Detecting structures below a cover film at the nanoscale resolution is of essential importance. In this work, we explored factors affecting subsurface material contrast and structural visibility in scattering-type scanning near-field optical microscopy (s-SNOM). A kind of multilayered reference samples containing different buried structures was fabricated and applied for s-SNOM imaging. The dependence of near-field optical contrast on structure geometry, dimension and cover thickness was investigated. Results demonstrate that distinguishing the buried slit pattern is easier than the circular hole with the same critical dimension. The s-SNOM can sense material difference under a more than 100 nm thick polymethyl methacrylate layer and it has a subsurface spatial resolution better than 100 nm.

中文翻译：

---

散射型扫描近场光学显微镜成像中亚表面纳米结构的可见性

以纳米级的分辨率检测覆盖膜下的结构至关重要。在这项工作中，我们探索了在散射型扫描近场光学显微镜（s-SNOM）中影响地下材料对比度和结构可见性的因素。制备了一种包含不同掩埋结构的多层参考样品，并将其用于s-SNOM成像。研究了近场光学对比度对结构几何形状，尺寸和覆盖厚度的依赖性。结果表明，与具有相同临界尺寸的圆形孔相比，区分掩埋的缝隙图案更容易。s-SNOM可以感应到厚度超过100 nm的聚甲基丙烯酸甲酯层下的材料差异，并且其次表面空间分辨率优于100 nm。