The Effect of Wafer Shape in Chemical Mechanical

Planarization

Researcher: Joseph LuPrincipal Investigator: Chris Rogers

Corporate Sponsors: Cabot CorporationIntel CorporationFreudenberg 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 RPMStruers RotoPol-31

Drill Press

Weighted Traverse

Two Aligned 12 BitCamera

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

10- 20 Microns

Friction Measurements

Coeff. of Friction =Friction Force

Downforce

(Fdrag )

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 Wafer Concave 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 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

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

slurryVpad

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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