g) Surface Cleaning and Micro-Structuring with Lasers
Previous
studies
have
shown
that
excimer
lasers
are
efficient
and
safe
tools
to
remove
securely
and
controlled layers of a certain thickness from the surface of icons and paintings.
Excimer
lasers
offer
significant
advantages
for
sur
-
face
cleaning
processes,
because
their
short
wave
-
lengths
(e.g.
248
nm)
can
be
focused
to
a
smaller
spot
size than visible or infrared light.
With
each
pulse
the
UV
light
can
remove
quite
pre
-
cisely
about
0.2
µm
of
dirty
material
.
In
com
parison:
A human hair is about 50 - 100 µm thick.
And
for
some
applications
even
more
important
(different
to
some
other
laser
types),
excimer
lasers
do
not
release
greater
fractions
of
heat,
which
could
cause
thermal
damage
to
surroun
-
ding
material.
These
attributes
make
excimer
lasers
well-suited
for
cleaning
sensitive
surfaces
like
pigment
lac
quer,
finishing
varnish
or
art
paintings,
but
also
for
manufacturing
of
all-poly
-
mer electronic compo
nents.
Excimer Laser Scanning Device for Sensitive Surface Cleaning
Automated,
non-polluting
cleaning
devices
are
of
rapidly
growing
interest
in
science
and
in
-
dustry.
Particularly
laser
cleaning
units
avoiding
wet
chemical
reactions
and
by
this
significantly
reducing
environmental
contamination,
have
proven
successfully
and
have
found
many
new
applications.
Most
of
these
laser
cleaning
units
are
designed
to
completely
remove
the
top
layer
of
a
surface
or
the
surface
itself,
e.g.,
removing
paint
as
a
preparatory
step
for
a
new
sealing
of
the
sur
-
face
(see
aeroplane
or
car
industry).
In
these
cases
it
is
important
to
make
sure,
that
no
re
-
maining lacquer is left.
Likewise
this
applies
to
the
cleaning
of
stone
faca
des,
antiques
or
other
objects
suffering
from dust and environmental impacts. The statue at the left was completely black like the base.
Lasers,
however,
offer
additional
significant
advantages
compared
to
conventional
cleaning
me
-
chanisms:
•
So,
soft
and
sensitive
surfaces
like
paint
or
plastics
may
be
treated
to
ablate
a
few
micro
-
meters
of
the
upper
layer
together
with
some
adherent
impurities
without
destroying
the
protecting function of the layer or the underlying structure.
•
In
semiconductor
epitaxi
or
optical
coating
fabrication
substrates
can
be
irradiated
to
re
-
move
monolayers
of
water
or
oxygen
from
the
surface
even
under
ultrahigh
vacuum
con
di
-
tions.
•
Toxic
chemicals
or
hazardous
bacteria
sticking
at
the
surface
can
be
cracked
and
vaporized
to sterilize instruments.
•
Lasers
can
be
used
to
decontaminate
some
equipment
which
was
radioactively
conta
-
minated.
We
developed
a
laser
cleaning
unit
de
sig
-
ned
for
an
automated
processing
and
cleaning of conta
minated samples.
Particularly
dust,
che
micals
or
radioactive
isotopes
sticking
at
var
nish,
lacquer
or
plastic
sealing
are
removed
together
with
a
few
µm
thin
film
of
the
surface
without
destroying the sealing itself.
While
for
complete
removal
of
a
sealing
it
may
be
favorable
when
the
laser
radiation
pene
trates
into
deeper
layers
and
causes
some
depth
effect,
ablation
of
only
a
thin
film
requires
deposition
of
the
laser
energy
into
the
top
layer
of
the
surface.
This
is
best
realized
with
lasers
operating
in
the
UV,
where
paint
and
plastics
show
sig
nificantly
increasing
absorption.
Therefore,
we
are
working
with
a
KrF-excimer
laser.
The
key
element
of
the
cleaning
device
is
a
beam
forming
and
scanning
unit.
To
improve
the
laser
beam
quality
for
homogeneous
irra
-
di
ation
of
sam
ples,
a
beam
homogenizer
was
developed
which
forms
a
rectangular
cross
se
-
ction
with
top-hat
beam
profile.
The
beam
is
fo
cused
down
to
2x2
mm
2
and
directed
across
the polluted surface by a beam scanner which uses two galvo mirrors.
The
scanning
rate
and
by
this
the
deflection
of
the
beam
is
adapted
to
the
pulse
repetition
rate
(up to 1 kHz) and therefore allows an extremely fast automated processing.
An
accurately
controlled
beam
positioning
together
with
the
top-hat
profile
ensures
a
very
ho
-
mo
geneous,
uniform
and
reliable
irradiation
of
each
surface
element
with
an
almost
identical
laser
fluence.
Our
investigations
with
this
set-up
show,
that
after
optimizing
the
relevant
laser
parameters
like
pulse
energy,
peak
intensity,
laser
repe
ti
-
tion
rate,
num
ber
of
pulses
and
beam
profile,
an
efficient
clea
ning
without
damage
of
the
surface
is
obtained.
A
computer
controlled
operation
of
the
system
gua
rantees
the
uni
-
form
and
continuous
cleaning
as
well
as
a
comfortable
handling.
The
unit
is
equip
ped
with
an
adapted
suction
nozzle
to
dispose
the
detached particles from the surface.
To
quantify
the
cleaning
efficiency
and
to
proof
the
applicability
of
laser
cleaning
even
for
radio
-
actively
contaminated
samples
varnished
plastic
plates
were
prepared,
contaminated
with
152
Eu
at
the
surface.
152
Eu
is
favorably
used
as
contaminating
test
material,
since
under
normal
con
-
ditions
it
is
not
radioactive
but
can
be
activated
well-aimed
by
neutron
radiation
to
a
meta
stable
configura
tion
with
a
half-life
of
9.5
h.
Therefore,
any
handling
of
the
plates
during
pre
paration
and cleaning can be done without danger of radioactivity.
The
laser
cleaning
efficiency
is
determined
by
measuring
the
radioactivity
of
the
plates
before
and
after
laser
irradiation.
We
found
that
with
a
fluence
of
1
J/cm²
only
one
or
two
pulses
per
position are necessary to bring the initial contamination level down to less than 5%.
The
same
set-up
can
also
be
used
for
cleaning
of
art
paintings
and
restoration
of
antiques.
The
scanner
unit
directs
the
excimer
laser
radi
ation
onto
the
painting
and
sweeps
the
beam
across
an
area
of
6x10
cm².
For
processing
of
larger
areas
the
painting
can
be
shifted
auto
mati
-
cally
by
step
per
motor
controlled
displace
units.
This
figure
shows
an
oil
painting
as
test
ob
-
ject
ir
radiated
with
different
concentrations
(pulses
per
position).
It
demonstrates
the
well
con
trollable,
homogeneous
treatment
and
the
efficiency
of
ex
cimer
laser
cleaning
of
art
ob
-
jects.
It
results
in
an
appealing
and
bright
appearance
of
the
processed
area
and
shows
the
suspicious
potential
for
future
excimer
laser cleaning appli
cations.
Doctoral Theses
B. Warm
Einsatz Adaptiver Optik zur Formung von Laserstrahlen
School of Electrical Engineering, Helmut-Schmidt-Uiversity, Hamburg 1994
R. Meixner
Herstellung und Charakterisierung wellenlängenselektiver organischer Feldeffekttransistoren
School of Electrical Engineering, Helmut-Schmidt-Uiversity, Hamburg 2007
K.-H. Steglich
Reinigung und Strukturierung empfindlicher Oberflächen mittels Excimerlaserstrahlung
- Entwicklung und Anwendung eines Applikationsgerätes -
School of Electrical Engineering, Helmut-Schmidt-Uiversity, Hamburg 2008
Refereed Publications in Journals and Conference Digests
K.-H. Steglich, H. Harde
Laser Cleaning of Radioactively Contaminated Surfaces
Proceedings of the Conference on Lasers and Electro Optics Europe 1998, IEEE Catalog No. 98TH8326,
ISBN: 0-7803-4233, Glasgow, Scotland, UK, p. 24 (1998)
K.-H. Steglich, H. Harde
Laser Scanner for Cleaning of Sensitive Surfaces
Conference on Lasers and Electro-Optics/Europe (CLEO/EUROPE 2000), IEEE Conference Digest, CWF 57,
Cat. No. 00TH8505, ISBN: 0-7803-6319-3, Nice, France, p. 215 (2000)
K.-H. Steglich, H. Harde
Sensitive Surface Cleaning using an Excimer Laser Scanner
Conference on Lasers and Electro-Optics (CLEO 2001), Technical Digest, CTuT 7, Cat. No. 01CH37170,
ISBN: 1-55752-676-1, Baltimore, MD, USA, CTuT 7, p. 233 (2001)
K.-H. Steglich, H. Harde
Sensitive Surface Cleaning Using an Excimer Laser Scanner
Conference on Lasers, Applications and Technologies (IQEC/LAT 2002),
Technical Digest, LMF 45, Moscow, Russia, p. 283 (2002)
K.-H. Steglich, H. Harde
Automated Surface Cleaning with an Excimer Laser
Conference on Laser-assisted Micro- and Nanotechnologies (ILATA-III 2003/LAM-X),
Technical Digest, PSII-1, 2003, St. Petersburg, Russia, p. 38 (2003)
K.-H. Steglich, H. Harde
Rapid Excimer Laser Cleaning of Plane Objects
Conference on Lasers and Electro-Optics/Europe (CLEO/EUROPE 2003), Conference Digest (CD-ROM,
Volume 27E), CK5W, ISBN 2-914771-15-0, Munich, Germany, p. 106 (2003)
K.-H. Steglich, H. Harde
Art Cleaning by Excimer Lasers
Eurolaser 1/2004, Verlagsgesellschaft Grütter GmbH & Co. KG, Coburg, ISSN: 1430-8274 (2004)
P.H. Thiesen, R. Meier, T. Fedorkova, K.-H. Steglich, H. Harde, B. Niemeyer
Die Bestimmung der Dicke laserbehandelter Polymerfilme mittels Ellipsometrie
Chemie Ingenieur Technik 2004, 76 No.9, Wiley-VCH, ISSN 0009-286X, p. 1385 (2004)
P.H. Thiesen, R. Meier, T. Fedorkova, K.-H. Steglich, H. Harde, B. Niemeyer
The Thickness of a Modified Polymere Film - An Ellipsometric Study
12. Wolfgang-Ostwald-Kolloquium, Kiel (2004)
R. Meixner, R. Wille, P. Schertling, H. Goebel, H. Harde, K.-H. Steglich, F.A. Yildirim, W. Bauhofer,
W. Krautschneider
Bottom Gate Organic Field Effect Transistors Made by Laser Structuring
Organic Electronics 7, pp. 586–591 (2006)
K.-H. Steglich, H. Harde
Oberflächenreinigung mit Lasern
Uniforschung, Forschungsmagazin der Helmut-Schmidt-Universität Hamburg, 14. Jahrgang, S. 12-15 (2004),
ISSN: 0940-8061
Contributions on National Conferences and Meetings
K.-H. Steglich, H. Harde
Reinigung kontaminierter Oberflächen mit Hilfe eines Excimer-Lasers
Frühjahrstagung der DPG, Sektion Kurzzeitphysik, Bayreuth, 10. März 1998,
Verhandl. DPG (VI) 33, 305 (1998)
K.-H. Steglich, H. Harde
Excimer-Applikationsverfahren zur sensitiven Reinigung radioaktiv kontaminierter Oberflächen
Frühjahrstagung der DPG, Fachverband Kurzzeitphysik, Heidelberg, 18. März 1999,
Verhandl. DPG (VI) 34, K 7.6, 288 (1999)
K.-H. Steglich, H. Harde
Reinigung radioaktiv kontaminierter empfindlicher Oberflächen mittels eines Excimer-Lasers
Poster Norddeutsches Laserkolloquium 1998, Hannover, 9. Dezember 1999
K.-H. Steglich, H. Harde
Excimer-Laser-Scanner zur sensitiven Reinigung radioaktiv kontaminierter Oberflächen
Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Fachverband Kurzzeitphysik,
Bonn, 6. April 2000, Verhandl. DPG (VI) 35, D3 (2000)
K.-H. Steglich, H. Harde
Excimer-Laser-Scanner zur Reinigung empfindlicher Oberflächen
Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Fachverband Kurzzeitphysik,
Bochum, 18.-21. März 2002, Verhandl. DPG (VI) 37, D3 (2002)