In-Situ Measurements for Chemical Mechanical Polishing

1. In-Situ Measurements for Chemical Mechanical Polishing James Vlahakis Caprice Gray CMP-MIC February 20, 2006

2. Outline • Slurry layer imaging using Dual Emission Laser Induced Fluorescence (DELIF) • Why DELIF works • How to take data • Ways to interpret data • In-Situ Force measurements • Experimental Equipment/Setup • Coefficient of Friction • Downforce frequency analysis

3. In Situ Slurry Layer Image Acquisition in Chemical Mechanical Planarization Caprice Gray PhD. Candidate Tufts University 20 February 2006 3

4. Dual Emission Laser Induced Fluorescence (DELIF) • Types of Measurements • Dye choice • pH, temperature, fluid layer thickness • How to make DELIF measurements • time averaged (no laser) • 2 Dye System • 1 Dye System • DELIF Images and Analysis • Qualitative examination of data • Calibration procedure for quantitative • Types of quantitative measurements

5. Is a DELIF system hard to set up? • YES

6. Types of Measurements Time averaged 1” 1 cm Low Resolution Instantaneous 1mm High Resolution Instantaneous

7. Pad Ratio = Slurry Division of 2 images cancels variations in image source intensity Why Examine 2 Emissions?

8. DELIF Light Paths Laser Mirror Laser Shot Camera Mirror Camera 1 Fluorescent Light Camera 2 Optics Box BK7 Optical Glass Wafer

9. Calcein Camera Pad Camera Optics Box

10. DELIF Spectral Analysis (1 dye)

11. Spectral Filter Regions

12. Variables I1f, I2f = Fluorophore fluorescent intensity IL = laser intensity Icam = light collected by camera F = quantum efficiency A = absorption l = wavelength z = passive scalar a, b, C, D = constants How DELIF works

13. Sources of Error • Measurements are independent of viewing geometry • Short wavelength absorber/emitter: • Independent of the passive scalar (type 3 conflict*) • Does not absorb its own emission • Does not absorb the long wavelength absorber’s emission • Long wavelength absorber/emitter: • Does not absorb its own emission • Does not absorb Laser emission • Absorption must be a linear function of z (true for thin films) • Choose a short wavelength filter band outside the absorption region of the long wavelength absorber/emitter (type 2 conflict*) • Choose filter bands where emissions do not overlap (type 1 conflict*) *Spectral conflict types as identified by Coppeta and Rogers Experiments in Fluids, 25 (1998) 1-15.

14. Choosing Dyes References: J. Copetta, C. Rogers. Experiments in Fluids, 25 (1998) 1-15. C. Hidrovo, D. Hart. Measurement Science and Technology, 12 (2001) 467-477 J. Lu, et. al. Journal of The Electrochemical Society, 151 (4) (2004)

15. UV Lamp Light Dye 2 Dye 1 z Slurry Layer Pad Time Averaged DELIF • NO LASER, uses UV lamp • Mostly qualitative – global slurry behavior • Quantitative- average fluid layer thickness, average pH, or average temperature • Must suppress the natural fluorescence of the pad with carbon black • Need 2 dyes

16. Laser Shot 355 nm Dye 1 Dye 2 z Slurry Layer Pad 2 Dye System • Laser allows instantaneous measurements • Need laser beam expander for low resolution images • Must suppress the natural fluorescence of the pad with carbon black

17. Laser Shot 355 nm Dye Particle z Slurry Layer Pad 1 Dye System • Laser allows instantaneous measurements • Must use pads with natural fluorescence and spectra that fit the model • Polyurethane based pads work well • Surface coatings are not good enough • Depending on laser power, may need beam expander to prevent pad burning

18. 1mm = 232 pixels Calibration Methods X-Y Calibration Capture image of millimeter ruler and measure pixels/mm • 1-Dye Calibration • Flat wafer shimmed by microscope slide • Need very flat pad • Must image near wafer edge (difficult) 2-Dye Calibration Inject dyed slurry between 2 microscope slide shimmed on 1 side

19. Most Recent Calibration Method • Etch wells into glass wafer to different depths • Depth must be greater than pad surface roughness • Relative calibration • Need wafers with 2 different well depths • Can acquire pixel to pixel slurry depth differences • Absolute calibration • Need wafers with at least 3 different well depths • Know slurry thickness under every pixel

20. Pad Images (Low Ra Flat) (a) Flat wafer (b) 14 um deep 1mm2 square well We can see striations in the pad due to the motion of the conditioner. Striations direction is along the dotted line. Slurry flow direction is indicated by arrows http://www.tuftl.tufts.edu/CMPWebsite2/Public/PictureGallery/pics.htm

21. Air Pockets Low Resolution High Resolution Air pockets get trapped in features Grooves help to transport air pockets under the wafer features

22. 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: e

23. Histogram Data Red line = 10psi, White Line = 0psi Histograms of 2mm2 regions at different points on the pad.

24. Pad Shape Near Wafer Features

25. DELIF Summary • How and why DELIF works • Must be very careful in choosing dyes/fluorophores and filter regions • Different ways to employ DELIF • Calibration methods • Types of image analysis • Qualitative: slurry starvation, air travel under the wafer • Quantitative: Pad compression using sub-region histograms, Pad shape near wafer features

26. Fruedenberg FX9 K-grooved Rodel IC1000 K-grooved Fruedenberg FX9 Pad Images (Low Ra Grooved) http://www.tuftl.tufts.edu/CMPWebsite2/Public/PictureGallery/pics.htm

27. Thin-grooved Experimental Pad xy-grooved experimental Pad Flat Experimental Pad Pad Images (High Ra) http://www.tuftl.tufts.edu/CMPWebsite2/Public/PictureGallery/pics.htm

28. Polishing Setups New Setup Old Setup