Copper shows a tendency to drift into contiguous dielectric material under bias and temperature stressing. The stability of different compositions (by changing silane gas flow rate) of Ti-Si-N-O films has been investigated using metal-oxide-semiconductor (MOS) capacitors. MOS samples preannealed at 250 degrees C and subjected to bias temperature stressing (BTS) at 150 degrees C, 200 degrees C under an electrical field of 0.5 or 1 MV/cm show stable capacitance-voltage behavior with no flatband voltage shift from as-annealed to 90 min of BTS for Ti-Si-N-O film with Si/Ti ratio of 0.48. The lack of flatband voltage shift indicates that Ti-Si-N-O film is able to prevent Cu ion penetration. It is found that the electrical stability of Ti-Si-N-O film is reduced with higher Si/Ti ratio. For Ti-Si-N-O film with Si/Ti ratio of 0.91, flatband voltage shifts 0.75 V after 90 min of BTS at 150 degrees C and 0.5 MV/cm, and this shift is attributed to the interface states at the Ti-Si-N-O/oxide interface that were generated during the plasma process and could not be fully healed after 250 degrees C annealing. Thus, it is suggested that with low silane gas flow rate, an electrically stable Ti-Si-N-O film can be achieved with fewer interface states. (c) 2006 The Electrochemical Society.