Strong Synergistic Effects between Ceria and Montmorillonite particles in Glass CMP Slurries
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Strong Synergistic Effects between Ceria and Montmorillonite particles in Glass CMP Slurries Mingming Fang, Michael Ianiro, Don Eisenhour, and Jason St. Onge Technical Center, Amcol International, Inc., 1350 West Shure Drive, Arlington Heights, IL 60004 ABSTRACT Glass substrate has superior shock resistance and higher stiffness for increased rpm and access time than Al/NiP substrate. The main barrier for the use of glass instead of Al/NiP in desktop computers has been the high cost of the glass substrate, which is mostly caused by its need for a long polishing time. Developing a glass CMP slurry that can deliver a higher polishing rate and fewer surface defects is a continuous challenge in the disk industry. We recently discovered that adding montmorillonite particles into a ceria-based glass CMP slurry can significantly increase the polishing rate without sacrificing the surface smoothness. It is the first time, to our knowledge, that this strong synergistic effect between ceria and montmorillonite particles was reported in the glass CMP area. Several physical properties of the ceria- montmorillonite slurries, such as viscosity, zeta potential, and particle size, are characterized in order to understand the mechanism of the synergistic effect.
INTRODUCTION Glass magnetic-memory disks are used as computer hard drives for storing data in lap-top and desk-top PCs for many years. In order to increase the storing capability of hard drives, these glass substrates must be planarized before the magnetic layers are deposited on their surfaces. Chemical Mechanical Planarization (CMP) is used to accomplish this task. Ceria (CeO2) particles are the most commonly used abrasive in the glass CMP slurry formulations due to thier unique chemical properties with silica surface at basic conditions. Different sizes and distributions of CeO2 were selected to formulate different glass CMP slurries in order to meet the requirements of polishing rate and surface roughness. Most glass disks suppliers, such as Hoya, Toyo Kohan, and Fujimi, use ceria-based CMP slurries to manufacture their products. Since the electronic industrial trend is always to minimize the sizes of electronic units and maximize the speed and capability of the storing devices, disk manufacturing companies are continuously looking for ways to improve their polishing rate while decrease the surface roughness. From a slurry point of view, one way to accomplish this is to use smaller CeO2 particles to decrease the surface roughness and add chemical additives to enhance the rate. While some progress has been made by this approach, it gets to a point that balancing the mechanical and chemical aspects of the slurry becomes very difficult. Another way to improve glass CMP slurries is to look for novel abrasives. Bentonite (industrial name of montmorillonite) has been widely used in industries as a viscosity modifier and suspension additive.1 2 Bentonite and other clay particles were also used in CMP slurries, but only as suspending agents3 4. Few literature sources
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