Analysis of the Tribological Mechanisms Arising in the Chemical Mechanical Polishing of Copper-Film Wafers When Using a Pad With Concentric Grooves

[+] Author and Article Information
Jen Fin Lin, Sheng-Chao Chen, Yu Long Ouyang

Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan

Ming Shih Tsai

 National Nano Device Laboratory, Hsinchu 300 Taiwan

J. Tribol 128(3), 445-459 (Mar 08, 2006) (15 pages) doi:10.1115/1.2194913 History: Received January 30, 2004; Revised March 08, 2006

An average Reynolds equation considering the effects of a pad’s annular grooves and surface roughness is developed in this study to examine mixed lubrication in the chemical mechanical polishing (CMP) of a copper-film silicon wafer. This equation is obtained on the basis of the principle that the pressure gradients and volume flow rates in the direction normal to the border of a groove and a plateau as well as on two sides of the border must be equal. The continuities of volume flow rates and hydrodynamic pressure on two sides of the border as well as in the direction normal to the border of a groove and a plateau are satisfied in order to develop this Reynolds equation. The removal rate model is obtained by taking the concentration of active abrasives in the slurry and the pad grooves into account. Theoretical results are also shown in order to investigate the effects of changing the groove depth and width on the removal rate and the nonuniformity of a copper-film wafer. The application of concentric grooves in general can lower the suction pressure (negative pressure) formed between the pad and the wafer, elevate the wear rate, and reduce the nonuniformity. However, the influences of the groove depth on wear rate and nonuniformity become insignificant when the depth is excessively large. The removal rate is reduced by increasing the groove width such that it finally approaches to the result of a nongrooved pad.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

The schematic representation of a wafer-polishing tool. It shows polish platen with the wafer carrier assembly (a) Top view. (b) Side view.

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Figure 2

Schematic representation of the compressed asperities of the pad under the hydrodynamic and solid contact pressures

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Figure 3

Schematic diagrams showing the two components of (a) the two pressure gradients and (b) the volume flow rates in the directions normal and tangential to the border of a groove and a plateau

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Figure 4

Balance of forces at the wafer

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Figure 5

Schematic representation of the compressed asperities of the pad fully covered by one layer of abrasive particles

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Figure 6

Schematic diagram of deformations arising in a spherical contact region

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Figure 7

Distributions of the hydrodynamic pressure at a wafer in the use of (a) a pad without grooves and (b) a pad with grooves

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Figure 8

Variations of the removal rate in the radial direction under the conditions of (a) (ωc,ωp)=(35rpm,35rpm), down-force pressure: 34.47kPa; (b) (ωc,ωp)=(25rpm,25rpm), down-force pressure: 34.47kPa; and (c) (ωc,ωp)=(35rpm,35rpm), down-force pressure: and 20.68kPa. They were produced in the pads with grooves.

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Figure 9

The analytical and experimental results of the removal rate versus the nonuniformity. They were obtained in the use of pads with grooves.

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Figure 10

Comparisons of the removal rates produced by the nongrooved pad and the pad with grooves

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Figure 11

Variations of the mean removal rate with the nonuniformity. They are obtained from the pad with grooves and the nongrooved pad.

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Figure 12

Effects of the change in the groove width on the removal rates varying in the radial direction of a wafer



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