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Friction Updates

Friction Updates. Last FtF Past issues & solutions Latest data CoF vs. slurry dilution CoF vs. rotation rate Fz vs. slurry dilution Laser displacement sensor tests Feasibility Specifications Thesis Roadmap Microscale friction and polishing model Macroscale measurements

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Friction Updates

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  1. Friction Updates • Last FtF • Past issues & solutions • Latest data • CoF vs. slurry dilution • CoF vs. rotation rate • Fz vs. slurry dilution • Laser displacement sensor tests • Feasibility • Specifications • Thesis Roadmap • Microscale friction and polishing model • Macroscale measurements • Questions/Requests • Future work • Jim Vlahakis • PhD. Candidate • Tufts University

  2. Friction Updates – Last FtF • External noise issues • New wafer motor power supply eliminated noise • Issues concerning slurry dilution • Moved from 9:1 to 3:2 dilution, more in line with industry practice • Data runs at 30/60rpm • Now using 60/120rpm (.5 & 1m/s), more in line with industry practice • Irregularities due to changes in wafer shape • Controls in place to monitor wafer shape

  3. Friction Updates – Latest Data • CoF vs. slurry dilution • 60rpm & 1.7psi • Note large CoF (and large σ) for pure slurry. A result of shear thickening? • CoF remains fairly constant over a wide range of slurry dilutions • CoF for pure H2O seems strongly dependent on pH • Next steps • study slurry compositions in the range of 1 part H2O to 2/3/5/7 parts slurry • Investigate pH dependence for H2O • Perform experiment “backwards”

  4. Friction Updates – Latest Data CoF vs. rotation rate, note development of CoF plots and spectra

  5. Friction Updates – Latest Data CoF vs. rotation rate, note development of CoF plots and spectra

  6. Friction Updates – Latest Data • Fx vs. slurry dilution • 60rpm - 1.7psi • Decrease in Fz tracks decrease in density of slurry as it is mixed with H20 • Increasing σ corresponds to increasing chatter (except for pure slurry case) • Next steps • study slurry compositions in the range of 1 part H2O to 2/3/5/7 parts slurry • Investigate pH dependence for H2O

  7. Friction Updates – Latest Data • CoF vs. rotation rate • 60rpm - 1.7psi • CoF remains fairly constant over a wide range of velocities • Below 30rpm data is unreliable – motion of wafer drive is noticeably non-uniform • Next step • Investigating deeper into the Stribeck curve will require lower pressures and much higher velocities. Likely not possible with our current setup

  8. Friction Updates – Laser Sensor • Feasibility of using multiple laser sensors to monitor wafer displacement • How much does support frame displace during worst case polishing • 60rpm–2.5psi–pure H20 (strong chatter) • Frame displacements are on the order of .1mm • Spectrum of displacement signal is very familiar • Safe to say that wafer motion won’t be lost in frame motion

  9. Friction Updates – Laser Sensor • Generate rough idea of wafer displacement • 60rpm-1.7psi-3:2 (minimal chatter) • range = +/- 1mm • Wafer regularly moving out of range • To be safe, we should require a range of at least +/- 2mm or even +/-5mm • Must design a system that allows for quick adjustment of sensor position • Given the accuracy of the laser (~1μ), is this a good way to measure fluid film thickness? • Sensor size is an important consideration

  10. Friction Updates – Thesis Roadmap • Develop a micro-friction model utilizing the expertise of the BostonCMP group • Identify the processes that contribute to CoF and/or MRR • Examples • CoF = μfluid+μpad+μparticles • Polishing is more a “plucking” (chemical) process, rather than a “plowing” (mechanical) process • Make changes on the microscale and measure their effect on the macroscale, for example • Vary roughness and moduli of pads • Various particle loads • Maintain constant particle loading, while varying the load of particles that participate in the polishing • Measure effect on both CoF and MRR • Which changes effect CoF or MRR only • Which effect both • Does this confirm our model or do we need to make adjustments? Microscale Changes and Their Effect on Macroscale Process Variables in Chemical Mechanical Planarization Submitted by James Vlahakis In Partial Fulfillment of the Requirements for a PhD. School of Engineering Tufts University May 2008

  11. Friction Updates - Questions/Requests Questions • How can we measure MRR? • Can we etch a radial channel in our wafers and measure the change in step heights? • Can we replace slurry silica particles with particles that do not participate in the chemistry? Requests • More slurry please! • Pads of various roughness and modulus

  12. Friction Updates – Future Work High Level View • Continue to develop models with Boston CMP group • Identify the experiments that will show the accuracy (or inaccuracy) of our models • Perform the experiments and, if necessary, iterate until our models can explain our data • Write it up! Low Level View • Complete CoF vs. slurry dilution experiments • Determine μ and shear thickening effects for various slurry dilutions • Purchase and begin installation of laser displacement package • Prepare for various conferences and papers

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