From “White Ribbon” to “Black Belt”: A Direct Observation of the Kooi Effect Masking Film by Transmission Electron Microscopy

A black micromasking film at the edge of bird’s beak along the localized oxidation of silicon edge is observed for the first time. It looks like an “eyelash” in the cross-sectional transmission electron microscope (XTEM) images and like a “black belt” in the top view TEM images. The defects responsible for the “white ribbon” in the “Kooi effect” are observed in the first few seconds of high resolution TEM before they are vaporized. These defects are shown to be a nonstoichiometric silicon oxynitride compound because they are not eliminated by etching with hot phosphoric acid.