Mechanism of Facet Formation During Epitaxial CoSi 2 Growth Using Co/Refractory Bilayers
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EPITAXIAL
CoSi 2
Jeong S. Byun, Kwan G. Rha, Woo S. Kim, and (*)Hyeong J. Kim, Semiconductor Research Laboratory Lab., GoldStar Electron Co. Ltd., 50 Hyangjeong -Dong Cheongju-Si, 360-480, Korea; (*)Dept. of Inorg. Materials Eng. Seoul National Univ., 151-742, Korea
ABSTRACT The formation mechanism of facets occurring during epitaxial growth of CoSi2 are described using a Co/Ta bilayer. At the early stage of annealing, the diffusion of Co atom occurs across the interlayed Ta layer, first forming a CoSi layer on the Si substrate. CoSi2 grains nucleate at the CoSi/silicon interface and grows laterally parallel to the surface. Due to the difference of dominant moving species in CoSi2 and CoSi, the CoSi2 grain at the interface impedes the interface movement, thereby, leading to the facet formation. Epitaxial CoSi2 grains nucleated at the non-epitaxial CoSi2/silicon interface and the faceted corner and grow laterally along the Si surface. With increasing annealing temperature, the epitaxial quality of the CoSi2 improves because of increased lateral growth rate of the CoSi2.
INTRODUCTION Cobalt silicide (CoSi2) is known to be the most promising material because of its low resistivity (less than 20 p D -cm), the high possibility of epitaxial growth on the Si-substrate, and process compatibilities in very large scale intergration (VLSI) technology[1,2]. Especially, the epitaxial growth of CoSi2 using a Co/refractory bilayer, such as, Co/Ti[3,4], Co/Ta[5], and Co/Zr[6], has been intensivily investigated with a special interest. The success of those epitaxial growth technique is believed to be due to the ability of the refractory to reduce the native oxide of the silicon substrate[7] (thus creating a clean, oxygen-free silicon surface), and to the fact that Co diffusion is slowed by the refractory layer. Most of the papers report that facets (or steps) are invariably formed at the CoSi2/silicon interface during the epitaxial CoSi2 layer growth, however, the cause of which is not fully understood. In this work, we have investigated the mechanisms of the facet formation at the CoSi2/silicon interface using transmission electron microscopy (TEM). The only assumption used for this study is that the dominant moving species in the CoSi2 and CoSi phases are Co atoms and silicon atoms, respectively[2]. This means that the diffusion of the silicon atoms from the silicon substrate to the outer CoSi layer can not occur, once the CoSi2 layer formed on the silicon surface.
453 Mat. Res. Soc. Symp. Proc. Vol. 355 01995 Materials Research Society
EXPERIMENT The (100) p-type silicon wafers with 10-20 £2-cm resistivity were used in this work. The substrate were cleaned in a dilute HF solution prior to loading it into an electron gun evaporator. A Ta film of 3.5 nm thickness and a Co film of 25 nm thickness were sequentially deposited on the substrate without breaking the vacuum. The chamber vacuum was maintained below 3X10-0 torr during deposition. The annealing was carried out at the temperatures of 500-8001 in a rapid thermal anneal
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