pad characterization update caprice gray nov. 9, 2006 cabot microelectronics aurora, il
TRANSCRIPT
Outline
• Review where we were last time• Non-DELIF imaging• DELIF Contact detection feasibility and
preliminary results• Thesis Outline• DELIF Modeling• Experimental Outline• Questions/Issue that should be resolved before
proceeding forward
Last Meeting Accomplishments
• Set up beam splitter aligner
• Replace poor quality optical filters with high quality filters
• Determined the source of ratio drift by modeling intensity sources for each camera
Source of Ratio Drift
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Calibration for all previous data sets that show ratio drift.
All Components the cameras actually measure
Primary Source of ratio drift
Experimentally Determined Constants
New Ratio Calculation
Determined by drift
Imaging Benchmarks: SEM
• Imaged in 3 regions of a used pad
1. Edge of wafer track (most glazed region)
2. Outside Wafer track (no glazing)
3. Center of wafer track (less glazing)
Imaging Benchmarks: SEM
Outside of wafer track
Edge of wafer track
Center of wafer track
In a grooveCenter of wafer track
Imaging Benchmarks: Confocal Microscopy
Similar to DELIF Resolution(scale bar = 160 m)
Zoomed image of a pore, a cross section near the pad surface
(scale bar = 40 m)
Imaging Benchmarks: Confocal Microscopy
• 24 images are taken every 2 mm
• Video start at the deepest layer and progresses to the surface
Rohm and Haas Pad-Wafer Contact Study
• Confocal Reflectance Interference Contrast Microscopy
• Images are taken through sapphire.– No slurry– Static
• Imaging region < 1 mm2
– Asperity Contact ~ 50 m2
• Pads studied:– IC1000– VP3000– Politex– Experimental
• Tested 0-6 psi, contact 0-6%, experimental contact ~ 20%
DELIF for Contact
• 360,000+ pixels 2% ~ 7200 pixels • 50 m2 ~ 7-8 pixels (6.7 m2/pixel)
– Focus must be really good– We are at the resolution limit for our system
• At this resolution, we are seeing contact region intensity smoothing
Data for static DELIF on CMC D100
CMC D100 Imaging Issues
• Experiment: 50 consecutive static images
• Image drift correction was nearly 100% of signal
• Focus is difficult because Ra>DOF– Must carefully focus at
tops of pixels– Out of focus light bleeds
into pixels that are in focus
Thesis Outline
• Introduction– Why are we looking for pad-wafer contact in CMP– Literature review of experimental pad-wafer contact
measurements– Project Goal = detect in-situ pad-wafer contact
• Methods– What is DELIF, and why use it– System model and calibration techniques– Hardware description– System limitations– Image Acquisition and Processing
In-Situ Detection of Pad/Wafer Contact with DELIF during CMP
Thesis Outline
• Experimental Outline– Description of variables and responses– Post acquisition image interpretation (histogram analysis, etc.)
• Results and Discussion– Comparison on contact on hard vs. soft pads– Static measurements vs. dynamic measurements– Pressure variation effect on contact %– Relate results to previously studied pad-wafer contact
measurements• Conclusions
– Summary of Experimental results– Contribution of results to current understanding of CMP– Could this technique be expanded to study multiple polishing
pad types?
DELIF Modeling
• Goals– Examine how comparable
our actual system is to current DELIF models
– Verify our linear calibration technique (Ratio Intensity Fluid layer thickness)
• Results– slurry particles quadratic
calibration– As slurry particle
concentration 0, calibration linear
Old Model
Current System
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Experimental Outline
• Finish Tweaking Optics to get repeatable static data
• Identify 2 types of polishing pads that will work optically with our system.– Similar Ra ~ 4-6 m– High and Low bulk modulus
• Proceed to DOE– Possible Variables: pressure, pad/wafer velocity, pad
type, slurry dilution, pH– Responses: Contact area %, Contact area size,
friction signature?
Open Questions
• Which 2 pads should I focus my study on and will I have a steady supply of them?
• Does slurry dilution matter?– Accurate depth measurements or minimize chatter?
• Should I continue to search for a static contact measurement benchmarking technique, or just use (the limited) data from literature?
• Which experimental variables should I concentrate on?– My variable preferences: pad modulus, pad-wafer
speed, down-force