usp upenn lsi fabrication of silicon probes for biosensors dr. marcelo bariatto a. fontes (post-doc)...

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



MICROPROBE FABRICATION

• Glass micropipette

• Carbon

• Metal

– Single electrode– Low reproducibility



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



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



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



FABRICATION STEPS• Boron etch stop

• Plasma etching

mask 1 probe shape

mask 2 lines / contacts

mask 3 windows

mask 1mask 1mask 2mask 3mask 1



FABRICATION RESULTS - SEM and AFM

• High reproducibility

• Roughness :12.5 nm (rms)– 16 % area



FABRICATION RESULTS - Si PROBES

• Etch stop

• Plasma etching

SIMS analyses[B]=1.25 1020 at./cm3



FABRICATION RESULTS - COMPLETE SEQUENCE

• Uncompensated mechanical stress– coverage and lines damaged



FABRICATION RESULTS - FINAL DEVICE



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)



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)



ACKNOWLEDGMENTS

• CNPq

• FAPESP

• CNPq/PADCT/CDCT

• Center for Sensor Technology at UPENN

usp upenn lsi fabrication of silicon probes for biosensors dr. marcelo bariatto a. fontes (post-doc)...

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