EPP Europe P2.2022

Bild: Microcare
Particulate contamination comes from the air,
from the abrasion of moving parts, from clothing,
or from dirty, unfiltered etching fluids
(Metal Oxide Semiconductor Field-Effect
Transistors) or other semiconductor components
are immersed in the heated fluid
for cleaning. Often, agitation helps enhance
the cleaning fluid’s effectiveness.
This is done by leveraging the boiling action
of the cleaning fluid, adding vibrating
ultrasonic energy or using a spray
wand to loosen the particulate off the
substrate. Once cleaned, the parts mechanically
transfer to the rinse sump. The
parts rinse in pure, uncontaminated fluid
or inside the fluid vapors themselves. The
components come out cool so they are
immediately ready for use or for the next
stage of processing. Unlike the commoner
aqueous cleaning, vapor degreasing combines
cleaning, rinsing and drying in one
step to maximize takt time. It takes as
little as 6–20 minutes per batch.
Moreover, vapor degreasers typically
have a smaller footprint than aqueous
cleaners. The systems take up less valuable
production space and, because vapor
degreasing cleaning is a simple, predictable
and repeatable process, it is easy to
qualify and validate for cleanroom use.
Good particle displacement
The displacement cleaning fluids used
inside vapor degreasers have chemical
and physical properties that are advantageous
to particle displacement and help
accelerate the cleaning process. Small
particles can be difficult to remove from
wafers since strong electrostatic forces
exist between the particles and the wafer
substrate. A particle adheres to the substrate
through adhesion forces, whether
it is an electrostatic charge or Van der
Waals force. This adhesion creates a friction
force parallel with the surface: static
friction if the particle is not moving, dynamic
friction if it is. To remove the contaminant,
the cleaning fluid must reduce
the thickness of the laminar boundary
layer, break the bond and allow the particles
to release from the substrate.
Some displacement fluids are a mixture
of hydrofluoro-olefin (HFO) and ethanol
that removes fine particulate down to the
micron or even sub-micron range. The alcohol
component forms hydrogen bonds
at the fluid-substrate interface, reducing
the intermolecular forces between the
particle and the substrate. This allows the
particulate to lift more easily from the
substrate.
Plus, the fluorocarbon-based fluids are
synthetically derived, allowing for a
higher purity level than traditional hydrocarbon-based
cleaning fluids. These
ultra-pure fluids dry quickly and completely
without leaving spots or residue
behind.
High density & low viscosity
Particulate displacement fluids are
dense: typically, 20–40% heavier than
water and 50% heavier than alcohol.
They also have a lower viscosity than IPA
(Isopropyl Alcohol), water or water with
surfactant additives. The combination of
the higher density and the lower viscosity
About the author
Elizabeth Norwood is a
Senior Chemist at MicroCare,
which offers precision cleaning
solutions. She has been in
the industry more than 25
years and has a BS in Chemistry
from the University of St.
Joseph. Norwood researches,
develops and tests cleaningrelated
products. She currently
has one patent issued
and two pending for her
work. For more information,
visit www.microcare.com.
THE FLEXIBILITY
FOR MASS
INTERCONNECT
ODU-MAC ®
GET YOUR
SOLUTION
NOW!
black-line@odu.de
Electromechanical version
Eight tensioning points
for equal connections
Flexible configuration with
ODU-MAC® modules
Including cable assembly
www.odu.de
EPP Europe » 11 | 2022 23