Effect of Ion Energy on Structural and Chemical Properties of Tin Oxide Film in Reactive Ion-Assisted Deposition (R-Iad)
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ABSTRACT Tin oxide films were deposited on in-situ heated Si (100)substrates using reactive ionassisted deposition and the effect of average impinging energy of oxygen ions on the crystalline structure and the stoichiometry of deposited films were examined. The transformation from SnO phase to Sn0 2 phase of the films was dependent on the change of the average impinging energy of oxygen ion (Ea), and the relative arrival ratio of oxygen to tin. Perfect oxidation of Sn0 2 was performed at Ea = 100, 125 eV/atom at as low as 400 A substrate temperature. The composition (No/Nsn) of films increased from 1.21 to 1.89, and was closely related to the average impinging energy of oxygen ion. The surface morphology of the films was also investigated by scanning electron microscopy. INTRODUCTION Sn0 2 films are widely used in a variety of application such as opto-electronic devices, solar-cells, antireflection coatings and gas sensors [1-4]. Several methods, e.g. reactive evaporation [5], chemical vapor deposition [6] and sputtering [7], each with its own advantages and disadvantages, have been employed to obtain Sn0 2 films. Chemical vapor deposition(CVD) processing of tin oxide films is, although inexpensive, being substituted by physical vapor deposition(PVD) processing which is more controllable and needs lower processing temperature, leading to thin films of better purity and outstanding optical and electrical properties. Although many reports have been published on the preparation of SnO2 films by traditional PVD techniques, no one has successfully deposited pure SnO2 films without a post annealing treatment at higher than 550 °C in oxygen ambient or air. Generally, in the case of evaporation or sputtering using Sn0 2 as evaporant or sputtering target, the SnOz phase decomposes in gaseous state and mainly SnO phase condenses onto the substrate. These films have to be oxidized to SnO 2 subsequently by post annealing treatment in oxygen ambient or air at temperatures higher than 550 1C [5,7]. Recently many thin films including dielectric oxides, fluorides, transparent conductors and nitrides have been grown successfully by ion-assist deposition [8-10], however, there have been few reports about deposition of SnO 2 films using this deposition method. This ion based-deposition technique has many benefits such as an elaborate control of film properties including composition and structure, an enhanced adhesion between film and substrate, and a reduction of substrate temperature for crystallization of films, etc. [11]. In particular, a major advantage of the ion-assisted deposition is that ion energy and ion flux are decoupled, allowing for independent variation of either parameter. Thus the stoichiometry of films is easily controlled by varing ion flux, and additional energy added to the growing film by bombardment with energetic ions during the deposition results in lower minimum substrate 313 Mat. Res. Soc. Symp. Proc. Vol. 504 ©1998 Materials Research Society
temperature for thin film formation. In this paper, reactive io
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