Fabrication of Silicon Probes for Biosensors

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Fabrication of Silicon Probes for Biosensors

• Dr. Marcelo Bariatto A. Fontes (Post-Doc) LSI /
  USP
• Dr. Rogério Furlan
  LSI / USP
• Dr. Jorge J. Santiago-Avilés UPENN

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MOTIVATION

• Biological applications
• neural activities
• intracellular recording
• ionic distribution
• electrical stimulation

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MICROPROBE FABRICATION

• Glass micropipette

• Carbon

• Metal

• Single electrode
• Low reproducibility

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SILICON MICROMACHINED PROBES

• Easy shape definition by computer-designed
  photomask
• Multidetection and spatial distribution
• High reproducibility
• IC compatible (smart sensors)
• Batch fabrication and
• Low cost

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MICROMACHINING TECHNIQUES

• Deep boron diffusion
• high temperature and time
• Lateral diffusion
• largedimensions
• Strong crystal orientation dependence

• Boron etch stop

• Plasma etching

• Low temperature process
• Better shape definition and thickness control
• without lateral diffusion
• Quick process
• Low silicon crystalline orientation dependence

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PROBE DESIGN

• Needle shape general purpose electrochemical
  system
• Multipoint and multispecies detection
• 2 to10 gold µelectrodes
• 90 to 340 µm tip
• Ag/AgCl reference
• Platinum auxiliary

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FABRICATION STEPS

• Boron etch stop

mask 1
mask 3
mask 1
mask 1
mask 2

• Plasma etching

mask 1 ? probe shape mask 2 ? lines /
contacts mask 3 ? windows
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FABRICATION RESULTS - SEM and AFM

• High reproducibility
• Roughness 12.5 nm (rms)
• 16 ? area

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FABRICATION RESULTS - Si PROBES

• Etch stop

SIMS analyses B1.25 1020 at./cm3

• Plasma etching

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FABRICATION RESULTS - COMPLETE SEQUENCE

• Uncompensated mechanical stress
• coverage and lines damaged

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FABRICATION RESULTS - FINAL DEVICE
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CONCLUSION

• High reproducible micromachined multidetection
  silicon probe (80)
• Several probe designs were explored by varying
  the number of the detection electrodes
• Plasma etching technique presented better
  characteristics of shape definition and
  processing time than etch stop
• Boron etch stop ? 2.4x1019 at./cm3 (SIMS)

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CONCLUSION - cont.

• Plain silicon probes of 15 µm were obtained
• Uncompensated mechanical stress between SiO2 and
  Si3N4
• Bent structures ? decrease the processing yield
• Increase of probe thickness by plasma etching ?
  45 µm
• Compatibility with silicon microelectronic
  technology
• New materials for interconnection and coverage
  (Poly-Si / Polymers)

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ACKNOWLEDGMENTS

• CNPq
• FAPESP
• CNPq/PADCT/CDCT
• Center for Sensor Technology at UPENN