Laser-Induced Formation of Thin TiO 2 Films from TiC1 4 and Oxygen an a Silicon Surface.
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LASER-INDUCED FORMATION ON A SILICON SURFACE.
OF
THIN TiO2
FILMS
FROM
TiC1 4
AND
OXYGEN
Tomoji KAWAI, Takahiro CHODA and Shichio KAWAI The Institute of Scientific and Industrial Research, Osaka University Mihogaoka, Ibaraki, Osaka 567 Japan
ABSTRACT A uniform thin TiO film with the rutile structure which is usually made at higher than 70Rt, can be formed at room temperature by the laser irradiation of adsorbed TiCl 4 followed by oxidation and repeated cycles of this procedure on a silicon(lO0) single crystal surface. The laser irradiation to gaseous mixture of TiCl 4 and oxygen from the direction parallel or perpendicular to the substrate, on the other hand, leads to the formation of a TiO 2 film consisting of amorphous fine particles. The mechanism of the film formation is briefly discussed.
I.
INTRODUCTION
Laser-Chemical Vapor Deposition (LCVD) has been recognized as a useful method for preparing a thin film at low temperature.[l] The advantages of LCVD over the traditional thermal CVD are that spatially controlled deposition is possible with a highly accurate deposition period at low temperatures utilizing photon energy. Furthermore, a particular set of chemical species could be selected to form a desired film by a selective photochemical reaction. The variety of parameters that control the deposition in LCVD is also an attractive feature for the fabrication of functional thin films. There have been many studies of LCVD to form metal, semiconductor and insulator films.[2) We report here the formation of thin TiO films with excimer laser excitation of gaseous TiCl 4 and oxygen or adsorbed TiCl 4 on the Si surface followed by oxidation. TiO2 films are attracting attentions as a typical inorganic thin film which can be used for optical or electronic devices because of its large dielectric constant. The purpose of this study is first to investigate the low temperature formation of the uniform Ti0 2 film taking advantage of light energy. The second purpose is to clarify the differences of the effect of gas phase excitation, adsorbate excitation and substrate excitation on the film formation, since LCVD generally involves the processes of excitation of gaseous species, adsorbed species and/or substrates. It was revealed in this work that a uniform thin TiO 2 film with rutile structure which is usually made at higher than 700°C can be formed at room temperature taking advantage of the laser-induced reaction of adsorbed TiC1 4 with oxygen and the repeated cycles of this procedure on a silicon(lO0) single crystal surface. On the other hand, the laser irradiation of gaseous mixture of TiC1 4 and oxygen led to the formation of a TiO 2 film consisting of amorphous fine particles.
Mat. Res. Soc. Symp. Proc. Vol. 75. c 1987 Materials Research Society
290
II. EXPERIMENTAL II-1. Film formation TiO2 films were formed on a silicon(100) single crystal surface. The substra~e surface was etched with 10% HF solution for two minutes, followed by washing in water and drying in vacuum for 30 minutes. The surface was then
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