Light absorptive underlayer enhanced excimer-laser crystallization of Si thin-film
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Light absorptive underlayer enhanced excimer-laser crystallization of Si thin-film Wenchang Yeh,a) Dunyuan Ke, Chunjun Zhuang, Hsiangen Huang, and Yubang Yang Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (Received 4 June 2007; accepted 7 August 2007)
A sample structure and method for superlateral-growth (SLG) enhancement in excimer-laser crystallization has been implemented and realized. The proposed sample structure is a Si film/buffer film/light-absorptive (LA) film/glass-stacked structure, with the irradiation of laser light from underneath a substrate. The influence of the absorption coefficient ␣ of the LA film has been found to be critical in this structure. By increasing ␣ from 0 to 12,000 cm−1, diameter of SLG grain has increased from 0.8 to 10 m, with the solidification term increased from 75 to 1050 ns, respectively. The radius of SLG grain was shown to be proportional to the solidification term with a slope of 5 m/s. This result suggests the average SLG growth rate is constant at 5 m/s, irrespective of the solidification term of Si film. The applicability of present method to both sequential lateral solidification method and micromelt seeding method was demonstrated. Overcoming of Si agglomeration has been shown to be important for applying the present method to the sequential lateral solidification (SLS) method.
I. INTRODUCTION
Rapid melting and recrystallization by excimer-laser crystallization (ELC) of amorphous silicon (a-Si) thin films have been applied to the production of lowtemperature polycrystalline silicon (poly-Si) for thin-film transistors (TFTs) on glass1 and plastic substrates.2 This is mainly because of the short pulse duration characteristics of excimer laser (10–200 ns), which result in minimal heat damage on the substrate. These TFTs are now used to construct not only pixel switches, but also peripheral driver circuits for active-matrix flat-panel displays. Their future evolution aims at the enlargement of the matrix/circuit scale and further system integration into the panel, which require the enhancement of the TFT mobility and device-to-device uniformity. However, since the grain size in the conventional ELC method is as small as several hundred nm and smaller than the channel
a)
Address all correspondence to this author. e-mail: [email protected] and [email protected] This paper was selected as the Outstanding Meeting Paper for the 2006 MRS Spring Meeting Symposium A Proceedings, Vol. 910. DOI: 10.1557/JMR.2007.0392 J. Mater. Res., Vol. 22, No. 11, Nov 2007
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length of TFTs,1 the carrier mobility is limited due to barrier height caused by trapped charges at the grain boundaries. Therefore, larger grain size is demanded for higher mobility TFTs. Controlled superlateral growth (C-SLG) of Si film was proposed and implemented in which the Si grain was grown at a controlled position with grain sizes of ∼2 m.3–7 Moreover, grains up to 200 m in length w
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