bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of ethylene oxide and propylene oxide chemisorbed on clean and oxygen precovered Ag(110)
Authors: Bare Simon R.
Published: July 2002

The adsorption of ethylene oxide and propylene oxide on clean and oxygen precovered Ag(110) was studied using temperature programmed desorption, low-energy electron diffraction (LEED), high-resolution electron energy-loss spectroscopy (HREELS), and x-ray photoelectron spectroscopy. Both ethylene oxide (C2H4O) and propylene oxide (C3H6O) adsorb weakly on the clean Ag(110) surface, with heats of adsorption of 9.5 and 10.6 kcal/mol, respectively. The heats of adsorption of both C2H4O and C3H6O increase by about 30% as the coverage of coadsorbed atomic oxygen is increased up to an oxygen coverage of 0.5, where the heat of adsorption decreases again. Ethylene oxide forms a c(2×2) LEED pattern at saturation coverage of the monolayer following adsorption at 90 K. A racemic mixture of C3H6O forms a (4×2)p1g1 LEED pattern, while the pure enantiomer (S)-C3H6O forms a c(2×2) pattern at the same saturation coverage of the monolayer. Models of the structures accounting for these data are proposed. The HREELS of C2H4O and C3H6O on clean Ag(110) are little perturbed from their gas phase spectra. The epoxide ring of C2H4O is close to normal to the surface, while that of C3H6O is inclined. There is little change in the vibrational frequencies of the normal modes of C2H4O or C3H6O on the oxygen precovered surface. The orientation of C3H6O is influenced by coadsorbed atomic oxygen.
Phase transition of the Si(111)–Au surface from √3 ×√3 to 5×1 structure studied by means of the low-energy electron diffraction, Auger electron spectroscopy, and Rutherford backscattering spectroscopy techniques
Authors: Yuhara Junji , Inoue Masahiko , Morita Kenji
Published: July 2002

The changes of the Au coverage and the structure of the Si(111)–√3×√3-Au surface induced by isothermal annealing in the temperature range of 500–575 °C have been studied by means of low-energy electron diffraction (LEED), Auger electron spectroscopy, and Rutherford backscattering spectroscopy techniques. It is found that the Au coverages by RBS and AES at each temperature decay exponentially down to 0.75 ML, above which only the LEED pattern of √3×√3 spots is observed, and decay biexponentially from 0.75 ML and a mix of √3×√3 + 5×1 spots is observed down to 0.54 ML at 575 °C, 0.52 ML at 550 °C, and 0.61 ML at 530 °C, below which only the LEED pattern of 5×1 spots is observed. From analysis of the decay curves of Au coverages, it is determined that the activation energies for Au atoms to be dissolved from the √3×√3 structure and the 5×1 structure into the bulk and for phase transition of the Au/Si(111) surface from the √3×√3 to the 5×1 structure are 2.5±0.5, 2.8±1.0, and 1.6±0.4 eV, respectively. The process for the phase transition is discussed.
Deposition system for the synthesis of modulated, ultrathin-film composites
Authors: Fister Loreli , Li Xiao-Mei , McConnell John , Novet Thomas , Johnson David C.
Published: July 2002

We have initiated a program using elemental superlattices as probes of the early stages of solid-state reactions. The main advantage of using superlattices as reactants is the ability to tailor their structure on an angstrom length scale to control reaction kinetics. Consequently, we designed and constructed a computer-controlled and monitored ultrahigh-vacuum chamber for the preparation of elemental superlattices. This system is capable of manufacturing three sets of three samples in one evacuation cycle. Up to six different elements can be incorporated into each sample. Elements can be deposited from independently controlled electron-beam sources, Knudsen, or evaporation cells. The sample drive mechanism combined with source shutters and computer control permit complex layer-repeat units within the composite. Layer thicknesses can be controllably varied from 4 Å upward. Various attributes of the chamber include its modular design, multiple layer thickness control options, reproducibility and quality of samples, flexibility, and extensive computer monitoring during sample preparation.
In situ investigation of temperature and bias dependent effects on the oxide growth of Si and Ge in an electron cyclotron resonance
Authors: Hu Y. Z. , Wang Y. Q. , Li M. , Joseph J. , Irene E. A.
Published: July 2002

The electron cyclotron resonance (ECR) plasma oxidation of Si and Ge was investigated using in situ spectroscopic ellipsometry at substrate temperatures of 80–400 °C and at bias voltages of −30 to +60 V. A study of the oxide growth kinetics by ECR plasma oxidation results in three distinct regions of growth with the first two being linear and the last parabolic. At the earliest linear stage the rate of oxide growth is the fastest, and corresponds to ∼3 nm film thickness which is not dependent on bias. Following this, the second linear region displays an oxide growth rate proportional to the bias with typical growth rates of 0.10, 0.32, and 0.60 nm/min for 0, +30, and +60 V, respectively, at 300 °C. The third region displays parabolic kinetics and corresponds to the Cabrera–Mott (CM) theory for the oxidation by charged species in the limit of a low electric field. Activation energies of 0.19 and 0.28 eV are obtained using the CM model for the ECR plasma oxidation of Si and Ge, respectively. Increasing the negative bias causes oxide sputter etching and surface damage, with no significant contribution to oxidation. A probable mechanism for the ECR plasma oxidation process is also discussed.
Spectroscopy and photochemistry of acetylene adsorbed on NaCl(100)
Authors: Dunn S. Keith , Ewing G. E.
Published: July 2002

Polarized infrared absorption spectroscopy is used to determine molecular tilt and orientation of acetylene physisorbed to NaCl(100). The spectra are qualitatively explained by an ordered structure similar to the low-temperature crystalline phase of acetylene. We also find evidence for a high-temperature, disordered lattice-gas phase of this system. Upon exposure to 184.9 nm light the lattice gas undergoes a hydrogen exchange reaction, while the structured phase is unreactive. In contrast to gas-phase photolysis, which yields a polymer, molecular hydrogen, and a collection of small hydrocarbons, no products other than acetylene isotopomers are observed in the surface-phase reaction. The rate of the reaction shows an exponential temperature dependence and is interpreted as being surface diffusion limited. We propose that this photochemical hydrogen exchange occurs by a radical chain reaction.
Adhesion measurement of Ti thin films on Si substrate using internal stress in overcoated Ni films
Authors: Kondo Ichiharu , Takenaka Osamu , Kamiya Toyoharu , Hayakawa Kaname , Kinbara Akira
Published: July 2002

Adhesion strength between sputtered Ti thin films and Si substrate has been evaluated by using an internal stress in Ni thin films deposited onto the Ti thin films. The adhesion of the Ni film to the Ti film is very strong and the internal stress in the Ni film was found to be large enough to peel off the Ti film from the Si substrates. The tensile stress generated by the internal stress in the Ni film at the interface between the Ti film and the Si substrate was evaluated by finite element method. By this method, it became clear that when the value of the Ni film internal stress times the Ni film thickness was 150 N/m, the corresponding tensile stress at the interface was 10 MPa and this stress was enough to peel off the Ti film on an Ar ion bombarded Si substrate.
Posthydrogenation study of a-Si films grown by reactive magnetron sputtering
Authors: Liang Y. H. , Abelson J. R.
Published: July 2002

Amorphous silicon thin films were deposited by dc reactive magnetron sputtering and posthydrogenated in order to investigate the H diffusion kinetics in a network originally free of H. A flux of atomic H was generated by dissociation of molecular hydrogen on a hot filament. Secondary ion mass spectroscopy was used to characterize the H profiles at various stages of diffusion. H profiles measured from secondary ion mass spectroscopy can be fitted by a complementary error function. The H diffusion exhibits a dispersive behavior, and the diffusivity in the a-Si is about 1×10−15 cm2 s−1 at 340 °C and t=240 min. The dispersive parameter α was estimated to be ∼0.4. The activation energy was ∼0.4 eV. In order to improve the sensitivity at low concentration, posthydrogenation was also done with deuterium. Secondary ion mass spectroscopy analysis shows that at high D concentration the profile follows a complementary error function behavior, while at low concentration D profile follows an exponential decay. These results show that the posthydrogenation in dc magnetron sputtered amorphous silicon can be described by the combined effects of deep and shallow traps.
Vacuum conditions for sputtering thin film TiNi
Authors: Jardine A. Peter
Published: July 2002

Sputter deposition of TiNi has been problematic due to the extreme reactivity of titanium. There are several advantages in depositing TiNi with other metals such as Ti and Cu since the shape memory effect properties can be changed selectively, including coring of the thin film. Simultaneous codeposition of cored material using sputter deposition becomes technically difficult as this implies that the sample to target distance increases. In this article, we discuss a relationship developed so that a basic base vacuum pressure can be found with target–sample distance and correlated to the observed phases for both Ti and TiNi samples. Practical limitations imposed by the vacuum system on both devices and device quality are discussed.
Surface spectroscopic studies of the deposition of TiN thin films from tetrakis-(dimethylamido)-titanium and ammonia
Authors: Corneille J. S. , Chen P. J. , Truong C. M. , Oh W. S. , Goodman D. W.
Published: July 2002

The adsorption and pyrolysis of tetrakis-(dimethylamido)-titanium (TDMAT), Ti[NMe2]4, on several metal substrates, were studied using x-ray photoelectron spectroscopy, Auger electron spectroscopy, infrared reflection absorption spectroscopy and thermal desorption mass spectrometry. TDMAT was found to decompose readily above ∼480 K on metallic substrates, producing TiCxNy films exhibiting a carbon-rich interface. However, in the presence of NH3, well below the threshold of gas-phase reactions (<10−4 Torr), the growth of low-carbon-content (≤8 at. %) titanium nitride films proceeds readily, via surface mediated reaction(s) of TDMAT and NH3 between 550 and 750 K. The effects of surface temperature and reagent pressures are reported and discussed.
Fluid simulations of particle contamination in postplasma processes
Authors: Garrity M. P. , Peterson T. W. , Garrett L. M. , O’Hanlon J. F.
Published: July 2002

Fluid flow and particle trajectories in postplasma processes are simulated using a commercially available computational fluid dynamics code. Two parallel plate geometries are modeled. Recirculation eddies are observed and particles of 0.01 μm diameter can be trapped in these zones. Gravity can be a dominant mechanism, resulting in particle deposition onto wafer and chamber surfaces. The collection efficiency of particles on the wafer is near unity for particles 0.1 μm or greater in diameter, and efficiency increases with pressure and flow rate. For example, for gas conditions of 20 sccm and 15 mTorr (2 Pa) 35% of 0.01-μm-diam particles are collected on the wafer when released 2 cm above the wafer, while at 20 sccm and 100 mTorr (13.3 Pa), collection increases to 95%. Particle deposition as a function of initial particle position depends on chamber configuration.
Oxidation and 6H-SiC–SiO2 interfaces
Authors: Hornetz B. , Michel H.-J. , Halbritter J.
Published: July 2002

For hexagonal SiC the oxidation is slower for the Si-terminated surface as compared to the C-terminated surface. This has been related to an unknown interface compound. Our angle resolved x-ray photoelectron spectroscopic (ARXPS) analysis of oxidized Si-(001) and C-(001̄) surfaces of 6H-SiC reveals the interface oxide Si4C4−xO2 (x≤2), seemingly a reaction product of a peroxidic O2 bond to a SiC double layer. This oxide occurs in larger thickness (≂1 nm) at the slowly oxidizing Si-(001) surface, whereas the C-(001̄) surface shows smaller amounts, only, diminishing fast with oxidation above 1000 K. Evidence is presented that the oxidation of SiC to SiO2 is retarded by a Si4C4−xO2 interface layer. Our ARXPS analysis is consistent with amorphous SiO2 containing less than 3% Si4C4O4 as oxidation product of Si4C4−xO2.
A radio-frequency bandpass mass filter for broad ion beams
Authors: Schlemm H.
Published: July 2002

A bandpass mass filter for broad ion beams based on mass selective radio-frequency acceleration of ions is described. The ions are extracted from a broad beam ion source by a conventional hole two-grid extraction system. The mass separation consists in multiaperture coaxial hole channels formed of seven grids. The dimensions of the channels are calculated. This arrangement is investigated by ion ray tracing and by experimental investigation. Results for mass resolution (M/ΔM), transmission, and beam current density are presented. For nitrogen, argon, and krypton a transmission of 5%, a beam current density of 4 μA/cm2, and a mass resolution of 4 are achieved.
Chemical microanalysis by reflected electron energy loss microscopy
Authors: Paparazzo E.
Published: July 2002

We test the potential of reflected electron energy loss microscopy (REELM) as a tool for imaging chemical change in systems that possess both lateral and in-depth inhomogeneities, as well as in insulator samples. Results obtained across the interface between an atomically clean InSb surface and the adjacent, heavily contaminated InSb surface show, in agreement with the findings of other workers, that the technique provides a much better chemical contrast than the one offered by scanning Auger microscopy (SAM). The depths probed by REELM span a range that is several times wider than by SAM, and REELM provides nondestructive depth profiling into the thickness of the contamination layer, as well as of the layer built up on the clean region after air exposure. Na metal, accumulated on the surface of long electron-irradiated NaF, is easily imaged by REELM despite the severe surface charging that prevented Auger spectra and SAM imaging. Following the anticipated findings that appeared in the literature some time ago [A. J. Bevolo, Scanning Electron Microsc. Part IV 1449 (1985)], this is the first experimental evidence that REELM is virtually immune to surface charging in insulator surfaces.
Changes in refractive index and in chemical state of synchrotron radiation irradiated fluorinated polyimide films
Authors: Maruo Yasuko Yamada , Sasaki Shigekuni , Haga Tsuneyuki , Kinoshita Hiroo , Horiuchi Toshiyuki , Tamamura Toshiaki
Published: July 2002

Changes in refractive index and in film thickness caused by synchrotron radiation are studied in a fluorinated polyimide (6FDA/TFDB). The index at 589.6 nm increased by 1.3% and the thickness decreased by 0.69% for 8-μm-thick film after 30 min irradiation. X-ray photoelectron spectroscopy analysis was performed on the modified surfaces after synchrotron radiation exposure. From the present data the synchrotron radiation leads to production of a fluorine-poor surface.
Issues of atomic-resolution structure and chemical analysis by scanning probe microscopy and spectroscopy
Authors: Wiesendanger R. , Bode M. , Pascal R. , Allers W. , Schwarz U. D.
Published: July 2002

The ultimate goal of high-resolution microscopy, i.e., the determination of structure and chemistry on the atomic scale, has not been achieved yet. In the case of scanning tunneling microscopy (STM), the superposition of atomic and electronic structure information was found to be a critical issue, particularly for semiconductor surfaces. Here, we show that, in the case of multicomponent systems with large unit cell size, the structural analysis is further complicated by the decay behavior of the surface wave functions, which drastically influences the distance dependence of STM images. The chemical analysis at the atomic level is generally prevented by the inaccessibility of core levels due to the low-energy scale of scanning probe microscopies. However, fingerprints for particular chemical species at the atomic level can be obtained from tunneling spectroscopy independent of the chosen substrate. Here, we will focus on a particular example of iron adsorbates on different metal substrates. Finally, the possibility of achieving chemical contrast on the nanometer scale by friction force microscopy and force spectroscopy methods will be discussed.
Interactions of small molecules with TiO2(110) surfaces: The role of defects
Authors: Wang Li-Qiong , Shultz A. N. , Baer D. R. , Engelhard M. H.
Published: July 2002

In this article, the adsorption behavior and the surface redox reactivity among small molecules including N2O, O2, H2O and HCOOH on TiO2(110) surfaces are compared. New measurements of the interaction of HCOOH with defect-free and defective TiO2(110) surfaces and initial results from N2O adsorption on defects are combined with earlier work involving O2 and H2O. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) were used to monitor the amount of species adsorbed on the surface and the presence of electronic defects. The defective surfaces were prepared by Ar+ bombardment and electron-beam exposure. Both O2 and N2O ‘‘heal’’ defects (defect healing means an observation of the reducing of defect state intensity in both XPS and UPS spectra) even if they do not readily stick on the TiO2(110) surfaces at 300 K. H2O also heals defects, but at a much slower rate than either O2 or N2O. In contrast, HCOOH exposure produces little healing even though the rate of adsorption for HCOOH (with saturation exposure of 103 L) is much faster than for H2O. The interactions of small molecules with defective TiO2(110) surfaces involve not only the adsorption and dissociation of molecules on the surface but also the surface redox reaction in which the reduced Ti states (such as Ti3+) are oxidized by the surface adsorbates to Ti4+, resulting in the reduced Ti 3d defect intensity.
Thin metal films deposited at low temperature for optoelectronic device application
Authors: He L. , Shi Z. Q.
Published: July 2002

Thin metal layers play an important role in the development of electronic devices. Thin metal films deposited at low temperature (LT=77 K) have shown some unique properties which enhance device performance. The microstructure properties of thin metal films formed at room temperature (RT=300 K) and LT were investigated in this work. An insulating substrate was used for Au, Ag, and Al metal deposition. The surface morphology and microstructure of the metal films was studied by transmission electron spectroscopy (TEM) and atomic force microscopy (AFM). The resistance of the thin films was measured in situ as a function of film thickness and temperature. It was found that all LT thin films become electrically continuous at a much lower thickness than the RT films. Electrical measurements determined that the LT films demonstrated several orders of lower resistance compared to RT film at very thin (less than 100 Å) thickness, which could lead to the potential applications of these films on electronic and optoelectronic devices. It is observed by both TEM and AFM that the LT films showed much lower density of grain boundaries than the RT samples at the same thickness. This is consistent with the resistance measurement results.
Solid phase epitaxy of β-FeSi2 on Si(100)
Authors: Chen H. , Han P. , Huang X. D. , Zheng Y. D.
Published: July 2002

Orthorhombic β-FeSi2 is a semiconducting material with a direct band gap of about 0.87 eV, which makes it an active component in light detectors and near-infrared sources. Solid phase epitaxy (SPE) has been used as the conventional method to grow epitaxial β-FeSi2 films. In this article, we report on the SPE of β-FeSi2 films using Fe/Si(100) heterostructures obtained by metalorganic chemical vapor deposition (MOCVD). The formation processing of the β-FeSi2 thin films includes the deposition of iron on Si(100) by MOCVD and a subsequent annealing. The highly textured Fe layer deposited on the silicon substrate was tested by x-ray diffraction (XRD) and electron microscopy techniques. The β-FeSi2 film was successfully formed after the annealing process. The better epitaxy of β-FeSi2 on Si(100) was evidenced by XRD measurements. It was also confirmed by Raman spectra measurements, in which some main Raman lines were clearly detected. Optical transmission measurements revealed a strong absorption of β-FeSi2 near 0.87 eV.
Strain gradients and normal stresses in textured Mo thin films
Authors: Malhotra S. G. , Rek Z. U. , Yalisove S. M. , Bilello J. C.
Published: July 2002

The high-resolution x-ray-diffraction technique was used to explore strain variations in sputtered Mo films with thicknesses of 170, 260, and 800 nm that possess a (110) out-of-plane texture. The strains in crystallographic planes perpendicular to the surface of each film were found to be nominally constant and compressive at all x-ray penetration depths. Near the surface of each film, the inclined-plane strains were compressive, and then relaxed as the penetration depths approached each entire film thickness. The strain tensor in a laboratory reference frame for each film, as a function of penetration depth, revealed that the normal strain εzz was tensile near the surface of each film, and then relaxed to a nominally constant value as the penetration depths approached the entire film thickness. The penetration depth over which the normal strain decayed to a nominally constant value increased as the total film thickness increased. A consequence of the large normal strains near the free surface of each film is that the corresponding normal stresses were nonzero.
Crystallographic and microstructural studies of BaTiO3 thin films grown on SrTiO3 by laser molecular beam epitaxy
Authors: Cui Da-Fu , Wang Hui-Sheng , Chen Zheng-Hao , Zhou Yue-Liang , Lu Hui-Bin , Yang Guo-Zhen , Ma Kun , Chen Hong , Li Lin , Liu Wei , Zhang Yun
Published: July 2002

A series of trial tests were carried out to grow BaTiO3 thin films on SrTiO3 substrates in our newly built laser molecular beam epitaxial system. The phase, crystallographic orientation and crystalline quality of the films were investigated by x-ray diffraction θ/2θ scan, symmetric and asymmetric rocking curves (ω scans) and φ scan. The interfacial microstructures of the BaTiO3/SrTiO3 and the surface morphology of BaTiO3 films were analyzed by cross-section transmission electron microscopy and atomic force microscopy. Under appropriate growth conditions, epitaxial, single-crystal films with fully c-axis oriented tetragonal structure were obtained. The tetragonality was calculated by using {303} asymmetric rocking curve for a BaTiO3 thin film to be 1.027, which is larger than the bulk value of BaTiO3. The BaTiO3/SrTiO3 interface is very abrupt with no transitional layer and the BaTiO3 film exhibits an atomically smooth surface.
Optimization of niobium thin films by experimental design
Authors: Knappe S. , Elster C. , Koch H.
Published: July 2002

The statistical methods of experimental design were applied to efficiently increase the quality of sputtered niobium thin films. A large number of potential factors and interactions were explicitly taken into consideration in order to optimize the particular fabrication process. Three factors were found to influence the intrinsic stress of niobium films; five further factors affected the residual resistance ratio. The process behavior was modeled and optimized using these factors. The process description presented is more comprehensive than typically reported, and the results deviate from published data.
Laser single-photon ionization mass spectrometry measurements of SiCl and SiCl2 during thermal etching of Si(100)
Authors: Materer N. , Goodman Rory S. , Leone Stephen R.
Published: July 2002

Pulsed laser single-photon ionization time-of-flight mass spectrometry is used to investigate the etch products resulting from thermal etching of Si(100) with molecular chlorine over a temperature range of 1023–1373 K and a pressure range of 10−5–10−4 Pa. In this regime, two thermal etch products, SiCl2 and SiCl, are directly observed by ionization without fragmentation using 118 nm light. Over this temperature and pressure range, the desorption fluxes of SiCl2 and SiCl are proportional to the dosing chlorine pressure. A phenomenological activation energy of 0.36±0.03 eV is observed for the SiCl desorption flux from an Arrhenius plot. The SiCl2 product flux exhibits a complex temperature dependence, first increasing and then decreasing, and thus this rate is controlled by at least two pathways. One pathway in the lower temperature regime may be a direct desorption channel. The other process at higher temperatures may be a competing reaction that limits the precursor species, most likely SiCl, for the formation of SiCl2 on the surface. The ability to detect the radical species without mass spectral cracking provides the potential to unravel such complex pathways.
Recombination at the silicon nitride/silicon interface
Authors: Elmiger J. R. , Schieck R. , Kunst M.
Published: July 2002

A contactless technique to study the characteristic quantities of the SiNx/Si interface is of great interest. To investigate this interface, the influence of the light-induced excess charge carrier concentration (Δnb) on the differential interface recombination velocity (Sdiff) at the SiNx/Si interface is studied using frequency resolved microwave conductivity measurements. Sdiff is determined for SiNx/Si systems with different doping types and doping concentrations of the Si substrate. The excess carrier concentration is measured independently from the determination of Sdiff by means of the method of the short circuit variation. Very good passivation of the Si surface by the SiNx film was observed with surface recombination velocities smaller than 10 cm/s. The experimentally obtained values of Sdiff as a function of Δnb show good agreement with calculations based on the Shockley–Read–Hall formalism. Capacity–voltage measurements enabled the determination of the interface defect density and the positive fixed charge density in the SiNx(Qf=2×1012 cm−2). The dependence of Sdiff on the excess carrier concentration is caused by the large positive fixed charge density and the high ratio of the charged-to-neutral acceptor capture cross sections (σca/σna). The comparison between the model and the experimental results yields acceptor capture cross sections of σca=5×10−15 cm2, σna=5×10−21 cm2 for n-Si and σca=1×10−14 cm2, σna=1×10−20 cm2 for p-Si. The influence of the donor capture cross sections on Sdiff can be neglected. Additionally, the experimentally determined interface defect density could be verified with model calculations.
Growth, morphology, and magnetic properties of ultrathin epitaxial Co films on Cu(100)
Authors: Coyle S. T. , Hembree G. G. , Scheinfein M. R.
Published: July 2002

The room temperature growth and morphology of epitaxial Co films on Cu(100) were studied from the initial nucleation of islands through thicknesses of several monolayers using in situ nanometer resolution ultrahigh vacuum scanning electron microscopy, Auger electron spectroscopy, and the surface magneto-optic Kerr effect. The films became ferromagnetic at room temperature at ∼1.7 ML (1 ML=1.53×1015 atoms/cm2). Roughening structures, seen as large inclusions into step bands and terrace pits from which Cu may have migrated, were observed. Minimization of surface energy along step edges is offered as a possible explanation for the observed morphology at the beginning stages of the formation of these structures. A second Co magnetic phase was detected in many films with out-of-plane remanence and a coercivity 5–10 times the in-plane value.
Effects of oxygen flooding on sputtering and ionization processes during ion bombardment
Authors: Tian C. , Vandervorst W.
Published: July 2002

The effects of oxygen flooding on the sputter and ionization yield of Si and SiO2 have been investigated. Additional processes in sputtering and ionization may be introduced by oxygen flooding beyond a simple chemical adsorption and knock-on process, leading to a larger reduction in sputter yield and a further enhancement in ionization yield for silicon sputtered from a Si substrate as compared to the values for silicon dioxide. A transient, particularly for the sputter yield, still remains, implying that the transient reduction is not as complete as desired.
Synergetic effects in ion beam energy and substrate temperature during hyperthermal particle film deposition
Authors: Marton D. , Boyd K. J. , Rabalais J. W.
Published: July 2002

A semiquantitative subplantation model for hyperthermal particle enhancement of epitaxy is proposed and applied to the system of Si+ ion beam homoepitaxial growth. The mechanism proposes that storage of a portion of the kinetic energy of the hyperthermal particles as interstitial atoms and subsequent release of this energy is a general phenomenon that is responsible for ion beam enhanced epitaxy and growth of metastable materials. A generalized epitaxial phase diagram which illustrates the energy-temperature synergism is constructed. This provides an understanding of the limited and unlimited silicon homoepitaxial growth from thermal (molecular beam epitaxy) and hyperthermal Si atoms, respectively. Four regions of energy-temperature space have been identified in reference to epitaxial growth: I. Unlimited epitaxy due to high thermal energy; II. Interstitial registry-limited epitaxial growth; III. Hyperthermal particle enhanced epitaxy; IV. Defect-limited epitaxial growth.
Development of electron cyclotron resonance and inductively coupled plasma high density plasma etching for patterning of NiFe and NiFeCo
Authors: Jung K. B. , Lambers E. S. , Childress J. R. , Pearton S. J. , Jenson M. , Hurst A. T.
Published: July 2002

Two different kinds of high density plasma reactors are found to be effective for dry etching of Ni0.8Fe0.2 and Ni0.8Fe0.13Co0.07. Using a Cl2/Ar plasma chemistry, electron cyclotron resonance and inductively coupled plasma system produce a factor of 2 higher etch rates than for pure Ar sputtering under the same conditions. The etch rates are a strong function of ion flux, ion energy, and plasma gas composition, all of which may be interpreted in terms of balancing formation of chloride etch products with efficient ion-assisted desorption of these products. Typical peak etch selectivities of ∼5 and ∼4, respectively, were obtained for NiFe over SiO2 and SiNx masks. Post-etch corrosion was also studied, and found to be strongly dependent on the conditioning of the reactor walls.
Deposition of diamond-like carbon films using the screen grid method in electron cyclotron resonance chemical vapor deposition
Authors: Yoon S. F. , Rusli  , Ahn J. , Zhang Q. , Wu Y. S. , Yang H.
Published: July 2002

The deposition of diamond-like carbon (DLC) films from a mixture of hydrogen and methane using the electron cyclotron resonance chemical vapor deposition method is reported. A new technique based on a dc bias applied to a two-tier screen grid positioned above the substrate has been used to provide an electric field to accelerate the ions towards the substrate during deposition. The structural characteristics of the DLC films have been studied using Raman spectroscopy. Under conditions of 400 W microwave power and 6.5 mTorr process pressure, films deposited using the screen grid method were found to be hard and diamond-like and to contain a low bonded hydrogen content, as opposed to films deposited conventionally with dc bias applied directly to the substrate holder. The results showed that the dc bias applied to the lower grid of the screen grid fixture has the effect of accelerating the ionic species to impinge onto the substrate, hence promoting DLC film growth.
Viscosity and velocity slip coefficients for gas mixtures: Measurements with a spinning rotor gauge
Authors: Bentz J. A. , Tompson R. V. , Loyalka S. K.
Published: July 2002

A selection of experimental measurements for He-Ar, He-N2, and He-Ne binary gas mixtures which were made with a spinning rotor gauge (SRG) are reported. All of the experiments were conducted in the slip regime. Theoretical results from a previous paper on the SRG are used to extract values of the viscosity and the velocity slip coefficient from the experimentally obtained data for each of the gas mixtures. The measured viscosities are in excellent agreement with existing literature values. Slip coefficients for binary gas mixtures have not previously been reported. An important issue here is whether the velocity slip coefficients for binary gas mixtures can be predicted accurately using separately measured tangential momentum accommodation coefficients. The calculation of slip coefficients from theory requires a knowledge of the accommodation coefficients of each constituent of the mixture. The dependence of these coefficients on the gas composition is not known and the simplest assumption is to regard them as being independent of the composition. The slip coefficients computed in conjunction with this work use this simple assumption in a theoretical expression for the slips. These computations led to reasonable agreement of the theoretical results with our data for the He-Ne mixture. Agreement in the cases of the He-Ar and He-N2 mixtures, however, was less than satisfactory.
Plasma induced copolymerization of hexafluoropropylene and octafluoropropane
Authors: Leezenberg Pieter B. , Reiley Timothy C. , Tyndall George W.
Published: July 2002

Ultrathin fluoropolymer films were deposited by a plasma-enhanced chemical vapor deposition process, from mixtures of hexafluoropropylene (C3F6) and octafluoropropane (C3F8) precursors. Different monomer feed compositions result in different rates of deposition. The C3F6 is the primary polymerizing species and C3F8 acts to reduce the deposition rate. The structure and composition of these films were characterized using Fourier transform infrared and angle-resolved x-ray photoelectron spectroscopy. The bulk F:C ratio is 1.1 for the homopolymer film (deposited from C3F6 only) and 1.4 for the copolymer film (deposited from C3F6+C3F8 monomer feed). The copolymer film has more –CF3 groups and has a more highly branched structure. The surface F:C ratio is 1.5 for the homopolymer and 1.7 for the copolymer film. The water contact angle increased with film thickness and with addition of C3F8 to the monomer feed. A mechanism is presented to describe how the addition of C3F8 modifies the polymerization process, causes a high surface F:C ratio of the copolymer films, and leads to reduced surface energy.
Photoenhanced reactive ion etching of III–V nitrides in BCl3/Cl2/Ar/N2 plasmas
Authors: Tempez A. , Medelci N. , Badi N. , Berishev I. , Starikov D. , Bensaoula A.
Published: July 2002

Gallium nitride (GaN) and boron nitride (BN) are known as superior semiconductor materials for UV optoelectronic and high power, high temperature applications. As a result of their high molecular bond strength these materials are extremely difficult to etch. In this article, reactive ion etching (RIE) tests were performed on GaN and BN thin films using respectively BCl3/Cl2/Ar and Cl2/Ar chemistries. In order to improve the etch rates at lower rf powers and thus reduce ion bombardment-induced damage, a photoassisted RIE process was investigated. The same plasma chemistries in combination with a xenon arc lamp were utilized. In an attempt to minimize surface nitrogen depletion, N2 was used instead of Ar as dilution gas. Photoenhancement was observed for both GaN and BN etching. As expected, the etch rate increased with rf power for both unassisted and photoassisted etching conditions. The combination of illumination and N2 led to a nitrogen-rich surface for GaN. In the case of BN, photoassisted etching in Ar resulted in a slightly lower surface nitrogen depletion. Chlorine was also detected on both etched GaN and BN films under illumination at a content of less than 1.7% and 2.5%, respectively.
Compositional variations in strain-compensated InGaAsP/InAsP superlattices studied by scanning tunneling microscopy
Authors: Grandidier B. , Feenstra R. M. , Silfvenius C. , Landgren G.
Published: July 2002

Cross-sectional scanning tunneling microscopy (STM) and scanning tunneling spectroscopy are used to study strain-compensated InGaAsP/InAsP superlattices grown by metalorganic vapor phase epitaxy, with or without an InP layer inserted in the InAsP barrier. A difference of contrast in the STM images is observed between the InAsP barrier grown over an InP layer compared with the InAsP grown over the InGaAsP well. The first ≈4 nm of the InAsP barrier layers grown over the wells are found to be compositionally intermixed, containing significant enrichment of both arsenic and gallium atoms. This intermixing is believed to be due to some carryover or surface segregation of these species when the growth is switched from well to barrier.
Characterization of thin metal films processed at different temperatures
Authors: Siewenie J. E. , He L.
Published: July 2002

Thin metal of Au, Ag, and Al films were deposited onto room temperature (RT) and low temperature (LT=77 K) substrates then subjected to five types of measurement: resistivity vs film thickness, resistivity vs substrate temperature, atomic force microscopy (AFM), transmission electron microscopy (TEM), and TEM electron diffraction. In all three cases, the LT films were continuous at lower thicknesses than the RT films during resistivity vs film thickness measurements. During resistivity vs substrate temperature testing of very thin films (<100 Å), all three LT films exhibited resistivities that were orders of magnitude lower than RT films of the same thickness. In general, TEM and AFM scans of LT films exhibited better substrate coverage at lower thicknesses, and RT films showed larger grain size. Resistivity vs film thickness measurements and TEM scans were done on Pd and Ni. LT Pd films exhibited larger resistivities than the RT films at all measured thicknesses. Ni RT film started with higher resistivity and became more conductive than the LT film at larger thicknesses.
Surface acoustic wave propagation properties of nitrogenated diamond-like carbon films
Authors: Kim Jin Yong , Chung Hun Jae , Kim Hyeong Joon , Cho Hyun Min , Yang Hyung Kook , Park Jong Chul
Published: July 2002

Nitrogenated diamond-like carbon (a-C:N) thin films on Si(100) were deposited by radio frequency magnetron reactive sputtering. Using ZnO piezoelectric thin films, the surface acoustic wave (SAW) propagation properties of a-C:N thin films on Si(100) have been experimentally investigated using bidirectional interdigital transducers between ZnO and a-C:N/Si(100). A generalized SAW mode with velocities between 5000 and 7000 m/s were observed. A high velocity pseudo-SAW mode was also observed and identified with simulated data, of which the velocity was 13 850 m/s. We calculated the film elastic constants from the phase velocities in the layered structure. The calculated constants for a-C:N thin films on Si were c11=392.1 and c44=185.7 GPa.
A review of recent advances in semiconductor superlattices
Authors: Chang L. L.
Published: July 2002

Very recent advances in semiconductor superlattices are reviewed. The emphasis is on electronic properties associated with energy quantization.
Band discontinuities and interface Fermi-level positions in Ge–GaAs(110) heterojunctions
Authors: Kowalczyk Steven P. , Grant R. W. , Waldrop J. R. , Kraut E. A.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) measurements were performed on (p)Ge–(p)GaAs(110) and (p)Ge–(n)GaAs(110) heterojunctions to investigate the possible influence of interface defect levels on valence-band discontinuities ΔEv. These XPS experiments indicate that ΔEv is independent of GaAs dopant type. Comparison of the present results with results from previous work shows that ΔEv is independent of the GaAs(110) surface preparation method (thermal, sputter and annealed, or cleavage) and Ge dopant type. No evidence is found for the presence of an intrinsic dipole layer associated with interface defect levels.
Initial reactions at the interface of Pt and amorphous silicon
Authors: Nemanich R. J. , Thompson M. J. , Jackson Warren B. , Tsai C. C. , Stafford B. L.
Published: July 2002

The initial reactions at the interface of Pt on a-Si:H are probed by interference enhanced Raman scattering, TEM, and Auger, and the atomic structural changes are correlated with electrical properties determined from current–voltage and internal photoemission measurements. It is shown that a disordered Pt–Si intermixed phase of less than 20 Å thick exists at the interface immediately after deposition, and this phase grows thicker with annealing to 150 °C. Annealing at 200 °C causes the nucleation of crystalline silicide phases. The Schottky diodes exhibit rectification over greater than ten orders of magnitude of current density. Initially, the as-deposited diodes exhibit an ideality parameter of ∼1.11. Subsequently, the value drops to 1.04 as the silicide develops. Internal photoemission results indicate deviations from expected behavior.
Palladium on GaAs: A reactive interface
Authors: Oelhafen P. , Freeouf J. L. , Kuan T. S. , Jackson T. N. , Batson P. E.
Published: July 2002

We have studied the formation and properties of ≊15 nm films of Pd on GaAs(100) and (110) substrates as a function of annealing temperature. Ultraviolet and x–ray photoelectron spectra (UPS and XPS) have established several distinctive phases; coupled with scanning electron microscopy studies, agglomeration has been observed at elevated temperatures. Transmission electron diffraction studies permit more detailed phase identification at specific temperatures. Electrical studies permit characterization of both interface properties and bulk transport properties of the reacted layer. In contrast to previous work, we find no Pd–As binary phases. After high temperature anneals (Ta >350 °C), only PdGa is observed; these films are not continuous, but form [often epitaxial on (100) substrates—with (110)PdGa‖‖ (100)GaAs and [1̄11]‖‖[011]GaAs] islands. After low temperature (≊250 °C) anneals of Pd films on (110) substrates, small crystallites of PdGa are imbedded in the dominant matrix of a ternary single crystal phase. Energy dispersive x-ray analysis and XPS core level intensities suggest that this phase has the nominal composition of Pd2GaAs. Metallic Ga is inferred after room temperature deposition from He ii UPS studies of the Ga 3d core level.
A simple model for the index of refraction of GaAs–AlAs superlattices and heterostructure layers: Contributions of the states around Γ
Authors: Leburton J. P. , Hess K.
Published: July 2002

We present a simple theory of the dielectric function in superlattices. The calculation is performed separately for different symmetry points of the band structure. We assume that among the contributing states only the Γ states are influenced substantially by size quantization and the electronic states at Γ are calculated by using a simplified k⋅p method. New features of the dielectric constant of superlattices are a fine structure due to zone folding (subbands) and a small anisotropy due to the lower symmetry. Except for these finer details, the index of refraction of a superlattice is well approximated by the corresponding constant for an alloy Alx̄Ga1−x̄As where x̄ is the averaged Al mole fraction of the superlattice.
High mobility insulated gate transistors on InP
Authors: Taylor M. J. , Lile D. L. , Nedoluha A. K.
Published: July 2002

The surface charge carrier transport of electrons in accumulation mode insulated gate FET’s fabricated on [100] oriented samples of semi-insulating InP has been investigated, both as a function of surface and dielectric preparation as well as of temperature over the range of 85 to 300 K. Results of these studies indicate that room temperature field-effect mobilities as large as 4200 cm2/V s and effective mobilities of 3300 cm2/V s can be achieved in the linear region on material whose bulk Hall mobility does not exceed 3000 cm2/V s.
Interface properties of Al–SiO2–In0.53Ga0.47As MIS devices
Authors: Shen C. C. , Pande K. P.
Published: July 2002

n-In0.53Ga0.47As MIS capacitors with SiO2 dielectric films have been investigated. The SiO2 films, which were deposited by a novel low temperature process, exhibit stoichiometric composition. The MIS devices show a sharp interface and a minimum interface state density of 7×1011 cm−2 eV−1. The devices also show small hysteresis effects.
Effect of interfaces upon atomic diffusion: Si and Zn in GaAs
Authors: Van Vechten J. A.
Published: July 2002

The activation energy for atomic diffusion often includes terms resulting from a change in ionization state of the diffusing species. It is argued that these terms ought to be affected by the electronic states of the material not only at the site of the diffusion but also within a range of order of the Debye screening length of it. Thus, atomic diffusion ought to be a nonlocal phenomenon with a scale comparable with modern device structures. Major increases in the rate of diffusion near interfaces, surfaces and dislocations are predicted and should be considered when modeling processes. GaAs–AlAs superlattices allow testing of these conclusions.
Plasma-enhanced CVD of titanium silicide
Authors: Rosler Richard S. , Engle George M.
Published: July 2002

The continuing trend toward smaller geometries and thinner junctions mandates that interconnect and gate materials have the lowest resistivity possible. Titanium silicide has the lowest resistivity of the refractory metal silicides and is, therefore, the prime candidate for advanced VLSI processing. This paper describes the CVD of titanium silicide in the ASM PECVD system. Reactor characteristics, deposition uniformities, and properties of the as-deposited and annealed films are discussed. Film resistivity, after a 10 min anneal at 650 °C, is typically 15 to 20 μΩ cm. This result is obtained at a lower temperature (by about 100 °C) and lower resistivity (by about 25%) than is usually attainable with sputter-deposited TiSix. Analysis using Rutherford backscattering spectrometry and Auger electron spectroscopy also indicates considerably better purity with these PECVD films. The step coverage of CVD TiSix is essentially conformal.
Impurity effects in transition metal silicides
Authors: Lien C.-D. , Nicolet M-A.
Published: July 2002

Impurities can affect the properties of silicides directly by virtue of their presence. Impurities can also influence the processes by which silicides are formed. The effect of impurities on the reaction of transition metal films with a silicon substrate induced by thermal annealing are well documented. The interpretation of these results is discussed. It is shown that impurity redistribution is a major factor in determining how significant the effect of an impurity is. Redistribution observed for dopant impurities is also discussed.
Fermi level position and valence band discontinuity at GaAs/Ge interfaces
Authors: Katnani A. D. , Chiaradia P. , Sang H. W. , Bauer R. S.
Published: July 2002

We present a photoemission study of the valence band discontinuity ΔEv and the Fermi level EF at the abrupt n-GaAs/Ge interface. We investigated these properties during the early stages of interface formation between different reconstructions of GaAs(100) and epitaxial Ge. While GaAs(100) As surface stoichiometry variations from 0.25 to 1.25±0.10 monolayers caused no change in ΔEv, the Fermi position indicated an increasingly n-type interface of >0.3 eV with the presence of As. Intentional As4 annealing of the Ge or addition into the growth environment only produced a more n-type barrier with no corresponding change in ΔEv. Variations in crystallographic orientations do not contribute to the band discontinuities by more than ±0.05 eV.