Paper Title (Use Style: Paper Title) s66

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: [email protected]

Topic : Synthesis, integration and assembly of new II. PREPARATION OF MOC materials The first step consists in mixing the metal-alcoxides precursors with the MAA in the following ratio M:MAA = Abstract—Metal oxo-cluster (MOC) prepared 1:8. After 5 minutes of stirring, a volume of 2ml of 1- from Zr, Ti or Hf precursors were synthetized propanol was added as a solvant. Then, after 10 minutes of and used as photocrosslinkable hybrid stirring, de-ionized water was added with a molar ratio M:H2O = 1:20. An additional volume between 2 to 8ml of building blocks for direct write lithography. 1-propanol was added to tune the viscosity of the Deep-UV irradiation (λ<250 nm) was used to formulation for adjusting the thin film thickness by spin- generate micro-nanopatterns by DUV-induced coating. Using such preparation conditions, the formulation condensation of the MOC for applications in could be kept during 2 months without any noticeable modification of its properties (including the optics, photonics, sensors or nanoelectronics. photosensitivity). [1]

I. 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 Figure 1. Metal oxo-clusters preparation scheme.[1] reactions.

Preparation of the starting building blocks (MOC III. NANOPATTERNING precursors) is first described. Photocrosslinking of Ti, Zr and Hf oxo-clusters was investigated by means of in situ Thin films for lithography were deposit by spin-coating. FTIR and spectroscopic ellipsometry. Finally, micro and The typical thickness was 100 nm (3000 rpm, 60 sec.) and nanostructures obtained by laser direct write are presented. the films were irradiated without any pre-treatment. Home- made 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 nanostructures with strong interest for practical applications 100 nm to 600 nm (line width resp. from 50 nm to 300 nm). in electronics, optics, photonics or biology since they can be The interferometric head is depicted in Figure 2. After used in other lithographic setup and they can be easily irradiation, the thin films were developed 30s in doped to obtain optical, magnetic or electrical properties. cyclohexanone to remove the non-irradiated part. A thermal or DUV annealing could be applied after development to This concept was extended recently to materials with mineralize the sample. electronic properties. In particular, we demonstrated that InGaZnO sructures can be achieved by laser lithography. The final material has semi-conductor properties after post- annealing at moderate temperature [5].

1.57mm 1.57mm 1.57mm 1.57mm 1.57mm 1.57mm

A A A 38.2 ° ° ° 38.2 38.2 38.2 2 mm mm mm 2 2 2

n=1.56 n=1.56 n=1.56

Ordre -1 74.8 Ordre +1 B 74.8 Gmax=1.88mm

Ordre +2 Ordre -2 C

Figure 2. Scheme of the interferometer used to generate periodical light patterns in the MOC thin film and application to nanopatterning. Figure 3. AFM images of 300nm wide structures prepared by DUV interferometric lithography starting from TiOC thin film. Left image IV. TYPICAL EXAMPLES OF MICROSTRUCTRUCTURES corresponds to structure after lithography and development and right images are the same structure after DUV or thermal annealing post- Using such lithographic tool and MOC precursors thin treatment. [1] films, it is possible to generate easily micro and nanopatterns over relatively wide areas (cm2) in limited times (few sec). [2] ACKNOWLEDGMENT Figure 3 presents typical examples accessible with This work was supported by ANR program TiOC precursors resins. The case of TiOC was studied with PHOTOMOC (N° ANR-14-CE26-0039-01). Authors much care because in this case, we could demonstrate that a gratefully acknowledge the Regional Council of Alsace for room-temperature mineralization of the material was fundings. possible, leading to amorphous TiO2 structures. Low temperature curing of sol-gel materials is getting increasing REFERENCES importance due to the challenge to develop optical or electronic devices on plastic substrates.[1] [1] Stehlin, F.; Wieder, F.; Spangenberg, A.; Le Meins, J.-M.; Soppera, High resolution patterning can also be achieved with O., Journal of Materials Chemistry C 2014, 2, 277-285.. structures widths as low as 50 nm [3] and also, multiple [2] Ridaoui, H.; Wieder, F.; Ponche, A.; Soppera, O. Nanotechnology 2010, 21. irradiation strategies allows preparing more complex [3] Stehlin, F.; Bourgin, Y.; Spangenberg, A.; Jourlin, Y.; Parriaux, O.; architectures [4]. Reynaud, S.; Wieder, F.; Soppera, O. Optics Letters 2012, 37, 4651. [4] Li, C.-H.; Stehlin, F.; Wang, K.-R.; Lin, Y.-H.; Wieder, F.; Soppera, V. CONCLUSION O.; Zan, H.-W.; Meng, H.-F., Applied Physics Letters 2013, 102 (16), 163305. These inorganic photoresists open new doors towards [5] H Lin, F Stehlin, O Soppera, H Zan, C Li, F Wieder, A Ponche, D room temperature preparation of high-resolution inorganic Berling, B Yeh, K Wang, Scientific Reports 2015, 5 ,10490.