This paper reports the effect of a SiCN/Ta bilayer barrier on the electrical properties and thermal stability of single damascene lines for Cu-ultra low k integration. By introducing an additional SiCN layer prior to a Ta barrier, breakdown voltage, line-to-line leakage current and thermal stability could be significantly improved. The increase in the line resistance could be minimized by optimizing the thickness of SiCN layer in the multilayer lines. (c) 2006 Elsevier B.V. All rights reserved.