1. 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

2. 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

3. 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

4. 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

5. 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

7. 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/min  9:1 dilution  0.5 g/L Calcein

8. 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

9. 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

10. 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

11. Pad Topology

12. 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.

13. Future Work Investigate much larger region, to view multiple contact points in one image  Ability 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?

14. The End Acknowledgements  Intel  Cabot Microelectronics  University of Arizona Questions?