Methods of deducing oxide thickness using calculated and measured scattering spectra are provided. Embodiments include depositing an oxide over a semiconductor wafer, reducing the oxide from a portion of the semiconductor wafer, and deducing a thickness of oxide remaining at a location within the portion using scatterometric metrology. Embodiments further include deducing the thickness by: calculating scattering spectra for a plurality of oxide thicknesses, producing calculated scattering spectra, monitoring scattering spectra at the location within the portion of the semiconductor wafer, comparing the monitored scattering spectra at the location to the calculated scattering spectra, determining a closest matching calculated scattering spectra to the monitored scattering spectra at the location, and obtaining an oxide thickness corresponding to the closest matching calculated scattering spectra.