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

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

Rotary CMP Polisher

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

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

Wafer- Pad Interaction Pad Asperities Wafer 10- 20 Microns Pad

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

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

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

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

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

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

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)

Pressure Measurements - Locations of 7 pressure taps on wafer

Non-Rotating Wafer Convex Concave Fluid Inlet Fluid Inlet High Pressure Low Pressure -60 RPM platen speed -3 Psi Downforce

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

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

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’

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

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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