Reactive Diffusion in Ni-Si Bulk Diffusion Couples
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Section I: Basic and Applied Research
Reactive Diffusion in Ni-Si Bulk Diffusion Couples S. Oukassi and F. Hodaj
(Submitted January 16, 2009; in revised form February 26, 2009) Reactive diffusion in the Ni-Si system has been studied using bulk polycrystalline Ni/Si wafer diffusion couples in the temperature range from 450 to 700 °C and with annealing times of up to 32 h. For all diffusion couples, three phases were detected Ni2Si, Ni3Si2, and NiSi. The thickness e of the reaction product is not homogeneous; its global growth kinetics satisfies the parabolic law and the total growth coefficient k2 (e2 = k2t) is found to be expressed by: k2 = 2.531024 exp (2160 kJ/RT ), in m2/s. The Ni2Si layer is homogeneous in thickness, and the value of its growth coefficient obtained by extrapolation at lower temperatures is more than two orders of magnitude smaller than the values obtained in thin-film experiments.
Keywords
binary diffusion, diffusion couples, experimental kinetics
1. Introduction Transition metal silicides play an active role in silicon semiconductor device technology, and thin-film metal/bulk silicon reactions have been studied extensively. The remarkable finding was that silicides can form at much lower temperatures in thin-film metal bulk/silicon couples than in bulk/bulk couples.[1] Moreover, it has been well known for several decades that reactive diffusion in thinfilm metal/silicon bulk couples usually demonstrates ‘‘oneby-one’’ (sequential) phase formation,[2,3] whereas in bulk/ bulk diffusion couples, intermediate phases were found simultaneously. The reaction of Ni and Si for possible use in microelectronics manufacturing has been extensively studied, starting in the mid-1970s.[2,4] Recently, interest in the low resistivity NiSi compound increased significantly because of its foreseeable use as a contact for the source, drains and gates of complementary metal-oxide-semiconductor (CMOS) devices. In the literature, the growth kinetics of intermediate phases in Ni-Si bulk diffusion couples is studied in the temperature range from 550 to 900 C, and Ni31Si12 (also referred to as Ni5Si2), Ni2Si, Ni3Si2, and NiSi phases were found simultaneously.[1,5-8] On the contrary, in Ni thin-film/bulk Si couples the growth kinetics of some intermediate phases is studied only in lower temperature ranges. For example, the growth kinetics of the Ni2Si phase has been studied only for temperatures below about 330 C (see, for example, Ref 9) because, at higher temperature, the Ni2Si phase disappears in favor of other phases (sequential phase formation). S. Oukassi and F. Hodaj, SIMAP—UMR CNRS 5266, Grenoble INP—UJF, BP 75 38402 St. M d’He`res Cedex, France. Contact e-mail: [email protected].
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In studies of thin-film interdiffusion couples, it has been recognized that the kinetic process is usually determined by grain-boundary diffusion in a fine-grained thin film, and, consequently, interdiffusion can occur faster than in bulk samples at lower temperatures. Although the differences between thin-film and bulk interdiffu
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