Successful recovery of moisture-induced TDDB degradation for Cu/ULK(k=2.5) BEOL interconnect

Abstract

Cu/ULK(k=2.5) dual Damascene back end of line(BEOL) dielectric degradation was studied with respect to post Cu CMP delay prior to dielectric diffusion barrier deposition. The threshold of the delay time was observed beyond which line-to-line leakage current increased rapidly while the dielectric breakdown voltage decreased. This air exposure-dependent degradation was attributed to moisture absorption by damaged ULK during integration, and caused premature TDDB (time-dependent dielectric breakdown) failure. It was found that combination of moisture removal by damage-free UV and mild plasma treatment was able to restore dielectric breakdown voltage as well as TDDB time to failure even well past the threshold of delay time.