Time-dependent dielectric breakdown (TDDB) of hydrogenated silicon carbon nitride (H:SiCN) and silicon carbide (H:SiC) thin films and the impact of copper (Cu) ions has been investigated using metal-insulator-semiconductor (MIS) capacitors with Cu gate electrodes. These films were deposited using a plasma-enhanced chemical vapor deposition technique. Bias temperature stress tests of the MIS capacitors were done at up to 275degreesC using an electric field up to 3.0 MV/cm. With the introduction of an electric field-dependent factor, the first law of thermodynamics was found to describe the experimental TDDB data of these films very well. The time to breakdown was found to decrease exponentially with an increase in the electric field and temperature, agreeing with the thermochemical E model excellently. The presence of Cu ions in these films was found to significantly accelerate the breakdown. It is believed that the electric field enhancement in the dielectric films at the cathode region due to the accumulation of positive Cu ions causes the breakdown acceleration. The data in this work suggest that the quick initial leakage current decrease during the TDDB tests of Cu-gated capacitors is caused by electron trapping instead of the Cu ion accumulation in the dielectric films. (C) 2004 The Electrochemical Society.