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

Device Overview

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

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

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

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

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

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

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

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

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

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

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

Fabrication 13. Release cantilevers with wet HF 13. Release cantilevers with wet HF HF Vapor available only at wbmetal HF Vapor available only at wbmetal No metal that is resistant to HF is allowed at wbmetal (Cr, Au, etc) 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%) 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) Instead, use a long etch (10-15 hours) in weak HF (20:1 BOE)

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

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

Questions and Suggestions