Growth of CVD graphene on copper by rapid thermal processing
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Growth of CVD graphene on copper by rapid thermal processing W. Kim1, J. Riikonen1, S. Arpiainen2, O. Svensk1, C. Li1, and H. Lipsanen1 1 Department of Micro- and Nanosciences, Aalto University, FI-00076, Espoo, Finland 2 VTT Microsystems and Nanoelectronics, FI-02044, Espoo, Finland ABSTRACT We have investigated the fabrication of graphene by chemical vapor deposition using a conventional rapid thermal processing system with infrared heating. Graphene films were grown on the pretreated copper foil in RTP at 935-960°C at pressure of 6~7 mbar. The grown films were characterized by scanning electron microscope and Raman spectroscopy to investigate morphology of graphene. The growth of graphene was initiated by small flakes that spread rapidly covering the whole copper surface as a single-layer film in ~20 seconds. Room temperature mobility and sheet resistance extracted by transfer-length method (TLM) for the graphene film transferred onto the SiO2/Si substrate were around 1,800 cm2/Vs and 260 Ω/ with the gate voltage, respectively. INTRODUCTION Since the successful synthesis by chemical vapor deposition (CVD) [1-3], graphene has been considered as a potential candidate for the transparent conductive electrodes widely used in optoelectronics due to its extraordinary physical properties. Among the methods known for the synthesis of graphene, CVD on a catalytic metal substrate is considered as the most suitable method for larger scale fabrication of high-quality graphene. Recently, the methods using fast photo-thermal CVD on nickel (Ni) [4] and slow (60 min growth time) rapid thermal processing (RTP) like CVD on copper (Cu) [5] have been reported. Compared to conventional resistive thermal furnace, cold-walled RTP with direct infrared heating has the advantages of fast operation in heating and cooling and accurate local temperature control in a large area growth. Furthermore, the use of cold -wall reactor allows less contamination to be induced during the process. In this study, we synthesized graphene by RTP from methane (CH4) and investigated growth behavior by observing the initial formation of carbon grains. The qualities of graphene layers identified by scanning electron microscope (SEM) and Raman spectroscopy are presented with room temperature mobility and sheet resistance obtained by device measurements. EXPERIMENTAL We prepared graphene on copper foil by RTP-CVD. The schematic for the growth setup is presented in Fig. 1. Infrared light from the halogen lamps was used as a heat source and intrinsic silicon wafer was used as a susceptor. Before the growth process, the Cu foil (nominal purity ~ 99.8%) was pretreated in acetic acid to remove native oxides followed by annealing under hydrogen (H2) environment at 800 qC for 30 minutes at atmospheric pressure. The pretreated Cu foil was placed onto the silica plate on the Si susceptor to prevent the reaction between copper and silicon. In the process, the silicon susceptor was first heated up to 935~950
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qC and kept for 5 minutes under H2 ambient at the pressure
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