Vertical Pillars for Biological Force Vertical Pillars for Biological Force SensingSensing

Class update – July 6thClass update – July 6th

Sarah Coulthard, Nahid Harjee, Nathan Klejwa, Ronald Sarah Coulthard, Nahid Harjee, Nathan Klejwa, Ronald KwonKwon

Device OverviewDevice Overview

TrainingTraining

Completed:Completed: MERL clean shop: AllMERL clean shop: All wafersaw: Ronwafersaw: Ron amtetcher: Nahidamtetcher: Nahid wbgeneral: Nathanwbgeneral: Nathan

To be completed:To be completed: innotecinnotec Critical point dryerCritical point dryer

FabricationFabrication 1. Quartz wafers – Obtained from 1. Quartz wafers – Obtained from

stockroomstockroom Glass vs. Quartz substrateGlass vs. Quartz substrate

Quartz More flexible when working at wet Quartz More flexible when working at wet benchesbenches

Glass etches 5~10x fasterGlass etches 5~10x faster Adhesion of SU-8 in HF will be final determinantAdhesion of SU-8 in HF will be final determinant

Fabrication (Alignment Fabrication (Alignment Marks)Marks)

Adhesion of resist to quartzAdhesion of resist to quartz Shipley 3612 or 3617mShipley 3612 or 3617m Isotropic or anisotropic etchIsotropic or anisotropic etch

(HF bath or amtetcher)(HF bath or amtetcher) Visibility on a transparent substrateVisibility on a transparent substrate Etch ratesEtch rates ““Frosting” of quartz in PiranhaFrosting” of quartz in Piranha11 or HF or HF

1 K. R. Williams, et al., J. Microelectromech. Syst., vol. 12, no. 6, pp. 761-778, 2003.

2. Etch alignment marks2. Etch alignment marks

Fabrication (Alignment Fabrication (Alignment Marks)Marks)

Process: Piranha, YES, svgcoat, karlsuss, Process: Piranha, YES, svgcoat, karlsuss, svgdev, inspection, 6:1 BOE, Piranhasvgdev, inspection, 6:1 BOE, Piranha

First attempt with 3612: interference ringsFirst attempt with 3612: interference rings Issues with 3617m:Issues with 3617m:

Bubbles in the lineBubbles in the line Coat program changedCoat program changed

Two more attempts with 3612 for exposureTwo more attempts with 3612 for exposure 120 s in 6:1 BOE, measured with dektak120 s in 6:1 BOE, measured with dektak

Fabrication (Alignment Fabrication (Alignment Marks)Marks)

Adhesion not an issue after HMDS Adhesion not an issue after HMDS primeprime

Shipley 3612 is adequateShipley 3612 is adequate No frosting in Piranha or HFNo frosting in Piranha or HF 110 nm/min in 6:1 BOE, in line with 110 nm/min in 6:1 BOE, in line with

Williams (130 nm/min in 5:1 BOE)Williams (130 nm/min in 5:1 BOE) Alignment marks visible on karlsussAlignment marks visible on karlsuss

FabricationFabrication 3. Spin 5 3. Spin 5 μμm SU-8 (Waiting on SU-8 2005)m SU-8 (Waiting on SU-8 2005)

4. Expose cantilevers 4. Expose cantilevers (Waiting on SU-8 2005)(Waiting on SU-8 2005)

FabricationFabrication 5. Develop SU-85. Develop SU-8 6. Deposit Cr then Au6. Deposit Cr then Au

Need to have 1000 Need to have 1000 ÅÅ of of Au to connect bondwireAu to connect bondwire

FabricationFabrication 7. Etch back metal (Mask 3) 7. Etch back metal (Mask 3)

Cr and Au etchant available at wbgeneralCr and Au etchant available at wbgeneral Need to test resistance of SU-8 to etchantsNeed to test resistance of SU-8 to etchants

FabricationFabrication 8. Spin 300 8. Spin 300 μμm SU-8 2100m SU-8 2100

New hotplate installed in MERL CleanshopNew hotplate installed in MERL Cleanshop Hotplate has NOT been calibratedHotplate has NOT been calibrated Several tests of 300 Several tests of 300 μμm SU-8 conductedm SU-8 conducted

Difficult get an even coating without bubblesDifficult get an even coating without bubbles Skin forms on baking SU-8 and causes non-Skin forms on baking SU-8 and causes non-

uniformityuniformity May need to use 2 layers each 150 May need to use 2 layers each 150 μμm thick m thick

FabricationFabrication 9. Expose pillars and spacers (Waiting)9. Expose pillars and spacers (Waiting)

10. Spin 35 10. Spin 35 μμm SU-8 (Waiting on SU-8 2035)m SU-8 (Waiting on SU-8 2035)

FabricationFabrication 11. Expose top of spacers (Waiting)11. Expose top of spacers (Waiting)

12. Develop SU-8 (Waiting)12. Develop SU-8 (Waiting)

FabricationFabrication 13. Release cantilevers with wet HF13. Release cantilevers with wet HF

HF Vapor available only at wbmetalHF Vapor available only at wbmetal No metal that is resistant to HF is allowed at wbmetal (Cr, Au, No metal that is resistant to HF is allowed at wbmetal (Cr, Au,

etc)etc) SU-8 may peel off Quartz in high concentration HF SU-8 may peel off Quartz in high concentration HF

(49%)(49%) Instead, use a long etch (10-15 hours) in weak HF Instead, use a long etch (10-15 hours) in weak HF

(20:1 BOE)(20:1 BOE)

FabricationFabrication 14. Critical Point Dry wafers after HF 14. Critical Point Dry wafers after HF

etch to prevent stiction (Waiting on etch to prevent stiction (Waiting on training)training)

FabricationFabrication

15. Dice15. Dice Use wafer saw to dice on backside (to Use wafer saw to dice on backside (to

avoid water and stiction)avoid water and stiction) Use etched wafer saw lanes as “scores” Use etched wafer saw lanes as “scores”

to snap quartzto snap quartz Use etched wafer saw lanes as guides Use etched wafer saw lanes as guides

for diamond scribe for diamond scribe Laser ablation?Laser ablation?

Questions and SuggestionsQuestions and Suggestions