Quantitative In-Situ Measurement of Asperity Compression Under

the Wafer During PolishingCaprice Gray

MRS Spring MeetingSan Francisco, CA

March 30, 2005

Overview

• Introduction• Experimental Setup

– Polisher– Dual Emission Laser Induced Fluorescence

• Pad Compression Experiments and Results– Static Compression– Dynamic Compression

• Conclusion

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 m/pixel

• In these experiments we use fluid thickness measurements to infer what is happening to pad asperities during polishing

Polishing Setup

Motor

Platen

RotoPol-31

Wafer

Force Table

Steel Table

DELIF

0

0.2

0.4

0.6

0.8

1

300 400 500 600

Wavelength (nm)

Inte

nsi

ty (

au)

Camera B Filter

Camera A Filter

Pad Em.392 nm

Calcein Abs492 nm

Calcein Em.530 nm

Pad Abs. 346nm

Laser Em.355 nm

Slurry Abs.

Slurry Em.

Why Examine 2 Emissions?

Pad

Slurry

=

Ratio

Division of 2 images cancels variationsin image source intensity

Experiments

• Pads: flat Fruedenberg FX9– Global vs. Local topography

• Static: flat glass wafer• Dynamic: etched glass wafer

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.

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: 0

0

Static Compression Results

= 133.9 - 22.2R2 = 0.7

0

10

20

30

40

50

60

0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Compression Factor

(S

lurr

y T

hic

knes

s) (

um

)

Dynamic Pad Compression

• Two wafers were etched and contain square wells– 14.5 m deep– 27 m 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

Dynamic Results

(7m)

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 m deep wells was greater than expansion into 14.5 m deep wells.

Acknowledgements

• Tufts– 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