Electron Beam Evaporation In Ultrahigh Vacuum Research Articles

Observations of self-assembled microscale triangular-shaped spikes in copper and silver thin films

We present observations on the formation of previously unreported self-assembled triangular-shaped morphological features in copper and silver thin films deposited at oblique and glancing vapor incidence angles by electron-beam evaporation in ultrahigh vacuum, and characterized them by using scanning electron microscopy (SEM). This systematic study investigates the morphology of 500nm thick copper and silver films, fabricated at vapor incidence angles between 0 and 85 degrees, from the substrate normal. Films fabricated at 50 degrees vapor incidence and greater exhibit triangular-shaped “microspikes” scattered seemingly randomly across the surface with areal densities on the order of 50 spikes per 10×10micrometer area. SEM analysis reveals that the microspikes increase in size with increasing vapor incidence angle. Films deposited at glancing vapor incidence angles (80 degrees and greater), are composed of inclined nanoscale columnar structures, with a high degree of interconnectivity between adjacent columns; where microspikes grow randomly from these tilted columns, and the spikes range in size from 100 to 2000nm in length.

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.

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.

Thirty-Day-Long Data Retention in Ferroelectric-Gate Field-Effect Transistors with HfO2 Buffer Layers

Metal–ferroelectric–insulator–semiconductor (MFIS) diodes and p-channel MFIS field-effect transistors (FETs) were fabricated and their electrical properties were characterized. These MFIS structures were formed using HfO2 as an insulating buffer layer, and SrBi2Ta2O9 (SBT) and (Bi,La)4Ti3O12 (BLT) as ferroelectric films. HfO2 buffer layers of about 8 nm physical thickness were deposited by ultrahigh-vacuum (UHV) electron-beam evaporation, then ferroelectric films of about 400 nm thickness were deposited by sol–gel spin coating. The fabricated p-channel MFIS-FETs with the SBT/HfO2 gate structure exhibited a drain current on/off ratio larger than 103 even after 30 days had elapsed. It was also found that the degradation of ferroelectricity was not pronounced even after applying 2.2×1011 bipolar pulses.

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.

Structure and thermal stability of (Zr0.6Al0.4)O1.8 thin film on strained SiGe layer

Zr0.6Al0.4O1.8 dielectric films were deposited directly on strained SiGe substrates at room temperature by ultra-high vacuum electron-beam evaporation (UHV-EBE) and then annealed in N2 under various temperatures. X-ray diffraction (XRD) reveals that the onset crystallization temperature of the Zr0.6Al0.4O1.8 film is about 900°C, 400°C higher than that of pure ZrO2. The amorphous Zr0.6Al0.4O1.8 film with a physical thickness of ∼12nm and an amorphous interfacial layer (IL) with a physical thickness of ∼3nm have been observed by high-resolution transmission electron microscopy (HRTEM). In addition, it is demonstrated there is no undesirable amorphous phase separation during annealing at temperatures below and equal to 800°C in the Zr0.6Al0.4O1.8 film. The chemical composition of the Zr0.6Al0.4O1.8 film has been studied using secondary ion mass spectroscopy (SIMS).

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.

AlN thin films fabricated by ultra-high vacuum electron-beam evaporation with ammonia for silicon-on-insulator application

The application of silicon-on-insulator (SOI) substrates to high-power integrated circuits is hampered by the self-heating effect due to the poor thermal conductivity of the buried SiO 2 layer. We introduce aluminum nitride (AlN) thin films formed by ultra-high vacuum electron-beam evaporation with ammonia as an alternative. The chemical composition, surface morphology, and electrical properties of these films were investigated. The film synthesized at 800 °C shows a high AlN content, low surface roughness with a root-mean-square value of 0.46 nm, and high electrical resistivity. Based on thermodynamic analysis and our experimental results, the mechanism of AlN formation is proposed.

Structure and electric property comparison between Ge nanoclusters embedded in Al2O3 and Al2O3/ZrO2

Metal-insulator-semiconductor (MIS) structures containing Ge nanocrystals embedded in both Al2O3 and ZrO2/Al2O3 are fabricated by an ultra-high vacuum electron-beam evaporation method. Secondary ion mass spectroscopy (SIMS) results indicate that Ge embedded in Al2O3 diffuses towards the surface of the Al2O3 layer after annealing at 800°C in N2 ambient for 30 min. Ge embedded in ZrO2/Al2O3 is stable, thus inducing less leakage current. Capacitance voltage studies indicate that annealing can effectively passivate the negatively charged trapping centers. Memory effect of the Ge nanoclusters is verified by hysteresis in the C-V curves in the Al2O3/Ge+Al2O3/Al2O3 and ZrO2/Ge+Al2O3/Al2O3 samples.

Heteroepitaxial diamond film growth: the a-plane sapphire–iridium system

A substrate system with suitable physical and chemical properties is a necessary component for achieving large-scale heteroepitaxial diamond growth. We have developed a two-stage process to produce (001) diamond films using a-plane (112̄0) α-Al 2O 3 (sapphire) as a substrate. Epitaxial (001) iridium films are first grown on terraced, vicinal a-plane sapphire by ultra-high vacuum electron-beam evaporation at 950 °C. The epitaxial relationship, Ir(100)‖Al 2O 3(112̄0) with Ir[011]‖Al 2O 3 [11̄00], was determined by analysis of X-ray and electron backscattering diffraction. For a 300-nm thickness of Ir, a (200) rocking curve yielded a linewidth of 0.2°. After transfer to a CVD system, a diamond film was grown on the Ir layer by low-pressure chemical vapor deposition using methane and hydrogen. A key step in the process is the initial exposure of the epitaxial Ir to a d.c.-biased plasma that leads to uniform coverage of the surface by a dense array of diamond crystallites prior to growth. A subsequent growth step for approximately 60 min yields a continuous and highly homogenous (001) diamond film over areas more than 50 mm 2. The epitaxial relationship between diamond and the Ir substrate is diamond(001)‖Ir(001) with diamond[100]‖Ir[100]. The films have also been characterized by AFM, SEM, TEM, and Raman. As a result of the superior thermomechanical properties of sapphire, this heteroepitaxial system may enable wafer-size heteroepitaxial diamond growth in the near future.

High frequency capacitance–voltage characterization of Al2O3/ZrO2/Al2O3 in fully depleted silicon-on-insulator metal–oxide–semiconductor capacitors

Al 2 O 3 / ZrO 2 / Al 2 O 3 gate stacks were prepared on ultrathin silicon-on-insulator (SOI) by ultrahigh vacuum electron-beam evaporation and postannealed in N2 at 450 °C for 30 min. A three clear nanolaminate layered structure of Al2O3 (2.1 nm)/ZrO2 (3.5 nm)/Al2O3 (2.3 nm) was observed with high-resolution cross-sectional transmission electron microscopy. High frequency capacitance voltage (C–V) characteristics of the fully depleted (FD) SOI metal–oxide–semiconductor (MOS) capacitor at 1 and 5 MHz were studied. It is the minority carriers that determine the high frequency C–V properties, which are opposite to the case of bulk MOS capacitors. And the series resistance of the SOI is the determinant factor of the high frequency characteristics of the FD SOI MOS capacitors.

Nanoscale silicon prepared on different substrates using electron-beam evaporation and their field-emission property

Silicon nanorods (about 10–35 nm height) on silicon and porous silicon substrates were synthesized using ultra-high vacuum electron-beam evaporation in the present of a Fe catalyst. Atomic force microscopy (AFM) is used to estimate the dimension and check the morphology of the silicon nanoclusters. The electron field emission is used to reveals the property of silicon nanorods grown on different substrates.

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.

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.