Reconstruction of (100) Silicon/Disilicide Interfaces
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RECONSTRUCTION OF (100) SILICON/DISILICIDE INTERFACES D. LORETITO*, J. M. GIBSON*, ALICE E. WHITE*, K. T. SHORT*, R. T. TUNG*, S. M. YALISOVE*, and J. L.BATSTONE** *AT&T Bell Laboratories, 600 Mountain Ave., Murray Hill, NJ 07974 "**Dept. of Materials Science and Engineering, The University, P. 0. Box 147, Liverpool, L69 3BX, U. K.
ABSTRACT A 2x1 reconstruction has been observed at the Si/NiSi 2 (100) and Si/CoSi 2 (100) interfaces. The reconstruction has been found in both ion-implanted (mesotaxial) material and in material grown by molecular beam epitaxy (MBE). The reconstruction is apparent in HREM images obtained from cross sections and in transmission electron diffraction (TED) patterns from (100) orientation samples. We propose that the reconstruction is due to a layer of dimerised silicon atoms at the interface. We conclude that the 2x1 reconstruction is a low energy state of the silicon/disilicide(100) interface.
INTRODUCTION The reordering, or reconstruction, of free crystal surfaces in ultra high vacuum (UHV) is a well known phenomenon which has been studied for many years. Recently however reordering at the interface between crystals has been reported by several workers: Akimoto and coworkers used X-ray diffraction to investigate reordering of the AI/GaAs(100) interface [1], the AlN/GaAs(100) interface [2] and between epitaxial Si(ll1) and boron-terminated Si(ll1) substrates [3]. and Bourret and coworkers[4], saw reconstruction of grain boundaries in germanium using HREM and transmission electron diffraction (TED). In this paper we study the reordering of the Si(100)/CoSi 2 (100) and the Si(100)/NiSi 2 (100) interfaces, produced by two different techniques: ion-implantation and Molecular Beam Epitaxy (MBE). We have used HREM and TED in this study. Since NiSi 2 and CoSi 2 have the fcc flourite structure with lattice constants close to silicon (smaller by 0.4% and 1.2% respectively) epitaxial disilicide/silicon systems with flat and abrupt interfaces can be grown. These systems have applications in silicon devices based on ballistic transport[5,6], where the interfacial structure is of particular importance. Previous studies of the disilicide(100)/silicon(100) interface using HREM have shown that the rigid shift across the interface is consistent with a model where the silicide is terminated by a plane of six-fold co-ordinated metal atoms [7,8]. In their HREM study of NiSi 2/Si(100) Chems and Hetherington saw an occasional doubling of the periodicity at the interface, which they attributed to either an interface reconstruction or to microfacetting [9], but they did not publish their findings. A structural investigation of an interface is most easily done with penetrating radiation (HREM, TED, X-ray diffraction), which has the advantage that, in cases where the incident beam is perpendicular to the interface, the scattering from the interface is weak and can therefore be interpreted relatively simply from a kinematical or single scattering model. The study of buried interfaces does not require high vacuum
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