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MAGNETIC STIRRING BAR FOR EXTREMELY ABRASIVE, HARSH CHEMICAL ENVIRONMENTS

IP.com Disclosure Number: IPCOM000008228D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2002-May-29
Document File: 2 page(s) / 113K

Publishing Venue

Motorola

Related People

James Vanell: AUTHOR

Abstract

In this work, I discuss the apparatus required for stirring/agitating extremely abrasive, harsh chemicals used with Chemical Mechanical Polishing (CMP) tools. The apparatus and methodology presented herein is applicable to both metal and oxide slurries from any of the recognized Suppliers of this type chemistry.

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MO-LA Technical Developments

MAGNETIC STIRRING BAR FOR EXTREMELY ABRASIVE, HARSH CHEMICAL ENVIRONMENTS

by James Vanell

ABSTRACT

  In this work, I discuss the apparatus required for stirring/agitating extremely abrasive, harsh chemicals used with Chemical Mechanical Polishing (CMP) tools. The apparatus and methodology presented herein is applicable to both metal and oxide slurries from any of the recognized Suppliers of this type chemistry.

STATEMENT OF PROBLEM

  Chemical Mechanical Polishing technology requires the use of extremely abrasive slurries containing silica or alumina particles suspended in solutions ranging in pH from I .8 to 12. It is crucial to the function of the slurry that the abrasive parti- cles be kept suspended in solution. As an example, one of the most promising slurries for Tungsten polishing shows almost immediate settling without constant stirring. Settling of the slurry affects the removal rate an,d can result in particle agglomera- tion. This agglomeration results in overly large abrasive particles with subsequent scratching during polish. In addition, slurry stirring methodologies must be relative'ly non-intrusive to prevent additional contamination due to material exposure and part wear, All the above-mentioned particle and contam- ination issues likely result in product loss. Process results are very dependent upon consistent particle size and concentration within the slurries and assumes no process contamination due to the stirring methodology. Any significant change in abrasive concentration of the slurty delivered to the polishing tool dramatically alters the removal rate and uniformity performance of the slurry.

  Standard methods of chemical mixing/agitation are not applicable to CMP slurries. These methods include: Magnetic stirrers, electrically- or pneumati- cally-driven impellers, shakers, homogenizers, and recirculating pumps. These methods present

problems resulting from metallic or polymer conta- mination due to wear, pose significant difficulty of implementation at point-of-use, are unacceptable in a clean room environment, and/or generally produce poor mixing results. Specifically, prior art using TeflonTM -over-Alnico magnets results in stirring bars which last approximately one week before the abrasive/barrel ridge combination have completely worn through the TeflonTM overcoat and exposed...