Action Mechanism of 2-Phosphonobutane-1,2,4-Tricarboxylic Acid on Co Barrier CMP in H 2 O 2 -Based Slurries: A Combined Dynamic and Static Electrochemical Study

The low-pressure cobalt (Co) barrier Chemical mechanical polishing (CMP) faces three critical challenges: achieving sufficient removal rate (RR) while obtaining the desired surface quality of Co and Cu, achieving the appropriate selectivity of Cu/Co RR, and suppressing galvanic corrosion of Cu/Co. To meet this challenge, this paper developed a novel CMP slurry by integrating 2-phosphonobutane -1,2,4-tricarboxylic acid (PBTCA) as a complex agent and Octanohydroxamic Acid (OHA) as an inhibitor. The optimized slurry (0.3 wt% PBTCA, 0.6 wt% H 2 O 2 , 4 wt% SiO 2 , 0.09 wt% OHA) achieves a Co RR of 301.5 Å min −1 and Cu RR of 267.5 Å min −1 , with a Cu/Co RR selectivity of 0.88:1.00; the potential difference of 9 mV effectively inhibiting galvanic corrosion of Cu/Co. The action mechanism of the opitized slurry is elucidated as follows: PBTCA enhances the RR of Co by forming stable complexes with Co ions, where the O atom of the phosphate group in PBTCA has stronger complexation ability than the carboxyl groups. Add OHA to the PBTCA-based slurry to achieve the desired surface quality of Cu/Co and an appropriate Cu/Co removal rate ratio. The surface roughness of Cu and Co after CMP is 0.653 nm and 0.309 nm, respectively, meeting the surface quality requirements.