Preparation and characterization of ultra-thin cobalt silicide for VLSI applications

Ultra-thin cobalt silicide (CoSi₂) was formed from 10 nm cobalt film by solid phase reaction of Co and Si by use of rapid thermal annealing (RTA). The Ge⁺ ion implantation through Co film caused the interface mixing of the cobalt film with the silicon substrate and resulted in a homogeneous silicide layer. XRD was used to identify the silicide phases that were present in the film. The metallurgical analysis was performed by RBS. XRD and RBS investigations showed that final RTA temperature should not exceed 800°C for thin (< 50 nm) CoSi₂ formation.     

Metal silicide-templated growth of quality Si films for Schottky-diodes

Quality Si films were grown on a metal silicide template and fabricated for a Schottky-diode. The thin metal was firstly deposited and reacted to the supplying Si and then formed the silicide layer, which is a template to grow quality Si film above it due to the lattice affinity to Si. Various types of metal (Co, Ni, and mixture of Co and Ni) were used as catalyst species. The morphological changes of Si grain sizes were systematically investigated. Two steps of Si supply condition were applied and revealed the formation of metal silicide phases and Si film growth.During the Si supply, Co was stable to form CoSi₂ and grew a crystalline Si (c-Si) film above it. However Ni firstly formed Ni rich silicide phases at low Si supply due to the fast Ni diffusion in Si. By increasing the Si supply, Ni diffusion has been staggered and formed NiSi₂ layer to grow a c-Si film above it. It has been also revealed that the NiSi₂ migration produced a c-Si film behind. Mixing of Co with Ni showed a stable silicide phase without a serious metal migration and improved the Si crystallinity providing an enhanced Schottky-diode performance.The investigation of silicide formation and quality Si film growth is presented. Transmission electron microscope analysis proves the volume growth of c-Si film above a metal disilicide of NiSi₂ or CoSi₂.     

Silicide formation with nickel and platinum double layers on silicon

Diffusion effects and silicide formation in double layers of electron-gun-evaporated thin films of nickel and platinum on 〈100〉 and 〈111〉 silicon substrates were studied by megaelectronvolt backscattering spectrometry, transmission electron microscopy and glancing angle X-ray diffraction as a function of heat treatment (200–900 °C) for both sequences of thin films. It was found for the Si/Ni/Pt(Si/Pt/Ni) system that Ni₂Si(Pt₂Si) starts growing first. When all the nickel (platinum) has been consumed by this compound growth, platinum (nickel) diffuses through the Ni₂Si(Pt₂Si) layer and accumulates at the SiNi₂Si(SiPt₂Si) interface. This platinum (nickel) diffusion seems to be a grain boundary diffusion.For 〈100〉 Si/Ni/Pt samples with thin platinum layers it has been shown that platinum acts as a marker for the moving species in the transition from Ni₂Si to NiSi. For thick platinum layers it was observed that similar processes occur, leading to essentially a four-layered silicide where the layers are alternately rich in nickel and rich in platinum (450 °C, 20 min). In the silicide for the 〈100〉 Si/Pt/Ni system the distribution of nickel and platinum is approximately the reverse of the asdeposited distribution (about 450 °C, 20 min). In the further evolution of the profiles the elemental distribution becomes smooth and flat for both sequences of the layers (750 °C, 20 min). We suggest the existence of a ternary of the type SiNi_1?xPt_x.     

Structural and chemical stability of Ta–Si–N thin film between Si and Cu

Thermal stability and barrier performance of reactively sputter deposited Ta–Si–N thin films between Si and Cu were investigated. RF powers of Ta and Si targets were fixed and various N₂/Ar flow ratios were adopted to change the amount of nitrogen in Ta–Si–N thin films. The structure of the films are amorphous and the resistivity increases with nitrogen content. After annealing of Si/Ta–Si–N(300 Å)/Cu(1000 Å) structures in Ar–H₂ (10%) ambient, sheet resistance measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Auger electron spectroscopy (AES) were employed to characterize barrier performance. Cu₃Si and tantalum silicide phase are formed at the same temperature, and the interdiffusion of Si and Cu occurs through the local defect sites. In all characterization techniques, nitrogen in the film appears to play an important role in thermal stability and resistance against Cu diffusion. A 300 Å thick Ta₄₃Si₄N₅₃ barrier shows the excellent barrier property to suppress the formation of Cu₃Si phase up to 800°C.     

Impurity effects in molybdenum silicide formation

The reaction between molybdenum thin films and single-crystal Si〈111〉 substrates was studied as a function of the concentrations of impurities (mainly oxygen) in the metal film. At a low oxygen concent (1–2 at.%), only the silicide phase MoSi₂ was observed, and a thickness proportional to the square root of time corresponding to an average activation energy of 3 eV in the temperature range 545–600 °C was found. During the formation of the silicide the oxygen originally present in the molybdenum films accumulates at the interface between the silicon and the MoSi₂.In contrast, a higher oxygen content (4–5 at.%) prevents the formation of any silicide phases in the above temperature range and leads to the formation of MoSi₂ and Mo₅Si₃ phases at temperatures near 800 °C. MoSi₂ was always observed at the inner interface with Mo₅Si₃ on the surface.The oxygen segregates from the silicides and accumulates at the Si-MoSi₂ and MoSi₂-Mo₅Si₃ interfaces to form a non-uniform layer of SiO_x(x ? 2).     

Surface and interface morphology of CoSi2 films formed by multilayer solid-state reaction

CoSi₂ is a promising material for self-aligned silicide (salicide) applications in sub-0.25 μm complementary metal–oxide–semiconductor (CMOS) technology. In conventional salicide technology, silicides are formed by a solid-state reaction (SSR) after source/drain formation. With the continued scaling down of junction depths, surface and interface roughness of silicides is a growing concern. In this work, a comparative study has been made to investigate the morphology and thermal stability of CoSi₂ formed by SSR of different structures, i.e. Co/Si, TiN/Co/Si, Ti/Co/Si, Co/Ti/Si and Ti/Co/Ti/Si. Atomic force microscopy and other techniques were used to characterize the morphology and thermal stability. Compared with the Co/Si reaction, TiN or Ti capping reduces the roughness and improves the thermal stability. The reaction with a Ti interfacial layer shows epitaxial growth of CoSi₂ on Si (100). The morphology and thermal stability of epitaxial CoSi₂ were significantly improved. The epitaxial CoSi₂ may be useful for contact in deep submicrometer CMOS devices.     

Effects of nitrogen annealing on surface structure,silicide formation and magnetic properties of ultrathin films of Co on Si(100)

Effects of nitrogen annealing on structural and magnetic properties of Co/Si (100) up to 700°C has been studied in this paper. Ultrathin Co films having a constant thickness of 50 Å were grown on Si (100) substrates using electron-beam evaporation under very high vacuum conditions at room temperature. Subsequently, the samples were annealed at temperatures ranging from 100–700°C in a nitrogen environment at atmospheric pressure. Sample quality and surface morphology were examined using atomic force microscopy. Silicide formation and the resultant variation in crystallographic arrangement were studied using X-ray diffractometer. The magnetization measurements done using a vibrating sample magnetometer indicate a decrease in coercivity and retentivity values with increase in annealing temperature. Resistivity of the samples measured using a four-point probe set up shows a decrease in resistivity with increase in annealing temperature. Formation of various silicide phases at different annealing temperatures and the resultant variation in the magnetic susceptibility has been thoroughly studied and quantified in this work.     

Structural and electrical properties of swift heavy ion beam irradiated Co/Si interface

Synthesis of swift heavy ion induced metal silicide is a new advancement in materials science research. We have investigated the mixing at Co/Si interface by swift heavy ion beam induced irradiation in the electronic stopping power regime. Irradiations were undertaken at room temperature using 120 MeV Au ions at the Co/Si interface for investigation of ion beam mixing at various doses: 8 × 10¹², 5 × 10¹³ and 1 × 10¹⁴ cm⁻². Formation of different phases of cobalt silicide is identified by the grazing incidence X-ray diffraction (GIXRD) technique, which shows enhancement of intermixing and silicide formation as a result of irradiation.I–V characteristics at Co/Si interface were undertaken to understand the irradiation effect on conduction mechanism at the interface.     

Effect of annealing parameters on the magnetic properties of NiZn ferrite thin films

Ni_0.5Zn_0.5Fe_2.0O_4.0 thin films (NZFs) were deposited on Si (100) substrate by a sol–gel method, and the effects of annealing parameters on the structure and magnetic properties of the proposed films were investigated. Moderate heating rate was beneficial to the nucleation of NZFs. When the heating rate was 2 °C/min the saturation magnetization (M _s) achieved its maximum and the coercivity (H _c) reached its minimum. Both the crystallization and M _s of NZFs enhanced with increasing annealing time; however, H _c changed contrarily. High quenching temperature produced a large stress and consequently deteriorated magnetic properties. The optimal annealing parameters of NZFs were annealed at 700 °C, heating rate 2 °C/min, annealing time 1 h, and gradually cooled to room temperature. Finally, NZFs showed a high magnetization of 320 emu/cm³ and low coercivity of 86 Oe.     

Solid state reactions of TaW thin films and Si single crystals

Contact reactions between a Si substrate and thin films of TaW bilayers and codeposited alloys have been studied. The interdiffusion and silicide formation have been analysed by Auger electron spectroscopy and X-ray diffraction. In the bilayer structures the formation of TaSi₂ and WSi₂ is observed at 700–750°C and 800–850°C, respectively. For the Ta-rich alloy of Ta₈₀W₂₀, TaSi₂ is formed at 700–750°C similarly to the bilayer case, but this is followed by the formation of Ta₅ Si₃ which disappears at higher temperatures. For the W-rich alloy of Ta₂₀W₈₀, silicide formation is delayed to higher temperatures due to alloying in the thin film.     

Growth mechanism of epitaxial CoSi2 on Si and reactive deposition epitaxy of double heteroepitaxial Si/CoSi2/Si

The growth mechanism of epitaxial CoSi₂ was studied using Co/Ti/Si multilayer solid phase reaction. Results showed that phase formation was controlled by diffusion of Co through the growing CoSi_x, although at the early stage of CoSi₂ growth the diffusion of Co could be controlled by a Ti layer. A reactive deposition technique was also evaluated by using a conventional magnetron sputtering system. Results showed that an epitaxial CoSi₂ layer was formed by controlling the Co sputtering rate not to exceed the Co diffusion rate through CoSi_x. However, the surface of CoSi₂ became rough when the deposition rate was much slower than the Co diffusion rate through CoSi_x. The roughness was caused by the formation of CoSi₂ (111) facets at the interface between CoSi₂ and the Si substrate. Si/CoSi₂/Si double heteroepitaxial structures were fabricated when Si and Co were sequentially sputter-deposited on a Si (100) substrate.     

Effects of annealing on the formation of Mg2Si film prepared by resistive thermal evaporation method

The effects of annealing time and temperature on the formation and structure of magnesium silicide (Mg₂Si) films were investigated. Magnesium films of 380 nm thickness were deposited on Si (111) substrates using resistive thermal evaporation method. The films were then annealed in an annealing furnace under a low vacuum atmosphere of 10^?1–10^?2 Pa. The results showed that the crystallization quality of Mg₂Si films was strongly affected by the annealing time and temperature. Annealing at 400 °C for 4 h was the optimal preparation conditions for Mg₂Si films.     

The growth and transformation of Pd2Si on (111), (110) and (100) Si

Thin Pd films on (111), (110), (100) and amorphous Si substrates form [001] fiber textured Pd₂Si in the temperature range 100°–700°C. The degree of texture is a function of substrate orientation, increasing in the order amorphous Si, (100) Si, (110) Si and (111) Si. Only on the (111) Si substrate is the Pd₂Si film epitaxially oriented. Temperature-dependent growth on this orientation can be characterized by [001] textured growth, epitaxial azimuth orientation at the Si interface and progressive layer by layer formation of the mosaic crystal to the thin film surface.During Pd deposition, rapid non-diffusion-controlled growth of epitaxial Pd₂Si on (111) Si occurs at substrate temperatures of 100° and 200°C. An unidentified palladium silicide of low crystallographic symmetry forms during Pd deposition onto a 50°C substrate. The diffusion-controlled growth of Pd₂Si on (111) Si follows a t^0.5 dependence. The velocity constant is

$\text{k = 7 × 10}{}^{\mathrm{?2}}\text{exp}\text{?}\text{29200±800}\text{RT}\text{cm}{}^2\text{/}\text{sec}$

Palladium deposited on 100°C (111) Ge substrates reacts during deposition to form epitaxially oriented Pd₂Ge. However, growth of this phase at higher temperatures results in a randomly oriented film. The transformation of Pd₂Ge to PdGe is kinetically controlled. After a 15 min anneal at 560°±10°C in N₂ only PdGe is detectable on (111) Ge.The high temperature stability of thin film Pd₂Si is controlled by time- temperature kinetics. For a given annealing cycle, the nucleation and growth rates of the PdSi phase are inversely related to the crystalline perfection of Pd₂Si. Decreasing transformation rates follow the order (100), (110), (111) Si. formation of thin film Pd₂Si occurs by the formation of PdSi and subsequent growth of Si within the PdSi phase. After a 30 min N₂ anneal, initial transformation occurs at 735°C on (100) Si, 760°C on (110) Si and 840°C on (111) Si. Extended high temperature annealing produces a two-phase structure of highly twinned and misoriented Si and small PdSi grains that penetrate as much as 3 μm into the Si.     

Formation and characterization of tungsten silicide layers

Tungsten silicide films formed via furnace annealing were studied. The tungsten layers were deposited either by evaporation or by r.f. sputtering onto Si(100) substrates as well as onto silicon layers deposited in situ. Tungsten deposited at room temperature yields poor silicides owing to the lack of permeability at the interface with silicon. This as well as the formation of voids in the substrate are discussed. Deposition onto substrates heated to 500 °C, however, always allows the formation of a silicide during subsequent annealing.     

Initial stages of silicon-iron interface formation

The formation of a silicon-iron (Si/Fe) interface has been studied in situ by the method of high-resolution photoelectron spectroscopy using synchrotron radiation. The experiments were performed under ultrahigh vacuum conditions (at a residual pressure of 3 × 10^?10 Torr) in a range of Si coating thicknesses within 0.04–0.45 nm. It is established that the process begins with the formation of a FeSi silicide and Fe-Si solid solution on the iron substrate surface. As the Si coating thickness increases, the solid solution converts into ferromagnetic (Fe₃Si) and nonmagnetic (FeSi) silicides. It is shown that thermostimulated solid-state reactions leading to the transformation of FeSi and Fe₃Si silicides into a semiconducting β-FeSi₂ silicide start at a temperature close to 600°C.     

Interdiffusion and compound formation in the Mo/Pd/Si thin film metallization system

The process of interdiffusion and compound formation in Mo/Pd/Si thin films was studied between 250 and 750°C via sheet resistance measurements, X-ray diffraction, Rutherford backscattering spectrometry and Auger electron spectroscopy. The results indicate that thermal annealing of the Mo/Pd/Si thin film couples between 250 and 475°C lead to PdSi interaction, Pd₂Si compound formation and consequently a small increase in the sheet resistance. In contrast, exposure of the Mo/Pd/Si thin films to temperatures higher than 475°C lead to MoPd₂Si interaction in addition to PdSi interaction, MoSi₂ compound formation and a dramatic increase in the sheet resistance. The influence of interdiffusion and compound formation on the interface morphology in the Mo/Pd/Si system was studied, and the implications of these observations to a very-large-scale integration contact metallization utilizing an Mo/Pd₂Si/Si system are discussed.     

Magnetic properties and structure of cobalt-platinum thin films

The magnetic properties of RF sputtered Co-Pt alloy thin films were studied as a function of Pt content from 0 to 80 at%. At room temperature, ferromagnetic films were obtained in the range 0-32 and 40-80 at% Pt. For Pt contents between 32 and 40 at%, discontinuities in the magnetization, magnetostriction, and coercivity versus Pt content were observed; however no discontinuity was observed in the resistivity. The structure of films containing about 25 at% Pt is a mixture of hexagonal and face-centered cubic (FCC) phases. At this composition the magnetostriction is small, but coercivities are large-700 to 2000 Oe-and dependent upon film thickness. The coercivities of these films do not change with heat treatment up to temperatures of 600°C but decrease markedly at 700°C. The properties of equiatomic Co-Pt film s are similar to those of bulk alloys. In particular the large coercivity observed in films after heal treatment at 500° to 700°C is due to the formation of an ordered tetragonal phase within the face-centered cubic matrix. The structure of films of about 75 at% Pt is initially a disordered face-centered cubic phase and with heat treatment beginning at 500°C an ordered face-centered cubic phase forms. The coercivity of these films (∼200 Oe) does not change with annealing at 500°C. It decreases slightly upon further annealing at 600°C to 700°C. Electron microscope observations were used to correlate the magnetic properties with film structure.     

Effects of Magnetic Annealing on Structure and Magnetic Properties of L10-FePt/Ag Films

The structural and magnetic properties of L1₀-FePt/Ag films were studied by X-ray diffraction and a vibrating sample magnetometer. The FeAg/Pt films were obtained by depositing FeAg thin films on thermally oxidized Si (001) substrates via magnetron sputtering and Pt layers on their surface after annealing FeAg thin films at 400 °C with and without an out-of-plane magnetic field of 10 kOe. These films were further annealed at various temperatures to obtain L1₀-FePt phase. The results indicated that the pre-annealing of FeAg thin films under 10 kOe magnetic field caused (001) orientation of Fe particles, and the deposition of Pt layer on such orientated underlayers reduced the ordering temperature of FePt in FeAg/Pt films, realizing the L1₀-FePt phase at 400 °C. The higher coercivity and ordering degree were also observed in the samples, compared with those pre-annealed without magnetic field at the same annealing condition.     

Structural properties of the PdSi interface: An investigation by reflection high energy electron diffraction

The first stages of the formation of silicide were studied at various temperatures during palladium deposition onto an Si(111) 7 × 7 surface using the reflection high energy electron diffraction technique.For temperatures below 200°C, the interaction of palladium with silicon leads to the formation of three-dimensional Pd₂Si crystallites.At more elevated temperatures (300–400°C) two-dimensional phases were distinguished that are denoted as follows: Si(111) √3 R(30°) Pd and Si(111) 2√3 R(30°) Pd.     

Annealing behaviour and magnetic properties of Co/Pt and Fe/Pt bilayer thin films

The annealing behaviour and magnetic properties of Co/Pt and Fe/Pt bilayer thin films are investigated. The coercivity of Co/Pt bilayer thin films increases with annealing above 450 °C and shows a peak value of 40 kA m⁻¹ in the range from 500 to 550 °C. This increase is due to both the formation of a CoPt solid solution and the optimization of grain diameters. Furthermore, the increase is promoted by multilayering. Similar results were obtained for Fe/Pt bilayer thin films.