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Effects of Pad Properties on Cu Dishing During CMP

Effects of Pad Properties on Cu Dishing During CMP. Caprice Gray PhD Student, Mechanical Engineering Tufts University, Medford, MA Intel Intern Presentation 8/18/05. Overview. Goal: Investigate Cu line dishing during CMP using polishing pads with varying properties

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Effects of Pad Properties on Cu Dishing During CMP

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  1. Effects of Pad Properties on Cu Dishing During CMP Caprice Gray PhD Student, Mechanical Engineering Tufts University, Medford, MA Intel Intern Presentation 8/18/05

  2. Overview • Goal: Investigate Cu line dishing during CMP using polishing pads with varying properties • Motivation: How do pad properties affect dishing as design rules shrink? • Topics Covered: • Automated dishing analysis for higher data throughput • Evaluated 9 different pad • Pad Properties Evaluated • Fiber size • Pad hardness • Hydrophobicity (Surface Tension) • Fibrous vs. Porous

  3. Cu Silicon Experimental Overview Cu FW Ta ILD up region

  4. Felt Nylon Polishing Pads Fibrous Porous Polyurethane impregnated Polyester felt Soft Silk Mohair Microfiber Soft Hard Polyurea/ Polyurethane Nanocomposit Tangled Polyester Microporous polyurethane Elastomer/ WSP Alloy

  5. Profile features and save data Data Evaluation attain average dishing Polish Wafers (vary polish time) Change Pads Analysis Process Data Modeling and effect screening

  6. 0 Erosion Dishing Automated Data Evaluation Isolate region of interest and apply data smoothing filter Import Raw Data Isolate feature width region Isolate features and calculate dishing Calculate average dishing and Erosion for each feature width

  7. Dishing Rate Results

  8. Dishing is Predictable Hardness Fiber/Pore Size Hydrophobicity Asperity Geometry Grooving Compressibility Density Material “Pad” is a convolution of many material properties Dishing Rate is a function of: Feature Width Feature Density Pad

  9. Evaluation of Variables Feature Width < 2um Feature Width > 2um 70% No Effect No Effect Feature Density 20% No Effect 70 Pad Hardness (Shore D) 20 20 Pores Fiber/Pore Size (um) Fibers 0 100 Contact Angle* (Hydrophobicity) *Soft Fibrous Pads Only 0 0 0 800 800 Dishing Rate (A/min) Dishing Rate (A/min)

  10. Summary and Conclusions • A LabView interface was developed to automate data analysis • Summary of design rule affects on Dishing Rates (DR) • Feature Width↓ DR↓ • Large Features  Large DR variation pad to pad • Small Features  Small DR variation pad to pad • Feature Density has minimal affect on DR • Summary of pad property affects on DR • Hardness↓  DR↑ for large features • Fiber size↑  DR↓ more so for large features • Hydrophobicity↑  DR↓ for porous pads, for large features • Hydrophobicity↑  DR↑ for fiberous pads, more so for large features • Recommendations • Large Features (FW > 2 um): Allied, JSR • Small Features (FW < 2 um): Allied, SUBA IV, TWI 711, (Polytex) • All Feature Scales (0.32um – 20 um): Allied, TWI 711, SUBA IV • Future Work • Determine the relationship between other pad properties and dishing • Examine erosion data • Is there different selectivity on the pads? (Cu vs. Ta vs. Oxide polish rates)

  11. Bonus Features

  12. Dishing Rate Normalized to Bulk Rate Oxide Polishing Pad

  13. Dishing Rate and Feature Density

  14. Effect of Feature Density by Pad

  15. Dishing Rate and Pad Hardness

  16. Normalized Dishing Rate with Pad Hardness

  17. Dishing Rate and Fiber Size

  18. Dishing Rate and Contact Angle Brushlon and TWI 711 behave completely differently Brushlon- fiberous, high dishing rate, contact angle = 0 TWI 711 – intermediate dishing rate (between allied and SUBA,90+ contact angle Porous Soft Fiberous

  19. Microfiber – 1 min Contact Angle Images WSP Elastomer Microfiber-initial Tangled Polyester Nanocomposit Soaks in near different grove-drop locations. Otherwise, no soak. Soaks in Does not soak in Soaks in Porous Felt Polyurethane Fibrous Felt Soaks in quickly Soaks in quickly Soaks in

  20. Processing Interface

  21. Evaluating Erosion Data • Long Scans Length  Scan Leveling Drift  Inaccurate Erosion Data • Can examine erosion amplitude • See planarity in time across entire structure • Lose information about feature width effects • Must Evaluate shorter scans for accurate erosion data

  22. Erosion Amplitudes

  23. Erosion v Dishing TWI 711 SUBA IV

  24. Can optically identify the presence on Ta inside Cu lines, but not outside the lines Overpolished Wafer Erosion Through Material Layers Ta no Cu Unpolished No Ta or Cu

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