Cobalt Silicide Films Research Articles

FMR Investigation of the Magnetic Anisotropy in Films Synthesized by Co+ Implantation into Si

Thin ferromagnetic films with the uniaxial magnetic anisotropy were synthesized by Co+ implantation into single-crystal silicon in the magnetic field. It was concluded that the formation of the induced magnetic anisotropy is due to the directional atomic pair ordering (Neel–Taniguchi model). The synthesized films were studied by the ferromagnetic resonance (FMR) method in the temperature range from 100 to 300 K. The FMR linewidth is almost independent of temperature, which is in agreement with the Raikher model describing the magnetic resonance of uniaxial magnetic particles. It is found that the temperature dependence of the anisotropy constant is linear. This dependence can be associated with the difference in the coefficients of thermal expansion of the Si (111) substrate and the ion-beam-synthesized cobalt silicide films.

Ion-Beam Synthesis of Ferromagnetic Films by the Implantation of Co+ Ions into Silicon

Thin ferromagnetic films of cobalt silicide are synthesized by implanting Co+ ions into single-crystal silicon plates under an external magnetic field. Scanning magnetopolarimetry shows that the samples implanted at a dose greater than 2 × 1017 cm–2 have uniaxial magnetic anisotropy. Based on the dose dependence of the anisotropy field and the experiment on switching the direction of the easy magnetization axes, it is concluded that the induced magnetic anisotropy in the resulting films is due to the directional atomic pair ordering. The absence of the effect of external mechanical stress created during implantation on the magnetic properties of cobalt-silicide films is revealed.

Scanning tunneling microscopy study of the early stages of epitaxial growth of CoSi2 and CoSi films on Si(111) substrate: Surface and interface analysis

We report scanning tunneling microscopy observations of solid-phase epitaxial growth of ultra-thin CoSi2 and CoSi films at heating temperatures in the range of 350–600°C using a disordered ‘(1×1)’ phase of Co/Si(111) as a pre-existing template. It is found that depending on the growth conditions two types of epitaxial cobalt silicide films can be formed. At coverages below ~2 ML (1 ML=7.83×1014atoms/cm2) of Co, CoSi2 phase grows in the form of flat two-layer patches spreading over the surface at elevation of the temperature. It consists of precisely two the completely filled Co layers and four Si layers above the interface. At coverages higher than ~2 ML of Co, the layer-by-layer growth of CoSi phase with the CsCl-type crystal structure also takes place. The CoSi phase consists of one or more Co-Si double layers, which are located on top of the second Si-Co-Si triple layer of CoSi2, i.e., it has а coherent double interface CoSi/CoSi2/Si(111). According to experimental findings and ab initio total-energy calculations, the structures with the eightfold coordination of interfacial Co atoms and lateral unit cells of the silicide layer and substrate mutually rotated by 180° prove to be the most stable ones.

On the Origin of the Gate Oxide Failure Evaluated by Raman Spectroscopy

The metal-oxide-semiconductor-field-effect-transistor (MOSFET) has been miniaturized for the high performance large-scale integrated-circuit (LSI). However, in the ultimately miniaturized MOSFET, the gate oxide failure with high leakage current is inevitable. In this study, we evaluated the origin of the gate oxide failure by Raman spectroscopy in conjunction with optical beam induced resistance change (OBIRCH) analysis. MOS capacitors were used as the samples. The 2.8 nm thick gate oxinitrid insulator film and the poly-Si gate electrode layer were formed on a P type Si substrate. The cobalt (Co) silicide film was formed on the poly-Si electrode. The SiH4 flow rate was 150 sccm or 350 sccm. The gate oxide integrity was evaluated by the test element group (TEG) measurements. As a result, Raman intensity increased at the failure position compared with the other positions in the sample deposited with 150 sccm of SiH4 flow rate. We consider that higher Raman intensity at the gate oxide failure positions reflects the irregular structure of poly-Si. Furthermore, the Raman peaks at failure positions shifted toward the lower wavenumber while the FWHMs are approximately constant with other positions. Thus, we found that there is no difference in the crystallinity of the poly-Si. The origin of the gate oxide failure was high tensile strain in the gate poly-Si electrode. In conclusion, we have successfully evaluated the gate oxide failure by Raman spectroscopy with a quasi-line excitation source.

Absorption modulation of terahertz metamaterial by varying the conductivity of ground plane

Most research focuses on varying the resonator and dielectric spacer to configure the absorption and resonant frequency of terahertz (THz) metamaterial absorbers (MAs), where a metal ground plane is used as a perfect reflector of incident THz waves. In this paper, we modulate the MAs absorption by varying the conductivity of the ground plane. Two THz MAs were fabricated by replacing the gold ground planes with cobalt silicide films, and the measured absorptivity decreases by 4% for the electric resonance and increases by 44% for the dipole resonance. Our quantitative analysis reveals that when the conductivity of the ground plane decreases from 1.8 × 107 S/m to 3.0 × 105 S/m, the absorptivity of the electric resonance decreases by 23%, while that of the dipole resonance increases by 62%. Our approach also provides a practical method to measure the electric conductivity of conductive films in the THz regime.

In-situ study of growth of carbon nanotube forests on conductive CoSi2 support

The growth of high density vertically aligned carbon nanotube forests on conductive CoSi2 substrate layers is characterized by in situ x-ray photoemission spectroscopy and x-ray diffraction. We use in situ silicidation to transform as loaded, low conductivity CoSi supports to highly conductive CoSi2 during nanotube growth. These cobalt silicide films are found to be stable against oxidation and carbide formation during growth and act as an excellent metallic support for growth of aligned nanotubes, resembling the growth on the insulating Fe/Al2O3 benchmark system. The good catalytic activity is attributed to interfacial reactions of the Fe catalyst particles with the underlying CoSi2 support. We obtain ohmic conduction from the support layer to the carbon nanotube forest.

Improvements in Thermal Stability of Cobalt-Silicide Films by Adding Nickel

We studied the diffusion of cobalt atoms into silicon substrates by using an X-ray diffraction experiment and molecular dynamics (MD) simulations to prevent open-circuit failures induced by the agglomeration of cobalt-silicide (CoSi2) film in semiconductor devices. The experimental results revealed that the agglomeration of cobalt-silicide films was caused by the diffusion of Co-atoms from CoSi2 films with a (111) texture into Si (001) substrates. The activation energy of Co-atom diffusion measured with sheet resistance (3.6eV) agreed well with that obtained from the MD simulations (3.7eV). We developed a CoSi2 film by adding nickel (Ni), because the MD simulation results indicated that the addition of Ni effectively reduced diffusion of Co-atoms. Its effectiveness was confirmed by measuring the sheet resistance. The agglomeration rate of CoSi2 film with Ni added was one digit smaller than that of CoSi2 film without it.

Effect of annealing on magnetic properties and silicide formation at Co/Si interface

The interaction of Co (30 nm) thin films on Si (100) substrate in UHV using solid state mixing technique has been studied. Cobalt was deposited on silicon substrate using electron beam evaporation at a vacuum of 4×10−8 Torr having a deposition rate of about 0·1 Å/s. Reactivity at Co/Si interface is important for the understanding of silicide formation in thin film system. In the present paper, cobalt silicide films were characterized by atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS) in terms of the surface and interface morphologies and depth profile, respectively. The roughness of the samples was found to increase up to temperature, 300°C and then decreased with further rise in temperature, which was due to the formation of crystalline CoSi2 phase. The effect of mixing on magnetic properties such as coercivity, remanence etc at interface has been studied using magneto optic Kerr effect (MOKE) techniques at different temperatures. The value of coercivity of pristine sample and 300°C annealed sample was found to be 66 Oe and 40 Oe, respectively, while at high temperature i.e. 748°C, the hysteresis disappears which indicates the formation of CoSi2 compound.

Synthesis and characterization of cobalt silicide films on silicon

Cobalt silicide has emerged as a leading contact material in silicon technology due to its low resistivity, high stability and small lattice mismatch. In this study, 0.2–0.4μm thick Co films were deposited on Si(100) wafers by RF magnetron sputtering at room temperature, and annealed at temperatures from 600 to 900°C in vacuum. As-deposited and annealed samples were characterized by Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Although the Si substrates were sputter cleaned before the deposition, all the samples showed a thin oxide layer at the Si/Co interfaces. Annealing up to 700°C did not alter the composition at the interface except small amount Co diffusion into Si. Annealing at 800°C promotes the evaporation of the oxides from the interface and, as a result, clean CoSi2 films were formed. Although the interface appeared to be sharp within the RBS resolution after high temperature annealing, the surface topography was relatively rough with varying size of crystal grains.

Formation of cobalt silicide films by ion beam deposition

Thin films of cobalt silicide are widely used as metallization in very large-scale integrated electronic circuits. In this study, Co ions were deposited on Si(111) wafers by a high beam current filter metal vacuum arc deposition (FMEVAD) system. Surface silicide films were formed after annealing from 500 to 700°C for 30min. The results show that a thin CoSi2 surface layer with both a smooth surface topography and sharp interface can be achieved by annealing at 700°C. The CoSi phase and O contamination were observed in the samples that were annealed at lower temperatures.

Characterization of Heating Elements with Cobalt Silicide Films for Inkjet Printer

Characterization of Heating Elements with Cobalt Silicide Films for Inkjet Printer

Preparation and properties of sputtered nitrogen-doped cobalt silicide film

It is the purpose of this study to develop tough hinge material for the application of the torsional springs. Nitrogen-doped cobalt silicide (CoSi x N y ) film is sputtered from cobalt silicide (CoSi 2) target in Ar/N 2 discharge. Stress and sheet resistance of CoSi x N y film are two major properties to be evaluated. Taguchi method is practiced in reactive sputtering deposition of CoSi x N y film. Process pressure is most critical to the CoSi x N y film stress and the optimum condition of 1000 W, 0.8 Pa, and 20% N 2 flow ratio, indeed results in low tensile CoSi x N y film stress, about 54. MPa. Reannealing process indicates that stability of CoSi x N y film is attained after first annealing process. Stress hysteresis behaviors of CoSi x and CoSi x N y films resemble that of metal film with a complete elastic manner in the second stage of heating and cooling. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses suggest that toughness and strength of the film is achievable. It is concluded that CoSi x N y film as a hinge material is feasible.

Preparation and properties of sputtered nitrogen-doped cobalt silicide film

It is the purpose of this study to develop tough hinge material for the application of the torsional springs. Nitrogen-doped cobalt silicide (CoSi x N y ) film is sputtered from cobalt silicide (CoSi 2 ) target in Ar/N 2 discharge. Stress and sheet resistance of CoSi x N y film are two major properties to be evaluated. Taguchi method is practiced in reactive sputtering deposition of CoSi x N y film. Process pressure is most critical to the CoSi x N y film stress and the optimum condition of 1000 W, 0.8 Pa, and 20% N 2 flow ratio, indeed results in low tensile CoSi x N y film stress, about 54. MPa. Reannealing process indicates that stability of CoSi x N y film is attained after first annealing process. Stress hysteresis behaviors of CoSi x and CoSi x N y films resemble that of metal film with a complete elastic manner in the second stage of heating and cooling. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses suggest that toughness and strength of the film is achievable. It is concluded that CoSi x N y film as a hinge material is feasible.

Effects of annealing temperature and surface preparation on the formation of cobalt silicide interconnects

Cobalt silicide films have been prepared by rapid thermal annealing of cobalt layers sputter deposited on silicon substrates. We report on the evolution of silicide phases, surface and interface roughness as a function of the annealing temperature and silicon surface preparation. The characterizations are carried out by atomic force microscopy, X-ray diffraction, X-ray reflectivity, Raman spectroscopy, and transmission electron microscopy. The cleaning procedure of the silicon substrate affects the interface roughness and the silicide thickness, whereas little effects are found on the surface. On the other hand, surface roughness increases with annealing temperature.

Influence of annealing ambience on the formation of cobalt silicides

By using two sets of Raman systems with excitation lines of 514.5 and 632.8 nm, the influence of annealing ambience was investigated on the formation of cobalt silicides. The results show that a more uniform, compact and thermal stable cobalt silicide film can be formed in the hydrogen annealing ambience than that in the Ar annealing ambience. Two characteristic bands located at 305 and 325 cm −1 , which may be assigned to the CoSi and CoSi 2, respectively, were found during the phase transition processes. The strong band which appeared at 325 cm −1 that can only be detected with the excitation line of 632.8 nm was found to be due to the resonant Raman effect.

Ultrathin cobalt silicide film formation on Si(100)

AbstractThe interfacial reaction between ultrathin Co film and substrate Si(100) was studied by in situ XPS using monochromatized Al Kα. When the Co is deposited on Si(100) at room temperature, CoSi2 is formed during the initial stage of Co deposition and then metallic Co starts to grow sequentially. For 8 ML Co deposition on Si(100) the interfacial reaction layer is relatively thin compared with the pure Co overlayer, which is not involved in the interfacial reaction in depth. The Co layers change rapidly to CoSi layers after annealing at 270°C, and then CoSi2 layers form after annealing at 540°C for 2 min. The CoSi2 layers are changed to CoSi2 islands by post‐annealing at >650°C. Copyright © 2003 John Wiley & Sons, Ltd.

Structural investigations in the formation of the epitaxial CoSi 2 layer using a Co/TiSi x bilayer on Si (1 0 0)

Epitaxial cobalt silicide layers were formed on the p-type Si (1 0 0) by co-sputtering of Ti and Si as the interlayer, using the Co/TiSi x bilayer structure and subsequent rapid thermal annealing (RTA) at high temperatures. The cobalt silicide films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and atomic emission spectrometry (AES) to identify the phases, surface and interface morphologies and the chemical compositions. The XRD analysis results show that the epitaxial CoSi 2 layer with a (2 0 0) crystallographic orientation has been successfully grown on the Si (1 0 0) substrate. Effects of the variation of the d.c. power of the sputtering process and the annealing temperature (up to 800 °C) during RTA were investigated. The presence of a Co–Ti–O spinel phase was detected during silicidation in the annealing temperature range 400–600 °C. The AFM micrographs of the surface of the annealed Co/TiSi x bilayer structure show that the RMS roughness increased sharply up to 600 °C and stabilized thereafter at a moderate value of 8.9 nm, implying the formation of a relatively smoother surface in spite of high-temperature annealing. The AES analysis results indicate that native oxide on the Si substrate are removed by Ti at the beginning of RTA and Co diffuses to the clean surface of the Si substrate so that an epitaxial CoSi 2 layer can form. The cross-sectional high-resolution transmission electron microscopy (HRTEM) analysis further reveals the epitaxial relationship between the CoSi 2 layer and the Si (1 0 0) substrate.

Suppressing boron penetration and cobalt silicide agglomeration in deep submicron p-channel metal–oxide–semiconductor devices

Two discrete processing techniques have been combined for the doping and silicidation of thin (∼125 nm) amorphous silicon (a-Si) film. One technique uses an implantation barrier consisting of a stack of low temperature cobalt silicide (CoSi) and a-Si. The other technique incorporates nitrogen (N2+) to suppress CoSi2 agglomeration. When combined, the implantation barriers consisting of the CoSi/a-Si stack or a-Si films reduce boron penetration in p-channel metal–oxide–semiconductor devices and the implanted N2+ hinders cobalt silicide agglomeration. The two processing approaches presented here differ only in the implantation sequence. TRIM (transport of ions in matter) simulation has been used to predetermine the approximate doses and energies of implantation species. Sheet resistances are measured to assess the silicide thickness and quality of the resulting films. Depth profiles for boron, nitrogen, fluorine and cobalt have been extracted analytically by secondary ion mass spectroscopy. Transmission electron microscopy micrographs have been included to show the silicide/Si interface and also to manifest that there is no grain boundary grooving in the resulting cobalt silicide film.

Imaging of the structure of ultra-thin cobalt silicide films by inelastically backscattered electrons

We have investigated the initial growth of cobalt silicide films in the Co/Si(111) system by incoherent medium-energy electron diffraction providing real-space imaging of the subsurface atomic structure. It is shown that deposition of the first few (1–3) monolayers of Co results in formation of cobalt silicide islands with composition and structure depending on the temperature. While, the clusters of B-type CoSi2 grow at elevated temperatures (T>300°C), the room temperature deposits consist of silicide grains of A- and B-type orientation. Further increase of the Co coverage results in both an enrichment of the probed layer with the metal and its disordering. Annealing of such samples at T>250°C gives rise to solid-phase reaction of Co and Si leading to gradual formation of the epitaxial disilicide layer and disappearance of A-type domains.

Comparison of epitaxial growth of CoSi 2 among Co/Ti, Co/Hf, and Co/Nb bilayers on (100)Si

Formation of epitaxial cobalt silicide film on (100)Si using Co/Ti, Co/Hf, and Co/Nb bilayers has been investigated. The degree of easiness in the epitaxial growth of CoSi 2 by annealing the metal bilayers on (100)Si at 800°C was found to strongly depend upon what thin metal layer was used as an epitaxy promoter. Perfect epitaxy of CoSi 2 was obtained using Co/Ti/(100)Si. Local epitaxy of CoSi 2 was obtained using Co/Ti/(100)Si, while epitaxy of CoSi 2 was not obtained for the Co/Nb/(100)Si system. Epitaxial growth of CoSi 2 in these Co/metal/Si systems seems to be related to the formation and decomposition of stable reaction barriers like Co–Ti–O and Hf–Si–O compounds at high temperatures. These stable reaction barriers formed at high temperatures make uniform diffusion of Co atoms possible, resulting in the growth of epitaxial CoSi 2.