at an upper level of the integrated circuit. The diffusion preventing barrier layer may be formed in-situ over the impurity containing dielectric material with the subsequent disposition of a metal layer thereover, and further processing of a multi-layer dielectric structure to include polishing. The in-situ deposition of the cap or barrier layer prevents the exposure of the impurity containing layer to atmosphere, thereby avoiding contamination of the layer by moisture absorption, hydrogen absorption, or the like.