Layer Transfer and Simultaneous Activation of Phosphorus Atoms in Silicon Films by Near-Infrared Semiconductor Diode Las
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Layer Transfer and Simultaneous Activation of Phosphorus Atoms in Silicon Films by Near-Infrared Semiconductor Diode Laser Irradiation Yoshitaka Kobayashi, Kohei Sakaike, Shogo Nakamura, Mitsuhisa Ikeda, Akio Ohta and Seiichiro Higashi Depertment of Semiconductor Electronics and Integration Science, Graduate School of Advanced Sciences of Matter, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima, 739-8530, Japan
ABSTRACT Layer transfer and simultaneous activation of phosphorus atoms in Si films induced by semiconductor diode laser (SDL) irradiation have been investigated. Phosphorus-doped a-Si films supported by columns on a starting substrate (quartz) and a counter substrate (glass) were closely contacted face-to-face, and an 812 nm light from a SDL was irradiated to the a-Si films from the backside of the starting substrate. After SDL irradiation, 20μm wide and 1000μm long Si films were transferred to the counter substrate and were crystallized simultaneously. From optical microscope images, it was confirmed that the original form was completely maintained after the film transfer. The electrical conductivity of transferred Si film was as high as 708 S/cm. Hall measurement of the films revealed very high electron concentration of 9.5×1020 cm-3, which indicated efficient doping is achieved by the laser transfer technique. INTRODUCTION For the realization of high-performance flexible electronics, the formation of high-crystallinity Si films on flexible substrate such as polyethylene terephthalate (PET) substrates is one of the most crucial technological issues. However, it is not easy to form high-crystallinity Si films on flexible substrate under limited thermal budget. Therefore, we have proposed and succeeded in layer transfer and simultaneous crystallization technique of large area (6×6 mm2) amorphous Si (a-Si) films to glass and PET substrates using mid-air structure [1]. We define the a-Si films with mid-air structure as the films supported by narrow quartz columns, which minimize the area of contact with the films. The advantage of this mid-air structure is that the Si film is quickly heated and transferred easily to a counter substrate. Our proposed method would be effectively applied to Si device fabrication on flexible substrate using layer by layer transfer of intrinsic and doped Si films. In this work, we have attempted layer transfer and doping simultaneously by SDL irradiation to phosphorus doped a-Si films with mid-air structure.
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EXPERIMENT 200-nm-thick phosphorus doped a-Si films were deposited on quartz substrate by a capacitively coupled plasma enhanced chemical vapor deposition (CCP CVD) of SiH4 and PH3 diluted with H2 with the substrate hearting at 250ºC. The PH3 flow ratio is defined by the flow rate of PH3 gas divided by the SiH4 + PH3 + H2 gas flow rates. During the a-Si film deposition, PH3 flow ratio was controlled at 0.29, 0.45, 0.60 and 0.75%. Dehydrogenation was performed at substrate temperature of 400ºC in N2 ambient for 1 hour. For the I-V measurement of transferred Si f
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