Suppression of Reaction between Si Substrate and Obliquely Deposited Fe Atoms
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KK8.8.1
Suppression of Reaction between Si Substrate and Obliquely Deposited Fe Atoms S. Jomori, M. Suzuki, K. Nakajima, K. Kimura Department of Engineering Physics and Mechanics, Kyoto University Yoshida-honmachi, Sakyo, Kyoto 606-8501, Japan
ABSTRACT We have investigated the initial stage of the growth of obliquely deposited Fe on a Si substrate held at 470 °C with atomic force microscopy (AFM) and high resolution Rutherford backscattering spectroscopy (HRBS). During the deposition from the normal direction, many Si atoms are displaced from their lattice position due to the reaction with the deposited Fe. On the contrary, the number of displaced Si atoms decreases significantly, and the nanoislands of a few 10 nm in diameter grow selectively when Fe is deposited at 85°. This is clear evidence that the local nucleation processes for the Fe silicide formation is modified by the geometrical deposition conditions.
INTRODUCTION Oblique angle deposition technique has attracted the interest of many researchers since it enables us to create unique nanostructures, such as zigzag [1] and helix [2]. In addition to these complex morphologies, the specific crystallographic phase has been selectively grown by oblique deposition as reported by Karabacak et al. They succeeded the selective growth of metastable β- W nanorods using an oblique-angle sputter deposition technique and attributed such peculiar selectivity to the dependence of the surface mobility of the deposited W atoms on the crystallographic phase [3]. Their concept may be extended to the modification of the initial growth stage of a reactive system such as metal silicide, since the local nucleation conditions strongly affect the phase of the resulting cluster of silicide [4, 5]. Among the various silicides we focus our attention on Fe-Si system, since iron silicides have diverse crystal structures and properties (semiconductor, metal, ferromagnetism, etc.) depending on their composition, such as FeSi, Fe3Si and FeSi2. They are also of increasing research interest as a strong candidate for device materials with small load to environment [6]. Although many efforts have been paid to clarify the growth mechanism [7-10] or to improve the film quality [11, 12] of iron silicides, control of the growth of iron silicide is insufficient for the practical applications. As mentioned above, the oblique angle deposition seems to be useful to modify the local nucleation conditions. However, there is no systematic study of reactive oblique-angel deposition (ROAD). In this paper, therefore, we report our first try to modify the local nucleation conditions by using ROAD, in which Fe was deposited on a hot Si substrate from oblique direction.
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EXPERIMENTAL DETAILS Samples were prepared in an ultrahigh vacuum (UHV) chamber which is connected to a 400 keV ion accelerator. After a surface oxidized n-type Si(001) wafer of 50×7×0.6 mm3 (resistivity ρ≈5.0 Ω cm) was loaded into the UHV chamber (base pressure 7×10-10 Torr), it was cleaned by annealing at 1200 ˚C for 3 s to remove
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