Photochemical Lamination of Low Refractive Index Transparent SiO 2 Film at Room Temperature for Antireflection Coating
- PDF / 283,310 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 75 Downloads / 249 Views
Y5.5.1
PHOTOCHEMICAL LAMINATION OF LOW REFRACTIVE INDEX TRANSPARENT SiO2 FILM AT ROOM TEMPERATURE FOR ANTIREFLECTION COATING Y. Ogawa and M. Murahara Department of Electrical Engineering, Tokai University 1117 Kitakaname, Hiratsuka-shi, Kanagawa 259-12, Japan ABSTRACT A transparent low refractive index SiO 2 film laminated on a glass substrate at room temperature by photochemical reactions with the Xe2 * excimer lamp (172nm). This SiO 2 film grown on the fused silica glass was proved to avoid reflection of light. A refractive index of the SiO 2 film was 1.36. After annealing the film for one hour at 200 degrees centigrade, the refractive index increased to 1.42. The refractive index increased as the F atom density in the SiO 2 film decreased. INTRODUCTION Low refractive index films such as MgF 2 film and TiO 2 film have been widely used for antireflection coating and clad materials for optical fibers. In addition to them, the SiO 2 film, which was doped the fluorine atom or boron atom, was used as antireflection coating for silica glasses. Kawamata of Olympus Optical Co. has fabricated the MgF 2 film by the sputtering method using the MgF 2 target in the presence of O2 gas [1]. This method, however, employed the different material from the glass substrate. In addition, Miyajima of Toshiba Co. has fabricated the fluorine atom doped SiO 2 film at 400 degrees centigrade substrate temperature by PE-CVD (plasma-enhanced chemical vapor deposition) method in the presence of tetraethylorthosilicate (TEOS), O2 and CF4 mixed gases [2]. Yoo of Novellus Systems Inc. has also fabricated the fluorine atom doped SiO 2 film at from 300 to 400 degrees centigrade substrate temperature by PE-CVD method in the presence of TEOS, O2 and CF4 mixed gases [3]. However, neither the Miyajima’s study report nor Yoo’s did refer to transparency. We have successfully fabricated a transparent and low refractive index SiO 2 film at room temperature by using Xe2 * excimer lamp [4-8]. In this paper, we reported on the new method, in which the deposition rate was enhanced with cooling the substrate.
Y5.5.2
PRINCIPLE OF SiO2 FILM LAMINATION The Xe2 * excimer lamp light was irradiated to the NF3 and O2 mixed gases in which a glass substrate and a piece of Si wafer were placed. The wavelength of the lamp is 172nm, and the photon energy is 166.1 kcal/mol. The binding energies of NF3 and O2 are 69 kcal/mol and 119.1 kcal/mol, respectively. Since the NF3 gas and the O2 gas have a strong absorption band in the wavelength of 172nm(Fig.1), they were photo-dissociated to produce F radicals and NO2 . The F radicals etched the surface of the Si wafer, producing SiF 4 , which was adsorbed on the glass substrate surface to produce one molecular layer of SiF 4 . The SiF 4 layer was then oxidized with the NO2 to grow one molecular layer of SiO 2 . By the adsorption of SiF 4 and oxidized reaction with NO2 , the SiO 2 film was automatically laminated on the glass substrate. Then, the fluorine atoms were doped in the SiO 2 film because the SiF 4 , which did not reac
Data Loading...
