Interaction Forces Between a Glass Surface and Ceria-Modified PMMA-Based Abrasives for CMP Measured by Colloidal Probe AFM

Abstract

Interaction forces between a glass surface and two types of ceria-coated poly(methyl methacrylate) (PMMA)-based terpolymer abrasive particles were investigated using colloidal probe atomic force microscopy and correlated with relevant chemical mechanical planarization (CMP) and post-CMP parameters. The composite particles were achieved by either creating chemical bonds by silane coupling agents (composite A) or tuning the pH in order to form electrostatic attractive interactions between the core and shell composite (composite B). Based on the average values of the pull-off force vs pH, a qualitative agreement between the measured adhesion forces and the material removal rate (MRR) was found. For pH 3, both the MRR and adhesion forces are larger for composite B with respect to composite A. Interestingly, for pH 10, composite B and ceria give almost the same MRR and similar adhesion force values. Nevertheless, in general, the adhesion forces measured at pH 10 are significantly smaller than those monitored at pH 3, whereas the MRR is significantly larger for pH 10. This suggests that factors other than adhesion, such as an enhanced silica dissolution rate, dominate and define the MRR at pH 10. The increase in repulsive force with increasing pH corresponds to a decrease in composite-glass adhesion. For pH between 2 and 7, the electrostatic attractive forces between polymer particles and the silica surface are responsible for high particle counts. To improve the particle removal efficiency after CMP with the ceria-based slurry, pH values higher than 7 are recommended.