Electrochemical Solubility Switching Enables Lateral Etching Toward Sub‐20 nm Nanopatterning

The miniaturization of patterns to sub-20 nm dimensions remains challenging, owing to the fundamental constraints of optical patterning and the increasing complexity and cost of advanced lithographic technologies such as extreme-ultraviolet lithography. Here, we introduce an electrochemical etching strategy that effectively decouples the final feature size from the optical diffraction limit by leveraging voltage-gated solubility switching in electro-responsive polymers. We discover that the redox-state-dependent solubility of rhodamine-based polymers (Poly-RhNNE-B) can be precisely modulated by applied potentials, enabling programmable electrochemical dissolution. Notably, redox-mediator-facilitated intermolecular charge transfer extends this solubility switching laterally beyond the electrode-contact regions. This electrochemical lateral etching enables electrically controlled post-patterning dimensional refinement, allowing the remaining feature width to be progressively reduced after the initial pattern has been defined and yielding a minimum remaining linewidth of ∼17 nm without requiring the final nanoscale dimension to be directly defined by high-resolution optical exposure. This approach introduces an electrochemical nanofabrication strategy that complements conventional lithographic techniques, potentially reducing process complexity in selected nanoscale pattern-refinement scenarios while enabling high-resolution micro/nano-structuring, thereby expanding the toolbox for next-generation precision nanomanufacturing.