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

Outline 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 Summary and conclusions

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

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

Wafer- Pad Interaction Pad Asperities Wafer Pad Microns

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

Convex vs Concave Wafers Wafers used are typically ~ 5  m convex or concave Glass (BK-7) windows – 0.5 in thick, 3 in diameter wafer Polishing Pad wafer Polishing Pad Convex WaferConcave Wafer

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 WaferConcave Wafer  Speed ->  Slurry Thickness ->  Coeff. Of friction  Speed ->  Slurry Thickness ->  Coeff. Of friction

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

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 Pad slurry V pad Angle

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 interaction may be characterized by coeff. of friction and slurry thickness data Slurry film thickness is not independent of the polishing pad’s response to process parameters There is measurable pressure differences between different wafer shapes

Conclusions & Future Work Lubrication regime is a function of slurry film thickness and friction –Convexities =  hydrodynamic lift –Concavities =  asperity contact Slurry thickness and friction are correlated –based on future work, friction can be used as end point detector in the planarization process Examine changes in slurry thickness and friction of a polishing wafer as it changes shape Examine localized frictional effects - ‘hot spots’

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