bluuebunny/crossref_metadata_2025 huggingface dataset:
Pattern profile control in magnetron reactive ion etching of poly-Si
Authors: Kimizuka Masakatsu , Watanabe Yoshio , Ozaki Yoshiharu
Published: July 2002

The effect of adding SF6 or C2H6 to Cl2 plasma to control the pattern profile in poly-Si etching has been studied using a magnetron reactive ion etching system. It is found that the sidewalls of patterns etched with pure Cl2 plasma are either sloped or vertical depending on whether a radio-frequency (rf) power of 700 W (0.9 W/cm2) or 600 W(0.77 W/cm2) is applied. By increasing the content of SF6 the angle of the sidewall taper of the pattern etched at 700 W rf power reaches 90°. Adding C2H6 makes it possible to adjust the slope of the sidewall over a range from 77° to 90° at a rf power of 600 W. These observed results are attributed to plasma polymerization.
Nonlinear optical effects in rotationally twinned CdTe and CdMnTe crystals
Authors: Becla P. , Witt A. F. , Dewey C. F.
Published: July 2002

The crystal growth conditions leading to the formation of rotational twins in binary CdTe and pseudobinary CdMnTe alloys were studied experimentally. Phase-matched second harmonic generation on periodic structures composed of rotational twins grown in this effort was tested. It is shown that alloying CdTe with MnTe is effective in increasing the tendency of twinning as well as the nonlinear coefficient deff.
Quantum Hall effect and setback modulation doping in HgTe–CdTe heterostructures
Authors: Hoffman C. A. , Meyer J. R. , Bartoli F. J. , Lansari Y. , Cook J. W. , Schetzina J. F.
Published: July 2002

HgTe–CdTe superlattices with electron concentrations up to 3×1017 cm−3 have been grown by photoassisted molecular-beam epitaxy with controlled indium doping of the CdTe barriers. Magnetotransport measurements indicate that the low-temperature electron mobility is relatively independent of donor concentration at large ND, in contrast to the Hg1−xCdxTe alloy system in which μn strongly decreases with ND. Also studied are the first Hg-based heterostructures with setback doping, i.e., with an undoped spacer layer between the donors in the middle of the barriers and the electrons in the quantum wells. A 43 Å setback is found to produce a factor of 2 mobility increase over any measured previously in heavily doped samples, and an 81 Å setback leads to further enhancement of μn. All superlattices with doping levels ≥8×1015 cm−3 display the quantum Hall effect. Quantization of the Hall conductivity in multiples of ≊NWe2/h indicates participation by nearly all of the 𝒩W periods in the superlattice, implying that the controlled doping is extremely uniform.
Orientation dependance of arsenic incorporation in metalorganic chemical-vapor deposition-grown HgCdTe
Authors: Elliott J. , Kreismanis V. G.
Published: July 2002

The influence of substrate orientation on p-type doping was investigated on three different CdTe crystallographic orientations: (111)B, (111)A4°→(110), and (100)4°→(110). Teritarybutylarsenic was used as the p-type dopant source in a conventional, atmospheric pressure direct alloy growth metalorganic chemical-vapor deposition growth process. Hall measurements on annealed baseline undoped growths showed high mobility and low carrier concentration material on all three orientations. At high Hg/Te ratios, it was possible to dope the (111)B to the low 1016/cm3 range and the (111)A4°→(110) and (100)4°→(110) to the low 1017/cm3 range.
Lateral p–n junctions between quasi-two-dimensional electron and hole systems at corrugated GaAs/AlGaAs interfaces
Authors: Harbury Henry K. , Porod Wolfgang , Goodnick Stephen M.
Published: July 2002

We report on a numerical study of the potential profile and energy states of lateral p–n junctions at the GaAs/AlGaAs interface. The junctions arise from the amphoteric nature of Si doping during molecular-beam epitaxial growth on {100} versus {111} surfaces and have been previously realized experimentally through selective chemical etching. We find that the occurrence of a lateral p–n junction is sensitive to the doping of the overlayer and for Si doping concentrations less than 5 × 1017 cm−3 in Al0.3Ga0.7As, the p–n junction vanishes. We have studied the formation of a quantum wire in a V-groove structure and show that a one-dimensional system is in fact formed which may be controlled by the reverse bias applied between the n and p regions.
Model for surface diffusion of aluminum–(1.5%) copper during sputter deposition
Authors: Cale Timothy S. , Jain Manoj K. , Taylor Donald S. , Duffin Robert L. , Tracy Clarence J.
Published: July 2002

Surface diffusion plays a critical role in improving the step coverage of sputter deposited aluminum–copper (Al–Cu) films, which are widely used in the microelectronics industry. Unfortunately, values of surface diffusivity as a function of temperature have not been published for aluminum copper films commonly used. We present a model for surface diffusion during sputter deposition of Al–Cu films and show that semiquantitative agreement with experimental Al–(1.5%)Cu film profiles can be obtained. This modeling and experimental work is a step toward developing a method to estimate diffusivity values using films deposited in process equipment, which would prove useful in process design. Al–(1.5%)Cu films were deposited at 303, 423, 523, and 623 K, into ‘‘infinite’’ trenches which have a variety of initial aspect ratios. No substrate bias was applied in order to minimize resputtering of deposited material. Surface diffusivity as a function of temperature was estimated by comparing experimental film profiles with profiles simulated using evolve, a physically based low pressure deposition process simulator. The equations which govern the deposition process and the required constitutive models for both curvature driven surface diffusion and deposition kinetics are discussed. Assuming a surface-free energy of 1100 erg/cm2, the expression for the surface diffusivity is D=6×10−4 exp(−5800/T) cm2/s with temperature in Kelvin. Our model predicts that step coverage increases with decreasing feature size, if all other deposition parameters are held constant, which is consistent with experiment.
Two precursor model for low-pressure chemical vapor deposition of silicon dioxide from tetraethylorthosilicate
Authors: IslamRaja M. M. , Chang C. , McVittie J. P. , Cappelli M. A. , Saraswat K. C.
Published: July 2002

The low-pressure deposition of SiO2 from tetraethylorthosilicate (TEOS) is studied. Experiments have been done to get the profile evolution in trenches of different aspect ratios and at various time steps until closure. A fast analytical simulator, using an adsorption/reemission model, which can handle multiple species, has been developed to simulate the profile evolution. The deposition profiles were simulated using a single or a two rate limiting precursor model. It has been previously shown that low-pressure chemical vapor deposition (LPCVD) of SiO2 from other sources, such as silane, can be modeled accurately using only one rate limiting precursor. Comparison of simulation results and experimental profiles of LPCVD of SiO2 from TEOS indicates that a deposition model which includes two rate limiting precursors is consistent with experiments. It is suggested that an intermediate species, having a very high reaction sticking coefficient (Sc∼1), is likely to be formed by gas phase reactions. This along with another species of low reaction sticking coefficient, thought to be from the source gas, react separately with the surface to deposit SiO2. Although a one precursor model gives approximate results for early stages of deposition or for thin coverages, it fails to predict the entire profile evolution, from the initial profile until closure. The two precursor model gives more accurate results for all profiles from the initial until closure. The pressure dependence of the step coverage and deposition rate is due to the change in the ratio of the partial pressures of the two rate limiting precursors with deposition pressure.
Two-dimensional fluid model of high density inductively coupled plasma sources
Authors: Stewart R. A. , Vitello P. , Graves D. B.
Published: July 2002

A two-dimensional (r,z) fluid model has been developed to study plasma transport in inductively coupled plasmas (ICP). Electron heating is treated by assuming a fixed, spatially varying power deposition profile in the electron energy balance equation. A high aspect ratio ICP reactor geometry has been studied, with two assumed power profiles: spatially uniform and localized to within several skin depths of the radial wall. The effect of neutral gas pressure on plasma uniformity is presented for an argon discharge over the range of 1–20 mTorr. Comparisons between the fluid model and predictions from a spatially averaged global model show similar scaling of plasma density, electron temperature, and plasma potential over a wide range of pressure and power.
Synthesis of monopole-and-quadrupole focusing columns
Authors: Mui P. H. , Szilagyi M.
Published: July 2002

Application of the simulated annealing and downhill simplex methods to the design of electrostatic monopole-and-quadrupole circular plate systems is investigated. The design objective is to minimize chromatic, relativistic, and third- and fifth-order geometric aberrations subjected to a set of predefined source parameters, source and image locations, and maximum allowed electrode potentials. Instead of searching for some optimal potential distributions, which may be extremely difficult to reconstruct in practice, a geometrically simple system consisting of circular plates is arbitrarily chosen at the start. These circular plate electrodes are each partitioned into four separate sectors so that a mixture of axially symmetric (monopole) and quadrupole fields can be generated by each individual plate. An algorithm for rapid repeated computations of the field and potential distributions is outlined. Methods of simulated annealing and downhill simplex are then invoked to find a locally optimal monopole and quadrupole potentials combination to achieve the smallest image spot size of an axial point source. Several promising results have been observed. The combination of monopoles and quadrupoles can achieve spot sizes more than two times smaller in radius than those obtained with just monopoles or quadrupoles alone. Finally, the patterns and properties of the optimal monopole and quadrupole potentials are studied in detail to gain some insight into the ideal general system behaviors and interactions.
Nanometer lithography on silicon and hydrogenated amorphous silicon with low energy electrons
Authors: Kramer N. , Jorritsma J. , Birk H. , Schönenberger C.
Published: July 2002

The oxidation of a hydrogen terminated Si surface can locally be induced with a scanning tunnelling microscope (STM) operating in air or with a beam of free electrons in a controlled oxygen environment. The oxidation mechanism of both processes was studied and compared. The oxidation with the STM in air depends strongly on the applied tip-substrate voltage and writing speed, but is not proportional to the tunnelling current. This is in contrast to the process with a beam of free electrons. The thickness of the electron beam induced oxide is studied as a function of electron energy, electron dose, and oxygen pressure. Oxide thicknesses of 0.5–3 nm are measured using Auger spectroscopy. The initial step of the oxidation process is the electron beam induced removal of hydrogen from the surface. The electron dose requirement for this step was determined as a function of electron energy. The dose is found to be minimal for 100 eV electrons, and is ≊4 mC/cm2. Oxide lines made with the STM on Si(110) were used as a mask to wet etch the pattern into the Si(110). With tetramethyl ammonium hydroxide, a selective anisotropic etch liquid, trenches with a width of 35 nm and a depth of 300 nm were made. We show that it is also possible to locally oxidize hydrogenated amorphous silicon (a-Si:H) and use the oxide as an etching mask. Hydrogenated amorphous silicon has the advantage that it can be deposited in very thin layers on almost any substrate and therefore has great potential as STM and electron-beam resist.
A study of silicon epitaxial growth on silicon substrates exposed to Ar electron cyclotron resonance plasmas
Authors: Buaud P. P. , Hu Y. Z. , Spanos L. , Irene E. A. , Christensen K. N. , Venables D. , Maher D. M.
Published: July 2002

Epitaxial growth of Si on Si(100) wafers was carried out at 700 °C in an Ar microwave electron cyclotron resonance plasma chemical vapor deposition system. Both plasma exposure prior to growth and epitaxial growth were monitored by real-time single-wavelength ellipsometry, first to determine an optimum end point for Ar plasma cleaning which would favor quality epitaxial growth, and second to follow the growth of the epitaxial film. Spectroscopic ellipsometry combined with cross-sectional transmission electron microscopy and atomic force microscopy were used to characterize the epitaxial films, the epitaxial film/substrate interface, and the surface morphology. Secondary-ion mass spectroscopy was used to evaluate the contamination levels at the film/substrate interface. Epitaxial films were successfully grown on both, smooth and rough (20–30 nm roughness layer) Si substrates. For both cases the top surface of the epitaxial film was smooth, but the interfaces were different.
Improved focusing-and-deflection columns
Authors: Mui P. H. , Szilagyi M.
Published: July 2002

Our earlier design procedures for constructing quadrupole columns are further expanded to include octupole corrector units and ‘‘octupole’’ deflectors with no third-order harmonics. The additional complications are finer partitioning of the plates and increased number of voltage controllers. Two sample designs, one having only the additional octupole deflectors and one having both the deflectors and the correctors, are presented and compared to our previous quadrupole system. The additional octupole components are shown to be capable of increasing the current density from 30% to more than 300% for a four-plate system, designed to focus and scan the electron beam over a circular area of 0.25 mm radius. The electron beam is assumed to have an initial divergence of ±2.3 mrad, an initial energy of 6 kV, a total energy spread of 1 eV, and a final acceleration of 30 keV. These systems are then slightly reoptimized for a superficial comparison with the commercially available column by Micrion Corporation. The numerical results indicate a potential for substantial improvements, demonstrating the power of this design procedure. Finally, a discussion is presented on how the individual components can interact with each other to reduce the various aberrations.
In situ etching and regrowth process for edge- and surface-emitting laser diodes with an AlGaAs/GaAs buried heterostructure
Authors: Ogura Mutsuo
Published: July 2002

An in situ dry etching and metalorganic chemical-vapor deposition regrowth process is developed to realize AlGaAs/GaAs buried heterostructure with an arbitrary shape and orientation, and is applied to edge-emitting laser diodes with a complex cavity structure and surface-emitting laser diodes (SELD). At present, threshold currents for both edge-emitting and surface-emitting lasers are similar to that of a conventional ridge-stripe waveguide laser or proton-isolated SELD, indicating that there is considerable surface recombination at regrown interfaces. Surface recombination velocity at the regrown interfaces is estimated from the size effect of lasing characteristics.
Compositional disordering of AlGaAs/GaAs superlattices by using the low-temperature grown GaAs
Authors: Tsang J. S. , Lee C. P. , Fan J. C. , Tsai K. L. , Chen H. R.
Published: July 2002

The use of low-temperature (∼200 °C) grown GaAs by molecular beam epitaxy to induce compositional disordering of AlGaAs/GaAs superlattices has been studied. After furnace annealing between 700 and 850 °C for 30 min, an obvious blue shift in the peak wavelength of the superlattice emission is observed by the 77 K photoluminescence (PL), indicating that the emission has been changed from that of the GaAs quantum wells to that of the intermixed AlGaAs. The PL shift and the depth profile of Al concentration measured by secondary ion mass spectrometry indicate that the superlattice is nearly totally disordered after 850 °C annealing.
Optically matched trilevel resist process for nanostructure fabrication
Authors: Schattenburg M. L. , Aucoin R. J. , Fleming R. C.
Published: July 2002

A novel trilevel resist process has been developed which enables high-contrast imaging of periodic structures with spatial periods down to 200 nm in thick resist on highly reflective substrates, using λ=351.1 nm argon-ion laser exposure. The process utilizes a 200-nm-thick, high-contrast, imaging resist layer, a thin (∼15-nm) evaporated dielectric interlayer, and a 300–600-nm-thick bottom antireflection coating (ARC) which suppresses reflections from the substrate. Our trilevel resist scheme has been implemented in a manufacturing process which utilizes a high-contrast interferometric lithography system for the formation of large-area, 200–1000 nm period grating and dot array images. The choice of interlayer is the most critical feature of this process. This material must have good deposition and adhesion properties, must be optically matched to the resist and ARC, must etch quickly during the reactive-ion etching (RIE) pattern transfer from the resist into the interlayer, must display very high selectivity to the ARC during the RIE pattern transfer into the bottom layer, and must be easily stripped after the trilevel resist structure has served its purpose. We also report on computer modeling which elucidates the factors influencing standing wave formation and present results of tests with several interlayer materials which display good optical matching and selectivities of up to 240:1 during RIE of the ARC.
Reliable substrate temperature measurements for high temperature AlGaAs molecular-beam epitaxy growth
Authors: Strite S. , Kamp M. , Meier H. P.
Published: July 2002

We describe a reproducible and precise temperature control system for the molecular beam epitaxial growth of AlGaAs at substrate temperatures in the 700 °C range. Coating of the optical pyrometer window was observed to dramatically affect the pryometer readings making it an unreliable temperature measurement technique. By observing pyrometer interference oscillations during both GaAs and AlGaAs epitaxy, the Ga desorption rate during AlGaAs growth was estimated. The known temperature dependence of the Ga desorption rate allowed the substrate temperature to be calculated, and corrected, when necessary, during the growth. This method allowed the absolute AlGaAs substrate temperature to be controlled within ±3 °C over a six month production cycle.
Nanometer metrology by means of backscattered electrons
Authors: Di Fabrizio E. , Grella L. , Gentili M. , Baciocchi M. , Mastrogiacomo L. , Maggiora R.
Published: July 2002

A metrological study with a Leica Cambridge (microfabrication) MF 10 cs/120 electron-beam (e-beam) machine on metal structures in the nanometer region is presented. The nanometer region (below 100 nm) considered in this study is very challenging when an e-beam machine is used in the metrological mode, because the feature sizes, in this work ranging between 60 and 170 nm, become comparable to the probe spot size. Thus, a more detailed analysis is necessary in order to extract metrological information properly. Electrons detected by an annular channel plate form the signal from which the metrological data are extracted. Based on this feature, two algorithms, one computational and the other graphical, are proposed and compared. A good agreement between e-beam-based and independent scanning electron microscope measurements is found. A statistical study shows an accurate reproducibility below 10 nm with high speed performances. Finally, dimensional control requirements are fulfilled, making the e-beam machine one of the most reliable metrological tools for metal structures even in the nanometer region down to 60 nm.
Scanning tunneling microscopy current–voltage characteristics of carbon nanotubes
Authors: Rivera W. , Perez J. M. , Ruoff R. S. , Lorents D. C. , Malhotra R. , Lim S. , Rho Y. G. , Jacobs E. G. , Pinizzotto R. F.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to obtain images and current–voltage (I–V) curves of carbon nanotubes produced by arc discharge of carbon electrodes. The STM I–V curves indicate that carbon nanotubes with diameters from 2.0 to 5.1 nm have a metallic density of states. Using STM, we also observe nanometer-size graphene sheets which are four graphite layers thick. The STM images of carbon nanotubes are in good agreement with transmission electron microscope images.
Surface morphology of metalorganic vapor phase epitaxy grown InAs and InGaAs observed by atomic force microscopy
Authors: Hsu C. C. , Xu J. B. , Wilson I. H.
Published: July 2002

We have studied the surface morphology of metalorganic vapor phase epitaxy grown InAs and InGaAs by atomic force microscopy. InAs monolayer steps were observed on an annealed InAs substrate. Monolayer steps and terraces were also observed on the grown InAs homoepitaxial layers. Step edges are smooth and straight on the grown samples. The growth mode is by step flow. In the case of InGaAs lattice matched to an InP substrate, steps are not as straight as those of InAs layers. This is due to a higher surface concentration gradient near step edges. Two-dimensional islands were observed on the monolayer terraces at a high growth rate of 1.2 nm/s.
Studies of low coverage adsorption of Li on Si(001): Observation of negative differential resistance and electron trapping
Authors: Johansson Mikael K.-J. , Gray Struan M. , Johansson Lars S. O.
Published: July 2002

We have studied the initial stages of Li adsorption onto the Si(001) surface with scanning tunneling microscopy and spectroscopy (STM/S). On p-type silicon samples, STS on the Li sites shows a region of strong negative differential resistance (NDR). In addition, with the tip held stationary above the Li sites, a digital switching is observed in the tunneling current, which we attribute to the existence of thermally activated electron traps. The changing occupation statistics of these traps as the voltage changes causes the NDR. Screening of the traps means that weaker NDR is also observed when the tip is positioned over unmodified Si dimers. Thus, very small amounts of Li have a dramatic effect on both local and extended length scales.
Scanning tunneling microscopy study of the interfacial structure of nickel silicides
Authors: Yoshimura M. , Shinabe S. , Yao T.
Published: July 2002

The growth of ultrathin silicide (∼monolayer) has been studied by scanning tunneling microscopy. Ni atoms react with the Si(111)-7×7 surface to form clusters at room temperature. With increasing annealing temperature, they gradually coalesce and form monolayer islands surrounded by √19×√19 ring structures. The surface structure shows √3×√3-R30° at 400 °C and 2×2 at 600 °C. The latter structure is a new finding for the Ni/Si system. It is suggested that the transformation of the surface structure on the monolayer island can be related to a change of the interfacial structure.
Spatially resolved electron tunneling spectroscopy on single crystalline Rb3C60
Authors: Jess P. , Hubler U. , Behler S. , Thommen-Geiser V. , Lang H. P. , Güntherodt H.-J.
Published: July 2002

A Rb3C60 single crystal (Tc=30.5 K) is investigated in the superconducting state at 2.8 K by scanning tunneling microscopy and scanning tunneling spectroscopy (STS). STS data reveals a spatial variation of the superconducting energy gap Δ on a scale of 50 nm (Δ=2.6–5.2 meV; 2Δ/kBTc=2.0–4.0). This behavior is attributed to varying stoichiometry on the sample surface. An investigation of a Rb3C60 facet shows that I(V) characteristics even vary on molecular scale. I(V) curves acquired between fullerene molecules exhibit a nonvanishing slope at zero bias whereas I(V) characteristics measured above molecules exhibit vanishing slope at zero bias.
Long term reproducibility of secondary ion mass spectroscopy measurements in silicon
Authors: Chu Paul K. , Smith Stephen P. , Bleiler Roger J.
Published: July 2002

The long term reproducibility of quantitative secondary ion mass spectroscopy (SIMS) analysis is assessed using three independent analytical procedures important to the microelectronics industry: the determination of oxygen, boron, and surface impurities in silicon. Thousands of measurements acquired from carefully selected statistical process control samples provide an excellent data base. The oxygen measurement yields a repeatability of +2% at a concentration of 28 ppma (instrumental background around 1.4 ppma). A relative standard deviation of 8.3% is achieved for the boron measurement. The boron concentration in the control sample is 5.8 ppba. Many different control samples have been monitored for surface SIMS contamination measurements, and the RSD ranges from 5% to over 100% depending on the element and magnitude of the areal densities. Our results indicate that SIMS is an excellent technique for long-term process control when rigorous analytical protocols are adopted. The oxygen and boron measurements as well as the measurement of surface sodium, aluminum, and potassium on silicon have been accepted by ASTM as standard procedures. Our analytical protocols have been extended to depth profiling analysis, such as ion implanter dose matching which is an important measurement for the semiconductor industry.
All solid source molecular beam epitaxy growth and characterization of strain-compensated 1.3 μm InAsP/InGaP/InP multiquantum well lasers for high-temperature operation
Authors: Toivonen M. , Savolainen P. , Asonen H. , Murison R.
Published: July 2002

Strain-compensated InAsP/InGaP/InP multiquantum well lasers emitting at 1.3 μm were grown by all solid source molecular beam epitaxy. A high characteristic temperature of 86 K was measured for temperatures between 20 and 120 °C for lasers with as-cleaved and high reflection coated facets. A low threshold current density of 115 A/cm2 per well was obtained for lasers with a cavity length of 1600 μm. Our results clearly demonstrate the suitability of a InAsP/InGaP strain-compensated system for lasers operating at elevated temperatures and the potential of all solid source molecular beam epitaxy for growth of optoelectronic devices.
Fundamental limits to imaging resolution for focused ion beams
Authors: Orloff Jon , Swanson L. W. , Utlaut M.
Published: July 2002

This article investigates the limitations on the formation of focused ion beam images from secondary electrons. We use the notion of the information content of an image to account for the effects of resolution, contrast, and signal-to-noise ratio and show that there is a competition between the rate at which small features are sputtered away by the primary beam and the rate of collection of secondary electrons. We find that for small features, sputtering is the limit to imaging resolution, and that for extended small features (e.g., layered structures), rearrangement, redeposition, and differential sputtering rates may limit the resolution in some cases.
Scanning near-field optical microscopy/spectroscopy of thin organic films
Authors: Nagahara L. A. , Tokumoto H.
Published: July 2002

We have used a scanning near-field optical microscope to investigate the optical properties of a thin organic film consisting of poly(phenylene vinylene) and tris(8-hydroxy)quinoline aluminum. Near-field optical images taken in transmission mode using a 488 nm laser light revealed numerous ‘‘dark spots’’ scattered randomly across the film; however, the dark spots were not related to the surface topography. These dark spots ranged in size from 100–300 nm in diameter. The nature of the dark spots was attributed to an increase in the absorption at 488 nm as a result of local variations in the poly(phenylene vinylene) film.
Gamble mode: Resonance contact mode in atomic force microscopy
Authors: O’Connor S. D. , Gamble R. C. , Eby R. K. , Baldeschwieler J. D.
Published: July 2002

Active noise reduction has been accomplished in atomic force microscopy by applying a high frequency, low amplitude vibration to the cantilever while it is in contact with a surface. The applied excitation (≳200 kHz; ∼1 nm) is acoustically coupled to the tip and dampens the resonance Q factors of the system. The applied frequency is well above the bandwidth of the acquisition system (50 kHz). We call this mode ‘‘gamble mode’’ or ‘‘resonance contact.’’
Monte Carlo simulation of inclined incidence of fast electrons to solids
Authors: Gueorguiev Y. M. , Mladenov G. M. , Ivanov D. I.
Published: July 2002

In the present work inclined incidence of accelerated electrons to solids is simulated using Monte Carlo technique. Spatial distributions of absorbed electron energy density in a 125 nm poly(methylmethacrylate) resist layer on bulk Si substrate are obtained for angles of incidence 30°, 45°, and 60° at two beam energies—25 and 50 keV—together with the energy and angular distributions of the backscattered electrons. The results show strong asymmetry of the exposure distributions. Their peaks are significantly lower, wider, and 40–100 nm shifted, and their shapes are different in comparison with those for normal incidence of electrons. The ratio between the maximum values of exposure distributions due to the forward scattered and the backscattered electrons decreases with decreasing angle of incidence. These peculiarities of exposure distributions may lead to enhanced proximity effects and cause deviation from required pattern shapes. Therefore, if inclined incidence of accelerated electrons to any surface occurs during electron beam lithography, it has to be taken into account.
Single-electron charging of a molecule observed in scanning tunneling scattering experiments
Authors: Nejo H. , Aono M. , Baksheyev D. G. , Tkachenko V. A.
Published: July 2002

Two extreme cases can be solved for electron charging effects where the first one ignores the electron correlation and the second one treats only one-electron scattering. So far, Coulomb blockade has been treated by the orthodox theory [Likharev, IBM J. Res. Dev. 32, 144 (1988)], where the charging energy is expressed as e2/2C using the capacitance C of a tunnel junction. On the other hand, one-electron scattering can be solved exactly by using the Schrödinger equation. But it is difficult to solve for a many-body system by the Schrödinger equation. In this article, stress is placed on the case where the electric field cannot be ignored anymore. A treatment of the charging energy is proposed using a screening model or an electromagnetic field model by employing a cavity model in the field of photon.
Tip–sample interactions: Extraction of single molecular pair potentials from force curves
Authors: Unger Marc A. , O’Connor Stephen D. , Baldeschwieler John D.
Published: July 2002

This article describes a method for extracting the true tip–sample potential from an experimental force curve in atomic force microscopy. This potential is not the negative integral of the force curve. Rather, the potential is a more complicated function of the force curve and cantilever spring constant. If information about the shape of the tip is known, a decorrelation may be performed to extract molecular pair potentials from the total tip–sample potential. Applications and limitations of this method are discussed.
Structural investigation of cytochrome f Langmuir–Blodgett films with scanning tunneling microscopy: Protein aggregation
Authors: Tazi A. , Boussaad S. , DeRose J. A. , Leblanc R. M.
Published: July 2002

We have imaged Langmuir–Blodgett (LB) films of cytochrome f (Cyt f), transferred onto a gold film on mica substrate which has been covered with arachidic acid (three monolayers), with the scanning tunneling microscope. From these images, we have determined the structure of the Cyt f LB films (two monolayers) as a function of surface pressure (Π) and ethanol concentration (ethanol:water) in the spreading solvent. We have observed aggregation of the Cyt f protein in films deposited at 15 and 20 mN/m with ethanol concentrations of 20%, 40%, and 80% in the spreading solvent. The LB films of Cyt f are mainly composed of aggregates a few hundred nm in size. Film morphology and aggregate sizes depend upon the ethanol concentration and the surface pressure for transfer onto the solid substrate.
InSb(1̄ 1̄ 1̄)3×1: New surface reconstruction
Authors: Björkqvist M. , Göthelid M. , Olsson L. Ö. , Kanski J. , Karlsson U. O.
Published: July 2002

Scanning tunneling microscopy studies of the InSb(1̄1̄1̄) surface have revealed highly ordered 3×1 symmetry reconstructions. The structures are produced at high annealing temperatures and are believed to be driven by the deficiency of Sb in the surface layer. The proposed model for the reconstruction involves two distinct structures: One constitutes a missing Sb row in the topmost double layer, and one comprises two missing Sb rows with an additional missing row of In.
Growth, doping, and etching of GaAs and InGaAs using tris-dimethylaminoarsenic
Authors: Dong H. K. , Li N. Y. , Wong W. S. , Tu C. W.
Published: July 2002

Growth, doping, and in situ etching of GaAs using cracked and uncracked tris-dimethylaminoarsenic (TDMAAs) in chemical beam epitaxy (CBE) have been studied. A reflection high-energy electron diffraction study indicates that the complete decomposition of TDMAAs occurs below 370 °C. Possible TDMAAs decomposition pathways, which are consistent with experimental data, are presented. The carbon level in undoped GaAs films and the hole concentration in carbon-doped GaAs films using uncracked TDMAAs are much lower than those using cracked TDMAAs, which may be due to atomic hydrogen released from the β-hydride elimination process of uncracked TDMAAs on the GaAs surface. The in situ GaAs etching effect was observed only when the substrate was exposed to uncracked TDMAAs. Possibly, reactive free radicals generated by uncracked TDMAAs on GaAs surfaces are responsible for the etching effect. Surface roughness in selective-area growth of GaAs and the poor interfaces in InGaAs/GaAs multiple quantum wells grown by CBE using uncracked TDMAAs may result from this etching effect.
Quantitative measurement of two-dimensional dopant profile by cross-sectional scanning capacitance microscopy
Authors: McMurray J. S. , Kim J. , Williams C. C.
Published: July 2002

Quantitative two-dimensional dopant profiling of a gatelike structure is achieved by scanning capacitance microscopy (SCM). A processed silicon wafer is sectioned then polished such that a cross section is made through a gatelike structure. This structure consists of two n+ doped regions separated by a lighter doped n region. The two-dimensional SCM data are converted to dopant density through a physical model of the SCM–silicon interaction. Improvements to the physical model and SCM data to dopant profile algorithm are discussed. Advances in sample preparation are described. Adjustment of the conversion model parameters allows for fitting of the SCM dopant profile to a vertical secondary-ion-mass-spectroscopy profile. The accuracy of this fit is better than 20%. This fit also gives strong evidence that the full two-dimensional profile is truly quantitative.
Observation of hot electron relaxation in GaAs/AlGaAs multiple quantum wells by excitation spectroscopy
Authors: Wu H. Z. , Liu J. H. , Dong G. O. , Wu J. Z. , Ye Z. Z. , Jiang X. B.
Published: July 2002

Hot electron relaxation in GaAs/AlGaAs multiple quantum well (MQW) structure was studied with the use of photoluminescence excitation (PLE) spectroscopy. Oscillation due to the emission of confined longitudinal optical (LO) GaAs phonons, by photoexcited electrons were observed in the (6 K) excitation spectra. The period of the oscillation is different from that observed in bulk GaAs. The calculation from a four-band Kane model, describing the mixing of heavy- and light-hole bands at wave vector away from k=0, was used to interpret the difference of oscillation features between the GaAs/AlGaAs MQW structure and bulk GaAs. The recorded PLE spectrum and calculated results show that photoexcited electrons can directly cascade downwards to the exciton energy state by LO phonon emissions.
Effects of water vapor and chlorine on the epitaxial growth of Si1−xGex films by chemical vapor deposition: Thermodynamic analysis
Authors: Lee I.-M. , Jansons A. , Takoudis C. G.
Published: July 2002

The effects of water vapor and chlorine on the Si1−xGex epitaxial growth are studied through thermodynamic analyses. Since Ge does not form chemical species with oxygen at an appreciable level, the water vapor and oxygen background level requirements for Si1−xGex epitaxial growth are mostly similar to the ones for Si growth. At large excesses of Ge gas phase sources and low system water vapor level, however, the critical temperature above which oxide-free epitaxial growth occurs decreases with increasing system pressure. Analyses of the results obtained suggest that there are two mechanisms for the removal of SiO2(s) from the surface: one is by forming volatile SiO, and the other is by forming gas phase H2O. The former one appears to dominate for most conditions studied; the latter one appears to dominate when the water vapor level of the system is very low and/or small amounts of the Si gaseous source are present. The boundary between etching and deposition of Si1−xGex films is examined for all Ge solid phase compositions. The etch/deposition boundaries for pure Si and pure Ge show opposite trends with increasing chlorine concentrations, because of the different affinities of Si and Ge to form chlorinated species. The chlorine concentration needed to reach etching increases with increasing system temperature for Si, whereas it decreases with increasing temperature for Ge. It is found that the formation of SiCl4 is favored over GeCl2 at low temperatures, while the opposite happens at higher temperatures. The etch/deposition boundary for Si1−xGex thin films is found to form a saddlelike contour because of the interaction of the different behaviors of Si and Ge. Overall, calculated results are seen to be in good agreement with available experimental results.
Anomalous behavior of resistance in Al alloy interconnections stacked with Ti layers during electromigration tests
Authors: Kouno T. , Hosaka M. , Niwa H. , Yamada M.
Published: July 2002

In Al alloy interconnections stacked with Ti layers, anomalous behavior of the line resistance was observed during electromigration tests. The line resistance monotonically decreased until it rapidly increased and the line failed. We found that the thickness of the Al lines, which showed the anomalous resistance change, increased uniformly between the anode end and the cathode one. This could explain the anomalous decrease of the line resistance. It was also found that in the resistance decreased lines extra Al grew on the original Al layer and it had the same crystal orientation as the original Al layer. In the case of Al lines with anti-reflective coating (ARC) of TiN/Ti (the upper/lower layer), extra Al grew not only on the original Al layer but also between ARC-TiN and Al3Ti which was formed by a reaction between the Al and Ti.
Extension of krypton fluoride excimer laser lithography to the fabrication of 0.18 μm devices
Authors: Ogawa Tohru , Uematsu Masaya , Takeuchi Koichi , Oda Tatsuji
Published: July 2002

This article presents the extension of krypton fluoride (KrF) excimer laser lithography. An 0.18 μm device can be fabricated by KrF excimer laser lithography when weak off-axis illumination is combined with an attenuated phase-shifting mask, a high-performance antireflective layer, and a high-numeral-aperture exposure tool. A 1.0 μm depth-of-focus can be achieved for 0.18 μm rule logic patterns. The weak off-axis illumination can reduce the influences of the secondary peak in the high-duty periodic patterns, and retain the depth-of-focus for isolated patterns when it is used in combination with an attenuated phase-shifting mask. A high-performance antireflective layer can increase the depth-of-focus because a uniformly exposed area in the photoresist can be formed when the light reflected from the substrate is eliminated.
Nanoscale etching of GaAs surfaces in electrolytic solutions by hole injection from a scanning tunneling microscope tip
Authors: Kaneshiro C. , Okumura T.
Published: July 2002

Controllable etching of GaAs(100) has been electrochemically achieved on a nanometer scale by using a scanning tunneling microscope (STM) in acidic solutions (pH=2–3). The realized features on n-GaAs(100) surface were as small as 10 nm. We studied the dependence of the etching rate on the potentials applied to the STM tip as well as the GaAs substrate. These results indicate that the hole injection from the tip is responsible for the local etching of GaAs surfaces in electrolytes rather than local charges induced by an electric field.
Modification of surface morphology and optoelectronic response in porous Si films by electrochemical methods
Authors: Yang Zhong-Hua , Zhang Peng , Wang De-Jun , Li Tie-Jin
Published: July 2002

The effect of varied H+concentration on surface morphology of porous silicon (PS) is observed by atomic force microscopy technique. A new mechanism of PS formation concerning H+ effect is proposed. The photoluminescence (PL) spectra of two typical PS samples have different responses in the short-wavelength region. Surface photovoltage spectra results imply that the short-wavelength PL band of the PS sample prepared in high H+ concentration may be related to direct band-gap transition.
Atomic force microscopy studies of Hg1−xCdxTe thin films grown by isothermal vapor phase epitaxy
Authors: Di Nardo S. , Lozzi L. , Santucci S. , Bernardi S.
Published: July 2002

Atomic force microscopy measurements have been performed in order to study mercury cadmium telluride thin films grown on hybrid substrates by means of a new method based on an isothermal vapor phase epitaxy process (iso-VPE). The morphology of the samples, grown both on sapphire and on silicon 2 in. substrates, was observed at the different steps of the iso-VPE process. In the case of the silicon substrate the absence of interdiffusion with the deposited film was detected by means of a cross sectional atomic force microscopy analysis of the sample. Moreover, the surface quality of the iso-VPE grown thin films has been found to be comparable with that of samples grown on hybrid substrates by means of conventional techniques like liquid phase epitaxy. Fourier-transform infrared measurements were also performed in order to prove the high optical goodness of the samples.
Fourier transform infrared study of porous silicon dipped into Cr3+ solution
Authors: Huang Y. M. , Zhai B. G.
Published: July 2002

We have measured Fourier transform infrared (FTIR) spectra of Cr3+ immersed porous silicon after annealing at different temperatures. After dipping porous silicon into Cr3+ solution, three additional peaks appear at 807, 886, and 940 cm−1 in the FTIR spectrum. When annealed in nitrogen at different temperatures for various durations, the peak at 807 cm−1 remains almost unchanged, the height of peak 886 cm−1 decreases gradually, while the peak at 940 cm−1 disappears quickly. This decay process occurs much faster at higher annealing temperature. These FTIR features reflect the surface chemistry change after immersed into Cr3+ solution.
Emission characteristic of diamond-tip field emitter arrays fabricated by transfer mold technique
Authors: Kim Seongjin , Ju Byeong Kwon , Lee Yun Hi , Park Beom Soo , Baik Young-Joon , Lim Sungkyoo , Oh Myung Hwan
Published: July 2002

Wedge-shaped diamond-tip field emitter arrays were fabricated and characterized. The tip radius of the diamond emitter fabricated by using a silicon mold was about 300 Å. The maximum current density of 800 μA/cm2 and the threshold voltage of 600 V were obtained from the diamond-tip field emitter array, which was a better electrical characteristic than that of a flat diamond film. The effects of vacuum pressure upon emission characteristics were investigated. The emission characteristic of the diamond-tip field emitter array was not varied over a wide range of vacuum pressure relatively to the flat diamond film.
Reactive ion etching of CHF3+BCl3 for ternary InxAl1−xAs and InxGa1−xAs (x=0.18, 0.3, 0.52) compounds using various In contents
Authors: Kao Hung-Chung , Lai Li-Shyue , Chan Yi-Jen
Published: July 2002

CHF 3 +BCl 3 reactive ion etching etching was used to study the etching of InxGa1−xAs and InxAl1−xAs layers with varied In contents (x=0.18, 0.3, 0.52). By adding CHF3 gas, it is possible to effectively reduce the etching rate of InxAl1−xAs, without any influence on the InxGa1−xAs. The etching rate of InxGa1−xAs decreased with the In content; however, InxAl1−xAs showed the opposite trend. The etching selectivity between the InxGa1−xAs and the InxAl1−xAs layers was increased by reducing the In content.
Cross-sectional nano-spreading resistance profiling
Authors: De Wolf P. , Clarysse T. , Vandervorst W. , Hellemans L. , Niedermann Ph. , Hänni W.
Published: July 2002

The nano-spreading resistance profiling (nano-SRP) method has been developed and improved such that it can now be used as an accurate tool for quantitative two-dimensional carrier profiling. Instrumental improvements include the use of batch-fabricated, conducting diamond-coated silicon probes, and a low-noise logarithmic current amplifier. The spatial resolution (10 nm), the dynamic range (1014–1020 atoms/cm3), and the sensitivity (1014 atoms/cm3) of the nano-SRP technique are illustrated by profiling a wide range of state-of-the-art device structures. Two-dimensional measurements of the carrier distribution inside fully processed metal–oxide–semiconductor transistors with gate lengths varying from 2 μm down to 0.25 μm illustrate the strength of the technique to map present and future devices. The nano-SRP method currently has sufficient resolution to demonstrate the small asymmetry in the source/drain profiles from transistors in which the sample was not rotated during the 7° implant. The electrical transistor characteristics confirm the nano-SRP results. As another example, the lateral diffusion of arsenic and phosphorus profiles is studied as a function of implantation conditions. All results are compared with conventional one-dimensional techniques (SRP and secondary ion mass spectroscopy).
Visualization of plasma uniformity in dry etching using the imaging plate
Authors: Arita Kiyoshi , Etoh Masahiro , Asano Tanemasa
Published: July 2002

Monitoring two-dimensional plasma uniformity in dry etching process by using the imaging plate has been investigated. It was found that the distribution of photostimulated-luminescence intensity of the imaging plate correlates well with the distribution of the ion density in the plasma measured with a Langmuir probe. The effect of ultraviolet light from the plasma has been investigated by covering the imaging plate with a quartz wafer. It was found that the imaging plate senses ultraviolet light from the plasma whose intensity is correlated with the ion density in the bulk plasma.
Molecular beam epitaxy growth of SiC on Si(111) from silacyclobutane
Authors: Chen J. , Steckl A. J. , Loboda M. J.
Published: July 2002

3C–SiC films have been grown by molecular beam epitaxy on Si(111) substrates using a single organosilane precursor (silacyclobutane-SiC3H8). Temperatures of 800 to 1100 °C and pressures of (1–5)×10−6 Torr were utilized. The growth rate of the SiC films obtained from secondary ion mass spectrometry depth profiles ranged from 1 to 6 Å/min. The SiC chemical bonding structure was confirmed by Fourier transform infrared spectrometry. The surface morphology and crystallinity of SiC films were studied by scanning electron microscopy (SEM), reflection high energy electron diffraction and x-ray diffraction. Typical triangular growth pits of various sizes were observed by SEM. X-ray diffraction reveals that SiC films grown in the presence of native oxide exhibit better crystallinity than those grown on surfaces from which the oxide is removed prior to growth.