Preparation of TiSi<Subscript>2</Subscript> via flash lamp processing of TiN/Ti/Si heterostructures

The structural and phase transformations induced in the TiN/Ti/Si system by flash processing with incoherent light have been studied by transmission electron microscopy and Auger electron spectroscopy. The conditions have been identified under which polycrystalline C49 or C54 TiSi₂ films grow.     

Phase formation and characteristics of r.f.-sputtered barium-strontium titanate thin films on various bottom layers

(Ba_0.7Sr_0.3)TiO₃ thin films were deposited by r.f.-magnetron sputtering on Pt/Ti/Si, Pt/TiSi₂/Si and Pt/Ti/SiO₂/Si substrates, respectively, and annealed at 650 C for 30s by Rapid Thermal Annealing (RTA). XRD (X-ray diffraction) patterns revealed that the BST films had perovskite structure without preferred orientation. Auger depth profiles of barium-strontium titanate (BST) films on various substrates were performed. In the Pt/Ti/Si and Pt/TiSi₂/Si structures, Si diffused into the BST film, but in the Pt/Ti/SiO₂/Si structure, the diffusion of Si into the BST film was prevented and the interface between the BST film and the electrode was stable. The dielectric constants were about 310–260 (100 kHz–1 MHz).     

Thermal stability of Al-1%Si-0.5%Cu/TiSi2 contact structure

Stable TiSi₂ was formed by rapid thermal annealing (RTA) on single-crystal Si. Subsequently a 600 nm-thick Al-1%Si-0.5%Cu layer was deposited on the top of the formed TiSi₂ followed by furnace annealing for 30 min at 400–600 C in N₂ ambient atmosphere. The thermal stability of Al-1%Si-0.5%Cu/TiSi₂ bilayer and interfacial reaction were investigated by employing four-point probe, scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The composition and the phase of precipitates formed by the reaction of Al-1%Si-0.5%Cu with TiSi₂ were studied by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). It was found that the TiSi₂ layer was consumed by the reaction between TiSi₂ and Al-1%Si-0.5%Cu layer, resulting in precipitates at 550 C. The results from EDS revealed that the precipitates were composed of Ti, Al and Si. The precipitates were identified as Ti₇Al₅Si₁₂ ternary compound from XRD analysis.     

Formation mechanism of titanium silicide by mechanical alloying

The syntheses of five titanium silicides (Ti₃Si, TiSi₂, Ti₅Si₄, Ti₅Si₃, and TiSi) by mechanical alloying (MA) have been investigated. Rapid, self-propagating high temperature synthesis (SHS) reactions were involved in producing the last three materials during room temperature high-energy ball-milling of elemental powders. Such reactions appeared to occur through ignition by mechanical impact in the fine powder mixture formed after a critical milling period. From in-situ thermal analyses, each critical milling period for the formation of Ti₅Si₄, Ti₅Si₃, and TiSi was observed to be 22, 35.5 and 53.5 minutes, respectively. However, the formation of Ti₃Si and TiSi₂ did not occur even after 360 minutes of milling of as-received Ti and Si powder mixture, due to the lack of homogeneity of the powder mixture. Other ball-milling procedures were employed for the syntheses of Ti₃Si and TiSi₂ using different sizes of Si powder and milling medium materials. Ti₃Si was synthesized by milling a Ti and 60 minutes premilled Si powder mixture for 240 minutes. -TiSi₂ and TiSi₂ were produced by high energy partially stabilized zirconia (PSZ) ball-milling for 360 minutes in a steel vial followed by jar-milling of a Ti and 60 min premilled Si powder mixture for 48 hr. The formation of Ti₃Si and TiSi₂ occurs through a slow solid state diffusion reaction, and the product(s) and reactants coexist for a certain period of time. The formation of titanium silicides by MA and the reaction rate appeared to depend on the homogeneity of the powder mixture, milling medium materials, and heat of formation of the product involved.     

Interface evolution of SiO2 glass ceramic and Ti–6Al–4V alloy joint brazed with Ag–Cu–Ti alloy

Abstract

In the present paper, SiO₂ glass ceramic and Ti–6Al–4V alloy were successfully brazed with Ag–21Cu–4·5Ti active braze alloy. The interfacial microstructure and evolution course of SiO₂ glass ceramic/Ti–6Al–4V joint were studied in detail. According to the experimental results, active element Ti plays a quite important role in the formation of reaction layers on the joint interface. The reaction products of the joint are TiSi₂, Ti₄O₇, TiCu, Cu₂Ti₄O and Ti₂Cu respectively. The interface evolution can be generally described by four stages, which are solution and diffusion of atoms, reaction among atoms, formation of reaction layers and precipitation of solid solution layers respectively.     

Interfacial reactions for the non-stoichiometric TiB x /(100)Si system

In order to evaluate the interfacial reactions in the TiB _x /(100)Si system and the thermal stability of non-stoichiometric TiB _x films (0 B/Ti 2.5), TiB _x /Si samples prepared by a co-evaporation process were annealed in vacuum at temperatures between 300 and 1000°C. The solid phase reactions were investigated by means of sheet resistance, X-ray diffraction, transmission electron microscopy, X-ray photo-electron spectroscopy, and stress measurement. For TiB _x samples with a ratio of B/Ti 2.0, an apparent structural change is not observed even after annealing at 1000°C for 1 h. For samples with a ratio of B/Ti < 2.0, however, there are two competitive solid phase reactions: the formation of a titanium silicide layer at the interface and the formation of a stoichiometric TiB₂ layer at the surface, indicating the salicide process. The sheet resistance and the film stress in the Ti/Si and TiB _x /Si systems are well explained by the solid phase reactions.     

Effects of rapid thermal treatments on Ti/TiN/Si structures for electrical contacts on silicon

Abstract

A possible new technique for metallisations in Si microelectronics technology has been prepared and characterised. Bilayers of TiN_x/Ti were deposited by sputtering over a Si substrate. The samples were annealed in a rapid thermal processing system, and further analysed using Auger electron spectroscopy and electrical measurements (Schottky barrier height and sheet resistance). Significant differences from the more usual silicidiltion process of a Ti/Si structure have been observed. The silicidation process of the TiN_x/Ti structures is mainly controlled by the presence of the intermediate TiN layer. The final structure was determined to be Si/TiSi_x/TiN_y/TiSi_z.

MST/3336     

Phase Relations in the KOH–TiO2–SiO2–H2O System at 500°C and 0.1 GPa

The compounds crystallizing in the system KOH–TiO₂(rutile)–SiO₂–H₂O at 500°C, 0.1 GPa, and different TiO₂, SiO₂, and KOH concentrations are K₂TiSi₆O₁₅ (Ti davainite structure), K₂TiSi₃O₉ (Zr wadeite structure), and K₂Ti₆O₁₃ (Ti jeppeite structure). The matrix-assembly model is used to examine the formation of the K₂TiSi₆O₁₅ structure (sp. gr. P ) from subpolyhedral structural units. A centrosymmetric cyclic 12-polyhedron cluster of composition K₂ M ₂ T ₁₀ is identified, in which the K atoms lie in center positions above and below the plane of the MT ring. The precursor cluster K₂ M ₂ T ₁₀ is identical in structure to the Cs₂ M ₂ T ₁₀ cluster in Cs₂TiSi₆O₁₅, a titanosilicate which has a topologically different MT framework. The mechanisms of the assembly of the three-dimensional MT frameworks in these titanosilicates differ at the level of primary MT chains: the condensation of the clusters in K₂TiSi₆O₁₅ involves five common corners, while that in Cs₂TiSi₆O₁₅ involves only three corners.     

Development of phases and texture in sol-gel derived lead zirconate titanate thin films prepared by three-step heat-treatment process

Lead zirconate titanate (PZT) films were fabricated by the addition of 10 mol% excess Pb to the starting solution which was spin-coated onto Pt/Ti/SiO₂/Si substrates. The effect of film thickness on texture was investigated, and it is clear that the (100) texture gradually increases and the (111) texture decreases with increasing film thickness. A Pt _x Pb intermetallic metastable phase was observed by X-ray diffraction, and it is found that the position of this peak shifted from 38.30° 2 (d : 0.2348 nm) to 37.10° 2 (d : 0.4213 nm) with increasing firing temperature from 350°C to 550°C. The (111) preferred orientation in the PZT film was promoted by the metastable Pt _x Pb phase. The formation of the (100) texture of perovskite phase in the multilayer films was mainly attributed to the effects of both substrates and crystal growth rates which depend on the crystal orientation.     

The effect of combined diffusion and kinetic transport barriers on multi-phase solid state reactions with a vapour reactant

Analytical models are presented for the rates of layer thickness growth of MoSi₂ and of Mo₅Si₃ that form by reaction of vapour-supplied Si with Mo or with partially silicided Mo. The models are applicable to other systems. Coupling of the diffusive flux of the reactive species Si with the rate of the chemical reactions determines the growth kinetics. The rate of chemical reaction is assumed to be proportional to the magnitude of a discontinuity in the Si activity at the physical boundary where the silicide reaction is occurring. Various combinations of diffusive versus chemical-kinetics-dominated transport in the two phases which grow in tandem are found to affect the functional dependence of the growth kinetics on time. Models include cases in which the host solid is heterogeneous, as occurs when the average composition of the host lies in a poly-phase region of the phase diagram.Nomenclature p porosity, (For examplep ₁ is the porosity of the MoSi₂ layer.) - q 1 — p - v _i volume fraction ofi in the unsilicided compact - V _i theoretical molar volume ofi - _i theoretical volume per gram atom of Si ini - _i (1 —p _i/_i ing atoms of Si per unit volume ini - D _i Diffusion coefficient of Si ini - K _i Kinetic rate constant for conversion of phasei to phasei+ 1 in g.At cm^–2s^–1 per C - J _i Flux of Si through phasei in g.Atcm^–2s^–1 - C ₀ in MoSi₂ at outer surface in equilibrium with Si vapour - C ₁ in MoSi₂ at boundary in equilibrium with Mo₅Si₃ - C ₂] in Mo₅Si₃ at boundary in equilibrium with MoSi₂ - C ₃ in Mo₅Si₃ at boundary in equilibrium with Mo - C ₄ in Mo at boundary in equilibrium with Mo₅Si₃ - C ₁ in MoSi₂ at boundary with Mo₅Si₃, but at a higher Si activity than the equilibrium value - C ₃ in Mo₅Si₃ at boundary with Mo, but at a higher Si activity than equilibrium value - C_ij C _i —C _j - A(Si) Atomic weight of Si - T elapsed time since start of siliciding in seconds - X, Y thicknesses of MoSi₂, Mo₅Si₃ layers in cm     

The influence of TiN on cosputtered (Ti+Si) blanket film

X-ray diffraction, transmission electron microscopy and Auger spectroscopy were used to study the formation of TiSi₂ from a cosputtered (Ti+Si) film with and without TiN capping. In all cases, a metal rich silicide identified as Ti₅Si₃, was the first phase to form from the amorphous (Ti+Si) regardless if a TiN overlayer was or was not present. At temperatures of 923 K and below it only Ti₅Si₃ was observed in all specimens. C54 TiSi₂ formation is enhanced in specimens having a TiN capping and its formation occurs at lower temperatures and at a faster rate at some appropriate temperature than in specimens without TiN. The effect of tensile stress induced by the TiN layer is suggested as the reason of C54 TiSi₂ formation.     

Sintering of (alumina + titanium) powder mixtures and elaboration of the corresponding cermets

We considered the possible formation of a bond between a ceramic (Al₂O₃) and a metal (titanium). We first concluded that a direct bonding of these two materials would be very unsatisfactory. We managed to obtain good bonding through an (Al₂O₃ +xTi) cermet placed between the two initial materials. Diffusion tests with Al₂O₃/Ti or (Al₂O₃ +xTi)/Ti couples have shown the appearance of densified layers in the diffusion zone. The study of the influence of the titanium content in the cermet permitted values ofx to be determined which give an appropriate continuity (10 x 25 wt%) across the interface. Measurements by micro probe have shown that the mobility of the Al³⁺ ion has a predominant influence in the process leading to the bonding. The nature of the sintering atmosphere plays an important role in the sintering capacity of (Al₂O₃ +xTi) cermet as well as the densification of the samples.     

Studies of BaTiO3 thin films on different bottom electrode

BaTiO₃ (BT) thin films were prepared on Pt/Ti/SiO₂/Si and Ru/Ti/SiO₂/Si substrates by a modified sol-gel technique. The microstructure of the films was characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy. The results showed that BT thin films crystallized with perovskite structure. Compared to BT film on Pt/Ti/SiO₂/Si substrate, BT thin film deposited on Ru electrode has similar dielectric constant, while it has higher dielectric loss. C–E curve for BT film on Pt/Ti/SiO₂/Si was more symmetrical around zero-bias field than C–E curve for BT film on Ru/Ti/SiO₂/Si substrate. The tunability was 52.02% for BT film on Pt electrode, which was 33.42% on Ru electrode, at 275 kV/cm and room temperature. The leakage current density of BT on Pt electrode was about an order of magnitude lower than BT film on Ru electrode at the applied electrical field below 150 kV/cm. The leakage conduction mechanism was investigated.     

Ti–Al–Si–N nanocrystalline composite films synthesized by reactive magnetron sputtering

A series of Ti–Al–Si–N nanocrystalline composite films with different Si contents were synthesized in a mixture gas composed of Ar, N₂ and SiH₄ by reactive magnetron sputtering. Energy dispersive spectroscopy, Auger electron spectroscopy, X-ray diffraction and transmission electron microscopy were employed to characterize the microstructures of these films; a nanoindenter was used to measure their mechanical properties. The results show that by changing the SiH₄ partial pressure in the mixture gas, Si content in the films can be easily controlled. After Si is added into the films, an interface phase TiSi_x appears. It prevents (Ti,Al)N and AlN grains from growing, as a result, the (Ti,Al)N and AlN phases exist as nanocrystals. Correspondingly, the films' hardness and elastic modulus arrive at their maximum values of 36.0 and 400 GPa, respectively, at 3.5 at.% Si. With a further increase of Si content, the films' mechanical properties decrease gradually.     

Electron microscopy observations of N2+ -implanted TiN films as diffusion barriers for very-large-scale integration applications

Titanium nitride films were prepared by implanting 40keV N₂⁺ ions into Si〈100〉n⁺/p shallow junctions coated with titanium layers of different thicknesses (from 80 up to 100nm). Using a suitable thermal annealing a film of TiSi₂ is formed at the TiN-Si interface, as demonstrated by transmission electron microscopy (TEM) observations on planar and cross-sectioned specimens, as well as by Rutherford backscattering spectrometry experiments. The effectiveness of these TiN films as diffusion barriers when placed in contact with a thick aluminium overlayer is evaluated, and their electrical performances are tested on suitable test patterns after thermal treatments up to 600°C. The variation in the structure of the interfaces in the TiSi₂/TiN/Al contacts is followed as a function of the heat treatment by cross-sectional TEM investigations and the results are presented.     

Phase Composition, Orientation, and Substructure of Iridium Silicide Films on Silicon

The phase composition, orientation, and substructure of iridium silicide films produced by electron-beam evaporation of Ir on (001) and (111) Si at substrate temperatures from 300 to 1000°C were studied by electron microscopy and diffraction. The results demonstrate that the sequence of silicide formation upon Ir deposition onto heated substrates is the same as upon heat treatment of Ir films deposited at room temperature. It is shown that oriented growth of Ir₃Si₅ and IrSi_0.7 is possible. The IrSi₃/Si interface is shown to be, to some extent, coherent, with the lattice mismatch being accommodated by dislocations in some directions and by elastic strain in other directions. The likely mechanism for the formation of a dislocation structure at the IrSi₃/Si interface is discussed.     

Ordering of Fe-Si phases

The microstructure of Fe-Si alloys containing 8 and 15.5 at % Si and heat-treated between 550 and 1200°C is studied by transmission electron microscopy, and the phase composition of alloys containing 19 and 23 at % Si is determined by x-ray diffraction. The Fe-15.5 at % Si alloy heat-treated above 700°C is found to consist of a disordered solid solution and B2 phase. The B2 particles can be thought of as portions of {100} layers consisting entirely of Si atoms and sandwiched between {100} layers of Fe atoms, that is, as a two dimensional phase. At t 675°C, a compositionally modulated microstructure develops in which the Si-enriched zones have the Fe₃ Si stoichiometry and DO₃ structure. At high temperatures, the Fe-19 at % Si alloy consists of the and B2 phases, and the Fe-23 at % Si alloy consists of the and DO₃ phases. These findings are at variance with the generally accepted Fe-Si phase diagram.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 28–35.Original Russian Text Copyright © 2005 by Ustinovshchikov, Sapegina.     

Growth mechanism of epitaxial CoSi2 on Si and reactive deposition epitaxy of double heteroepitaxial Si/CoSi2/Si

The growth mechanism of epitaxial CoSi₂ was studied using Co/Ti/Si multilayer solid phase reaction. Results showed that phase formation was controlled by diffusion of Co through the growing CoSi_x, although at the early stage of CoSi₂ growth the diffusion of Co could be controlled by a Ti layer. A reactive deposition technique was also evaluated by using a conventional magnetron sputtering system. Results showed that an epitaxial CoSi₂ layer was formed by controlling the Co sputtering rate not to exceed the Co diffusion rate through CoSi_x. However, the surface of CoSi₂ became rough when the deposition rate was much slower than the Co diffusion rate through CoSi_x. The roughness was caused by the formation of CoSi₂ (111) facets at the interface between CoSi₂ and the Si substrate. Si/CoSi₂/Si double heteroepitaxial structures were fabricated when Si and Co were sequentially sputter-deposited on a Si (100) substrate.     

Investigations of surface structure for thermally evaporated silicon on a Cu(111) surface

The surface structure and composition of semiconductor/Cu(111) films prepared by thermal evaporation in an ultrahigh vacuum condition have been investigated. As Si atoms were deposited on a Cu(111) surface, diffused spots were observed up to 2 monolayers while 1 × 1 spots become dimmer as revealed using low-energy electron diffraction technique. Because of a larger electron affinity of Si than that of Cu, the Cu L₃M₄₅M₄₅ Auger line shifts to a lower kinetic energy. Annealing treatments at 425 K causes a splitting of the Cu L₃M₄₅M₄₅ line. This shows the interdiffusion at the Si/Cu interface and the formation of a Cu-rich surface layer. After annealing treatments, the domains grow and aggregate to form larger domains as revealed by the decreasing full-width at half maximum of diffraction spots. Ge/Cu(111) shows 1 × 1 structure as annealing up to 500 K. Lack of a dominant structure and a large valence diameter of Ge result in different structures as compared to Si/Cu(111).     

Characteristics of sol-gel derived PZT thin films with lead oxide cover layers and lead titanate interlayers

The sol-gel derived PbZr_0.53Ti_0.47O₃ (PZT) films were fabricated on the bare Pt/Ti/SiO₂/Si substrates or the same substrates coated by the PbTiO₃ (PT) interlayers. The post-deposition annealing temperature and time were optimized when the PbO cover layers and PbO vapour-containing atmosphere were compared with each other and adopted as the method to diminish the lead-loss problem during the high-temperature post-deposition annealing. The X-ray diffraction patterns, microstructures, and electrical properties such as relative permittivity, _r, remanent polarization, P _r, and coercive electrical field, E _c, were investigated in relation to the annealing conditions. The PZT films deposited on the bare Pt/Ti/SiO₂/Si substrates under the PbO vapour-containing atmosphere showed better electrical properties. This indicates that the PbO vapour-containing atmosphere may be the better method of lead-loss-prevention to process the lead-containing films rather than the PbO cover layer method. The electrical characteristics of the PZT films, _r=1150, a dissipation factor of 0.039, P _r=26 C cm^–2, and E _c=40.5 kV cm^–1 were measured at 1 kHz. When PZT films were deposited on substrates coated by the PT layers, PZT-PT films with single perovskite phase were derived by post-deposition annealing at 500 °C for 1 h. However, the relative electrical properties are very poor, i.e. E _r=160, P _r=2.0 C cm^–2 and E _c=75 kVcm^–1. The optimum combination for preparing PZT-PT films is a 40 nm PbTiO₃ interlayer and annealing conditions of 6 h at 550 °C in a PbO vapour-containing atmosphere; the derived films exhibit electrical properties of E _r=885, P _r=21.5 C cm^–2 and E _c=64 kV cm^–1. The combination of inserting a PT interlayer and annealing in a PbO vapour-containing atmosphere can prevent the formation of electrical short paths. In this case, nearly pin-hole-free PZT films can be grown on the PT (interlayer) /Pt/Ti/SiO₂/Si substrates. It is believed that it is possible to prepare the PZT films with nano-scale uniformity, reproducible quality, which may be worth considering for commercial applications.