Real-Time Evolution of the Indium Tin Oxide Film Properties and Structure During Annealing in Vacuum

Indium tin oxide (ITO) is widely applied as a transparent conductive oxide coating. A standard and successful industrial route of production is its deposition by magnetron sputtering from a compound (oxide) target [1]. To increase cost efficiency, it would be preferable to sputter reactively from a metal target at sufficiently high partial pressure of oxygen. However, under this condition, a satisfactorily low resistivity of the films cannot readily be obtained, [2] so that a deposition on heated substrates or post-deposition annealing is necessary. So far, the annealing processes for reactively sputtered ITO [3,4] have only been studied for metal-rich films, in contrast to comprehensive studies after magnetron sputtering from ceramic targets [5-10]. Moreover, mainly isothermal heat treatment is considered in the literature, although annealing using a temperature ramp is of more relevance for practical application. Several investigations report on real-time in situ monitoring of the ITO film resistivity and reflectivity [9,10], which is used for an indirect characterization of the crystalline structure of the films. This approach requires simplifying assumptions on the linear dependence of the resistivity or reflectivity on the crystalline fraction, and the stability of the film roughness during annealing. Direct investigations of the influence of heat treatment on the ITO film structure are so far limited to post-annealing studies by X-ray diffraction (XRD) and scanning or transmission electron microscopy [3-5,7,8,11].