Propagation of Si-Network in Hr-Cvd and Spontaneous Chemical Deposition
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PROPAGATION OF Si-NETWORK IN HR-CVD AND SPONTANEOUS CHEMICAL DEPOSITION JUN-ICHI HANNA*, AKIRA KAMO**, MASANOBU AZUMA**, NAOKI SHIBATA**, HAJIME SHIRAI** AND ISAMU SHIMIZU** Tokyo Institute of Technology Imaging Science and Engineering Laboratory*, Graduate School at Nagatsuta** Nagatsuta Midori-ku Yokohama, 227 Japan ABSTRACT In comparison with the Si:H films the conformational changes in the Si:H(F) networks of the films prepared by HRCVD and Spontaneous Chemical Deposition were investigated systematically in terms of the effects of the substrate temperature and the promoters. Fluorine participation in the chemical processes of the film growth favored the reduction of terminators without degradation of the Si network and promoted the propagation of closely packed Si network, leading to the crystal growth at a low temperature. 1.INTRODUCTION Thin films of a-Si have been established as a large area electronic material, applied to solar cells, electrophotographic drums, TFT arrays for flat panel display devices, image pick-up tubes and so on.') Some of the device performances, however, are not necessarily good enough to replace the counterparts manufactured from the conventional materials which limits the practical application. The improvement in the device qualities requires improvement in the electronic properties of the films such as photoconductivity and hole transport and doping characteristics, in addition to a reduction in the 2 notorious photo-induced effect, i.e., Steabler-Wronski effect. ) In comparison to crystal growth at high temperature, the a-Si is prepared at such a low temperature that the thermal equilibrium cannot be established in the condensation, where the kinetics dominates the growth. Therefore, the structure and properties in the films depend on how they are prepared. We have attacked the problem by recognizing the importance of controlling the Si network structure in the films, which dominates the properties as described above, resulting in a new technique for the preparation of Si thin 3films from 0 fluorides, HR-CVD (Hydrogen Radical Enhanced CVD). )-1 ) The essence of the HR-CVD technique lies in the control of the chemical processes of the film deposition with the 4 aid of atomic hydrogen which is generated by microwave plasma. ) Thus, the HR-CVD not only relaxes the preparation condition for the a-Si:H(F) films from fluorides compared to the conventional rf-glow discharge of the gaseous mixture of SiF4 4 and H2, ) but also provides us several advantages over the conventional method of rf-glow discharge of SiH4 as follows: 1)Controllability of the Si network structures from "amorphous" to "epitaxial growth" at a low temper0 ature less than 300 C.6) 2)High quality films of Si and its related alloys at high deposition rates more than 1OA/sec.5) 3)Non-dispersive hole transport at ambient temperature characterized by Tc of < 300K. 9 ) Mat. Res. Soc. Symp. Proc. Vol. 118. '1988 Materials Research Society
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4)High doping efficiency in microcrystalline films. 6 ) We have recently developed
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