Immersion Scatterometry for Nanoscale Grating Topography Extraction.

Abstract

The objective of optical scatterometry is to determine the geometrical parameters of a periodic structure, such as a surface-relief grating, from its ellipsometric spectrum. There is particular interest in applying this technique to semiconductor metrology, where it can be used for wafer-to-wafer process monitoring and control of lithographic and etching processes.

In this thesis, immersion scatterometry is investigated to improve feature resolution for nanoscale surface-relief gratings. Improved resolution may come in the form of reduced uncertainty in estimated parameters, or reconstruction of previously unresolved features. The rationale behind immersion scatterometry is that increasing the ambient refractive index reduces the effective wavelength, which means that scattered modes that are evanescent in atmosphere may be propagating modes in the immersion case. Additional propagating reflected modes create the potential for more features in the specular-mode ellipsometric spectrum, which can convey additional information about the sample under investigation.

Initial experimental results for immersion ellipsometry and topography extraction of gratings are reported. Potential sources of systematic error in immersion ellipsometry are investigated. The effects of these error sources are quantified, and mitigation strategies are evaluated. These strategies should also aid in reducing errors in other applications of immersion ellipsometry, including electrochemistry, biology, and medicine.