A strategy using a copper/low-k BEOL process to prevent negative-bias temperature instability (NBTI) in p-MOSFETs with ultra-thin gate oxide

This paper is a report on the effect of processing to form interconnects by using copper and a material with a low dielectric constant (copper/low-k) on the negative-bias temperature instability (NBTI) of p-MOSFETs. We found that the NBT-stress lifetime of copper/low-k interconnects is shorter than that of aluminum/SiO/sub 2/ interconnects. The NBTI strongly depends on the cap layer over the copper/low-k layer, on the intermetal dielectric (IMD) film, on the barrier-metal film, and on the temperature of post-metal annealing (PMA). Based on these results, we developed methods for reducing the NBTI in next-generation MOSFETs.