Crystallinity Analysis of Amorphous-Crystalline Mixed Phase Silicon Films Using EXAFS Method
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CRYSTALLINITY ANALYSIS OF AMORPHOUS-CRYSTALLINE MIXED PHASE SILICON FILMS USING EXAFS METHOD
Masatoshi Wakagi*, Toshiki Kaneko*, Kiyoshi Ogata** and Asao Nakano** *Hitachi Research Laboratory, Hitachi Ltd., 4026 Kuji-cho, Hitachi-shi, 319-12 Japan. "Production Engineering Research Laboratory, Hitachi Ltd., 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, 244 Japan. ABSTRACT
The crystalline phase fraction (Xc) of amorphous-crystalline mixed phase Si films prepared by thermal annealing of a-Si:H films and by plasma CVD and chemical annealing methods was investigated by the EXAFS method. The EXAFS spectra of these films were represented by linear-combination of a-Si:H and c-Si EXAFS spectra. The values of Xc were analyzed by least-square curve fitting. The crystallinity was also analyzed by a Raman scattering method measured from both sides of the films. Then, the Xc values analyzed by the Raman method were calibrated by the EXAFS analysis results. INTRODUCTION
Amorphous-crystalline mixed phase Si materials, including microcrystalline Si (Igc-Si), have attracted much attention in the past few years for their application to solar cells,' thin film transistors 2 and other devices. For characterization of these materials, it is important to determine the crystalline phase fraction. Raman scattering methods are widely used for this analysis. However, uncertainty of Raman scattering cross section of amorphous and crystalline phases cause difficulties for estimation of the absolute value. Extended X-ray Absorption Fine Structure (EXAFS) reflects the short range order of network structure can be used to analyze amorphous phases as well as crystalline phases. Therefore, the crystallinity of amorphous-crystalline mixed phase can be analyzed by the EXAFS method. The crystallinity of evaporated Ge films has. been investigated from the3 second- and third-nearest neighbor peak height in EXAFS radial distribution functions. However, the crystalline phase fraction was not determined quantitatively by this method. As opposed to the Raman scattering cross sections, X-ray absorption cross sections for amorphous and crystalline phases are identical when their compositions are same. These characteristics can be utilized for determination of the crystalline phase fraction of amorphouscrystalline mixed phase materials. In this paper, a new EXAFS method for quantitative analysis of the crystalline phase fraction is presented. The crystalline phase fraction was analyzed for amorphous-crystalline mixed phase Si films prepared by thermal annealing of aSi:H films and by plasma CVD and chemical annealing (CA)4 deposition methods. Furthermore, TO mode Raman scattering analysis for crystalline phase fraction was examined and compared with the EXAFS analysis results. EXPERIMENTAL
Hydrogenated amorphous Si (a-Si:H) films were prepared by a conventional plasma CVD (PCVD) method using SiH4 and H2 gases. The SiH4 gas portion to the total gas flow (PSiH4) was 0.6. The films with thickness of 21tm were deposited on 10itm thick Be foil. The sarmples were an
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