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TECHNICAL PAPERS

A Scratch Intersection Model of Material Removal During Chemical Mechanical Planarization (CMP)

[+] Author and Article Information
Wei Che, Yongjin Guo

Department of Mechanical Engineering,  Iowa State University, Ames, IA 50011

Abhijit Chandra1

Department of Mechanical Engineering,  Iowa State University, Ames, IA 50011achandra@iastate.edu

Ashraf Bastawros2

Department of Aerospace Engineering,  Iowa State University, Ames, IA 50011bastaw@iastate.edu

1

Also at the Department of Aerospace Engineering, Iowa State University.

2

Also at the Department of Mechanical Engineering, Iowa State University.

J. Manuf. Sci. Eng 127(3), 545-554 (Oct 12, 2004) (10 pages) doi:10.1115/1.1949616 History: Received July 21, 2003; Revised October 12, 2004

A scratch intersection based material removal mechanism for CMP processes is proposed in this paper. The experimentally observed deformation pattern by SEM and the trends of the measured force profiles (Che , 2003) reveal that, for an isolated shallow scratch, the material is mainly plowed sideway along the track of the abrasive particle with no net material removal. However, it is observed that material is detached close to the intersection zone of two scratches. Motivated by this observation, it is speculated that the deformation mechanism changes from ploughing mode to shear-segmentation mode as the abrasive particle approaches the intersection of two scratches under small indentation depth for ductile metals. The proposed mechanistic material removal rate (MRR) model yields Preston constant similar to those observed experimentally for CMP processes. The proposed model also reveals that the nature of the slurry-pad interaction mechanism, and its associated force partitioning mechanism, is important for determining the variation of MRR with particle size and concentration. It is observed that under relatively soft pads, small particles and low particle concentration, the pad undergoes local deformation, yielding an increased MRR with increasing particle size and concentration. At the other extreme, the intact walls of the surface cells and the connecting cell walls between the surface pores deform globally, resembling a beam or a plate, and a decreasing trend in MRR is observed with increasing particle size and concentration. The predicted MRR trends are compared to existing experimental observations.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 2

An AFM scan of a representative scratch cross section during single grit scratching of copper (depth of cut 3μm). The volume in the trench is about the same as the pile-up volume.

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Figure 8

Schematic of volume of detached flake at intersection

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Figure 9

A schematic of particle motion in the CMP process

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Figure 10

A schematic of particle train motions relative to the unit cell

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Figure 11

MRR variation with pressure for copper CMP data

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Figure 12

MRR variation with velocity (copper CMP)

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Figure 13

MRR variation with particle size for a fixed 2 wt. % concentration (SiO2 CMP)

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Figure 14

MRR variation with concentration for particle size of 0.2μm (SiO2 CMP)

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Figure 15

MRR variation with particle size for a fixed 10 wt % concentration (SiO2 CMP)

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Figure 16

MRR variation with particle size (SiO2 CMP)

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Figure 1

Schematic diagram of a CMP process

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Figure 3

Flow chart for calculating the MRR in a typical CMP process

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Figure 4

SEM image of an IC1000 pad. The pad surface is tilted 60 deg of the viewing axis to show the relative surface topography. The average pore diameter is about dp=50μm.

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Figure 5

Schematic representation of the multiscale of the wafer∕pad contact. (a ) Long wavelength multi asperity contact; (b ) details of individual pad asperity contact under local pressure, P; (c , d ) cell level deformation as a local indentation (with no, partial, or full contact of the wafer∕pad interface); (d ) bending of the entire cell.

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Figure 6

Characteristic detachment length variation with the scratch depth

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Figure 7

Schematic of scratch intersection

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