Fabrication of Poly-silicon Thin Films on Glass and Flexible Substrates using Laser Initiated Metal Induced Crystallizat
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0910-A21-10
Fabrication of Poly-silicon Thin Films on Glass and Flexible Substrates using Laser Initiated Metal Induced Crystallization of Amorphous Silicon Husam H. Abu-Safe, Hameed A. Naseem, and William D. Brown Arkansas Photovoltaic Research Center, Department of Electrical Engineering, University of Arkansas, Fayetteville, AR, 72701 ABSTRACT Poly-silicon thin films on glass and Kapton® substrates are fabricated using laser initiated metal induced crystallization method. Amorphous silicon films of 200 nm thickness were deposited on the two substrates. The films were capped with 200 nm aluminum films. The annealing laser was a cw Argon-ion laser system. Laser power densities ranging from 4 to 9 W/cm2 were used in the annealing process. The samples were irradiated for various periods of time. X-ray diffraction patterns from the initial results indicated the crystallization of the films. Scanning electron microscopy showed dendritic growth in the annealed samples. The composition analysis of the samples indicated aluminum-silicon alloy regions in the films. INTRODUCTION The formation of polycrystalline silicon (poly-Si) by annealing its amorphous precursor has been receiving a great deal of attention due to the immense potential it has in large area microelectronic applications. Poly-Si thin films can be used to fabricate thin film solar cells, thin film transistors for active matrix liquid crystal displays (AMLCDs), image sensors and 3D microelectronics. While there are many techniques to make poly-Si thin films by direct deposition or by crystallizing amorphous silicon (a-Si) films deposited on foreign substrates, metal induced crystallization (MIC) has been viewed as one of the best technique so far to fabricate continuous thin polycrystalline films on cheap substrates like glass and plastic. It is well known that a-Si, when in contact with certain metals and subjected to thermal annealing crystallizes at very low temperatures. Various metals such as aluminum, sliver, nickel and gold have been used to crystallize a-Si films using this method. In the case of aluminum, temperatures as low as 150˚C have been reported [1]. The excitation sources for the interaction between metalSi interfaces in most of the studies were thermal annealing, microwave annealing, ion beam sources and electric field. Laser crystallization (LC) technique has been widely investigated in the creation of poly-Si thin films for more than a decade [2]. Until now, all studies based on MIC used thermal annealing as an excitation source. In the current study, we show the results of using laser powers to initiate the MIC of a-Si on glass and Kapton substrates. EXPERIMENT Two sets of samples were prepared for the study. In the first set, 0.15 mm thick clean cover glass (Soda lime glass) substrates were used, whereas for the second set, 7 µm-thick flexible Kapton sheets were used instead of the glass substrates. Hydrogenated amorphous silicon (a-Si:H) films of 200 nm thickness were deposited on the substrates using plasma enhanced chemical vapor dep
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