Optimization and characterization of LPCVD TiB2 for ULSI applications

Choi,Ruggles,Osburn,Xing

, p. 3053 - 3061 (1991)

The chemical vapor deposition of TiB2 from gaseous mixtures of TiCl4, B2H6, and H2 onto various substrates was studied. A thermodynamic analysis using the SOLGASMIX computer program indicated that at an input gas ratio corresponding to the stoichiometry of TiB2, the amount of secondary-phase deposition would be considerably reduced compared to that of TiB2. For nonstoichiometric input gas mixtures, other solid phases, including oxides and silicides, are expected to result from the reaction with substrates. Experimental depositions of films were carried out in a cold wall system over a broad range of temperatures, pressures, and input gas flow rates. X-ray diffraction and x-ray photoelectron spectroscopy data indicate that the as-deposited films are very fine grained polycrystalline or amorphous, and the films RTA-annealed above 900°C are crystalline TiB2. Below 550°C, surface reactions are the dominant factor for the kinetics of TiB2 deposition, while mass transport is a limiting step for deposition above 550°C. At higher temperatures the deposition rate increases linearly with flow rate and total pressure, suggesting the deposition mechanism is reactant limited. The B/Ti ratio determined via Auger electron spectroscopy approaches the stoichiometric value of two in higher temperature films, while the presence of excess boron and chlorine was detected for low-temperature films. Stoichiometric TiB2 films were deposited over a wide range of input gas mixture B/B + Ti ratios ranging from 0.4 to 0.71. Depletion effects of input gas were observed at low flow rate and high pressure where the residence time of reactants is longer than 10 s.

Chemical and electrochemical behavior of titanium diboride in cryolite-alumina melt and in molten aluminum

Devyatkin,Kaptay

, p. 107 - 109 (2000)

Titanium diboride is the most perspective material for protection of the cathode lining of aluminum electrolysis cells. One of the possible methods for obtaining a titanium diboride coating is an electrochemical synthesis from cryolite melt containing oxides of titanium and boron. In the present paper the behavior of oxides of titanium and boron in cryolite melt is considered. Coherent coating of titanium diboride has been deposited from the molten system Na3AlF6 - Al4B2O9 - CaTiO3. (C) 2000 Academic Press.

Preparation of TiB2 and ZrB2. Influence of a mechano-chemical treatment on the borothermic reduction of titania and zirconia

Millet,Hwang

, p. 351 - 355 (1996)

TiB2 and ZrB2 have been synthesized by a mechano-chemical treatment of a mixture of titania or zirconia powder and amorphous boron followed by a relatively low temperature annealing (1100°C). Both the temperature and the kinetics of the borothermic transformations are affected by the mechano-chemical treatment when the size of the particles obtained after thermal annealing of the sample milled for a short time remains in the sub-micron range. The reaction paths are different for TiB2 and ZrB2 with the formation of TiBO3 and Ti2O3 as intermediate compounds in the case of the borothermic reduction of titania, while in the zirconia/boron system a direct borothermic reduction of zirconium oxide is observed.

Processing and properties of TiB2 with MoSi2 sinter-additive: A first report

Murthy,Basu,Balasubramaniam,Suri,Subramanian,Fotedar

, p. 131 - 138 (2006)

The densification of non-oxide ceramics like titanium boride (TiB 2) has always been a major challenge. The use of metallic binders to obtain a high density in liquid phase-sintered borides is investigated and reported. However, a non-metallic sintering additive needs to be used to obtain dense borides for high-temperature applications. This contribution, for the first time, reports the sintering, microstructure, and properties of TiB 2 materials densified using a MoSi2 sinter-additive. The densification experiments were carried out using a hot-pressing and pressureless sintering route. The binderless densification of monolithic TiB2 to 98% theoretical density with 2-5 μm grain size was achieved by hot pressing at 1800°C for 1 h in vacuum. The addition of 10-20 wt% MoSi2 enables us to achieve 97%-99%ρth in the composites at 1700°C under similar hot-pressing conditions. The densification mechanism is dominated by liquid-phase sintering in the presence of TiSi2. In the pressureless sintering route, a maximum of 90%ρth is achieved after sintering at 1900°C for 2 h in an (Ar+H2) atmosphere. The hot-pressed TiB2-10 wt% MoSi2 composites exhibit high Vickers hardness (～26-27 GPa) and modest indentation toughness (～4-5 MPa·m12).

Effect of KCl, NaCl and CaCl2 mixture on volume combustion synthesis of TiB2 nanoparticles

Nekahi, Atiye,Firoozi, Sadegh

, p. 1377 - 1383 (2011)

Preparation of titanium diboride (TiB2) nanoparticles was carried out by volume combustion synthesis. TiO2, B2O 3 and elemental Mg were mixed with 0-60% salt mixture of KCl, NaCl and CaCl2 with increment of 15% as a low melting temperature diluent. Compressed samples were synthesized in a tubular furnace at a constant heating rate under argon atmosphere. Thermal analysis of the process showed that the addition of the low melting temperature salts mixture led to a significant decrease in ignition and combustion temperatures. Synthesized samples were then leached by nitric and hydrochloric acids to remove impurities. The samples were examined by XRD, SEM and DLS analysis. The results showed the formation of fine deagglomerated particles with the addition of the salts mixture. The results revealed that 45% salts mixture had the smallest average particle size of about 90 nm.

Mechanochemical synthesis and pressureless sintering of TiB2-AlN composites

Kim, Hyung-Jong,Choi, Heon-Jin,Lee, June-Gunn

, p. 1022 - 1024 (2002)

TiB2-AlN composites have been fabricated by the pressureless sintering of a mechanochemically processed Ti, Al, and BN powder mixture. TiB2-AlN powder was obtained from the mixture of Ti, Al, and BN, which had a composition corresponding to 45.7 wt% TiB2-54.3 wt% AlN, after mechanochemical processing for longer than 24 h. X-ray diffraction and transmission electron microscopy analysis showed that the powder subjected to mechanochemical processing for 60 h consisted of crystallites less than 300 nm in size with a disordered crystal structure. TiB2-AlN composites with 95% relative density, a flexural strength of 172 MPa, a fracture toughness of 4.6 MPa·m1/2, a hardness of 12.0 GPa, and an electrical resistivity of 1488 μΩ·cm were obtained by pressureless sintering at 1700°C for 2 h of the powder subjected to mechanochemical processing for 60 h.

Champagne, B.,Dallaire, S.,Adnot, A.

, p. L21 - L26 (1984)

Ball milling-induced combustion in powder mixtures containing titanium, zirconium, or hafnium

Takacs

, p. 75 - 84 (1996)

Ball milling induces self propagating high temperature reactions in many highly exothermic powder mixtures. This phenomenon has been studied in a variety of reactions with titanium, zirconium, and hafnium. Several oxides (CuO, Cu2O, NiO, Fe3O4, and ZnO) were reduced with Ti, Zr, and Hf and the borides, carbides, silicides, and sulfides of these metals were prepared from elemental mixtures. The ignition time is much shorter with Zr than with either Ti or Hf whenever oxygen or sulfur is involved in the reaction, but no similar variation is observed for the formation of borides, carbides, and silicides. It is suggested that the fast diffusion of oxygen in ZrO2 and very likely of sulfur in ZrS2 are responsible for this behavior.

Influence of stearic acid on mechanochemical reaction between Ti and BN powders

Byun, Jung-Soo,Shim, Jae-Hyeok,Cho, Young Whan

, p. 149 - 156 (2004)

The influence of stearic acid as a process control agent on the mechanochemical reaction between Ti and BN to form TiN/TiB2 nanocomposite powder by high energy ball milling has been investigated. A powder mixture of pure Ti and hexagonal BN powders with a molar ratio of 3:2 was milled for up to 40 h with up to 1.75 wt.% of stearic acid. The XRD analysis shows that an intimate mixture of TiN and TiB2 crystalline powders was formed during milling by a displacement reaction. It has been observed by monitoring the temperature of the vial surface during the milling process that the addition of over 1.5 wt.% of stearic acid changed the reaction mode from a mechanically induced self-propagating reaction (MSR) to a gradual reaction. It has also been found by XRD and TEM analyses that the MSR produces TiN and TiB2 particles initially of sub-micron size, which are reduced gradually by further milling. However, there still remain some coarse TiB2 particles larger than a few hundred nanometers even after 16-h milling due to their extremely high hardness. On the other hand, the gradual reaction induced by stearic acid successfully inhibits the formation of coarse TiB2 particles and eventually decreases the crystallite size of the products below 40 nm after 16 h of milling.

Mechanism of the cathode process in the electrochemical synthesis of TiB2 in molten salts. I. The synthesis in an all-fluoride electrolyte

Makyta,Matiasovsky,Taranenko

, p. 861 - 866 (1989)

The mechanism of the cathode process in the electrochemical synthesis of titanium diboride in molten LiF-KF supporting electrolyte containing potassium hexafluorotitanate and tetrafluoroborate as electrochemically active components has been determined by

Properties of titanium and zirconium diborides obtained by self-propagated high-temperature synthesis

Radev,Marinov

, p. 48 - 51 (1996)

Self-propagated high-temperature synthesis (SHS) of TiB2 and ZrB2 is carried out in a steel reactor under Ar. The SHS is initiated by a current pulse of 60 A and 40 V. It is shown that the interparticle contacts play a significant role in the successful proceeding of the synthesis reactions. The products obtained have similar morphology. X-ray data show the presence of welt-crystallized phases of TiB2 and ZrB2. Chemical analyses indicate a high boron content in the products. The properties of TiB2 powders synthesized from the same initial titanium and boron reagents by both SHS and mechanochemical synthesis are compared.

Properties of TiB2 powders obtained in a mechanochemical way

Radev,Klisurski

, p. 39 - 41 (1994)

Mechanochemical synthesis of TiB2 powders was achieved in a planetary mill. The product obtained, whose physical and chemical properties were investigated, was a single-phase powder, possessing submicronic particle size. Microstrain of the lattice was registered by X-ray studies. The amount of combined boron was comparatively high. These properties were preconditioned for high activity of the substances obtained, especially during sintering. A mechanism for the synthesis is proposed.

Nowotny, H.,Benesovsky, F.,Brukl, C.,Schob, O.

, (1961)

A reduction-boronation route to nanocrystalline titanium diboride

Chen, Luyang,Gu, Yunle,Shi, Liang,Yang, Zeheng,Ma, Jianhua,Qian, Yitai

, p. 231 - 233 (2004)

Nanocrystalline titanium diboride (TiB2) has been prepared through a reduction-boronation route by using Ti powders and BBr3 as titanium and boron sources, and metallic sodium as reductant at 400 °C. X-ray powder diffraction (XRD) pattern can be indexed as hexagonal TiB 2 with the lattice constants of a=3.028 and c=3.223A?. Transmission electron microscopy images show particle morphology with average size of 15 nm. Selected area electron diffraction patterns confirm the preparation of the hexagonal TiB2.

Effect of Cu content on the reaction behaviors of self-propagating high-temperature synthesis in Cu-Ti-B4C system

Liang,Wang,Yang,Zhao,Jiang

, p. 113 - 118 (2008)

The SHS reaction behaviors of the Cu-Ti-B4C system with various Cu content were investigated. Theoretical calculation of the adiabatic temperatures reveals that the reaction in the Cu-Ti-B4C system is self-sustainable for the presence of 0-72.22 wt.% Cu in the reactants without any preheat. With the increase of Cu content, the adiabatic temperatures, combustion temperatures and wave velocity decrease greatly, while the ignition time shows first a remarkable decrease and then an increase with the minimum value at 20 wt.% Cu. Moreover, with the increase of Cu content, the sizes of the TiC and TiB2 grains decrease considerably.

A facile one-step route to nanocrystalline TiB2 powders

Chen, Luyang,Gu, Yunle,Qian, Yitai,Shi, Liang,Yang, Zeheng,Ma, Jianhua

, p. 609 - 613 (2004)

Nanocrystalline titanium diboride (TiB2) has been prepared by the reaction of TiCl4 with NaBH4 in the temperature range of 500-700°C in an autoclave. X-ray powder diffraction (XRD) patterns can be indexed as hexagonal TiB2 with the lattice constants of a=3.032 and c=3.229A?. Transmission electron microscopy (TEM) image shows particle morphology, with average size of 15nm for the powder obtained at 600°C. Selected area electron diffraction (SAED) pattern confirms the prepared hexagonal TiB2. The oxidation behavior of TiB2 is studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA).

Structure of TiB2 produced by dynamic ion mixing

Riviere,Guesdon,Delafond,Denanot

, p. 477 - 486 (1988)

The technique of dynamic ion mixing is based on the use of a high energy ion beam to homogenize at the atomic scale and to improve the adherence of a growing film on any substrate. TiB2 films of stoichiometric composition were produced either by co-evaporation or by dynamic ion mixing using 100 keV Ar+ ions. The characterization of the films was performed by transmission electron spectroscopy (TEM). The ion mixing of the growing film has a crucial importance with regard to the resulting microstructural state. Amorphous TiB2 films are produced by conventional co-evaporation although crystalline TiB2 films of hexagonal structure are produced by dynamic ion mixing. The TiB2 amorphous phase appears to be very stable since crystallization starts only at about 1170 K, and complete transformation into the hexagonal crystalline structure is obtained at 1280 K. Relatively thick TiB2 coatings have been prepared with e=1 μm and studied by TEM on cross-sectional preparations. The microhardness of crystalline TiB2 films is about 2800 kgf mm-2 and is in good agreement with the value reported for bulk TiB2.

Electrochemical deposition of TiB2 in high temperature molten salts

Fastner,Steck,Pascual,Fafilek,Nauer

, p. 32 - 35 (2008)

The electrochemical deposition of TiB2 out of a NaCl-KCl-NaF-KBF4-K2TiF6 electrolyte at 600 °C was tested on steel and molybdenum substrates using various current programs. The characterisation of the deposited layers has been carried out by X-ray diffraction methods, scanning electron microscopy and microhardness measurements. The pulse sequences and the current densities used influence in a significant way the homogeneity of the layers deposited, the crystal size, the texture and other physical properties like electrical and thermal conductivity. The microhardness range was up to 2900 HV, smooth and dense layers were prepared at a pulse frequency of 100 Hz.

Preparation of titanium diboride nanopowder

Kravchenko,Torbov,Shilkin

, p. 614 - 616 (2010)

We have studied the reaction between NaBH4 and TiCl4 at elevated temperatures in the range 570-1020 K and pressures of up to 10 MPa, with no solvent. The results indicate that nanoparticulate tita- nium diboride forms at temperatures

Preparation of TiB2 sintered compacts by hot pressing

Itoh, Hideaki,Naka, Shigeharu,Matsudaira, Tsuneaki,Hamamoto, Hiroshi

, (1990)

A sintered compact of titanium diboride (TiB2) was prepared by hot pressing of synthesized TiB2 powder which was obtained by a solid-state reaction between TiN and amorphous boron. Densification occurred at 20 MPa and 1800°C for 5 to

Low temperature electrical resistivity studies and search for superconductivity in Ti-B system

Kutty,Pillai,Karunakaran,Vaidya

, p. 1123 - 1126 (1989)

Resistivity of TiBx alloy has been measured for three different compositions. The alloys contain the three known phases TiB2, TiB and Ti3B4 and unknown phase/phases. Resistivity measurements between room temperature and 77 K show that there is no superconducting transition in this range of temperature contrary to some recent reports. Resistivity shows a small anomaly at low temperature which is attributed to the unknown phase.

Formation of titanium nitride by mechanical milling and isothermal annealing of titanium and boron nitride

Ding,Yao,Qiu,Bai,Guo,Xue,Wang,Zhou,Su

, p. 77 - 81 (2005)

The formation of titanium nitride with rock salt structure (δ-TiNx) was studied by mechanical milling of a mixture of Ti and hexagonal boron nitride (h-BN) powders and isothermal annealing of the mixture after milling for 70 h under argon atmosphere. The mole ratio of Ti to h-BN is 22:78. In the milling process, an amorphous Ti-N alloy was formed firstly by a diffusion reaction between Ti and BN, and then the amorphous Ti-N alloy transformed into δ-TiNx driven by mechanical milling. However, in the annealing process, a Ti(N) solid solution was formed firstly by incorporation of N into Ti, and the N content in the Ti(N) increased with increasing annealing temperature. When the N content exceeded the solubility limit of the Ti(N) at some annealing temperature, the Ti(N) decomposed into δ-TiNx and Ti(N) with the solubility limit. No self-sustaining reaction occurs in the present work. No TiB2 is observed to form in the two processes. The thermodynamic and kinetic mechanisms of formation of the δ-TiNx are discussed.

Consolidation of combustion-synthesized titanium diboride-based materials

Hoke,Meyers

, p. 275 - 284 (1995)

The quasi-static consolidation in uniaxial compression of combustion-synthesized TiB2-based materials was investigated. Consolidation was carried out in insulated containers upon completion of the combustion reaction, while the porous reaction products were ductile. Since the consolidation is not an isothermal process, the temperature change during consolidation was monitored and recorded. The effect of the addition of metallic elements to the elemental powders was established, and it was found that nickel and chromium provide the best compact integrity. The partial densification is sufficient to show significant differences between the effects of metallic additives. A phenomenological (not based on the micromechanisms of densification) constitutive model was applied to the hot and porous reaction products incorporating the temperature dependence of flow stress. The activation energy for the temperature dependence of the flow stress is established and indicates that, in addition to diffusion-induced plastic deformation, other processes occur, such as fracturing of ligaments.

Synthesis of TiB2 by electric discharge assisted mechanical milling

Calka,Oleszak

, p. 346 - 348 (2007)

In this study, synthesis of titanium diboride from elemental powders of Ti and B by electric discharge assisted mechanical milling technique was investigated. This recently developed technique has the following advantages: rapid reaction rate, controlled

A mild solvothermal route to nanocrystalline titanium diboride

Gu, Yunle,Qian, Yitai,Chen, Luyang,Zhou, Fu

, p. 325 - 327 (2003)

Titanium diboride (TiB2) has been synthesized via a benzene-thermal reaction of metallic sodium with amorphous boron powder and titanium tetrachloride at 400°C in an autoclave; the temperature was much lower than that of traditional methods. The X-ray diffraction (XRD) pattern can be indexed with the hexagonal cell of TiB2 and the lattice constants a = 3.027 and c = 3.228 A?. X-ray photoelectron spectroscopy (XPS) results show the mole ratio of Ti:B as 1:1.766. Transmission electron microscope (TEM) images indicate that the average particle size is in the range of 15-40 nm in diameter.

New criteria for the applicability of combustion synthesis: The investigation of thermodynamic and kinetic processes for binary Chemical Reactions

Tan, Xiaoming,Su, Xianli,Yan, Yonggao,Uher, Ctirad,Zhang, Qingjie,Tang, Xinfeng

supporting information, (2021/01/07)

Combustion synthesis is a novel technique that utilizes the exothermic heat of a chemical reaction to maintain the reaction and to rapidly prepare materials. But, hitherto, none of unified criterion for the validation of combustion synthesis has been proposed. Herein, we proposed the conditions need to be met. In terms of kinetics, at the adiabatic temperature (Tad), the diffusion distance of atoms (lTad) within 0.1 s should be larger than the particle size of the reactants(d), that is, lTad≥d. For systems that satisfy Tad/Tm,L≥1(where Tm,L is the melting point of the low-melting point component of the reactants), the presence of a liquid phase significantly increases the atomic diffusion distance from nanometers to tens of microns, making the criterion lTad≥d simplified to Tad/Tm,L≥1 in most situations. In terms of thermodynamics, the system needs to ensure that the reaction components are in an activated state, that is, Tad/Tm,H ≥0.7, where Tm,H is the melting point of the high-melting point component. The criteria for the SHS reactions proposed in this study further improve the theoretical understanding of SHS reactions, and provide guidance for exploring the ultra-fast synthesis of binary and multicomponent compounds.

Sequence of phase evolution during mechanically induced self-propagating reaction synthesis of TiB and TiB2via magnetically controlled ball milling of titanium and boron powders

Oghenevweta,Wexler,Calka

, p. 380 - 391 (2017/02/05)

Mechanically induced self-propagating reaction synthesis of titanium boride and diboride was investigated for elemental mixtures of titanium and amorphous boron in starting atomic ratios of Ti50B50and Ti34B66. Samples were milled for different periods leading up to and after an ignition point which was determined by in-situ monitoring of the mill temperature. Methods of X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy were used to determine product evolution. For both compositions, a partial crystallisation of amorphous boron commences during the early stages of milling and progresses through to the ignition point. At later stages and prior to ignition, HRTEM combined with electron diffraction revealed the formation of nanocrystalline titanium diboride, which was confirmed by Raman spectroscopy to be of an off-stoichiometric, boron-lean composition; TiB2-x.This phase is believed to have formed by solid-state reaction at the interface of the heavily deformed Ti and amorphous B via a mechanism which parallels the formation of nanocrystalline off-stoichiometric Ti1+xC1-xprior to the self-propagating synthesis of TiC from Ti and graphite. After ignition, the product for Ti34B66comprised relatively large facetted grains of TiB2, liquid phase sintered by thin regions of unreacted Ti which had melted due to high heat of reaction. In contrast, the product of Ti50B50comprised platelike TiB particles, and spheroidal dispersions of TiB2in unreacted Ti and B. Likely mechanisms for the different product evolution routes for the two compositions are proposed and discussed.

Densification, characterization and oxidation studies of novel TiB2+EuB6compounds

Murthy, T.S.R.Ch.,Sonber,Vishwanadh,Nagaraj,Sairam,Bedse,Chakravartty

, p. 85 - 95 (2016/08/12)

TiB2+EuB6ceramic samples with different EuB6contents were fabricated using hot -pressing technique. The introduction of EuB6promoted the sinterability, fracture toughness and oxidation resistance of TiB2. 98.7% TD achieved by adding 2.5% EuB6to TiB2by hot pressing at a relatively low temperature of 1750?°C, 35?MPa, 1h. Formation of complete solid solution of TiB2+EuB6observed for all the samples by XRD, EDS and EBSD. Hardness of all samples is measured in the range of 24–27?GPa ～50% higher fracture toughness value of 5.2?MPa?m1/2was obtained in the 2.5% EuB6contained sample compared to monolithic TiB2. Enhancement of oxidation resistance of TiB2was observed by EuB6addition due to the formation of EuBO3and Eu2O3. Oxidized cross section of TiB2+EuB6sample was measured as 340?μm, which is ～35% less than that of monolithic TiB2(520?μm), after oxidation at 1400?°C for 8h.