Silicide-Silicon Interface States
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E.S. YANG,* X. WU,* H.L. EVANS,* AND P.S. HO** * Columbia Radiation Laboratory and Center for Telecommunication Research, Columbia University, New York, NY10027 **IBM T.J. Watson Research Center, Yorktown Heights, NY 10598 ABSTRACT The existence and nature of localized states at metal-semiconductor interfaces are long-standing scientific issues that have not been resolved. As device dimensions continue to shrink and packing density continues to increase, interfaces at silicide-silicon contacts will be increasingly influential in determining the circuit behavior. Characterization of these interfaces, whether as ohmic contacts or rectifying junctions, is a necessity for microelectronics. Therefore, the study of silicide-silicon interfaces are important both scientifically and technologically. In this talk, we shall review the theoretical models of the Schottky barrier and the importance of interface states. We shall then introduce available experimental tools for interface state studies. In particular, we shall discuss the measurement of silicide-silicon interface states by an accurate-phase capacitance spectroscopy (APCS). Some of the devices were fabricated with standard chemical cleaning before metal evaporation. Others were prepared in an UHV chamber with heat cleaning before metal deposition. For palladium silicide diodes, the behavior of both chemically-cleaned and UHV-prepared samples is similar. The peak position of the capacitance spectrum correlates with the barrier height, and the magnitude of the peak decreases by a factor of three after annealing. In the case of nickel silicide diodes, a comparison between epitaxial and non-epitaxial interfaces shows much lower interface state density for the former. Experimental data indicate that silicide formation and interfacial perfection are important in specifying the Fermi level. I.
INTRODUCTION
Although the rectifying properties of a metal-semiconductor contact have been known for almost fifty years, the barrier formation is still not understood. Yet, the Schottky barrier is such a fundamental device in microelectronics that a thorough knowledge is needed to realize its full potential. The difficulty of the problem lies with the lack of information on the metal-semiconductor interface, i.e., experimental data of the electronic structure and interface states. In this paper, an attempt is made to review the current status of the relationship between interface states and the formation of the Schottky barrier. We shall restrict our discussion to silicide-silicon interfaces because of the following reasons: (1)silicide contacts are readily reproducible, (2) clean and controlled interfaces have been fabricated with both epitaxial and non-epitaxial structures, (3) these interfaces are well characterized by spectroscopic and micro-analytical techniques, and (4) silicide junctions are important in both bipolar and MOS technology. We shall begin with a survey of the important models of the Schottky barrier. Relevant data from surface spectroscopies will be presented to
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