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Chemical-mechanical polishing, or planarization (CMP), has emerged as an increasingly important technology for integrated-circuit manufacturing. Consumables used during CMP interact in a complex manner with the polishing tool, the process conditions, and the wafer being polished. In this article, several advanced analytical methods are used to analyze the properties of slurries and pads under conditions similar to those found during CMP processing. Some of the key findings are that under these process conditions, pads can be stabilized with a heat treatment prior to installation on the polisher; pads absorb slurries at different rates, and slurries also react with the pads; and the mechanical properties of the pads are dependent on the orientation of the grooves on the pad. Dynamic rheometry was used to detect de-agglomeration in sheared slurries.

Chemical Mechanical Planarization has become a method of choice for planarization of metal and oxide layers in microelectronics industry. A CMP process includes up to 16 variables that need to be controlled to achieve a stable CMP process [1]. One of the major variables in CMP is related to slurry compositions. In particularly, a uniform distribution of the sizes of the abrasive particle in slurry is crucial for a stable CMP performance. The agglomerates can be unstable, since their size depends on addition of chemical additives and shearing during the CMP process.In this work, the authors studied agglomeration of the fumed and colloidal silica-based slurries using dynamic rheometry, zeta potential tests, and an accusizer.Slurry viscosity, determined using a steady state rheometry, was correlated to the particle charge, characterized by zeta potential, and to the particle sizes obtained using the particle size analyzer. Additionally, rheometer was used for slurry shearing to study effect of shear on slurry characteristics. Particle agglomeration due to slurry shearing and storage was observed and corroborated using rheometry, zeta potential, and particle size measurements.

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.

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