Laser Crystallization of Silicon for Large Area Electronics
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0989-A16-01
Laser Crystallization of Silicon for Large Area Electronics Toshiyuki Sameshima Graduate School of Engineering, Tokyo University of Agriculture & Technology, 2-24-16, Nakamachi, Koganei, 184-8588, Japan
ABSTRACT Laser crystallization of silicon is discussed for forming polycrystalline silicon thin films used to fabricate polycrystalline silicon thin film transistors (poly-Si TFTs). Laser-induced rapid heating is important for crystalline film formation with a low thermal budget. Structural and electrical properties of poly-Si films are discussed. Reduction of electrical active defects located at grain boundaries is essential for achieving poly-Si TFTs with high performances. The internal film stress is attractive to increase the carrier mobility. Recent development in laser crystallization methods with pulsed and continuous wave (CW) lasers is then reviewed. Control of the heat flow results in crystalline grain growth in the lateral direction, which is essential for fabrication of large crystalline grains. We also report an annealing method using a high power infrared semiconductor laser. High power lasers will be attractive for rapid crystallization of silicon films over a large area and activation of doped regions.
INTRODUCTION The technologies of polycrystalline silicon thin film transistors (poly-Si TFTs) have been developed in recent twenty years. TFTs have been applied to switching elements for liquidcrystal-flat-panel displays used in note book type personal computers, mobile phone and TV [1]. Poly-Si TFTs have been also been applied to logical integrated circuits because of their possibility of a high operation frequency [2,3]. Fabrication of TFT circuits on plastic films is also attractive for cheap, flexible and light devices [4]. For this purpose, fabrication processes of TFTs at a low temperature are important because of low heat resistivity of glass and plastic materials. Sameshima et al. developed excimer-laser-induced crystallization of amorphous silicon films formed on glass substrates [5]. They reported poly-Si TFTs using laser crystallization with a low processing temperature of 270∫C. Many works on pulsed laser crystallization have been done to improve the low temperature fabrication processing of poly-Si TFTs [6-8]. The equipment of crystallization has been developed using the excimer laser at the present stage. Furthermore, crystallization of silicon films in the lateral direction has been widely investigated in order to fabricate poly-Si TFTs with high performances. In this paper, laser crystallization technology is reviewed for low temperature fabrication processing. Structural and electrical properties of poly-Si films are argued. Passivation of SiO2/Si interface and grain boundaries is also discussed for fabrication of TFTs with a high mobility and a low threshold voltage. Crystallization of silicon films in the lateral direction using pulsed laser as well as continuous wave laser is also referred for TFTs with high performances. We also
introduce infrared semiconductor indu
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