Materials Characterization of Alternative Gate Dielectrics
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Materials
Characterization of Alternative Gate Dielectrics
Brett W. Busch, Olivier Pluchery, Yves J. Chabal, David A. Muller, Robert L. Opila, J. Raynien Kwo, and Eric Garfunkel Abstract Continued scaling of microelectronic devices is demanding that alternatives to SiO2 as the gate dielectric be developed soon. This in turn has placed enormous pressure on the abilities of physical characterization techniques to address critical issues such as film and interface structure and composition, transport properties, and thermal or chemical stability. This article summarizes the strengths and capabilities of four techniques used for the materials characterization of alternative gate dielectrics: scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), medium-energy ion scattering (MEIS), infrared-absorption spectroscopy (IRAS), and x-ray photoelectron spectroscopy (XPS). The complementary nature of these techniques has allowed for a detailed picture of the various properties of alternative gate dielectrics, and in particular of the dielectric/silicon interface. Critical issues and features of several important alternative gate dielectrics, ZrO2, Al2O3, Y2O3, and Gd2O3, are explored in light of the well-studied SiO2 /Si system. Keywords: chemical structure, electron energy-loss spectroscopy (EELS), highdielectric-constant materials, high- dielectrics, medium-energy ion scattering (MEIS), infrared-absorption spectroscopy (IRAS), physical characterization, scanning transmission electron microscopy (STEM), thin films, x-ray photoelectron spectroscopy (XPS).
Introduction One of the more difficult aspects of engineering a viable, alternative high- gate dielectric stack has been to determine the structure and composition of a given film. This is especially relevant at the interface, where in order to maintain the advantage of a high- material, namely, achieving low electrical thickness (or higher gate capacitance) with a larger physical thickness, one must prevent the formation of a low- SiOx layer during or after film deposition. To this end, physical characterization techniques are necessary in which the composition of a dielectric layer can be determined with a resolution approaching the angstrom level, or alternatively, with a sensitivity better than one monolayer.
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In this article, we discuss several powerful experimental methods that we have used to examine high- films, focusing on the nature and accuracy of information that they yield. Because of the complexity of the problem, the complementary information that these tools provide is necessary if we are to build up a full atomic-scale understanding of high- gate stacks, including their ultimate electrical properties. A key goal of our physical and chemical characterization has been to determine the composition and structure as a function of depth and processing history, with a special emphasis on interface behavior and SiO2 composition. We first briefly outline key features of each technique, citing some
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