Physical Behavior of Fluorine Atoms in the Fabricated Transparent SiO 2 Thin Film at Room Temperature

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H.lizuka, M.Murahara Faculty of Electrical Engineering, Tokai University 1117 Kitakaname, Hiratuka, Kanagawa, 259-1292, Japan

Abstract This paper describe the growth of a transparent SiO 2 thin film performed by using Xe 2" excimer lamp at room temperature. In this study, NF., and 02 mixture gases was employed as a reaction gas. A silicon substrate was placed in a reaction chamber, which was filled with NF3 and 02 mixture gases. The mixture gases were exposed to the Xe 2 " excimer lamplight, and SiF 4 and NO 2 gases were produced by photochemical reaction. Subsequently SiF 4 adsorbed onto the Si substrate. SiO2 was formed by oxidation reaction between SiF,, and NO 2. These processes occur spontaneously, and SiO 2 film is grown. The refractive index of fabrication SiO 2 thin film is 1.32. By annealing at 200'C, the refractive index of this filn was increased to 1.44. Further increase in the annealing temperature, resulted in a higher refractive index and lower density of fluorine atoms.

Introduction Silicon dioxide films are generally fabricated by a high temperature oxidation of a silicon wafer. The high temperature processing, however, has many disadvantages such as dopant diffusion and thermal stress in the films. To solve these problems, a low temperature process is required. There are many reports on silicon dioxide deposition by the Photochemical Vapor Deposition (photo CVD) or Plasma CVD at low temperatures [1,2]. However, these processes require a heat treatment of approximately 500 degrees. One of a few techniques to fabricate thin films at low temperature, atomic layer epitaxy (ALE) has been reported [3-6]. We investigated a new method for a fabrication of Si0 2 thin film at room temperature with irradiation of Xe 2" excimer lamplight [7-10]. In this method, NF. and 02 gas mixtures are employed as a reaction gases. These gases were photodissociated by irradiation of Vacuum Ultra Violet (VUV) light, to form SiF 4 and NO 2 gases. SiF 4 gas is highly unstable, but this method can produce an amply amount of SiF 4 gas for the growth of SiO 2 film. Thus, by repeating SiF 4 adsorption and oxidization reaction with NO 2, the SiO 2 thin layer was spontaneously grown on the substrate. This reaction mechanism was investigated by using Fourier Transform InfraRed (FT-IR) and Vacuum Ultra-Violet (VUV) spectroscopes. Moreover, the fabricated Si0 2 film thickness, refractive index, a composite and a dielectric constant characteristic were measured to evaluate the characteristics of the formed Si0 2 film.

283 Mat. Res. Soc. Symp. Proc. Vol. 555 01999 Materials Research Society

Photochemical reaction A substrate was placed in a reaction chamber, which was filled with SiF 4 gas, when the SiF4 absorbed about 10A thickness on the substrate. Objects of this work that have formed Si0 2 film oxidized the absorbed SiF 4 mono layer. The Si substrate was placed in a reaction chamber, where SiF4 and NO 2 gases were sealed in. The SiF 4 gas absorbed at a silicon surface. This absorbed SiF 4 was occurred the oxidized reaction with

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