A major challenge in modern semiconductor, photonic, and quantum technology is the accurate characterization of ultrathin (100 nm) patterns with ever-decreasing lateral feature sizes (25 nm). In this study, we showcase ellipsometric porosimetry (EP) as an alternative, scalable metrology for model channel hole patterns. The critical dimensions of such features are typically below 100 nm, and thus their diameters can be determined via in situ optical observation of capillary evaporation-driven refractive index changes based on classical thermodynamic principles. We demonstrate that the EP-derived diameters of the model structures correlate well with both the expected values and those obtained from optical critical dimension (OCD) metrology. Since the accuracy of OCD decreases when probing deep into the subwavelength regime (190 nm), EP emerges as a complementary metrology candidate, as its highest accuracy is typically for feature sizes of 1–25 nm. The method presented here can also be extended to more complex anisotropic structures.
Füredi et al. (2026) studied this question.