Micro-raman spectroscopic investigation of NiSi films formed on BF 2 + - , B + - and nonimplanted (100) Si substrates
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Micro-raman spectroscopic investigation of NiSi films formed on BF2+-, B+-and nonimplanted (100) Si substrates S. K. Donthua , D. Z. Chia, A. S. W. Wonga, S. J. Chuaa,b and S. Tripathyb a) Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602 b) Centre of Optoelectronics, Department of Electrical Engineering, National University of Singapore, 2 Engineering Drive, Singapore 119260 ABSTRACT Micro-Raman spectroscopic technique was used to investigate vibrational properties of NiSi thin films formed on three different (100) Si substrates: non-implanted, 20-keV BF2+-implanted, and 20-keV B+-implanted. Raman spectroscopy was also performed on NiSi powder to identify various phonon modes associated with different selection rules of group theory. It was found that Raman peaks of NiSi thin films formed on BF2+ implanted substrate were broader and shifted to lower frequency side compared to films formed on other substrates. The broadening of the Raman peaks in these films, which also exhibit much improved thermal stability, is attributed to small grains resulting probably from fluorine segregation to grain boundaries and interface. It is further proposed that besides grain boundary segregation, the excess fluorine in the film influences the stress-state in the silicide film resulting in shift of phonon peak positions. INTRODUCTION Nickel mono-silicide (NiSi) has been considered as a potential alternative to the currently used silicides (TiSi2 and CoSi2) for 0.1 or sub 0.1-micron generation complementary metal-oxidesemiconductor (CMOS) devices due to its linewidth-independent resistivity, low silicon consumption and one-step annealing process [1-2]. On the other hand, Raman spectroscopy has proven to be an effective technique for in-situ characterization of silicide formation and thus can be used for process development [3-5]. Raman spectrum serves as a material fingerprint with each peak in the spectrum corresponding to a unique vibrational mode of the lattice. Besides phase identification, raman spectroscopy can also provide other valuable information such as strain state, nucleation site density and grain size in a silicide material [6]. Though raman spectroscopy was used extensively to study titanium and cobalt silicide reactions, its application for NiSi characterization remains largely underdeveloped. This is partly due to the unavailability of characteristic raman spectrum for NiSi [7]. In this paper, we report polarized raman spectra of NiSi film as well as NiSi powder and identify phonon modes associated with different selection rules of group theory. We further report the results of studies performed on NiSi films formed on (100) Si substrates implanted with different dopants and demonstrate the feasibility of using raman spectroscopy technique to study the effect of dopants, fluorine in particular, on phase stability of NiSi. EXPERIMENTAL Micro-raman spectroscopy was performed using 514.5-nm line of argon ion laser. The scattered light was dispersed through JY-T64000 triple monochromator
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