Cu and Dilute Binary Cu(Ti), Cu(Sn) and Cu(Al) Thin Films: Texture, Grain Growth and Resistivity

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Cu AND DILUTE BINARY Cu(Ti), Cu(Sn) AND Cu(Al) THIN FILMS: TEXTURE, GRAIN GROWTH AND RESISTIVITY A. Gungor, K. Barmak, A. D. Rollett, C. Cabral, Jr.1, J. M. E. Harper1 Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213 1 IBM T. J. Watson Research Center, P. O. Box 218, Yorktown Heights, NY 10598 ABSTRACT Annealing Cu and dilute Cu(Ti), Cu(Sn) and Cu(Al) alloy films resulted in the strengthening of film texture, with the strongest fiber texture being found for Cu(Ti). Annealing also resulted in a decrease of electrical resistivity and the growth of grains, with the largest grain size and lowest resistivity being seen for pure Cu itself. Among the alloy films, the lowest resistivity was found for Cu(Ti) and the largest grain size for Cu(Al). Electron beam evaporated films with compositions in the range of 2.0-3.0 at% and thicknesses in the range of 420-540 nm were annealed at 400˚C for 5 hours. Four point probe resistance measurement, xray diffraction and transmission electron microscopy were used to follow the changes in film resistivity, texture and grain size. INTRODUCTION The performance and reliability of metal interconnections are increasingly dependent on aspects of microstructure such as grain size and crystallographic orientation (texture) as line widths approach 100 nm. A recently proposed scheme to control the microstructure of Cu via alloying is to use the energy released by the decomposition of Cu-alloys - in addition to grain boundary, surface, and strain energy minimization – to drive grain growth and texture evolution[1]. Based on this scheme, in a study reported by Barmak et al., the impact of alloying elements on the decomposition and electrical resistivity of a group of dilute binary, Cu alloy films annealed at a constant heating rate up to 950˚C was investigated [2]. In this work, we focus on the evolution of resistivity, grain size and texture in dilute binary Cu(Ti), Cu(Al) and Cu(Sn) alloy films that are annealed isothermally at 400˚C. We compare and contrast the behavior of the alloy films with that for a pure Cu film. We find that for all films, including the pure Cu film, annealing lowers film resistivity, causes the grains to grow and strengthens film texture. However, the alloy films all have higher resistivities and smaller grain sizes than the pure copper film. The best combination of resistivity (relatively low) and fiber texture (strong), for an alloy film, is found for Cu(Ti), while the best combination of resistivity (low) and grain size (large) is found for pure Cu itself. EXPERIMENTAL Pure Cu and dilute binary Cu(Ti), Cu(Al) and Cu(Sn) alloy films were electron beam evaporated onto thermally oxidized silicon wafers. The composition and thickness of the films are listed in Table I. The films were isothermally annealed at 400˚C for 5 hours in a nitrogen atmosphere. The sheet resistance of the films before and after annealing was measured by a fourpoint probe technique. J3.2.1 Downloaded from https://www.cambridge.org/core. Columbia Univer

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