bluuebunny/crossref_metadata_2025 huggingface dataset:
A direct approach to the modeling of polydihexylsilane as a contrast enhancement material
Authors: Loong Wen-an , Pan Hong-tsz
Published: July 2002

In our study the polydihexylsilane(PDHS), as a contrast enhancement material, we found that the values of A, B, and C of Dill’s modeling parameters of PDHS are irregularly dependent on its film thickness, and also refractive index decreases during exposure. These difficulties make Dill’s model inadequate for the simulation of contrast enhanced lithography. A new model was derived to simulate the nonlinear photobleaching curves of PDHS with varying thickness. Linearity was found with parameters in this equation as a function of PDHS film thickness. The thicker PDHS film does not improve the contrast within the usually used thickness range of 0.1–0.6 μm. This equation also models the nonlinear bleaching curve of p-diazo-N,N-dimethylaniline-chloride zinc chloride and the reported bleaching curve of CEM-2 quite well.
Scanning tunneling microscope images of fatty acid Langmuir–Blodgett bilayers
Authors: Kuroda R. , Kishi E. , Yamano A. , Hatanaka K. , Matsuda H. , Eguchi K. , Nakagiri T.
Published: July 2002

The molecular arrangements of a fatty acid [behenic acid; CH3 (CH2)20COOH ] bilayer have been observed with a scanning tunneling microscope. The sample was deposited onto a highly oriented pyrolytic graphite substrate by the Langmuir–Blodgett technique. We observed two types of molecular arrangements. One type has two periodicities of 3 and 0.4 nm, and the other type has those of 6 nm (with subperiodicity of 3 nm) and 0.4 nm. In both types the directions of the two periodicities cross at a right angle. The 3 nm/6 nm periodicity corresponds to one/double length of the molecule, and the 0.4 nm periodicity corresponds to the width of the molecule. These results suggest that the molecules lie parallel to the substrate.
Fundamental and practical aspects of differential scanning tunneling microscopy
Authors: Stoll E. P. , Gimzewski J. K.
Published: July 2002

Phase-sensitive techniques can be used to measure differential surface topography in noisy environments, such as those encountered in technological applications. We present a variety of atomic resolution images of the Au(110) (1×2), Cu(111), and stepped surfaces recorded in the conventional and differential modes. Reconstruction of the topography from the differential image reveals that, although the technique suppresses most noise, an undesirable amplification of the 1/f component occurs in agreement with theoretical analysis. We demonstrate that such noise can nevertheless be removed with suitable filtering techniques.
Tunneling microscopy and spectroscopy on cross sections of molecular-beam-epitaxy-grown (Al)GaAs multilayers
Authors: Salemink H. , Albrektsen O.
Published: July 2002

We report scanning tunneling microscopy (STM) observations of topography and spectroscopy on molecular-beam-epitaxy (MBE)-grown (Al)GaAs multilayers. The experiments were done on ultrahigh vacuum (UHV)-cleaved, MBE-grown GaAs–AlGaAs multilayer structures, exposing the (110) plane which is cross sectional to the 〈001〉 growth direction. A UHV scanning electron microscopy (SEM) is used for easy guidance towards the epitaxial structure. The atomic registry is clearly observed in the epitaxial GaAs, in the AlGaAs layer as well as in their interfaces. The transition between these materials, as seen by STM, takes place over a region of 1–2 unit cells. The GaAs layers have a very homogeneous appearance, in contrast to the AlGaAs layers, which show a patchy texture in the atomic resolution images. This is attributed to an inhomogeneous distribution of the local density of states in the AlGaAs. Furthermore, the current–voltage characteristics in the AlGaAs indicate variations in the position of conduction band with respect to the valence band. These features are indicative of composition fluctuations on the nanometer scale, which are directly observed by our tunneling electron probe. We present results from current–voltage spectra, taken over a GaAs/AlGaAs interface: the transition in valence band position is observed over a length scale of six unit cells (3.5 nm). A marked distinction between the GaAs and the AlGaAs material is the chemisorbed coverage, which takes place on the Al compound at a high rate, even under the UHV condition of <5×10−11 mbar.
Two-dimensional atomic force microprobe trench metrology system
Authors: Nyyssonen D. , Landstein L. , Coombs E.
Published: July 2002

This article describes the extension of atomic force microprobe (AFM) technology to two dimensions (2D) for accurate measurement of submicron critical dimensions (CDs). The system utilizes a vibrating tip with heterodyne-interferometer sensor similar to that introduced by Martin, Williams, and Wickramasinghe. [Y. Martin, C. C. Williams, and H. K. Wickramasinghe, J. Appl. Phys. 61, 4723 (1987)]. However, the tip vibrates in 2D with dual heterodyne detection. The sample is moved relative to the tip by means of coarse- and fine-motion stages whose position is monitored with 3D interferometry. The system does not scan the sample, but operates like a nanorobot sensing the approach of the tip to the surface by means of the vibration damping. A special three-point tip has been fabricated by Lee [K. L. Lee, D. W. Abraham, F. Serord, and L. Landstein, Proceedings of the 35th ISEIPB Conference, Seattle, WA, May 28–31, 1991 (unpublished), paper K1] with 0.1 μm shank diameter which allows measurement of submicrometer trench widths up to 2 μm in depth with accuracy and repeatability at the nanometer level. Measurements are made under computer control. The system design and operating characteristics are discussed.
Electron-beam induced tungsten deposition: Growth rate enhancement and applications in microelectronics
Authors: Kohlmann-von Platen K. T. , Buchmann L.-M. , Petzold H.-C. , Brünger W. H.
Published: July 2002

Electron-beam induced deposition (EBID) of tungsten from the precursor gas W(CO)6 was investigated with the aim of enhancing the growth rate of the process. By varying dwell and loop time over a limited range, experimental deposition rates were compared to a time dependent model developed to describe the focused ion beam induced deposition. We found the cross section σ for EBID at 30 keV beam energy to be 1.2±0.2×10−16 cm−2. Based on these data, we predicted the achievable growth rate as a function of the current density. Moreover, EBID was used for x-ray and open stencil mask repair, the generation of etch masks and the deposition of electrically conductive lines. The resistivity of the latter was found to be affected by the beam energy and current; the best value achieved was 10−2 Ω cm.
Self-assembled monolayer electron-beam resists on GaAs and SiO2
Authors: Lercel M. J. , Tiberio R. C. , Chapman P. F. , Craighead H. G. , Sheen C. W. , Parikh A. N. , Allara D. L.
Published: July 2002

It was demonstrated that self-assembled monolayers of n-octadecanethiol [ODT; CH3(CH2)17SH] on GaAs and n-octadecyltrichlorosilane [OTS; CH3(CH2)17SiCl3] on SiO2 act as self-developing positive electron beam resists with electron-beam sensitivities of ∼100–200 μC/cm2. For the OTS monolayer on a silicon native oxide, atomic force microscopy (AFM) images of the exposed layer before etching demonstrate the removal of all or part of the layer upon electron-beam exposure. Features as small as 25 nm were resolvable in a 50 nm period grating. A resist contrast curve for OTS was obtained from AFM depth measurements as a function of dose. An ammonium hydroxide water etch was used to transfer patterns into the GaAs to a depth of at least 30 nm and buffered HF was used for pattern transfer into the SiO2 to a depth of at least 50 nm.
Electron-beam lithography for advanced device prototyping: Process tool metrology
Authors: Rosenfield M. G. , Thomson M. G. R. , Coane P. J. , Kwietniak K. T. , Keller J. , Klaus D. P. , Volant R. P. , Blair C. R. , Tremaine K. S. , Newman T. H. , Hohn F. J.
Published: July 2002

Direct write electron-beam lithography is the most flexible technique for sub-0.25 μm imaging in an advanced development environment. The resolution and custom exposure capabilities of electron-beam lithography, as well as the rapid turnaround for new device designs, provide early device/technology feasibility demonstration, learning, and proof-of-concept not easily obtainable with other lithographies. We have used a 50 kV shaped-beam system for advanced complementary metal–oxide–semiconductor (CMOS), bipolar, BiCMOS, and DRAM device prototyping as well as for front-end and back-end process development, metrology standard fabrication, exploratory device fabrication, and x-ray mask fabrication. The high throughput, as compared to vector scan systems, of shaped-beam electron-beam lithography was found to be essential in satisfying the requirements of advanced development programs. The key to success has been a complete understanding and integration of the interaction of the resist process, tool, proximity correction, and metrology at 0.25 μm and below. In this article, we will describe the processes used to obtain minimum dimensions down to 0.1 μm in negative and positive resists with 3σ linewidth variation typically better than 0.025 μm. Accurate and precise scanning electron microscopy metrology will be shown to be critical for process development and inspection of device wafers. In addition, tool set-up techniques and proximity correction for sub-0.25 μm lithography will be discussed. Working room temperature CMOS devices and circuits, with physical gate widths as small as 0.1 μm, have been fabricated using e-beam lithography for the critical gate level and optical lithography for all other levels. A mixed lithography approach was found to be the most effective use of the e-beam, lithography capabilities.
Ultrahigh vacuum scanning tunneling microscopy studies of platinum on graphite
Authors: Clark G. W. , Kesmodel L. L.
Published: July 2002

The surface morphology of submonolayer coverages of platinum vapor deposited onto highly oriented pyrolytic graphite (HOPG) has been studied. With coverages of 5%–30% of a monolayer, we have observed both three-dimensional clusters and two-dimensional (2D) islands of Pt on the substrate. Our studies concentrated on the 2D islands of Pt, which exhibited several interesting features. Small islands exhibited epitaxial growth on the HOPG with markedly small Pt–Pt bond lengths, as well as occasional features of larger spacings. Similar larger structures on graphite islands and near graphite steps on the clean HOPG surface were observed. Results of scanning tunneling spectroscopy show that spectra on platinum deposits exhibit a broader character than those on clean graphite and show some structure consistent with bulk Pt.
Experimental observations and modeling of ultra-shallow BF2 and As implants in single-crystal silicon
Authors: Tasch A. F. , Yang S.-H. , Morris S. , Lim D.
Published: July 2002

The achievement of ultra-shallow doping profiles by ion implantation requires low energy implants and minimum thermal budgets. In this case, the profile is generally more sensitive to the implant parameters, including implant angles and dose. A detailed study has been performed of the dependence of boron and arsenic profiles on tilt angle, rotation angle, and dose for energies down to 15 keV for BF+2 and As+ implants in (100) Si wafers. The major axial and planar channels have been determined using critical angle analysis and are in agreement with experimental observations. In addition, computationally efficient models have been developed for BF2 and As implants which accurately account for the boron and arsenic profile dependence on tilt angle, rotation angle, and dose in addition to energy.
Capacitive sensors coupled to a scanning tunneling microscope piezoscanner for accurate measurements of the tip displacements
Authors: Desogus S. , Lányi Š. , Nerino R. , Picotto G. B.
Published: July 2002

This article studies the use of capacitive sensors for in situ calibration of the piezoscanner of a scanning tunneling microscope (STM). Nonlinearities, hysteresis, and creeps of piezoactuators are the main sources of the uncertainty in the tip position while scanning the sample surface to be imaged. In order to compensate for these effects in the reconstruction of the surface topography, capacitive sensors have been coupled to a piezoscanner of a STM operating in air. This scanner provides x,y,z displacements up to about 130 μm×130 μm×30 μm, and consists of bimorph plates mounted in a parallelogram arrangement. The capacitive sensors are inserted in a differential configuration to minimize capacitance variations due to changes in humidity and temperature of the air and to compensate for thermal drifts of the structure. As a performance test, the piezoscanner displacements were independently measured by means of a differential interferometer. A linearity within 3% and a deviation within 0.3% from the expected capacitance versus displacement dependence were achieved for scanner range up to 130 μm, with a resolution of 5 nm. Perspective improvements of the present setup are also discussed.
Scanning force microscopy of E. coli OmpF porin in buffer solution
Authors: Schabert F. A. , Hoh J. H. , Karrasch S. , Hefti A. , Engel A.
Published: July 2002

The extracellular and periplasmic surface topography of the E. coli outer membrane protein OmpF reconstituted into 2D crystals in the presence of phospholipids were investigated with a scanning force microscope in buffer solution. Topographs exhibiting 2 nm lateral resolution are in good agreement with data from electron microscopy and x-ray crystallography, and indicate the exciting possibility to monitor structural changes of ‘‘live systems’’ at molecular resolution by scanning force microscopy.
Micromachining of metal surfaces by scanning probe microscope
Authors: Sumomogi T. , Endo T. , Kuwahara K. , Kaneko R. , Miyamoto T.
Published: July 2002

This paper describes micromachining of pure metal surfaces in air by a scanning probe microscope that has a very sharp diamond tip mounted on the end of a cantilever beam. Samples of pure metals, such as Ni, Cu, and Au, were prepared by vapor deposition or mechanical polishing of bulk metals. Sample surfaces were scratched with x-y scanning of 3 μm x direction span, 30 nm y direction feed and 0.98–19.6 μN loading force, and topographies of the scratched area were observed. On the scanning-scratched surfaces of Cu and Au, the ridge caused by the adhesion of removed materials were observed. On the other hand, in the case of Ni, flat square hollows of 5–50 nm depth were obtained. The mechanism of micromachining should be determined by several factors such as plasticity, adhesive property, and oxide surface of metals. The method presented here will be powerful for micromachining of various materials.
Fabrication of nanometer-scale structures on insulators and in magnetic materials using a scanning probe microscope
Authors: Hosaka S. , Koyanagi H. , Kikukawa A. , Miyamoto M. , Imura Ryo , Ushiyama J.
Published: July 2002

Field evaporation and electron induced local heating in scanning probe microscopes [atomic force microscope, scanning tunnel microscope (STM), and magnetic force microscope (MFM)] are investigated for a nanometer-sized structure fabrication on an insulator and for a fine magnetic domain formation in a magnetic material. Application of negative voltage to the gold-coated AFM probe can be provided to make gold lines 40 nm wide and dots 20 nm in diameter on SiO2/Si by field evaporation. Reversely, in a positive voltage, thermal processes are dominant, one of which is the formation of nanometer-sized magnetic domains produced by electron induced local heating using STM and MFM. The proposed MFM recording can form 60×240 nm2 domains in a Pt/Co multilayer magnetic film and they can be observed with the same probe.
Ultrathin nitride layers grown by molecular-beam epitaxy and their effects on interface states in silicon metal–insulator–semiconductor field-effect transistors
Authors: Fayfield R. T. , Chen J. , Hagedorn M. S. , Higman T. K. , Moy A. M. , Cheng K. Y.
Published: July 2002

In this experiment the ultrahigh vacuum environment of a molecular-beam epitaxy reactor equipped with ammonia was used to thermally nitride silicon. The resulting thin silicon nitride films were incorporated as gate insulators of metal-insulator-semiconductor field-effect transistors. The fabrication of field-effect transistors enabled very accurate interface state characterization of the silicon–silicon nitride interface by the charge pumping technique. The ammonia nitridation of silicon was also investigated as a surface passivation technique for scanning probe microscope (both conductive tip atomic force microscope and scanning tunneling microscope) lithography techniques.
Field emission and atom probe field ion microscope studies of palladium-silicide-coated silicon emitters
Authors: King R. A. , Mackenzie R. A. D. , Smith G. D. W. , Cade N. A.
Published: July 2002

Palladium-silicide-coated field emitters were prepared by palladium thermal evaporation onto silicon tips, followed by annealing at 675 K. Pulsed laser atom probe analysis showed a clean near stoichiometric, Pd2Si layer with a thin silicon-enriched surface. In spite of the higher work function of palladium silicide compared to silicon, enhanced emission was obtained from the silicide-coated tips. Field ion and field emission imaging of the tips showed that this enhanced emission was due to the roughness of the silicide layer. Pulsed laser atom probe analysis of a palladium silicide tip exposed to air for four days showed that the silicon-rich surface layer was converted to an oxidized layer 2–4 monolayers thick. The field emission characteristics of silicide tips exposed to air were similar to those observed previously in oxidized silicon tips. After an initial current burst which corresponded to the disruption of the oxide layer, intense emission was observed from sharp areas around the circumference of the tip.
Effect of tip shape on surface roughness measurements from atomic force microscopy images of thin films
Authors: Westra K. L. , Thomson D. J.
Published: July 2002

The distortion of images by the finite radius of the tip is a significant artifact in atomic force microscopy (AFM) imaging of thin films. This article examines the effect of the finite radius of the AFM tip on the measurement of five surface roughness parameters: Ra and Rrms roughness, horizontal roughness, bearing ratio, and power spectral density. The effect of the finite size of the AFM tip on the measurement of these roughness parameters was studied using simulations. We found that the vertical roughness measures (Ra and Rrms) were the least affected by the tip induced distortion. For a spherical tip, the error in Ra and Rrms roughness was less than 15% as long as the radius of the major features in the AFM image (RAFM) was greater than twice the radius of the tip (Rtip). The horizontal roughness of the surface was sensitive to the distortion due to the tip. For distorted AFM images (RAFM/Rtip=5) the bearing ratio curve was similar in shape to the curve for the original surface. The bearing ratio curve of the severely distorted profile (RAFM/Rtip=1.5) was significantly different from the curve for the original trial surface. The general shape of the power spectral density (PSD) curves for the original and both distorted profiles were similar. However, the lower frequency peaks in the PSD curves for the distorted profiles differed from those in the PSD curve for the original surface.
Pattern transfer of electron beam modified self-assembled monolayers for high-resolution lithography
Authors: Lercel M. J. , Rooks M. , Tiberio R. C. , Craighead H. G. , Sheen C. W. , Parikh A. N. , Allara D. L.
Published: July 2002

Self-assembled monolayers of octadecylsiloxane and octadecylthiol have been modified by high-resolution electron beam lithography. Focused electron beams from 1 to 50 keV and scanning tunneling microscopy at ∼10 eV have been used as patterning tools. The patterns have been transferred into many substrates by wet, dry, and combinations of wet and dry etches. Wet etching almost always results in a positive tone, but reactive ion etching of GaAs with Cl2 at very low dc biases (<10 V) results in a negative tone. The effect of electron beam damage on the monolayers and the subsequent etching reactions has been explored through x-ray photoelectron spectroscopy.
Photoacid bulkiness effect on dissolution kinetics in chemically amplified deep ultraviolet resists
Authors: Itani Toshiro , Yoshino Hiroshi , Fujimoto Masashi , Kasama Kunihiko
Published: July 2002

The photoacid bulkiness effect on dissolution characteristics was investigated in a three-component chemically amplified deep ultraviolet positive resist system. The resist consisted of a tert-butoxycarbonyl (t-BOC) protected polystyrene, benzenesulfonic acid derivative photoacid generator and an additional dissolution inhibitor (t-BOC protected bisphenol A). For the benzenesulfonic acid photoacid generator, four types of substituents; 4-fluoro, 4-chloro, 2,4-dimethyl, and 4-tert-butyl, were studied. Dissolution contrast (Rmax/Rmin) increased and the pattern profiles became rectangular with increasing substituent bulkiness. The reason for this is that bulky substituents such as 2,4-dimethyl and 4-tert-butyl increased resist hydrophobic strength in both bulk and surface regions, thereby strengthening the surface inhibition effect. Next, in order to investigate the bulkiness effect on acid mobility, diffusion length during postexposure bake time was determined by means of the ion conductivity method. Diffusion length decreased and resist profiles became rectangular with increasing photoacid bulkiness, and T-topping profile was observed in 4-tert-butyl substituent. It is believed that the acid catalytic reaction number decreases in the case of a shorter diffusion length. Therefore, the surface inhibition effect becomes strong, and then the T-topping profile was observed in 4-tert-butyl substituent.

In order to understand the details of surface inhibition effect, resist pattern profile simulation was carried out using PROLITH/2 version 3.0. Simulation results of pattern profiles coincided with the actual resist pattern by adjusting the parameters of the surface inhibition effect (relative surface rate and inhibition depth). It was found that the photoacid bulkiness effect on pattern profiles can be explained by the surface inhibition effect. Based on the analysis of the dissolution characteristics, acid diffusion behavior and profile simulation, it was concluded that the resist pattern profile, especially its top rectangularity, can be controlled by changing the substituent group of photogenerated benzenesulfonic acid. By combining the modification of the base resin structure (protection ratio and molecular weight) and acid structures, both high resolution capability and rectangular resist pattern profiles can be achieved.
Fabrication and analysis of a silicon tip avalanche cathode
Authors: Jo Sung Ho , Lee Jong Duk , Kwon Sang Jik
Published: July 2002

As an attempt to develop a cathode with low operation voltage for the vacuum microelectronic devices, a new cathode-silicon tip avalanche cathode (STAC) has been fabricated and analyzed. STAC is a silicon field emitter with a shallow n+-p+ junction formed on the tip. The emission characteristics of the fabricated STAC show that the gate voltage at which the emission initiates is considerably lowered and the gate voltage required to produce a desired emission current is reduced. These characteristics of STAC result from the emission of the hot electrons generated and accelerated by the avalanche breakdown in the n+-p+ junction on the tip. However, a large current is needed for the avalanche breakdown and this results in low emission efficiency. A simple analysis is presented to explain the measured emission characteristics of the fabricated STAC.
Optimization of quantum well structures for field emission applications
Authors: Litovchenko V. G. , Kryuchenko Yu. V. , Il’chenko L. G.
Published: July 2002

A theoretical analysis is made of the effect of field emission from films with a quantized electron spectrum. Dependences of emission current on film thickness demonstrate oscillatory behavior due to oscillations in screening constant. Certain critical thicknesses are found at which the jumplike changes in the value of field emission intensity occur. It is shown that a large positive effect (increase of the field emission efficiency) may be obtained for the case of nonplanar emitters covered by thin quantized films due to the superposition of two important factors (electric field strengthening near emitter tips and electron spectrum quantization in the film).
Spatially and rotationally oriented adsorption of molecular adsorbates on Ag(111) investigated using cryogenic scanning tunneling microscopy
Authors: Chen X. , Frank E. R. , Hamers R. J.
Published: July 2002

The molecular adsorption of thiophene and 2,5-dimethylthiophene on Ag(111) surfaces is studied using a cryogenic scanning tunneling microscope (STM) operating at 120 K. Thiophene molecules are observed to adsorb preferentially at step edges, occupying the upper step edge at lowest coverage, and additionally occupying the lower step edge at higher coverage. The adsorption site and rotational orientation of 2,5-dimethylthiophene were identified. Molecules at step edges are observed to cluster, indicating an attractive interaction between molecules at step edges. As the coverage increases, a phase transition corresponding to a transition from a planar to a tilted geometry is observed.
Monolayers of fluorinated silanes as electron-beam resists
Authors: St. John Pamela M. , Craighead H. G.
Published: July 2002

Self-assembled monolayers made from long chain hydrocarbon trichlorosilanes have been used previously as very thin self-developing resists, ideal for electron-beam lithography. We are currently studying the physical and chemical effects of additional functional groups at the monolayer terminus by varying the electron-beam dose and etching procedures for the fluorinated trichlorosilanes. These monolayers are attractive candidates for ultrathin electron-beam resists because they are typically inert towards concentrated alkalis and acids thereby making them resistant to chemical attack. These materials can be used as positive resists on oxide surfaces at various electron-beam energies and doses. A wet chemical etch is used to transfer exposed patterns to substrates.
Influence of a ZnTe buffer layer on the structural quality of CdTe epilayers grown on (100)GaAs by metalorganic vapor phase epitaxy
Authors: Leo G. , Longo M. , Lovergine N. , Mancini A. M. , Vasanelli L. , Drigo A. V. , Romanato F. , Peluso T. , Tapfer L.
Published: July 2002

The influence of a ZnTe buffer layer on the structural quality of CdTe epilayers grown on (100)GaAs substrates by metalorganic vapor phase epitaxy has been investigated by both x-ray diffraction and ion channeling Rutherford backscattering spectrometry measurements. Single-crystal (100) oriented CdTe epilayers of good structural quality have been obtained after inserting a ZnTe buffer layer of a thickness ranging between 300 and 500 nm. The influence of the buffer layer thickness on the crystalline quality and the morphology of the CdTe epilayer has been related to the defect distribution and the surface roughness of the ZnTe buffer layer. The crystalline quality and the surface strain have been thus studied as a function of the CdTe thickness on samples having optimal ZnTe layer thickness. The initial compressive mismatch between CdTe and ZnTe, f=−5.8%, appears to be almost fully relaxed for a CdTe thickness around 200 nm. A residual compressive in-plane strain (about −0.02%), independent of the CdTe epilayer thickness, has been found above 300 nm which can be ascribed to thermal strain and indicates a complete relaxation of the lattice misfit at the growth temperature.
Comparison of masking materials for high microwave power CH4/H2/Ar etching of III–V semiconductors
Authors: Lee J. W. , Crockett R. V. , Pearton S. J.
Published: July 2002

Patterned photoresist, SiO2, SiNX, and W were compared as masking materials for GaAs and other III–V semiconductors during CH4/H2/Ar plasma etching. The use of electron cyclotron resonance conditions is a much more severe test of the mask integrity in comparison to reactive ion etching. Ar flow rate, microwave power and rf power have significant effects on mask erosion (or polymer deposition on the mask), while process pressure is found to have little effect over the range 1.5–10 mTorr. SiNX retains high geometrical integrity and displays little erosion under electron cyclotron resonance conditions, while SiO2 is quickly coated with a polymer that can degrade critical dimensions. Morphological changes in both W and photoresist films during exposure to electron cyclotron resonance CH4/H2/Ar discharges indicate that these are less desirable choices than SiNX.
Latent image formation: Nanoscale topography and calorimetric measurements in chemically amplified resists
Authors: Ocola L. E. , Fryer D. , Nealey P. , dePablo J. , Cerrina F. , Kämmer S.
Published: July 2002

The characterization of photoresists during the image formation process has traditionally relied on bulk methods during or after development. This article shows that it is not necessary to develop the photoresist in order to obtain significant information about the image formation process in x-ray, electron beam, and UV lithography. The characterization of the image formation process in chemically amplified photoresists prior to development is difficult due to their sensitivity to electrons used in scanning electron microscopy and the weak changes in dielectric constant needed for optical microscopy. The advent and development of the atomic force microscope (AFM) have allowed local surface measurements of exposure induced changed in photoresists with sub-μm scale resolution and negligible modification of the sample. A series of chemically amplified resists, positive and negative, have been studied with a variety of exposure radiation (electron beam, x-ray, and UV). The results discussed in this article focus on two of these resists: SAL 605 (−), and TOK 010 (+). Both positive and negative chemically amplified resists exhibit significant changes in topography and calorimetric properties during the image formation process. Interpretation of the resist topography in negative resists is given by a semi-empirical model that assumes Fickian diffusion of resist material during post-exposure bake (PEB) and verified with AFM data. The glass transition temperature, Tg, of wafer spun thin films of SAL 605 has been measured, prior to exposure, to be 75±3°C with an ellipsometric technique. The PEB temperature, 105°C, is much greater than the Tg of SAL 605, thereby providing some justification for our Fickian diffusion model. These results are preliminary until a chemical map can be done on the resist at sub-μm resolution, which at present time is not possible. The need for detecting intrinsic material property changes due to the image formation process motivates the exploration of calorimetric properties of the resist. Interpretation of the calorimetric data is still unclear. Both cases of positive and negative photoresists exhibit an increase of heat absorbed in the exposed regions. Photoacid ions produced by exposure to radiation may be considered responsible for such an increase.
Analysis of distortion in interferometric lithography
Authors: Ferrera Juan , Schattenburg M. L. , Smith Henry I.
Published: July 2002

We present a mathematical model to describe the spatial phase of gratings produced by interferometric lithography, as well as a set of experiments to verify the model’s validity and to measure any distortions introduced when the lithography is performed. The implementation of two methods to measure the phase progression of these gratings is described. We find the results obtained from an initial set of experiments to be in good agreement with the theoretical model, i.e., the absence of significant distortions, such as coherent phase noise, is confirmed. These results are also applicable to the metrology of grids.
Influence of patterning in silicon quantum well structures on photoluminescence
Authors: Namatsu Hideo , Furuta Tomofumi , Nagase Masao , Kurihara Kenji , Iwadate Kazumi , Murase Katsumi , Makino Takahiro
Published: July 2002

This article reports on a study of the photoluminescence (PL) characteristics of SiO2/Si/SiO2 quantum well structures formed by the thermal oxidation of Si lines with rectangular cross sections and (111) side planes. The PL spectra have a peak at a wavelength of 760 nm regardless of Si width, indicating that the emission is due to the recombination of carriers at the Si/SiO2 interface. The Si width required to obtain the maximum emission is about 5 nm, which is thicker than theoretically predicted. The reason for this is clarified by measuring the difference in the PL characteristics for patterned and unpatterned SiO2/Si/SiO2 film structures. In the film structures, the characteristics are found to vary by the patterning of the ultrathin Si layer, followed by oxidation; the Si thickness yielding the maximum intensity increases and a wide range of Si thickness contributes to the emission. This behavior is consistent with that of the oxidized Si lines and is possibly due to pattern deformation caused by oxidation. The stress accompanying the deformation is probably the reason for the increase in the PL intensity in thicker Si. Therefore, the PL characteristics for Si are strongly influenced by the patterning and subsequent oxidation.
Electronic magnetic and structural coupling in colossal magnetoresistive (La,Ca)MnO3
Authors: Pickett Warren E. , Singh David J.
Published: July 2002

The local spin density approximation (LSDA) is used to investigate the interrelationships between electronic properties, magnetism, structure, and transport in La1−xCaxMnO3. The LSDA is shown to provide a realistic description of the endpoint compounds, including magnetic and structural symmetry. Mn–O hybridization is strong and spin dependent. Supercell calculations for x=1/4 and x=1/3 yield ferromagnetic configurations. Strong local La–Ca cation effects are found, which lead to localization of the low density of minority spin carriers in this regime. Implications of this effectively half-metallic electronic structure are discussed.
Measurement of interfacial shear (friction) with an ultrahigh vacuum atomic force microscope
Authors: Carpick R. W. , Agraït N. , Ogletree D. F. , Salmeron M.
Published: July 2002

We have studied the variation of frictional force with externally applied load for a Pt-coated atomic force microscope tip in contact with the surface of mica cleaved in ultrahigh vacuum. At low loads, the frictional force varies with load in almost exact proportion to the area of contact as predicted by the Johnson–Kendall–Roberts (JKR) theory [K. L. Johnson, K. Kendall, and A. D. Roberts, Proc. R. Soc. London Ser. A 324, 301 (1971)] of elastic adhesive contacts. The friction-load relation for a deliberately modified tip shape was proportional to an extended JKR model that predicts the area-load relation for nonparabolic tips. The tip shape was determined experimentally with a tip imaging technique and was consistent with the predicted friction behavior. This demonstrates that the frictional force is proportional to the area of contact between the tip and sample. Using the JKR/extended JKR model, interfacial surface energies and shear strengths can be estimated.
High-temperature stable Ir–Al/n-GaAs Schottky diodes: Effect of the barrier height controlling
Authors: Lalinský T. , Osvald J. , Machajdík D. , Mozolová Z̆. , S̆is̆olák J. , Constantinidis G. , Kobzev A. P.
Published: July 2002

We report on novel Ir–Al/n-GaAs Schottky contact systems based on sequentially evaporated Ir–Al multilayers which enable us to control the barrier height at the interface with annealing temperature. Auger depth profiling and Rutherford backscattering methods were applied to analyze the Ir–Al composition and the interfacial reaction stability. An increase of the barrier height with annealing temperature has been indicated for all the Schottky contact systems. Barrier heights as high as 0.95 V were measured for annealed Schottky diodes with the first aluminum or very thin iridium interfacial layer. A model of the barrier height enhancement based on a solid phase epitaxy of a graded AlxGa1−xAs layer at the interface at elevated annealing temperatures was considered to explain the electrical properties of the contacts. The model contributions to the formation of a metal/AlxGa1−xAs/GaAs heterojunction diodes with required barrier height and thermal stability are discussed.
Properties of TaNx films as diffusion barriers in the thermally stable Cu/Si contact systems
Authors: Takeyama Mayumi , Noya Atsushi , Sase Touko , Ohta Akira , Sasaki Katsutaka
Published: July 2002

The properties of Ta2N and TaN compound films as a diffusion barrier between Cu and Si have been investigated by examining compositional depth profiles obtained by Auger electron spectroscopy. The use of a Ta2N barrier is effective for improving the thermal stability of the contact system by raising the silicide formation temperature as compared with the use of a Ta barrier. The contact system of Cu/TaN/Si is fairly stable due to annealing for 1 h even at 750 °C. This is interpreted by the stability of the TaN compound, which is chemically inert to Si as well as Cu at this temperature. Eliminating the grain growth of TaN due to annealing is also effective for suppressing the physical diffusion through the barrier.
Spark-gap atomic emission microscopy. II. Improvements in resolution
Authors: Van Patten P. G. , Noll J. D. , Myrick M. L.
Published: July 2002

Experimental methods are described which enhance performance in spark-gap atomic emission microscopy (SGAEM) experiments. SGAEM is a recent innovation that permits elemental analysis of scanning tunneling microscopy substrates with high spatial resolution while maintaining tip–surface registry. Detectable sparks have been generated with bias pulses as small as 5 V, and intense atomic emission has been observed in such sparks. Small (∼1 nF), high-voltage capacitors and tungsten tips prepared by thermal etching (a new technique described) have been used in these experiments to yield a SGAEM spatial resolution better than 1 μm2, and an absolute detection limit for Cu of less than 25 fmol.
Numerical modeling of the disk-edge field emitter triode
Authors: Wang Chen , Wang Baoping , Zhao Hongwei , Sin Johnny K. O. , Poon M. C.
Published: July 2002

In this article, a new numerical algorithm, a finite-difference method in a nonorthogonal curvilinear coordinate system, is presented. This algorithm can be used for efficient simulation of a disk-edge field emitter. With the boundary-conforming coordinate lines, this method can deal with arbitrary microemitter shapes. Simulation results are presented for a unit cell, consisting of a disk-edge field emitter with “cocktail glass” structure. Dependence of the field enhancement factor, electron trajectories, and emission current upon geometrical factors are presented.
Diamond cold cathodes for electron guns
Authors: Givargizov E. I. , Zhirnov V. V. , Chubun N. N. , Voronin A. B.
Published: July 2002

Sharp silicon tips, coated with diamond, were tested concerning electron gun application. Emission stability, reproducibility of current–voltage characteristics, and beam confinement in the vacuum of 10−6 Torr were studied. No hysteresis or shift of emission characteristics during long term testing have been found. Low frequency current fluctuations were less than 10%. The electron source was tested over a 120 h period and the current decrease was within 10% of the initial value at the end of the test period. The divergence half-angle of emitted electrons was found to be within 3°.
Barrier height at clean Au/InAs(100) interfaces
Authors: Ohler C. , Daniels C. , Förster A. , Lüth H.
Published: July 2002

Using photoelectron spectroscopy, we have reexamined the barrier height at Au/InAs(100) contacts prepared under ultrahigh vacuum conditions. The n-barrier height is 0.010±0.050 eV: the Fermi level at the interface is right at the InAs conduction band edge. This result is expected from models based on charge transfer into metal-induced gap states but contrasts with previously published experimental values. Depending on the preparation procedure, the surface of InAs(100) grown using molecular-beam epitaxy shows c(4×4) or (2×4) reconstruction; the barrier height, however, is independent of the surface reconstruction prior to gold deposition.
Robotic nanomanipulation with a scanning probe microscope in a networked computing environment
Authors: Baur C. , Gazen B. C. , Koel B. , Ramachandran T. R. , Requicha A. A. G. , Zini L.
Published: July 2002

This article describes the initial phase of the development of a high-level programming system for robotic manipulation with a scanning probe microscope (SPM). A SPM server has been developed, which runs in the WINDOWS environment of the PC that controls the microscope. Client programs running on Unix work stations or other computers connected to the Internet can send remote commands to the SPM through the server. The clients can be sophisticated artificial intelligence programs that reason about robotic tasks and sensory data acquired by the SPM. A first set of intermediate-level commands has also been developed for sensing and manipulation. The system is being tested by pushing colloidal gold nanoparticles with dimensions in the order of 15–30 nm on a mica substrate in noncontact atomic force microscope mode. The test programs image the sample, search for nanoparticles in the presence of thermal drift, turn feedback on and off for pushing, and so on. The particles are being moved reliably.
Evidence of near-surface localization of excited electronic states in crystalline Si
Authors: Mantese L. , Bell K. A. , Rossow U. , Aspnes D. E.
Published: July 2002

Surface- and interface-related spectra, obtained either directly by techniques such as reflectance-difference (-anisotropy) spectroscopy or indirectly by subtracting pseudodielectric function spectra obtained ellipsometrically on surfaces with different chemical termination, exhibit features related to energy derivatives of the bulk dielectric function. We argue that these spectra provide direct evidence that the excitations involved are localized both in space and time. These data unequivocally indicate that critical point energies obtained from above-band-gap ellipsometric or reflectrometric optical spectra are not necessarily equal to bulk values, and that surface chemical and structural termination is at least one contributing factor. Present surface-optical calculations do not include these effects, which may explain, in part, remaining discrepancies between theory and experiment.
Writing and reading bit arrays for information storage using conductance change of a Langmuir–Blodgett film induced by scanning tunneling microscopy
Authors: Takimoto K. , Kuroda R. , Shido S. , Yasuda S. , Matsuda H. , Eguchi K. , Nakagiri T.
Published: July 2002

We demonstrate writing and reading bit arrays for information storage using an atomic force microscope with an electrically conducting probe and a medium consisting of a polyimide Langmuir–Blodgett film. In this system, data bits of 10 nm in diameter were written by application of voltage pulses with the conducting probe, and were read out by detecting the change in current. Topographical change was hardly observed at the data bits. A bit array of about 103 bits which contained information such as binary encoded characters was written and was successfully read out. The way to write and read the data bits with higher rate is discussed.
Fully large-scale integration-process-compatible Si field emitter technology with high controllability of emitter height and sharpness
Authors: Takemura Hisashi , Furutake Naoya , Nisimura Miyo , Tsuida Shunji , Yoshiki Masayuki , Okamoto Akihiko , Miyano Soichiro
Published: July 2002

We developed a fully large-scale integration (LSI)-process-compatible technology with excellent control of emitter shape for the first time. The fabricated emitter tip configuration has two-step-cone shape whose upper and lower cone configurations are controllable independently. While the upper parts determine the emitter tip sharpness and the apex angle, the lower parts determine the emitter height by utilizing two-step thermal oxidation for emitter tip sharpening in addition to anisotropic reactive ion etching for the emitter height control. The stable and uniform thermal oxidation for sharpening emitters produces excellent uniformity, and the process, without liftoff, is matched with Si LSI technology completely. The obtained 1944 tip emitter with 800 nm gate diameter showed low threshold voltage of 35 V.
Cell attachment on silicon nanostructures
Authors: Turner S. , Kam L. , Isaacson M. , Craighead H. G. , Shain W. , Turner J.
Published: July 2002

Advances in neural probe technology are currently hindered by a lack of understanding of the cues and mechanisms responsible for rejection and isolation of probes implanted in the central nervous system. To gain additional insight into this topic, the attachment of astrocytes on nanoscale textured silicon surfaces was investigated. Silicon surfaces were textured using a reactive ion etch process designed to produce nanometer-scale columnar structures in silicon (“silicon grass”). Standard photolithographic techniques were used to pattern the surface thereby allowing selective modification of the surface texture by a wet chemical etch for silicon. The resulting surface allowed a side-by-side presentation of different surface textures to cells grown in culture. The silicon surfaces were characterized by scanning electron microscopy (SEM) and scanning Auger electron microscopy. The cell attachment and morphology were observed with laser scanning confocal microscopy and SEM. Transformed astrocytes from a continuous cell line showed a preference for wet-etched regions over grassy regions. In contrast, primary cortical astrocytes from neonatal rats showed a preference for silicon grass over the wet-etched surface. For the transformed astrocytes cells, the degree of response was continuous with the degree of wet-etch modification.
Use of atomic force microscopy for analysis of high performance InGaAsP/InP semiconductor lasers with dry-etched facets
Authors: Whaley R. D. , Gopalan B. , Dagenais M. , Gomez R. D. , Johnson F. G. , Agarwala S. , King O. , Stone D. R.
Published: July 2002

We report on the use of an atomic force microscope (AFM) to directly measure the quality of InGaAsP/InP laser facets formed by a CH4:H2:Ar reactive ion etching process. From the AFM data, we obtain values for rms surface roughness and transverse angular tilt that have previously only been estimated through laser operating characteristics or inferred from scanning electron microscope analysis. The etched facet reflectivity, calculated from device slope efficiency data and far-field beam profiles, is in excellent agreement with AFM measurements. We show methane-based dry etching can achieve a rms facet roughness of 22 nm. This value surpasses the generally accepted roughness parameter of λ/10 and is competitive with the best chlorine-based facet etching to date. We also report a transverse angular facet tilt of 2°, which we believe to be the most vertical, CH4-based facet etch reported to date. The output performance of these devices is nearly identical to cleaved devices.