Amorphous, 10‐nm‐thick tantalum‐silicon‐nitride (TaSiN) layers were found to be effective diffusion barriers between copper and thermal silicon dioxide. The films were electrically evaluated using TaSiN/Cu/TaSiN‐oxide‐silicon capacitors and bias thermal stress (BTS) treatments; the capacitors were stressed at 300 °C with electric fields in excess of 1 MV/cm for up to 80 h. High frequency capacitance versus voltage characteristics were recorded at room temperature before and after BTS treatment. Based upon comparisons between these (C–V) curves, barrier failure was concluded to have not occurred. ©1995 American Institute of Physics.