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Replacement Metal Gate application (RMG) required an excellent flat surface underneath the gate at STI (Shallow Trench Isolation) level but also after POP (Poly-Si Open Process) CMP. This work investigated the role that process selectivity plays on final CMP topology particularly for STI buffing process and POP process. Tests were focused on acidic slurries chosen for their good defectivity performances and also for their good tunable selectivities by dilution. At STI level, inappropriate slurry selectivity can increase dishing value or create edge over erosion issue. In a more complex case as POP process, where 3 materials are involved, selectivity becomes a major contributor to the gate height loss. By understanding the contribution that each selectivity has on dishing or on final gate shape, better slurry specifications can be determined for STI and POP CMP process. Finally, this work brings a better understanding of the gate profile evolution over the different CMP RMG process steps. Keywords: Selectivity, Dishing, Gate height loss, Topology, Shallow Trench Isolation, STI, Buffing STI, Replacement Metal Gate, RMG, Poly Open Process, POP.