In Situ Friction Measurements in Chemical Mechanical Planarization Jim Vlahakis PhD. Candidate Tufts University 20 February 2006 1
Jan 21, 2016
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
• Sources of Error• Final thoughts
Experimental Setup
• 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
Equipment
Motor – ½ hp Dayton
Wafer – transparent BK7
Table – 136kgs, steel
Platen – 12” diameter
Force table – AMTI
Polisher – Struers RotoPol31
Motor
Platen
RotoPol-31
Wafer
Force Table
Steel Table
Equipment - Issues
• 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 - Force Table
• Decomposes the loading into orthogonal components (forces and moments),
• Accuracy– 355 bits/lb in x and y– 710 bits/pound in z
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
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
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”
Data Analysis
• 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
Results & Discussion Coefficient of Friction
Ungrooved FX9 pad
Results & Discussion Coefficient of Friction
Circular grooved FX9 pad
Results & Discussion Coefficient of Friction
xy grooved IC1000 pad
Results & Discussion Coefficient of Friction
xy grooved IC1000 pad – low slurry flow rate
Results & Discussion Coefficient 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
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
Results & Discussion Frequency Analysis
Ungrooved FX9 pad
Results & Discussion Frequency Analysis
Circular grooved FX9 pad
Results & Discussion Frequency Analysis
xy grooved IC1000 pad
Results & Discussion Frequency Analysis
xy grooved IC1000 pad – low slurry flow rate
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?
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
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