Characterization & Analysis of Sub-Grain Boundaries in Sequential Lateral Solidification Processed SOI Films
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Characterization & Analysis of Sub-Grain Boundaries in Sequential Lateral Solidification Processed SOI Films M. A. Crowder, A. B. Limanov, B. A. Turk1 , and James S. Im Division of Materials Science and Engineering, Department of Applied Physics and Applied Mathematics, School of Engineering and Applied Science, Columbia University, New York, New York 10027 Abstract The nature of the formation of sub-grain boundaries within sequential lateral solidification (SLS) processed thin silicon films has been examined using single crystal Si films as a precursor material. Experimental details include the use of an excimer laser projection system and straight-slit beamlets to produce directionally solidified microstructures. Within the SLS processed silicon-on-insulator (SOI) films, three microstructurally distinct regions are identified: (1) an initial planar defect-free area (the extent of which can depend on laser fluence and orientation); (2) a transitional area within which the sub-grain boundaries appear and propagate in a well-defined direction relative to the crystallographic orientation; and (3) a final area characterized by sub-grain boundaries aligning approximately to the scan direction, and the in-plane texture becoming more random. We discuss the results within the context of a plastic deformation model of sub-grain boundary formation.
Introduction Sequential lateral solidification (SLS) is a pulsed-beam induced crystallization method [1, 2] that can produce grain-boundary location engineered microstructures. Such a capability is attained during crystal growth by controlling the locations, shapes, and extent of melting induced by the incident energy-beam pulses and iteratively irradiating and sequentially translating the films [3]. The resulting ability to manipulate the locations of high-angle grain-boundaries in the crystallized films can be used to realize low defect-density crystalline Si films with various microstructures, ranging from large-grained and grain-boundary-location controlled polycrystalline films to locationcontrolled single-crystal regions [1]. The SLS method is flexible and can be implemented using various beam sources and beam shaping schemes [4, 5]. In general, a variety of planar defects can be found within SLS processed Si films, with subgrain boundaries being the most prevalent intragrain defect [1, 2]. The general pattern of the subgrain boundaries consists of a river-like structure where sub-grains can be either eliminated by adjacent sub-grains, or bifurcated by the appearance of a sub-grain boundary within the central region of the sub-grain. Sub-grain boundary spacing in SLS processed a-Si films In the previous investigations [6], the average spacing between boundaries were analyzed and characterized with respect to external processing parameters such as film thickness, incident energy density, and per-pulse translation distance. It was found that the average spacing remains approximately constant after a short transition region within which the majority of the large number of 1
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