We have investigated the leakage mechanism of amorphous SiCN (a-SiCN) films after bias-temperature-stress (BTS) with Cu electrode. The leakage current became very large and breakdown due to the Cu ions penetration after strict BTS condition. The distribution profile of Cu penetration was depicted by SIMS spectrum. It is apparent that Cu ions penetrated into the a-SiCN film and even reached to the interface between a-SiCN/Si due to BTS. The Cu ions existing in a-SiCN would be taken as trap states and could enhance the carriers to transport. The main characteristics of post-breakdown a-SiCN followed the space-charge-limited current (SCLC) mechanism at 298 K. With decreasing the temperature to 100 K, the Fowler-Nordheim tunneling dominated the conduction in medium fields. However, electrons obeyed the SCLC again in high fields (>3.3 MV/cm) at 100 K. We purpose a physical model to interpret the leakage mechanism of breakdown a-SiCN films due to Cu ions. (C) 2004 Elsevier B.V. All rights reserved.