High polishing selectivity ceria slurry for formation of top electrode in spin-transfer torque magnetic random access memory

During the formation of the top electrode (T.E.) in spin-transfer torque magnetic random access memory, a slurry with a high polishing rate of SiO2 and a low polishing rate of metal (T.E. material) is required in the chemical mechanical planarization application area. We used a ceria-based slurry with a polymeric additive to maintain the high polishing rate of SiO2 while it suppresses the polishing rate of the T.E. material, tantalum and ruthenium. We found ruthenium showed a significantly higher selectivity than tantalum in the ceria-based slurry. X-ray photoelectron spectroscopy was used to investigate the adsorption characteristics of the polymeric additive on the T.E. material. Except for the adsorbed polymeric additive, we found that zeta potential of the T.E. material played a critical role in determining the polishing selectivity of SiO2-to-T.E. material.

► High selective chemical mechanical planarization (CMP) slurry was investigated.
► The slurry has a high selectivity of SiO2-to-metals like tantalum and ruthenium.
► Spin-transfer-torque magnetic memory requires such high selectivity slurry.
► Surface zeta potential was used to explain CMP mechanism.
► tantalum and ruthenium have different rate-determining steps during CMP.