BioMEMS DeviceFabrication Procedure

Theresa Valentine

8/19/03

Electrode Fabrication• Begin with Pyrex wafer, 100 mm diameter, 0.5 mm thickness• Metal deposition

– E-beam evaporate 90Å Cr and 2000Å Au– Must provide Au target– Tom Loughran, ECE clean room, tcl@glue.umd.edu

• Resist patterning– 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– 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• 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)

• 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

RPM1: 240 RPM2: 500 RPM3: 1200

RAMP4: 1

RAMP1: 1 RAMP2: 1 RAMP3: 1

TIME1: 3 TIME2: 7 TIME3: 20

Fluid Control Layer Fabrication• 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)

• Bake wafer in box furnace for 2 hours at 70°C– 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

– Use extra methanol squirted on wafer to allow fine alignment• Dry wafer gently with a wiper or let dry in air

RPM1: 100 RPM2: 200 RPM3: 500 RAMP4: 3

RAMP1: 1 RAMP2: 1 RAMP3: 1

TIME1: 3 TIME2: 17 TIME3: 60