Ultra-high Vacuum Electron Beam Research Articles

Investigation of E-Beam Evaporated Silicon Film Properties for MEMS Applications

This paper investigates the crystallinity, microstructure, surface morphology, stress characteristics, and Young’s Modulus of ultrahigh vacuum (UHV) electron-beam (E-beam) evaporated silicon films with a low thermal budget. The films are evaporated at various substrate temperatures ranging from 200 °C–625 °C, deposition rates ranging from 50 to 400 nm/min, and annealed at 600 °C for various durations. Some of the preliminary results were reported by Michael and Kwok. The results indicate that the film characteristics of the evaporated silicon films are significantly different from and better suited for microelectromechanical systems (MEMS) applications than low pressure chemical vapor deposition silicon films, commonly used for MEMS devices. The very attractive properties of UHV E-beam deposited silicon films are remarkably low residual stress (both average and gradient), very smooth surface morphology, and thick layers at a low thermal budget with reasonably large deposition rates. Two different mechanisms have been identified as responsible for initiating the formation of crystal grains in these films: 1) kinetic energy of evaporated silicon atoms; and 2) thermal energy from the substrate heating. The first mechanism leads to fine columnar grains responsible for the smooth surface morphology and easily controllable low stress characteristics. The second mechanism results in coarse grain formation with a relatively higher proportion of (111) oriented grains. Cantilever beams of 30- $\mu \text{m}$ thickness have been fabricated from such films with rms roughness of $\mu \text{m}$ with Young’s Modulus of 169 GPa. [2015-0096]

Hydride formation in single palladium and magnesium nanoparticles studied by nanoplasmonic dark-field scattering spectroscopy.

Scrutinizing functional nanosystems and relating details in their size, chemistry, and geometry to functionality remains a significant experimental challenge. Following the concept of indirect nanoplasmonic sensing (INPS), the exploitation of truncated Au nanocones with functionalized tips, nanofabricated in a one step, are used as single nanoplasmonic sensors for dark-field scattering spectroscopy measurements of the hydride formation Au in single Pd and Mg nanoparticles.

MeV Au ion induced modifications at Co/Si interface

We report on room temperature MeV Au ion induced modifications at the Co/Si interfaces. Nanometers size thin film of Co and Si were grown by ultra high vacuum (UHV) electron beam evaporation technique on Si(1 1 1) surface and were irradiated by 1.5 MeV Au 2+ ions at a fluence of 5 × 10 14 ions cm −2. High-resolution transmission electron microscopy (HRTEM) along with energy filter imaging technique has been employed to study the formation of Co–Si alloy at the interface. Formation of such surface alloy has been discussed in the light of ion-matter interaction in nanometer scale regime.

Epitaxial Fe3Si films on GaAs(100) substrates by means of electron beam evaporation

This paper presents results on the preparation, structural, electrical and magnetic properties ofFe3Si films as a representative for a Heusler alloy-like compound which are known as half-metallicmaterials with ferromagnetic behaviour. The films have been prepared by means of ultra-highvacuum (UHV) electron beam evaporation with the aim of achieving epitaxial growth onGaAs(100) substrates. The main focus of this work is the structural characterization of theFe3Si films grown on GaAs by means of high resolution transmissionelectron microscopy (TEM) to confirm the epitaxial growth. ForFe3Si with a composition in the vicinity of stoichiometry an almost lattice-matched growth onGaAs(001) has been observed characterized by a high crystalline quality and a goodinterface perfection. Besides the studies on cross-sectional samples by TEM data fromreflection high energy electron diffraction (RHEED) and x-ray diffraction (XRD) werealso included into the discussion. The electrical and magnetic parameters of thefilms studied are found to be in good agreement with data reported for the bestFe3Si molecular beam epitaxy (MBE) layers. As evidenced by x-ray diffraction, transmission electronmicroscopy, resistivity and magnetic measurements, we find an optimum growth temperature of 280–350 °C to obtain ferromagnetic layers with high crystal and interface perfection as well as a highdegree of atomic ordering.

Study of defects and thermal stability of ultrathin Cu films on Ta(110) and Ta(100) by thermal helium desorption spectrometry

Thermal helium desorption spectrometry has been used to study the interaction of helium with defects in Cu films (5–300 Å) deposited on Ta(110) and Ta(100) single crystals by ultrahigh vacuum electron beam evaporation. The thermal stability of the Cu films was also investigated. Cu films on Ta(110) and Ta(100) at room temperature are metastable and on heating, the films transform into islands. The temperature at which this takes place is strongly dependent on the Cu film thickness and for a given thickness (> 40 Å) occurs at a lower temperature on Ta(100) than on Ta(110). The activation energy for island formation is 1.6 ± 0.4 eV for 50 Å Cu/Ta(110) and 0.8 ± 0.1 eV for 100 Å Cu/Ta(100) obtained by Kissinger analysis. The geometry of the Cu islands resulting from annealing 50 Å Cu films at 1000 K for 10 s depends strongly on the Ta substrate orientation. There is evidence for the stressed states of both the Cu films and the Ta substrates. Helium release from monovacancies and vacancy clusters in Cu films (> 75 Å) on Ta(110) and Ta(100) was detected at ~ 750 K and ~ 800–1000 K respectively. The sublimation of the Cu films from the Ta substrates could be observed by the release of retained helium at ~ 1300 K.

Influence of preparing process on total-dose radiation response of high- k Hf-based gate dielectrics

The purpose of this paper is to report some total-dose radiation response experimental results of Hf-based dielectric films including HfON film prepared by ion beam enhanced deposition method (IBAD) and HfO 2 film by ultra high vacuum electron beam evaporation system (UV-EBE). MIS structures with HfON and HfO 2 gate dielectrics were irradiated by10 keV X-rays with the dose from 0 to1 × 10 6 rad (Si). Electrical measurement results showed that trap charge density and interface trap charge density of HfON dielectric films are much smaller than HfO 2 dielectric films, and the flatband and midgap voltage shifts in HfON films are also smaller than that in HfO 2 film. AFM and XRD results show that HfON films are smooth and thermal stability even under 800 °C high temperature annealing.

High Speed Photon Number Resolving Detector with Titanium Transition Edge Sensor

We have developed new photon number resolving detectors with titanium transition edge sensors (Ti-TESs) for a high counting rate operation in quantum information. The titanium superconducting films were fabricated by ultra-high vacuum electron beam evaporation, and showed a sharp superconducting transition at 359 mK. The device was coupled to a single mode optical fiber, and cooled down to 100 mK. Some of optical responses of the devices were measured by illuminating heavily attenuated laser pulses at wavelengths of 405 and 1550 nm. As a result, the device showed a fast decay time constant of 300 ns, which enables the operation at the counting rate of 400 kcps. The energy resolution was 0.76 eV at 405 nm and 0.68 eV at 1.5 µm, that make it possible to clearly resolve the number of photons of incident laser pulses. These features of the high counting rate operation and the reasonable energy resolution are very promising for quantum information field.

Preparation of one-dimensional photonic crystal with variable period by using ultra-high vacuum electron beam evaporation

One-dimensional photonic crystal with variable period has been prepared by using the method of ultra-high vacuum electron beam evaporation. Advantage of this method is gaining variable period easily. The transmittance of the photonic crystal has been also studied.

Self-Assembled Nanostructures on VSe2Surfaces Induced by Cu Deposition

Analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have been applied for the characterization of evolution, lateral arrangements, orientations, and the microscopic nature of nanostructures formed during the early stages of ultrahigh vacuum electron beam evaporation of Cu onto surfaces of VSe2 layered crystals. Linear nanostructure of relatively large lateral dimension (100-500 nm) and networks of smaller nanostructures (lateral dimension: 15-30 nm; mesh sizes: 500-2000 nm) are subsequently formed on the substrate surfaces. Both types of nanostructures are not Cu nanowires but are composed of two strands of crystalline substrate material elevating above the substrate surface. For the large nanostructures a symmetric roof structure with an inclination angle of approximately 30 degrees with respect to the substrate surface could be deduced from detailed diffraction contrast experiments. In addition to the nanostructure networks a thin layer of a Cu-VSe2 intercalation phase of 3R polytype is observed at the substrate surface. A dense network of interface dislocations indicates that the phase formation is accompanied by in-plane strain. We present a model that explains the formation of large and small nanostructures as consequences of compressive layer strains that are relaxed by the formation of rooflike nanostructures, finally evolving into the observed networks with increasing deposition time. The dominating contributions to the compressive layer strains are considered to be an electronic charge transfer from the Cu adsorbate to the substrate and the formation of a Cu-VSe2 intercalation compound in a thin surface layer.

Metal-induced nanostructures on surfaces of layered chalcogenides

The development of layered dichalcogenide crystal surfaces during early stages of metal deposition has been investigated, using ultra-high vacuum electron beam evaporation of copper at ambient temperature onto (0 0 0 1) VSe 2 crystal surfaces as model case. Analytical transmission electron microscopy techniques, scanning electron microscopy, and atomic force microscopy have been combined to characterize the microscopic nature of the surface structures and the self-assembled formation of surface nanostructures that form as large nanostructures (lateral dimensions > 100 nm) and as networks of smaller nanostructures (lateral dimensions ∼ several 10 nm). Nearly contiguous ultrathin layers of a copper-rich crystalline surface phase are observed for deposition stages at a nominal Cu coverage of 1 nm and above. The observations indicate that compressive in-plane strains are induced in the VSe 2 surface layers by the formation of a copper-rich crystalline phase by intercalation, with possible contributions of an electronic charge transfer from copper atoms to the substrate during the earliest deposition stages. Above a critical value the surface layer strains are relaxed by formation of surface folds, nanostructure networks and interface dislocations.

Studies on Al2O3/ZrO2/Al2O3 high K gate dielectrics applied in a fully depleted SOI MOSFET

Al2O3/ZrO2/Al2O3 gate stacks were prepared on ultrathin SOI (Silicon on insulator) substrates by ultrahigh vacuum electron beam evaporation and post-annealed in N2 at 450°C for 30 min. Three clear nanolaminate layered structure of Al2O3(2.1 nm)/ZrO2(3.5 nm)/Al2O3(2.3 nm) was observed with a high-resolution cross-sectional transmission electron microscope (HR-XTEM). High frequency capacitance voltage (C-V) characteristics of a fully depleted (FD) SOI MOS capacitor at 1 and 5 MHz were studied. The minority carriers determine the high frequency C-V properties, which is opposite to the case of bulk MOS capacitors. The series resistance of the SOI substrate is found to be the determinant factor of the high frequency characteristics of FD SOI MOS capacitors.

Interfacial stability between zirconium oxide thin films and silicon

We studied the interfacial properties of ZrO 2 thin films deposited by ultra-high vacuum electron beam evaporation (UHV-EBE). Some samples were annealed in O 2 ambient by rapid thermal annealing (RTA) at different temperatures ranging from 300 to 700 °C. X-ray photoelectron spectroscopy (XPS) of all films, whether annealed or not, revealed that the binding energies of Zr3d 5/2 and Zr3d 3/2 are 183.5 and 185.7 eV, respectively, which are the typical peak values of Zr 4+. X-ray diffraction (XRD) results showed that the as-deposited film was amorphous, and it remained stable up to the annealing temperature of 600 °C. But when the temperature increased further attaining 700 °C, it began to crystallize. All the surfaces of the thin films were smooth and uniform. The typical RMS roughness ranged from 0.546 to 0.666 nm across an area of 50×50 μm. Steep and clear interfaces between zirconium oxide thin film and Si substrate were obtained both by spreading resistance profile (SRP) and cross-sectional transmission electron microscopy (XTEM). High quality of the interface without interfacial oxide was achieved when the annealing temperatures were kept under 600 °C, but when the temperature was raised to 700 °C, ∼1-nm thick oxide product was detected by XTEM. The component of the oxide product is not exactly known yet, but may be SiO x or ZrSi x O y .

Interfacial and microstructural properties of zirconium oxide thin films prepared directly on silicon

Zirconium oxide thin films were deposited directly on Si by ultra high vacuum electron beam evaporation (UHV-EBE) and rapid thermal annealed (RTA) in O 2 ambient at different temperatures ranging from 300 to 800 °C. X-ray photoelectron spectroscopy (XPS) revealed zirconium is in the fully oxidized state of Zr 4+. X-ray diffraction (XRD) results showed that as-deposited thin films were amorphous. When the annealing temperature increased higher than 700 °C, the films began to crystallize. The surface topology was studied with atomic force microscopy (AFM) and the surface of the 700 °C-annealed sample was more rougher than that of the 600 °C-annealed sample, due to its potentially faceted interfaces. And the typical RMS roughness ranged from 0.546 to 0.666 nm across an area of 50 μm×50 μm. Sharp interfaces between ZrO 2 and Si were obtained both by spreading resistance profile (SRP) and cross-sectional transmission electron microscope (XTEM). The interfacial oxide (∼1 nm) was not detected until annealing temperature amounting to 700 °C and the exact compositions were not known yet.

Dominant diffusing species in the growth of amorphous interlayer between Yb metal thin films and crystalline Si

The dominant diffusing species in the formation of an amorphous interlayer between Yb thin films and crystalline Si substrates have been determined by a Mo cluster marker experiment. Metal thin films with multilayered structures were deposited on both (111) and (001)Si substrates in an ultrahigh vacuum electron beam evaporation system. The positions of the Mo cluster markers relative to the Si substrates, before and after heat treatment, were determined by high-resolution transmission electron microscopy and energy dispersive analysis of x-ray as well as autocorrelation function analysis. The displacement of the Mo cluster markers in the amorphous interlayer during the Yb–Si interdiffusion indicates that Si atoms constitute the dominant diffusing species during the growth of amorphous interlayer.

Silicon-on-Insulator Structure Fabricated by Electron Beam Evaporation of Si on Porous Si and Epitaxial Layer Transfer

Epitaxial monocrystalline Si was grown on porous silicon by ultra-highvacuum electron beam evaporation. Results of reflection high-energyelectron diffraction, atomic force microscopy, cross-sectiontransmission electron microscopy and Rutherford backscatteringspectrometry and channelling (RBS/C) show that the epitaxial layeris of a good quality. Furthermore, silicon-on-insulator materials weresuccessfully produced by bond and etch back of porous silicon. Thequality of the silicon-on-insulator samples was investigated by RBS/Cand spreading resistance profiling. Experimental results show that boththe crystalline quality and electrical quality are good. In addition,the interface between the top Si layer and SiO2 buried layer is verysharp.

X-ray multilayer optics: growth and characterization

Growth of X-ray multilayer optics is done using an ultra high-vacuum electron beam deposition. High-vacuum reflectometer station on Indus-1 synchrotron source is described. Representative studies on Mo/C X-ray multilayers are presented.

Synthesis and Properties of Al-Based Amorphous and Microcrystalline Thin Films

ABSTRACTAmorphous metal alloys are ideally suited for interconnects in micro-electromechanical sys- tems (MEMS) because of their resistance against stress- and electromigration, and their stability in chemically aggressive environments, which should both lead to a substantial improvement of lifetime and reliability of robust sensors. While amorphous refractory metal alloys and amor- phous silicides are excellent interconnect materials for devices operating at elevated tempera- tures, these systems lack the cost-effective and easy interconnect processing of the prevalent polycrystalline aluminum alloy metallizations. Amorphous aluminum alloys are applicable to devices operating at up to 200°C, and their stressmigration resistance and chemical stability is far superior to conventional polycrystalline aluminum alloys. These new metallizations are very promising for processing interconnects, in particular because of their high strength and ductility, though having low density, and their relatively low electrical resistivity compared to other amor- phous metal alloys. Therefore these metallizations are especially suited for surface acoustic wave (SAW) sensors, where the interconnects are exposed to considerable mechanical strains. In this work amorphous Aluminum Yttrium alloy thin film metallizations deposited on appropriate sub- strates at room temperature (R.T.) by ultra-high vacuum (UHV) electron beam evaporation will be presented, and their mechanical and electronic properties together with their temperature sta- bility will be investigated.

Giant magnetoresistance and structural properties in Co/Cu/Co sandwiches with Si and Cr buffer layers

Cobalt 5.5 nm/Cu 3 nm/Co 5.5 nm sandwiches with Si and Cr buffer layers were prepared by ultra-high vacuum electron beam evaporation. A large in-plane anisotropy of the giant magnetoresistance (GMR) effect was found in Si buffered sandwiches when the buffer layer thickness was equal to or larger than 0.9 nm. In the easy axis, the GMR effect reached a value of 5.5% with a high field sensitivity of approximately 0.7%/Oe, while in Cr-buffered Co/Cu/Co sandwiches, the GMR effect showed only in-plane isotropic properties with a maximum GMR value of 6%. The XRD spectrum and HRTEM image revealed that there exists a Co 2Si compound between the Si buffer and the lower Co magnetic layer. All these results indicate that the anisotropic GMR effect in Si-buffered sandwiches results from the cobalt silicide between the Si buffer and the lower Co magnetic layer.

A study of the NiSi to NiSi 2 transition in the Ni–Si binary system

The growth mechanisms of the transition from polycrystalline NiSi to single-crystal NiSi 2 have been investigated. Samples were prepared by depositing Ni on 〈100〉 Si substrates by ultra high vacuum electron-beam deposition followed by vacuum annealing to form a silicide. Experiments were carried out at the transition temperature of 750°C for different annealing times. Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM), scanning electron microscopy (SEM), Auger emission spectroscopy (AES) and X-ray diffraction (XRD) were employed with special emphasis placed on scanning and transmission electron microscopy. Cross-sectional examination in the transmission electron microscope reflects the coexistence of nickel monosilicide and nickel disilicide for samples annealed at 750°C. Scanning electron microscopy shows interesting surface morphology of samples in which island-like NiSi 2 growth takes place in an NiSi thin film. Grain boundaries in the initial and final stages of NiSi 2 formation are characterized by holes which extend from the surface to the silicon substrate. A mechanism is proposed to account for these observations by involving the following: lattice diffusion of Ni into the Si substrate, the conversion of NiSi grains to NiSi 2 via nucleation and diffusion processes and lateral grain growth resulting in accumulation of vacancies on grain boundaries resulting in holes.

Structural and electrical characterization of AIN thin films obtained by nitridation of Al/Si substrate

AlN thin films have been grown on Al-covered Si(100) substrates using nitridation in high-purity nitrogen ambient, where the Al layer was previously deposited by ultrahigh vacuum (UHV) electron beam evaporation. The temperature of nitridation plays an important role in the formation of AlN films. The films have been characterized by x-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy, transmission electron microscopy, and spreading resistance profile. Results indicate that the AlN films formed by nitridation at 1000°C for 30 min exhibit the preferred orientation of (002), with spreading resistance above 108Ω.