Silver Metallization with Reactively Sputtered TiN Diffusion Barrier Films
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Silver Metallization with Reactively Sputtered TiN Diffusion Barrier Films L. Gao1, J. Gstöttner1, R. Emling1, Ch. Linsmeier2, M. Balden2, A. Wiltner2, W. Hansch1, D. Schmitt-Landsiedel1 1 Institute for Technical Electronics, Technical University Munich, D-80333, Munich, Germany 2 Max-Planck-Institut für Plasmaphysik, EURATOM Association, D-85748, Garching, Germany
ABSTRACT The physical and electrical properties as well as thermal stability of reactively sputtered titanium nitride (TiN) film serving as a diffusion barrier was studied for silver (Ag) metallization. The thermal stability of Ag/TiN metallizations on Si with 12-nm-thick TiN barriers, as-deposited and after annealing at 300-6500C in N2/H2 for 30 min, was investigated with sheet resistance measurement, X-ray diffraction, focused ion beam-scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. According to electrical measurement no change of sheet resistance was found after annealing at 6000C, but an abrupt rise appeared at 6500C annealing. There are two causes by which the Ag/TiN/Si structure became degraded. One is agglomeration of the silver layer, and the other is oxidation and diffusion which are also associated problems during thermal annealing. INTRODUCTION A high performance interconnection network on a chip is becoming increasingly important for ultra large-scale integration (ULSI) of Si integrated circuits. Continued shrinking of devices has led to a discrepancy between the transistor and interconnect performance [1]. Because of its high electrical conductivity and its good electromigration properties, copper replaces aluminum in some microelectronic applications [2]. However, Cu resistivity increases substantially in sub100-nm technology due to the size effect. Silver, with the lowest bulk resistivity among the conductor metals and similar or even higher electromigration resistance, is one of the best potential candidates for future interconnect metallization [3-5]. Until now, a large number of barriers against Cu diffusion have been investigated. The usage of Ag interconnects in Si ULSI devices requires also development of barrier layers which prevent Ag diffusion into the Si substrate and SiO2 insulators at elevated temperatures. Thin aluminum oxynitride (AlxOyNz) diffusion barriers have been formed in high temperature by annealing Ag/Al bilayers on oxidized Si substrates in ammonia ambient, in which Ag is deposited by electron-beam evaporation [6]. Diffusion and electromigration behavior was investigated for sputtered Ag lines with different barrier layers of Al2O3, Si3Ni4 and Ti [5]. Titanium nitride (TiN) barriers, which are thermally stable at high temperature, have been widely investigated to prevent interdiffusion of Cu in ULSI [7,8]. This report discusses process development and characterization of TiN as a diffusion barrier for silver metallizations. The sample structure in this work is Ag (200 nm)/TiN (12 nm)/Si. Finally, a possible failure mechanism of TiN barrier in preventing Ag diffusio
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