Instantaneous Fluid Film Imaging in Chemical Mechanical Planarization

Daniel Apone, Caprice Gray, Chris Rogers, Vincent P. Manno, Chris Barns, Mansour Moinpour, Sriram Anjur, Ara Philipossian

Motivation

Microelectronic devices continue to decrease in size; current features are routinely smaller than 100nm

The semiconductor industry requires a deeper understanding of the physical processes involved in CMP to help attain smoother surfaces

Using Dual Emission Laser Induced Fluorescence (DELIF) we can measure instantaneous fluid film thicknesses (and temperatures) during a polishing run

Here we look at how the pad conforms to features on a wafer

Polishing Setup

Struers RotoPol-31 table top polisher

Polisher sits atop a force transducer table capable of measuring down and shear forces during a polish

Optical Setup

Evolution VF 12 bit digital cameras Region of Interrogation:

3 cm across on pad Second ROI: 3mm on

pad

355 nm Nd-YAG Laser provides excitation light Laser Pulse Length: 6ns

Dual Emission Laser Induced Fluorescence

Calcein in slurry solution UV light excites Pad’s natural fluorescence Pad’s emission excites Calcein Each emission is captured by a camera Taking the ratio of the two emissions normalizes

the image by initial excitation intensity

0

0.2

0.4

0.6

0.8

1

300 400 500 600

Wavelength (nm)

Inte

ns

ity

(au

)

Calcein Fluorescence Calcein Absorbance Laser Emission Pad Fluorescence

Pad Absorbance Slurry Absorbance Slurry Fluorescence

Camera B FilterCamera A Filter

392 492 530346

355

Experimental Parameters Freudenberg FX9 Pad Wafer & Platen Rotation: 30 rpm

Relative Velocity: 0.34 m/s Downforce: 1.8 PSI Slurry

Flow Rate: 50 cc/min9:1 dilution0.5 g/L Calcein

Results Images are 3 cm

viewing area on pad

Air bubbles contained in a wave of slurry

Striations made by conditioner

Small circles are shadows of dried slurry on top of wafer

Previous Work

Film thickness increases as pad speed increases

Inverse relationship for downforce and thickness

Film thickness are measured from the wafer surface down to some mean height within the pad

Searching for Contact…. Images are 3 mm

viewing area on pad; can see individual asperities

Dark areas have less fluid, indicate peaks

Bright areas are holes in pad, more fluid there

10psi static image, to make sure contact was occurring

Contact points seem to be few and far between

Pad Topology

Conclusion

Pad topology seems to be the governing factor as to whether or not Pad/Wafer contact is occurring.

Wafer seems to be supported by only a few peaks at any given time, the vast majority of asperities do not reach up to the wafer.

Future Work

Investigate much larger region, to view multiple contact points in one imageAbility to resolve individual asperities is

necessary to determine if contact is occurring Correlate applied pressure with amount of

contact? Correlate amount of contact with changes

in friction data?

The End

Acknowledgements IntelCabot MicroelectronicsUniversity of Arizona

Questions?