Alumina-Ti Interface Reactions Studied by AES and UPS
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H. Lefakis*, M. Liehr, G.W. Rubloff and P.S. Ho IBM T.J Watson Research Center Yorktown Heights, New York 10598
ABSTRACT The interaction of Ti with A12 0 3 under UHV conditions has been studied by AES and UPS. Ti was deposited by iterated and successively thicker evaporations (up to a total thickness of 91, A) under UHV conditions onto the alumina substrate at room temperature. The oxide substrate was grown on AI/Si(111) in an adjacent VHV preparation chamber. The last deposition was followed by in situ annealing. It was found that, contrary to indications of thermodynamic considerations using bulk equilibrium data, Ti interacts strongly with alumina at room temperature, dissociating it to metallic Al and forming TiO 2 at the interface. This reaction is limited, resulting in an interface width of ~-10 Xand allowing subsequent evaporations to homogeneously cover the products. Annealing to 5000C does not produce any evidence of outdiffusion or extensive interface reactions, implying that the interface oxide is stable and an effective barrier to Al (and/or Ti) diffusion up to this temperature.
I. INTRODUCTION The unique combination of excellent mechanical, electrical and chemical properties which aluminas possess, makes them attractive for microelectronic applications such as high-end packaging modules or, potentially, metal oxide semiconductor (MOS) devices. In these capacities the stability of and/or interactions at the alumina-metal interface become very important, especially when, to a first approximation, the heat of formation of an oxide of the adjacent metal is comparable to that of alumina. Titanium is an excellent case in point since it is both widely used in the microelectronics technology and known to spontaneously oxidize. Studies of a similar interface, namely SiO 2,/Ti, have shown that Ti interacts with silica even at room temperature [1-3]. This interaction is also clearly favored by thermodynamic considerations based on bulk equilibrium data of standard heats of formation [1]. The same considerations, using corresponding bulk thermodynamic data, do not indicate the existence of a strong driving force for reaction at the A120 3/Ti interface [4]. However, this is contrary to the results reported by Lofton and Swartz [5], who examined thin Ti films (
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