bluuebunny/crossref_metadata_2025 huggingface dataset:
Technology and applications of broad-beam ion sources used in sputtering. Part I. Ion source technology
Authors: Kaufman H. R. , Cuomo J. J. , Harper J. M. E.
Published: July 2002

The technology of broad-beam ion sources used in sputtering applications is reviewed. The most frequently used discharge chambers are described, together with procedures for predicting performance. A new, compact ion source is described. Ion acceleration is reviewed, with particular emphasis on recent low-energy techniques. Some of these techniques include three-grid, small-hole two-grid, and one-grid ion optics. A new material for fabrication of high-precision ion optics is silicon. Because no stresses are introduced with the etching techniques used, the finished grid can be held to very close tolerances. A recent innovation for sputtering applications is the use of Hall-current acceleration. This technique uses a magnetic field interacting with an electron current to provide the accelerating electric field, thereby avoiding the usual space-charge limit on ion current density that is associated with gridded optics. Electron emission is also reviewed, with new hollow cathodes promising improved lifetimes. The overall picture is one of greatly improved ion source capability, with particularly large improvements in low-energy ion current densities.
Computer simulation of line edge profiles undergoing ion bombardment
Authors: Rangel/ow I. W.
Published: July 2002

A computer model of dry etching was used to predict line edge profiles obtained by the ion etching device built in our Institute. For the simulation, the etch rates as a function of impact angle data for gold, silicon, and chromium, resists AZ 1350 and PMMA were determined. These characteristics were approximated by means of analytical functions. It has been found that the accuracy of the etch rate versus impact angle is of great importance. The influence of this dependence on the predicted contour evolution has been investigated for the case of a gold hemisphere approximated by two-dimensional semicircular profile. The model was compared with known analytical results. The experimental verification of the model has been made on patterns developed in AZ 1350 on silicon, AZ 1350 on Al, and PMMA on Au. SEM observations of the evolution of edges under ion milling show good agreement between the experimentally obtained pattern profile and computer predictions.
Interfacial chemistry of electrical contacts on GaAs and Al0.3Ga0.7As
Authors: Buonaquisti A. D. , Wang Y. -X. , Holloway P. H.
Published: July 2002

Thermal restructuring of oxides of GaAs and Al0.3Ga0.7As substrates has been studied using Auger electron spectroscopy and both neutral and secondary ion mass spectrometry. The oxide underwent restructuring at ≳250 °C while gallium oxides desorbed at temperatures depending upon the type of oxide. Reoxidation at low oxygen pressures resulted in surface oxygen species different from those in native oxides. These species desorbed at ∼520 °C while native oxides desorbed at 600 °C. Carbon-containing contaminants did not desorb. The implications of these results for electrical contacts are discussed.
The use of metallic glasses in fabrication of ICF targets
Authors: Johnson W. L. , Lee Mark C.
Published: July 2002

The fabrication of Au-base metallic glass spheres and microballoons used for ICF targets is described. Alloys of composition Au55Pb22.5Sb22.5 were used because of its low melting point and high Z number. Metallic glass microspheres have a high degree of sphericity and surface smoothness and deform homogeneously and isotropically under the high strain rates involved in an ICF implosion. (AIP)
Local space-charge forces and broadening of energy distribution in electron beams
Authors: Sasaki Tateaki
Published: July 2002

Let the space-charge force Fsp be divided into two parts, average force Fav and local force Floc. This paper analyzes the Floc and gives a simple theoretical view for the phenomenon of energy broadening for which we have no good theory yet. We first analyze Floc for electron gas in thermal equilibrium and then investigate a case which simulates electron beams. The analysis gives us not only the average value of F2loc but also the probability function of the distribution of F2loc. Applying the results of analysis to electron beam forming a crossover, we obtain a theoretical formula which explains the results of our computer simulation on energy broadening not only almost qualitatively but also quantitatively within a factor of about 2.
Noble metal/Si(111) interfaces studied by MeV ion scattering
Authors: Ito T. , Gibson W. M.
Published: July 2002

The displacement-sensitive MeV ion-scattering measurement has been performed on Si(111) surfaces covered with Au and/or Ag evaporated at room temperature. For single metal depositions, the reactivity of Ag atoms with Si atoms was very low compared to Au. For sequential depositions of both Ag and Au, the reactivity of the system was dominated by the more reactive material Au while the onset of the Si displacement depends on the amount of both metals for 0.5–2.0 ML coverage of predeposited materials (1 ML=7.83×1014 atoms/cm2). No significant differences were observed between Au/Si(111) 7×7 and Au-stabilized 3×1 surfaces for subsequent Ag depositions. The mechanism of the reaction between the noble metal and Si atoms is discussed in terms of current models.
An Auger electron spectroscopy/electron energy-loss spectroscopy study on the oxidation of WSi2 thin film
Authors: He Jian-Wei , Mo/ller Preben J. , Chen Jiann-Ruey
Published: July 2002

The room-temperature oxidation of a high-temperature-annealed thin film of WSi2 vapor deposited upon a Si(111) crystal surface was studied by Auger electron spectroscopy (AES) and electron energy-loss spectroscopy (EELS) after 105 L oxygen exposure under UHV conditions. It is found that the LVV 92-eV silicon AES signal does not show any splitting and that the surface after oxidation is only partly covered by silicon oxides. Based upon an analysis of the AES and EELS structures the oxidation process is discussed.
Advances in vacuum contamination control for electronic materials processing
Authors: O’Hanlon John F.
Published: July 2002

The demand for devices with improved performance and yield and fabricated with reduced processing costs is driving advances in electronic materials processing. A most important consideration is the reduction of defects resulting from particulate contamination during processing. Since many of the steps in device processing use vacuum equipment, their requirements are shaping the design of new tools. In this paper we describe the sources of contamination during processing, the techniques used for their reduction, and note vacuum issues that relate to the use of new processing technologies.
Quantitative surface electron spectroscopies: Application to the study of corrosion of metals and glasses
Authors: Maschhoff B. L. , Zavadil K. R. , Nebesny K. W. , Armstrong N. R.
Published: July 2002

The surface chemical reactions of extremely reactive metals such as lithium have been explored using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Corrosion processes which occur at the lithium surface, or corrosion reactions occurring at lithium/glass interfaces, are difficult to characterize by normal ex situ analyses which may damage the interface of interest. Starting with atomically clean surfaces, XPS and AES can be used to help construct a surface with controlled composition passive layers which can then be immersed into electrochemical environments and systematicaly studied. Careful analysis of the XPS or AES data is needed to provide reliable molecular information and quantitation of the actual metal surface regions.
Scanning tunneling microscopy of Kish graphite and highly oriented pyrolytic graphite in air
Authors: Morita S. , Tsukada S. , Mikoshiba N.
Published: July 2002

The atomic images of single-crystal graphite (Kish graphite) in air were compared with those of highly oriented pyrolytic graphite (HOPG) using a scanning tunneling microscope. In the usual topography mode, the Kish graphite showed an anomalous atomic corrugation ΔZ up to 175 Å, larger than that of HOPG, whereas both the atomic corrugations in Kish graphite and HOPG increased with decreasing tunnel resistance RT. On the other hand, in a (variable) current mode, the Kish graphite showed a ratio of the tunneling current modulation ΔIT/〈IT〉 several times smaller than that of HOPG, while both the current modulations in Kish graphite and HOPG were nearly independent of the tunnel resistance RT in contrast to the atomic corrugation.
Cross-sectional transmission electron microscopy of the interfaces between physical vapor deposited TiNx coatings and steel substrates
Authors: Erdemir A. , Cheng C. C
Published: July 2002

The functional lifetime of surface coatings for mechanical, tribological, and metallurgical applications is strongly related to their structural and interfacial characteristics. In this study, cross-sectional transmission electron microscopy (XTEM) and electron energy-loss spectroscopy were concurrently employed to investigate the structural and chemical states of the TiN films and interfaces formed during sputter deposition and ion plating. The effects of deposition temperatures and processes on the solid-state interactions between the film and substrate materials are reported. In addition, convergent beam electron diffraction studies were incorporated in the present study to assist in interpreting the XTEM observations. The results show that exposure to high temperatures during ion plating strongly influences the microstructural as well as chemical states of the TiN films and the film–substrate interfaces.
Structural characterization of multilayer metal phosphonate film on silicon using angular-dependent x-ray photoelectron spectroscopy
Authors: Akhter S. , Lee H. , Hong H.-G. , Mallouk T. E. , White J. M.
Published: July 2002

A trilayered film of (Hf, Y, Zr) 1,10-decanebisphosphonate was grown on Si wafer and characterized by variable angle take-off x-ray photoelectron spectroscopy. The angular dependence of the metal intensities is consistent with a sequentially layered arrangement with no intermixing of the metal ions. This implies that the C10 alkyl chains are fully extended and stacked in an ordered layered structure. The angular dependence of the Si 2p electrons (1150 eV) yields a mean free path of 315 ± 80 Å.
Structure of platinum ultrafine particles in Pt/C catalyst observed by scanning tunneling microscopy
Authors: Komiyama Masaharu , Kobayashi Jun’ichi , Morita Seizo
Published: July 2002

Ultrafine platinum metal particles (few nanometers in diameter) dispersed on the surface of a vacuum-deposited carbon film were examined by scanning tunnelling microscopy. In this system that simulates an industrial Pt/C supported metal catalyst, the observed shape of the Pt particles appeared close to hemispherical, bounded by several relatively flat faces. The particle shapes were fitted well with halves of cubo-octahedra, providing a model for the structure of ultrafine Pt metal particles in the industrial Pt/C supported metal catalysts.
Sloped niobium etching using CF4 and O2
Authors: Sasserath Jay N. , Vivalda John
Published: July 2002

A sloped etching process for Nb is developed for pilot line operations. Reactive ion etching and plasma processes are compared for a CF4/O2 parallel plate etch system. The higher pressure etches were found to have better characteristics for the numerous combinations of independent variables examined. Process settings tested include rf power, chamber pressure, and etchant flow rates. Higher Nb etch rates, photoresist:niobium etch rate selectivity of 1:1, and adequate selectivity over SiO2 were obtained with the plasma etches. For both types of processes, control of plasma loading affects were determined to be crucial to accomplish successful patterning. Finally, mathematical models of the etch process were derived from the data and used to determine basic etch mechanisms occurring within the reactor.
Field emitter tips for vacuum microelectronic devices
Authors: Chin K. Ken , Marcus R. B.
Published: July 2002

The design criteria for two forms of field emitters (cone and wedge) for vacuum microelectronic applications are discussed. Effects of practical variations in geometry on emission current, spatial and temporal dispersion of electron emission, and emitter heating are calculated by simulation. Several design guidelines for the geometry of the emitter–anode complex are suggested. A sharp silicon tip processing method is presented, which is based on the oxidation inhibition of silicon at regions of high curvature. Methods for forming emitters of other materials are also discussed.
Slippage of simple liquid films adsorbed on silver and gold substrates
Authors: Krim J. , Watts E. T. , Digel J.
Published: July 2002

The amplitude of vibration of a quartz crystal oscillator decreases slightly when a film adsorbs on its surface. Measurement of this decrease in amplitude allows one to quantitatively deduce the solid–liquid interfacial viscosity and the degree to which the film ‘‘slips’’ due to the oscillatory motion. Experiments have been carried out on various ‘‘model interfaces,’’ including xenon and nitrogen on gold, and water and cyclohexane on silver. Monolayers and bilayers of these films are observed to exhibit greater average slippage than thick films of the corresponding bulk material. The more massive monolayers are observed to exhibit shorter slip times.
Surface reconstructions induced by thin overlayers of indium on Si(111)
Authors: Cornelison D. M. , Chang C. S. , Tsong I. S. T.
Published: July 2002

We have used the technique of impact collision ion scattering spectrometry (ICISS) to study the in-plane geometry of both the 7/8 × 7/8 and 4×1 reconstructions of indium on Si(111). For the 7/8 × 7/8 reconstruction the In adatoms are generally thought to lie on either threefold hollow (H3) sites or on fourfold atop (T4) sites. Our ICISS polar-angle scans agree with computer simulations of the T4 model. Separations of the In and Si layers have also been determined from our experimental data, in agreement with predictions from total energy calculations. The 4×1 reconstruction is known to consist of double rows of adatoms running in 〈1̄10〉 directions, from scanning tunneling microscopy images. Assuming the top layer adatoms to be indium, we perform ICISS polar-angle scans to determine whether the adatom positions lie in H3 or T4 sites. Our results show general agreement with the simulations for the H3 sites in the 4×1 geometry.
The effect of surface roughness on reflection high-energy electron diffraction rocking curves and impact on reflection high-energy electron diffraction intensity oscillations
Authors: Fan W. C. , Ignatiev A.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) rocking curves have been studied for the Si(111)-((3)1/2×(3)1/2) R30°–Ag structure as a function of varying degrees of surface roughness as generated by Ar+ ion bombardment. Under increased surface roughness, most peaks in the rocking curves showed a characteristic change represented by splitting, shifting, and variation in intensity. This characteristic change in the rocking curves is identified as a result of surface step generation accompanied by modulation of the surface potential barrier. This surface roughness effect well explains the behavior of RHEED intensity oscillations during epitaxial growth and identifies the origin of phase differences of different beams.
New method for calculating the molecular flux from an inclined Knudsen cell
Authors: Fujiwara Akio
Published: July 2002

A new theoretical treatment of an inclined Knudsen cell in the molecular-beam epitaxy (MBE) system is presented. Clausing’s integral equation method is generalized to obtain numerically the angular distribution, transmission probability, and film thickness distribution for the inclined cell. This treatment, which greatly reduces the calculation time as compared with conventional methods, provides optimization of the MBE system design.
The absence of contamination of mercury from a stainless steel molecular beam epitaxy mercury source
Authors: Mohnkern L. M. , Harris K. A. , Yanka R. W. , Myers T. H. , Frame E. M. Skelly
Published: July 2002

The use of stainless steel in the construction of a molecular-beam epitaxy (MBE) Hg source has been the subject of concern because of the possibility that Hg could dissolve the stainless steel constituents which would contaminate the growing epilayer. Because of this concern, quartz has been touted to be the material of choice for constructing an MBE Hg source. However, quartz fabrication is difficult and costly, and the final product is susceptible to fracture. We show, by inductively coupled plasma emission spectroscopy and neutron activation measurements, that the detectable (<0.1 ppm) trace metal content of Hg contained in our heated, stainless steel Hg source is no different from the highest purity Hg commercially available. This significant result indicates that stainless steel is a suitable, noncontaminating material for the construction of an MBE Hg source.
Probe position controller for plasma parameter measurement in vacuum
Authors: Abraham R. L. , Hayes M. A.
Published: July 2002

A probe controller capable of determining both the axial and radial positions of a probe tip to better than 1 mm is described. This controller has an axial span of nearly 40 cm, and a radial span of better than 8 cm. The probe controller system incorporates the electrical feedthroughs for the probe bases, which accept a variety of probe tips. The carriage system is low in profile, so little compromise of experimental volume has resulted from its installation. Our vacuum base pressure, which is approximately 10−7 Torr, has not been affected by either installation or use of this system. Graphs displaying axial and radial plasma profiles taken with the controller are presented.
Nonresonant multiphoton ionization of rare gases
Authors: Kokubun Kiyohide , Ichimura Shingo , Hashizume Hiroko , Shimizu Hazime , Oowadano Yoshiro , Matsumoto Yuji , Endo Kazuhiro
Published: July 2002

For the purpose of applying the laser-ionization method to measuring gas pressure, the dependence of the ionization output signals of rare gases on the gas pressure and the laser intensity were studied using XeCl, KrF, and ArF excimer lasers. The proportional relation between the ionization signal and the gas pressure was experimentally verified to below 10−8 Torr. In the case of Kr gas, the dependence of the ionization signal on the laser intensity was in agreement with the theory of nonresonant multiphoton ionization, and saturation of ionization in the case of Xe was observed.
Analysis of time-of-flight spectra
Authors: Gibson E. M. , Foxon C. T. , Zhang J. , Batey J. H. , Joyce B. A.
Published: July 2002

A simplified method of data analysis for time of flight measurements of the velocity of molecular beams sources is described. This method does not require the complex data fitting previously used in such studies. The method is applied to the study of Pb molecular beams from a true Knudsen source and has been used to show that a VG Quadrupoles SXP300H mass spectrometer, when fitted with an open cross-beam ionizer, acts as an ideal density detector over a wide range of operating conditions.
Deposition by etching-enhanced reactive sputtering: A new high-rate deposition method for SiO2 and TiO2
Authors: Ross Randall C.
Published: July 2002

This paper introduces a new hybrid thin film deposition technique that combines reactive sputtering and plasma etching. Using this technique, increases in deposition rates of SiO2 by 30 times and TiO2 by 10 times have been obtained on conventional dc magnetron sputtering equipment. The technique is named deposition by etching-enhanced reactive sputtering, or DEERS. The background of DEERS’s conception and experimental results of Cl-based DEERS of SiO2 and TiO2 as well as other potential DEERS systems are described.
Etch characterization of a broad-beam electron cyclotron resonance ion source
Authors: Ghanbari E. , Nguyen T. , Bui S. , Ostan E.
Published: July 2002

We present some of the ion beam and etch characteristics of a broad-beam electron cyclotron resonance (ECR) ion source. The source offers two modes of operations suitable for uniform ion beam etching. The low energy mode, 25<E<200 eV, is characterized by 0.30–1 mA/cm2 ion density with the beam uniformity, within ±5%, spanning over 10 cm of the beam diameter. Argon beam etching of gold and aluminum targets give etch rates of 349–2183 Å/min and 277–834 Å/min for each material, respectively. A preliminary reactive ion beam etching of aluminum targets with Cl2 indicates an increase in the etching rates by factors of 1.5 to 2 over argon ion beam etching.
Characterization of Rh films on Ta(110)
Authors: Jiang L. Q. , Ruckman M. W. , Strongin Myron
Published: July 2002

The surface and electronic structure of Rh films on Ta(110) up to several monolayers thick on Ta(110) are characterized by photoemission, Auger emission, low-energy electron diffraction (LEED) and low-energy ion scattering (LEIS). From the variation of the Rh Auger peak-to-peak intensity as a function of evaporation time, Rh appears to grow in the Stranski–Krastanov mode at room temperature. However, the LEIS data show that the Rh adatoms begin to cluster on Ta(110) before growth of the monolayer is completed. Diffuse LEED scattering suggests that the Rh films are disordered. Photoemission shows that Rh chemisorption on Ta(110) generates two peaks located at −1.5 and −2.5 eV binding energy during the initial phase of thin-film growth (0<θ<0.5 ML). By 0.75 ML Rh coverage, these states merge into a broad structure centered near −2 eV binding energy. Photoemission peaks typical of a Rh(111) surface are seen at higher coverages (θ>3.7 ML). CO dissociates on the Rh/Ta(110) surface for Rh coverages<2.5 ML and the surface develops a site capable of molecular CO adsorption above 0.3-ML Rh coverage.
Preparation of well-ordered, oxygen-rich SnO2(110) surfaces via oxygen plasma treatment
Authors: Cavicchi R. , Tarlov M. , Semancik S.
Published: July 2002

The problems involved in preparing well-defined metal oxide surfaces are well known. We are investigating low power rf oxygen plasma treatment as a method for producing metal oxide surfaces of controlled stoichiometry and structure. The effects of exposing a 300 K oxygen deficient SnO2(110)−4×1 surface to an oxygen plasma (0.1 Torr) have been examined using low-energy electron diffraction (LEED), x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), ion scattering spectroscopy (ISS), and surface conductivity measurements. Results from the plasma-exposed surface have been compared to those obtained from a thermally oxidized (1 Torr O2, 700 K) SnO2(110) surface. LEED observations indicate that low energy ion bombardment processes associated with plasma exposure do not significantly damage (disorder) the surface. In addition, band gap states associated with oxygen vacancies are eliminated as shown by UPS. This is in accord with XPS data that show an increase in the surface O/Sn ratio. The elimination of oxygen vacancies, which act as donors in tin oxide, causes a drop in surface conductivity of two orders of magnitude and a band bending of approximately 0.5 eV compared to the sputter-annealed surface. The comparatively higher ISS O/Sn ratios as well as the larger band bending suggest that a more oxygen-rich tin oxide surface is obtained by room temperature plasma exposure than by high temperature oxidation at considerably higher O2 pressures.
Physical vapor deposition equipment evaluation and characterization using statistical methods
Authors: Dharmadhikari Vineet S. , Lynch R. O. , Brennan W. , Cronin W. , Rastogi R.
Published: July 2002

More stringent quality and performance demands are being imposed on the maturing semiconductor industry, and as a result, evaluation and characterization methods become important in selecting new process equipment. Statistical design of experiments (SDE) which can provide information not only on selection but also for successful installation of a tool are discussed. The data are taken from actual qualification runs made in a commercially available physical vapor deposition (PVD) system used for deposition of aluminum alloy. Manufacturability related factors such as process variance (run-to-run, wafer-to-wafer, within-wafer uniformity) and process capability indices (Cp and Cpk) are baselined with respect to film sheet resistance, deposition rate, and uniformity, and are used for further process optimization. We found this to be a very reliable and practical method for accomplishing a rapid process startup.
The effects of polymer film formation on photoresist (OFPR-800) during plasma etching in C2F6/CHF3/He
Authors: Thomas J. H. , White L. K. , Miszkowski N.
Published: July 2002

Experiments were performed to study the effects of fluorocarbon erosion of photoresist and the changes in photoresist surface chemistry as a function of the plasma conditions in a commercial etching system using C2H6–CHF3–He gas mixtures used in SiO2 etching. Fluorocarbon thin film formation is observed on the photoresist surface. The composition and thickness of the surface layers are determined using computations from x-ray photoemission data. The composition of the polymer layer is mostly constant within the parameter space studied. It becomes fluorine rich when the source gas is CHF3/He. The measured etch rate of the resist film is correlated to polymer film thickness of the fluorocarbon layer remaining on the surface of the resist in the parameter space studied [total gas flow, C2H6:CHF3 flow (0–40 sccm), variable He flow (40–100 sccm), variable power (350–500 W), and variable pressure (2–2.6 Torr)]. Fluorocarbon polymer deposition is correlated with a zero photoresist erosion rate. In the matrix studied, this occurs when the pressure is maximum, power is minimum, and the He flow is minimum or when the gas is a mixture of CHF3 and He.
Columnar microstructure and stress measurements in amorphous W0.75Si0.25 thin films
Authors: Thomas R. E. , Perepezko J. H. , Wiley J. D.
Published: July 2002

Columnar microstructure has been observed in direct-current sputter deposited amorphous metal thin films of W0.75Si0.25. Transmission electron microscopy was used to examine the films, both in cross section and plan view. Individual columns are 50–150 Å in diameter and the morphology is typical of a zone 1 structure. In contrast, films of the same composition deposited by magnetron sputtering did not exhibit a columnar microstructure. The dc sputtered films were also found to be in tensile stress when deposited on silicon substrates. Measured stresses ranged from 6.5×108 Pa for 4000 Å films with a linear increase to 8×108 Pa for 33 000 Å films. For films thinner than 4000 Å the stress in the films dropped off rapidly. The linear increase in stress seen was attributed to mutual attractive forces between adjacent columns.
Metal–insulator semiconductor properties of molecular-beam epitaxy grown HgCdTe heterostructures
Authors: Goodwin M. W. , Kinch M. A. , Koestner R. J.
Published: July 2002

By using a new device concept, the limitations of high dark and tunnel currents in metal–insulator semiconductor (MIS) infrared detectors with cutoff wavelengths greater than 10 μm may be reduced. The concept is an MIS device fabricated on an N-isotype heterostructure which consists of a thin (approximately 1 μm) wide-band gap HgCdTe layer on top of a thicker (approximately 5 μm) narrow-band gap HgCdTe layer. The wide-band gap layer increases the tunnel breakdown field and reduces the dark currents of the narrow-band gap detector layer. We report here measurements on this type of device structure which has been fabricated from molecular-beam epitaxy (MBE) grown HgCdTe. On one MIS heterostructure with cutoff wavelengths ranging from 9.2 to 11.5 μm a decrease in dark currents by a factor of 2 compared with MIS dark currents in Texas Instrument’s (TI’s) standard solid-state-recrystallized (SSR) HgCdTe is found. In addition the breakdown field for the heterostructure is increased from approximately 0.6 V/μm found in SSR HgCdTe of comparable band gap to 1.4 V/μm. The MIS heterostructure can also be operated as a two-color detector. Along with these results, analysis and interpretation of the data and modeling of the MIS heterostructure design are presented.
Improved flux control from the Sentinel III electron impact emission spectroscopy system
Authors: Kubiak R. A. , Newstead S. M. , Powell A. R. , Parker E. H. C. , Whall T. E. , Naylor T. , Bowen K.
Published: July 2002

Measures taken to improve the sensitivity and stability of the Sentinel III electron impact emission spectroscopy evaporation controller are described, allowing calibration factors of up to 50 times to be used. Si and Ge deposition rates from 0.3 nm s−1 down to 0.004 and 0.001 nm s−1, respectively, have been achieved, with stable control over growth periods of many hours. Use of these low deposition rates allows access to low SiGe alloy compositions and eliminates the occurrence of alloy fluctuations due to flux noise and finite substrate rotation speeds, by allowing monolayer deposition times of several seconds to be used. A marked nonlinearity in response of the Sentinel sensor to Si flux is also described.
Optimizing the conductance of right-angle valves
Authors: Hablanian M. H. , Nuzzi F. J. , Pflanz T. L.
Published: July 2002

The design of a valve to some degree is dictated by the size of the required connections. But the internal geometry, which establishes the conductance of the valve, should be based on the three-dimensional examination of overall conductance. Following published Monte Carlo calculations, the internal designs of small right-angle valves have been optimized by choosing the right combinations of the seat diameter, internal body diameter, and the length of the stroke. Using this approach, in the case of electromechanically operated valves, the expensive bellows (for compensating the force of the sealing spring) can be entirely eliminated. Comparative experimental verification for the optimal design are presented.
Nonevaporable getter investigation at the National Synchrotron Light Source
Authors: Halama Henry J. , Guo Yaohua
Published: July 2002

We report H2, CO, and CO2 pumping speed measurements on a linear pump using NEG strip St 707 (Saes Getters Inc.) as a function of both adsorbed gases and number of activations. To simulate the conditions of an operating storage ring a gas mixture of 50% H2, 35% CO, and 15% CO2 is used in all measurements. Initial measured pumping speeds of >450 ℓ m−1 s−1 decrease to 200 and 100 ℓ m−1 s−1 for H2 and CO, respectively, after 70 air exposures. A further drop to 50 ℓ m−1 s−1 for CO occurs at CO loading of 1×10−2 Torr ℓ m−1. CO2 and CO pumping speeds are about the same. The photon stimulated desorption for both baked and activated strips is an order of magnitude lower than that for stainless steel.
A comparison of one-dimensional and two-dimensional smoothing algorithms for Auger depth profiling
Authors: Gaarenstroom Stephen W.
Published: July 2002

The technique of Auger depth profiling is widely used for the chemical analysis of thin film materials. Depth profile data are typically smoothed when they are displayed. This work compares selected smoothing algorithms [one-dimensional (1D) Savitzky–Golay polynomial least squares smooth, two-dimensional (2D) Savitzky–Golay smooth, and factor analysis]. The smoothing routines were judged by comparing the resultant spectral energy resolutions, depth resolutions, and signal-to-noise of spectra and profiles for an anodic oxide film on tantalum metal. The 2D routines were superior to the more conventional 1D smooths for all the criteria considered. The 2D routines also provide the analyst with additional flexibility to trade-off performance in resolution, signal-to-noise, and data acquisition time. The factor analysis procedure was more complex, but gave depth profiling results as good as the best 2D smoothing results.
Defect and impurity effects on the initial growth of Ag on Si(111)
Authors: Zuo J.-K. , Wendelken J. F.
Published: July 2002

Step and impurity effects on the initial growth of a thin film have been demonstrated in the ( 7/8 × 7/8 )R30° (or simply 7/8 ) domain growth of Ag on Si(111) using high angular resolution low-energy electron diffraction. Anisotropy in the 7/8 domain shape and growth during deposition are found on the stepped Si(111) with the preferential growth along the step edge direction. The 7/8 superlattice grows with coverage principally by domain coalescence at the temperature T∼450 °C and is self-similar at different coverages (scaling) as observed on a flat Si(111). The size distribution is shown to follow a Gamma distribution by a simple model calculation. A dramatic change in the growth mechanism is observed when oxygen impurities [≤0.02 monolayer] appear. The 7/8 domains in the presence of impurities grow with coverage more randomly and isotropically in contrast with the step edge effects and coalescence is inhibited. As a result, the 7/8 superlattice stays in a microdomain morphology without long range order.
Attempt to grow diamond phase carbon films from an organic solution
Authors: Namba Yoshikatsu
Published: July 2002

Diamond phase carbon films have been grown on silicon substrates at temperatures of less than 50 °C by using an organic solution. Substrates were negatively biased with sufficient dc potential to simulate ionized deposition conditions used in physical vapor deposition. The surface morphology, crystal structure, and some physical properties of the films were examined by scanning electron microscopy, transmission electron microscopy, x-ray photoemission spectroscopy. It was confirmed that the film is composed of small grains of diamond phase or diamondlike structure.
New concepts in turbomolecular pump design
Authors: Hablanian M. H.
Published: July 2002

Modern turbopumps were introduced in 1958 and are now widely used in industrial and laboratory applications. At the present time, three types of turbine-type pumps are in existence: axial flow turbomolecular pumps, turbodrag pumps, and hybrid pumps combining the two types on the same axis. Recent emphasis on oil-free vacuum pumping systems has revived the interest in pumps which can tolerate higher discharge pressures. When exit pressures reach 10 mbar (or higher), the well-established molecular flow analysis cannot be used. It appears that the existing turbomolecular and turbodrag pumps, which take their basic design from historical models, are not optimized in regard to their speed and throughput performance. Following a simple concept of bulk velocity variation, which can be used for assessing the density continuum (despite the existence of molecular flow through parts of the pump) an optimized pumping speed and compression staging arrangement was developed which demonstrates a practical improvement in compression ratios of as high as 40 times for light gases (helium and hydrogen), without increasing the size and power, compared to a conventional pump. Turbine-type pumps, unlike oil-vapor jet and high-vacuum cryopumps, permit practical engineering solutions for expanding the pressure regime to almost arbitrary high pressure. This makes it possible to use oil-free backing pumps at intermediate pressures of 10–100 mbar using relatively small changes in design.
Radio-frequency magnetron sputtering of pure and mixed targets of Li4SiO4, Li3PO4, and Li2O
Authors: Dudney N. J. , Bates J. B. , Robertson J. D.
Published: July 2002

Pure and mixed targets of Li4SiO4, Li3PO4, and Li2O were sputtered in both argon and argon/oxygen process gases using a 1-in. diam radio-frequency planar magnetron source. The appearance of the sputter target, the self-bias voltage of the target, the film deposition rate, and the optical emission of the plasma were monitored during film growth. The films were analyzed by energy dispersive x-ray spectrometry, proton induced gamma emission, and atomic spectrometry. Films grown from targets of Li3PO4 were found to be near stoichiometric. In contrast, films grown from targets of, or containing, Li4SiO4 were lithium deficient due to the decomposition and segregation of Li2O away from the sputtered area on the surface of the target. A similar redistribution of material was observed for Li2O targets as well. Reproducible and homogeneous film compositions with stoichiometric lithium concentrations can best be achieved by codeposition with independently controlled sputter sources onto a rotating substrate.
Work-function oscillations during Cu film growth on an oxygen precovered Ru(0001) surface: A basically old technique as a powerful film growth monitor
Authors: Schmidt M. , Wolter H. , Nohlen M. , Wandelt K.
Published: July 2002

In the present work it is demonstrated how dynamical measurements of the work function may be used to investigate the growth of thin epitaxial metal films. A special setup of a basically old technique—a redesign of a Kelvin probe—is applied to monitor work function changes not only during gas adsorption but also during metal deposition with high precision. Such dynamical work function change measurements clearly demonstrate the layer-wise growth of thin Cu films on an oxygen precovered Ru(0001) surface. This is revealed by the observation of multiple ΔΦ-oscillations with a period corresponding to the deposition of a single Cu(111) layer. Furthermore the role of the oxygen as a surfactant for layer-by-layer growth is concluded from the fact that under similar conditions such oscillations have never been observed during Cu evaporation on the clean Ru(0001).
Role of Ga2O in the removal of GaAs surface oxides induced by atomic hydrogen
Authors: Ide Yuichi , Yamada Masamichi
Published: July 2002

The role of Ga2O in the removal of GaAs surface oxides induced by atomic hydrogen (H⋅) has been studied using temperature-programed desorption (TPD), x-ray photoelectron spectroscopy, and low-energy electron diffraction (LEED). GaAs(001) substrates with ‘‘Ga2O3-like’’ surface oxides formed in vacuo, as well as those ‘‘as-loaded’’ from air, were treated by thermally generated H⋅ at substrate temperatures ranging from 210 to 410 °C. Formation of Ga2O-like oxides was indicated by TPD performed after H⋅ treatment. Above the onset temperature of Ga2O desorption, which was 350–400 °C, oxide removal was rapid. Below the onset temperature, oxide removal was slow and incomplete, suggesting that Ga2O-like oxides act as a mask against H⋅ irradiation. When treated by H⋅ at 210 °C, the amount of Ga2O-like oxides formed did not increase with the treatment time. Moreover, prolonged H⋅ treatment at 210 °C resulted in a Ga-rich LEED pattern. We attribute this to a further reaction of H⋅ with Ga2O, resulting in Ga and water. In practice, H⋅ treatment at temperatures above the Ga2O desorption onset is desirable for rapid and complete oxide removal, which results in a stoichiometric surface.
Photoemission spectroscopy study of thin Cr overlayers on NH3/GaAs(100)
Authors: Park Ken T. , Cao Jianming , Gao Y. , Ruckman M. W.
Published: July 2002

The interface formation of Cr/NH3/GaAs(100) and its temperature dependence using synchrotron radiation photoemission and resonance photoemission spectroscopies have been investigated. We observed that at T=90 K the initial deposition of Cr stimulated nitridation of the GaAs substrate and subsequent interface reaction was characterized by Cr-induced substrate disruption. Annealing of the thus formed interface to room temperature and above caused further Cr–GaAs reaction. The metallicity of the Cr overlayer was examined using constant initial-state spectroscopy (CIS) of Cr 3d with Ei=1.7 eV below the Fermi level. The CIS spectra showed a maximum at the photon energy hν=50.0 eV followed by a second broad maximum centered at hν=56–58 eV depending on the stage of the interface formation. As the nominal Cr coverage increases from 1 to 10 Å, the valence band photoemission spectra show a shift of the Cr 3d band toward the Fermi level. At the same time, the second maximum in CIS gradually dominates over the first, suggesting the evolution of the Cr overlayer to a more metallic state. The sensitivity of the second maximum in its peak position and intensity to the density of states near the Fermi level indicates that this maximum likely results from many body electron interactions. The results show that CIS can provide valuable information about the transition of a thin overlayer to a metallic state.
Morphology of precursors and CuIn1−xGaxSe2 thin films prepared by a two-stage selenization process
Authors: Dhere Neelkanth G. , Kuttath Shanker , Moutinho Helio R.
Published: July 2002

The morphology of sequentially sputtered metallic precursors and CuIn1−xGaxSe2 thin films prepared using a novel two-stage selenization process was found to change from initially very smooth layers with a root-mean-square (rms) surface roughness of <10 Å to coalescing grains with a fine (∼200 Å) subgrain structure, three-dimensional ∼9000 Å size islands, and finally to compact, well-faceted, large ∼1 μm grain-size CuIn1−xGaxSe2 thin films with a rms roughness of 950–1500 Å. In situ homogenization of Cu-rich precursors prior to the first selenization and a maximum selenization temperature of 550–560 °C that provided beneficial fluxing action of copper selenide improved the morphology of completed CuIn1−xGaxSe2 thin films and the photovoltaic conversion efficiency of the solar cells.
H2O adsorption kinetics on Si(111)7×7 and Si(111)7×7 modified by laser annealing
Authors: Wise M. L. , Okada L. A. , Sneh O. , George S. M.
Published: July 2002

The adsorption kinetics of H2O on Si(111)7×7 and Si(111)7×7 modified by laser annealing were studied using laser-induced thermal desorption and temperature-programmed desorption techniques at temperatures between 180 and 800 K. The laser-annealed Si(111)7×7 surface displayed an enhanced initial reactive sticking coefficient for H2O compared with the unmodified Si(111)7×7 surface. At 180 K, the initial reactive sticking coefficient was S0=6.9×10−1 on laser-annealed Si(111)7×7 compared with S0=1.9×10−2 on unmodified Si(111)7×7. This larger initial sticking coefficient is attributed to the creation of a more reactive surface structure formed by the laser annealing process. At higher oxygen coverages, the reactivity of the laser-annealed surface changed and displayed much slower H2O adsorption rates that were similar to the kinetics on Si(111)7×7. The decreasing initial reactive sticking coefficient versus increasing surface temperature suggested a precursor-mediated adsorption mechanism on both the Si(111)7×7 and laser-annealed Si(111)7×7 surfaces. After long H2O exposures, the oxygen coverage saturated at θO≊0.35 monolayers on Si(111)7×7 for temperatures between 300 and 700 K. At higher surface temperatures, the saturation coverage increased prior to SiO desorption at temperatures above 900 K. This increase was attributed to the creation of additional dangling bond adsorption sites following H2 desorption at temperatures above 700 K.
The correlation between selective oxide etching and thermodynamic prediction
Authors: McNevin S. C.
Published: July 2002

This article will report the qualitative connection between chemical predictions based on thermodynamics and the selective oxide etching in a hot wall commercial high-density plasma system. The relationship between the experimentally observed protective carbon-based deposit on nonoxide surfaces such as Si and the theoretically predicted selective deposition of carbon will be explored. While carbon is deposited on both Si and SiO2, the oxygen in the SiO2 leads to the ion-enhanced removal of this deposited carbon so that plasma etching of the oxide can continue. It will be shown that CO gas and the chamber/wafer temperature play a major role in this carbon deposition. The chemical role of H in increasing this deposit will also be examined. The model predicts that the carbon deposition increases exponentially with chamber temperature, and that this deposition occurs only on the nonoxide underlying layer at the bottom of the contact. This is consistent with the experimental observation that increasing chamber temperature increases the protective deposition on the underlying Si, but does not deposit on the SiO2 side walls and change their angle. This is not to suggest that such a simple thermodynamic model can quantitatively explain all of the observed effects, but it clearly is very effective in understanding the qualitative dependence on such ‘‘chemistry’’ process parameters as temperature, gas flow, and chemical composition.
Plasma-based surface engineering processes for wear and corrosion protection
Authors: Matthews A. , Leyland A. , Dorn B. , Stevenson P. R. , Bin-Sudin M. , Rebholz C. , Voevodin A. , Schneider J.
Published: July 2002

Vacuum plasma-based coating and treatment methods have considerable potential for reducing wear and corrosion. However, they have not been widely applied to engineering components other than tools such as those used in metal cutting. This is due to several factors, not least of which are cost and an unsuitability for cheaper substrate materials. Here we discuss six plasma-based processing routes that can widen the applicability of these processes and ensure greater market penetration. These methods are: (i) duplex plasma nitriding plus physical vapor deposition (PVD) coating, (ii) low temperature plasma diffusion treatment, (iii) postcoat plasma nitriding, (iv) layered diamondlike carbon/metal carbide PVD/chemical vapor deposition coating, (v) thick metal/metal nitride PVD coating, and (vi) duplex electroless nickel plus PVD coating. The characteristics of these methods are discussed, especially with regard to their beneficial influence on wear or corrosion.
Growth of ultrathin crystalline Al2O3 films on Ru(0001) and Re(0001) surfaces
Authors: Wu Yutong , Garfunkel Eric , Madey Theodore E.
Published: July 2002

Ultrathin aluminum oxide films (≤20 Å thick) on Ru(0001) and Re(0001) surfaces have been grown by depositing aluminum in an oxygen ambient (0.5–1×10−5 Torr), and have been characterized by x-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), low energy electron diffraction (LEED), and high resolution electron energy loss spectroscopy. No LEED pattern is observed from the films of thickness ≳5 Å deposited on either surface at 300 K. Long range order of the films is achieved by depositing aluminum in ambient oxygen at elevated substrate temperatures (≥970 K). The LEIS results indicate three-dimensional growth for the films on these substrates at 1170 K. Films on Re(0001) show sharper LEED patterns than those on Ru(0001) substrates. Analysis of the XPS Al 2s/O 1s area ratios indicate that the films are stoichiometric.
Schottky barrier at the Au/Gap (110) interface
Authors: Fanfoni M. , Goletti C. , Chiaradia P. , Ng W. , Cerrina F. , Hwu Y. , Terrasi A. , Margaritondo G.
Published: July 2002

The Schottky-barrier formation of the Au/GaP (110) interface has been investigated by photoemission, in the presence of large surface photovoltage effects induced by the intense photon beam of a synchrotron-radiation source. The surface photovoltage has been measured with a Kelvin probe. The largest surface photovoltage shift observed in the photoemission spectra was almost 1 eV. The Schottky barrier appears to be fully established at about 8 Å, while the surface photovoltage does not disappear until about 16 Å. The Schottky-barrier height is 1.35±0.1 eV. The Kelvin-probe results demonstrate directly that the photoemission data must be corrected for the surface photovoltage during the formation of the barrier but are insensitive to it once full coverage is obtained.