Photoelectron Spectroscopy Depth Profiling Research Articles

XPS Depth Profile Analysis of a Thin Non-Conducting Titanate Superlattice

New BaTiO 3 -SrTiO 3 (BTO-STO)-superlattices which may be interesting for future electronic applications have been investigated by X-ray photoelectron spectroscopy (XPS) depth profiling. At first XPS measuring conditions were optimized for that non-conducting and thin layer systems (21 nm double layer thickness) considering the practical instrumental limitations. Second a simulation of the sputtering process for the concrete experimental conditions were done by a dynamic T-DYN code. By comparison of experimental and simulated depth profiles the maximum sample roughness could be estimated to be in the range of 2 nm.

Hydrogen plasma etching method for depth analysis by x-ray photoelectron spectroscopy

An etching device using a hydrogen plasma has been developed for x-ray photoelectron spectroscopy (XPS) depth profile analysis of organic compounds. The effect of the hydrogen plasma discharge was investigated using a photoresist film containing benzene rings, C– O bonds and C– F bonds formed on an Si(100) wafer. The condenser-type discharge tube employed is composed of electrodes, an etch tunnel (shield tube) and a quartz glass tube. Both the electrodes and etch tunnel have many holes. Experimental results show that the etching rate of the photoresist film is 26.7 nm min−1 at an r.f. power of 200 W, a gas flow rate of 6.0 cc min−1 and a hydrogen gas pressure of 26.6 Pa. This rate is higher than that achieved by the use of a conventional high-speed etching ion gun. It is observed that the etched surface is flatter than that obtained by parallel plate electrodes and an Ar ion beam. The amounts of C, O and F after hydrogen plasma etching were not remarkably different from those before etching, and the shape of the C 1s spectrum did not show any change, indicating no change in chemical bonding. The results show that hydrogen plasma etching is very effective for depth profile analysis of organic polymers by XPS. Copyright © 2000 John Wiley & Sons, Ltd.

Evidence of transition metal diffusion during hydrothermal ceramic film growth: Ba(Ti,Zr)O3on layered Ti–Zr alloy

Ti–Zr alloy thin films of 20–60 nm in thickness were evaporated on Pt-coated silicon wafers. The films exhibited a layered Ti–Zr depth distribution. The films were then treated hydrothermally in 0.25 M Ba(OH)2at 150 and 200 °C for 4–8 h. Films treated at 150 °C did not exhibit reflections from the Ba(TixZr1−x)O3perovskite structure by x-ray diffraction, although a slight barium content was detected by x-ray photoelectron spectrometry. On the other hand, the films treated hydrothermally at 200 °C revealed reflections corresponding to perovskite Ba(TixZr1−x)O3. These films exhibited a homogeneous titanium and zirconium depth distribution, as shown by x-ray photoelectron spectroscopy and Auger depth profiles, proving that either titanium or zirconium ions diffuse during the hydrothemal treatment. The initial Ti–Zr film was completely consumed during the hydrothermal process, leading to a film of homogeneous composition (Ba, Ti, and Zr) up to the interface with the platinum layer.

A comparison of Schottky-limited and space-charge-limited currents in SrBi2Ta2O9 thin films

Stoichiometric SrBi2Ta2O9 (SBT)-Pt contact exhibits a Schottky contact with a barrier height of 0.9 eV, but small amounts of excess Bi produce ohmic contacts at low voltages, followed by perfectly quadratic space-charge-limited current-voltage dependences (SCLC). Attempts to fit Schottky models to the temperature dependence of leakage currents in Bi-rich SBT films yield unphysical results, including a negative barrier height. We have generalized the SCLC theory of Rose to incorporate the temperature dependence of the dielectric constant. This theory has a single parameter T* which is a measure of trap energy distribution. A single T* value fits our data at all temperatures and all voltages. These macroscopic leakage current data are correlated with X-ray photoelectron spectroscopy (XPS) depth profiles that show how excess Bi has diffused into the electrode-ferroelectric interface region.

Characterizaton of Pecvd Fluorinated Silicon Oxides and Stabilization of Interaction with Metals

ABSTRACTFluorinated silicon oxide films were prepared in a plasma enhanced chemical vapor deposition reactor using TEOS, O2, and either C2F6 or NF3. Properties such as deposition rate, film refractive index, dielectric constant, density, and fluorine concentration were investigated as a function of experimental conditions. Based on nuclear reaction analysis (NRA) and Fourier Transform Infrared (FTIR) measurements, no single linear relationship was found between fluorine concentration or film density and dielectric constant. Special attention was paid to the interaction of fluorine with metals. NRA and X-ray photoelectron spectroscopy (XPS) depth profiles showed that fluorine diffuses rapidly through aluminum and piles up at the free surface. The effect of various plasma treatments was investigated to passivate the surface of fluorinated silicon oxide. CF4 - O2 plasma treatment of the fluorinated oxide before aluminum deposition produced significant improvement in inhibiting fluorine diffusion into aluminum without increasing the dielectric constant.

Experimental obviousness of the necessity for a thin Ni interfacial layer to obtain highly ordered photoconductive MoS2 films

It is shown that photosensitive films can be obtained by solid state reaction, induced by annealing, between the constituents Mo and S sequentially deposited in thin film form if the substrate is coated with a thin (10–20 nm) NiCr layer. The thin Mo and S layers are deposited in the atomic ratio Mo : S=1 : 3. The substrates used are mica sheets. An annealing at 1073 K for 30 min under argon flow allows one to obtain highly 2H–MoS2 crystallized films. The thickness of the crystallites is similar to that of the films; they have their c-axes perpendicular to the plane of the substrate. After crystallization, X-ray photoelectron spectroscopy (XPS) depth profiles show that Ni is diffused all over the thicknesses of the films and that 1 at% of Ni is visible at the surfaces of the films. The direct current (d.c.) conductivity of these films is nearly similar to that of single crystals. The films are photosensitive. The room temperature photoconductivity, which results from interband transitions, allows one to measure the direct band gap that is similar to that of a single crystal. When bare mica substrates (without Ni) are used MoS2 films are obtained but they are poorly crystallized and not photoconductive, which shows an NiCr interfacial layer is necessary. Probably a melting phase NiSx forms, which increases the mobility of the atom at grain boundaries.

Epitaxial growth of aluminum nitride layers on Si(111) at high temperature and for different thicknesses

We present the epitaxial growth by rf reactive sputtering of aluminum nitride on Si(111) at high temperature. The grain size of the obtained films was sufficient to obtain a good low energy electron diffraction (LEED) pattern from which we determined a lattice parameter of 3.1 Å, indicative of fully relaxed films. The surface of the film was examined in situ by Auger electron spectroscopy (AES); no contamination was detected, with the exception of low levels of oxygen. The film and its interface were studied by high resolution electron energy loss spectroscopy (HREELS), x-ray photoelectron spectroscopy (XPS) depth profiling, and transmission electron microscopy (TEM). Again, a low concentration of oxygen and no carbon contamination were detected by XPS. Three different growth methods were applied to the deposition of aluminum nitride at high temperature. The obtained films were studied in order to determine the influence of the methods on the interface, on the ‘bulk structure’ of the film, and on its surface. Each has been shown to have particular characteristics. The first one, performed at a temperature of 1000 °C, and including a cleaning of the surface by exposure to Al flux, was characterized by an interfacial layer with no long-range order and increasing the interaction between the film and the substrate. The second growth consisting of deposition at the same high temperature has shown a good surface quality for very thin layers (<50 Å ) and the absence of an interfacial layer. The last method, based on a first step of growth at low temperature (700 °C), resulted in good quality thick layers which allowed us to determine the infrared dielectric constants of aluminum nitride by HREELS.

Si-YBaCuO intermixing and reactive patterning technique

A novel Si-YBaCuO intermixing technique has been developed for patterning YBaCuO superconducting thin films on both insulating oxide substrates (MgO) and semiconductor substrates (Si). The electrical, structural, and interfacial properties of the Si-YBaCuO intermixed system have been studied using resistivity, x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy and Auger depth profiling measurements. The study showed that the reaction of Si with YBaCuO and formation of silicon oxides during a high temperature process destroyed superconductivity of the film and created an insulating film. On a MgO substrate, the patterning process was carried out by first patterning a silicon layer using photolithography or laser-direct-writing, followed by the deposition of YBaCuO film and annealing. For a silicon substrate, thin metal layers of Ag and Au were patterned as a buffer mask which defines the YBaCuO structures fabricated thereafter. Micron-sized (2-10 Μm) superconducting structures with zero resistance temperature above 77 K have been demonstrated. This technique has been used to fabricate current controlled HTS switches and interconnects.

The Epitactic Growth of Oxides on Si

The epitactic growth of oxides on Si requires structural and chemical compatibility between the substrate and film. The growth of (Ba0.7,Sr0.3)TiO3 (BST) by pulsed laser deposition on HF-cleaned Si (001) and Si with a buffer layer of CaF2 was studied. The BST can form a low misfit interface with Si and CaF2 but chemical reactions between the BST and the Si prevented the epitactic growth on Si. An x-ray photoelectron spectroscopy (XPS) depth profile indicated that the BST had reacted to form a silicate and titanium silicide. The BST on CaF2 -Si(00l) substrate was partially epitactic and formed a 45° rotated orientation relationship such that the Si (110) is parallel to the BST (100).

Use of Si-YBaCuO Intermixed System for Patterning of Superconducting Thin Films

AbstractA Si-YBaCuO intermixed system has been formed using rapid thermal annealing (RTA) of Cu/BaO/Y2O2/Si layered structures, which were deposited on MgO substrates by electron-beam evaporation. The electrical and structural properties of the Si-YBaCuO system have been analyzed by resistivity, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy and Auger depth profiling measurements. It was found that Si mixed with YBaCuO during annealing, thus creating an insulating film. This effect has been used to pattern YBaCuO films. The patterning process was carried out on an underlying silicon layer, rather than the YBaCuO film itself, using conventional photolithography or laser etching. After YBaCuO film deposition and RTA, the patterned region became superconducting separated by Si-YBaCuO intermixed areas. Micron-sized line features with Tc's above 77 K have been demonstrated.

Quantitative depth profile and bulk analysis with high dynamic range by electron gas sputtered neutral mass spectrometry

The need for quantification in thin‐film and surface analysis has increased the interest in sputtered neutral mass spectrometry (SNMS) since this method is less affected by matrix effects than secondary ion mass spectrometry (SIMS) and in addition does not suffer from preferential sputtering like Auger electron spectroscopy and x‐ray photoelectron spectroscopy depth profiles, as it measures sputtered fluxes instead of surface concentrations. Among the different postionization techniques, electron gas SNMS [H. Oechsner and W. Gerhard, Z. Phys. B 221, 41 (1975)] using a hot and high‐density rf‐coupled plasma, is the one most established. Its field of applications has until recently been limited by two artifacts: mass resolved residual gas line interferences in SNMS spectra and structureless background induced by photons and electrons of the plasma. Both problems are overcome by a new ion optical arrangement which combines a three‐electrode retarding field configuration, adjusted to the maximum of plasma pot...

Ag/Ai schottky contacts on n-InP

Schottky contacts have been fabricated onn- InP using a Ag/Al/InP configuration where the Ag and Al thicknesses are 1000 and 40-50A, respectively. Diodes fabricated on InP substrates withn ≈ 7 x 1016 cm-3, have effective barrier heights, Obeff, of 0.4 eV and reverse bias leakage current densities of >4 A/cm2 atVr = - 3V. Appropriate heat treating at temperatures between 400–500° C raises barrier heights by as much as 0.25 eV, resulting in Obeff ≈ 0.65 eV and reverse bias leakage current densities less than 0.002 A/cm2. Diode characteristics are found to vary dramatically with different surface preparations prior to metallization; results of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profiling studies indicate that native oxides which are predominantly InPO4 produce superior contacts and that aluminum first reacts with the native oxide and then migrates through the silver to the free metal surface which results in the dramatic improvements observed upon annealing.