bluuebunny/crossref_metadata_2025 huggingface dataset:
Helicon wave plasma reactor employing single-loop antenna
Authors: Jiwari Nobuhiro , Fukasawa Takayuki , Kawakami Hiroshi , Shindo Haruo , Horiike Yasuhiro
Published: July 2002

Helicon wave plasma excited by a single-loop antenna and etching characteristic of Si and SiO2 is studied on a basis of plasma parameters and wave patterns measurements. A wide variety of wavelength with space is observed in the single-loop antenna, and because of no external boundary for the wavelength, the best match of the rf source with plasma is possible. This fact is ascribable to the density enhancement rather than in the conventional double-loop antenna. A condition that the magnetic field is lowered in the antenna portion is also effective on the density enhancement. This is explained by a longer time in resonance of the electron. The etching uniformity is also improved by using a larger diameter one-loop antenna, with a great usefulness.
Investigation of plasma etch induced damage in compound semiconductor devices
Authors: Shul R. J. , Lovejoy M. L. , Hetherington D. L. , Rieger D. J. , Vawter G. A. , Klem J. F. , Melloch M. R.
Published: July 2002

We have investigated the electrical performance of mesa-isolated GaAs pn-junction diodes to determine the plasma-induced damage effects from reactive ion and reactive ion beam etching (RIBE). A variety of plasma chemistries (SiCl4, BCl3, BCl3/Cl2, and Cl2) and ion energies ranging from 100 to 400 eV were studied. We have observed that many of the reactive ion etching BCl3/Cl2 plasmas and RIBE Cl2 plasmas yield diodes with low reverse-bias currents that are comparable to the electrical characteristics of wet-chemical-etched devices. The reverse-bias leakage currents are independent of surface morphology and sidewall profiles.
Smart thin film TiNi/piezoelectric heterostructures
Authors: Mercado P. G. , Jardine A. P.
Published: July 2002

Thin film layers of shape memory alloys and ferroelectric ceramics can produce a family of ‘‘smart’’ heterostructures capable of performing both sensing and actuating functions. Important issues in the synthesis of these active structures are the ability to generate the appropriate crystalline phases of each material while producing defect-free homogeneous high quality films. The compatibility of sol–gel processed Pb(Zr,Ti)O3 (PZT) thin films with thin film shape memory effect TiNi substrates were investigated. Thin film TiNi was deposited on quartz substrates by physical sputter deposition utilizing a TiNi target in a ultrahigh vacuum chamber, which was followed by in situ vacuum annealing. The ferroelectric tetragonal phase of PZT was deposited on TiNi by sol–gel and spin coating processes followed a by 600 °C anneal for 5 min in air. The heterostructures obtained were nominally defect-free, unlike those obtained through deposition onto bulk TiNi substrates.
Reflectance anisotropy spectroscopy: A probe for surface chemistry on Na2S-passivated and (NH4)2S-passivated (001) GaAs
Authors: Paget D. , Berkovits V. L. , Gusev A. O.
Published: July 2002

We have investigated the surface optical transitions on (NH4)2S-passivated, Na2S-passivated, and unpassivated GaAs as a function of annealing temperature. The change of the reflectance anisotropy (RA) spectrum allows us to distinguish several annealing stages, which we identify as desorption of the protective overlayer, desorption of residual impurities, and breaking of Ga–S bonds. For the case of impurity desorption, we find a very good connection between the increase of dimer concentration, as found from the RA spectrum, with the decrease of impurity concentration, as monitored by Auger spectroscopy. We find significant differences between the Na2S- and the (NH4)2S-passivated surfaces. Unlike the Na2S-passivated surface, most of the arsenic atoms situated on the (NH4)2S-passivated surface before annealing are found to be dimerized, so that they are not involved in any chemical bonds with the overlying protective layer. Thus, in this last case, As–S bonds detected by photoemission spectroscopy are situated in the protective overlayer.
Adsorption of perfluorinated n-alkanoic acids on native aluminum oxide surfaces
Authors: Wallace R. M. , Chen P. J. , Henck S. A. , Webb D. A.
Published: July 2002

We have examined the reaction of solution and vacuum vapor deposited long chain perfluorinated n-alkanoic acids CF3(CF2)nCOOH (n=8–16) with the native aluminum-oxide surface using x-ray photoelectron spectroscopy and infrared reflection absorption spectroscopy. Adsorption from solution results in slightly higher acid surface coverage than that achieved from vacuum deposition. We also find that adsorption of acids from either deposition method results in a canted, monodentate configuration. Thermal degradation is observed from the elevated temperatures employed in the vacuum deposition approach. We also find evidence of degradation of the acids from exposure to a nonmonochromatic x-ray source.
Spectroscopic characterization of thin vanadium carbide films on a vanadium (110) surface: Formation, stability, and reactivities
Authors: Chen J. G. , DeVries B. D. , Frühberger B. , Kim C. M. , Liu Z.-M.
Published: July 2002

The surface properties of thin vanadium carbide films, produced on a V(110) surface, have been investigated by using a combination of high-resolution electron energy-loss spectroscopy, fluorescence-yield near-edge x-ray absorption spectroscopy (FYNES), and Auger electron spectroscopy (AES). Our results indicate that thin carbide films with a stoichiometry of VC can be produced by exposing V(110) to olefin molecules at 600 K. A comparison of the bulk-sensitive FYNES data with the relatively surface-sensitive AES results suggests that the average thickness of the VC film is greater than the penetration depth of Auger electrons for the C(KLL) and V(LMM) transitions. Upon heating to 600–1050 K, the thin VC films most likely undergo a thermally induced clustering process, which is followed by a diffusion of carbon atoms into the bulk V(110). The surface reactivities of the carbide-modified surfaces are significantly different from those of either clean V(110) or oxygen-modified V(110), as will be demonstrated by the interactions of these surfaces with CO and ethylene molecules.
Improved method of nonintrusive deposition rate monitoring by atomic absorption spectroscopy for physical vapor deposition processes
Authors: Lu C. , Guan Y.
Published: July 2002

We have developed a novel optical scheme named COPACT (common optical path for automatic correction of transmission) to improve the long-term stability of monitoring the deposition rate by atomic absorption spectroscopy. In previously developed atomic absorption monitors, the signal changes caused by the vapor flux could not be separated from those caused by viewport coating and minor optical alignment shifts once the deposition process is in progress. The new optical design is capable of measuring the atomic absorption independent of changes in optical system transmission, thus allowing the concentration of atoms in the vapor flux to be unambiguously determined in real-time. Experimental results confirmed the ability of this new optical design to achieve high sensitivity and long-term stability.
InGaN/AlGaN blue-light-emitting diodes
Authors: Nakamura Shuji
Published: July 2002

Highly efficient InGaN/AlGaN double-heterostructure blue-light-emitting diodes (LEDs) with an external quantum efficiency of 5.4% were fabricated by codoping Zn and Si into an InGaN active layer. The output power was as high as 3 mW at a forward current of 20 mA. The peak wavelength and the full width at half maximum of the electroluminescence of blue LEDs were 450 and 70 nm, respectively. Blue-green LEDs with a brightness of 2 cd and a peak wavelength of 500 nm were fabricated for application to traffic lights by increasing the indium mole fraction of the InGaN active layer.
Roughness in Si1−xGex/Si superlattices: Growth temperature dependence
Authors: Headrick R. L. , Baribeau J.-M.
Published: July 2002

Structural measurements of buried interfaces utilizing x-ray specular reflectivity profiles and diffuse scattering are discussed in this article. Evolution of roughness is kinetically limited at growth temperatures less than or equal to 400 °C. Then, the configuration of the growth surface is frozen, and leads to a vertical correlation of microroughness. For intermediate growth temperatures near 550 °C, the amplitude of roughness is minimized, since there is sufficient surface diffusion to smooth out short length scale roughness, but not enough for the surface to become unstable. Roughness reappears at higher growth temperatures, driven by strain in the SiGe layers, and the surface evolves on a time scale comparable to the layer growth, reducing the cross correlation between interfaces.
Annealing study of gold films using scanning tunneling microscopy
Authors: Porath D. , Bar-Sadeh E. , Wolovelsky M. , Grayevsky A. , Goldstein Y. , Millo O.
Published: July 2002

We have studied thermal annealing effects on the surface morphology of 800 Å thick gold films, using scanning tunneling microscopy. The gold films were thermally evaporated onto glass substrates and were then measured with the scanning tunneling microscope at room temperature before and after annealing. The annealing treatments were done at temperatures between 200 and 500 °C and for periods ranging from 1 to 60 h. We present data showing the evolution of the average surface-grain size and rms roughness amplitude of the gold films as a function of annealing temperature and duration. Our data suggest that surface diffusion is the main process active at low annealing temperatures of 300 °C and below. The activation energy for surface self-diffusion of gold in our samples was around 1.1 eV. Other mechanisms seem to be dominant at higher temperatures.
Metal overlayers on organic functional groups of self-organized molecular assemblies. V. Ion scattering spectroscopy and x-ray photoelectron spectroscopy of Ag/COOH interfaces
Authors: Herdt G. C. , Czanderna A. W.
Published: July 2002

In the present work, x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) were used to characterize mercaptoundecanoic acid [MUA, HS(CH2)10 COOH] and mercaptohexadecanoic acid [MHA, HS(CH2)15COOH] self-assembled monolayers (SAMs) before and after depositing up to 1.0 nm Ag at ∼10−7 Torr. Results from XPS O 1s, Ag 3d, and C 1s spectra do not indicate that a complex is formed (no chemical shifts) between Ag and the COOH of MUA or MHA at 295 K. Although no direct evidence for Ag/COOH interactions is evident, the initial value for ISS Ag peak intensities for 1.0 nm of Ag on COOH of MHA is unchanged after 1 h and is only reduced to 68% of the initial value after 15 h. For MUA, the ISS Ag peak intensity for 1.0 nm is constant for about 5 min and is gradually reduced until it is not detectable about 90 min after Ag deposition. These results and those we obtained earlier for Ag on octadecanethiol [ODT, HS(CH2)17CH3] might be explained by weak or no interactions between Ag and COOH and by different defect densities in the SAMs. The initial Ag ISS peak intensity for 1.0 nm Ag on MHA increases from 295 K as the SAM temperature is reduced to reach a maximum at about 200 K. The increased ISS intensity from Ag/COOH vs Ag/CH3 is consistent with lower defect densities in the MHA vs ODT.
Measurements of pulsed-power modulated argon plasmas in an inductively coupled plasma source
Authors: Ashida Sumio , Shim M. R. , Lieberman M. A.
Published: July 2002

The behavior of pulsed-power (square wave) modulated argon plasmas generated by an inductively coupled plasma (ICP) source is experimentally investigated. The apparatus is an ICP source with a flat coil geometry equipped with a cylindrical Langmuir probe on the axis of the cylindrical chamber. The evolution of the plasma density is determined from the wave forms of ion saturation currents. The rise and fall of the density had a time scale of a few tens of microseconds. The time average plasma density is also measured as a function of pulse frequency and duty ratio, holding the average absorbed power constant. When the plasma is modulated, the density is larger than that for a continuous wave excitation of the same average power. Larger densities are obtained for smaller duty ratios. The density increases monotonically as the period is decreased down to 100 μs. This agrees qualitatively with the modeling result, which accounts for the higher density by the difference of time scales for the generation and the loss of charged particles. The results for electron temperature measurements also show good agreement with the model quantitatively during the pulse ‘‘on’’ times. If the period is long enough, it is found that the electron temperature rises abruptly at the initial stage of power application, in agreement with the calculation.
Experimental studies of two-dimensional and three-dimensional structure in a crystallized dusty plasma
Authors: Pieper J. B. , Goree J. , Quinn R. A.
Published: July 2002

Coulomb crystallization of monodisperse 9.4-μm-diam spheres confined in a plasma is investigated in a modified GEC rf Reference Cell using various gases and electrode topographies. For some plasma conditions, planar electrodes confine particles radially in a few horizontal layers due to the curvature of the sheath boundary, and a two-dimensional (2D) hexagonal lattice is observed which structural analysis shows to be consistent with the intermediate ‘‘hexatic’’ phase of KTHNY 2D melting theory. A depression in the electrode surface causes a corresponding depression in the sheath and allows trapping of more layers in a three-dimensional (3D) structure, which is viewed in cross section by video imaging of a plane illuminated by a horizontal laser sheet. To synthesize 3D images, a stack of 2D images is made by moving the laser sheet and camera focal plane vertically through the particle cloud. This reveals regions of two stable 3D configurations within the cloud: body-centered-cubic and simple hexagonal with vertically aligned particles.
Detection of dust particles in the plasma by laser-induced heating
Authors: Stoffels W. W. , Stoffels E. , Kroesen G. M. W. , de Hoog F. J.
Published: July 2002

Heating of dust particles suspended in a low pressure discharge by means of a high power pulsed laser was analyzed. A detailed model of particle heating and thermal decomposition was developed and experimentally verified using 1 μm Teflon-like particles in a radio-frequency argon discharge. Laser-induced heating results in blackbody-like emission from the particles. This radiation can be easily recorded and a particle temperature of about 3500 K is determined by fitting the emission spectra. From the model it follows that the time resolved emission intensity gives valuable information about the particles: the time delay between the onset of the laser pulse and the blackbody-like emission corresponds to the heating time of the clusters and is dependent on their size. Moreover, the absolute emission intensity is proportional to the particle density.
Microstructural evolution and preferred orientation change of radio-frequency-magnetron sputtered ZnO thin films
Authors: Lee Yong Eui , Lee Jae Bin , Kim Young Jin , Yang Hyung Kook , Park Jong Chul , Kim Hyeong Joon
Published: July 2002

Crystallographic orientation and microstructural changes of ZnO thin films deposited by rf-magnetron sputtering were investigated with changing deposition parameters. Positional dependence of texture orientation and microstructural features, which might be attributed primarily to bombardment of high energetic oxygen species on the film in the region of the target erosion area, were observed. The films deposited at low temperature and/or using pure argon had (002) preferred orientation and a smooth columnar structure. At increasing substrate temperature and/or oxygen partial pressure, c-axis orientation of the film was severely degraded and abnormal elongated crystallites were also developed. As the films became thicker, c-axis orientation changed from normal to the substrate to parallel to the substrate. In this case, the microstructure was altered from a smooth fine columnar structure to abnormally grown elongated crystallites that were developed to a faceted texture structure.
Properties of transparent conducting oxides formed from CdO and ZnO alloyed with SnO2 and In2O3
Authors: Wu X. , Coutts T. J. , Mulligan W. P.
Published: July 2002

In this article we examine the structural, electrical, and optical properties of several ternary alloy thin films. The alloys are zinc oxide and cadmium oxide, each of which was reacted with both indium oxide and tin oxide to form sputtering targets. The films were deposited by rf sputtering. X-ray diffraction spectroscopy showed that cadmium stannate, cadmium indate, and zinc stannate films were all polycrystalline spinel phase, but only when deposited at room temperature in pure oxygen and then annealed in argon/cadmium sulfide. The fourth alloy, zinc indate, exhibited a hexagonal phase when prepared under identical conditions. Cadmium stannate has one of the lowest resistivities of any transparent conducting oxide (TCO), has low absorbance in the visible spectrum, and is an excellent compromise between electrical and optical requirements. For this material, we show that a single phase is essential for the highest electrical conductivity and lowest optical absorbance. Zinc stannate has a resistivity more than one order of magnitude higher than cadmium stannate but, because of a larger band gap, has an even lower absorbance. We conclude that there is no “best” TCO, and the decision regarding which to use depends on the specific application and the weighting given to electrical versus optical properties. The zinc-bearing alloys are nontoxic, which may also be an attractive feature for many applications.
Crystalline alumina deposited at low temperatures by ionized magnetron sputtering
Authors: Schneider Jochen M. , Sproul William D. , Voevodin Andrey A. , Matthews Allan
Published: July 2002

Ionized magnetron sputtering based on the work of Rossnagel and Hopwood [J. Vac. Sci. Technol. B 12, 449 (1994)] has been used to deposit alumina films containing orthorhombic κ alumina and monoclinic θ alumina at substrate temperatures of 370 to 430 °C. An inductively coupled rf Ar/O2/Al discharge between the sputter source and the heated substrate table was used to effectively ionize not only Ar but more importantly Al and O2. Both ion energy as well as the ion flux to the substrate influence the structure and properties of the coatings. The ion energy was controlled by the substrate bias potential, and the ion flux by means of the rf power supplied to the coil. The effect of the degree of ionization and therefore the ion flux to the substrate was studied at a constant substrate bias potential of −70 V. It was found that as the ion flux to the substrate was increased, the film crystallinity increased (i.e. the Bragg diffraction peaks were sharper and had higher intensity). It was shown that the formation temperature for κ alumina can be drastically decreased if high fluxes of reactive Al ions are employed to increase the energy at the substrate. Depending on the ion energy and ion flux, films with hardness values usually reported for chemical vapor deposition (CVD) κ alumina could be deposited at a maximum substrate temperature of 430 °C as opposed to ∼1000 °C by CVD. The process described allows for the first time the deposition of κ alumina onto metallic substrates such as hardened high speed steel without softening it.
Metal pattern fabrication using the local electric field of a conducting atomic force microscope probe
Authors: Brandow Susan L. , Calvert Jeffrey M. , Snow Eric S. , Campbell Paul M.
Published: July 2002

Two approaches were developed using an ambient atomic force microscope (AFM) to pattern metal in either positive or negative tone. The difference in surface chemical reactivity between exposed and unexposed regions was used to selectively attach colloidal Pd(II) nanoparticles capable of initiating the deposition of electroless (EL) Ni. In one case, EL Ni was selectively deposited in the unexposed regions of an organosilane film. In the second case, EL Ni was selectively deposited directly on an AFM oxide pattern. Based on the different binding selectivities of the Pd(II) catalysts, selective deposition on AFM patterns was attributed to the presence of a carbon residue in AFM oxide patterns formed under ambient conditions. The patterned Ni films were used as a mask for pattern transfer into the underlying substrate by reactive ion etching.
Carbon nucleation on Si(100) using a negative carbon ion beam
Authors: Ko Y. W. , Kim S. I.
Published: July 2002

The initial nucleation stages of carbon film on Si(100) substrates were investigated by low energy electron diffraction (LEED) and Auger electron spectroscopy. In the initial stages, energetic carbon ions lead to a phase transformation from a two domain p(2×1) to a (1×1) LEED structure pattern after about 6×1015 carbon ion/cm2 dose (3 atomic layers). At room temperature, the energetic carbon ions are deposited as silicon carbide (SiC) up to a thickness of about 10 atomic layers. As the deposition temperature increases to 300 °C, the thickness of the SiC interlayer increases to 30 atomic layers. An increased carbon ion dose leads to the formation of sp3 or sp2 rich carbon film depending on the carbon ion energy and the deposition temperature. Higher energy (150 eV) C− ion beams and lower deposition temperatures (room temperature) produce sp3 rich carbon films. At 150 eV ion energy, the transition temperature from sp3 to sp2 rich carbon film during deposition is about 150 °C. Lower energy (<50 eV) C− ion beams at room temperature produce sp2 rich carbon films. During postdeposition annealing, the sp3 rich carbon film deposited at room temperature was converted to an sp2 rich carbon film above 740 °C.
Parametrization of the Laframboise theory for cylindrical Langmuir probe analysis
Authors: Mausbach Michael
Published: July 2002

In this investigation we parametrize the numerical results of Laframboise with the function f(χ)=a(b+χ)c, where a, b, and c are fit parameters and χ is the normalized probe potential. The fits show a clear relation between these fitting parameters and the probe characteristic. With these parameters we construct a self-consistent algorithm to fit measured cylindrical probe characteristics of a Maxwellian plasma without any assumption for the relation of the characteristic Langmuir probe dimension to the Debye length. The measured probe characteristics of an anodic Cu-vapor vacuum arc are analyzed by means of this nonlinear fitting algorithm. From the determined plasma parameters we obtain clear indications for hot ions. The mean deviation of the calculated theoretical probe characteristic from the measured characteristic is <2%.
Ion distribution functions in inductively coupled radio frequency discharges in argon–chlorine mixtures
Authors: Woodworth J. R. , Riley M. E. , Miller P. A. , Nichols C. A. , Hamilton T. W.
Published: July 2002

We report on measurements of positive ion energies, current densities, and angular distributions at the grounded electrode of inductively coupled discharges in mixtures of argon and chlorine. We also report on ion species and Langmuir probe measurements for these discharges. The inductive drive in our gaseous electronics conference reference cell produced high plasma densities (1011–1012/cm3) and stable plasma potentials. As a result, ion energy distributions consisted of a single peak well separated from zero energy. At pressures of 2.5–20 mTorr and constant rf power, the addition of Cl2 to an Ar discharge lowered ion current densities, reduced ion energies, and reduced the width of the ion energy distributions. Half-widths of the ion angular distributions ranged from 4.5° to 8.5° with the distributions broadening with increases in pressure or rf power. The addition of Cl2 to Ar discharges made the angular distributions less sensitive to total pressure. Cl+ replaced Ar+ as the dominant ionized species when small amounts of chlorine were added to Ar discharges.
Air bake-out to reduce hydrogen outgassing from stainless steel
Authors: Bernardini M. , Braccini S. , De Salvo R. , Di Virgilio A. , Gaddi A. , Gennai A. , Genuini G. , Giazotto A. , Losurdo G. , Pan H. B. , Pasqualetti A. , Passuello D. , Popolizio P. , Raffaelli F. , Torelli G. , Zhang Z. , Bradaschia C. , Del Fabbro R. , Ferrante I. , Fidecaro F. , La Penna P. , Mancini S. , Poggiani R. , Narducci P. , Solina A. , Valentini R.
Published: July 2002

Hydrogen outgassing is the most significant factor limiting the attainment of outgassing rates below 10−12 mbar l s−1 cm−2 in stainless steel vacuum systems. This limit turns out to be crucial in very large vacuum systems, like the VIRGO vacuum tubes (2 tubes 1.2 m diam, 3000 m length). Heating the raw material at 400 °C in air was suggested as a money saving alternative to the classical vacuum heating at 950 °C. We report the results of hydrogen content analysis performed on stainless steel samples submitted to different treatments, and also the measurement performed on a prototype tube (1.2-m-diam, 48-m-long). We concluded that air bake-out drives out most of the hydrogen absorbed in the bulk stainless steel, while the presence of an oxide layer does not reduce the hydrogen outgassing.
In situ infrared ellipsometry study of the growth of plasma deposited silica thin films
Authors: Bertrand N. , Drévillon B. , Bulkin P.
Published: July 2002

The evolution during growth of the vibrational properties in several plasma deposited a-SiO2 thin films is studied. We mainly compare dense a-SiO2 deposited either at low pressure in an integrated distributed electron cyclotron resonance (IDECR) reactor or at higher pressure in a dual mode reactor. The latter system also allows one to vary the a-SiO2 film density. Growth is studied by in situ infrared ellipsometry on stainless steel and c-Si substrates in the 1000–1400 cm−1 region. This region corresponds to the Si–O–Si asymmetric stretching mode which is split into transverse optical (TO) and longitudinal optical modes. Vibrational modes are revealed by inflection points in the ellipsometric angle Δ. LO modes are predominantly observed with metallic substrates, whereas on c-Si TO and LO modes are simultaneously observed. Vibrational properties of the IDECR films are found to be very close to the reference thermal silica over the whole range of thicknesses (up to more than 1000 nm), whereas the dual mode plasma deposited oxides have their vibrational modes shifted towards small frequencies and are broadened. This difference is mainly found in films with a higher H concentration which were deposited at high pressure (>9%) rather than in the IDECR film (<2%). The study of the Δ inflection point frequencies versus film thickness also shows differences in the interface formation. Contrary to the IDECR case, the vibrational properties of the dual mode plasma deposited oxides are stable only at large thicknesses. Vibrational properties are then compatible with two Lorentz oscillators: a strong one near 1050 cm−1 (with a strength F=0.65 and width 50 cm−1) and a weaker one near 1175 cm−1. In contrast, at small thicknesses, upward shifts in the LO frequency are observed. An interpretation in terms of disorder induced mode coupling at the interface between the two vibrations is proposed. We discuss the possible role of nucleation processes, due to high pressure, in correlation with the observed influence of film morphology and the nature of the substrate.
Growth and characterization of GaN thin films by magnetron sputter epitaxy
Authors: Singh P. , Corbett J. M. , Webb J. B. , Charbonneau S. , Yang F. , Robertson M. D.
Published: July 2002

Single crystal epitaxial gallium nitride films on GaN buffer layers were grown on (0001) sapphire using magnetron sputter epitaxy. The films were characterized using x-ray diffraction, photoluminescence, scanning electron microscopy and transmission electron microscopy. In the layers investigated thus far, the optimum buffer layer had a thickness of 500 Å at a growth temperature of 550 °C, while the optimum growth temperature range for the active GaN epilayer was found to be 900 °C–950 °C. The growth rates for the buffer layer and GaN epilayer were 0.2 and 0.35 μm/h, respectively. In general, photoluminescence studies showed emission from a broad defect band centered around 2.4 eV and a strong exciton peak at 3.48 eV. The exciton/defect intensity ratio was strongly dependent on crystal quality at constant excitation intensity. The transmission electron microscopy studies revealed highly epitaxial GaN films, showing a kind of columnar growth structure. GaN films grown at 950 °C appeared to have the best structural quality.
Magnetic nanostructures produced by electron beam patterning of direct write transition metal fluoride resists
Authors: Streblechenko Dmitry , Scheinfein M. R.
Published: July 2002

Transition metal (TM) fluoride electron beam sensitive resists suitable for the in situ fabrication of arbitrarily shaped nanometer scale magnetic structures have been developed. 20 nm thick TM fluoride films are prepared by thermal evaporation onto thin carbon films. Nanopatterns are written directly into the TM fluoride film in a scanning transmission electron microscope using a 0.5 nm diameter electron probe. Electron energy loss spectroscopy measurements indicate that as fluorine is released, the TM coalesces. Electron micrographs of exposed patterns show that the resist resolution is on the order of nanometers. Exposure of broad areas leads to coalescent TM layers which cap the remaining fluoride and decrease the rate of fluorine removal. The cross section for the removal of a fluorine atom and the cross section for the same process in the presence of an arbitrarily thick capping layer were measured. An electron dose of 1000 C/cm2 at 100 keV will remove 90% of the fluorine from a 20 nm thick CoF2 film.
Probe diagnostics in a full wave resonator radio-frequency discharge
Authors: Vinogradov G. K. , Menagarishvili V. M. , Yoneyama S.
Published: July 2002

A full wave or lambda resonator (λ-R) is a capacitively balanced radio-frequency (rf) inductive plasma source. It has three separate inductive excitation zones with opposite magnetic momenta strictly located at their axial positions. The 2 kW, 27 MHz, 1.4 Torr pressure discharge in oxygen was studied by means of movable single rf compensated fine cylindrical Langmuir probes. Flat wall probes were also used to reveal the distribution of positive ion flux and floating potentials on the chamber wall. The electron density in the λ-R discharge varies from 107–108 cm−3 at 5–10 mm distance from the wafer to 2×1011 cm−3 in the central plasma toroid. One of the main problems of the probe operation is high gas temperature of ∼1500 K in the plasma toroid and high-power dissipation on the probe surface. That is why not only fine cylindrical but also 100–130 μm diam spherical probes were used. The probe technique and preliminary results are presented.
Studies on structural, electrical, compositional, and mechanical properties of WSix thin films produced by low-pressure chemical vapor deposition
Authors: Santucci S. , Lozzi L. , Passacantando M. , Picozzi P. , Petricola P. , Moccia G. , Alfonsetti R. , Diamanti R.
Published: July 2002

Tungsten silicide (WSix) thin films have been deposited by low-pressure chemical vapor deposition using silane (SiH4) and tungsten hexafluoride (WF6) at different fluxes ratio ranging from 44 to 745 onto planar Si(100) wafers covered by 130 Å of SiO2 and 2000 Å of phosphorus-doped polysilicon layers to reproduce the control gate structure of a FLASH-EEPROM. The deposited films have been annealed in oxygen ambient at 900 °C. The composition of as deposited films as well as annealed films has been studied by x-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, and secondary ion mass spectroscopy. Cross section scanning electron microscopy and atomic force microscopy have been employed to study the thickness and the surface morphology of the deposited layers. The resistivity and the mechanical properties of the films have been also investigated. The as-deposited films have shown, growing the SiH4/WF6 ratio, an increase of the Si/W stoichiometric ratio (until 3), a decrease of the film thickness and stress while there is an increase of the sheet resistance. In the case of annealed films, which pass from amorphous state to crystalline structure, as detected by x-ray diffraction, there is a strong decrease of the sheet resistance values as well as of the silicide film thickness depending on the SiH4/WF6 ratio, while the presence of a silicon oxide layer with different thickness has been also detected on top of the silicide layer.
Kinetic energy distribution of nitrogen ions in an electron cyclotron resonance plasma
Authors: Fan Z. Y. , Newman N.
Published: July 2002

In this article, the kinetic energy distribution of atomic and molecular nitrogen ions is reported for two electron cyclotron resonance (ECR) sources. Methods to reproducibly tune the kinetic energy of ionic species from 3 eV to 35 eV have been developed in order to produce monoenergetic ion beams for the demanding requirements of selective energy epitaxy. This article also describes methods to avoid the discontinuous hysteretic transitions between stable ECR modes. The changes in the ion energy distribution resulting from these abrupt transitions are characterized.
X-ray photoelectron spectroscopy study of the heating effects on Pd/6H-SiC Schottky structure
Authors: Chen Liang-Yu , Hunter Gary W. , Neudeck Philip G. , Knight Dak
Published: July 2002

X-ray photoelectron spectroscopy is used to study the effects of heat treatment on the Pd/6H-SiC Schottky diode structure. After heating the structure at 425 °C for 140 h, a very thin surface layer of PdO mixed with SiOx formed on the palladium surface of the Schottky structure. Heat treatment promoted interfacial diffusion and reaction which significantly broadened the interfacial region. In the interfacial region, the palladium concentration decreases with depth, and the interfacial products are PdxSi (x=1,2,3,4). In the high Pd concentration regions, Pd4Si is the major silicide component while PdSi and Pd2Si are major components in the low Pd concentration region. At the center of the interface, where the total palladium concentration equals that of silicon, the concentrations of palladium associated with various palladium silicides (PdxSi, x=1,2,3,4) are approximately equal. The surface passivation layer composed of PdO and SiOx may significantly affect the electronic and catalytic properties of the surface of the Schottky diode which plays a major role in gas detection. The electronic properties of the Schottky structure may be dominated by a (Pd+PdxSi)/SiC interface. In order to stabilize the properties of the Schottky structure the surface and interface diffusion and reactions must be controlled.
Ultraviolet-ozone jet cleaning process of organic surface contamination layers
Authors: Moon D. W. , Kurokawa A. , Ichimura S. , Lee H. W. , Jeon I. C.
Published: July 2002

To understand the ultraviolet (UV)-ozone jet cleaning process of organic surface contamination layers, adventitious hydrocarbon layers on Si, self-assembled octadecyltrichlorosilane monolayers on Si, and self-assembled C60H–(CH2)12–SH monolayers on Au were cleaned with pure ozone jet and UV irradiation. Cleaned surfaces were analyzed with in situ x-ray photoelectron spectroscopy measurements. Ozone molecules could react with the unsaturated C–C bonds in self-assembled C60H–(CH2)12–SH monolayers on Au surfaces at room temperature. However, the saturated C–C bonds in OTS hydrocarbon molecules adsorbed on Au surfaces reacted not with ozone molecules but with oxygen radicals generated by the dissociation of ozone molecules under UV irradiation. For adventitious carbon contamination on Si surfaces, only a fraction could be cleaned by ozone at room temperature but it could be almost cleaned with UV-ozone jet.
Heterogeneous recombination of atomic bromine and fluorine
Authors: Kota Gowri P. , Coburn J. W. , Graves David B.
Published: July 2002

Recombination coefficients (γ) of Br and F atoms have been measured for crystalline Si, quartz, photoresist, anodized aluminum, poly-Si, WSix, tungsten and stainless steel surfaces for a range of temperatures. The γBr and γF values are compared to our previously reported measurements of γCl [G. P. Kota, J. W. Coburn, and D. B. Graves, J. Vac. Sci. Technol. A 16, 270 (1998)]. In general, the Br-, Cl- and F-atom recombination coefficients decrease as the surface temperature increases. The γBr values are similar to the γCl values for the various surfaces. At room temperature, γBr is highest (>0.4) for stainless steel and tungsten, moderate (0.1–0.4) for poly-Si, WSix and anodized Al, and lowest (<0.05) for c-Si, quartz and photoresist. However, γF, at room temperature, is no greater than 0.05 for all the surfaces. γF increases slightly as the temperature is decreased to 80 K but is still below 0.1 for all the surfaces. The recombination coefficient data as a function of temperature for all surfaces are fit to a phenomenological model developed previously for γCl (see the above reference). The model assumes that the incident halogen atoms physisorb on a surface that is saturated with chemisorbed halogen atoms. The physisorbed atoms are assumed to diffuse on the surface and either desorb before recombining or recombine and then desorb. The recombination rate is assumed to be first order in physisorbed atom coverage.
Formation of β-FeSi2 films by pulsed laser deposition using iron target
Authors: Liu Zhengxin , Okoshi Masayuki , Hanabusa Mitsugu
Published: July 2002

Semiconducting β-FeSi2 films were formed by pulsed laser deposition on silicon (100) substrates. The phase and crystallinity were examined by x-ray diffraction spectrometry. In the simplest scheme a single phase β-FeSi2 film was formed by depositing an iron layer on the silicon at 600 and 700 °C. At lower deposition temperatures, metastable FeSi was present in addition to β-FeSi2. At 800 °C metallic α-FeSi2 was mixed into the film. We used a laser target made of iron and silicon in addition to the iron target to form a multilayer of thin iron and silicon films. However, no significant benefit was obtained. Also, we formed the β-FeSi2 film by depositing iron on silicon at room temperature and then annealing at 650 °C for 120 min. Alternately, iron was deposited at 450 or 550 °C, and the β-FeSi2 film was formed by annealing at 600 °C. It was concluded that the best way to produce single phase β-FeSi2 is to deposit iron at 600 °C without any additional heat treatment. The interface between the β-FeSi2 film and silicon substrate was abrupt.
Photon shield for atomic hydrogen plasma sources
Authors: Nienhaus H. , Gergen B. , Bergh H. S. , Majumdar A. , Weinberg W. H. , McFarland E. W.
Published: July 2002

Atomic hydrogen sources are usually strong photon emitters. To produce an atomic hydrogen beam and suppress the undesired photon flux, a small but effective light blocking device has been developed which fits into the quartz tube of a hydrogen plasma source. The device is made of stainless steel and uses angled passages and offset throughholes to absorb plasma generated photons while permitting hydrogen atoms and molecules to pass. The photon flux was reduced by a factor of at least 104, whereas an attenuation of the H atom flux was not observed. By measuring the average velocity of the H atoms passing through the light blocker it has been shown that this device in the microwave plasma tube produces a room temperature thermalized atomic hydrogen beam.
Ultrahigh rate, wide area, plasma polymerized films from high molecular weight/low vapor pressure liquid or solid monomer precursors
Authors: Affinito J. D. , Gross M. E. , Mounier P. A. , Shi M.-K. , Graff G. L.
Published: July 2002

A new process has been developed for the high rate vacuum deposition of solid films from high molecular weight/low vapor pressure liquid, or even solid, monomer precursors. The gas resulting from the flash evaporation of a liquid monomer mixture or from a suspension of liquid monomer and insoluble solid particles is used as the support medium for a glow discharge in a plasma enhanced chemical vapor deposition-like process. Due to the high molecular weight/low vapor pressure nature of the precursors, the plasma of the flash evaporated gas cryocondenses at an extremely high rate on substrates at ambient, and higher, temperatures. Upon condensation the liquefied plasma immediately begins to polymerize to form a solid film due to the high concentration of radicals and ions contained in the liquid film. The process has been successfully implemented in a vacuum roll coating system in a roll-to-roll deposition process. Polymer films and molecularly doped polymer composite films of polymer and light emitting organic molecules have been deposited at thicknesses ranging from about 0.1 to 24 μm at web speeds between 96 and 0.5 linear meters per minute. This new deposition process will be discussed along with some properties of the films fabricated with this new process.
Nanometer-scale compositional variations in III-V semiconductor heterostructures characterized by scanning tunneling microscopy
Authors: Yu E. T. , Zuo S. L. , Bi W. G. , Tu C. W. , Allerman A. A. , Biefeld R. M.
Published: July 2002

Nanometer-scale compositional structure in InAsxP1−x/InNyAsxP1−x−y//InP heterostructures grown by gas-source molecular beam epitaxy and in InAs1−xPx/InAs1−ySby/InAs heterostructures grown by metalorganic chemical vapor deposition has been characterized using cross-sectional scanning tunneling microscopy. InAsxP1−x alloy layers are found to contain As-rich and P-rich clusters with boundaries formed preferentially within (1̄11) and (11̄1) crystal planes. Similar compositional clustering is observed within InNyAsxP1−x−y alloy layers. Imaging of InAs1−xPx/InAs1−ySby superlattices reveals nanometer-scale clustering within both the InAs1−xPx and InAs1−ySby alloy layers, with preferential alignment of compositional features in the [1̄12] direction. Instances are observed of compositional features correlated across a heterojunction interface, with regions whose composition corresponds to a smaller unstrained lattice constant relative to the surrounding alloy material appearing to propagate across the interface.
Properties of Si1−xGex three-dimensional islands
Authors: Sullivan J. S. , Mateeva E. , Evans H. , Savage D. E. , Lagally M. G.
Published: July 2002

Thin, coherently strained films of SiGe were deposited on Si(001) to form faceted, dislocation-free, three-dimensional (3D) islands via the Stranski–Krastanov (SK) growth mode. Deposition was interrupted to determine the saturation island number density as a function of alloy composition, substrate temperature during growth, and growth rate. To control the shape of buried islands during encapsulation with Si, the 3D islands were embedded and overgrown at various temperatures. The temperature dependence of the island number density yields an approximate activation energy of 0.7 eV for diffusion of Ge dimers on a Ge covered Si(001) surface. The dependence of the 3D-island number density on growth rate cannot be understood without modifying the classical model of nucleation and growth to account for the wetting layer present in SK systems. To explain the island number density as a function of alloy composition, a simple linear elastic model is developed in which the island number density is proportional to the inverse square of the Ge mole fraction in the alloy plus a constant. Finally, cross-sectional transmission electron microscopy reveals that the island shape changes dramatically during encapsulation, but the morphology can be kinetically preserved.
Cathodoluminescence spectroscopy of nitrided SiO2–Si interfaces
Authors: Young A. P. , Bandhu R. , Schäfer J. , Niimi H. , Lucovsky G.
Published: July 2002

We use cathodoluminescence spectroscopy (CLS) to investigate the electronic states of ultrathin gate dielectrics with nitrided SiO2–Si interfaces, known to improve reliability in advanced complementary metal–oxide–semiconductor devices. The 5 nm thick films investigated were: (i) as-deposited (at 300 °C) structures, (ii) 400 °C hydrogen anneal, (iii) 900 °C rapid thermal anneal (RTA), and (iv) a combination of both anneals. CLS emission energies and intensities versus excitation energy were essentially unchanged for the as-deposited interface compared to non-nitrided plasma-processed interfaces. In the near-infrared, features appear at 0.8 and 1.0 eV, with the 1.0 eV peak Si substrate intensity increasing with increasing depth. From depth variation measurements at higher photon energy, a 3.4 eV peak is also shown to arise from the Si substrate, and a 2.7 eV feature is shown to come from the interface region. After hydrogenation, the CLS is essentially the same as for non-nitrided interfaces, except for an increase in the relative intensity of a broad background luminescence ranging from 1.5 to 2.5 eV. However, the RTA and the combination of the RTA and hydrogenation do not completely suppress emission near 2.0 eV feature as for non-nitrided interfaces. From the behavior of the CLS features, we are able to clearly distinguish between interfacial defects and substrate features, which are significantly reduced by the combined RTA/hydrogen anneal, and features that are not reduced by the annealing procedures.
Analysis of P adsorption and desorption on the (001) InP surface using surface photoabsorption
Authors: Lee Tae-Wan , Hwang Heedon , Moon Youngboo , Yoon Euijoon , Kim Young Dong
Published: July 2002

We present an in situ study of P desorption and adsorption on the (001) InP surface using surface photoabsorption (SPA). The SPA spectra show three peaks at 2.1, 2.9, and 3.1 eV. Here, based on previous studies, we have identified them as a P dimer related and two surface In dimer related peaks, respectively. The initial sharp drop and the slow recovery of the SPA signal at 430 nm after PH3 is switched on implies that at least two steps are involved in the P desorption process. We also observed a structure at 3.1 eV in the spectrum of the In-stabilized surface. We have determined from temperature dependent desorption measurements that the activation energy for P desorption from this surface is 3.36 eV.
Negative ion resputtering in Ta2Zn3O8 thin films
Authors: Rack Philip D. , Potter Michael D. , Woodard Andrew , Kurinec Santosh
Published: July 2002

Thin films have been deposited by radio frequency magnetron sputtering from a stoichiometric Ta2Zn3O8 ceramic target (3ZnO+1Ta2O5). Negative ion resputtering effects have been observed in the stoichiometric Ta2Zn3O8 target and have been attributed to O− ion formation from primarily Ta–O bonds. Zinc deficient thin films were deposited as a result of the preferential resputtering of Zn versus Ta. The negative ion resputtering effects are exacerbated at higher powers and lower pressure. This observation is correlated to the oxygen ion transport through the dark space and the plasma, which ultimately controls the energy distribution of the oxygen particles that arrive at the substrate. Another ceramic target with excess ZnO (6ZnO+1Ta2O5) was also sputtered under similar conditions, however predominantly ZnO films were deposited. Finally, a mosaic ZnO–Ta target was sputtered, which resulted in stoichiometric and luminescent thin films.