Chemical Vapor Deposition of Antimony‐Doped Tin Oxide Films Formed from Dibutyl Tin Diacetate

Abstract

A CVD process for the preparation of transparent conducting layers of antimony-doped tin oxide has been developed utilizing dibutyl tin diacetate, antimony pentachloride, O2, H20, and N~ as carrier gas at a substrate temperature of 400~176It was designed to fulfill a need for more highly conducting coatings than those obtainable without doping, in the sheet resistance range 50-100 ohm/square, but still possessing an optical transmission in excess of 80% throughout the visible spectrum. Coatings to this specification are used extensively for a variety of electro-optic devices. A set of optimized deposition conditions is presented together with important optical, electrical, structural, and chemical properties of the films. Typical SnO2: Sb films have film thicknesses ranging from 1500-3600A with a sheet resistance of 50-150 ohm/ square, a specific resistivity of 0.0015-0.0032 ohm-cm, an n-type carrier concentration of 1.2 • 1020 cm -3, and a Hall mobility of 23 cm2/V-sec. They exhibit a light transmission of 85-91% net, and have an optimum dopant concentration within the range of 0.6-2.7 atomic per cent of antimony. The films are free of volatile chlorine, are chemically inert, and may be heated in air for prolonged periods without noticeable deterioration. Samples on sapphire substrates were heated in air to 1000~ for several hours without change in the sheet resistance.Transparent, electrically conducting thin films are required in many modern opto-electronic devices. Numerous materials, prepared by a variety of physical and chemical techniques (1,2), have been reported but in practice only two materials, tin oxide doped with antimony and indium oxide doped with tin, are widely used. Antimony-doped tin oxide coatings are conventionally prepared by spray hydrolysis of tin tetrachloride-antimony chloride mixtures (1-16), but for the high quality coatings required in electronic devices more sophisticated deposition techniques are needed. Sputtering techniques (1, 2, 17-20) have been used with better success. Chemical vapor deposition (21-22) could offer economic advantages of lower equipment cost and simpler processing.A chemical vapor deposition process for the preparation of transparent conducting coatings of nonstoichiometric tin oxide has been described in a previous paper (22). The subject of the present investigation is an important modification of this basic process by which a controlled quantity of an antimony dopant, which greatly increases the conductivity of the film, is introduced into the tin oxide. A full description of the apparatus and the proposed advantages of the CVD technique over spray hydrolysis were presented in the previous paper (22). Also given were extensive literature references on undoped tin oxide films; references in the present paper are therefore confined essentially to antimony-doped tin oxide films.In addition to lower conductivity, a second disadvantage of the undoped tin oxide is that it is nonstoichiometric and is therefore only a metastable phase. If it is subjected to any hig...

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