Effect of Complexing Agent in Slurry on CMP Property for Barrier Material Cobalt

Recently, Cobalt (Co) is focused as the barrier material for the next-generation copper interconnects technology, owing to its superiority in anti-diffusibility for barrier effects and adhesion. In this work, Chemical Mechanical Polishing (CMP) samples were prepared by Direct current (DC) magnetron sputtering, CMP tests were done by the polisher (nspire-6EC from Revasum Company), the thickness of Co films pre-CMP and post-CMP were measured by step-profiler and their surface roughness were characterized by Atomic Force Microscope (AFM). In order to optimize the CMP slurry recipe, the effects of different complexing agents (including citric acid and acetic acid) on material removal rate (MRR) and root mean square (RMS) roughness are firstly compared. And the concentration effects of complexing agents on MRR and RMS roughness were also discussed. CMP results show that the optimized MRR could reach 457.8 nm/min when 0.4 wt% acetic acid was used as complexing agent and the number of RMS roughness would decrease from 8.19 nm to 5.98 nm, which confirms that acetic acid is a more suitable complexing agent for CMP slurry of Co.