Nanometer-scale crystallinity in In–Ga–Zn-oxide thin film deposited at room temperature observed by nanobeam electron diffraction

Abstract

We report a detailed analysis of the nanoscopic structure of an In–Ga–Zn-oxide (IGZO) thin film deposited at room temperature. Using nanobeam electron diffraction (NBED) with a 1-nm-diameter probe, we analyzed a nanoscopic region of the IGZO thin film in which the diffraction spots of crystal were unobservable in a macroscopic region using selected-area electron diffraction (SAED) with about 300-nm-diameter probe. However, they were clearly recognized in a NBED pattern. They indicate a minute crystalline structure in the film. We further confirm the presence of crystals by observing a NBED pattern with spots distributed with six-fold symmetry in a specimen thickness thinned down to10 nm. To check the effect of the electron-beam irradiation during a transmission electron microscopy (TEM) and NBED measurements, we examine changes in crystal size as a function of the cumulative electron dose. No crystal growth during the electron beam irradiation was observed in the film. These results allow us to conclude that the IGZO thin film is not amorphous but a nanocrystalline (nc)-IGZO thin film, composed of nanometer-size crystals.