SiO 2 Film Coatings with VUV Excimer Lamp CVD
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Dept. of E&E Eng., University of Miyazaki, Miyazaki 889-2192, Japan Phone: +81 985 572811; Fax: +81 985 581672; E-mail: [email protected] ABSTRACT Silica film coatings were demonstrated using photo-chemical vapor deposition with a 172-nm Xe excimer lamp. Tetraethoxyorthosilicate (TEOS) molecules were successfully dissociated into SiO 2+2C 2H 5-OH+(residual C and H) with the 7.2-eV photons. The films were deposited onto a quartz or A120 3 single crystal substrate with the deposition rate of 1 nm/min. The films were uniform and smooth enough for optical applications. INTRODUCTION According to an advent of high power lasers, they have become indispensable tools to a wide field of materials processings. In particular, short-wavelength lasers have attractive characteristics for materials processings such as large absorption coefficients and high-density deposition within several ns duration, and thus they have been succeeded in preparing high-melting points materials and superlatives with an advantage of the precise thickness-control [1-4]. There are, however, some problems to be overcome such as temperature rise inducing undesirable damages on substrates and pre-deposited materials and occurrence of debris. Under such situations, rare gas excimer lamps using dielectric barrier discharge, that are very compact and have a high-efficiency, have become an attractive light-source of high-energy photons in the wavelength region difficult for laser oscillation [5-8]. Furthermore, uniform processings over a large area without thermal damages and speckling or interference fringes are possibly expected [9-11], because the excimer lamp outputs are intrinsically incoherent and quasi-continuous radiation. In this paper, we propose a new technique of materials processings by using incoherent excimer lamps, and show some results when they are tried to prepare silica thin films. A xenon excimer lamp emits incoherent radiation at 172-nm wavelength, 7.2-eV photon energy, which surmount bonding energies of many kinds of chemical bonds such as C-H (4.3 eV), C-O (3.9 eV), C=C (6.4 eV) and C=N (6.7 eV). In a molecule of tetraethoxyorthosilicate (Si(OC 2H5) 4 : TEOS), all of bonds besides Si-O (-9.0 eV) must be broken with 7.2-eV photons. Silica films are prepared base on this ides and we will show some optical characteristics of the films.
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Mat. Res. Soc. Symp. Proc. Vol. 555 01999 Materials Research Society
EXCIMER LAMPS Rare gas excimers are generated
Transparent
by dielectric barrier discharge or silent discharge. In Fig. l(a) is illustrated a
typical barrier discharge configuration.
Dichrg Gs
In most cases, the gas mixture is hermetically sealed in a quartz envelope.
HV Generator
Typical filling pressures are of the order of 1 bar. AC voltage of a few kV is
Dielectric Barrier
Transparent
(a)
Electrode
applied to the electrodes and ignites the discharge. The dielectric barrier discharges consist of a large number of micro-discharges with nanosecond duration. Typical 3 plasma parameters are _10-4 cm" electron
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