Single-Axis Projection Scheme for Conducting Sequential Lateral Solidifica-tion of Si Films for Large-Area Electronics
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Single-Axis Projection Scheme for Conducting Sequential Lateral Solidification of Si Films for Large-Area Electronics Alexander LIMANOV*, Institute of Crystallography Russian Academy of Sciences, Moscow Vladimir BORISOV, TRINITI, Troitsk, Moscow region ABSTRACT This paper deals with some results of research in SLS performed in the excimer laser laboratory of TRINITI research institute, Russia, where different types of excimer lasers have been developed and manufactured. The research used a new simple SLS approach based on single-axis (i.e., cylinder) projection optics. The method employs a long single melting line extended many centimeters in length. The line is formed by projection through a single slit in a bulk metal mask. Some aspects of the efficiency, potential, and technical challenge of the method are discussed. This method is particularly useful with low pulse energy and high frequency excimer lasers, and one of the most efficient ways of providing directionally crystallized Si films over a large area. Several types of excimer lasers were tested for the SLS technique. It was found that among various parameters, pulse duration is a more important one, e.g., an increase in pulse duration from 25 to 150 ns results in enlargement of lateral growth distance by about three times. 1. INTRODUCTION Since the beginning of the nineties, Excimer Laser Crystallization (ELC) has been considered a promising technique to produce advanced TFTs for large area application. Indeed, conventional ELC technique has already produced polycrystalline silicon films on glass for the first generation of commercial poly-Si AMLCDs. Meanwhile, some advanced ELC methods have been capable of obtaining excellent quality and location controlled c-Si film on glass with electron mobility up to 500 cm2/Vs [1]. Such a result opens a way to produce a System-on-glass, e.g., a computer built on glass/plastic board together with a screen’s TFTs. The progress in ELC is mainly related to research in the transformation scenario of Si thin film pulsed crystallization [2,3]. The most important finding of the research was the establishment and understanding of the super lateral growth (SLG) phenomenon [3,4], which takes place during near-complete melting of a large film area followed by lateral growth from small solid islands surviving at the film-substrate interface. It was found that: (1) large grains can be produced only by lateral growth through the melt, (2) only unmelted initial film rather than nucleation (!) can provide seeding to grow perfect large grains, (3) location control for the seeding is a key for location controlled crystallization. These findings pushed forward R&D in controlled super lateral growth (C-SLG) methods [5]. The first C-SLG techniques were realized by internal manipulation (e.g., by patterning of precursor Si film [6], or by patterning of an additionally deposited layer [7] ) with a heat source induced within Si film by laser irradiation. However, grain size in this case is limited by single extension of lateral growth. A bre
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