Cu Dual-Damascene Interconnects with Direct Chemical Mechanical Polishing Process on Porous Low-$k$ Film

To reduce the effective dielectric constant ($k_{\text{eff}}$) value for 32 nm node technology and beyond, the effects of a direct chemical mechanical polishing (CMP) process on porous low-$k$ film without a protective cap layer were investigated. It was confirmed that a capless structure on porous low-$k$ film is effective in reducing the resistance--capacitance (RC) products, but it causes degradation of wire-to-wire breakdown voltage characteristics. The most important point of a direct CMP process is to control the amount of damage to the polished surface. In this study, two types of low-$k$ film were compared in combination with a variety of CMP process conditions. As results, we found that a direct CMP process has a positive effect on wire-to-wire current leakage and time-dependent dielectric breakdown (TDDB) reliability where a porous low-$k$ film deposited by modified conditions is used. By optimizing the deposition and curing conditions, it is possible to control the distribution of different pore sizes in porous low-$k$ film, which allows us to realize a highly reliable capless structure.