Research Papers: Friction & Wear

Coffee Stain Ring Effect and Nonuniform Material Removal in Chemical Mechanical Polishing

[+] Author and Article Information
Jianguo Xin

Department of Mathematics and Statistics, University of North Carolina, Charlotte, NC 28223jxin@uncc.edu

J. Tribol 132(4), 041605 (Oct 07, 2010) (6 pages) doi:10.1115/1.4002108 History: Received November 16, 2009; Revised June 12, 2010; Published October 07, 2010; Online October 07, 2010

When a drop of coffee dries on the counter-top, it leaves a dense, ringlike stain along its perimeter. Solids immersed in a drying drop will migrate toward the edge of the drop and form a solid ring. Such phenomena create ringlike stains and happen for a wide variety of surfaces, solvents, and solutes. It is referred to as the coffee stain ring effect. The phenomenon is caused by the outward microfluidic flow of the solute within the drop, which is driven by the evaporation of solvent. We show that the mechanism for the ring effect contributes to the nonuniform material removal in chemical mechanical polishing (CMP), specifically, at edges of blanket wafers causing the edge effect or at edges and corners of protrusive features on patterned wafers inducing the doming effect; metal dishing and dielectric erosion. By controlling the evaporation profile of the solvent in the slurry layer between the wafer surface and the polishing pad, such as making grooves or embedding the abrasive particles on the pad, or delivering the slurry from the bottom of the pad, one can improve the uniformity of material removal during the CMP process.

Copyright © 2010 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 1

Shape function for contact pressure distribution with wafer radius R=0.1 m and the parameter β=655/m

Grahic Jump Location
Figure 2

A drop of elongated coffee containing about 1% weight solids has dried to form a perimeter ring, intensified in regions of relatively high curvature. The longest distance between two points on the perimeter is about 22 mm.

Grahic Jump Location
Figure 3

Schematic showing the mechanism of the coffee stain ring effect: as the solvent evaporates, an outward radial microfluidic flow of the solution particles indicated with arrows is generated

Grahic Jump Location
Figure 4

Evaporation of the slurry solvent can only occur near the edge of a wafer but not through its surface



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