Transcript BioMEMS Device Fabrication

BioMEMS Device
Fabrication Procedure
Theresa Valentine
8/19/03
Electrode Fabrication
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Begin with Pyrex wafer, 100 mm diameter, 0.5 mm thickness
Metal deposition
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Resist patterning
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E-beam evaporate 90Å Cr and 2000Å Au
Must provide Au target
Tom Loughran, ECE clean room, [email protected]
Clean wafer with acetone/methanol/IPA
Dehydrate for 10 minutes on hotplate at 100°C
Cover wafer with HMDS primer while on spinner
Wait exactly 1 minute
Spin HMDS at 5000 rpm for 30 s
Apply one pipette of Shipley 1813 photoresist to wafer
Spin 1813 at 5000 rpm for 30 s
Soft bake for 1 minute at 100°C on hotplate
Expose at 150-200 mJ/cm2 dose
Develop for 30 s in Shipley 352 developer
Wash immediately
Hard bake at 120°C for a few minutes
Metal etching
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Etch Au in Transene TFA etchant, 28Å/s (1 min 40 s works well for 2000Å)
Etch Cr in Transene 1020 etchant, 40Å/s (20 s works well for 90Å)
Mold Fabrication
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Remove SU-8 from refrigerator at least 2 hours before process
Begin with bare Si wafer, 100 mm diameter, 0.5 mm thickness
Clean wafer with acetone/methanol/IPA if not fresh from box
Dehydrate for 10 minutes on hotplate at 100°C
Cover 2/3 of wafer with SU-8/50 (from bottle) while wafer is on spinner
Spin SU-8 (recipe for 220 microns)
RPM1: 240
RPM2: 500
RPM3: 1200
RAMP1: 1
RAMP2: 1
RAMP3: 1
TIME1: 3
TIME2: 7
TIME3: 20
RAMP4: 1
Pre-bake SU-8 (220 microns) for 100 min on hotplate at 95°C, 300°C/min ramp, auto
off
Let wafer cool on hotplate for 30 min after auto-off
Expose with 900 mJ/cm2 dose
Post-bake for 30 min on hotplate at 95°C, 300°C/min ramp, auto off
Let wafer cool on hotplate for 30 min after auto-off
Develop for 22 min in SU-8 developer
Rinse wafer in fresh SU-8 developer (never water!) and let dry
Fluid Control Layer Fabrication
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Place SU-8 mold wafer in 0.1M SDS solution (1.44 g SDS powder per 50 mL water) for 2 minutes
Remove wafer and let dry naturally (no nitrogen)
Mix PDMS (Sylgard 184) in a plastic cup with curing agent in 10:1 weight ratio
Cover wafer with PDMS while wafer is on the spinner
Spin PDMS (recipe for ~130 microns)
RPM1: 100
RPM2: 200
RPM3: 500
RAMP1: 1
RAMP2: 1
RAMP3: 1
TIME1: 3
TIME2: 17
TIME3: 60
Bake wafer in box furnace for 2 hours at 70°C
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Hold in “Set” to program, press enter, select program “0” and press enter
SP1=70, time1=0.01 (1 min), SP2=70, time2=2.00, SP3=22, time3=off, JC=0 to ramp to 70°C as fast as
possible, remain for 2 hours, turn off to room temperature
Remove wafer from box furnace, turn off furnace, and let wafer cool
Submerge wafer in a dish of methanol and loosen PDMS edges with razor blade or tweezers
Pull one side of PDMS gently from wafer until entire layer is free
Keep PDMS layer under methanol while aligning to electrode wafer
Remove electrode wafer with PDMS from methanol and check alignment under microscope
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RAMP4: 3
Use extra methanol squirted on wafer to allow fine alignment
Dry wafer gently with a wiper or let dry in air