Post ash chemical treatments were evaluated for improving the reliability of Cu/low-k structures. The RC delays, leakage current, ramp-voltage-breakdown and timedependent- dielectric-breakdown lifetimes resulting from different treatments were compared. The pitch dependence of capacitance and breakdown was also evaluated. Post ash chemical treatments were more beneficial for the smaller line spaces. FTIR and TEM/EELS analysis were performed to determine the chemical changes occurring at the sidewall due to the post ash chemical treatments. The analysis showed that the chemical treatments increased the carbon content at the trench sidewalls. The post ash treatments were found to improve the electrical characteristics.