bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation of UVIIHS resist chemistry to dissolution rate measurements
Authors: Thackeray J. , Fedynyshyn T. H. , Kang D. , Rajaratnam M. M. , Wallraff G. , Opitz J. , Hofer D.
Published: July 2002

This article describes the correlation of UVIIHS resist chemistry to dissolution rate measurements as a function of resist processing conditions. The acid generation efficiency, α, for the UVIIHS photoacid generator is high, 0.027 cm2/mJ. The dissolution rate versus exposure curves show the excellent developer selectivity of UVIIHS, with n values >8 for all processes. The rmax values for this resist are above 20 000 Å/s, which is higher than any positive resist previously reported. The extent conversion for deprotection is directly related to the dissolution rate changes; ∼30% deprotection correlates to the E0 dose for all process conditions evaluated. At 30%–40% acid produced, all of the deprotection chemistry is essentially completed. The chemical contrast, as measured by extent conversion versus exposure dose, is strongly affected by the postexposure bake (PEB) temperature, with 140 °C PEB showing higher chemical and lithographic contrast than the 130 °C PEB. Mack’s dissolution model has been shown to work for these data sets.
Suppression of electron shading effect by a counter radio frequency bias in plasma etching
Authors: Kamata T. , Arimoto H.
Published: July 2002

We investigated the suppression of the charge buildup caused by the electron shading effect using a counter rf bias, which produces high energy electrons reflected from the counter electrode. We expected that these high energy electrons could overcome the potential barrier formed at the entrance of high aspect-ratio hole patterns and to decrease the charge buildup at the bottom of these patterns. We directly investigated the charge buildup by measuring dc self-bias potential differences between high aspect-ratio hole patterns and open-space pattern. The dc self-bias potential difference increased, independent of the hole pattern aspect ratio, at the lower substrate rf bias voltage and they tended to saturate at the following higher substrate rf bias voltage. The dc self-bias potential difference reached about 100 V with a substrate rf bias voltage of 400 V for an aspect ratio of 2. The dc self-bias potential difference dramatically decreased from 100 to 20 V by increasing the counter rf bias voltage. In addition, we investigated this suppression effect by changing the phase difference between counter and substrate bias voltages when both bias frequencies were set to 13.56 MHz. We found that there is a variation of the suppression effect with respect to the phase difference. This indicates that high energy electrons, which were accelerated in an oscillation sheath, could reach the bottom of the holes.
Polysilicon gate etching in high density plasmas. III. X-ray photoelectron spectroscopy investigation of sidewall passivation of silicon trenches using an oxide hard mask
Authors: Bell F. H. , Joubert O.
Published: July 2002

The characteristics of poly-Si trench etching in high density plasma processes was studied by x-ray photoelectron spectroscopy. Poly-Si films on SiO2-covered Si(100) substrates were masked with a 200-nm-thick oxide hard mask. The 200 mm wafers were then etched downstream using a helicon high density plasma source and a chlorine-based gas chemistry. After etching, samples were transferred under ultrahigh vacuum to a surface analysis chamber equipped with an x-ray photoelectron spectrometer. Regular arrays of trenches were used to determine the photoelectron signals originating from the tops, sidewalls, and bottoms of the features. A thin oxide film was found on the sides of the oxide masked poly-Si trenches. The origin of this film can be related to the sputtering and redeposition of oxide from the quartz tube of the helicon source located in the plasma generation region. A substantial amount of chlorine was present on the poly-Si sidewall of the features, whereas less chlorine was found on the oxide surfaces. The poly-Si sidewalls were covered by a small amount of oxygen.
Correlation of Raman and optical studies with atomic force microscopy in porous silicon
Authors: Filios Adam A. , Hefner Susan S. , Tsu Raphael
Published: July 2002

Atomic force microscopy images of porous silicon samples prepared with different conditions have been correlated with photoluminescence (PL) and Raman spectra, allowing a clear classification of two types of samples, ‘‘gently’’ etched versus ‘‘heavily’’ etched. The gently etched samples show a significantly improved morphology and uniformity, as well as consistent correlation in PL and Raman results with the quantum confinement model for the light emission.
Use of multiple analytical techniques to confirm improved optical modeling of SnO2:F films by atomic force microscopy and spectroscopic ellipsometry
Authors: Ruzakowski Athey P. , Urban F. K. , Holloway P. H.
Published: July 2002

Variable angle of incidence spectroscopic ellipsometry, reflectance, and transmittance techniques were used to determine the optical constants of a fluorine doped tin oxide film deposited by chemical vapor deposition onto a hot soda-lime-silica glass ribbon. To improve the optical characterization, an additional analytical technique, atomic force microscopy (AFM), was used to incorporate information about surface roughness into the optical model. Our earlier work demonstrated the necessity of including a surface roughness layer as six sublayers in the optical model. The present work further confirms the method and demonstrates its accuracy with additional analytical techniques. These include: (1) cross sectional in-lens field emission scanning electron microscopy to measure total film thickness, determine presence of interface roughness and extent of surface roughness; (2) secondary ion mass spectrometry to give a first approximation of the film layer structure for optical modeling by depth profiling the film composition; (3) Hall measurements to identify the semiconductor carrier density and mobility; (4) x-ray diffraction to identify the crystalline phase and preferential growth orientation. The use of AFM surface images and surface roughness plus the other compositional and structural information to improve ellipsometric modeling of thin films has been confirmed.
Graded electron affinity electron source
Authors: Shaw J. L. , Gray H. F. , Jensen K. L. , Jung T. M.
Published: July 2002

We describe a new electron source using electric field and low electron affinity semiconductor materials to bring charge to potential energy levels near the vacuum level while still in the solid. The basic idea involves moving some of the potential barrier from the surface to the bulk, and distributing the barrier over a thin layer below the surface. In so doing, the emission physics is changed fundamentally from a quantum mechanical tunneling process largely controlled by surface properties to a classical transport process largely controlled by the band structure of a wide bandgap semiconductor. The composition of the thin layer below the surface would be graded such that the conduction band minimum changes from an energy close to the substrate Fermi level to an energy significantly closer to the vacuum level. Electrons from the substrate would be drawn into the graded composition layer with an electric field produced by a pointed emitter structure and extraction gate similar to that used in field emitter arrays. Relative to a conventional field emitter array, the new source is expected to require lower extraction fields and exhibit improved emission uniformity, stability, and noise. The I–V characteristics are not Fowler–Nordheim and may include a saturation effect at high current densities that could be engineered to improve reliability and uniformity. The group III nitrides can be grown with a continuous range of composition that provides the range of electron affinity needed to produce the proposed electronic structure.
Low-voltage electron-beam lithography with scanning tunneling microscopy in air: A new method for producing structures with high aspect ratios
Authors: Kragler K. , Günther E. , Leuschner R. , Falk G. , von Seggern H. , Saemann-Ischenko G.
Published: July 2002

A new lithography method for patterning an electron-beam resist employed in microelectronic technology with low energetic electrons from a scanning tunneling microscopy tip is presented. The method utilizes a thin electron-sensitive, chemically amplified top resist (positive mode) and amorphous diamondlike carbon as conductive bottom resist which allows one (in contrast to other scanning probe microscopy techniques) to achieve aspect ratios larger than five. The exposure response curve of the employed top resist is presented and compared with high-energy e-beam results. It is shown that the exposure with low-energy electrons leads to a direct cleavage of the functional group of the resist polymer responsible for development. Furthermore, the achievable writing speed for scanning tunneling microscopy exposure is estimated. The successful application of the scanning-tunneling-microscopy-based lithography is demonstrated especially with respect to the high aspect ratio on various substrates (Al, Si, SiO2, and poly Si).
Studying membranes with scanning force microscopy and patch-clamp technique
Authors: Mosbacher J. , Häberle W. , Hörber J. K. H.
Published: July 2002

The application of scanning probe techniques to biological molecular structures is a rapidly developing field. Here, we describe the combination of a scanning force microscope with the electrophysiological patch-clamp technique. The latter technique allows electrical control of a membrane preparation and direct measurement of the function of transmembrane proteins like ion channels. In addition, the solution composition of either side of the membrane can be controlled and membrane tension can be varied by applying pressure or suction to the patch pipette. We show results of our investigation of the mechanical and electro-mechanical properties of excised membrane vesicles and inside-out patches from Xenopus oocytes. Our observations favor the theory that parts of the cytoskeleton are excised together with the plasma membrane. They seem to stabilize the lipid bilayer leading to a relatively high elasticity of the membrane patch.
Enhanced dry etching of silicon with deuterium plasma
Authors: Iwakuro Hiroaki , Kuroda Tsukasa , Shen Dian-Hong , Lin Zhangda
Published: July 2002

The etching of Si and SiO2 for H2 and D2 plasma exposure has been investigated. The Si is etched rapidly by a factor of 34 for D2 plasma exposure compared with H2 plasma exposure. On the other hand, the etching rate of SiO2 does not change. This suggests a possibility of dry etching of Si with D2 gas.
Growth of silicon nanowires via gold/silane vapor–liquid–solid reaction
Authors: Westwater J. , Gosain D. P. , Tomiya S. , Usui S. , Ruda H.
Published: July 2002

Silicon nanowires (whiskers) have been grown on Si(111) via the vapor–liquid–solid (VLS) reaction using silane as the Si source gas and Au as the mediating solvent. The silane partial pressure and temperature ranges were 0.01–1 Torr and 320–600 °C, respectively. Growth at high partial pressure and low temperature leads to the growth of Si nanowires as thin as 10 nm. These wires are single crystals but exhibit growth defects such as bending and kinking. Lowering the silane partial pressure leads to an increase in the wire width and a reduction in the tendency to form growth defects. At low pressure, 40–100 nm wide well-formed wires have been grown at 520 °C. The VLS reaction using silane allows the growth of Si wires, which are significantly thinner than those grown previously using SiCl4.
High quality interfaces in GaAs–AlAs quantum wells determined from high resolution photoluminescence
Authors: Reynolds D. C. , Look D. C. , Jogai B. , Kaspi R. , Evans K. R. , Estes M.
Published: July 2002

High resolution photoluminescence (PL) measurements performed on several GaAs–AlAs quantum well structures revealed sharp excitonic transitions separated in energies corresponding to roughly half-monolayer fluctuations in well size. The narrow linewidths correlate with interface island structure whose lateral extent is either much larger or much smaller than the exciton diameter. The half-monolayer separation results from a sharply peaked PL intensity response occurring around those areas of the laterally nonuniform interface which have roughly 50% island coverage, with the average island size much smaller than the exciton diameter, about 225 Å.
Equipment simulation of SiGe heteroepitaxy: Model validation byab initiocalculations of surface diffusion processes
Authors: Hierlemann M. , Werner C. , Spitzer A.
Published: July 2002

Incorporation of very little Ge into a Si surface significantly increases deposition during chemical vapor deposition. This is due to the fact that hydrogen and chlorine desorb faster from the SiGe surface making available additional surface sites for adsorption. Two mechanisms are discussed to explain the observed catalytic effect: (i) the diffusion model where surface diffusion of H and Cl atoms from Si to Ge sites opens up an energetically more favorable path for H and Cl desorption via Ge surface sites and (ii) the collective model where incorporation of Ge into Si stimulates an overall change of the electronic structure of the surface, thus leading to increased desorption. Ab initio cluster calculations are used in this work to evaluate both models. Binding energies of H and Cl atoms on Si, Ge, and SiGe surfaces are calculated. It is observed that Si–H, Ge–H and Si–Cl, Ge–Cl binding energies do not change whether their neighboring surface atoms are Si atoms or Ge atoms. An overall change of the electronic structure of the surface due to Ge incorporation cannot be observed, making the collective model highly unprobable. To evaluate the diffusion model transition states for migration between different surface sites need to be located and the activation barriers need to be calculated. Surface diffusion of H and Cl atoms from Si to Ge is found to be energetically more favorable than desorption of H2, HCl, or SiCl2 from Si. Surface diffusion on mixed SiGe surfaces leads to enhanced desorption via Ge surface sites. Thus the diffusion model is considered a valid description. Macroscopic reactor simulations prove that the diffusion model can accurately describe enhanced deposition to explain the observed catalytic effect encountered during growth of SiGe heterolayers.
Electrostatic tip-surface interaction in scanning force microscopy: A convenient expression useful for arbitrary tip and sample geometries
Authors: Zypman Fredy R. , Eppell Steven J.
Published: July 2002

The electrostatic energy between a dielectric scanning force microscope (SFM) tip and a point charge is obtained in closed form as a function of the separation of the two objects. Applications of this result to both spherical and arbitrary tip shapes are discussed. Also, utilizing kinematic data, a method is given to experimentally extract the force due to the tip-sample interaction from a typical SFM instrument. This is done by analyzing the time dependent motion of the tip. The result is based on the use of a time dependent analysis of the force distance curve which is unavoidable in motion regimes in which the tip accelerates, as in the snap-to-contact process.
Dual scanning tunneling microscope mode of the surface diffusion metal ion source: Li transfer and scanning
Authors: Gupalo M. S. , Yarish I. L. , Zlupko V. M. , Suchorski Yu.
Published: July 2002

Application of the new solid-state lithium surface diffusion metal ion source in the scanning tunneling microscope (STM) mode under ultrahigh vacuum conditions is reported. By applying positive voltage pulses to a Li-covered tungsten STM tip placed within tunneling range, single nanosized Li hillocks and stripe-shaped Li formations are created on the Pt(110) surface in a well-reproducible way. The transfer of Li to the sample surface occurs in a noncontact way via chemically assisted field desorption of Li from the apex of the tip. The supply of Li to the apex surface sites is provided by surface diffusion from a Li monolayer deposit on the shank of the tip. The topography and evolution of the fabricated Li nanoformations are probed in situ using the same tip in the conventional STM imaging mode.
Metal–oxide–semiconductor-compatible silicon based single electron transistor using bonded and etched back silicon on insulator material
Authors: Köster T. , Hadam B. , Hofmann K. , Gondermann J. , Stein J. , Hu S. , Altmeyer S. , Spangenberg B. , Kurz H.
Published: July 2002

We present a fabrication method for a single electron transistor in silicon. The process is based on bonded and etched back silicon on insulator material with a very thin silicon top layer. Tunnel junctions are realized by electron beam lithography in combination with a two layer resistsystem. The pattern is transferred by anisotropic reactive ion etching and the lateral dimensions are reduced further by thermal oxidation. The process technology is, apart from the e-beam lithography, fully metal–oxide–semiconductor compatible. We electrically characterized samples with four tunnel junctions in series. At 6 K the I/U characteristics reveals a Coulomb blockade as well as a Coulomb staircase, which can be attributed to the asymmetry in the system. Additionally, the temperature dependence and the variation of the background electrostatic potential of the islands were investigated.
Synchrotron radiation photoemission spectroscopy studies of the thermal nitridation of GaAs(100) with ammonia
Authors: Huh Chul , Park Seong-Ju , Ahn Sook , Han Jeong Yeul , Cho Keum Jae , Seo Jae Myung
Published: July 2002

The thermal nitridation of GaAs(100) with ammonia was investigated by synchrotron radiation photoemission spectroscopy and atomic force microscope. This study revealed the chemical composition, chemical states, and morphological changes in the nitridated surface layer. We observed that ammonia can be decomposed to an activated nitrogen atom above 700 °C forming GaN on the surface. Thermally nitridated layers were composed of metallic Ga and GaN islands that are elongated along the [011] direction to relax the tensile strain in the [01̄1] direction. As the nitridation temperature increased, the composition of GaN increased in the nitridated layer due to the efficient thermal decomposition of NH3 and the subsequent incorporation of the N atom into the metallic Ga. The surface morphology of the nitridated layer, on the other hand, became substantially roughened at higher temperatures.
Ultrashallow secondary ion mass spectroscopy depth profiling of doping spikes and Si/SiGe/Si heterostructures using different primary species
Authors: Krüger D. , Iltgen K. , Heinemann B. , Kurps R. , Benninghoven A.
Published: July 2002

We present high resolution secondary ion mass spectroscopy (SIMS) depth profiles for characterization of Si/SiGe/Si heterojunction bipolar transistors (HBT). We show by device simulation that to achieve transit frequencies of more than 90 GHz for a given HBT, it is necessary to keep the decay length of the B profile in the SiGe base layer smaller than 2.5 nm. This formulates stringent requirements for the processing technology and for profile characterization techniques. In time-of-flight secondary ion mass spectroscopy (TOF-SIMS) depth profiling (dual-beam mode), we used a low energy (0.5–3 keV) sputter gun operating with different sputter gases (Ar, O2, SF6) to achieve a profile decay length below 2.5 nm. The full width at half-maximum (FWHM) of 3 nm B doping spikes in HBT structures is well-characterized using an Ar+ ion beam of 1 keV. To measure B base doping with a decay length of about 1 nm it is necessary to lower the energy of the sputtering ion beam to less than 2 keV for SF6 and to 0.6 keV for Ar sputtering. The decay length depends linearly on the sputtering ion beam energy in the low energy range. The slope of this dependence is smaller for SF6 sputtering than for Ar sputtering.
Quantifying distortions in soft lithography
Authors: Rogers John A. , Paul Kateri E. , Whitesides George M.
Published: July 2002

This article describes a moiré technique for determining distortions in soft lithography. We use the technique to investigate distortions when soft lithography is performed in a variety of configurations; a method is identified for limiting maximum distortions to less than 1 μm over areas ∼1 cm2. We also suggest an approach for actively controlling these distortions, and we demonstrate in a simple way its feasibility.
Formation of ultrathin oxynitride layers on Si(100) by low-temperature electron cyclotron resonance N2O plasma oxynitridation process
Authors: Chakraborty Sahana , Yoshida Toshiyuki , Hashizume Tamotsu , Hasegawa Hideki , Sakai Takamasa
Published: July 2002

We have undertaken the characterization of the low-temperature direct electron cyclotron resonance (ECR) N2O plasma process on the technically important Si(100) surface by the combined use of the newly developed ultrahigh vacuum (UHV)-based contactless capacitance–voltage (C–V) and x-ray photoelectron spectroscopy (XPS) techniques. An UHV-based contactless C–V measurement system allowed for the first time a direct in situ assessment of electronic properties of “free” Si surfaces and the surfaces covered with an ultrathin insulator layer. The UHV contactless C–V analysis indicated that a oxynitride/Si interface with a minimum interface state density of 1×1011 eV−1 cm−2 could be realized by the ECR N2O oxynitridation process at 400 °C. The angle-resolved XPS study showed that the formation of a phase-separated Si3N4/SiO2 structure is important to realize such a interface at low temperatures. The electronic and the chemical properties of the interfaces were found to be strongly correlated.
Bromine/methanol wet chemical etching of via holes for InP microwave devices
Authors: Trassaert S. , Boudart B. , Piotrowicz S. , Crosnier Y.
Published: July 2002

We report on the realization of via holes on InP material (for the first time to our knowledge) using bromine/methanol wet chemical etching. Typical dimension of the via holes is about 80 μm in diameter. A specific layout has been accomplished to obtain the via hole equivalent circuit. Measurements have been performed from 50 MHz to 30 GHz. They exhibit losses of 0.1 dB at 30 GHz. The via hole equivalent circuit is found to be a resistance and an inductance in serial configuration with typical values of 0.4 Ω and 26 pH, respectively.
Transient and stationary field emission currents from semiconductors computed by a simple semi-classical method
Authors: Filip V. , Nicolaescu D. , Plavitu C. N. , Okuyama F.
Published: July 2002

The transient emission current densities from flat band semiconductors and the stationary emission from graded electron affinity devices are computed by a combined semi-classical transport+transmission coefficient method. A rapid sequence of sharp current overshoots can be obtained in the first case for a wide range of built-up speeds of the external field. Their amplitudes and frequencies are field dependent and can be diminished by previous “heating” of the electronic system. In the second case, low field saturation and temperature assisted emission enhancement were found as expected. Several practical conclusions are drawn.
Characteristics and circuit model of a field emission triode
Authors: Nam Jung Hyun , Uh Hyung Soo , Lee Jong Duk , Ihm Jeong Don , Kim Yeo Hwan , Choi Kyu Man
Published: July 2002

A circuit model for a field emission triode has been proposed. The model parameters have been extracted from the fabricated silicon tip array and verified by being compared to the results simulated by circuit simulator (SPICE). The cutoff frequency can be calculated from the parametric capacitance and the transconductance values extracted from measurements. For the field emission triode, the capacitance of 3.45 fF/tip and the transconductance of 0.94 nS/tip have been measured under the emission current of 4.1 nA/tip. From these values, the cutoff frequency is predicted to be 43 kHz but the measured one came out to be 6 kHz because of the parasitic capacitance components.
High-speed Si/SiGe technology for next generation wireless system applications
Authors: Larson Lawrence E.
Published: July 2002

Si/SiGe integrated circuit technology represents a revolutionary opportunity to combine high-performance digital, analog, and rf circuits on a common substrate. The outstanding high-frequency performance of the Si/SiGe devices, combined with the high levels of integration of complementary metal–oxide–semiconductors will contribute to a long-term “paradigm shift” in the architectural partitioning of high-frequency high-performance wireless systems. This article outlines the key future systems applications for the technology.
Electron emission characteristics of boron nitride films synthesized by plasma-assisted chemical vapor deposition
Authors: Sugino Takashi , Kawasaki Seiji , Tanioka Kazuhiko , Shirafuji Junji
Published: July 2002

Boron nitride (BN) films are synthesized using BCl3 and N2 as source gases by plasma-assisted chemical vapor deposition. The BN film consists of hexagonal grains of 3 nm in size. The energy gap is estimated to be as wide as 6.0 eV from ultraviolet-visible optical transmission measurement. The electrical resistivity is estimated to be 2×1011 and 1.3×102 Ω cm for undoped and sulfur-doped BN films, respectively. The electron emission current is detected at electric fields higher than 9 V/μm. The tunneling barrier height is estimated to be 0.1 eV from the Fowler–Nordheim plot. BN-coated Si tip field emitter arrays are fabricated. The electron emission occurs at electric field as low as 6 V/μm. It is demonstrated that the electron emission characteristic of Si tip array is much improved by BN coating.
Ultrahigh vacuum sample heating stage for molecular beam epitaxy applications with transfer mechanism to a remote scanning tunneling microscope
Authors: Mendus T. , Chambers A.
Published: July 2002

An ultrahigh vacuum (UHV) sample heating stage and sample holder are described which utilize radiant and electron bombardment heating to achieve sample temperatures up to 1300 K. The sample surface is widely accessible by the various beams associated with surface preparation, monitoring, and deposition. The design is based on a commercially available Omicron scanning tunneling microscope (STM) sample holder and allows transfer to an auxiliary mobile UHV system and thence to a STM and other UHV facilities.
Method for angular sputter yield extraction for high-density plasma chemical vapor deposition simulators
Authors: Kapur P. , Bang D. S. , McVittie J. P. , Saraswat K. C. , Mountsier T.
Published: July 2002

High-density plasma chemical vapor deposition (HDP CVD) is a deposition method of current interest for gap fill of intermetal and interlevel dielectrics in semiconductor circuits. In HDP CVD processes the silicon dioxide film is often sputter etched as it is being deposited. The resputtering of the deposited film is a crucial process component in determining the final surface topography. Hence, it is imperative that the process simulators take this effect into consideration. In this work, we propose a method to extract the angle-dependent sputter yield for the HDP CVD process. This method constitutes the usage of our test structure. The extracted angular yield distribution is, then, used to simulate the final silicon dioxide profile. The distribution validity is determined by comparison of the simulated profile against the experimental profile. SPEEDIE (Stanford profile emulator for etching and deposition in integrated circuit engineering), a deposition and etching simulation program, was used as the simulator while experiments were performed on a HDP CVD system. A reasonably, good agreement was obtained between simulated and experimental profiles, indicating an accurate angular yield extraction. The extracted angular yield curve was compared with other such curves from literature for different ion energies. This comparison showed a trend of increase in the angle at which maximum yield occurs as the ion energy increased.
Epitaxial growth and properties of III–V magnetic semiconductor (GaMn)As and its heterostructures
Authors: Tanaka Masaaki
Published: July 2002

We present epitaxial growth, structures, magnetization, magneto-transport, and magneto-optic properties of (GaMn)As thin films and (GaMn)As/AlAs superlattice heterostructures grown by molecular beam epitaxy (MBE) on GaAs substrates. (Ga1−xMnx)As is a new class of III–V based magnetic alloy semiconductor grown by low temperature MBE, which contains a large amount of Mn atom (Mn concentration x up to 8%) far above the equilibrium solubility of Mn in GaAs. The feasibility of preparing such a III–V based magnetic semiconductor and its heterostructures gives a new degree of freedom in the materials design of III–V systems, offering new opportunities to explore spin-related phenomena as well as potential device applications using both magnetic and electronic/optical functions in III–V semiconductors.
Fabrication of submicron suspended structures by laser and atomic force microscopy lithography on aluminum combined with reactive ion etching
Authors: Boisen A. , Birkelund K. , Hansen O. , Grey F.
Published: July 2002

We report a simple fabrication method for suspended submicron silicon and silicon oxide structures. The structures are defined by laser and atomic force microscopy (AFM) writing on a 7-nm-thick aluminum film. For laser writing the minimum obtained linewidth is 500 nm, whereas for AFM it is approximately 100 nm. During AFM writing, aluminum oxide is formed, whereas during laser writing, a compound containing aluminum and silicon is formed. For both processes the nonpatterned aluminum can be dissolved selectively in a wet chemical etch leaving the patterned areas as an etch mask. Alternatively, the aluminum oxide can be etched to form a positive etch mask. Aluminum and aluminum oxide are both excellent etch masks for reactive ion etching (RIE) of silicon and silicon oxide. Hence, by combinations of RIE processes, a variety of structures can be fabricated from the aluminum based masks. To illustrate the flexibility of this technique we demonstrate fabrication of submicron cantilevers and bridges defined in silicon and silicon oxide.
Influence of edge roughness in resist patterns on etched patterns
Authors: Namatsu Hideo , Nagase Masao , Yamaguchi Toru , Yamazaki Kenji , Kurihara Kenji
Published: July 2002

We report on the linewidth fluctuations in resist patterns and their influence on etched patterns. The linewidth fluctuations observed as line edge roughness are mainly caused by polymer aggregates in the resist materials. Polymer aggregates more than 30 nm in diameter are observed in both the positive and negative resist films. Because the polymer aggregates are not dissolved but extracted during development, they remain stuck on the pattern sidewall and cause linewidth fluctuations. When substrates, such as Si, are etched using resist patterns as a mask, the linewidth fluctuations of the resist patterns are faithfully transferred to the substrate. This means that the linewidth fluctuations in device patterns are originally due to the polymer aggregates in the resist films. The linewidth fluctuation is also found to decrease through substrate etching, depending on resist thickness loss. This possibly results from degradation of the resist patterns in lateral directions through etching. However, it does not provide a sufficient decrease in linewidth fluctuations because the large thickness loss of the resist during etching results in critical dimension loss. Therefore, the reduction of the effect of the aggregate size, for example, by using the resist with small aggregates, such as hydrogen silsesquioxane, is necessary.
Atom-by-atom analysis of microtip emitter surfaces by the scanning atom probe
Authors: Nishikawa O. , Watanabe M. , Ohtani Y. , Maeda K. , Tanaka K. , Sekine T. , Itoh J.
Published: July 2002

Unique capabilities of the scanning atom probe, atomically high resolution and atom-by-atom mass analysis, were utilized to investigate the compositional distribution in the individual apexes of a silicon microtip array and fine grains of chemical vapor deposition diamonds. The dry-etched silicon tips contain a large amount of carbon and hydrogen and the HF-treated tips contain even oxygen and fluorine. Although the carbon concentration of the uppermost surface layer is as high as 50% for the dry-etched tip, it decreases to less than 10% for the second layer and approaches to the constant concentration of less than 2% at the depth of 20 nm suggesting the carbon intermixture during the fabrication and/or etching process of the microtip array. The carbon concentration in the HF-treated tip decreases from 18% to 8% at the depth of 30 nm. On the other hand, the oxygen concentration stays fairly constant at around 25% throughout the analysis. The high hydrogen concentration in the diamonds is attributed to the large difference between the activation energies for hydrogen desorption, 21 kcal/mol, and for methane adsorption, 7.3 kcal/mol.
Microelectron gun integrating a point-source cathode
Authors: Hammadi Zoubida , Gauch Michel , Morin Roger
Published: July 2002

A structure integrating a sharp field emission tip inside a coaxial structure with an overall diameter as small as 60 μm is described. It can emit nA electron current with a minimum kinetic energy of 50 eV. It is demonstrated that this structure behaves like an electron gun and is able to produce a low-energy, divergent and highly coherent electron beam at distances as small as 100 μm from the tip.
Novel scanning near-field optical microscopy/atomic force microscope probes by combined micromachining and electron-beam nanolithography
Authors: Zhou H. , Midha A. , Bruchhaus L. , Mills G. , Donaldson L. , Weaver J. M. R.
Published: July 2002

We have developed novel probes which allow scanning near-field optical microscopy to be performed in a conventional atomic force microscope (AFM). Direct-write electron-beam lithography and silicon micromachining have been used in a reliable batch process which allows the production of many probes at once without resort to handicraft. The aperture is situated at the hollow tip apex of a conventional silicon nitride AFM cantilever. Since there is no waveguide cutoff, the overall light throughput is dramatically enhanced. The integration of a conventional force microscope cantilever with the aperture allows more reliable and better control of the aperture-sample distance than that obtained by “shear-force” detection. In addition, since the apertures are defined by lithographic means, the size and shape of apertures are well controlled and reproducible. We present the first results of near-field optical imaging and luminescence imaging using these probes demonstrating excellent light throughput and also good spatial and spectral resolution.
Micromachined, reusable shadow mask for integrated optical elements grown by metalorganic chemical vapor deposition
Authors: Peake G. M. , Zhang L. , Li N. Y. , Sarangan A. M. , Willison C. G. , Shul R. J. , Hersee S. D.
Published: July 2002

Precise three-dimensional control of micro-optical elements has recently been achieved using shadow masked metalorganic chemical vapor deposition (MOCVD) with an epitaxial mask. However, the epitaxial shadow mask used to deposit these precision micro-optics limits the size and shape of the available structures. In this work, a reusable shadow mask was fabricated by deep-Si reactive ion etching and employed in the growth of circular microlenses. This novel, reusable mask makes the shadow masked MOCVD process more rapid and less expensive and also allows more flexibility in the shape and size of the micro-optical elements that can be deposited. The micromachined shadow mask is held in place during growth by fusion bonding, it can be released by rapid cooling and it is easily cleaned for reuse. Microlenses with apertures as large as 500 μm, fabricated under the micromachined mask, did not flatten at the center and formed accurate quadric surfaces.
Peak and integrated reflectivity, wavelength and gamma optimization of Mo/Si, and Mo/Be multilayer, multielement optics for extreme ultraviolet lithography
Authors: Stuik R. , Louis E. , Yakshin A. E. , Görts P. C. , Maas E. L. G. , Bijkerk F. , Schmitz D. , Scholze F. , Ulm G. , Haidl M.
Published: July 2002

Reported is the optimization of the fabrication of Mo/Si multilayer systems produced by e-beam evaporation and ion-beam smoothening. The impact of a number of coating parameters is verified such as variation of the mirror’s center wavelength and the metal fraction of the bilayer (Γ ratio), resulting in reflectivities up to 68.6% at normal incidence. Parallel to this experimental work, a numerical optimization based on experimentally determined multilayer properties is carried out on the throughput of multimirror lithographic systems for the 11–15 nm wavelength region using Mo/Si and Mo/Be coatings. The center wavelength, Γ ratio and layer stack have been optimized. The calculations show an optimum throughput for a 10-mirror Mo/Si system at 14.4 nm, assuming a light source with a wavelength independent spectrum.
Correlation of atomic force microscopy sidewall roughness measurements with scanning electron microscopy line-edge roughness measurements on chemically amplified resists exposed by x-ray lithography
Authors: Reynolds Geoffrey W. , Taylor James W.
Published: July 2002

As critical dimensions of resist features shrink, roughness of the features may contribute significantly to the variation in critical dimension. Measuring and understanding the causes of this roughness will become increasingly important with smaller sizes. To date, mainly two techniques have been used to measure the roughness: atomic force microscopy (AFM) and scanning electron microscopy (SEM). Topdown SEM measurements provide an easy and expedient measure of the variation in the profile of the resist feature. These measurements are often called “line-edge roughness” (LER). AFM measurements are considerably more time consuming, but provide information on the entire sidewall surface of the resist, rather than just the profile in line-edge roughness. Our recent AFM measurements on the positive-tone resist APEX-E and UV5 have shown that the sidewall roughness of the resist is depth dependent; resist near the substrate is smoother than resist at the top surface of the resist. For instance, APEX-E may have a roughness on the order of 3 nm rms near the substrate, which may increase to 7 or so nm rms at the top of the resist line. This article will correlate measurements made by both AFM and SEM and explore how the depth-dependent roughness in AFM data may affect the magnitude of the roughness measured by topdown SEM.
High-performance silicon dioxide etching for less than 0.1-μm-high-aspect contact holes
Authors: Samukawa Seiji , Mukai Tomonori
Published: July 2002

We describe a method for controlling radicals in high-performance SiO2 etching of contact holes smaller than 0.1 μm using nonperfluorocompound gases (CF3I and C2F4) in an ultrahigh-frequency (UHF) plasma. Because this method allows the independent control of polymerization and etching through the selective generation of CF2 and CF3 radicals, both high etching selectivity and a high etching rate were achieved without microloading and etching stop, even for a 0.05 μm contact hole. Using this new gas chemistry, we achieved an optimum balance between polymerization and etching in 0.05-μm-diameter contact holes by controlling the flow ratio of C2F4/CF3I gas
Atom-by-atom analysis of diamond, graphite, and vitreous carbon by the scanning atom probe
Authors: Nishikawa Osamu , Ohtani Yoshikatsu , Maeda Kiyoshi , Watanabe Masafumi , Tanaka Keiji
Published: July 2002

Various artificial diamonds, graphite and vitreous carbon were atom-by-atom mass analyzed by a scanning atom probe (SCAP). Carbon clusters were detected in all specimens and the abundance of the clusters was found to be high for graphite and vitreous carbon. Nearly 90% of the carbon atoms field evaporated from 99.99% pure graphite were detected as clusters up to C11. After soaking in acid (H2SO4:HNO3:H2O=1:1:1) for 15 min no clusters were detected in the high-pressure high-temperature (HPHT) diamond which exhibited mass peaks of the clusters up to C6. The number of clusters formed by odd numbers of carbon atoms was larger than that formed by even numbers. The hydrogen concentration in chemically vapor deposited diamonds appeared to be related to the percentage of hydrogen in the mixed reaction gas while growing the diamonds. Few hydrogen ions were detected in the HPHT diamond and vitreous carbon. The hydrogen and oxygen distributions in the 99.8% graphite were rather uniform while those in the 99.99% graphite were localized. The present results suggest that the mass analysis by the SCAP may shed light on even the binding state of the analyzed materials.
Atomic level analysis of silicon emitters utilizing the scanning atom probe
Authors: Nishikawa O. , Watanabe M. , Ohtani Y. , Maeda K. , Tanaka K.
Published: July 2002

In order to examine the effect of chemical treatment on silicon emitter surfaces, photolithographically processed, mechanically grooved, and crushed silicon specimens were atom-by-atom mass analyzed before and after the soakage in hydrofluoric acid (HF) by the scanning atom probe. Silicon microtips fabricated by the photolithography were found to be most heavily contaminated before the HF treatment. After the acid soakage, the (111)-oriented silicon surface is found to be most resistive to the HF treatment while other specimens are vulnerable to contaminants, possibly due to defects and disorders on the surface layers. The Fowler–Nordheim (FN) curves were plotted for all specimens. Generally, the HF treatment lowered the work function of the specimens which field evaporate hydrogen as H+ and H2+.
Epitaxial perovskite thin films grown on silicon by molecular beam epitaxy
Authors: Yu Z. , Ramdani J. , Curless J. A. , Finder J. M. , Overgaard C. D. , Droopad R. , Eisenbeiser K. W. , Hallmark J. A. , Ooms W. J. , Conner J. R. , Kaushik V. S.
Published: July 2002

Thin film perovskite-type oxide SrTiO3 has been grown epitaxially on Si(001) substrate by molecular beam epitaxy. Reflection high energy electron diffraction and x-ray diffraction analysis indicate high quality SrTiO3 heteroepitaxy on Si substrate with SrTiO3(001)//Si(001) and SrTiO3[010]//Si[110]. The SrTiO3 surface is atomically as smooth as the starting substrate surface, with a root mean square roughness of 1.2 Å observed by atomic force microscopy. The thickness of the amorphous interfacial layer between SrTiO3 and Si has been engineered to minimize the device short channel effect. An effective oxide thickness <10 Å has been obtained for a 110 Å thick dielectric film. The interface state density between SrTiO3 and Si is 6.4×1010 cm−2 eV−1, and the inversion layer carrier mobilities are 221 and 62 cm2 V−1 s−1 for n- and p-channel metal–oxide–semiconductor devices with 1.2 μm effective channel length, respectively. The gate leakage in these devices is two orders of magnitude smaller than a comparable SiO2 gate dielectric metal–oxide–semiconductor field effect transistors.
Magnetization Precession by Hot Spin Injection
Authors: Weber W. , Riesen S. , Siegmann H. C.
Published: July 2002

As electrons are injected at various energies into ferromagnetic material with their spin polarization vector perpendicular to the axis of the magnetization, we observe precessional motion of the spin polarization on the femtosecond time scale. Because of angular momentum conservation, the magnetization vector must precess as well. We show that spin injection will generate the precessional magnetization reversal in nanosized ferromagnetic bits. At reasonable injected current densities this occurs on the picosecond time scale.
Continuous Mantle Melt Supply Beneath an Overlapping Spreading Center on the East Pacific Rise
Authors: Dunn Robert A. , Toomey Douglas R. , Detrick Robert S. , Wilcock William S. D.
Published: July 2002

Tomographic images of upper mantle velocity structure beneath an overlapping spreading center (OSC) on the East Pacific Rise indicate that this ridge axis discontinuity is underlain by a continuous region of low
P
-wave velocities. The anomalous structure can be explained by an approximately 16-kilometer-wide region of high temperatures and melt fractions of a few percent by volume. Our results show that OSCs are not necessarily associated with a discontinuity in melt supply and that both OSC limbs are supplied with melt from a mantle source located beneath the OSC. We conclude that tectonic segmentation of the ridge by OSCs is not the direct result of magmatic segmentation at mantle depths.
Carbon Dioxide Degassing by Advective Flow from Usu Volcano, Japan
Authors: Hernández P. A. , Notsu K. , Salazar J. M. , Mori T. , Natale G. , Okada H. , Virgili G. , Shimoike Y. , Sato M. , Pérez N. M.
Published: July 2002

Magmatic carbon dioxide (CO
2
) degassing has been documented before the 31 March 2000 eruption of Usu volcano, Hokkaido, Japan. Six months before the eruption, an increase in CO
2
flux was detected on the summit caldera, from 120 (September 1998) to 340 metric tons per day (September 1999), followed by a sudden decrease to 39 metric tons per day in June 2000, 3 months after the eruption. The change in CO
2
flux and seismic observations suggests that before the eruption, advective processes controlled gas migration toward the surface. The decrease in flux after the eruption at the summit caldera could be due to a rapid release of CO
2
during the eruption from ascending dacitic dikes spreading away from the magma chamber beneath the caldera.
Collaboration Between CC- and A-Adding Enzymes to Build and Repair the 3'-Terminal CCA of tRNA in
Aquifex aeolicus
Authors: Tomita Kozo , Weiner Alan M.
Published: July 2002

The universal 3′-terminal CCA sequence of all transfer RNAs (tRNAs) is repaired, and sometimes constructed de novo, by the CCA-adding enzyme [ATP(CTP):tRNA nucleotidyltransferase]. This RNA polymerase has no nucleic acid template, yet faithfully builds the CCA sequence one nucleotide at a time using cytidine triphosphate (CTP) and adenosine triphosphate (ATP) as substrates. All previously characterized CCA-adding enzymes from all three kingdoms are single polypeptides with CCA-adding activity. Here, we demonstrate through biochemical and genetic approaches that CCA addition in
Aquifex aeolicus
requires collaboration between two related polypeptides, one that adds CC and another that adds A.
Electrical Anisotropy Below Slow- and Fast-Moving Plates: Paleoflow in the Upper Mantle?
Authors: Bahr Karsten , Simpson Fiona
Published: July 2002

Upper mantle electrical conductivities can be explained by hydrogen diffusivity in hydrous olivine. Diffusivity enhances the conductivity of olivine anisotropically, making the
a
axis the most conductive of the three axes. Therefore, the hypothesis that plate motion induces lattice-preferred orientation of olivine can be tested with the use of long-period electromagnetic array measurements. Here, we compared electrical anisotropies below the slow-moving Fennoscandian and fast-moving Australian plates. The degree of olivine alignment is greater in the mantle below the Fennoscandian plate than below the Australian plate. This finding may indicate that convection rather than plate motion is the dominant deformation mechanism.