Surface Kinetics Model for SiLK Chemical Mechanical Polishing

The surface mechanism for SILK removal by chemical mechanical polishing (CMP) is modeled quantitatively using modified Langmuir-Hinshelwood surface reaction kinetics to define the boundary condition on the wafer surface for three-dimensional diffusive mass-transport equations. The model generates slurry concentration distributions between the pad and wafer as well as a CMP removal rate profile along the wafer diameter. Mathematically predicted removal rates of 15-200 nm/min accurately represent experimental data for concentrations of 0.0015-0.024 M potassium-hydrogen phthalate slurry. Three-dimensional model fits to experimental data for a range of velocity and pressure indicate that the SILK CMP removal rate is controlled by a combination of (i) chemical reaction altering the SILK surface layer and (ii) physically enhanced desorption of the reacted surface layer into the surrounding slurry.

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