Abstract
To overcome the difficulty in measuring the extremely slow erosion of transparent silica, we apply spectroscopic ellipsometry (SE) optical critical dimension measurements on a subwavelength surface relief grating instead of a blank silica substrate. By analyzing the nano-grating SE spectra, we find that the H2SO4-H2O2 Piranha cleaning widely used for organic contaminants removal also etches silica slowly—up to a molecular monolayer is partially removed from the silica surface by each cleaning cycle. Based on these findings, we conclude that silica dissolution is an important factor to be considered in applications such as template cleaning in nanoimprint lithography.
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