An Advanced 405-nm Laser Diode Crystallization Method of a-Si Film for Fabricating Microcrystalline-Si TFTs

Kiyoshi MORIMOTO  Nobuyasu SUZUKI  Kazuhiko YAMANAKA  Masaaki YURI  Janet MILLIEZ  Xinbing LIU  

IEICE TRANSACTIONS on Electronics   Vol.E94-C   No.11   pp.1733-1738
Publication Date: 2011/11/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E94.C.1733
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Section on Electronic Displays)
laser crystallization of a-Si,  thin film transistor,  microcrystalline silicon,  heat flow simulation,  

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This report describes a crystallization method we developed for amorphous (a)-Si film by using 405-nm laser diodes (LDs). The proposed method has been used to fabricate bottom gate (BG) microcrystalline (µc)-Si TFTs for the first time. A µc-Si film with high crystallinity was produced and high-performance BG µc-Si TFTs with a field effect mobility of 3.6 cm2/Vs and a current on/off ratio exceeding 108 were successfully demonstrated. To determine the advantages of a 405-nm wavelength, a heat flow simulation was performed with full consideration of light interference effects. Among commercially available solid-state lasers and LDs with wavelengths having relatively high optical absorption coefficients for a-Si, three (405, 445, and 532 nm) were used in the simulation for comparison. Results demonstrated that wavelength is a crucial factor for the uniformity, efficiency, and process margin in a-Si crystallization for BG µc-Si TFTs. The 405-nm wavelength had the best simulation results. In addition, the maximum temperature profile on the gate electrode through the simulation well explained the actual crystallinity distributions of the µc-Si films.