Adhesive Bonding with SU-8Advanced microtechnology course (P)

Maria Berdova

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Wafer Bonding

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Adhesive Bonding

W. B

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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

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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 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

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MicronozzelsThermal 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

Sensors and Actuators A 147 (2008) 672–676

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

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Calorimetric flow sensorBy 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, exposurePMMA 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 KaptonPMMA substrate

60 µm SU-8 to define inlet and outlet connections

Bonding Removal

from 0 ul/min to 25ul/min

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Thank You!