Cobalt Silicide Research Articles

Optimizing Cobalt Silicide Interfaces With Carbon PAI: Enhanced Thermal Stability and Reduced Specific Contact Resistivity for DRAM Applications

Optimizing Cobalt Silicide Interfaces With Carbon PAI: Enhanced Thermal Stability and Reduced Specific Contact Resistivity for DRAM Applications

Simultaneous optimization of power factor and thermal conductivity via charge transfer effect and enhanced scattering of phonons in Si80Ge20P1/CoSi2 composites

SiGe based alloy is a promising medium-high temperature thermoelectric material that has been applied in the field of aerospace exploration. So far, utilizing the second phase to promote the scattering of phonons is a common way to improve the thermoelectric performance of SiGe based alloy, but this often deteriorates the electrical properties. In this study, the Si80Ge20P1/CoSi2 composites have been prepared by mechanical alloying and spark plasma sintering, and the content of cobalt silicide (CoSi2) nanoparticles have been manipulated. Since the CoSi2 nanoparticles possess higher carrier concentration and smaller work function than the Si80Ge20P1 matrix, the carrier concentrations of composites have been pushed up due the charge transfer effect. Meanwhile, the formation of nano-sized phase interfaces and stacking faults in the composites has enhanced the scattering of low-frequency phonons. As a result, the optimal power factor of 3.41 mW⋅m−1⋅K−2 and thermal conductivity of 2.29 W⋅m−1⋅K−1 have been achieved, and the corresponding zT reaches up to 1.3 in the Si80Ge20P1+0.5% CoSi2 (in mole) composite at 873 K. This work provides a new idea for developing the performance of SiGe based alloy.

Structural, chemical, and magnetic investigation of a graphene/cobalt/platinum multilayer system on silicon carbide

We investigate the magnetic interlayer coupling and domain structure of ultra-thin ferromagnetic (FM) cobalt (Co) layers embedded between a graphene (G) layer and a platinum (Pt) layer on a silicon carbide (SiC) substrate (G/Co/Pt on SiC). Experimentally, a combination of x-ray photoemission electron microscopy with x-ray magnetic circular dichroism has been carried out at the Co L-edge. Furthermore, structural and chemical properties of the system have been investigated using low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS). In situ LEED patterns revealed the crystalline structure of each layer within the system. Moreover, XPS confirmed the presence of quasi-freestanding graphene, the absence of cobalt silicide, and the appearance of two silicon carbide surface components due to Pt intercalation. Thus, the Pt-layer effectively functions as a diffusion barrier. The magnetic structure of the system was unaffected by the substrate’s step structure. Furthermore, numerous vortices and anti-vortices were found in all samples, distributed all over the surfaces, indicating Dzyaloshinskii–Moriya interaction. Only regions with a locally increased Co-layer thickness showed no vortices. Moreover, unlike in similar systems, the magnetization was predominantly in-plane, so no perpendicular magnetic anisotropy was found.

Heterostructured Cobalt Silicide Nanocrystals: Synthesis in Molten Salts, Ferromagnetism, and Electrocatalysis.

Nanoscale heterostructures of covalent intermetallics should give birth to a wide range of interface-driven physical and chemical properties. Such a level of design however remains unattainable for most of these compounds, due to the difficulty to reach a crystalline order of covalent bonds at the moderate temperatures required for colloidal chemistry. Herein, we design heterostructured cobalt silicide nanoparticles to trigger magnetic and catalytic properties in silicon-based materials. Our strategy consists in controlling the diffusion of cobalt atoms into silicon nanoparticles, by reacting these particles in molten salts. By adjusting the temperature, we tune the conversion of the initial silicon particles toward homogeneous CoSi nanoparticles and core-shell nanoparticles made of a CoSi shell and a silicon-rich core. The increased interface-to-volume ratio of the CoSi component in the core-shell particles yields distinct properties compared to the bulk and homogeneous nanoparticles. First, the core-shell particles exhibit increased ferromagnetism, despite the bulk diamagnetic properties of cobalt monosilicide. Second, the core-shell nanoparticles act as efficient precatalysts for alkaline water oxidation, where the nanostructure is converted in situ into a layered cobalt silicon oxide/(oxy)hydroxide with high and stable oxygen evolution reaction (OER) electrocatalytic activity. This work demonstrates a route to design heterostructured nanocrystals of covalent intermetallic compounds and shows that these new structures exhibit very rich, yet poorly explored, interface-based physical properties and reactivity.

Influence of Si surface preparation on CoSi2 formation and agglomeration

In microelectronics, despite a difficult nucleation of cobalt silicide CoSi2 in small dimensions, the CoSi2 based contacts remain interesting for some specific devices designed in 65 nm technology. Therefore, to promote the formation of CoSi2 in 65 nm technologies, it is possible to interfere on the formation of CoSi, that occurs during RTA1. To this end, the surface preparation of the Si substrate, before the Co deposition, may have an influence on the cobalt silicide phases formation. In this work, different surface preparations (SiCoNi, HF followed by SC1 and HF only), as well as several Soft Sputter Etch, SSE, processes have been applied on Si(100) wafers before the deposition of Co and TiN layers. Depending on the surface preparation, the formation temperatures and/or crystalline orientations for the Co silicide phases, including CoSi2, are different, as observed by XRD and/or EBSD. Four-point probes measurements also show a strong dependency of the CoSi2 agglomeration to the surface preparation scheme. These results highlight the influence of surface preparation on the Co silicides formation and agglomeration and its importance for the integration of CoSi2 films in a 65 nm CMOS technology.

Semimetallic Orbital Hybridization by Particular Surface Engineering in Ternary Cobalt Silicide to Accelerate Oxygen Evolution Reaction

The oxygen evolution reaction (OER) plays an important role in efficient energy conversion, but needs excellent catalysts to overcome the sluggish reaction kinetics. The classic reaction kinetics implies that catalytic activity strongly depends on the electronic‐state occupation at surface active sites. Herein, a semimetallic orbital‐hybridization strategy is suggested to optimize the reaction activity of metal site at ternary cobalt silicide surface by particular interlayer electronic‐state coupling, which is completely different from the atomic configuration with double‐layered metal surface. The detailed analysis about electronic structure demonstrates that the semimetallic orbital hybridization is responsible for reducing OER activation barrier, due to a proper bonding strength. Instead, the stronger metallization cannot benefit a fast intermediate dissociation, which requires a higher activation barrier at OER. Herein, a new insight into accelerating OER by a particular surface engineering is provided.

Investigation of thermally stimulated conductivity of cobalt silicide

Mono- and disilicide of cobalt were obtained in the near-surface region of diffusion-doped silicon by cobalt atoms. The thermally stimulated conductivity (TSC) of cobalt disilicide was investigated. The energy of the adhesion levels of 0.32 eV was determined for the structures of cobalt disilicide – doped silicon - cobalt disilicide. The influence of the illumination intensity on the TSC curves is investigated and it is shown that the illumination intensity does not affect the shape of the curve and weakly affects the magnitude of the maximum of the current peak.

Mesostructure and Magnetic Properties of SiO2-Co Granular Film on Silicon Substrate

Granular films SiO2(Co) exhibit unusual magnetic and magnetotransport properties which are strongly dependent on the composition of the film and material of a substrate. For example, the injection magnetoresistance (IMR) coefficient reaches a giant (GIMR) value of 105% at room temperature in SiO2(Co) films on an n-GaAs substrate. However, the IMR effect is negligible in the case of a similar granular film deposited on the n-Si substrate. In this report, the structural and magnetic properties of granular film SiO2(Co) on Si substrate are studied with the aim to understand the cause of the difference in IMR coefficients for SiO2(Co) thin film deposited on n-GaAs and on n-Si substrates. Investigations were carried out using complementary methods of Polarized Neutron Reflectometry, Grazing Incidence Small-Angle X-ray Scattering, X-ray Reflectometry, Scanning Electron Microscope, and SQUID magnetometry. It is shown that the interface layer between the granular film and Si substrate exhibits metallic rather than magnetic properties and eliminates the GIMR effect. This interface layer is associated with the Si diffusion to Co nanoparticles and the formation of the metallic cobalt silicides.

A novel nanoprobing analysis flow by using multi-probe configuration to localize silicide defect in MOSFET

It is demonstrated that nanoprobing technique is superior in localizing silicide defect rapidly in metal-oxide-semiconductor field-effect transistor (MOSFET). Cobalt silicide (CoSi2) as an interfacial material below tungsten contact plug, various types of defects about CoSi2 often cause leakage current in MOSFET, so close studies of problematic silicide is significant regarding MOSFET reliability enhancement. When one MOSFET in a combinational logic circuit is suspected of anomaly, because this kind of circuit is composed of several devices which are sometimes arranged in an active area (AA) of unique geometric shape, it is impossible to collect MOSFET characteristic correctly based on regular nanoprobing flow since conventional method hits limit for combined circuits measurement. Such circumstance almost impedes failure analysis (FA) in device level. Nevertheless, relying on our alternative strategy of multi-probe configuration, a novel nanoprobing analysis flow is adopted for device examination. It is shown that exact I-V characteristic of failed device can be captured by proposed workflow. Following I-V curve analysis further reveals an evident electrical signature of abnormal abrupt junction. It corresponds to an active area shorting with its surrounding nwell region. In addition, sophisticated leakage current behaviors are exhaustively interpreted by simplified models. Eventually, we confirmed CoSi2 encroachment from the active area into nwell by the means of transmission electron microscopy (TEM) analysis. This paper presents an effective analysis to identify leaky junction of MOSFET in logic circuit that is rarely reported before. Furthermore, our exploration exhibits impressive flexibility of nanoprobing analysis in terms of localizing unusual silicide defect, so nanoprobe analysis is clearly an attractive option to optimize MOSFET manufacturing.

Spintronic Terahertz Emitters in Silicon-Based Heterostructures

Integration of active elements into silicon wafers is the first step towards their usage in modern electronic devices based on nanometric structures. Spintronic terahertz emitters, typically composed of nanometer-thin magnetic multilayer, have the outstanding capability of producing high-quality, broadband terahertz pulses using extremely simple heterostructures. A question remains on whether an efficient and cheap integration with other silicon-based technologies can be achieved. We show here that simply having a ferromagnetic layer on silicon produces remarkably efficient spintronic terahertz emission despite the low spin-orbit coupling of the individual components. We achieve this by leveraging on the natural formation of silicides at the interface of a transition metal and silicon. The cobalt silicide layer has good spin-to-charge conversion efficiency that reaches around 1/6 as that of the prototypical spintronics THz-emitter heterostructure cobalt/platinum.

Focused Ion Beam vs Focused Electron Beam Deposition of Cobalt Silicide Nanostructures Using Single-Source Precursors: Implications for Nanoelectronic Gates, Interconnects, and Spintronics

Focused Ion Beam vs Focused Electron Beam Deposition of Cobalt Silicide Nanostructures Using Single-Source Precursors: Implications for Nanoelectronic Gates, Interconnects, and Spintronics

Study of Multi-layered Cobalt Silicide Nanostructured Thin Films Prepared by Ion Beam Sputtering

Aims: This work focuses on the different existing techniques for synthesis of nanomaterials, the selection of potential process for preparation of Co/Si and Co/Si/Co such that material with optimum characteristics may be obtained. Background: The process of synthesis plays a crucial role in physical properties and associated phenomena acquired by them, and hence is a deciding factor in various potential applications of the materials. Objective: The aim of the study was to investigate the properties of multi-layered cobalt silicide nanostructured thin films prepared by ion beam sputtering. Method: The cobalt silicide is selected for synthesis using IBS technique owing to vast scope of its application in manufacturing microelectronic devices. Result: The formation of nanostructured layers has been confirmed through XRD and XRR patterns. Conclusion: The role of substrate thickness, interface quality and crystalline structure is very important in deciding properties of multilayer nano-structured thin films.

Growth kinetics of anodic oxide layers on cobalt silicides in sulphuric acid solutions

Growth kinetics of anodic oxide layers on cobalt silicides in sulphuric acid solutions

Влияние интеркаляции золота на электронную структуру графена на Co-Si/SiC(0001)

Investigation of graphene on an ultrathin CoSi/CoSi2 cobalt silicide layer on a SiC(0001) substrate after the Au intercalation has been carried out. It was shown that deposition of Au and subsequent annealing of the system at a temperature of 500°C leads to the intercalation of Au atoms and the formation of gold silicide under graphene with a stoichiometry close to that of Au2Si. The study of the electronic structure of the system in the region of the K point of the surface Brillouin zone revealed the quasi-freestanding character of graphene with a linear spectrum of π states and a Dirac point near the Fermi level. The measurements using photoelectron microscopy showed the homogeneity of the work function along the surface of the sample on a micrometer scale.

Кинетика роста анодных оксидных пленок на силицидах кобальта в растворах серной и фтороводородной кислот

The growth kinetics of anodic oxide layers was studied on cobalt silicides Co2SiandCoSi2in 0,5 mol/l H2SO4 solution with addition of 0,005 or 0,01 mol/l HF using chronoamperometric measurements at different oxide formation potentials. The kinetics of oxide growth can be described on the basis of the high field model. The current responses to potential steps for Co2Si electrode appear as damped oscillations. The oscillating processes were explained from the standpoint of the theory of linear electric circuits and from the consideration of chemical interaction of the oxide film with the solution.

In situ synthesis of cobalt silicide particle reinforcing and coloring Si3N4 ceramics

AbstractIn this paper, silicon nitride (Si3N4) ceramics with black color and high toughness were fabricated by gas pressure sintering and characterized by X‐ray diffraction, Raman, scanning electron microscopy, EDS, and transmission electron microscopy. The in situ formed cobalt silicide was confirmed to contribute to the black color through the introduction of CoO. Due to the addition of CoO, the growth of β‐Si3N4 grains is promoted, forming elongated grains, and eventually forms the self‐reinforcing microstructure. However, with adding excessive CoO, interfacial debonding is found between cobalt silicide and Si3N4 matrix and a decrease in strength was resulted. The optimum composition is 1 mol% CoO in Si3N4, with the fracture toughness of 9.9 ± 0.3 MPa m1/2, flexural strength of 826.1 ± 46.0 MPa, and a much darker black color. The mechanism of color formation is discussed where the black color derives mainly from the metallic silicon and additionally the porosity.

Direct Writing of Cobalt Silicide Nanostructures Using Single-Source Precursors.

Two new precursors for focused electron beam-induced deposition (FEBID) of cobalt silicides have been synthesized and evaluated. The H3SiCo(CO)4 and H2Si(Co(CO)4)2 single-source precursors retain the initial metal ratios and show low sensitivity to changes in the FEBID parameters such as acceleration voltage, beam current, and precursor pressure. The precursors allow the direct writing of material containing ∼55 to 60 at % total metal/metalloid content combined with high growth rates. During the deposition process an average of ∼80% of the carbonyl ligands are cleaved off in these planar deposits. Postgrowth electron curing does not change the deposits' composition, but resistivities decrease after the curing procedure. Temperature-dependent electrical properties indicate the presence of a granular metal for both cured samples and the as-grown Co2Si deposit, while the as-grown CoSi material is on the insulating side of the metal-insulator transition. The observed magnetoresistance behavior is indicative of tunneling magnetoresistance and is substantially reduced upon postgrowth irradiation treatment.

Электронная структура графена на карбиде кремния, интеркалированного атомами кремния и кобальта

The results of ab initio calculations of the spin-polarized band structure of graphene on silicon carbide intercalated with cobalt and silicon atoms are presented. It is shown that metal and silicon atoms during intercalation are localized between the substrate and the buffer layer of carbon atoms. Initially, the cobalt layer is strongly coupled with the buffer layer. The subsequent intercalation of silicon and the formation of cobalt silicide leads to a transition from hybridized state to the formation of quasi-freestanding bilayer graphene on the surface of the system due to the transformation of the buffer layer to the second graphene layer.

Effect of a Ti diffusion barrier on the cobalt silicide formation: solid solution, segregation and reactive diffusion

Diffusion barriers play an important role in numerous phase formation processes. A well known example in microelectronics is the reactive diffusion growth of silicide thin films which are applied as contact materials. In this work, the effect of a Ti interlayer on the kinetics of the formation of CoSi by reactive diffusion is investigated. Therefore, Co(100nm)/Ti(5nm) deposited on Si(111) is annealed at various temperatures. Transmission electron microscopy and atom probe tomography allow to study the evolution of microstructure and local compositions after each annealing. It is observed that the CoSi growth starts at the Ti/Si interface and it is controlled by Co diffusion through the Ti interlayer. The Ti interlayer keeps its microstructure during the growth of CoSi. At higher annealing temperatures, Si diffusion through the Ti interlayer to the Co layer is evidenced. First, it segregates at grain boundaries of the polycrystalline Co layer on top of the Ti interlayer before it reacts to cobalt silicides. Also Ti diffusion to the CoSi/Si interface occurs that may affect diffusion processes and phase formation reaction at this interface. Beyond the experimental observations, a model is developed to quantify the diffusivity of Co in the Ti interlayer on the base of the investigated CoSi growth. Furthermore, a model is developed in order to estimate the diffusivity of Si in the Ti interlayer on the base of the formed solid solution and segregation in the Co layer. Both models can be generally applied for similar material configurations to estimate diffusivities in interlayers or to predict phase growth.

A study of nickel and cobalt silicides formed in the Ni/Co/Si(1 0 0) system by thermal annealing

Abstract In this work, the Ni/Co/Si system was annealed at temperatures ranging from 300 °C to 800 °C. The samples were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and sheet resistance measurement. The XRD and Raman spectroscopy results showed that the formation of nickel and cobalt silicides (CoSi, Co2Si, Ni2Si, NiSi, NiSi2, CoSi2) is an annealing temperature dependent diffusion process. The diffusion phenomenon was evidenced by RBS. The low values of the sheet resistance which were correlated with the films surface roughness were attributed to the formation of both CoSi and NiSi phases.