bluuebunny/crossref_metadata_2025 huggingface dataset:
Dot lithography for zero-dimensional quantum wells using focused ion beams
Authors: Kubena R. L. , Joyce R. J. , Ward J. W. , Garvin H. L. , Stratton F. P. , Brault R. G.
Published: July 2002

A 50-keV focused Ga+ beam formed in a two-lens microprobe column with prefinal lens deflection was used to expose dot arrays in a negative-acting bilevel resist. Dot arrays 600×600 μm with 600-Å-diam resist posts on 0.6-μm centers (incorporating 1024×1024 dots) were fabricated with ion exposure times of 18 s (beam dwell times of 16 μs/post). By reducing the beam dwell time by a factor of 2, roughly 300-Å-diam posts were fabricated. Since the ions stop in the bottom resist layer and do not enter the substrate, the optical properties of underlying material should not be altered by damage from the exposure process.
Investigation of reactive ion etching induced damage in GaAs–AlGaAs quantum well structures
Authors: Wong H. F. , Green D. L. , Liu T. Y. , Lishan D. G. , Bellis M. , Hu E. L. , Petroff P. M. , Holtz P. O. , Merz J. L.
Published: July 2002

We report on the use of a novel technique to study reactive ion etching (RIE) induced damage using multiple quantum wells of 20-, 40-, 60-, and 90-Å widths as in situ probes. Cathodoluminescence (CL) at low temperature, using a finely focused electron beam, allows sensitive determination of the quality of individual quantum wells before and after RIE damage. There is a correspondence between individual luminescence peaks and the depth of the particular quantum well. We can therefore use the CL spectral information to provide a sensitive profile of the depth of RIE induced damage. Various etching conditions and the effects of postetch anneals are examined. Pure Ar sputtering and enhanced chemical etching using CCl2F2/BCl3 at different bias voltages are investigated. Our results reveal that the degree and spatial extent of damage increase with increasing ion energy and decreasing ion mass.
X-ray photoelectron spectroscopy surface charge buildup used to study residue in deep features on integrated circuits
Authors: Thomas J. H. , Bryson C. E. , Pampalone T. R.
Published: July 2002

A major problem is encountered in characterizing the surfaces at the bottom of submicrometer holes formed by plasma etching operations in the fabrication of submicrometer circuitry. Using monochromated x rays to excite photoemission spectra, surface charge buildup can occur on insulating surfaces causing the spectra to shift relative to the spectra of electrically conductive surfaces. In the case of silicon dioxide on Si, the oxide surface can charge up to a significant voltage relative to the silicon substrate making the two regions spectroscopically resolvable. When an electron flood gun is used in conjunction with monochromatic x rays, the insulated regions can be made to shift in kinetic energy relative to the substrate thereby allowing precise identification of various electrically different regions. In this initial study, residues at the bottoms of 0.75-μm-wide paths etched in 0.9-μm-thick silicon dioxide were identified. Patterns were etched in silicon dioxide using Freon-based plasma etching and various final cleaning procedures. The residue layers observed are similar to those observed on CHF3 etched silicon.
On the mechanism of energy distribution in liquid metal ion sources
Authors: Komuro Masanori , Arimoto Hiroshi , Kato Takao
Published: July 2002

A theoretical model on the generation of a singly charged ion in a liquid metal ion source is proposed based on field evaporation, free space field ionization (FI), and charge transfer collision (CT) with neutral atoms. Calculated results for Ga+ from a Ga source show that the FI peak appears at an energy deficit of ∼9 eV for an emitter radius of 1 nm and an electric field of 16 V/nm, that a calculated ion flux for the FI is about five times as large as for the CT collision between Ga+ and Ga, and that an energy distribution curve for the CT exponentially decreases with a decay factor expressed by the product of the emitter radius and the electric field. These are in good agreement with the energy distribution curves of Ga+ experimentally obtained. This model is also applied to the energy distributions for the singly charged ions from Au60Si26Be14 (at. %) alloy source in which tails in the high ion energy region appear due to the CT collision between the doubly charged ions and the atoms, in addition to the low energy tail. It is shown theoretically and experimentally that both tails also exponentially decrease. The intensity ratio between the high- and low-energy tails indicates that the ions in the low-energy tail are mainly produced by the CT collision between the doubly charged ions and the atoms.
Optimized eight-inch extraction system for reactive ion beam etching
Authors: Korzec D. , Engemann J.
Published: July 2002

A methodology of ion extraction system optimization is proposed, taking into account the influence of the ion density variation in plasma at the plasma sheath. Software tools for extraction grids design and machining have been developed, allowing compensation for the current, divergence, and deflection of a single beamlets. Simulation was used to predict the properties of the three-grid single beamlet. The measurement of the radial ion saturation current density distribution in plasma using a double Langmuir probe for an axial magnetic field up to 16 mT, vacuum chamber pressure ranging from 4×10−5 to 2×10−3 and rf power from 100 to 900 W has been performed. These distributions were used to calculate the grid compensation functions. An extraction system was optimized for the reference magnetic field in the air coil B=7.20 mT, vacuum chamber pressure p=2.0×10−4 mbar, rf power Prf=500 W, and net acceleration voltage Vnet=300 V with argon as a working gas. The ion current density distributions for optimized and nonoptimized extraction systems have been measured and compared with predictions of the model. A maximum detectable variation in the ion current density across the 8 in. target can be reduced to < 3%.
Microfabrication cellular phosphors
Authors: Deckman H. W. , Dunsmuir J. H. , Gruner Sol M.
Published: July 2002

Phosphor screens with densely packed cellular arrays of ∼108 μ and sub-μ diam CsI phosphor columns having ∼10:1 aspect ratios were prepared using microfabrication techniques. Uniformly sized, optically isolated phosphor columns were formed in screens designed for micron-resolution imaging of 5–15 keV x-rays in a microtomography application. Micron-sized cells were prepared by etching fiberoptic faceplates, and smaller cells were formed from a lithographic mask of monodisperse spherical polymer colloidal particles. A defect free lithographic mask of monodisperse colloidal particles was created using a ‘‘Langmuir–Blodgett like’’ coating technique. The cells were then uniformly loaded with CsI (Na activated) phosphor so that variations in the quantum efficiency across the screen were less than 33%.
Tip–sample interaction forces in scanning tunneling microscopy: Effects of contaminants
Authors: Meepagala S. C. , Real F. , Reyes C. B.
Published: July 2002

We have made simultaneous measurements of the tunnel current and the force of interaction as a gold-coated cantilever approaches towards and recedes from a gold sample in atmosphere. We will describe the effects arising from the surface contaminant layer. We also have made an estimation of the minimum value of the contact (repulsive) force that should be present for tunneling between gold and gold in air to be observed.
Desktop computer-based management of images and digital electronics for scanning tunneling microscopy
Authors: Robinson R. S. , Kimsey T. H. , Kimsey R.
Published: July 2002

Experimental prototype scan-control electronics that implement via hardware many features from an earlier software-based scanning control system have been engineered. The goals include faster scanning speed to support research involving real-time monitoring of surface changes during electrochemical reactions. The STM z-axis motion is controlled with a novel type of digital integrator/error-correction circuit, facilitating novel STM operational modes. The digital feedback and analog integration methods are compared. To address particular aspects of STM image management, which may differ substantially from traditional scientific image processing, software was designed for scanning and management of images. The software is described.
Atom-resolved surface chemistry: The early steps of Si(111)-7×7 oxidation
Authors: Avouris Ph. , Lyo In-Whan , Bozso F.
Published: July 2002

The early stages of Si(111)-7×7 oxidation using scanning tunneling microscopy and scanning tunneling and photoemission spectroscopies have been studied. It has been found that there are at least two different oxygen-containing sites being formed. Their different surface site distributions and behavior as a function of O2- exposure show them to be two distinct early products. By correlating the spectroscopic results and the results of theoretical calculations one is able to identify one of these products as involving an O atom tying up an adatom dangling bond with a second O atom inserted in one of the adatom back bonds, while the other involves a single O atom inserted in an adatom back bond. The preference of these products for the faulted half of the 7×7 unit cell and for corner-adatom sites is explained in terms of a site-dependent sticking coefficient involving a process analogous to the gas-phase ‘‘harpooning’’ processes. It is shown that the majority of the resulting molecular precursors involve O2 interacting with a single dangling-bond site. Finally, mechanisms are proposed for the early steps of the oxidation process.
Anisotropic etching of GaAs using a hot Cl2 molecular beam
Authors: Ono Tetsuo , Kashima Hideo , Hiraoka Susumu , Suzuki Keizo , Jahnke Andreas
Published: July 2002

Anisotropic etching of GaAs(100) is performed using a hot Cl2 molecular beam produced by free expansion of gas heated in a furnace. The etch rate is 1.5 μm/min at a furnace temperature of 800 °C and a substrate temperature of 120 °C. An aspect ratio of ten and an almost smooth bottom surface are obtained under this condition.
A comparison of the measurement of ion damage in silicon surfaces using differential reflectance and spectroscopic ellipsometry
Authors: Burns T. M. , Chongsawangvirod S. , Andrews J. W. , Irene E. A. , McGuire G. , Chevacharoeukul S.
Published: July 2002

Differential reflectance (DR) spectroscopy has recently been reported to be effective in measuring the damage imparted to a Si surface by ion beams. Spectroscopic ellipsometry (SE) has been used extensively for this measurement. The present study compares DR and SE, ‘‘head-to-head,’’ from both high energy ion implanted samples (60–180 keV) and low energy (0.1–1.5 keV) ion exposures. In most cases DR and SE yield the same information, but SE has a greater analytical capability at the present time. DR is shown to be quite useful for buried layers and being simpler in terms of hardware requirements, perhaps more suitable for process monitoring.
Thickness dependence of the dielectric behavior of SiO2 films fabricated by microwave electron cyclotron resonance plasmas
Authors: Chau T. T. , Mejia S. R. , Kao K. C.
Published: July 2002

Dielectric behavior of SiO2 films fabricated by microwave electron cyclotron resonance (ECR) plasmas under high-electric stresses has been studied on the basis of the current–voltage (I–V) characteristics, the capacitance–voltage (C–V) characteristics, and the effects of the ramp rate as functions of film thickness. In the region from the current at the onset of Fowler–Norheim (FN) injection to the current at the onset of trapped space charge effects, the I–V characteristics follow closely the FN relation, implying that at least in this region the motion of the electrons is controlled by their interaction with the lattice rather than by their interaction with traps in the forbidden gap. The width of this current region increases with increasing film thickness for a given ramp rate of applied field indicating that the injected electrons may travel quite a distance before being effectively trapped. This also implies that the effects of this trapped space charge on the reduction of the field at the cathode and hence the injecting current become important at a lower field for thinner films. There is no evidence of electron impact ionization taking place prior to dielectric breakdown. After the onset of FN injection,the current density in the leading filament could reach a value as high as 10 A/cm2 at the breakdown field, which could therefore cause thermal instability in the filament. Dielectric breakdown may be initiated by thermal destruction and followed by impact ionization leading to a sharp increase in current at the breakdown field.
A transmission electron microscopy study of hillocks in thin aluminum films
Authors: Ericson Fredric , Kristensen Nils , Schweitz Jan-Åke , Smith Ulf
Published: July 2002

Hillocks, small outgrowths on a film surface, form when compressional stresses in an aluminum film are relaxed at elevated temperature (≥90 °C), for instance during the phase of rising temperature in an annealing cycle. This paper reports a study of hillock formation in Al films of thicknesses in the interval 0.25–2.2 μm and which have been deposited by electron beam evaporation. Hillock sizes, shapes, number and formation temperatures were determined, the latter on a heating stage in situ in a scanning electron microscope. The internal structure of the hillocks was studied by cross-sectional transmission electron microscopy technique. These studies provided strong support for the idea that hillocks are formed by migration of material along grain boundaries, presumably at triple junctions, up to the surface where it is deposited in a growing hillock. Initially, the hillocks are separated from the original film surface by a grain boundary-like interface, but prolonged annealing will cause underlaying grains to grow into the hillocks, until they become integrated in the film.
Low temperature thermal oxidation sharpening of microcast tips
Authors: Akamine S. , Quate C. F.
Published: July 2002

The authors report the fabrication of sharp tips by casting a tip material into a sharpened silicon mold whose original shape was modified by the growth of a nonuniform, low temperature, thermal oxide. The addition of the oxide layer is the only significant difference between this process and processes currently being used by the majority of commercial producers of atomic force microscope force sensing cantilevers. While commercially available molded tips typically have radii of curvature of approximately 500 Å and aspect ratios of 0.5 or less, tips made in the modified molds have radii of curvature as low as 110 Å and aspect ratios of 0.95. This technique is useful when sharpness, uniformity, and low cost are required.
Atomic scale survey of III–V epitaxial interfaces
Authors: Salemink H. W. M. , Albrektsen O.
Published: July 2002

A novel scanning tunneling microscopy technique is reported, which displays the atomically resolved lattice sites on ultrahigh vacuum cleaved (110) cross sections of epitaxially grown semiconductor multilayers. Voltage selective imaging is used to display either the group III (empty state) sites or the group V (filled state) sites on GaAs–AlGaAs and InP–InGaAsP heterojunctions grown by molecular-beam epitaxy and metalorganic vapor phase epitaxy. The interfaces can be defined to an accuracy of ±1 unit cell. Charge density maps of the group III (Al–Ga) sublattice in AlGaAs and of the group V (As–P) sublattice in InGaAsP are generated for the first time, and these reflect the composition fluctuations on the atomic scale. A tentative assignment is given to the individual Al and Ga sites and the ‘‘roughness’’ of such interfaces on the atomic scale is discussed.
Numerical simulation of field emission from silicon
Authors: Jensen K. L. , Ganguly A. K.
Published: July 2002

A common method for estimating current from semiconductor field emission is to assume that the potential inside the semiconductor is the same as that which would occur if no current were emitted [zero emitted current approximation (ZECA)], and then to use the calculated density at the surface in a standard Fowler–Nordheim analysis familiar from metallic field emission calculations. At high fields, it is obvious that this method fails, as the effect of current is no longer negligible in the calculation of the band bending effects. In this work, we shall present methods for calculating the band bending effects at arbitrary fields in the ZECA model; a comparison of the Wentzel–Kramers–Brillouin and Fowler–Nordheim approaches to field emission for silicon will be compared to the airy function approach of evaluating the transmission coefficient (TC) in the ZECA model; and finally, the limits of ZECA for field emission from silicon will be analyzed by comparing the TC calculations to Wigner distribution function (WDF) simulations performed with full band bending effects and scattering. As anticipated, the ZECA model, whether calculated by the TC or WDF approach, diverges from the full band bending WDF model for high fields. A discussion of this behavior is given in light of the density and current profiles.
First indications of spontaneous ordering in ZnSe0.50Te0.50 alloy
Authors: Luo H. , Samarth N. , Short S. W. , Xin S. H. , Furdyna J. K. , Ahrenkiel P. , Bode M. H. , Al-Jassim M. M.
Published: July 2002

We describe our study of II–VI alloy ZnSe0.5Te0.5 in search of spontaneous ordering. Samples were prepared by molecular beam epitaxy in a variety of structure configurations and growth temperatures, in order to scan a wide range of parameters and identify a favorable condition for ordering. Transmission electron microscopy was carried out on these samples and revealed indications of spontaneous ordering in several samples, where regions with stacking of atoms that appear to be different from the zinc-blende structure were observed. Preliminary study shows that such regions have the CuAu [i.e., the (100) superlattice] structure.
Two-dimensional delineation of semiconductor doping by scanning resistance microscopy
Authors: Shafai C. , Thomson D. J. , Simard-Normandin M.
Published: July 2002

A new technique for the two-dimensional delineation of P–N junctions is presented using a scanning resistance microscope (SRM). The SRM uses a conducting probe to perform localized resistance measurements over a surface. These resistance measurements are used to delineate between regions of different doping type and concentration. Theoretical simulation shows that the SRM is able to delineate between p-type and n-type regions of a surface, and between regions of high and low dopant concentration. By using contact forces of 10−4 N, the contact area is estimated to be 30 nm. Experiments have shown that this technique can localize a P–N junction with a lateral spacial resolution of less than 35 nm, over dopant concentrations ranging from 1015 to 1020 atoms/cm3. In addition, during resistance measurements the SRM is capable of performing simultaneous surface topography measurements.
Use of boundary element methods in field emission computations
Authors: Hartman Robert L. , Mackie William A. , Davis Paul R.
Published: July 2002

The boundary element method is well suited to deal with some potential field problems encountered in the context of field emission. A boundary element method is presented in the specific case of three-dimensional problems with azimuthal symmetry. As a check, computed results are displayed for well-known theoretical examples. The code is then employed to calculate current from a field emission tip and from the same tip with a protrusion. Finally an extension of the boundary element code is employed to calculate space-charge effects on emitted current.
High-performance multilevel blazed x-ray microscopy Fresnel zone plates: Fabricated using x-ray lithography
Authors: Di Fabrizio E. , Gentili M. , Grella L. , Baciocchi M. , Krasnoperova A. , Cerrina F. , Yun W. , Lai B. , Gluskin E.
Published: July 2002

Diffractive lenses are becoming the optical elements of choice for many applications. One type of diffractive lens, the binary zone plate, has already demonstrated high-resolution performance experimentally. However, in order to increase the diffraction efficiency of these zone plates, a blazed grating profile must be used. This can best be approximated by a staircase grating profile, created by multilevel exposures. Using x-ray lithograph, we fabricated for the first time circular, linear bi- and trilevel zone plates, with gold structures 0.75 μm thick (per level), on silicon nitride substrates. The zone plates were designed for use at a wavelength of 1.54 Å, and had a theoretical efficiency of 68.5% for bilevel and 81.5% for trilevel zone plates. Due to the large depth of focus and high resolution inherent to x-ray lithography, the finished zone plate exhibits very steep sidewall profiles, with linewidth resolution down to 0.25 μm. Such vertical sidewalls are essential for achieving high lens efficiency. Fabrication errors, such as thickness variation in the electroplated gold and misalignment, were considered, and their effect on the optical efficiency of the zone plate was estimated. Alignment errors between levels were minimized, achieving a best result of 25 nm (3σ). In fabricating the zone plates, we employed standard integrated device tools, such as a Leica Cambridge Electron Beam microfabricator (EBMF) 10cs/120 electron-beam writer for the x-ray mask fabrication, and a Suss 200 x-ray stepper for the multilevel exposures. Thus, we have shown that it will be possible to fabricate many lenses, with a variety of optical characteristics, in one wafer.
FeP precipitates in hydride-vapor phase epitaxially grown InP:Fe
Authors: Luysberg M. , Göbel R. , Janning H.
Published: July 2002

Fe-doped InP was grown by hydride-vapor phase epitaxy. Doping levels up to 8×1018 cm−3 were determined by secondary ion mass spectrometry. Additionally performed photoluminescence measurements revealed a homogeneous distribution of electrically active Fe atoms. From microstructural investigations by analytical transmission electron microscopy, spherical-shaped precipitates were detected in plan-view samples. These precipitates with diameters up to 13 nm are homogeneously arranged in the epilayer. For conglomerates of precipitates a distinct enrichment with Fe and P was measured by a comparative energy dispersive x-ray analysis. The lattice plane distances of the precipitates were deduced from the electron diffraction patterns and from high-resolution electron micrographs. A comparison with calculated values for different Fe–P alloys indicates that the precipitates consist mainly of orthorhombic FeP.
Photocatalytic oxidation for point-of-use abatement of volatile organic compounds in microelectronics manufacturing
Authors: Raupp Gregory B.
Published: July 2002

In gas–solid heterogeneous photocatalytic oxidation (PCO), volatile organic compounds (VOCs) present in process air or air vents can be rapidly and completely oxidized to innocuous by-products over a near-ultraviolet (UV) illuminated titanium dioxide thin film catalyst at room temperature. This class of advanced oxidation processes appears to be well-suited for point-of-use VOC abatement in the microelectronics manufacturing industry. In this article, we review industrial requirements and unresolved technical issues in the context of the recently published Semiconductor Industry Association roadmap. The specific requirements for VOC abatement from a typical photolithography track are presented. Bench-scale PCO kinetics for target VOCs are reviewed to demonstrate the typical process behavior expected.
Domain structure and polarization reversal in ferroelectrics studied by atomic force microscopy
Authors: Gruverman A. , Kolosov O. , Hatano J. , Takahashi K. , Tokumoto H.
Published: July 2002

The ferroelectric domain structure and its dynamics under applied electric field have been studied with nanoscale resolution by atomic force microscopy (AFM). Two mechanisms responsible for the contrast between opposite domains are proposed: large built-in domains are delineated in friction mode due to the tip–sample electrostatic interaction, and small domains created by an external field are imaged in topography mode due to piezoelectric deformation of the crystal. The ability of effective control of ferroelectric domains by applying a voltage between the AFM tip and the bottom electrode is demonstrated. It is experimentally confirmed that the sidewise growth of domain proceeds through the nucleation process on the domain wall.
Excimer laser assisted etching of AlGaAs and GaAs
Authors: Takatani Shinichiro , Yamamoto Seiji , Takazawa Hiroyuki , Mochiji Kozo
Published: July 2002

Laser assisted etching of AlGaAs and GaAs by chlorine using ArF and KrF excimer lasers was investigated. The etching rate of AlGaAs was shown to be larger than that of GaAs. Quadrupole mass spectroscopy analysis of the etching products for KrF assisted etching showed intense Ga+ and As+ signals from AlGaAs. It is suggested that a laser-induced neutral atom desorption process is enhanced in the AlGaAs etching. Hall measurements of a shallow channel heterostructure sample and GaAs Schottky diode characterization demonstrated the low damage of the etching process. The etching profile was examined by scanning electron microscopy and feasibility for field effect transistor gate recess etching was shown.
Diffusion and channeling of low-energy ions: The mechanism of ion damage
Authors: Chen Ching-Hui , Green Debora L. , Hu Evelyn L.
Published: July 2002

A simple model, including both channeling and diffusion effects, has been developed for the understanding of the mechanism of low-energy ion-induced damage. This model provided much better agreement with our experimental data, and yields a value for the effective diffusivity of defects during ion bombardment as ∼3×10−15 cm2/s. The numerical results support our experimental data that diffusion of defects, even at room temperature, plays an important role in determining the profile of ion-induced damage and suggests that some enhancement of defect diffusion occurs during ion bombardment. In addition, since the majority of defects are located in the near-surface region (within ∼50 Å of the surface), even modest etch removal of the surface can dramatically alter the damage profile. Therefore, surface removal has also been considered in our model to find the influence of etch rate on the ion damage profile.
Manufacturing issues of electrostatic chucks
Authors: Wright D. R. , Chen L. , Federlin P. , Forbes K.
Published: July 2002

In the past few years, electrostatic chucks (ESCs) have become much more widespread in semiconductor manufacturing equipment. In addition to the elimination of moving parts, ESCs hold the promise to decrease the wafer edge exclusion, that is, to allow more good chips to be made on each wafer. A number of technical, material, and business challenges remain in making ESCs workable and reliable in all tools across the semiconductor factory, or fab. We will discuss issues of clamping force, clamping and declamping time, and wafer temperature control, describing how they affect design and choice of materials. The effect of these choices on adapting ESCs to various tools over various temperature ranges will also be discussed. The role of models and test results in accelerating development will be addressed. Finally, we will list some of the business challenges to implementing ESCs. Despite technical successes, many high-volume fab lines are always reluctant to risk installing new technology, despite promises of improvement. SEMATECH has addressed these issues with the Working Groups that address standard specifications, study early testing results, and share manufacturing performance data.
Low-distortion electron-beam lithography for fabrication of high-resolution germanium and tantalum zone plates
Authors: David C. , Kaulich B. , Medenwaldt R. , Hettwer M. , Fay N. , Diehl M. , Thieme J. , Schmahl G.
Published: July 2002

In this work, an e-beam tool consisting of a commercial pattern generator and a scanning electron microscope is used for the fabrication of high-resolution zone plates for x-ray microscopy applications. In order to avoid misplacement of the zone plate structures, which would result in a deterioration of the imaging properties, various possible distortions of the lithography system are investigated. Misscaling and nonorthogonality of the deflection axes are eliminated by a simple alignment routine using contamination marks. Drift is found to be sufficiently small after several hours of thermal stabilization. The nonlinearity error is measured by the exposure of Moiré patterns. We were able to reduce the total misplacement of the zone plate structures to less than 3×10−4 of the zone plate’s diameter. The resist patterns can be transferred in germanium and tantalum by reactive ion etching using trilevel processes resulting in structures with linewidths down to 26 nm. The quality of the dry etching process is shown by measurement of the x-ray diffraction efficiency. Imaging an e-beam-generated test object with the fabricated zone plates at λ=2.4 nm proves that the total distortions of the e-beam tool were sufficiently reduced.
Fabrication of CdZnSe/ZnSe quantum dots and quantum wires by electron beam lithography and wet chemical etching
Authors: Illing M. , Bacher G. , Kümmell T. , Forchel A. , Hommel D. , Jobst B. , Landwehr G.
Published: July 2002

We have developed a versatile and low-damage technology to realize quantum dots and quantum wires based on CdxZn1−xSe/ZnSe heterostructures. Electron beam lithography was used for pattern definition. The pattern transfer into the semiconductor was performed by a wet etch process based on a K2Cr2O7:HBr:H2O solution. Preferential etching along crystallographic planes leads to well-defined sidewalls of the freestanding dot and wire structures. Dot sizes down to 28 nm and wire sizes down to 13 nm have been achieved. High photoluminescence efficiencies, even in the narrowest structures, allow the study of lateral confinement effects. We observe a size dependent blueshift of up to 20 meV in the photoluminescence emission spectrum of the narrowest nanostructures. The measured energy shifts can be modeled based on a rectangular lateral potential well and the measured sizes of the structures.
Molecular beam epitaxy grown ZnSe studied by reflectance anisotropy spectroscopy and reflection high-energy electron diffraction
Authors: Zettler J. -T. , Stahrenberg K. , Richter W. , Wenisch H. , Jobst B. , Hommel D.
Published: July 2002

In this work we report on the in situ investigation of MBE grown ZnSe surfaces performed simultaneously by reflectance anisotropy spectroscopy (RAS) and reflection high-energy electron diffraction (RHEED). Reconstructions and anisotropic reflectance of the ZnSe(001) surface are studied in the temperature range from 50 °C to 380 °C. With increasing temperature the ZnSe surface evolves from a Se-rich c(2×2)Se via a Se-rich (2×1) to a Zn-rich c(2×2)Zn surface reconstruction with the transition temperatures depending on whether the surface is Se stabilized or not. Each surface reconstruction as verified by RHEED is accompanied by a characteristic RAS spectrum. Time resolved measurements of the RAS signal at fixed photon energies allowed to determine the activation energy (0.7 eV) for the Se desorption from the (2×1) reconstructed ZnSe(001) surface.
Commercial heterojunction bipolar transistor production by molecular beam epitaxy
Authors: Streit Dwight C. , Oki Aaron K. , Block Thomas R. , Lammert Michael D. , Hoppe Matthew M. , Umemoto Donald K. , Wojtowicz Michael
Published: July 2002

We have developed the first commercial heterojunction bipolar transistor (HBT) production line based on GaAs–AlGaAs–InGaAs HBT material grown by molecular beam epitaxy. We have demonstrated sustained high-yield production of HBT integrated circuits for commercial applications using molecular beam epitaxy growth and processing techniques originally developed for high-reliability applications. TRW HBT parts such as cellular power amplifiers, digital radio chip sets, Darlington gain blocks, and analog-to-digital convertors are now inserted in high volume commercial products such as cellular phones, local area networks, and digital oscilloscopes. HBT monolithic microwave integrated circuits allow these products to achieve functions and performance never before available for consumer applications.
Oxide growth on silicon (100) in the plasma phase of dry oxygen using an electron cyclotron resonance source
Authors: Kim Keunjoo , An M. H. , Shin Y. G. , Suh M. S. , Youn C. J. , Lee Y. H. , Lee K. B. , Lee H. J.
Published: July 2002

Silicon dioxide films were grown using an oxygen plasma generated by an electron cyclotron resonance (ECR) source at several low temperatures. The plasma oxidation rate was investigated by varying the growth parameters. The oxide thickness parabolically increases with microwave power but decreases with increasing pressure or flow rate. A complementary model of the Deal–Grove oxidation theory is suggested for the plasma oxidation, and kinetic parameters are compared with the other plasma and thermal oxidation cases. The diffusion rate constant in O2 plasma oxidation at room temperature is enhanced up to the level of the diffusion rate in thermal oxidation and the reaction rate constant is much larger than the thermal oxidation case. This may imply that, due to oxygen atoms dissociated by the ECR plasma, plasma oxidation is related to the atomic diffusion through oxide layer and the atomic chemical reaction at the Si–SiO2 interface. The high quality of the ultrathin oxide film was characterized with a breakdown field of 14.8 MeV/cm and an interfacial state density of 1.2×1010 eV−1 cm−2.
In situ control and analysis of the scanning tunneling microscope tip by formation of sharp needles on the Si sample and W tip
Authors: Heike S. , Hashizume T. , Wada Y.
Published: July 2002

Sharp needles on the Si(111)7×7 and Si(100)2×1 surfaces are formed in a controlled manner by applying a sample bias Vs ranging from +5.0 to +10.0 V while keeping the scanning tunneling microscope (STM) tunneling current constant. The size of the needle-shaped structure is 1–20 nm in height and 1–5 nm in diameter depending on the bias voltage and duration (1–30 s). The needle structures are utilized to counter image the scanning tip with an atomic resolution (needle formation and tip imaging=NFTI). The STM resolution for the Si(111)7×7 structure is evaluated in relation to the atomic structure of the scanning tip imaged by the NFTI method. When a bias voltage of Vs=−10.0 V is used, needle formation on the scanning tip is observed. The NFTI method gives us a conventional technique to modify and monitor in situ the scanning tip of STM.
Electron emission from the pyramidal-shaped diamond after hydrogen and oxygen surface treatments
Authors: Yamada T. , Ishihara H. , Okano K. , Koizumi S. , Itoh J.
Published: July 2002

The emission properties of the pyramidal-shaped diamond after hydrogen and oxygen surface treatments were discussed. There was a shift in C1s binding energy peak in the x-ray photoelectron spectrum due to the surface treatments. The lowest turn-on voltage in the emission current versus anode voltage characteristics is observed after the hydrogen treatment. The emission barrier height ratios against the as-prepared surface are found to be 0.68 for hydrogen treated and 2.1 for oxygen treated surfaces, respectively, from the slopes of the Fowler–Nordheim characteristics. The change in the barrier height is speculated to be explained by the dipole formed at the diamond surface. The emission stability is also confirmed, and this remarkable feature was obtained for a hydrogen-treated surface.
Measurement of band offsets in Si/Si1−xGex and Si/Si1−x−yGexCy heterojunctions
Authors: Stein B. L. , Yu E. T. , Croke E. T. , Hunter A. T. , Laursen T. , Bair A. E. , Mayer J. W. , Ahn C. C.
Published: July 2002

Realization of group IV heterostructure devices requires the accurate measurement of the energy band offsets in Si/Si1−xGex and Si/Si1−x−yGexCy heterojunctions. Using admittance spectroscopy, we have measured valence-band offsets in Si/Si1−xGex heterostructures and conduction-band and valence-band offsets in Si/Si1−x−yGexCy heterostructures grown by solid-source molecular-beam epitaxy. Measured Si/Si1−xGex valence-band offsets were in excellent agreement with previously reported values. For Si/Si1−x−yGexCy our measurements yielded a conduction-band offset of 100±11 meV for a n-type Si/Si0.82Ge0.169C0.011 heterojunction and valence-band offsets of 118±12 meV for a p-type Si/Si0.79Ge0.206C0.004 heterojunction and 223±20 meV for a p-type Si/Si0.595Ge0.394C0.011 heterojunction. Comparison of our measured band offsets with previously reported measurements of energy band gaps in Si1−x−yGexCy and Si1−yCy alloy layers indicates that the band alignment is type I for the compositions we have studied and that our measured band offsets are in quantitative agreement with these previously reported results.
Scanning tunneling microscopy and ballistic electron emission spectroscopy studies of molecular beam epitaxially grown Pt/CaF2/Si(111) structures
Authors: LaBella V. P. , Schowalter L. J. , Ventrice C. A.
Published: July 2002

The electronic and morphological properties of ultrathin Pt/CaF2/Si(111) metal insulator semiconductor structures have been characterized in situ by scanning tunneling microscopy (STM) and ballistic electron emission microscopy (BEEM). Platinum thickness from 2 Å to 20 Å grown on 5 Å epitaxial CaF2 have been characterized. The STM images of the Pt/CaF2/Si(111) structures show the atomic steps of the underlying CaF2 morphology, as well as the formation of Pt nodules. These nodules have been observed to coalesce into bigger grains when left at room temperature under ultrahigh vacuum conditions for over 24 h. For ultrathin Pt coverages (2 Å) the STM images at different tip biases reveal different topography, depending on the value of the tip bias relative to the conduction band minimum (CBM) of the CaF2 intralayer (3.3 eV). The STM images at biases well above the CBM of the CaF2 show similar features to bare CaF2/Si(111), while images at the CBM show features of the deposited Pt. BEEM spectra of the 10 Å sample show a peak at ∼4.5 eV due to the density of states of the CaF2 intralayer and an additional peak at 2 eV, which has not been observed in previous studies of metal/CaF2/Si(111) structures.
Fabrication and characterization of room temperature silicon single electron memory
Authors: Guo Lingjie , Leobandung Effendi , Zhuang Lei , Chou Stephen Y.
Published: July 2002

A single electron memory was demonstrated in crystalline silicon that has a transistor channel width of ∼10 nm and a nanoscale floating gate of dimension ∼(7 nm × 7 nm × 2 nm), patterned by electron beam lithography, lift-off, and reactive ion etching. Quantized shift in the threshold voltage and self-limited charging process have been observed at room temperature. Analysis has shown that these quantized characteristics are the results of single electron charging effect in the nanoscale floating gate.
Evidence of Ge island formation during thermal annealing of SiGe alloys: Combined atomic force microscopy and Auger electron spectroscopy study
Authors: Tételin C. , Wallart X. , Stiévenard D. , Nys J. P. , Gravesteijn D. J.
Published: July 2002

The effect of thermal annealing on the composition and morphology of the surface of strained SiGe layers grown on Si is investigated in the temperature range 400–900 °C. We show that Ge segregation starts at 400 °C and increases with increasing temperature. Above 700 °C, strain relaxation leads to the formation of islands on the surface. By combining atomic force microscopy and Auger electron spectroscopy we demonstrate that these islands are Ge rich and that at 900 °C rather pure Ge islands are formed on a Si rich underlying layer.
Fourier transform infrared spectroscopy of corona-processed silicon dioxide films
Authors: Landheer D. , Sayedi S. M. , Landsberger L. M. , Kahrizi M.
Published: July 2002

The application of corona discharge during the thermal oxidation of Si substrates has been shown to dramatically enhance the growth rate at low temperatures. Fourier transform infrared spectroscopy (FTIR) of the films shows that these films have properties close to those of untreated oxides. No-hydrogen related impurities are introduced into these films by the corona processing. However, subtle changes in the shape and intensity of the main Si–O–Si asymmetric (AS) stretch vibration at 1070 cm−1 indicate that the films have a different structure than that of standard thermal SiO2 films. The changes in frequency and full width half maximum (FWHM) of the AS peak are described as a function of corona-treatment parameters. The peak frequency and FWHM of positive-corona-treated films shift in a direction consistent with relaxation of thermal SiO2 films. However, for negative-corona-treated films the shifts are in the opposite (unexpected) direction. Coupled FTIR and etch-back measurements indicate that both positive- and negative-coronaprocessed films are homogeneous.
Compositional dependence of luminescence of lithium zinc gallate phosphor
Authors: Suh Kyung-Soo , Jang Soon-Ju , Cho Kyoung-Ik , Nahm Sahn , Byun Jae-Dong
Published: July 2002

The photoluminescence (PL) and cathodoluminescence (CL) characteristics of lithium gallate and lithium zinc gallate were investigated as a function of composition and firing temperature. As Li/Ga of lithium gallate decreased, the emission peak shifted from about 420 to 390 nm under ultraviolet (UV) excitation. Similar results were obtained under cathode ray (CR) excitation. PL spectra of lithium gallates fired at high temperature were most similar to those of Li-deficient lithium gallate. This result clearly indicates that lithium gallate fired at high temperature is Li deficient. The PL and CL emission spectra of lithium zinc gallate consisted of a single broadband under UV and CR excitation. The emission peak of the composition of (1−x)Li0.5Ga2.5O4–xZnGa2O4 shifted from 406 to 440 nm as x increased under UV excitation and the peak intensity decreased with x. However, the intensity increased with x under CR excitation. When the composition of lithium zinc gallate was 0.4Li0.5Ga2.5O4–0.6ZnGa2O4, the brightest CL was observed.
Investigation of Pt/Ta diffusion barrier using hybrid conductive oxide (RuO2) for high dielectric applications
Authors: Yoon Dong-Soo , Baik Hong Koo , Lee Sung-Man , Lee Sang-In , Ryu Hyun , Lee Hwack Joo
Published: July 2002

The Pt/Ta diffusion barrier using hybrid conductive oxide (RuO2) for dynamic random access memory and ferroelectric random access memory capacitor bottom electrodes is proposed. The thermal stability of Pt+RuO2 (50 nm)/Ta+RuO2 (50 nm)/TiSi2/poly-Si/SiO2/Si contact system is investigated and compared to that of the Pt(50 nm)/Ta(50 nm)/TiSi2/poly-Si/SiO2/Si contact system. The Pt+RuO2/Ta+RuO2/TiSi2/poly-Si/SiO2/Si contact system sustained its structure up to 650 °C, whereas Pt/Ta/TiSi2/poly-Si/SiO2/Si contact system was completely degraded after annealing at 650 °C. In the former case, the addition of ruthenium dioxide (RuO2) into the Pt bottom electrode layer led to retardation of the oxygen indiffusion, preventing the indiffusion of oxygen up to 650 °C. In addition, the Ta+RuO2 diffusion barrier showed an amorphous structure and RuO2 is bound to the Ta matrix, inhibiting the interdiffusion of O, Pt, and Si through grain boundaries which can act as fast diffusion paths up to high temperatures. Therefore, it appeared that the barrier properties of Pt/Ta diffusion barrier are improved by using hybrid conductive oxide (RuO2).
Characterization of TiN barriers against Cu diffusion by capacitance–voltage measurement
Authors: Rha Sa-Kyun , Lee Seung-Yun , Lee Won-Jun , Hwang Yong-Sup , Park Chong-Ook , Kim Dong-Won , Lee Youn-Seoung , Whang Chung-Nam
Published: July 2002

Sputtered TiN was studied as a diffusion barrier in Cu/TiN/Ti/Si and Cu/TiN/Ti/SiO2/Si multilayer structures using various characterization methods, and their sensitivities for detecting breakdown of the barrier were compared. It was confirmed by scanning electron microscopy and Auger electron spectroscopy that breakdown of the TiN barrier occurred through out-diffusion of Si in addition to in-diffusion of Cu. Breakdown temperatures varied by more than 100 °C depending on characterization methods, and capacitance–voltage (C–V) measurement was most sensitive for detecting the failure of the TiN barrier. The effects of rapid thermal annealing (RTA) on barrier properties of TiN were investigated, and it was found by C–V measurement that the TiN(400 nm) RTA treated at 700 °C in a NH3 ambient was stable up to 590 °C for 2 h, while the reference TiN (400 nm) was stable up to 450 °C for 2 h.
Ohmic contacts to p-type GaN using a Ni/Pt/Au metallization scheme
Authors: Jang Ja-Soon , Park Kyung-Hyun , Jang Hong-Kyu , Kim Hyo-Gun , Park Seong-Ju
Published: July 2002

We report a new Ni/Pt/Au trilayer metallization scheme for the formation of ohmic contact to p-GaN. Metal thin films with a thickness of 20 nm for Ni, 30 nm for Pt, and 80 nm for Au were deposited on the p-GaN layer (Na=9.4×1016 cm−3) by electron beam evaporation. The samples, annealed at 500 °C for 30 s in a rapid thermal anneal system, showed a high quality ohmic contact with a low specific contact resistance of 2.1×10−2 Ω cm2. Auger electron spectroscopy analysis of the contact layers suggests that Pt plays an important role in the formation of ohmic contact, indicating that a Ni/Pt/Au trilayer can be used and that it is a promising material system for ohmic contact to p-GaN.
Distributed, multiple variable shaped electron beam column for high throughput maskless lithography
Authors: Groves T. R. , Kendall R. A.
Published: July 2002

The ultimate resolution obtainable with focused electron beams is, for practical purposes in lithography, unlimited. Existing e-beam lithography systems are too slow to be practical for high volume manufacturing of semiconductor devices, however. The usable current in probe forming systems is limited by the stochastic Coulomb interaction in the beam path, which causes loss of resolution at high current. This is due to the need to pass all of the writing current through an aperture. Distributed systems, by contrast, do not suffer from this problem, as the current is spread over a large volume. The purpose of this article is to propose a distributed system, employing multiple, variable shaped beams for direct write (maskless) lithography. We call this system DiVa, to emphasize the key attributes of distributed writing current, and variable beam shaping. It utilizes a planar cathode, patterned with a rectilinear array of square emitters. Focusing is accomplished by a uniform, axial magnetic field, oriented along the optic axis. This transfers a one-to-one image of the emitters onto the writing surface. Deflection plates between adjacent rows of beamlets effect motion in one Cartesian axis, while mechanical translation of the stage effects motion in the orthogonal axis. Theoretical resolution is diffraction limited to 4.6 nm at 50 kV. Experimental results are presented which demonstrate the first order optics using a rudimentary apparatus.