Tin-Oxo Nanocluster Composite Films as Positive-Tone Photoresist for Extreme UV Lithography

As high-numerical aperture extreme UV lithography (EUVL) approaches commercial deployment, driving a need for innovation in photoresist technology, extensive research has identified tin-oxo nanoclusters (TOCs) as promising next-generation photoresist platforms. This study proposes a method for achieving TOC-based photoresists that increase their solubility upon exposure to EUV radiation, addressing the current lack of suitable candidates. Lewis-acidic alkylated TOCs undergo ligand dissociation upon exposure to high-energy electron beams or EUV light. This structural change enhances further the Lewis acidity of the resulting compounds, enabling the selective dissolution of exposed regions in a Lewis-basic aqueous developer to form a positive-tone stencil. This strategy is successfully demonstrated using DSBTOC, which contains bulky counter-anions but lacked sufficient patterning performance and stability for high-resolution pattern formation. A modified formulation combining DSBTOC with 10 wt.% dendritic hexaphenol (DHP) that acts as both a Lewis base and a radical scavenger exhibited improved thin-film properties and chemical stability. EUVL testing of films made from this mixture produced a positive-tone stencil with a line width of 13 nm. It is expected that TOC-based positive-tone resists to complement their negative-tone counterparts in producing high-performance semiconductor chips.