Large particle counting

Reproduced from Characterization of abrasive particle distribution in CMP slurries, in Proceedings from the 16th Annual International Symposium on Chemical Mechanical Planarization, August 8, 2011, sUde 24, sponsored by Clarkson University, Potsdam, NY. 

Calibration with known size particles (such as polystyrene latex beads) is used to relate the size of the electrical pulse to the size of the particle. So, the particle counter not only detects that a particle has been detected in the fluid but also the size of the particle. The size threshold determines whether the pulse is large enough to be considered a particle detected or if below the threshold then relegated to just background noise. Liquid chemical particle counters are available for the size range of 0.04—20 pm. 

Used with permission from Particle Measuring Systems, Boulder, Colorado. 

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Remsen EE, Anjur S, Boldridge D, Kamiti M, Li S, Johns T, Dowell C. Analysis of large particle count in fumed silica slurries and its correlation with scratch defects generated by CMP. J Electrochem Soc 2006 153(5) G453-G461. 

FIGURE 18.33 (a) Large particle counts variation in different size bins for silica-H slurry recirculation in MLC pump at 7600 rpm and 63.4tumovers/h (Test 7) (b) Particle counts variation in different size bins for silica-H slurry recirculation in AOD pump at 28psi backpressure, 63.4turnovers/h (Test 8) and (c) Cumulative particle counts variation in different bins for silica-H slurry recirculation in MLC pump Test 7 and AOD pump Test 8. 

Remsen, E.E., Anjur, S.P., Boldridge, D., Kamiti, M., Li, S., 2005. Correlation of defects on dielectric surfaces with large particle counts in chemical-mechanical planarization (CMP) slurries using a new single particle optical sensing (SPOS) technique. MRS Pioc. Cambridge Univ Press. 

However, the large particle count for SIS is considerably lower than for PA and is independent of flow rate. Since the flow rate ordering was randomized and SIS was alternated with PA at each flow, the result is robust every time that SIS was installed the removal rate increased and the defect count decreased, and every time the standard slurry wand was reinstalled the rate decreased and defects increased. 

If the particles are sufficiently large for counting, and can be determined, the nominal diameter (diameter of a sphere of equal volume) can be calculated at once. In this case a9 = 7r/6, so that the nominal diameter dH is given by the expression... 

Continuous curves of the type illustrated in Fig. 2.2 are often used to show the difference in size distributions of aerosol number, surface area, or mass, with the same aerosol. These differences arise when there are large numbers of small particles present in an aerosol. These particles contribute greatly to total particle count but little to total particle mass or surface area. 

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