Epitaxial growth of copper nanowire arrays grown on H-terminated Si(110) using glancing-angle deposition
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We report the growth of epitaxial nanowire arrays using the technique of glancingangle deposition with substrate rotation. Epitaxial copper nanowire arrays were deposited on H-terminated Si(110) using electron beam evaporation. The nanowire arrays were characterized by x-ray diffraction, atomic force microscopy, and scanning electron microscopy. Individual nanowires were confirmed to be single crystalline by examination with transmission electron microscopy. The epitaxial growth involves twin formation with the epitaxial orientation relationships: Cu(111)//Si(110) with Cu[11¯0]//Si[001] and Cu[1¯10//Si[001] for each of the twins. As the angle of incidence is increased, Cu grows as isolated columns with a spacing that increases as the angle of incidence is increased. However, the thickness limit for epitaxial growth is reduced as the angle of incidence is increased, and it is reduced to approximately 300 nm for a deposition angle of 75°. The x-ray rocking curves for samples deposited at increasing polar angles show steadily improving crystal orientation up to a deposition angle of about 35°. Beyond 65° deposition angle, the rocking curves show significantly sharper split diffraction peaks indicating that there are distinct orientations. In addition, the split peaks have a much lower full width at half maximum. The observed behavior is explained based on arguments involving unidirectional diffusion arising from adatom parallel momentum.
I. INTRODUCTION
Due to the wide range of industrial and technological applications in relation to the production of semiconductor, electronic, and magnetic devices, thin film epitaxy has been the subject of extensive study in recent decades. Epitaxial growth of copper on silicon is one of the wellknown examples of heteroepitaxy and has been discussed in several papers.1–3 The epitaxial orientation relationship of copper on silicon depends on the lattice symmetry of the silicon surface. Epitaxial copper films grown on Si(100) have the Cu[100] crystallographic orientation normal to the substrate. Copper deposited on Si(111) or Si(110) substrates show Cu[111] texture. Cu(111) on Si(110) possess better epitaxial qualities due to the lower lattice misfit. Epitaxial films grown using glancing-angle deposition (GLAD) with substrate rotation, however, have not been reported to date. GLAD employs oblique angle deposition and substrate motion to engineer thin-film structure on a nanometer
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0465 3620
J. Mater. Res., Vol. 19, No. 12, Dec 2004
scale in three dimensions. In this process, a fibrous structure of highly oriented nanoarrays is deposited by physical evaporation or sputtering. The pitch, orientation, diameter, and porosity can be controlled by the film growth parameters.4 GLAD has the advantage that large arrays of structures can be made with spacing between the elements on the order of tens to hundreds of nanometers. The size of the individual elements is determined by materials propert
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