Phase formation during reactive molybdenum-silicide formation

Abstract

Silicide formation due to thermal treatment of thin (5–10 nm) molybdenum films on single-crystal, polycrystalline, and hydrogenated amorphous silicon substrates in the temperature range of 100 to 1000 °C was studied, with an emphasis on the initial interactions. The molybdenum deposition, annealing, and characterization using Raman scattering and Auger electron spectroscopy was carried out in UHV in order to minimize the effects of contaminants. Raman spectroscopy is used to distinguish between tetragonal (t-MoSi2) and hexagonal MoSi2 (h-MoSi2). The Raman spectrum of bulk tetragonal MoSi2 exhibits two prominent lines which are associated with the A1g (325 cm−1) and Eg (440 cm−1) modes. The only silicide phases detected in the thin film experiments were t-MoSi2 and h-MoSi2. While hexagonal MoSi2 does not appear in the bulk phase diagram, it is the first silicide phase formed in thin film reactions at a temperature between 300 and 400 °C. The nucleation temperature of h-MoSi2 was the same for Si〈100〉, Si〈111〉, and amorphous Si. Indirect evidence for disordered intermixing of silicon and molybdenum before nucleation of h-MoSi2 is found. Annealing at approximately 800 °C causes the silicide to transform from the hexagonal phase to the tetragonal phase for all substrates. Contaminants interfere with the formation of h-MoSi2 and also retard the transformation of h-MoSi2 to t-MoSi2. For the thin films considered here, the transformation to t-MoSi2 is accompanied by islanding of the silicide film. A lower interfacial energy between the silicon and silicide for h-MoSi2 has been proposed to explain the nucleation of h-MoSi2 before t-MoSi2.

Combustion wave structure during the MoSi2 synthesis by Mechanically-Activated Self-propagating High-temperature Synthesis (MASHS): In situ time-resolved investigations

“…The current observations are also in agreement with those reported by Park et al [42] who investigated the volume ignition of mechanically activated MoC2Si pellets. Their works support the solid-state reaction assumption for which the ignition temperature is lower when crystallite size decreases.…”

“…Thus, the formation of the bulk of a-MoSi 2 by MASHS can involve, in the early stage of the reaction, a solid-state diffusion process; the latter is certainly enhanced by the nanometric nature of the reactants, the intimate mixing between reactants and by the larger number of defects introduced during ball-milling. As reported by Doland et al [42], deposition of molybdenum thin film (5-10 nm thick) onto amorphous silicon subtract leads to the formation of molybdenum disilicide after annealing at a temperature between 300 and 400 8C. As a result, the polyinterfaces created at a nanometer scale would promote low temperature solidstate diffusion.…”

Solution growth of crystalline silicon on glass in the In–Si–Mo system

“…To assure the presence of h-MoSi 2 in the film, Raman spectra were recorded for wavenumbers from 200 to 530 cm À 1 . The characteristics of spectra match those reported for h-MoSi 2 by other authors [11,12]. We found the absolute positions of the phonon modes being in good agreement with the data of the cited authors (our data: 249, 347, 386, 412 cm À 1 , Doland et al: 210, 260, 395, 420 cm À 1 and weaker features between 260 and 395 cm À 1 , Reinig et al: 257, 354, 395, 426 cm À 1 ).…”

“…These measurements were supplemented by Raman spectroscopy. All spectra were recorded for wavenumbers from 200 to 530 cm À 1 , where molybdenum disilicides and crystalline silicon exhibit Raman-active phonon modes [11,12]. A He-Ne laser which operates at a wavelength of 632.8 nm was used for excitation.…”

Low-temperature synthesis of α- and β-MoSi2 powders using Na

“…␤-MoSi 2 powders have been prepared as mixtures with ␣-MoSi 2 , Mo, or an amorphous phase by MA [8][9][10]13] and by plasma spray methods [15,16] thin films were fabricated by annealing Mo and Si layers deposited on thermally oxidized Si wafers at 873 K [17], by annealing Mo films deposited on Si substrates at 773-963 K [18,19], and by As-ion implantation to Mo films deposited on Si substrates [20].…”