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

Abstract

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.

Measuring shape and size of micrometric particles from the analysis of the forward scattered field

“…1 The need of continuous, non-invasive, in-line monitoring of powder suspensions in fluids is increasing, in connection with the rapid development of materials and devices through the bottom-up approach [2][3][4][5][6][7][8] as well as the need of characterizing small particles in the traditional topdown processes. [9][10][11][12][13][14][15] Quite recently, attention has been given to the possibility of driving the interactions through specific shapes of the building blocks to be assembled, [16][17][18][19] thus mimicking the behavior of atoms and molecules with chemical bonds. Over the last decades, very powerful techniques for the characterization of small particles became available.…”

Accurate sizing of ceria oxide nanoparticles in slurries by the analysis of the optical forward-scattered field

“…Basically, industry needs to guarantee both the stability of PSD and concentration upon time to prevent the surfaces from scratches and to accurately control the removal rates (Nicholes et al 2003;Remsenz et al 2006). Among the possible issues, the formation of aggregates and the contamination by other materials (metals, chemicals) are common (DeNardis et al 2005;Li 2008). Also, the presence of nano-and micro-bubbles is possible.…”