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Directional Field Aided Lateral Crystallization of Amorphous Silicon Thin Films Marek A. T. Izmajlowicz, Neil A. Morrison, Andrew J. Flewitt and William I. Milne Engineering Department, Cambridge University, Cambridge, CB2 1PZ, U.K. ABSTRACT For application to active matrix liquid crystal displays (AMLCDs), a low temperature (< 600 oC) process for the production of polycrystalline silicon is required to permit the use of inexpensive glass substrates. This would allow the integration of drive electronics onto the display panel. Current low temperature processes include excimer laser annealing, which requires expensive equipment, and solid phase crystallization, which requires high temperatures. It is known that by adding small amounts of metals such as nickel to the amorphous silicon the solid phase crystallization temperature can be significantly reduced. The rate of this solid phase metal induced crystallization is increased in the presence of an electric field. Previous work on field aided crystallization has reported crystal growth that either proceeds towards the positive terminal or is independent of the direction of the electric field. In this work, extensive investigation has consistently revealed directional crystallization, from the positive to the negative terminal, of amorphous silicon thin films during heat treatment in the presence of an electric field. This is the first time that this phenomenon has been reported. Models have been proposed for metal induced crystallization with and without an applied electric field in which a reaction between Ni and Si to produce NiSi is the rate-limiting step. The crystallization rate is increased in the presence of an electric field through the drift of positive Ni ions.

INTRODUCTION Low temperature (< 600 oC) formation of poly-Si thin films on glass substrates is required for the purpose of integrating drive electronics onto active matrix liquid crystal display (AMLCD) panels. The most widely used method of poly-Si preparation is the deposition of amorphous silicon (a-Si) and its crystallization by post-annealing using techniques such as solid phase crystallization (SPC) [1, 2] or excimer laser annealing (ELA) [3]. SPC has many advantages over ELA, such as simplicity, low cost, uniformity, and large-area capability. However, the high crystallization temperature (> 600 oC) required for crystallization in a short industrial timescale necessitates the use of expensive quartz substrates and prevents the commercial application of SPC. The SPC temperature of a-Si can be lowered by the addition of some metals [4, 5] but this phenomenon has not been applicable to the fabrication of thin film transistors (TFTs) because of metal incorporation into the Si. Selective deposition of nickel on a-Si thin films was found to induce crystallization of a-Si, with little metal contamination, outside of the metal coverage, a phenomenon known as metal induced lateral crystallization (MILC) [6, 7]. The application of an electric field during annealing has been shown to increase the rate o