Dielectric failure mechanisms in advanced Cu/low-k interconnect architecture

Time-dependent dielectric breakdown (TDDB) reliability is increasingly becoming a critical reliability concern with the introduction of lower dielectric constant materials and shrinking of metal spacing in the back-end-of-line technology. Therefore, there is a need to investigate the factors causing the leakage and dielectric breakdown in advanced Cu/low-k interconnects and understand the failure mechanisms involved. In this work, specially designed test structures i.e. line end (S1) and corner (S2) interconnect layouts were used to investigate the failure mechanisms. This is due to its electric field enhancement effects and thus enabling more stringent reliability assessments, and also due to its efficacy in failure analysis. Two failure mechanisms were observed and they were delamination at the SiC(N) dielectric cap and SiOCH low-k dielectric interface and Ta migration from the anode sidewall. The delamination resulted in a lower TDDB activation energy (~0.2eV) for S1 and S2 structures due to field enhancement effects while Ta migration increased the interconnect leakage. This implies that the capping layer properties and its adjacent interface adhesion quality as well as the sidewall barrier integrity degrade TDDB reliability. However, the TDDB reliability was found to be improved in stand-alone and self-aligned CoWP-capped interconnect architecture with lower leakage and higher TDDB activation energies (0.66eV – 0.96eV). This is due to its TDDB dependence on the inter-metal dielectric properties alone instead of the additional interface adhesion quality of the dissimilar interface between the dielectric cap and inter-metal dielectric in dielectric-capped interconnects.