bluuebunny/crossref_metadata_2025 huggingface dataset:
Energies and symmetries in interface formation: In/GaP(110) and Ga/InP(110)
Authors: Vitomirov I. M. , Aldao C. M. , Schabel M. , Waddill G. D. , Anderson S. G. , Weaver J. H.
Published: July 2002

We have used high-resolution synchrotron radiation photoemission to study adatom–substrate interactions and growth morphologies for In/GaP(110) and Ga/InP(110). Room-temperature experiments reveal extensive adatom clustering, but also substrate disruption and cation segregation for both interfaces, with greater amounts for Ga/InP(110). Ga deposition in InP(110) at 60 K also results in substrate disruption, but with kinetic trapping of the released In atoms close to the interface and a greater tendency toward layer-by-layer growth. In constrast, the deposition of preformed metallic Ga clusters shows no evidence for substrate disruption. We conclude that atom condensation and coalescence are responsible for disruption, with different activation barriers being present for cluster deposition and atom deposition because of the details of surface and interface bonding. For Ga deposition on n-type InP(110) at 60 K, the appearance of states at the Fermi level is correlated to changes in band bending. Metal cluster deposition leads to pinning positions that can be related to surface unrelaxation around the perimeter of the clusters; we find no evidence for metal induced gap states or defect levels.
Isotropic plasma etching of doped and undoped silicon dioxide for contact holes and vias
Authors: van den Hoek W. G. M. , Wicker T. E. , Westlund B. F. , Powell G. B.
Published: July 2002

Isotropic plasma etching of doped and undoped oxides has been studied as an alternative to the ‘‘wet’’ isotropic step in the ‘‘wet–dry’’ contact etch approach. Czochralski grown p-type 〈100〉 100-mm-diam silicon substrates with either 0.1-μm low-temperature chemical vapor deposition oxide (LTO) and 0.5-μm borophosphosilicate glass (BPSG, 2.5 wt. % B and 7 wt. % P), or 0.6-μm thermally oxidized silicon were used. These substrates were masked with a resist pattern with contact holes whose diameters were between 10.0 and 0.75 μm. Subsequently, they were isotropically etched in a Matrix System One etcher. In this step 0.3 μm of the oxide was removed. The remaining oxide was anisotropically etched in an AME 8110 hexode etcher in a CHF3 / CO2 /He mixture at 72 mTorr and 1250 W. The isotropic oxide etch process was characterized using a multilevel statistical experimental design with pressure, 13.56-MHz rf power, and total gas flow (50% NF3 in He) as the variables. Optimized etch conditions resulted in an etch rate uniformity of less than ±3.0% (one sigma divided by the average for 9 points), a BPSG etch rate in excess of 0.3 μm/min, a thermally oxidized silicon etch rate of 0.12 μm/min, and a resist etch rate of <14 nm/min. The scanning electron miscroscope measurements showed a critical dimension variation of <0.1 μm total in the contact hole diameter at the LTO–silicon interface as compared to the contact hole diameter at the resist–BPSG interface before etch.
Comparison of M-region x-ray and Auger electron spectra for near-threshold electron excitation of metallic and oxidized lanthanum
Authors: Wachter Joseph R. , Liefeld Robert J.
Published: July 2002

The M-region x-ray yield and Auger electron spectra of metallic and oxidized lanthanum were measured for electron excitation near the M5 and M4 ionization energies. The measurements show a chemical shift of 2.3 eV in the x-ray excitation spectra for the two species but no corresponding shift in the Auger electron spectra. This supports the hypothesis that two distinct excitation processes occur near the M5 and M4 ionization energies. One process results in an excited state which can decay through ‘‘characteristic’’ channels while the second process leads to a state which decays only by radiative emission.
Infrared analysis of film growth on the silicon surface in room air
Authors: Olsen J. E. , Shimura F.
Published: July 2002

Two infrared internal reflection spectroscopic techniques are used to analyze the composition of the film that grows on hydrophobic silicon at room temperature. A conventional internal reflection technique with a silicon internal reflectance element shows that the silicon surface adsorbs hydrocarbons from the atmosphere. A modified internal reflection technique showed <0.2 nm of SiO and SiO1.5 on the silicon surface one month after a hydrofluoric acid strip. Compared to the rate of contamination, the rate of silicon oxidation at room temperature is considered negligible.
Effects of anodic fluoro-oxide on the thermal stability of Hg1−xCdxTe photoconductive arrays
Authors: Mainzer Nili , Weiss Eliezer , Laser Daniel , Shaanan Michael
Published: July 2002

Hg1−xCdxTe (x∼0.2) photoconductive arrays passivated with anodic fluoro-oxides show an improved thermal stability relative to arrays fabricated with anodic oxides. The performance of the photoconductors with the anodic fluoro-oxide is only slightly degraded by annealing at temperatures up to 100–105 °C, in contrast to the monotonic decrease observed in arrays passivated with an anodic oxide caused by annealing above 70 °C. The improved stability of the fluoro-oxides does not depend much on the bath composition, as long as it is a solution of hydroxyl and fluoride ions. Both secondary ion mass spectroscopy and low-energy proton induced nuclear reaction, which is very sensitive to fluorine atoms, were used as depth profile probes. It was found that the fluorine concentrated at the anodic film–semiconductor interface as well as on the film surface. A mechanism by which fluorine is deposited in such a manner is advanced.
Microstructure analysis of thin films deposited by reactive evaporation and by reactive ion plating
Authors: Guenther Karl H. , Loo Boon , Burns David , Edgell Jo , Windham Debbie , Müller Karl-Heinz
Published: July 2002

Electron microscopy, stylus-type surface profilometry, and Raman microprobe characterization show distinct differences between thin films deposited by reactive evaporation and by reactive ion plating. Reactive evaporation yields thin films with the well-known columnar microstructure with appreciable surface roughness and other deficiencies. Low-voltage, high-current reactive ion plating deposition produces thin films which are smooth and dense. Cross-section electron micrographs of ion plated coatings reveal a densely packed polycrystalline structure for ZrO2 , while TiO2 appears to form vitreous films. Molecular dynamics computer simulation of the film formation process is in good qualitative agreement with the experiments. The results suggest the expansion of the Movchan–Demchishin structure zone model with an additional zone 4 for the vitreous phase, resulting from superthermal film formation conditions (thermal spiking).
Emission characteristics of a hafniated oriented tungsten thermal field emission source
Authors: Troyon M. , Pandey A. K. , Orlikowski J. P.
Published: July 2002

The paper presents the results of investigations into the possibility of using the oxygen processed and hafniated 〈100〉 oriented tungsten (HfO/W) tip as a stable thermal field emission source. This cathode was found to resemble in its characteristics ZrO/W <100> cathodes. The optimum operating temperature range is found to be 1750–1850 K. A limited amount of life testing indicates a life of more than 1000 h and this source was found to work well under a modest vacuum of a few 10−9 Torr. In the operating temperature region an rms relative noise of 0.26% in the frequency interval of 0.1 to 1000 Hz was measured and the emission current drift is <0.5% per hour. Energy spread of 0.67 eV was measured for a probe current of 15 nA obtained in an illuminating semi-angle of 0.57 mrad. The work function of these cathodes was evaluated to be ≂2.7 eV.
Novel 〈110〉 growth processes in vacuum evaporated calcium fluoride films on 〈001〉 silicon
Authors: Srivatsa A. R. , Narayan J. , Radpour F. , Singh R.
Published: July 2002

Novel microstructures in calcium fluoride films deposited by vacuum evaporation were observed on 〈001〉 silicon substrates as a function of deposition temperature. The microstructure consists of two sets of 〈110〉 oriented crystallites on the 〈001〉 silicon. A set of {110} planes in each of these two kinds of crystallites is aligned with a set of {110} planes of silicon, leading to a film morphology with mutually perpendicular, elongated, rodlike features running along a 〈110〉 direction of each set of crystallites. Both scanning electron microscopy and transmission electron microscopy were used to examine these features. The growth of this microstructure is discussed in the context of a combination of 〈110〉 textured growth and ‘‘planar-matching epitaxy.’’
Etching results and comparison of low pressure electron cyclotron resonance and radio frequency discharge sources
Authors: Cook J. M. , Ibbotson D. E. , Foo P. D. , Flamm D. L.
Published: July 2002

As the lateral dimensions of ultra-large-scale integration (ULSI) circuit features approach a few-tenths of a micron, demands on the etch transfer of patterns into thin films become increasingly challenging. These demands, combined with the greater susceptibility to create damage, require that new methods are evaluated and compared for etching fine structures in order to establish processing technologies. Submicron polysilicon etching has been performed on a single-wafer etcher using two different sources that sustain intense discharges at low pressure (≲10−3 Torr). The first is an electron cyclotron resonance (ECR) source operated at 2.45 GHz. The second source is a simple helical resonator (HR) structure operated at radio frequencies (RF). The comparisons made between the two sources were the etched profiles of polysilicon, material selectivity, polysilicon etch rates, and etch uniformity. These preliminary experiments show that both systems have great promise to successfully pattern ULSI structures. The advantages and disadvantages of ECR and improved HR sources will be discussed.
Epitaxial growth of silicon on Si(001) by scanning tunneling microscopy
Authors: Hamers R. J. , Köhler U. K. , Demuth J. E.
Published: July 2002

The epitaxial growth of silicon on Si(001)-(2×1) substrates at temperatures between 580 and 850 K is studied using scanning tunneling microscopy (STM). The growth is strongly anisotropic, forming long narrow structures only a few dimers wide but more than 100 Å long. Models are proposed for the two types of antiphase boundaries that are observed on the epitaxially grown surfaces.
Ballistic electron emission spectroscopy of noble metal–GaP(110) interfaces
Authors: Ludeke R. , Prietsch M.
Published: July 2002

Ballistic electron emission microscopy (BEEM) was used in an UHV environment to investigate the current–voltage spectra of Cu, Ag, and Au films on cleaved n-type GaP(110). Current thresholds, which occur when the applied tip-to-metal bias exceeds the Schottky barrier height, were remarkably uniform to within ±0.02 V for any particular metal–GaP interface, but varied for interfaces with different metals. The fitted threshold voltage Vo depends on the model used for the interface current transport. Its value varies by ∼0.05 V between a prior model that predicts a (V−Vo)2 dependence near threshold and a new (V−Vo)5/2 dependence proposed here. The latter includes an energy dependent transmission coefficient for transport across the metal–semiconductor interface. Significant BEEM current variations and fluctuations were observed, which are associated with topographic gradients of the metal surface and sudden changes in the tunneling geometry during the experiment. The transport model is further developed to include average angles of incidence of the injected electrons that are off-normal at the metal–semiconductor interface, a condition that occurs when the tunneling tip is scanning over nonplanar surface features. Model predicted current variations are consistent with the range of surface gradients observed in the topographic images of the noble metal films on GaP.
Development of foam shells for cryogenic laser fusion target
Authors: Chen C. , Norimatsu T. , Takagi M. , Katayama H. , Yamanaka T. , Nakai S.
Published: July 2002

Spherical hollow polymer foam shells used as a sustainer of cryogenic fuel for the inertial fusion target have been developed. Foam shells which have 500–1000 μm diameter with a 30–100 μm uniform wall, 4 μm cell size and 40 mg/cm3 density, have been fabricated using a dual-nozzle droplet generator and a freeze-dry technique. Requirements to obtain a uniform thick wall and fine cell size are discussed.
On the effect of an oxygen beam in sputter depth profiling
Authors: Meuris M. , Vandervorst W. , Jackman J.
Published: July 2002

Experiments of depth resolution measurements on silicon with secondary ion mass spectrometry reveal that oxygen primary particles provide always a smaller decay length (better depth resolution) compared with other primary particles for the same penetration depth of the particle. This deviation from the classical collisional mixing model can be explained by a model which does take the incorporation of the primary particle during sputtering into account. For oxygen particles the incorporation is so high that it leads to a different matrix composition at the surface compared with the bulk of the Si sample and it results in a target swelling at the surface. It is now important to realize that the displacements of the atoms are only important relative to the position of the Si atoms in the expanded lattice and that movements with respect to the incorporated oxygen atoms does not matter. The model presented quantifies this effect and gives an accurate estimate of the reduction of the decay lengths. The model predicts a similar behavior for all primary particles with low matrix sputter yield and high incorporation of the primary particle.
Surface roughness analysis by scanning tunneling microscopy and atomic force microscopy
Authors: Files-Sesler Leigh Ann , Hogan Tim , Taguchi Tomoaki
Published: July 2002

This report demonstrates the use of scanning tunneling microscopy and atomic force microscopy to obtain surface roughness parameters for semiconductor materials. Correlation between figures of merit and physical properties such as bondability and reflectivity has been demonstrated. Eutectic bond strength for silicon die attachment is shown to be inversely proportional to the roughness of the backside of the silicon die. Reflectivity of aluminum metallization has been shown to decrease with increasing roughness. We also illustrate that in some metal systems the surface structure is independent of the grain size as determined by planar transmission electron micrographs. Our work relies heavily on generating numerical data, which can be used to understand critical relationships and develop processing solutions.
Pumping characteristics of sputter ion pumps with high-magnetic-flux densities in an ultrahigh-vacuum range
Authors: Ohara Kenji , Ando Ichiro , Yoshimura Nagamitsu
Published: July 2002

Pumping characteristics of sputter ion pumps with anode cells of 17, 24, and 29 mm diameters, respectively, were measured for N2 at three magnetic fields (i.e., ∼0.15, ∼0.2, and ∼0.3 T) in an ultrahigh-vacuum range between 1×10−8 and 1×10−6 Pa. The pumping speed of the pump with 17-mm-diam cells increased significantly with increasing magnetic fields. However, the pump with 17-mm-diam cells and a magnetic field of 0.3 T evidenced negligible pumping speed at pressures <1.5×10−8 Pa. The pump with 24-mm-diam cells and a magnetic field of 0.3 T showed a fairly high pumping speed in the range between 1×10−8 and 1×10−6 Pa. The pump with 29-mm-diam cells and 0.3 T showed the highest pumping speed among all the test pumps at pressures <2×10−8 Pa, though its speed in the 10−7 Pa range was comparatively low.
Errors in curve fitting of profilometer data
Authors: Selverian John H.
Published: July 2002

The measurement of stresses in thin films on sybstrates requires in thin films determining films’ radius of curvature. It is shown that the accuracy of profilometer measurements depend crucially on the signal-to-noise ratio. (AIP)
Atom assisted sputtering yield amplification
Authors: Berg S. , Barklund A. M. , Gelin B. , Nender C. , Katardjiev I.
Published: July 2002

At first sight one might assume that it is unlikely to influence the sputtering yield of a specific ion/substrate combination by any external means. However, we have found that such an influence may well be introduced. The sputtering yield is predominantly determined by the ion/substrate momentum transfer efficiency and the energy of the incoming ion. Sputter erosion of, e.g., carbon atoms by argon ions from a carbon substrate exhibits a very low sputtering yield. Due to the difference in masses between carbon and argon much of the momentum is transferred into the bulk of the carbon substrate. This situation could be changed by simultaneous codeposition of Pt atoms onto the carbon substrate surface during the argon sputtering. Keeping the argon flux at a level well above what is needed to sputter remove all the deposited Pt atoms the following effect occurs. Some of the deposited Pt atoms will be forward implanted by the energetic argon ions into the near surface region of the carbon substrate. Collision between both argon (M=40) and carbon (M=12) atoms with the implanted Pt atom (M=195) can result in reflection of some of the light atoms. Therefore implanted Pt atoms will act as effective reflection centers pushing the collision cascade to take place closer to the surface region, thereby contributing to an effective increase of the number of collision cascades in this region. This reflection effect will result in a substantial increase of the sputtering yield of carbon atoms. Experimental verification of this effect for the (Ar+C+Pt) and the (Ar+Si+Pt) systems will be presented. It will be also shown that this sputter amplification process can be predicted from computer simulations using the t-dyn version of the Monte Carlo trim code.
Carrier injection and scanning tunneling microscopy at the Si(111)-2×1 surface
Authors: Cahill David G. , Feenstra R. M.
Published: July 2002

Surface photovoltage at the Si(111)-2×1 surface is measured using a scanning tunneling microscope by simultaneously modulating the sample bias and the intensity of illumination from a He–Ne laser. In the limit of small tunneling current, the dependence of surface photovoltage on light intensity measured for p- and n-type Si gives the Fermi level at the surface, 0.46±0.03 eV. Tunneling out of the surface injects bulk carriers that reduce band bending at the surface of n-type Si. Tunneling into the surface reduces the surface photovoltage on p-type Si and increases the photovoltage on n type demonstrating that the tunneling current changes the surface potential by charging of surface electronic states or through bulk spreading resistance. Spatial variations in the surface photovoltage measured at positive sample bias and large tunneling current are observed at surface defects.
Spatial distributions of electron density and temperature in audio frequency and radio frequency magnetron glow discharges
Authors: Fusselman S. P. , Yasuda H. K. , Javedani J. B. , Chiang J. , Prelas M. A.
Published: July 2002

The spatial distributions of electron density and temperature in parallel plate audio frequency (AF) (40 kHz) and radio frequency (RF) (13.56 MHz) magnetron discharges were obtained using double Langmuir probes. At 30 W and 580 mTorr argon, electron density ranged from 5×108/cm3 to 1.5×109/cm3 and electron temperature ranged from 3.4 to 4.6 eV in the AF discharge. For 30 W net power and 580 mTorr argon in the RF discharge, electron density ranged from 2×109/cm3 to 8×109/cm3 and electron temperature ranged from 2.5 to 3.6 eV. Electron temperature in the AF discharge increases as the discharge axis is approached, and is independent of axial position. In the RF discharge electron temperature increases near the electrode surface. Electron density distributions in both discharges show the influence of magnetic fields, with the maximum electron density occurring at the position where the radial component of the magnetic field (parallel to the electrode surface) is at a maximum. In the AF discharge, this influence is no longer apparent at axial distances from the electrode surface beyond 2.5 cm. In the RF discharge, radial variations in electron density characteristic of magnetic confinement are observed throughout the plasma, even at the center plane between electrodes.
Decomposition of NO2 on metal surfaces: Oxidation of Ag, Zn, and Cu films
Authors: Rodriguez José A. , Hrbek Jan
Published: July 2002

The dissociation probability of O2 on Cu(111), Ag(111), and Zn(001) surfaces is quite low (<10−2). The oxidation process using molecular oxygen is not practical for work under ultrahigh vacuum conditions. We have found that NO2 is a very good oxygen source for the oxidation of Ag, Zn, and Cu surfaces. At elevated temperatures (300–500 K), the dissociation probability of NO2 on thick Ag, Zn, and Cu films supported on Ru(001) is close to one. The decomposition of NO2 produces a large amount of adsorbed oxygen and gaseous NO and N2. The thermal stability and electronic properties of the O/Ag, ZnOx, and CuOx films were examined using temperature desorption spectroscopy, x-ray photoelectron spectroscopy (XPS), and x-ray Auger electron spectroscopy. Large amounts of oxygen can be adsorbed and dissolved in Ag films without oxidation of the noble metal. The zinc oxide films displayed the typical O 1s XPS and Zn L3M4,5M4,5 Auger spectra of polycrystalline ZnO. In addition, the high-resolution electron energy-loss spectroscopy spectra of these films exhibited the characteristic phonon losses of bulk ZnO. In the case of Cu films the NO2-oxidation leads to the formation of a mixture of CuO and Cu2O. The CuO species is relatively unstable and can be reduced to Cu2O by annealing at 700 K (2 CuO→Cu2O+1/2O2) or by direct reaction with metallic Cu at 300 K (CuO+Cu→Cu2O).
Dose–time relation in BF3 plasma immersion ion implantation
Authors: Shao Jiqun , Round Mark , Qin Shu , Chan Chung
Published: July 2002

Etching and deposition rates of silicon and SiO2 during BF3 plasma immersion ion implantation are measured. The relation between total dose and plasma immersion ion implantation processing time is developed through computer modeling. The results are in very good agreement with the experimental data. Comparison with a previously published model is also given.
Secondary electrons in liquid metal ion sources
Authors: Czarczynski Wojciech
Published: July 2002

The computer investigation of secondary electron trajectories in liquid metal ion sources (LMIS) is reported. Calculations show the possibility of electron focusing on the ion emitter needle apex. Secondary electron focusing appears in the electrode configuration that is very common in the needle type LMIS. The secondary electrons may deliver considerable power to the needle apex. A simple theoretical model based on the heat flow equation for the evaluation of secondary electron heating has been proposed. The ion transit time-dependent heating cycle is discussed as a possible mechanism of ion current oscillations in the MHz range.
Stresses in a coated solid due to shear and normal boundary tractions
Authors: Zheng Lanshi , Ramalingam S.
Published: July 2002

Mismatch in elastic and mechanical properties of the film–substrate interface is common when engineering alloys are hard coated. Knowledge of interface stresses due to applied external tractions can be useful in evaluating propensity for coating failure as a function of material properties and for coating design. Using plane strain modeling and displacement formulation, interface stresses are calculated and presented here as a function of elastic modulus ratios. Results are also discussed from application perspectives.
Investigation of pyroelectric characteristics of lead titanate thin films for microsensor applications
Authors: Deb K. K. , Bennett K. W. , Brody P. S.
Published: July 2002

Pyroelectric PbTiO3 thin films deposited on Si(100) substrates (Pt/Ti/SiO2/Si) by sol-gel processing have been characterized in some detail to determine the usefulness of these films for uncooled detector applications. The films have been deposited without substrate heating. The amorphous films were than annealed in air for a half hour at 400–700 °C. X-ray diffraction patterns taken on these films showed single-phase tetragonal perovskite structure with a slight c-axis preference. The grain size was in the range of 0.2–0.3 μm. The D–E hysteresis loop characteristics were performed, as well as measurements of the dielectric and pyroelectric properties versus temperature and frequency. The influence of dc bias treatment on the dielectric and pyroelectric properties was investigated. The results of measurements show that PbTiO3 thin films exhibit a relatively high pyroelectric coefficient relative to the dielectric permittivity, contributing to a very high figure of merit for voltage responsivity that is competitive with PbTiO3 single crystal and PZT thin films.
Low temperature deposition of silicon nitride films by distributed electron cyclotron resonance plasma-enhanced chemical vapor deposition
Authors: Sitbon S. , Hugon M. C. , Agius B. , Abel F. , Courant J. L. , Puech M.
Published: July 2002

Silicon nitride thin films have been deposited via distributed electron cyclotron resonance plasma-enhanced chemical vapor deposition, without intentional substrate heating, using SiH4 and N2 gas mixtures. The effects of N2/SiH4 gas flow (1.5–19) and microwave power (800–1500 W) on deposition rate, refractive index, composition, chemical bonds, and etch rate were studied by ellipsometry, MeV ion beam analysis techniques, and Fourier transform infrared spectroscopy. All parameters examined indicate that a highly diluted SiH4 gas phase and a microwave power of 1500 W help to prepare quasistoichiometric films with a high density (2.9 g/cm3) and a refractive index of 1.98. The effects of film density and film stoichiometry (N/Si) on refractive index are discussed through the Lorentz–Lorenz relation. The first electric results show that, under the optimized deposition parameters, a critical field of 2.3 MV/cm and an interface state density of 5×1010 eV−1 cm−2 can be achieved.
Optical emission study of reaction mechanisms in the deposition of nitrogen-containing amorphous hydrogenated carbon films
Authors: Durrant Steven F. , Rangel Elidiane C. , Bica de Moraes Mário A.
Published: July 2002

The reaction mechanisms taking place in a film-forming radio frequency discharge of a mixture of acetylene, nitrogen, and helium have been investigated using optical emission spectroscopy. A transient actinometric method was employed, based on the interruption of the flow of one of the feed gases (either C2H2 or N2), and the subsequent observation of the time-dependent changes in the discharge environment, specifically of the concentrations of CH and CN species, two possible precursors of film formation. Both N2 and C2H2 affect the CH and CN concentrations. Nitrogen strongly enhances the rate of formation of CH, very probably via gas phase reactions between atomic nitrogen and C2H2 or other species containing carbon and hydrogen. On the other hand, the relatively high CH concentration observed in discharges without nitrogen is taken to indicate that fragmentation of the C2H2 molecules by the discharge is another important mechanism of formation of the CH species. For the CN species, gas phase reactions between carbon- and nitrogen-containing species are expected to contribute to its appearance. However, a relatively high CN concentration could be detected even in discharges without C2H2 in the gas feed, so long as a nitrogen-containing polymer film was previously formed on the inner wall of the chamber. This is taken as evidence that interactions between the plasma and the polymer surface play an important role in the generation of the CN species. Further measurements of the CN concentration in a plasma of 100% He, produced in the chamber immediately after the formation of a nitrogen-containing polymer film, indicate that a possible reaction mechanism for the formation of the CN species is the detachment of nitrile groups (—C≡N) from the polymer surface upon cleavage of the carbon bond linking the nitrile terminations to the polymer chains.
Tunnel channels, charge transfer, and imaging mechanisms in scanning tunneling microscopy
Authors: Repphun G. , Halbritter J.
Published: July 2002

In scanning tunneling microscopy operation tip and object are routinely covered by adsorbates, hydroxides, or oxides. These undesirable layers are difficult to identify and to control in ultrahigh vacuum, high vacuum, or air. In an electrolytic environment the potentials of electrolyte–tip or electrolyte–substrate change the interfaces and, hence, the intermediate tunneling states, in a well-controlled way. Intermediate states nl(x) yield tunnel channels parallel to the direct one: I∝ exp(−2d√m2φ/ℏ) with d as the gap distance and φ≂φvac as the tunnel barrier height. With a uniform density nl the tunnel current decays exponentially with deff=d/(n+1) by n≥1 intermediate states thus simulating a reduced tunnel barrier height φeff=φ0(n+1)−2≪φvac. Exchanging nl(x) with x yields nonexponential I(d) dependences. Using the dependences of I on distance and voltage, the charge transfer processes, tunnel channels, and intermediate states in the oxide, hydroxide, and solid part of the electrolytic double layer can be identified. Atomic resolution has been found for n≤4 intermediate states. The localized states are proposed to be related to dipole resonances in the polarized and ordered interface HOH–HO− layers. Beside charge transfer between tip and substrate, dipole resonance also results in charge transfer along the polarized layer. So a floating electrode and, hence, imaging of organic molecules or Coulomb barriers, are possible.
SiO2/poly-Si electron beam resist process for nanofabrication
Authors: Wada T. , Haraichi S. , Ishii K. , Hiroshima H. , Komuro M. , Hirayama M.
Published: July 2002

An inorganic electron beam resist process for nanofabrication is described. Si-based bilayer inorganic electron beam resists, SixOy/Si3N4, Si3N4/SiO2, and SiO2/poly-Si were investigated. The SiO2/poly-Si system was found to be the most suitable for attaining deep undercut structures with fine patterns for metal–insulator–metal ultrasmall tunnel junction fabrication. Utilizing the multiple-angle deposition–oxidation deposition method, we have fabricated Al/Al2O3/Al tunnel junctions for which a clear Coulomb staircase was observed in the I–V characteristics at 12 K.
Sputtered gold films for surface-enhanced Raman scattering
Authors: Maya L. , Vallet C. E. , Lee Y. H.
Published: July 2002

Sputtered gold films in a pure form or as nanocomposites in silica or silicon nitride were screened for surface-enhanced Raman scattering (SERS) activity using Rhodamine 6G as a probe. The films were prepared by sputtering pure gold or solidified Au–Si alloys in plasmas generated in a dc glow discharge apparatus. The plasmas were produced with argon, nitrogen, or argon–oxygen as the sputtering gas to directly deposit gold films or in the latter case a gold oxide intermediate. The alloys produce nanocomposite films in a silicon nitride or silica matrix depending on the plasma gas. SERS activity was detected in some of the films thus leading to a search for the critical parameters that controlled this phenomenon. The films were characterized by profilometry, x-ray diffraction, and atomic force microscopy. SERS activity was found to be correlated to crystallite size in the 10–25 nm range and to roughness larger than 15 nm, and it was independent of film thickness. Sputtered gold films, particularly those containing the gold as a nanocomposite in silica are attractive media for SERS because of excellent adherence, ruggedness, and simplicity in preparation.
Laser pulse desorption under scanning tunneling microscope tip-Cl removal from single site on Si(100)
Authors: Dohnálek Z. , Lyubinetsky I. , Yates J. T.
Published: July 2002

The desorption of pairs of chlorine atoms influenced by the tip of a scanning tunneling microscope is achieved at preselected sites on the Cl-saturated Si(100)-(2×1) surface using nanosecond laser pulse irradiation of the tip within the tunneling range. Bright features observed for the empty state topographic images after a laser pulse sequence are interpreted to be due to bare Si–Si dimers formed by laser induced desorption of two Cl atoms underneath the tip. The Cl desorption mechanism involves the enhancement of the sample-tip interaction due to laser pulse induced tip heating and tip expansion.
Electron energy-loss spectroscopy of (DMe–DCNQI)2Cu
Authors: Mochida Michihiro , Shimada Toshihiro , Koma Atsushi
Published: July 2002

Electron energy-loss spectroscopy (EELS) has been applied to in situ prepared (DMe–DCNQI)2Cu (DMe–DCNQI=2,5-dimethyl-N,N-dicyanoquinonediimine). The intensity of the loss peaks changed significantly with the primary electron energies. It is probably due to the matrix element effects of the EELS. In conjunction with photoelectron spectroscopy using synchrotron radiation, the nature of the unoccupied levels has been elucidated.
Effects of the axial external magnetic field on the reduction of the dielectric window damage due to capacitive coupling in the inductively coupled plasma
Authors: Kim Jung-Hun , Lee Ho-Jun , Kim Youn-Taeg , Whang Ki-Woong , Joo Jung-Hoon
Published: July 2002

The degree of the capacitive coupling in the radio frequency inductively coupled plasma was estimated by measuring the dc shift of the potential at the central inner side of the dielectric window. Its value was −82.2 V for the condition examined (1.1 kW, 1.5 mTorr, C4F8 plasma, flow rate 20 sccm) and the dielectric window was severely damaged owing to this potential difference from the plasma potential, which could be confirmed with the quadrupole mass spectrometry. When an axial external magnetic field was applied, the mass spectrometer signals, which indicate the damage of the dielectric window, decreased drastically in addition to the improvement of the power transfer efficiency. This was mainly caused by the transition from the etching of the dielectric window to polymer formation due to the reduced window potential as a result of the application of magnetic field.
On the relation between preferential emission and bulk composition in binary alloy sputtering
Authors: Zheng Li-Ping , Li Ri-Sheng , Li Shu-You
Published: July 2002

Under simulated 1 keV Ar ion bombardment at low temperatures, the angular distributions of the steady sputter state of Cu–Ni alloys have been studied with the help of a dynamic Monte Carlo program. Calculations show the preferential emission of Ni in the near-normal direction, but that of Cu at oblique angles. Calculations also show that these preferential emissions strongly depend on the bulk composition.
Multiterm solution of the reactive space–time-dependent Boltzmann equation
Authors: White R. D. , Robson R. E. , Ness K. F.
Published: July 2002

The effect of spatial gradients, whether associated with surfaces or otherwise, on charged particle phase-space distribution functions and transport properties is a long-standing problem in the kinetic theory of gases. This article first discusses the necessary ingredients for an accurate kinetic theory analysis of the space–time behavior of electrons in gases and compares the different approaches currently in use. We then focus upon the electrons in a radio-frequency discharge away from the walls, where gradients are weak, and point out that the fundamental kinetic theory of even the boundary-free problem still warrants more careful attention than has been given to it in much of the contemporary literature. We highlighted the importance of careful analysis by presenting results for the first comprehensive “multiterm” solution of Boltzmann’s equation furnishing the complete set of hydrodynamic transport coefficients for electrons in an ac field undergoing ionization and attachment.
Layer-by-layer etching of GaAs (110) with halogenation and pulsed-laser irradiation
Authors: Han B. Y. , Cha C. Y. , Weaver J. H.
Published: July 2002

We have investigated the effect of laser irradiation on the terrace morphology of Br-covered GaAs (110). Layer-by-layer etching of GaAs (110) is demonstrated through laser-induced etching and atomic desorption. Nanosecond pulsed-laser irradiation (hν=2.3 eV, pulse power ∼35 mJ cm−2) of Br–GaAs (110) initially produces a high density of small, single-layer etch pits as Br is consumed. Continued laser irradiation causes Ga and As desorption from pit edges so that pits grow and thereby remove the remnant of the top GaAs layer. When there is Br on the surface, pit growth reflects the Br chemisorption structure (elongated along [001]) but subsequent atom desorption favors growth along [11̄0].
Conversion of tungsten nitride to pure tungsten
Authors: Lin Jun , Tsukune Atsuhiro , Suzuki Toshiya , Yamada Masao
Published: July 2002

The properties of W2N thin films deposited on Si, SiO2, and Ta2O5 by plasma-enhanced chemical vapor deposition, with and without an electron cyclotron resonance plasma formed SiO2 (ECR-SiO2) top layer are comparatively investigated. The ECR-SiO2 top layer can effectively promote the conversion of W2N to pure W while samples are annealed at high temperature. After annealing at 900 °C, W2N with the ECR-SiO2 top layer fully converts to W without occurrence of silicidation but that without the ECR-SiO2 top layer partially, or does not convert to W at all. The resistivity for the 900 °C annealed samples with the ECR-SiO2 top layer is only 1/3–1/10 of that without the ECR-SiO2 top layer. The conversion of W2N to W and enhancement of this conversion by the top ECR-SiO2 layer are discussed and explained.
Thermal and excimer laser assisted growth of Si(1−x)Gex alloys from Si2H6 and GeH4 monitored by on line single wavelength ellipsometry and ex situ atomic force microscopy
Authors: Larciprete R. , Cozzi S. , Pieretti S. , Vianey I. , Padeletti G. , Masetti E. , Montecchi M.
Published: July 2002

Single wavelength ellipsometry was used to monitor the growth of Si(1−x)Gex alloys obtained by ultrahigh vacuum chemical vapor deposition (CVD) at 570 °C on Si and to evaluate the effect of sample irradiation by KrF excimer laser pulses at an energy density above the threshold for surface melting. Laser irradiation was performed during or after the CVD growth. When the Si(1−x)Gex alloys were grown without laser assistance, the recorded ellipsometric curves indicated the presence of pronounced surface roughness, which was confirmed by atomic force microscopy analysis. On line ellipsometry during multiple pulse postgrowth irradiations showed a sudden increase of the ellipsometric angles Ψ and Δ corresponding to the first laser pulse. This behavior attested to the smoothing of the surface microroughness induced by the melt–recrystallization cycle. The excimer laser assisted CVD growth of Si(1−x)Gex alloy layers was also followed. By changing the ratio between the thermal growth rate and the irradiation frequency the kinetics of surface roughening was studied.
Low-pressure metalorganic vapor phase epitaxy of InP on (111) substrates
Authors: Ababou Y. , Masut R. A. , Yelon A.
Published: July 2002

We present a low-pressure metalorganic vapor phase epitaxy study of InP layers on (111)A and (111)B substrates, both normal and off-oriented 1° towards the [011̄] and [2̄11] directions. The optimal temperature was 650 °C for growth of specular surfaces on normal (111)A substrates, a slight increase compared to that for (001) substrates. Higher photoluminescence intensity was obtained compared to (001) InP epilayers. Specular surfaces could not be obtained on normal (111)B substrates over the wide range of growth temperatures and V/III ratios explored. However, the (111)B surface morphology was considerably improved at 600 °C using misoriented substrates, particularly with the [2̄11] direction of tilt. There are reasons to expect that this morphology, which still shows a few elongated defects, may be further improved using the nonequivalent opposite [211¯] tilt direction.
Control of structural, electrical properties of (Ba,Sr)TiO3/RuO2 thin films by the application of amorphous (Ba,Sr)TiO3 layer
Authors: Paek Su-Hyon , Lee Kong-Soo , Seong Jin-Yong , Choi Duck-Kyun , Kim Boum-Seock , Park Chi-Sun
Published: July 2002

The structural, electrical properties of (Ba,Sr)TiO3[BSTO]/RuO2 thin films were controlled by the addition of amorphous BSTO layers between crystalline BSTO film and RuO2 substrate. We prepared BSTO films with double-layered structure, that is, amorphous layers deposited at 60 °C and crystalline films. Crystalline films were prepared at 550 °C on amorphous BSTO layers. The thickness of amorphous layers was varied from 0 to 170 nm. During the deposition of crystalline films, the crystallization of amorphous layers occurred and the structure was changed to circular while crystalline BSTO films showed columnar structure. Due to insufficient annealing effect, amorphous BSTO phase was observed when amorphous layers exceeded 30 nm. Amorphous BSTO layer could also prevent the formation of oxygen deficient region in RuO2 surface. Leakage current of total BSTO films decreased with increasing amorphous layer thickness due to structural modifications. Dielectric constant showed maximum value of 343 when amorphous layer thickness was 30 nm at which the improvement by grain growth and the degradation by amorphous phase were balanced.
Efficiency improvement in low temperature metal-oxide-semiconductor solar cells by thin metal film deposition on photon receiving area
Authors: Lee Kuo-Chung , Hwu Jenn-Gwo
Published: July 2002

The recent discovery of the trap assisted tunneling property of low temperature liquid phase deposition (LPD) oxide is beneficial for metal-oxide-semiconductor (MOS) solar cells. Although the thickness of LPD oxide is up to 7 nm, the trap-assisted tunneling currents are still large enough for solar cell’s application. In this work, we fabricate and study the MOS solar cells with oxide prepared by LPD. The I–V curve for LPD oxide grown on bare Si is much different from that on native oxide. The larger tunneling current for LPD oxide grown on bare Si may be due to the boundaries between oxide seeds’ domains. For solar cells application, it’s better to use LPD oxide grown on bare Si. The conduction mechanism of LPD MOS solar cells is also discussed. For solar cells without additional thin transparent Al film, the minority carriers were collected from the accumulation region outside the main electrodes. For solar cells with additional thin transparent Al film, the thin Al electrode can directly collect the minority carriers from the weak inversion region underneath the thin Al film. For a cell exposed under 20 mW/cm2, short circuit current density JSC up to 13.2 mA/cm2, open circuit voltage VOC up to 433 mV, fill factor FF up to 66 and exposure area effective conversion efficiency η* up to 18.9% are obtained for this structure.
Noncontact method for measuring coefficient of linear thermal expansion of thin films
Authors: Rafla-Yuan H. , Hichwa B. P. , Allen T. H.
Published: July 2002

We measured the coefficient of linear thermal expansion of ZnSe thin films with a temperature regulated spectroscopic ellipsometer. The change in the film thickness was found to be a quadratic function of temperature whereas the coefficient of linear thermal expansion varied linearly in the temperature range between 295 and 413 K. While spectroscopic ellipsometry is recognized as a measurement technique to determine thin film optical constants and film thickness, the present work expands upon this technique to measure temperature induced dimensional change in the Å range.
Patterning of fluorine-, hydrogen-, and carbon-containing SiO2-like low dielectric constant materials in high-density fluorocarbon plasmas: Comparison with SiO2
Authors: Standaert T. E. F. M. , Matsuo P. J. , Allen S. D. , Oehrlein G. S. , Dalton T. J.
Published: July 2002

Successful pattern transfer of 0.36–0.62 μm features into fluorinated silicon dioxide, hydrogen silsesquioxane (HSQ), and methyl silsesquioxane (MSQ) has been demonstrated in a transformer coupled plasma (TCP) source using fluorocarbon feedgas chemistries. These films have a lower dielectric constant than conventional SiO2. It is this property that makes them attractive for implementation in future integrated circuit technology. The etching of these novel dielectrics was compared to conventional SiO2. We have observed that the different chemical makeup of these SiO2-like dielectrics does not affect the etching when weakly polymerizing gases are used, such as CF4. In this case, the etch rate is primarily dependent on the ion energy. For more polymerizing chemistries, like CHF3 or C3F6/H2 gas mixtures, x-ray photoelectron spectroscopy analysis showed that an increasing steady state fluorocarbon film thickness limits the ion and neutral flux at the interface of the various dielectrics. It is suggested that, as the fluorocarbon film thickness increases, the etching becomes more dependent on neutral species from the gas phase. In this case, hydrogen and carbon impurities in HSQ and MSQ, respectively, limit the etch rate. On the other hand, fluorine in the fluorinated SiO2 film enhances the etch rate as compared with the etch rate of conventional SiO2. In line with these observations, we conclude that fluorine from the gas phase is most likely the controlling etchant as the fluorocarbon film increases beyond the ion penetration depth.
Bias-assisted etching of polycrystalline diamond films in hydrogen, oxygen, and argon microwave plasmas
Authors: Zhang W. J. , Sun C. , Bello I. , Lee C. S. , Lee S. T.
Published: July 2002

Bias-assisted etching of diamond films was performed in a microwave plasma chemical vapor deposition system. Hydrogen, hydrogen/oxygen, and hydrogen/argon mixtures were used as reactant gases. The effects of both the reactant gas compositions and applied substrate bias on the etching rate, surface morphology, and phase variation were investigated by scanning electron microscopy and Raman spectroscopy. The contribution of ions of different reactant gases to the etching of diamond films was discussed.
Thermally actuated microbeam for large in-plane mechanical deflections
Authors: Kolesar Edward S. , Allen Peter B. , Howard Jeffery T. , Wilken Josh M. , Boydston Noah C.
Published: July 2002

The design, finite-element analysis, and experimental performance evaluation of a microelectromechanical systems (MEMS) device, known as a thermally actuated beam, is presented. The behavior of the thermal beam has been characterized so that it can be considered as an actuator in future MEMS applications. A MEMS polysilicon thermally actuated beam uses resistive (Joule) heating to generate thermal expansion and movement. To be a useful MEMS device, a thermally actuated beam will need to produce in-plane tip deflections that span 0–10 μm; while generating force magnitudes on the order of 10 μN. The thermally actuated beam design was accomplished with the L-Edit® software program. The devices were fabricated using the Multi-User Microelectromechanical Systems Process foundry service at the Microelectronics Center of North Carolina. The finite-element modeling analysis was accomplished with the IntelliCAD® computer program. These analyses predicted thermal beam tip deflections (0–13 μm) consistent with experimental observations. The average tip force generated by the thermal beam was measured to be 8.5 μN. The resonant frequency associated with in-plane motion, without damping, was calculated to be 75.16 kHz. The average resonant frequency measured in ambient air was 69.73 kHz. As a relative measure of reliability, it was observed that the thermal beam could be activated well in excess of three million cycles.