Adhesive Bonding with SU-8

Report
Adhesive
Bonding with
SU-8
Advanced microtechnology
course (P)
Maria Berdova
2
Wafer Bonding
3
Adhesive Bonding
W. Brockmann, P. L. Geiß, J. Klingen, B. Schröder, Adhesive
Bonding, Materials, Applications and Technology, 2009.
4
SU-8
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Epoxy-based negative photoresist
Thickness <1um to >300um
Formulated in gamma butyrolactone (GBL) solvent (or in
cyclopentanone)
High chemical and thermal stability
Can be used for building rigid mechanical structures
HAR 40:1
Relatively cheap, easy to process
The strongest adhesion to Ti and TiO2
J. Micromech. Microeng. 17 (2007) R81–R95
5
Drawbacks of SU-8
 Difficult
removal after curing
 High coefficient of thermal expansion (52
ppm/◦C, for silicon and glass ~ 3 ppm/◦C)
 High level of tensile stress
 Poor adhesion to Ni substrates
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General bonding procedure
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Clean silicon and Pyrex wafers in piranha solutions then
dehydrate the wafers at 200◦C for at least 40 min
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Deposit, pre-bake, expose, post-bake and develop the first
SU-8 layer on the silicon wafer
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Spin-coat and pre-bake the second SU-8 layer on the Pyrex
wafer
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Join the two wafers at different bonding temperatures then
apply pressure to eliminate trapped air bubbles with a pair of tweezers
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After the bonded stack cools to room temperature, blanket
expose the second SU-8 layer through the Pyrex wafer
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Post-bake the stack with temperature ramping while applying
pressure
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Low cooling to reduce thermal mismatch stresses in the layers
J. Micromech. Microeng. 13 (2003) 732–738
Sensors and Actuators A 120 (2005) 408–415
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Micronozzels
Thermal oxidation
Litho from unpolished back side
Etching of SiO2 in BHF
DRIE
Patterning of 10 µm SU-8
Etching of SiO2 membranes
Spinning and backing SU-8 on Pyrex
Contact of Si and Pyrex substrates
Exposure through the Pyrex wafer
and post bake
J. Micromech. Microeng. 13 (2003) 732–738
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Micronozzels (leakage tests)
J. Micromech. Microeng. 13 (2003) 732–738
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Capacitive pressure sensor
Bonding with a pressure of 60N by pumping 1 h
with a surrounding pressure of 10−4 Pa, then
heating in ramp for 1 h to 70 ◦C and 100 ◦C, and
finally cooling down to room temperature
Sensors and Actuators A 147 (2008) 672–676
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Calorimetric flow sensor
By applying an electrical signal to
the heater element, the
surrounding liquid is heated up.
Then, temperature distribution is
measured by means of resistance
change at the downstream and
upstream sensors
20 µm SU-8, exposure
PMMA substrate
Ti/Pt, lift-off
Ox treatment for
cleaning
5 µm SU-8 to prevent
contact Me/liquid
125 µm Kapton
PMMA substrate
60 µm SU-8 to define inlet
and outlet connections
Bonding
Removal
20 µm SU-8 to define
microchannel
from 0 ul/min to 25ul/min
11
Thank You!

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