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  • Print publication year: 2010
  • Online publication date: July 2014

8 - Interdiffusion and reaction in thin films



Modern microelectronic semiconductor devices use layered thin films on Si wafers. Interdiffusion and reaction between two neighboring thin-film layers has been a technological issue from the point of view of yield and reliability of the devices. On a piece of Si chip the size of a fingernail, there are now more than several hundred millions of FETs, each of them with source, drain, and gate contacts. These contacts are typically made of silicides, which are IMCs of metal and Si, and each of the contacts must be the same or have the same electrical properties. Hence, in manufacturing VLSI circuits on a Si chip, the formation of silicide contacts and gates has been a critical processing step. So the controlled formation of silicide by depositing and reacting a thin metal film on a Si substrate has been a very active area of study [1–4]. What is unique in the thin-film interfacial reaction is the requirement of “single-phase formation” [5]. This means that we need to form a specific single-silicide phase in all the contacts and gates. Why it is unique is because of the difference between the reaction in bulk diffusion couples and that in thin-film couples. Multiple phases are formed simultaneously in the bulk couples, but multiple phases are formed sequentially one-by-one in thin films, so we can have single-phase instead of multiple-phase formation in thin-film reactions.

[1] J. W., Mayer, J. M., Poate and K. N., Tu, Thin films and solid-phase reactions, Science, 190 (1975), 228-234.
[2] K. N., Tu and J. W., Mayer, “Silicide Formation,” Ch. 10 of Thin Films: Interdiffusion and Reactions, eds J. M., Poate, K. N., Tu and J. W., Mayer (Wiley-Interscience, New York, 1978).
[3] Marc-A., Nicolet and S. S., Lau, “Formation and characterization of transition-metal sili-cides,” in VLSI Electronics, Vol. 6, eds N. G., Einspruch and G. B., Larrabee (Academic Press, New York, 1983).
[4] L.J., Chen and K. N., Tu, “Epitaxial growth of transition-metal silicides on silicon,” Materials Science Reports 6 (1991), 53-140.
[5] U., Goesele and K. N., Tu, “Growth kinetics of planar binary diffusion couples: thin film case versus bulk cases”, J. Appl. Phys. 53 (1982), 3252.
[6] S. H., Chen, L. R., Zheng, C. B., Carter and J. W., Mayer, “Transmission electron microscopy studies on the lateral growth of nickel silicides”, J. Appl. Phys. 57 (1985), 258.
[7] H., Foell, P. S., Ho and K. N., Tu, “Cross-sectional TEM of silicon-silicide interfaces”, J. Appl. Phys. 52 (1981), 250.
[8] R. T., Tung and J. L., Batstone, “Control of pinholes in epitaxial CoSi2 layers on Si(111)”, Appl. Phys. Lett. 52 (1988), 648.
[9] Kuo-Chang, Lu, Wen-Wei, Wu, Han-Wei, Wu, Carey M., Tanner, Jane P., Chang, Lih J., Chen and K. N., Tu, “In-situ control of atomic-scale Si layer with huge strain in the nano-heterostructure NiSi/Si/NiSi through point contact reaction,” Nano Letters 7:8 (2007), 2389–94, s.
[10] Y. C., Chou, W. W., Wu, L. J., Chen and K. N., Tu, “Homogeneous nucleation of epitaxial CoSi2 and NiSi in Si nanowires,” Nano Lett. 9 (2009), 2337–42.