Ni2 Si Research Articles

Customized development of promising Cu-Cr-Ni-Co-Si alloys enabled by integrated machine learning and characterization

Two types of alloys, Cu-Ni-Co-Si and Cu-Cr-Zr, are considered candidate materials for next-generation integrated circuits due to their superior comprehensive performance. However, the rapid development of these two types of alloys remains difficult using conventional simulation techniques. Machine learning offers a new tool for accelerating the design and discovery of new materials with required property profiles. Herein, composition-process-property database of the six-element Cu-Cr-Ni-Co-Si-Zr alloys were established, and a novel strategy of customized performance design for different application environments was proposed. Then, four alloys with different performance characteristics were rapidly screened from 850,500 candidates using a multi-property segmented screening method, and the predicted results agreed well with the experimental results. Importantly, the developed Cu-1.0Cr-1.0Ni-2.5Co-0.8Si alloy was used as a bridge alloy to link the Cu-Ni-Co-Si and Cu-Cr-Zr alloys together, filling the gap in the mid-segment performance (220–240 HV, 45–65% IACS) of Cu-based alloys. Interestingly, the studied alloy was a dual-phase precipitation-strengthened alloy. It was found that the small spherical (Co, Ni)2Si phase was the main influence on the micro-hardness and strength, while the large rod-shaped Cr3Co5Si2 phase was the main reinforcing phase that affected ductility and electrical conductivity. The design method proposed in this paper accelerates the development of the Cu-Cr-Ni-Co-Si alloy system, which has great potential for application in integrated circuits and heat sinks.

Nickel silicide formation with rapid thermal treatment in the heat balance mode

The formation of nickel silicide layers on (111)-Si substrates during rapid thermal annealing in the heat balance mode was studied by the Rutherford backscattering method, X-ray diffraction, transmission electron microscopy, and electrophysical measurements. Nickel films of about 70 nm thickness were deposited by magnetron sputtering at room temperature. The rapid thermal treatment was carried out in a heat balance mode by irradiating the substrates backside with a non-coherent light flux of quartz halogen lamps in the nitrogen medium for 7 seconds up to the temperature range of 200 to 550 °C. The redistribution of nickel and silicon atoms to monosilicide NiSi composition starts already at a temperature of 300 °С and almost ends at a temperature of 400 °С. In the same temperature range, the orthorhombic NiSi phase with an average grain size of about 0.05–0.1 μm is formed. At a rapid thermal treatment temperature of 300 °C, two phases of silicides (Ni2 Si and NiSi) are formed, while a thin layer of unreacted Ni is retained on the surface. This fact can be explained by the high heating rate at the initial annealing stage, at which the temperature conditions of the NiSi phase formation occur earlier than the entire Ni layer manages to turn into the Ni2 Si phase. The layers with a simultaneous presence of three phases are characterized by a high roughness of the silicide-silicon interface. The dependence of the specific resistivity of nickel silicide layers shows an increase to the values of 26–30 μOhm · cm in the range of rapid thermal treatment temperatures of 200–250 °C and a subsequent decrease to the values of about 15 μOhm · cm at a rapid thermal treatment temperature of 400 °C. This value of specific resistivity is characteristic of the high conductivity of the NiSi phase and correlates well with the results of structure studies.

Joining SiC ceramic and metal Mo with AuPdCoMnNi alloy and interfacial reactions

For high-temperature joining of SiC ceramics, a multi-element AuPdCoMnNi alloy was designed and used as filler metal to join SiC ceramics to metal Mo. The brazing experiment was conducted under the condition of 1150 °C for 5 min and 10 min, respectively. The results show that numerous micro-cracks are visible in the directly brazed Mo/SiC joints, which are continuously distributed in bands of (Co, Ni)-Si and (Pd, Ni)2Si compounds. SiC was further joined to Mo using a Kovar interlayer under the same brazing conditions, and the metallurgical quality of the joints was evidently improved compared with the joints without this interlayer. The joining layer was mainly composed of (Au, Mn)ss layer mixed with element C, (Fe, Co, Ni, Mo)-Si compound layer and (Fe, Co, Ni)-Si compound with discontinuous (Pd, Ni)2Si phases and some small fragments of (Fe, Co, Ni, Mo)-Si compounds. In addition, the shear strength of the joints with Kovar interlayer reaches 55.36 MPa, remarkably higher than the void. The joining mechanism was also discussed.

Effect of V Addition on Microstructure and Properties of Cu-1.6Ni-1.2Co-0.65Si Alloys

To obtain high strength and high electrical conductivity at the same time, the microstructure and properties of 0.2 wt.% V-added, 0.1 wt.% V-added and V-free Cu-1.6Ni-1.2Co-0.65Si(-V) alloys were investigated. We examined with electrical conductivity and hardness measurements, tensile test, optical microscope and transmission electron microscope (TEM). The results show that Cu-1.6Ni-1.2Co-0.65Si-0.1V alloy obtains excellent combination properties: electrical conductivity is 46.12% IACS, hardness is 293.88 Hv, and tensile strength is 782 MPa, which are produced by 65% cold rolling + aging at 500 °C for 480 min. The addition of vanadium (V) can accelerate the precipitation of solute atoms from the copper matrix, improve the hardness and electrical conductivity of Cu-1.6Ni-1.2Co-0.65Si alloys, and greatly accelerated the aging response. δ-(Co,Ni)2Si and β-Ni3Si phases are detected in Cu-1.6Ni-1.2Co-0.65Si-0.1V alloy. The Orowan mechanism and grain boundary strengthening play a major role in the yield strength strengthening due to δ-(Co,Ni)2Si phase.

Precipitation behavior of Cu-3.0Ni-0.72Si alloy

CuNiSi alloys have been widely applied in electronic and electrical industries. The precipitation behavior of some of the CuNiSi alloys is still not well understood. In this study, the precipitation behavior of the Cu-3.0Ni-0.72Si alloy aged at 600 °C for different times was investigated by transmission electron microscopy, atom probe tomography and phenomenological theory of precipitation crystallography. A new orientation relationship (OR) between the precipitates and the Cu matrix was found in the over-aged condition and a coarsening mechanism of the metastable precipitates was put forward. The two- and three-dimension invariant line theories were successfully applied in interpreting the evolution of the ORs and the morphologies in the Cu/δ-Ni2Si (Cu/δ) system. At the early stage of aging, the fine metastable δ’-(Cu, Ni)2Si precipitates are coherent with the Cu matrix, with a quasi-Bain OR of (110)Cu||(100)δ′ and [001]Cu||[001]δ′, and four pairs of parallel conjugate planes: (1¯1¯1)Cu||(3¯01)δ′, (111)Cu||(301)δ′, (1¯11)Cu||(021)δ′, and (11¯1)Cu||(02¯1)δ’. The precipitates have a δ-Ni2Si structure, with some Ni atoms substituted by Cu atoms. During growth, the core region of the metastable δ’-(Cu,Ni)2Si precipitate transforms into stable δ-Ni2Si, with a quasi-NW OR of (1¯11)Cu||(021)δ and [110]Cu||[100]δ, while a layer of metastable δ’- (Cu, Ni)2Si still exists around the core. With prolonging aging time, the δ-Ni2Si precipitates with the OR of (1¯11)Cu||(021)δ and [110]Cu||[100]δ grow two-dimensionally to form a plate-like shape, while those with the OR of (111)Cu||(301)δ and [1¯10]Cu||[010]δ grow one-dimensionally to form a fiber-like shape.

Microstructure and Properties of a Novel Cu–Ni–Co–Si–Mg Alloy with Super-high Strength and Conductivity

The Cu–4.5Ni–1.2Co–1.0Si–0.15Mg alloy with super-high strength and high electrical conductivity was designed, and a two-step thermo-mechanical treatment was applied to improve the mechanical and electrical properties of the alloy. The microstructure and properties of the alloy were investigated by transmission electron microscope observation, tensile test, hardness and electrical conductivity measurements. The results show that the final alloy treated by two-step thermo-mechanical process has a hardness of 329 HV, a yield strength of 1086 MPa, an elongation of 3.6%, and an electrical conductivity of 30.1%IACS, respectively. The nanoscale β-Ni3Si and δ-(Co,Ni)2Si precipitates form during the thermo-mechanical process, and the addition of the Co could promote the precipitation of δ-(Co,Ni)2Si particles. The orientation relationship (OR) between Cu matrix and the precipitates is: (022)Cu//(011)β//(010)δ and [100]Cu//[100]β//[001]δ. Comparing with the directly aging treatment and one step thermo-mechanical treatment, precipitates that form during the two-step thermo-mechanical process are much smaller and distributed more densely, resulting in the better comprehensive properties of the alloy.

Effect of cobalt additions on soft magnetic θ-(Fe,Ni)2Si

The effects of cobalt additions to Fe56.7Ni10Si33.3 and Fe51.7Ni15Si33.3 on phase stability and magnetic prop- erties of the soft magnetic phase h-(Fe,Ni)2Si are explored. The addition of 5 at.% Co increases the temperature of the eutectoid decomposition of the h-phase from 738 to 760 C as well as Curie temperatures and magnetic saturation, while the coercive field is reduced. Lattice parameter measure- ments indicate magnetostriction.

Corrosion properties of thermally annealed and co-sputtered nickel silicide thin films

The corrosion properties of nickel silicide thin films are addressed by means of polarisation experiments in combination with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) characterisation before and after the polarisation runs. The thin films studied included two pairs of nickel silicide of different compositions fabricated on Si wafer by means of ion-beam sputter deposition technique. For one pair, thin films were prepared by co-sputtering Si and Ni targets. To achieve higher crystallinity, the other pair was prepared by Ni sputter deposition followed by subsequent thermal annealing at 280 °C and 480 °C to develop single silicide phase of Ni 2Si and NiSi in individual film, respectively. The variation of the binding energy (BE) of Ni 2p 3/2 core-level peak in the XPS measurement in accordance with the Si content for this binary system follows a Boltzmann's relationship. The electrochemical polarisation tests conducted in 1.00 M HCl solution showed almost the same behaviour for the tested specimens irrespective of structure or film composition, still, the SEM and XPS studies together with optical microscopy showed that the Ni 2Si, leaner in Si, experienced thin film corrosion, whilst the NiSi appeared to be more resistant. Clearly, composition is found to be a more important design factor to tailor the corrosion properties than the structure for this binary silicide system.

Study of nickel silicide formation on Si(1 1 0) substrate

Nickel silicide formation on Si(1 1 0) and Si(1 0 0) substrate was investigated in this paper. It is confirmed that nickel monosilicide (NiSi) starts to form after 450 °C annealing for Si(1 0 0) substrate, but a higher annealing temperature is required for NiSi formation on Si(1 1 0) substrate, which is demonstrated by X-ray diffraction (XRD) and Raman scattering spectroscopy. The higher formation temperature of NiSi is attributed to the larger Ni 2Si grain size formed on Si(1 1 0) substrate. Ni silicided Schottky contacts on both Si(1 0 0) and Si(1 1 0) substrates were also fabricated for electrical characteristics evaluation. It clearly reveals that the rectifying characteristics of NiSi/n-Si(1 1 0) Schottky contacts is inferior to that of NiSi/n-Si(1 0 0) Schottky contacts, which is attributed to a lower Schottky barrier height and a rougher contact interface. The formation kinetics for nickel silicide on Si(1 1 0) substrate is also discussed in this paper.

Influence of different SiC surface treatments performed prior to Ni ohmic contacts formation

This work is dealing with the influence of surface treatment on ohmic contacts to hexagonal N-type SiC with medium doping level. The contact materials were Ni and Ni 2Si. The structures had to be annealed at high temperatures in order to reach ohmic behavior. A number of surface treatment methods were tested: wet cleaning, plasma etching, intentional oxidation with etching, H 2 annealing and their combinations. After some types of cleaning, the SiC surface was immediately analysed using the XPS method. The results of the analyses showed that the composition of the surface was not much influenced by these treatments. At lower annealing temperatures (approx. up to 850 °C) the prepared contacts showed Schottky behavior with large scatter of parameters. After annealing at approx. 960 °C, where the onset of ohmic behavior is expected, the structures were truly ohmic and of good parameters. Cleaning methods had just a negligible influence on the electrical parameters of the ohmic contacts. An explanation for these observed facts is suggested: Although – already on the basis of the XPS results – we could speak about a negligible influence of the cleaning onto the contact parameters, there might come across also other mechanisms coming from interaction of contact materials with SiC, which caused similar behavior of ohmic contacts on differently treated surfaces.

Nano granular magnetic phase by interfacial intermixing in [formula omitted]/Si bilayer structure

The bilayer structures of Fe 50Ni 50 films on silicon substrate have been studied before and after the swift (∼100 MeV) Fe 7+ ion irradiation. The AFM (atomic force microscopy) study of the structures shows the formation of clear ellipsoidal grains of nano dimensions. XRD (X-ray diffraction) data of the structures show the formation of magnetic silicide phases of Fe 5Si 3, Ni 3Si 2 and Ni 2Si. Electronic flow across the interface has been found to significantly increase by two orders of magnitude on the irradiation. Moreover the electronic flow shows a low magnetic field (of ∼500 G) sensitivity for the irradiated structures and not for the unirradiated ones. The M – H (magnetization versus magnetic field) characteristics show the typical behaviour of nano magnetic grains which are antiferromagnetically coupled in a paramagnetic phase. The observed results have been understood in the realm of interfacial intermixing (which has been further tailored by the irradiation) to result the nano granular phases of magnetic silicides (of ∼50 nm). The intermixing seems to make the interface intimate enough to result in a significant increase of current across interface of the bilayer and its sensitivity for an in plane low magnetic field.

The graphitization of carbon nanofibers produced by catalytic decomposition of methane: Synergetic effect of the inherent Ni and Si

The catalytic effect of the inherent Ni and Si on the graphitization of carbon nanofibers produced by catalytic decomposition of methane is reported. The participation of the inherent Ni and Si metals as co-catalysts in the graphitization of the carbon nanofibers through the formation of Ni 2Si and SiC was inferred. Taking advantage of this catalytic effect, graphite materials showing structural characteristics comparable to oil-derived graphites which are employed in several industrial applications have been prepared from the carbon nanofibers. Unlike SiC which is further descomposed to graphite, the role of Ni 2Si remains unclear. At the CNFs heat treatment temperatures employed, Ni 2Si is in a liquid state where the carbon can be dissolved to form a supersaturated solution from which the SiC can be produced by segregation, thus being an intermediate stage in the catalytic graphitization of the carbon nanofibers. Further work are currently in progress to go insight this issue.

Oxygen distribution in nickel silicide films analyzed by time-of-flight secondary ion mass spectrometry

The oxygen distribution in Ni 2Si and NiSi films formed during a two-step silicidation process was analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS mass spectra revealed that both silicon and nickel reacted with oxygen at the Ni 2Si surface. In addition, silicon nitride was formed at the surface by the reaction of silicon with nitrogen in the TiN capping layer during the first silicidation annealing. The amount of nitrogen at the NiSi surface varied with silicidation annealing temperature and with the formation conditions of the TiN capping layer. We also showed that a small amount of oxygen was penetrated into the NiSi film and strongly affected the level of junction leakage current in n +–p junctions in n-channel MOSFETs. The oxygen concentration in the NiSi film decreased with an increase in the amount of nitrogen at the NiSi surface.

Three-dimensional composition mapping of NiSi phase distribution and Pt diffusion via grain boundaries in Ni 2Si

The formation of Ni silicide alloyed with Pt has been analyzed by atom probe tomography. A 300 °C/1 h anneal results in simultaneous growth of the NiSi and Ni2Si phases: the Ni2Si phase is a continuous layer with columnar grains, while the NiSi phase forms a discontinuous layer. Direct evidence of Pt diffusion short-circuits via Ni2Si grain boundaries is shown. The presence of Pt in the grains and interphase boundaries may explain the change in the Ni silicide formation for the Ni(5% Pt)/Si system.

Spike Annealing as Second Rapid Thermal Annealing to Prevent Pure Nickel Silicide From Decomposing on a Gate

To create a nickel-monosilicide (NiSi) film with superior electrical properties, two-step rapid thermal annealing (RTA) was optimized. Using <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> chemical dry cleaning and increasing initial RTA temperature makes it possible to macroscopically transform nickel into NiSi without causing oxygen contamination. Nevertheless, di-nickel silicide (Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si) remaining on the top surface of NiSi on p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -doped gate degrades the electrical properties of the NiSi film. This top-surface Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si is formed by decomposition of NiSi by conventional second RTA and appears as a disconnection of the NiSi film on the logic test device or agglomeration of silicon and nickel on the blanket NiSi film with activation energy of 2.92 eV. Using ldquospike RTArdquo with higher temperature suppresses the decomposition of NiSi and activates transformation of Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si to NiSi. It is concluded that the proposed two-step RTA significantly improves the uniformity of the electrical properties of NiSi in 65-nm-node logic devices.

Microstructure analysis of boronized pure nickel using boronizing powders with SiC as diluent

In this study, boronizing of 99.9% pure nickel was performed by means of a powder-pack method using Commercial LSB-II powders (that contained SiC) at 850, 900 and 950 °C for 2, 4, 6 and 8 h, respectively. The coated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and hardness tests. The presence of boride (Ni 2B) and silicide (Ni 5Si 2, Ni 2Si) phases, formed on the surface of boronized pure nickel, were confirmed by X-ray diffraction analysis. The Ni 3Si phase was found when pure nickel was boronized at 850 °C for 2 h. Depending on boronizing time and temperature, the thickness of coating layer ranged from 36 to 237 μm. The hardness values were 832 HV 0.01 for the silicide layer, 984 HV 0.01 for boride layer, and 139 HV 0.01 for the Ni substrate.

Irradiation induced effects on Ni 3N/Si bilayer system

The irradiation effect in Ni 3N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10 14 ions/cm 2 was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni 2Si and Si 3N 4 phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni 3N thin films. It was observed that after irradiation (Ni 2p 3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10 −4 torr, were examined using Au ions. In-situ I– V measurements on Ni 3N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.

Measurement of As diffusivity in Ni 2Si thin films

The lattice and grain boundary diffusion coefficients of As in 260 nm-thick Ni 2Si films were measured. The Ni 2Si layers were prepared via the reaction between a Si layer deposited by low pressure chemical vapor deposition and a Ni layer deposited by magnetron sputtering on a Si substrate covered with a SiO 2 film. As was implanted in the silicide. Its concentration profiles were measured using secondary ion mass spectroscopy before and after annealing (550–700 °C). 2D finite element diffusion simulations taking into account lattice diffusion and grain boundary (GB) diffusion were performed based on the microstructure of the samples. They were found to fit accurately the measured profiles and allowed to measure the diffusion coefficients for each temperature. Lattice diffusion is characterized by a pre-exponential factor D 0 v ∼ 1.5 × 10 −1 cm 2 s −1 and an activation energy Qv ∼ 2.72 eV. In the case of GB diffusion P 0 = sδD 0 gb = 9.0 × 10 −3 cm 3 s −1 and the activation energy was found to be higher than for lattice diffusion with Qgb ∼ 3.07 eV. Existing data concerning diffusion in silicides and other materials is used to discuss these results. The diffusion of As in Ni 2Si could be reduced due to impurity segregation in GBs.

Kinetic study of interfacial solid state reactions in the Ni/4H–SiC contact

Investigation of the relatively low temperature reaction between Ni nanolayer film and 4H–SiC substrate provides valuable insights into studies of the fundamental properties of SiC Schottky diodes. A quantitative description of chemical kinetics of Ni/SiC contact formation has been studied via deposition of about 50 nm Ni film on 4H–SiC (Si terminated surface) by magnetron sputtering and subsequent annealings at temperatures of 500–700 °C. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) techniques were used to investigate the interface reaction products upon annealing and element distribution across the reaction layer. It is found that the thermodynamically stable silicide Ni 2Si begins to form at the contact interface as a result of sample annealing above 600 °C, which associated with producing carbon distributed at the surface and at the interface of the silicide with the SiC substrate. The kinetic process is described to mainly include the solid state interface reactions and the diffusion of components through the produced layer of silicides. When the diffusion layer is thick enough (more than 100 nm), the kinetic feature is thought to be diffusion controlled, which follows the parabolic law. The active energy of Ni silicide formation was derived as (135.0 ± 19.51) kJ mol −1.

Atomic-scale redistribution of Pt during reactive diffusion in Ni (5% Pt)–Si contacts

The NiSi silicide that forms by reactive diffusion between Ni and Si active regions of nanotransistors is used nowadays as contacts in nanoelectronics because of its low resistivity. Pt is added to the Ni film in order to stabilise the NiSi phase against the formation of the high-resistivity NiSi 2 phase and agglomeration. In situ X-ray diffraction (XRD) experiments performed on material aged at 350 °C (under vacuum) showed the complete consumption of the Ni (5 at% Pt) phase, the regression of Ni 2Si phase as well as the growth of the NiSi phase after 48 min. Pt distribution for this heat treatment has been analysed by laser-assisted tomographic atom probe (LATAP). An enrichment of platinum in the middle of the NiSi phase suggests that Pt is almost immobile during the growth of NiSi at the two interfaces: Ni 2Si/NiSi and NiSi/Si. In the peak, platinum was found to substitute for Ni in the NiSi phase. Very small amounts of Pt were also found in the Ni 2Si phase close to the surface and at the NiSi/Si interface.