bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanometer-scale observations of the corroded surfaces of metallic glass Fe40Ni38Mo4B18
Authors: Watanabe Yoshihisa , Nakamura Yoshikazu , Hirayama Shigekazu , Taniguchi Nobuki
Published: July 2002

The change in the surface morphology of metallic glass Fe40Ni38Mo4B18 during the early stages of corrosion by nital has been observed by atomic force microscopy. The effects of crystallization on the corrosion process have been studied. The corrosion behavior of the as-quenched specimen is summarized as: (1) protrusions, whose height is less than 10 nm before corrosion, appear from the matrix with the progress of corrosion; (2) the average surface roughness increases, approximately from 1 to 5 nm, during 30 min of corrosion. This result can be explained by the assumptions that (1) protrusions are metal–boride crystallites which show a resistance, (2) the matrix is corroded because of its iron-rich composition, and (3) crystallites buried in the matrix appear due to the corrosion of the matrix. Corrosion of the annealed specimen is similar to that of the as-quenched specimen. However, the protrusions are much larger and the average surface roughness increases approximately from 5 to 25 nm during 30 min of corrosion. These results indicate that the corrosion resistance of this metallic glass is lowered by crystallization.
Progress towards λ/20 extreme ultraviolet interferometry
Authors: Goldberg K. A. , Beguiristain R. , Bokor J. , Medecki H. , Attwood D. T. , Jackson K. , Tejnil E. , Sommargren G. E.
Published: July 2002

Diffraction-limited optical imaging systems for extreme ultraviolet (EUV) lithography require wave front aberrations to be limited to a fraction of the EUV wavelength. Surface figure metrology and wave front measurement at this level of accuracy represent key challenges in the development of EUV lithography. We have constructed and operated a wave front measuring interferometer at 12–13 nm wavelength. This interferometer is being used to measure the aberrations in 0.1 numerical aperture Fresnel zone plate lenses. Factors limiting the resolution and accuracy of the interferometer were studied. Substantial progress toward λ/20 wave front measurement accuracy has been made.
High resolution x-ray mask repair
Authors: Blauner Patricia G.
Published: July 2002

Repair of gold absorber x-ray masks with ground rules down to 250 nm is now accomplished using commercially available focused ion beam (FIB) tooling. Chief among the challenges in extending this technology to below 250 nm is that presented by the redeposition of absorber material during opaque repair. This article examines several techniques which have been proposed to minimize redeposition, including the use of thinner absorbers, gas assisted etching, and simple postrepair trimming. In addition, the capabilities of the current tooling is demonstrated and a comparison of the FIB etch characteristics of several different absorber materials proposed for future mask fabrication (Au, W, and TaSiN) is presented.
High synchrotron radiation durability microwave plasma chemical vapor deposition diamond x-ray mask membrane
Authors: Tsuboi Shinji , Okuyama Hiroshi , Ashikaga Kinya , Yamashita Yoshio
Published: July 2002

Diamond is a very attractive material for x-ray mask membranes since it has high Young’s modulus, high transmission under exposure to soft x rays (in the exposure wavelength region of 0.5–1.5 nm), and good thermal conductivity. However, there remains a drawback of synchrotron radiation damage. Microwave plasma chemical vapor deposition diamond membranes under several kinds of deposition conditions have been evaluated. It is found that x rays attack only the nondiamond component of the membrane, and a diamond membrane having good crystallinity shows high x-ray irradiation durability.
Numerical analysis on field emission for the effects of the gate insulators
Authors: Ahn Ho Young , Lee Chun Gyoo , Lee Jong Duk
Published: July 2002

A program to solve the Poisson equation by a finite element method has been developed to simulate accurately the distributions of potential and electric field of the field emission microtriode. The emission current can be calculated by this method more accurately and efficiently than the finite difference method. Moreover, we can consider the effect of a gate insulator structure that cannot be treated by boundary element method. The optimal gate insulator is investigated from the viewpoint of the multilayer structure and the edge shape of the insulator. The emission current can be improved more than 85% using a gate insulator with a vertical edge shape and double-layer structure with different permittivities.
Atomic force microscopy study of electron beam written contamination structures
Authors: Amman M. , Sleight J. W. , Lombardi D. R. , Welser R. E. , Deshpande M. R. , Reed M. A. , Guido L. J.
Published: July 2002

Electron radiation induced hydrocarbon contamination can be either a problem or a useful tool in electron beam analyses and lithographies. We have used atomic force microscopy to study electron beam written contamination structures. Contamination is shown not only to arise from the primary electron beam but also from the energy scattered outside of the direct impingement area. The size of the contamination structures correlates well with that expected from electron scattering theory. By varying the geometry of the written structures, the rate at which the electron dose is deposited, and the nearby hydrocarbon surface density, we show that surface diffusion of hydrocarbon molecules plays a primary role in the formation of the contamination structures.
Comparison of damage created by a chemical downstream etcher and plasma-immersion system in metal–oxide–semiconductor capacitors
Authors: Brożek Tomasz , Dao Thuy , Viswanathan Chand R.
Published: July 2002

The effect of a chemical downstream etching (CDE) environment on the oxide integrity and electrophysical properties of thin oxide metal–oxide–semiconductor capacitors was investigated with respect to the poly-buffered local oxidation process. CDE plasma-related effects were compared to that caused by exposure to high-density plasma. Two types of plasma-induced damage were isolated for both plasma exposures; one due to plasma charging manifests itself through antenna dependence of gate oxide integrity, while the other results in generation of defects (generation-recombination centers) in the silicon substrate. Experiments revealed that CDE is not a completely charging-free process; the charging effect was found to be lower than for the plasma-immersion system. Both types of plasma exposure may also cause defect generation in the silicon substrate. The level of damage, affecting oxide integrity, charge trapping, interface degradation, and defect density in the near-surface silicon region is significantly lower for CDE than for plasma-immersion systems.
Importance of determining the polysilicon dopant profile during process development
Authors: Debusschere I. , Deferm L. , Vandervorst W.
Published: July 2002

During the development of a 0.5 μm, n-type poly, complementary metal–oxide–semiconductor (MOS) process the influence of different process steps on the PMOS gate doping level was investigated. The application of spreading resistance measurements and secondary ion microscopy analysis for determination of the polysilicon dopant profile allowed us to define critical process conditions within which the process could be optimized using short loop tests. The influence of the polysilicon thickness and phosphorus doping level, of the p+ source/drain implantation dose, of the subsequent temperature steps, and of the silicidation were all investigated. It was concluded that a combination of certain process conditions, such as a polysilicon implant dose of 4.0×1015 combined with a p-plus dose of 3.0×1015, does lead to unacceptably low active carrier concentrations, which are proven to result in gate depletion. Furthermore, it was noted that in case of low net impurity concentrations the modification of any of the processing conditions has a large influence on the final polysilicon spreading resistance probe profile. A detailed discussion of the different parameters and the resulting doping profiles are given in the article. Based on the results of the short loop tests the p-plus implant dose was fixed at 2.0×1015. A full transistor lot was processed in which the remaining parameter, i.e., the polysilicon implantation dose, was varied. The device characteristics determined on this lot are in agreement with predictions, based on the results of the experiment.
Secondary ion mass spectroscopy ultrashallow depth profiling for Si/Si1−xGex/Si heterojunction bipolar transistors
Authors: Krüger D. , Kurps R. , Heinemann B. , Herzel F. , Zeindl H. P.
Published: July 2002

Starting from a theoretical dopant and composition profile of a Si/Si1−xGex/Si heterojunction bipolar transistor (HBT), the requirements for high depth resolution secondary ion mass spectroscopy (SIMS) measurements are discussed. To characterize the boron out-diffusion from the Si1−xGex base, which can crucially degrade the transit frequency fT, a depth resolution of better than about 3 nm is necessary. SIMS measurements have been performed using low energy oxygen primary beams at normal incidence to characterize sharp B profiles in Si and Si1−xGex layers. Graded Ge concentrations have been measured quantitatively using cesium primary beams and MCs+ secondary ion detection. It is shown that in the limit of low energy primary beams, the leading edges of the SIMS profiles with upslopes of 1–2 nm/decade show sufficient resolution for many of the HBT applications. For better characterization of effects which are located on the trailing edge of the profile, deconvolution procedures are necessary.
Characterization of B and Sb delta-doping profiles in Si and Si1−xGex alloys grown by molecular-beam epitaxy
Authors: Krüger D. , Gaworzewski P. , Kurps R. , Zeindl H. P.
Published: July 2002

Boron and antimony deltalike doping spikes in Si and Si1−xGex layers with x=0 to x=0.25 deposited by molecular-beam epitaxy (MBE) have been investigated as candidates for p and n delta- doping MBE technology. They were characterized by high depth resolution secondary ion mass spectrometry (IMS) measureements using oxygen and cesium primary ion beams in the energy range from 2 to 12 keV and by high depth resolution spreading resistance measurements. Deltalike doping profiles with a full width at half-maximum of less than 2.7 and 3 nm have been measured by SIMS for Sb and B, respectively, with corresponding upward slopes of 0.4 and 1 nm. For Si1−xGex growth segregation effects, the electrical activity of B decreases with increasing Ge content, and the steepness of the B spikes increases. The behavior of B spikes during annealing is investigated.
Improved sensitivity and depth resolution for analyses of shallow p-n junctions in silicon with secondary ion mass spectrometry
Authors: Erickson Jon W. , Brigham R.
Published: July 2002

The analysis of shallow p-n junctions by standard secondary ion mass spectrometry with oxygen primary ion bombardment can be significantly enhanced in two ways. The sensitivity can be increased about 100-fold by using both instrumental means and chemical modification (in situ oxidation). The depth resolution can be improved about twofold in many cases (e.g., for B), by phenomena accompanying oxidation. It is known that chemical segregation of As may adversely affect depth resolution, so analyses for different elements must be treated on a case-by-case basis.
One- and two-dimensional characterization of power metal–oxide–semiconductor structure by spreading resistance profiling: From the profiles to the I–V curves
Authors: Privitera V. , Saggio M. G. , Magrì A.
Published: July 2002

In the last four years the two-dimensional spreading resistance profiling (2D-SRP) technique has been developed and improved such that it can be considered by now an accurate tool for junction delineation. As a consequence, the reliability of process simulators can be tested by comparing both 2D-SRP and, of course, 1D-SRP experimental results with relative simulations. In this work we apply the 1D- and 2D-SRP techniques to a power metal–oxide–semiconductor field effect transistor device structure to characterize the doped layers and to measure the channel length. A channel length of 0.95 μm has been measured with an accuracy of 0.03 μm. Attesting to the accuracy of the process simulation, by the use of the experimental results, has an importance which goes beyond the simple confirmation of the implemented modeling. The process simulation results are used as input for device simulation. Therefore, we further checked the reliability both of the measurements and the process simulations by comparing the experimental I–V curves of the characterized power metal–oxide–semiconductor structure with those obtained by the device simulations. This work shows that the use of 1D- and 2D-SRP measurements allows us to obtain accurate I–V curves going through process and device simulation.
Properties of probe tip/Si contacts and their connection to spreading resistance analyses
Authors: Gaworzewski P. , Roos B. , Borngräber J. , Höppner K. , Höppner W. , Henniger U.
Published: July 2002

Current spreading resistance analyses of ultrashallow dopant profiles in Si take into account effects of carrier spilling and calculate the spreading resistance using a multilayer correction algorithm. However, the analysis of profiles with the dopant sequence lowly doped layer on highly doped layer or substrate does not give accurate results. Reasons for this behavior are investigated by studying effects of probe tip penetration and plastic deformation of Si. Results of loading–unloading experiments on the system OsW probe/Si let us conclude that a metallic Si phase is present beneath the loaded contact. The spatial extent of this metallic phase zone is estimated. The penetration of the probes into the Si samples and the geometry of the probe indents are independent of conductivity type and dopant concentration as shown by atomic force microscopy and scanning electron microscopy investigations. Three-dimensional model calculations check the effect of the depth distribution of penetrating microcontacts of the OsW probes.
Reflectance spectra of plasma etched silicon
Authors: Engstrom Herbert
Published: July 2002

Plasma etching of oxide on silicon using fluorine ion bombardment results in the formation of an amorphous fluorosilyl (SiFx) layer on the surface of the crystalline silicon. Consequently, all reflectance spectra of plasma etched oxide on silicon wafers are very well fitted by a stack consisting of oxide on modified amorphous silicon on silicon. This model fit wafers having an oxide layer of nonzero thickness and wafers that were overetched. Use of such a model in a thin film reflectometer allows the accurate determination of the oxide thickness, measurements which were previously very inaccurate. Examples of such spectra and their analysis are presented together with the results of electron spectroscopy for chemical analysis and mechanical profilometer measurements.
Acid-diffusion suppression in chemical amplification resists by controlling acid-diffusion channels in base matrix polymers
Authors: Yoshimura Toshiyuki , Shiraishi Hiroshi , Terasawa Tsuneo , Okazaki Shinji
Published: July 2002

We have investigated the suppression of acid diffusion during postexposure baking (PEB) of chemical amplification resists in terms of the molecular control of base matrix polymers to control acid-diffusion channels. According to a previously proposed model, acid diffuses along acid-diffusion channels in chemical amplification resists. The acid-diffusion channels are composed of OH groups outside the base matrix polymers (active OH groups) and vacancies in the matrices. The negative-type chemical amplification resists used in this work consisted of cresol novolak with controlled molecular-weight distributions as the base matrix polymers, an acid-catalyzed crosslinker of melamine resin, and acid generators of onium salt. Measurements of the dependence of the pattern sizes of isolated lines on the PEB time made it clear that acid diffusion defines the resist pattern sizes based on Fick’s law. The densities of the active OH groups play a critical role in acid diffusion, and a base matrix polymer with fewer active OH groups is expected to result in less acid diffusion. Therefore, we can suppress acid diffusion by reducing the number of oligomers in the base matrix polymers by a precipitation method, since these oligomers stereochemically include many active OH groups. We have obtained high resolution by using a resist with an oligomer-free resin. The acid-diffusion model was also confirmed based on infrared absorption spectroscopy and thermal analysis. We conclude that acid diffusion can be suppressed by controlling the acid-diffusion channels.
Fabrication of a refractive microlens integrated onto the monomode fiber
Authors: Babin S. , Weber M. , Koops H. W. P.
Published: July 2002

The fabrication of microlenses using a dry resist process is described for the first time. Characteristics of the totally dry process were investigated. A technique for lens positioning and exposure was developed for a scanning electron microscope equipped with an image processor beam control system. The microlenses have a computer generated hyperbolic profile. Microlenses of cylindrical, ring, and elliptical geometry were fabricated on a Si wafer and on the end of a monomode quartz fiber. Focusing of visible and infrared light by a fabricated microlens is demonstrated.
Experimental and simulated estimation of new super resolution technique
Authors: Kamon Kazuya , Matsui Yasuji
Published: July 2002

In order to support next-generation devices, a super resolution technique having wide applicability and effective resolution enhancement has been proposed and some simulation results were demonstrated. It has been experimentally proven that the depth of focus of the new optics is 1.5 times wider than the modified illumination, which shows good agreement to previous simulation results. From the evaluation of the mask stage repeatability, 0.1 μm (on mask) alignment accuracy or lens distortion between the first and second mask is acceptable for the new optics.
Characterization and correction of optical proximity effects in deep-ultraviolet lithography using behavior modeling
Authors: Yen Anthony , Tritchkov Alexander , Stirniman John P. , Vandenberghe Geert , Jonckheere Rik , Ronse Kurt , Van den hove Luc
Published: July 2002

We present the characterization of optical proximity effects and their correction in deep-UV lithography using an empirically derived model for calculating feature sizes in resist. The model is based on convolution of the mask pattern with a set of kernels determined from measuring the printed test structures in resist. The fit of the model to the measurement data is reviewed. The model is then used for proximity correction using commercially available proximity correction software. Corrections based on this model is effective in restoring resist linearity and in reducing line-end shortening. It is also more effective in reducing optical proximity effects than corrections based only on aerial image calculations.
Three-dimensional electron-beam lithography using an all-dry resist process
Authors: Babin S. , Koops H. W. P.
Published: July 2002

Micromechanics, microelectronics, and micro-optics favor structurization of three-dimensional surfaces. Dry resist processes present fewer hazards to personnel and environment than conventional wet resist processes. The negative tone dry resist octavinylsilsesquioxan is investigated in its applicability to three-dimensional structurization of surfaces having a high relief. This resist, also known as V-T8, enables coating of arbitrary substrates by evaporation in high vacuum. After exposure it is developed in high vacuum by a dry thermal treatment at 200 °C. The resist is characterized with electron exposures with an energy ranging from 5 to 50 keV. Its sensitivity is 40 μC/cm2 at 20 keV. The resist exhibits high dry etch resistivity. Its contrast is increased from 0.7 to 2.1 using plasma etching in CF4 as a postdevelopment step. The dry resist is employed to structure 250 μm deep steep surface steps and to modify fabricated three-dimensional structures with dot gratings for metrology applications.
Development of focused ion-beam machining techniques for Permalloy structures
Authors: Thaus D. M. , Stark T. J. , Griffis D. P. , Russell P. E.
Published: July 2002

The ability to micromachine Permalloy (Ni–Fe alloys) has become important for the development of magnetically actuated microelectromechanical systems devices and for the development of computer disk read-write heads. In this work, focused ion-beam micromachining (FIBM) of Permalloy using Ga+ and with I and Cl chemical enhancement (CE) has been investigated. Micromachining of Permalloy with Ga+ resulted in a material removal rate of only 0.10 μm3/nC and the topography of the micromachined cuts increased in roughness with increased depth reaching micrometer dimensions for the deeper cuts. In comparison to Ga+ only FIBM, I2 CE-FIBM increased the material removal rate by a factor of 8–30 (0.83–3.0 μm3/nC) for bulk and edge micromachining, respectively, with much reduced micromachining induced topography. Procedures were developed to prevent the formation of I2 CE-FIBM related postmicromachining reaction products. Chlorine CE-FIBM, using C2Cl4, CCl4, and C2HCl5, as noncorrosive chlorine sources, provided a Permalloy material removal rate enhancement versus Ga+-only FIBM of approximately a factor of 2 and ≊100 Å topography.
Molecular orientation in polymers from near-field optical polarization measurements
Authors: Williamson R. L. , Miles M. J.
Published: July 2002

A combined noncontact shear force and scanning near-field optical microscope has been used to study the structure of a spherulitic polyhydroxybutyrate specimen. Using polarized light, the birefringence structure of the spherulite revealed a concentric ring structure with submicron resolution. Optical images could be correlated with the topographic images, recorded simultaneously, of the same area. This demonstrated directly the correlation between the twisting structure of the ribbonlike polymer crystallites and the birefringent concentric ring structure, and demonstrates the capability of scanning near-field optical microscopy for studying molecular orientation as a function of topographic structure.
Thermally stable InGaP/GaAs Schottky contacts using low N content double layer WSiN
Authors: Shiojima Kenji , Nishimura Kazumi , Tokumitsu Masami , Nittono Takumi , Sugawara Hirohiko , Hyuga Fumiaki
Published: July 2002

This article describes thermally stable Schottky contacts using low N content double layered WSiN for InGaP/(In)GaAs metal–semiconductor field-effect transistors with self-aligned ion-implanted n+ layers. Transmission electron microscopy observations show that the microscopic interfacial reaction between WSiN and GaAs is completely suppressed when N content in the WSiN is 10% or less. As a result, a WSiN/GaAs-cap/InGaP Schottky contact shows high thermal stability after annealing at 800 °C for 100 min, even though the GaAs cap is as thin as 25 Å. Moreover, the double-layer WSiN structure suppresses reduction in the carrier concentration in the channel during activation annealing. The carrier concentration of the GaAs-cap (40 Å)/InGaP (100 Å)/ InGaAs-channel (100 Å) film, 6.5×1018 cm−3, decreases to less then 2×1018 cm−3 with low N content WSiN (N=10%, 4000 Å) after annealing at 900 °C for 0.1 s, but it remains 3.8×1018 cm−3 with the double layered WSiN (N=37%, 3800 Å/N=10%, 200 Å).
Probing surface and thin film magnetic structure with circularly polarized synchrotron radiation
Authors: Waddill G. D. , Tobin J. G. , Guo X. , Tong S. Y.
Published: July 2002

A new group of techniques predicated on the availability of a tunable source of circularly polarized soft x-rays show tremendous potential for advancing the understanding of magnetic nanostructures. These techniques involve use of circularly polarized radiation as probes in x-ray absorption and x-ray photoemission and photoelectron diffraction studies, and provide unique information about the element specific magnetic moments and magnetic structure of thin films, interfaces, and surfaces. Examples of each technique will be discussed with emphasis given to the recently demonstrated first observation of spin-dependent photoelectron diffraction using circularly polarized x-rays. This technique promises the direct, element specific determination of local magnetic structure on an atomic scale, and will be of tremendous utility in the effort to establish structure-property relationships in magnetic nanostructures. Circularly polarized x-rays are used to produce spin-polarized photoelectrons from the Fe 2p spin-orbit doublet. Intensity asymmetries of up to ∼3% are observed for the 2p3/2 sublevel. These asymmetries depend on the relative orientation of the x-ray polarization vector and the sample magnetization as well as upon the photoelectron kinetic energy and emission direction. Multiple scattering calculations are found to reproduce both the observed energy and angular asymmetry variations. Strategies to increase the measured effect are also discussed.
Magnetic x-ray dichroism in the spectroscopy of ultrathin magnetic alloy films
Authors: Tobin J. G. , Goodman K. W. , Mankey G. J. , Willis R. F. , Denlinger J. D. , Rotenberg E. , Warwick A.
Published: July 2002

The magnetic structure of nanoscale alloy films has been probed using the magnetic x-ray linear dichroism in photoelectron spectroscopy and magnetic x-ray circular dichroism in x-ray absorption spectroscopy. FeNi and CoFe epitaxial films were grown on Cu(001), in situ and using MBE techniques. Because soft x-rays were used to probe the 2p and 3p core levels, both elemental selectivity and magnetic sensitivity were achieved simultaneously. Correlation of these magnetic techniques with compositional and structural information will be done. Ultimately, from studies such as this a complete determination of the structure-property relationships will be achievable.
Silicon dioxide chemical vapor deposition using silane and hydrogen peroxide
Authors: Gaillard Frédéric , Brault Pascal , Brouquet Pierre
Published: July 2002

SiH4 and H2O2 have been successfully used for the deposition of silicon dioxide for shallow trench isolation. With this chemistry, it is possible to fill up trenches without voids up to an aspect ratio 2.3:1. The very good gap filling is due to the presence of SiOH groups in the oxide film. To obtain a density close to that of thermal oxide, the film must be annealed at high temperature. The electrical characteristics are equivalent to those obtained using thermal silicon dioxide.
Analysis of molecular beam epitaxy grown Ga1−xAlxAs/Ga1−yAlyAs dielectric stack mirrors using complex indices of refraction
Authors: Strachan W. J. , Reiner J. , Goodhue W. D. , Karakashian A. S. , Casasanta V. , Geller J. D.
Published: July 2002

Dielectric stack mirrors consisting of alternating layers of Ga1−xAlxAs/Ga1−yAlyAs, grown by solid source molecular beam epitaxy, are evaluated using reflection spectroscopy and a complex index of refraction model. The dielectric stack mirrors have asymmetric reflectivity spectra in the near infrared. We contend that this asymmetry is due to loss in the mirror stack and propose that the loss may be caused by defects introduced during the growth process. These reflectivity spectra are compared to a model that includes loss by utilizing complex indices of refraction. Calculated spectra reproduce this asymmetry using small imaginary index components. This study demonstrates the validity of using a theory that includes loss for modeling the reflectivity spectra of a dielectric stack mirror in the spectral range of 0.7 to 0.9 μm.
Large blueshift in the photoluminescence of pseudomorphic InGaAs/GaAs quantum wells grown in patterned (100) GaAs grooves and ridges with vertical sidewalls
Authors: Kamath K. , Phillips J. , Singh J. , Bhattacharya P.
Published: July 2002

Molecular beam epitaxial growth of pseudomorphic InGaAs quantum wells on (100) GaAs substrates, patterned with vertical sidewalls using reactive ion etching, were studied. Contrary to the redshift observed in the photoluminescence from the ridges and grooves of patterned substrates with (n11) sidewalls, we have observed a blueshift in the case of vertical sidewalls. The possibilities of change in the strain tensor and the change in composition of the InGaAs grown in the grooves or on the ridges were considered in order to explain this increase in band gap. We believe that the vertical sidewalls act as kink sites for the migrating adatoms instead of sources, as in the case of (n11) sidewalls. We have demonstrated a blueshift of up to 50 meV without any degradation in the intensity and linewidth of the photoluminescence spectra.
Interaction of hydrogen ions with oxidized GaAs(100) and AlAs(100) surfaces
Authors: Chang Ying-Lan , Cao R. , Spicer W. E. , Pianetta P. , Shi Song , Hu Evelyn , Merz James
Published: July 2002

We have performed photoemission experiments, using a tunable soft x-ray synchrotron radiation source to study the chemical changes of oxidized GaAs and AlAs surfaces subject to exposure from hydrogen ions. Results indicate that the net effects for hydrogen ion irradiation are (i) the reduction of arsenic and (ii) the growth of the cation oxide components. The reduction of arsenic can result from the formation/desorption of arsine. The oxide overlayer after hydrogen ion treatments is dominated by cation oxides which are the more stable chemical species as described in the phase diagram. This oxide layer should then remain stable in atmosphere. These results can provide insight into the chemical reaction between hydrogen ions and oxidized AlGaAs surfaces.
Role of structural and chemical contributions to valence-band offsets at strained-layer heterojunctions: The GaAs/GaP (001) case
Authors: Di Ventra M. , Peressi M. , Baldereschi A.
Published: July 2002

We calculate with the ab initio pseudopotential method the valence-band offset (VBO) of GaAs/GaP lattice-mismatched heterojunctions pseudomorphically grown on GaAsxP1−x(001) substrates (0≤x≤1). The resulting value of 0.76 eV for the GaP substrate supports the highest among the experimental data available. We show that the VBO for any substrate can be easily obtained from that calculated for one substrate following standard band-structure theory since the interface-dependent contribution to the VBO, which is the electrostatic potential lineup, has no significant variation with the substrate. Such variation, however, can be taken into account accurately by a simple analytic scaling law, which is demonstrated here. Finally, we show that the VBO of GaAs/GaP (001) is due to structural and chemical effects, and we propose an operative method for identifying and separating the two contributions, whose dependence on strain is also discussed.
Fabrication of sub-0.5 μm diameter cobalt dots on silicon substrates and photoresist pedestals on 50 cm×50 cm glass substrates using laser interference lithograph
Authors: Spallas J. P. , Boyd R. D. , Britten J. A. , Fernandez A. , Hawryluk A. M. , Perry M. D. , Kania D. R.
Published: July 2002

We have fabricated arrays of 120-nm-diam cobalt dot masks on 300 nm centers using laser interference lithography. The density of the cobalt dot arrays is ≳109 dots/cm2. The standard deviation of the average cobalt dot diameter is 7.4% over a 5-cm-diam silicon substrate. Single crystal silicon pedestals were formed using a chrome dot mask array to demonstrate that these subquarter micrometer features can be used to fabricate high density self-aligned gated field emitter arrays. We have exposed uniform photoresist pedestals on 50 cm×50 cm glass substrates using laser interference lithography to demonstrate that this technique can be scaled to expose large areas. The base diameter of the photoresist pedestals is 330 nm and the height is 250 nm. The center-to-center spacing is 670 nm. The standard deviation of the base diameter of the photoresist pedestals is 3% over an 8 μm×8 μm region.
Reactive ion etching GaAs and AlAs: Kinetics and process monitoring
Authors: Franz Gerhard , Hoyler Charlotte , Kaindl Josef
Published: July 2002

The BCl3/(Ar,He) etching process for AlGaAs layers is described and analyzed. It was thoroughly investigated whether the mechanism of plasma etching could be evaluated using the loading effect. Very smooth sidewalls of the structures were obtained with using an optimized process to treat the photoresist after its development. It is shown that various end point detection methods can complement each other and enable etch depth monitoring with a depth resolution of significantly better than 50 nm at a total depth of more than 2.5 μm.
X-ray mask fabrication technology for 0.1 μm very large scale integrated circuits
Authors: Oda M. , Uchiyama S. , Watanabe T. , Komatsu K. , Matsuda T.
Published: July 2002

X-ray mask fabrication using a subtractive process and a 30 kV acceleration voltage electron beam writer was investigated. The dose margin for delineation of fine resist patterns is increased by reducing the resist thickness. Delineation of 0.1 μm patterns in a 0.1-μm-thick resist has approximately the same dose margin as that of 0.2 μm patterns in a 0.3-μm-thick resist. Width error in SiO2 patterns used as an etching mask is decreased by reducing the thickness and adding SF6 to CF4 etching gas. Tantalum absorbers can be etched very accurately with electron cyclotron resonance ion stream etching by taking microloading effects and undercutting into account. Using the 0.1-μm-thick resist, x-ray masks with 0.1 μm large scale integrated circuit patterns are almost perfectly produced and have a critical dimension accuracy of 13 nm.
Spin-resolved x-ray photoemission studies of ferromagnetic metals
Authors: Klebanoff L. E.
Published: July 2002

Recent spin-resolved x-ray photoelectron spectroscopy (SRXPS) studies of ferromagnetic metals are reviewed. SRXPS studies of metallic Fe, Co, Co66Fe4Ni1B14Si15, and Ni demonstrate that core-level photoemission, and the itinerant electron response to core-hole creation, are highly spin-dependent. The exchange splitting of the Fe 2p3/2 level is found to be 0.48±0.05 eV. Lifetime broadening results for the Fe 2p3/2 N↑ (majority spin) and N↓ (minority spin) components indicate conservation of spin in core-hole filling processes involving the valence band. SRXPS study of the Fe 2p3/2 peak asymmetry α reveals a dependence of electron–hole excitation on the spin of the core hole. Spin analysis of the Fe 3s XPS line shape shows it to be a three-component spectrum, rather than the two-component line shape assumed previously. A photon energy dependence of one of the Fe 3s components explains disagreement among previous Fe 3s XPS results. Comparisons of SRXPS from Co metal and Co66Fe4Ni1B14Si15 directly demonstrate the effect of a reduced atomic magnetic moment on the spin dependence of core-level XPS. The behavior of lifetime broadenings for the N↑ and N↓ Co 2p3/2 components show that the reduced Co magnetic moment found in the Co66Fe4Ni1B14Si15 amorphous glass is due to the transfer of ↑-spin valence electron density to the ↓-spin valence band upon glass formation. SRXPS also allows investigation of spin-dependent core-hole screening processes and satellite production, as demonstrated in SRXPS studies of ferromagnetic Ni. Future directions of SRXPS are also explored.
Magnetic circular dichroism in reflection electron energy loss spectroscopy?
Authors: Harp G. R. , Farrow R. F. C. , Marks R. F.
Published: July 2002

We evaluate the possibility of using dichroic electron energy loss spectroscopy (DEELS) as an alternative to x-ray magnetic circular dichroism (XMCD). It is well known that electron energy loss spectroscopy and x-ray absorption spectroscopy provide similar information. A simple semiclassical model suggests that reflection DEELS might have a magnetic sensitivity similar to that of XMCD. This sensitivity will be reduced, however, by multiple scattering of the probe electron before and after the energy loss event. Thus, it is difficult to predict the magnitude of the DEELS effect. Experiments were performed at the L edges of polycrystalline Fe, Co, and Ni thin-film samples prepared in situ with a uniaxial magnetic bias. Even in these most favorable cases, the DEELS effect is limited to less than one-tenth of related effects in XMCD.
Fabrication of Si field emitters by dry etching and mask erosion
Authors: Rakhshandehroo M. R. , Pang S. W.
Published: July 2002

A Cl2 plasma generated by an electron cyclotron resonance source was used to etch field emitter arrays in Si. Compared to wet etching, emitter arrays with sharper emitter tips and higher packing density can be formed by dry etching. Mask erosion was used to control the etch profile in Si. SiO2 masks with different profiles were patterned by wet and dry etching, and the effects of the initial SiO2 masks slope and etch conditions on the resultant Si profile were investigated. The lateral etch rate of SiO2 decreased from 363 to 150 nm/min as the SiO2 slope increased from 17° to 45°. As a result, the slope of the Si etch profile increased from 52° to 78° after dry etching to a depth of 1.8 μm. The ion flux and energy, controlled through coupled microwave and rf power, were used to obtain the desired etch rate and basewidth of the emitters. By increasing the pressure during etching, the lateral etch rate of SiO2 was reduced and more vertical Si profiles were developed. As pressure was increased from 0.5 to 10 mTorr, the lateral etch rate of SiO2 reduced from 414 to 144 nm/min while the vertical Si etch rate did not change significantly. This caused the slope of the Si etch profile to increase from 42° to 69°. Using the above technique, arrays of sharp emitter tips in Si with 2.2 μm basewidth and 11 μm height were fabricated and packing densities up to 1×107 tip/cm2 were achieved.
Driven nonlinear atomic force microscopy cantilevers: From noncontact to tapping modes of operation
Authors: Sarid Dror , Ruskell Todd G. , Workman Richard K. , Chen Dong
Published: July 2002

A numerical model of the operation of an atomic force microscope with a driven cantilever is presented. This model takes into account the attractive van der Waals and repulsive indentation forces acting between tip and sample. The time-dependent displacement amplitude and phase of the tip oscillations, and the magnitude, duration, and sign of the short bursts of tip–sample force are derived. It is shown that the stiffness of the tip and sample materials is an important factor in determining the magnitude and duration of the tip–sample repulsive force and the magnitude of sample indentation. The model covers typical operating ranges of vibrating cantilever atomic force microscopes, from the noncontact to the tapping modes.
In situ investigation of the passivation of Si and Ge by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiO2
Authors: Wang Y. , Hu Y. Z. , Irene E. A.
Published: July 2002

In situ real time single wavelength ellipsometry and spectroscopic ellipsometry were used to monitor electron cyclotron resonance plasma enhanced chemical vapor deposition of SiO2 on Si and Ge at substrate temperatures from floating temperature (<50 °C) to 400 °C. Dielectric layers were evaluated by capacitance–voltage measurements. Single wavelength ellipsometry and x-ray photoelectron spectroscopy results show that oxidation occurred along with SiO2 deposition at the initial stage of plasma enhanced chemical vapor deposition. The real time oxidation analysis shows that the subcutaneous oxidation follows parabolic growth kinetics during SiO2 deposition. The parabolic rate coefficient is proportional to the voltage drop across the subcutaneous oxide layer, and yields temperature activated transport. The subcutaneous oxidation of Ge yields a Ge rich oxide that degrades the electrical properties of metal–oxide capacitors. A thin Si layer deposited at room temperature before SiO2 deposition protects the Ge surface from undesirable oxidation during SiO2 deposition. The required thickness of Si layer is predicted. Electron cyclotron resonance plasma oxidation at 400 °C after SiO2 deposition reduces the slow trap states. An Al/SiO2/Si/Ge structure shows improved electrical properties of metal–oxide Ge capacitors. For c-Si substrates, a rapid thermal anneal of the deposited SiO2 in high vacuum can effectively eliminate the OH group incorporation, and thus reduces both interface trapped charge and slow trap states.
Nanoscale fabrication on a clean TiO2(110)1×2 surface by scanning tunnel microscopy
Authors: Berkó A. , Kriván E.
Published: July 2002

The nanoscale restructuring process induced by the tunneling current was studied on a TiO2(110)1×2 reconstructed surface. The threshold parameters of 0.1 nA and +3.5 V were found. Below the critical voltage (even in the case of two orders of magnitude higher tunneling current), no change of the original surface structure appears. Above the threshold bias, the evolution of the process depends on the current: (i) for lower current (0.1–1 nA), only an outrising feature (average diameter of 3 nm, corrugation 1 nm) appears and the process saturates in the time scale of 10–20 s; (ii) for the higher currents 1–10 nA, the structural transformation begins with an increasing hump formation followed by a developing of a craterlike hollow structure (etching process). According to the results of the spectroscopic measurements, it is very likely that the created humps are composed of more reduced stoichiometric oxide phase. The facts that the presented process starts only above a threshold bias and the intensity of the tunneling current has great influence on the volume of the created structure strongly suggest a mechanism where a resonant electron excitation induced surface decomposition plays an important role.
Polysilicon gate etching in high density plasmas. V. Comparison between quantitative chemical analysis of photoresist and oxide masked polysilicon gates etched in HBr/Cl2/O2 plasmas
Authors: Bell F. H. , Joubert O.
Published: July 2002

We have used x-ray photoelectron spectroscopy (XPS) to study the chemical constituents present on the surfaces after etching of poly-Si features masked with photoresist or oxide patterns. The wafers were etched in a low pressure, high density plasma, helicon source using a HBr/Cl2/O2 gas mixture. The O2 gas flow rate was tuned to obtain anisotropic etching profiles by forming an SiO2 like layer on the sidewalls of the features and maximizing the polysilicon/gate oxide selectivity. Electrostatic charging of insulating surfaces and geometric shadowing of photoelectrons by adjacent photoresist lines were performed to differentiate the photoemission signals from the tops, sidewalls, and bottoms of the features. XPS analyses have shown that the passivation layer formed on the polysilicon sidewalls during etching is a chlorine rich silicon oxide film with both type of masks. This film contains a low carbon concentration when resist is used as a mask. The similar thickness and constitution of the sidewall for oxide and photoresist masked poly-Si samples indicate that the nature of the mask material has no significant effect on the sidewall passivation mechanism.
Comparison of Si and GaAs/interfaces resulting from thermal and plasma oxidation
Authors: Lefebvre P. R. , Irene E. A.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) analyses of oxides produced by thermal and plasma oxidation of GaAs show that electron cyclotron resonance (ECR) plasma oxidation favors what is thought to be the more desirable (from the point of view of electronic passivation) As+5 oxidation state while thermal oxidation favors the lower oxidation state, As+3. Thermal oxidation produces a Ga-rich oxide, whereas the ECR plasma oxides are nearly stoichiometric. Also, thermal oxidation removes As(0) during the initial stage. XPS shows that thermal and ECR plasma Si oxides have different structures. In situ and real time ellipsometry studies indicate that thermal and ECR plasma oxidations yield different film growth kinetics for both GaAs and Si. In particular there are no strong substrate orientation effects for the ECR plasma oxidation of GaAs and Si in the initial stage of oxidation. The similarities in our Si and GaAs oxidation results enable models to emerge based on the dominance of the highly reactive plasma generated oxidant species for plasma oxidation and molecular oxygen for the thermal case.
Si- and C-rich structure of the 6H-SiC(0001) surface
Authors: Li L. , Hasegawa Y. , Sakurai T.
Published: July 2002

The reconstructions of the 6H-SiC(0001) surface under both Si-rich and C-rich conditions were studied using field ion-scanning tunneling microscopy (FI–STM). The sample was cleaned by in situ Si beam etching at 900–1000 °C. The as-cleaned surface showed a (√3×√3) structure. The Si-rich phases were produced by annealing the sample in a Si flux. With increasing Si concentration, (2×2), (2√3×6√3), (3×3), and (7×7) reconstructions were observed. Reaction of the Si-rich phases with C2H2 molecules at 1050 °C resulted in the formation of a C-rich surface, which exhibited a (2×2)/(6×6) reconstruction. A structure model for (√3×√3) reconstruction is proposed, and possible applications of using the surface reconstruction to selectively grow SiC polytype is discussed.
Magnetic property of NiO ultrafine particles with a small Ni core
Authors: Sako Sanshiro , Ohshima Kazunari , Sakai Masahiro , Bandow Shunji
Published: July 2002

The magnetic nature of a NiO shell and a Ni core were separately investigated in the temperature dependence of the magnetization curve of the samples with the average sizes of 1.6, 2.0, 2.2, 2.5, 2.8, 3.0 and 3.2 nm. The superparamagnetism of the NiO shell and Ni core were observed in specific temperature ranges. The increase of the magnetic moment per atom in the metallic free cluster with decreasing size were not observed in the small Ni core with the NiO shell though the proper saturation magnetization of Ni core was estimated.
Calculation of electronic energy levels in artificially confined cavities of a sphere and a circular cylinder
Authors: Zhao Yong Fang , Jing Xiao Gong , Li Lin Song , Wang Li Jun , Hui Zheng , Li Tie Jin
Published: July 2002

Based on the results of experiments of the nanostructured materials, the electronic structures of the spherical and circular cylindrical well in nanometer scale are calculated using a constant potential by direct solution of the Schrödinger equation. According to the result of the bound states existing only under certain conditions, the calculated results show that the energy level structures of these modes are quite distinct from that of the hydrogen atom. The number of energy levels is finite and it depends strongly on the potential parameter. The order of energy levels is E1s<E2p<E3d<E2s<E3p<E4d<… in the case of the artificially confined cavity of the sphere. It was exactly consistent with an investigation reported by T. Inoshita et al. [Phys. Rev. Lett. 57, 2560 (1986)]. The calculated results of the circular cylindrical wells have similar properties on the level structure compared with that of a square spherical artificial atom well.