Positive-tone Tin-oxo Nanoclusters for Extreme UV lithography

In this study, we propose a strategy to achieve positive metal oxide resists (pMORs) based on tin-oxo nanoclusters (TOCs) for extreme ultraviolet (EUV) lithography in high-performance semiconductor integrated circuit manufacturing. TOC possesses Lewis acidic properties and becomes more strongly acidic upon ligand dissociation when exposed to high-energy radiation, such as electron beam (e-beam) and EUV. During the subsequent development process using an aqueous solution of tetramethylammonium hydroxide (TMAH), a Lewis base, the exposed regions undergo Lewis acid-base interactions, leading to increased hydrophilicity. Ultimately, this results in enhanced solubility, enabling the formation of positive-tone patterns. To address the limitations of TOCs, particularly in terms of process margin and chemical stability, we mixed TOCs with small organic molecules containing phenolic hydroxyl groups, which act as Lewis bases. This modification effectively mitigated the shortcomings of TOCs. A TOC formulation containing 10% dendritic polyphenol (DPP) exhibited an improved dissolution contrast while simultaneously enhancing chemical stability. Using this in EUV lithography, we successfully achieved high resolution positive-tone patterns with a line width of 13 nm.