bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion beam analysis for depth profiling
Authors: Knapp J. A. , Barbour J. C. , Doyle B. L.
Published: July 2002

New techniques in the application of ion beam analysis to depth profiling in solids are briefly surveyed. These include (1) non-Rutherford backscattering analysis using high energy beams, (2) resonant nuclear reaction analysis, (3) time-of-flight elastic recoil detection spectrometry, and (4) heavy ion backscattering spectrometry. The last can be used for very precise depth profiling in one configuration, or as a very sensitive trace contaminant analysis in another configuration.
Oxidation of Mg adsorbed on Ru(001): A photoemission study
Authors: Malik I. J. , Hrbek J. , Shek M.-L. , Bzowski A. , Kristof P. , Sham T. K.
Published: July 2002

We studied the interaction of oxygen with Mg overlayers adsorbed on Ru(001). Soft x-ray synchrotron radiation was used to explore photoemission from the valence band, the O 2p, O 2s, and Mg 2p levels, as well as intra- and interatomic Auger processes. The photoemission results are complemented by thermal desorption data. The O/Mg/Ru system shows photoemission features characteristic of molecular orbitals of a dioxygen species.
Applications of ab initio quantum molecular dynamical relaxation: Silicon(111)-5×5 surface reconstruction and aluminum deposited on silicon(100)
Authors: Adams Gary B. , Sankey Otto F.
Published: July 2002

We present two applications of a first principles quantum molecular dynamics technique. In the first, we have determined the relaxed atomic geometry and the corresponding electronic structure of the Si(111) surface in the 5×5 dimer–adatom-stacking fault structure. We find a unique low temperature behavior for this surface, namely, corrugation of the adatoms on each side of the 5×5 unit cell, which we verify by the use of perturbation theory. In a second application, we have determined the relaxed atomic geometry and the corresponding electronic structure of the Al:Si(100) surface in both the 2×2 and the 2×3 reconstructions. In particular, we find that the Al dimers on this surface are parallel to, rather than perpendicular to, the Si dimer direction.
Energy surface and dynamics of Si(100)
Authors: Gryko Jan , Allen Roland E.
Published: July 2002

Our earlier first-principles-based simulations indicated that Si(100) exhibits unusual dynamical behavior. Here we report a calculation of the total energy surface that helps one to understand this behavior, and additional simulations that show some new features.
Observation of atomic step morphology on silicon oxide surfaces
Authors: Homma Yoshikazu , Suzuki Mineharu , Yabumoto Norikuni
Published: July 2002

Atomic step structures on oxidized Si(111) surfaces are investigated by scanning electron microscopy with grazing incidence of the primary electron beam and by scanning force microscopy. Atomic step structures similar to those on clean Si(111) are preserved on a thermally oxidized surface at 900 °C in dry O2 as well as on a naturally oxidized surface in air. The atomic step structures are also discernible on the SiO2/Si interface when a 20-nm-thick oxide layer is removed by HF etching. These results indicate that once a clean surface with atomic steps and terraces is formed, the surface morphology is stable against oxidation, and that the initial surface morphology is preserved as oxidation proceeds.
Structural and chemical composition investigation of thin lead zirconate titanate films
Authors: Huffman M. , Goral J. P. , Al-Jassim M. M. , Echer C.
Published: July 2002

Thin lead zirconate titanate (PZT) ferroelectric films are currently being used in a variety of applications. One of the more novel uses is in nonvolatile random access memory devices. As part of such a memory device, these PZT films undergo a significant amount of thermal cycling during standard semiconductor processing. Therefore, it is of considerable importance to understand the evolution of the PZT film morphology and composition as a function of temperature. The ferroelectric domain and PZT grain boundary evolution in sputtered and sol-gel deposited PZT films has been recorded. Hot stage transmission electron microscopy has been used for this investigation between room temperature and 600 °C. The ferroelectric domains in all the samples are very distinct. The transition from the tetragonal to the cubic paraelectric phase was observed at Curie temperatures (TC) close to those expected for the various compositions analyzed. Zr/Ti ratios in these films ranged from 48/52 to 30/70. Since the films are polycrystalline and some compositional inhomogeneity exists from crystallite to crystallite, a distribution of transition temperatures has been observed throughout a single PZT film. This result fits very well with electrically measured values of TC, which exhibit very broad maxima. Nanoprobe analysis of the composition of these films was performed before and after heating to see if there are any significant changes. Line scans were used to analyze grain and grain boundary composition in both plan view and cross section. The difficulties of obtaining reliable analytical results are explored in detail.
Electron donor–electron acceptor interactions in surface metal–metal bonds: The Cu/Re(0001) and Pd/Re(0001) systems
Authors: Rodriguez José A. , Campbell Robert A. , Goodman D. Wayne
Published: July 2002

The interaction of Cu and Pd with Re(0001) has been examined by means of temperature programmed desorption and x-ray photoelectron spectroscopy. A Cu monolayer desorbs from Re(0001) at a temperature of 1180 K and has an electron density similar to that of the surface atoms of Cu(100). Pd adatoms on Re(0001) are electronically perturbed with respect to surface atoms of Pd(100), desorbing at a temperature of 1450 K. By comparison of these results with those previously presented in the literature for Pd and Cu adlayers, we found that there is a correlation between the electronic perturbations in the adlayers, the strength of the admetal–substrate bonds, and the ability of the adatoms to chemisorb CO. The results indicate that formation of a surface metal–metal bond leads to a gain in electrons by the element initially having the larger fraction of empty states in its valence band. This behavior is contrary to that observed in bulk alloys, indicating that the electronegativities of the surface atoms are substantially different from those of the bulk. A method to establish a scale of surface electronegativities is proposed.
Reactive ion etching of HgCdTe with methane and hydrogen
Authors: Elkind J. L. , Orloff Glennis J.
Published: July 2002

Reactive ion etching (RIE) of HgCdTe using hydrogen and methane/hydrogen mixtures has been studied. The hydrogen RIE was found to form a Cd-rich residue which resulted in a very rough surface and which gradually inhibited via formation. The addition of methane (∼25%) resulted in smoother etched surfaces and ultimately deeper vias without the residue. Aspect ratios (via depth to width) of ∼0.9 were attained using this RIE process. A very strong HgCdTe surface orientation dependence was noted regarding both etch rate and etched surface morphology. For short etch times, the [111B] surface etched faster than the [100] surface, which etched faster than the [111A] surface. On the other hand, the [111A] etched surface was far smoother than either the [111B] or [100] surfaces.
Hybrid Cu–Al beam pipe for KEK B factory
Authors: Ishimaru Hajime , Momose Takashi , Suetsugu Yusuke , Hirayama Hideo
Published: July 2002

A hybrid Cu–Al beam pipe is proposed for the KEK B factory. The pipe design is based on the idea that the best characteristics of each material should be utilized to obtain lower cost and a photodesorption yield comparable to that of an all-copper vacuum beam pipe. Copper is used in the part directly irradiated by synchrotron radiation photons while aluminum alloy is used in the parts irradiated only by reflected photons. A fabricated model of the hybrid Cu–Al beam pipe is presented, and can be realized using standard manufacturing techniques. For the present, the desorption yield of aluminum alloy is estimated as about five times higher than that of copper. Using this value, the estimated photodesorption yield is about three times higher than that of an all-copper beam pipe, at a photon dose greater than 1021 photons/m. The photodesorption yield of the aluminum alloy must be reduced, and several methods are suggested to obtain a yield comparable to copper. Using EGS4, the estimated radiation levels outside of the hybrid beam pipe in the normal bending sections of both the high energy ring and the low energy ring for the KEK B factory are comparable with those in the existing TRISTAN accumulation ring. In the wiggler sections, however, an additional order of magnitude in shielding is required to reach the same levels. The present estimated cost of the hybrid beam pipe is one third that of an all-copper beam pipe and is 0.6 million yen per meter.
Perspectives and limitations of vacuum microtubes
Authors: Mil’shtein S. , Paludi C. A. , Chau P. , Awrach J.
Published: July 2002

The edge or blade type emitter is the basic element of design for vacuum microtubes presented in this article. Several devices are tested which consist of vertical and horizontal structures with two (diode), three (triode), and four (tetrode) electrodes. The experimental results show some correlation with Fowler–Nordheim (FN) theory. In cases where emission occurs, but FN theory is not followed, the results indicate limitations in the ability to model, and to account for those factors which control emission. The cold emission from the grid (gate) electrode, and the phenomena of ‘‘forming’’ a metal surface are also discussed. The difficulty in controlling cold emission makes these devices inflexible. One can conclude from analyzing the experimental results presented in this paper, as well as similar results obtained from other research, that cold emission devices have a number of drawbacks and limitations regardless of the design of the emitter. To mitigate these drawbacks and limitations, a new design for a vacuum microtube is presented which operates on the basis of photoemission, and offers an alternate control mechanism for more stable emission.
Infrared reflection–absorption spectroscopy of a model catalyst in a flow reactor: CO oxidation on Pt(100)
Authors: Hong Seongsik , Richardson Hugh H.
Published: July 2002

Infrared and mass spectral data from a continuous flow ultrahigh vacuum reactor of CO oxidation over Pt(100) are presented. Steady states corresponding to a high reaction rate branch and a low reaction rate branch are observed. For surface temperatures below 460 K, the adsorption of CO is detected in the high reaction rate branch as a new band at 1630 cm−1. A transition between the high reaction rate branch and the low reaction rate branch is seen at an unstable stationary point, where the 1630 cm−1 band disappears and vibrational bands corresponding to island growth of an adlayer of CO grow in. CO in the adlayer is adsorbed in top and bridged sites (bands at 2089 and 1880 cm−1) and the island growth is inferred from the lack of frequency shift with band growth. At surface temperatures of 460 K and greater, only bands from the adlayer of CO are observed and they are only detected in the low reaction rate branch. The transition from the low reaction rate branch to the high reaction rate branch goes through another unstable stationary point, where the disappearance of the CO adlayer is seen. A hysteresis in the CO2 production rate with CO partial pressure is observed between the high and low reaction rate branches.
Experimental scaling laws for multipolar electron cyclotron resonance plasma sources
Authors: Sze F. C. , Asmussen J.
Published: July 2002

The performance of five different diameter multipolar electron cyclotron resonance (ECR) plasma sources is evaluated by comparing (1) ion production energy costs, (2) microwave coupling efficiency, (3) electron temperatures and ion energies, and (4) discharge absorbed power density versus input power and pressure. The experimental measurements demonstrate that ECR plasma source performance is a function of operating pressure, gas type, input power, discharge size, and applicator size. When using 2.45 GHz excitation the most efficient and optimum plasma source sizes have diffusion lengths of 1.5–2.5 cm and associated discharge diameters of 12.5–25 cm. Microwave coupling efficiencies are in excess of 90% and ion production energy costs are 600–700 eV/ion or less and absorbed power densities are less than 1 W/cm3. The 25 cm diam discharges are the most efficient with ion energy production costs of 400–200 eV/ion and absorbed power densities are less than 0.2 W/cm3. Small sources have lower microwave coupling efficiencies and much higher ion production energy costs and operate with very high absorbed power densities and electron temperatures. When the applicator size is increased to 30 cm or more, performance of a source excited with 2.45 GHz is limited by the ability to control the exciting electromagnetic modes.
Characterization of the virtual source in an electron-beam evaporation system
Authors: Miller Mark D. , Biltoft Peter J. , Benapfl Mike
Published: July 2002

We have determined the size and location of the ‘‘distributed virtual source’’ of an electron-beam evaporation source using a mask/shadowing technique. By depositing copper through slit masks onto glass witnesses, then measuring the width of the deposition pattern it was possible to calculate the size and location of the virtual source. We determined the source size to be 3.9±1.0 cm side to side, 4.8±0.5 cm front to back, 4.4±0.5 cm across one diagonal and 4.4±0.5 cm across the other diagonal while its location was 9±3 cm above the hearth. The size of the virtual source is dramatically larger than the area created by the electron beam rastering across the surface of the muffin. This data may be useful when high-tolerance vapor deposition into porous materials is desired (as in microchannel plates). In this application, the angle between the virtual source and the substrate may be critical for effective coating of the channels.
Reaction pathways for ArF excimer laser assisted tungsten chemical vapor deposition from a WF6–H2 gas mixture
Authors: Heszler P. , Carlsson J. O. , Mogyorósi P.
Published: July 2002

Photolytic tungsten chemical vapor deposition by an ArF excimer laser from a WF6/H2/Ar gas mixture is a very complicated process with reactions occurring both in series and in parallel. In this article different reaction pathways were modeled and compared with experimental deposition rate data. The absorption cross section for WF6 was measured to 1.7×10−18 cm2 at the ArF excimer laser wavelength of 193 nm. From a rate equation model, it was concluded that the direct photolytic contribution to the deposition rate was negligible. Moreover, reduction of tungsten subfluorides by hydrogen atoms, formed in reactions between photolytically released fluorine atoms and molecular hydrogen, was also found to be negligible. However, photolysis in combination with various radical reactions generate a relatively high concentration of tungsten subfluorides (WF3, WF4, and WF5). Thermochemical calculations indicate that H2 reduction of tungsten subfluorides to solid tungsten, forming clusters in the vapor, is highly probable. Among the different cluster nucleation mechanisms polymerization of tungsten subfluorides seems to be an important step. This also explains the influence of WF6 partial pressure on the deposition rate.
Corrosion behavior of steel coated with thin film TiN/Ti composites
Authors: Hübler R. , Schröer A. , Ensinger W. , Wolf G. , Stedile F. C. , Schreiner W. H. , Baumvol I. J. R.
Published: July 2002

Thin film multilayered TiN/Ti composites are investigated as a possible alternative for protective coating of steels. Corrosion tests based in cyclovoltametry made in a buffered acetic acid solution reveal that multilayered coatings of this kind with total thickness of 0.5 μm perform as well as 3 μm single layered coatings. A discussion is presented on the influence of the multilayer parameters on this beneficial effect.
Nitridation of GaAs(110) using energetic N+ and N+2 ion beams
Authors: DeLouise L. A.
Published: July 2002

X-ray photoelectron spectroscopy is used to monitor surface stoichiometric and electronic changes that result from reactive nitrogen ion beam bombardment of GaAs(110) at room temperature. This treatment leads directly to the formation of a thin GaN reaction layer. The nitride layer thickness is found to depend on ion dose, incident energy (0.5–3 keV) and composition (N+, N+2) in a manner that suggests that the growth kinetics are limited by sputter desorption of the growth surface. A comparison of results is made between 1 keV Ar+ and 1 keV N+2 bombarded surfaces to distinguish to what extent changes in the surface composition and band bending are physical bombardment or chemically induced. We demonstrate that bombardment-induced crystal lattice imperfections are a dominant source of electronically active band gap acceptor states. From band bending measurements evidence is given that suggests N+2 ion bombardment yields a lower concentration of charge acceptor states in comparison to Ar+ ion bombardment. We attribute this behavior to the formation of strong GaN bonds that help to minimize the group V surface depletion and lattice disorder.
Dependence of etch characteristics on charge particles as measured by Langmuir probe in a multipolar electron cyclotron resonance source
Authors: Sung K. T. , Juan W. H. , Pang S. W. , Dahimene M.
Published: July 2002

A multipolar electron cyclotron resonance (ECR) plasma source was characterized by Langmuir probe measurements and the charged particle energy and density are related to photoresist etch rate. Ion density was found to increase with microwave power but decrease with source distance, and is independent of rf power and flow rate. Among the different gases investigated, Ar plasma was found to have higher ion density compared to O2, N2, and Cl2 discharge. Ion density peaked at 5 mTorr for Ar and 2 mTorr for O2 plasma. For a N2 plasma, the maximum ion density was found to occur at 10 mTorr at 3 cm and 2 mTorr at 23 cm below the ECR source. Electron temperature is ∼3 eV for pressure ranging from 1 to 5 mTorr but decreases to 2 eV at 20 mTorr. Photoresist etch rate follows the same trend as ion density. It increases with microwave power and decreases with source distance. On the other hand, photoresist etch rate increases with rf power and flow rate, even though the ion density remains constant. This suggests that photoresist etching also depends on ion energy and concentrations of neutral species. Ion density uniformity of ±1% for a N2 plasma was measured across the central 24 cm along the stage at 23 cm below the source. For a source distance between 3 and 23 cm, uniformity of ±3% was obtained over a 12 cm diam region on the stage. In an O2 plasma, photoresist etch rate uniformity of ±2% was measured for a 10 cm diam wafer and the corresponding ion density uniformity was ±1%.
Characterization of electron cyclotyron resonance microwave plasma under critical configuration of magnetic field
Authors: Bai Peiguang , Liu Jian , Parikh Nalin , Swanson Max
Published: July 2002

We have constructed a chemical vapor deposition/etching system consisting of a 2.45 GHz microwave generator (ASTeX S-1000) and two movable coaxial magnetic coils. A unique rotatable planar Langmuir probe was designed to characterize the plasma. The Langmuir probe measurements showed an anisotropic character of the plasma which was mainly a result of the magnetic field gradient and propagation direction of the microwaves. By placing the coils at certain distances from the microwave window and adjusting the current through the coils, a critical condition was established, known as ‘‘high mode plasma.’’ In this high mode, the plasma ion density was more than four times that in the normal mode. The physical basis of the high mode involved placing the electron cyclotron resonance critical field (875 G) just in front of the microwave window with a positive magnetic field gradient toward the direction of microwave propagation. This condition produced a high absorption of microwave power and also prevented charged particles from escaping from the plasma.
Characterization of hydrogen and oxygen atoms in SiN films produced by plasma-enhanced reactive sputtering
Authors: Sugimoto Iwao , Yanagisawa Keiichi , Kuwano Hiroki , Nakano Satoko , Tago Akio
Published: July 2002

Silicon nitride films are prepared by helium-excited magnetron radio-frequency sputtering. Excitation energy transfer from He to N2 and existence of hydrogenation and oxidation source (O+ and OH⋅) in the plasmas are confirmed by optical emission spectroscopy. The structure and characteristics of the resultant films depend on the gas pressure during sputtering: Films produced at pressures above 5 Pa are etched rapidly in a buffered hydrogen fluoride solution and have low refractive indices because their structure is coarse and rich in oxygen and hydrogen or both.
Enhancement of Schottky barrier height to n-GaAs using NiAl, NiAl/Al/Ni, and Ni/Al/Ni layer structures
Authors: Chen C.-P. , Chang Y. A. , Kuech T. F.
Published: July 2002

The Schottky barrier height of NiAl/n-GaAs, NiAl/Al/Ni/n-GaAs, and Ni/Al/Ni/n-GaAs diodes has been studied by the current–voltage (I–V) and the capacitance–voltage (C–V) techniques. A NiAl alloy with 50 at. % Al was sputter deposited. An overall concentration of 50 at. % Al in NiAl/Al/Ni/n-GaAs contact structure, and two different overall concentrations of 25 and 60 at. % Al in Ni/Al/Ni/n-GaAs contact structure were prepared by sputter depositing different thicknesses of Ni and Al. An enhancement of the Schottky barrier height ranging from 0.1 to 0.13 eV was observed for each of the above contacts. The maximum barrier heights range from 0.95 to 0.98 eV for both the alloy and layered structure contacts, with ideality factors smaller than or equal to 1.1. The interfacial stability between the contacts and GaAs has been examined by cross-sectional transmission electron microscopy, glancing angle x-ray diffraction, and scanning Auger microscopy. A planar interface between contacts and GaAs was observed for both the alloy and layered contacts. A regrowth mechanism has been demonstrated to explain the enhancement of Schottky barrier height for these contacts.
X-ray absorption near edge structures of sulfur on gas-phase polysulfide treated InP surfaces and at SiNx/InP interfaces
Authors: Kwok R. W. M. , Huang L. J. , Lau W. M. , Kasrai M. , Feng X. , Tan K. , Ingrey S. , Landheer D.
Published: July 2002

The effects of a gas-phase polysulfide treatment on InP were studied by x-ray absorption near-edge structures (XANES) of both the sulfur L-edge and K-edge, and by x-ray photoelectron spectroscopy (XPS). Some passivated InP samples were encapsulated with about 4 nm of remote plasma deposited silicon nitride, and the chemical structure of the sulfur atoms at the interface was again determined by angle dependent K-edge XANES. Both XPS and L-edge XANES confirmed the presence of indium to sulfide bonding on the surface exposed to gas-phase polysulfide, and XPS confirmed the presence of more than one sulfide species. The angle dependence in K-edge XANES indicated that most of the surface sulfur atoms had their sigma bonds oriented along the (110) azimuth with a polar tilt angle of about 40°–60°. It is thus plausible that these sulfur atoms terminated the indium atoms on InP (100) in the form of In–S–In bridging bonds along the (110) azimuth. Vacuum annealing was found to cause desorption of some surface sulfide species and conversion of the residual sulfide species into one sulfide species, and to enhance the XANES angle dependence which again indicated the presence of the In–S–In bridging bonds along the (110) azimuth. Further angle dependent K-edge XANES analyses showed that such a sulfur bonding configuration was preserved even after the gas-phase polysulfide passivated InP surface was capped with silicon nitride deposited by remote plasma chemical vapor deposition.
Oscillating behavior of NO reduction reactions over rhodium studied on the atomic level
Authors: van Tol M. F. H. , Wouda P. T. , Nieuwenhuys B. E.
Published: July 2002

Rate oscillations during the reduction of NO by H2 and NH3 over Pt(100) have been studied earlier in our laboratories. A vacancy model involving the surface coverages of NO, O, and the hydrogen source (H or NHx) was proposed. This paper describes the NO–H2 reactions over Rh studied by field-emission microscopy (FEM). Oscillations in both electron emission current and the images observed were recorded. The dynamic behavior of these reactions, such as traveling wave fronts moving over the surface in an oscillatory manner and the occurrence of surface explosions, was displayed on a fluorescent screen with a spatial resolution of 20 Å. All processes were recorded in real time with a charged coupled device video camera. The results obtained for the NO reduction over Pt(100) are compared with the FEM results obtained with Rh, where many crystal planes were studied at the same time. Several types of oscillatory behavior have been observed, with large differences in periodicity, frequency, and amplitude. The type of oscillation is determined by the NO–H2 ratio, the temperature, and the surface structure. Using probe-hole FEM local oscillations were observed on several surfaces. The nature of the wave fronts observed during oscillatory behavior of the NO–H2 reaction over Rh involves the removal of the adlayer by reaction of NO and its dissociation fragments with hydrogen.
Existence of metastable molecular precursors to dissociative oxygen chemisorption on Si(111) and Si(100) at 40 K
Authors: Seo J. M. , Kim K. J. , Yeom H. W. , Park Ch.
Published: July 2002

The presence of metastable molecular precursor to dissociative oxygen chemisorption has been identified, for the first time, on Si(100) and Si(111) surfaces using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy at 40 K. Density of valence states for such species shows three distinct peaks at 1.8, 3.4, and 4.9 eV below the Fermi energy of substrates. The precursor stabilized on Si(100) at 40 K induces a large work-function increase of 1.5 eV at saturation coverage. It also gives rise to a shoulder to O 1s photoemission spectrum that is located at 1.2 eV lower binding energy than the O 1s peak of stable and dissociated oxygen species. It has been concluded that the major reason of a larger work-function increment at 40 K is the existence of a molecular precursor, of peroxy radical type, on Si(100) and Si(111). These results strongly suggest that there exists a general mechanism of oxygen adsorption onto silicon surfaces.
Test results for a sputter-ion pump with a new cell structure
Authors: Suetsugu Yusuke
Published: July 2002

A test model of a sputter-ion pump using a new cell structure was fabricated, where the magnets reside within the Penning cell assembly. The magnetic field intensity in the cell, pressure (P) dependence of discharge current, and pumping speed are measured. An axial magnetic field larger than 700 G is created inside the cells using commercial magnets with a remanent magnetism of 12 kG. The discharge current (I) is proportional to P1.0–P1.6 in the measured pressure range from 7.5×10 −9 to 1×10−6 Torr. Pumping speed for nitrogen is proportional to P0.6 on the average in the pressure range from 2×10−8 to 1×10−6 Torr and can be written as 0.05 I/P for P≥1×10−7 Torr. The test model is almost less than a half, in both volume and weight, compared to conventional ion pumps with almost the same nominal pumping speeds. It was confirmed experimentally that the new cell structure has the possibility of becoming a compact and light ion pump. The problem remains to optimize the cell sizes to moderate the pressure dependence of the discharge current, i.e., the pumping speed.
Importance of the molecular identity of ion species in reactive ion etching at low energies
Authors: Bello I. , Chang W. H. , Lau W. M.
Published: July 2002

Surface reactions on Si and SiO2 induced by CF+ and CF+2 from a mass-separated ion-beam system were studied with x-ray photoelectron spectroscopy. The bombardment energies were varied from 100 to 2±0.6 eV. We found that the surface reactions induced by fluorocarbon molecular ion bombardment largely depended on the molecular identity of the ion species, its degree of molecular dissociation upon impact, and the reactivity of the substrate surface. Four examples are shown to illustrate this new approach in altering reaction pathways. (1) CF+ bombardment at 2 eV: This led to molecular adsorption on both Si and SiO2and to SiFx formation on Si but little reaction with SiO2. (2) CF+/20 eV: This led to a higher probability of molecular dissociation upon impact and thereby opened the channel for CF disproportionation. The energy carried by the fragment was sufficiently high that the reaction channels with SiO2 was also opened. (3) CF+/100 eV: This resulted in efficient molecular dissociation and incorporation of atomic fragments rather deeply into the substrate. The channel for fluorocarbon formation was closed and those for SiC and SiF formation were opened. A silicon compound layer was formed on both substrates. (4) CF+2/100 eV: This resulted in molecular dissociation but the average energy per fragment was low. The channel for deep penetration was closed and most reactants were confined in the very top surface. CF disproportionation became a viable channel on both Si and SiO2 and a new channel was opened for etching SiO2 due to the availability of a sufficiently high local concentration of fluorine.
Accelerator based secondary-ion mass spectrometry for impurity analysis
Authors: Anthony J. M. , Kirchhoff J. F. , Marble D. K. , Renfrow S. N. , Kim Y. D. , Matteson S. , McDaniel F. D.
Published: July 2002

A Cs based secondary-ion mass spectrometry (SIMS) instrument has been constructed and coupled to a 3 MV tandem accelerator to produce an accelerator mass spectrometry system for impurity detection in materials. Exposed surfaces of the ion optical elements and sample holder hardware are fabricated from semiconductor grade Si to reduce sputter contamination of samples. The mass analyzed Cs beam generates negative secondary ions from the sample which are injected into the accelerator. Passage of the ions through the accelerator causes dissociation of the molecular interferences, so the system represents a truly ‘‘atomic’’ mass spectrometer. Quantification of the system is similar to SIMS, and sub parts per 109 detection limits of most transition metals have been demonstrated.
Growth, structural characterization, and stability of thin Cr/δ -Mn(001) superlattices
Authors: Pohl J. , Malang E. U. , Köhler J. , Bucher E.
Published: July 2002

We report on the epitaxial growth of Mn in the bcc high temperature modification δ-Mn on Cr(001) surfaces at room temperature using molecular-beam epitaxy (MBE). The growth of the individual layers can be well fitted by the layer-by-layer mode, and the Cr/Mn system forms separate layers. Cr/δ-Mn(001) superlattices with equal individual layer thicknesses show an increase of the average lattice parameter c with increasing superlattice spacing Λ, with a maximum stretching of 4% at layer thickness of about 11.5 Å each compared to the bulk value of Cr. A stretching of 6% was found for a Ge(001)Fe20(Cr30Mn7)×12.5 superlattice with different individual layer thicknesses. The in-plane lattice parameters are not affected with varying layer thicknesses. Increasing Mn-layer thicknesses to values larger than ≊23 Å lead to a phase transition of the δ-Mn. These results were obtained by means of Auger electron spectroscopy, reflection high energy electron diffraction, and x-ray diffraction.
Ion and neutral argon temperatures in electron cyclotron resonance plasmas by Doppler broadened emission spectroscopy
Authors: Tsu David V. , Young R. T. , Ovshinsky S. R. , Klepper C. C. , Berry L. A.
Published: July 2002

Neutral and ionic gas temperatures (Tn and Ti) are crucial parameters in the plasma processing of materials (etching and film deposition). Here we evaluate a method used for obtaining the temperatures, i.e., the Doppler broadening, of emission lines. We focus on Ar lines from microwave electron cyclotron resonance plasmas. We use the same technique for both ions and neutrals. Three factors are important in achieving accuracy: (1) knowing the correct instrument width at the central wavelength of each ion and neutral line, (2) understanding the noise-dependent variation in the measured widths, and (3) knowing how the magnetic field affects the spectra. We find that T can be determined to within ∼100 °C. Ti and Tn are typically found to be ∼0.5 and <0.1 eV, respectively for 0.5 mTorr Ar.
Effect of substrate pretreatment on growth of GaN on (0001) sapphire by low pressure metalorganic chemical vapor deposition
Authors: Hwang C.-Y. , Schurman M. J. , Mayo W. E. , Li Y. , Lu Y. , Liu H. , Salagaj T. , Stall R. A.
Published: July 2002

GaN films were grown on c-plane sapphire substrates by low pressure metalorganic chemical vapor deposition using a GaN buffer layer grown at lower temperatures. The quality and surface morphology of the GaN films were strongly affected by the surface pretreatment of the sapphire substrate before the growth of the GaN buffer layer and the GaN epitaxial layer. The films grown on pre-nitrided sapphire substrates exhibit improved electrical and optical properties over those of the films grown on unnitrided substrates even though the surface morphology became rougher. We have achieved a carrier concentration in the range of 2×1016–5×1017 cm−3 and electron mobility in the range of 250–300 cm2/V s at room temperature. The GaN films were evaluated by photoluminescence, Hall measurement, x-ray rocking curve, and transmission electron and scanning electron microscopies.
New method of tubular material inner surface modification by plasma source ion implantation
Authors: Sun Mu , Yang Si-ze , Li Bing
Published: July 2002

Plasma source ion implantation is a non-line-of-sight ion implantation technique for surface modification of materials, but that technique is only suitable for outer surface modification of hollow targets, not for inner surface modification. In this article we present a new method that applies to inner surface implantation. Preliminary experimental results show that this new method increases plasma density and uniformity inside the tubular target with the inner surface, generates a plasma sheath between the inner surface of the target and the plasma to implant the inner surface of the target effectively, and achieves a dose uniformity that is acceptable for industrial applications.
Designing low pressure systems with continuum models
Authors: Singh Vikram , Berney Butch , Krishnan Anantha
Published: July 2002

The predictions of a commercial Computational Fluid Dynamics (CFD−ACE) code were compared with experimental data to assess the validity of continuum models at the low operating pressures typical of plasma etch and chemical vapor deposition reactors. Pressure data for nitrogen flow (ranging from 100 to 500 sccm) in a fully automated vacuum test cell, were collected at Lam Research Corporation for comparison [P. K. Shufflebotham, T. J. Bartel, and B. Berney, J. Vac. Sci. Technol. B 13, 1862 (1995)]. Both two- and three-dimensional model predictions of pressure profiles at different sections of the test chamber were compared with data. Good agreement was observed between the measured and predicted values of pressure over the range of flow rates investigated. However, as expected, better agreement was observed for the higher flow rate (higher pressure) cases as compared to the lower flow rates. Further improvements in model predictions are anticipated with the inclusion of slip boundary conditions at solid surfaces.
Characterization of as-grown and annealed thin SiO2 films formed in 0.1 M HCl
Authors: Allegretto E. M. , Bardwell J. A.
Published: July 2002

Anodic oxidation at constant voltage has been used to produce oxide films of thickness 10–440 Å on Si(100). The electrolyte was 0.1 M HCl. Both annealed and as-grown samples were characterized by ellipsometry and Fourier transform infrared spectroscopy (FTIR), as well as by etch rate measurements in dilute HF. For as-grown samples, the voltage dependence of the thickness was determined. FTIR results for the as-grown films showed that the properties were dependent on the oxide thickness and not directly on the formation voltage. These results also provided a basis of comparison for the annealed samples. Demonstrably higher quality oxide films were characteristic of the annealed samples in comparison to the as-grown samples. The higher quality of the annealed samples was confirmed by measurement of the etch rate.
Effect of a surface layer on the stress relaxation of thin films
Authors: Thouless M. D. , Rodbell K. P. , Cabral C.
Published: July 2002

The salient features of the deformation mechanisms that can be obtained from stress–temperature plots of thin films deposited on substrates are discussed in this article. It is shown that the slope of the cooling portion of these plots at low temperatures indicates when dislocation-glide-dominated mechanisms are important and whether these occur without changes in microstructure. Furthermore, the behavior of the films during and after isothermal holds gives important information about the relaxation processes. Some of these general principles have been demonstrated by experimental observations on the shape of the stress–temperature curves for 1-μm-thick copper, silver, and aluminum films deposited on silicon. Two specific observations can be made based on these results. First, for the materials and conditions examined, isothermal holds do not affect the residual stress state upon subsequent cooling. Second, while the behavior of the copper and silver films can be qualitatively described by constitutive models appropriate for bulk forms of those materials, the behavior of aluminum is anomalous. It is believed that the properties of the aluminum film are dictated by the presence of the native oxide which suppresses relaxation mechanisms associated with diffusion and dislocation climb. To support this contention, copper, silver, and aluminum films were passivated by SiO2 layers. The shape of the stress–temperature plots for copper and silver changed qualitatively from one consistent with bulk relaxation mechanisms to one consistent with dislocation-glide mechanisms. The behavior of the aluminum film was unaffected by passivation.
Transient characteristics of nitrogen gas-pulsed electron cyclotron resonance plasma
Authors: Park Young Ju , Ozasa Kazunari , O’Keeffe Patrick , Aoyagi Yoshinobu , Min Suk-Ki
Published: July 2002

Transient optical emission characteristics of a nitrogen gas-pulsed electron cyclotron resonance (ECR) plasma have been investigated as a first step towards understanding the nature of a nitrogen gas-pulsed plasma. We observed different transient optical emission profiles for the first negative N+2, the second positive N2*, and the first positive N2* emission bands in nitrogen gas-pulsed ECR plasma that are closely related to the pressure changes in a discharge cavity of the plasma source. On the basis of the transient emission profiles, optical emission spectra over the wavelength range 300–700 nm were obtained for three specific time regions within the pulse. During the gas-pulsed injection period large ratios of N2*/N+2 (2.5–7.1) and low electron temperatures (1.2 eV) were observed. On the other hand, small ratios of N2*/N+2 (0.3) and high electron temperature (2.5 eV) were recorded 0.65 s after stopping the gas-pulsed injection. These observed N2*/N+2 ratios are interpreted in terms of different excitation processes and electron temperatures (Te) due to the surge of neutral N2 gas. The N2*/N+2 ratios in an ECR gas-pulsed plasma are 5–7 times higher than those in continuous wave plasma. Through timing optimization of the transient characteristics, nitrogen gas-pulsed ECR plasma is considered to be a useful candidate for high efficiency p-type high doping in Zn(Se,Te) semiconductors or for the plasma deposition of nitride films.
Epitaxy above 10−5 Torr: A student’s introduction to thin film growth and characterization
Authors: Longiaru Minsu , Krastev E. T. , Tobin R. G.
Published: July 2002

Highly oriented Cu films are grown under ‘‘dirty’’ conditions by simple thermal evaporation onto Si(100) substrates prepared by wet chemical etching. The films are grown and characterized using equipment and techniques appropriate to an advanced undergraduate laboratory. These experiments can provide students with an accessible introduction to advanced thin film techniques. The etched Si surface is extraordinarily chemically inert, enabling high surface quality to be maintained while the substrates are transferred in air into a low-vacuum (10−5 Torr) resistive evaporator during deposition. After deposition of ∼100 nm of Cu, the films are characterized by θ–2θ x-ray diffraction, using a student diffractometer with low x-ray intensity, detection sensitivity, and resolution. Clear evidence of oriented growth is found for the etched substrates, whereas films grown on unetched substrates are disordered. Other measurements suggest that the oriented films are in fact fully epitaxial.
Effect of Al ion implantation on the adhesion of Al films to SiO2 substrates
Authors: Su X. W. , Yang J. , Zhang Q. Y. , Cui F. Z.
Published: July 2002

The effects of Al ion implantation on the adhesion of Al films to SiO2 substrates were investigated. The thickness of the Al films was about 100 nm. 70 keV Al ion implantation was performed with doses of 5×1015 and 5×1016 Al+/cm2. The adhesion was measured by scratch test. It was found that the film adhesion could be improved by more than ten times after implantation. The composition depth profiles of Auger electron spectroscopy showed that implantation results in the formation of Al2O3 at the interface and interface mixing and/or roughening. These factors enhanced the film adhesion. However, tensile stress develops at high implantation dose, which is deleterious to the film adhesion. Transmission electron microscopy and x-ray diffraction investigation indicates that the grains of the film were refined by implantation.
Transparent and conductive Ga-doped ZnO films grown by low pressure metal organic chemical vapor deposition
Authors: Li Y. , Tompa G. S. , Liang S. , Gorla C. , Lu Y. , Doyle John
Published: July 2002

Highly transparent conductive Ga-doped zinc oxide (ZnO:Ga) has been deposited on 3 in.×4 in. Corning 7059 glass and other substrates using a high speed rotating disk reactor low pressure metal organic chemical vapor deposition system. Diethylzinc, oxygen, and triethylgallium were used as precursors. The films exhibit low resistivity, ∼2.6×10−4 Ω cm, high optical transparency (>85%) in the visible range, good adhesion, and are highly stable. The film properties were correlated with the growth conditions, including flow rate, temperature, pressure, and doping concentrations. The microstructural properties of the films, such as surface and interface morphology, crystallinity, and composition were studied using scanning electron microscopy, x-ray diffraction, and secondary ion mass spectroscopy. The resistivity and transmittance of the films were investigated by four-point probe measurements, photoluminescence spectroscopy, and optical absorption spectroscopy. In order to meet the needs for application to flat panel displays, the thermal stability of the Ga-doped ZnO films have been tested by a dc biased heater. The feasibility of film processing was also investigated through patterning and wet chemical etching.
Silicon crystal heating and thermocouple mounting designs
Authors: Nishino H. , Yang W. , Dohnálek Z. , Ukraintsev V. A. , Choyke W. J. , Yates J. T.
Published: July 2002

New mounting methods for a silicon crystal and a thermocouple are described. The sample mounted using this design exhibited a very uniform temperature distribution when resistively heated. Deviations between the silicon temperature and the mounted thermocouple temperature have been measured. Metal contamination on the surface of the sample mounted with a thermocouple by the new method was found to be below the detection limit of Auger electron spectroscopy. In addition, the emissivity data at 0.65 μm for silicon as a function of temperature has been fitted to a useful equation.
Intrinsic stress dependence of c-axis orientation ratio in PbTiO3 thin films deposited by reactive sputtering
Authors: Kweon S. Y. , Yi S. H. , Choi S. K.
Published: July 2002

Highly c-axis oriented lead titanate (PbTiO3) thin film, having a perovskite structure, was prepared on magnesium oxide (MgO) (100) single crystal using multiple cathode dc-magnetron sputtering at 600 °C. The film was annealed at 700 °C for up to 8 h. Both the c-axis orientation ratio P and c-axis lattice parameter of the film decreased with the increase of the annealing time. It was confirmed that the decrease of the c-axis lattice parameter with the annealing time was due to the relaxation of the intrinsic stress generated during deposition. These experimental results suggested that P was related to the intrinsic stress. The film deposited at various working pressures was examined in detail to confirm the intrinsic stress effect of P. P of 95% at 8 mTorr decreased to 60% at 70 mTorr. The pressure dependence of P was explained by the intrinsic stress change. Regardless of the sputtering condition, all P’s were reduced to 40% after annealing at 700 °C for 8 h. The difference in P between the before and after annealing was caused by the relaxation of the intrinsic stress. It was supposed that the remaining 40% of P after the heat treatment was caused, in the most part, by the ferroelectric phase transition.
Two-dimensional imaging of CF2 density by laser-induced fluorescence in CF4 etching plasmas in the gaseous electronics conference reference cell
Authors: McMillin Brian K. , Zachariah Michael R.
Published: July 2002

Spatially resolved two-dimensional maps of the relative CF2 density in low-pressure radio-frequency Ar/CF4/O2 discharges generated within a parallel-plate Gaseous Electronics Conference reference cell have been obtained using planar laser-induced fluorescence imaging. The experiments cover a wide range of pressure, composition, flow rate, and power deposition conditions (13.3–133.3 Pa, 1%–100% CF4, 1%–10% O2, 5–100 sccm, 3–35 W). Typically, the centerline (r=0) axial CF2 distribution was symmetric with the local peak occurring near the center of the electrode gap, but, in all cases, significant radial variations in CF2 density were observed (14%–45% standard deviation from the mean) with the peak density occurring near the edge of the discharge region. Varying the pressure led to significant changes in both the magnitude and spatial distribution of CF2 density, while varying the composition, flow rate, and power primarily affected only the magnitude of the CF2 density, with only modest changes in the spatial distribution. Based on image-averaged comparisons, the CF2 density increased with power, pressure, and CF4 mole fraction, decreased with addition of oxygen, and varied nonmonotonically with flow rate.