Nucleation-Control and Enhancement of Solid-Phase-Crystallization of SiGe-Heterostructure
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NUCLEATION-CONTROL AND ENHANCEMENT OF SOLID-PHASE-CRYSTALLIZATION OF SiGe-HETEROSTRUCTURE S. YAMAGUCHI, S. K. PARK, and N. SUGII* Hitachi Research Lab., Hitachi Ltd., Tokyo 185-8601, Japan; [email protected] *Central Research Lab., Hitachi Ltd., Tokyo 185-8601, Japan ABSTRACT The crystallization of SiGe-heterostructure in which a thin Ge layer put between Si layers has been investigated. When the Ge layer is inside the Si layer, the crystallization phenomena are similar to those of SiGe alloy layer; Ge completely diffuses in Si layer during the crystallization. When the Ge layer is at the interface between the Si layer and the quartz substrate, significant enhancement of crystallization has been found. In this structure, decrease in surface free-energy increases the nucleation rate at the interface and causes anomalous localization of Ge at the interface. When the Ge layer is on the surface of the Si layer, the crystallization property is quite different from the other structures. The underlying Si layer has large and aligned grains when the furnace annealing is assisted by the laser-annealing. A part of this work was carried out under the ASET program supported by NEDO, Japan. INTRODUCTION Polycrystalline Si on insulating substrate is of interest for the fabrication of polycrystalline gate-electrodes and thin film transistors (TFT). The thermodynamic phenomena of a solid-phase-crystallization (SPC) of pure Si have been studied in detail [1,2]. The incubation and the crystallization times are simple activation-type phenomena. The activation-energy of SPC of pure Si is about 2.7 eV [2]. During the crystallization, the random nucleation occurs primarily at the interface between Si layer and the substrate. The largest grain size of Si is 5 m, but it consists of a number of small domains [3]. Estimated single-domain size is about 500-600 nm. This size is not enough to reduce the carrier scattering at grain boundaries in the practical TFT channel. The grain size and grain boundaries are key parameters to obtain a high quality Si layer. The enhancement of crystallization, which is equivalent to reducing the nucleation rate, and control of nucleation site are essentially needed. Ge-doping into Si is a major approach to change material property of Si. Ge significantly enhances both the nucleation and SPC in Si. Si0.47Ge0.53 alloy, for example, has 100 lower SPC temperature than that of Si [2]. It has been reported, however, that grain size of crystallized Si1-xGex significantly decreases with increase of Ge concentration (x) [3] because the enhancement of the nucleation in SiGe alloy is relatively higher than that of SPC rate. To avoid the high nucleation in SiGe alloy, Ge has been investigated as a seed material for crystallization; Ge is partially deposited on the Si layer by conventional photolithography process before SPC [4]. Ge diffusion, however, often causes the
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SiGe-alloying and high crystal quality has not been obtained. In this study, the nucleation-control and the enhancement of SPC using Si
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