bluuebunny/crossref_metadata_2025 huggingface dataset:
IBM-personal computer data acquisition and processing system to upgrade an out-of-date mass spectrometer
Authors: López Callejas R. , Pozas Cárdenas M. J. , Cruz Cruz G. , Meléndez Lugo L. , Chávez Alarcón E. , Valencia Alvarado R. , Olayo González M. G. , Flores Orta A.
Published: July 2002

A versatile, inexpensive, and easy to use module, giving an IBM-compatible personal computer format of the residual gas analysis spectra obtained by old mass spectrometers, and the associated software are described. The code includes options for postacquisition spectrum processing. With this module, old mass spectrometers can be converted into an efficient computer-based tool for residual analysis.
Ion-assisted Si/XeF2-etching: Influence of ion/neutral flux ratio and ion energy
Authors: Vugts M. J. M. , Hermans L. J. F. , Beijerinck H. C. W.
Published: July 2002

The Ar+ ion-enhanced Si(100)/XeF2 reaction at 300 K is studied quantitatively in a molecular beam setup. Measurements are done for XeF2-fluxes from 0.1 up to 3.4 monolayer/s, Ar+-fluxes from 8×10−4 up to 8×10−2 monolayers/s and Ar+-energies of 500, 1000 en 2000 eV. Both the XeF2 consumption and the SiFx production are measured by mass spectrometry. It is concluded that physical and chemical sputtering are the only significant ion-induced mechanisms: damage-enhanced etching and enhanced spontaneous etching can be neglected. The flux dependence of the etch process is found to be solely determined by the ratio of the ion over the neutral flux. This behavior is described by a simple kinetic model. From the energy dependence it is concluded that both the physical and the chemical sputtering contributions scale with the square root of the ion energy. The ion-enhanced Si/XeF2 reaction is most efficient for ion/neutral ratios of 0.1 and higher: 80% of the XeF2 is then consumed in the reaction process versus 10% during spontaneous etching. It is concluded from the mass spectrometer signals that under these conditions between 35% and 61% of the SiFx products are released by physical sputtering and the remainder desorbs by chemical sputtering.
Analysis of aluminum nitride epitaxial growth by low pressure metal organic chemical vapor deposition
Authors: Buggeln R. C. , Meyyappan M. , Shamroth S. J.
Published: July 2002

Epitaxial growth of aluminum nitride films by low pressure metal organic chemical vapor deposition is modeled. The feed gas mixture consists of trimethyl aluminum, ammonia, and hydrogen. The governing fluid flow, energy, and species conservation equations are solved numerically in two dimensions. The effects of process variables on growth characteristics is investigated in the mass transport limited regime. Results are presented in terms of flow patterns, species distributions, and growth parameters for various reactor pressures and growth temperatures. In the low pressure regime (50–150 Torr) the growth rate is nearly independent of temperatures between 600 and 1200 °C. The growth rate increases approximately linearly with pressure at 1200 °C.
Feature scale simulation studies of TEOS-sourced remote microwave plasma-enhanced chemical vapor deposition of silicon dioxide: Role of oxygen atom recombination
Authors: Virmani Moneth , Levedakis Dimitri A. , Raupp Gregory B. , Cale Timothy S.
Published: July 2002

Experimental data and feature scale simulations are combined to test a kinetic model proposed for remote microwave plasma-enhanced chemical vapor deposition (RμPECVD) of silicon dioxide from tetraethylorthosilicate (TEOS) and oxygen. The constitutive relationships used are refinements of those developed for the direct capacitively coupled rf PECVD of SiO2, using TEOS and oxygen. We discriminate between a first order and a second order oxygen atom recombination reaction on the surface of the feature based on simulation results obtained using EVOLVE, a physically based low pressure simulator. We then use film profiles inside features to estimate the oxygen atom flux to the water surface and the kinetic parameters used in the rate expressions for the deposition reaction and the oxygen atom recombination reaction. Results indicate that under the conditions of our experiments, the thermally activated oxygen atom recombination reaction on the growing silicon dioxide surface is second order in oxygen atoms. This recombination reaction consumes reactive oxygen and leads to gradients in oxygen atom flux in the feature. Because this surface reaction is thermally activated, the magnitude of the gradient increases as the water surface is increased, which results in significant degradation of step coverage.
Response surface study of resist etching in high density oxygen plasma and interactions of O2 plasma with NiFe, Cu, Ta, and Al2O3
Authors: Hsiao R. , Miller D. , Kellock A.
Published: July 2002

Etching of a photosensitive polymer in high density oxygen plasma was studied. The polymer is a commonly used insulation material in a magnetic recording head. A quantitative relationship between etch rate and inductive power, bias power, and pressure was established by using the response surface method. Etch rate was found to increase with both inductive power and bias power, and a maximum etch rate was found at about 5 mTorr pressure. The effect of exposing the commonly used materials in magnetic recording heads such as NiFe (81/19 wt %), Cu, Ta, and Al2O3 to high density oxygen plasma was also investigated. Electron spectroscopy for chemical analysis and Rutherford backscattering spectroscopy were used to characterize the plasma-exposed samples. It was found that exposure to high-density oxygen plasma caused rapid oxidation of Cu, segregation and oxidation of Fe at the surface of NiFe, relatively slight oxidation of Ta, and no change in the physical thickness or the composition of Al2O3.
Particle formation rates in sulfur hexafluoride plasma etching of silicon
Authors: Garrity Mary P. , Peterson Thomas W. , O’Hanlon John F.
Published: July 2002

Particle formation during low pressure SF6/argon etching of silicon in a single wafer parallel plate reactor is studied. Particles are extracted from the exhaust and collected on the wafer. Particle composition and morphology depend on plasma power, etch time, gas composition, and pressure. Primary particles of tens of nm in diameter and spherical and chain aggregates as large as 5 μm are observed. Critical powers and etch times are required for the formation of these aggregates. The presence of major gas phase species is determined using mass spectrometry and optical emission spectroscopy. Mechanisms for describing the formation processes of particles are presented, including gas phase precursor formation, nucleation, and coagulation. Precursor formation is determined from plasma-dependent, homogeneous, gas-phase reactions and etch product distributions predicted from electrical and etch rate measurements of the plasma. Dissociation of SF6 into lower molecular weight SFx species and unsaturated SiFex species is primarily responsible for initial particle formation.
Effect of nonstoichiometry upon optical properties of radio frequency sputtered Al–N thin films formed at various sputtering pressures
Authors: Wang Dao-yuan , Nagahata Yukio , Masuda Masataka , Hayashi Yasunori
Published: July 2002

Colored Al–N films can be easily made through changing the content of nitrogen gas at various sputtering pressures. For films deposited at 5×10−2 Torr, with only slight change in the proportion of nitrogen gas from 0% to 2.5%, 5%, 7.5%, and 10%, the respective visual appearance changed from silver–gray to gray, gray, green–yellow to transparent. With the further increase in the content of nitrogen gas up to 100%, the obtained films were all transparent. For films formed at 5×10−1 Torr, with the content of nitrogen gas being 0%, 2.5%, 5%, 7.5%, 10%, and 20%, the corresponding visual appearance of the films were silver–gray, black, dark-green–yellow, green–yellow, light-yellow and transparent. When the content of nitrogen gas changed from 20% to 100%, there was almost no difference in the visual appearance. For films formed at 1 Torr, when the content of nitrogen gas was only over 2.5%, the film became clear. Measurements of transmittance, reflectance, and thickness, calculations of the absorption coefficient, refractive index, and extinction coefficient, and an x-ray photoemission spectroscopy analysis show that the coloration is mainly due to the nonstoichiometry induced by lower content of nitrogen gas at various sputtering pressures. Furthermore, the calculated extinction coefficients are found to have a much closer relationship with the coloration than other parameters, such as, refractive index and thickness. The optical band gap of the obtained stoichiometric AlN films is 5.85–5.9 eV.
Formation of titanium nitride coatings by nitrogen plasma immersion ion implantation of evaporated titanium films
Authors: Hartmann J. , Ensinger W. , Königer A. , Stritzker B. , Rauschenbach B.
Published: July 2002

Titanium was deposited onto silicon by electron beam evaporation in high vacuum. The Ti films were treated by plasma immersion ion implantation (PIII) with energetic nitrogen ions extracted from a plasma which was generated by electron cyclotron resonance microwave excitation. The elemental composition of the films was measured by Rutherford backscattering spectrometry and the different phases were identified by x-ray diffraction. The results show that nitrogen PIII treatment leads to nitrogen ion incorporation with nitride phase formation, accompanied by an increase in density. Two mechanisms for the incorporation of nitrogen can be distinguished: implantation and radiation enhanced diffusion.
Effect of a vacuum ion gauge on the contamination of a hydrogen-passivated silicon surface
Authors: Yun Sun Jin , Lee Seung-Chang , Lee Jae-Jin , Lee Jeong Yong
Published: July 2002

The effect of operating a vacuum ion gauge on carbonaceous (C) contamination of a hydrogen (H)-passivated Si surface before epitaxial growth was investigated. The dependence of C contamination on the residence time in the loading chamber, tlc, was determined with or without operating a vacuum ion gauge. The results showed that C contamination of a H-passivated surface was greatly increased by use of the ion gauge. With ion gauge operation in a vacuum of 1×10−6–1×10−7 Torr in the loading chamber, the configuration of the ion gauge and upside down-stacked wafers is shown to be a dominant factor of C contamination of the Si surface. The presence of C contaminants could be determined by observing SiC diffraction patterns using in situ reflection high energy electron diffraction (RHEED), since the C contaminants reacted with Si to produce single crystalline SiC at a temperature as high as 850 °C. The RHEED patterns demonstrated that the single crystalline SiC had a zinc-blende structure. Single crystalline SiC islands with an ellipsoidal cross section were observed by high resolution transmission electron microscopy. In the subsequent epitaxial growth of Si, a well oriented single crystalline Si layer could be grown over the SiC islands although the effect of C contamination on the electrical characteristics of the interface was not clarified. Longer tlc with the ion gauge also required a higher temperature to achieve a 2×1 reconstructed surface structure from the H-passivated Si surface.
Vacuum arc deposition of Mo films
Authors: Vershinin Nikolay , Straumal Boris , Gust Wolfgang
Published: July 2002

Mo coatings on Cu substrates were deposited with the aid of an unfiltered vacuum arc at a deposition voltage of 31 V. Dependencies of the deposition rate Rd on the discharge current I (in the interval from 80 to 180 A) and the distance L between the cathode and substrate were investigated. Rd increases monotonically with increasing I and decreases with increasing L. If the substrate is parallel to the cathode surface, Rd is much higher than it is for substrates which are perpendicular to the cathode surface. Rd values as high as 15 nm/s were reached. The reasons for this behavior are analyzed. It is also shown that Mo macroparticles are well incorporated into the coating building an integral part of it.
Dynamics of molecular chemisorption of N2 on the Ru(001) surface
Authors: Seets D. C. , Wheeler M. C. , Mullins C. B.
Published: July 2002

The chemisorption of N2 on Ru(001) has been studied using supersonic molecular beam techniques. The initial molecular chemisorption probability, S0, was measured as a function of incident energy, Ei, from 0.021 to 0.90 eV and angle of incidence, θ, from 0° to 60° at a surface temperature of 77 K. At a normal angle of incidence, the value of S0 decreases with increasing kinetic energy in the low and intermediate energy regimes and is constant in a higher energy (0.4 eV<Ei<0.7 eV) regime. As the angle of incidence increases, the value of S0 decreases more rapidly with Ei at low energies. At θ=60°, S0 decreases with increasing kinetic energy, passes through a local minimum near Ei=0.2 eV, and then increases to the same constant value as in the normal incidence case. At Ei=0.90 eV, the most energetic beam used in this study, the value of S0 decreases slightly from this constant value. Similar measured trends in the angular and energy dependence, particularly at intermediate energies, have not been reported previously for a molecular chemisorption system, and we qualitatively describe this behavior by combining a trapping-mediated mechanism (dominant at low incident energies) and a direct molecular chemisorption mechanism (dominant at high incident energies). We also report measurements of the initial dissociative chemisorption probability of N2 on Ru(001) and conclude that this probability at Ei=1.25 eV and normal incidence does not exceed 1×10−3 at a surface temperature of 600 K.
Reflective coatings for large-area solar concentrators
Authors: Martin P. M. , Affinito J. D. , Gross M. E. , Stewart D. C. , Bennett W. D. , Kelley R. J. , Horne W. E.
Published: July 2002

Reflective/protective coatings were applied to pre-formed 2.5-m-long solar concentrator panels by the magnetron sputtering process. Low-cost manufacturing processes such as hydrostatic forming of aluminum solar concentrator panels are needed to keep the costs of domestic power generation low. Without treatment, the specular reflectance of the aluminum panels was less than 20%. As expected, silver (Ag) and aluminum (Al) coatings applied directly over the untreated panels did not significantly increase specular reflectance. To provide a specular base surface, approximately 100-μm-thick urethane layers were applied to the panels before deposition of the reflective coating. This smoothing layer filled in scratches and defects. Reflective Ag and Al layers, with protective overcoats of Al2O3 and Si3N4, were deposited onto the urethane-coated panels by reactive magnetron sputtering with ion assist in Pacific Northwest National Laboratory’s 3 m coating chamber. The specular reflectance of the panels increased to an average of 92% at visible wavelengths, very near the reflectance of Al coatings on highly polished glass. Panels with Ag metal layers displayed similar increases. The optical performance uniformity of the coating was better than ±5%. The measured primary concentration ratio of the panels was 800:1, which far exceeded the design ratio of 500:1. The total concentration ratio was 2400:1. The coatings passed MIL-spec environmental and durability tests. Field testing of the concentrator dishes and coatings is continuing, and test results will be reported.
Reactions of diethylgermane, triethylgermane, and ethyl groups on Ge(100)
Authors: Chen Jihong , Greenlief C. Michael
Published: July 2002

The adsorption and decomposition of diethylgermane and triethylgermane on the Ge(100) surface are investigated. These molecules are potential Ge sources for the deposition of epitaxial Ge thin films. Room temperature adsorption of either ethylgermane leads to the formation of surface germanium hydrides and ethyl groups. The ethyl groups decompose at higher temperatures and form ethylene via a β-hydride elimination reaction. Isotopic labeling experiments are used to confirm this reaction step. This is in contrast to the Si(100) surface where both α- and β-hydride elimination is observed for the decomposition of surface ethyl groups. Low energy electron diffraction is used to evaluate the quality of the deposited germanium films.
Adsorption of N2H4 on silicon surfaces
Authors: Tindall C. , Li L. , Takaoka O. , Hasegawa Y. , Sakurai T.
Published: July 2002

The chemistry of N2H4 on Si(100)2×1 and Si(111)7×7 has been studied using scanning tunneling microscopy (STM). On Si(100), the STM images show that the predominant pathway for adsorption is across the silicon dimers with the N–N bond parallel to the surface. On Si(111)7×7, the molecule behaves in a manner which is similar to NH3. That is, at low coverages the molecule adsorbs preferentially at center adatoms due to the greater reactivity of these sites, while at higher coverages it also reacts with the corner adatoms.
Improved mass spectrometer measurements using a pulsed gas sampling system
Authors: Sodal I. E. , Hanna D. A.
Published: July 2002

A method which provides continuous background subtraction in the mass spectrometer measurement while continuously sampling gas into the ion source is described. The method employs a pulsed gas sampling system that is capable of continuously admitting gas into the closed ion source from a wide range of sample gas pressures. This gas sampling system, when combined with synchronous detection by a digital filter, allows the mass spectrometer to be operated in ac mode so that only the signal derived from the gas sample entering the ion source is measured. The signals generated from varying gas background in the vacuum chamber, drift due to environmental temperature changes, pump instability, drift in the ion detection circuitry, and line signals are excluded. The stability of the mass spectrometer measurement is therefore greatly improved. The sampling system can be operated in molecular flow at low sampling gas pressures or viscous flow when sampling from a high pressure environment. The stability of the flow regime has been investigated and data showing the overall performance of the system are reported. This method can potentially improve the measurement capability of mass spectrometers used in a variety of applications such as residual gas measurements in industrial process control, medical gas monitoring, and trace gas monitoring in the atmosphere.
Orientation-dependence of elastic strain energy in hexagonal and cubic boron nitride layers in energetically deposited BN films
Authors: Cardinale G. F. , Medlin D. L. , Mirkarimi P. B. , McCarty K. F. , Howitt D. G.
Published: July 2002

Using anisotropic elasticity theory, we analyze the relative thermodynamic stabilities of strained graphitic (hexagonal) BN and cubic BN (cBN) single-crystal structures for all orientations of biaxial stress and strain fields relative to the crystallographic directions. In hBN, the most thermodynamically stable orientation has the graphitic basal planes oriented roughly 45° relative to either the plane of stress or strain. For cBN, the lowest-energy configuration differs for the constant stress or constant strain assumptions. Importantly, these most-stable orientations of hBN and cBN differ from those found experimentally for graphitic BN and cBN in polycrystalline BN films produced by energetic deposition processes. Therefore, the observed textures are not those that minimize elastic strain energy. We discuss possible origins other than elastic strain–energy effects for the observed textures.
Stability of rapidly annealed reactive sputter deposited nitrided silicon dioxide
Authors: Eftekhari G.
Published: July 2002

The effect of incorporation of nitrogen atoms into the structure of reactively sputtered SiO2 was examined. It was determined that the presence of a controlled concentration of nitrogen atoms improves the electrical properties of the oxide. This could be achieved at partial pres-sure of nitrogen of about 10%. High temperature annealing improved the oxide properties. The nitrided oxides showed a better resistance to high current stress.
Sputtering investigation of boron nitride with secondary ion and secondary neutral mass spectrometry
Authors: Zhang J. , Bhattacharjee S. , Shutthanandan V. , Ray P. K.
Published: July 2002

Sputtering of boron nitride with xenon ions was investigated using secondary ion (SIMS) and secondary neutral (SNMS) mass spectrometry. The ions generated from the ion gun were incident on the target at an angle of 50° with respect to the surface normal. The energy of ions ranged from 100 eV to 3 keV. A flood electron gun was used to neutralize the positive charge buildup on the target surface. The intensities of sputtered neutral and charged particles, including single atoms, molecules, and clusters, were measured as a function of ion energy. Positive SIMS spectra were dominated by the two boron isotopes whereas BN− and B− were the two major constituents of the negative SIMS spectra. Nitrogen could be detected only in the SNMS spectra. The intensity–energy curves of the sputtered particles were similar in shape. The knees in p-SIMS and SNMS intensity–energy curves appear at around 1 keV, which is significantly higher than the 100–300 eV energy range at which knees appear in the sputtering of medium and heavy elements by ions of argon and xenon. This difference in the position of the sputter yield knee between boron nitride and heavier targets is due to the reduced ion energy differences.
Experimental study on the scaling law of the outgassing rate with a pumping parameter
Authors: Akaishi K. , Kubota Y. , Motojima O. , Nakasuga M. , Funato Y. , Mushiaki M.
Published: July 2002

The outgassing rate of a small test chamber made of type 304 stainless steel has been measured as a function of pumping speed in the range from 0.3 to 200 ℓ/s. The chamber was first exposed to air and then pumped with different pumping speeds for three days at 20 °C without baking. Typical outgassing rates of the chamber are determined from the measurement of steady pressures at the pumping time of 72 h. It is found, as a result, that measured outgassing rates q obey a set of power laws of q1=C1(S/A)m1 and q2=C2(S/A)m2, where S/A is the ratio of pumping speed S to the surface area A of the chamber, C1 and C2 are constants, the exponents m1 and m2 are 0.8282 for S/A⩾10−3 ℓ/s cm2 and 0.4655 for S/A⩽10−3 ℓ/s cm−2. It is shown that the observed power law can be derived from theoretical consideration and is useful to estimate the ultimate pressure of an unbaked vacuum system.
Comparison of low-temperature oxidation of crystalline Si and B with a-Si:B alloy: An x-ray photoelectron spectroscopy study
Authors: Yang G.-R. , Zhao Y.-P. , Abburi M. , Dabral S. , Tong B. Y.
Published: July 2002

The low-temperature (25–600 °C) oxidation of amorphous silicon boron alloy (a-Si:B) prepared by low-pressure chemical-vapor deposition, with varying boron contents (0%–25%), has been qualitatively studied using x-ray photoelectron spectroscopy. The oxidation of these amorphous a-Si:B films has been compared to that of crystalline silicon (c-Si) and boron (c-B). It was found that higher boron concentration in the Si:B alloy caused faster oxidation of both the Si and B components in the amorphous alloy as compared to either c-Si or c-B. At room temperature, suboxides were formed (Si+, Si2+, Si3+, B+, B2+) as opposed to oxides (Si4+, B3+). At higher temperature the oxidation was faster, as expected. In addition, at higher temperatures the SiO2 and B2O3 oxides were preferentially formed by the conversion of the suboxides. All the evidence suggests that the availability of three-coordinated B bonds in the Si:B alloy accelerates the oxidation process when compared to the oxidation of the tightly bounded c-Si or c-B.
Production evaluation of real-time statistical process control on a sub-0.5 μm inductively coupled metal etch process
Authors: Boskin Eric D. , Dalton Timothy J.
Published: July 2002

The semiconductor manufacturing industry is demanding improved algorithms for the detection and isolation of equipment faults. The real-time statistical process control (RTSPC) algorithm analyzes real-time sensor and actuator data for the detection of such faults. The software was evaluated using SECS-II (Serial Equipment Communication Standard) data from several commercial plasma etchers. These data were used to build statistical models which were then applied to data recorded during subsequent wafer processing. RTSPC was able to detect several faults related to failure of rf matching networks. For one of the rf match failures, the RTSPC alarm preceded the component failure by several weeks. This alarm was correlated to a shift in the critical dimension of wafers processed in this etcher. The statistical data filters included within RTSPC are discussed, as well as the characterization of the real-time data. Emphasis is placed on whether uni-variate, multivariate, or time-varying statistics are required to detect the faults seen on the etchers, and additional algorithms which would enhance the fault detection capability.
Wafer-transfer robot for use in ultrahigh vacuum
Authors: Kanetomo Masafumi , Kashima Hideo , Suzuki Takamichi
Published: July 2002

A polar coordinate wafer-transfer robot has been developed that enables thin-film manufacturing to be done in an ultrahigh vacuum. This robot features a frictionless spring structure that operates in a vacuum and is magnetically driven by a motor in the atmosphere (Nikkei Mechanical 1993.5.17). The spring arms are made of sheet springs and rigid plates and were optimized by simulation using the finite element method. All moving parts in the vacuum environment have a minimum of two bearings. As a result, a repeat position precision of 0.2 mm or less was able to be achieved in the atmosphere. Also, a maximum transfer distance of 800 mm and a transfer speed of 400 mm/s were achieved at a pressure of 10−7 Pa. After operation in a clean room at atmospheric pressure, only three particles above 0.1 μm in size were observed. Using this wafer-transfer robot, the area needed for film manufacturing in a multichamber ultrahigh vacuum can be reduced about 30% compared with using a conventional linear-magnet–coupling wafer-transfer robot.
Selective scanning tunneling microscope-induced light emission from self-assembled monolayer-covered Au surfaces
Authors: Evoy S. , Pardo F. D. , St. John P. M. , Craighead H. G.
Published: July 2002

We have studied the scanning tunneling microscope-induced light emission from Au surfaces in air. The effect of adsorbates on the light emission was investigated. Atmospheric contaminants appear as nonemissive clusters in the luminescence images. Preliminary results suggest that UV/ozone exposure partially reverses the effect of atmospheric contamination. Self-assembled monolayer chemisorption was also studied. The presence of an octadecylthiol (ODT) monolayer on the Au surface decreases the light emission intensity by one order of magnitude. Selective inhibition of luminescence is demonstrated using a microcontact printed pattern of ODT.
Transport properties along a finite-length atomic chain
Authors: Yamada Toshishige
Published: July 2002

We study the electron transport properties of a finite-length atomic chain created on an insulating substrate. Discrete energy levels are formed due to the finite length, and they are expected to show some trace in the I–V characteristics that are not predicted by an infinite chain model. Practically, electrodes are necessary for an electrical measurement but they cause complications: energy level broadening in the chain, chain charging due to the work function difference, Coulomb interaction through an effective capacitance, and mode selection resistance. If certain conditions are satisfied, depending on whether the highest occupied level is fully or partially filled in the chain, there is, respectively, an offset voltage for the current onset corresponding to the discrete energy separation, or the current rises rapidly for an infinitesimal voltage with a finite differential conductance on the order of quantum unit of conductance.
Oxygen fixing on Cu due to electron-beam damage during Auger spectroscopy
Authors: Heras J. M. , Viscido L.
Published: July 2002

We report on the electron stimulated adsorption of oxygen produced by the electron beam of an Auger spectrometer on Cu(100) samples at ≈100 K and 300–350 K. The OKLL, as well as the Cu LMM and M23VV Auger signals were monitored. The Cu target was discontinuously exposed to O2 up to saturation of the OKLL signal (440 langmuir, L), irradiating between doses with electron-beam energies in the range 100–2000 eV. The M23VV doublet of Cu at 59–61 eV became unresolvable as the exposure of the adsorbed O2 to the electron beam progressed. The effect of O2 with the sample at 100 K was practically the same as that previously found for H2O with the sample at 350 K, the kinetics of the process being governed by the sticking coefficient. A lateral composition profile taken after stabilization by annealing at 300 K showed a circular region centered at the point of incidence of the beam in which the OKLL signal had values ≈20 times higher than all around. This surface chemical modification was stable upon annealing during 10 min at 573 K, but annealing at T>1000 K practically restored the initial resolution condition of the M23VV doublet. From the collision number of O2 molecules, considering (i) the low sticking coefficient on Cu(100), and (ii), that the chemisorbed species are atoms, an overall efficiency of ≈10−6 can be estimated for the electron-beam assisted oxidation of the bulk.
Structure analysis of Ge dimer on Si (001) by medium-energy ion scattering blocking profiles from embedded Ge layers
Authors: Sumitomo Koji , Nishioka Takashi , Ogino Toshio
Published: July 2002

We propose a novel technique for determining the surface structure quantitatively and accurately by modifying the substrate, and apply it to the structure analysis of Ge dimers on the Si (001) surface. One or two atomic layers of Ge were embedded below 4–12 ML of Si overlayer by molecular-beam epitaxy and with atomic scale layer precision. The ions scattered from embedded Ge layers are blocked by the reconstructed surface atoms. Since the origin of the signals are restricted, the scattering-blocking pairs are uniquely assigned. In addition, the effect of thermal vibration can be minimized by choosing a distance between scattering and blocking atoms that is suitable for analysis. Therefore, we can observe the sharp and simple blocking profile of embedded Ge signals, and can determine the atomic displacements of reconstructed surfaces. The bond length of the Ge–Ge dimer on Si (001) surface was determined by this method to be 2.4 Å.
Effects of oxygen ion assist at 1–10 eV on growth of Bi2(Sr,Ca)2CuOx films at 540 °C by ion–beam sputtering
Authors: Endo T. , Yan H. , Abe K. , Nagase S. , Ishida Y. , Nishiku H.
Published: July 2002

Thin films of Bi2(Sr,Ca)2CuOx were prepared by ion-beam sputtering with low-energy (1–10 eV) oxygen ion assist. The 2201 phase with good crystallinity can be grown dominantly at very low temperature using only oxygen gas at a substrate temperature Ts=540 °C and average oxygen partial pressure Po=0.75 mTorr without assist. Single phase 2201 can be grown with assist under the same Ts and Po conditions. The assist exhibits other effects, such as promotions of 2201 growth and oxidation for lower Ts and Po and suppression of 2201 phase decomposition for higher Ts. The assist enhances Cu atom incorporation, and reduces excess Bi-composition and Bi-related impurity phases in the film. The assist also has effects on surface smoothing and modifies the c parameter. These depend more strongly on the assist ion flux than on energy, indicating that the enhancement of 2201 nucleation is the important mechanism for these effects, as well as the preferential resputtering by the assist ions.
Method for the study of grain boundary diffusion effects by Auger electron spectroscopy sputter depth profiling
Authors: Lee Y. S. , Lim K. Y. , Chung Y. D. , Whang C. N. , Woo J. J. , Lee Y. P.
Published: July 2002

We investigated the effects of grain boundary diffusion (GBD) at elevated temperatures on Auger electron spectroscopy sputter depth profiles of Co-Ag bilayers by using the modified surface accumulation method which is proposed for the first time to our knowledge. The results agree well with our previous ones done by the surface accumulation method. The GBD parameters for Ag in Co along the grain boundaries were found to be as follows: the activation energy and pre-exponential factor for GBD are 0.425±0.025 eV and ∼1×10−7cm2, respectively. These indicate that the modified method is an effective alternative in studying the effects of GBD, and may be applied to complicated systems for which the previous method does not hold.
Evidence for covalent attachment of purple membrane to a gold surface via genetic modification of bacteriorhodopsin
Authors: Brizzolara Robert A. , Boyd Jennifer L. , Tate Ann E.
Published: July 2002

The objective of this work is to covalently attach bacteriorhodopsin (BR) to a gold surface via genetic substitution of cysteine for serine (S35C) at the 35th amino acid position. Samples of BR-containing purple membrane (PM) on gold were evaluated using atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). AFM images reveal a surface coverage of S35C-containing PM fragments of approximately 25%. XPS measurements reveal a small excess of sulfur for S35C-containing PM on gold, and a much larger excess of sulfur on wildtype-containing PM on gold. In both cases, the excess sulfur is covalently bound to the gold surface and appears to originate from dissociated methyl mercaptan groups from methionine residues on the external surfaces of BR. We conclude that the quantity of excess sulfur is smaller for S35C than for wildtype because the S35C’s sulfhydryl binds some PM fragments to the surface, reducing the quantity of methyl mercaptan that can bind to the surface. It then follows that the rather low coverage of S35C-containing PM fragments on gold is due to interference of the methyl mercaptan groups with the binding of S35C-containing PM fragments to the surface. Coverage might be increased by immobilizing S35C-containing fragments on a functionalized surface using a heterobifunctional cross-linker, thereby preventing dissociation of methyl mercaptan groups from BR, and by using smaller PM fragments.
Fowler–Nordheim stressing of polycrystalline Si oxide Si structures: Observation of stress induced defects in the oxide, oxide/Si interface, and in bulk silicon
Authors: Jiang J. , Awadelkarim O. O. , Werking J. , Bersuker G. , Chan Y. D.
Published: July 2002

Deep level transient spectroscopy and capacitance voltage measurements were used to study the Fowler–Nordheim (FN) stress induced defects in n+-polycrystalline-Si/90-Å-thick-SiO2/p-Si substrate capacitors. These capacitors were fabricated using a 0.5 μm complementary metal–oxide–silicon process flow. The capacitors were subjected to constant voltage FN stress at temperatures between 300 and 50 K. At all stress temperatures positive charge buildup was observed to take place in the gate oxide, whereas at stress temperatures ⩾150 K a band of hole traps centered at 0.55 eV above the top of the valence band and ∼0.2 eV wide was seen to be induced by the stress. However, FN stress below 150 K was observed to induce two bulk silicon defects 600 to 1000 Å from the SiO2/Si interface. One of these defects is configurationally bistable with electronic states at 0.35 and 0.30 eV below the conduction band edge Ec. The second defect gives rise to an electron trap located at Ec−0.37 eV.
Surface chemistry of the N-containing precursor dimethylhydrazine on Cu
Authors: Sun Y.-M. , White J. M. , Kamath A. , Kwong D. L.
Published: July 2002

This article focuses on the surface chemistry of an N-containing precursor, dimethylhydrazine (DMH), on Cu. DMH both adsorbs and decomposes on clean Cu at room temperature. N–N, C–N, and N–H bonds are cleaved, resulting in the immediate desorption of N2 and CH4 and leaving DMH species that, during subsequent heating, lead to N2 and CH4 desorption. There is evidence that CH3 groups dehydrogenate to form methylene, CH2, that inserts into Cu–C and Cu–N bonds, and leads to C2H4, C2H5N; C3H7NH2, and C3H6NH2. The activation energy of DMH decomposition on the clean surface is about 10.8 kJ/mol. The 300 K reactivity of a clean Cu surface is reduced by repeated DMH doses and temperature programmed desorption. Passivation is attributed to the alteration of active surface sites by small amounts of retained reaction products, presumably containing C, the concentration of which lie below x-ray photoelectron spectroscopy detection limits. DMH decomposition and surface synthesis pathways are discussed.
Comparison between ultraviolet-photoelectron spectroscopy and reflection high-energy electron diffraction intensity oscillations during Si epitaxial growth on Si(100)
Authors: Enta Y. , Irimachi H. , Suemitsu M. , Miyamoto N.
Published: July 2002

In ultraviolet-photoelectron spectroscopy on a Si(100) surface during solid-source or gas-source molecular-beam epitaxy (MBE), intensity oscillations of photoelectrons from the valence-band surface states are observed. Recent studies by authors [Enta et al., Surf. Sci. 313, L797 (1994)] have revealed that the photoelectron intensity oscillations (PIOs) most probably originate from an alternation between the 2×1 and the 1×2 surface reconstructions during growth. This model consequently suggests that the period of the oscillations corresponds to the growth time of 2 ML. To confirm this relation, reflection high-energy electron diffraction (RHEED) intensity oscillation was measured during gas-source MBE, using Si2H6 under identical growth conditions with those used for PIO observations. The oscillation period at the half-order diffraction spots of RHEED agreed well with that of PIO at various Si2H6 pressures, providing a direct support for the above interpretation for the origin of PIO.
Effect of interface on the characteristics of functional films deposited on polycarbonate in dual-frequency plasma
Authors: Klemberg-Sapieha J. E. , Poitras D. , Martinu L. , Yamasaki N. L. S. , Lantman C. W.
Published: July 2002

Functional coatings are used in increasingly demanding applications that require specific optical characteristics, resistance to damage and good adhesion to different types of substrate materials, including polymers. In the present work we investigate thin films fabricated by low pressure plasma-enhanced chemical vapor deposition, using a dual-mode microwave/radio-frequency (MW/RF) plasma approach. The substrates are exposed to the principal dense microwave (MW, 2.45 GHz) plasma, while applying a RF-induced negative bias voltage. This technique provides independent control of the energy and flux of bombarding ions, and it allows one to deposit dense films at ambient substrate temperature at a high rate over large areas. We optimized the deposition process for amorphous hydrogenated silicon nitride (SiN1.3) obtained from SiH4/NH3 mixture. Using an average ion energy of about 150 eV, we obtained low-stress (<100 MPa) films with a refractive index of 1.89, at deposition rates around 30 Å/s. MW plasma pretreatments with different gases have been investigated in order to further enhance adhesion of the SiN1.3 coatings on polycarbonate (PC) substrates—the highest adhesion, determined by the microscratch- and the adhesive-tape peel tests, was found when PC was pretreated in N2 plasma. The adhesion is related to the thickness and chemical structure of the interface. In fact, spectrophotometry and x-ray photoelectron spectroscopy analysis suggest the presence of a graded interface region, up to 40 nm thick, part of which contains Si–C, Si–O–C, and Si–N–C chemical links.
Minimizing metal etch rate pattern sensitivity in a high density plasma etcher
Authors: Gabriel Calvin T. , Zheng Jie , Abraham Susan C.
Published: July 2002

The variation of metal etch rate with spacing between metal lines was measured from scanning electron microscopy micrographs of TiN/Al–0.5%Cu/TiN wafers etched in a high density inductively coupled plasma metal etcher. The metal etch rate was found to depend on the spacing between metal lines, with etch rate significantly decreasing in very narrow spaces for a conventional Cl2/BCl3 chemistry. The effect of several process parameters on this etch rate dependence was studied. It was found that the dependence could be reduced significantly, and the traditional rolloff of etch rate as spacing decreases could be eliminated, by the choice of process gases. Addition of 15% CHF3 to a BCl3/Cl2 mixture resulted in a 50% reduction of the effect, and addition of both CHF3 and Ar under certain process conditions resulted in almost complete reduction or even inversion of the effect. A mechanism is proposed for this improvement: sidewall passivants like CHF3 reduce the sticking coefficient of chlorine on aluminum, boosting reactant flux to the bottom of high aspect ratio openings.
Synchrotron radiation induced H2O desorption from aluminum surfaces
Authors: Chen J. R. , Hsiung G. Y. , Huang J. R. , Chang C. M. , Liu Y. C.
Published: July 2002

Photon stimulated desorption from aluminum surfaces was studied by irradiating an aluminum chamber in the 1.3 GeV electron storage ring at the Synchrotron Radiation Research Center. Experiments on aluminum samples were also performed in an experimental station. The behavior of water vapor, the main concern in this work, was quite different from that of the other gases. A time delay between the peak of the H2O signal and the starting time of irradiation was observed. Effects due to different conditions such as beam current, pumping speed, and beam dose of the storage ring were investigated.
Application of a high critical temperature superconductor bearing for high vacuum measurement
Authors: Chew A. D. , Chambers A. , Troup A. P.
Published: July 2002

A novel and ultrahigh vacuum compatible, high critical temperature superconductor suspension is described in its application to a rotating disc vacuum gauge. The noncontacting and robust suspension comprises a permanent magnet (and attached disc) suspended freely in a vacuum and below a liquid nitrogen cooled YBa2Cu3O7 pellet which is held outside the vacuum chamber. This configuration supersedes a fiber suspension. Molecular torque developed from a high speed disc accelerates the suspended disc and facilitates a measurement of total pressure. The offset of the superconductor suspension (analogous to that of the spinning rotor gauge) is about 5×10−6 mbar, nitrogen equivalent. After 50 h the offset reduced by up to 21% of its initial value. In the range 1.6×10−3–3.6×10−6 mbar, the pressure measured using this device was within ±20% of that measured by a spinning rotor gauge; at lower pressures the agreement with an ionization gauge degraded to ±80%. Improvements in pellet structure reduce internal losses in the bearing and in the offset term, by a factor of 10, and should enable measurements in ultrahigh vacuum.
Intermixing in Fe/Cr (001) multilayers: Density functional calculations
Authors: Singh David J.
Published: July 2002

Fe/Cr (001) multilayers containing perfect as well as intermixed interfaces were investigated using density functional calculations and an ordered supercell approach. The results show that the qualitative differences between theoretical expectations for perfect interfaces and experimental data for real Fe/Cr multilayers can be understood in terms of intermixing. Both phase shifts and reductions in magnitude of the coupling are found.
Surface chemical analysis: Comparing and exchanging data
Authors: Seah M. P.
Published: July 2002

The current status of repeatability and reproducibility in interlaboratory studies in surface analysis using Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), dynamic and static secondary ion mass spectrometries (SIMS), and sputtering are briefly reviewed. Repeatabilities are governed by the quality of the instrument design and the procedure for instrument use. Reproducibility from laboratory to laboratory requires the use of transfer standards which may be technique wide, as in the cases of AES and XPS, or sample specific as in the case of dynamic SIMS. Repeatabilities of intensity ratios with good instruments and procedures should be better than 2% for all techniques for suitable samples. Repeatabilities of the energy scale in good electron spectrometers average around 0.025 eV. The reproducibilities in quantification have improved to around 10% relative standard deviation. The measurement infrastructure is developing well and it needs to be reinforced by the relevant documentary standards to enable analysts to transfer and exchange data, at the above levels, and to improve it where necessary. The analyst needs methods of validating both equipment and software and the laboratory management, in turn, needs methods of testing the analyst’s proficiency. These aspects need development of appropriate documentary standards, as pioneered by ASTM Committee E-42 on Surface Analysis and, at an international level, by the International Standards Organization Technical Committee 201 on Surface Chemical Analysis.
MAXMIND—Data storage and evaluation environment in surface analysis
Authors: Brandl K. W. , Störi H.
Published: July 2002

The problem of surface-analytical data exchange for multi-method analysis has to be solved in order to use data from a number of different surface analytical instruments [such as Auger electron spectroscopy (AES), scanning Auger microscopy, x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy, scanning tunneling microscopy, atomic force microscopy, etc.] in a synergistic manner. As only a standardized data exchange format can guarantee the independence of proprietary measurement systems without adaptation of existing software, the public domain software package called the management and exchange of method independent data (MAXMIND), was developed based on the hierarchical data format. A first key feature of MAXMIND is the strict separation of the software design and the development of data dictionaries (sets of parameters for various methods); thus data dictionaries can be modified without recompiling the software. The data dictionaries included in the present version of MAXMIND are in the case of AES and XPS based on published guides.12345 Dictionaries for other methods have been set up by the authors and are to be considered as preliminary. Besides a graphical user interface based on the X11 interface, a second key feature is that interfaces have been made from MAXMIND to the “matrix laboratory” (MATLAB) and a processing package from Khoral Research, Inc. (KHOROS), which are both well-known data analysis environments in the surface analysis and image processing community. Using one of these interfaces, a combination of either MATLAB or KHOROS in conjunction with MAXMIND forms an integrated data storage and evaluation environment.
Reaction of hydrogen with O/Ru(001) and RuOx films: Formation of hydroxyl and water
Authors: Li S. Y. , Rodriguez J. A. , Hrbek J. , Huang H. H. , Xu G.-Q.
Published: July 2002

The interaction of gas phase atomic hydrogen with chemisorbed oxygen on Ru(001) and RuOx films has been investigated by means of Auger electron spectroscopy and thermal desorption spectroscopy at surface temperatures between 120 and 320 K. Although molecular hydrogen does not adsorb on oxygen saturated Ru(001) or RuOx films even at 120 K, atomic hydrogen reacts with oxygen on Ru(001) surfaces, and both D2 and D2O desorb at temperatures below 500 K. The 2Dgas+Oad→D2Ogas reaction is approximately six times faster at 310 K than at 120 K. For RuOx films, a unity reaction probability was found at oxygen coverages above 3 monolayers (ML), while it decreased to 0.4 at Θ0<3 ML. Such variation can be attributed to a change in the structure of the oxide film. The reaction probably follows an Eley–Rideal mechanism where gas phase atomic hydrogen reacts with oxygen prior to thermal accommodation within the surface. The desorption of water is the rate limiting step at surface temperatures below 200 K, whereas the formation of water is the rate limiting step at higher temperatures.