Electrical Properties of Epitaxial Silicide-Silicon Interfaces
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R. T. TUNG,* A. F. J. LEVI,* J. M. GIBSON,* K. K. NG* AND A. CHANTRE** *AT&T Bell Laboratories, Murray Hill, New Jersey 07974 **CNET, Grenoble, France
ABSTRACT The Schottky barrier heights of single crystal NiSi 2 layers on Si(l 1l) have been studied by current-voltage, capacitance-voltage and activation energy techniques. Near ideal behavior is found for Schottky barriers grown on substrates cleaned at -820"C in ultrahigh vacuum. The Fermi level positions at the interfaces of single crystal type A and type B NiSi 2 are shown to differ by -0.14 eV. Transmission electron microscopy demonstrated the epitaxial perfection of these silicide layers. At a cleaning temperature of 1050"C, the near surface region of lightly doped n-type Si was converted to p-type. The presence of a p-n junction was directly revealed by spreading resistance measurements and resulted in a high apparent Schottky barrier height (>0.75 eV) which no longer bears immediate relationship to the interface Fermi level position.
INTRODUCTION Epitaxial single crystal metal-semiconductor interfaces are ideal systems for Schottky barrier height (SBH) studies. Because of the homogeneity in their interface structure and electronic properties, direct correlation between the observed SBH and the physical parameters is possible. The system consisting of NiSi 2 on Si(l 11) has been shown to be nearly perfect in epitaxial structure [1]. The atomic structure of the interface has been modelled by high resolution transmission electron microscopy (TEM) [2-31 and ion channeling [41, making the system an ideal case for SB studies. Moreover, a unique comparison is offered in that NiSi 2 layers can be formed on Si(l 11) with either one of the two epitaxial orientations, type A or type B [I]. An A-type NiSi 2 layer has the same orientation as the Si(l 11) substrate, while a B-type layer shares the normal axis with the substrate but is rotated 180° about this axis with respect to the substrate. With the observed interface structure differing only by third nearest neighbor atoms and beyond, the A and B interfaces are identical in all bulk parameters which are thoughte to affect the SBH. The experimentally determined interface atomic positions are accurate to -0.•A, however a substantial difference of 140 mV between SBH's of type A and type B was observed experimentally [5]. This was a significant discovery because the variation of SBH with orientation was not in agreement with previous SBH experiments on polycrystalline systems and was also in conflict with the predictions of many existing SB models. A mechanism of intrinsic nature is suggested by such a correlation of SBH with details of interface microstructure. In this paper, we present results of a recent exhaustive study of the SBH's and structures of the epitaxial NiSi 2-Si(I 11) interfaces. EXPERIMENTAL PROCEDURES Float-zone and Czochralski-grown Si wafers with doping concentration between ND - IX l014 and 6 3 3x101 cm- were used in this study. These wafers were cut to within 0.5 of the (11) plane. Borondoped p-typ
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