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In Situ Friction Measurements in Chemical Mechanical Planarization

In Situ Friction Measurements in Chemical Mechanical Planarization. Jim Vlahakis PhD. Candidate Tufts University 20 February 2006. 1. Introduction. Experimental setup Equipment Data generation Data analysis Results & Discussion Coefficient of Friction (COF) Frequency Analysis

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In Situ Friction Measurements in Chemical Mechanical Planarization

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  1. In Situ Friction Measurements in Chemical Mechanical Planarization • Jim Vlahakis • PhD. Candidate • Tufts University • 20 February 2006 1

  2. Introduction • Experimental setup • Equipment • Data generation • Data analysis • Results & Discussion • Coefficient of Friction (COF) • Frequency Analysis • Sources of Error • Final thoughts

  3. Must accommodate our DELIF experiments transparent wafer 9:1 water diluted slurry to avoid polishing Framework supports optics Process parameters must be modified to account for laboratory scaling Wafer size = 3” dia. Default ω = 60rpm Flow rate ~ 50cc/min Experimental Setup

  4. Motor Wafer Platen Steel Table RotoPol-31 Force Table Equipment Motor – ½ hp Dayton Wafer – transparent BK7 Table – 136kgs, steel Platen – 12” diameter Force table – AMTI Polisher – Struers RotoPol31

  5. Alignment of polisher and force table Mechanical isolation Support frame Alignment of wafer drive belt In our setup, Fz, also includes the weight of any fluid in the system Platen runout can influence Fz Equipment - Issues

  6. Equipment - Force Table • Decomposes the loading into orthogonal components (forces and moments), • Accuracy • 355 bits/lb in x and y • 710 bits/pound in z

  7. Equipment - Polisher • Struers RotoPol 31 table top polisher. • Rests directly on top of the force platform • Real time measurements of the wafer/pad interaction forces • Fz – process downforce • Fx, Fy - friction due to polishing • Custom LabView software allows us to select a rotation rate from 0 – 100rpm

  8. Equipment - Wafer • Transparent glass BK7 wafer • Wafer concavity mates with drive shaft • Drive plate (red plastic) ensures positive engagement with wafer drive pins • Decent amount of “play” allows the wafer some freedom of movement

  9. Data Generation • Custom LabView software controls force table, digital amplifier and I/O settings • Front panel seems complicated but is pretty straightforward • Most settings are “set and forget”

  10. Data format - 6 columns, tab delimited Each column represents one component (Fx, Fy, etc.) Sampling rate = 2kHz Each data run ~ 20sec Data file sizes up to tens of megabytes (ie manageable) Accuracy Issues .007N/bit in x and y .097N/bit in z Force table/polisher alignment Data Analysis

  11. Results & DiscussionCoefficient of Friction Ungrooved FX9 pad

  12. Results & DiscussionCoefficient of Friction Circular grooved FX9 pad

  13. Results & DiscussionCoefficient of Friction xy grooved IC1000 pad

  14. Results & DiscussionCoefficient of Friction xy grooved IC1000 pad – low slurry flow rate

  15. Results & DiscussionCoefficient of Friction • For unvented pad • Larger spread in instantaneous COF, ranging from 0.0 to 3.0 • Indicates the lubrication regime is alternating from hydrodynamic to boundary lubrication • Larger average COF and larger variation in COF • Higher velocity decreases COF slightly • For vented pads • Smaller spreads in COF and smaller average COF • Indicates more consistent lubrication regime • Venting seems to moderate the changes in COF • high Fz-30rpm-IC1000 dataset seems to show some sort of resonance effect

  16. Results & Discussion Frequency Analysis • Examine the downforce frequency spectrum • Which frequencies contribute the most • Can we learn anything about the various polishing parameters based on the frequency signature

  17. Results & Discussion Frequency Analysis Ungrooved FX9 pad

  18. Results & Discussion Frequency Analysis Circular grooved FX9 pad

  19. Results & Discussion Frequency Analysis xy grooved IC1000 pad

  20. Results & Discussion Frequency Analysis xy grooved IC1000 pad – low slurry flow rate

  21. Results & Discussion Frequency Analysis • Features at 120Hz/240Hz/360Hz are grounding issues. Must be filtered out in the future. • Resonant case (highFz-30rpm-IC1000 pad) shows a strong peak at ~190Hz. May be related to pad’s natural frequency • Which features are important? What scale should we be looking at?

  22. Sources of Error • Mechanical Issues • Isolation from external inputs • Bearing runout, unbalanced rotating components • Electronic Issues • Noise from other equipment • Appropriate sampling rates • Appropriate filtering

  23. Final Thoughts • What, exactly, do we want to learn? • How to identify failure modes • A polishing end point • Correlate removal rates with COF • What are the relevant variables? • Which regions of parameter space do we want to explore? • What is the best way to present this data? • Thanks to • Intel & Cabot for their sponsorship • Our advisors Vin Manno & Chris Rogers • Fellow researchers at U. of Arizona • Howard Stone at Harvard and Gareth McKinley at MIT

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