Iron Implantation Research Articles

Silicide formation and structural evolution in Fe-, Co-, and Ni-implanted silicon

Silicide formation and structural evolution in Fe-, Co-, and Ni-implanted silicon have been studied with use of extended x-ray-absorption fine-structure, x-ray-diffraction, and Rutherford backscattering spectrometry. Si(100) wafers were implanted at elevated temperatures, typically 350 \ifmmode^\circ\else\textdegree\fi{}C, to doses ranging from 1\ifmmode\times\else\texttimes\fi{}${10}^{16}$ to 1\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ions/${\mathrm{cm}}^{2}$. In the Co-implanted system, ${\mathrm{CoSi}}_{2}$ forms with doses as low as 1\ifmmode\times\else\texttimes\fi{}${10}^{16}$ Co/${\mathrm{cm}}^{2}$ and up to 3\ifmmode\times\else\texttimes\fi{}${10}^{17}$ Co/${\mathrm{cm}}^{2}$, where the CoSi phase starts to form. At higher doses (8\ifmmode\times\else\texttimes\fi{}${10}^{17}$ Co/${\mathrm{cm}}^{2}$), ordered CoSi and a CoSi-like short-range-ordered phase coexist. The silicide formation observed in the Ni-implanted system is similar to that in the cobalt-implanted system. In the case of iron implantation, Fe is coordinated with about eight Si atoms in the (1--3)\ifmmode\times\else\texttimes\fi{}${10}^{17}$ Fe/${\mathrm{cm}}^{2}$ range as in the tetragonal ${\mathrm{FeSi}}_{2}$. However, the ${\mathrm{FeSi}}_{2}$ phase forms only at around 5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ Fe/${\mathrm{cm}}^{2}$. At even higher doses, a substantial amount of iron is in disordered states in addition to the ordered FeSi phase. Upon annealing at 900 \ifmmode^\circ\else\textdegree\fi{}C, semiconducting \ensuremath{\beta}-${\mathrm{FeSi}}_{2}$ forms in all the Fe-implanted samples independent of the dose. Mechanisms for silicide formation in these ion-implanted systems are discussed with respect to crystal structure, diffusion, and implantation damage.

Ion-beam-enhanced adhesion of iron films to sapphire substrates

The effect of implantation of different ion species on the adhesion of iron films to sapphire substrates was investigated. The implantation energies were adjusted to ensure that the ion concentration profiles, damage profiles, and recoil distributions were the same for each species. For all implantations, the peak ion concentration was at the film-substrate interface. The adhesion of the films was measured by a pull test and a scratch test. For a fluence of 1 × 10 15 ions cm -2, implantation of chromium (300 keV) and iron (320 keV) increased the bond strength whereas implantation of nickel (340 keV) did not. The effect is proposed to be due to changes in the interfacial energy resulting from the presence of the ion species at the interface. Only a narrow zone is affected; the mixing at the interface is less than 10 nm.

Fabrication and Evaluation of Ternary Co-Fe-Si Structures Produced by Ion Beam Synthesis

ABSTRACTDual implantation of cobalt and iron into silicon (100) wafers and subsequent annealing has been used to form layers containing mixtures of CoSi2 and FeSi2. The structure and properties of the layers were followed by Secondary Ion Mass Spectrometry (SIMS), cross-sectional transmission electron microscopy (XTEM), Transmission Electron Diffraction (TED), Rutherford Backscattering Spectroscopy (RBS), and photoluminescence (PL). When a high dose of both species was implanted, segregation of the cobalt and iron occurred which for 1000°C anneals, resulted in an epitaxial layer of αFeSi2 upon a CoSi2 layer. The epitaxial quality of both of these layers was superior to those previously fabricated by single species implants. For a low dose cobalt implant followed by a high dose iron implant, a single phase solid solution was formed and segregation did not occur. Photoluminescence at 1.54 urn was observed from this layer, but with a much lower intensity and a broader line width than that from a pure βFeSi2 layer.

Ion beam synthesis of buried FeSi 2 in (100) silicon

The formation of iron silicide by high dose implantation of iron ((2–5)×10 17 Fe + cm −2, 300 KeV) at 350°C and subsequent two-step annealing was investigated. The depth distribution of iron was studied by Rutherford backscattering spectrometry, in particular the change in iron concentration for the phase transition from β-FeSi 2 to α-FeSi 2. Using X-ray diffraction, an admixture of FeSi in addition to FeSi 2 was detected in all samples in all samples investigated, and also in the as-implanted state. Cross-sectional transmission electron microscopy indicated preferred epitaxial growth of the silicide. The transition from the semiconducting to the metallic state as a result of high temperature annealing was detected by sheet resistivity measurements.

Microstructural and chemical effects in Al2O3 implanted with iron at 77 K and annealed in oxidizing or reducing atmospheres

Implantation of Fe (160 keV) into α–Al2O3 at 77 K produces an amorphous surface layer for fluences in the range of 1016 to 1017 Fe/cm2. Measurements of short-range order were made by extended energy loss fine structure analysis (EXELFS). The structure of amorphous Al2O3 produced by implantation of iron at 77 K exhibits short-range order that differs from that produced by stoichiometric (Al + O) implants. This difference is manifested by changes in the Al–O near-neighbor bond length. The local environments of implanted iron were determined from conversion electron Mössbauer spectroscopy (CEMS). The iron resides in several different local environments consistent with the electronic states of Fe2+, Fe4+, and Fe0. The relative amount of each environment depends upon the concentration (fluence) of the implanted iron ions. Regrowth of the amorphous zone during annealing occurs in the sequence amorphous → γ–Al2O3 ↠ α–Al2O3. The kinetics of regrowth and phase separation vary with implanted fluence and with annealing atmosphere. The higher the concentration of implanted iron, the slower the formation of iron-aluminum oxide precipitate phases in oxidizing atmospheres and α–Fe precipitates in reducing atmospheres.

Copper, iron and zirconium implantation into polycrystalline α-Al 2O 3

Polycrystalline α-Al 2 O 3 samples have been implanted by 10 17 Zr, Fe or Cu ions/cm 2 at 110 keV in order to form oxide precipitates in the near-surface region after annealing in air. A chemical and microstructural characterization has been performed on the as-implanted surface and on the samples annealed in the temperature range from 600 to 1600°C. The nature of the chemical phases and the precipitate evolution have been characterized by combining RBS, XPS, GXRD, CEMS, TEM and SEM techniques. XPX, CEMS and TEM experiments on as-implanted specimens detect copper, iron and zirconium as Cu° (small metallic precipitates), Fe° (small α-iron precipitates), Fe II (associated with FeAl 2O 4), and Fe IV (metastable state), Zr° and Zr IV (ZrO 2) in the as-implanted region. Analyses carried out after heat treatments between 600 and 1000 °C indicate a complete surface oxidation in this temperature range. Additionally, some precipitates appear along grain boundaries. Annealing at temperatures ranging from 1000 to 1600°C leads to drastic surface composition changes. The stability and size of the different observed precipitates (ZrO 2, AlFeO 3, Fe 2O 3, Fe 3O 4, CuO, CuAl 2O 4) strongly depend on the annealing temperature.

Microscopic aspects of copper, zirconium and iron ion implantation in alumina

Polycrystalline α-Al 2O 3 samples implanted at room temperature with 55, 110 and 220 keV copper, iron and zirconium ions in the range (0.2–1) × 10 17 ions cm -2 have been investigated by means of scanning transmission electron microscopy and X-ray energy-dispersive spectroscopy. As-implanted specimens retain their crystallinity in the case of copper and iron implantation and a precipitation of the implanted element is observed. The spinel phase is also present after iron implantation. An amorphous-like layer is detected in the case of zirconium implantation with a tendency to form zirconia crystals. Annealings have been performed (1000–1400 °C for 1 h in air). The copper spinel expands with epitaxial relations between the precipitates and the matrix. The zirconium is entirely oxidized in the form of tetragonal and then monoclinic ZrO 2 phases.

An analytical model of diffusion current in intrinsically gettered structures based on intentional contamination experiments

The authors used the results of intentional iron implants into bulk wafers with intrinsic gettering (IG) to develop an analytical model suitable for calculating the diffusion current in both bulk and epitaxial wafer structures. The model is used to compare the improvement in diffusion current an epitaxial wafer provides over a bulk wafer. For typical structures factor reductions in diffusion current of 10 to 100* are predicted when using epitaxial wafers. Iron incorporated into a MOSFET device during its fabrication was seen to be effectively removed from the device by the presence of an adjacent region of IG. More important is the observation that the gettered impurities reside close to the device in the IG region and still act to increase the diffusion current into the junction. >

High dose iron implantation into silicon and metals

High dose implantations of Fe into metals and semiconductors have been performed with beam energies up to 1 MeV at the UNILAC-injector at GSI. Unusual high concentrations of 70 atomic % for Si and 20 atomic % for Cu have been obtained, with doses of 1018 Fe/cm2 in the case of Si and several 1017 Fe/cm2 in the case of Cu. For Si the thickness of the layers were determined by Rutherford backscattering to be 4500 A. These results are consistent with calculations, which show that these high concentrations are due to the reduction of the sputter yield at the relative high particle energies. Samples have been characterized using several complementary methods (Mossbauer Spectroscopy (MS), Rutherford Backscattering Spectroscopy (RBS), Auger electron Spectroscopy (AES). Scanning Electron Microscopy (SEM), X-ray diffraction (XRD)).

High-dose iron implantation into silicon and metals

High-dose implantations of Fe into metals and semiconductors have been performed with energies up to 1 MeV at the UNILAC injector at GSI. Unusually high concentrations of 70 at.% for Si and 20 at.% for Cu have been obtained, with doses of 10 18 Fe/cm 2 in the case of Si and several times 10 17 Fe/cm 2 in the case of Cu. For Si the thicknesses of the layers were determined by Rutherford backscattering to be 4500 Å. These results are consistent with calculations, which show that these high concentrations are due to the reduction of the sputter yield at the relatively high particle energies. The cases of Si, Cu and Pb will be discussed. Samples have been characterized using several complementary methods (Mossbauer spectroscopy (MS), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and X-ray diffraction (XRD)).

The structure of Al 2O 3 implanted with iron at 77 K

Implantation of iron in the fluence range of 1 × 10 16 to 1 × 10 17 ions/cm 2 (160 keV) produces an amorphous surface layer in Al 2O 3 if the substrate temperature is approximately 77 K during implantation. Conversion electron Mössbauer spectroscopy (CEMS) measurements on the implanted 57Fe show a distribution of the iron among the charge states of Fe 2+, Fe 0, and the unusual Fe 4+ state. The Mössbauer parameters indicate that there are two Fe 2+ and two Fe 4+ states present in amounts that vary with fluence. No Fe 3+ was detected. The fine structure of the electron energy loss spectra indicates that the short-range order in amorphous Fe-implanted Al 2O 3 differs from that in amorphous Al 20 3 created by stoichiometric (2 Al + 3 O) implantation.

DC current transport in iron-implanted MgO single crystals

The electrical conductivity of MgO single crystals has been enhanced using iron implantation. Using the four probes technique and iron profiles obtained from Rutherford backscattering analysis, the dc conductivity of crystals implanted at room temperature with 100 keV iron ions and doses ranging from 3 × 10 16 up to 10 17 cm −2 has been derived in the temperature range of 300–500 K. The room temperature conductivity increases by four orders of magnitude when the iron dose increases from 3 × 10 16 to 10 17 ions cm −2 reaching the value ∼ 10 −3 Ω −1 cm −1. The conductivity is thermally activated, and the activation energy decreases continuously from 0.47 to 0.16 eV when the Fe content increases. Using conversion electron Mössbauer spectroscopy iron has been identified in different states which allowed us to discuss the observed electrical conductivity modification.

Conversion electron Mössbauer spectroscopic study on phosphorus implanted iron

Implantation of iron with phosphorus ions at different implantation energies (50, 100, and 200 keV) and different implantation doses (1 and 5 × 10 17 cm −2) is studied by conversion electron Mössbauer spectroscopy. Implantation results in an amorphization of the implanted range. In samples implanted with 1 × 10 17 cm −2 amorphous iron-phosphorus alloys with Fe 3P-like short range order are formed. Contrary to this and to other known amorphous alloys which are ferromagnetic, samples implanted with 5 × 10 17 cm −2 show a short range order similar to Fe 2P which is paramagnetic. Annealing the samples up to 400° C results in a precipitation of Fe 3P and Fe 2P, respectively. A further annealing in every case allows the formation of crystalline Fe 3P. Temperatures of 600° C and more initiate diffusion processes and the phosphorus begins to migrate out of the investigated region.

Titanium and carbon implantation of iron

Pure iron foils have been implanted with Ti and with Ti plus C and characterized by conversion electron Mossbauer spectroscopy (CEMS) and Auger electron spectroscopy (AES). Both paramagnetic and magnetic phases are observed and attributed to amorphous Fe−Ti−C alloys of differing Ti and C contents. Estimates of the thicknesses of the amorphous layers based on the CEMS data are in good agreement with the AES concentration depth profiles.

Precipitation phenomena in high-dose iron-implanted silica and annealing behavior

The effects of high-dose iron implantation into high-purity fused silica have been investigated by conversion-electron Mössbauer spectroscopy, transmission electron microscopy, Rutherford backscattering, and optical spectroscopy. In addition to isolated Fe2+ ions, samples subjected to doses of 4⊠1016 and 6 ⊠ 1016 ions cm−2 were found to contain homogeneously dispersed, equidimensional, crystalline particles ⋍2 nm, similar to Fe3O4. Precipitated spherical particles of metallic α-Fe⋍4 nm were observed in samples receiving a dose of ⋍ 1017 ions cm−2; as the dose was raised to 2.5 ⊠ 1017 ions cm−2 the mean size of these particles reached ⋍ 30 nm. Annealing in air to 800°C resulted in the growth of acicular grains of α-Fe2O3 ⋍ 20–300 nm. The optical spectra of the implanted layers are compared with the predictions of small particle theory.

Influence of the implantation of transition metal ions on the electrocatalytic activity of carbon materials

The influence of implantation of titanium, vanadium, chromium iron, cobalt, nickel, zirconium, molybdenum, silver, tungsten, iridium and platinum ions on the catalytic activity of polycrystalline graphite and glassy carbon for the electrochemical hydrogen evolution reaction has been studied. The factors causing an increase of material activity as a result of ion beam modification were determined. Implanted layers were investigated by XPS and voltammetric measurements. The formation of metastable states of implanted transition metal atoms in the carbon matrix has been established. These states are characterized by an unexpected high extent of unoccupancy of d-electronic valence levels. The transition of the implanted system in the equilibrium state occurs by metal atom diffusion and precipitation. Active sites of electronic exchange in the near-surface substrate region are bound to implanted metal atoms or their precipitates. These phenomena result in an increase of adsorptivity and considerable decrease of hydrogen overpotential on modified electrodes.

A comparison between ion implantation and laser alloying of iron for oxidation resistance improvement

A comparison between ion implantation and laser alloying of iron for oxidation resistance improvement

A comparison between ion implantation and laser alloying of pure iron for oxidation resistance improvement

Following previous results concerning boron alloying by ion implantation or laser surface melting, we study the role of aluminium to improve the high temperature oxidation of iron. Laser alloying has a greater efficiency than ion implantation. The aluminium containing phases formed at the metal-scale interface are responsible for the observed protection. The behaviour of the laser surface alloy is quite comparable to that of conventional alloys Fe-5Al. These two techniques, ion implantation and laser irradiation, seem to be of importance for future developments of corrosion protection.

Study of iron implanted MgO crystals by low-energy electron induced X-ray spectroscopy

Magnesium oxide crystals implanted with Fe + ions have been studied by means of Low-Energy-Electron-Induced X-ray Spectroscopy. All the implantations were carried out with 100 or 150 keV ion energy, at doses in the range from 10 15 to 10 17 ions cm −2. The structure of the Fe L II, L III X-ray emission bands provides information about the iron chemical state. Fe L II/L III band intensity ratio measurements have been performed with a 3 keV electron excitation in order to investigate the whole implanted layer. In addition, by using a filtered Fourier transform technique on observed spectra, some modifications in the oxygen K emission band can be observed in implanted MgO crystals after thermal annealings in air. The oxygen spectrum fine structure suggests that the MgO matrix, partially destroyed by iron implantation, is restored after high temperature treatments. All the implantation, is restored after high temperature treatments. All the results are discussed on the basis of previous Mössbauer Spectroscopy studies and ion channeling investigations.

Electrochemical investigations of ion-implanted oxide films

Oxide films (passive films) of 40–50 nm thickness were prepared by anodic polarization of hafnium and titanium electrodes up to 20 V. Multiple-energy ion implantation of palladium, iron and xenon was used in order to obtain modified films with constant concentration profiles of the implanted ions. Rutherford backscattering, X-ray photoelectron spectroscopy measurements and electrochemical charging curves prove the presence of implanted ions, but electrochemical and photoelectrochemical measurements indicate that the dominating effect of ion implantation is the disordering of the oxide film. The capacity of hafnium electrodes increases as a result of an increase in the dielectric constant D. For titanium the Schottky-Mott analysis shows that ion implantation causes an increase in D and the donor concentration N. Additional electronic states in the band gap which are created by the implantation improve the conductivity of the semiconducting or insulating films. This is seen in the enhancement of electron transfer reactions and its disappearance during repassivation and annealing. Energy changes in the band gap are derived from photoelectrochemical measurements; the absorption edge of hafnium oxide films decreases by approximately 2 e V because of ion implantation, but it stays almost constant for titanium oxide films. All changes in electrochemical behavior caused by ion implantation show little variation with the nature of the implanted ion. Hence the dominating effect seems to be a disordering of the oxide.