Metal-oxo clusters (MOCs) with atomically precise structural configurations have become the optimal choice for nanolithography materials due to their uniformly nanosized components, high etch resistance, appropriate absorption characteristics, and facilitation of investigations into structure-function relationships. From the perspective of elements with strong resonance to extreme ultraviolet(EUV) radiation, such as In, Sn, Zn and Zr, their metal-oxo clusters exhibit superior lithography performance as innovative photoresists.

However, most of them are still in the research and development stage and cannot be used on commercial extreme ultraviolet lithography(EUVL) scanners. Up to now, only the targeted formulation resist developed by Inpria Corporation, based on Sn12-oxo cluster, has stood out. It achieved a resolution of 13 nm at a dose of 35 mJ/cm² on Advanced Semiconductor Material Lithography(ASML)’s NXE:3300B scanner. This highlights its tremendous potential for commercial applications, hence research into tin-oxo cluster-based photoresists holds significant promise.

In a study published in Angew. Chem. Int. Edit, the research group led by Prof. Jian Zhang from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences, reported the improving the lithography sensitivity of atomically precise tin-oxo nanoclusters via heterometal strategy.

The researchers proved heterometallic MOCs can fully leverage the synergistic effects between different components to achieve exceptional performance, playing a vital role in the realm of photolithography. From this perspective, the researchers introduced different metal dopants into the tin-oxo clusters and further explored the relationship between the patterning performance and dopant’s coordination geometry.

The researchers synthesized the isostructural heterometallic Sn-M oxo clusters (M=In3+, Fe3+ and Al3+), and increased the coordination number via introducing the N-containing ligands. All these cluster compounds demonstrated excellent solubility, dispersibility, and stability, facilitating the preparation of high-quality films via spin-coating for lithographic applications.

In order to obtain the deeper understanding of thin film properties, the researchers carried out AFM-infrared (Atomic Force Microscopy based Infrared Spectroscopy), neutron reflectivity (NR), and X-ray reflectivity (XRR) measurements, confirming the homogeneity of the oxo cluster-based photoresists.

Besides, the researchers used electron beam lithography (EBL) to evaluate their pattering performance, and all four materials achieved 50 nm line patterns. Among these, the compound with indium dopants and unsaturated coordination demonstrated the highest lithography sensitivity, illustrating the impacts the types of metal dopants and their coordination geometries on nanolithography performance. Furthermore, they validated the exposure mechanisms by  x-ray photoelectron spectroscopy(XPS).

This study not only explores the structural influence of various metal dopants, but also further investigates coordination geometries on the performance of organotin-oxo clusters in nanolithography.

The precise modification of tin-oxo clusters via the heterometal strategy, specifically varying the metal dopants and their coordination geometries, has resulted in SnOC-1(In), SnOC-1(Al), SnOC-1(Fe), and SnOC-2, thereby tuning their distinct lithography performance. (Image by Prof. ZHANG’s group)

Contact:

Prof. ZHANG Jian

Fujian Institute of Research on the Structure of Matter

Chinese Academy of Sciences

E-mail: zhj@fjirsm.ac.cn