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Vertical Pillars for Biological Force Sensing

Vertical Pillars for Biological Force Sensing. Sarah Coulthard, Nahid Harjee, Nathan Klejwa, Ronald Kwon. Class update – July 6th. Device Overview. Training. Completed: MERL clean shop: All wafersaw: Ron amtetcher: Nahid wbgeneral: Nathan To be completed: innotec Critical point dryer.

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Vertical Pillars for Biological Force Sensing

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  1. Vertical Pillars for Biological Force Sensing Sarah Coulthard, Nahid Harjee, Nathan Klejwa, Ronald Kwon Class update – July 6th

  2. Device Overview

  3. Training • Completed: • MERL clean shop: All • wafersaw: Ron • amtetcher: Nahid • wbgeneral: Nathan • To be completed: • innotec • Critical point dryer

  4. Fabrication • 1. Quartz wafers – Obtained from stockroom • Glass vs. Quartz substrate • Quartz More flexible when working at wet benches • Glass etches 5~10x faster • Adhesion of SU-8 in HF will be final determinant

  5. Fabrication (Alignment Marks) • 2. Etch alignment marks • Adhesion of resist to quartz • Shipley 3612 or 3617m • Isotropic or anisotropic etch(HF bath or amtetcher) • Visibility on a transparent substrate • Etch rates • “Frosting” of quartz in Piranha1 or HF 1 K. R. Williams, et al., J. Microelectromech. Syst., vol. 12, no. 6, pp. 761-778, 2003.

  6. Fabrication (Alignment Marks) • Process: Piranha, YES, svgcoat, karlsuss, svgdev, inspection, 6:1 BOE, Piranha • First attempt with 3612: interference rings • Issues with 3617m: • Bubbles in the line • Coat program changed • Two more attempts with 3612 for exposure • 120 s in 6:1 BOE, measured with dektak

  7. Fabrication (Alignment Marks) • Adhesion not an issue after HMDS prime • Shipley 3612 is adequate • No frosting in Piranha or HF • 110 nm/min in 6:1 BOE, in line with Williams (130 nm/min in 5:1 BOE) • Alignment marks visible on karlsuss

  8. Fabrication • 3. Spin 5 μm SU-8 (Waiting on SU-8 2005) • 4. Expose cantilevers (Waiting on SU-8 2005)

  9. Fabrication • 6. Deposit Cr then Au • 5. Develop SU-8 • Need to have 1000 Å of Au to connect bondwire

  10. Fabrication • 7. Etch back metal (Mask 3) • Cr and Au etchant available at wbgeneral • Need to test resistance of SU-8 to etchants

  11. Fabrication • 8. Spin 300 μm SU-8 2100 • New hotplate installed in MERL Cleanshop • Hotplate has NOT been calibrated • Several tests of 300 μm SU-8 conducted • Difficult get an even coating without bubbles • Skin forms on baking SU-8 and causes non-uniformity • May need to use 2 layers each 150 μm thick

  12. Fabrication • 9. Expose pillars and spacers (Waiting) • 10. Spin 35 μm SU-8 (Waiting on SU-8 2035)

  13. Fabrication • 11. Expose top of spacers (Waiting) • 12. Develop SU-8 (Waiting)

  14. Fabrication • 13. Release cantilevers with wet HF • HF Vapor available only at wbmetal • No metal that is resistant to HF is allowed at wbmetal (Cr, Au, etc) • SU-8 may peel off Quartz in high concentration HF (49%) • Instead, use a long etch (10-15 hours) in weak HF (20:1 BOE)

  15. Fabrication • 14. Critical Point Dry wafers after HF etch to prevent stiction (Waiting on training)

  16. Fabrication • 15. Dice • Use wafer saw to dice on backside (to avoid water and stiction) • Use etched wafer saw lanes as “scores” to snap quartz • Use etched wafer saw lanes as guides for diamond scribe • Laser ablation?

  17. Questions and Suggestions

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