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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. 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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  1. Quantitative In-Situ Measurement of Asperity Compression Under the Wafer During Polishing Caprice Gray MRS Spring Meeting San Francisco, CA March 30, 2005

  2. Overview • Introduction • Experimental Setup • Polisher • Dual Emission Laser Induced Fluorescence • Pad Compression Experiments and Results • Static Compression • Dynamic Compression • Conclusion

  3. 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

  4. Motor Wafer Platen Steel Table RotoPol-31 Force Table Polishing Setup

  5. DELIF

  6. Pad Slurry Why Examine 2 Emissions? Ratio = Division of 2 images cancels variations in image source intensity

  7. Experiments • Pads: flat Fruedenberg FX9 • Global vs. Local topography • Static: flat glass wafer • Dynamic: etched glass wafer

  8. 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.

  9. 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

  10. Static Compression Results

  11. 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

  12. Dynamic Results (7mm)

  13. 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.

  14. 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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