Effect Of Nickel In Large Grain Poly-Si Film Formed By Nickel Induced Lateral Crystallization and New Grain Enhancement
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Effect Of Nickel In Large Grain Poly-Si Film Formed By Nickel Induced Lateral Crystallization and New Grain Enhancement Method
W.Y. Chan, A.M. Myasnikov, M.C. Poon, C.Y. Yuen, P. G. Han1, M. Chan, P.K. Ko Department of Electrical and Electronic Engineering, Hong Kong University of Science & Technology, Sai Kung, Hong Kong 1 Department of Electronic Engineering, City University of Hong Kong, Kowloon Tung, Hong Kong ABSTRACT Large grain poly-silicon film (poly-Si) with high material quality and uniformity can have numerous novel applications such as providing a low cost alternative to form silicon-on-insulator (SOI) substrates and a breakthrough technology to ultra-dense 3-dimensional multi-layer SOI like devices and circuits. Nickel Induced Lateral Crystallization (NILC) of amorphous Si (a-Si) has been studied intensively, yet the grains are still small (~ 1 µm). Recently, we have reported a novel method by combining NILC and a new annealing (at above 900 ºC) to form poly-Si film with very large grains ranging from 10 µm to 100 µm. The film has good quality and the TFTs formed are highly comparable to SOI TFTs. This work further reports the effect of Ni to the new large-grain poly-Si film.
INTRODUCTION Nickel Induced Lateral Crystallization has been studied as an alternative to solid-phase crystallization (SPC) of amorphous silicon (a-Si) and nickel (Ni) was found to be a very good material for inducing crystallization of a-Si outside its coverage area [1], [2], [3]. The polycrystalline silicon thin film formed by this novel method is largely free of metal contamination, with better crystallinity than those produced by SPC and resulting in better performing thin film transistors. In addition, such film can have numerous novel applications such as providing a low cost alternative to form SOI substrates and a key technology for ultra-dense circuit integration including SRAM. However, the TFT’s performance has not been optimized because the quality of the NILC poly-Si is a function of nickel amount, time and temperature and maybe more. In addition, the large amount of nickel in recrystallized films may lead to the problem of metal A31.6.1
contamination and degradation of devices formed in these films. Therefore we should comply the balance in the amount of nickel in recrystallized films. In this paper, we try to define the nickel concentration in amorphous silicon and to study the effect of nickel on the nickel induced lateral crystallization for different sizes and lengths of nickel sources.
EXPERIMENTAL DETAILS 7000 Å thick oxide was formed by wet oxidation at 1000 °C on (100) 20 Ω-cm p-Si wafers. Then, 1000 Å of a-Si was deposited on the oxide by LPCVD at 550 °C, and followed by the deposition of 3000 Å of low temperature oxide (LTO) at 425 °C. Windows were then patterned (see Figure 1) and 50 Å and 200 Å Ni was deposited onto the a-Si using an electron beam evaporator where the Ni thickness was monitored by a quartz resonator. Prior to the Ni deposition, the native oxide on the a-Si film was removed by dipping i
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