Advances in the Characterization of Particle Size Distributions of Abrasive Particles used in CMP
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0991-C04-03
Advances in the Characterization of Particle Size Distributions of Abrasive Particles used in CMP Mungai Kamiti, Stacey Popadowski, and Edward E. Remsen R&D-Enabling, Cabot Microelectronics Corp., 870 N. Commons Drive, Aurora, IL, 60543
ABSTRACT The use of density gradient stabilized centrifugal sedimentation (disc centrifugation) for the characterization of abrasive particles in CMP slurries is reported. For slurries prepared with ceria and colloidal silica abrasives, the technique is demonstrated as capable of providing highly repeatable analyses of the abrasiveís apparent particle size distribution (PSD). The addition of water soluble organic additives to the slurries is shown to produce large shifts in the apparent PSD relative to the PSD of the pure abrasive particles. Particle-additive interactions driving the shift in apparent PSD could not be interpreted with confidence due to the lack of accurate densities for particle-abrasive complexes formed in the slurry. To address this problem, sucrose density gradients prepared using H2O and D2O were tested as spin fluids of different densities to analyze a colloidal silica standard with a narrow PSD. Preliminary results comparing experimental disc centrifuge data with theoretical simulations of the disc sedimentation pattern suggest that this technique can potentially characterize both the particle diameter and density of abrasive particles in a CMP slurry.
INTRODUCTION Commercial development of microelectronic devices containing ever-increasing numbers of integrated circuits per unit area of wafer surface demands minimal surface defect creation in conjunction with optimal polishing and planarization via chemical-mechanical planarization (CMP).1 It is widely accepted in the IC industry that the fraction of particles in CMP slurries with diameters less than 0.5 µm drives essential polishing and planarization processes. By contrast, the fraction of particles with diameters greater than 0.5 µm is treated as the principal source of surface defects on processed wafers. As a result, highly accurate and precise size analysis is essential over the entire abrasive particle size distribution of CMP slurries. A wide range of ensemble techniques and fractionation methods are available for particle size distribution determination.2 Of particular interest among these methods is density gradient stabilized centrifugal sedimentation (disc centrifugation)3 which has been demonstrated recently4 for the high resolution analysis of abrasive particle size distributions in CMP slurries. An additional important capability of disc centrifugation is the analysis of intermolecular interactions in aqueous solution. This feature has been exploited in the analytical ultracentrifugation characterization of intermolecular interactions in biological systems such as protein-protein interactions5and enzyme-substrate binding6. The ability to characterize binding
interactions between abrasive particles and the components used in CMP slurries is highly attractive as a means to identify
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