Thermal and Stress Modeling for the Flash Lamp Crystallization of Amorphous Silicon Films
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0910-A21-15
Thermal and Stress Modeling for the Flash Lamp Crystallization of Amorphous Silicon Films Mark P. Smith1, Richard A. McMahon1, Keith A. Seffen1, Dieter Panknin2, Matthias Voelskow2, and Wolgang Skorupa2 1 Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, Cambridgeshire, CB2 1PZ, United Kingdom 2 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, Dresden, Saxony, Germany ABSTRACT Thin poly-crystalline silicon films are attractive for the fabrication of active matrix liquid crystal displays. We investigate the use of flash lamp annealing to crystallize amorphous silicon layers on glass substrates as a low cost manufacturing route. In this process amorphous silicon (a-Si) can be crystallized by solid phase crystallization (SPC) or in the super lateral growth (SLG) regime. We present a thermal model incorporating the phase transitions during annealing; providing a valuable tool for optimizing the process conditions. Another consideration is the evolution of stress resulting from the transient thermal loading of the substrate material. Results are presented for various substrate geometries and important scalability issues are addressed. INTRODUCTION Thin polycrystalline Si (pc-Si) films are extensively used for flat panel active matrix liquid crystal displays [1,2], with the quality of these films being crucial for the performance of these devices. To realise low cost, large area substrates, the polycrystalline silicon is generally formed on cheap glass substrates, therefore the process temperatures must not exceed the softening point of the glass, which is around 600 ˚C [3]. There are several established methods of film preparation that are compatible with the constraint on processing temperature. These are: (i) direct deposition of polycrystalline silicon and (ii) furnace annealing, metal induced or laser crystallization of amorphous silicon. Whilst direct deposition of polycrystalline silicon can be readily achieved, the small grains are highly defective and show roughness in the surface. Alternatively, a-Si films can be deposited followed by SPC. For furnace annealing, the growth is mediated by the formation of twins, forming large heavily defective grains. Metal induced crystallization is also possible but the contamination due to the metal impurities jeopardises the material quality. The best pc-Si films are formed by laser crystallization of a-Si films. The disadvantages of this method are the poor uniformity and low scanning speed of the laser, decreasing material quality and raising processing costs. This paper reports on initial studies into the feasibility of flash lamp annealing (FLA) of amorphous silicon films for the production of high-quality polycrystalline films, including the development of thermal and stress models, uniformity and application to large substrate areas. The thermal model includes both the thermal response of the wafers and the phase transition scenarios. Predictions from the thermal model correlate well with e
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