Altering shear thickening in fumed silica suspensions using nanoparticles


Project ID: D2018-58



Silicon chips can contain over one billion transistors in one square centimeter of surface area.  In order to interconnect such a large number of electrical elements, materials must be planarized with nanometer-scale precision while leaving the exposed surface free of defects, such as scratches, gouges, or pits.  Chemical mechanical polishing (CMP) is the current technique used to perform this task. In response to market needs, CMP slurry manufacturers began favoring chemically active slurries over those that were mechanically active. However, this method has led to problems with corrosion, etching, and defects. Individual fumed silica particles can form larger agglomerates, causing a spike in viscosity at a critical shear rate, and thus scratches


Invention Description

Researchers have identified additives for a CMP slurry that can be used to control the critical shear rate. The CMP slurry recipe consists of salt and spherical silica and has been shown to move the critical shear rate from 10,000 to greater than 100,000 s-1. By pushing the critical shear rate, manufacturers will lose less material to defects.



•       CMP is a critical processing technology used by the semiconductor industry to produce a wide variety of materials, including logic devices, memory chips, and microelectronic machines (MEMs)

•       CMP technology is widely used to polish silicon dioxide, copper, tantalum, tantalum nitride, aluminum and tungsten, with application to many other materials being considered by semiconductor development scientists and engineers



•       Prevent defects from CMP processing

•       Capable of pushing critical shear rate beyond what is seen with fumed silica


IP Status:       Patent pending


Publication:              Shear thickening and defect formation in chemical mechanical polishing.

                     N Crawford, K Williams, D Boldridge, M Liberatore


Patent Information:
For Information, Contact:
Yuriy Yatskiv
Licensing Associate
The University of Toledo
Matthew Liberatore
Ehsan Ffakhrabadi
Chemical mechanical polishing
Critical shear rate
Fumed silica