Study of copper drift during TDDB of intermetal dielectrics by using fully passivated MOS capacitors as test vehicle

A fully passivated Metal-Oxide-Semiconductor (MOS) capacitor [Tőkei Zs. Barrier integrity and reliability in copper low-k interconnects. ISTC 2005; 386–95] is used to study the intrinsic properties of a barrier between copper and dielectric in Back-End-Of-Line interconnects. Several barriers are studied and compared to each other. The test vehicle is also used to thoroughly investigate the role of thermal diffusion or field assisted ionic copper drift during Time-Dependent-Dielectric Breakdown (TDDB) by investigating the breakdown of dielectrics without a barrier at very low voltages.Comparing different barriers revealed that a “standard” PVD-based Ta barrier has a significantly better TDDB-performance compared to an 8 nm SiCN-barrier.For samples without barrier, it was found that long thermal anneals without the application of a stress voltage changes the distribution of failure times. Furthermore, the possibility of a bimodal distribution was argued when stressing these devices at a wide range of fields. A corollary is that, in presence of copper, both the E-model and the root-E-model do not apply for describing the experimental data obtained on these samples without barrier.