Impact of low-K dielectrics and barrier metals on TDDB lifetime of Cu interconnects

Time-dependent dielectric breakdown (TDDB) in Cu metallization and the dependence on the presence of barrier metal, barrier metal thickness, the kind of barrier metals and the Low-K dielectrics, is investigated. There is a distinct difference in TDDB degradation mechanism with and without barrier metals. TDDB degradation of Cu interconnects without and with barrier metal is caused by bulk mode and CMP-surface mode, respectively. TDDB characteristic with barrier metal is almost the same for different barrier metal thickness and depends much more strongly on the electric field strength than the MIS structure. Additionally, both degradations, related to Cu-ion diffusion, are mainly caused not by thermal stress but by electrical stress. The barrier properties of Ta and TaN are better than those of TiN against Cu-ion diffusion into dielectrics, for TDDB. In the case of Low-K structure, TDDB property with barrier metal also depends on the CMP-surface. With low-K dielectrics the electric field strength is concentrated near the CMP-surface and the TDDB lifetime reduces as K-value becomes lower. However, all low-K structures in this study are able to satisfy the 10-year TDDB reliability specifications for the capacitor.