Quantitative in situ measurement of asperity compression under the wafer during polishing
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Quantitative In-Situ Measurement of Asperity Compression Under the Wafer During Polishing. Caprice Gray MRS Spring Meeting San Francisco, CA March 30, 2005. Overview. Introduction Experimental Setup Polisher Dual Emission Laser Induced Fluorescence Pad Compression Experiments and Results

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Quantitative In-Situ Measurement of Asperity Compression Under the Wafer During Polishing

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Quantitative in situ measurement of asperity compression under the wafer during polishing

Quantitative In-Situ Measurement of Asperity Compression Under the Wafer During Polishing

Caprice Gray

MRS Spring Meeting

San Francisco, CA

March 30, 2005


Overview

Overview

  • Introduction

  • Experimental Setup

    • Polisher

    • Dual Emission Laser Induced Fluorescence

  • Pad Compression Experiments and Results

    • Static Compression

    • Dynamic Compression

  • Conclusion


Introduction

Introduction

  • DELIF is used to collect grayscale images that represent properties under the wafer during polishing

    • pH, temperature, fluid layer thickness

  • Previous thickness measurement

    • time averaged

    • low spatial resolution

  • New DELIF Setup

    • Laser enables instantaneous imaging

    • Larger distance between lens and CCD – 4 mm/pixel

  • In these experiments we use fluid thickness measurements to infer what is happening to pad asperities during polishing


Polishing setup

Motor

Wafer

Platen

Steel Table

RotoPol-31

Force Table

Polishing Setup


Delif

DELIF


Why examine 2 emissions

Pad

Slurry

Why Examine 2 Emissions?

Ratio

=

Division of 2 images cancels variations

in image source intensity


Experiments

Experiments

  • Pads: flat Fruedenberg FX9

    • Global vs. Local topography

  • Static: flat glass wafer

  • Dynamic: etched glass wafer


Static pad compression

Static Pad Compression

  • 2 Images were taken in a single section of the pad.

    • 0 kPa

    • 70 kPa

  • 17 total sections were imaged and analyzed.


Histogram analysis

Histogram Analysis

  • The asperity size distribution is the same shape as the fluid layer thickness distribution.

  • When force is applied to the wafer, the distribution changes both shape and location.

  • Standard deviation comparison → pad compression

  • Peak location → fluid layer thickness.

  • Compression factor: e


Static compression results

Static Compression Results


Dynamic pad compression

Dynamic Pad Compression

  • Two wafers were etched and contain square wells

    • 14.5 mm deep

    • 27 mm deep

  • Asperities can expand under these wells.

  • Histograms from regions 1 and 2 are compared

  • Run Conditions:

    • Pad/wafer rotation: 30 RPM

    • Continuous conditioning

    • Slurry flow: 50 cc/min

    • Force applied to wafer: 10 kPa


Dynamic results

Dynamic Results

(7mm)


Conclusions

Conclusions

  • DELIF can be used to measure slurry film thickness with asperity scale resolution.

  • Over the 6 mm2 regions imaged, Different amounts of fluid can be displaced due to the same applied global forces.

  • Pad topography deformation can be inferred from fluid layer thickness measurements.

    • During a static application of force, local pad compression is roughly linearly related to the amount of fluid displaced by the compression

    • In the dynamic case, asperity expansion into 27 mm deep wells was greater than expansion into 14.5 mm deep wells.


Acknowledgements

Acknowledgements

  • Tufts

    • Professor Chris Rogers

    • Professor Vincent P. Manno

    • Dan Apone

    • TUFTL

  • Intel Corporation

    • Chris Barns

    • Mansour Moinpour

  • Cabot Microelectronics

    • Sriram Anjur

  • University of Arizona

    • Ara Philipossian


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