SU-8 and Its properties

SU-8 And Its Features
Anne Samuel
• Introduction
- photoresist
- positive vs negative photoresist
• SU-8
- photosenstivity of SU-8
- process
- features
- application
• References
• Photoresists consists of three components.
- Resin( binder that provides adhesion,
chemical resistance etc- poly(cis-isoprene))
- Sensitizer(photoactive compound such as
bis(aryl)azide,t-butyl benzoic acid)
- Solvent( which keeps the resist liquid)
Positive Vs Negative Photoresists
• Positive Photoresists(PMMA)
- developer is not a solvent.
- resolution is 0.5(mm) and contrast is 2.2
- higher resistance to plasma etching
• Negative Photoresists( rubber based resists)
-provides good adhesion and tougher films for wet etching.
- more sensitive,so faster reaction(exposure energy is 10
mJ/cm^2 vs 100 mJ/cm^2).
-contrast is ~ 1.5
- lower % of sensitizer, so these resists are cheaper.
- not sensitive to over-developing.
What is SU-8?
- a negative epoxy based photoresist
- near UV sensitive
- consists of multifunctional highly branched
polymeric epoxy resin
- dissolved in a organic solvent along with
photoacid generator.
• SU-8 was first formulated at IBM as early as
What is SU-8?
• A single molecule
contains 8 epoxy
groups in a bisphenolA novalac glycidyl
• 8 in SU-8 means the 8
epoxy groups.
• SU-8 polymer
Photosensitivity of SU-8
• The photo acid generator
with the epoxy resin in
SU-8 is triarylsulfonium
• When SU-8 is exposed
to light or photon, it is
absorbed and
photochemical reaction
takes place.
< http ee250a/lectures
• The photochemical /EE250A_Lecture_09_Thick-Film_Lithography_SUreaction produces an 8_files/frame.htm>
Photosensitivity (cont’d)
The acid formed in the
photochemical reaction acts
as a catalyst in the exposed
regions during post baking
exposure (PEB).
To promote a cross linking
During cross linking, a
zipping process occurs
between the epoxy groups
creating a three dimensional
In order for the cross linking
to takes place PEB must be
above Tg
Cross-linking causes the film < http ee250a/lectures
to shrink and become more
SU-8 Process
• A typical SU-8 process consists of
- Spin-coating
- Soft Bake
- Exposure
- Post Exposure bake(PEB)-to cross link exposed regions
of the film
- Development
- Rinse & dry
- Hard Bake (or curing-optional)
- Imaged material
- Remove (optional)
Features of SU-8
• Why should we use SU-8?
• Good adhesion
• Near UV- Sensitive
• Broad range of thickness can be
obtainted from one spin with a
conventional spin coater (750
nm to 500 mm)
• High aspect ratios ( ~15 for lines
and 10 for trenches).
Applications of SU-8
• Some of the applications include
- Electroplating molds
- Sensors
- Actuators
- Micro-to Milli scale structures
- Microfluidic channels
1. Judy, Jack. “Thick film Lithography & SU-8”. 2003.
2. IBM Research -Zurich Research Laboratary. “ Epon SU-8
3. Micro.Chem.“Nano-SU-8: Negative Tone Photoresist Formulations”
4. Lorenz,H, Guerin,L . “ SU-8 Technologies at EPFL”. June 2002.

similar documents