bluuebunny/crossref_metadata_2025 huggingface dataset:
A new silicon phosphide, Si12P5: Formation conditions, structure, and properties
Authors: Carlsson J. R. A. , Madsen L. D. , Johansson M. P. , Hultman L. , Li X.-H. , Hentzell H. T. G. , Wallenberg L. R.
Published: July 2002

The formation conditions, structure, and properties of the recently discovered phosphide, Si12P5 (initially assigned Si7P3), have been studied using x-ray diffraction, high-resolution transmission electron microscopy, photospectrometry, and a four-point probe. The phosphide formed in amorphous Si–P alloy thin films with 30, 35 and 44 at. % P after annealing at 1000 °C for 30 min. During annealing at 1100 °C, the phosphide dissociated through P evaporation. The Si12P5 phase is proposed to have rhombohedral symmetry with a P3̄1m space group and a C5W12 structure. The hexagonal lattice parameters measured were a=6.16±0.05 Å and c=13.17±0.01 Å. The optical band gap and the electrical resistivity of the phosphide were determined to be 1.55 eV and 5 mΩ cm, respectively. The Gibbs free energy diagram for the Si–P system was modified to include this new Si12P5 phase.
Silicon and germanium nanoparticle formation in an inductively coupled plasma reactor
Authors: Gorla C. R. , Liang S. , Tompa G. S. , Mayo W. E. , Lu Y.
Published: July 2002

We have studied the formation of Si nanoparticles in a SiH4–Ar plasma discharge generated in a helical resonator type inductively coupled plasma reactor. It is observed that Si particles vary in sizes from 5 to 15 nm under different conditions. The particles were mostly spherical and made up of a crystalline core with a 1–2 nm thick amorphous shell. The size distribution was narrow for particles formed at a pressure of 200 mTorr, plasma power of 400 W and silane flow rate of 20 sccm (+980 sccm Ar). The effect of a dc bias applied to the particle collecting grids has also been studied. It is found that a negative bias (−25 to −100 V) applied to the grids used for particle collection results in a large increase in the number of Si nanoparticles collected, while a positive bias does not change the collection efficiency considerably, suggesting that the particles are positively charged. Under very low flow rates and under high plasma powers, the Si particle density decreases considerably and a film like deposition occurs on transmission electron microscopy grids placed in the reactor for collecting the particles. We have also studied the formation of Ge particles (50–200 nm) in a GeH4–Ar plasma generated in the same reactor. These particles are crystalline with a spherical morphology.
Highly reliable fitting for gas delivery systems
Authors: Ikeda Nobukazu , Shirai Yasuyuki , Ohmi Tadahiro , Yamaji Michio
Published: July 2002

After confirming the basic characteristics of two types of metal gasket fittings, which are used in construction of ultrapure gas delivery systems for semiconductor manufacturing, it is noticed that the pipe usually twists at the time the fitting is tightened. This may be the possible cause of an external leak, therefore a twist leak test was undertaken to confirm the reliability of the seal during assembly. As a result, it was found that one type of fitting leaked and another type of fitting did not leak. This later type did not leak (leak rate is less than 2.98×10−16 Pa m3/s) even after 70° of twisting.
Plasma process induced surface damage removal
Authors: Brooks C. B. , Buie M. J. , Vaidya K. J.
Published: July 2002

As device geometries continue to shrink below 0.5 μm, previously acceptable levels of silicon contamination and lattice damage from energetic ion bombardment in reactive ion etchers are beginning to affect device performance and reliability through increased junction leakage and higher contact resistance. The Applied Materials remote plasma source (RPS), an isotropic chemical downstream etcher, was used to remove surface residues, impurity penetration, and silicon lattice damage to recover a device quality surface. Several diagnostic methods, including transmission electron microscopy, Rutherford backscattering, and x-ray photoelectron spectroscopy, are used to investigate the effectiveness of a controlled silicon etch process in the RPS chamber.
Interactions of low-energy (20–800 eV) nitrogen ions with Cu(100): A combined temperature programmed desorption and electron energy loss spectroscopy study of chemisorption and entrapment states
Authors: Yu H. , Leung K. T.
Published: July 2002

The interactions of low-energy (20–800 eV) nitrogen ions with Cu(100) at room temperature have been investigated by using temperature programmed desorption (TPD) mass spectrometry and high-resolution electron energy loss spectroscopy. The desorption feature observed at 760 K can be attributed to adsorption of surface atomic nitrogen on fourfold-hollow sites. When the impact energy (IE) of the nitrogen ions used for the irradiation exceeded 75 eV, our TPD results further revealed a new desorption feature at 520 K, which can be tentatively assigned to ion-implanted atomic and/or molecular nitrogen. The intensities and temperatures of the desorption maxima of the surface (chemisorption) and ion-implantation (entrapment) features were found to greatly depend on the IE and the dosage of the ions. Other effects including the creation of defect sites as a result of the ion irradiation are also investigated.
Real-time observation of VO2 thin films in phase transition by laser scanning microscopy
Authors: Nagashima M. , Wada H.
Published: July 2002

The surfaces of vanadium dioxide thin films (VO2) in phase transition were studied at visible wavelength by laser scanning microscopy (LSM). Samples were laser ablated VO2 on Al2O3 and SiO2/Si substrates at different temperatures and in different oxygen pressures. Using the differential interference method in the observation by LSM, real-time surface images for the samples in transition were successfully obtained by changing their temperature. The results showed the strong influence of deposition temperature, the oxygen pressure and the substrate type on the clarity and orientation of transition areas, which appeared as the difference of the brightness in the images.
Film properties of Ti/TiN bilayers deposited sequentially by ionized physical vapor deposition
Authors: Cerio Frank , Drewery John , Huang Eon , Reynolds Glyn
Published: July 2002

Ionized physical vapor deposition (iPVD) has received much attention as a method for depositing material at the bottom and on the sidewalls of the high aspect ratio features proposed for sub-0.25 micron integrated circuits. In this article, we describe the film properties of Ti/TiN bilayers deposited sequentially using the iPVD technique. The experimental configuration consisted of a planar magnetron sputtering source in combination with an inductively coupled RF plasma. TiN was reactively sputtered from a titanium target which remained non-nitrided throughout the deposition, a process commonly referred to in non-ionized PVD as operating in the non-nitrided mode (NNM). These films were analyzed by cross-sectional scanning electron microscopy and transmission electron microscopy, automated four-point sheet resistance probe, x-ray diffraction, x-ray fluorescence, stress gauge, and Rutherford backscattering. Highly oriented 〈111〉 TiN was observed on 〈002〉 oriented Ti underlayers. At via aspect ratios of 4:1 with vertical sidewalls, bottom coverage approaching 100% was obtained. Varying process parameters did not change the bulk resistivity significantly, and values as low as 23 μΩ cm were measured for the NNM TiN films. Mechanical stress was strongly influenced by substrate temperature, as has been observed for both conventionally sputtered and collimated Ti/TiN. Below 200 °C, the films were highly compressive, but values below 2 GPa were obtained at 400 °C. RF plasma power and pressure were also found to affect stress. Deposition rates of 900 Å/min were measured, corresponding to a specific deposition rate of 1.8 Å/kW s.
Effects of “processing parameters” in plasma deposition: Acrylic acid revisited
Authors: Candan Sennur , Beck Alison J. , O’Toole Liam , Short Robert D.
Published: July 2002

In this article we explore the relationship between the plasma-phase chemistry and deposit in the plasma deposition of acrylic acid. This is achieved through systematic variation of some of the plasma deposition variables, termed “processing parameters.” The surface chemical composition of deposits has been investigated by means of x-ray photoelectron spectroscopy. Changes in the surface chemical composition with the ratio of plasma power-to-monomer flow rate, P/φ, substrate position (in the reactor), nature of the substrate, and washing and aging (of the deposit) are examined. Based on these, we provide a qualitative description of the deposits’ molecular structure, and how this changes with P/φ. The plasma-phase chemistry has been probed by means of mass spectrometry and attention given to the effect of P/φ on the neutral and ionic components of the plasma. The major plasma-phase reactions are elucidated, and a knowledge of these help to explain how the molecular structure of plasma deposits are affected by P/φ and other processing parameters.
Metrology of sub-0.5 μm silicon epitaxial films
Authors: Chen Weize , Reif Rafael
Published: July 2002

Non-destructive thickness measurement of sub-0.5 μm silicon epitaxial films has been performed using spectroscopic ellipsometry (SE) in the near infrared to visible range (0.75–3 eV). The undoped epitaxial films were grown on heavily doped substrates by chemical vapor deposition at 700–900 °C. The effect of heavy doping on the optical properties of crystalline silicon in the spectral range 0.75–3 eV is precisely described by the Drude free carrier model. It is shown that SE can simultaneously determine the substrate dopant concentration, the thicknesses of the epitaxial film and native oxide, and if present, the thickness of the transition layer between the epitaxial film and the substrate. The epitaxial film thicknesses measured by SE were in excellent agreement with results of secondary ion mass spectrometry (SIMS). The substrate dopant concentrations measured by SE also agree well with SIMS results for n-type substrates, but are consistently higher than SIMS values for p-type substrates. It was also demonstrated that SE can be used for process monitoring in low temperature silicon epitaxy. This study identifies a non-destructive thickness measurement technique for sub-0.5 μm silicon epitaxial films which are expected to be widely used in future semiconductor devices.
Onset of oscillations during growth on a vicinal surface
Authors: Harris S.
Published: July 2002

We determine the conditions describing the transition from step flow during growth on a vicinal surface. The analysis is based on a mean field model of the generalized Burton, Cabrera, Frank equation together with a “gedanken” experiment that allows us to use the steady state solution to predict the onset of oscillations in the total coverage and step density. Results are obtained for the case where both steps absorb and where the up step absorbs and the down step prevents interlayer transport. These results are also compared with previous results for the transition condition which are based on a criterion that is less directly related to the surface morphology.
Growth of SiC films via C60 precursors and a model for the profile development of the silicon underlayer
Authors: Levinson Joshua A. , Hamza Alex V. , Shaqfeh Eric S. G. , Balooch Mehdi
Published: July 2002

We report on an experimental and theoretical study of the growth of SiC films and of the profile development of the silicon underlayer. SiC features were grown via the direct reaction of the silicon substrate with C60 precursors. Two masking configurations were used to investigate the effects of bulk and surface diffusion on SiC film growth. Without a diffusion barrier (i.e., a patterned SiO2 mask with regions of silicon initially exposed directly to C60), voids formed in the substrate beneath the growing SiC layer, which ultimately controlled the final thickness of the SiC film. Pronounced faceting was observed at the early stages of growth on crystalline silicon. When a tungsten diffusion barrier was used to prevent bulk diffusion (i.e., tungsten covering silicon in non-SiO2 masked regions), significant undercutting resulted beneath the oxide and SiC layers without void formation. A profile simulation was developed to model the time evolution of the silicon underlayer when this diffusion barrier is used. The simulation incorporated an adatom hopping and surface diffusion model to describe the generation and transport of silicon atoms along the evolving profile. A single fitting parameter was required. The agreement between simulation and experiment was good, and a corresponding value of the hopping coefficient was calculated. As an alternative to direct reaction with the silicon substrate, we also demonstrate experimentally that silicon atoms can be co-sublimed with fullerenes to produce SiC films on wafer surfaces, which avoids the consumption of substrate material. Co-sublimation was used to create SiC membranes and also to coat silicon microcantilevers. Force-deflection measurements for the microcantilevers revealed that the stiffness properties were enhanced with the application of a SiC film and that the co-sublimed SiC had mechanical properties like those of bulk material.
High performance Al–N cermet solar coatings deposited by a cylindrical direct current magnetron sputter coater
Authors: Zhang Qi-Chu , Zhao K. , Zhang B.-C. , Wang L.-F. , Shen Z.-L. , Lu D.-Q. , Xie D.-L. , Li B.-F.
Published: July 2002

High efficiency Al–N cermet solar selective coatings have been designed using a numerical computer model and deposited experimentally. In numerical modeling calculations, Bruggeman approximations of dielectric function for composite materials were employed. Aluminum is used as a metallic component and AlON as a ceramic component in cermet. Numerical calculation results show that the double cermet layer film structure has the highest photothermal conversion efficiency for the Al–AlON cermet solar selective coatings. The optimized film has a solar absorptance of 0.958 and a hemispherical emittance of 0.035 at 80 °C. The optimized film yields two cermet layers with metal volume fractions of 0.143 and 0.275, and with layer thicknesses of 43 and 80 nm, going from the antireflection coating to the infrared reflector layer. In the optimized double cermet layer film the solar radiation is efficiently absorbed internally and by phase interference. Thermal loss is also efficiently reduced by using thin cermet layers with such low metal volume fractions, which are substantially transparent in the main wavelength region of blackbody radiation within the temperature range of interest, 50–200 °C. The predicted film structure has been used as a guide for the experimental deposition. The Al–N cermet solar selective coatings with double cermet layer film structure have been deposited onto batches of solar collector tubes using a commercial-scale cylindrical dc magnetron sputter coater. Two Al–N cermet solar absorber layers are deposited by dc reactive sputtering in a gas mixture of argon and nitrogen. The different metal volume fractions in the cermet layers are achieved by changing the reactive nitrogen gas flow rate, while the sputtering current is fixed. A solar absorption of 0.96 and a normal emittance of 0.08 at 80 °C have been achieved for deposited Al–N cermet solar coatings. The baking process, for 1 h at 400 °C in vacuum, hardly affects solar absorptance, however the emittance reduces about 0.01 at 80 °C. These high-performance low-cost Al–N cermet solar collector tubes may be a less-polluting replacement for black chromium solar collectors produced by electrochemical methods.
Silicon nitride films deposited at substrate temperatures <100 °C in a permanent magnet electron cyclotron resonance plasma
Authors: Doughty C. , Knick D. C. , Bailey J. B. , Spencer J. E.
Published: July 2002

Deposition of silicon nitride at low temperatures by plasma-enhanced chemical vapor deposition requires an efficient source of activated precursors and high-current, low-energy ion assist. We report the deposition of silicon nitride at substrate temperatures <100 °C using a permanent magnet electron cyclotron resonance plasma reactor capable of generating uniform plasmas over 300 mm diameters. The effects of gas mixture, silane flow, pressure, and microwave power on the film deposition rate, composition and bonding, index of refraction, stress, and etch rate in buffered oxide etch solution are reported. The N2/SiH4 flow ratio and microwave power both influence the film index and hydrogen content and bonding. For a SiH4 flow of 30 sccm and N2/SiH4 ∼0.75, hydrogen is equally distributed between Si–H and N–H sites and total hydrogen content is minimized. At a deposition rate of 500–600 Å/min, a threshold in microwave power of ∼1100 W exists, above which films with buffered oxide etch rates <150 Å/min result. Near the threshold microwave power compressive stress <400 MPa is observed, with increasing stress at higher microwave powers.
Desorption of fragment ions from condensed Si(OCH3)4 by localized inner-shell electron excitation at the silicon, oxygen, and carbonKedges
Authors: Baba Y. , Sekiguchi T.
Published: July 2002

Desorption of fragment ions from condensed Si(OCH3)4 (tetramethoxysilane) following localized inner-shell electron excitation at the silicon, oxygen, and carbon K edges has been investigated using monochromatized synchrotron radiation in the soft x-ray region. For Si K-edge excitation, the predominant species of the desorbed ions were Si(OCH3)n+ where n=2, 3, 4, which resembles the cracking pattern of gas-phase molecules excited by 70 eV electrons. In contrast, the CH3+ ions were the main species of the desorbed ions for the C and O K-edge excitations. The photon-energy dependencies of the CH3+ yield at the C K edge revealed that the CH3+ desorption happens only at the resonant excitation from C 1s to the σ* orbit localized at the C–O bond, which suggests that the core-to-valence resonant excitations are localized around the C–O bond until the C–O bond breaks. These results shed light on the possibility of low-temperature SiO2 deposition on a silicon surface by an x-ray-induced photochemical reaction through selective C–O bond scission using monochromatized synchrotron radiation.
Silicon nanodots fabricated on a Si(100) surface via thermal nitridation and oxygen etching reactions
Authors: Ha Jeong Sook , Park Kang-Ho , Yun Wan Soo
Published: July 2002

Silicon nanodots with very uniform sizes have been fabricated on a Si(100) surface via a thermal nitridation followed by oxygen etching reaction. N2 gas was exposed to a clean Si(100) surface at 800 °C and this surface was subsequently reacted with O2 gas at 700 °C. Scanning tunneling microscope measurement of surface morphology showed that silicon nanodots with an average size of 5 nm were formed as a result of selective oxygen etching of the silicon surface. Silicon nitride islands of a few nanometers acted successfully as masks against oxygen etching at high temperatures. The number density of silicon nanodots is estimated to be 1×1012/cm2. The lowering of nitridation temperature to 700 °C resulted in similar silicon nanodots with a little bit smaller sizes, indicating that silicon nitride islands formed even at this temperature can be successfully used as masks for oxygen exposure. Owing to the relatively low thermal mobility of nitrogen species, Si nanodots with uniform sizes could be obtained on the Si(100) substrate.
100 keV focused ion beam system with a E×B mass filter for maskless ion implantation
Authors: Shiokawa Takao , Kim Pil Hyon , Toyoda Koichi , Namba Susumu , Matsui Takao , Gamo Kenji
Published: July 2002

Various liquid metal alloy ion sources and a 100 keV mass separated focused ion beam system have been fabricated and their basic characteristics have been measured. These are mass spectra, energy spread and angular current intensity for ion sources, and focusing characteristics of the system. It was observed that Be–Si–Au ternary alloy ion sources produce doubly charged Be and Si ions and the importance of these ion sources is demonstrated by fabricating a GaAs JFET using a maskless ion implantation technique and by PMMA resist exposure.
Quantum-well charge-coupled devices for charge-coupled device-addressed multiple-quantum-well spatial light modulators
Authors: Goodhue W. D. , Burke B. E. , Nichols K. B. , Metze G. M. , Johnson G. D.
Published: July 2002

We have demonstrated a new type of GaAs/AlGaAs charge-coupled device (CCD) in which the charge is confined to a quantum-well channel. The MBE-grown quantum-well CCD (designated QWCCD) has a channel consisting of a 140 Å GaAs layer clad on both sides by AlGaAs layers. This structure was grown on a multiple-quantum-well (MQW) structure consisting of 60 periods of GaAs and AlGaAs layers of about 100 Å thickness each. Large optical modulation effects involving quantum-confined excitons were observed in the MQW structure when a bias was applied perpendicular to the plane of the layers. The combination of QWCCD and MQW structures has promise as a high-speed spatial light modulator for applications in optical signal processing.
Selective area deposition of metals using low-energy electron beams
Authors: Kunz R. R. , Allen T. E. , Mayer T. M.
Published: July 2002

We have investigated the use of low-energy electron beams to nucleate and stimulate the deposition and growth of thin films of metals. Selective area growth of Fe from Fe(CO)5 using low-energy focused electron beams (<5 keV) has been deomnstrated. Low-energy electron-beam irradiation (0.5–3.0 keV) can be used to nucleate growth of Fe on a Si surface. Subsequent thermal decomposition of Fe(CO)5 on Fe is ∼900 times faster than on Si at 125 °C resulting in thick, polycrystalline Fe films deposited only in areas irradiated by the electron beam. We have demonstrated nucleation and growth of 150 nm Fe features using 3 keV, 100-nm-diam electron beam. Fluxes and energies of low-energy electrons passing through the surface (primaries, secondaries, backscatters) are calculated by a Monte Carlo technique using an accurate scattering cross section for low-energy electrons. Spatial distributions of backscatters and secondaries at primary energies <3000 eV are seen to be confined primarily to a radius of <10 nm from the point of impact, and it appears that scattering contributes little to the spatial distribution of deposited film. Minimal electron scattering at low-energy makes this regime attractive for direct write, selective area processing.
Electrical damage induced by ion beam etching of GaAs
Authors: Scherer A. , Craighead H. G. , Roukes M. L. , Harbison J. P.
Published: July 2002

We have examined the electrical damage induced in GaAs by ion milling and ion beam assisted etching, relevant to the fabrication of small conducting structures. The depth of the damage was measured by Schottky barrier measurements with in situ deposited gold contacts and by resistance and mobility measurements of etched two-dimensional electron gas structures. The effect of exposed etched sidewalls on the conductivity of narrow wires was examined for GaAs/AlGaAs structures. We find that it is possible to create wires narrower than surface depletion lengths by defining the structures through ion beam induced damage without exposing the sidewalls. In particular, narrow conducting wires can be defined solely by etching the thin-undoped-GaAs cap layer atop the modulation doped material.
Mask bias in submicron optical lithography
Authors: Mack Chris A. , Kaufman Patricia M.
Published: July 2002

The effects of mask bias on the performance of an optical lithographic process are examined theoretically and experimentally. By studying the effects of bias on the aerial image, the fundamental reasons for process improvement with bias are made clear. Simulations are used to examine mask linearity and exposure and focus latitude as a function of bias. Experimental data confirm the improvement in latitude for isolated lines with bias. The proximity effect is investigated and shown to be not well understood. Two possible explanations for the proximity effect: image flare and developer depletion, are studied.
Adsorbate-induced surface states and Fermi-level pinning at semiconductor surfaces
Authors: Mönch Winfried
Published: July 2002

Adatoms on semiconductors are inducing surface states and surface dipoles. These adatom-induced surface states are responsible for the pinning of the Fermi level at adsorbate-covered semiconductor surfaces. Adatom-induced surface dipoles, on the other hand, are changing the ionization energy of the surface. Metal atoms evaporated on, for example, GaAs(110) surfaces held at low temperatures were observed to induce surface states of donor character while with nonmetal adatoms such as chlorine, sulfur, and oxygen, on the other hand, adatom-induced surface acceptors were observed. The energy levels of the metal-induced surface donors were found to be linearly correlated with the first ionization energies of the metal atoms. For metal adatoms with one outer s electron, this chemical trend is explained in a surface–molecule or bond picture by using a simple tight-binding approach. In the band picture, on the other hand, adatom-induced surface dipoles are described by the tails of the electron wave functions of the adatoms into the semiconductor. These tails are derived from the virtual gap states of the complex band structure of the semiconductor.
GaAs/InP and InAs/InP heterojunction band offsets measured by x-ray photoemission spectroscopy
Authors: Waldrop J. R. , Grant R. W. , Kraut E. A.
Published: July 2002

X-ray photoemission spectroscopy (XPS) has been used to measure the unstrained valence-band offset ΔEv for the x=0 and x=1 end points of the Inx Ga1−x As/InP (100) heterojunction system. Although the GaAs/InP (100) and InAs/InP (100) pseudomorphic interfaces investigated are strained because of lattice mismatch, the ΔEv values obtained by the XPS measurement analysis used are interpreted as characteristic of an unstrained interface. Strain-free values of ΔEv (GaAs/InP)=0.19 eV and ΔEv (InAs/InP)=0.31 eV are reported. A linear interpolation of these x=0 and x=1 unstrained values gives ΔEv (In0.53 Ga0.47 As/InP)=0.25 eV (ΔEc/ΔEv =58/42) for the lattice-matched interface.
Molecular-beam epitaxial growth of metastable Ge1−xSnx alloys
Authors: Piao J. , Beresford R. , Licata T. , Wang W. I. , Homma H.
Published: July 2002

Substrate-stabilized, metastable, single-crystal Ge1−xSnx films can be grown by molecular-beam epitaxy (MBE). We have grown for the first time single crystal Ge1−xSnx alloys on lattice matched GaSb (with x=0.5) and InP (with x=0.26) substrates up to a thickness of 0.3 μm. Reflection high-energy electron diffraction (RHEED) observations and x-ray measurements show that even at very small lattice mismatch (less than 0.05%), single crystal Ge1−xSnx films cannot be grown thicker than 0.3 μm. Our x-ray results suggest that the critical thickness of α-Sn and Ge1−xSnx single crystal films is mainly determined by a phase transition mechanism, and the dislocation generation equivalent critical thickness is an overestimate. Under practical MBE growth conditions, it is very difficult to grow thick films, due to the sensitivity of the critical thickness to composition fluctuations. We have shown that even under an exact lattice match between substrate and film, the critical film thickness is limited.
In-plane solvent diffusion in a soluble polyimide lift-off structure
Authors: Shih D-Y. , Galligan E. , Cataldo J. , Paraszczak J. , Nunes S. , Serino R. , Graham W. , McGouey R.
Published: July 2002

The mechanism that governs the in-plane solvent (N-methyl pyrrolidinone) diffusion in a soluble polyimide [3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride and diaminophenylindane (BTDA-DAPI)] lift-off structure was investigated. Using a metal-on-polyimide test pattern along with a surface profilometer, the solution process was shown to occur in three stages. A thermal-activated diffusion process which follows the t1/2 Fick’s law was observed as solvent molecules diffuse laterally (parallel to the film plane) underneath the metal pad, which serves as a solvent diffusion barrier, into the soluble polyimide film. The diffusion coefficients are described by the expression: D=0.0005 exp(−3600 cal/RT) cm2/s, over the 40–85 °C temperature range. Behind the diffusion front was a region of solvent/polyimide (PI) swollen gel with increasing solvent concentration away from the front. After a maximum solvent concentration was reached, the swollen gel began to disintegrate into the solvent bath. This gradually led to a completely dissolved region behind the swollen gel. The rate of solvent diffusion was very close to that of dissolution. Both were governed by the peak PI curing temperature, solvent temperature, and the types of solvent used. Based on this study, the total time required to lift off evaporated metal on top of the stencil can be calculated from the diffusion coefficients and the induction time obtained at each temperature.
Numerical modeling of electron and ion optics on personal computers
Authors: Munro Eric
Published: July 2002

Dramatic advances in the power and cheapness of personal computers (PCs) over the past decade, combined with the development of new computer-aided design software, now enable most aspects of electron and ion optical system design to be carried out on PCs. The latest desktop computers, such as the new 80486-based systems and the IBM RISC System/6000, offer computing speeds faster than many mainframes, and enable complete electron optical systems to be designed quickly and cheaply before they are built. The paper describes and illustrates major areas of electron optical design which can now be routinely computed on PCs, including design of individual electron lenses and deflectors, optimization of complete electron or ion optical columns for lithography and inspection (including dynamic focusing and stigmation), discrete Coulomb interactions, analysis of electron guns, multipole systems for beam transport and aberration correction, tolerancing of individual components and complete electron optical columns, design of photomultiplier tubes, fully three-dimensional (3D) field computation and ray tracing in systems with combined electrostatic and magnetic fields, and the 3D modeling of electron-specimen interactions and charging problems in the scanning electron microscope.
Successive oxidation stages and annealing behavior of the Si(111) 7×7 surface observed with scanning tunneling microscopy and scanning tunneling spectroscopy
Authors: Pelz J. P. , Koch R. H.
Published: July 2002

Scanning tunneling microscopy and spectroscopy reveal at least a two-stage reaction process which occurs at adatom sites on Si (111) 7×7 surfaces exposed to oxygen at 300 K. Reacted adatoms in the first stage have a slightly modified electronic spectrum and show a preference for the faulted half and the corners of the 7×7 unit cell, while second stage adatoms appear similar to ‘‘missing’’ or ‘‘lowered’’ adatoms in topographic images. Annealing the surface to ∼625 K causes large changes in the number and site preference of the two stages.
Surface-photovoltage effects on adsorbate-covered semiconductor surfaces at low temperatures
Authors: Kampen T. U. , Troost D. , Hou X. Y. , Koenders L. , Mönch W.
Published: July 2002

Surface photovoltage (SPV) needs to be considered in optical studies of electronic properties of semiconductor surfaces. We used a Kelvin probe (CPD), ultraviolet photoemission spectroscopy (UPS), and electric-field-induced Raman spectroscopy (EFIRS) to investigate the effect of SPV on adsorbate-induced variations of surface band bending at InP(110) and GaAs(110) surfaces at low temperatures. On InP(110) surfaces, which were exposed to Cs, H, and Cl2 at ≊170 K, the SPV was found to depend on the type of adsorbate and its coverage. After the light was switched off, the SPV was found to decay with time constants varying between some minutes up to a few hours. For GaAs(110) surfaces exposed to atomic hydrogen at 140 K, we observed the light of a discharge lamp to flatten the bands. By using EFIRS, on the other hand, the buildup of surface band bending was unambiguously detected as a function of exposure to atomic hydrogen. The H-induced changes of surface band bending determined from variations of the work function measured in the dark with a Kelvin probe and of the ionization energy evaluated from the widths of UPS spectra excellently agree with the EFIRS-derived data.
Nanofabrication of metal structures in gold films deposited on mica
Authors: Silva L. A. , Laitenberger P. , Palmer R. E.
Published: July 2002

A technique is described for fabricating simple metal structures with the scanning tunneling microscope (STM) which have dimensions of 10’s to 100’s of nanometers and are partially electrically isolated from their environment. The basic idea is to deposit a very thin metal film on an insulating substrate, and use the tip to machine gaps through the film where lateral electrical insulation is desired. A brief account is given of the technical issues involved in using the STM in this way. These include locating the metal–insulator interface, tip selection criteria, and variations in the tip’s machining properties. A 190 Å thick gold film deposited on mica is used to demonstrate the technique. Two potentially useful structures are shown which have been machined in this film: a wire segment 70 nm wide, and metal pads with widths of 240 nm and 50 nm.
Scanning tunneling microscopy/scanning electron microscopy combined instrument
Authors: Asenjo A. , Buendía A. , Gómez-Rodríguez J. M. , Baró A. M.
Published: July 2002

A new scanning tunneling microscope/scanning electron microscope (STM/SEM) combined system has been developed based on an ultrasmall size STM that can be placed and removed from a SEM commercial chamber without breaking the vacuum. The STM device allows three-dimensional coarse positioning of the tip by means of inertial drive mechanisms. The total XY movement is 1 mm2 with a resolution of 50 nm. In that way STM images can be obtained on any preselected spot of the sample under simultaneous tip and sample SEM inspection. The stability of the microscope is high enough as to obtain atomic resolution on highly oriented pyrolithic graphite.
Scanning tunneling microscopy/spectroscopy study of V2O5 surface with oxygen vacancies
Authors: Oshio Takanori , Sakai Yoshiyuki , Ehara Shaw
Published: July 2002

The geometric and electronic structures of the V2O5(010) surface with oxygen vacancies were studied by means of scanning tunneling microscopy/spectroscopy. Vanadyl oxygens which play an important role in an oxidization catalyst are found to be easily desorbed in a line along the c axis by annealing the sample above 500 °C. We obtained the current images of vanadium V4+ ion rows caused by the desorption of vanadyl oxygens and also the images of V5+ ion rows distinctively. Periodic vanadium ion rows having about a half-space of lattice constant a of V2O5 were observed when almost all vanadyl oxygens were desorbed from the surface.
Profile modeling of high density plasma oxide etching
Authors: Han Joseph S. , McVittie James P. , Zheng Jie
Published: July 2002

The mechanisms of the oxide etching process are studied using the overhang test structures etched on the Applied Materials inductively coupled plasma oxide etcher. The results from the overhang test structures clearly show many details of the surface interactions that etched trenches would not show. Together with results obtained with standard trench structures etched with the same process, a new model for oxide etching is developed to explain the observed profiles and trends. The two neutral, simultaneous deposition and etching model contains several key features. Components controlling the deposition behavior are: (1) polymer chemical vapor deposition, (2) ion enhanced deposition, and (3) angle dependent polymer sputtering. The etch rate is simulated with a saturation model, where the rate can be ion or neutral flux limited. The model is incorporated into the profile simulator SPEEDIE and the simulations are run with one set of parameters. The simulation results show good agreement with the scanning electron microscopy experiment results for both profile and lag trends.
Negative resist corner rounding. Envelope volume modeling
Authors: Hagouel Paul Isaac L. , Neureuther Andrew R. , Zenk Andrew M.
Published: July 2002

A pronounced feature of negative resist developed profiles is corner rounding. Almost all of the current resists are composed of polymeric materials and negative resists depend on cross-linking during exposure for feature delineation after development. The envelope sphere polymer molecule modeling describes the creation of the rounded profile at corners of resist lines during dissolution. A cellular automata dissolution model incorporates the envelope model, simulates the mechanics of the etching process, and predicts the corner rounding. We used Shipley SNR-248 negative resist for the experimental profiles. The experimental results confirm the dependence of the dissolution rate Eri,j on the differential etch rate between exposed and unexposed regions (volumes) of the resist. High postexposure bake temperatures and higher development environment temperatures modify the profiles.
Fabrication of micromechanical switches for routing radio frequency signals
Authors: Randall John N. , Goldsmith Chuck , Denniston David , Lin Tsen-Hwang
Published: July 2002

Micromechanical switches have several advantages over other switch technologies for the routing of microwave and mm-wave signals. They offer low loss, low switching power, very low standby power, and are extremely linear. The switching speeds are very slow compared to solid state switches; however, for a number of applications, their specifications appear attractive. For instance, electronically steerable antenna arrays operating at 10, 20, and 30 GHz need phase shifters for each antenna element. Micromechanical RF switches that offered lower losses could find significant applications as phase shifters for telecommunications applications. We describe the fabrication of membrane micromechanical RF switches that switch signals of 10 GHz and higher. Dry etching plays a critical role in fabrication. In particular the isotropic removal of a sacrificial polymer layer between the bottom electrode and the membrane is a critical process. Reasonable rates must be obtained at moderate temperatures and there must be as little residue as possible. A high degree of selectivity over that of the capacitor dielectric is also a requirement. Our process should be compatible with microwave monolithic integrated circuit (MMIC) processing technology allowing integration with RF amplifiers and other components.
Investigation of low temperature SiO2 plasma enhanced chemical vapor deposition
Authors: Deshmukh Shashank C. , Aydil Eray S.
Published: July 2002

Low temperature (<270 °C) plasma enhanced chemical vapor deposition (PECVD) of SiO2 thin films using tetraethylorthosilicate (TEOS) and O2 plasma was investigated. Depositions were carried out in a PECVD reactor with a helical resonator discharge source. Transmission infrared spectroscopy, spectroscopic ellipsometry, and wet etch rate measurements were used to characterize the deposited films as a function of rf power, gas composition, and substrate temperature. Most pronounced effects were observed when the substrate temperature and TEOS:O2 flow ratio ℜR were varied. Good quality SiO2 films can be obtained at high temperature and/or low ℜR. For R≳0.1, while the deposition rate was weakly dependent on temperature between 260 and 100 °C, it increased almost by a factor of 2 between 100 and 45 °C. This is also accompanied by drastic changes in film properties such as refractive index, increase in OH and –OC2H5 content, and decrease in film density. Studies using in situ attenuated total reflection Fourier transform infrared (ATR FTIR) spectroscopy indicated that stable good quality SiO2 films without any SiOH at higher temperature (250 °C) and with very little SiOH at room temperature could be deposited using very low R. Based on the understanding provided by ATR FTIR, films with properties approaching to those of thermal oxide have been deposited at room temperature.
High temperature surface degradation of III–V nitrides
Authors: Vartuli C. B. , Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Lambers E. S. , Zolper J. C.
Published: July 2002

The surface stoichiometry, surface morphology, and electrical conductivity of AlN, GaN, InN, InGaN, and InAlN were examined at rapid thermal annealing temperatures up to 1150 °C. The sheet resistance of the AlN dropped steadily with annealing, but the surface showed signs of roughening only above 1000 °C. Auger electron spectroscopy (AES) analysis showed little change in the surface stoichiometry even at 1150 °C. GaN root mean square (rms) surface roughness showed an overall improvement with annealing, but the surface became pitted at 1000 °C, at which point the sheet resistance also dropped by several orders of magnitude, and AES confirmed a loss of N from the surface. The InN surface had roughened considerably even at 650 °C, and scanning electron microscopy showed significant degradation. In contrast to the binary nitrides, the sheet resistance of InAlN was found to increase by ∼102 from the as grown value (3.2×10−3 Ω cm) after annealing at 800 °C and then remain constant up to 1000 °C, while that of InGaN increased by two orders of magnitude between 700 and 900 °C. The rms roughness increased above 800 and 700 °C, respectively, for InAlN and InGaN samples. In droplets began to form on the surface at 900 °C for InAlN and at 800 °C for InGaN, and then evaporate at 1000 °C, leaving pits. AES analysis showed a decrease in the N concentration in the top 500 Å of the sample for annealing ≥800 °C in both materials.
High-vacuum versus ‘‘environmental’’ electron beam deposition
Authors: Folch Albert , Servat Jordi , Esteve Joan , Tejada Javier , Seco Miquel
Published: July 2002

Electron beam deposition (EBD) provides an inexpensive way to fabricate nanostructures of various materials in a scanning electron microscope (SEM). However, the purity of metals deposited from an organometallic precursor gas is impaired by simultaneously deposited carbon coming both from the organometallic molecule and the residual contamination gas in the SEM chamber. We discuss carbon-contamination EBD in a standard high-vacuum SEM and compare it to EBD of Au in an environmental SEM (ESEM). The ESEM allowed us to perform ‘‘environmental’’ EBD (E-EBD), i.e., EBD in the presence of an environmental gas (1–10 Torr) in addition to the organometallic precursor gas. We built a simple device that contains a reservoir for the organometallic precursor and goes on the sample stage of the ESEM. With this device we were able to highlight the advantages of E-EBD over conventional, high-vacuum EBD. We discuss the basic chemical reactions underlying the E-EBD process.
Plasticity study of deformed materials by in situ atomic force microscopy
Authors: Coupeau C. , Girard J. C. , Grilhé J.
Published: July 2002

The emerging of a single dislocation at a surface creates a step with a height equal to the Burgers vector component normal to the surface. By coupling an atomic force microscope with a tensile tester, the fine slip line structure can be analyzed. This equipment is particularly suitable to follow the course of plastic flow from the emergence of the first few dislocations from bulk crystal to the stages of work hardening. The motivations, instrumentation and results on LiF single crystal are described.
Preparation of N-doped hydrogen-free diamondlike carbon and its application to field emitters
Authors: Moon Jong Hyun , Chung Suk Jae , Han Eun Jung , Jang Jin , Jung Jae Hoon , Ju Byeong Kwon , Oh Myung Hwan
Published: July 2002

We have studied the electrical, optical and field emission properties of nitrogen gas-phase doped hydrogen-free diamondlike carbon (DLC) films. The N-doped hydrogen-free DLC films were deposited by an alternating layer deposition technique using plasma enhanced chemical vapor deposition, in which deposition of a thin layer of gas-phase doped DLC and CF4 plasma exposure on its surface were carried out alternately. The optical band gap of the DLC films decreases from 1.8 to 1.55 eV with an increase of the [N2]/[CH4] ratio from 0% to 24% because of an increase of the graphite phase (π state). The emission current density and onset field are strongly related to the gas-phase doping concentration in the DLC films. The optimum [N2]/[CH4] flow rate ratio for efficient electron emission was found to be 9%. The onset field and the effective barrier energy at 9% are 7.2 V/μm and 0.02 eV, respectively. The material appears to be modified into a carbon-nitrogen alloy when it exceeds 9%. We have also studied the enhanced field emission characteristics of nitrogen gas-phase doped hydrogen-free DLC films on Mo tip field emitter arrays. The maximum emission current for each pixel increased from 160 μA to 1.52 mA with the addition of a 200 Å thick N doped hydrogen-free DLC coating on the Mo tips.
A study of the relationship between Si/SiO2 between interface charges and roughness
Authors: Lai L. , Hebert K. J. , Irene E. A.
Published: July 2002

This study examines the correlation between interface roughness and charges. Atomic force microscopy (AFM) and a newly developed area roughness function which couples two roughness parameters, root-mean-square (rms) and fractal dimension (DF), are used to reliably and accurately characterize surface roughness. Interface charges (Dit and Qf) are measured using high frequency and quasistatic capacitance–voltage methods. This study is divided into three parts where smooth, purposely roughened, and purposely smoothened Si substrates are used to make metal–oxide–semiconductor capacitors for measurements. Purposely roughened substrates are obtained using a chemical acid etch solution. Purposely smoothened substrates are initially roughened with the chemical acid etch solution and smoothened through thermal oxidation. We report that the increases of Dit and Qf with Si roughness are due entirely to the area increase and orientation changes the result from roughness.
Process sensing and metrology in gate oxide growth by rapid thermal chemical vapor deposition from SiH4 and N2O
Authors: Lu Guangquan , Tedder Laura L. , Rubloff Gary W.
Published: July 2002

Active sampling mass spectrometry has been used for process sensing in gate oxide growth by rapid thermal chemical vapor deposition from SiH4 and N2O. Equipment and process behavior throughout the short process cycle were revealed in the detailed time-dependent changes of downstream mass spectroscopic signals. A H2 reaction product was clearly identified during SiO2 deposition for SiH4/N2O ratios of 0.5%–2.0% at 5 Torr total pressure and in the temperature range 750–850 °C. No H2O product was observed, suggesting that the process is dominated by a two-step reaction involving SiH4 pyrolysis and subsequent N2O oxidation of the deposited Si to form SiO2. The evolution of the H2 product signal during a process was then used as a process indicator. The integrated H2 signal was found linearly proportional to the deposited oxide thickness, providing the basis for real-time, noninvasive thickness metrology applications. This work demonstrates that properly configured real-time mass spectrometry is capable of providing not only time-dependent chemical information about system behavior, but also quantitative metrology for the film deposition process.