Growth of Tin Oxide Film Deposited by a Hybrjd Ion Beam
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Partially ionized beam(PIB)[5] has many advantages such as low temperature film growth, fast nucleation of material on substrate, and smooth surface of the films, etc. with controlling particles' energy instead of substrate temperature. Moreover, PIB has some difference with other ion-based film formation processes in the deposition of energetic materials itself which can be adjusted by ionization potential and acceleration energy during the deposition, and crystallographic structure, composition, and properties of the depositing films could be optimized by control of ionization values. [6,71 By using this technique, many high quality oxide films such as TiO2 on Si[6], A120 3 on sapphire[7], optical films, etc. have been fabricated. In this study, we deposited nonstoichiometric/stoichiometric undoped tin oxide thin films by the hybrid ion beam system which was composed of a partially ionized metal beam and a cold hollow cathode gas ion beam. The PIB source was used for Sn metal evaporation and the gas ion beam was applied for assisting ionized oxygen, respectively. EXPERIMENTAL The metal ion source can be divided into mainly three parts like other P1B source[5,8]:Generating part of metal particles, an ionizer, and an acceleration electrode. Vaporized metal particles from the carbon crucible by electron bombardment heating were ejected through small nozzle(1 mm(4)) x 1 mm(L)) and then partially ionized by electron impact in the 611
Mat. Res. Soc. Symp. Proc. Vol. 396 * 1996 Materials Research Society
ionization region and subsequently accelerated to the substrate with various acceleration voltages(Va). The PIB source was described in detail previously. [8] A 5 cm gridded cold hollow gas ion source were served to assist ionized oxygen during Sn metal evaporation. Deposition was carried out in two different ways:The first method, tin metal was evaporated at various acceleration voltages of 0 - 4 kV by the PIB and concurrently reactive oxygen gas(99.995+ %) was blown near the Si(100) substrate with the size of 1 cm x 1 cm by a ring-type nozzle gas feeder. The other method, instead of flowing neutral oxygen gas, ionized oxygen was assisted by the gas ion source during the deposition of Sn metal. Within the ejection angle of ± 6 - 8 ° at a distance of 45 cm from each source, the ion beam current density showed over 50 % uniformity of the maximum value for the PIB metal ion source and 90 % uniformity for a gas ion gun, respectively, and therefore at these conditions tin oxide thin films could be homogeneously deposited by using the hybrid ion beam. The base pressure of the reaction chamber was 1 X 10-6 Torr and deposition was carried out at 2 x 10-4 Torr. Crystalline structure and composition of deposited tin oxide films were investigated through x-ray diffraction(XRD;Phillips), Auger electron spectroscopy(AES;PHI 670) and x-ray photoelectron spectroscopy(XPS; Surface Science Instruments 2803-S spectrometer, Al ka xray (hv=1486.6 eV)). Atomic force microscope(AFM; Park Scientific Instrument) studies were carried out to
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