bluuebunny/crossref_metadata_2025 huggingface dataset:
Detailed study of scanning capacitance microscopy on cross-sectional and beveled junctions
Authors: Duhayon N. , Clarysse T. , Eyben P. , Vandervorst W. , Hellemans L.
Published: July 2002

In this work we have done a systematic study with scanning capacitance microscopy (SCM) on cross-sectional and beveled structures. A study was made on the practical problem of contrast reversal as well as on the effect of carrier spilling related to bevel angle, steepness and substrate concentration of the doping profile. A comparison has been made with the results achieved with spreading resistance profiling and also with theoretical predictions. Finally, the junction displacement for cross-sectional and beveled junctions is studied as a function of the applied bias. It is shown that the junction displacement is much smaller on the beveled surface after demagnification. Furthermore, the large extension of the profile along the beveled surface allows us to study the bias induced variation of the SCM signal within the depletion layer in great detail.
Amorphous boron coatings produced with vacuum arc deposition technology
Authors: Klepper C. C. , Hazelton R. C. , Yadlowsky E. J. , Carlson E. P. , Keitz M. D. , Williams J. M. , Zuhr R. A. , Poker D. B.
Published: July 2002

In principle, boron (B) as a material has many excellent surface properties, including corrosion resistance, very high hardness, refractory properties, and a strong tendency to bond with most substrates. The potential technological benefits of the material have not been realized, because it is difficult to deposit it as coatings. B is difficult to evaporate, does not sputter well, and cannot be thermally sprayed. In this article, first successful deposition results from a robust system, based on the vacuum (cathodic) arc technology, are reported. Adherent coatings have been produced on 1100 Al, CP–Ti, Ti–6Al–4V, 316 SS, hard chrome plate, and 52 100 steel. Composition and thickness analyses have been performed by Rutherford backscattering spectroscopy. Hardness (H) and modules (E) have been evaluated by nanoindentation. The coatings are very pure and have properties characteristic of B suboxides. A microhardness of up to 27 GPa has been measured on a 400-nm-thick film deposited on 52 100 steel, with a corresponding modulus of 180 GPa. This gives a very high value for the H/E ratio, a figure-of-merit for impact resistance of the film. A number of applications are contemplated, including corrosion/abrasion protection for die-casting dies and improved wear resistance for biomedical implants.
Dielectric Materials in Semiconductor Devices
Authors: Chu T. L.
Published: July 2002

Dielectric films are used extensively in semiconductor technology for masking against the diffusion of dopants into semiconductors, fabrication of active and passive components, electrical isolation between components, and surface passivation of devices. Silica is the most widely used dielectric in silicon devices at present, the preparation and properties of silica films are reviewed. However, silica is structurally porous, resulting in the high permeability of silica films toward impurities and the migration of impurity ions in silica films. Considerable efforts have been made to investigate other dielectrics during the past few years. The preparation and properties of several important dielectric films are discussed. Silicon nitride and aluminum oxide have been shown to be superior to silica in several respects. Various silica-silicon nitride and silica-alumina combinations have provided new and improved devices.
Dry process technology (reactive ion etching)
Authors: Bondur James A.
Published: July 2002

Dry process technology represents a new and exciting technique for defining images in insulators, semiconductors, and metals. It is attractive for application in the semiconductor industry because it results in increased dimensional and shape control for etched images. In addition, it represents a potentially less expensive process which is inherently safer for the people involved. Several different plasma etch system configurations are available for experimentation. Each has unique capabilities for different films. The different equipment configurations are described, including their ability to etch particular films, and the effects of the process on the etched image formed. Information is presented on other halogenated gases that may have potential application as a part of the dry process technology. Since experimental evidence is not available to explain the mechanisms involved in this technology, the published information speculating as to whether radicals, ions, or neutrals are responsible for etching are reviewed.
Thermal processing and encapsulation of solids in metal tubulations
Authors: Kayser F. X. , Stowe G. L.
Published: July 2002

A vacuum processing technique is described that permits encapsulation of the sample in metal tubing by application of a cold-weld pinch-off. It is particularily useful for annealing samples of materials that are capable of gettering glass surfaces. The hardware involved are standard commerical items.
Stability of rf-sputtered aluminum oxide
Authors: Gardner R. A. , Peterson P. J. , Kennedy T. N.
Published: July 2002

The chemical and thermal-mechanical stability of sputtered aluminum oxide films are examined. Sputtered alumina is quite soluble in bases and phosphate-containing solutions. Carbon dioxide was detected in the films by infrared spectroscopy and by mass spectroscopy during thermal gravimetric analysis; the presence of CO2 is likely due to adsorption on the sputtered film. Heating and cooling of sputtered alumina results in an irreversible expansion of the film. The anomalous expansion is cumulative with additional higher temperature heating, similar to a thermal ratchet effect, until a temperature of 850°C is reached. At temperatures above 850°C rapid argon evolution from the sputtered film occurs and is accompanied by film contraction.
Effect of impurities on the PtSi–Si interface and the PtSi surface
Authors: Crider C. A. , Poate J. M. , Rowe J. E. , Sheng T. T. , Ferris S. D.
Published: July 2002

Platinum silicides have been prepared by depositing Pt thin films under UHV and controlled impurity ambients. The interfaces and surfaces have been characterized by Rutherford backscattering spectroscopy, cross sectional TEM techniques and SEM. Clean depositions yielded planar interfaces whereas increasing oxygen contamination produced nonuniform interfaces and surfaces. No differences in interfacial and surface uniformity, reaction rates, and phase growth sequence were observed between samples cleaned with normal device processing steps and UHV sputter cleaned and annealed samples provided the Pt films were impurity free. The influence of interfacial oxides on silicide kinetics has also been determined.
Copper coated laser fusion targets using molecular beam levitation
Authors: Rocke M. J.
Published: July 2002

A series of diagnostic experiments at the Shiva laser fusion facility required targets of glass microspheres coated with 1.5–3.0 μm of copper. Previous batch coating efforts using vibration techniques gave poor results due to microsphere sticking and vacuum welding. Molecular beam levitation (MBL) represented a noncontact method to produce a sputtered copper coating on a single glass microsphere. The coating specifications that were achieved resulted in a copper layer up to 3 μm thick with the allowance of a maximum variation of 10 nm in surface finish and thickness. These techniques developed with the MBL may be applied to sputter coat many soft metals for fusion target applications.
Clustering and second-neighbor interactions in semiconductor alloys
Authors: Porod W. , Ferry D. K. , Jones K. A.
Published: July 2002

The virtual-crystal approximation in the framework of the tight-binding method is extended to include interactions between unlike second-nearest neighbors for semiconductor alloys. These interactions are determined by taking the experimentally observed bowing parameters of the energy gap as input information. Conclusions concerning the question of clustering are drawn and compared to experiment.
Radio frequency sputtering—the significance of power input
Authors: Horwitz Chris M.
Published: July 2002

Radio frequency (rf) sputtering is used for the deposition and etching of thin layers. In both cases the target etch rate must be controlled, and often power input has been used as one of the controlling parameters. An earlier paper has shown that the applied rf target voltage (Vpp) was a more useful parameter, and here new data is presented which indicates that the peak-to-peak voltage remains the preferable parameter for both etch rate control and in transferring between machines. However, a new method is described here which obtains the discharge power by subtracting losses from the total power reading. This discharge power is shown to be related to etch rates, and can thus be used as an aid in the scaling of system sizes. In addition, this discharge power exhibits interesting behavior as the pressure is varied, at constant applied rf voltage. Three main regions are evident when etching Si with CF4: at low pressures directional ion-induced etching is obtained; in an intermediate region the input power rises rapidly with pressure and the etching is less directional resulting in overhang profiles; and at high pressures an isotropic etching component results in undercut profiles. The two extreme regions correlate with the commonly identified regimes of: (a) low power input, low pressure reactive sputter etching, and (b) high power input, high pressure plasma etching.
Mechanisms of voltage controlled, reactive, planar magnetron sputtering of Al in Ar/N2 and Ar/O2 atmospheres
Authors: Affinito J. , Parsons R. R.
Published: July 2002

The relationships between processes occurring on the target surface, substrate surface, and in the glow discharge of a dc planar magnetron are studied for the purpose of controlling film stoichiometry. The positive feedback mechanisms which lead to the well-known transitions between bare and covered target surfaces are correlated with glow discharge characteristics. These data are found in agreement with a model we have developed which allows for two distinct mechanisms of target coverage: chemisorption, and ion plating of reactive gas species to the target surface. This model allows estimation of the stability of the glow discharge against these positive feedback mechanisms, which indicates under what circumstances voltage control of the glow discharge will permit operation at all degrees of target coverage without abrupt transitions between the extreme states of target coverage. It is shown that with this method of voltage control there is a one-to-one relationship between cathode voltage and film stoichiometry. Futhermore, a method is presented for calculating the film composition from the glow discharge characteristics alone and, related to this, a single target technique for producing thin film cermets is presented.
Edge region hydrogen line emission in the PDX tokamak
Authors: McNeill D. H. , Bell M. G. , Grek B. , LeBlanc B.
Published: July 2002

Measurements of the Hα line shape and of the spatial distribution of Hα emissivity in the PDX tokamak are interpreted in terms of molecular dissociation reactions at the plasma edge. The in-flux of molecules is shown to be roughly proportional to the edge emission intensity over a wide range of temperatures. The H2 particle lifetime is estimated for various types of discharges in PDX.
Anomalous transport properties of a new compositionally modulated semiconductor–semimetal system: PbTe–Bi
Authors: Shin Sung C. , Hilliard J. E. , Ketterson J. B.
Published: July 2002

Compositionally modulated structures (CMS) of PbTe–Bi with wavelengths between 38–140 Å were prepared by thermal evaporation on muscovite mica substrates. There was a well defined epitaxy with the (111) plane and the [11̄0] axis of the CMS parallel to (001) and [100] of the mica. The dc resistivity, Hall coefficient, and magnetoresistance were measured in the temperature range of 1.8 to 300 K and for magnetic fields up to 50 kG. All samples displayed an anomalous logarithmic increase in the resistance at low temperature. The magnetoresistance increased logarithmically with magnetic field H in large fields for the samples with thick PbTe layers (≳45 Å), while it went as H1/2 for the samples with thin PbTe layers (≲30 Å). The sign of the Hall coefficient changed from negative to positive with increasing Bi layer thickness and the positive Hall coefficient could be changed in sign by increasing the PbTe layer thickness.
Simultaneous gas- and plasma-driven hydrogen transport in solids
Authors: Brice D. K. , Doyle B. L.
Published: July 2002

The transport parameter formalism for evaluating the steady-state hydrogen (tritium) inventory, permeation rate, and recycle time for surfaces exposed to the plasma of an operating magnetic confinement fusion reactor has been extended to include synergistic effects of gas- and plasma-driven permeation. This steady-state formalism includes hydrogen trapping, recombination barriers to release at inner and outer surfaces, diffusion, and effects of thermal gradients (e.g., Ludwig–Soret effect) and is applicable to simultaneous plasma-driven and gas-driven hydrogen injection. In addition to providing a simple way of calculating the magnitude of these important tritium-related concerns, the transport parameter together with the ratio of the recombination coefficients at the two surfaces can also be used to classify the nature of these processes as to whether they are rate limited by bulk diffusion or surface recombination. New simple equations are derived which define these various regimes, and a new regime is identified which could influence permeation-probe measurements of plasma-edge fluxes.
Phenomena produced by ion bombardment in plasma-assisted etching environments
Authors: Winters Harold F.
Published: July 2002

The emphasis of this review paper will be to summarize recent experimental results, describe and evaluate contemporary concepts in the etching field, and to provide references to recent work.
Detection of atomic surface structure on NbSe2 and NbSe3 at 77 and 4.2 K using scanning tunneling microscopy
Authors: Coleman R. V. , Giambattista B. , Johnson A. , McNairy W. W. , Slough G. , Hansma P. K. , Drake B.
Published: July 2002

Scanning tunneling microscopy (STM) studies have been performed on NbSe2 and NbSe3 at 77 and 4.2 K. The surface atomic structure has been clearly resolved, but evidence of charge-density wave (CDW) modulation has only been observed at 4.2 K in NbSe3. CDW’s exist in NbSe2 at 4.2 K and in NbSe3 at 77 K, but the CDW amplitude is either too small or is screened by the remaining conduction electrons. The linear chain structure in NbSe3 has been clearly resolved and the STM profiles are dominated by the heights and effective charges of the surface Se atoms. Improved sensitivity and resolution will be required to study any details of the CDW structure in both compounds.
Anomalous nitrogen-metal bonding on Cr(110) and Cr/W(110) overlayers
Authors: Shinn N. D. , Tsang K.-L.
Published: July 2002

Valence and core-level synchrotron photoemission studies of molecular nitrogen chemisorption on Cr(110) and Cr/W(110) overlayers have revealed unusual metal:molecule bonding. On Cr(110), a single molecular adsorption state (α-N2) is populated via a mobile precursor at 90 K and characterized by valence orbital peaks at binding energies of 12.7 (weak), 8.4, and 7.1 eV with respect to the Fermi level. This is indicative of highly perturbed α-N2 valence orbitals and a molecular electronic structure similar to that of ‘‘π bonded’’ α-N2 on Fe(111). Nitrogen (1s) core-level spectra are used to identify three co-existing nitrogen species on the monolayer and bilayer Cr/W(110) surfaces at 80 K: weakly chemisorbed molecules (γ-N2), a stronglychemisorbed molecular dissociation intermediate (α-N2), and atomic nitrogen (β-N). A multiply coordinated species, Cr N=N Cr, is proposed for the α-N2 binding states, in spite of the absence of deep hollow sites usually invoked to account for this anomalous metal:nitrogen bonding. However, a high-symmetry local binding site requires a reconsideration of the ultraviolet photoelectron spectroscopy (UPS) peak assignments for α-N2.
Simulation and measurement of density variation in Mo films sputter deposited over oxide steps
Authors: Tait R. N. , Smy T. , Brett M. J.
Published: July 2002

A density profile for sputtered metal deposited over a step is generated using simulation by ballistic deposition (simbad), a two-dimensional computer simulation of thin film growth by ballistic deposition of hard disks. By postdeposition etching of a real Mo film deposited over a similar step, regions with high etch rate are identified. As etch rate is related to density, these are assumed to be low density sections, and are in fact found to agree well with low density regions predicted by the simulations.
Local bonding environments of Si–OH groups in SiO2 deposited by remote plasma-enhanced chemical vapor deposition and incorporated by postdeposition exposure to water vapor
Authors: Theil J. A. , Tsu D. V. , Watkins M. W. , Kim S. S. , Lucovsky G.
Published: July 2002

We have deposited thin films of SiO2 by remote plasma-enhanced chemical vapor deposition and have identified similar infrared (IR) spectroscopic signatures of Si–OH groups incorporated during either film growth, or the cooling down process in the deposition chamber. These films can also be hygroscopic and, on postdeposition exposure to atmospheric water vapor, they show changes in the IR spectra associated with the incorporation of additional Si–OH groups. These changes are (i) the development of a new symmetric feature, centered at about 3350 cm−1, within the asymmetric O–H stretching band generated during growth and/or cooling down; (ii) the development of a new spectral feature at 925 cm−1; and (iii) a shift in the Si–O bond-stretching band to higher wavenumber. We show that the first two changes in the IR spectra are due to near-neighbor Si–OH bonding groups that result from the reaction between water vapor and the Si–O–Si bonds of the SiO2 host network. These spatially correlated Si–OH groups have different spectral features, due to relatively strong hydrogen bonding interactions, from the randomly distributed Si–OH groups that are incorporated initially during film growth and/or cooling down. The shift in the frequency of the Si–O stretching band derives from a preferential reaction of water with strained and highly reactive Si–O–Si bonding groups, i.e., those with the smallest Si–O–Si bond angles which are attacked by water vapor, resulting in the formation of near–neighbor pairs of Si–OH bonding groups.
An investigation of cluster formation in an ionized cluster beam deposition source
Authors: McEachern R. L. , Brown W. L. , Jarrold M. F. , Sosnowski M. , Takaoka G. , Usui H. , Yamada I.
Published: July 2002

We have investigated the concentration of Agn clusters (25<n<1600) in a vapor of Ag expanding from the nozzle of a crucible heated to temperature as high as 1950 K (which corresponds to a silver vapor pressure of about 30 Torr). The goal of the experiment was to determine whether there were enough of these clusters present to have a significant effect on the ion-enhanced deposition of Ag films, as postulated for ion cluster beam (ICB) deposition. Time-of-flight mass spectra were obtained by using an excimer laser at 248 nm (KrF) or 193 nm (ArF) to photoionize a fraction of the vapor. The ions were extracted normal to the direction of average velocity of the neutral species and detected with a Faraday plate after a 20 cm field-free flight path. At the level of experimental uncertainty, no convincing evidence for the presence of large clusters was found for Ag vapor pressures in the 2–30 Torr range (typical for ICB). We conclude that under the conditions of our experiment, not more than one atom in 5000 is contained in a cluster with between 25 and 1600 atoms.
Radiative substrate heating for high-Tc superconducting thin-film deposition: Film-growth-induced temperature variation
Authors: Westerheim A. C. , Choi B. I. , Flik M. I. , Cima M. J. , Slattery R. L. , Anderson Alfredo C.
Published: July 2002

We have examined the problem of substrate temperature changes during the growth of YBa2Cu3O7−x (YBCO) thin films on LaAlO3 when the substrate is radiatively heated. Substrate temperature variations sufficient to degrade film quality occur unless the heater temperature is controlled during growth. At a heater temperature of 900 °C, the temperature of a LaAlO3 substrate was measured to be only 540 °C, while a similar substrate with a 2000-Å YBCO film reached 640 °C. The experimental data and calculations indicate that the heater temperature must be as high as 1240 °C to heat LaAlO3 to 730 °C, and must be decreased by over 200 °C during the first 500 Å of film deposition to maintain a constant substrate temperature during film growth. This study shows the need for an in situ noncontact substrate temperature measurement technique.
Interaction of atomic hydrogen with native oxides on GaAs(100)
Authors: Petit E. J. , Houzay F. , Moison J. M.
Published: July 2002

GaAs (100) covered with its native oxides is exposed to increasing doses of low energy atomic hydrogen in order to test the possibility of using it for surface cleaning at moderate temperatures. Hydrogen molecules are dissociated using a hot filament, and samples are exposed to atomic hydrogen at room temperature and at 300 °C with doses between 100 L and 100 kL of H2. The chemical modifications are characterized by ultraviolet and x-ray photoelectron spectroscopies. Exposures to atomic hydrogen contribute to clean the surfaces at both temperatures. At room temperature, As oxides completely desorb below 30 kL. The substrate is not degraded but one monolayer (ML) of C and Ga oxides remain on the surface upon hydrogenation up to 100 kL. Heating the sample to 300 °C stimulates the reaction of As oxides with the substrate and the desorption of reaction products to a larger extent. Above 10 kL, the thickness of the remaining contaminating layer is inferior to 1 ML. After exposures above 5 kL, superficial As depletion is observed in the substrate before complete cleaning is achieved, however no traces of metallic Ga are detected.
Metal/metal homoepitaxy on fcc(111) and fcc(001) surfaces: Deposition and scattering from small islands
Authors: Sanders David E. , Halstead David M. , DePristo Andrew E.
Published: July 2002

For systems of a single chemical species, we investigate the dynamics of adsorption of a metal atom on a clean fcc(111) metal substrate and on a pyramidal defect built on the fcc(001) substrate; the defect extends three layers above the surface, with nine, four, and one atoms in each layer, respectively. Each face thus forms a small part of an fcc(111) face. Molecular dynamics (MD) simulations are used where the interaction energy and the corresponding forces are generated from the recently developed non-self-consistent density functional based corrected effective medium (CEM) method in its simplest and computationally most efficient semiempirical MD/MC-CEM formulation. In previous work, the MD/MC-CEM form has been shown to predict the geometric and energetic properties of clean and adsorbate covered surfaces accurately. We show that there is no transient mobility for the Cu/Cu(111) system at a surface temperature of 80 K and an incident gas atom kinetic energy of 0.25 eV at incident angles up to 45° from the surface normal. This finding should hold for other homogeneous metal deposition systems since it arises from the fact that energy dissipation to the metal substrate is so efficient. For the Cu system, we determine that the cross section for sticking on the sides of the 14 atom pyramid varies from 9.0 to 37.2 Å2 for two MD/MC-CEM based potential energy surfaces (PES) differing only in the energetics of low coordination binding. Normalized to the aiming area, these give probabilities of 8.6% to 35.7%. Thus, it is shown that the low coordination region of the interaction strongly impacts the determination of growth modes, shifting from a funneling method giving two-dimensional (2D) layer by layer growth to a 3D mode, producing a rougher surface.
N2H4 and NH3 as precursors for silicon nitride thin film growth
Authors: Slaughter Elizabeth A. , Gland John L.
Published: July 2002

The thermal decomposition of ammonia (NH3) and hydrazine (N2H4) on the Si(100) surface has been characterized using Auger electron spectroscopy (AES), temperature programmed desorption, and low energy electron diffraction (LEED). Successive cyclic dosing of the Si(100)-(2×1) [E. A. Wood, J. Appl. Phys. 35, 1306 (1964); H. H. Farrell, F. Stucki, J. Anderson, D. J. Frankel, G. J. Lapeyre, and M. Levinson, Phys. Rev. B 30, 721 (1984)] surface with the nitride precursor resulted in the formation of an amorphous nitride layer as indicated by LEED. Hydrazine nitrided the Si(100)-(2×1) surface much more rapidly than ammonia, as shown by a comparison of the AES nitridation curves for NH3 and N2H4. These nitridation curves have very different slopes and clearly have different functional forms. The marked difference in nitride formation rates during cyclic dosing and heating, along with the absence of NH3 desorption during N2H4 decomposition, suggest that NH3 and N2H4 may result in the formation of different types of nitride overlayer and/or have different thermal decomposition mechanisms.
Laser-assisted nitridation of GaAs: Mechanisms
Authors: Zhu X.-Y. , Wolf M. , White J. M.
Published: July 2002

A nitride layer can be formed at low temperatures on GaAs(100) by simultaneous exposure to ammonia and UV photons in an ultrahigh vacuum environment. This process is a result of nonthermal photodissociation of adsorbed ammonia, initiated both by direct photon absorption and by attachment of hot substrate carriers. The nitride layer consists of a mixture of thermally stable GaN and volatile AsN; the latter desorbs below 800 K.
Effects of ion bombardment in plasma etching on the fluorinated silicon surface layer: Real-time and postplasma surface studies
Authors: Oehrlein Gottlieb S.
Published: July 2002

The silicon–fluoride reaction layer formed on silicon surfaces when etched in low pressure discharges of CF4 and SF6 has been characterized using ellipsometry in real time and x-ray photoemission spectroscopy (XPS) after sample transfer in vacuum. By comparing reactive ion etching (sheath voltage Vs=50–500 eV) and plasma etching (Vs≂30 eV) over the pressure range 10–250 mTorr and by using different rf power levels, the effects of ion bombardment on the SiFx layer were examined. The thickness of the SiFx layer depends primarily on the sheath voltage of the discharge, which determines the maximum energy of the bombarding ions. For low ion bombardment etching the apparent thickness of the SiFx layer is ≂0.5 nm. It increases up to ≂1.7 nm as the sheath voltage is increased. Nondestructive profiling of the SiFx layer was performed by angle-resolved photoemission to determine the variation of the various fluorosilyls (SiF, SiF2, SiF3, and SiF4) as a function of depth. SiF3 has the highest intensity at the surface of the SiFx layer and drops off rapidly in relative importance as the reacted layer is probed deeper. At the largest depth, SiF becomes the dominant species. SiF2 and SiF4 are also peaked at the surface, but their relative importance is always smaller than that of SiF and SiF3. The initial stages of fluorination of the Si surface were monitored in real time using ellipsometry. Within the first seconds of exposure to the plasma, a damaged Si layer is introduced which is subsequently fluorinated and partly consumed. The steady-state SiFx layer thus formed and present on the crystal during etching is stable when the discharge is terminated. This finding validates the use of postplasma XPS analysis for the study of the SiFx layer. The ellipsometric measurements demonstrate that an increase in the sheath voltage of the discharge results in increased surface damage and deeper fluorination of the Si surface. These results are in conflict with the predictions of several models of ion-enhanced etching and indicate that ion-induced mixing and generation of damage may play an important role in ion-enhanced etching reactions.
Measurements of radical densities in radio-frequency fluorocarbon plasmas using infrared absorption spectroscopy
Authors: Haverlag M. , Stoffels E. , Stoffels W. W. , Kroesen G. M. W. , de Hoog F. J.
Published: July 2002

Densities of CF2 radicals, rotational temperatures, and the degree of dissociation in radio-frequency fluorocarbon plasmas have been measured using Fourier transform infrared absorption spectroscopy and tunable diode laser infrared absorption spectroscopy. The CF2 densities obtained in CF4, CHF3, C2F6, and CF2Cl2 plasmas indicate that the partial pressure of CF2 is around 1%–5% of the total pressure. From the spatial dependence of the CF2 density it was established that at high pressure, CF2 is produced either on the rf electrode or close to the rf electrode. Furthermore, a comparison between measured absorption spectra and a simulation of the rotational distributions has revealed that the rotational temperatures of CF4, CF2, and HF are all close to room temperature. FTIR spectra indicate that in plasmas of gases with a low F/C ratio (due to the presence of H or Cl) the source gas is converted for a significant part into other species.
Modeling and simulation of glow discharge plasma reactors
Authors: Lymberopoulos Dimitris P. , Economou Demetre J.
Published: July 2002

Large scale numerical simulations of the spatiotemporal plasma flow in low-pressure (0.1–1 Torr) radio-frequency capacitively coupled reactors were performed using a global plasma reactor model. Two-dimensional argon glow discharge simulations coupled with neutral (metastable) transport and reaction provided insight on the discharge structure and radial plasma uniformity. A one-dimensional simulation of a strongly electronegative (Cl2) discharge was also performed using the global model. Global model results suggested a ‘‘boundary layer’’ approach in which the reactor is separated into two regions: bulk plasma and sheath. The two-region model was applied successfully to the Cl2 discharge.
Modification of aluminum thin films
Authors: Park M. , Lane K. R. , Parpia J. M. , Isaacson M. S.
Published: July 2002

We have utilized several processing techniques to locally modify the superconducting transition temperature and the normal state resistivity of aluminum thin films. The techniques of ion implantation, application of a magnetic overlayer, and reactive ion etching have been used to fabricate S-N interfaces with controlled differences in transition temperatures and normal state resistances. Lithographic techniques and CF4 reactive ion etching at low power and pressure reliably produce two-dimensional S-N structures of desired dimensions in the limit where the transition temperatures and normal state electronic properties of the two regions are close to each other.
Commercial helium permeation leak standards: Their properties and reliability
Authors: Abbott P. J. , Tison S. A.
Published: July 2002

Standard leaks or leak artifacts are used extensively in industrial and research environments, typically for the calibration of helium leak detectors. The most commonly used leak is the helium permeation type, which uses a glass, quartz, or polymer barrier to restrict the flow of helium via diffusion. Physical leaks, on the other hand, use a physically restrictive element to limit the flow. This article will discuss the properties and reliability of helium permeation standard leaks, based on eight years of accumulated calibration data. Physical helium leaks will not be discussed since relatively few have been calibrated at the National Institute of Standards and Technology.
In situ observation of the oxidation and reduction processes on Fe-Cr alloys
Authors: Walls M. G. , Ponthieux A. , Rondot B. , Owen R. A.
Published: July 2002

We present atomic force microscopy (AFM) observations on the micron and submicron scale of the surface morphology evolution of Fe-Cr alloys during oxidation-reduction cycles. Industrial Fe-17%Cr, which contains impurity inclusions, exhibits a specific type of corrosion behaviour during the initial stages of oxidation. The inclusions, which are rich in silicon, undergo a very rapid oxidation process which leads to a large increase in their volume. This in turn leads in many cases to the ejection of the enlarged precipitates from the sample, leaving a pitted surface. Purer material is free from this type of attack. Apart from the precipitate behaviour, the oxidation-reduction cycle appears to proceed in most cases similarly in the pure and industrial Fe-17%Cr alloys. Both also contain Cr-rich particles which behave differently from the rest of the sample. Fe-5%Cr and pure Fe samples do not exhibit enhanced activity compared to the 17% samples either during oxidation or reduction. Indeed, in the case of the pure Fe sample it is often quite difficult to observe any changes at all. For these mechanically polished surfaces, which are similar to those used in most electrochemical studies and encountered in real corrosion problems, the AFM observations at the scale of a few microns illustrate that chemical heterogeneities on this scale have more influence than polishing scratches, but that other heterogeneous effects sometimes exist which do not appear to be connected with either property. The usefulness of in situ observations carried out on this scale is underlined.
Temperature dependence of a-C:H film deposition in a CH4 radio frequency plasma
Authors: Mutsukura Nobuki , Saitoh Kazuhiko
Published: July 2002

The hydrogenated hard carbon films were deposited at elevated temperature in planar rf CH4 plasmas. The deposition rate and mechanical properties of the carbon films deposited at substrate temperature between room temperature and 400 °C were examined. The behavior of the film deposition rate indicated the negative temperature slope, and activation energies of around 0.04–0.05 eV at gas pressures of 40–100 mTorr were obtained from the Arrhenius plots of the deposition rates. Both the temperature behavior and the value of the activation energy suggest that the spontaneous incorporation of physisorbed CH3 precursor into the growing film is negligible, and the chemical reaction between the CH3 molecules and hydrocarbon ions bombarding the film surface is most probable in the present deposition process. The dense carbon films having film densities up to 2.7 g/cm3 were obtained at 40 mTorr.
High temperature oxidation of thin CrN coatings deposited on steel
Authors: Milošev I. , Abels J. M. , Strehblow H.-H. , Navinšek B. , Metikoš-Hukovič M.
Published: July 2002

Chromium nitride coatings were deposited on steel substrates by the tetrode plasma-beam sputtering technique at 200 °C. The coatings exhibit a dense, smooth, and homogeneous structure with the appearance of occasional pinhole defects, as shown by scanning electron microscopy (SEM) and atomic force microscopy. The thickness of the coatings was sufficiently small (0.34 μm) to allow the study of the compositional changes induced by the high temperature oxidation throughout the oxide and nitride phases, as well as at the inner interface between the nitride coating and the substrate. The CrN coatings were oxidized in an oxygen flow at temperatures up to 750 °C. After oxidation at temperatures higher than 450 °C the formation of a Cr2O3 layer as a separate phase on the top of the nitride coating is observed. It is suggested that the mechanism of CrN oxidation proceeds by the progressive replacement of nitrogen by oxygen. As the temperature is raised the thickness of the Cr2O3 layer increases and its grain structure becomes more pronounced. Besides oxidation of CrN to Cr2O3 another parallel process is taking place, namely the oxidation of iron from the substrate. This process leads to the formation of FeO islands, which represent defect spots on the surrounding Cr2O3 surface. The number of these defects depends on the temperature and time of oxidation. In order to study the failure mechanism, various surface analytical techniques were applied, i.e., x-ray photoelectron-spectroscopy, Auger electron spectroscopy, energy dispersive x-ray spectroscopy, and SEM. It is suggested that the penetration of iron through the coating starts at the pinholes present in the coating. At higher temperatures, however, this is not the dominating mechanism, and the diffusion process is further facilitated by the mismatch in the thermal expansion coefficients between the substrate and the nitride coating. Thermal stress thus established leads to the loss of adhesion at the inner substrate/coating interface and therefore creates additional paths for the diffusion of iron.
In situ characterization of the transient behavior of particles in low pressure plasmas
Authors: Schmidt Ursula I. , Graves David B.
Published: July 2002

Contamination due to plasma-generated particles is one of the major issues affecting the yield loss in microelectronics fabrication. Laser light scattering performed in situ during the process provides important information about particle distributions both spatially resolved and as a function of time. It is therefore well suited for the investigation of the transient behavior of process-generated particles that can influence the performance of etching or deposition plasmas. The present light scattering system allows the quantitative determination of particle size and number density by detecting the scattering intensity at two separate angles (angular dissymmetry) and/or at two different polarization states (polarization dissymmetry), respectively. A special calibration procedure is required in order to obtain quantitative results for particle size and number density. Based on this analysis, we report the temporal evolution of the spatial distribution of aluminum particles in an argon discharge. We examine the transition from a continuous cloud of particles filling the entire interelectrode gap to a narrow band of intense scattering near the grounded electrode. Other changes of light scattering patterns with time have been observed under other conditions. The implications of these observations in terms of particle generation and evolution in gas discharge plasmas are discussed.
On the recovery of the spectroscopic image in atomic force microscopy
Authors: Sokolov Igor Yu.
Published: July 2002

The principle possibility of the detection of the sort of material a surface consists of (in other words, obtaining the spectroscopic, or ‘‘Hamaker constant’’ image of the surface) is proven for the atomic force microscopy method. It is shown that the problem can be reduced to the Fredgolm integral equation of the first kind with a core of the Hilbert–Schmidt type. This problem is demonstrated to have a unique solution, provided the model case of exact measurements and the surface topography is known in advance. It is shown that the latter can be considered as the topography obtained in the contact mode. The possibility of the spectroscopic image recovery for the measurements with errors is discussed. As an example, obtaining the Hamaker constant is demonstrated for an example of the surface consisting of two different materials.
Standardized procedure for calibrating height scales in atomic force microscopy on the order of 1 nm
Authors: Suzuki M. , Aoyama S. , Futatsuki T. , Kelly A. J. , Osada T. , Nakano A. , Sakakibara Y. , Suzuki Y. , Takami H. , Takenobu T. , Yasutake M.
Published: July 2002

We propose a standard stepped sample and specify a procedure for determining the step height for height-scale calibration of atomic force microscopy (AFM) instruments on the order of sub-nm to nm. The stepped Si(111) surface structure was confirmed to be the most appropriate for the standard sample by a series of round-robin measurements carried out by a group comprising AFM instrument manufacturers and user organizations. By specifying a standard measurement procedure, the mean standard deviation of the step heights is decreased by 50%. It is also confirmed that the measured Si step height is accurate to ±5%, which is consistent with the accuracy obtained for higher step standard samples. A prototype common data processing software program containing the algorithm of the specified procedure was used to allow direct comparison of the untreated measurement data from each organization.
Optical properties of cobalt oxide films deposited by spray pyrolysis
Authors: Athey P. Ruzakowski , Urban F. K. , Tabet M. F. , McGahan W. A.
Published: July 2002

The optical constants of Co3O4 films were determined by analyzing variable angle of incidence spectroscopic ellipsometry data and normal incidence transmittance data, between 3500 and 17 000 Å. Absorption was taken to be nonzero for the soda–lime–silica float glass substrate. The absorption of the soda–lime–silica float glass was fitted by an ensemble of four Gaussian oscillators over the entire measured spectral range. Surface roughness of the film was measured with atomic force microscopy and included in the optical model. The films were deposited by spray pyrolysis of cobalt acetylacetonate onto heated soda–lime–silica float glass and fused silica substrates. Fused silica was used to observe film absorption without the effect of substrate absorption. The oxide film phase was identified with thin-film x-ray diffraction analysis. Simultaneous fits of ellipsometry and transmittance data from coated samples were computed to obtain the film thickness, optical constants, and the amplitudes of the four Gaussian oscillators representing the glass substrate absorption. This analysis was done by treating the optical constants at each wavelength as simple fitting parameters or as variables with a Kramers–Kronig consistent parametric model. Spectra for the most accurate optical constants of Co3O4 films deposited by spray pyrolysis onto both substrates are presented.
Atomic scale flattening and hydrogen termination of the Si(001) surface by wet-chemical treatment
Authors: Morita Yukinori , Tokumoto Hiroshi
Published: July 2002

An ultrahigh vacuum scanning tunneling microscopy has been applied to analyze wet-chemically prepared Si(001) surfaces in an atomic scale. The surface treated by 2.5% HF is atomically rough and is covered by featureless corrugations resulting from an etching by OH ions in the solution. The surface treated by HF:HCl=1:19 mixed solution without controlling an oxide-removal direction is also atomically rough, but is characterized by a kinkful morphology, which reflects the crystallographic nature of the Si(001) surface. On the other hand, the surface treated by the same mixed solution but by controlling the oxide-removal direction is covered by regular monatomic steps and the ordered dihydride phase on the terrace. From these facts, we have confirmed that these factors, the concentration of the OH ions and the way of the oxide-removal, play roles in the preparation of the atomically flat Si(001) surface.
Super-resolution fluorescence imaging of single dye molecules in thin polymer films
Authors: Bopp M. A. , Tarrach G. , Lieb M. A. , Meixner A. J.
Published: July 2002

We report on the imaging of single dye molecules in thin polymer films under ambient conditions by means of scanning near-field optical microscopy. The long-term mechanical stability and high detection efficiency of our instrument allow the imaging of single dye molecules over several hours with a high signal-to-noise ratio. The local excitation by the near-field tip, the low excitation power and the fact that the dye molecules are embedded in the three dimensional polymer structure drastically reduce photodestruction as compared with conventional microscopy. The observation of many molecules in the same film allows to probe them under identical experimental conditions and to statistically analyze their global behavior. We find that the molecules diffuse and rotate within the polymer matrix. The single dye molecules act as nanometer-sized probes and reflect the local structure of the polymer.
Cl2 plasma etching of Si(100): Damaged surface layer studied by in situ spectroscopic ellipsometry
Authors: Layadi N. , Donnelly V. M. , Lee J. T. C. , Klemens F. P.
Published: July 2002

Spectroscopic ellipsometry was applied to study the damage induced by chlorine plasma etching of crystalline silicon (100). Two etching modes (with different dc bias voltages) were investigated; (1) reactive ion etching with radiofrequency (rf) power applied only to the wafer stage and (2) a high density helicon plasma with and without rf power on the stage. Bias voltages from 0 to −350 V were employed. A two layer model was used to interpret the ellipsometry data. The interfacial layer was modeled as a mixture of amorphous silicon (a-Si), crystalline silicon (c-Si), and chlorinated silicon (SiClx), and the top surface was modeled as a mixture of a-Si and SiClx. The evolution of the damaged surface layer was investigated as a function of plasma exposure time and dc bias. Real-time measurements show that the damaged surface layer reaches a saturated thickness and composition after about 4 s of plasma exposure. The thickness of the surface layer increases with mean ion energy (i.e., negative dc bias voltage) from 9 Å at 0 V to 32 Å at −350 V. Ion energy also increases the equivalent thicknesses of a-Si and SiClx within the surface layer. In addition, real-time ellipsometric traces indicate that the stable surface layer present after etching critically depends on the sequence and delay between the extinction of the plasma source and the stage power. When power is turned off abruptly, the surface that was present during etching does not change with time (in the absence of air exposure) indicating that post-plasma surface diagnostic measurements such as x-ray photoelectron spectroscopy reflect the surface that is present during etching.
Atomistic simulations of the nanometer-scale indentation of amorphous-carbon thin films
Authors: Sinnott S. B. , Colton R. J. , White C. T. , Shenderova O. A. , Brenner D. W. , Harrison J. A.
Published: July 2002

Molecular dynamics simulations are used to examine the nanometer-scale indentation of a thin film of amorphous carbon with a nonrigid sp3 bonded carbon tip. The simulations show in detail the atomic-scale mechanism of the indentation process and compare the bonding character of the film before and after indentation. The computationally determined elastic modulus of the amorphous-carbon film is found to be 243 GPa, in good agreement with experiment.
Investigation of a SF6 helicon plasma
Authors: Chabert P. , Boswell R. W. , Davis C.
Published: July 2002

We present a study of a helicon plasma with SF6 gas, operating at 13.56 MHz and powers between 0 and 2000 W, pressure between 0.3 and 7.5 mTorr, and flow rates between 4 and 40 sccm. All the measurements of plasma and gas parameters were made in the downstream diffusion chamber, below the helicon source. Two main regimes have been observed: at low power (typically <200 W), the plasma is not luminous in the source and ionization takes place in the diffusion chamber where there is an electric field. At high power, the plasma is strongly dissociated and the ionization occurs in the source for pressure above 0.9 mTorr and in the diffusion chamber when the pressure is below. The fluorine atom concentration increases with power until a saturation level [F]sat is reached. The gas flow rate determines the power required to reach the saturation whereas [F]sat is proportional to the pressure. The power required for the dissociation can be an important part of the power injected into the reactor leaving less power for ionization. This leads to a decrease of the plasma density when the flow rate increases at constant pressure.