Formation Of MoSi2 Research Articles

Oxide Barriers to the Formation of Refractory Silicides

ABSTRACTAn investigation of the formation of refractory metal (tungsten, molybdenum and tantalum) silicides by reaction of the metal with crystalline and polycrystalline silicon at temperatures above 900°C indicates that WSi2 formation can be inhibited by certain processing techniques. These techniques utilize the growth of an SiO2 diffusion barrier about 20 Å thick on crystalline silicon and the deposition of tungsten films in vacuum ambients that will ensure oxygen incorporation (P ≥ 2 × 10−7 Torr). The reactivity of vacuum-deposited tungsten films results in the formation of an isolating oxide between the deposited silicon and tungsten films and the maintenance of the stability of the SiO2 diffusion barrier between tungsten films and a crystalline silicon substrate. This barrier is effective up to 1050°C in hydrogen ambients containing 15–20 ppm H2O. These procedures, however, are ineffective in preventing the formation of MoSi2 or TaSi2 at or above 900°C. A possible explanation for these results is that the tungsten film contains some level of oxygen due to the gettering of residual oxygen in the vacuum. In addition, the outgassing of the silicon source may enhance the level of oxygen at the evaporated W-Si interface. When the composite layer is annealed at high temperatures in a hydrogen ambient, the oxygen diffuses readily out of the bulk of the tungsten film to the interface, probably forming Sio2 which is more stable than WO3.The resulting thin SiO2 film has sufficient integrity to prevent silicon diffusion into the tungsten, thereby preventing WSi2 formation. This property of tungsten makes it inherently useful for buried-metal films in silicon devices.

The formation of silicides in Mo-W Bilayer films on si substrates: A marker experiment

Use is made of the metallurgical similarity between Mo and W, and of their different atomic weights to study the diffusive formation of MoSi2 and WSi2. Thin film bilayers of Mo and W were deposited via e-beam evaporation upon Si single crystal substrates and annealed in an inert atmosphere at temperatures up to 1000‡C. The annealed samples were analysed by means of Rutherford backscattering and x-ray diffraction. The results indicate that Si is the dominant diffusing species. Observations on the formation of WSi2 are consistent with a process dominated by grain boundary diffusion through the W film.

A Penning ion source for a mass spectrometer: H Böhm and K G Günther, Vakuum-Technik, 14(7), Oct 1965, 192–193, (in German).

The synthesis and formation of MoSi2, Mo5Si3, and Mo3Si compounds by the mechanical alloying of MoSi powder mixtures has been investigated. Ball-milling experiments were conducted for the composition range of 10–80 at.% Si. The formation of molybdenum silicides, especially MoSi2, during mechanical alloying and the relevant reaction rates markedly depended on the powder composition. The spontaneous formation of αMoSi2 during mechanical alloying at 67 at.% Si (MoSi2 stoichiometry) proceeded by a mechanically-induced self-propagating reaction (MSR), the mechanism of which is analogous to that of the self-propagating high-temperature synthesis (SHS). At the compositions of 54 and 80 at.% Si, however, the formation of MoSi2 proceeded by the gradual formation of both the α and /gb phases instead of the MSR mode. The formation of Mo5Si3 during mechanical alloying was characterized by a slow reaction rate as the reactants and product coexisted over a long period. The milling of Mo-rich powder mixtures up to 150 h did not lead to the direct formation of Mo3Si. The Mo3Si phase appeared only after brief annealing at temperatures of 800°C and above.

Design of NASA-Lewis space propulsion facility: D J Pearse, Sixth Annual Symposium on Space Environmental Simulation St. Louis, Missouri, May 1965, 18 pages.

The synthesis and formation of MoSi2, Mo5Si3, and Mo3Si compounds by the mechanical alloying of MoSi powder mixtures has been investigated. Ball-milling experiments were conducted for the composition range of 10–80 at.% Si. The formation of molybdenum silicides, especially MoSi2, during mechanical alloying and the relevant reaction rates markedly depended on the powder composition. The spontaneous formation of αMoSi2 during mechanical alloying at 67 at.% Si (MoSi2 stoichiometry) proceeded by a mechanically-induced self-propagating reaction (MSR), the mechanism of which is analogous to that of the self-propagating high-temperature synthesis (SHS). At the compositions of 54 and 80 at.% Si, however, the formation of MoSi2 proceeded by the gradual formation of both the α and /gb phases instead of the MSR mode. The formation of Mo5Si3 during mechanical alloying was characterized by a slow reaction rate as the reactants and product coexisted over a long period. The milling of Mo-rich powder mixtures up to 150 h did not lead to the direct formation of Mo3Si. The Mo3Si phase appeared only after brief annealing at temperatures of 800°C and above.

超耐熱材料の研究(第1報) MoSi<sub>2</sub>の生成條件について

超耐熱材料の研究(第1報) MoSi<sub>2</sub>の生成條件について