bluuebunny/crossref_metadata_2025 huggingface dataset:
Density of states and hot electron effects in ballistic electron emission spectroscopy
Authors: Ludeke R.
Published: July 2002

Ballistic electron emission microscopy (BEEM) and BEEM spectroscopy are reported for thin (≊50 Å) Cr layers on n-type GaP(110). BEEM images reveal that current transport across the interface occurs primarily in the vicinity of grain boundaries where the Cr is thinnest, and on small (<200 Å in diameter) surface patches that are relatively smooth and parallel to the interface. For the conventional electron injection mode, the collector current Ic exhibits pronounced but broad structures near tip biases VT of 4 and 6 V, whose origin is attributed to density of states effects in the semiconductor. For VT≳7 V, Ic was frequently observed to exceed the (constant) scanning tunneling microscope tip current. Under reverse bias (electron extraction) a novel hole current was observed for VT≳1.7 V, which, following an initial rise with increasing bias, would saturate and then decay, often leading to a polarity reversal for VT≳5.5 V. This behavior, as well as the large Ic observed at high forward bias, is attributed to impact ionization in the depletion region of the semiconductor. In addition to the conventional threshold in Ic at 1.31 V, attributed to electron transmission across the Schottky barrier into the X1 conduction band minima, a second, more pronounced threshold at 1.69 V was observed for the first time for GaP. It is assigned to electron transfer into the higher lying L1 and X3 conduction band minima.
Hydrogen chemisorption on ferromagnetic thin film surfaces
Authors: Mankey G. J. , Kief M. T. , Huang F. , Willis R. F.
Published: July 2002

We report measurements of hydrogen desorption and its effect on the magnetism of pseudomorphic ultrathin films of Fe, Co, and Ni on Cu(001). Hydrogen desorption is measured with thermal desorption spectroscopy (TDS) and changes in the magnetic properties with saturation hydrogen coverage are measured with the surface magneto-optic Kerr effect (SMOKE). TDS of hydrogen shows that Co films less than 2.5 monolayers thick do not completely cover the substrate, and that Co deposited at 300 K does not alloy with the Cu(001) substrate. By carefully controlling the thickness of the Ni films, we can tune the ferromagnetic Curie temperature to below the hydrogen desorption temperature. The thermal desorption of hydrogen from the paramagnetic Ni thin film surface is similar to that from bulk ferromagnetic Ni(001) indicating magnetism has no measurable effect on thermal desorption kinetics. Hydrogen is more weakly chemisorbed on ferromagnetic Co thin film surfaces and more strongly chemisorbed on ferromagnetic Fe thin film surfaces as compared to Ni(001). SMOKE measurements show hydrogen chemisorption produces a magnetically ‘‘dead’’ surface layer on Ni films, a reduction in the surface layer magnetism on Co films, and an enhancement in the surface layer magnetism on Fe films.
In situ detection of InGaAs strained-layer relaxation by laser light scattering
Authors: Celii F. G. , Files-Sesler L. A. , Beam E. A. , Liu H.-Y.
Published: July 2002

The utility of in situ laser light scattering (LLS) to monitor molecular beam epitaxy growth of InGaAs/GaAs strained layers is demonstrated. LLS signatures were correlated with ex situ characterization by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. Desorption of GaAs native oxide resulted in surface pit formation (3–10 nm depth, 30–100 nm width, density of 109–1010 cm−2) which caused a slight increase in LLS signal. Deposition of a GaAs buffer layer reduced the surface pitting, then formed a wavy surface morphology, with step deviations of ∼5 monolayers which were aligned in the (011̄) direction. InGaAs layer growth at 515 °C resulted in a rapid increase in LLS intensity, after an initial onset time, because of the increasing density and height of surface steps generated by misfit dislocations. Critical thickness was determined in situ from the LLS onset time, which depended inversely on the InGaAs composition, and was compared to equilibrium model predictions. By rotating the wafer, contributions to the LLS signal from misfit dislocations could be separated from isotropic surface roughness. Three-dimensional (island) growth occurred in films with In content above 25%. Observations of relaxation dynamics included the continuing increase of LLS signal even afer InGaAs layer growth was terminated. During GaAs cap layer growth, a decrease in the density ratio of α(011̄) to β(001) dislocations was also observed.
Model for charge movement after the radio frequency excitation is extinguished
Authors: Overzet Lawrence J.
Published: July 2002

A fluid equation model for charge movement in the afterglow of a parallel plate radio-frequency discharge was developed which can closely simulate the time averaged flux of negative ions to the grounded electrode of the system. While the percentage of the negative charge carried by electrons at the beginning of the afterglow influences the time dependence of the negative ion flux to the grounded electrode during the afterglow, it does not influence the time integrated negative ion flux significantly. This is because the electron attachment lifetime tends to be less than the ambipolar diffusion lifetime for electrons of several hundred microseconds. As a consequence, nearly all of the negative charge in the body of the afterglow exits as negative ions rather than as electrons independent of the initial percentage of electrons in the active glow. A change in the concentration of a negative ion during the active glow will still affect its time integrated flux to the grounded electrode during the afterglow in a nearly linear fashion provided the percentage of negative charge carried by electrons during the active glow remains nearly constant. As a consequence, measured changes in the negative ion signal from a discharge afterglow can accurately relate changes in the negative ion concentration of the active glow.
Second-harmonic generation in Si–SiO2 heterostructures formed by chemical, thermal, and plasma-assisted oxidation and deposition processes
Authors: Bjorkman C. H. , Shearon C. E. , Ma Y. , Yasuda T. , Lucovsky G. , Emmerichs U. , Meyer C. , Leo K. , Kurz H.
Published: July 2002

Second-harmonic generation (SHG) on vicinal Si(111) surfaces, ∼4° off axis, was studied by varying the chemical bonding state of the surface atoms. O-terminated surfaces were prepared by thermal oxidation, plasma deposition, and chemical oxidation. H-terminated surfaces were prepared by removing the oxide layers and subjecting the Si surfaces to RCA cleans terminated by rinses in dilute HF solutions. SHG experiments were performed in the s- and p-polarization modes, using the 1053 nm emission from a Nd:YLF laser. An angular anisotropy, characteristic of vicinal Si(111) surfaces, and including a distinctive SHG feature polarized in the [112̄] direction of the surface steps, was enhanced by the presence of an oxide layer, independent of how the Si–SiO2 interface was prepared. We show for the first time that H-terminated Si surfaces exhibited a similar angular anisotropy, and that the SHG signal polarized in the [112̄] step direction was reduced, rather than enhanced by the change in the surface bonding chemistry. Using model calculations, we illustrate that this apparent reduction in SHG signal is due to a change in the relative phase of the background and step-induced contributions to the SHG signal.
Synthesis of carborane and boron-rich films from solid diborane using synchrotron radiation
Authors: Ruckman M. W. , Murray M. F. , Mowlem J. K. , Strongin D. R.
Published: July 2002

Photoemission and boron K-edge spectra from solid diborane on silver or graphite surfaces were measured before and after exposure to synchrotron radiation at 78 K. Exposing condensed diborane on a silver support to synchrotron radiation produced a boron-rich film that was retained on the surface at 300 K. A surface phase whose valence and near-edge spectra resembled o-carborane was created by a photon or photoelectron-induced reaction between graphite and diborane.
Interfacial chemistry of a perfluoropolyether lubricant studied by x-ray photoelectron spectroscopy and temperature desorption spectroscopy
Authors: Herrera-Fierro Pilar , Jones William R. , Pepper Stephen V.
Published: July 2002

The interfacial chemistry of Fomblin Z25, a commercial perfluoropolyether used as lubricant for space applications, with different metallic surfaces—440 C steel, gold, and aluminum—was studied. Thin layers of Fomblin Z25 were evaporated onto the oxide-free substrates and the interfacial chemistry studied using x-ray photoelectron spectroscopy and temperature desorption spectroscopy. The reactions were induced by heating the substrate and by rubbing the substrate with a steel ball. Gold was found to be completely unreactive towards Fomblin at any temperature. Reaction at room temperature was observed only in the case of the aluminum substrate, the most reactive towards Fomblin Z25 of the substrates studied. It was necessary to heat the 440C steel substrate to 190 °C to induce decomposition of the fluid. The degradation of the fluid was indicated by the formation of a debris layer at the interface. This debris layer, composed of inorganic and organic reaction products, when completely formed, passivated the surface from further attack to the Fomblin on top. The tribologically induced reactions on 440C steel formed a debris layer of similar chemical characteristics to the thermally induced layer. In all cases, the degradation reaction resulted in preferential consumption of the difluoroformyl carbon (–OCF2O–).
Study of epitaxial growth of Ag on hydrogen terminated Si(111) and Si(100) surfaces
Authors: Naik R. , Kota C. , Rao B. U. M. , Auner G. W.
Published: July 2002

We have employed reflection high energy electron diffraction (RHEED) to study Ag films grown on hydrogen terminated Si(111) and Si(100) substrates by molecular beam epitaxy. X-ray diffraction (XRD) and RHEED studies indicate 〈111〉 oriented growth of Ag on Si(111) substrates both at room temperature and at 275 °C with [011]Ag∥ [011]Si. Scanning electron microscopy (SEM) studies showed an island growth (island size ∼3000 Å) for the samples grown at 275 °C. While XRD showed predominantly 〈100〉 oriented growth of Ag on Si(100) at room temperature, RHEED observations did not indicate a good epitaxial growth. The Ag films grown on Si(100) substrates at 275 °C showed a 〈100〉 oriented epitaxial growth with [001]Ag∥ [001]Si. SEM showed an island growth (island size∼3000 Å) for the samples grown at 275 °C.
Factors influencing the quantitative compositional analysis of powders in sputtered neutral mass spectrometry
Authors: Dang Tuan A. , Hilliard Clinton
Published: July 2002

Sputtered neutral mass spectrometry (SNMS), which decouples ionization from sputtering, has greatly reduced the effect of the sample matrix. Its application to the quantification of powders has, however, resulted in many other uncertainties. An investigation of artifacts associated with the quantification of powders was carried out using W and Cr powders and several binder systems including Ag, Au, and C. The signal intensity detected in SNMS was significantly affected by the powder’s particle size and its preparation for analysis. The binder used in forming a pellet caused spectral interference and coating artifacts. Pressing powders onto In foil eliminated these problems, but did not result in a consistent foil coverage. Regardless of the preparation method, the particle size of powders had a strong influence on the intensity of the detected signal. The surface area of the powders can be used to project the intensity of the signal measured.
Evolution of atomic-scale roughening on Si(001)-(2×1) surfaces resulting from high temperature oxidation
Authors: Seiple J. V. , Pelz J. P.
Published: July 2002

Scanning tunneling microscopy was used to study surface morphology on Si(001)-(2×1) samples following elevated temperature O2 exposure as a function of pressure (1×10−8<Pox<5×10−6 Torr), temperature (500<Ts<700 °C), and dose [10–800 langmuir (L)]. At low O2 doses (Dox<50 L; Ts≥600 °C and Pox<1×10−7 Torr) preferred B-type step retraction is observed, but single A-domain formation is prevented due to step pinning by nucleated oxide clusters. These pinning centers roughen the surface via step ‘‘fingering’’ at low doses, while at higher doses result in the formation of three-dimensional conical islands, similar to oxidation-induced ‘‘growth features’’ reported previously by Smith and Ghidini [J. Electrochem. Soc. 129, 1300 (1982)] at higher temperatures. Surface etching rates were determined by measuring the island heights as a function of exposure, and a sticking coefficient s of 0.04 (±0.02) was estimated for O2 reaction on Si(001) at 600 °C. For moderate O2 doses (<1000 L) surface etching was found to dominate SiO2 growth up to pressures several orders of magnitude above the commonly accepted oxidation ‘‘critical line,’’ causing significant atomic-scale roughening under these oxidation conditions.
Tungsten etching using an electron cyclotron resonance plasma
Authors: Maruyama T. , Fujiwara N. , Shiozawa K. , Yoneda M.
Published: July 2002

Electron cyclotron resonance (ECR) plasma etching is one of the most suitable methods to realize a highly selective and highly anisotropic etching because the ECR is able to generate a high density plasma at low pressure. We applied this technique to W etching using sulfur hexafluoride (SF6) and octafluoro cyclobutane (C4F8) mixture gases at the etching chemistry. The characteristics of the W etching using ECR plasma were investigated. Consequently, high selectivity to photoresist is obtained without biasing rf power. Furthermore, it is clear that the addition of C4F8 to the plasma decreases the reactive ion etching lag effect in W etching. Both our simulations and mass spectral analysis with changing orifice aspect ratios show the surface reaction coefficients of the precursors to increase with increasing molecular weight. For example, the surface reaction coefficient of the parent species of the C4F+9 fragment is estimated to be about 0.12. Furthermore, in our simulation, the flux of these parent species is lowered below 60% in the 2.5-aspect-ratio trench pattern.
Film deposition and surface modification using intense pulsed ion beams
Authors: Meli C. A. , Grabowski K. S. , Hinshelwood D. D. , Stephanakis S. J. , Rej D. J. , Waganaar W. J.
Published: July 2002

High-power pulsed ion beams have been used to ablate material for ultrahigh-rate film deposition and to treat the surfaces of alloys. Pulsed ion beams were provided by the high-power-density Gamble II facility at the Naval Research Laboratory [high voltage (∼900 keV), short pulse (60 ns)] and the lower-power-density Anaconda facility at Los Alamos National Laboratory [lower voltage (∼300 keV), longer pulse (400 ns)]. Peak film deposition rates after target ablation reached 1 mm/s. Films of pure Al, pure Ta, YBCO, and Ni–Zn ferrite were deposited on glass and single-crystal substrates, in some cases heated. The film deposition process was studied with framing photography, a bolometer, and other diagnostics to gain an understanding of the ablation, transport, and deposition steps. Stoichiometric deposition of multicomponent targets has been demonstrated. Film morphology remains poor, but has steadily improved, and our present understanding points the way to further improvement. Lower fluences (∼5 J/cm2) were used to investigate rapid thermal processing of metal surfaces for the enhancement of corrosion resistance. The results in this area have been negative, but here again the knowledge gained through these experiments allows us to propose directions for improvement.
Development of 111 texture in Al films grown on SiO2/Si(001) by ultrahigh-vacuum primary-ion deposition
Authors: Kim Y. W. , Petrov I. , Greene J. E. , Rossnagel S. M.
Published: July 2002

A high degree of 111 preferred orientation with minimal mosaic spread has been shown by many researchers to be essential for electromigration resistance in Al-based interconnects. We have found that 111 texture can be greatly enhanced through the use of low-energy self-ion irradiation during deposition. In these experiments, 300-nm-thick Al layers were grown on SiO2 at 65 °C from highly ionized beams provided by an ultrahigh-vacuum primary-ion deposition (PID) source. Al+ ion energies EAl+ and ion/neutral ratios JAl+/JAl were independently varied from 10 to 120 eV and from 0% to 68%, respectively. All PID Al films exhibited very strong 111 preferred orientations, which increased with increasing EAl+ and/or JAl+/JAl, and azimuthally symmetric x-ray diffraction pole figures with no measurable tilt. The full width at half-maximum intensity Δω of 111 ω-rocking curves decreased continuously from 9.6° with EAl+=10 eV and JAl+/JAl=68% to 2.2° with JAl+/JAl=120 eV compared to 10.6° for films deposited by thermal evaporation. This was accompanied by a continuous decrease in the average grain size from 370 nm for thermal deposition to 90 nm with EAl+=120 eV. The PID Al films exhibited a columnar microstructure with weak competitive column growth. Changing the beam energy after the formation of a continuous layer had only a minor effect on film texture, indicating that the degree of ion-irradiation-induced preferred orientation is controlled during nucleation and/or coalescence while local pseudomorphic forces dominate thereafter. ω-rocking curves from a bilayer film consisting of a 20-nm-thick Al buffer layer grown by PID followed by a 280-nm-thick thermally evaporated Al overlayer were essentially identical to those obtained from 300-nm-thick single-layer PID Al films.
Application of the Monte Carlo method to pressure calculation
Authors: Suetsugu Yusuke
Published: July 2002

The Monte Carlo method, which has been used for simulation of steady-state molecular flow and estimation of static pressure in relation to vacuum science, is applied to a calculation of the time dependent pressure distribution in a vacuum system. The calculation follows the usual simulation process, but the locations of the test particles are recorded at various values of time. In this way the pressure distribution in a vacuum system can be obtained at any time from the beginning of gas desorption. The pressure propagation along a beam line and the steady-state pressure distribution in a vacuum system with an orifice and a pump are presented as two examples.
Effects of surface oxide on the rapid thermal nitridation of Si(001)
Authors: Copel M. , Tromp R. M. , Timme H.-J. , Penner K. , Nakao T.
Published: July 2002

We have investigated the role of surface oxygen on the rapid thermal nitridation of Si(001) by NH3 using medium energy ion scattering. For short times, typical of rapid thermal processing, monolayer quantities of oxygen are sufficient to reduce nitridation. The oxide remains on the surface after nitridation, which may adversely influence subsequent nitride chemical vapor deposition.
Reactive magnetron sputter deposited CNx: Effects of N2 pressure and growth temperature on film composition, bonding, and microstructure
Authors: Zheng W. T. , Sjöström H. , Ivanov I. , Xing K. Z. , Broitman E. , Salaneck W. R. , Greene J. E. , Sundgren J.-E.
Published: July 2002

The effects of growth processes on the chemical bond structure, microstructure, and mechanical properties of carbon–nitride (CNx) thin films, deposited by reactive magnetron sputtering in a pure N2 discharge, are reported. The film deposition rate RD increases with increasing N2 pressure PN2 while N/C ratios remain constant. The maximum N concentration was ∼35 at. %. RD was found to be dependent upon the film growth temperature Ts. For a given PN2, RD decreased slightly as Ts was increased from 100 to 600 °C. The variations in RD with both PN2 and Ts can be explained by ion-induced desorption of cyano radicals CNx from both the target and growth surfaces during deposition. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (FTIR) analyses showed that N atoms in films grown at Ts≳350 °C with low nitrogen partial pressures PN2, ∼2.5 mTorr, were bound to C atoms through hybridized sp2 and sp3 configurations. For low Ts=100 °C and higher PN2, 10 mTorr, triple-bonded C≡N was detected by FTIR. Two types of microstructures were observed by high-resolution transmission electron microscopy, depending on Ts: an amorphous phase, containing crystalline clusters for films deposited at Ts=100 °C, while a turbostraticlike or fullerenelike phase was observed for films deposited at Ts≳200 °C CNx films deposited a higher Ts and lower PN2 were found to have higher hardness and elastic modulus.
Thermal stability of Cu/W/Si contact systems using layers of Cu(111) and W(110) preferred orientations
Authors: Takeyama Mayumi , Noya Atsushi , Fukuda Tomoyuki
Published: July 2002

A thermally stable Cu/W/Si contact system using Cu(111) and W(110) films with preferred orientations has been developed. The application of the W diffusion barrier with the [110] preferred orientation effectively suppresses the grain boundary diffusion of Si as well as the fast diffusion of Cu through the barrier due to annealing, resulting in raised silicidation temperatures above 670 °C and an effective suppression of Cu diffusion. The contact system tolerates annealing at 690 °C for 1 h, at which the W layer also stands as an effective barrier, although the W barrier is uniformly consumed by the silicidation reaction at the W/Si interface.
Fluoroether bonding to carbon overcoats
Authors: Cornaglia Laura , Gellman Andrew J.
Published: July 2002

A set of small fluorocarbon ethers (CF3CF2OCF2CF3 , CF3OCF2OCF3 , and –CF2OCF2OCF2–) and their hydrocarbon analogs have been used in a model study of the bonding of fluoroether lubricants to the amorphous-carbon (a-CH) overcoats used to protect the surfaces of magnetic storage media. These small ethers allow measurement of desorption kinetics and allow study of the heats of adsorption, a property that cannot be measured directly using the perfluoropolyalkylether lubricants themselves. The a-CH films used in this investigation were provided by three commercial manufacturers of magnetic storage disks. In all cases, the heat of adsorption of the hydrocarbon ether was greater than that of the corresponding fluorocarbon ether, suggesting that the ethers are bonded to the films through donation of the electron pairs on the oxygen atom. The a-CH films are heterogeneous, exposing a variety of adsorption sites at which the ethers bond with a range of interaction strengths. The hydrogen content of the a-CH films was varied by heating, which induced dehydrogenation at temperatures in excess of 500 K. Most interestingly, systematic dehydrogenation of the films results in an increase in the heats of adsorption of all ethers. We propose a model in which the electropositive nature of the hydrogen in the a-CH films weakens the extent of electron donation from the ether lone pairs and, hence, weakens the bonding of the ethers to the a-CH films. The implication of this model is that it should be possible to control the interaction of lubricants with a-C films by varying the types and concentrations of heteroatoms in the films.
Microcrystalline oxide-incorporated new diffusion barrier for dynamic random access memory and ferroelectric random access memory capacitor electrode
Authors: Yoon Dong-Soo , Baik Hong Koo , Lee Sung-Man
Published: July 2002

Microcrystalline oxide-incorporated new diffusion barrier for dynamic random access memory (DRAM) and ferroelectric random access memory (FRAM) capacitor electrodes is proposed. The thermal stability of the Pt/Ta+CeO2/TiSi2/poly-Si/SiO2/Si contact system is investigated and is compared to that of the Pt/Ta/TiSi2/poly-Si/SiO2/Sicontact system. The Pt/Ta+CeO2/TiSi2/poly-Si/SiO2/Si contact system retained its structures up to 800 °C without increase in electrical resistivity but the Pt/Ta/TiSi2/poly-Si/SiO2/Si contact system was completely degraded after annealing at 650 °C. In the former case, since the addition of cerium dioxide (CeO2) led to the stuffing of microcrystalline oxide along the grain boundaries in Ta matrix and CeO2 was much heavier atomic weight than any stuffed elements, it prevented the interdiffusion of O, Pt, and Si through grain boundaries which can act as fast diffusion paths to high temperatures. It appears that the barrier properties of the microcrystalline oxide-incorporated new diffusion barrier are superior to polycrystalline transition metal barriers, polycrystalline nitride barriers, ternary amorphous compound barriers, and N2- and O2-stuffed barriers.
Comparison of initial oxidation of Si(111)7×7 with ozone and oxygen investigated by second harmonic generation
Authors: Nakamura Ken , Kurokawa Akira , Ichimura Shingo
Published: July 2002

Initial oxidation by high purity ozone and molecular oxygen of Si(111)7×7 was investigated by second harmonic generation (SHG) with a 1.064 μm Nd:YAG laser. Decrease of second harmonics (SH) intensity to almost zero after 5 L ozone gas exposure, in spite of the fact that molecular oxygen kept SH intensity for the same amount of exposure, indicated that ozone is inserted into the Si–Si backbond in the subsurface layers more effectively than molecular oxygen. In the initial exposure, rates of rapid decrease in SH intensity for both ozone and oxygen adsorption were in the same order of magnitude, although O 1s x-ray photoelectron spectroscopy (XPS) intensity showed high reactivity of ozone. This is because of a difference in the information depth between SHG and XPS so that oxygen species in the subsurface layers are not effective in decreasing SH intensity. This indicates that the process of attacking backbonds is underway even with an initial exposure of <5 L.
Automated tuning of an electron cyclotron resonance cavity to a microwave power source
Authors: Hanish C. K. , Grizzle J. W.
Published: July 2002

One of the drawbacks to using an electron cyclotron resonance (ECR) plasma source in a production reactive ion etch tool is that, typically, the matching of the source load to the microwave power generator must be done manually, and hence is prone to error. This can lead to large variability in the power delivered to the plasma, that in turn may cause inconsistent etch results. In addition, if the reflected power due to mismatch between the generator and plasma is large enough, significant damage can be done to the equipment. This article documents an automated method for matching an ECR cavity to a microwave power generator. The algorithm is demonstrated on a Wavemat ECR high density source coupled to an AsTex S-1500i microwave power generator.
Some investigations on the effective short time outgassing depth of metals
Authors: Schindler N. , Riemann T. , Edelmann Chr.
Published: July 2002

Outgassing rates of aluminium samples coated with Al, Fe, and B were studied as a function of the surface composition at and near room temperature. The surface was changed by diffusion processes caused by heating in argon at atmospheric pressure and in vacuum. Achieved effects of these preparations were studied by x-ray photoelectron spectroscopy depth profiling, scanning electron microscopy, and atomic force microscopy measurements. It can be shown that the outgassing rate is independent on the atomic concentration of O, C, Al, Fe, and B in the nanometer range for many 105 s, when the samples were prepared in this way. The samples coated and heated at 500 °C in vacuum and the aluminum surface cleaned with ethanol have nearly the same outgassing behavior after air exposure. Therefore it can be concluded that the short time outgassing is only controlled by contamination and desorption.
Surface productions of CF and CF2 radicals in high-density fluorocarbon plasmas
Authors: Suzuki C. , Sasaki K. , Kadota K.
Published: July 2002

Spatial distributions of CF and CF2 radical densities in high-density fluorocarbon plasmas were measured by laser-induced fluorescence spectroscopy. In both pulsed and continuous-wave (cw) C4F8 discharges, the radical densities were lower in the center of the discharge and higher near the walls. Namely, hollow-shape profiles of the radical densities were maintained in the C4F8 discharges. This indicates the presence of surface productions of the radicals on the chamber wall. The rf power dependences of the radical fluxes from the wall, which were estimated from the density gradients, showed similar trends to the gas-phase radical densities. This result revealed that the surface productions predominantly determine the gas-phase CF and CF2 radical densities in high-density C4F8 plasmas. In contrast to C4F8, almost uniform profiles of the radical densities were always observed in cw CF4 discharges, while hollow profiles were observed in pulsed CF4 discharges. The CF2 flux from the wall in the pulsed CF4 discharge was one or two orders smaller than that in the C4F8 discharge, and the rf power dependence of the CF2 flux showed a dissimilar trend to the gas phase CF2 density. The large difference in the radical flux from the wall observed in the C4F8 and CF4 discharges suggests that heavy neutral species (CxFy, x⩾2) in the C4F8 plasma make great contributions to the film deposition on the wall where the deposited films enhance the surface productions of CF and CF2 radicals.
Can photoemission accurately probe the bulk electronic structure of the complex oxides?
Authors: Choi Jaewu , Waldfried C. , Liou S.-H. , Dowben P. A.
Published: July 2002

The surface of the complex oxides, in particular the manganese perovskites, is dominated by a different free enthalpy at the surface. This can be demonstrated by surface segregation after annealing the samples. By comparing relative x-ray photoelectron spectroscopy intensities of the manganese perovskite La1−xCaxMnO3 (x=0.1, 0.35) for different emission angles, the profile of elemental concentration was determined. Analysis shows evidence for pronounced surface segregation of calcium. Our results suggest that there are strong differences between surface and bulk enthalpies without segregation or surface relaxation. This is consistent with the previously observed surface resonance in the electronic band structure.
Etching of diamond (100) surface by atomic hydrogen: Real-time observation by reflection high energy electron diffraction
Authors: Komatsu Shojiro , Okada Katsuyuki , Chou Sung-Baek , Aizawa Takashi , Shigetani Hisashi , Tanaka Junzo , Sato Yoichiro
Published: July 2002

Progress of etching of diamond (100) surface by atomic hydrogen was observed in real time with the help of reflection high energy reflection diffraction. The initial 1×1 pattern that indicates smooth two dimensional extension of the crystal surface transformed into the pattern corresponding to the (110) reciprocal lattice plane that indicates surface roughening. Ex situ atomic force microscope observation of the etched surface revealed a lot of shallow etch pits with a few nm in depth and a few degrees in the slope of the pit. It is supposed that deposition is effective against etching in actual chemical vapor deposition conditions partially because of the difference in their favorable temperatures, in addition to the absolute difference in their rates.
Influence of residual stress and film thickness on crystallographic orientation in Al thin films deposited by bias sputtering
Authors: Choi H. M. , Choi S. K.
Published: July 2002

Al thin films with various residual stress and film thickness were deposited by bias sputtering. Residual stress and relative intensity of the (200) to (111) plane of Al thin films were measured by x-ray diffraction. When film thickness is fixed at 1 μm below the residual stress of ∼80 MPa, Al thin films have a (111) orientation, but above this stress, a (100) orientation. If Al thin films are in the high residual stress of ∼145 MPa, crystallographic orientation changes to a (100) from a (111) orientation as film thickness increases to 2 μm from 1 μm. However, Al thin films with the residual stress of ∼25 MPa have a (111) orientation regardless of film thickness. Total energy for Al thin films of a (100) and a (111) orientation was calculated as a function of residual stress and film thickness. These experimental results could be explained by the minimization of the sum of strain energy and surface energy in the films.
Laser-induced thermal desorption analysis of the surface during Ge etching in a Cl2 inductively coupled plasma
Authors: Young Choe Jae , Herman Irving P. , Donnelly Vincent M.
Published: July 2002

Laser desorption laser-induced fluorescence (LD-LIF) detection of GeCl was used to determine in situ the surface coverage of chlorine during the etching of germanium by Cl2 in an inductively coupled plasma (ICP) reactor. The ICP operated in the dim mode for radio frequency (rf) power ≲350 W and in the bright mode for higher powers. The etch rate was 3.5 μm/min with 540 W rf power and −40 V substrate bias. The chlorine surface coverage was about 2× that with chlorine flow only and the plasma off, both with dim- and bright-mode operation, and was independent of rf power within each mode for laser repetition rates of 0.2, 5, and 15 Hz. Similarly, the chlorination of the adlayer did not change when the ion energy was increased from 16 to 116 eV by increasing the substrate bias voltage, both with dim- and bright-mode operation. This was confirmed by x-ray photoelectron spectroscopy measurements in a similar high density reactor, where it was found that the surface density of chlorine was ∼2.6×1015 Cl/cm2. As the ion energy increases from 16 to 116 eV, the etch yield of ions increases from 1 to 3 atoms/ion. “Wait and probe” measurements show that the GeClx adlayer is quite stable. Since the same adlayer chlorine content was measured by LD-LIF under high ion current/fast etch conditions (bright mode) and low ion current/slow etch conditions (dim mode), both the adlayer chlorine content and the etch rate seem to be controlled by the ion current to the wafer. Previously reported work in Si etching in this ICP [J. Vac. Sci. Technol. A 15, 3024 (1997)] showed a similar independence of adlayer chlorination with rf power, but much slower chlorination and an increasing chlorination of the adlayer with increasing ion energy.
A new and simple variable-angle accessory for infrared specular reflectance
Authors: Polo M. C. , Ferrer N. , Romero M. , Pérez J. , Quevedo M. , Vilardell F.
Published: July 2002

A simple, low-cost accessory (patent pending) with only two flat mirrors and a new variable-angle mechanism has been developed for infrared specular reflectance measurements. The system allows the angles of incidence to be varied continuously from 15° (near normal incidence) to 85° (near grazing angle) without losing the alignment of the accessory. The reflectivity of boron nitride thin films deposited on metallic substrates has been measured at different angles of incidence to demonstrate the utility of this accessory.
Improvements to the analysis of x-ray photoelectron spectra using a maximum entropy method for deconvolution
Authors: McIntyre N. S. , Do T. , Piao H. , Splinter S. J.
Published: July 2002

X-ray photoelectron spectra are typically broadened by the inclusion of contributions from the exciting X radiation, as well as the spectrometer itself. A procedure for removal of much of this broadening using a version of the maximum entropy method is described. This method uses a nonlinear functional (the spectral “entropy” or information content) to stabilize the noise amplification problem inherent to deconvolution of real data. A less ambiguous solution is therefore obtained compared to previous approaches which use linear estimates. This algorithm avoids the subjective nature of many previous deconvolution methods by assuming that the informational uncertainty is always maximized within the constraint of the data provided. This large scale, nonlinear optimization problem can be solved on a fast personal computer using a sequential quadratic programming algorithm. For spectra with adequately high signal/noise, the linewidths produced approach the limiting core hole lifetime values. The method is applied to study the extended growth of an oxide layer on clean polycrystalline aluminum surfaces following exposure to water vapor. For the early growth stages, the spectral detail is comparable to recent synchrotron-based studies where one or more precursor phases are detected at the interface prior to the nucleation of the extended oxide film. In a related study of the oxidation of gold–aluminum alloy surface films, the evolution of the gold–aluminum near-surface phase could be followed through changes in the Au(4f ) and the Al(2p) spectra. From the latter, the surface oxides grown on the alloy surface are seen to differ distinctly from those on pure aluminum.
Disappearance of element-specific Kikuchi bands from fluoride surfaces
Authors: Omori Shinji , Nihei Yoshimasa
Published: July 2002

We measured scanned-angle x-ray photoelectron diffraction (XPED) patterns from both SrF2(111) and MgF2(001) surfaces, which exhibit complex element-specific characteristics: (1) A set of Kikuchi bands due to Bragg reflection of photoelectrons by {111} planes are detectable for Sr 3p3/2 emission, but not for F 1s emission from SrF2(111). (2) By contrast, {111} bands are observed for F 1s emission, but not for Mg 2s emission from MgF2(001). (3) {110} bands are weak for F emission and strong for Mg emission from MgF2(001). We have used the simple two-beam model of the Kikuchi-band formation to interpret the phenomena and found out that the two kinds of element-specific extinction of the Kikuchi bands occur in completely different ways; the extinction mechanisms have been confirmed by multiple-scattering cluster calculation, another more accurate approach to simulating XPED patterns.
Low-energy electron diffraction study of the multilayer relaxation of Cu(211)
Authors: Seyller Th. , Diehl R. D. , Jona F.
Published: July 2002

The multilayer relaxation of Cu(211) at 110 K was determined by a dynamical low-energy electron diffraction study. This study indicates that the first and second interlayer spacings are contracted by 0.11±0.03 Å (15±4%) and 0.08±0.03 Å (11±4%), respectively, while the third interlayer spacing is expanded by 0.06±0.03 Å (8±4%). These results compare well with the predictions of two theoretical studies of this surface [C. Y. Wei, S. P. Lewis, E. J. Mele, and A. M. Rappe, Phys. Rev. B 57, 10062 (1998); S. Durukanoglu, A. Kara, and T. S. Rahman, Phys. Rev. B 55, 13894 (1997)].
Hydrogenated amorphous carbon nitride films on Si(100) deposited by direct current saddle-field plasma-enhanced chemical vapor deposition
Authors: Jang H. K. , Kim G. , Lee Y. S. , Whangbo S. W. , Whang C. N. , Yoo Y-Z. , Kim H. G.
Published: July 2002

Hydrogenated amorphous carbon nitride [a-C:H(N)] films were deposited on p-type Si(100) at room temperature with a substrate bias voltage of 200 V by direct current saddle-field plasma-enhanced chemical vapor deposition using methane and nitrogen as source gases. The structural and compositional changes of the a-C:H(N) films induced by the differential ratio of N2 to CH4(nN2/nCH4) were investigated using Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. Initially, as nitrogen is added to the pure methane, the deposition rate decreases quite rapidly then less so as nN2/nCH4 rises above 0.5. The deposition rate continues to gradually decrease with the increase of the nN2/nCH4. The ratio of N to C of the films saturated at 0.25 at the maximum of nN2/nCH4. The number of N–H and C≡H bonds in the films increased with nN2/nCH4 but the number of C–H bonds decreased. The optical band gap energy of the films, as determined by the Tauc relation was lowered from 2.53 to 2.3 eV as the nN2/nCH4 of the source gas changed from 0 to 4.
Influence of the plasma pressure on the microstructure and on the optical and mechanical properties of amorphous carbon films deposited by direct current magnetron sputtering
Authors: Jacobsohn L. G. , Freire F. L.
Published: July 2002

The influence of the plasma pressure on the microstructure and on the mechanical and optical properties of amorphous carbon films deposited by dc-magnetron sputtering was investigated. A modified version of the computer code TRIM 98.01 was employed to simulate the thermalization of the sputtered carbon atoms. In this way, it provided the efficiency of transport and the amount of energy deposited at the growing surface per sputtered carbon atom as a function of the plasma pressure and according to Sigmund’s energy distribution of sputtered particles. Several techniques were employed to characterize the films properties: ion beam analysis provided the composition and areal density; profilometry provided the thickness and film/substrate bending, with which the internal stress could be calculated through Stoney’s equation, and nanoindentation provided the film hardness. In addition, the disorder of the amorphous network was characterized by Raman spectroscopy, while infrared spectroscopy provided information about chemical bonding. Transmission and reflection spectroscopies were carried out in the 400–2500 nm range, and the optical gap was obtained through the Tauc plot. The index of refraction was obtained at 1.3 μm according to the Abelès method. All these quantities were related to the growing conditions, providing a clear picture of the growth of polymer-like or diamond-like films. Finally, the present models for a-C films are reviewed in light of experimental results.
Alternating ion bombardment technique for wall surface control in depositive plasma processing
Authors: Nakamura K. , Ohwaki M. , Yoneda S. , Sugai H.
Published: July 2002

In order to improve the process repeatability of silicon dioxide etching, surface control of reactor wall based on ion bombardment is proposed. In this new technique, a reactor wall is almost fully covered with two floating bias walls, and rf bias is applied between the two walls with transformer coupling at 400 kHz. The biased walls are alternately bombarded by energetic ions in the negative phase of the rf bias. This alternating ion bombardment (AIB) technique enables us not only to suppress the polymer deposition during dielectric etching but also to clean the walls deposited with polymer during run-to-run etching. The AIB has little influence on electron density and plasma potential during etching. The radical diagnostics revealed that, during the AIB, mainly CF and CF2 densities increase due to ion-enhanced desorption from the wall at the rate estimated from the removal rate of the fluorocarbon polymer layer.
Evaluation of single- and multilayered amorphous tantalum nitride thin films as diffusion barriers in copper metallization
Authors: Chen G. S. , Chen S. T. , Yang L.-C. , Lee P. Y.
Published: July 2002

This study evaluates 40-nm-thick amorphous Ta2N (a-Ta2N) thin films with various compositions and metallurgical designs as diffusion barriers for copper metallization. Results based on sheet resistance measurements, x-ray diffraction analyses, and transmission and scanning electron microscopies consistently follow a sequence of coarsening copper grains, transforming a-Ta2N into a crystalline phase, and finally forming {111}-faceted pyramid Cu3Si precipitates and TaSi2. The degradation of the single-layered stoichiometric Ta2N (a-Ta67N33) barriers is primarily triggered by a premature crystallization of the amorphous barrier layers at temperatures as low as 450 °C. However, as adequately designed double-layered (20 nm Ta67N33/20 nm Ta62N38) amorphous barriers can be subjected to high-temperature annealing without crystallization, the effectiveness of the double-layered barriers can be significantly improved, elevating the degradation temperature by approximately 100 °C.
Epitaxial growth and surface structure of cuprous halide thin films
Authors: Wake Tomoko , Saiki Koichiro , Koma Atsushi
Published: July 2002

The surface atomic and electronic structures of cuprous halide CuX (X=Cl, Br, and I) films, which were grown on various GaAs faces, have been studied by reflection high-energy electron diffraction, Auger electron spectroscopy, and electron energy loss spectroscopy. Epitaxial growth in a layer by layer fashion was observed commonly on all GaAs faces, except on a GaAs (111) As 2×2 face. The growth mode at the initial stage was affected by the lattice misfit of CuX to GaAs. Auger electron spectra and electron energy loss spectra of CuX depend on the crystal face of the substrate. These results indicate that CuX have both ionic and covalent features in the film growth process.
Synergism of transmission measurements with spectroscopic ellipsometry measurements in the analysis of a nearly opaque bimetal film stack on glass
Authors: Tompkins Harland G. , Tasic Sonja
Published: July 2002

For a bimetal stack (Pt) and (Au) which is nearly opaque, we used transmission measurements along with spectroscopic ellipsometry measurements to determine the thicknesses of each metal layer as well as the optical constants of both materials. The key role of the transmission measurements is discussed.
Estimation of surface kinetic parameters and two-dimensional simulation of InP pattern features during CH4–H2 plasma etching
Authors: Rhallabi A. , Houlet L. , Turban G.
Published: July 2002

A two-dimensional simulation of reactive ion etching (RIE) of InP trench profiles is developed. The local equation of etching rate on each string is established considering the Langmuir adsorption concept. The etching rate takes into account the chemical etching on both the covered and uncovered surface fractions by the neutrals and the ion sputtering on both the covered and uncovered fraction of surface elements. Surface kinetic parameters of InP RIE process are estimated by using a minimization method to fit the experimental data of etching rate as a function of percent CH4 in the CH4–H2 plasma mixture. Such parameters are then used to simulate the etch surface profile evolution in time under the RIE process. The effect of ratio of the ion flux to the neutral flux on the anisotropy of the profiles is shown as well as the aspect ratio on the etching rate evolution in time.
Motion of atomic steps on ultraflat Si(111): Constructive collisions
Authors: Finnie P. , Homma Y.
Published: July 2002

The motion of atomic steps was studied using ultraflat Si(111) substrates which have flat terraces of up to 50 μm in width separated by monoatomic steps. The motion is revealed in time lapse movies made by in situ scanning electron microscopy. When samples are heated to high temperatures (∼1000 °C) the surface erodes in a step-flow mode: steps retreat in an orderly fashion, one after the other. Here, steps are forced to collide constructively, providing a means to probe step interactions. Diffusion theory is used to explain the collision dynamics, allowing the extraction of physical parameters. After colliding, double steps continue to move at speeds simply related to the precursor steps’ velocities.
UV photoemission study of low temperature oxygen adsorption on GaAs(110)
Authors: Frankel D. J. , Anderson J. R. , Lapeyre G. J.
Published: July 2002

The adsorption of oxygen on the (110) cleaved surface of GaAs is studied by first physisorbing molecular O2 on the surface at a temperature of approximately 45 K and then warming the surface to 300 K. The transformation from a state with molecular O2 physisorbed on the surface to one with chemisorbed atomic oxygen is studied with ultraviolet photoemission spectroscopy (UPS) using a helium resonance lamp as a source. The physisorbed state shows a set of emission peaks with spacings equal to the gas phase values. The sample temperature is not cold enough to obtain multiple layers of condensed oxygen. As the temperature of the sample is then increased from T=45 to 300 K, the UPS spectrum changes dramatically; by T=60 K the molecular O2 peaks have disappeared and by 170 K the spectra have taken on a form characteristic of chemisorbed atomic oxygen. Evidence is found for one or more intermediate states during the transformation of the physisorbed molecular O2 to chemisorbed atomic oxygen.