High Temperature Post-Deposition Annealing Studies of Layer-by-layer (LBL) Deposited Hydrogenated Amorphous Silicon Film
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1153-A05-01
High Temperature Post-Deposition Annealing Studies of Layer-by-layer (LBL) Deposited Hydrogenated Amorphous Silicon Films Goh Boon Tong, Siti Meriam Ab. Gani, Muhamad Rasat Muhamad and Saadah Abdul Rahman Low Dimensional Materials Research Center, Department of Physics, University of Malaya, 50603 Kuala Lumpur, Malaysia ABSTRACT High temperature post-deposition annealing studies were done on hydrogenated amorphous silicon thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) using the layer-by-layer (LBL) deposition technique. The films were annealed at temperatures of 400 oC, 600 oC, 800 oC and 1000 oC in ambient nitrogen for one hour. Auger electron spectroscopy (AES) depth profiling results showed that high concentration of O atoms were present at the substrate/film interface and at film surface. Very low concentration of O atoms was present separating silicon layers at regular intervals from the film surface and the substrate due to the nature of the LBL deposition and these silicon oxide layers were stable to high annealing temperature. Reflectance spectroscopy measurements showed that the onset of transformation from amorphous to crystalline phase in the LBL a-Si:H film structure started when annealed at temperature of 600 oC but the X-ray diffraction (XRD) and Raman scattering spectroscopy showed that this transition only started at 800oC. The films were polycrystalline with very small grains when annealed at 800 oC and 1000 oC. Fourier transform infrared spectroscopy (FTIR), measurements showed that hydrogen was completely evolved from the film at the on-set of crystallization when annealed at 800 oC. The edge of the reflectance fringes shifted to longer wavelength decrease in hydrogen content but shifted to shorter wavelength with increase in crystallinity. INTRODUCTION Transformation of hydrogenated amorphous silicon (a-Si:H) from amorphous metastable phase to stable crystalline phase has been the subject of interest for many years. The interest was mainly due to its potential applications in thin film transistors and solar cells as the polycrystalline Si films formed when annealed at high temperature had higher mobility, higher conductivity and larger breakdown voltages at metal-oxide-semiconductor interface compared to the amorphous Si films [1, 2]. The transformation from amorphous to crystalline phase has been monitored by studying the effects of thermal annealing on the various properties of a-Si:H films [3]. Monitoring the crystallization of a-Si:H films grown by layerby-layer (LBL) deposition technique using our home-built radio-frequency plasma enhanced chemical vapour deposition (rf-PECVD) system as a result of high temperature annealing is the focus of this work. The LBL deposition technique involved periodic interruptions of the deposition process whereby the plasma discharge of silane diluted in hydrogen was stopped for a fixed period of time during which the growth surface was treated with hydrogen plasma discharge. The effects of high temperature annealing on
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