USP
Fabrication of Silicon Probes
for Biosensors
LSI
Dr. Marcelo Bariatto A. Fontes (Post-Doc) LSI / USP
Dr. Rogério Furlan
LSI / USP
Dr. Jorge J. Santiago-Avilés
UPENN
UPENN
INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
MOTIVATION
• Biological applications
– neural activities
– intracellular recording
– ionic distribution
– electrical stimulation
http://www.lsi.usp.br/~bariatto/
SBmicro 2000 - Manaus - Amazonas
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
MICROPROBE FABRICATION
• Glass micropipette
• Carbon
• Metal
– Single electrode
– Low reproducibility
http://www.lsi.usp.br/~bariatto/
SBmicro 2000 - Manaus - Amazonas
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
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
http://www.lsi.usp.br/~bariatto/
SBmicro 2000 - Manaus - Amazonas
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
MICROMACHINING TECHNIQUES
• Boron etch stop
• Deep boron diffusion
– high temperature and time
• Lateral diffusion
– “large”dimensions
• Strong crystal orientation
dependence
• Plasma etching
http://www.lsi.usp.br/~bariatto/
• Low temperature process
• Better shape definition and
thickness control
– without lateral diffusion
• Quick process
• Low silicon crystalline orientation
dependence
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
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
http://www.lsi.usp.br/~bariatto/
SBmicro 2000 - Manaus - Amazonas
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
FABRICATION STEPS
• Boron etch stop
mask 123
• Plasma etching
mask 1  probe shape
mask 2  lines / contacts
mask 3  windows
http://www.lsi.usp.br/~bariatto/
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
FABRICATION RESULTS - SEM and AFM
• High reproducibility
• Roughness :12.5 nm (rms)
– 16 %  area
http://www.lsi.usp.br/~bariatto/
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
FABRICATION RESULTS - Si PROBES
• Etch stop
SIMS analyses
[B]=1.25 1020 at./cm3
• Plasma etching
http://www.lsi.usp.br/~bariatto/
SBmicro 2000 - Manaus - Amazonas
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
FABRICATION RESULTS - COMPLETE SEQUENCE
• Uncompensated mechanical stress
– coverage and lines damaged
http://www.lsi.usp.br/~bariatto/
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
FABRICATION RESULTS - FINAL DEVICE
http://www.lsi.usp.br/~bariatto/
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
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)
http://www.lsi.usp.br/~bariatto/
SBmicro 2000 - Manaus - Amazonas
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
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)
http://www.lsi.usp.br/~bariatto/
SBmicro 2000 - Manaus - Amazonas
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INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
ACKNOWLEDGMENTS
• CNPq
• FAPESP
• CNPq/PADCT/CDCT
• Center for Sensor Technology at UPENN
http://www.lsi.usp.br/~bariatto/
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