Synchrotron Radiation Patterning of Plasma Polymerized Organo Silicons

Journal
of Photopolymer
Volume 7, Number
Communication
Synchrotron
of Plasma
Radiation
Polymerized
in Oxygen
G.K. Vinogradov,
3(1994)
Science
and
615-618
Technology
©1994TAPJ
Patterning
Organo
Silicons
Atmosphere
C. Shao,
K. Sends,
and S. Morita
Center for Cooperative Research
in Advanced Science and Technology,
Nagoya University, Nagoya 464-OY, Japan.
1. Introduction
Recently some reports have been published on the development of new approaches for
all dry photo lithographic processing based on silicon containing plasma polymerized
resists
[1,2]. Silylation technology is well known and widely used in micro lithography [3,4]. Silicon
containing crosslinked thin films, on the other hand, were plasma polymerized for different
purposes of surface coating such as optical, mechanical, and electrical [5,6]. It was also shown,
that Si-Si network can be plasma polymerized from, for example, aromatic silanes undergoing
particularly scission of Si-CH3 and Si-H bonds [7]. Silylated resists have been patterned by UV
irradiation in an oxygen atmosphere as well. However, only the combination of plasma
polymerization of silicon containing networks with their UV irradiation in the presence of
oxygen gives a breakthrough for all dry photo lithographic processing [1,2].
Uv lithography being the only candidate for a recent mass production will be probably
replaced in the future with X-ray processing having much lower critical dimension. All the
merits of X-ray lithography can be revealed with ultra thin perfect resist layers, which can be
deposited and processed exclusively in dry technology cycles. The present paper describes our
preliminary results on plasma polymerization
containing organic films in an oxygen ambient.
and synchrotron
X-ray patterning
of silicon
2. Experimental
Plasma Polymerization.
Silicon organic films were deposited in RE capacitively coupled plug
flow box-type reactor [S]. The reactor represents a rectangular prism with a well shaped uniform
gas flow and a plasma volume, strictly limited with the rectangular copper thermal stabilized
Received April 4 , 1994
Accepted May 9, 1994
615
I Photopolym. Sci. Technol., Vol. 7, No.3, 1994
electrodes,
teflon
stainless
chamber.
Two
walls,
sets
and a copper
of
discharge
hexamethyldisilazane/Ar
mixture
mesh.
condition
have
The last was applied
of polymer
Film thickness
The distributions
deposition
of film thickness
with an automatic
Patterned
been
and low frequency
hexamethyldisilazane.
structure.
The reactor
used:
pulse
to suppress
was monitored
was mounted
discharge
of
time modulated
discharge
of pure
features.
Synchrotron
X-ray patterning.
15 microns
beryllium
foil.
Deposited
and cross linking
crystal
microbalance.
along the gas flow were measured
The facility
of UVSDR
Japan., was used. The wavelength
0.8
nm.
A stainless
diaphragm
supplied
sample
chamber
a differential
after
was
connected
pumping
resists
copper mesh (100 lines/inch,
deposited
system
ring
in
for about
through
a possibility
the
to irradiate
Ton.
on silicon samples were covered
as a mask, irradiated
and then removed
Science
corresponds
synchrotron
providing
of about 0.3-0.5
50% transparent)
of oxygen,
of Molecular
X-ray intensity
to the
to reveal their self
with an X-ray beam through
at the Institute
of maximum
high oxygen pressure
Plasma polymerized
profilometer
films have been irradiated
Okazaki,
time in the presence
20%
ellipsometer.
development
samples under relatively
formation
in situ with a quartz
samples have been scanned with a mechanical
with
the cylindrical
continuous
particulate
on silicon substrates
inside
with a microscope
for a prescribed
period
of
to the ambient atmosphere.
3. Results and Discussion
All
irradiated
samples
being
negative
type
resists
demonstrate
however
well
distinguished self development features (Fig. 1). Irradiated areas become harder and thinner. The
minimum X-ray
dose in our experiments was about 0.2 Jlcm2 , which is essentially low. The
irradiated area can be easily distinguished
from non-irradiated
by colors for all irradiated
samples. Initial steep low dose part of the curve corresponds for initial high rate oxidation
reactions. Under the higher doses the rate of thickness decrease is probably dealt with increasing
of the degree of oxidation and less probably with a partial polymer ablation.
The data known from literature suggest, that the level of sensitivity of best silicon
organic polymer resists to oxidation under UV 193 nm irradiation and adjacent wet development
is about 35-60 mJlcm2 [9] and can be even improved with chemical sensitizers. Total dose of
about
1.2 JIcm2 transferred
silicon containing
plasma
deposited
polymers
to the level
eharacteri- stir of stochiometric Si0 2 [1].
The efficiency of X-ray synchrotron oxidation, and especially Be filtered radiation, must
be essentially lower in compare with UV processing, taking into consideration lower absorption
and mechanisms of energy transfer from high energy penetrating X-ray photons to low energy
chemical bonds accompanied with several energy dissipating processes.
616
J. Photopolym. Sci. Technol., Vol. 7, No.3,
Color
exhibit
microphotographs
also
some
interferometric
colors
films.
Bright
areas
corresponding
as
the
the
changing
gray.
under
to dark
is
increasing,
from
dark
to
phenomenon
X-ray
beam
mesh
mask.
reddish
definitely
the
mesh
difficult
oxygen.
X-rays
gas
Secondary
can be a
excited
metastable
can promote
of the X-ray
molecules.
species,
component
oxygen,
and
states.
Every
2
rough
in
thus
these
distributed
decreasing
the
exposure.
shows
a
profilometer
sample.
thus
radiative
of
appropriately
of the films
Fig.
of the film deposited
by
dissipation
excited
mechanical
absorbed
energy
electronically
contrast
Fig. I. Self-development
in a pulsed
discharge.
activated
of
atomic
oxidation
the
areas
oxygen
surface
of
origin
processes
molecules,
part
probable
are partly
ionized
explain
below
with
phase
produce
to
some
of masked
interaction
film
as well.
most
direct
bright
polymer
with
The
is
oxidation
redistributed
of oxidation
signal
from
the
for
high
dose
The
typical
surface
compare
of masked
with
exhibiting
some
reactions.
Similar
noisy
areas
be found
on
can
blue
areas
such
squares
minimum
of unexposed
the copper
very
a
color
modifying
irradiated
intact
self developed
dose
It is rather
the
the
are changing
It manifests
reactions
of
for
irradiation
while
change
of
yellowish
of 0.2 JIcm2
1994
profile
low
the
areas
irradiated
surface
of
etching
samples
increased
load on the profilometer's
stylus.
hardness
of irradiated
non-irradiated
Fig. 2. Mechanical
prlofile
of the
patterned
resist. Initial thickness
200 nm, continuous
discharge.
unexposed
dose
and
is
under
In that case
areas
the effect
and indentation
is caused
of the
stylus
by the
difference
inside
the
of
polymer
film.
617
J. Photopolym. Sci. Technol., Vol.7, No. 3, 1994
Further
now
experiments
on X-ray
oxidative
patterning
and
vet and plasma
development
are
in progress.
Conclusion
X-ray
Silicon
containing
exposure
in
irradiated
Clear
areas
optical
images
phenomena
gas phase
oxidative
have
resist
Typical
been
been
developed
of the
resists
films
have
X-ray
patterning
observed
under
in all samples
have
been
been
patterned
by
by
synchrotron
self development
any
doses
from
including
those
with the lowest
modified
to the
secondary
processes
silicon
films
be
under
the
high
of energy
about
X-ray
dissipation
0.2
doses
of
JIcm2.
dose.
as well.
through
the
candidates
for
oxygen.
deposited
X-ray
ambient.
films
can be assigned
activated
Plasma
have
areas
polymerized
oxygen
of polymer
Unexposed
This
an
plasma
photo
organo
lithography
can
considered
in all dry microelectronics
as promising
technology
cycles.
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