Achievement of non-selectivity barrier slurry by adding H3PO4 and its application in patterned wafers CMP

Copper metallization is achieved by combining the dual damascene techniques followed by chemical mechanical planarization (CMP). Tantalum and its nitride have been identified as the diffusion barrier layer for copper metallization. However, the wide differences in properties between copper and tantalum layers result in selectivity problems during CMP process. The aim of this work is to obtain a non-selectivity alkaline slurry for copper and tantalum removal by adding phosphoric acid (H₃PO₄) and investigates the effects of H₃PO₄ concentration, pH on the material removal rate (MRR) in CMP of Cu and Ta. It was found found that the MRR of Ta has a improvement at first until reach the maximum, and then decreased. When the pH value is 8.5, the Ta/Cu polish rate selectivity is nearly 1:1. The results indicate that due to the introduction of H₃PO₄, the slurry has an inhibiting effect on copper removal and has acceleration on the removal of Ta. The polishing properties of the obtained slurries were also evaluated on pattern wafers, the results show that the non-selectivity slurry has a lower dishing and excellent surface roughness compared with a commercially slurry.