Structural Properties of Polycrystalline Silicon Films Formed by Pulsed Rapid Thermal Processing
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State laboratory for Surface Physics, Institute of Semiconductors & Center for Condensed Matter Physics, Chinese Academy of Science, P.O.Box 912, Beijing 100083, China ** Beijing Solar Energy Research Institute, Beijing 100083,China *
ABSTRACT A novel pulsed rapid thermal processing (PRTP) method has been used for realizing the solid-phase crystallization of amorphous silicon films prepared by PECVD. The microstructure and surface morphology of the crystallized films are investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The results indicate that this PRTP is a suitable postcrystallization technique for fabricating large-area polycrystalline silicon films with good structural qualities such as large grain size, small lattice microstain and smooth surface morphology on low-cost substrate. INTRODUCTION Polycrystalline silicon (poly-Si) is a material of great importance in microelectronics, photovoltaics and display technologies [1-5]. In recent years, there is growing interest in developing practical techniques for fabricating larger-area and high-quality poly-Si films on lowcost glass substrate at a low temperature. Generally, post-crystallization of amorphous silicon is thought to be a preferred technique for this purpose [6,7]. Compared to those as-grown, the poly-Si films prepared by post-crystallization have perfect structure and smooth surface morphology that are required for critical applications. Several post-crystallization methods have been reported. Among them, zone melt recrystallization (ZMR) can produce large-grain poly-Si films [8], but the very high process temperature (>1000 'C) makes the use of low-cost substrate actually impossible; Conventional furnace annealing requires several tens of hours at the temperature around 600 TC (softening point of glass) [9,10], which means high thermal budget and low throughput, diseconomic for large-scale production; Rapid thermal processing (RTP) can greatly shorten the process time [11,12], but due to the continuous thermal exposure to high temperature, the damage to the glass substrate is inevitable; Although laser beam annealing can realize the crystallization at lower temperature [13,14], it is very expensive and also needs to take a long time to scan over a large area; Post-crystallization using a metal as seed can also be carried out at the temperature lower than 600 0C [15-17], but the contamination of metal impurity to the Si film is induced. So developing a new effective method to prepare poly-Si films on lowcost substrate is still an attractive and challenging target. Currently, we have presented an improved rapid thermal processing method---pulsed rapid thermal processing (PRTP), which involves a number of cycles of thermal process. In each cycle, a 60-s thermal bias of 550 TC is used for preheating the films to a "critical state" of crystallization, so that the rapid nucleation and grain growth can be triggered by a following 1-s high-temperature thermal pulse of 850 TC. By using this annealing method, solid-phase crystallizati
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