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USP
UPENN
LSI
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
http://www.lsi.usp.br/~bariatto/ SBmicro 2000 - Manaus - Amazonas 2
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 3
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 4
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 5
INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
MICROMACHINING TECHNIQUES
• Boron etch stop
• Plasma etching
• Deep boron diffusion– high temperature and time
• Lateral diffusion – “large”dimensions
• Strong crystal orientation dependence
• Low temperature process
• Better shape definition and thickness control
– without lateral diffusion • Quick process• Low silicon crystalline orientation
dependence
http://www.lsi.usp.br/~bariatto/ SBmicro 2000 - Manaus - Amazonas 6
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 7
INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
FABRICATION STEPS• Boron etch stop
• Plasma etching
mask 1 probe shape
mask 2 lines / contacts
mask 3 windows
mask 1mask 1mask 2mask 3mask 1
http://www.lsi.usp.br/~bariatto/ SBmicro 2000 - Manaus - Amazonas 8
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/ SBmicro 2000 - Manaus - Amazonas 9
INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
FABRICATION RESULTS - Si PROBES
• Etch stop
• Plasma etching
SIMS analyses[B]=1.25 1020 at./cm3
http://www.lsi.usp.br/~bariatto/ SBmicro 2000 - Manaus - Amazonas 10
INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
FABRICATION RESULTS - COMPLETE SEQUENCE
• Uncompensated mechanical stress– coverage and lines damaged
http://www.lsi.usp.br/~bariatto/ SBmicro 2000 - Manaus - Amazonas 11
INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
FABRICATION RESULTS - FINAL DEVICE
http://www.lsi.usp.br/~bariatto/ SBmicro 2000 - Manaus - Amazonas 12
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 13
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 14
INTEGRATED MICROSYSTEMS GROUP - DMI - LSI - USP
ACKNOWLEDGMENTS
• CNPq
• FAPESP
• CNPq/PADCT/CDCT
• Center for Sensor Technology at UPENN
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