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FORMATION AND SILICON BEHAVIOR IN TITANIUM TANTALUM LAYERED ALUMINUM FILMS.

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B.W. Shen.* J.M. Anthony,** P-H. Chang.** J. Keenan.** R. Matyi**. and H.L. Tsai** * Semiconductor Process and Design Center, ** Central Research Laboratory, Texas Instruments, Inc. P.O. Box 225621. M.S. 944. Dallas, Texas 75265. ABSTRACT Thin film interaction in the material systems of titanium and tantalum-layered Al- 1% Si films has been studied using advanced material characterization techniques. Compound phase formation was analyzed based on results from X-ray diffraction analysis. AI3Ti was identified in the titanium-layered film after 450°C sintering. TaSi2 and unreacted Ta, however, were identified after the sintering. Silicon participated in the phase formation process by incorporating itself as a solute in the AI3Ti while transforming Ta into its silicide. This behavior is to be interpreted based on available ternary phase diagrams. Cross-sectional transmission electron microscopy results indicate that well defined layered films and columnar grains of aluminum were obtained which are believed to be the primary reasons for the observed electromigration improvement over the base metal. INTRODUCTION Aluminum films when layered with transition metals have been shown to significantly improve the electromigration properties over that of the base aluminum [1.2]. Howard et al. [1] first reported electromigration results on Cr. Ti. and Ta layered films of AI-4%Cu. Mean time to failure(MTTF) improvement by as much as 100 times was reported. Shen et al. [2] recently reported their results on Ti layered AI-1%Si. improvement of MTTF by 15 times was observed. Similar improvement has been reported when layered with titanium silicide [3]. It was also reported that significant hillock suppression was observed and a smoother surface was produced after sintering [2.41. making this material extremely interesting for its potential application in VLSI multilevel interconnection. Reaction kinetics between pure aluminum and some transition metals between 325"C to 575°C have been investigated by Howard et al.[5]. The effects of Cu addition to aluminum on Hf and Ti reaction with aluminum were reported by Huang and Wittner [6] at temperature range of 325°C to 450°C. Similar work in copper doped aluminum/vanadium system between 410'C to 500°C was reported by Colgan et al. [7]. While Cu was reported to retard the reaction kinetics, refractory metalaluminides were always the observed phases in these reports. No refractory metalcopper compound phases were ever reported. Silicon addition to the aluminum is commonly used in IC manufacturing to prevent junction penetration. Effect of silicon and its behavior in the refractory metal-layered aluminum films, to the best knowledge of these authors, have never been systematically studied. We have applied advanced material characterization techniques like x-ray diffraction(XRD). secondary ion mass spectroscopy(SIMS). Rutherford backscattering(RBS). and transmission electron microscopy(TEM) to study the compound ph