Low-temperature Preparation of Metal-oxide Nanostructures by DUV
Lithography from Metal-oxo Clusters
Fabrice Stehlin, Chun-Cheng Yeh, Dominique Berling, Fernand Wieder, Arnaud Ponche, Arnaud
Spangenberg, Olivier Soppera
Institut de Science des Matériaux de Mulhouse (IS2M), CNRS - UMR 7361
Université de Haute Alsace, 15 rue Jean Starcky, Mulhouse, France
Contact author: olivier.soppera@uha.fr
Topic : Synthesis, integration and assembly of new
materials
Abstract—Metal oxo-cluster (MOC) prepared
from Zr, Ti or Hf precursors were synthetized
and used as photocrosslinkable hybrid
building blocks for direct write lithography.
Deep-UV irradiation (λ<250 nm) was used to
generate micro-nanopatterns by DUV-induced
condensation of the MOC for applications in
optics, photonics, sensors or nanoelectronics.
I.
II.
PREPARATION OF MOC
The first step consists in mixing the metal-alcoxides
precursors with the MAA in the following ratio M:MAA =
1:8. After 5 minutes of stirring, a volume of 2ml of 1propanol was added as a solvant. Then, after 10 minutes of
stirring, de-ionized water was added with a molar ratio
M:H2O = 1:20. An additional volume between 2 to 8ml of
1-propanol was added to tune the viscosity of the
formulation for adjusting the thin film thickness by spincoating. Using such preparation conditions, the formulation
could be kept during 2 months without any noticeable
modification
of
its
properties
(including
the
photosensitivity). [1]
INTRODUCTION
Among other functional materials, metal oxides are of
highest interest for a wide range of applications like optics,
photonics, microelectronics, magnetism, photocatalysis, and
photovoltaic,... However, their integration into complex
systems or devices usually requires multistep processes,
involving vacuum deposition or high temperature processes.
A major challenge is to enable nanopatterning of the metal
oxide material with a low temperature process, even, if
possible room-temperature process. Such characteristic is a
key-point for implementing functional inorganic
nanostructures in devices comprising organic materials or
on plastic substrates.
A versatile, fast and easy route towards metal-oxide
nanostructures prepared by full-optical method, at room
temperature is presented here. The concept relies on the
preparation of photosensitive metal-oxo clusters (MOC)
that can be crosslinked and mineralized in a single step
process, by Deep-UV (DUV) irradiation (ArF laser
emission band at 193 nm). The oxo-clusters are prepared by
complexation between metal alkoxides and methacrylic
acids followed by a partial hydrolysis. These molecular
building blocks are designed to absorb DUV light and they
can react from excited stated to give rise to crosslinking
reactions.
Preparation of the starting building blocks (MOC
precursors) is first described. Photocrosslinking of Ti, Zr
and Hf oxo-clusters was investigated by means of in situ
FTIR and spectroscopic ellipsometry. Finally, micro and
nanostructures obtained by laser direct write are presented.
Figure 1. Metal oxo-clusters preparation scheme.[1]
III.
NANOPATTERNING
Thin films for lithography were deposit by spin-coating.
The typical thickness was 100 nm (3000 rpm, 60 sec.) and
the films were irradiated without any pre-treatment. Homemade DUV interferometric setup was used for patterning.
An ArF laser (Braggstar from Coherent), was used as
irradiation source at 193 nm. Several phase masks were
used to generate regular patterns with periods ranging from
100 nm to 600 nm (line width resp. from 50 nm to 300 nm).
The interferometric head is depicted in Figure 2. After
irradiation, the thin films were developed 30s in
cyclohexanone to remove the non-irradiated part. A thermal
or DUV annealing could be applied after development to
mineralize the sample.
in electronics, optics, photonics or biology since they can be
used in other lithographic setup and they can be easily
doped to obtain optical, magnetic or electrical properties.
This concept was extended recently to materials with
electronic properties. In particular, we demonstrated that
InGaZnO sructures can be achieved by laser lithography.
The final material has semi-conductor properties after postannealing at moderate temperature [5].
3 mm
1.57mm
1.57mm
A
2 mm
38.2 °
n=1.56
Ordre -1
74.8
B 74.8
Ordre +1
Gmax=1.88mm
Ordre +2
Ordre -2
C
D
Figure 2. Scheme of the interferometer used to generate periodical light
patterns in the MOC thin film and application to nanopatterning.
IV.
TYPICAL EXAMPLES OF MICROSTRUCTRUCTURES
Using such lithographic tool and MOC precursors thin
films, it is possible to generate easily micro and
nanopatterns over relatively wide areas (cm2) in limited
times (few sec). [2]
Figure 3 presents typical examples accessible with TiOC
precursors resins. The case of TiOC was studied with much
care because in this case, we could demonstrate that a roomtemperature mineralization of the material was possible,
leading to amorphous TiO2 structures. Low temperature
curing of sol-gel materials is getting increasing importance
due to the challenge to develop optical or electronic devices
on plastic substrates.[1]
High resolution patterning can also be achieved with
structures widths as low as 50 nm [3] and also, multiple
irradiation strategies allows preparing more complex
architectures [4].
V.
CONCLUSION
These inorganic photoresists open new doors towards
room temperature preparation of high-resolution inorganic
nanostructures with strong interest for practical applications
Figure 3. AFM images of 300nm wide structures prepared by DUV
interferometric lithography starting from TiOC thin film. Left image
corresponds to structure after lithography and development and right
images are the same structure after DUV or thermal annealing posttreatment. [1]
ACKNOWLEDGMENT
This work was supported by ANR program
PHOTOMOC (N° ANR-14-CE26-0039-01). Authors
gratefully acknowledge the Regional Council of Alsace for
fundings.
REFERENCES
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[2]
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[5]
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