Ru-Ta Alloy Research Articles

Growth-Inhibited Nucleation Enhancement: from High Density Nanoparticle Deposits to Nanometer Thin Continuous Films

In our group, we have been working on the electrochemical nucleation and growth of high island density deposits of copper, indium, nickel, cobalt and iron deposits for more than a decade. From simple electrolyte solutions, all metal systems seem to saturate at an island density of few times 1011 islands per cm2 at most or about 20-30nm spacing per particle. From direct copper plating for damascene processes, we know that the island density can be augmented by the introduction of growth inhibiting species such as the chloride-polyether suppressor additive combo. In this case, the Cl-suppressor adsorbs on the copper island as soon as it is formed. As the current-potential curve for the Cl-suppressor covered copper is polarized more negative with respect to the non-suppressed copper, the overpotential is driven more negative during galvanostatic deposition allowing higher island density [1]. As such the island density can be driven higher than 1013 cm-2 (spacing of about 3nm per particle) on oxide-poor noble metals such as Pt and up to 1012 cm-2(spacing of about 10nm per particle) for oxide-prone surfaces like RuTa alloys [2]. Note that these values are extrapolated as islands can no longer be distinguished from films at this point (coalescence thickness of 5nm and 2nm for hemispherical particles, respectively). The adsorbed suppressor typically also introduces flattened particle shapes helping to bring the effective coalescence thickness even lower. On platinum and cleaned RuTa surfaces, closed copper films with thicknesses down to 2-3nm could be obtained. From our study, it became apparent that the surface condition and overpotential were the two drivers.Based on the know-how from copper, several typical growth inhibiting additives (e.g. saccharine, 2-butyne-1,4-diol, PEG) were tried to increase the Ni and Co nanoparticle density. However, with no avail, as the adsorption and inhibition was typically too slow. In copper deposition, the additives already form complexes with the cuprous intermediate formed during copper deposition. As such the adsorption is very fast, whereas for Ni and Co, the additives need to adsorb via a physisorption which happens too late to affect the nucleation stage. Recently we found that the Ni particle density is strongly affected by the boric acid concentration [3]. The formation of growth inhibiting hydroxides gives the desired effect for growth-inhibited nucleation. However, the local pH cannot rise to fast as otherwise precipitation from solution already occurs in the depletion layer. Therefore a small concentration of boric acid was still needed at 5mM NiCl2 concentration to allow nickel growth to proceed long enough. At the best trade-off conditions a density of 4x1011 cm-2 Ni nanoparticles on TiN was obtained. By tuning the NiCl2 concentration, the growth-inhibited nucleation process could be extended to higher Ni island densities resulting in nanometer thin nickel films [4]; similar to what was achieved for copper. In this paper, we will go in on the mechanism of growth-inhibited growth for the fabrication of high density particles or (sub)nanometer thin films of Cu and Ni. “The Effect of Polyether Suppressors on the Nucleation and Growth of Copper on RuTa Seeded Substrate for Direct Copper Plating” M. Nagar, A. Radisic, K. Strubbe, P.M. Vereecken Electrochim. Acta, 127, 315-326 (2014).“Systematic studies of electrochemical nucleation and growth of copper on Ru-based substrates for damascene process”, Magi Margalit Nagar, PhD thesis, Universiteit Gent. “Enhanced nucleation of Ni nanoparticles on TiN through H3BO3-mediated growth inhibition” Johannes Vanpaemel, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe Vereecken, Electrochimica Acta 109, 411-418 (2013).“Electrochemical deposition of sub-nanometer Ni films on TiN” Johannes Vanpaemel, Masahito Sugiura ,Daniel Cuypers, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe M. Vereecken, Langmuir, 30 (8), 2047–2053 (2014).

Effects of N Doping in Ru-Ta on Barrier Property and Reliability Performance for Cu Interconnects

The effects of N doping in Ru-Ta alloy on film property, barrier property against Cu diffusion and reliability performance in Cu interconnects were investigated. RuTa(N) film which was doped with N in Ru-Ta alloy was applied as a diffusion barrier layer in Cu interconnects, and barrier property and reliability performance with RuTa(N) barrier were mainly evaluated. As RuTa(N) film was annealed, N desorbed easily from RuTa(N) film due to its low thermal stability and the crystal size became larger because of the recrystallization. RuTa(N) film had the poor barrier property against Cu diffusion due to the structure of high-angle grain boundaries despite the crystal size of RuTa(N) increases and the density of grain boundaries decreases after annealing. Reliability performance of via electromigration could be improved by using Ru-Ta based alloy barrier. However, there was remarkable difference of reliability performance between RuTa and RuTa(N) barrier, and RuTa(N) had inferior reliability performance of via electromigration. On the other hand, RuTa had both good barrier property and superior reliability performance. It was found that doping N in Ru-Ta alloy degraded barrier property and reliability performance. Consequently, it is appropriate to apply RuTa single film as the diffusion barrier layer for Cu interconnects.

The Development of Cu Filling and Reliability Performance with Ru-Ta Alloy Barrier for Cu Interconnects

Ru-Ta alloy was investigated as the diffusion barrier layer in Cu dual damascene interconnects, and Cu filling property and reliability performances with RuTa/RuTa(N) stacked barrier structure were mainly evaluated. RuTa strongly orientated to Ru(002) and the lattice misfit between Ru(002) and Cu(111) was lower than that between Ta(110) and Cu(111). The wettability of Cu seed on RuTa was much better than that on Ta. The barrier property against Cu diffusion of RuTa/RuTa(N) stacked barrier structure kept the equivalent barrier property of conventional Ta/TaN one. Filling property of Cu electroplating was improved by using Ru-Ta alloy barrier, and trenches of 45 nm in width could be filled successfully due to the suppression of the agglomeration of Cu seed on the sidewall of trench. Via resistance with RuTa/RuTa(N) barrier was much lower than that with Ta/TaN one due to its low resistivity. The estimated life time of via electromigration with RuTa/RuTa(N) barrier was longer than that with Ta/TaN one because of the good wettability and filling property inside via. Consequently, Cu filling property and reliability performance can be improved with RuTa/RuTa(N) stacked barrier structure in Cu interconnects.

The Effect of the Substrate Characteristics on the Electrochemical Nucleation and Growth of Copper

We have deposited copper electrochemically, from acidic copper sulfate solutions with and without presence of different polyether molecules, on as-received RuTa alloy substrates, electrochemically-treated RuTa alloys and on Pt. We focused on the effect of substrate properties on the nucleation and growth processes during galvanostatic deposition, especially formation of Cu underpotential layer, and its influence on the island shape and final island density. Analysis of the galvanostatic transients showed that an exponential dependence could be used to describe the relationship between the island density and the actual deposition overpotential for all three substrates. For Pt and as-received RuTa alloy, a general equation is proposed for determining final island density irrespective of solution composition and deposition parameters, making it easier to predict the potential use of the given substrates in applications where direct plating is required. We also use various physical characterization techniques to determine the point of minimum coalescence thickness for Cu on Pt as a model substrate, and extrapolate the validity of the exponential formulas to island sizes beyond the resolution of our scanning electron microscopes.

From High Density Nanoparticle Deposits to Nanometer Thin Continuous Films By Growth-Inhibited Nucleation Enhancement

In our group, we have been working on the electrochemical nucleation and growth of high island density deposits of copper, indium, nickel, cobalt and iron deposits for about a decade. From simple electrolyte solutions, all metal systems seem to saturate at an island density of few times 1011 islands per cm2 at most or about 20-30nm spacing per particle. From direct copper plating for damascene processes, we know that the island density can be augmented by the introduction of growth inhibiting species such as the chloride-polyether suppressor additive combo. In this case, the Cl-suppressor adsorbs on the copper island as soon as it is formed. As the current-potential curve for the Cl-suppressor covered copper is polarized more negative with respect to the non-suppressed copper, the overpotential is driven more negative during galvanostatic deposition allowing higher island density [1]. As such the island density can be driven higher than 1013 cm-2 (spacing of about 3nm per particle) on oxide-poor noble metals such as Pt and up to 1012 cm-2(spacing of about 10nm per particle) for oxide-prone surfaces like RuTa alloys [2]. Note that these values are extrapolated as islands can no longer be distinguished from films at this point (coalescence thickness of 5nm and 2nm for hemispherical particles, respectively). The adsorbed suppressor typically also introduces flattened particle shapes helping to bring the effective coalescence thickness even lower. On platinum and cleaned RuTa surfaces, closed copper films with thicknesses down to 2-3nm could be obtained. From our study, it became apparent that the surface condition and overpotential were the two drivers.For the application of dense CNT forests, we were interested in fabrication of densely packed Ni, Co and Fe nanoparticles. We have shown that the density of the ECD catalyst particles is directly translated to the CNT density; the highest density of 2x1011cm-2 from an alkaline NiNO3-NH4Cl bath [3]. Based on the know-how from copper, several typical growth inhibiting additives (e.g. saccharine, 2-butyne-1,4-diol, PEG) were tried to increase the Ni and Co nanoparticle density. However, with no avail, as the adsorption and inhibition was typically too slow. In copper deposition, the additives already form complexes with the cuprous intermediate formed during copper deposition. As such the adsorption is very fast, whereas for Ni and Co, the additives need to adsorb via a physisorption which happens too late to affect the nucleation stage. Recently we found that the Ni particle density is strongly affected by the boric acid concentration [4]. The formation of growth inhibiting hydroxides gives the desired effect for growth-inhibited nucleation. However, the local pH cannot rise to fast as otherwise precipitation from solution already occurs in the depletion layer. Therefore a small concentration of boric acid was still needed at 5mM NiCl2 concentration to allow nickel growth to proceed long enough. At the best trade-off conditions a density of 4x1011 cm-2 Ni nanoparticles on TiN was obtained. By tuning the NiCl2concentration, the growth-inhibited nucleation process could be extended to higher Ni island densities resulting in nanometer thin nickel films [5]; similar to what was achieved for copper. In this paper, we will go in on the mechanism of growth-inhibited growth for the fabrication of high density magnetic metals such as Ni, Co and Fe.“The Effect of Polyether Suppressors on the Nucleation and Growth of Copper on RuTa Seeded Substrate for Direct Copper Plating” M. Nagar, A. Radisic, K. Strubbe, P.M. Vereecken Electrochim. Acta, 127, 315-326 (2014).“Systematic studies of electrochemical nucleation and growth of copper on Ru-based substrates for damascene process”, Magi Margalit Nagar, PhD thesis, Universiteit Gent."Electrochemical tailoring of catalyst nanoparticles for CNT spatial-dimension control" A. Romo-Negreira, D. J. Cott, K. Maex, M. M. Heyns and P. M. Vereecken, JES 157, K47 (2010).“Enhanced nucleation of Ni nanoparticles on TiN through H3BO3-mediated growth inhibition” Johannes Vanpaemel, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe Vereecken, Electrochimica Acta 109, 411-418 (2013).“Electrochemical deposition of sub-nanometer Ni films on TiN” Johannes Vanpaemel, Masahito Sugiura ,Daniel Cuypers, Marleen H. van der Veen, Stefan De Gendt, Stefan and Philippe M. Vereecken, Langmuir, 30 (8), 2047–2053 (2014).

Improved ON-State Reliability of Atom Switch Using Alloy Electrodes

Cu-alloy active-electrode coupled with Ru-alloy inert electrode is proposed to improve the ON-state reliability of nonvolatile Cu atom switch. The high rupture temperature (Tr > 400 °C) of the nanometer-scale Cu bridge with high thermal resistance (Rth) is realized by the Cu(AlTi)-alloy without increasing programming current. The anti-Cu diffusive Ru(Ta) alloy contributes to improve the retention of the ON-state at 150 °C and endurance to > 104 cycles. The metallurgical prescription on the electrodes is a key to improve the stability of the nanometer-scale conducting bridge while keeping the switching power low.

Unexpected Constrained Twin Hierarchy in Equiatomic Ru-Based High Temperature Shape Memory Alloy Martensite

Among the different systems for high temperature shape memory alloys (SMA’s), equiatomic RuNb and RuTa alloys demonstrate both shape memory effect (SME) and MT temperatures above 800°C. Equiatomic compounds undergo two successive martensitic transformations, β (B2) → β’ (tetragonal) → β’’ (monoclinic), whereas out of stoechiometry alloys exhibit a single transition from cubic to tetragonal. In the case of two successive martensitic transformations, we expect to have a finer microstructure of the second martensite because it is supposed to develop inside the smallest twin elements of the former one. In equiatomic Ru-based alloys, if the first martensitic transformation is “normal”, the second one gives different unexpected microstructures with, for instance, twins with a thickness which is larger than the smallest spacing between twin variants of the first martensite. In fact, the reason for this unexpected hierarchy of the twins size is that the second martensitic transformation takes place in special conditions: geometrically, elastically and crystallographically constrained.

Phase Transformation and Shape Memory Effect in Ru-Based High Temperature Shape Memory Alloys

Among the different systems for high temperature shape memory alloys (SMA’s), equiatomic RuNb and RuTa alloys demonstrate both shape memory effect (SME) and MT temperatures above 800°C. For both systems, it is interesting to find a way to control the transformation temperatures while keeping the shape memory effect. One way to change the transformation temperatures is to change the composition in the binary alloys; another is to add a ternary element like Fe. The eight investigated alloys show two different space groups at room temperature. The monoclinic alloys undergo two successive displacive transformations on cooling, starting from the high temperature β phase field: β (B2) à β’ (tetragonal) à β’’ (monoclinic). The tetragonal alloys exhibit a single transition from cubic to tetragonal. A multiple twinned microstructure can be found in all alloys. Transformation temperatures decrease with lower Ru content and with the addition of Fe. The β’ à β transformation seems to be the main responsible for the SME. Compression tests performed in the martensitic phase give a quantitative result of the shape memory effect. In the binary alloys, the SME decreases with decreasing Ru content, which is in accordance with the evolution of the lattice parameters of martensites. A lower SME in the ternary alloys can also be linked to the lattice parameters and seems to be quite reliable to predict the evolution of the shape memory effect.

The effect of Fe additions on the shape memory properties of Ru-based alloys

Equiatomic RuNb and RuTa alloys exhibit a shape memory effect (SME) and high transformation temperatures (>800 °C). Controlling the transformation temperatures while retaining the SME can be achieved either by changing the alloy composition or by adding a ternary element such as Fe. Eight alloys are investigated. The SME decreases with decreasing Ru content, which is in accordance with the evolution of the lattice parameters of martensite.

Hf-Based High-kDielectrics: Process Development, Performance Characterization, and Reliability

Abstract In this work, the reliability of HfO2 (hafnium oxide) with poly gate and dual metal gate electrode (Ru–Ta alloy, Ru) was investigated. Hard breakdown and soft breakdown, particularly the Weibull slopes, were studied under constant voltage stress. Dynamic stressing has also been used. It was found that the combination of trapping and detrapping contributed to the enhancement of the projected lifetime. The results from the polarity dependence studies showed that the substrate injection exhibited a shorter projected lifetime and worse soft breakdown behavior, compared to the gate injection. The origin of soft breakdown (first breakdown) was studied and the results suggested that the soft breakdown may be due to one layer breakdown in the bilayer structure (HfO2/SiO2: 4 nm/4 nm). Low Weibull slope was in part attributed to the lower barrier height of HfO2 at the interface layer. Interface layer optimization was conducted in terms of mobility, swing, and short channel effect using deep submicron MOSFE...

Impact of Ge on integration of HfO2 and metal gate electrodes on strained Si channels

Tensile-strained Si epitaxial layers (7.5nm–17nm) were grown on relaxed Si0.5Ge0.5 virtual substrates by ultrahigh-vacuum rapid thermal chemical vapor deposition. Metal-oxide-silicon capacitors were fabricated with SiO2 or HfO2 as gate dielectrics and Ru–Ta alloy or TaN as the metal gate electrodes. The results indicate that the interface trap density (Dit) increased as the strained silicon thickness decreased, which was attributed to the presence of Ge in the strained Si layer. Higher Dit was observed with SiO2 which may be due to Si consumption during oxidation, leading to a higher density of Ge at the interface. Leakage current density (Jg) was also observed to increase with increasing strained silicon thickness. This trend of increasing Dit and Jg with decreasing strained silicon thickness did not change after rapid thermal annealing. Both Ru–Ta and TaN gate electrodes were found to exhibit as good a performance on strained Si as on bulk Si.

Beyond microelectronics: materials and technology for nano-scale CMOS devices

The scaling of CMOS devices into the nanometer regime has required the introduction of new materials in field effect transistor fabrication. Foremost of these is the introduction or new gate dielectrics to replace the ultra-thin SiO2 films traditionally used. It has been found that these materials, such as ZrO2, HfO2 and Al 2O3, reduce gate leakage currents by 2–5 orders of magnitude. Unfortunately these new high-κ materials have also resulted in substantial electron and hole mobility reduction. However, with the introduction of strained silicon, in which mobilities have been recovered to the extent that even with the high-κ gate dielectrics improvements have been noted approaching 60%. Further increases in electron and more importantly hole mobilities have been discovered with the use of silicon substrates of either (110) or (111) orientations. However, the electron mobility had a significant decrease with the same substrates. Finally the introduction of metal gates has allowed scaling to continue by eliminating the capacitance of the poly-Si gate. Even though the requirements for such metal gates are quite restrictive, a number of candidates have been found. Such metal systems that might be used include particular Ru-Ta alloys gates for both nFETs and pFETs can be fabricated and perform as desired. Similarly, the use of a variety of nitrogen concentrations in TiN and TaN yields a range of acceptable work functions which might be applicable to either or both FET types. The introduction of these materials increases device performance but it is their integration into CMOS processes that will determine their utility. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A Capacitance-Based Methodology for Work Function Extraction of Metals on High-<tex>$kappa$</tex>

This letter presents a methodology to accurately extract the work function of metal electrodes on high-/spl kappa/ dielectrics with various charge distributions. A mathematical analysis including sources of errors was used to study the effect of charge distribution in gate dielectric stacks on the flatband voltage of the device. The calculations are verified by experimental results obtained for Ru-Ta alloys on HfO/sub 2/ and SiO/sub 2/ gate dielectric stacks. It is shown that accounting for the appropriate charge model is imperative for accurate calculation of workfunction on high-/spl kappa//SiO/sub 2/ gate dielectric stacks.

Effect of Ta content on martensitic transformation behavior of RuTa ultrahigh temperature shape memory alloys

Effects of Ta content on martensitic transformation (MT) behavior of Ru 100− x Ta x ( x=46–54 at.%) alloys have been investigated by differential scanning calorimetry, dilatometry, X-ray diffraction and optical microscopy. Ta content significantly affects the MT behavior of RuTa alloys. The one-stage reservible MT occurs in Ta-poor RuTa alloys with Ta content less than 49 at.%. The two-stage reservible MT takes place in near-equiatomic RuTa alloys. No reservible MT is observed in Ta-rich alloys with Ta content more then 52 at.% Ta. The MT temperatures and hysteresis of RuTa alloys decrease with increasing Ta content. The aged and thermal cycled processes are nearly no effect on the MT behavior of these alloys. The deforming way of RuTa alloys is twinning. The Ru 50Ta 50 alloy is of the most excellent MT behavior among these RuTa alloys.

Electrical properties of Ru-based alloy gate electrodes for dual metal gate Si-CMOS

In this letter, low resistivity Ru and Ru-Ta alloy films, deposited via reactive sputtering, were evaluated as gate electrodes for p- and n-MOSFET devices, respectively. MOSFETs fabricated via a conventional process flow indicated that the work functions of Ru and Ru-Ta alloys were compatible with p- and n-MOSFET devices, respectively. Both of the metal gated devices eliminated gate depletion effects. Good MOSFET characteristics, such as I/sub DS/-V/sub GS/ and mobility, were obtained for both Ru-gated PMOSFETs and Ru-Ta gated NMOSFETs.

Thermoelastic Properties of Super High Temperature Ru-Ta Shape Memory Alloy

ABSTRACTEquiatomic Ru-Ta alloy can show a thermoelastic phase transformation at super high temperatures above 1000°C. The temperature of shape memory effect of this alloy seems to be remarkably higher by two times than those of the formerly reported high temperature NiMnAl alloy and it seems very interesting as one of the new high temperature SMAs, however, detailed thermoelastic properties of Ru-Ta system alloy have not been clarified. The present paper investigates the basic material properties of Ru-Ta alloy, i.e. each transformation temperature, temperature hysteresis range, heat absorption by DSC measurement and metallurgical compounds by X-ray diffraction that depend on alloy composition by changing the Ru content from 46–5 4at%. Effect of heat treatment at solution temperature and aging temperature on thermoelastic phase transformation points is investigated and the thermal cyclic stability is also studied for engineering applications as high temperature actuator/sensor materials.

Rapid-Solidified Metallic Actuator Materials Developed by Electromagnetic Nozzleless Melt Spinning Method

AbstractElectro-magnetic nozzleless melt-spinning method was developed by combining the control of the flow down of the molten metals after electromagnetic float-melting(i.e. levitation) with rapid solidification by rotating roll. The metallurgical grain microstructures can be changed by rotating roll speed. It was confinned that the produced, intermetallic TiNi and NiAl system alloy thin plates showed the strong crystal anisotropy, higher shape memory functional properties than those of the conventionally processed melt-worked samples having its same origin. As new SMAs by using this method, ferromagnetic shape memory, FePd alloy having very large magnetostriction and super high temperature shape memory, RuTa alloy having the transformation over 1000°C were developed. Moreover, our recent study on the advanced rapid-solidification machine to produce many kinds of short fibers as well as ribbons is introduced. Finally, harmonic material design for sensor/actuator stacking composite system, namely “Smart Board” for aircraft structures will be introduced.

Native ruthenium in tantalum carbide concentrates from the Ural mountains, USSR

Native Ru has been found in several samples of tantalum carbide collected in the Urals before 1914. Ru crystallized with a rectangular habit but now has hexagonal symmetry. The chemical composition is Ru-Ta alloy (Ta = 7.56 ± 0.7 wt%) and it is entirely devoid of other PGEs. This unusual composition, the fact that PGMs are not found intergrown with the Ru, and that magnetite and ilmenite, rather than chromite, are found among the associated placer minerals, indicates that the petrological affinity of the Ru is pyroxenitic, rather than dunitic or peridotitic. It is suggested that pure native Ru is more widespread than hitherto observed and that identification may be impeded by specific detection difficulties which were met with during this study (i.e., extremely small sizes, strong adhesive properties, unfavourable optical properties).