Large Particle Counts Research Articles

Reduction of Large Particles in Ceria Slurry by Aging and Selective Sedimentation and its Effect on Shallow Trench Isolation Chemical Mechanical Planarization

The effect of aging and selective sedimentation of ceria slurry on the slurry characteristics, such as the particle size distribution, the large-particle count, and the dispersion stability, and on the number of defects on the wafer surface during the shallow trench isolation (STI) chemical mechanical planarization (CMP) process was investigated. The aging time and temperature were considered as important variables giving great influence on the slurry characteristics and STI–CMP. By applying aging and selective sedimentation, the number of large particles produced by either strong agglomeration or soft flocculation in ceria slurry was successfully reduced, and the dispersion stability of the ceria particles was also improved. A CMP evaluation demonstrated that the number of defects on the wafer surface was significantly reduced, while maintaining the reasonable oxide removal rate and oxide-nitride selectivity.

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 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 . 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 . 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 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.

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

AbstractA dual-sensor single particle optical sensing method (SPOS) is described for the measurement of the large particle count (LPC) in fumed silica polishing slurries. LPC values were expressed on a silica sphere-equivalent diameter scale rather than a polystyrene latex-equivalent size basis. Linear correlations between LPC and scratch counts on SiO2 surface films for wafers polished under clean room and table-top CMP conditions are demonstrated. However, these correlations were obtained for a limited set of model slurries; and further investigation will be needed to assess the general applicability of dual-sensor SPOS for oxide scratch defect prediction in CMP slurries.

Investigating the Effects of Diluting Solutions and Trace Metal Contamination on Aggregation Characteristics of Silica-Based ILD CMP Slurries

AbstractOne of the major drawbacks to CMP is the tendency for abrasive particles in slurries to form aggregates, which have the potential to cause defects on wafer surfaces. Therefore, it is crucial to understand the mechanisms by which aggregates are formed so appropriate metrology can be implemented that will identify defect-causing slurries before they are used in the fab. Single particle optical sensing (SPOS) techniques are commonly used to obtain large particle counts (LPC) for slurries. The SPOS technique requires slurry dilution before measuring and the instrument continues to dilute the sample during a measurement. Other techniques that can be used to characterize slurries are particle size distribution by static light scattering (SLS), mean particle size (MPS) by dynamic light scattering (DLS), and zeta potential (ZP) measurements. Like SPOS, all of these techniques require that slurry be diluted prior to measuring and the current method for doing so is with UPW. Diluted slurry demonstrates significantly different ionic strength than the undiluted slurry, and electrolyte concentration has been shown to affect aggregation and electric double layer characteristics of silica particles 2–6. An alternative diluting solution was formulated that simulates the conductivity and pH of the original slurry to mimic the conditions to which particles are actually exposed. It is crucial to identify the metrology that is compatible with high pH solutions and the impact of these solutions on measurements. A second objective of the study is to examine aluminum contamination in slurries. To date, the aluminum content of silica-based CMP slurries and effects on performance have not been well studied. Aluminum is known as a potential contaminant during abrasive and/or slurry manufacturing processes. Known defect free slurries were doped with aluminum and effects on particle aggregation were observed. Specifically, it is of interest to identify the metrology and techniques that may be useful (and those that are not) in monitoring aluminum induced aggregation.