Intra-level dielectric reliability in deep sub-micron copper interconnects

Abstract

As interconnects are scaled down to deep sub-micron regime, some of the back-end-of-line (BEOL) dielectric reliability issues such as intra-level leakage current, dielectric breakdown strength and time-dependent dielectric breakdown (TDDB) are becoming increasingly important. By varying some of the process steps such as surface treatments and dielectric barriers, we are able to determine the origin of the leakage currents, their probable leakage pathways as well as the dielectric breakdown mechanisms. From the carrier transport modeling, it was deduced that the trap density at the BEOL dielectric surfaces is the major cause of intra-level leakage current. Besides, it was also shown that Cu ion drift into neighboring BEOL dielectric can have major impact on both BEOL dielectric breakdown strength as well as TDDB performance. Soft breakdown phenomenon was observed in intra-level comb capacitor structures. The occurrence of soft breakdown was irregular and it poses practical measurement problems.