Electron Cyclotron Resonance Ion Beam Research Articles

Controlling the optical properties of hafnium dioxide thin films deposited with electron cyclotron resonance ion beam deposition

The effects of reactive and sputtering oxygen partial pressure on the structure, stoichiometry and optical properties of hafnium oxide (HfO2) thin films have been systematically investigated. The electron cyclotron resonance ion beam deposition (ECR-IBD) technique was used to fabricate the films on to JGS-3 fused silica substrates. The amorphous structure of HfO2 films were determined by X-ray Diffraction. Energy-dispersive X-ray Spectroscopy and Rutherford Backscattering Spectrometry were carried out for the composition and stoichiometry analysis, where this suggests the formation of over-stoichiometric films. The data suggests that the O:Hf ratio ranges from 2.4 – 4.45 to 1 for the ECR-IBD fabricated HfO2 films in this study. The transmission and reflectance spectra of the HfO2 films were measured over a wide range of wavelengths (λ = 185 – 3000 nm) by utilizing a spectrophotometer. The measured spectra were analyzed by an optical fitting software, which utilizes the model modified by O'Leary, Johnson and Lim, to extract the optical properties, refractive index (n) and the bandgap energy (E0). By varying the reactive and sputtering oxygen partial pressure, the optical properties were found to be n = 1.70 – 1.91, and E0 = 5.6 – 6.0 eV. This study provides a flexible method for tuning the optical properties of HfO2 coatings by controlling the mixture of reactive and sputtering gas.

Alternating silicon oxy-nitride and silicon oxide stripe formation by nitric oxide (NO+) ion implantation

We report nitric oxide ion (NO+) beam induced nanoscale pattern formation on Si (100) surface. The patterns are found to be structurally as well as chemically periodic. A highly reactive 14 keV NO+ beam is developed in an Electron Cyclotron Resonance ion beam system and implanted on Si (100) surface at oblique angles to form a periodic nano-ripple pattern with specific silicon oxide and silicon oxy-nitride enriched sectors with different dielectric constants. Well-defined ripple patterns start to form at comparatively lower ion fluences due to an additional instability generation by the chemical reaction of NO+ ions with silicon. The chemical shift of the Si 2p peak in the x-ray photoelectron spectroscopy study of an ion irradiated sample confirms the formation of silicon oxide and silicon oxy-nitride, whereas the local chemical nature of the ion induced ripple patterns, probed by electron energy loss spectroscopy, approves spatially resolved silicon oxide and silicon oxy-nitride stripe pattern formation. The ion modified layer thickness measured by cross-sectional transmission electron microscopy has an excellent agreement with Monte Carlo simulations. The optical sensitivity of an NO+ bombarded chemically patterned Si surface is also studied by UV–Visible spectroscopy. Formation mechanisms and potential applications of such nano-scale spatially graded materials are discussed.

Growth of highly (110)- and (111)-textured SrTiO3 thin films on Pt(111)/α-Al2O3(0001) substrates by ECR ion beam sputter deposition

SrTiO3 (STO) thin films were directly grown on Pt(111)/α-Al2O3(0001) substrates without Ti buffer layer using electron cyclotron resonance ion beam sputter deposition. Highly (110)- and (111)-textured STO films were obtained at 600 and 750°C, respectively. The structural, morphological and electrical properties of both textured films were studied and compared. From high-resolution X-ray diffraction data and in-plane pole figure analysis, highly (110)-textured STO film was found to contain three orientation variants related by a 120° in-plane rotation, while highly (111)-textured STO film had two orientation variants related by a 180° in-plane rotation. The presence of rod- and triangular-shaped grains was observed for the (110)- and (111)-textured film surfaces, respectively. Their grain orientations were also consistent with the structural analysis. The leakage current characteristics of Pt/STO/Pt capacitors were found to follow the Schottky emission and Poole–Frenkel conduction mechanisms. A larger dielectric constant of (111)-textured film (320 at 100kHz) was obtained in comparison with that of (110)-textured film (238 at 100 kHz) due to the effect of biaxial in-plane tensile strain and larger grain size.

Optical and mechanical properties of transparent SrTiO3 thin films deposited by ECR ion beam sputter deposition

AbstractSrTiO3 (STO) thin films have been deposited on glass substrates by electron cyclotron resonance (ECR) ion beam sputter deposition at different substrate temperatures (100–600 °C). The structural characteristics of the deposited films show a transition from amorphous phase to polycrystalline phase at 600 °C. The films exhibit good transparency with an interference pattern in the visible region and a very smooth surface without cracks. The refractive index of the films increases with an increase of the substrate temperature, and their dispersion was analyzed by a single‐oscillator model. The extinction coefficient of the films in the visible region is of the order of 10−3–10−2. The estimated values of the direct and indirect bandgap energies for the polycrystalline STO film are 3.80 and 3.32 eV, respectively. Its density is almost identical to the bulk STO single crystal, which is relatively high in comparison with those prepared by other techniques. The mechanical stability of the films is also improved with an increase of substrate temperature. Young's modulus and hardness of the polycrystalline STO film are 194.1 ± 15.5 and 22.5 ± 2.0 GPa, respectively.

Fabrication and characterization of epitaxial SrTiO3/Nb-doped SrTiO3 superlattices by double ECR ion beam sputter deposition

Epitaxial oxide superlattices (SLs) of SrTiO3 (STO) and Nb-doped SrTiO3(STNO) were fabricated on LaAlO3 (LAO) (001) substrates by an ion beam sputter deposition (IBSD) system having double electron cyclotron resonance (ECR) ion guns. The [STOx/STNOy]10 SLs were epitaxially grown at different stacking sequences (x = 6 nm, y = 1–6 nm) and maintained the periodicity z of 10. Structural properties and surface morphology are found to be strongly dependent on the STNO sublayer thickness (y). Highly strained SLs with two-dimensional growth mode is observed at smaller STNO sublayer thickness (y = 1 nm). With increasing to a critical thickness (y = 4 nm), the SLs are freely strained and transformed to three-dimensional growth mode. The results demonstrate that the double ECR-IBSD is a versatile technique for the growth of high-quality oxide SLs.

Fabrication and Characterization of an FeBNdNb Magnetic Metallic Glass Thin Film

We have fabricated an Fe67.46B22.5Nd6.3Nb3.74 magnetic metallic glass thin film on a (100) silicon substrate by electron cyclotron resonance ion beam sputtering. We confirmed the metallic glass state of the thin film by observing its crystallographically amorphous state using X-ray diffractometry and transmission electron microscopy, and we obtained the glass transition temperature using differential scanning calorimetry. We also confirmed the magnetization of the thin film using a physical property measurement system. The thin film showed the largest reported width of the supercooled liquid region (96 K) and the smallest reported value of coercivity (7.5 A/m) among the existing magnetic metallic glass thin films. This study is expected to lead to an increase in the variety of materials available and greater knowledge of the physical properties of magnetic metallic glass thin films and to facilitate research on developing magnetic metallic glass thin films as base materials for magnetic microelectromechanical systems.

Effect of annealing on magnetic properties of Nd-Fe-B thin films prepared by ECR ion beam sputtering method

Nd-Fe-B thin films were prepared by electron cyclotron resonance (ECR) ion beam sputtering and subsequent annealing. The influence of annealing on the magnetic properties and X-ray diffraction patterns of the product films was investigated. Amorphous films deposited at room temperature were annealed at temperatures between 600 and 800 °C. The c-axis oriented crystallization of the Nd2Fe14B phase did not appear by annealing of the buffer layer and magnetic Nd-Fe-B layer deposited at room temperature, and the hysteresis loops of the films indicated magnetic isotropy.

Low resistive copper films deposited using the ion beam sputtering method with an ultra-high purity target

Electric conductivities of copper thin films were investigated aiming toward low-loss metallization materials in energy-saving MEMS devices. The copper thin films were deposited with the goal of reducing impurities significantly and expecting to minimize scattering cross sections by relevant exclusion of scattering factors such as crystalline grain boundaries. Electron cyclotron resonance ion beam sputtering deposition (ECR-IBS) using an ultra-pure copper target was employed as the film process. Two indexes of the conductive properties, i.e. the resistivity at direct current and the mean free time extracted from optical transmission/reflection measurements at the plasma frequency, were employed in the evaluations and optimum conditions of the thin film processing were investigated. As a result, significant improvement in conductivity using the optimized conditions of temperature (430 K) and purity of the target (8N) was achieved for a thickness range of 10–300 nm.

Magneto-optic properties of electron cyclotron resonance ion beam sputtered and magnetron sputtered Co/Pt multilayers

An investigation of the magneto-optic properties of single Co films sandwiched by Pt films is presented. The films are grown via electron cyclotron resonance ion beam sputtering and magnetron sputtering. Kerr rotation and ellipticity are measured for the multilayers, varying Pt cap, Co, as well as Pt buffer layer thickness. The set of data allows the separation of optic and magneto-optic contributions to the Kerr signals. The magneto-optic constants (Voigt constants) are determined and compared with literature values. The striking result is the strong difference of the magneto-optic constants for ultrathin and thick Co films. The analysis of the data reveals that for ultrathin films, the Kerr signals have contributions that come presumably from the interfaces, indicative of polarized Pt.

A new mask blank deposition tool

A new ion beam sputter deposition tool (Seg-IonSys-1900) for EUV mask blanks has been developed. Different novel concept ideas were implemented in the tool to overcome the actual critical points of low particle generation and their embedding in the deposited layers, high homogeneity of layer thickness and very high mask blank throughput. For this it has been used a vertical position of the mask blanks for transportation and deposition without any kinds of substrate clamping. The Mo and Si layer deposition were realized by a segment controlled linear electron cyclotron resonance ion beam source. With it the ion beam profile can be adjusted to homogenize the layer thickness without rotation of the substrate. The focussed three grid system cause a deposition rate at 1000 eV Xe ions of 0.25 nm/s for Mo and 0.35 nm/s for Si. Thus, by optimization of the process parameters a 50 Mo/Si multilayer stack can be produced within 1 h.

Morphology and magnetic properties of ECR ion beam sputtered Co/Pt films

We report the fabrication of magnetic films using electron cyclotron resonance ion beam sputtering. The films consist of a Pt buffer layer, a thin magnetic Co layer and a Pt cap. Varying the thickness of the layers, we can tune the magnetic properties and a uniaxial perpendicular magnetic anisotropy can be obtained. Materials like amorphous silicon oxide, amorphous carbon, glass, mica and potassium bromide have been used as substrates. We have analyzed the structure of Co/Pt films on amorphous carbon by means of transmission electron microscopy. The analysis reveals that the buffer layers are polycrystalline with a (1 1 1)-texture, which increases with Pt thickness. The average grain-size is linearly correlated with the total thickness of the Pt buffer layer. While Co grows predominantly in its HCP stacking with c -axis aligned parallel to the surface normal, FCC grains with a strong (1 1 1) texture are also found. Scanning tunneling microscopy investigations reveal an average surface roughness of the Pt buffer layer of 3.0 Å . For buffer thickness ⩾ 60 Å we find similar magnetic properties for all Co films, not depending on the substrate materials. Co films of 4–8 Å thickness exhibit a perpendicular easy axis of magnetization, while a spin reorientation transition is found in a thickness range of 8–13 Å. Above 13 Å an in-plane easy axis of magnetization is obtained.

A slab-shaped electron cyclotron resonance ion beam source for in-line running target treatments

The possibility of industrial surface treatments of broad metallic rolls by appropriate ion beams has motivated our study of an immersed electron cyclotron resonance slab-shaped ion source composed of a number of elementary microwave modules fed in parallel through a linear power divider. We describe the performances of a single module implemented by a 45-mm-height ionization chamber of 80×15 mm cross section surrounded by a set of permanent magnets in a multipole configuration. A current density of 5 mA/cm2, uniform to within 10% over a 60 mm width, has been obtained for argon as well as for oxygen and nitrogen under a 500 W input power and a gas pressure of 5–8×10−3 mbar in the ionization chamber. Moreover, we have investigated the case of the non-normal incidence of the ion beam onto the running target. For 30° and 60° incidence angles with respect to the normal, the current density loss is 15% and 25%, respectively.

A compact electron cyclotron resonance source for 200-2000 eV ion beams

Ion-beam-sputtered and -assisted deposition technologies need medium energy, 100-2000 eV, ion beams of current density 1-3 mA cm-2, operated in a reactive and corrosive gas environment. We designed, built and characterized a compact electron cyclotron resonance ion beam source generating 2 cm diameter ion beams with currents of 2-8 mA and energy 200-1700 eV. Continuous wave microwave power (2.45 GHz, P1=0-300 W) was introduced into a 5 cm diameter plasma chamber via a 50 omega cable and a half-wavelength antenna. A ceramic cup sealed the plasma chamber and separated the antenna from the plasma. Boron nitride spacers electrically isolated the high-voltage plasma from the earthed chamber walls. Two Sm-Co ring-shaped magnets formed a circular electron cyclotron resonance surface in the plasma generation zone near the microwave introduction point. An external magnetic coil generated in the chamber an axial magnetic field, which helped to ignite the plasma and to control the plasma shape and density. The ignition microwave power was 5-40 W, with operational (argon) pressures in the beam line of 2*10-5 to 2*10-4 Torr. An argon ion beam was extracted using two multi-aperture pyrolitic graphite grids: a positive plasma grid and a negative electron suppression grid. The ion beam current increased linearly with microwave power; the beam half-angle divergence near the target was alpha /2=4-6.

Surface treatment of a–axis EuBa2Cu3O7−y thin films by an electron cyclotron resonance ion beam

An electron cyclotron resonance (ECR) ion beam has been utilized for a developing surface cleaning process of high-Tc superconducting thin films. By means of silver-contact resistivity measurements, and ex situ surface analysis using x-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED), the effects of ECR treatment on an air-exposed surface of a-axis EuBa2Cu3O7−y (EBCO) films are examined. Ag/EBCO contacts are made with exposure of the EBCO surface to an ECR oxygen ion beam with ion current densities of 100 μA/cm2 at room temperature for about 30 min and the in situ deposition of silver. The contacts, which are not annealed in oxygen, exhibit low contact resistivity in the 10−8–10−7 Ω cm2 range. These values are about five orders of magnitude lower than those of samples fabricated without ECR treatment. Based on XPS and RHEED data, change in the EBCO surface caused by ECR treatment is surmised.

Orientation Control of AlN Film by Electron Cyclotron Resonance Ion Beam Sputtering

Orientation control of aluminum nitride (AlN) films deposited on a-SiN/(110)Si was investigated by controlling the assisted nitrogen ion beam. Films were deposited using an electron cyclotron resonance (ECR) dual ion beam sputtering system having an ECR ion gun for irradiation and Kaufman-type ion gun for sputtering. It was found that AlN films with perpendicular and parallel orientation to the substrate could be obtained. These films consisted of micrograins. However, it was confirmed from reflection high energy electron diffraction (RHEED) and selected area electron diffraction (SAED) patterns that the former was c-axis oriented film and the latter was nearly single crystal.

Plasma diagnostics of an ECR ion beam system

It has been customary in the past to characterize plasma properties by referring to the power which was supplied by the generating system. Usually values of forward and reflected power are given. However, only physical parameters such as ion density or electron temperature can give a realistic picture of the plasma itself. In this work the Langmuir probe technique was used to obtain information about the properties of an electron cyclotron resonance (ECR) plasma in order to optimize the parameters of the system.