Inverted PAINT for Material-Specific Super-Resolution Fluorescence Imaging of Semiconductors.

Recent advances in super-resolution fluorescence microscopy have extended its application beyond traditional biological samples to include various organic materials such as polymers and lipid layers. However, its application to inorganic materials, including semiconductor substrates, still remains limited due to technical challenges associated with their thickness, optical opacity, and the lack of effective fluorophore labeling methods. To overcome these challenges, a label-free Inverted point accumulation for imaging in nanoscale topography (PAINT) imaging method is developed for thick and non-transparent inorganic nanomaterials by addressing the limitations of conventional PAINT imaging. By placing the sample in an inverted orientation and utilizing electrostatic interactions to control dye movement against gravity, silica-specific and silicon-specific nanoimaging of silica-silicon line- and hole-patterned semiconductor wafers, respectively is achieved. Through systematic optimization of polymer coating, dye charge, pH, refractive index, and dye concentration, it is demonstrated that the Inverted PAINT imaging method successfully visualizes sub-100 nm line patterns with a resolution of ≈12 nm, as well as enables multi-color and 3D nanoimaging. The method is anticipated to serve not only as a non-destructive and material-specific nanoimaging technique for a variety of inorganic nanomaterials, but also as a next-generation tool for semiconductor metrology and defect inspection.