1. Principal Investigator: Chris Rogers
The Effect of Wafer Shape on Lubrication Regimes in Chemical Mechanical Planarization
Researcher: Joseph Lu
Principal Investigator: Chris Rogers
Corporate Sponsors:
Cabot Corporation
Intel Corporation
Freudenberg Nonwovens
VEECO Insturments

2. Outline Advantages of chemical mechanical planarization
Laboratory scale CMP setup
Slurry film thickness measurement technique
Friction measurement technique
Define wafer shapes
Effects of wafer curvature on slurry film thickness and coefficient of friction
Effects of wafer curvature on fluid pressure distribution
Summary and conclusions

3. Rotary CMP Polisher

4. Polishing Platform Drill Press Weighted Traverse Two Aligned 12 Bit
100 RPM
Struers
RotoPol-31
Drill Press
Weighted Traverse
Two Aligned 12 Bit
Camera
Three Way Solenoid Valve
Tagged Slurry
Slurry

5. DELIF Technique Measurement Ratio Calibration of passive scalar Color
Separation
Detection
Calibration
Ratio
Measurement
of passive scalar
Ratio
Calibration

6. Wafer- Pad Interaction
Pad Asperities
Wafer
Microns
Pad

7. Friction Measurements
Friction Force (F )
drag
Coeff. of Friction =
Downforce

8. Convex vs Concave Wafers
Polishing Pad
Polishing Pad
Convex Wafer
Concave Wafer
Wafers used are typically ~ 5 mm convex or concave
Glass (BK-7) windows
0.5 in thick, 3 in diameter

9. Slurry Thickness vs. Pad Speed
Increasing pad speed = Increasing slurry thickness
Repeatable and consistent data
Convex Wafer

10. Coefficient of Friction vs. Pad Speed
Increasing pad speed = Decreasing friction
Repeatable and consistent data
Convex Wafer

11. Wafer Shape & Pad Speed Effects
Convex Wafer
Concave Wafer
 Speed ->  Slurry Thickness
->  Coeff. Of friction
 Speed ->  Slurry Thickness
->  Coeff. Of friction

12. Wafer Shape & Downforce Effects
Convex Wafer
Concave Wafer
 Downforce ->  Slurry Thickness
->  Coeff. of Friction
 Downforce ->  Slurry Thickness
-> -- Coeff. of Friction

13. Coefficient of Friction Coefficient of Friction
Lubrication Regimes
Boundary Lubrication
1.0
Mixed Lubrication
0.1
Turbulence
Coefficient of Friction
Coefficient of Friction
0.01
0.001
Full Fluid Film
Lubrication
0.0001 1 10
100
1,000
100,000
ZN/P
ZN/P
Z= Viscosity (poise) N= Speed (RPM) P= Pressure (Psi)

14. Pressure Measurements
- Locations of 7
pressure taps on
wafer

15. Non-Rotating Wafer Convex Concave
Fluid
Inlet
Fluid
Inlet
High Pressure
Low Pressure
-60 RPM platen speed Psi Downforce

16. Rotating Wafer Convex Concave -60 RPM platen speed -3 Psi Downforce
Pressure (Psig)
Pressure (Psig)
% Wafer Radius
% Wafer Radius
-60 RPM platen speed
-3 Psi Downforce

17. Summary
Clear difference in slurry film thickness and coeff. of friction trends between convex and concave wafers
Convex wafers seem to be able to support a thicker slurry layer than a concave wafer
Pad - wafer lubrication regime may be characterized by the coeff. of friction and slurry thickness data
Slurry film thickness is not independent of the polishing pad’s response to process parameters
There are significant pressure differences between different wafer shapes

18. Conclusions & Future Work
Lubrication regime = f (slurry film thickness, friction, fluid pressure)
Convexities = +pressure =  hydrodynamic lift
Concavities = suction =  asperity contact
Slurry thickness, friction, and fluid pressure are correlated
The understanding of the relationship of these parameters can improve the control of the planarization process
Examine changes in slurry thickness and friction of a polishing wafer as it changes shape
Examine localized feature scale effects - ‘hot spots’

19. Acknowledgements Cabot Corporation Intel Corporation Tufts University
Frank Kaufman
Intel Corporation
Mansour Moinpour, Ara Philipossian
Tufts University
Chris Rogers, Vincent Manno, Alicia Scarfo

20. Visit our web site at

21. Wafer Angle of Attack
Convex wafer AOA much greater than Concave wafer AOA
Very small AOA for concave wafer
Measurement error ~0.003
 AOA may support thicker fluid film
Angle
slurry
Vpad
Pad