bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement and modeling of moisture adsorption properties of 316 stainless steel tubing samples
Authors: Siefering Kevin L. , Whitlock Walter H.
Published: July 2002

A technique has been developed using an atmospheric pressure ionization mass spectrometer to measure the submonolayer equilibrium adsorption properties of moisture on tubing surfaces. This technique has been used to generate isobar data for moisture on 316 stainless steel surfaces with various commercially available surface treatments. Both a dissociated absorption model based on a Temkin energy distribution and a semiempirical adsorption model have been fit to the data. Though differences in the isobar data were clear, moisture absorption did not vary strongly with tube surface treatment. The implications of these results on tubing dry-down dynamics were confirmed by running controlled dry-down tests from an initial level of 200 ppb using an inlet gas at 0.2 ppb. The ranking of dry-down times (fastest to slowest) was the same as predicted by the isobar data. The difference between the dry-down time of the fastest and slowest responding tubes was approximately a factor of 4.
Observation of the reaction of gas-phase atomic hydrogen with Ru(001)-p(1×2)-O at 100 K
Authors: Xie Jun , Mitchell William J. , Lyons Kevin J. , Wang Youqi , Weinberg W. Henry
Published: July 2002

The interaction of gas-phase atomic hydrogen with chemisorbed oxygen on Ru(001) has been investigated with high-resolution electron energy loss spectroscopy. As gas-phase hydrogen atoms impinge on the p(1×2) oxygen overlayer at surface temperatures below 100 K, water is formed, a reaction which has not been observed in previous studies of coadsorbed hydrogen and oxygen on Ru(001). The water molecules which are produced exist as adsorbed monomers initially but form clusters at greater extents of reaction. Since this reaction occurs at low surface temperatures, an Eley–Rideal-like mechanism is suggested in which hydrogen atoms from the gas phase react with adsorbed oxygen before being thermally accommodated to the surface. More than 50% of the saturation coverage of oxygen can be removed by means of gas-phase atomic hydrogen. Complete removal of the oxygen overlayer is inhibited by the water that is produced in the reaction.
Adsorbate-induced surface stress
Authors: Ibach H.
Published: July 2002

The physical origin of surface stress is discussed. Based on these considerations a general functional form of the dependence of the adsorbate-induced surface stress on the coverage is proposed. Experimental data on the adsorption of oxygen, sulfur, and carbon on Ni(100) are in agreement with this proposition. It is shown further that the p4g reconstruction of the Ni(100) surface upon carbon deposition is caused by the compressive stress induced by the carbon atoms. Recent results on CO on Ni(100) are, however, at variance with the simple reasoning concerning all aspects of the induced surface stress—the sign, the magnitude, as well as the coverage dependence.
Comparison of boranol and silanol reactivities in boron-doped SiO2 chemical vapor deposition from trimethyl borate and tetraethyl orthosilicate
Authors: Bartram M. E. , Moffat H. K.
Published: July 2002

For the first time, the relative rates of consumption of surface boranols and silanols reacting with tetraethyl orthosilicate [TEOS, Si(OCH2CH3)4] have been measured. This comparison has direct bearing on understanding the growth of doped SiO2 films from TEOS and trimethyl borate [TMB, B(OCH3)3] sources since surface boranols and silanols are expected to be present during the thermal chemical vapor deposition process. The measurements were accomplished by first derivatizing a porous silica substrate with boranols and silanols via hydrolysis of the products from an initial trimethyl borate (TMB) chemisorption step. TEOS exposures in the mTorr pressure regime were then carried out in a cold-wall reactor. Reaction products on the surface were identified with Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy in analysis chambers adjoining the reactor. Although TEOS does not react with SiOH at 300 K, it does react with BOH at this temperature. Using the deuterated species (SiOD and BOD) to measure the relative rates of hydroxyl consumption without interference from concurrent hydroxyl formation, the reaction rate constant for boranols with TEOS at 1000 K was determined to be twice that of silanols. At 1000 K, subsequent decomposition of the TEOS chemisorption products regenerates both BOH and SiOH.
Formation of secondary phases in evaporated CuInS2 thin films: A surface analytical study
Authors: Scheer R. , Lewerenz H.-J.
Published: July 2002

The surface composition of coevaporated Cu-In-S films for photovoltaic applications has been investigated by x-ray and ultraviolet photoelectron spectroscopy. A comparison of the front and back surface, i.e., the interface between the Cu–In–S film and the Mo back contact, is made for films with different stoichiometries. We find that In-rich films are covered at both surfaces by an In-rich second phase which has the cation ratio of CuIn3S5. The front surface of Cu-rich films shows a segregation of CuS that is not found at the back surface. The formation of binary and ternary second phases in nonstoichiometric CuInS2 films and their implications on the growth mechanism are discussed.
Transition metal induced ring-cluster structures on Si(111)
Authors: Parikh S. A. , Lee M. Y. , Bennett P. A.
Published: July 2002

We characterize a ‘‘ring-cluster’’ (RC) structure produced by high temperature annealing of transition metals on Si(111), studied by scanning tunneling microscope and low-energy electron microscopy. This structure consists of a single metal atom on a substitutional site in the top layer of Si(111) plus an overlying ring of six Si adatoms with an unusual bridge bonded topology. We find that the same structure occurs for all near noble metals specifically Fe, Co, Ni, Pd, Pt and Ir. It does not occur for refractory metals (Ti, W) or for noble metals (Cu, Ag). Clear phase separation of clean Si(111)-7×7 and large triangular domains containing a lattice gas of RCs occurs only for quenching from above the 7×7 to 1×1 phase transition at T=840 °C. The density of RCs within a domain increases with average metal coverage. The domain orientation is defined by its boundary with the faulted half of 7×7 unit cells. The large scale morphology for RC induced structures and its dependence on quench rate suggests a precipitation reaction. Dissolution rate of nickel RCs into bulk Si was found to be t=20 s at 800 °C assuming exponential decay.
Growth of layered semiconductors by molecular-beam epitaxy: Formation and characterization of GaSe, MoSe2, and phthalocyanine ultrathin films on sulfur-passivated GaP(111)
Authors: Hammond C. , Back A. , Lawrence M. , Nebesny K. , Lee P. , Schlaf R. , Armstrong N. R.
Published: July 2002

Studies of the sulfur passivation of GaP(111) surfaces with solution treatments, and the subsequent molecular-beam epitaxy growth and characterization of ultrathin films of layered semiconductors on those surfaces are presented in this article. Simple solution passivation procedures allow formation of a S–GaP(111) semiconductor surface which will support the growth of highly ordered layers of GaSe (Eband gap=2.05 eV). These thin GaSe layers then permit the further growth of ordered layers of a semiconductor like MoSe2 (Eband gap=1.0 eV) or an organic dye such as a phthalocyanine. Reflection high energy electron diffraction and angle-resolved x-ray photoelectron spectroscopy have been used to determine the structure and composition of the surface layers formed at each stage of the deposition process. Absorption spectra are used to characterize the band edge and A1,2 exciton energies of the MoSe2/GaSe S–GaP(111) thin films, and the position and shape of the phthalocyanine Q band.
Si1−xGex/Si multiple quantum wells on Si(100) and Si(110) for infrared absorption
Authors: Kreifels T. L. , Hengehold R. L. , Yeo Y. K. , Thompson P. E. , Simons D. S.
Published: July 2002

Optical emission and absorption properties of Si1−xGex/Si superlattices grown on (100) and (110) Si substrates were investigated to determine the optimal growth conditions for these structures to be used as infrared detectors. Fully strained Si1−xGex/Si superlattices were grown by molecular beam epitaxy (MBE) and examined using low-temperature photoluminescence to identify no-phonon and phonon-replica interband transitions across the alloy band gap. Phonon-resolved emission was most intense for undoped quantum wells grown at 710 °C for both silicon orientations. Room-temperature absorption measurements were conducted on (100) and (110) Si1−xGex/Si superlattices using Fourier transform spectroscopy while varying incident electric field polarization. Strong intersubband absorption was observed at 7.8 μm from a sample composed of 15 quantum wells of 40 Å Si0.8Ge0.2 separated by 300 Å of Si grown on (100) Si by MBE at 550 °C. Valence band wells were doped with a boron concentration of 5×1019 cm−3. No intersubband transitions were observed on similar (110) Si1−xGex/Si superlattices ranging in boron dopant from 1×1019 to 8×1019 cm−3, nor from any structure grown at 710 °C. This peak was most likely masked by free-carrier absorption which dominated the spectrum.
Large-area pulsed laser deposition: Techniques and applications
Authors: Greer J. A. , Tabat M. D.
Published: July 2002

Pulsed laser deposition (PLD) has quickly emerged as a unique tool with which to grow high quality films of complex chemical compounds. It is estimated that at present the number of different materials which have been deposited by PLD now exceeds two hundred. Scientists have used this process primarily as a laboratory tool to deposit films of various compounds that are typically difficult to synthesize by other techniques, and then quickly evaluate the relevant material properties. Deposition techniques such as ion-beam, rf, or dc magnetron sputtering, electron-beam evaporation, molecular beam epitaxy, chemical vapor deposition, and metal organic chemical vapor deposition, have all achieved wide-spread acceptance as processes with which to grow various types of electronic and optical films. In order for PLD to emerge as a real production process, it must be demonstrated that PLD is capable of depositing material over useful substrate sizes with acceptable uniformity. PLD must also compete with more established growth techniques or provide film properties which are otherwise unobtainable with these alternatives. Furthermore, as with any commercial process, PLD will become viable only if it is cost effective. Due to its unique capabilities, it is expected that PLD will emerge as a production tool for several applications in the near future. However, such applications are expected to be relatively low volume with high value added to the end product by the laser-deposited film.
The growth and characterization of layered, binary thin-film oxides: MgO–NiO and CaO–NiO
Authors: Xu C. , Oh W. S. , Guo Q. , Goodman D. W.
Published: July 2002

Layered, binary thin-film oxides of NiO, MgO and CaO have been prepared and characterized using low energy electron diffraction, Auger electron spectroscopy, energy loss spectroscopy, ion scattering spectroscopy, and temperature programmed desorption using probe molecules. Epitaxial growth was observed for the NiO–MgO and CaO–NiO systems; however, superior wetting was found for NiO–MgO relative to CaO–NiO. The thermal stabilities of the supported monolayer oxide vary significantly for the four systems studied, i.e. NiO/MgO, NiO/CaO, MgO/NiO and CaO/NiO, with NiO/CaO having the lowest thermal stability and CaO/NiO, the highest.
Photoluminescence measurements in the phase transition region for CdS thin films
Authors: Ariza-Calderon H. , Lozada-Morales R. , Zelaya-Angel O. , Mendoza-Alvarez J. G. , Baños L.
Published: July 2002

CdS polycrystalline thin films were grown by the chemical bath deposition technique at 80 °C onto glass substrates. The films grow in the cubic crystalline structure as determined by x-ray diffraction analysis. After thermal annealing in S2 and Ar atmospheres, the CdS changes from the metastable zinc blende phase to a stable wurtzite one. The cubic-to-hexagonal transition temperature has been determined to be 370 °C, as seen by the photoluminescence spectra and the x-ray diffraction patterns of the different samples. These spectra show the well-known green emission band of the CdS centered at 2.4 eV for the as-grown sample, which shifts to 2.25 eV for the sample annealed at 365 °C just before the phase transition takes place. For the sample annealed at 374 °C, an abrupt blueshift of the green band occurs going back to an energy value of 2.4 eV, when the crystalline phase transition occurs.
Effects of Y or Gd addition on the structures and resistivities of Al thin films
Authors: Takayama Shinji , Tsutsui Naganori
Published: July 2002

The addition of Y or Gd to Al thin films markedly decreases the grain size of the Al matrix and largely suppresses growth of hillocks at high temperatures (350–450 °C) associated with a large number of segregated metallic compounds, mostly at grain boundaries. The resistivities of the films after annealing at those high temperatures are less than 50 nΩ m. These tendencies also hold true for other Al rare-earth alloy systems. The breakdown voltage of anodically oxidized films of Al–Y and Al–Gd alloys is higher than that of pure Al thin films.
Model for ion-induced nucleation based on properties of small ionic clusters
Authors: Girshick S. L. , Rao N. P. , Kelkar M.
Published: July 2002

A method is presented for calculating ion-induced nucleation rates. Whereas classical ion-induced nucleation theory makes the approximation that small ionic clusters are charged droplets whose properties equal their values for the bulk liquid, the method presented gives a nucleation rate in the form of a summation over discrete cluster properties. The summation converges rapidly around the critical cluster size, which is often as small as a few atoms. This approach allows the direct utilization of experimental and/or computational data for cluster properties. Sample calculations are presented for nucleation of silicon particles via condensation of neutral silicon vapor onto silicon anions for conditions representative of microelectronics processing plasmas. As the temperature increases the predicted nucleation rates show a transition from the collision-limited regime to the condensation–evaporation regime, where nucleation rates drop sharply with temperature. The value of the temperature where this occurs depends on the condensible vapor concentration.
Integrated processing of silicon oxynitride films by combined plasma and rapid-thermal processing
Authors: Hattangady S. V. , Niimi H. , Lucovsky G.
Published: July 2002

Silicon oxynitride (OXN) gate dielectric thin films have been prepared in a cluster tool using a low thermal-budget process combining plasma and rapid-thermal step. This N2-based process has (i) increased process latitude for the formation of N-rich alloys, and (ii) resulted in lower bonded-H concentrations, in comparison to NH3-based processes. On-line Auger electron spectroscopy and off-line infrared spectroscopy have been used to characterize chemical bonding, showing that the deposited films are pseudobinary alloys, (SiO2)x(Si3N4)1−x. The processing steps are (i) a 300 °C plasma-assisted oxidation, (ii) a 300 °C plasma-assisted chemical vapor deposition of oxynitride films, and (iii) a 30 s, 900 °C postdeposition rapid-thermal anneal. Electrical characterization of O–OXN–O structures in metal–oxide–semiconductor capacitors was performed using capacitance–voltage techniques to evaluate the effect of alloy composition on midgap interface state density, Dit, and flat-band voltage, Vfb.
Chemical dry etching of silicon nitride and silicon dioxide using CF4/O2/N2 gas mixtures
Authors: Kastenmeier B. E. E. , Matsuo P. J. , Beulens J. J. , Oehrlein G. S.
Published: July 2002

The chemical dry etching of silicon nitride (Si3N4)and silicon nitride (SiO2) in a downstream plasma reactor using CF4, O2, and N2 has been investigated. A comparison of the Si3N4 and SiO2 etch rates with that of polycrystalline silicon shows that the etch rates of Si3N4 and SiO2 are not limited by the amount of fluorine arriving on the surface only. Adding N2 in small amounts to a CF4/O2 microwave discharge increases the Si3N4 etch rate by a factor of 7, but leaves the SiO2 etch rate unchanged. This enables etch rate ratios of Si3N4 over SiO2 of 10 and greater. The Si3N4 etch rate was investigated with respect to dependence of tube length, tube geometry, and lining materials. Argon actinometry has shown that the production of F atoms in the plasma is not influenced by the addition of N2 to the discharge. Mass spectrometry shows a strong correlation between the Si3N4 etch rate and the NO concentration. X-ray photoelectron spectra of the silicon nitride samples obtained immediately after the etching process show that F atoms are the dominant foreign species in the reaction layer, and that N2 addition to the feed gas enhances the O atom incorporation. Based on these data, we propose a mechanism for the etch rate enhancement of N2 addition to a CF4/O2 discharge.
Determination of chemistry and microstructure in SiOx (0.1<x<0.8) films by x-ray photoelectron spectroscopy
Authors: Shallenberger Jeffrey R.
Published: July 2002

The stoichiometry of a series of low pressure chemical vapor deposition deposited SiOx films was determined using x-ray photoelectron spectroscopy (XPS) by two different methods. The first, more traditional, method involved applying relative sensitivity factors to the integrated O 1s and Si 2p peaks, taking into consideration differences in photoemission probabilities of oxidized and elemental silicon. In the second method the Si 2p spectra were curve fit into five peaks corresponding to Si0+SiH (99.4 eV), Si1+ (100.3 eV), Si2+ (101.2 eV), Si3+ (102.0 eV), and Si4+ (103.0 eV). The five valence states of silicon corresponding to tetrahedrally coordinated silicon bonded to 0, 1, 2, 3, and 4 oxygen atoms. The relative areas of the peaks were combined with the known oxygen coordination numbers to yield stoichiometries. Rutherford backscattering and hydrogen forward scattering were done to verify the XPS quantification and to measure the hydrogen concentration of the films, respectively. The fraction of elemental silicon present as a function of oxygen concentration was compared with the fraction predicted by a random bonding model of silicon and oxygen atoms. The experimental fraction of Si0+SiH measured by XPS was greater than the fraction predicted by the random bonding model consistent with distinct regions (or possibly crystallites) of elemental silicon in the oxide matrix. Also, it was established that 3 kV argon sputtering does not preferentially sputter oxygen from either SiO2 or SiOx films contrary to previous reports.
X-ray studies on (110) fiber texture in FeTaN films using Ti underlayers
Authors: Klemmer T. J. , Inturi V. R. , Barnard J. A.
Published: July 2002

The (110) fiber texture observed in FeTaN sputtered films is characterized using several x-ray diffraction techniques including the high angle and glancing angle geometries, rocking curves, and pole figure tilt scans. These techniques are compared with respect to their geometries and the textural information that they yield. The magnetically soft FeTaN films have potential for use in inductive write heads and their properties are known to depend strongly on the preferred crystallographic orientation. It is shown that the use of a strongly oriented (0002) Ti underlayer enhances the strength of the (110) fiber in the FeTaN, decreases its skew, and decreases random orientations with respect to films that do not have an underlayer.
Three-dimensional deposition of TiN film using low frequency (50 Hz) plasma chemical vapor deposition
Authors: Shimozuma M. , Date H. , Iwasaki T. , Tagashira H. , Yoshino M. , Yoshida K.
Published: July 2002

Titanium nitride (TiN) films have been deposited on three-dimensional substrates by low frequency (50 Hz) plasma chemical vapor deposition method using a TiCl4+N2+H2 mixture at a substrate temperature of 550 °C with a substrate bias circuit using two diodes. The maximum value of the deposition rate was 1200 nm/h at a substrate bias voltage VB of −150 V and the ratio of flow rate k(N2/TiCl4)=2. The maximum value of Vickers hardness of deposited TiN films using Micro–Vickers hardness tester was about 2400 Hv at k=2 and VB=−150 V bias voltage. There were practically no differences between the deposition rates and Vickers hardness on vertical and horizontal substrate surfaces against the surface of electrodes. Resistivity of the films was about 80 μΩ cm at VB from 40 to −150 V with k=2. However, the hardness of deposited film with no substrate bias was about 1000 Hv. This demonstrates the importance of the substrate bias to make uniform and high quality film deposition on three-dimensional substrate surfaces by setting the substrate in the middle of the interelectrode gap. The composition of deposited TiN films was measured by Auger spectra method. It was found that Ti, N, Cl, O, and C were contained in the deposited TiN films. The at. % value of the Cl content [=Cl/(Ti+N+O+C+Cl)] in the TiN films was about 2% with substrate bias voltage, and the ratio of N/Ti was about 1.2.
Integrated plasma equipment model for polysilicon etch profiles in an inductively coupled plasma reactor with subwafer and superwafer topography
Authors: Hoekstra Robert J. , Grapperhaus Michael J. , Kushner Mark J.
Published: July 2002

Above wafer topography of the substrate, such as wafer clamps, is known to impact adjacent feature profiles during plasma etching of microelectronic devices. The consequences of subwafer topography, such as electrostatic chucks and cooling channels, on feature profiles is less well characterized. To investigate these issues we have developed and integrated a plasma equipment model and a Monte Carlo feature profile model, and applied the integrated model to investigate polysilicon etching in an inductively coupled plasma reactor. We find that, when using low conductivity wafers, subwafer topography reduces the sheath potentials above the wafer which results in lower ion energies incident on the wafer. Etch rates sensitive to ion power are therefore also reduced. Due to the perturbation of the presheath and sheath, subwafer topography can also affect the angular distribution of the ion flux incident on the wafer which then results in asymmetric etch profiles. Superwafer structures perturb both the magnitude and angular distribution of the ion flux due to shadowing at the edge of the wafer. This leads to lower etch rates and asymmetric etch profiles. Inhibitor fluxes can be used to control the etch profile shape but only at relatively low magnitudes of those fluxes.
Analysis and characterization of native oxide growth on epitaxial Si1−xGex films after a chemical clean
Authors: Lee I.-M. , Takoudis C. G.
Published: July 2002

Ellipsometry, contact angle goniometry, atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS) are used to study native oxide growth on SiGe films (with Ge content of 0%, 20%, 40%, and 100%) after a chemical clean. Ellipsometry suggests that the presence of Ge affects the initial oxide thickness right after the clean but it does not affect the rate of native oxide growth. Roughness of SiGe samples as measured by AFM does not appear to be affected by the native oxide growth or the Ge content in the film. The decrease in advancing (and receding) contact angles of SiGe samples after the chemical clean is apparently the result of both increasing oxide thickness and oxide solid phase composition. XPS results suggest that increasing Ge content in the film increases the oxidation of SiGe surface atoms. The chemical shifts in the Si 2p and Ge 3d spectra suggest that both Si and Ge react with oxygen to form SiO2 and GeO2. Such data suggests that contact angle measurements could be a rapid method to determine the state and passivation characteristics of a silicon substrate surface as a function of time; however, such a technique would not be as effective for SiGe films, the chemical composition of their native oxides of which would also change as a function of time.
Surface cleaning aluminum foil with ozone gas
Authors: Momose Takashi , Hayasaka Eisyuh , Saitou Katuhiro , Nagayama Katuya , Abe Sin’ya
Published: July 2002

Residual oil on rolled aluminum foil prevents good adherence of print or paint. Ozone gas exposure shows promise of effectively reducing the surface hydrocarbons to acceptable levels for industrial coatings (<10% surface carbon). Ozone and thermal treatments performed on laboratory- and industrial-scale samples which were surface analyzed using x-ray photoelectron spectroscopy and further characterized with H2O contact angle measurements. The samples were exposed to oxygen gas including ozone 630 ppm at a flowing rate of 0.5 l/min. Two treatments, heating treatment and ozone treatment with heating, are compared at a heating temperature, 200 °C for 6 h exposure time for laboratory-scale samples and 200 °C for 30 min and for 160 min at higher than 100 °C for industrial-scale samples. The atomic concentration % of carbon (C) proportional to the quantity of oil on the surface was determined to be 9.8% for the laboratory-scale sample and 7.4% for the industrial-scale sample.
Comparison of the submicron particle analysis capabilities of Auger electron spectroscopy, time-of-flight secondary ion mass spectrometry, and scanning electron microscopy with energy dispersive x-ray spectroscopy for particles deposited on silicon wafers with 1 μm thick oxide layers
Authors: Diebold Alain C. , Lindley Patricia , Viteralli Jim , Kingsley Jeff , Liu Benjamin Y. H. , Woo Keung-shan
Published: July 2002

Future particle analysis methods must be capable of determining the composition of 100 nm and smaller particles. Determination of the oxidation state is a part of this capability. In this study, we compare Auger, scanning electron microscopy equipped with energy dispersive x-ray spectroscopy, and time-of-flight secondary ion mass spectrometry using a sized set of Al, Al2O3, and TiO2 deposited on silicon wafers having 1 μm of thermally grown oxide.
Adsorption and thermal decomposition of C2D5I on the (110) and (111) planes of NiAl: A temperature programmed deposition and x-ray photoelectron spectroscopy study
Authors: Chaturvedi Sanjay , Strongin Daniel R.
Published: July 2002

This study investigates the adsorption and the subsequent thermal decompoistion of d5-iodoethane (C2D5I) on the (110) and (111) planes of NiAl using temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). Both I 3d5/2 and C 1s XPS data show that C2D5I adsorbs molecularly on both NiAl surfaces at 120 K. Upon heating the sample, the C–I bond starts to cleave and the scission of this bond is complete on NiAl(110) and NiAl(111) by 150 and 300 K, respectively. It is suspected that this cleavage results in the formation of C2D5(ad) and I(ad). TPD results show that the thermal decomposition of C2D5(ad) yields C2D4 and D2 as the main products on both the surfaces. The main difference in the decomposition products of C2D5(ad) species on the two surfaces is that desorption of C2D4 occurs on NiAl(111) at ∼315 K, ∼50 K higher than the corresponding value for NiAl(110).
Measurement of electron energy distribution function in an argon/copper plasma for ionized physical vapor deposition
Authors: Lu Z. C. , Foster J. E. , Snodgrass T. G. , Booske J. H. , Wendt A. E.
Published: July 2002

The electron energy distribution function (EEDF) has been measured under a variety of conditions in an Ar/Cu plasma for ionized physical vapor deposition. The EEDF is directly measured in a system including a direct-current magnetron sputter source for copper and a radio frequency (rf) induction plasma, using a Langmuir probe with a modulated bias voltage in combination with a lock-in amplifier. The experimental data indicate that at fixed rf ionization power, the electron population in the tail of the EEDF is depleted by the introduction of copper vapor, and the electron average energy decreases slightly. Observed changes in the EEDF are attributed to inelastic collisions with copper atoms, which have lower threshold energies for excitation and ionization as well as larger cross sections as compared to argon, and the resulting reduction in the measured plasma potential.
Non-neutral plasma expansion induced by electron-neutral collisions in a Malmberg–Penning trap
Authors: Chao Edward H. , Davidson Ronald C. , Paul Stephen F.
Published: July 2002

Single species non-neutral plasmas have very robust confinement properties because the conservation of canonical angular momentum in a system with azimuthal symmetry provides a powerful constraint on the allowed radial positions of the particles. If no external torques act on the plasma, the plasma cannot expand radially to the wall. However, collisions with a background neutral gas will exert a torque on the rotating plasma thus allowing the mean-square radius to increase. In the electron diffusion gauge experiment, a pure electron plasma is confined in a Malmberg–Penning trap and the radial density profile is measured as a function of time. The base pressure is 5×10−10 Torr and purified helium is injected to pressures ⩾5×10−9 Torr. The magnetic field is varied between 100 and 600 G. The experimentally measured radial density profile shape is found to match closely the theoretically predicted (expanding) equilibrium profile, where a single free parameter proportional to the electron temperature T is varied to best fit the experimental data. The best-fit value of the temperature T is found to stay approximately constant even as the plasma expands and the electrostatic energy decreases. The measured plasma expansion rate is found to scale with magnetic field strength as 1/B3/2 instead of the expected 1/B2 scaling. This modification in scaling may be caused by field asymmetries, which are believed to be an important factor in plasma expansion for the pressure ranges examined here. Nevertheless, the expansion rates are observed to increase with increasing background pressure, and the absolute scaling with pressure is consistent with theoretical predictions.
Oxygen adsorption on well-defined gold particles on TiO2(110)
Authors: Bondzie V. A. , Parker S. C. , Campbell C. T.
Published: July 2002

Very tiny Au particles on TiO2 show excellent activity and selectivity in a number of oxidation reactions. We have studied the vapor deposition of Au onto a TiO2(110) surface using x-ray photoelectron spectroscopy, low energy ion scattering, low energy electron diffraction, and temperature programmed description (TPD) and found that we can prepare Au islands with controlled thicknesses from one to several monolayers. In order to understand at the atomic level the unusual catalytic activity in oxidation reactions of this system, we have studied oxygen adsorption on Au/TiO2(110) as a function of Au island thickness. A hot filament was used to dose gaseous oxygen atoms, since O2 gas does not readily dissociatively adsorb on Au. The saturation coverage of oxygen adatoms on Au particles approaches 1.0 ML, similar to that found on bulk Au(110) and (111). TPD results show higher desorption temperatures (645 K) for ultrathin gold particles on TiO2(110) than thicker particles (520–545 K). This implies that Oa bonds much more strongly to ultrathin islands of Au. Thus from Brönsted relations, ultrathin gold particles should be able to dissociatively adsorb O2 more readily than thick gold particles. We postulate that the catalytic activity in oxidation reactions demonstrated by thin (small) Au particles on TiO2 is related to the positive influence this stronger bonding to oxygen has on the dissociative adsorption rate of O2. © 1999 American Vacuum Society.
Differences in radical generation due to chemical bonding of gas molecules in a high-density fluorocarbon plasma: Effects of the C=C bond in fluorocarbon gases
Authors: Samukawa Seiji , Mukai Tomonori
Published: July 2002

We investigated the differences in radical generation due to chemical bonding of fluorocarbon gas molecules in the plasma. We found that dissociation of the C=C bond is five times easier than that of the C–C bond in a fluorocarbon gas plasma. As a result, a C2F4 plasma could generate a higher density of CF2 radicals than a C4F8 plasma. Additionally, the same dissociation processes occurred in the C3F6 and C5F8 plasma, which both have the C=C bond and C–C bond in their molecules. In the C3F6 plasma, the density of generated CF2 radicals was 3.5 times higher than that for CF or CF3 radicals, whose radical densities were the same. The C5F8 gas plasma mainly produced CF2 and CF radicals, and the CF radical density was higher in comparison to other fluorocarbon gas plasmas.
Etch rate control in a 27 MHz reactive ion etching system for ultralarge scale integrated circuit processing
Authors: Tatsumi T. , Hikosaka Y. , Morishita S. , Matsui M. , Sekine M.
Published: July 2002

The etch rates of SiO2, photoresist, Si, and SiN in a 27 MHz reactive ion etching system at constant ion flux of 6×1016 cm−2 s−1 and ion energy of 1450 V were studied. Typical incident flux densities of CF2 and CF+ were on the order of 1017 and 1016 cm−2 s−1, respectively. The SiO2 etch rate was determined by the balance of the energy supplied by the total ion flux and the amount of the C–F reactive species supplied by radicals and ions. When we roughly assumed the surface reaction probabilities of F, CF, CF2 and CF3 to be 0.1, 0.1, 0.1, and 0.5, the SiO2 etch rate could be expressed well as a function of the total number of F in the net radical fluxes. To clarify the dominant flux including radicals and ions, however, further research on surface reaction probabilities on the actual etched surface must be conducted because the incident fluxes strongly depend on these constants of the surface reaction probability. Lowering the total ion flux or ion energy decreased the etch rate of SiO2. A higher ion flux or higher ion energy is required to obtain higher etch yields. When excess C–F reactive species exist on the etched surface, they disturb the etching reaction by wasting the energy of incident ions. Under these conditions, a reactive species is no longer an “etchant,” but an “inhibitor.” Therefore, it is important to control the amount of total reactive species according to the ion conditions. Oxygen contributed to the removal of these excess C–F species, resulting in a higher etch yield. In contrast, the etch rates of a photoresist, Si, and SiN did not depend on flux of the C–F reactive species, but on the oxygen concentration. It is concluded that a process with high selectivity requires low oxygen concentration, high ion flux, and optimized flux of C–F reactive species.
Growth of carbon nanotubes by microwave plasma-enhanced chemical vapor deposition at low temperature
Authors: Choi Young Chul , Bae Dong Jae , Lee Young Hee , Lee Byung Soo , Park Gyeong-Su , Choi Won Bong , Lee Nae Sung , Kim Jong Min
Published: July 2002

Carbon nanotubes have been grown on Ni-coated Si substrates by microwave plasma-enhanced chemical vapor deposition with a mixture of methane and hydrogen gases at temperatures ranging from 520 to 700 °C. The density and the length of the carbon nanotubes increased with increasing growth temperature. At a growth temperature of 520 °C, the carbon nanotubes were curly, whereas the nanotubes were straight and self-aligned upward at temperatures above 600 °C. Images from high-resolution transmission electron microscopy showed that the nanotubes were multiwalled, with a few wall structures. The graphitized structures were also confirmed by Raman spectra. We show that the size of Ni grains on Si substrates is correlated to the diameters of the grown carbon nanotubes.
Focused ion beam microlithography using an etch-stop process in gallium-doped silicon
Authors: La Marche P. H. , Levi-Setti R. , Wang Y. L.
Published: July 2002

We have found that silicon, when implanted with doses of gallium in excess of 1013 ions/cm2, experiences little or no etching in aqueous caustic solutions. By exploiting a finely focused 40–50 keV gallium ion beam (0.05–0.1 μm diameter) in our scanning ion microscope, we have shown that it is possible to fabricate structures with submicrometer (0.1 μm) features. The silicon behaves as a negative resist with a sensitivity of about 1 μC/cm2. This etch-stop process is largely insensitive to crystallographic orientation, except for the highly insoluble (111) plane in which damage-promoted etching occurs.
Etch products from the reaction of XeF2 with SiO2, Si3N4, SiC, and Si in the presence of ion bombardment
Authors: Winters Harold F.
Published: July 2002

Modulated beam mass spectrometry has been used to identify the etch products desorbed during ion bombardment of SiO2, Si3N4, SiC, and Si in the presence of XeF2. The major silicon-containing product from all of these materials is SiF4 as judged by the intensity of the SiF+3 peak. The radicals SiF and SiF2 are observed but in much smaller quantities. N2 and O2 are major etch products from Si3N4 and SiO2, respectively. No other compounds of oxygen or nitrogen were observed. The major ‘‘carbon-containing’’ product from SiC was not identified. The product distributions are relatively independent of XeF2 flux, ion energy, and the type of ion (i.e., Ar+ or CF+3). Rough estimates for the relative etch rates of these materials have also been obtained. The product distributions are consistent with an interpretation which suggests that ‘‘chemical sputtering’’ is the dominant (but not the only) mechanism for producing ion-enhanced etching.
Molecular level fabrication techniques and molecular electronic devices
Authors: Carter Forrest L.
Published: July 2002

In anticipation of the continued size reduction of switching elements to the molecular level, new approaches to materials, memory, and switching elements have been developed. Two of the three most promising switching phenomena include electron tunneling in short periodic arrays and soliton switching in conjugated systems. Assuming a three-dimensional architecture, the element density can range from 1015 to 1018 per cc. In order to make the fabrication of such a molecular electronic device computer feasible, techniques for accomplishing lithography at the molecular scale must be devised. Three approaches possibly involving biological and Langmiur–Blodgett materials are described.
CO on Ni[100]: Stark effect and electroreflectance vibrational spectroscopy
Authors: Lambert David K.
Published: July 2002

Electroreflectance vibrational spectroscopy (EVS) has been used to study the stretch vibrational mode of CO on Ni[100] at 300 K. The Stark tuning rate of terminally bonded CO is measured to be 1.3×10−6 cm−1/(V/cm), acting to decrease frequency as the electric field out of the surface is increased. The present measurement is in close agreement with the Stark tuning rates for CO on Ni[100] and on Pt in an aqueous electrolyte. In addition to the Stark effect, another signal source is observed that is tentatively identified with an electric-field-induced change in the angle some CO molecules have with respect to the surface normal. Recent advances in the EVS measurement technique are also described.
A parametric study of interband absorption in GaAs–AlxGa1−xAs quantum wells
Authors: Porod W. , Pötz W. , Ferry D. K.
Published: July 2002

Calculations of the optical transitions in GaAs–AlxGa1−xAs heterostructures are undertaken, with an eight-band k ⋅ p method. The sensitivity of the resulting spectrum to structural, as well as to material, parameters is studied. For a rectangular quantum well, we find that the available data do not allow a unique determination of the conduction band offset Qe. By accounting for experimental uncertainties, we find that any value in the range 0.5–0.9 is compatible. For parabolic wells, however, we can narrow this range to 0.5–0.65.
Micromachining of silicon mechanical structures
Authors: Kaminsky G.
Published: July 2002

Refined and very exact processing procedures for producing geometrically highly precise silicon structures are described. The structures are micromachined utilizing wet chemical orientation and/or concentration etching techniques. The use of a specially designed and highly effective etching system is a significant refinement in the processing procedure. The structures have excellent large and small scale uniformity. Relief structures having features as small as 0.2 μm have been produced. We report on devices for three specific research applications: (1) Very high Q torsional oscillators useful for high sensitivity measurements in the study of the mechanical properties of single crystal silicon and also in the study of thin freely suspended liquid crystal films, (2) unstrained focusing x-ray mirrors, and (3) μm level mechanical ‘‘shadow masks’’ useful for noncontaminative, in situ patterning of thin films deposited in MBE and/or other deposition systems.
The effects of germanium concentration on the compound formation and morphology of gold-based contacts to gallium arsenide
Authors: Kim Taeil , Chung D. D. L.
Published: July 2002

Alloyed Au–Ge thin films on n-GaAs are widely used for fabricating Ohmic contacts to n-type GaAs. This paper presents a systematic study of the effects of Ge concentration on the compound formation and morphology in the metallization. The lowest annealing temperature at which the compound formation at 10−6 Torr was observed for Au–Ge contacts with Ge concentrations of 0, ∼0.6, 3, and 12 wt. % Ge was 500, 500, 450, and 350 °C, respectively. Hence, Ge was found to decrease the compound formation temperature. Au7Ga2 was observed in contacts with low Ge concentrations (0 and ∼0.6 wt. % Ge), whereas α′-AuGa (or Au7Ga), a tentatively identified Au3Ga phase, and a AuGeAs ternary phase were observed in contacts with a Ge concentration of 12 wt. %. At an intermediate Ge concentration (3 wt. % Ge), both Au7Ga2 and α′-AuGa were observed. The morphology after compound formation was sensitive to the Ge concentration. In Au–Ge contacts, a change in the Ge concentration from 0 to ∼0.6 wt. % caused a sharp decrease in the aspect ratio of the aligned Au7Ga2 rectangular particles; a change from 3 to 12 wt. % Ge caused a change from a GaAs-rich matrix to a Au-rich matrix with the appearance of characteristically shaped AuGeAs patches.
Strain-dependence of localized states in quantum-well structures
Authors: Pötz W. , Ferry D. K.
Published: July 2002

A k⋅p model is developed to describe confined states in strained-layer heterostructures fabricated from III–V compounds and their alloys. Unlike the case of simple one-band models, the presence of intrinsic strain not only shifts the band edges but also modifies the effective masses associated with the individual bands. Results for InGaAs/GaAs and InGaAs/InP are presented. We show that the presence of strain can have significant influence on the electronic properties of these systems such as intersubband transition energies and the band offsets. The importance of strain effects on the determination of band offsets from optical data is discussed.
The reaction of Si(100) 2×1 with NO and NH3: The role of surface dangling bonds
Authors: Avouris Ph. , Bozso F. , Hamers R. J.
Published: July 2002

We present the results of a detailed study of the reactions of Si(100) 2×1 with NO and NH3. We use several electron spectroscopies and ion scattering to study the reactivity of the surface and to determine the nature of the rate limiting steps of the above reactions over a wide temperature range (90–1200 K). We find that the Si(100) 2×1 surface is quite reactive and can dissociate NO or NH3 even at 90 K. The reactions are, however, self-limiting. The released O or H atoms tie up the surface dangling bonds and passivate the surface. The N atoms, on the other hand, occupy mostly subsurface sites. Sustained reactivity and thin film growth occurs only at temperatures sufficiently high enough to desorb the surface oxygen or hydrogen and regenerate the surface dangling bonds. We find, however, that electron-stimulated desorption of the hydrogen can be used to nonthermally regenerate the surface dangling bonds and allow silicon nitride thin film growth even at 90 K. Because of the crucial role the top layer plays in the film growth mechanism we investigate its nature using the new technique of scanning tunneling microscopy (STM). This is the first in situ study of a surface chemical reaction by STM. The STM topographs indicate that the 2×1 reconstruction is preserved after exposure of the Si(100) 2×1 surface to NH3. The topographs and the tunneling current versus voltage curves suggest the formation of a Si(100) 2×1 monohydride-like surface layer.
Sublattice allocation and antiphase domain suppression in polar-on-nonpolar nucleation
Authors: Kroemer Herbert
Published: July 2002

One of the first problems that must be solved if device-quality GaAs is to be grown on Si substrates is that of suppressing antiphase disorder. Recent experimental evidence shows that such disorder can be suppressed not only on the (211) orientation, but also on (100), through a combination of slight misorientation and a high-temperature surface anneal, which lead to the pairing of all Si surface steps into a particular kind of double-height steps. A recent model by Aspnes of Ihm explains the energetic preference for this kind of step via a drastic reconstruction of the atomic configuration at the step edge involving the formation of a π-bonded chain running along the step. Another unexpected puzzle is posed by the recent observation that on a given Si (100) surface, antiphase disorder-free growth with both possible Ga–As sublattice allocations can be achieved, depending on initial nucleation conditions. A detailed nucleation model is presented that explains these observations, involving a site interchange between Si atoms and incoming As atoms under Ga-rich nucleation conditions.
Laser ablative chemical etching of SiO2
Authors: Agrawalla B. S. , Dai B. T. , Allen S. D.
Published: July 2002

The cw CO2 (λ=10.6 μm) laser ablative chemical etching of fused SiO2 in the presence of several etchant gases shows rapid removal rates, 0.4–8×106 μm3/s for a laser intensity of 9 kW/cm2 and yields smooth, high quality surfaces. The etchant gases HF, HCl, H2, Cl2, NF3, and CF3Br are all transparent to the laser wavelength used and the SiO2 substrate absorbs the radiation strongly. Etching occurs mainly by ablation of SiO2 and the etchant gases react with the hot, partially ionized plume containing SiOx particles to yield differing extent of cleanliness. A laser-induced plasma formation accompanies the etching process.
Silicon dioxide fine patterning by reactive fast atom beam etching
Authors: Kuwano Hiroki , Shimokawa Fusao
Published: July 2002

A fast atom beam technique is applied to silicon dioxide substrate pattern fabrication. A modified Mcllraith (saddle field) fast atom source having a charge exchange cell in front of the cathode grid is studied under several discharge conditions. High pressure in the source is shown to increase the proportion of high-energy neutral particles in the beam. The tendencies of the neutralizations are in accordance with calculations based on resonance charge transfer. Maximum etch rates for Si and SiO2 using a CF4 +O2 gas mixture are achieved at a relative CF4 gas flow rate of 0.76, and the etch rate for SiO2, unlike that for Si, is found to depend linearly on the discharge current. The etched sidewalls at a discharge voltage of 1.2 kV were nearly perpendicular. Reactive fast atom beam etching proved capable of producing highly accurate 0.2-μm-wide pattern formations.