Extensive Raman spectroscopic investigation of ultrathin Co1−xNixSi2 films grown on Si(100)

Abstract

Ultrathin silicide films were formed by starting from 1–8 nm thick Co1−xNix (x = 0, 0.25, 0.5, 0.75, and 1) at 350 °C–900 °C. For each composition x, there exists a critical thickness above which the transition temperature from monosilicides CoSi and NiSi to a disilicide-like phase increases with increasing film thickness. Below this thickness, the disilicide phase seems to form without exhibiting the monosilicides within the detection resolution limits of transmission electron microscopy and Raman spectroscopy. Raman spectroscopic analysis seems to indicate that Ni could be dissolved in the CoSi lattice to a certain fraction despite the fact that CoSi and NiSi are distinct with different crystallographic structures. Moreover, the disorder-induced Raman scattering in NiSi2 is found to be enhanced by Co incorporation. The observed annealing behaviors are attributed to variations in free energy change for phase transition caused by differences in metal thickness.

Investigation of mixing Co in ultra-thin NiPt silicide films

“…The bumps of Raman spectra for the 16 nm (NiCoPt)-samples annealed at 500 o C and 550 o C in Fig. 3 also demonstrate that monosilicide is formed [6]. When the temperature increases to 650 o C, the bumps disappear and disorder-induced Raman scattering (DIRS) occurs in Fig.…”

“…When the temperature increases to 650 o C, the bumps disappear and disorder-induced Raman scattering (DIRS) occurs in Fig. 3, which indicates that disilicide for 16 nm (NiCoPt)-samples is formed [6,7]. What's more, the XTEM micrograph along with two EDS line-scans and the diffraction patterns shown in Fig.…”

“…Formation of epitaxially aligned silicide, which requires low lattice mismatch between the formed silicide and the underlying silicon, is an effective way to reduce the surface energy and hence increase the structural stability of the silicide. Since the lattice mismatch between Co 1-x Ni x Si 2 and Si is rather small [6], in this work, Co is mixed in the NiPt silicide system in an attempt to improve the structural stability of the ultra-thin NiPt films.…”

A Study on the Electrodeposition and Silicidation of Nickel-Cobalt Alloys for Silicon Photovoltaic Cell Metallization

“…21,24,[37][38][39][40][41][42][43][44] Although the interest was later shifted to the nickel monosilicide for that application, the ternary silicide was then of interest as alternative to CoSi 2 because the addition of Ni improves the nucleation of Co disilicide and reduces the silicide roughness and Si consumption. Therefore, not only all those studies 21,24,[37][38][39][40][41][42][43][44] were based on vacuum deposited extremely thin films but also most of them focused on the disilicide formation from Co rich alloys at high temperatures above 500 • C. One article, 41 however, reported the silicidation of Ni 50 Co 50 films. While a much thinner film, 10 nm, and a much higher temperature, 700 to 1100 • C, were used, the Ni concentration peak was found slightly deeper than Co, consistent with the observation in Figure 3.…”

“…21,24,[37][38][39][40][41][42][43][44] Although the interest was later shifted to the nickel monosilicide for that application, the ternary silicide was then of interest as alternative to CoSi 2 because the addition of Ni improves the nucleation of Co disilicide and reduces the silicide roughness and Si consumption. Therefore, not only all those studies 21,24,[37][38][39][40][41][42][43][44] were based on vacuum deposited extremely thin films but also most of them focused on the disilicide formation from Co rich alloys at high temperatures above 500…”