New Particle Metrology for CMP Slurries
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0991-C09-01
New Particle Metrology for CMP Slurries S. Kim R. Williams1, Ilyong Park1, Edward E. Remsen2, and Mansour Moinpour3 1 Chemistry and Geochemistry, Colorado School of Mines, 1500 Illinois St., Golden, CO, 80401 2 Cabot Microelectronics Corporation, 870 North Commons Drive, Aurora, IL, 60504 3 Intel Corporation, 2200 Mission College Blvd., Santa Clara, CA, 95054 ABSTRACT A new particle sizing and counting method based on the coupling of flow field-flow fractionation (FFF) with dual-sensor, single particle optical sensing (SPOS) detection is reported. The integration of FFF and SPOS systems was accomplished by means of a dilution interface that preserved the resolution of FFF-separated particles. Analysis of a model mixture of polystyrene latex standards of different diameters established that the FFF-SPOS system can resolve particles into discrete peaks for subsequent particle counting. Application of this method for the analysis of a colloidal silica standard demonstrated its use for materials commonly employed as CMP abrasives. Further development and refinement of the technique will enable compositional and structural analyses of heterogeneous large particle populations constituting commercial CMP slurries. INTRODUCTION A central tenet of integrated circuit manufacture states that the larger particle fraction in chemical mechanical planarization (CMP) slurries used to process surface films on silicon wafers produces micro-scratches on commercial microelectronic devices.1 The most compelling evidence for this assertion comes from experimental studies2, 3, 4 demonstrating the correlation between the large particle count (LPC) and wafer scratch defect counts. However, the chemical and structural nature of these particles can not be determined from SPOS measurements4, 5 commonly used to determine the LPC. This lack of detail prevents the assignment of specific large particle types in the LPC as micro-scratch generators. In addition, a relative ranking of the micro-scratching potential for the different large particle types is also beyond the reach of conventional SPOS techniques. Findings reported in the present study for model particle mixtures indicate that a new method combining size separation of particles via flow field-flow fractionation (FFF)6 and particle detection using dual-sensor SPOS can be applied in the detailed analysis of the larger particle populations typically found in CMP slurries. The FFF separation utilizes laminar flow conditions to induce a parabolic flow profile with its characteristic maximum flow rate at the center of the channel and decreasing flow velocities towards the channel walls. The FFF process commences with the transport of particulate sample to a membrane accumulation wall by a crossflow of fluid (see Figure 1A). Since the closest distance of approach to the wall is limited to one particle radius, small particles will have a center of mass that is closer to the wall than large particles and will be transported to the detector at a lower flow velocity. Consequently, smal
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