Sub-grain Boundary Spacing in Directionally Crystallized Si Films Obtained via Sequential Lateral Solidification
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Sub-grain Boundary Spacing in Directionally Crystallized Si Films Obtained via Sequential Lateral Solidification M. A. Crowder, A. B. Limanov, 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 In this paper, we report on the average linear density of sub-grain boundaries that are found in directionally solidified microstructures obtained via sequential lateral solidification of Si thin films. Specifically, we have characterized the dependence of the sub-grain boundary density on the film thickness, incident energy density, and per-pulse translation distance. The investigation was confined to analyzing directionally solidified microstructures obtained using straight-line beamlets. It is found that the average spacing of the sub-grain boundaries depended approximately linearly on the film thickness, where it varied from 0.28 m at a ˚ to 0.75 m at 2,000 A. ˚ In contrast, variations in either the energy density thickness of 550 A or the per-pulse translation distance within the investigated SLS process parameter domain were found to have a negligible effect on the spacing. Discussion is provided on a preliminary model that invokes polygonization of thermal-stress generated dislocations, and on implications of the dependence of device performance on the film thickness.
Introduction Sequential lateral solidification (SLS) is a pulsed-beam based crystallization method [1, 2] that permits flexible control of grain boundaries. Such a capability during crystal growth is attained by controlling the locations, shapes, and extent of melting induced by the incident laser pulses and iteratively irradiating and sequentially translating the films [3]. This ability to manipulate the locations of high-angle grain-boundaries in the crystallized films can be used to realize low defectdensity crystalline Si films with various microstructures, including (1) large-grained and grainboundary-location controlled polycrystalline films, (2) directionally solidified microstructures, or (3) location-controlled single-crystal regions [4]. In general, there can be a variety of intragranular structural defects that may form during the growth in a crystallization process [5]. Previously, we have identified that sub-grain boundaries constitute the most prevalent intragrain defect found in SLS processed Si films [1, 2]. (Twins constitute additional intragrain defects observed in SLS processed Si films [6]). Since crystalline defects within the active portion of the semiconductor can only degrade the performance of microelectronic devices, it is important to characterize and analyze the extent to which the defects appear, particularly as a function of primary external parameters. Such quantitative analysis of the sub-grain boundaries has not been previously conducted, and to accomplish this constitutes the primary goal of this paper. The results obtained in this investigation r
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