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Nanocrystalline silicon (nc-Si) film thin film transistor (TFT) may be a promising device for various application including flat panel display due to rather simple process compared with poly-Si TFT and better performance compared with a-Si TFT. Conventional plasma enhanced chemical vapor deposition (PECVD) method has been widely reported to deposit nc-Si film. It is known that inductively coupled plasma (ICP) mode can generate high density plasma[1-2], so that ICP-CVD may also provide a certain advantages such as high deposition rate and improved crystallinity over PECVD. The purpose of our work is to report nc-Si film fabricated by (ICP-CVD) suitable for ultra low temperature TFTs which can be applied to flexible eletronics. The flexible electronic devices may have certain merits compared with the present rigid one. For flexible displays, it is inevitable to limit the process temperature to avoid deforming substrates like plastics. We deposited nc-Si film by ICP-CVD at 150 o C. ICP power was 400W. The process gas was SiH4 diluted with He as well as H2 and He/H2 mixture. The flow rate of He, H2 was varied from 20 sccm to 60 sccm and that of SiH4 was 3sccm. The crystalline volume fractions evaluated from the Raman spectrum of the nc-Si film were above 70%. X-ray diffraction (XRD) patterns of the nc-Si films were measured. From the the XRD measurements results of nc-Si films deposited by ICP-CVD, the properties of Si film deposited under each condition were studied. The XRD spectra of Si films with 30nm, 50nm and 100nm thickness were shown in Fig. 1. Fig . 1 (a), (b) and (c) show the graphs of Si film prepared at He:SiH4=40:3, He:H2:SiH4=20:20:3 and H2:SiH4=40:3, respectively. In Fig. 1 (a), there is no (2θ=28 o ) and (2θ=47 o ) peak when the thickness of Si film is 30nm. As the thickness increased over 50nm, significant peaks were detected. On the other hand, in the case of He/H2 dilution, the and peaks were observed at thickness of 30nm and the peaks increased highly at thickness of 50nm, 100nm as shown in Fig. 5 (b). However, in the case of H2 dilution in Fig. 5(c), the peak was first detected at the thickness of 100nm. This means the nucleation of this Si film is carried out slowly and the incubation layer can be thick. The fast grain growth in Fig. 5 (b) may be attributed to the effect of combination of He dilution and H2 dilution. He dilution is believed to reduce the energy barrier for substrate reaction and to increase thermal conductivity at the |
