Diffusion barrier performance of nanoscale TaNx thin-film

TaNx nanoscale thin-films and Cu/TaNx multilayer structures were deposited on P-type Si（100） substrates by DC reactive magnetron sputtering. The characteristics of TaNx films and thermal stabilities of Cu/TaNx/Si systems annealed at various temperatures were studied by four-point probe（FPP） sheet resistance measurement, atomic force microscopy（AFM）, scanning electron microscope-energy dispersive spectrum （SEM-EDS）, Alpha-Step IQ Profilers and X-ray diffraction（XRD）, respectively. The results show that the surfaces of deposited TaNx thin-films are smooth. With the increasing of N2 partial pressure, the deposition rate and root-mean-square（RMS） decrease, while the content of N and sheet resistance of the TaNx thin-films increase, and the diffusion barrier properties of TaNx thin-films is improved. TaNi.09 can prevent interdiffusion between Cu and Si effectively after annealing up to 650℃ for 60 s. The failure of TaNx is mainly attributed to the formation of Cu3Si on TaN/Si interface, which results from Cu diffusion along the grain boundaries of polycrystalline TaN.     

Effects of Nitrogen Content on the Phase and Resistivity of TaN Thin Films Deposited by Electron Beam Evaporation

A series of amorphous electron beam evaporated Ta and TaN films with N/Ta ratio from 0 to 1.15 were deposited on Si/SiO₂ substrates at 200°C. As N/Ta ratio increases, the TaN films undergo phase changes from pure metallic Ta to a mixture of Ta, Ta₂N, and nitrogen-rich TaN films. The electrical resistivity of the Ta and TaN films increased from 242 µΩ-cm to 1126 µΩ-cm with increasing N/Ta ratio. X-ray diffraction patterns revealed the development of different phases of TaN that are in agreement with the TaN phase diagram. The presence of different phases on the film surface was also confirmed by x-ray photo-emission spectroscopy (XPS) analysis. Groups of Ta4f doublet related to different TaN phases were observed in the core-level spectra of TaN films. Field-emission scanning electron microscopy images revealed that surface morphology also varied with the phase change in TaN films. The N/Ta ratios from energy-dispersive x-ray generally agreed with those from the XPS analysis.     

Effects of processing parameters on the properties of tantalum nitride thin films deposited by reactive sputtering

The effects of processing parameters on the properties of tantalum nitride thin films deposited by radio frequency reactive sputtering have been investigated. The influence of the N₂ partial and (Ar + N₂) total gas pressures as well as the sputtering power on the microstructure and electrical properties is reported. Rising the N₂ partial pressure, from 2 to 10.7%, induces a change in the composition of the δ-TaN phase, from TaN to TaN_1.13. This composition change is associated with a drastic increase of the electrical resistivity over a 7.3% N₂ partial pressure. The total gas pressure is revealed to strongly affect the film microstructure since a variation in both composition and grain size is observed when the gas pressure rises from 6.8 to 24.6 Pa. When the sputtering power varied between 50 and 110 W, an increase of the grain size related to a decrease of the electrical resistivity is observed.     

Optimization of electrolyte concentration for surface modification of tantalum using plasma electrolytic nitridation

Plasma Electrolytic Nitriding (PEN) is a cathodic atmospheric plasma process which has shown a promising deposition of metal coatings that exhibits a significant adhesion to the substrate as well as high deposition rates. The structure of tantalum alloy, microhardness and corrosion resistance behavior after cathodic plasma electrolytic nitriding (PEN) in electrolyte containing urea and distilled water were investigated. An Optical microscope (OM), X-ray diffractometer and scanning electron microscopy (SEM) were used to characterize the phase composition of the modified layer and its surface morphology. The corrosion resistance properties of nitrided tantalum alloy are investigated. It was shown that various electrolytes provided metallic tantalum (Ta), TaN_0.43, TaN_0.1, Ta₄N, Ta₄N₅ and TaN phases and nitrogen solid solution in tantalum. The cathodic PEN with 78 wt% urea and 21.6 wt% distilled water had a microhardness of 1198.18 VHN, which was selected as the best sample in term of electrolyte composition.     

Fabrication and diffusion barrier properties of nanoscale Ta/Ta-N bi-layer

One of the most important processes in Cu metallization for ultra large scale integrated circuits (ULSI) is to fabricate better diffusion barrier. In this paper, Ta/Ta-N films were fabricated by dc magnetron reactive sputtering (DCMS) in N₂/Ar ambient, then Cu/Ta/Ta-N/Si multi-structures were prepared in suite. The thin-film samples were rapid thermal annealed (RTA) at variational temperatures in N₂ ambient. Alpha-Step IQ Profiler, four-point probe (FPP) sheet resistance measurer, atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD) and tape test were used to characterize the microstructure and diffusion properties of the thin-films. The results show that the nanoscale Ta/Ta-N thin-films have smooth surface, and the thermal stability and barrier performance are good. After 600 °C/300 s RTA, Ta (40 nm)/Ta-N (60 nm) thin-films can effectively block against Cu diffusion and keep good adhesion strength with Cu films. After higher temperature RTA process, Cu atoms penetrated through the barrier and reacted with silicon, the barrier fail.     

The evolution of diffusion barriers in copper metallization

Refractory metal nitride thin films have been widely developed as the diffusion barriers for the aluminum or copper interconnects in integrated circuits. This study reviewed the evolution of diffusion barriers in copper metallization. First, materials characteristics and electrical properties of various diffusion barriers, titanium nitride (TiN), tantalum nitride (TaN), and titanium zirconium nitride (TiZrN), were examined. These diffusion barriers were prepared by reactive magnetron sputtering in N₂/Ar gas mixtures. Next, barrier performance was evaluated by annealing the Cu/barrier/Si systems at 400–1,000°C for 60 min. in vacuum as well as the measurements of copper diffusion coefficients. The results suggest that TiZrN films can be used as a diffusion barrier for copper metallization better than the well-known TaN films. Therefore, the evolution of diffusion barriers in copper metallization, from TiN to TaN and then from TaN to TiZrN, is addressed.     

Ta–Rh binary alloys as a potential diffusion barrier between Cu and Si: Stability and failure mechanism of the Ta–Rh amorphous structures

Thermodynamic calculations were carried out to derive the Gibbs free energy diagram for the amorphous and crystalline phases in the Ta–Rh system. These calculations predicted that the compositional range for the amorphous Ta–Rh phase was within 37–66 at.% Ta, which was validated by X-ray diffraction (XRD) analysis, high-resolution transmission electron microscopy (HRTEM) observations and resistivity measurements of as-deposited films. The thermodynamic modeling provided a valuable guide for selecting an amorphous composition suitable for diffusion barrier applications. The stability and metallurgical failure mechanism for TaRh_x diffusion barriers in contact with Cu and/or Si were investigated by resistivity measurements, XRD analysis and detailed electron microscopy on samples annealed in 5% H₂/95% N₂ gas for 30 min at various temperatures. Amorphous TaRh_x in contact with the Si substrate was stable up to 700 °C, whereupon TaRh_x decomposed and reacted to form TaSi₂ and RhSi. Si/amorphousTaRh_x (13 nm)/Cu stacks, on the other hand, were stable only up to 550 °C. Failure occurred by reaction of Rh with the Si substrate to form RhSi at the interface. The large density of defects formed in the barrier layer as a result of outward diffusion of Rh facilitated diffusion of Cu to the Si/TaRh_x interface to form Cu₃Si particles. The formation of Cu₃Si was observed to trigger further silicidation of the barrier to form a discontinuous TaSi₂ layer.     

Growth of conformal copper films on TaN by electrochemical deposition for ULSI interconnects

Seedless copper electrochemical deposition (ECD) becomes a potential interconnect technology while device dimension keeps shrinking in ULSI design. In seedless copper ECD on TaN, which is a widely used diffusion barrier, uniform growth of copper film on TaN is hindered because a robust native Ta₂O₅ exists on TaN surface. Complete removal of the native Ta₂O₅ can be attained using a saturated KOH solution that is assisted by an anodic voltage. This then permits that copper film grows on the pretreated TaN surface in a copper-citrate (Cu-Cit) complex electrolyte. Its growing morphology and deposition rate are dependent on the etching depth of as-deposited TaN in the KOH solution. Even for a very short etching time of 0.8 s, thin Ta₂O₅ is totally etched off and the activated TaN surface appears. Thin and conformal copper films grown in a layer-by-layer mode on the TaN surface are proper to function as an ECD seed or metal lines for ULSI interconnects.     

Nb、Cu金属层厚度对Si3N4/Nb/Cu/Ni/Incone l600接头组织和性能的影响

采用Nb／Cu／Ni作中间层，在连接温度为1403K、连接时间为50min、连接压力为7．5MPa的条件下，采用不同尺寸的中间层进行了Si3N4陶瓷与Inconel 600高温合金的部分液相扩散连接。通过改变Nb层、Cu层厚度，研究了Cu层、Nb层厚度变化对Si3N4／Nb／Cu／Ni／Inconel 600接头的组织和性能的影响。研究发现，当Cu层厚度小于0．05mm时，随着Cu层厚度的增加，接头中的Cu—Ni合金层厚度增加，接头强度快速增加；当Cu层厚度超过0．05mm时，接头中的Cu—Ni合金层厚度由于压力的作用不明显增加，接头强度增加缓慢。随着Nb层厚度的增加，反应层厚度增加，接头的强度先增大后减小。     

不同工艺对TaN薄膜摩擦磨损性能影响研究

采用微波增强的反应磁控溅射和离子注入法以及两者相结合的工艺制备了TaN系薄膜。通过X射线衍射(XRD)分析了薄膜的晶体结构,用微磨损仪和白光轮廓仪对样品的摩擦系数和磨损情况进行了检测和分析。结果表明,Ta离子注入与TaN沉积相结合的方式制备的薄膜耐磨损性能较好,其中Ta离子注入后沉积的Ta/TaN多层膜耐磨性能最好。说明此种工艺有效整合了两种工艺的优点,有利于薄膜力学性能的改善。     

Corrosion behaviour of TaN thin PVD films on steels

Abstract

The corrosion behaviour of tantalum nitride (TaN) thin films deposited on AISI 1018 carbon steel, AISI M2 tool steel and AISI 304 stainless steel has been investigated in an aqueous sodium chloride solution. The films were produced by means of magnetron sputtering plasma deposition. Morphological and microstructuctural characteristics of the films were studied by atomic force microscopy and X-ray diffraction analysis. Potentiodynamic polarisation, electrochemical impedance spectroscopy and cyclic voltammetry techniques were used for electrochemical characterisation. The TaN films displayed lower corrosion current densities than those of the substrates. A relaxation time in the impedance analysis was observed in the 1018/TaN system, two relaxation times were observed in the M2/TaN system, and a diffusion process was found in the 304/TaN system. This indicates that the substrates were not completely isolated from the solution and the defects in the films appear to be detrimental owing to electrolyte penetration through the defects which caused localised corrosion. The corrosion behaviour of the films depends mainly on the electrochemical properties of the substrate.     

A comparative study of CrN, ZrN, NbN and TaN layers as cobalt diffusion barriers for CVD diamond deposition on WC-Co tools

Chromium, zirconium, niobium and tantalum nitrides layers have been sputtered onto WC-12 wt.% Co substrates as diffusion barriers and buffer layers for improving performances of diamond surface coating. X-ray diffraction shows under specific reactive sputtering conditions, only MN (M = Cr, Zr, Nb, Ta) type phase exits. Their electric resistivity has been measured on samples deposited onto silica under the same conditions and related to those published.Surface and transverse scanning electron microscopy shows a dense columnar morphology.Thermo chemical computing proves the stability of those nitrides against Co, hydrogen and methane up to 1150 K (877 °C). A computed diagram of nitrogen partial pressure is given for their carburization with methane showing the highest stability for ZrN and TaN. Diamond deposition for 5 h up to 1153 K (880 °C) highlights a different behaviour for each of those materials. Auger Electron Spectroscopy (AES) profiles show a massive diffusion of cobalt through the decomposed CrN layer, a transformation of TaN and NbN into carbide without diffusion of cobalt while ZrN is outstandingly well preserved.     

Transmission electron microscopy study of the failure mechanism of the diffusion barriers (TiN and TaN) between Al and Cu

Failure mechanisms of transition metal nitride thin film diffusion barriers, such as TiN and TaN (10 nm in thickness), between Al and Cu were investigated by transmission electron microscopy (TEM), scanning transmission electron microscopy, and energy dispersive spectroscopy. After annealing at 450 °C during 30 min, the TiN diffusion barrier initially failed due to an interfacial reaction between TiN and Al forming TiAl3. When the annealing temperature was increased to 500 °C, Cu-Al intermetallic compounds were formed by the interdiffusion of Al and Cu through the diffusion barrier. In the case of the Al/TaN/Cu structure, no interfacial reaction products were observed after annealing up to 550 °C. On the other hand, it failed after annealing at 550 °C due to the inter-diffusion of Cu and Al through the diffusion barrier. TEM also identified Cu to be the rapid diffusing species in both systems. The results are discussed based on the thermodynamic stability of the interface predicted by the ternary phase diagram and the diffusion kinetics of Al and Cu through the diffusion barrier. The results show that both the thermodynamic stability of the diffusion barrier between Al and Cu and the diffusion kinetics of Al and Cu through the diffusion barrier, which are dependent on the microstructure of the diffusion barrier, should be considered carefully when selecting diffusion barrier materials between Al and Cu.     

Effects of TaN nanoparticles on microstructure,mechanical properties and tribological performance of PEEK coating prepared by electrophoretic deposition

In order to solve the friction, wear and lubrication problems of titanium, a series of TaN/ployether- ether-ketone (PEEK) coatings were developed by electrophoretic deposition, and the effects of TaN nanoparticles on the microstructure, mechanical properties and tribological performance of coatings were explored. Results manifest that the introduction of TaN nanoparticles into PEEK coatings could improve the deposition efficiency, enhance the resistant deform capacity, increase the hardness, elastic modulus and adhesive bonding strength. Compared with the pure PEEK coating, the friction coefficient of P-TN-3 was greatly reduced by 31.25%. The wear resistance of P-TN-3 was also improved in huge boost, and its specific wear rate was decreased from 9.42×10^-5 to 1.62×10^-5 mm³·N^-1·m^-1. The homogeneous composite TaN/PEEK coatings prepared by electrophoretic deposition were well-adhered to the titanium alloy substrate, TaN nanoparticles could improve the strength of PEEK coating, and provide wear-resistance protection for titanium alloys.     

Multilayer coatings by chemical vapor deposition in a fluidized bed reactor at atmospheric pressure (AP/FBR-CVD): TiN/TaN and TiN/W

TiN/W and TiN/TaN multilayer coatings were deposited on stainless steel by Chemical Vapor Deposition in a Fluidized Bed Reactor at Atmospheric Pressure (AP/FBR-CVD). First, the conditions for the deposition of TiN single layers were investigated, both from the experiment and thermochemical estimations. TiN was deposited from TiCl₄ and NH₃ at temperatures in the range of 750-950 °C. In the synthesis of multilayers, the W- and Ta-based layers were obtained by reduction of tungsten chloride or tantalum chloride with H₂. During the deposition of the TiN layers on top of the Ta layers, Ta reacted with NH₃ to form a mixture of tantalum nitrides. Multilayer coatings were characterized by means of GD-OES, AES and XRD. Preliminary results of nanoindentation hardness and oxidation resistance are also presented. Our results show for the first time that AP/FBR-CVD can be tuned for the deposition of multilayered coatings with periodicities in the submicron range.     

Carbo-oxidising of titanium by diffusion treatment in carbon–oxygen containing media

Abstract

The surface engineering of titanium with TiC_xO_1?x coatings through diffusion carbo-oxidising from graphite in oxygen containing media is investigated. The effect of oxygen partial pressure on phase composition of coatings during carbo-oxidising is evaluated. The interval of oxygen partial pressure allowing the carbo-oxide TiC_xO_1?x to form is defined as 10^?2–10³ Pa. The effects of process temperature and time on evolution of TiC_xO_1?x composition and morphology of surface layer have been investigated. It is determined that increases in temperature and process time favour an increase in carbon content in TiC_xO_1?x. It is revealed that at temperatures above the transformation temperature T_α?β, TiC_xO_1?x is formed not only in coating but also throughout grain boundaries of diffusion layer. The stages of carbo-oxide formation during diffusion carbo-oxidising of commercially pure titanium are explained as follows: surface saturation with oxygen; formation of TiO₂ film; oxide dissolution and formation of diffusion layer; formation of non-stoichiometric TiC_x and TiO_x and their interaction resulting in TiC_xO_1?x formation. Corrosion properties of carbo-oxide coatings tested in 80%H₂SO₄ are compared with nitride and oxide coatings. It is revealed that carbo-oxide coating demonstrates better corrosion resistance. The tribological properties of carbo-oxide, nitride and oxide coatings tested with bronze counterbody are compared, and carbo-oxide coating demonstrates better wear resistance.     

锌对SnxZn/Cu界面微空洞的影响

通过向锡钎料中添加不同含量的Zn元素,系统研究了锌对SnxZn/Cu(x=0,0.2,0.5,0.8(质量分数,％))界面处柯肯达尔空洞形成的影响.结果表明,经热老化处理后,纯Sn/Cu接头中的Cu3 Sn层和Cu3 Sn/Cu界面出现了大量柯肯达尔空洞.然而随着Zn元素含量的增加,反应界面处的Cu3Sn层逐渐变薄甚至消失,柯肯达尔空洞也随之显著减少或消失;锌在反应界面处的富集现象越来越显著.锌参与了界面反应,形成了(Cu,Zn)6Sn5相、Cu6(Sn,Zn)5相和Cu-Zn固溶合金,其中Cu-Zn固溶合金层可以显著影响铜的界面扩散.Zn元素直接参与了界面扩散,在很大程度上缓和铜和锡的不平衡扩散,从而有效抑制了柯肯达尔空洞的形成.     

Investigation on Oxygen Chemical Diffusion Properties of Perovskite Oxides (La1?x Pr x )0.6Sr0.4Co0.8Fe0.2O3?δ

Perovskite oxide samples of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (x = 0.2, 0.4, 0.6, 0.8) are obtained by solid-state reaction method. The oxygen chemical diffusion properties of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ are determined by electrical conductivity relaxation technique. The results show that the conductivity of (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ increases with the increase of oxygen partial pressure. The (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ samples have a high oxygen chemical diffusion coefficient, which decreases linearly with a decrease in temperature and an increase in Pr content. The oxygen chemical diffusion coefficient D _chem remains fairly constant at high PO₂. The oxygen chemical diffusion coefficient is the highest for (La_1−x Pr _x )_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ with x = 0.2, and attains a value of 9.41 × 10⁻⁵ cm² s⁻¹ at 600 °C. This shows the material’s promise as a cathode material for intermediate temperature solid oxide fuel cells.     

Hydrogen absorption and desorption in Ti−Al alloys

Binary Ti_1−xAl_x and ternary Ti_0.75−xAl_0.25M_x (M=V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Pd, Hf, Ta and W; x=0.15 and 0.25) alloys reacted slowly with 5.0 MPa H₂ at room temperature for different periods. The hydrogen absorption capacity, the 50% hydrogen desorption temperature (T _d) and the structures of their hydride were investigated. Amorphous and fcc type hydrides formed by hydrogenation of the binary Ti−Al alloys. As the Al concentration increased in the Ti−Al alloys, the hydrogen absorption capacity decreased, while the hydrogen desorption temperature decreased at once and then increased again. Amorphous, fcc, bcc and C14 Laves type hydrides formed by hydrogenation of the ternary Ti₃Al− based alloys. The hydrogen absorption capacity was reduced despite whatever elements were substituted for Ti in Ti₃Al. Ni, Co, Mn and Nb have the ability to reduceT _d of Ti_0.75−xAl_0.25M_x. This article based on a presentation made in the symposium “The 2nd KIM-JIM Joint Symposium: Hydrogen Absorbing Materials”, held at Hanyang University, Seoul, Korea, October 27–28, 2000 under the auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Improved oxidation and hot corrosion resistance of Ta-doped NiAlY alloy at 750°C

The oxidation and hot corrosion behaviors of the NiCrAlY, NiAlY, and Ni–xTa–Al–Y alloys (x = 1, 3, 5, and 10 wt%) were investigated at 750°C. The doped Ta promoted the formation of the protective α-Al₂O₃ scales. The NiTaAlY alloys exhibited an improved oxidation resistance compared with the NiAlY alloy. Under the NaCl-induced hot corrosion test, the addition of Ta reduced the consumption of Al and inhibited the internal corrosion of the alloys. The Ni–xTa–Al–Y alloys (x = 1, 3, 5, and 10 wt%) showed better resistance to the NaCl-induced hot corrosion. Moreover, the hot corrosion mechanism of the tested alloys was also discussed.