Annealing Effects of Indium-Tin Oxide Films Produced by Atmospheric RF Plasma Deposition Technique
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ABSTRACT Thin-films of indium-tin oxide (ITO) on soda-lime-silicate (SLS) glass were fabricated using an atmospheric RF plasma mist deposition process. Some of the films were deposited at substrate temperatures between 400 C and 500 C, and were subsequently annealed at 400 C and 530 C for 1 hour. Conductivity was improved due to post-annealing. Film thickness, particle size, film morphology and crystallite size were characterized. The structural changes on the glass and the ITO film were investigated by DRIFT spectroscopy. INTRODUCTION Oxide films are usually deposited to achieve the desired electrical, mechanical and optical properties by various techniques. Most deposition techniques require vacuum systems for film quality. However, such requirements will limit the size and production rate. Recently, we developed an RF plasma mist deposition process in atmosphere that may be applied to large scale applications [1]. Conductive and transparent indium-tin oxide (ITO) thin films have many applications, including flat panel liquid crystals, conductive filters and electrochromic windows, etc. Our previous results have shown that the resistivity of plasma fabricated films varies with In/Sn ratio, and the minimum resistivity is of approximately 0.1 0-cm at 10% Sn [2]. As compared to other vacuum deposition films, resistivity from the plasma deposited film is relatively higher. In this paper, a post-annealing step is added to reduce the resistivity of the plasma fabricated films. EXPERIMENT The RF plasma process consists of the following systems; material assembly, plasma reactor chamber, and the substrate assembly, as shown in Figure 1. The ITO mist formed by ultrasonic nebulizer enters the torch where it is subjected to the plasma field, and is vaporized. The vaporized material travels through the plasma field, into the flame, and is deposited on the substrates. ITO film was deposited onto soda-lime-silicate glass (SLS) with substrate temperatures of 400 C and 500 C (+/- 20 C). Starting solutions were indium nitrate, and tin tetra-chloride, at 75 g/L concentrations. Controlled deposition rate produces a desired thickness of 300-500 nm. Heat treatments were done on the substrates in an argon atmosphere environment at 400 C and 530 C for 1 hour. Film thickness and particle sizes were calculated by using the NIH imaging program. Resistivity measurements were done from a 4-point resistance system. Crystallite sizes were found from XRD data by SHADOW program. The structural changes on glass and ITO film were investigated with a Nicolet 60 SXR FT-IR spectrometer equipped with a Spectra Tech DRIFT (diffuse reflectance infrared Fourier transform) cell. 429 Mat. Res. Soc. Symp. Proc. Vol. 403 01996 Materials Research Society
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