1. Caprice Gray MRS Spring Meeting San Francisco, CA March 30, 2005
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. Polishing Setup
Motor
Platen
RotoPol-31
Wafer
Force Table
Steel Table

5. DELIF

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

7. Experiments Pads: flat Fruedenberg FX9 Static: flat glass wafer
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 Intel Corporation Cabot Microelectronics
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