Ultra-Low Temperature Poly-Si Thin Film by Excimer Laser Recrystallization For Flexible Substrates
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Ultra-Low Temperature Poly-Si Thin Film by Excimer Laser Recrystallization For Flexible Substrates Sang-Myeon Han, Min-Cheol Lee, Su-Hyuk Kang, Moon-Young Shin, Min-Koo Han School of Electrical Engineering (#50), Seoul National University, Seoul, 151-742, Korea Phone : +82-2-880-7992, Fax : +82-2-883-0827, E-mail:[email protected] Abstract An ultra-low temperature (< 200oC) polycrystalline silicon (poly-Si) film is fabricated for the plastic substrate application using inductively coupled plasma chemical vapor deposition (ICP-CVD) and excimer laser annealing. The precursor active layer is deposited using the SiH4/He mixture at 150oC (substrate). The deposited silicon film consists of crystalline component as well as hydrogenated amorphous component. The hydrogen content in the precursor layer is less than 5 at%. The grain size of the precursor active silicon film is about 200nm and it is increased up to 500nm after excimer laser irradiation. Introduction Polycrystalline silicon thin film transistor (poly-Si TFTs) fabricated at low temperature under 200oC has been widely investigated for flexible substrate application such as transparent plastic substrate. [1-3] Unlike the TFT process using glass substrate, the maximum process temperature should be lower than 200oC in order to avoid thermal damage on flexible substrate. The amorphous silicon film deposited by sputtering has been studied due to the drastic decrease of hydrogen content in the silicon thin film. [1] However, some amount of sputter source gases such as Ar, He incorporated in silicon film may restrict the laser annealing process window. On the other hand, amorphous or polycrystalline silicon precursor prepared by conventional plasma enhanced chemical vapor deposition(PECVD) method has been also researched with laser dehydrogenation. [4] The hydrogen content larger than 10% is inherently incorporated in precursor silicon film deposited by conventional PECVD at the temperature less than 200oC [5]. Step-by-step excimer laser dehydrogenation [4] could be a candidate to decrease the hydrogen content in silicon film, however, this method would be limited by the hydrogen eruption during excimer laser irradiation. In this paper, we report the characteristics of silicon film deposited by ICP-CVD at
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150oC using He/SiH4 gas mixture. High-density plasma of ICP mode may easily decomposite silane gas. [5] The deposited silicon film is characterized by various analysis methods such as FT-IR, Raman and SEM. Our experiments show that the hydrogen content in the silicon film is reduced to 4 at% and crystalline components are contained in the silicon film. The helium dilution would provide more effective decomposition of silane gas and ion bombardment effect [6] so that the crystalline component can be increased at the
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