Monocrystalline Si Films from Transfer Processes for Thin Film Devices
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MRS Spring Meeting, San Francisco, 16. - 20. April 2001 to be published in Mat. Res. Soc. Symp. Proc. 685E, xxx (2001)
Monocrystalline Si Films from Transfer Processes for Thin Film Devices Ralf B. Bergmann, Christopher Berge, Titus J. Rinke, and Jürgen H. Werner Universität Stuttgart, Institut für Physikalische Elektronik, Pfaffenwaldring 47, D-70569 Stuttgart, Germany ABSTRACT The transfer of thin monocrystalline silicon films to foreign substrates is of great interest for a number of applications such as silicon on insulator devices, active matrix displays and thin film solar cells. We present a transfer approach for the fabrication of monocrystalline Si films on foreign substrates based on the formation of quasi-monocrystalline Si-films. Our transfer approach is compatible with high temperature processing such as epitaxial growth at 1100°C, thermal oxidation and phosphorous diffusion. Reuse of Si host wafers is demonstrated by the subsequent epitaxial growth of three monocrystalline Si films on a single host wafer. Monocrystalline Si films with a thickness of 15 µm and a diameter of 3” are transferred to glass and flexible plastic substrates. The typical light point defect density in films transferred from virgin wafers ranges between 10 to 100 cm-2, while stacking fault and dislocation densities are ≤ 100 cm-2. The minority carrier diffusion length in the epitaxial Si films is around 50 µm.
INTRODUCTION The formation of crystalline Si films on foreign substrates [1] is a key technology for the fabrication of silicon-on-insulator (SOI) circuits [2] and other advanced electronic applications such as active matrix displays [3] and thin film solar cells [4]. As the presence of grain boundaries deteriorates the electronic quality and homogeneity of polycrystalline Si films [5], the use of monocrystalline Si films is highly desirable. Historically, apart from the SOS technology, SIMOX [6] was the first technology to provide monocrystalline SOI films suitable for integrated circuit applications. The SIMOX process forms a thin Si film on SiO2 by Implantation of Oxygen into a Si wafer followed by high-temperature annealing. While this process provides an SOI technology based on a Si wafer, for many applications the use of Si substrates is unsuitable: For liquid crystal displays, a transparent substrate with a large area is needed, while for thin film solar cells a Si wafer is too expensive as a substrate material. For other advanced applications such as wearable electronics, Si films must be flexible [7]. As a consequence, processes that transfer monocrystalline Si films to (arbitrary) foreign substrates are being developed at various companies and research institutions. Transfer processes start with the formation of a monocrystalline Si film that can − by some means − be separated from the host wafer. The host wafer is bonded or otherwise attached to an oxidized Si wafer or a foreign substrate and the monocrystalline Si film is subsequently detached from the host wafer. In most processes, the host wafer serves for mu
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