Diffusion of Atoms Implanted in Poly Silicon Layer on Insulator
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DIFFUSION OF ATOMS IMPLANTED IN POLY SILICON LAYER ON INSULATOR M. TAKAI, M. IZUMI, T. YAMAMOTO, A. KINOMURA, K. GAMO, T. MINAMISONO*, AND S. NAMBA Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan *Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan ABSTRACT Diffusion of arsenic implanted in poly-silicon on insulator structures after furnace and rapid thermal annealing (RTA) has been investigated by Rutherford backscattering (RBS) and Hall effect measurements. The diffusivity for As in joly-Si on insulator is represented by D = 3.12 x 104 exp ( - 3.86 /kT) cm /sec for the tail region after both RTA and furnace annealing and D = 34.0 exp ( - 3.42 /kT) cm2 /sec for the peak region after RTA. Poly-Si layers after implantation and annealing were found to have tensile stresses of 3.0 - 4.0 kbar. INTRODUCTION Poly silicon-on-insulator structures have recently attracted great attention because of their potential for application in thin film transistors (TFT) such as switching devices for flat panel displays or driving circuits for image sensors. Improvement in electrical properties of poly-Si TFT is possible by optimi7ing processes to fabricate TFT structures, such as short channel devices, or by reducing defects in poly-Si layers. Implanted-impurity behavior in SOI structures such as redistribution of impurities in poly-Si layers during various heat treatments has not been studied in detail though it is very important factors for device applications [1,2]. Arsenic (As) implantation followed by annealing is one of the possible doping process for TFT in poly-Si layers with SOI structures, where precise controls of impurity profiles, i.e., junction depth, are necessary. Diffusions of implanted As in poly-Si layers on crystalline Si [3.4] or on Si0 2 after furnace annealing [1], or RTA [2], have been measured. The obtained profiles or diffusivity of As depend on the preparation process of the interface between poly-Si and underlying crystalline Si layers [4] or on the grain size of poly-Si, where fast diffusion of As through grain boundaries occurs [1,2]. In our previous study [2], As was implanted at 100 keV with a dose of 101 5 /cm 2 in poly-Si on insulator structures to obtain the diffusivity of As in poly-Si during RTA or furnace annealing. Diffusivities of D = 0.28 exp ( - 2.84 /kT) cm2 /sec for RTA and D = 1.81 exp ( - 3.14 /kT) cm2 /sec for furnace annealing were obtained at and nearby the peak region of the implanted As profiles. In this study, As profiles in poly-Si layers on insulator (Si0 2 ) structures after RTA and conventional furnace annealing have been measured by Rutherford backscattering (RBS) to investigate parameters 1 5 suitable for 2 Implantation dose ranged from 5 x 10 /cm to 1 x As profiles. shallow 16 2 10 /cm , where faster diffusion took place in the tail region of the As profiles than in the peak region. Hall effect measurements in combination with successive layer removal techniques were used to obtain activated carrier and mobility distributions. The As d
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