Interfacial reactions in the Si/TaC/Cu system T. Laurila a, * , J. Molarius b , J.K. Kivilahti a a Laboratory of Electronics Production Technology, Helsinki University of Technology, P.O. Box 3000, FIN-02015 HUT, Espoo, Finland b VTT Microelectronics, P.O. Box 1208, FIN-02044 VTT, Espoo, Finland Received 11 November 2003; received in revised form 12 January 2004; accepted 3 February 2004 Abstract Interfacial reactions in the Si/TaC/Cu metallization system were investigated by utilizing transmission electron microscopy and a combined kinetic and thermodynamic analysis. The formation of an amorphous Ta[C,O] layer was observed at the TaC/Cu interface at 600 °C. After annealing at the same temperature a thin amorphous layer was detected also at the Si/TaC interface. After annealing at 750 °C the thickness of the amorphous layer at the Si/TaC interface had increased and a mixture of crystalline and amorphous phases could be detected inside the TaC layer. This was anticipated to be the preliminary stage of the formation of SiC and TaSi 2 that occurred at 800 °C. Overlapping with thickening of the amorphous layer formation of large Cu 3 Si precipitates took place and the layered metallization structure was partially destroyed. In order to obtain more information on the reactions at the Si/TaC interface and the effect of oxygen on the stability of TaC the ternary Si–Ta–C and Ta–C–O phase diagrams were evaluated from the assessed binary data. Activity diagram was also calculated to evaluate the possible reaction sequence at the Si/TaC interface. The observed reaction structure was found to be consistent with the thermodynamics of the ternary system. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Thermodynamics; Diffusion barrier; Tantalum carbide 1. Introduction The current trend of scaling down the dimen- sions of integrated circuits in order to achieve better electrical performance places serious de- mands for materials used in silicon-based devices. In particular, thin film interconnections are be- coming the limiting factor in determining perfor- mance and reliability of integrated circuits. Aluminum has been the most widely used material for metallization in very-large-scale integration (VLSI) and ultralarge-scale integration (ULSI) circuits during the past decades. However, as crit- ical dimensions of devices have approached sub- micron dimensions, reliability requirements has ruled out the possibility of using pure aluminum. In order to improve reliability, alloys with several additives such as Si, Cu, Ti, Pd, Cr, Mg and Mn, have been tested [1]. The improvement in the elec- tromigration performance thus achieved remains to date limited and is offset by the corresponding increase in interconnection resistivity [1,2]. * Corresponding author. Tel.: +35894514990; fax: +35894515 776. E-mail address: tomi.laurila@hut.fi (T. Laurila). 0167-9317/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2004.02.002 www.elsevier.com/locate/mee Microelectronic Engineering 71 (2004) 301–309