bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of porous silicon field emitter properties
Authors: Boswell E. C. , Huang M. , Smith G. D. W. , Wilshaw P. R.
Published: July 2002

The field emission properties and structure of silicon field emitter tips, covered with a porous silicon layer, have been studied. Emission produced with a variety of porous silicon morphologies, thickness, and different substrate types has been investigated and in each case improved characteristics are found compared to plain silicon emitters. Bright-and dark-field transmission electron microscope analysis has been carried out and for all p- and n-type porous emitters, a crystalline core is observed covered with a layer of amorphous porous silicon. This core has an improved aspect ratio over the original emitter shape. Single porous silicon tips have also been examined in a field-ion/field-emission microscope, allowing the emission image to be studied. It is concluded that field emission originates from sharp surface asperities present at the surface of porous silicon.
Combined calculation of lens aberrations, space charge aberrations, and statistical Coulomb effects in charged particle optical columns
Authors: Jiang X. R. , Barth J. E. , Kruit P.
Published: July 2002

Optimizing a charged particle optical system utilizing a high brightness source requires the inclusion of the effect of Coulomb interactions in the evaluations. A new computer program package, named ANALIC, has been developed to perform the combined calculation of lens aberrations, space charge aberrations, and statistical Coulomb effects in a complete instrument. By making use of an analytical slice method, valid for weak/incomplete collisions, to calculate the Coulomb interactions, the program combines reasonable accuracy with high speed. Using ANALIC, an optical system with an arbitrary number of lenses and apertures, an arbitrary mode of imaging, and an arbitrary distribution of the beam energy can be analyzed directly. The functions, features, organization, and calculation approach of the program are reported. As an example of the use of the program, a four lens electron probe instrument is analyzed for the demonstration of the combined calculation and optimization process of a particle optical system.
Fabrication of gold nanostructures on a vicinal Si(111) 7×7 surface using ultrahigh vacuum scanning tunneling microscope and a gold-coated tungsten tip
Authors: Fujita Daisuke , Jiang Qidu , Nejoh Hitoshi
Published: July 2002

We have demonstrated that nanometer-scale gold dots can be deposited on a vicinal Si(111) 7×7 surface using the field-assisted atom transfer from the gold-coated tungsten tip of a scanning tunneling microscope operating in ultrahigh vacuum. With the application of negative voltage pulses to the tip, gold nano-mounds with the size ranging from ∼3 to ∼20 nm across at the base and 0.6–1 nm high can be created on the surface. The deposition is found to be more favored on the step edges than the (111) terraces. Since atomically resolved images of the Si(111) 7×7 structure can be observed even after many cycles of atom transfer using the gold-coated tip, the shape of the tip apex has been kept very stable. The overall findings clearly suggest that the atom-transfer technique proposed here is proven to be a good candidate for fabricating nanometer-scale devices.
Effects of etch products and surface oxidation on profile evolution during electron cyclotron resonance plasma etching of poly-Si
Authors: Tuda Mutumi , Ono Kouichi , Nishikawa Kazuyasu
Published: July 2002

Evolution of etched profiles has been numerically investigated during electron cyclotron resonance (ECR) Cl2/O2 plasma etching of polycrystalline Si. The calculations included the processes of chemically enhanced ion etching and passivation layer formation, which are important in such low-pressure, high-density plasma etching environments. The sidewall passivation was modeled by taking account of the redeposition of etch products on sidewalls of etched features. In addition, the effect of surface oxidation was also included in the model. Etched profiles were then simulated to examine effects of the neutral-to-ion flux ratio onto the substrate, sticking coefficient of etch products, and additional incident fluxes of etch products and oxygen atoms. Numerical results indicated that in typical ECR plasma etching environments, where the gas pressure is P0≲1 mTorr and the ion current density is Ji∼10 mA/cm2 onto the substrate, the chlorinated surface coverage α is microscopically nonuniform on sidewalls and bottom surfaces of etched features: α≲0.3 at the bottom and α≊1 on the sidewalls. This microscopic nonuniformity in coverage was found to lead to inversely tapered etched profiles without any sidewall passivation. These profiles changed to vertical and further tapered, when simultaneous redeposition of etch products were taken into account with their sticking coefficients Sp≳0.1. Furthermore, it was shown that in the presence of oxidation, the sidewall surfaces are easily oxidized, and the lateral etching is effectively reduced during overetch.
First-principles study of Si 2p core-level shifts at water and hydrogen covered Si(001)2×1 surfaces
Authors: Pasquarello Alfredo , Hybertsen Mark S. , Car Roberto
Published: July 2002

Using a first-principles approach, we study Si 2p core-level shifts at water and hydrogen covered Si(001)2×1 surfaces. After allowing for full relaxation of the surface structures, core-level shifts are calculated including core-hole relaxation effects. We find that dissociated water on the Si(001)2×1 surface induces a core-level shift of 1.1 eV to higher binding energies, in good agreement with experiment. In the case of the hydrogen terminated Si(001)2×1 surface, calculated surface shifts are small (about 0.2 eV) and comparable to shifts of subsurface Si atoms.
Interfacet mass transport and facet evolution in selective epitaxial growth of Si by gas source molecular beam epitaxy
Authors: Xiang Qi , Li Shaozhong , Wang Dawen , Wang Kang L. , Couillard J. Greg , Craighead Harold G.
Published: July 2002

Facet formation and competition in selective epitaxial growth (SEG) of Si on SiO2− masked nanometer growth windows were studied experimentally and theoretically in gas source molecular beam epitaxy. The windows were patterned along [110] on Si(100) substrates. Mass accumulation around the edge of the SEG mesa top surface was observed and believed to be due to the interfacet mass transport from sidewalls to the top surface. Sidewall facet evolution from the initial (311) to (111) was observed. The facet evolution is due to the growth rate anisotropy among (100), (311), and (111). The interfacet mass transport is believed to affect growth rate of each facet and increase the growth rate anisotropy. As a result, it controls the size dependence of SEG growth rate and promotes the facet evolution. A theoretical model has also been developed for modeling the facet competition and evolution. Both the interfacet and intrafacet surface migration processes were taken into account in the model. The simulation results explain our experimental observations and provide an improved understanding of the facet growth on patterned substrates.
In situ and ex situ spectroscopic investigation of low temperature grown gallium arsenide by molecular beam epitaxy
Authors: Eyink Kurt G. , Capano M. A. , Walck S. D. , Haas T. W. , Streetman Ben G.
Published: July 2002

Low temperature growth of GaAs not only provides useful semi-insulating layers in a variety of devices, but also is interesting from a materials and crystal growth point of view. In this work we have utilized an in situ spectroscopic ellipsometer having 44 wavelength regions in the range 4000–8000 Å to monitor the low temperature growth of GaAs. Several different regions of growth have been observed, in agreement with earlier studies utilizing single wavelength ellipsometry. An initial region of homogeneous growth is followed by regions of material that exhibit varying optical properties. The complex refractive index of the epitaxial LT-GaAs films have been extracted from the real-time data acquired during the homogenous growth region. Ex situ characterization of these films was performed using high-resolution x-ray diffraction to determine the excess As concentration. Films in which the low temperature growth was stopped within the homogeneous growth regime have been characterized with a multiwavelength variable angle ellipsometer, and the complex refractive index of these films in the range 4000–17 000 Å have been extracted.
Calculation of electronic properties of defects in diamond: Application to electron emission
Authors: Miskovsky N. M. , Cutler P. H. , Huang Z.-H.
Published: July 2002

Electron field emission from diamond or diamond coated surfaces has been known experimentally to yield large currents at low fields. It has been speculated by the authors [Z.-H. Huang, P. H. Cutler, N. M. Miskovsky, and T. E. Sullivan, Appl. Phys. Lett. 65, 2562 (1994); J. Vac. Sci. Technol. B 13, 526 (1995)] that electron transport through band-gap states can be responsible for sustaining such currents. These states may be generated by point and/or extended defects such as vacancies and grain boundaries in chemical-vapor-deposition diamond films. Electronic and atomic properties of these defects are calculated using a tight binding approach. The model consists of a single vacancy or H substitution in a repeated extended cell consisting of 27 carbon atoms. The presence of vacancies or H substitution produces states that are spatially localized and whose energies lie in the gap. These states span an energy spectrum of about 1–2 eV just above the top of the valence band. The calculations for a concentration of about 1019 cm−3 suggest that these defect states are too low in energy to couple to those states which can produce the tunneling current in field emission. Additional work is needed to clarify the transport mechanism and how it depends on vacancy concentration including the possibility of vacancy–vacancy interaction which can lead to broadening of the discrete states into bands.
Spatial mapping of ordered and disordered domains of GaInP by near-field scanning optical microscopy and scanning capacitance microscopy
Authors: Leong J-K. , McMurray J. , Williams C. C. , Stringfellow G. B.
Published: July 2002

Imaging of topography, locally induced photoluminescence and Fermi-level pinning in adjacent ordered and disordered domains on a cleaved GaInP sample is performed using a near-field scanning optical microscope and scanning capacitance microscope at room temperature in air. Highly localized photoluminescence spectra obtained by the near-field scanning optical microscope on these domains show spectral peaks at 680 nm (ordered) and 648 nm (disordered) GaInP. The near-field scanning optical microscope and scanning capacitance microscope data confirm previously published data, indicating that the electronic surface structure of ordered GaInP is significantly different from that of disordered GaInP. Both approaches indicate that the Fermi-level at the surface of ordered GaInP is pinned, while the Fermi-level at the surface of disordered GaInP is not pinned. The size, structure, and position of the ordered and disordered domains observed by the near-field scanning optical microscope and scanning capacitance microscope agree with those obtained by cathodoluminescence and Kelvin probe force microscopy.
Dewetting dynamics and nucleation of polymers observed by elastic and friction force microscopy
Authors: Overney R. M. , Leta D. P. , Fetters L. J. , Liu Y. , Rafailovich M. H. , Sokolov J.
Published: July 2002

Dewetting dynamics of immiscible liquid polymer bilayers were studied by atomic force microscopy. Morphological changes of the phase-separated liquids were correlated with friction and local elastic properties, and the dewetting pattern classified in terms of the relative bulk viscosities. Topographical atomic force microscopy measurements revealed that the dewetting process did not occur on the liquid–liquid interface as expected. Rather the process is three-dimensional with an apparent shear plane ‘‘deep’’ inside the low viscosity liquid film. The depth of the shear plane is immediately established in the nucleation process which was studied two and three dimensionally by friction force microscopy and compliance measurements. Since this mechanism has not been observed previously in simple liquids, the role of entanglements of these polymers is discussed together with the application of the atomic force microscopy as a three-dimensional material property specific tool capable of studying processes below the surface.
Scanning force and friction microscopy at highly oriented polycrystalline graphite and CuP2(100) surfaces in ultrahigh vacuum
Authors: Müller T. , Kässer T. , Labardi M. , Lux-Steiner M. , Marti O. , Mlynek J. , Krausch G.
Published: July 2002

We present a novel scanning force and friction microscope for applications in ultrahigh vacuum (UHV) using the optical beam deflection method for detection. All optical components are positioned on the air side enabling a simple way of adjustment, the possibility of good decoupling of topography and lateral signal, and the absolute estimation of lateral force values. We demonstrate lateral atomic resolution on mica surfaces freshly cleaved in UHV. As model systems, we investigate the complex CuP2(100) surface on the unit cell level which exhibits a wide range of atomic stick-slip phenomena. In addition, first results on the friction behavior at step edges on highly oriented polycrystalline graphite surfaces are presented.
Electron-stimulated desorption of hydrogen from the Si(111) surface by scanning tunneling microscopy
Authors: Schwartzkopff M. , Radojkovic P. , Enachescu M. , Hartmann E. , Koch F.
Published: July 2002

Preparation of suitable silicon (111) wafers in weakly alkaline HF solutions results in the formation of atomically flat, hydrogen-terminated surfaces. Under high-vacuum conditions, the scanning tunneling microscope has been employed to selectively desorb the passivating hydrogen from nanometer-sized surface regions. The hydrogen depassivation process is studied as a function of current and applied bias voltage, voltage polarity, and exposure time to incident electrons either on individual surface locations or by varying the speed of tip motion to control the electron dose. The experimental findings are interpreted in terms of two distinct desorption mechanisms and the respective desorption yields are specified.
Imaging conducting surfaces and dielectric films by a scanning capacitance microscope
Authors: Lányi Š. , Török J. , Řehůřek P.
Published: July 2002

Scanning capacitance microscopes can be used to imaging the topography of conducting surfaces, both free and covered by an insulating film, and also the local properties of the films. Such local properties may be the variations of the dielectric constant and/or the dielectric losses, caused by the presence of certain defects. It is usually assumed that the resolution is tip radius limited. However, below an optimum radius of a few tens of nanometers, approximately twice the tip/surface distance, the resolution does not improve, only the signal-to-noise ratio is reduced. In the case of thick dielectric films limiting becomes the thickness. In spite of that appreciable local resolution may be achieved in the surface layer of the film on the side of the probe, although at reduced contrast. While close to the probe axis the contribution of the surface layer is dominating, at larger distances sensitivity reversal may occur.
Scanning tunneling microscopy study of SiC(0001) surface reconstructions
Authors: Owman Fredrik , Mårtensson Per
Published: July 2002

Scanning tunneling microscopy has been used to study the reconstructions of Si-terminated SiC(0001) surfaces observed after heat treatment at increasing temperatures. For the √3×√3 reconstruction, obtained by heating at temperatures around 950 °C, the images can be explained by a model composed of 1/3 monolayer of Si or C adatoms in threefold symmetric sites on top of the outermost Si–C bilayer. For surfaces heated above 1050 °C the images show growing fractions of quasiperiodic 6×6 and 5×5 reconstructions. Heating above 1250 °C results in a partial graphitization of the surface which modifies the observed 6×6 structure.
Noncontact scanning force microscopy using a direct-oscillating piezoelectric microcantilever
Authors: Itoh T. , Ohashi T. , Suga T.
Published: July 2002

This article describes noncontact scanning force microscopes that make use of a new type of direct-oscillating unimorph piezoelectric microcantilever. Since the scanning force microscope system using the piezoelectric cantilever requires no external deflection detector, it is very simple, compact, and is easy to operate in comparison with the conventional system using the optical sensors. In the noncontact operation mode, the piezoelectric cantilever is more preferred to other deflection detectable cantilevers, because it can be directly oscillated by applying voltage to itself. The methods used to detect the resonance shift due to force gradients acting the tip are slope detection and frequency modulation detection. In the slope detection technique, the resonance shift is detected by measuring the change of the amplitude or phase of the induced piezoelectric current. In frequency modulation detection, the resonance shift is detected by direct measurement of the resonance frequency of the current. The piezoelectric microcantilever serves as a resonator in this technique. The constructed noncontact scanning force microscope has been used to obtain the slope detection image of the Au film surface with grains of about 50 nm diam. The measured characteristics data of the fabricated cantilevers allow us to study the dependence of minimum detectable force gradients on the lever dimensions. We have discussed the design of the cantilever for noncontact operations.
Surface structures of thermoplastic and thermoset films after modification by graft copolymerization: Comparative study by x-ray photoelectron spectroscopy and atomic force microscopy
Authors: Loh F. C. , Tan K. L. , Kang E. T. , Li S. F. Y.
Published: July 2002

Thermal and near ultraviolet-light induced graft copolymerization of pristine, argon-plasma, oxygen-plasma, and ozone-pretreated thermoplastic [high-density polyethylene, poly(tetrafluoro- ethylene), and poly(ethylene terephthalate)], partial thermoset (polyimide), and thermoset (cross-linked polyaniline) films with hydrophilic monomers, such as acrylamide, acrylic acid, and sodium salt of styrene sulfonic acid, were carried out. The microstructures and compositions of the modified surfaces were studied by angle-resolved x-ray photoelectron spectroscopy and atomic force microscopy. In most cases, the density of surface grafting is enhanced by the pretreatment processes. In the case of thermoplastic films, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer which is richer in substrate chains to form a stratified surface structure. In the case of partial thermoset films, the grafted chains form either a surface layer uniformly intermixed with the substrate, or a graft-rich surface layer in a migration that is sterically hindered due to the presence of the grafted chains. In the case of thermoset films, the hydrophilic graft remains predominantly at the outermost surface of the substrate. The surface microstructures are further supported by dynamic water contact angle measurements. The differences in the surface structure and morphology of the pristine, pretreated, and graft copolymerized surfaces are also revealed by atomic force microscopy images.
Potentials and challenges for lithography beyond 193 nm optics
Authors: Canning John
Published: July 2002

The growth of the semiconductor industry continues to be driven to a large extent by steady advances in microlithography. Renewal of the Semiconductor Industry Association Roadmap is underway and accelerating requirements are predicted. The 130 nm generation is anticipated to be available in the year 2003, but the path to get there is not obvious. To meet the needs of its members, SEMATECH is embarking on a program to explore and narrow the technology options on the roadmap. The goal is to make a data-driven decision by late 1997. As an introduction to this Special Session on 0.13 Micron Lithography for Manufacturing, this article reviews the Lithography Technology Working Group requirements and potential solutions for roadmaps. The SEMATECH program to narrow the options beyond 193 nm optics is presented in detail, including the critical issues for each technology.
Diffusional attractions between voids on a Si(111)7×7 surface
Authors: Ter Ovanesyan E. , Manassen Y. , Ramesh Rao N. , Olami Z.
Published: July 2002

Ostwald ripening or coarsening is a term which describes the growth of large domains at the expanse of small ones in the final stages of any phase separation process. Several theories were developed in order to explain this process. All of them are based on the Lifshitz, Slyozov, and Wagner (LSW) model which predicts an increase in the average radius of domains r̄(t)∝t1/3 and a reduction of the number density of domains as a function of time N(t)∝t−1. The LSW model assumes static and circular domains, which are distributed at random. These assumptions were found to be incorrect by many experiments. And more advanced theories were necessary to explain these observations. In our work, we study the coarsening of voids formed in a Si(111)7×7 surface covered by 0.8 bilayers (BL). Besides the expected increase in the diameter of voids and the decrease in the number density, very strong attractions and rapid motion of voids towards each other were clearly observed. The result of the attraction between the voids is coagulation of voids and an increase in the spatial correlations between voids, as the coarsening process progresses, as we indeed observed. This is contradictory to the “ideal gas” picture which is the basis of the LSW model. Basically, this can be explained by a concentration gradient which develops between two voids of different size and the growth of voids in the direction of the larger concentration. However, this model cannot explain the large diffusional motions observed in our experiments. It is proposed that an amplification mechanism exists, whereby the arrival of a diffusing vacancy to the boundary of the void causes the release of several adatoms from the boundary. This process causes a much larger motion than expected by a single vacancy absorption. This picture, which is consistent with the structure of the steps, demonstrates how the microscopic details might have a significant affect on the global coarsening process.
Low-energy focused-ion-beam exposure characteristics of an amorphous Se75Ge25 resist
Authors: Lee Hyun-Yong , Chung Hong-Bay
Published: July 2002

Ion-beam exposure and patterning characteristics of an amorphous Se75Ge25 thin film which acts as a positive resist in focused-ion-beam (FIB) lithography have been studied using low-energy Ga+ ion sources below 30 keV. The a-Se75Ge25 resist exposed to 10 keV defocused-Ga+ ion beam with the dose of 5.0×1014 to 9.3×1015 ions/cm2 results in increasing the optical absorption, which was also observed in the film exposed to an optical dose of 4.5×1020 photons/cm2. The absorption edge shift of 0.3 eV for the resist exposed to a dose of 9.3×1015 ions/cm2 at 10 keV is about twice that of photo exposure. These large shifts could be estimated as due to an increase in disorder, considering a decrease in the slope of the Urbach tail and a broad pattern of x-ray diffraction. For the exposure of a 30 keV Ga+ ion beam and above a dose of 1.4×1015 ions/cm2, a 590-Å-thick resist film is completely etched by dipping for 10 s in 1:1:3 HNO3:HCl:H2O solution (25 °C), and then the etching rate is about 60 Å/s. As the incident energy increases from 10 to 30 keV, the threshold dose decreases from 4.0×1015 to 1.4×1015 ions/cm2 and then the imaging contrasts appear to be about 0.5 and 2.5, respectively. The decrease of the threshold dose with increasing the exposure energy is evidence that a predominant factor in the FIB exposure characteristics is the energy transfer rather than the implanted ions themselves. When 30 keV Ga+ FIB exposure with a multiscan diameter of 0.2 μm and the above-mentioned development are employed, a resist pattern with a linewidth of about 0.225 μm is obtained.
Structural and optical characterizations of single three-dimensionally confined GaAs/AlAs structures grown on patterned GaAs (001) substrates
Authors: Kasai Jun-ichi , Tanaka Sigehisa , Higuchi Katsuhiko , Katayama Yoshifumi
Published: July 2002

We report structural and optical characteristics of single three-dimensionally (3D) confined GaAs/AlAs structures grown by molecular beam epitaxy on 〈100〉 oriented square mesas patterned onto GaAs (001) substrates. By fabricating single structures and using AlAs barrier layers, we were able to clearly attribute luminescent spectral peaks to spatial origins in the grown structures. Observation with a scanning electron microscope and an atomic force microscope indicated that the structures on the mesas were pinched-off or truncated pyramids limited by sidewall {011} facets and a mesa-top facet. The observation also led to estimation of lateral width in the 3D confined structures, which decreased in proportion to a decrease in pattern width ranging from 1.6 to 0.2 μm. This proportionality can be explained by adatom migration on the sidewalls towards the bottom region of the patterned substrates. The optical properties of the grown structures were investigated by microphotoluminescence measurements at 8 K. Photoluminescence (PL) images were first measured to attribute luminescent spectral peaks to quantum-well (QW) heterostructures spatially originating in a truncated pyramidal structure. We next performed spectroscopy on single 3D confined structures of various lateral widths by positioning and holding the mesa top of one isolated pyramidal structure at a time under laser illumination. The PL and PL excitation spectra exhibited distinct exciton peaks about 10 meV wide. As the lateral width decreased, the vertical layer thickness estimated by their emission wavelength increased, but it saturated at smaller lateral widths. The saturation can also be explained by the adatom migration on the sidewalls. When excitation power was lowered, PL spectra became a cluster of sharp peaks. Each sharp peak may be due to the recombination of the exciton trapped in QW layer thickness fluctuation. The cluster thus suggests that the broad spectral width is caused mainly by wide variation in QW layer thickness of 3D confined structures.
Surface roughness of nitrided (0001) Al2O3 and AlN epilayers grown on (0001) Al2O3 by reactive molecular beam epitaxy
Authors: Kim Wook , Yeadon M. , Botchkarev A. E. , Mohammad S. N. , Gibson J. M. , Morkoç H.
Published: July 2002

Nitridation of c-plane sapphire followed by deposition of a low temperature AlN or GaN buffer is commonly employed in the growth of GaN-based structures which have received a great deal of attention recently. In order to gain some needed insight, we undertook an investigation of nitridation of sapphire followed by the subsequent growth of AlN buffer layers in a reactive molecular beam epitaxy environment. Atomic force microscopy was used to characterize the surface roughness of samples after exposure to various nitridation conditions. Nitridation at higher temperatures was found to yield smoother substrate surfaces possibly due to smoothing of scratches introduced during substrate preparation. Incorporation of nitrogen into sapphire surfaces during the nitridation process was verified using x-ray photoelectron spectroscopy by observing the development of the N 1s peak with nitridation time. The surface roughness of AlN layers deposited on these nitrided surfaces was found to increase dramatically with thickness due to a significant coarsening of the surface topography. Surface roughness was found to decrease with increasing growth rate, the smoothest films being obtained with a growth rate of 140–200 nm/h at a substrate temperature of 800 °C.
Evaluation of alignment accuracy in processed wafers and SiC masks on a scattered-light alignment system for x-ray aligners
Authors: Miyatake Tsutomu , Hirose Masaoki , Shoki Tsutomu , Ohkubo Ryo , Yamazaki Kuniaki
Published: July 2002

The alignment performances of the video-based scattered-light alignment (SLA) system for 0.1 μm lithography are described in this article. The SLA system has high sensitivity to the silicon carbide (SiC) mask without an antireflection coating (ARC). This article especially focuses on the alignment accuracy in processed wafers and the dependency of the alignment accuracy on the SiC membrane thickness. A series of alignment tests was done on a lab-based vertical wafer stage using the SiC masks. In order to evaluate the alignment accuracy in processed wafers, we prepared four processed wafer types: nitride, oxide, poly-Si, and aluminum. The high position sensing repeatability in the range of 4.8–6.4 nm (3σ) was obtained using the combination of the four processed wafers and a 2-μm-thick SiC membrane without the ARC. We also obtained the alignment accuracy using the wafer alignment marks only, resulting in an alignment accuracy of 10.0, 8.8, 9.1, and 35.7 nm (3σ) for the nitride, oxide, poly-si, and aluminum wafers, respectively. In addition, the dependency of the alignment accuracy on the SiC membrane thickness was obtained using the membranes with thicknesses of 2, 3, 4, and 5 μm. An improvement of the alignment accuracy in the aluminum is discussed.
Latent image characterization of postexposure bake process in chemically amplified resists
Authors: Ocola L. E. , Cerrina F. , May Tim
Published: July 2002

The demand of smaller device dimensions drives the need to improve the lithographic and the metrology tools to produce them. Characterization of the image formation during the lithography process is key to any process control effort. Scanning probe microscopy (SPM) on exposed, unbaked and baked, undeveloped photoresist shows morphological details of the image formation process unachievable with other techniques. The use of micro-Fourier transform infrared (μ-FTIR) spectroscopy will be investigated for latent image chemical analysis. Both of these techniques will be used in the study of the dependence of the latent image of a negative novolac-based chemically amplified resist, SAL 605 (Shipley), with postexposure bake (PEB) conditions. The objective of the experiment is to understand how the thermal properties of the resist and the linking reaction taking place are related to each other during PEB. Experimental results indicate that resist from unexposed regions diffuse into the exposed resist during PEB. SPM results show that this diffusion increases as the PEB temperature rises above the glass transition temperature of the unexposed resist. μ-FTIR results show that the linker component of the resist, hexamethoxymethylmelamine, has been identified as one of the resist components that diffuses into the exposed regions during PEB.
C
60
-incorporated nanocomposite resist system for practical nanometer pattern fabrication
Authors: Ishii T. , Nozawa H. , Tamamura T. , Ozawa A.
Published: July 2002

We propose a nanocomposite resist system that incorporates sub-nm size fullerene C60 molecules into a highly sensitive and moderately dry-etching resistant electron-beam positive resist, ZEP520. C60 incorporation leads to carbon reinforcement in the original resist material and enhances resist performance for nanometer pattern fabrication. 10 wt % C60 incorporated ZEP520 shows enhancements of etching resistance (∼15%), thermal resistance (∼30 °C), and mechanical resistance (3.5–5.5 in the aspect ratio). By applying this new resist system to x-ray mask fabrication, an ultrafine mask with the minimum dimension of 45 nm has been successfully fabricated.
Dry etching and consequent burring regrowth of nanosize quantum wells stripes using an in situ ultrahigh vacuum multichamber system
Authors: Yoshikawa T. , Sugimoto Y. , Kohmoto S. , Kitamura S. , Makita K. , Nambu Y. , Asakawa K.
Published: July 2002

Dry etching and consequent burring regrowth using an in situ ultrahigh vacuum multichamber system were investigated for nanometer-size fine patterns. Narrow stripe patterns with width variations from 30 to 5000 nm were fabricated on GaAs/AlGaAs single quantum wells using electron-beam lithography. The wafer was then etched and regrown in an in situ multichamber system. Using this in situ process along with a H-plasma treatment before regrowth, the surface nonradiative recombination velocity was able to be greatly reduced to 6.8×104 cm−1 from that of as-etched wafers (1.9×105 cm−1) estimated by measuring time-resolved photoluminescence (PL). Also, the size dependence of the PL intensity was able to be greatly improved to a degree that exceeded the InGaAs/InP wafers.
Nonstraight discharge path guided by a laser beam
Authors: Hoshi Yoshinobu , Yoshida Hiro
Published: July 2002

An electric discharge inducing method along curved discharge paths in a vacuum using a laser beam has been found. The discharge path in the present method is considered to be controlled by the passage of thermoelectrons along the electric field. Therefore, the path can trace not only a straight line but also curved lines. The thermoelectrons are emitted from a metal plasma, which is generated by a laser beam irradiation onto a metal surface (an electrode). Based on the present inducing principle, the discharge can be induced from an anode even to the back surface of the cathode through a hole in the cathode.
In-plane anisotropy of ZnTe nanoparticle-doped glass thin films fabricated by simultaneous oblique deposition from two opposing directions
Authors: Takeda Yasuhiko , Motohiro Tomoyoshi , Hioki Tatsumi , Noda Shoji
Published: July 2002

ZnTe nanoparticle-doped glass thin films which have quite unique anisotropies in microscopic structures and in optical properties in the thin film plane were fabricated by introducing ZnTe into nanometer-scaled voids included in well-known columnar structures of obliquely deposited SiO2 films. ZnTe and SiO2 were simultaneously deposited on substrates from two opposing oblique directions and then the samples were annealed. The samples consisted of two kinds of portions with planar shape; the portions of amorphous ZnTe (as-deposited samples) or condensing ZnTe nanocrystallites (postannealed samples) were stacked alternatively with SiO2 portions in the thin film plane in the direction parallel to the plane including the two deposition directions. In-plane anisotropies in the refractive indices, the absorption coefficients, and the third-order nonlinear optical susceptibilities were evaluated. The anisotropies in the optical properties were revealed to be due to the fact that the distribution of the electric field of the incident light in the composite (inhomogeneous) samples depends on the polarization because of the structural anisotropy.
Electronic properties of Si/Si1−x−yGexCy heterojunctions
Authors: Stein B. L. , Yu E. T. , Croke E. T. , Hunter A. T. , Laursen T. , Mayer J. W. , Ahn C. C.
Published: July 2002

We have used admittance spectroscopy and deep-level transient spectroscopy to characterize electronic properties of Si/Si1−x−yGexCy heterostructures. Band offsets measured by admittance spectroscopy for compressively strained Si/Si1−x−yGexCy heterojunctions indicate that incorporation of C into Si1−x−yGexCy lowers both the valence- and conduction-band edges compared to those in Si1−xGex by an average of 107±6 meV/% C and 75±6 meV/% C, respectively. Combining these measurements indicates that the band alignment is type I for the compositions we have studied, and that these results are consistent with previously reported results on the energy band gap of Si1−x−yGexCy and with measurements of conduction band offsets in Si/Si1−yCy heterojunctions. Several electron traps were observed using deep-level transient spectroscopy on two n-type heterostructures. Despite the presence of a significant amount of nonsubstitutional C (0.29–1.6 at. %), none of the peaks appear attributable to previously reported interstitial C levels. Possible sources for these levels are discussed.
Fabrication of thin-film cold cathodes by a modified chemical vapor deposition diamond process
Authors: Weiss B. L. , Badzian A. , Pilione L. , Badzian T. , Drawl W.
Published: July 2002

Thin-film cold cathodes have been grown on molybdenum by a modified microwave assisted plasma chemical vapor deposition diamond process. Electron field-emission tests have been performed on the devices. The modification from the chemical vapor deposition diamond process includes the addition of N2 and O2 into the plasma during the growth stage. Characterization of these films indicates a disordered tetrahedral carbon structure. Raman spectroscopy shows a disturbance in the cubic symmetry of the lattice and x-ray diffraction indicates a disordered tetrahedral structure. Electron emission testing indicate low turn-on voltages. Current densities from 1 to 8 mA/cm2 can be obtained for applied fields of 5–8 V/μm. The results are explained in terms of a change in the electronic band structure and the formation of states in the band gap.
Theory of FeSi2 direct gap semiconductor on Si(100)
Authors: Miglio Leo , Meregalli Valeria
Published: July 2002

In this article we show by theory predictions how the gap nature of β-FeSi2 could be suitably tailored in heteroepitaxial growth on Si(100) substrates where a Si–Ge buffer layer is used to set the lattice parameter and, in turn, the amount of strain in the FeSi2 film.
Microstructure and composition of InAsN alloys grown by plasma-source molecular beam epitaxy
Authors: Beresford R. , Stevens K. S. , Schwartzman A. F.
Published: July 2002

A series of growths conducted at different substrate temperatures and V:III ratios is analyzed by x-ray diffraction to determine composition. A metastable InAsN alloy plus pure InAs are obtained for temperatures in the range 450–500 °C and total V:III ratio of approximately unity. The InAs fraction in the alloy phase increases at lower temperatures, the maximum observed is 13%. For higher temperatures or higher V:III ratio only separated phases of InAs and InN are found.
Novel global planarization technology for interlayer dielectrics using spin on glass film transfer and hot pressing
Authors: Machida K. , Kyuragi H. , Akiya H. , Imai K. , Tounai A. , Nakashima A.
Published: July 2002

Global planarization technology based on a new concept comprised of spin on glass (SOG) film transfer and hot pressing is proposed for interlayer dielectrics. The technology basically involves coating a SOG film onto a sheet film in advance and then transferring it from the sheet film to a Si substrate by pressing and heating it in a vacuum. Planarization and filling of the interlayer dielectrics can be carried out by this process. For this technology, perhydrosilazane, which has a high viscosity for a thick formation during coating and a low viscosity for the flow during heating, is used as the SOG material. Experimental results show that the SOG thickness is reduced by the pressing and heating process and that its uniformity can be improved by the press force. By applying this technology to Al interconnection, it is found that planarization and filling can be completely realized. Therefore, this technology is very promising for simple and inexpensive global planarization.
SiGeC: Band gaps, band offsets, optical properties, and potential applications
Authors: Brunner K. , Schmidt O. G. , Winter W. , Eberl K. , Glück M. , König U.
Published: July 2002

Studying the structural and photoluminescence properties of pseudomorphic Si1−yCy and Si1−x−yGexCy multiple quantum well (QW) structures on (001) Si substrates offer a quantitative characterization of the band gap and band offset shifts caused by C alloying for y<3%. The main features of Si1−yCy alloys, which are a reduced lattice constant and a strong lowering of the conduction band energy, promise that C may serve as a counterpart to Ge in Si heteroepitaxy. The photoluminescent properties of Si1−yCy and SiGeC QWs are comparable to SiGe. Novel pseudomorphic Si1−yCy/SiGe coupled QW structures and Si1−yCy/Ge quantum dot structures result in a strong enhancement of the photoluminescent efficiency. The ternary SiGeC material system offers a higher degree of freedom in strain and band edge engineering of structures. We focus on our recent results on Si1−yCy and SiGeC QW layers embedded in Si concerning the growth by solid-source molecular beam epitaxy, structural properties, thermal stability, optical properties, and band offsets. The prospects of SiGeC alloys for realization of optoelectronic structures are discussed. First characteristics from 0.75 μm p-channel modulation-doped field-effect transistor devices containing an active SiGeC layer demonstrate good electrical properties.
Effect of hydrogenation on misfit dislocations in SiGe/Si structures for photovoltaic applications
Authors: Daami A. , Bremond G. , Caymax M. , Poortmans J.
Published: July 2002

Thick Si0.9Ge0.1 relaxed layers grown by chemical vapor deposition on Si(100) oriented substrates are investigated by photoluminescence (PL) spectroscopy. Resolved excitonic near-band-gap luminescence is observed in as-grown and hydrogen treated samples. Phonon assisted transitions are also well identified. The effect of hydrogenation is to enhance the luminescence related to the near-band gap. This enhancement is correlated with a quenching in the dislocation related PL especially for the D3–D4 bands and the T band. This indicates that hydrogenation passivates radiative centers inside dislocation cores which are responsible, beside nonradiative channels, for the quenching of SiGe band-gap edge luminescence.
Electrical characterization and annealing behavior of defect introduced in Si during sputter etching in an Ar plasma
Authors: Deenapanray P. N. K. , Auret F. D. , Myburg G.
Published: July 2002

We have employed current–voltage and capacitance–voltage measurements in conjunction with deep level transient spectroscopy to characterize the defects induced in n-Si during rf sputter etching in an Ar plasma. The reverse current, at a bias of 1 V, of the Schottky barrier diodes fabricated on the etched samples decreased nonmonotonically with etch time to a minimum at 6 min and, thereafter, increased. The reverse current also increased with decreasing plasma pressure. The barrier heights of the diodes followed the opposite trend. Six prominent electron traps were introduced in the substrate during Ar sputter etching. A comparison with the defects induced during high-energy alpha-particle and electron irradiation of the same material revealed that sputter etching created the VO and VP centers and V2−/0. The V2=/− charge state of the divacancy was not detected in our plasma etched samples. We have attributed the nondetection of V2=/− to the presence of defect-induced stress fields in the etched samples. A secondary defect with an energy level at Ec−0.219 eV was introduced during annealing and was found to be stable at 650 °C. This defect was introduced at the expense of a sputter-etching induced defect P4, which has similar electronic and annealing properties as EAr201 (Ec−0.201 eV), created in Ar-ion bombarded n-type Si.
Current oscillations in thin metal–oxide–semiconductor structures observed by ballistic electron emission microscopy
Authors: Wen H. J. , Ludeke R. , Schenk Andreas
Published: July 2002

Quantum interference oscillations of electrons in a thin SiO2 layer were observed by ballistic electron emission microscopy (BEEM). With BEEM, electrons are injected across the gate of a metal–oxide–semiconductor (MOS) structure and directly into the conduction band of the SiO2. The MOS capacitor consisted of a 5 nm thick Pd film deposited on a 2.8±0.2 nm oxide thermally grown on Si(100). Oscillations with up to four peaks in an energy range of 0–3 eV above the injection threshold were noted. Their magnitude is of the order of 30% of the underlying BEEM current. The oscillations were most salient and their energy location repeatable at points of the sample that were previously not exposed to the electron beam. Even modest exposures caused a buildup of positive charge. This charge resulted in energy shifts, as well as a weakening of the oscillations, both of which are a consequence of the added scattering and local field inhomogeneities associated with the random distribution of the positive charge. Solutions of the Schrödinger equation that included a built-in oxide potential of 0.20 V and image force effects at both interfaces gave excellent fits to the experimental data for an effective electron mass in the oxide mox=0.63±0.09mo. The uncertainty in mox arises from an uncertainty of ±0.2 nm in the determination of the oxide thickness by ellipsometric methods. Nevertheless, the obtained value is well above the generally accepted value of 0.5mo.
Dielectric-assisted trilayer lift-off process for improved metal definition
Authors: Ryan R. W. , Kopf R. F. , Hamm R. A. , Malik R. J. , Masaitis R. , Opila R.
Published: July 2002

We have developed a simple, trilayer lift-off process for obtaining metal of various thickness while retaining good feature definition down to 1 μm, using only standard photoresist and developer, and e-beam evaporated dielectric. This process has been implemented for fabrication of high speed circuits using InP/InGaAs/InP double heterojunction bipolar transistor devices. This structure is nonplanar, with a topography of about 1.3 μm from the top of the emitter to the substrate level for interconnects. Clean edges are obtained for all of the metallization steps. Metal lift-off with our trilayer process is easily accomplished by gentle rinsing with acetone, and does not require the use of high pressure spray or any heat treatment, such as boiling in a solvent to aid lift-off. This new process has greatly improved our circuit yield.
Negative electron-beam nanofabrication resist using acid-catalyzed protection of polyphenol provided by phenylcarbinol
Authors: Uchino Shou-ichi , Yamamoto Jiro , Migitaka Sonoko , Kojima Kyoko , Hashimoto Michiaki , Shiraishi Hiroshi
Published: July 2002

A high-resolution negative electron-beam (EB) lithography resist based on an acid-catalyzed protection reaction of a polyphenol enabled by a phenylcarbinol has been developed for nanofabrication. Polyphenol-3, which is synthesized by condensation of α,α,α′-tris(4-hydroxyphenyl)1-ethyl-4-isopropylbenzene with m-cresol, was selected as the most suitable matrix resin for the resist. 1,3,5-tris[1-(1-hydroxyethyl)]benzene (Triol-2) was found to be the best protection reagent among the six phenylcarbinols evaluated. Line-and-space patterns of 80 nm with edge roughness of less than 10 nm were delineated by using a resist composed of Triol-2, diphenyliodonium triflate, and polyphenol-3 in conjunction with an EB writer (20 μC/cm2 at 50 kV). Spectroscopic studies clearly showed that the acid-catalyzed protection reaction of the polyphenol brought about by Triol-2 is responsible for the resist insolubilization.
Focused ion-beam patterning of nanoscale ferroelectric capacitors
Authors: Stanishevsky A. , Aggarwal S. , Prakash A. S. , Melngailis J. , Ramesh R.
Published: July 2002

A 50 kV Ga+ focused ion beam was applied for milling submicron Pt-(La0.5Sr0.5)CoO3–Pb(NbxZryTiz)O3–(La0.5Sr0.5)CoO3–Pt-based ferroelectric capacitor heterostructures prepared by pulsed laser and sol-gel deposition techniques. The milling yields were found to be 0.22±0.02 μm3/nC for Pb(NbxZryTiz)O3, 0.3.4±0.01 μm3/nC for (La0.5Sr0.5)CoO3, and 0.34±0.06 μm3/nC for Pt layers. The influence of the ion beam current and its scan strategy, as well as depth of milling, on the quality of fabricated structures was studied. The minimum sizes down to 0.017 μm2 for the top electrode, and 0.04 μm2 for the capacitor structures milled to the bottom electrode were achieved without an additional sacrificial layer. A scanning probe microscopy technique was employed to test the properties of the milled capacitor structures.