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Proceedings Paper

Frenkel defect process in amorphous silica
Author(s): Koichi Kajihara; Masahiro Hirano; Linards Skuja; Hideo Hosono
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Paper Abstract

Point defects strongly influence optical properties of synthetic amorphous silica (synthetic a-SiO2) used in excimer laser photolithography and their properties are intensively studied. Decomposition of an Si-O-Si bond into a pair of oxygen vacancy and interstitial oxygen species is an intrinsic defect process in a-SiO2. It is similar to the creation of vacancy-interstitial pairs in crystalline materials and is regarded as "Frenkel defect process" in an amorphous material. Oxygens are also known to be emitted from a-SiO2 surfaces under irradiation with vacuumultraviolet (VUV) light or electron beam. However, the anion part of the Frenkel pair in a-SiO2, interstitial oxygen atom, lacks reliable spectroscopic signatures. Therefore, Frenkel process has been studied much less than another intrinsic defect process in a-SiO2, a simple cleavage of an Si-O bond, yielding a pair of silicon and oxygen dangling bonds. Interstitial oxygen molecule (O2), a common form of the interstitial oxygen species in a-SiO2, exhibits characteristic infrared photoluminescence (PL) at 1272 nm. This PL band allows interstitial O2 to be detected selectively with a high sensitivity, and is useful in studying Frenkel defect processes in both a-SiO2 and crystalline SiO2. The Frenkel process is dominant over the formation of the dangling bond pairs in highpurity synthetic a-SiO2. Both these processes are influenced by the degree of the structural disorder of a-SiO2characterized by distribution of Si-O-Si angles. Fluorine doping promotes the structural relaxation and is useful in decreasing the concentration of "strained" Si-O-Si bonds, which have Si-O-Si bond angles widely different from the relaxed angle and are vulnerable to radiation. Moderate fluorine doping is effective in improving both UV-VUV transparency and radiation hardness, whereas heavy fluorine doping tends to enhance defect processes involving the Frenkel mechanism and to degrade the radiation hardness.

Paper Details

Date Published: 18 May 2011
PDF: 12 pages
Proc. SPIE 8077, Damage to VUV, EUV, and X-ray Optics III, 80770R (18 May 2011); doi: 10.1117/12.886698
Show Author Affiliations
Koichi Kajihara, Tokyo Metropolitan Univ. (Japan)
Masahiro Hirano, Tokyo Institute of Technology (Japan)
Linards Skuja, Univ. of Latvia (Latvia)
Hideo Hosono, Tokyo Institute of Technology (Japan)

Published in SPIE Proceedings Vol. 8077:
Damage to VUV, EUV, and X-ray Optics III
Libor Juha; Saša Bajt; Richard A. London, Editor(s)

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