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

One 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.