Formation Of Molybdenum Silicides Research Articles

Combustion features in the Mo–Si–B system. Part 1. Mechanism and kinetics

The article describes the investigation of reaction mix combustion kinetics and mechanisms as well as to producing ceramic materials in the Mo–Si–B ternary system by SHS method. For mixes enriched by silicon, the driving force of the SHS-reaction is shown to be silicon fusion, produced melt sprea- ding over the surface of molybdenum and boron solid particles with dissolution of the latter in it and formation of Mo 3 Si intermediate silicide film. The subsequent silicon diffusion in molybdenum results in occurrence of MoSi 2 grains, thus molybdenum boride grains are formed as a result of mo- lybdenum diffusion into the melt. In the compositions with high boron content and low silicon fraction, MoB formation can carry by means of gas- phase mass transfer of МоО 3 suboxide to boron particles. Investigations of chemical transformation succession have been carried out in combustion wave. The obtained data testify of the possibility of parallel and subsequent flowing of molybdenum silicide and boride formation reactions, this sti- pulates the combustion transfer from fusion mode to detachment mode and vice versa. In the detachment mode, molybdenum silicide formation re- action is leading one, and molybdenum boride formation occurs with short time detachment. Using the power SHS-compaction, targets for magne- tron deposition are produced.

Self-propagating high-temperature synthesis of advanced ceramics in the Mo–Si–B system: Kinetics and mechanism of combustion and structure formation

The goal of this work is to investigate the combustion mechanisms of reactions in the Mo–Si–B system and to obtain ceramic materials using the SHS method. It is concluded that the following processes are defined by the SHS for Si-rich Mo–Si–B compositions: silicon melting, its spreading over the surfaces of the solid Mo and B particles, followed by B dissolution in the melt, and formation of intermediate Mo3Si-phase film. The subsequent diffusion of silicon into molybdenum results in the formation of MoSi2 grains and molybdenum boride phase forms due to the diffusion of molybdenum into B-rich melt. The formation of MoB phase for B-rich compositions may occur via gas-phase mass transfer of MoO3 gaseous species to boron particles. The stages of chemical interaction in the combustion wave are also investigated. The obtained results indicate the possibility of both parallel and consecutive reactions to form molybdenum silicide and molybdenum boride phases. Thus the progression of combustion process may occur through the merging reaction fronts regime and splitting reaction fronts regime. Molybdenum silicide formation leads the combustion wave propagation during the splitting regime, while the molybdenum boride phase appears later. Finally, targets for magnetron sputtering of promising multi-phase Mo–Si–B coatings are synthesised by forced SHS compaction method.

Combustion synthesis of MoSi 2 and MoSi 2–Mo 5Si 3 composites: Multilayer modeling and control of the microstructure

In this work, we present a multilayer modeling for the formation of molybdenum silicides in the exothermic reaction between Mo and Si under the influence of a temperature pulse. The heating rate can either be a well-controlled ramp or be generated spontaneously by the propagation of a combustion synthesis front. The model addresses the specific situation above the melting point of silicon and describes the solid–liquid reaction taking place in a single representative particle of molybdenum surrounded by the melt of silicon. We obtain a set of kinetic equations for the propagation of the interfaces between the different layers (Mo/Mo 5Si 3 and Mo 5Si 3/MoSi 2) in the solid particle and the change in composition of the melt. This approach enables one to understand the specific microstructure observed during the formation of molybdenum silicides and to assess the role of parameters of combustion synthesis such as the initial size of the particles, the combustion temperature or the stoichiometric coefficient.

Single shot damage mechanism of Mo/Si multilayer optics under intense pulsed XUV-exposure

We investigated single shot damage of Mo/Si multilayer coatings exposed to the intense fs XUV radiation at the Free-electron LASer facility in Hamburg - FLASH. The interaction process was studied in situ by XUV reflectometry, time resolved optical microscopy, and "post-mortem" by interference-polarizing optical microscopy (with Nomarski contrast), atomic force microscopy, and scanning transmission electron microcopy. An ultrafast molybdenum silicide formation due to enhanced atomic diffusion in melted silicon has been determined to be the key process in the damage mechanism. The influence of the energy diffusion on the damage process was estimated. The results are of significance for the design of multilayer optics for a new generation of pulsed (from atto- to nanosecond) XUV sources.

Control of the reactivity at a metal∕silica interface

The reactivity at the Mo∕SiO2 interface is studied as a function of the method of preparation of the silica layer. Three preparation methods for the silicon substrate are considered: plasma-enhanced chemical vapor deposition, and wet and dry thermal oxidations. Respective hydrogen contents in the silica layer of 3.4, 0.5, and 0.4at.% are induced. We report on the formation of molybdenum silicides (MoSi2 and Mo5Si3) at the Mo∕SiO2 interfaces from an x-ray emission spectroscopy study of the interfacial Si 3p occupied valence states. The interfacial reactivity increases with the hydrogen content of the silica film, which is explained by the ease with which the Si–H bonds break during the early stage of the deposition of the metal by cathodic sputtering.

Improved reflectance and stability of Mo-Si multilayers

Commercial EUV lithographic systems require multilayers with higher reflectance and better stability than those published to date. This work represents our effort to meet these specifications. Interface-engineered Mo-Si multilayers with 70% reflectance and 0.545-nm bandwidth at 13.5-nm wavelength and 71% reflectance with 0.49-nm bandwidth at 12.7-nm wavelength were developed. These results were achieved with 50 bilayers. These new multilayers consist of alternating Mo and Si layers separated by thin boron carbide layers. Depositing boron carbide on the interfaces leads to reduction in molybdenum silicide formation of the Mo-on-Si interfaces. Bilayer contraction is reduced by 30%, implying that there is less intermixing of Mo and Si to form silicide. As a result, the Mo-on-Si interfaces are sharper in interface-engineered multilayers than in standard Mo-Si multilayers. The optimum boron carbide thicknesses have been determined and appear to be different for the Mo-on-Si and Si-on-Mo interfaces. The best results were obtained with 0.4-nm-thick boron carbide layers for the Mo-on-Si interfaces and 0.25-nm-thick boron carbide layers for the Si-on-Mo interfaces. The increase in reflectance is consistent with multilayers having sharper and smoother interfaces. A significant improvement in oxidation resistance of EUV multilayers has been achieved with ruthenium-terminated Mo-Si multilayers. The best capping-layer design consists of a Ru layer separated from the top Si layer by a boron carbide diffusion barrier. This design achieves high reflectance and the best oxidation resistance during EUV exposure in a water-vapor (oxidizing) environment. Electron-beam exposures of 4.5 h (in an effort to simulate EUV exposure perturbation of the top layers) in the presence of 5×10 - 7 -Torr water-vapor partial pressure show no measurable reflectance loss and no increase in the oxide thickness of Ru-terminated multilayers.

Synthesis and formation mechanisms of molybdenum silicides by mechanical alloying

The synthesis and formation of MoSi 2, Mo 5Si 3, and Mo 3Si compounds by the mechanical alloying of Mo Si 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 MoSi 2, during mechanical alloying and the relevant reaction rates markedly depended on the powder composition. The spontaneous formation of αMoSi 2 during mechanical alloying at 67 at.% Si (MoSi 2 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 MoSi 2 proceeded by the gradual formation of both the α and /gb phases instead of the MSR mode. The formation of Mo 5Si 3 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 Mo 3Si. The Mo 3Si phase appeared only after brief annealing at temperatures of 800°C and above.

Formation of molybdenum silicides by mechanical alloying : U. Mizutani et al. (Nagoya University, Nagoya, Japan). J. Japan Soc. Powder Powder Metall., vol 42, no 2, 1995, 200–204. (In Japanese.)

Formation of molybdenum silicides by mechanical alloying : U. Mizutani et al. (Nagoya University, Nagoya, Japan). J. Japan Soc. Powder Powder Metall., vol 42, no 2, 1995, 200–204. (In Japanese.)

Studies on the formation of MoSi 2[sbnd]SiC by reaction of Si 3N 4 with molybdenum and carbon

Si 3N 4 powder was reacted with Mo powder and carbon black at 1200–1600°C in an argon atmosphere. The effects of carbon content and pressure on the formation of molybdenum silicides were studied. MoSi 2 and SiC formed at all temperatures. With a low initial carbon content or on conducting the reaction under a positive pressure of argon, the formation of Mo 5Si 3 and Mo 3Si can be suppressed. However, at higher temperatures (1500 and 1600°C), the formation of large quantities of SiC, Mo 5Si 3, and Mo 3Si was observed. Vapor—liquid—solid whisker type morphology was observed at lower temperatures. At higher temperatures various types (hexagonal, trigonal, polyhedral) of SiC particulate formed. The tendency of the reaction product to agglomerate was found to increase with a decrease in the carbon content.

On the formation of molybdenum silicides in MoSi multilayers: the effect of Mo thickness and annealing temperature

The present work deals with the formation of molybdenum silicides in all-sputtered a-Si/Mo/a-Si/Mo/a-Si/c-Si(100) multilayers. The structure were prepared without breaking the vacuum and the substrates were not intentionally heated during the sputtering. After deposition, the multilayers were annealed at 500 or 700°C. Grazing incidence X-ray diffraction and XPS techniques were used to characterize the Mo/a-Si and a-Si/Mo structures first and then the a-Si/Mo/a-Si/Mo/a-Si/c-Si(100) multilayers. The essential results can be summarized as follows: 1.(1) The nature of the interface formed in the unannealed structures depends strongly on the order of the deposits: if Si is sputtered onto sputtered Mo films, the a-Si/Mo interface is found to be abrupt while in the reverse order the deposit leads to a diffuse Mo/a-Si interface.2.(2) The thermal treatment has a significant effect only if the temperature is of the order of 700°C. In this case, the result depends on the a-Si and Mo thickness: for thickness lower than ≈200 Å only MoSi2 is formed, with predominance of the hexagonal phase, while for thicknesses greater than ≈200°C, we simultaneously observe the tetragonal phases MoSi2 and Mo5Si3.

Phase formation during reactive molybdenum-silicide formation

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.

Boron-doped glass-coated Mo-Si interaction

This letter gives the first report of molybdenum silicide formation by interaction of 1000-A-thick sputtered molybdenum film and an N-Si

Rapid Annealing Using Halogen Lamps

A few seconds halogen lamp annealing (HLA) technology is evaluated from the viewpoint of practical application to complementary metal oxide semiconductor (CMOS) very large scale integration (VLSI) processing. , 11B, and 31P ion‐implanted silicon layers have been investigated on their isothermal short‐time annealing behavior of junction leakage current, recrystallization, activation, and junction depth. We have found that a few seconds annealing of 800°C is enough to crystalline regrow the or 31P ion‐implanted amorphous layer, to activate or 31P ion‐implanted dopants, to form titanium silicide, and to reduce the area leakage current of both n+‐p− and p+‐n− junctions without dopant diffusion. But activation of 11B+ ion‐implanted dopants, reduction of perimeter leakage current, molybdenum silicide formation, and phosphosilicate glass (PSG) reflow require a little higher temperature heat‐treatment.

Impurity effects in molybdenum silicide formation

The reaction between molybdenum thin films and single-crystal Si〈111〉 substrates was studied as a function of the concentrations of impurities (mainly oxygen) in the metal film. At a low oxygen concent (1–2 at.%), only the silicide phase MoSi 2 was observed, and a thickness proportional to the square root of time corresponding to an average activation energy of 3 eV in the temperature range 545–600 °C was found. During the formation of the silicide the oxygen originally present in the molybdenum films accumulates at the interface between the silicon and the MoSi 2. In contrast, a higher oxygen content (4–5 at.%) prevents the formation of any silicide phases in the above temperature range and leads to the formation of MoSi 2 and Mo 5Si 3 phases at temperatures near 800 °C. MoSi 2 was always observed at the inner interface with Mo 5Si 3 on the surface. The oxygen segregates from the silicides and accumulates at the Si-MoSi 2 and MoSi 2-Mo 5Si 3 interfaces to form a non-uniform layer of SiO x ( x ⩽ 2).

Reaction kinetics of molybdenum thin films on silicon (111) surface

Silicon-metal systems are highly susceptible to solid-solid reactions which modify their electrical and mechanical properties. Although many works are dealing with silicide formation, the molybdenum-silicon system has not yet been investigated in detail to our knowledge. In this paper we present a He+ ion backscattering study of the molybdenum-silicide formation by interaction of a thin molybdenum layer and a silicon 〈111〉 wafer. The silicide phases Mo3Si and MoSi2 have been identified by x-ray diffraction and transmission electron microscopy. Surface transformations were observed by scanning electron microscopy. For an 800-Å Mo layer sputter deposited on silicon, we have found a time-square growth rate for MoSi2 with an average activation energy of 2.4 eV in the temperature range 475–550 °C. The fundamental roles of the cleaning of the silicon surface, of the substrate temperature during sputtering, and of the stresses in the layer are pointed out.

Silicidbildung in dünnen molybdän- und wolframschichten auf einkristallinen siliziumsubstraten bei relativ niedrigen temperaturen

Polycrystalline thin films of molybdenum and tungsten have been evaporated onto single-crystal silicon slices by electron beam. Silicide formation in the evaporated films could be detected by X-ray diffraction methods. According to the literature a temperature rise δ T of up to 500 °C can appear during the evaporation process. Annealing at T=550 °C results in enhaned silicide formation. It is concluded from X-ray measurements that the molybdenum silicide formation is diffusion limited at this annealing temperature. The silicide formation is discussed in connection with thin film diffusion.

Thermodynamic Properties of the System Molybdenum–Silicon

Gibbs energies of formation of molybdenum silicides have been determined by the Knudsen-effusion vapour-pressure method between 1410 and 1675 K. The results have been combined with data from the literature and the whole evaluated to give a set of self-consistent thermodynamic properties. The various inconsistencies between the data from the different investigations are discussed.

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.