Dependency of dishing on polish time and slurry chemistry in Cu CMP

In this paper the influences of slurry chemistry and thickness of the copper layer on dishing will be discussed. The dishing is studied for different patterns and variable polishing times. We found that the concentration of the oxidizer and the thickness of copper layer have a strong impact on dishing. The larger Cu features develop dishing at a higher rate than smaller structures during overpolishing. The experimental results lead to the following hypothesis for the Cu removal and surface passivation. The oxidizer (H₂O₂) reacts with Cu in an acidic slurry (pH 4) and Cu²⁺ ions are formed. The anions of the carboxylic acid react with Cu²⁺ ions and form an insoluble salt (R(COO)₂Cu) which passivates the surface. This passivation layer is removed in protruding areas by mechanical abrasion. Once removed from the surface, the `metallic soap' particles are swept away by the turbulent motion in the slurry .