bluuebunny/crossref_metadata_2025 huggingface dataset:
50 nm GaAs/AlAs wire structures grown on corrugated GaAs
Authors: Miller David J. , Harris James S.
Published: July 2002

Electron beam lithography has been used to investigate the growth of GaAs wires in finely corrugated GaAs. Electron beam lithography was used to define 100 nm corrugations along the [110] and [11̄0] directions; anisotropic etching revealed grooves that were V-shaped ([11̄0]) or dovetailed ([110]). Here, AlAs resharpens the groove profile during growth, provided the barrier thickness is not less than 30–40 nm. Also, GaAs exhibited an enhanced growth rate in both groove directions, with an increase of 60% over the nonpatterned growth rate for the [11̄0] direction. Growth in grooves along [11̄0] preserved the V shape of the groove, while [110] growth showed evidence of deposition masking and microvoiding.
Chemical beam epitaxy of strain balanced GaP/GaAs/InP/GaAs superlattices
Authors: Bensaoula A. H. , Freundlich A. , Bensaoula A. , Rossignol V. , Ponchet A.
Published: July 2002

This work addresses the chemical beam epitaxy (CBE) growth and interface properties of a new type of GaP(n)/GaAs(m)/InP(n)/GaAs(k) pseudomorphically strained superlattice structures. The structural properties of these highly strained heterostructures are discussed in light of high-resolution x-ray diffraction and transmission electron microscopy observations. In spite of the large lattice mismatch between the individual GaP, GaAs, and InP layers in the superlattice structures, it is demonstrated that due to a nearly perfect strain balance between GaP (in extension) and InP (in compression) layers, GaP/GaAs/InP/GaAs superlattices with thicknesses up to 1 μm can be achieved with CBE.
Characterization of plasma etch processes using measurements of discharge impedance
Authors: Bose F. , Patrick R. , Baltes H. P.
Published: July 2002

Actual power delivered to the discharge, rf voltage, rf current, phase angle, and dc bias have been measured using commercially available impedance and power meters placed directly on the powered electrode of a parallel-plate diode etcher. The variation of these electrical quantities as discharge parameters such as power, pressure, electrode spacing, gas mixing ratio, and total flow are varied has been investigated for both electropositive and electronegative gases. It was found that the transfer efficiency of the matching network depends significantly on the process conditions and can be as low as 55% of the generator output. Polysilicon etch rate experiments were performed to determine the effect of varying the actual power delivered to the discharge and possible interaction with other process parameters such as pressure, as opposed to considering solely the rf generator output. End point was detected by measuring the change in the discharge impedance while etching through a polysilicon film. The sensitivity of this technique was compared with that of more commonly used optical emission methods.
Probing by in situ scanning tunneling microscopy the influence of an organic additive on Si etching in NaOH
Authors: Allongue P. , Bertagna V. , Kieling V. , Gerischer H.
Published: July 2002

The etching of Si in alkaline solution is used to fabricate microstructures. A recent study has described the etching reaction at a molecular level. The present paper studies, with in situ scanning tunneling microscopy, the effect of a surfactant (triton) on Si etching and its consequences regarding the resulting surface topography, which is an important question in the preparation of substrates.
Structural characterization of plasma-doped silicon by high resolution x-ray diffraction
Authors: Chapek D. L. , Conrad J. R. , Matyi R. J. , Felch S. B.
Published: July 2002

High resolution x-ray diffraction methods have been used to characterize boron-doped silicon fabricated using low energy plasma source ion implantation (PSII). Double-crystal rocking curves recorded using the asymmetric (113) reflection show increasing intensity in the low-angle tail as the ion dose was increased from 1.1×1015 to 4.4×1015 cm−2. Scans of the diffuse intensity around the 113 point in reciprocal space using triple crystal diffraction showed no significant differences in the magnitude of diffuse kinematic scattering from an unimplanted control sample and the plasma doped silicon; in all cases, negligible diffuse scattering was observed. This suggests that the doping by PSII is accompanied by negligible amount of crystallographic damage. Postimplant rapid thermal annealing was found to cause no change in the level of diffuse scattering; however, the asymmetry in the double-crystal rocking curves switched to the high-angle side. Dynamic simulation of the rocking curves has been used to estimate the strain distribution in the as-implanted and annealed samples.
Atom probe analysis and field emission studies of silicon
Authors: King R. A. , Mackenzie R. A. D. , Smith G. D. W. , Cade N. A.
Published: July 2002

Single ungridded silicon tips have been studied by field emission current–voltage characterization, field emission imaging, field ion imaging, and pulsed laser atom probe (PLAP) analysis. Changes in field emission characteristics were observed as a thin contaminant layer (oxygen, hydrogen, carbon, and carbon monoxide) formed on the surface of clean field evaporated silicon tips. Removal of the contaminant layer by pulsed laser-assisted field desorption restored the original field emission characteristics. Clean silicon tips that were oxidized in air began to emit at half the voltage required for unoxidized tips. As the voltage was increased, a sudden irreversible increase in field emission current was observed. PLAP analysis and field emission imaging showed that this effect was caused by the disruption of the oxide layer shortly after the onset of field emission. After the oxide disruption, field emission occurred from regions of sharp local geometry around the circumference of the tip. Removal of these regions by field evaporation or PLAP produced field emission characteristics very similar to those obtained from clean silicon tips. This explains a long-standing problem in understanding the ‘‘switch-on’’ behavior of silicon emitters.
Nanometer-scale imaging characteristics of novolak resin-based chemical amplification negative resist systems and molecular weight distribution effects of the resin matrix
Authors: Shiraishi Hiroshi , Yoshimura Toshiyuki , Sakamizu Toshio , Ueno Takumi , Okazaki Shinji
Published: July 2002

Molecular weight distribution effects of novolak resin-based chemical amplification negative resist systems are investigated for electron-beam lithography. The resist systems investigated consist of onium salts as an acid generator, a methoxymethyl melamine crosslinker, and a conventional/fractionated novolak resin matrix. Delineated patterns of both types of resist systems are compared to evaluate submicron-scale resolution. The conventional novolak resin-based system shows higher contrast than the fractionated one. High aspect ratio patterns are resolved for the conventional novolak-based resist, whereas poor results are obtained for the fractionated resin-based one on the submicron scale. Very thin films (30 nm) of both resist systems are delineated with a finely focused electron beam (diameter: approximately 2 nm at 5 kV) from a scanning electron microscope. Nanometer-scale edge roughness (nanoedge roughness) is observed for the conventional novolak resin-based resist. On the contrary, the degree of nanoedge roughness is greatly reduced for the fractionated one.
Scanning tunneling microscope observation of the cleavage fracture surfaces of titanium aluminide
Authors: Zhang Yue , Chu W. Y. , Wang Y. B. , Qiao L. J. , Xiao C. M. , Wang Z. H. , Bai C. L.
Published: July 2002

The brittle fracture surfaces of titanium aluminide were investigated by the scanning tunneling microscope in the range of nanometers. The results showed that there were some river marks and/or fan patterns, ditches, dimples, and cleavage steps on the cleavage fracture surfaces. This was similar to that observed by the scanning electron microscope. The height and width of the cleavage step and the dimple size were in nanometer or quasiatomic scale.
Characterization of latent image by surface energy determined by contact angle measurements
Authors: Fadda E. , Berenguer M. , Clarisse C.
Published: July 2002

The resist processes used for optical lithography are mainly positive tone, based on the use of DNQ/novolac photoresists. The decrease in feature size requires a good knowledge and control of each step. The formation of the latent image is one of the more critical steps as it is very difficult to control and the quality of the subsequent steps is mainly governed by the quality of this image. This paper proposes to use contact angle measurements to follow resist surface modifications occurring during exposure. This technique leads to the determination of the different components of the surface energy. The correlation between Fourier transform infrared analysis and surface energy components has shown that contact angle measurements allow the latent image formation to be followed.
Effect of CO and CO2 addition to the CF4/O2 gas system on the etching of a low-pressure chemical vapor deposition tungsten film
Authors: Kwon Sung Ku , Kim Kyung Nam , Nam Chul Woo , Woo Seong Ihl
Published: July 2002

The effect of CO and CO2 addition to a CF4/O2 plasma on the etching characteristics of a low-pressure chemical vapor deposition tungsten film has been studied in a reactive ion etching reactor. Mass spectrometry and optical emission spectroscopy were used to monitor gas phase species at various compositions of etching gas. The main role of CO is scavenging F and O atoms, while that of CO2 is increasing the concentration of the O atom. The addition of a small amount of CO (1 sccm) to a CF4/O2 plasma enhances the etch rate of tungsten. With the addition of CO2, the etch rate of tungsten increases until the flow rate increases up to 5 sccm. The selectivity of W to SiO2 by adding CO and CO2 are 3.2 and 4.1, respectively. These values are relatively high when compared with the maximum selectivity of 2 in a CF4/O2 gas system.
Flat panel display prototype using low-voltage carbon field emitters
Authors: Tcherepanov A. Y. , Chakhovskoi A. G. , Sharov V. B.
Published: July 2002

A new flat panel display technology is based on low-voltage self-aligned field emission micro-triodes made from graphite material. Experimental displays demonstrated brightness of 130 candelas/m2 at gate voltages in the range 20–50 V and screen bias in the range 300–1000 V. Complete control of brightness was achieved with a small signal of 10–20 V about the gate voltage. The best devices operated at gate voltages of 22 V in the dc and pulse mode; 60%–90% of the emitters worked. The power loss in the gate was less than 20%. Certain design and fabrication ideas may be developed to achieve significantly higher performance of cathodes and displays fabricated with the described technology.
Dose contribution of heating in electron-beam lithography
Authors: Svintsov A. A. , Zaitsev S. I.
Published: July 2002

We present further results of a new fast method of simulating heating effects in e-beam lithography. The method suggested allows direct calculation of additional dose due to heating, and not only temperature distribution as in earlier articles. It predicts heating influence which exceeds the technological level beginning from 3–5 A/cm2 for current density and 1–2 μC/cm2 for resist sensitivity (rather modest values for modern powerful e-beam machines). As the first step of heating correction we suggested and realized a procedure considering the internal effect only, which showed remarkable improvement and high efficiency.
Magnetic force microscopy analysis of the micromagnetization mode of double-layered perpendicular magnetic recording media
Authors: Homma T. , Kurokawa Y. , Nakamura T. , Osaka T. , Otsuka I.
Published: July 2002

The micromagnetization mode of double-layered (DL) perpendicular magnetic recording (PMR) media, as well as the single-layered one, was investigated by a magnetic force microscopy (MFM) in order to clarify the origin of their recording characteristics. The DL media were flexible disks consisting of a CoNiReP PMR layer and a CoB (soft magnetic) or CoNiP (hard magnetic) underlayer, which were recorded using a ring-type head. Due to the variation in the underlayer characteristics, a clear difference in the stray field gradient at the transition region of the recorded magnetization was observed for the first time, which proved the validity of the presumed model for their magnetization mode. Such a direct analysis of the micromagnetization mode is possible only by MFM, and this technique is considered to be indispensable for optimizing the total design of PMR systems.
In situ observation of the tip shape of AuGe liquid alloy ion sources using a high voltage transmission electron microscope
Authors: Driesel W. , Dietzsch Ch. , Mühle R.
Published: July 2002

A AuGe liquid alloy ion source was observed in situ under various operating conditions in a 1 MeV transmission electron microscope. The formation of a field-stabilized liquid cone, the change in the cone shape as a function of ion emission current, spatial shifts of the liquid cone, and microdroplet emission were investigated. Below the onset voltage the shape of the tip covered with liquid AuGe alloy is spherical. At the onset voltage a Taylor cone is formed. At ion emission currents Ie larger than 4 μA a jetlike protrusion at the Taylor cone vertex can definitively be seen. At lower emission currents possible jet formation cannot be identified unambiguously. The cone half-angle α decreases linearly with the ion emission current, while the jet length and the jet diameter increase linearly with Ie. Emission of microdroplets was observed from the surroundings of the Taylor cone region. Microdroplets with a radius between 80 and 2300 nm are emitted in time intervals of about 0.1 s and more.
Theory of beam-induced substrate heating
Authors: Groves T. R.
Published: July 2002

In all electron, ion, and photon beam systems, the beam unavoidably deposits heat in the target substrate. Resist sensitivity varies with temperature, causing unwanted linewidth variation. Substrate heating has been studied by finite element analysis solution of the heat equation. The four-dimensional nature of the problem, three spatial dimensions together with time, leads to prohibitively long computation time. This limits our ability to obtain a physical understanding of the problem. Alternatively one can superimpose elementary analytic solutions, which have simple space-time dependency, to construct cases of practical interest. The purpose of this article is to describe mathematically the basic building blocks of a general analytic theory of beam heating, with the aim of efficiently and quickly computing temperature rise due to beam-induced substrate heating. Beam heating is most critical in writing of quartz reticles. Because of the poor thermal conductivity of quartz, the temperature rise at 10 μC/cm2, 30 A/cm2, and 50 kV is 45–85 °C, depending on pattern density. Heating is also significant for direct writing on silicon. At 10 μC/cm2, 50 A/cm2, and 100 kV, the temperature rise is 0.4–48 °C, depending on pattern density. Beam heating depends directly on the incident energy per unit area, which is given by the dose times the beam voltage. The dose is, in turn, proportional to the beam voltage, due to the increased transparency of resist layers at high voltage. Beam heating therefore increases with the square of the beam voltage. These trends suggest fast resist and low voltage as the best means of containing the effect. The latter conflicts with the need for high resolution, which requires high beam voltage. This suggests an optimum beam voltage for a given set of conditions.
HPR 506 photoresist used as a positive tone ion resist
Authors: Bruenger W. H. , Buchmann L.-M. , Torkler M. , Sinkwitz Stephan
Published: July 2002

A positive tone photo resist HPR 506 (Olin Microelectronic Materials) has been investigated for its performance under ion exposure. Experiments have been conducted with light ions (H+ and He+) in the ion projector IPLM 02 (IMS; Vienna) at an energy of 75 keV. The resist resolution proved to be ∼180 nm which is not as good as the projector resolution of below 80 nm as demonstrated with Polymethylmetacrylate. The sensitivity of HPR 506 resist in positive tone amounts to 1.2×1013 H+ ions/cm2 and 6×1012 He+ ions/cm2 with contrast numbers of 3.3 and 3.2, respectively. The dose gap between positive and negative mode is sufficiently high (factor of 3) to guarantee a good process stability. The exposure latitude for He+ exposure has a value of 15 nm. The sensitivity does not oscillate with resist thickness like in optical lithography. These performance data confirm that HPR 506 resist can be used for mix and match exposure in ion projectors and i-line steppers.
Etching processes for fabrication of GaN/InGaN/AlN microdisk laser structures
Authors: Lee J. W. , Vartuli C. B. , Abernathy C. R. , MacKenzie J. D. , Mileham J. R. , Pearton S. J. , Shul R. J. , Zolper J. C. , Hagerott-Crawford M. , Zavada J. M. , Wilson R. G. , Schwartz R. N.
Published: July 2002

Several new wet and dry etch processes required for fabrication of microdisk lasers in the III nitrides have been developed. ICl/Ar electron cyclotron resonance plasmas produce etch rates of 1.3 μm/min for GaN and 1.15 μm/min for InN at 1000 W microwave power and 250 W of rf power. These rates are substantially faster than previously investigated Cl2/Ar or CH4/H2 plasma chemistries. Selectivities of 5–6 over AlN are obtained for these materials. Wet chemical etching of AlN and InXAl1−XN in KOH-based solutions was found to be a strong function of etch temperature and material quality. The activation energy for these materials was in the range 2–6 kcal/mol, typical of diffusion-controlled processes. The KOH solutions did not etch GaN or InN at temperature as high as 80 °C.
Gate quality Si3N4 prepared by low temperature remote plasma enhanced chemical vapor deposition for III–V semiconductor-based metal–insulator–semiconductor devices
Authors: Park D. G. , Tao M. , Li D. , Botchkarev A. E. , Fan Z. , Wang Z. , Mohammad S. N. , Rockett A. , Abelson J. R. , Morkoç H. , Heyd A. R. , Alterovitz S. A.
Published: July 2002

We report the properties of silicon nitride films deposited by the electron cyclotron resonance remote plasma enhanced chemical vapor deposition method on Si substrates using SiH4 and N2. The effects of nitrogen/silane gas ratio (R=N2/SiH4), electron cyclotron resonance power, substrate temperature, and H on growth, refractive index, chemical composition, and etch rate were investigated. Nominally stoichiometric Si3N4 films were obtained with a refractive index of 1.9∼2.0 at a wavelength of 632.8 nm. The etch rate of the films in a buffered HF solution (7:1) was low (∼0.7 nm/min) and increased with increasing H2 gas flow rate and decreasing substrate temperature during deposition. Fourier transform infrared spectroscopy and high temperature thermal evolution experiments showed very small amounts of H in the films. A leakage current less than 100 pA/cm2 at a field of 2 MV/cm, a resistivity of ≳4×1017 Ω cm, and breakdown strengths of 6–11 MV/cm at a current density of 1 μA/cm2 were observed. These properties are comparable to those of Si3N4 prepared by conventional high temperature (700 °C) chemical vapor deposition. The performance of GaAs-based field-effect-transistors in switching and power applications can be enhanced substantially by employing a metal-insulator-semiconductor structure. By taking advantage of an in situ process approach, insulator-GaAs structures were successfully gated with excellent interfacial properties.
Reflectance anisotropy spectroscopy study of GaAs overlayer growth
Authors: Sobiesierski Z. , Westwood D. I. , Woolf D. A.
Published: July 2002

Reflectance anisotropy spectroscopy (RAS) has been employed to characterize the overlayer growth of GaAs onto sub to one monolayer coverages of Si δ layers deposited on the GaAs(001)-c(4×4) surface. The low growth temperature (400 °C), required to avoid spreading of the dopant away from the δ plane, has meant that the study of a RAS feature related to the linear electro-optic (LEO) effect is complicated by disordering at the GaAs surface. This disordering is induced not only by the growth temperature, but also by the presence of the Si δ layer itself. Variable thickness studies indicate that the LEO-induced signal is dependent on the field profile in the surface layer. It has been observed that the intensity of the LEO feature, as a function of Si coverage, reaches a maximum at ∼0.01 ML (∼6.4×1012 atoms cm−2) in agreement with previous studies of the site occupancy of Si δ layers.
Morphology and dissolution processes of metal sulfide minerals observed with the electrochemical scanning tunneling microscope
Authors: Higgins S. R. , Hamers R. J.
Published: July 2002

We report the use of a novel electrochemical scanning tunneling microscope (STM) in the study of surface topography and dissolution phenomena on naturally occurring metal sulfide minerals. Real time dissolution studies of galena in sulfate solution showed that at pH=2.7, the step edges are oriented with outward normal vectors parallel to 〈110〉. Atomic resolution images obtained in acidic perchlorate solution showed single vacancy sites, demonstrating the ability of the STM to resolve individual atomic species under electrolyte solutions. A novel syringe pump system was used to directly determine the effect of chloride ions on the surface structure at the onset of the adsorption process. STM images show the chloride ion produces small pits in the outermost layer of the surface. These observations underscore the importance of anionic species and their effects on the surface topography and dissolution rates. Initial investigations on pyrite and covellite suggest a potentially wide application to metal sulfide minerals, while more detailed investigations on galena illustrate some important aspects of the mineral/electrolyte interface.
Chromosome classification by atomic force microscopy volume measurement
Authors: McMaster T. J. , Winfield M. O. , Baker A. A. , Karp A. , Miles M. J.
Published: July 2002

Historically, metaphase chromosomes have been differentiated (or karyotyped), within a species using chemical banding techniques and optical microscopy. This chemical approach alters the structure of the chromosomes. Following successful work on high-resolution imaging of plant chromosomes, the volumes of complete metaphase sets of maize and barley chromosomes have been calculated from three dimensional atomic force microscopy data. These results correlated extremely well with classification by arm lengths and ratios. This study demonstrates the novel application of atomic force microscopy as a high-resolution measuring instrument for volumes of biological systems, a hitherto underused facility of the microscope. This approach will permit chromosomes to be identified and experiments performed on them without recourse to destructive chemical treatment.
Scanning thermal microscopy: Subsurface imaging, thermal mapping of polymer blends, and localized calorimetry
Authors: Hammiche A. , Hourston D. J. , Pollock H. M. , Reading M. , Song M.
Published: July 2002

We have used a platinum/10% rhodium resistance thermal probe to image variations in thermal conductivity or diffusivity at micron resolution and to perform localized calorimetry. The probe is used as an active device that acts both as a highly localized heat source and detector; by generating and detecting evanescent temperature waves, we may control the maximum depth of sample that is imaged. Earlier work has shown that subsurface images of metal particles buried in a polymer matrix are consistent with computer simulations of heat flows and temperature profiles, predicting that a 1 μm radius probe in air will give a lateral resolution of ∼200 nm near the surface, with a depth detection of a few μm. We have a special interest in polymer blends, and we present zero-frequency mode and temperature-modulation mode thermal images of some immiscible blends in which the image contrast arises from differences in thermal conductivity/diffusivity between single polymer domains. The behavior of domains is observed in real time as the blends are subjected to a slow temperature rise. We have also achieved localized differential thermal analysis of a number of polymers, and recorded events such as glass transitions, meltings, recrystallizations, and thermal decomposition within volumes of material estimated at a few μm3. This opens the way forward towards calorimetric imaging, by which it should be possible to distinguish between different regions undergoing either reversible or irreversible changes as the temperature is varied.
Fabrication and field emission study of gated diamondlike-carbon-coated silicon tips
Authors: Lee Sanjo , Ju Byeong Kwon , Lee Yun Hi , Jeon D. , Oh Myung Hwan
Published: July 2002

We have fabricated a gated silicon field emitter array for which the silicon tips are coated with a diamondlike-carbon film (DLC). Silicon oxide disks were patterned on the silicon substrate, and the tips were formed using conventional dry etching. With the oxide caps covering the tips, the insulating layer, molybdenum gate film, and aluminum parting layer were deposited. At this stage the oxide caps were removed to expose the silicon tips and a DLC-carbon film was deposited onto the tips.
Spatial-phase-locked electron-beam lithography with a delay-locked loop
Authors: Goodberlet J. , Ferrera J. , Smith Henry I.
Published: July 2002

A delay-locked loop is used in a one-dimensional demonstration of the global-fiducial-grid mode of spatial-phase-locked electron-beam lithography. A pattern-placement precision of σ∼5 nm is demonstrated under nonideal conditions. Results compare well with numerical simulations.
Programmable aperture plate for maskless high-throughput nanolithography
Authors: Berry I. L. , Mondelli A. A. , Nichols J. , Melngailis J.
Published: July 2002

One of the most serious challenges to extending lithography (by whatever radiation) into the sub-100 nm regime is mask manufacturing technology. We propose and analyze a pattern writing concept somewhat like a dot matrix printer that can expose resist with 25 nm pixels at rates needed for production lithography. It consists of a programmable aperture plate which defines an array of 3000×3000, 5 μm×5 μm apertures on 20 μm centers which is illuminated by a collimated beam of either ions or electrons. Each aperture can be blanked off by suitable electrodes and is individually addressed. The image of the array is demagnified on the wafer by 200×. The pattern is entered into the array from one edge only and is toggled across the array by shift registers. The wafer is moved in synchronism. Each pixel on the wafer is exposed 750 times by 750 different pixels to accumulate the total dose. If ions are used (e.g., H+) and a total maximum current of 3 μA is passed down the ion optical column, consistent with space charge limits, then the writing speed with 25 nm×25 nm pixels on the wafer is 1 cm2/s for an ion resist sensitivity of 3 μC/cm2. The aperture plate can be fabricated from a sandwich of 3 Si membranes and will exploit the high aspect ratio etching of 〈110〉 Si to achieve the structures that hold the blanking plates. The aperture array will measure 6 cm×6 cm. The shift register circuits clocking at about 10 MHz will be built in the spaces between the apertures and are feasible with state of the art devices.
Fabrication of multiple microcolumn array combined with field emission array
Authors: Park Jeong-Young , Lera Jared D. , Yakshin M. A. , Choi S. S. , Lee Y. , Chun K. J. , Lee J. D. , Jeon D. , Kuk Young
Published: July 2002

We made a multiple electron microcolumn array. The electron source was made of either a Si based field emission array or a nickel coated array to keep the distances among sources equal. Laser micromachining was used to obtain a self-aligned microcolumn with five lenses: an extractor, an accelerator, and an Einzel lens. The aberration of each column was greatly improved compared to anodically bonded Si lens microcolumns. The field emission electron beam pattern was obtained from a multiple microcolumn. Its I–V dependence and possible application to the electron beam lithography with high throughput is discussed.
Effective three-dimensional simulation of field emitter array and its optimal design methodology using an evolution strategy
Authors: Jung Jaehoon , Lee Byoungho , Lee Jong Duk
Published: July 2002

An effective three-dimensional finite element method analysis of electrical field is performed to obtain electric fields at field emitter tips in an array form. Considering the periodic characteristic of tips in an array form, the region for numerical analysis is reduced to a single cell with proper Neumann and Dirichlet boundary conditions. The evolution strategy is also adopted to find the optimal design condition. As an example, the maximum current density per anode area is found by the evolution strategy with design parameters of tip height and tip spacing.
Metastable-atom-activated growth of an ultrathin carbonaceous resist for reactive ion etching of SiO2 and Si3N4
Authors: Thywissen J. H. , Johnson K. S. , Dekker N. H. , Prentiss M. , Wong S. S. , Weiss K. , Grunze M.
Published: July 2002

A thin carbonaceous resist was grown by exposing a substrate to a beam of neutral metastable argon atoms in the presence of siloxane vapor. X-ray photoelectron spectroscopy and Auger electron spectroscopy data show that the resist was composed primarily of carbon. Near edge x-ray absorption fine structure spectra of samples exposed to metastable atoms show that carbon double bonds were formed during exposure. The deposited material was used as a resist for reactive ion etching into SiO2 and Si3N4. Lines in SiO2 were fabricated with widths as small as 20 nm, aspect ratios >2:1, and sidewalls as steep as 7:1.
Experimental study of field emission characteristics as a function of the emitter to anode distance
Authors: Ashihara Kazuto , Nakane Hideaki , Adachi Hiroshi
Published: July 2002

It was obtained experimentally that the fluctuation of the field emission current was increased as the anode was approached to the emitter, under a low level of the vacuum condition. It is numerically solved that the number of generated gas molecules and ions by electron stimulated desorption on the anode surface come to the emitter surface. Under ultrahigh vacuum, the number was not so different for the distance. On the other hand, under low level vacuum condition, the number was increased largely as the anode approached the emitter. So the fluctuation can be increased when the anode approaches the emitter under low level vacuum condition.
Electron-beam nanolithography, acid diffusion, and chemical kinetics in SAL-601
Authors: Dobisz Elizabeth A. , Fedynyshyn Theodore N. , Ma David , Shirey Loretta M. , Bass Robert
Published: July 2002

The work presents a unique investigation of the role of postexposure bake (PEB) on resist insolubility, PEB reaction kinetics, and the high resolution behavior of Microposit™ SAL-601. Patterns of 20–100 μm rectangles and single pass isolated lines were written on a JEOL JBX-5DII e-beam lithography system operated at 50 kV. The effects of PEB temperatures of 90–110 °C for periods of 1–11 min on resist insolubility and linewidth were examined. The samples were developed in MF-322 or acetone. The range of patterns allowed measurement of both the resist exposure curves and the line spread for each PEB condition. Insolubility in MF-322 can result from protection reactions and/or crosslinking reactions. Acetone insolubility, a characteristic of crosslinked resist, was observed at PEB temperatures of 100 °C and above. At 90 °C, acetone insolubility (crosslinking) was observed only after a PEB of 11 min. From the resist exposure curves for a sequence of PEB times, reaction orders for the PEB processes that led to resist insolubility were determined. At temperatures of 100–110 °C, reaction orders of 2.4 and 2.1 were obtained for reactions that led to insolubility in MF-322 and acetone, respectively. At 90 °C the order of reaction leading to MF-322 insolubility was 1.8. PEBs at 90 °C for 3 and 6 min produced the finest lines, with linewidths ⩽50 nm over an order of magnitude range in dose. An acid diffusion mth order reaction model, which allows for H+ loss to the surface, was introduced to analyze the linewidth measurements. In the 105–110 °C temperature range, the model best fit the data with diffusion coefficients of 4–8 nm2/s and acid loss rates of 0.003–0.005%/s.
Scanning tunneling microscope-induced luminescence of GaN at threading dislocations
Authors: Evoy S. , Craighead H. G. , Keller S. , Mishra U. K. , DenBaars S. P.
Published: July 2002

We have studied the scanning tunneling microscope-induced luminescence of GaN at low temperature. The emitted photons are investigated using bias spectroscopy techniques. Near band edge emission is detected at low temperature at tip biases exceeding Vt=3.25 V. Corresponding luminescence images reveal a correlation between threading dislocations and nonradiative recombination. A hole diffusion length of LD=30–55 nm is evaluated from the extent of the nonluminescent areas. Preliminary assessment of luminescence morphology is performed with standard cathodoluminescence.
Properties of plasma enhanced chemical vapor deposition diamond-like carbon films as field electron emitters prepared in different regimes
Authors: Evtukh A. A. , Litovchenko V. G. , Klyui N. I. , Marchenko R. I. , Kudzinovski S. Yu.
Published: July 2002

The influence of the diamond-like carbon (DLC) films deposited in different conditions on electron field emission of silicon tips has been investigated. Arrays of square based pyramidal cathodes were fabricated in n-type Si(100) using wet etching in an acid mixture. Undoped and nitrogen doped DLC films were grown by plasma enhanced chemical vapor deposition method from CH4:H2 and CH4:H2:N2 gas mixtures, correspondingly. During nitrogen doped DLC films deposition the nitrogen content in gas mixture was varied from 0% to 45%. The DLC films thickness was changed in range from 10 to 100 nm. Refractive indexes of DLC films were lower for thinner layers. The effect of preparation conditions of the DLC films on their electron emission properties (work function, threshold voltage, etc.) has been studied. For comparison of the emission properties of the structures with DLC films deposited in different conditions the threshold (onset) voltages, field enhancement factors, effective emission areas, calculated from Fowler–Nordheim plots, have been used. It was confirmed that for DLC coatings the electron field emission was substantially increased in comparison with the emission from silicon tips without the coatings, although the nonmonotonous dependence of effective work function on the refractive index of DLC films has been observed. In this context, optimization experiments with respect to the minimal value of the effective work function, which in some cases was less than 1 eV, have been performed. It was found that for the structures with nitrogen doped DLC films the emission appears at lower voltages and the calculated effective work function is 0.1 eV less than for case of the best undoped DLC films. The obtained results can be used for the development of the high efficient field emission cathodes. The model for explanation of the experimental results is presented and the role of carbon–carbon, carbon–hydrogen, and carbon–nitrogen bonds is discussed.
Study of crystal orientation in Cu film on TiN layered structures
Authors: Abe Kazuhide , Harada Yusuke , Onoda Hiroshi
Published: July 2002

The effect of underlayer texture on Cu film orientation has been studied. Cu texture correlates well with the underlayer texture. The Cu〈111〉 crystallographic orientation is enhanced on TiN film with a strong TiN〈111〉 orientation. Cu preferred orientation can be controlled by choosing an appropriate underlayer. Cross-sectional transmission electron microscope observation revealed that the Cu(111) plane grows epitaxially on the TiN(111) plane in spite of the large lattice mismatch between Cu and TiN. The atomic arrangement between Cu(111) and TiN(111) planes in TiN film deposited on Cu film has a rotational angle within ±10° around the 〈111〉 axis. On the other hand, in Cu film deposited on TiN film, there are two rotational angles: a rotational angle of 25°–30° in large Cu grain region and little rotation with rotational angle distributions less than 10° in a small Cu grain region. These results can be explained by consideration of superlattice mismatch. Cu(111) plane rotation occurs so as to have more energy stable position at coalescence stage.
Role of As4 in Ga diffusion on the GaAs(001)-(2×4) surface: A molecular beam epitaxy-scanning tunneling microscopy study
Authors: Yang H. , LaBella V. P. , Bullock D. W. , Thibado P. M.
Published: July 2002

The role of As4 molecules in Ga diffusion on the GaAs(001)-(2×4) reconstructed surface has been studied using a combined molecular beam epitaxy and scanning tunneling microscopy multichamber facility. We deposited 10% of a plane of Ga atoms onto an otherwise pristine surface, while exposed to two separate As4 beam equivalent pressures of 10−5 and 10−6 Torr. The higher As4 flux resulted in the production of fewer and larger islands, indicating that increasing the As4 flux increases the total interrogation area available to the Ga atoms before forming islands.
Surface potential of ferroelectric thin films investigated by scanning probe microscopy
Authors: Chen X. Q. , Yamada H. , Horiuchi T. , Matsushige K. , Watanabe S. , Kawai M. , Weiss P. S.
Published: July 2002

Scanning probe microscopy was used to form local polarized domains in ferroelectric thin films by applying a voltage between the gold-coated cantilever and the conductive substrate in contact mode. Two methods of visualizing the poled areas are described. The first is to detect the piezoelectric response of the films by applying a small oscillating voltage between the probe tip and the substrate. This measurement determines the local ferroelectric polarity and domain structure directly. The second method is to measure the surface potential of the poled films using scanning Maxwell stress microscopy. This does not directly address the ferroelectric behavior of the film, but rather the potential due to surface charge. We determined the surface potential dependence on pulse voltage and duration applied to the ferroelectric film. The results demonstrate that the charged area will increase rapidly, but the surface potential will saturate as the pulse voltage and duration are increased. The resultant stable localized surface charge features indicate that lead zirconate titanate thin films are promising candidates for high-density charge storage media.
Selectivity to silicon nitride in chemical vapor deposition of titanium silicide
Authors: Maa J. S. , Howard D. J. , He S. S. , Tweet D. J. , Stecker L. , Stecker G. , Hsu S. T.
Published: July 2002

A high selectivity to silicon nitride in the chemical vapor deposition of titanium silicide is needed to avoid deposition on the spacer region along the sidewalls of polysilicon structures. Deposition was performed in a rapid thermal chemical vapor deposition system using a mixture of TiCl4, SiH4, SiH2Cl2, and H2. Silicide film was found to deposit on silicon nitride film at conditions when deposition on oxide was not observed. The selectivity was found to depend on the flow rate of TiCl4. A higher flow rate reduced the silicide deposition on the silicon nitride, but also increased the consumption of substrate silicon. Good selectivity to silicon nitride at a lower TiCl4 flow was achieved at a lower wafer temperature. The Si/N ratio of the nitride film also affects silicide growth, but it is not a primary factor. The effect of SiH2Cl2 flow on selectivity was not detected. It is proposed that the growth on silicon nitride starts from the formation of a finely grained TiN film followed by the formation of TiSi2.
Moving boundary transport model for acid diffusion in chemically amplified resists
Authors: Croffie Ebo , Cheng Mosong , Neureuther Andrew
Published: July 2002

We propose a general model for latent image formation in chemically amplified resists. The model is based on a moving boundary acid transport concept that incorporates transient free volume generation and densification. It is based on experimental observation of negligible acid diffusion in polyhydroxysterene below Tg. The model offers insight into the post exposure bake (PEB) reaction mechanism that governs the relief image formation in chemically amplified resists. During PEB, there is a thermally induced deprotection catalyzed by the photogenerated acid that produces volatile by-products thereby generating free volume in the resist polymer. The free volume enhances local diffusivity of the acid. The rapid loss of the volatile products is followed by relaxation of the polymer matrix which eliminates the transient free volume and densifies the polymer. The densified polymer inhibits the diffusion of any acid trapped in the deprotected sites. We present cases where the model reduces to Fickean and case II type reaction driven diffusion models under some simplifying assumptions. The model was implemented in simulation tools for resist models to simulate one-dimensional and two-dimensional profiles. The results imply that the relief image formation depends strongly on both the mechanical the chemical properties of the resist. This model provides new directions for resist process optimization.
Study of acid diffusion in a positive tone chemically amplified resist using an on-wafer imaging technique
Authors: Lu Bing , Taylor James W. , Cerrina Franco , Soo Choi Pheng , Bourdillon Antony J.
Published: July 2002

In this article, the acid diffusion coefficient of Shipley positive tone resist, UV-III, in an as-spin coated film is determined by using an on-wafer imaging technique. This technique involves incorporation of a pH-dependent fluorescence material, 5-aminofluorescence, into the resist. This fluorescence material images the acid distribution by generating fluorescence intensity contrast under a confocal microscope. Using a laser beam of 488 nm wavelength and an objective lens of 100× (with oil immersion), the nominal feature sizes of 0.20 μm can be resolved with a high signal-to-noise ratio. The acid diffusion coefficient is determined from 1 μm lines and spaces (1:9), which are generated by e-beam writing under different post exposure baking (PEB) times. The value obtained during the PEB is smaller than 3.5×10−13 cm2/s. The resist properties (e.g., sensitivity, resolution, and thermal stability) are not changed significantly by the low loading of the fluorophore because the dose to size and the printed linewidth are very close to the conditions for resist processing without the fluorophore.
X-ray multilevel zone plate fabrication by means of electron-beam lithography: Toward high-efficiency performances
Authors: Di Fabrizio Enzo , Gentili Massimo
Published: July 2002

X-ray microscopy is a research area in which enormous progress has been made in the last years. The advent of third-generation synchrotons, together with the progress made in the fabrication of new optical devices, such as zone plate, are the two main factors that have influenced the interest around microscopy science. The article will treat the fabrication, by means, exclusively, of electron-beam lithography, of high-efficiency zone plates for x rays in the energy range of hard x rays. We were able to fabricate four-level zone plates made of gold and nickel, whose total thickness is 2.1 μm for gold, and 4.0 μm for nickel. The resolution, of the last level, is equal to 0.5 μm. These zone plates have experimental efficiency of about 38% in the case of gold, and 55% in the case of nickel, at the first diffraction order and at 7 keV x-ray energy. To our knowledge, the nickel zone plates have the highest efficiency ever obtained at x-ray wavelengths.
Two dimensional dopant and carrier profiles obtained by scanning capacitance microscopy on an actively biased cross-sectioned metal–oxide–semiconductor field-effect transistor
Authors: Zavyalov V. V. , McMurray J. S. , Stirling S. D. , Williams C. C. , Smith H.
Published: July 2002

Scanning capacitance microscopy (SCM) was developed to measure two dimensional (2D) dopant and carrier profiles on passive semiconductor devices. This capability has now been extended for the first time to electrically biased cross-sectional devices. An electrical bias is applied to the source/drain of a device while a SCM image is being acquired. 2D SCM profiles are obtained as a function of applied bias, providing a method for determining the carrier distribution in a functioning device. The acquired SCM data is converted to carrier density using a physical conversion model developed for 2D dopant profiling. The SCM carrier profiles agree qualitatively with the predictions of device simulation. The SCM imaging of actively biased devices provides a means to directly compare electrical device characteristics with electrical device and process models. The measured carrier profiles may eventually be used to improve the accuracy of the 2D dopant profile extracted from the SCM data.
Field emission properties of carbon nanotubes
Authors: Gröning O. , Küttel O. M. , Emmenegger Ch. , Gröning P. , Schlapbach L.
Published: July 2002

We have investigated the field emission properties of nanotube thin films deposited by a plasma enhanced chemical vapor deposition process from 2% CH4 in H2 atmosphere. Depending on the deposition of the metallic catalyst [Fe(NO3)3 in an ethanol solution or sputtered Ni] the nanotube films showed a nested or continuous dense distribution of tubes. The films consisted of multiwalled nanotubes (MWNTs) with diameters ranging from 40 down to 5 nm, with a large fraction of the tubes having open ends. The nanotube thin film emitters showed a turn-on field of less than 2 V μm−1 for an emission current of 1 nA. An emission site density of 10 000 emitters per cm−2 is achieved at fields around 4 V μm−1. The emission spots, observed on a phosphorous screen, show various irregular structures, which we attribute to open ended tubes. A combined measurement of the field emitted electron energy distribution (FEED) and the current-voltage characteristic allowed us to determine the work function at the field emission site. In the case of the MWNT thin films and arc discharge grown MWNTs we found work function values around 5 eV, which agree well with the global work function of 4.85 eV we determined by photoelectron spectroscopy. From the shape of the FEED peaks we can conclude that the field emission originates from continuum states at the Fermi energy, indicating the metallic character of the emission site. In the case of single-walled nanotubes we found significantly lower work function values of around 3.7 eV compared to those of MWNTs. We attribute this to a size dependent electrostatic effect of the image potential, which lowers the work function for small (<5 nm) structures.