bluuebunny/crossref_metadata_2025 huggingface dataset:
A new method to obtain Cu films with lower resistivity and higher interface adhesion on different substrates
Authors: Yang Jie , Wang Chen , Tao Kun , Fan Yudien
Published: July 2002

An ion beam assisted deposition (IBAD) method was used to obtain metal (Cu or Ti) intermediate layers. These intermediate layers were between the evaporated Cu surface films (SF) and different types of substrates (Si, glass, and polycrystalline Al2O3). How these intermediate layers effect the microstructure and properties of the Cu surface films was studied. Trends in crystallographic texture, crystal size, and resistivity of Cu surface films with different IBAD layers on different substrates are significantly different. The IBAD intermediate layer changed the crystallinity of Cu SF and increased the interface adhesion between the Cu SF and substrates. Rutherford backscattering spectroscopy, transmission electron microscopy, scanning electron microscopy, and x-ray diffraction analyses methods have been used for the study of the synthesized films. The experimental results show that films with lower resistivity and higher interface adhesion could be obtained by this combined IBAD–physical vapor deposition technique. This method has the potential to be used in electronic packaging and other thin film industries.
Permanent magnet electron cyclotron resonance plasma source with remote window
Authors: Berry Lee A. , Gorbatkin S. M.
Published: July 2002

An electron cyclotron resonance (ECR) plasma has been used in conjunction with a solid metal sputter target for Cu deposition over 200 mm diameters. The goal is to develop a deposition system and process suitable for filling submicron, high-aspect ratio ULSI features. The system uses a permanent magnet for creation of the magnetic field necessary for ECR, and is significantly more compact than systems equipped with electromagnets. A custom launcher design allows remote microwave injection with the microwave entrance window shielded from the copper flux. When microwaves are introduced at an angle with respect to the plasma, high electron densities can be produced with a plasma frequency significantly greater than the electron cyclotron frequency. Copper deposition rates of 1000 Å/min have been achieved.
Direct analysis of contamination in submicron contact holes by thermal desorption spectroscopy
Authors: Aoki Hidemitsu , Teraoka Yuden , Ikawa Eiji , Kikkawa Takamaro , Nishiyama Iwao
Published: July 2002

Thermal desorption spectroscopy (TDS) has been applied to detect contamination, produced in deep-submicron contact holes during plasma etching. AlF and other Al-containing fragments were observed as constituents of the contamination. The contamination is found to be accumulated in the holes, depending on an overetch time, acting as an inhibitor against achieving sufficiently low contact resistance. The effects of cleaning by Ar+ ion sputtering after contact-hole fabrication are also investigated. The sputtering improves the contact resistance significantly. The sharp TDS peaks of AlF and AlC clearly decreased in good relation to the improvement in the contact resistance. The TDS method has proven to be an effective tool in evaluating contamination in the submicron contact holes.
Interface exciton luminescence: An indication of interface inhomogeneities in single GaAs/GaAlAs heterostructures
Authors: Bessolov V. N. , Evstropov V. V. , Lebedev M. V.
Published: July 2002

A specific luminescence band originating from a heterointerface (H band) has been observed in the photoluminescence spectrum (at 1.7 K) of a single GaAs/GaAlAs heterostructure. Threshold effect of epitaxial temperature on interface luminescence has been found. A model has been proposed which attributes interface luminescence to annihilation of the interface heterodimensional exciton which is composed of a two-dimensional (2D) electron (2D hole) in the notch at the interface and a three-dimensional (3D) hole (3D electron) in the GaAs bulk region near the interface. The exciton binding energy decreases when the interface ruggedness increases. In the case of large inhomogeneities (ruggedness of chemically abrupt interface) such an exciton cannot form and the corresponding H band is not observed in the spectrum. Thus, the luminescence of the interface heterodimensional exciton can serve as an indication of the interface ruggedness.
Thermogravimetric analysis of selected condensed materials on a quartz crystal microbalance
Authors: Phillips Terry E. , Bargeron C. Brent , Benson Richard C.
Published: July 2002

Employing a quartz crystal microbalance and a quadrupole mass spectrometer in a vacuum chamber, thermogravimetric analyses (TGA) and mass spectrometer analyses have been performed at low temperature (90–190 K) on depositions of ammonia, acetone, methanol, toluene, isopropyl alcohol, water, para-xylene, and selected combinations of these materials. Deposition of a single species yielded a TGA curve characteristic of a pure substance. Homogeneous binary mixtures, like methanol and water, exhibited a desorption curve which contained structure in addition to that observed for the pure materials. Sequential layering of one material on top of another also altered the TGA response, suggesting substantial interlayer interactions, and the TGA curve shape was found to be a function of the top-layer thickness for the water-on-methanol system. Backfilling the chamber with nitrogen or argon at a pressure of 1 Torr increased the apparent desorption temperature of water by about 20 K.
Use of an inexpensive solid state differential sensor as a 0–35 mbar pressure gauge
Authors: Fleury Marc , Smullin Louis D.
Published: July 2002

We describe a simple setup that enables a solid state differential pressure sensor, normally designed to operate around 1 atm with a range of 70 mbar (−35/+35 mbar), to operate in high vacuum and act as a 0–35 mbar pressure gauge.
Study of ion mixing during Auger depth profiling of Ge–Si multilayer system. II. Low ion energy (0.2–2 keV) range
Authors: Menyhard M. , Barna A. , Biersack J. P. , Järrendahl K. , Sundgren J.-E.
Published: July 2002

Auger electron spectroscopy depth profiling was carried out on amorphous Ge–Si multilayer structures of 2 and 3 nm layer thicknesses using a dedicated Auger depth profiling instrument that rotates the specimen during sputtering and applies a grazing angle of incidence. Ion energy was in the range of 0.2–2 keV. The depth profiles of these multilayer systems are oscillating functions. The authors show that the amplitude of the oscillation versus the square root of the ion energy curve is linear in the energy range used. The depth profile cannot be described either by Gaussian broadening or the Liau model. Simulations using the dynamic transport of ions in matter code reproduce the slopes of the amplitude of oscillation versus the square root of ion energy curves, but the simulated and measured intercepts are different. The ratios of the measured and simulated intercepts are constant and do not depend on the layer thickness. This is used to give a recipe for a ‘‘normalization’’ of the simulated curves.
Electron cyclotron resonance plasma reactor for SiO2 etching: Process diagnostics, end-point detection, and surface characterization
Authors: Wan Zhimin , Liu Jian , Lamb H. Henry
Published: July 2002

An electron cyclotron resonance plasma reactor for low-pressure etching of SiO2 layers on Si is described. Under typical operating conditions of 1.1 mTorr neutral pressure, 5 sccm CF4/46 sccm He, and 400 W net microwave power, an average etch rate of 35–40 nm/min is obtained. Ion densities were measured by using a quadrupole mass analyzer (QMA) immersed in the downstream plasma; an optical multichannel analyzer was used for actinometric measurements of atomic F and O concentrations. The results are correlated with process variables and SiO2 etch rates. Real-time end-point detection was effected by actinometry and by monitoring the concentrations of etch products using a differentially pumped QMA. H2 addition inhibits SiO2 etching but improves SiO2/Si etch selectivity. For selective etching, in situ, off-line surface analysis by Auger electron spectroscopy demonstrated an increase in the surface C concentration during SiO2 etching and deposition of a fluorocarbon layer at the end point which strongly inhibits Si etching.
Negative ions in a CCl2F2 radio frequency discharge
Authors: Stoffels E. , Stoffels W. W. , Vender D. , Kroesen G. M. W. , de Hoog F. J.
Published: July 2002

The electron and negative ion densities in rf etching plasmas in pure CCl2F2 and its mixtures with argon have been measured using a microwave resonance technique in combination with photodetachment. It has been found that the dominant negative ion is Cl−. These ions are about 100 times more abundant than electrons and other negative ions (most likely F− and Cl2−). Typical densities reach 1017 m−3 for Cl− and 1015 m−3 for the electrons in a 30 mTorr discharge with 50 W rf input power. The decay time of the photodetached electrons towards the steady state gives an estimate for the effective electron attachment rate in the plasma. This rate (typically 2–5×10−15 m3s−1) appears to be substantially higher than the attachment rate to pure CCl2F2. Moreover it depends on plasma conditions, e.g., it increases with power and decreasing pressure. This is attributed to dissociative attachment to active species, such as radicals and vibrationally excited molecules, formed in the plasma. The total charge density in Ar/CCl2F2 mixtures is about ten times higher than that in a pure argon discharge, whereas the electron density is ten times lower. This effect is due to the presence of negative ions. A transition between an electropositive and an electronegative discharge occurs when a small amount of CCl2F2 is added to a pure Ar plasma. Measurements of energy resolved positive ion fluxes to the grounded electrode show that in an electronegative discharge the positive ion loss rate to the wall is about 10 times lower than that in an Ar plasma. This proves that the Bohm velocity in an electronegative plasma is much lower than that in an electropositive discharge.
New method to predict corrosion characteristics of Zn-metallized thin films for film capacitors
Authors: Na J. G.
Published: July 2002

The relationship between the microstructural parameters, e.g., grain size and preferred orientation, and the corrosion characteristics of Zn-metallized thin films was investigated. The Zn-metallized thin films with various grain sizes and preferred orientations were prepared by changing evaporation conditions, e.g., the temperature of the Zn source and the substrate temperature. By increasing the temperature of the Zn source and decreasing the substrate temperature, the grain size and the values of full width half-maximum (FWHM) of the (002) x-ray diffraction peaks of Zn decreased. From measurements of resistivity change in the thin films a function of time at the temperature of 40 °C and the relative humidity of 80%, it was found that the relative change in the value of Ω/sq decreased by decreasing the grain size and the FWHM values of the (002) peaks of Zn. It suggests that the FWHM measurement of the (002) peak of Zn is a simple method by which to predict the corrosion characteristics of Zn-metallized thin films.
Laterally resolved measurements of cesium iodide quantum yield
Authors: dell’Orto Tiziana , Almeida J. , Coluzza C. , Conforto E. , De Stasio Gelsomina , Margaritondo G. , Paic G. , Braem A. , Piuz F. , Tonner B. P.
Published: July 2002

Spatially resolved x-ray secondary electron photoemission spectra revealed lateral changes in quantum efficiency and chemical composition of polycrystalline cesium iodide photodetectors. Such changes depend on the substrate (stainless steel or aluminum). These results emphasize the limitations of conventional, spatially integrated quantum efficiency measurements, and shed new light on the chemical properties of inhomogeneous polycrystalline cesium iodide.
Thermal effects on GaAs(001) surface prepared by deoxygenated and de-ionized water treatment
Authors: Hirota Y. , Ogino T. , Watanabe Y. , Oshima M.
Published: July 2002

A study of n-type GaAs(001) surface prepared by deoxygenated and de-ionized water (DODIW) treatment as a function of temperature is presented. Synchrotron-radiation photoelectron spectroscopy was used to perform chemical and electrical characterization. Excess elemental arsenic on the surface decreases due to evaporation with heating to 400 °C. The surface structure changes from (1×1) to (2×4) with heating the substrate from 450 to 500 °C. The surface Fermi level lies almost 0.9 eV above the valence band maximum before heating, moves toward the midgap during heating, and returns to the near-flat-band position (1 eV) after cooling to room temperature. Ultraviolet photoelectron spectroscopy supports the near-flat-band position of the surface Fermi level at room temperature after cooling. This reversible movement of the surface Fermi level suggests that the DODIW-treated GaAs(001) surface has the possibility of a low density of surface states and that the surface Fermi level is not related to the surface structure after heating below 500 °C.
Silicon nitride encapsulation of sulfide passivated GaAs/AlGaAs microdisk lasers
Authors: Hobson W. S. , Ren F. , Mohideen U. , Slusher R. E. , Lamont Schnoes M. , Pearton S. J.
Published: July 2002

SiNx encapsulation of sulfide passivated GaAs/AlGaAs surfaces was examined with respect to the SiNx deposition conditions and applied to GaAs/AlGaAs microdisk lasers. The SiNx encapsulation is a method for preserving the positive effects (e.g., reduced surface recombination velocity, Sv) of the sulfide passivation by inhibiting the oxidation process of the air-exposed semiconductor. GaAs-based microdisks, with diameters of 2–10 μm, provide a very sensitive probe of the surface recombination since the resonator mode is in close proximity to the edge of the disk (∼<0.5 μm) and the carrier diffusion length is typically several microns. An ammonium sulfide solution was used for the S passivation. The SiNx was deposited by plasma-enhanced chemical vapor deposition (PECVD) at 50 or 300 °C, with and without post-deposition annealing (300–400 °C), or by electron cyclotron resonance chemical vapor deposition (ECR-CVD) at 100 °C. Photoluminescent measurements of GaAs/InGaP epitaxial structures provided an indication of the relative change in Sv. The GaAs/AlGaAs microdisks do not lase without sulfide treatment when optically pumped at 77 K. With the sulfide treatment alone, cw lasing was achieved but the lifetime was only several seconds. A dramatic increase in the laser lifetime was obtained using PECVD-deposited SiNx at 300 °C. The laser output for the PECVD SiNx (300 °C) encapsulated microdisks could be increased by nearly an order of magnitude by annealing at 400 °C for 300 s or by cw operation for several hours. Initial results using the ECR-deposited SiNx films suggest improved performance (lower threshold, stability) compared to the PECVD SiNx. The laser performance is correlated with the photoluminescence results.
Processing of PbTiO3 thin films. II. In situ investigation of stress relaxation
Authors: Li Chen C. , Desu Seshu B.
Published: July 2002

Stress relaxation in PbTiO3 films was investigated by the in situ stress measurement technique. A simple viscous flow model was successfully used to interpret the kinetics and behavior of stress relaxation of PbTiO3 thin films. The activation energy responsible for stress relaxation was estimated to be 190 kJ/mole, which was accounted for by the lattice diffusion of vacancies. A Nabarro–Herring creep model was successfully employed to correlate the relationships among the viscosity, lattice diffusion coefficient, and grain size of the PbTiO3 films, and an estimate of the lattice diffusion coefficient of vacancy motion during relaxation was obtained. Also, the observed time required for complete relaxation was found to be in accord with theoretical values. Hillock formation resulting from grain boundary sliding is believed to contribute to stress relaxation in its early stage. Thereafter, grain growth resulting from lattice diffusion is believed to play a major role in the stress relaxation.
CFX radical generation by plasma interaction with fluorocarbon films on the reactor wall
Authors: Miyata Koji , Hori Masaru , Goto Toshio
Published: July 2002

CFX (X=1–3) radicals were found to be generated from fluorocarbon films deposited on the reactor wall when the films are irradiated with plasmas. In this process, the fluorocarbon films were first formed on the reactor wall by electron cyclotron resonance (ECR) etching plasmas employing C4F8 and C4F8/H2 gases, and subsequently irradiated with an ECR-Ar plasma. CFX radical densities were measured during the Ar plasma by infrared diode laser absorption spectroscopy. CF3 radical density in the Ar plasma was estimated to be the same order as that in the C4F8 plasma. the fluorocarbon films deposited on the reactor wall were investigated by x-ray photoelectron spectroscopy. These results will offer valuable information for the production mechanism of CFX radicals in the etching process employing fluorocarbon gases.
Metal ion production by ion bombardment
Authors: Yamashita Mutsuo
Published: July 2002

A novel ion bombardment type metal ion production apparatus for ion-based thin film formation was constructed. In this apparatus, a plasma exciting high-frequency coil was mounted inside the metallic ion production chamber. A stable dense plasma of the order of 1012/cm3 could be obtained. When a Ti rod target, 4 mm (or 5 mm) in diameter and 45–100 mm in length, was fitted in the center of the HF coil and was negatively biased at −460 V, the top of the rod target was melted by heating due to the ion bombardment; vaporization of the target material occurred rapidly. The vaporized Ti atoms were ionized efficiently by the Penning effect and/or by the direct collision with many thermoelectrons emitted from the high temperature target surface. When the optimum perpendicular magnetic field (around 20 G) was applied to the plasma region, the plasma density increased and the operating gas pressure could be diminished to a lower limit of about 2×10−2 Pa. The main ion species were Ti+ and Ar+ in the mass spectrum of the extracted ion beam. The Ti+ ion current increased with Ar gas pressure and reached a maximum around 4 Pa. When a Cr target was used, the extracted ion beam was almost completely composed of Cr+ ions.
Grain size and hillock growth of vacuum-evaporated SnO2 thin films
Authors: Man W. K. , Yan H. , Wong S. P. , Wilson I. H. , Wong T. K. S.
Published: July 2002

In this study, tin-oxide (SnO2) thin films were prepared by a two-step process. With a vacuum-evaporation method, pure tin thin films were first deposited on Si and glass substrates at substrate temperatures from 50 to 300 °C. Then the metallic thin films were thermally oxidized with dry oxygen from 300 to 500 °C. The surface morphology of the SnO2 thin films was observed by scanning electron microscopy and atomic force microscopy. It was found that metallic hillocks are formed only for SnO2 thin films for which the substrate temperature during tin deposition was lower than 150 °C. The hillock growth is associated with stress inhomogeneity during the oxidation process. Grain size of the SnO2 thin films is also found to increase with the film thickness and the oxidation temperature. Kinetics of the grain growth is discussed in terms of a three-dimensional diffusion limited process.
Calibration issues for total reflection x-ray fluorescence analysis of surface metallic contamination on silicon
Authors: Diebold Alain C.
Published: July 2002

Total reflection x-ray fluorescence (TXRF) spectroscopy is used during process development and production process monitoring. Instruments used for these applications require measurement calibration and reproducibility. During 1994, a set of Ni dosed silicon wafers (approximately 1×1011 atoms/cm2) was fabricated and used in a ‘‘spoke in wheel’’ type of analysis round-robin. In this case, a set of samples was fabricated, analyzed by TXRF, and then smaller sets of three wafers were sent to five individual laboratories for analysis. The TXRF data demonstrated the reproducibility of TXRF results when samples have a uniform distribution across the surface. This work also points to the need for reference materials ≤ 1×1010 atoms/cm2. Gupta has previously shown that vapor phase decomposition (VPD) of Ni contamination is difficult, and we also report on VPD analysis of Ni [Gupta et al., Electro-Chem. Soc. Proc. 94-9, 200 (1994)]. We discuss the reproducibility of TXRF analysis of nonuniform surface contamination.
Unintentional hydrogenation of GaN and related alloys during processing
Authors: Pearton S. J. , Abernathy C. R. , Vartuli C. B. , Lee J. W. , MacKenzie J. D. , Wilson R. G. , Shul R. J. , Ren F. , Zavada J. M.
Published: July 2002

Atomic hydrogen plays an important role in GaN, passivating the electrical activity of Mg acceptors during cooldown after metal organic chemical vapor deposition growth, and thereby preventing achievement of high p-type doping levels unless an annealing step is performed. We have found that hydrogen is easily incorporated into GaN and related materials during many different process steps, including boiling in water, wet chemical etching in KOH-based solutions, dielectric deposition using SiH4 or dry etching in Cl2/CH4/H2Ar electron cyclotron resonance plasmas. In each of these cases we have employed deuterated chemicals and detected the incorporation of deuterium into GaN using high sensitivity secondary ion mass spectroscopy measurements. Hydrogen is found to have a diffusivity of ≳10−11 cm2 s−1 at 170 °C, and to passivate the electrical activity of Mg and C acceptors and also the native shallow donors in InGaN and InAlN. Annealing at 450–500 °C restores the electrical activity, but the hydrogen does not physically leave the films until much higher (∼800 °C) temperatures. The activation energies for dopant reactivation are of the order of 2.5 eV in bulk samples, where hydrogen retrapping is expected to be significant.
Reduction of gap states of ternary III–V semiconductor surfaces by sulfur passivation: Comparative studies of AlGaAs and InGaP
Authors: Seo J. M. , Kim Y.-K. , Lee H. G. , Chung Y.-S. , Kim S.
Published: July 2002

The effects of sulfur passivation on liquid-phase-epitaxy-grown n-type InGaP and AlGaAs surfaces have been studied using x-ray photoelectron spectroscopy. The surfaces were simultaneously prepared through degreasing and the use of an aqueous (NH4)2Sx treatment in air. For InGaP, sulfur atoms initially reacted with both surface In and Ga atoms and reacted negligibly with P atoms. The band bending was reduced by 0.7 eV compared to a sputter-cleaned surface. Presumably, sulfur eliminated P-vacancy-related gap states by occupying P sites and forming In–S and Ga–S bonds. By postheat treatment at 180 °C, S atoms were not removed from the surface and band bending was reduced further by 0.1 eV. For AlGaAs, S atoms initially reacted with Ga and As, but this treatment could not remove the Al oxide previously formed in the air. Postheat treatment at 180 °C simply induced S redistribution from As to Ga and As desorption, which reduced the band bending by 0.3 eV compared to the sputter-cleaned surface—a result similar to that for GaAs.
Sample charging of insulators with rough surfaces during Auger electron spectroscopy analysis
Authors: Park Jae-Won
Published: July 2002

A way to circumvent the sample charging in the analysis of insulators with rough surfaces during Auger electron spectroscopy (AES) has been studied. It is very difficult to handle the charging of insulators with rough surfaces during AES because of the irregular electron accumulations on the irradiated surface. This irregularity is attributed to various incident beam angles due to the surface roughness, which produce various electron excitation volumes in an electron rastering area. The charging problem of an insulator with rough surfaces during AES could be controlled by properly selecting the analysis position and area on the top of a protrusion or a particle on the surface of the insulating sample. This simple technique uses high spatial resolution of AES and the surface topography of an insulator, aiming at reducing the electron excitation volume as well as increasing the total electron yield.
Image force effects and the dielectric response of SiO2 in electron transport across metal–oxide–semiconductor structures
Authors: Wen H. J. , Ludeke R. , Newns D. M. , Lo S. H.
Published: July 2002

Hot electrons of variable energy were injected from a scanning tunneling microscope tip into a Pd/SiO2/Si(100) metal–oxide–semiconductor structure. An analysis of the emerging collector current in the Si substrate, a technique known as ballistic electron emission microscopy, revealed a monotonic barrier height lowering with increasing positive oxide bias, in excellent agreement with a scaled classical image force theory. Calculations using the WKB approximation suggest a negligible contribution to the observed shifts from electrons tunneling through the barrier. From an extrapolation to zero oxide field the Pd–SiO2 barrier height of 4.08±0.02 eV was deduced. An image-force dielectric constant of 2.74 in between the so-called optical (2.15) and static (3.9) dielectric constant was determined. In order to understand this intermediate value, a theoretical calculation of a retarded image force on the moving electron is carried out for the first time. The calculations yield an image-force dielectric constant of 2.69, that is consistent with the experimentally determined value. This intermediate dielectric constant is evidence for electron–phonon interaction and corresponds to an average dielectric response integrated over the time of progression of the electron in SiO2.
Etching of boron nitride in radio frequency plasmas
Authors: Schaffnit C. , Thomas L. , Rossi F.
Published: July 2002

This work demonstrates that ion assisted etching of hexagonal boron nitride is possible in addition to sputtering because of the ion bombardment in rf plasma environments. In order to study the presence of possible physical and chemical mechanisms, post treatments of boron nitride coatings were performed using pure argon, Ar/H2, and Ar/Cl2 plasma mixtures. This study reveals the effects of ion bombardment, H/H2 atoms, and Cl/Cl2 on the h-BN content in the films. It was found that, in addition to ion bombardment, hydrogen atoms and even more efficiently Cl and/or Cl2 can be used as chemical etchants for sp2 bonded boron nitride.
Design of a new sensor for mass flow controller using thin-film technology based on an analytical thermal model
Authors: Rudent P. , Navratil P. , Giani A. , Boyer A.
Published: July 2002

Thermal mass flow controllers are widely used in the semiconductor industry to deliver accurate process gas compositions and concentrations to the processing chamber. The sensor, a stainless-steel capillary tube, is the most critical part of the mass flow controller. We have designed a new sensor using thin-film technology in order to improve its reliability and to decrease its response time. The two temperature sensors are deposited platinum on an electrical insulating layer directly upon the capillary tube (without exposure to the gas stream) whereas the sensor is constantly heated by a resistive wire. The so-obtained sensors are very promising and the new design and technology could give us improvements which the old design and technology (two resistive coils) would not have been able to give us. The physical mechanisms of this new sensor are described by a third-order steady-state analytical thermal model which gives good results when compared with experiments. This fundamental study also includes the evolution of the correction factors as a function of the flow. We present here the thermal model, the new structure of the sensor, and its advantages.
Vacuum ultraviolet to visible emission of some pure gases and their mixtures used for plasma processing
Authors: Fozza A. C. , Kruse A. , Holländer A. , Ricard A. , Wertheimer M. R.
Published: July 2002

The vacuum ultraviolet (VUV) to near infrared emissions (112⩽λ⩽880 nm) from molecular gases (H2 and O2) and molecular gas–noble gas mixtures (H2–Ar and O2–Ar) have been investigated with two separate spectrophotometric instruments. We report the influence of plasma parameters such as gas composition, pressure, and microwave power upon the plasma emission. In the case of mixtures with noble gases, we selected a range of plasma parameters so as to obtain very intense VUV emissions, which can be useful for the photochemical treatment of polymer surfaces. Some kinetics mechanisms involved are discussed.
Asymmetric interface broadening in epitaxial Mo/W (001) superlattices grown by magnetron sputtering
Authors: Svedberg E. B. , Birch J. , Ivanov I. , Münger E. P. , Sundgren J.-E.
Published: July 2002

The interfacial structure in epitaxial Mo/W(001) superlattices, grown by magnetron sputtering on MgO(001) substrates has been studied. The films were grown in Ar and Kr discharges at a substrate temperature of 700 °C, and the as-deposited samples were analyzed by x-ray diffraction and found to be epitaxial with no high-angle grain boundaries. The degree of interfacial intermixing, caused by fluxes of different energetic species impinging on the growth surface, was estimated using a combination of Monte Carlo binary collision computer codes and a gas scattering computational model. In the Ar discharge case, large asymmetries in the Mo/W and W/Mo interfaces were found, with the W/Mo interface being more than a factor of 2 broader than the Mo/W interface. Simulations of x-ray reflectivity curves using the calculated interface profiles as input parameters without any additional fitting parameters agreed very well with measured data. The overall good fit between the calculated and measured reflectivity curves using the calculated compositional profiles is an indicator that the growth simulations using TRIM based codes provides interface profiles that are reasonably accurate, which can be used as a starting point for further refinements of the details of the interface structures.
Recent developments in the design, deposition, and processing of hard coatings
Authors: Zabinski J. S. , Voevodin A. A.
Published: July 2002

Coatings that offer protection from wear, low friction coefficients, and corrosion resistance are required for many applications ranging from tool inserts to bearings. The precise demands placed on these coatings varies by application, but to meet new requirements a useful approach is to use established coatings in new applications or create new materials by adjusting chemistry and microstructure. To achieve significant advancements in coating properties, we must go beyond single-layer/single-phase materials. Functionally gradient, multilayer, and composite coatings permit blending of properties traditionally considered mutually exclusive; for example, hardness and toughness. To facilitate growth of these types of coatings, improved deposition techniques must be developed. Discussion in this article focuses on the development of coating materials and deposition processes at the Air Force Materials Laboratory/Materials Directorate. Materials include nitrides/carbides and diamond-like carbon in functionally gradient, multilayer, and nanocomposite architectures. The magnetron assisted pulsed laser deposition process which permits the growth of infinitely variable gradients as well as sharp interfaces will be highlighted.
Study of substrate bias effect on corrosion susceptibility of thin film magnetic disks by accelerated chemical tests
Authors: Wang Charles C. , Chia Ray W. J. , Lee Jerry K. , Tang Wing T.
Published: July 2002

In this study, the characteristics of two relatively fast pore decoration techniques used for studying corrosion susceptibility of thin film disks with the structure CoCrTa/Cr/NiP/AlMg are discussed. The first technique employs HCl vapor. Since the HCl vapor reacts with both the cobalt alloy and the NiP layers, it has the capability of revealing pores in the sputtered layers with different sizes and depths that have an opening at the disk surface. The other technique uses a concentrated nitric acid solution. Because concentrated nitric acid reacts only extensively with the NiP layer, it is used to reveal the deeper pores in the sputtered layers with depth reaching the NiP layer. The tests are used to study the corrosion susceptibility of thin film disks with different substrate bias voltages during growth of the magnetic and chromium layers. By the use of these two accelerated chemical tests, the pinhole densities of sputtered films are found to decrease with increasing bias due to ion bombardment on the growing film that densifies the film structure. The porosity results obtained are compared with those conventional corrosion tests, including the environmental chamber test and hot water ion extraction. Good correlation among the different tests has been established.
MgO(100) surface relaxation by symmetrized automated tensor low energy electron diffraction analysis
Authors: Ferry D. , Suzanne J. , Panella V. , Barbieri A. , Van Hove M. A. , Bibérian J.-P.
Published: July 2002

We present a low energy electron diffraction study of the surface relaxation of MgO(100) at T=80 K down to the second atomic layer using in situ cleaved MgO crystals. We find that the main perturbation from the bulk structure is a topmost surface layer rumpling of 3.3±1.5% and a very small second layer rumpling of 0.2±2%. In both cases the oxygen atom is displaced outward. The first interlayer spacing is slightly reduced by 0.2±0.7% whereas there is no change in the second interlayer spacing.
Effect of fractal crystallization on the depositing sequence of a Pd/Ge thin film system
Authors: Zhiwen Chen , Shuyuan Zhang , Shun Tan , Jianguo Hou , Yuheng Zhang
Published: July 2002

The behavior of fractal crystallization in a Pd/Ge thin film system of various ratios of thickness (or composition) after annealing has been investigated by transmission electron microscope. It is difficult for coevaporated Pd–Ge films to obtain fractal crystallization. The fractal structure in Pd/a-Ge bilayer films can form more easily than in a-Ge/Pd bilayer films. The fractal crystallization was restricted because of the formation of the compounds (Pd2Ge and PdGe) in the Pd/Ge thin film system. Growth of the fractal structure depends on the competition between the two processes of amorphous germanium (a-Ge) crystallization and compound formation. Fractal formation can be explained by a random successive nucleation model.
Use of a new type of atomic hydrogen source for cleaning and hydrogenation of compound semiconductive materials
Authors: Kagadei V. A. , Proskurovsky D. I.
Published: July 2002

This article describes a source of atomic hydrogen (AH) based on a reflected Penning arc discharge with a hollow cathode and a self-heating electrode, designed for treating semiconductor materials with atomic hydrogen in technological processes. The source can readily be incorporated in industrial systems for thin-film deposition, ion implantation, and molecular beam epitaxy. In experiments on treatment of semiconductor structures the source was operated at a discharge operating voltage of 200 V and a current of 2 A. Measurements of the activation energy of AH etching have been preformed for GaAs (0.13 eV) and InP (0.19 eV) anode oxides and for a SiO2 film produced by chemical vapor deposition method (0.15 eV). The thickness of the native oxide layer has been investigated as a function of temperature and treatment time. The oxide film was completely removed in 1–2 min at a specimen temperature of T=400 °C and in 3–5 min at T=350 °C. It has been shown that when the AH cleaning of the GaAs surface and deposition of a metal film (AuGe, Ti, Ni) are accomplished in a unified vacuum cycle, no contaminant is present at the film–substrate interface. This, in particular, improves the characteristics of structures with a Schottky barrier. It has been found experimentally that the AH treatment of the GaAs surface reduces the rate of the subsequent oxidation of the surface in air. The AH source was also used for hydrogenation of the near-surface layers of semiconductor structures. The devices manufactured from the hydrogenized structures showed improved performance.
Twin-source plasma chemical vapor deposition for high rate deposition of SiO2 films
Authors: Nonogaki Ryozo , Nakai Shinji , Yamada Suzuya , Wada Tetsuya
Published: July 2002

A twin-source plasma chemical vapor deposition (p-CVD) method has been designed and tested for high rate deposition of SiO2 films. In the p-CVD system, two kinds of source gases are decomposed in the plasma generators independently, and then introduced onto the substrate. The gas in front of the substrate is excited successively by a third plasma generated by coupling of rf power into the electrode just below the substrate. The films were formed at room temperature. The setup increased the collision probability of reactive O* and SiHx*, and a high deposition rate of 1.9 μm/min was achieved by the high density of the precursors.
Symmetry of, and polarized-laser-induced reactions on, Si (111)/Cl2 surfaces studied by second-harmonic generation
Authors: Haraichi Satoshi , Sasaki Fumio
Published: July 2002

The surface symmetry of, and the polarized-laser-induced reactions on, Si (111)/Cl2 surfaces have been studied using second-harmonic generation (SHG). The outermost surface originated SHG signals, generated by 1.1, 1.3 and 2.0 eV probe, show the modified 3 m symmetries enhanced along the [21̄1̄] direction, probably because of a macroscopic asymmetric surface structure along the [21̄1̄] orientation. On the other hand, the SHG signals originated by the direct bulk transition, generated by 1.6 and 1.7 eV probe, show good 3 m symmetries rather reflecting the symmetry of bulk Si. The threshold power densities of the laser-induced Si (111)/Cl reaction showed significant dependence on the pump polarization with respect to the crystal orientation of the sample surface, and no important dependence on that with respect to the plane of incidence.
Diffusion behavior study of Yb+ and Er+ implanted into polyimide (C22H10N2O5)n
Authors: Wang Ke-Ming , Lu Fei , Meng Ming-Qi , Huang Mu-Bin , Wu Bo , Li Wei , Liu Xiang-Dong , Liu Ji-Tian
Published: July 2002

Polyimide (C22H10N2O5)n films were irradiated at room temperature by 200, and 300 keV Yb+ and 400 keV Er+. The dose was 1×1015 ions/cm2. The Rutherford backscattering technique has been used to study the diffusion behavior and the depth distribution of implanted Yb+ and Er+ in polyimide (C22H10N2O5)n. The results show that (1) for the sample annealed at lower temperature, the migration of Yb+ and Er+ into the overlying polyimide is faster than into the undamaged polyimide, but there is a significant non-Fickian tail extending deep into the undamaged polyimide film, (2) oxygen loss was observed, and (3) the depth distributions of “as implanted” Yb+ and Er+ were nearly Gaussian in all cases. The x-ray photoelectron spectroscopy was used to study the structural modification. After ion implantation, the binding energy of carbon 1s, nitrogen 1s and oxygen 1s in polyimide was decreased.
Diamond nucleation on nonscratched Si substrate pretreated by pulsed high-temperature and high-density CH4-plasma beam
Authors: Jiang Ying-Bing , Zhang Hong-Xia , Liu Chi-Zi , Liu Bin , Lin Zhangda , Wu Cheng , Yang Si-Ze
Published: July 2002

While great interest has been focused on low-temperature plasma chemical vapor deposition, the pulsed high-temperature and high-density plasma beam was utilized to enhance diamond nucleation on Si substrate without damaging the smoothness of Si surface, and a nucleation density up to 109 cm−2 was obtained. Scanning electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy results indicated that after pretreated by this high power CH4 plasma, an amorphous modified layer rich in sp3-hybridized carbon was formed on the Si surface. This layer was believed to provide large amounts of nucleation sites for diamond.
Abnormal steady states in reactive sputtering
Authors: Zhu Shenglong , Wang Fuhui , Wu Weitao
Published: July 2002

For a sputter system equipped with a constant current power supply and under reactive gas flow control, certain compositions of film are usually not accessible in the normal steady states because of the transition of steady state and the hysteresis effect. Theoretical studies in this article indicated that there exist abnormal steady states where films of intermediate compound contents may possibly be produced. However, the experimental endeavors to attain these states in a system under current/flow control failed. Further theoretical studies in this work indicated that not only are the abnormal steady states difficult to establish, but also they are sensitive to tiny drifts in parameter. In other words, in a sputter system with constant discharge current and constant reactive gas flow, the abnormal steady states can only be achieved and maintained when the parameters are set and kept in point sharply. These theoretical results revealed why it is not practically possible to operate steadily between the metal sputtering region and the compound sputtering region when a sputter system is under flow/current control.
Measurements of trace gaseous ambient impurities on an atmospheric pressure rapid thermal processor
Authors: Kondoh Eiichi , Vereecke Guy , Heyns Marc M. , Maex Karen , Gutt Thomas
Published: July 2002

Gaseous impurities in nitrogen ambient in the chamber of an atmospheric pressure rapid thermal processor were quantitatively measured. We employed atmospheric ionization mass spectrometry (APIMS) for this purpose. APIMS is the most sensitive technique to detect trace impurities in a gas at atmospheric pressure. A wide dynamic range (0.1 ppb→10 ppm) measurement was successfully performed, which allowed real-time monitoring of impurities during rapid thermal annealing. This work reports fundamental behavior of the ambient impurities originating from different sources. The sources discussed in this article are fourfold: source gas, system background, air (wafer loading), and wafer itself. The contribution of the source gas was found to be negligible, whereas the air and the wafer were found to be most crucial. Ambient management requires a better understanding of the independent contribution of each source to processing. It is shown how in situ measurements help to define process recipe for different types of wafers.
Ionized plasma vapor deposition and filtered arc deposition; processes, properties and applications
Authors: Martin P. J. , Bendavid A. , Takikawa H.
Published: July 2002

Recent innovations in vacuum arc deposition have resulted in the development of the filtered arc source as a deposition tool for a range of technologically important materials. The vacuum arc was recognized early on as a potentially useful source of energetic, ionized material and a practical high rate method for depositing thin films with bulk properties and the deposition of new materials. The inherent problem of microdroplet contamination was overcome by several approaches, the toroidal magnetic duct being the most prevalent. The present state-of-the-art of filtered arc deposition is discussed in terms of the current understanding of the emitted fluxes, the properties of the materials deposited by these devices and new applications.
Growth of Ag rows on Si(5 5 12)
Authors: Song H. H. , Jones K. M. , Baski A. A.
Published: July 2002

Our scanning tunneling microscopy studies show that Ag deposited onto Si(5 5 12) and annealed to moderate temperatures (400–450 °C) forms well-ordered overlayer rows. These rows have aspect ratios up to 150:1 and therefore are possible candidates as “nanowires.” As the Ag coverage is increased, the rows grow in length and number until the surface forms a periodic array of such structures at ∼0.25 monolayer (ML). A statistical analysis of these rows reveals a linear increase in median row length as a function of coverage with a median length of 67 nm at full coverage (∼0.25 ML). At higher annealing temperatures (>500 °C), Ag continues to form row-like structures, but the rows are wider and cause local faceting of the underlying Si substrate. We can therefore conclude that the lower temperature Ag rows are actually a metastable arrangement of the surface.
Consequences of mode structure on plasma properties in electron cyclotron resonance sources
Authors: Kinder Ronald L. , Kushner Mark J.
Published: July 2002

Low pressure (<50 mTorr) electron cyclotron resonance plasma sources are being developed for downstream etching and deposition and for production of radicals for surface treatment. The spatial coupling of microwave radiation to the plasma is a concern due to issues related to the uniformity of dissociation, electron heating, and ultimately process uniformity. To investigate these issues, a finite-difference-time-domain simulation for microwave injection and propagation has been developed, and has been incorporated as a module in the two-dimensional Hybrid Plasma Equipment Model. Results from parametric studies of N2 plasmas suggest that obtaining uniform fluxes to the substrate may require a power deposition profile that is peaked off axis. An increase in power deposition tends to reinforce nonuniformities in the ion flux profile. At higher pressures (>10 mTorr) the sensitivity of the ion flux to the substrate to the angle of the magnetic field at the substrate decreases, while the uniformity of the ion flux improves. Due to the dependence of the collision frequency on electron temperature, losses from cross-field diffusion are enhanced in both the low and high pressure regimes. Results also suggest that there is an optimal pressure for maximizing both the magnitude of the ion flux to the substrate surface and its uniformity.
Analysis of silicon oxynitrides with spectroscopic ellipsometry and Auger spectroscopy, compared to analyses by Rutherford backscattering spectrometry and Fourier transform infrared spectroscopy
Authors: Tompkins Harland G. , Gregory Richard B. , Deal Paul W. , Smith Steven M.
Published: July 2002

This work addresses the issues of whether spectroscopic ellipsometry, using the effective medium approximation (SE-EMA), may be used meaningfully to analyze plasma-enhanced chemical vapor deposition silicon nitride films. We use Rutherford backscattering spectrometry and Fourier transform infrared spectroscopy as reference methods and compare the results to the results of SE-EMA analyses and Auger analyses. The results are that Auger analysis, using properly determined sensitivity factors, gives compositions which are within the uncertainty of the reference methods. SE-EMA, on the other hand, always overestimates the oxide contribution and underestimates the nitride contribution. Probable causes are discussed.