Epitaxy-Like Growth of Polycrystalline Silicon on the Seed Crystallites Grown on Glass
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GROWTH OF POLYCRYSTALLINE SILICON ON THE SEED CRYSTALLITES GROWN ON GLASS
Y.Miyamoto, A. Miida and I. Shimizu, The Graduate School, 4259 Nagatsuta, Midori-ku, Yokohama, Japan 226 ABSTRACT Polycrystalline silicon thin films were grown on glass by two-steps, i.e., deposition of seeds on glass (1) and growth epitaxy-like on the seeds (2). For the growth of seeds, the surface reaction was intentionally enhanced by impingment of atomic hydrogen at rather high temperature (450 C). Strongly textured polycrystalline Si exhibiting (220) preferential orientation was grown epitaxy-like on the seeds. INTRODUCTION
In recent years, the thin film solar cells made of microcrystalline (pc-) silicon have become a current topic because of the excellent stability for light soaking and rather high energy conversion efficiency as high as 8 % or more. [1], [2] High quality polycrystalline(poly-) silicon thin films have been fabricated as well by Plasma Enhanced (PE-) CVD or Hot Wire techniques in an analogous manner to the fabrication of gc-Si. [3], [4] However, these thin films grown at rather low temperature are characterized by a structure that depends strongly on the thickness since the chemical reactions on the growing surface are ruled greatly by the topology of the surface. [5] In particular, it is quite difficult to make a crystalline film in the vicinity of the glass substrate. In this study, we attempted to grow poly-Si thin films from fluorinated precursors (SiFmH,: n+m=3) on glass substrates by the two steps, i.e., the deposition of seeds on glass (1) and the growth epitaxy-like on the seeds (1).
EXPERIMENT A remote type PE-CVD apparatus was used to grow the poly-Si from a gaseous mixture of SiF4 and H2 as described elsewhere. [3] A spectroscopic ellipsometer (SE) (Jovin Yvon) was equipped on the reactor for in situ real time monitoring of the growing surface. For the growth of seeds on glass, the deposition of a very thin layer (4 nm thick) and the treatment with atomic hydrogen were alternately repeated to enhance the crystallization (Layer-bylayer (LBL-) technique. [3] The structures of the films were evaluated from the measurements of SE, XRD, Raman and RHEED. The measurements of the depth proffiles of impurities 995 Mat. Res. Soc. Symp. Proc. Vol. 452 ©1997 Materials Research Society
such as F, H and 0 were made by SIMS, which provide information on the structures depending on the thickness. Schottky diodes were fabricated by stacking N-type seed crystals, undoped poly-Si and Pt top electrode deposited in this order on ZnO coated glass. RESULTS AND DISCUSSION Growth of seeds on glass substrate High quality poly-Si thin film consisting of grains (200 nm dia) was made on glass at TS=300 "C by LBL from fluorinated precursors. [3] However, amorphous-rich layer was grown at the vicinity of glass substrate. Some device performances were limited by the properties of these thin layers. Generally speaking, it is quite difficult to make [tc-Si or poly-Si exhibiting an abrupt interface on glass substrate when the films are gro
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