1. 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 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

6. General bonding procedure
Clean silicon and Pyrex wafers in piranha solutions then
dehydrate the wafers at 200◦C for at least 40 min
Deposit, pre-bake, expose, post-bake and develop the first
SU-8 layer on the silicon wafer
Spin-coat and pre-bake the second SU-8 layer on the Pyrex
wafer
Join the two wafers at different bonding temperatures then
apply pressure to eliminate trapped air bubbles with a pair of tweezers
After the bonded stack cools to room temperature, blanket
expose the second SU-8 layer through the Pyrex wafer
Post-bake the stack with temperature ramping while applying pressure
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

7. 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

8. Micronozzels (leakage tests)
J. Micromech. Microeng. 13 (2003) 732–738

9. 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

10. 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
20 µm SU-8 to define microchannel
125 µm Kapton
PMMA substrate
60 µm SU-8 to define inlet
and outlet connections
Bonding Removal
from 0 ul/min to 25ul/min

11. Thank You!