Surface Modification of Sputtered SiO 2 Thin Films by Metal Doping
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Surface Modification of Sputtered SiO2 Thin Films by Metal Doping Satoshi Takeda and Makoto Fukawa Research Center, Asahi Glass Co., Ltd. 1150 Hazawa-cho, Kanagawa-ku, Yokohama 221-8755, Japan ABSTRACT The effects of metal doping on the surface properties of sputtered silicon dioxide (SiO2) thin films were investigated. The aluminum (Al), titanium (Ti) or zirconium (Zr) doped SiO2 thin films were deposited onto glass by RF magnetron sputtering. The optical transmission spectra of the films were almost same as that of undoping film when the doping concentration was lower than ~3 at %. The contact angle of water droplets was measured for the films as a function of elapsed time. The hydrophobicity, resulting from the adsorption of organic substances in the atmosphere, was significantly altered by the metal doping. The surface reactivity of the film with a fluoroalkyl isocyanate silane was also changed. These alternations were due to the difference in surface OH group density of the film, which was induced by the metal doping. These results suggest that the surface properties can be modified by controlling the surface OH group density of the films.
INTRODUCTION Silicon dioxide (SiO2) thin films are widely used in various fields such as passivation layers of electronic devices, protection layers of optical disks, and anti-reflective (AR) coatings of displays because of its excellent chemical stability and optical transmittance with low refractive index [1,2]. To control the surface properties of the film is significantly important because the surface properties of the film may be changed when some organic substances are adsorbed on the film from the atmosphere, causing serious problems for product quality. In previous papers [3,4], we have investigated the relationship between the wettability and the surface OH group density of metal oxide films or commercial glasses, and reported that the surface OH groups play an important role on the surface properties since it can work as effective adsorptive or reactive sites. Furthermore, it has been found that the hydrophobicity, resulting from the adsorption of organic substances in the atmosphere, was different among the films or glasses, and that the origin of the difference was attributed to the difference in the amount of adsorbed carbon substances on the surfaces. The amount of the carbon substances adsorbed from the atmosphere has been dependent on the surface OH group density of the films or glasses. In the present study, we applied these findings to modify the surface properties of sputtered SiO2 thin films. The purpose of this study is to modify the surface properties of the films by controlling the surface OH group density of the films without change in optical properties. Here, the effects of metal doping in the films on the surface OH group density
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were investigated. The aluminum (Al), titanium (Ti) or zirconium (Zr)-doped SiO2 thin film was prepared from a metal-doped silicon target. The relationship between the surface OH group density and the w
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