Ion Beam Sputtering Deposition System Research Articles

Effects of fixture rotation on coating uniformity for high-performance optical filter fabrication

Abstract Coating uniformity is critical in fabricating high-performance optical filters by various vacuum deposition methods. Simple and planetary rotation systems with shadow masks are used to achieve the required uniformity [J. B. Oliver and D. Talbot, Appl. Optics 45, 13, 3097 (2006); O. Lyngnes, K. Kraus, A. Ode and T. Erguder, in ‘Method for Designing Coating Thickness Uniformity Shadow Masks for Deposition Systems with a Planetary Fixture’, 2014 Technical Conference Proceedings, Optical Coatings, August 13, 2014, DOI: http://dx.doi.org/10.14332/svc14.proc.1817.]. In this work, we discuss the effect of rotation pattern and speed on thickness uniformity in an ion beam sputter deposition system. Numerical modeling is used to determine statistical distribution of random thickness errors in coating layers. The relationship between thickness tolerance and production yield are simulated theoretically and demonstrated experimentally. Production yields for different optical filters produced in an ion beam deposition system with planetary rotation are presented. Single-wavelength and broadband optical monitoring systems were used for endpoint monitoring during filter deposition. Limitations of thickness tolerances that can be achieved in systems with planetary rotation are shown. Paths for improving production yield in an ion beam deposition system are described.

Corrosion resistance and mechanism of CeN, TiN and CeN/TiN bilayer composite film deposited by dual ion beam sputtering

Uranium (U) is an important engineering material in nuclear energy industry. Its environmental instability, however, posed challenges on its applications. Due to the active property and similar electronic configuration, Cerium (Ce) can be used as a reference metal to simulate the protection of uranium from corrosion. In order to improve the corrosion resistance of Ce, ceramic CeN, and ceramic TiN and CeN/TiN bilayer composite film were prepared by dual ion beam sputtering deposition system (DIBD). The crystal structure of films was identified by X-ray diffraction (XRD) and the chemical states of CeN film were characterized by the X-ray photoelectron spectroscopy (XPS). The Surface morphology and structure changes in atmospheric environment were examined by scanning electron microscopy (SEM) and XRD, The corrosion behavior was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The experimental results indicate the single film of CeN or TiN shows poor corrosion resistance, but the CeN/TiN bilayer composite film has better corrosion resistance. Based on the XPS, SEM and impedance analysis, we supposed that the loose of integrity and passivity breakdown on as deposited coating may be the corrosion inducement.

Improving the growth of Ge/Si islands by modulating the spacing between screen and accelerator grids in ion beam sputtering deposition system

Ge islands were fabricated on Si buffer layer by ion beam sputtering deposition with a spacing between the screen and accelerator grids of either 1mm or 2mm. The Si buffer layer exhibits mixed-phase microcrystallinity for samples grown with 1mm spacing and crystallinity for those with 2mm spacing. Ge islands are larger and less dense than those grown on the crystalline buffer because of the selective growth mechanism on the microcrystalline buffer. Moreover, the nucleation site of Ge islands formed on the crystalline Si buffer is random. Ge islands grown at different grid-to-grid gaps are characterized by two key factors, namely, divergence half angle of ion beam and crystallinity of buffer layer. High grid-to-grid spacing results in small divergence half angle, thereby enhancing the sputtering energy and redistribution of sputtered atoms. The crystalline volume fraction of the microcrystalline Si buffer was obtained based on the integrated intensity ratio of Raman peaks. The islands show decreased density with decreasing crystalline volume fraction and are difficult to observe at crystalline volume fractions lower than 72%.

Development of an Ion Beam Sputter Deposition System for Producing Complex-Shaped X-ray Mirrors

We developed a figuring system based on sputter deposition with the aim of establishing a fabrication method for complex-shaped X-ray mirrors. The spatial resolution is essentially determined by the size of the spot profile. In this study, we developed a sputter deposition apparatus using minute pinholes to limit the deposition area, with which deposition spots less than 100μm in diameter could be produced. Interferometric measurements revealed that surface profiles of the deposition spots were smooth enough to reflect X-rays without scattering.

Spetroscopic ellipsometry study on electrical and elemental properties of Sb-doped ZnO thin films

Room-temperature spectroscopic ellipsometry data has been analyzed to determine the complex dielectric functions, ɛ(E) = ɛ1(E) + iɛ2(E) of as-deposited Sb-doped ZnO (SZO) thin films grown on n-Si(100) substrates by dual ion beam sputtering deposition system for different growth temperatures (Tg). The dielectric functions have been obtained from ellipsometry data analyses using Cody-Lorentz oscillator in the GenOsc model. A gradual reduction in the value of electron concentration and finally the conversion of doping characteristics from donor type to acceptor type was observed with the rise in Tg. This, in turn, resulted in the decline of broadening of ɛ1 peaks, and hence in the increase of excitonic lifetime. Optical band-gap energy was observed to decrease with increase in Tg from 200 to 300 °C, and then rise continuously with further increase in Tg. X-ray diffraction measurements showed that all SZO films had (002) preferred crystal orientation. Hall measurement and X-ray photoelectron spectroscopy analysis confirmed that the change in the electrical conduction from n-to p-type was due to the enhancement in the value of Sb5+/Sb3+ ratio and SbZn–2VZn complex formation in SZO films.

Blue electroluminescence from Sb-ZnO/Cd-ZnO/Ga-ZnO heterojunction diode fabricated by dual ion beam sputtering.

p-type Sb-doped ZnO/i-CdZnO/n-type Ga-doped ZnO was grown by dual ion beam sputtering deposition system. Current-voltage characteristics of the heterojunction showed a diode-like rectifying behavior with a turn-on voltage of ~5 V. The diode yielded blue electroluminescence emissions at around 446 nm in forward biased condition at room temperature. The emission intensity increased with the increase of the injection current. A red shifting of the emission peak position was observed with the increment of ambient temperature, indicating a change of band gap of the CdZnO active layer with temperature in low-temperature measurement.

Influence of annealing temperature on ZnO thin films grown by dual ion beam sputtering

We have investigated the influence of in situ annealing on the optical, electrical, structural and morphological properties of ZnO thin films prepared on p-type Si(100) substrates by dual ion beam sputtering deposition (DIBSD) system. X-ray diffraction (XRD) measurements showed that all ZnO films have (002) preferred orientation. Full-width at half-maximum (FWHM) of XRD from the (002) crystal plane was observed to reach to a minimum value of 0.139° from ZnO film, annealed at 600 °C. Photoluminescence (PL) measurements demonstrated sharp near-band-edge emission (NBE) at ~ 380 nm along with broad deep level emissions (DLEs) at room temperature. Moreover, when the annealing temperature was increased from 400 to 600 °C, the ratio of NBE peak intensity to DLE peak intensity initially increased, however, it reduced at further increase in annealing temperature. In electrical characterization as well, when annealing temperature was increased from 400 to 600 °C, room temperature electron mobility enhanced from 6.534 to 13.326 cm2/V s, and then reduced with subsequent increase in temperature. Therefore, 600 °C annealing temperature produced good-quality ZnO film, suitable for optoelectronic devices fabrication. X-ray photoelectron spectroscopy (XPS) study revealed the presence of oxygen interstitials and vacancies point defects in ZnO film annealed at 400 °C.

Behavior of dual ion beam sputtered MgZnO thin films for different oxygen partial pressure

Mg-doped ZnO (MgZnO) films were grown on p-Si (001) substrates by dual ion beam sputtering deposition system at a constant growth temperature of 600 °C for different oxygen partial pressure. The impact of oxygen partial pressure on the structural, electrical, elemental and morphological properties was thoroughly investigated. X-ray diffraction (XRD) spectra revealed that the deposited MgZnO films were polycrystalline in nature with preferred (002) crystal orientation. The peak of MgZnO (101) plane was reduced significantly as oxygen partial pressure was increased and disappeared completely at 80 and 100 % O2. The maximum electron concentration was evaluated to be 5.79 × 1018 cm−3 with resistivity of 0.116 Ω cm and electron mobility of 9.306 cm2/V s at room temperature, for MgZnO film grown with 20 % O2. Raman spectra shows a broad peak at 434 cm−1 corresponded to E 2 high phonons mode of MgZnO wurtzite structure. The peak at 560 cm−1 corresponded to the E1 (LO) mode and was associated with oxygen deficiency in MgZnO films. Raman intensity at 560 cm−1 reduced, on increasing oxygen partial pressure. A correlation between structural, electrical, elemental and morphological properties with oxygen partial pressure was also established.

P-type conduction from Sb-doped ZnO thin films grown by dual ion beam sputtering in the absence of oxygen ambient

Sb-doped ZnO (SZO) thin films were deposited on c-plane sapphire substrates by dual ion beam sputtering deposition system in the absence of oxygen ambient. The electrical, structural, morphological, and elemental properties of SZO thin films were studied for films grown at different substrate temperatures ranging from 200 °C to 600 °C and then annealed in situ at 800 °C under vacuum (pressure ∼5 × 10−8 mbar). Films grown for temperature range of 200–500 °C showed p-type conduction with hole concentration of 1.374 × 1016 to 5.538 × 1016 cm−3, resistivity of 66.733–12.758 Ω cm, and carrier mobility of 4.964–8.846 cm2 V−1 s−1 at room temperature. However, the film grown at 600 °C showed n-type behavior. Additionally, current-voltage (I–V) characteristic of p-ZnO/n-Si heterojunction showed a diode-like behavior, and that further confirmed the p-type conduction in ZnO by Sb doping. X-ray diffraction measurements showed that all SZO films had (002) preferred crystal orientation. X-ray photoelectron spectroscopy analysis confirmed the formation of SbZn–2VZn complex caused acceptor-like behavior in SZO films.

Investigation of dual ion beam sputtered transparent conductive Ga-doped ZnO films

Ga-doped ZnO (GZO) transparent conducting films were deposited on sapphire (0001) substrates using dual ion beam sputtering deposition system. The impact of growth temperature on the structural, morphological, elemental, optical, and electrical properties was thoroughly investigated and reported. X-ray diffraction measurements explicitly confirmed that all GZO films had (002) preferred crystal orientation. The film deposited at 400 °C exhibited the narrowest full-width at half-maximum value of 0.24° for (002) crystalline plane and the lowest room temperature electrical resistivity of 4.11 × 10−3 Ω cm. The Raman spectra demonstrated the vibrational modes at 576 and 650–670 cm−1, associated with native oxygen vacancies and elemental Ga doping in ZnO lattice, respectively. All doped films showed an overall transmittance of above 95 % in the visible spectra. A correlation between structural, optical, elemental, and electrical properties with GZO growth temperature was established.

Influence of in-situ annealing ambient on p-type conduction in dual ion beam sputtered Sb-doped ZnO thin films

Sb-doped ZnO (SZO) films were deposited on c-plane sapphire substrates by dual ion beam sputtering deposition system and subsequently annealed in-situ in vacuum and in various proportions of O2/(O2 + N2)% from 0% (N2) to 100% (O2). Hall measurements established all SZO films were p-type, as was also confirmed by typical diode-like rectifying current-voltage characteristics from p-ZnO/n-ZnO homojunction. SZO films annealed in O2 ambient exhibited higher hole concentration as compared with films annealed in vacuum or N2 ambient. X-ray photoelectron spectroscopic analysis confirmed that Sb5+ states were more preferable in comparison to Sb3+ states for acceptor-like SbZn-2VZn complex formation in SZO films.

Effect of oxygen partial pressure on the behavior of dual ion beam sputtered ZnO thin films

Undoped ZnO thin films were grown on p-type Si (1 0 0) substrates at different oxygen partial pressure by dual ion beam sputtering deposition system at a constant growth temperature of 400 °C. The crystallinity, surface morphology, optical, elemental and electrical properties of these ZnO thin films was studied. The minimum value of full-width at half-maximum of the θ-rocking curve obtained from x-ray diffraction of the ZnO (0 0 2) plane, was reported to be 0.1865° from ZnO film grown at 50% of (O2/(O2 + Ar))%. Crystalline property of ZnO films was observed to degrade with the increase in oxygen partial pressure. Photoluminescence measurements demonstrated sharp near-band-edge emission at ∼381 nm at room temperature. X-ray photoelectron spectroscopy study revealed presence of oxygen interstitials and vacancies as point defects in ZnO films. Electrical resistivity of ZnO was found to increase with the increase in oxygen partial pressure.

Effect of growth temperature on structural, electrical and optical properties of dual ion beam sputtered ZnO thin films

ZnO epitaxial thin films were grown on p-type Si(100) substrates by dual ion beam sputtering deposition system. The crystalline quality, surface morphology, optical and electrical properties of as-deposited ZnO thin films at different growth temperatures were studied. Substrate temperature was varied from 100 to 600 °C at constant oxygen percentage O2/(O2 + Ar) % of 66.67 % in a mixed gas of Ar and O2 with constant chamber pressure of 2.75 × 10−4 mBar. X-Ray diffraction analyses revealed that all the films had (002) preferred orientation. The minimum value of stress was reported to be −0.32 × 1010 dyne/cm2 from ZnO film grown at 200 °C. Photoluminescence measurements demonstrated sharp near-band-edge emission (NBE) was observed at ~375 nm along with deep level emission (DLE) in the visible spectral range at room temperature. The DLE Peak was found to have decrement as ZnO growth temperature was increased from 200 to 600 °C. The minimum FWHM of the NBE peak of 16.76 nm was achieved at 600 °C growth temperature. X-Ray photoelectron spectroscopy study revealed presence of oxygen interstitials and vacancies point defects in ZnO film grown at 400 °C. The ZnO thin film was found to be highly resistive when grown at 100 °C. The ZnO films were found to be n-type conducting with decreasing resistivity on increasing substrate temperature from 200 to 500 °C and again increased for film grown at 600 °C. Based on these studies a correlation between native point defects, optical and electrical properties has been established.

Monochromatic X-rays for Low-Dose Digital Mammography

The feasibility of using monochromatic x-ray imaging generated from an x-ray tube and a multilayer reflector for digital mammography with a low radiation dose was examined. A multilayer mirror was designed to select the x-ray peak with an energy of 21.5 keV generated from an x-ray tube with a tungsten target and was fabricated by the ion-beam sputtering deposition system. Monochromatic x-ray images were obtained from an experimental digital mammography setup with a scanning stage. The performance of the system was evaluated using a breast phantom, a spectrometer, and a radiation dosimeter. We measured the contrast-to-noise ratio and performed the 10% modulation function test to determine image quality and resolution. The monochromatic beam from the multilayer reflector had a full-width-at-half-maximum of 0.9 keV at 21.5 keV, and the reflectivity was 0.70, which was 90% of the designed value. The polychromatic and monochromatic x-rays showed radiation doses of 0.497 and 0.0415 mGy, respectively. The monochromatic x-ray image shows fibers, calcifications, and masses more clearly than the polychromatic x-ray images do. The image contrast of the monochromatic x-rays was 1.85 times higher than that of the polychromatic x-rays. The experimental mammography setup had a spatial resolution of 7 lp/mm with both x-rays. Monochromatic x-rays generated using a multilayer mirror may be a useful diagnostic tool for breast examination by providing high contrast imaging with a low radiation dose.

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.

Monochromatic X-ray Imaging System Using a W/C Multilayer Mirror

The possibility of monochromatic X-ray imaging using a conventional X-ray tube and a tungstencarbon (W/C) multilayer mirror was examined. The W/C multilayer mirror was designed to choose the characteristic X-ray (17.5 keV) generated from an X-ray tube with a molybdenum target and was fabricated by using an ion-beam sputtering deposition system. The X-ray reflectivity and the monochromaticity of the W/C multilayer mirror combined with the X-ray tube were 0.62 and 0.26 keV, respectively. Monochromatic X-ray slit images for a test sample were obtained from the monochromatic X-ray imaging system with a scanning stage. The slit images were combined together, and a full sample image was obtained. The monochromatic X-ray imaging system showed a spatial resolution of 26 lp/mm at 10% MTF, a better contrast, and a better signal-to-noise ratio compared with polychromatic X-ray imaging.

In-Plane and Out-of-Plane Exchange Biases in Epitaxial FePt-FeMn Multilayers With Different Crystalline Orientations

A systematic study of in-plane and out-of-plane exchange biases in FePt/FeMn multilayers epitaxially deposited onto MgO(100), MgO(110), MgO(111) substrates by ion beam sputter-deposition system was performed. It is found that the surface and volume anisotropy constants are largest when samples are growth in (100) direction. While the FePt thickness dependence of the blocking temperature show a similar behavior for samples grown with different crystalline orientations, the dependences of exchange bias field and the unidirectional anisotropy constant on FePt thickness behave differently for different orientations. The ratio of in-plane and out-of-plane exchange biases is not only strongly dependent on crystalline orientation but also on thickness of FePt layers suggesting that the spin structure at the interface in multilayer thin films may not be the same as that of the antiferromagnetic bulk.

Effect of crystalline orientation on parallel and perpendicular exchange biases in FePt∕FeMn multilayers

A systematic study of parallel and perpendicular exchange biases in FePt∕FeMn multilayers epitaxially deposited onto MgO(100), MgO(110), and MgO(111) substrates by ion beam sputter-deposition system was performed. The ratio of parallel and perpendicular exchange biases is not only strongly dependent on crystalline orientation but also on the thickness of FePt layers. The result suggests that the spin structure at the interface in multilayer thin films may not be the same as that of the antiferromagnetic bulk.

Perpendicular exchange bias mechanism in FePt∕FeMn multilayers

A systematic study of parallel and perpendicular exchange biases in FePt∕FeMn multilayers fabricated onto MgO(001) substrates by ion beam sputter deposition system was conducted. The blocking temperature of parallel exchange bias was found to be higher than that of the perpendicular one. The discrepancy was interpreted as due to the spin canting out of plane at the interface. A systematic simulation based on the Landau-Lifshitz-Gilbert equation was carried out, which was in reasonable agreement with the assumption of spin canting out of plane, suggesting the state of nonuniform distribution of spin direction at the interface.

Magnetic properties and structure of FePt/FeMn multilayers

A systematic study of the magnetic properties by ion beam sputter-deposition system, was conducted in conjunction with the structure of FePt/FeMn multilayers fabricated onto MgO(0 0 1) substrates. Both parallel and perpendicular exchange biases were observed in the multilayers and were found to decrease drastically, as the deposition temperature is higher than 350 °C, which is evidently due to the interdiffusion at the interface. The thickness dependence study shows that the perpendicular magnetic anisotropy observed in the multilayers originates from surface anisotropy, being consistent with the decrease of perpendicular magnetic anisotropy as the deposition temperature is increased. The difference between parallel and perpendicular blocking temperatures that was clearly observed, is possibly due to the spin canting out of plane at the interface.