Processing and Properties of CW Laser-Recrystallized Silicon Films on Amorphous Substrates
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Hess,
and Sigmon,
eds.
Laser and Electron-Beam Solid Interactions and materials Processing
463
PROCESSING AND PROPERTIES OF CW LASER-RECRYSTALLIZED SILICON FILMS ON AMORPHOUS SUBSTRATES N. M. JOHNSON, D. K. BIEGELSEN, AND M. D. MOYER Xerox Palo Alto Research Centers, 3333 Coyote Hill Road, Palo Alto, California 94304 ABSTRACT CW laser recrystallization has been used to process silicon thin films as an integral step in semiconductor device fabrication. On continuous films of polycrystalline silicon, a silicon-nitride encapsulant is used to control surface morphology during laser recrystallization. For thin films on bulk glass substrates it is necessary to pattern the silicon layer in order to minimize microcracking as well as to control recrystallization. Over single crystal silicon substrates, test devices have been fabricated in silicon islands on dual-dielectric layers. Materials and device evaluation included TEM, current-voltage, capacitance-voltage, and EBIC measurements, and the test devices consisted of p-n junction diodes, MOS capacitors, and MOS field-effect transistors. INTRODUCTION Laser-recrystallized silicon thin films are of technological interest as a materials/processing system for the fabrication of high-performance thin-film transistors. On insulating layers over single-crystal silicon wafers, such semiconducting films could provide the essential ingredient for a three-dimensional VLSI technology. While on bulk glass substrates, such devices could find immediate application in large-area displays. Laser recrystallization is used to increase the grain size of deposited polycrystalline silicon films to dimensions that are comparable to those of the transistor structure, thereby
minimizing the detrimental effects of grain boundaries on device operation. Devices fabricated in single-crystal thin films should exhibit the highest performance and most reproducible operational characteristics. In this article we discuss the processing and properties of devices fabricated in CW laser-recrystallized silicon films on amorphous substrates. Both the materials configurations and laser-annealing techniques for promoting thin-film crystal growth are described in detail elsewhere [1]. Here, specific materials configurations are discussed from the standpoint of device processing, and results are presented for MOS field-effect transistors, MOS capacitors, and p-n junction diodes. Materials and device evaluation included TEM, current-voltage, capacitance-voltage, and EBIC measurements. CONTINUOUS SILICON THIN FILMS There have been several recent reports on the fabrication of MOS thin-film transistors in laser-recrystallized continuous layers of polycrystalline silicon [2-4]. The materials configuration consisted of a polycrystalline silicon film, typically 0.5-im thick, deposited on either a silicon-dioxide or silicon-nitride layer which covered a single-crystal silicon substrate. In the references cited above it is stated that for successful laser annealing of the silicon layer it was necessary to thermally an
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