As the technology nodes in integrated circuit (IC) fabrication continue to approach molecular dimensions, the defectivity and planarization provided by conventional chemical mechanical planarization (CMP) processes are no longer sufficient. Therefore, it is necessary to develop new chemistries and innovative screening techniques to solve difficult CMP challenges, including the use of new materials such as cobalt in advanced IC fabrication. For advanced nodes at 14 nm and below, cobalt is currently being implemented on top of Ta/TaN barrier layers and below the copper seeds for the first few metal lines, due to its better conformational coverage within high aspect ratio features and good adhesion to copper. In addition, replacing copper with cobalt in the trenches of interconnect lines for the first few metal layers in the BEOL has demonstrated lower resistivity at smaller dimensions, therefore cobalt interconnects are being considered for < 10 nm nodes for M1 and M2. All these new integration schemes require CMP to achieve planarity with requirements such as low dishing, defectivity, roughness, and tunable selectivity depending on the stack.

Under CMP conditions, however, cobalt can suffer from corrosion and static-etch issues, especially when in contact with copper (galvanic corrosion), due to the lower standard reduction potential of cobalt in aqueous solutions across a broad pH range. The corrosion issues must be solved in CMP slurries that deal with cobalt processes (both liner and bulk/plug) to successfully commercialize cobalt-based IC design for next generation semiconductor manufacturing. In this poster, we will discuss the results and learnings from corrosion inhibitor screening techniques such as electrochemical, static-etch, and quartz crystal microbalance (QCM) studies and their correlation with polishing results for developing cobalt slurry formulation platforms. Furthermore, fundamental understanding on the effects of pH and slurry components such as complexors/oxidizers/corrosion inhibitors on the corrosion and removal rate behavior of cobalt films will be discussed.