Niobium nitride films formed by rapid thermal processing (RTP): a study of depth profiles and interface reactions by complementary analytical techniques

The nitridation of niobium films approximately 250 and 650 nm thick by rapid thermal processing (RTP) at 800 °C in molecular nitrogen or ammonia was investigated. The niobium films were deposited by electron beam evaporation on silicon substrates covered by a 100 or 300 nm thick thermally grown SiO₂ layer. In these investigations the reactivity of ammonia and molecular nitrogen was compared with regard to nitride formation and reaction with the SiO₂ substrate layer. The phases formed were characterized by X-ray diffraction (XRD). Depth profiles of the elements in the films were recorded by use of secondary neutral mass spectrometry (SNMS). Microstructure and spatial distribution of the elements were imaged by transmission electron microscopy (TEM) and energy-filtered TEM (EFTEM). Electron energy loss spectra (EELS) were taken at selected positions to discriminate between different nitride, oxynitride, and oxide phases. The results provide clear evidence of the expected higher reactivity of ammonia in nitride formation and reaction with the SiO₂ substrate layer. Outdiffusion of oxygen into the niobium film and indiffusion of nitrogen from the surface of the film result in the formation of oxynitride in a zone adjacent to the Nb/SiO₂ interface. SNMS profiles of nitrogen reveal a distinct tail which is attributed to enhanced diffusion of nitrogen along grain boundaries.     

Vanadium Nitride Films Formed by Rapid Thermal Processing (RTP): Depth Profiles and Interface Reactions Studied by Complementary Analytical Techniques

The nitridation of vanadium films in molecular nitrogen and ammonia using a RTP‐system was investigated. The V films were deposited on silicon substrates covered by 100 nm thermal SiO₂. For a few experiments sapphire substrates were used. Nitride formation at high temperatures (900 and 1100 °C) and interface reactions and diffusion of oxygen out of the SiO₂‐layer into the metal lattice at moderate temperatures (600 and 700 °C) were studied. For characterisation complementary analytical methods were used: X‐ray diffraction (XRD) for phase analysis, secondary neutral mass spectrometry (SNMS) and Rutherford Backscattering (RBS) for acquisition of depth profiles of V, N, O, C and Si, transmission electron microscopy (TEM) in combination with electron energy filtering for imaging element distributions (EFTEM) and recording electron energy loss spectra (EELS) to obtain detailed information about the initial stages of nitride, oxide and oxynitride formation, respectively, and the microstructure and element distributions of the films. In these experiments the SiO₂‐layer acts as diffusion barrier for nitrogen and source for oxygen causing the formation of substoichiometric vanadium oxides and oxynitrides near the V/SiO₂‐interface primarily at temperatures ≤ 900 °C. At a temperature of 1100 °C just a small amount of oxynitride forms near the interface because rapid diffusion of nitrogen and fast formation of VN (diffusion barrier for oxygen) inhibit the outdiffusion of oxygen into the metal layer. In the 600 °C regime, in argon atmosphere oxynitride phases observed in the surface region of these films originate from reaction of residual oxygen in the argon gas, whereas NH₃ as process gas does not lead to oxide or oxynitride formation at the surface (apart from the oxidation caused by storage). NH₃ seems to support the diffusion of oxygen out of the SiO₂‐layer. During the decomposition of ammonia at higher temperatures hydrogen is formed, which could attack the SiO₂. In contrast, sapphire substrates do not act as oxygen source in the 600 °C regime and change the nitridation behaviour of the vanadium films.     

Characterization of transition metal nitride formation in rapid thermal processing (RTP)

The potential of RTP for the preparation of transition metal nitrides by reaction of metal thin films in molecular nitrogen was investigated. The films and the nitridation process were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive x-ray analysis (EDX) in a scanning electron microscope (SEM) and secondary neutral mass spectrometry (SNMS). The chemical states of vanadium at the utmost surface, detected by XPS, are related to V₂O₅ before RTP and to vanadium nitride, oxide and oxynitride after RTP. The deposition of a 3 nm Si top layer prevents V from oxidation and its selective removal before RTP enhances the proportion of nitride determined by XPS after RTP. From comparative experiments in a conventional tube furnace the advantages of RTP became obvious. With short process times of the RTP technique the integral amount of residual oxygen is kept low and oxide formation is largely avoided. The nitrogen content and the different polycrystalline phases formed by varying process time and temperature provide information about reactivity and the nitridation process. The nitrogen to vanadium ratio was determined by EDX and SNMS, revealing that the N content reaches saturation after only 5 seconds at 1100?°C.     

Nitridation of niobium oxide films by rapid thermal processing

The possibility of forming niobium oxynitride through the nitridation of niobium oxide films in molecular nitrogen by rapid thermal processing (RTP) was investigated. Niobium films 200 and 500 nm thick were deposited via sputtering onto Si(100) wafers covered with a thermally grown SiO₂ layer 100 nm thick. These as-deposited films exhibited distinct texture effects. They were processed in two steps using an RTP system. The as-deposited niobium films were first oxidized under an oxygen atmosphere at 450 °C for various periods of time and subsequently nitridated under a nitrogen atmosphere at temperatures ranging from 600 to 1000 °C for 1 min. Investigations of the oxidized films showed that samples where the start of niobium pentoxide formation was detected at the surface and the film bulk still consisted of a substoichiometric NbO_x phase exhibited distinctly lower surface roughness and microcrack densities than samples where complete oxidation of the film to Nb₂O₅ had occurred. The niobium oxide phases formed at the Nb/substrate interface also showed distinct texture. Zones of niobium oxide phases like NbO and NbO₂, which did not exist in the initial oxidized films, were formed during the nitridation. This is attributed to a “snow-plough effect” produced by the diffusion of nitrogen into the film, which pushes the oxygen deeper into the film bulk. These oxide phases, in particular the NbO₂ zone, act as barriers to the in-diffusion of nitrogen and also inhibit the outdiffusion of oxygen from the SiO₂ substrate layer. Nitridation of the partially oxidized niobium films in molecular nitrogen leads to the formation of various niobium oxide and nitride phases, but no indication of niobium oxynitride formation was found. Figure Schematic representation of the phase distribution in 200 nm Nb film on SiO₂/Si substrate after two steps annealing using an RTP system. The plot below represents the SIMS depth profiles of the nitridated sample with the phase assignment     

Annealing of thin B/Nb<Subscript>2</Subscript>N bilayers,B/Nb bilayers and Nb/B/Nb trilayers via rapid thermal processing (RTP)

B/Nb and B/Nb₂N bilayers and Nb/B/Nb trilayers of about 550 nm total thickness have been deposited on Si(100) wafers with 100 nm thermally grown oxide. Nb and B layers were deposited by magnetron sputtering. Nb₂N layers were prepared by nitridation of Nb films via rapid thermal processing (RTP). The samples were annealed subsequently at temperatures between 600 and 1,200 °C in an RTP system under Ar or NH₃ gas flow to study interdiffusion and reactivity of niobium, boron and nitrogen. Formation of phases was investigated by X-ray diffraction (XRD); surface morphology and roughness were studied via scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. Elemental depth profiles of selected samples were recorded by secondary ion mass spectrometry (SIMS). Annealing of the B/Nb bilayers and Nb/B/Nb trilayers under Ar leads to the formation of Nb₃B₂ at 1,200 °C at the B/Nb interface. At lower temperatures the high oxygen content in the boron layer is supposed to hinder the formation of borides due to formation of glass-like boron oxides. In NH₃ several niobium nitrides are formed but no boride phases. Here again the reactivity of boron with niobium is suppressed by the high oxygen content and boron oxide formation. During annealing of the B/Nb₂N bilayers no borides were formed indicating that well-formed Nb₂N is an effective diffusion barrier for B.     

Oxidizing valve metals: effect of electronic properties of the oxide films

Photocurrents emerging during the formation of anodic oxide films (AOF) on such valve metals as W, Ti, Zr, Nb, Ta are measured during an increase (direct run) and a decrease (reverse run of voltammetric curves) in the anodic potential. Capacitances of AOF formed at certain potentials are measured at potentials below the AOF formation potential. Effect of semiconductor properties on the AOF growth is considered through the formation of a Schottky barrier at the oxide/electrolyte interface. Calculated thicknesses of AOF and the depleted layer are compared. The donor-concentration drop in AOF with the distance from the metal/oxide interface is a condition for the growth of thick semiconductor oxide films. The measured potential dependence of the semiconductor-film capacitance is used to plot the donor concentration drop as a function of the distance from the Nb₂O₅/Nb interface in the oxide layer on a niobium electrode. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth.     

Prepared Low Stress Cubic Boron Nitride Film by Physical Vapor Deposition

We present low stress cubic boron nitride (cBN) films with a transition layer deposited on the metal alloy substrates by tuned substrate radio-frequency magnetron sputtering. The films were characterized by Fourier transform infrared spectroscopy and transmission electron microscopy (TEM). The IR peak position of cubic boron nitride at 1006.3 cm⁻¹, which is close to the stressless state, indicates that the film has very low internal stress. The TEM image shows that pure CBN phase exists on the surface of the film. Several phases of boron nitride were found at the medium implantation dose. It is believed that the transition from the low ordered phases to cBN phase occurred during implantation.     

SNMS and XRD investigations of laser deposited YSZ buffer layers

Summary Secondary Neutral Mass Spectrometry (SNMS) and X-Ray Diffraction (XRD) were used to find optimum parameters for the in-situ pulsed laser deposition of ZrO₂/Y₂O₃ (YSZ) buffer layers on silicon (100) substrates. Homogeneous and nearly stoichiometric concentration depth profiles were found by SNMS for the laser deposited YSZ films. A peak of the SiO intensity during profiling of the YSZ/Si interface points to a SiO₂ intermediate layer. An increasing Y-deficit of the YSZ films was found by decreasing the laser energy density at the target. Epitaxial growth of the YSZ thin films was observed at an oxygen partial pressure lower than 10^–3 mbar, a substrate temperature of 600–800°C and a laser energy density at the target of about 8 J/cm².     

Darstellung und Kristallstruktur von Niob-Tantal-Nitridphasen (Nb,Ta)N∼1

Preparation and Crystal Structures of Niobium-Tantalum-Nitride Phases (Nb, Ta)N_～1 Ta? Nb alloys with graduated composition are nitrided with NH₃ at 1100–1450°C. The mononitrides formed are investigated by X-ray diffraction. Their nitrogen content is evaluated by chemical analysis. Seven Ta? Nb nitride phases are observed. Depending on the temperature, the phases appear in a strictly defined sequence along the variation of the Ta:Nb relation. Corresponding to this sequence, the density (formula volume) of this nitride phases varies.     

Effects of nitrogen composition on the resistivity of reactively sputtered TaN thin films

Nanocrystalline tantalum nitride (TaN) thin films have been deposited by reactive direct current magnetron sputtering technique on Si/SiO₂ (100) substrate with nitrogen flow rate ranging from 0, 3, 5, 7, 9 to 11 standard cubic centimeter per minute (sccm). Structural properties, surface morphology, chemical composition and and resistivity of the TaN films were investigated by X‐ray diffraction (XRD), field emission scanning electron microscopy, X‐ray photoemission spectroscopy (XPS) and four‐point probe measurements, respectively. In the XRD spectra, a classical formation sequence of tantalum nitride phases in the order of Ta‐Ta₂N‐TaN‐Ta₄N₅ and decreasing amount of metallic Ta were observed with increasing nitrogen flow. The electrical resistivity of the TaN film was found to increase with increasing N/Ta ratio as a result of the increased electron scattering from interstitial N atoms. In the XPS analysis, two groups of Ta4f doublets relating to different TaN phases were observed in the core level spectra of TaN films. No strong coupling was observed between the Ta4f doublets and the Ta4p and the N1s groups. The appropriate nitrogen flow was believed to be helpful in the bonding and formation of stoichiometric TaN. Copyright © 2014 John Wiley & Sons, Ltd.     

Clarification by TEM and SIMS of abnormal Ti depth distribution in chemical solution-deposited SrTiO3/La0.5Sr0.5CoO3

A chemical solution-deposited multilayer system of SrTiO3 ("STO")/La0.5Sr0.5CoO3 ("LSCO") on a platinized wafer with a layer sequence Pt/TiO2/SiO2/Si(bulk) has been investigated by dynamic SIMS (secondary ion mass spectroscopy) and TEM (transmission electron microscopy); element determination was performed with EELS (electron energy-loss spectroscopy). The STO layer is intended to serve as a dielectric layer for a microelectronic capacitor; the conducting LSCO layer is a buffer layer intended to eliminate fatigue effects which usually occur at the STO/Pt interface. The SIMS depth profiles obtained for the main components revealed intense diffusion processes which must have occurred during the deposition/crystallization processes. Ti is found to diffuse from the (insulating) STO layer into the conductive LSCO layer where a region of constant concentration is observable. TEM-EELS experiments showed that these Ti plateaus are caused by precipitates approximately 20-80 nm in diameter.     

Gold and silver nanorings formed at the air/water interface

Gold nanorings were prepared at the air/water interface through reduction of AuCl₄⁻ ions by UV-light irradiation or formaldehyde gas treatment at room temperature templated by thin films of phthalocyanine derivatives. Silver nanorings were produced at the air/water interface via reduction of Ag⁺ ions by UV-light irradiation templated by poly(9-vinylcarbazole) (PVK) thin films. These nanostructures were investigated by transmission electron microscopy (TEM), selective-area electron diffractometry (SAED), and high-resolution TEM (HRTEM). It was found that the gold nanorings are composed of close-packed nanoplates whose (1 1 0) crystal planes are parallel to the air/water interface; while silver rings are composed of nanoparticles. It is demonstrated that the ring-like aggregates formed by parallel linear supramolecules of the phthalocyanine derivatives and the ring-like structure of PVK supramolecules are responsible for the formation of the gold and silver nanorings, respectively.     

Surface analytical investigations on the oxidation behaviour of TiAl-base intermetallics

Summary The oxidation behaviour of TiAl-base intermetallics has been investigated at 800°C in air. The main emphasis was placed on the mechanism by which niobium additions decrease the oxidation rate of titanium aluminides. For this purpose specimens of Ti50Al and Ti45Al10Nb were oxidized in a two-stage oxidation technique using an ¹⁸O-tracer. The scale formed during this oxidation process was analyzed by SNMS. It was found that niobium is mainly incorporated in the titanium dioxide and the nitride scale which forms beneath the initially formed alumina layer. The effect of this behaviour of the niobium on the oxide scale growth rates is discussed.     

Microstructural evolution of protective La–Cr–O films studied by transmission electron microscopy

Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS) were performed to study the microstructural evolution of La–Cr–O thin films deposited by radio frequency (RF)-magnetron sputtering on stainless steel substrates. Chromium L edges and oxygen K edges are analyzed to determine the valence states of the chromium and elucidate the phase evolution of the thin film. The as-deposited amorphous thin film crystallized to LaCrO₄ and finally transformed to the LaCrO₃ stable phase during annealing at 800°C. An intermediate Cr/Mn oxide layer was formed in all annealed samples. The thickness of this oxide layer stabilizes after 700°C, which indicates that the LaCrO₃ thin film plays a role in inhibiting the growth of an oxide layer on the metal surface.     

Characteristics of Ti–Nb,Ti–Zr and Ti–Al containing hydrogenated carbon nitride films

Nanocomposite Me–C–N:H coatings (Me is TiNb, TiZr or TiAl), with relatively high non-metal/metal ratios, were prepared by cathodic arc method using TiNb, TiZr and TiAl alloy cathodes in a CH₄ + N₂ atmosphere. For comparison purposes, a-C–N:H films were also produced through evaporating a graphite cathode in a similar atmosphere. The films were characterized in terms of elemental and phase compositions, chemical bonds, texture, hardness, adhesion and friction behavior by GDOES, XPS, Raman spectroscopy and XRD techniques, surface profilometry, hardness and scratch adhesion measurements, and tribological tests. The nanocomposite films consisted of a mixture of crystalline metal carbonitride and amorphous carbon nitride. The non-metal/metal ratio in the films composition was found to range between 1.8 and 1.9. For the metal containing nanocomposites, grain size in the range 7–23 nm, depending on the metal nature, were determined. As compared with the a-C–N:H, the Me–C–N:H films exhibited a much higher hardness (up to about 39 GPa for Ti–Zr–C–N:H) and a better adhesion strength, while the coefficients of friction were somewhat higher (0.2–0.3 for Me–C–N:H and 0.1 for a-C–N:H).     

液相烧结碳化硅晶界内氮化反应的研究

碳化硅 ( Si C)由于其高度的共价键结合特性而具有高硬度、耐磨性和高化学稳定性等优异性能而成为热机、高温环境和化学化工等领域的研究应用对象 .碳化硅材料的无压烧结最早是由 Prochazka[1] 实现的 .2 0世纪 80年代初期 ,Omori[2 ] 通过采用氧化物 ( Al2 O3,Y2 O3和稀土氧化物等 )添加剂的手段大大降低了无压烧结的温度 .这些氧化物具有较低的共熔点 ,在高温下易形成液相 ,从而促进了碳化硅的晶粒重排和晶体生长 .2 0世纪 90年代以来 ,氮化物和氧化物的混合添加剂 (如 Al N- Y2 O3) [3]被广泛应用于碳化硅的液相烧结 .这是因为氮在…     

Chemical Composition and Structure of Thin Films Produced by Chemical Vapor Deposition

This paper reports results from studies of the chemical composition and structure of semiconducting, dielectric, and metallic films produced from molecular precursors by the chemical vapor deposition method. A study was made of films of zinc sulfides, mixed copper, cadmium, and zinc sulfides, boron nitride, carbonitride, silicon carbonitride, and iridium films. It is shown that the use of metal compounds with different ligands (zinc and manganese) enables production of zinc sulfide films in which manganese ions are uniformly incorporated into the zinc sulfide crystal lattice to substitute zinc at the lattice sites. For the films of simple and mixed cadmium, copper, and zinc sulfides, the film structure depends on the type of substrate. The thin layers of mixed cadmium and zinc sulfides are asubstitution solution with a hexagonal structure. The thin layers of boron nitride produced from borazine exhibit a nanocrystalline structure and are a mixture of cubic and hexagonal phases. Composite layers were produced from alkylamine boranes and their mixtures with ammonia. Depending on synthesis conditions, the layers are mixtures of hexagonal boron nitride, carbide, and carbonitride or pure boron nitride. Using silyl derivatives of asymmetric dimethylhydrazine containing Si—N and C—N bonds in the starting molecule, we produced silicon carbonitride films whose crystal habit belongs to a tetragonal structure with lattice parameters a = 9.6 and c = 6.4 . The iridium films obtained by thermal decomposition of iridium trisacetylacetonate(III) on quartz substrates in the presence of hydrogen have a polycrystalline structure with crystallite sizes of 50 to 500 . A method for determining grainsize composition was proposed, and grain shapes for the iridium films were analyzed. The influence of substrate temperature on the internal microstructure and growth of the iridium films is demonstrated. At the iridium–substrate interface, a transition layer forms, whose composition depends on the substrate material and deposition conditions.     

Assembly of metal nanoparticle-carbon nanotube composite materials at the liquid/liquid interface

Carbon nanotubes (CNTs)-mediated self-assembly of metal (Au and Ag) nanoparticles at the liquid/liquid interface in the form of a stable nanocomposite film is reported. The metallic luster results from the electronic coupling of nanoparticles, suggesting the formation of closely packed nanoparticle thin films. The interfacial film could be transferred to mica substrates and carbon-coated transmission electron microscopy (TEM) grids. The transferred films were very stable for a prolonged time. The samples were characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), TEM, and X-ray photoelectron spectroscopy (XPS). SEM and TEM results show that the films formed at the liquid/liquid interface are indeed composite materials consisting of CNTs and nanoparticles. XPS measurements further indicate the presence of the interaction between nanoparticles and CNTs.     

Effect of atmospheric nitrogen on the oxidation mechanism of aluminum alloys with rare-earth metals

Interaction (25–620°C) of aluminum and its alloys with an atmosphere saturated with nitrogen was studied to determine the role played by rare-earth metals in the mechanism by which nitride phases are formed in oxidation of Al + REM alloys in air. The ellipsometric method and Auger electron spectroscopy were used to determine that, under the given experimental conditions, metallic aluminum is subjected to the greatest extent to the nitridation process, which is competing with the oxidation process. The process is initiated by the conversion of the amorphous oxide film to γ-Al₂O₃. The surface of Al + REM alloys interacts with nitrogen at the outer part of the oxide layer. The rare-earth metal actively reacts with impurity oxygen present in the atmosphere under study and hinders formation of nitride/oxynitride layers.     

Nitridation of niobium films by rapid thermal processing: different behaviour of films on oxydized silicon and monocrystalline sapphire substrates

By electron beam evaporation and RF magnetron sputtering 500 nm thick niobium films were deposited on thermally oxidized Si-(100)-wafers and by RF magnetron sputtering on monocrystalline sapphire-(1-102)-wafers. Investigations by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed differences of the film morphology depending on the substrate used: films deposited on SiO₂ exhibited an even surface with small crystallites, films on sapphire showed parallel surface structures with relatively large and well-shaped crystallites pointing at regular crystal growth influenced by the substrate. These differences in film morphology were also reflected in different reflection intensities of the films in XRD patterns, indicating that the films deposited on sapphire were strongly textured. In a first set of experiments nitridation in molecular nitrogen and ammonia was investigated. In a second set of experiments, it was tried to form oxynitrides of niobium by annealing the nitrided films in molecular oxygen. Particularly by X-ray-diffraction the formation of different nitride and oxide phases in dependence of the reaction temperature was examined. Further, elemental depth profiles were recorded by secondary ion mass spectrometry (SIMS) to track the position of the phases formed in the film. The different substrates led to disparate film reactivities, resulting in different nitridation grades of the films at similar reaction temperatures. In general, larger crystallite sizes resulted in less chemical reactivity of the films: even after nitridation at 1000 °C metallic niobium was still present in films deposited on sapphire. However, no evidence was obtained for the formation of oxynitrides by the process sequence observed.