Analysis of large particle count in fumed silica slurries and its correlation with scratch defects generated by CMP

The large particle count (LPC) of fumed silica slurries was evaluated and correlated with scratch counts created on Si O2 films by table-top, chemical-mechanical planarization (CMP). Particle sizing results obtained by static light scattering, capillary hydrodynamic fractionation, and dual-sensor single particle optical sensing (SPOS) pointed to the latter as the superior method for quantitative analyses of the LPC. Dual-sensor SPOS is a new technique that determines the LPC on a silica sphere-equivalent, light-scattering diameter scale for particles as small as 0.469 μm. LPC measurements used in combination with dark-field optical microscopy for scratch metrology afforded linear correlations between scratch counts and the LPC. Particles producing scratches had silica sphere-equivalent, light-scattering diameters exceeding 0.68 μm. Inclusion of these particles in the LPC produced a two-fold increase in the number of scratch-forming particles in the correlation relative to correlations generated via single-sensor SPOS measurements of LPC. Experimental uncertainty in scratch counts limited the correlation as a scratch predictor. Slurries differing in LPC by a minimum of 1.8× 105 particles gslurry had statistically different predicted scratch counts at the 95% confidence level. Additional method development is needed to extend LPC-based scratch prediction to other CMP processes producing scratch defects.