Leakage current and conduction mechanism of low-dielectric constant (low-k) carbon-doped silicon oxide (SiCO) for back-end-of-line (BEOL) dielectric are investigated in this work. Temperature-dependent leakage, Schottky emission and Poole-Frenkel emission for dense and porous low-k SiCO are analyzed respectively. Furthermore, time-dependent dielectric breakdown (TDDB) study at low electrical field verifies a square root of electrical field behaviour for low-k SiCO lifetime prediction. Besides, TDDB with regard to lifetime distribution, failure mode, thermal activation energy, and length scaling effect are also investigated. Finally, TDDB characterization of dense and porous low-k SiCO is carried out for the reference of process improvement and risk assessment. (C) 2008 Elsevier B.V. All rights reserved.