Tuan Tran1 Lukas Jablonka2 Zhen Zhang2 Daniel Primetzhofer1

1, Department of Physics and Astronomy, Uppsala University, Uppsala, N/A, Sweden
2, Solid State Electronics, The Ångström Laboratory, Uppsala University, Uppsala, , Sweden

Metal silicide, as a contact material, has played a vital role in advancing the performance of electronic devices due to its excellent electrical properties and thermal stability. As the device dimension is constantly reduced, precise understanding of the scaling behaviour of the silicide materials as well as silicide-Si interfaces is very crucial for both process integration and the device performance. For example, the typical phase evolution of nickel silicide (Ni-Si) with increasing temperature is, in general, from the metal-rich phase Ni2Si to mono-silicide NiSi and finally the silicon-rich phase NiSi2. The intermediate phase NiSi is often desired because it has the lowest resistivity and is stable up to 600 - 700oC [1]. However, it is reported that for a film thickness lower than 6 nm NiSi2 can directly grow epitaxially, bypassing the formation of the two former phases [2]. The morphologically stability of NiSi phase has been improve by the incorporation of platinum 5 - 10% (Pt) [3]. With the current fast-paced development of electronic devices, there is a substantial demand for the precise control of the silicide layer thickness at the scale of less than 5 nm, leading to the requirement of advanced characterization techniques.
Rutherford backscattering spectrometry (RBS) has been a versatile method for material research for more than five decades [4]. It can measure the composition, the thickness and the crystallinity of the materials in a non-destructive way. However, conventional RBS at the energy of 2 MeV is only effective for depth profiling films with thickness larger than 20 nm. The depth resolution can be improved by using low and medium energy ion scattering (LEIS and MEIS). The achievable depth resolution of this instrument is below 2 nm [5]. Moreover, an advanced detection method such as a position-sensitive time-of-flight (TOF) detector is able to acquire the blocking pattern of the scattered beam and reveal the crystal structure of the materials, particularly at the near surface.
In this presentation, an in-situ characterization of the silicide formation will be presented for film thicknesses of 5 - 20 nm. For this aim the samples are subjected to thermal annealing from 100 - 600oC in the high vacuum scattering chamber of the ToF-MEIS system. We study in details the phase evolution of the silicide films as indicated by the film compositional profile. In parallel, we attempt to analyse the blocking patterns for the epitaxial layers and the role of Pt in stabilizing the NiSi phase. The real-time studies will provide insights into the silicidation process, relevant for fine-tuning the manufacturing pathways.

[1] C. Lavoie, F. M. d’Heurle, C. Detavernier, and C. Cabral, Microelectronic Engineering 70, 144 (2003).
[2] R. T. Tung, J. M. Gibson, and J. M. Poate, Physical Review Letters 50, 429 (1983).
[3] Z. Zhang et al., Applied Physics Letters 97, 252108 (2010).
[4] W.-K. Chu, Backscattering spectrometry (Elsevier, 2012).
[5] M. K. Linnarsson, A. Hallén, J. Åström, D. Primetzhofer, S. Legendre, and G. Possnert, Review of Scientific Instruments 83, 095107 (2012).