bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of field-emission columns for next-generation MEBES® systems
Authors: Pearce-Percy H. , Abboud F. , Garcia R. , Mankos M.
Published: July 2002

To support device generations below 250 nm mask writing systems must improve productivity for smaller design address grids and simultaneously provide higher dose to support high resolution processes. Combining multipass writing techniques with higher pixel rate provides improved productivity and increased dose; however, many high resolution processes require even higher dose delivery. The optimization of field-emission systems for maximum effective brightness has been discussed previously, but the inclusion of electron-electron (e-e) interactions in the optimization process is a significant complication. There is little discussion in the general literature, except for Brodie and Meisburger [A. D. Brodie and W. D. Meisburger, Microelectron. Eng. 17, 399 (1992)] about the impact of e-e interactions on the design of columns for electron-beam lithography systems. This article discusses several formulations of the problem and the solutions. Closed-form solutions for particular special cases (spherical- and chromatic-aberration limited systems) have been derived using the computer algebra code Mathematica and will be presented. The design of an improved field-emission gun and column is described, based on these general considerations, and on an acceleration-mode gun lens with particularly low chromatic aberration. Several improvements in the column design are discussed. These include optimization of the gun and the column for highest dose (800 A/cm2) without increasing the beam energy of 10 keV. Although the transmission-line beam blanker design in the current MEBES column is sufficient for higher pixel rate requirements, the blanker driver rise and fall times need improvement. Early results from the new driver have been described previously [A. Muray, D. Colby, R. Teitzel, and M. Gesley, J. Vac. Sci. Technol. B 13, 2488 (1995)]. Later improvements and experimental results are discussed, including 250 ps rise and fall times and leading as well as trailing edge TAP settings.
Surface micromachined membranes for tunnel transducers
Authors: Wong Joyce , Scherer Axel , George Thomas
Published: July 2002

We have developed low-temperature surface micromachining procedures for the fabrication of suspended SiO2/Si3N4 membranes. This fabrication method was integrated with electron beam lithography, anisotropic ion etching, and electroplating to construct electrostatically deflectable tunnel transducers. We show the structures and some preliminary measurements on the performance of these monolithic devices.
Direct epitaxial growth of thin-film structures
Authors: Eres Gyula , Hui Frank Y. C. , Thundat T. , Joy D. C.
Published: July 2002

In this article we describe a method for direct epitaxial growth of thin-film structures using a combination of resistless electron beam lithography and supersonic molecular beam epitaxy. Electron beam irradiation of a surface hydride layer on silicon induces hydrogen desorption and hence alters the surface reactivity of the exposed area. Introduction of a source gas concurrently with, or immediately following electron beam exposure results in a pattern formation on the exposed area. Continuous silicon oxide patterns with linewidths below 0.1 μm have been achieved. The resulting pattern can be also used as a mask for subsequent selective growth on the unexposed area. Supersonic molecular beam epitaxy is a highly nonequilibrium film growth method that uses translationally hot source gas species generated by a high pressure gas expansion. Since the reactivity of the source gas molecules depends exponentially on the incident kinetic energy, the chemical selectivity of the film growth process can be altered by tuning the incident kinetic energy. Arbitrary patterns with linewidths on the order of 0.1 μm have been achieved with Si, Ge, and SiC epitaxy on Si (100) and Si epitaxy on Ge (100).
Selective etching of AlGaAs/GaAs structures using the solutions of citric acid/H2O2 and de-ionized H2O/buffered oxide etch
Authors: Kim Jong-Hee , Lim Dae Ho , Yang Gye Mo
Published: July 2002

Etching results using the solution system of citric acid/H2O2 and de-ionized H2O/buffered oxide etch are shown to provide good selective wet etching of AlGaAs/GaAs structures. For AlxGa1−xAs (x<0.5) layers the selective characteristics of each Al composition strongly depend on the volume ratio of the citric acid/H2O2 solution. The turning volume ratio of the solution, at which etching starts, sensitively depends on Al composition. Additionally, the etch rate of AlyGa1−yAs (y>0.7) quickly decreases with decreasing Al composition in de-ionized H2O/buffered oxide etch solution, providing a high degree of etching selectivity. These simple selective etching processes have been applied to define AlAs/GaAs distributed Bragg reflector mesas in a vertical-cavity surface-emitting laser structure.
Current status of single ion implantation
Authors: Shinada Takahiro , Kumura Yoshinori , Okabe Jun , Matsukawa Takashi , Ohdomari Iwao
Published: July 2002

The current status of single ion implantation (SII) which has been proposed as a novel technology to suppress the fluctuation in dopant number in fine semiconductor structures is reported. The key to control the ion number is to detect secondary electrons (SEs) emitted from a target upon ion incidence. By improving the SE detection system, we have achieved the efficiency of 90% which ensures the reduction in the fluctuation of dopant number to 30% compared to the conventional ion implantation. The improvement for the better SE detection efficiency has turned out to also be effective for the precise beam alignment. The single ion incident position can now be successfully controlled with an error of less than 0.3 μm.
Hole transport investigation in unstrained and strained SiGe
Authors: Bufler F. M. , Graf P. , Meinerzhagen B. , Fischer G. , Kibbel H.
Published: July 2002

Ohmic majority and minority drift mobilities are calculated for holes in unstrained and strained SiGe up to Ge contents of 30% and doping concentrations of 1020 cm−3. The transport model is based on three analytical hole bands and is therefore suitable for Monte Carlo simulations of npn heterojunction bipolar transistors with position-dependent Ge profiles. The band parameters have been adjusted to full band structure data obtained by the nonlocal empirical pseudopotential method including spin-orbit interaction. In strained SiGe the theoretical in-plane mobility component is compared to literature data and new experimental measurements. The theoretical results indicate an appreciable increase of the mobility for the highest Ge concentrations. In addition, the effective valence-band densities of states are computed.
Nanometer scale selective etching of Si(111) surface using silicon nitride islands
Authors: Ha Jeong Sook , Park Kang-Ho , Yun Wan Soo , Lee El-Hang
Published: July 2002

Formation of silicon nanopillars via selective oxygen etching of Si(111) surface using silicon nitride islands in the initial stage of nitridation was investigated by scanning tunneling microscopy and low energy electron diffraction. Silicon nitride islands with diameters of 6–15 nm, which were formed by low energy nitrogen ions, were resistive to O2 exposure at high temperatures resulting in silicon nanopillars as high as 2–3 nm. Existence of high density silicon nitride islands is considered to suppress the step flow etching of nearby silicon surfaces, resulting in a spatially nonuniform etching of silicon.
Incremental-growth model for the deposition of spatially modulated thin film nanostructures
Authors: Hodgkinson Ian , Wu Qi Hong , McPhun Adrian
Published: July 2002

An incremental-growth model is described for the deposition of thin dielectric films with spatially modulated columnar nanostructures. Expressions, relating the ratio of the peak-to-peak modulation depth and the spatial wavelength or pitch to extreme deposition angles, are listed for the special cases of sinusoidal modulations in the deposition plane and helical columns that grow normal to the substrate. The deposition of a nanostructure modulated perpendicular to the deposition plane is, as well, demonstrated. In each case simulations made using the model display features that are similar to those shown in scanning electron microscope photographs recorded for fractures in appropriate planes.
Evaluation of trifluoroiodomethane as SiO2 etchant for global warming reduction
Authors: Fracassi F. , d’Agostino R.
Published: July 2002

The utilization of CF3I in the plasma assisted dry etching of SiO2 has been studied in order to reduce the environmental impact of microelectronics device fabrication. The results show that CF3I is a promising substitute of CF4 in oxide etching since its utilization reduces 3–3.5 times the contribution to the global warming, nevertheless it still has a consistent effect on the environment for the plasma assisted formation of perfluorocompounds.
Metrology study of structural transfer accuracy in fabrication of high-aspect-ratio microelectromechanical systems: From optical mask to polished electroplated parts
Authors: Malek C. Khan , Wood R. , Dudley B. , Genova P.
Published: July 2002

This article focuses on some fabrication issues and characterization at various steps of the LIGA [German acronym for Lithorgraphy, Galvanoplasty, and molding (Abformung)] process, in particular on the acuity of pattern transfer through the various steps of the process, from the optical mask to planarized electroplated parts for basic LIGA processing (single level). Metrology data on the accuracy of the LIGA process as currently applied in the high-aspect-ratio microelectromechanical systems (HI-MEMS) Alliance at various stages of the process are presented and the sources of process biases are investigated. Some potential areas for improvement with respect to dimensional control will also be highlighted.
Characterizing GHOST proximity effect correction effectiveness by determining the worst-case error
Authors: Watson G. Patrick , Berger Steven D. , Liddle J. Alexander
Published: July 2002

Background proximity effect corrections such as GHOST and the proposed SCALPEL correction technique have been analyzed to determine how well they can perform in situations where the correction dose distribution is not ideal. A technique has been developed that evaluates the largest possible correction dose error by determining the worst-case exposure pattern. This pattern is found to be unlikely to occur in integrated circuit patterns, so that the dose errors found in realistic situations are expected to be much smaller. For Gaussian shaped GHOST correction energy distributions, the worst-case pattern resembles a disk or a bull’s eye. The optimal correction dose distribution has a width parameter of about 90% of the backscatter width. The worst-case background dose error is less than +/−2% for a backscatter coefficient of 0.40. For a correction dose that resembles a disk of constant intensity, the worst-case error is typically larger than the case of a Gaussian shape. The smallest worst-case error occurs with a correction disk radius of 1.2 times the backscatter range for a backscatter coefficient of 0.50. The smallest worst-case error is +/−10% or one half of that, +/−5%, for practical pattern density ranges. The SCALPEL correction dose profile is ring shaped and the worst-case background error can be nearly as large as the backscatter coefficient. The worst-case error concept is used to search for the optimum ring shape; a worst-case error as small as +/−3% is possible with the appropriate correction ring characteristics.
Lie algebraic aberration theory and calculation method for combined electron beam focusing-deflection systems
Authors: Hu Kangyan , Tang T.-T.
Published: July 2002

Lie algebraic deflection aberration theory is presented and applied to combined magnetic focusing-deflection systems. Employing this new algebraic tool, all third- and fifth-order canonical aberrations (including canonical position and momentum aberrations at arbitrary observation planes) for combined systems are derived. The results are complete with concise forms. An example of an in-lens deflection system is calculated for high-order geometric aberrations through fifth order. This article lays the groundwork for further studies on the computation and optimized design for higher-order aberrations of scanning probe systems.
In situ Ga+ focused ion beam definition of high current density resonant tunneling diodes
Authors: See P. , Linfield E. H. , Arnone D. D. , Rose P. D. , Ritchie D. A. , Jones G. A. C.
Published: July 2002

Results are presented for small embedded tunnel area (<100 μm2), high current density resonant tunneling diodes (RTDs) fabricated using a combination of in situ Ga+ focused ion beam (FIB) implantation with molecular beam epitaxial regrowth. In such devices, the tunnel current path is defined by the highly resistive disordered lattice (from the Ga+ FIB lithography) and confined to the undamaged regions. Postgrowth optical processing is then straightforward to perform. The success of this novel technique is demonstrated by systematically varying the wet etched mesa dimensions, the FIB defined tunneling area, and the ion implantation dose, with experimental data discussed in each case. Furthermore, it is shown that this approach allows a common and easy connection to an array of individual RTDs, which is of considerable interest for microwave and millimeter wave power combining applications.
Real-time Fourier transform infrared spectroscopy study of the kinetics of acid-catalyzed negative-tone resists based on hexamethoxymethylmelamine and phenolic resins
Authors: Dentinger Paul M. , Taylor James W.
Published: July 2002

The kinetics of the acid-catalyzed reaction in the novolac-based, negative-tone resist SAL 605 (Shipley Co.) and similar formulations were studied with Fourier transform infrared spectroscopy with an in situ hot plate. Real-time measurements of the reaction kinetics were made in a matrix identical to the lithographic conditions and without interference from the development step. The reaction order in the acid concentration was measured to be 1.2±0.15 at 113 °C, and the overall activation energy was measured to be 113±11 kJ/mol for SAL 605. A kinetic model was explored to explain the observed results. The model invoked the general acid catalysis shown in a prior publication [P. M. Dentinger, K. G. Knapp, G. W. Reynolds, J. W. Taylor, T. H. Fedynyshyn, and T. A. Richardson, Proc. SPIE 3331, 568 (1998)], and that the rate constant for the first link of a hexamethoxymethylmelamine (HMMM) was significantly greater than the rate constant for a second link. This model can be simplified to aid in chemically amplified resist modeling efforts and all parameters may be determined experimentally under similar conditions as the lithography and without interference from the dissolution process. A direct comparison of novolac-based and poly(4-hydroxy)styrene (PHS)-based negative resist formulations showed that the reaction rate was slightly faster for the PHS resin near lithographic bake times. The PHS system also appeared more able to form additional links per HMMM than novolac. However, a difference in dose to print between similar formulations of the two phenolic resins appears to arise largely from a reaction of the resin/HMMM matrix to the developer and is only a small function of the postexposure bake kinetics.
Lifetime and reliability results for a negative electron affinity photocathode in a demountable vacuum system
Authors: Sen P. , Pickard D. S. , Schneider J. E. , McCord M. A. , Pease R. F. , Baum A. W. , Costello K. A.
Published: July 2002

Negative electron affinity photocathodes may have useful applications as electron sources for high-throughput microlithography [A. Baum et al., J. Vac. Sci. Technol. B 15, 2707 (1997)]. However, the nature of such a system has raised questions about the lifetime and reliability of a cathode during operation. In this article, we report on the lifetime and reliability of cathode operation under various conditions applicable to lithography. To perform these measurements, a 632 nm laser was focused onto a spot smaller than 10 μm in diameter on the back surface of the cathode (active area 0.5–2.0 μm thick). The emitted electrons were accelerated to 5 kV to form a magnified image of the cathode on a phosphor screen 1 m away. The 1/e lifetime of the cathode was measured as a function of the cathode current, which turned out to be an inverse relationship. Additionally, a wafer coated with SAL-601 resist was substituted for the phosphor screen to determine if resist outgassing induced by exposure affected operating lifetime. It was found that the cathode had a lifetime (75 h at 165 nA) that was the same as that obtained without the wafer under similar conditions. Lifetime was also found to be a function of initial level of cesiation of the surface and cesium levels during activation. In particular, when the cathode was initially overcesiated, the Faraday cup current (in the plane of the phosphor) was found to be stable to 2% for up to 3 days at 200 nA, indicating that the cesium level that optimizes lifetime is not necessarily the same level that optimizes quantum efficiency.
Mask membrane deflection caused by mask tilt during the wafer stepping motion in x-ray steppers
Authors: Uchida Norio
Published: July 2002

A new analysis method for deflection of the mask membrane during the wafer stepping motion in x-ray steppers has been developed. The deflection is caused by the wedge action of the gas film between the mask and the wafer if the mask tilts slightly relative to the plane on which the wafer is traveling. The deflection is not only detrimental to the throughput of x-ray steppers, it may also damage the mask membrane. Lees’ difference approximation method is applied to Reynolds’ equation for the gas film and the equation of motion for the membrane. The results calculated show good agreement with the experimental results (Ref. 1) obtained by Canon Inc. (1) The larger the tilt angle of the mask and the narrower the mask-to-wafer gap, the larger the deflection of the mask membrane. (2) In order to maintain the deflection of the membrane within 1 μm in the calculated mask, the tilt angle of the mask must be within 20 μrad under conditions of a 15 μm mask-to-wafer gap, a 30 mm stepping distance, and a wafer velocity of 100 mm/s. If the stepping distance becomes longer, the tilt angle must be more strictly controlled.
Enhancement of emission characteristics for field emitters by N-doped hydrogen-free diamond-like-carbon coating
Authors: Kang Ho Kwan , Kim To Hoon , Moon Sung , Jung Jae Hoon , Oh Myung Hwan
Published: July 2002

The nitrogen-doped diamond-like-carbon (DLC) coating on the molybdenum field emitter arrays (Mo-FEAs) was reported to improve the electron emission characteristics. The plasma enhanced chemical vapor deposition method using a layer-by-layer technique was applied to deposit DLC films. Field emission characteristics were measured and the possibility of applying N-doped DLC coated emitters to high frequency vacuum devices was reported. The turn-on voltage of DLC coated FEAs was decreased from 75 to 55 V and the emission current was more stable than that of noncoated FEAs. The total transconductance of FEAs was increased and the effective work function of emitters was reduced by the N-type DLC coating.
Self-organization in Si/CoSi2(111) heteroepitaxy
Authors: Meyer T. , Klemenc M. , Graf T. , von Känel H.
Published: July 2002

We present a scanning tunneling microscopy study of the initial stages of epitaxial Si overgrowth of CoSi2(111) films. Under suitable growth conditions the silicon was found to decorate the steps of the silicide. This opens up the possibility of creating arrays of parallel silicon wires on a CoSi2 substrate. After oxidation of the silicon by exposing it to air the silicide in between the wires can be removed by wet etching, leaving an array of expitaxial CoSi2 wires. The mechanism leading to the formation of the silicon wires was identified as strongly enhanced diffusion of adatoms on a silicide surface compared to a silicon surface and preferential nucleation on upward steps.
Electric-field modified atomic beam holography
Authors: Fujita Jun-ichi , Kishimoto Tetsuo , Mitake Satosi , Shimizu Fujio
Published: July 2002

We report a demonstration of electric-field modulated atomic beam holography. The phase of the Ne atomic wave is modified by the quadratic Stark effect when an atom passes through the hologram. A combination of an electrode array and a two-dimensional through-hole hologram works as the phase hologram. Such a phase hologram not only eliminates nondiffracted images, but also makes real-time pattern modification possible.
Interferometric at-wavelength flare characterization of extreme ultraviolet optical systems
Authors: Naulleau Patrick , Goldberg Kenneth A. , Gullikson Eric M. , Bokor Jeffrey
Published: July 2002

The extreme ultraviolet (EUV) phase-shifting point diffraction interferometer (PS/PDI) has recently been developed to provide the high-accuracy wave-front characterization critical to the development of EUV lithography systems. Here we describe an enhanced implementation of the PS/PDI that significantly extends its measurement bandwidth. The enhanced PS/PDI is capable of simultaneously characterizing both wave front and flare. PS/PDI-based flare characterization of a recently fabricated EUV 10×-reduction lithographic optical system is presented.
Comparative evaluation of electron-beam sensitive single layer top surface imaging and bilayer chemical amplification of resist lines process for stencil mask making
Authors: Elian K. , Irmscher M. , Butschke J. , Letzkus F. , Reuter C. , Springer R.
Published: July 2002

Hardmask-less stencil mask making requires resist masks with a high aspect ratio. Single layer top surface imaging (TSI) and bilayer chemical amplification of resist lines (CARL) were evaluated and compared, with respect of generating irregular resist features below 180 nm in a film thickness of 850 nm. Special methods for eliminating the resolution-limiting effect of the glass transition temperature (Tg) drop are described. Optimized plasma etching conditions for both thin layer imaging (TLI) techniques were developed. Finally, results of a deep silicon etching process using the TLI resist masks are presented.
Simulation of roughness in chemically amplified resists using percolation theory
Authors: Patsis G. P. , Glezos N. , Raptis I. , Valamontes E. S.
Published: July 2002

A simulator for e-beam exposure and development (SELID) is combined with molecular modeling in order to investigate the various side effects of the gelation process in the case of chemically amplified resists (CARs). The procedure is demonstrated in the case of the negative tone epoxy resist but the method is equally applicable for other resist systems (positive and negative tone) and development mechanisms. A conventional resist simulator is not sufficient for the description of characteristics related to the detailed gel structure of the resist film and it needs to be combined with a molecular model. Molecular modeling is a suitable method for the simulation of the microscopic changes occurring during the post-exposure bake and development processes in the case of CARs. Macroscopic feature changes such as free volume size, cluster formation, and surface roughness can be effectively described using percolation theory. In order to construct a molecular model of a complex resist system a 3D square lattice is considered. The lattice size is equal to the mean radius of the spherical volume occupied by a monomer, in our case about 1 nm. The lattice is filled with the polymer chains by a random walk process and the photoacid generator is randomly distributed in the lattice according to its percent content in the actual material. In the case of an actual resist pattern exposure, SELID provides the energy deposition profile after e-beam exposure. The deposited energy stored into each cell of the lattice induces acid generation and subsequent reactions. Reaction progress is simulated using the molecular model. Using the above process it has been possible to reproduce the actual experimental contrast curves and to simulate line edge roughness.
Extension of x-ray lithography to 50 nm with a harder spectrum
Authors: Khan Mumit , Han Geng , Bollepalli Srinivas B. , Cerrina Franco , Maldonado Juan
Published: July 2002

To be competitive with the next-generation lithography technologies, synchrotron-based proximity x-ray lithography (PXRL) must prove to be extendible to produce minimum feature sizes of 70 nm and below. We present here a relatively simple and practical method to improve the PXRL system performance for the replication of features down to 50 nm with reasonable process latitude at large (g≈15μ) mask–wafer gaps. Contrary to previous conclusions indicating λ=1 nm as the best operating region, we find that a significant improvement can be achieved by a modest decrease in the effective wavelength of present PXRL systems, and by the use of non-silicon-based materials in beamline filters and masks. The proposed PXRL system requires a synchrotron storage ring with slightly higher energy than older rings such as Aladdin, but well within the design parameters of the newer generation of synchrotrons, and some beamline modifications. In addition, a diamond mask substrate is also utilized to eliminate the x-ray absorption due to the Si-absorption edge at 1.75 keV.
Space-charge-induced aberrations
Authors: Winograd G. I. , Meisburger W. D. , Pease R. F. W.
Published: July 2002

The effect of Coulomb interactions in electron-beam lithography systems are usually described in terms of the blur induced by stochastic electron–electron interactions. Here, we show both by an efficient Monte Carlo simulation and by a global space-charge model, that the aberrations induced by the lensing action of global space charge can be equally significant. For a 4:1 telecentric reduction projection optics operating at 100 kV beam energy and 25 μA total current, we obtain about 150 nm blur independent of any stochastic effects. The global space-charge model requires less than 5 min computation on a 450 MHz workstation. The aberration coefficients of the global space-charge-induced lens can be evaluated, and because they scale directly with the perveance of the beam, can be used to evaluate the global space-charge effect over a wide variety of conditions. When the Monte Carlo and global space-charge models are used together, the stochastic-only portion of the beam blur can be extracted.
PREVAIL: Operation of the electron optics proof-of-concept system
Authors: Gordon M. S. , Lieberman J. E. , Petric P. F. , Robinson C. F. , Stickel W.
Published: July 2002

A proof-of-concept (POC) system was built to prove the electron optics concept of PREVAIL as a viable technology for next generation lithography (NGL), and is described elsewhere (H. C. Pfeiffer et al., J. Vac. Sci. Technology B, these proceedings; W. Stickel et al. ibid., these proceedings). The primary objective of the PREVAIL POC system is the embodiment of the curvilinear variable-axis lens (CVAL) optics which provides superior performance in terms of minimum geometric aberrations over unusually large deflection distances off the system axis (see Stickel et al.). Another major benefit of the CVAL is the minimization of the Coulomb interaction blur, since this approach permits the reduction of the column length to the smallest practical dimensions. The implementation of the PREVAIL CVAL requires a much higher degree of complexity than that of probe-forming systems, even of those which incorporate variable-axis immersion lenses [M. A. Sturans et al., J. Vac. Sci. Technol. B 8, 1682 (1990)] in the projection optics. The procedure used to establish the proper curvilinear variable-axis trajectory has required the development of hardware and software tools and is semiautomated. In this article we describe the means employed to properly establish the imaging conditions and the curvilinear trajectory of the deflected beam. Proper adjustment of the components is verified by comparison with the theoretically predicted excitation values for the deflection and axis-shifting yokes. Performance results presented by Pfeiffer et al. in terms of image blur and subfield distortion provide the proof of concept for the CVAL imaging conditions.
High emittance source for the PREVAIL projection lithography system
Authors: Golladay S. D. , Kendall R. A. , Doran S. K.
Published: July 2002

In the PREVAIL proof of concept electron beam projection lithography system, 1 mm×1 mm sq reticle subfields are illuminated and imaged to a wafer with 4× demagnification. A relatively large beam semiangle (5–8 mr at the wafer) is required to optimize resolution at the beam currents (5–15 μA) needed for high-throughput lithography. A high emittance source and illumination system have been developed which can uniformly illuminate the reticle subfield with a beam semiangle up to 16.3 mr (1/e) at the wafer. The source utilizes a tantalum single crystal 10 mm in diameter. The crystal is heated by electron bombardment incident on the side opposite the emitting surface, which is a low work function crystal plane. A variation of the “critical Köhler” illumination scheme is utilized wherein the cathode surface is imaged approximately to a square shaping aperture, and the shaping aperture is conjugate to the reticle (and the wafer). The emission is temperature limited, so care must be taken to obtain a uniform temperature distribution across the emitter surface. Long term emission current stability better than 1% is provided by servo control of the bombardment heating power. Illumination uniformity has been measured at the wafer plane using a pinhole detector. The measured 3σ variation in current density is 3.2%. On the basis of these results, the tighter specifications required for a commercial PREVAIL projection system appear achievable.
Pattern displacement measurements for Si stencil reticles
Authors: Uchikawa K. , Takahashi S. , Katakura N. , Oshino T. , Kawata S. , Yamaguchi T.
Published: July 2002

We have fabricated Si stencil reticles that are employed by a new type of e-beam projection lithography system (EB stepper). We applied a stress reduction technique to the Si membrane to improve the pattern placement accuracy. The residual stress of Si membranes which were fabricated by anisotropic etching of B-doped Si wafers in KOH aqueous solution was reduced by annealing at 1150 °C. We carried out pattern-displacement measurements for a Si stencil reticle made of a Si membrane where the residual stress was reduced to 10 MPa, and we observed that the pattern displacement error was reduced to less than 20 nm. Furthermore, the pattern displacement in the stencil reticle had a high correlation with the displacement determined from a simulation based on a finite element model. However in the same reticle, we discovered additional, comparatively small displacements in random directions, which was not expected in a membrane that had a homogeneous tensile stress. As a cause of the pattern displacement in random directions, we identified a pattern-width broadening in the dry etching process.
Influence of the mask-scattered electrons in the cell-projection lithography
Authors: Kotera M. , Yamaguchi K. , Okagawa T. , Matsuoka K. , Kojima Y. , Yamabe M.
Published: July 2002

The influence of the mask-scattered electron on the pattern exposed at the wafer surface is simulated in the cell-projection lithography optical system. In order to obtain accurate distributions in the intensity and its direction of the scattered electron from the cell mask, the so called direct simulation of the elastic and inelastic scattering events of electron trajectories is performed in the mask material. In this treatment, the mask-scattered electrons are produced not only by the multiple scattering of the primary electrons, but also by the cascade multiplication of electrons in the mask. In the present simulation model all the electron trajectories above and below the cell mask are traced considering the cell-projection lithography optical system. In the present study we will discuss the thickness necessary for the cell mask to work as the stencil mask in the projection lithography system, and the transmittance of the mask-scattered electrons and the contrast of the exposure pattern at the wafer surface is obtained.
Raster shaped beam pattern generation
Authors: Rishton S. A. , Varner J. K. , Veneklasen L. H. , Boegli V. , Sagle A. L. , Hofmann, U. , Kao H. , Wang W.
Published: July 2002

We propose a new approach to electron-beam (e-beam) pattern generation, in which the best attributes of raster scan writing are combined with beam shaping. The maximum dimension of the variable shaped flash is equal to the minimum feature size required in the pattern. The limited shaping range allows the use of very high speed, limited-resolution, digital-to-analog conversion circuits and amplifiers to form the shapes, and also allows thermal field emission cathode and optics to be used effectively, providing a very high current density. The system should support a sustained flash rate of at least 100 MHz, which is much higher than that found in conventional variable shaped beam architectures. The throughput is pattern independent and attractive for photomask fabrication at the 130 and 100 nm wafer technology nodes.
157 nm: Deepest deep-ultraviolet yet
Authors: Rothschild M. , Bloomstein T. M. , Curtin J. E. , Downs D. K. , Fedynyshyn T. H. , Hardy D. E. , Kunz R. R. , Liberman V. , Sedlacek J. H. C. , Uttaro R. S. , Bates A. K. , Van Peski C.
Published: July 2002

Lithography at 157 nm is rapidly emerging as the industry-preferred technology for the post-193 nm era. Its target application is for the 100 to 70 nm generations, and it is therefore widely viewed as a “bridge” technology before the next-generation lithographies are ready for insertion into manufacturing. Its attractiveness stems from the overlap in many areas with current practice and shared infrastructure developed for longer wavelengths. This article will review the present status of 157 nm lithography, emphasizing the technological challenges in the various subsystems: lasers, optical materials and coatings, photomask materials, photoresists, and projection tool development. Viewed as a whole, recent developments in these diverse areas are cause for cautious optimism that indeed 157 nm lithography will be ready in time, without encountering unforeseen obstacles.
Models and methods: Effective use of technology-computed aided design in the industry
Authors: Mouli Chandra V.
Published: July 2002

Modeling and simulation of semiconductor processes and devices are gaining importance in the semiconductor industry. Technology-computer aided design (TCAD) tools have the potential for rapid, inexpensive simulation experiments. But their effective use in the industry has been hampered by several limitations. This article highlights some of the problems and discusses possible approaches for the effective use of TCAD in the industry.
Modeling of ultrashallow spreading resistance probe calibration curves
Authors: Hillard R. J. , Ramey S. M. , Ye C. Win
Published: July 2002

Accurate determination of resistivity and carrier density from spreading resistance (SR) data depends heavily on the quality of the SR probes. This quality can be assessed by the shape of the calibration curve, which primarily depends on the properties and behavior of the point contact diodes. In this article, we demonstrate that the SR calibration curve can be simulated using an accurate representation of the SR equivalent circuit. This simulation includes physical models for the point contact diodes, the traditional geometric spreading resistance, and all parasitic resistances. Modeling of the point contact diode is emphasized based on measurements and analysis of the full current/voltage relationships for bulk p-type material.
Production of shallow ion-implanted layers using rapid electron-beam annealing under the condition of transient-enhanced outdiffusion
Authors: Kagadei V. A. , Proskurovsky D. I.
Published: July 2002

The effect of the transient-enhanced outdiffusion of P, As, and Sb from ion-doped silicon layers on the diffusion of the impurity into the specimen bulk during rapid electron-beam annealing has been studied. For specimens doped with P+ and As+ ions, it has been established that the average coefficient of diffusion of the impurity into the bulk under the condition of transient-enhanced outdiffusion is a fraction of that in a case where no evaporation of the impurity takes place. For specimens doped with Sb+ ions, no diffusion of antimony into the bulk of silicon under the condition of evaporation of the impurity has been revealed, but, on the contrary, a decrease in the depth of position of the impurity has been detected. The data obtained indicate that the evaporation of the impurity, in particular, its transient-enhanced outdiffusion occurring early in the process of rapid thermal annealing, slows down the diffusion of the impurity into the bulk of silicon. The possibility of harnessing this effect for the production of supershallow-doped layers is discussed.
Study of pre-equilibrium sputter rates for ultrashallow depth profiling with secondary ion mass spectrometry
Authors: Ronsheim P. A. , Murphy R. J.
Published: July 2002

Sputter rates for sub-keV primary beam energies are investigated with atomic force microscopy measurements of crater step heights. Using a 800 eV O2+ sputtering beam at an incidence angle of 50° with oxygen flooding, the surface swells as the implanted oxygen forms an altered layer. After a fluence of 1E17 O/cm2, the sputter rate reaches equilibrium. Characteristic parameters such as the depth scale offset, zd0, and the apparent initial silicon surface zSi0, are extracted from the data (0.6 and −1.3 nm, respectively), and the magnitude of the profile shift is discussed in terms of the final profile accuracy.
Effects of radio frequency bias frequency and radio frequency bias pulsing on SiO2 feature etching in inductively coupled fluorocarbon plasmas
Authors: Schaepkens M. , Oehrlein G. S. , Cook J. M.
Published: July 2002

The effect of radio frequency (rf) bias frequency on SiO2 feature etching using inductively coupled fluorocarbon plasmas is investigated. It is found that the rf bias frequency can have an important effect on SiO2 feature etch rate, microtrenching phenomena, and SiO2-to-photoresist etch selectivity. In addition, the effect of rf bias pulsing on inductively coupled fluorocarbon plasma SiO2 etching has been studied and a model that describes the data well is presented. The model assumes that fluorocarbon deposition occurs while the rf bias is off, fluorocarbon etching occurs during the first part of time that the bias is on, and substrate etching occurs once the fluorocarbon material has been removed from the substrate.
Simulation of focusing field emission devices
Authors: Lan Y. C. , Lai J. T. , Chen S. H. , Wang W. C. , Tsai C. H. , Tsai K. L. , Sheu C. Y.
Published: July 2002

Several focusing field emission devices are simulated by the MAGIC particle-in-cell code program. The emission current, anode current, and focusing effect are compared and analyzed. The results show that the coaxial focusing structure has the smallest electron dispersion width, the coplanar focusing structure has good focusing effect and simplest fabrication process, and the ridge focusing structure has the largest anode current. The overall consideration reveals that the coplanar focusing structure is the better choice for display application.
Eu
3
+
-
activated silica prepared by the alkoxide sol–gel method
Authors: Županc-Mežnar Lea , Cerc-Korošec R. , Bukovec P. , Padežnik Gomilšek J.
Published: July 2002

For the preparation of europium(III) activated silica tetraethoxysilane and europium(III) chloride were used as precursors. Powders and monoliths were prepared. The products were characterized by thermal analysis, scanning electron microscopy, ultraviolet-visible absorption spectroscopy, fluorescence spectroscopy, cathodoluminescent measurements, and extended x-ray absorption fine structure (EXAFS) analysis. With EXAFS analysis we elucidated the environment of Eu3+ ions in amorphous samples. The Eu–O distance was 0.248 nm in xerogel and 0.23–0.26 nm in the powder after heating.
Molecular-beam epitaxial growth of high electron mobility AlGaN/GaN heterostructures
Authors: Li L. K. , Turk B. , Wang W. I. , Syed S. , Simonian D. , Stormer H. L. , Lang D. V.
Published: July 2002

We report the growth of high quality AlGaN/GaN heterostructures on sapphire by ammonia gas-source molecular-beam epitaxy. By inserting a low-temperature-grown AlN interlayer during the growth of the thick GaN buffer, the piezoelectrically-induced two-dimensional electron gas (2DEG) in the unintentional doped AlGaN/GaN heterostructures exhibited substantially increased mobility. With the optimized AlN interlayer thickness of 30 nm, electron mobilities as high as 1500, 10 310, and 12 000 cm2/V s were obtained at room temperature, 77 and 0.3 K respectively. Sheet densities of 9×1012 and 6×1012 cm−2 were measured at room temperature and 77 K, respectively. The 2DEG was confirmed by strong and well resolved Shubnikov–de Haas oscillations starting at 2.8 T. Photoluminescence measurements and atomic force microscopy revealed that the densities of native donors and grain boundaries were effectively reduced in the AlGaN/GaN heterostructures with AlN interlayers.
Growth and characterization of patterned ZnCdSe structures for application in integrated R-G-B II–VI light-emitting diodes
Authors: Luo Y. , Elmoumni A. , Guo S. P. , Tamargo M. C. , Kelly S. , Ghaemi H. , Asnin V. , Tomkiewicz M. , Pollak F. H. , Chen Y. C.
Published: July 2002

We report the growth and characterization of patterned ZnCdSe structures on GaAs substrates as our initial attempt to use shadow mask selective area molecular-beam epitaxy (MBE) to integrate II–VI (Zn,Cd,Mg)Se-based red-green-blue (R-G-B) light-emitting diodes (LEDs). Patterned ZnCdSe thick layers and ZnCdSe/ZnSe quantum wells (QWs) were grown on GaAs substrates using a silicon shadow mask mounted on a mask fixture that allows the mask to be placed and removed within the MBE growth system. Excellent pattern definition and good optical properties were obtained. Integration of patterned ZnCdSe/ZnSe QWs having different thickness and Cd composition, therefore different emission wavelengths, on a single GaAs substrate was also achieved. These results will be applied to the (Zn,Cd,Mg)Se material system to integrate R-G-B LEDs on a single InP substrate.
Gas source molecular beam epitaxial growth of 77 GHz InP Gunn diodes for automotive forward looking radar applications
Authors: Franklin J. , Kuo H. C. , Liu J. , Vizcarra R. , Pao Y. C. , Cheng K. Y. , Pickrell G.
Published: July 2002

Phosphorous based gas source molecular beam epitaxy for the production application of growing millimeter wave Gunn diode structures on sulfur doped indium phosphide substrates for automotive forward looking radar applications is described. Procedures for obtaining silicon doping control in the 1015 range are outlined. Hall mobility and low temperature photoluminescence results comparable to the best results obtained using metal-organic molecular beam epitaxy and metal-organic chemical vapor deposition are reported. Process control and repeatability are discussed. 77 GHz Gunn diode radio-frequency performance results are reported.
New approach to the independent ohmic contact formation in the structures with two parallel isotype quantum wells
Authors: Sadofyev Yu. G. , Yevstigneev S. V. , Kopaev Yu. V. , Shipitsin D. S. , Shmelev S. S.
Published: July 2002

A method of forming a nonalloyed selective ohmic contact to a system of quantum wells with the same conductivity type is suggested. It is experimentally shown that for quantum wells in compositionally different layers (GaAs and InGaAs) such a contact with an InGaAs quantum well can be made by vacuum evaporation of aluminum on the mesa sidewalls.
Molecular-beam epitaxy growth and nitrogen doping of hexagonal ZnSe and ZnCdSe/ZnSe quantum well structures on hexagonal ZnMgSSe bulk substrates
Authors: Lin W. , Tamargo M. C. , Wei H. Y. , Sarney W. , Salamanca-Riba L. , Fitzpatrick B. J.
Published: July 2002

Hexagonal ZnMgSSe bulk substrates have been synthesized as attractive alternatives for the homoepitaxial growth of II–VI device structures. Hexagonal ZnSe epilayers and ZnCdSe/ZnSe quantum well structures were grown on these substrates by molecular-beam epitaxy. The cross-sectional transmission electron microscopy image shows that the ZnSe epilayer replicated the hexagonal structure of the substrate. The 6 K photoluminescence (PL) spectra of the hexagonal ZnSe layers show strong impurity-bound-exciton emissions at about 2.796 eV. No Y-line (defect-related emission) is observed in the spectra suggesting good substrate preparation and growth conditions. The 77 K PL spectra of hexagonal quantum well structures show dominant emission from the ZnCdSe well layer. Double-crystal x-ray rocking curves indicate that the ZnSe epitaxial layers and the substrates are near lattice matched. Doping of hexagonal ZnSe with nitrogen was performed. Photoluminescence spectra suggest that these samples exhibit donor-acceptor-pair emission with typical characteristics of heavily doped (compensated) samples.
Comparison of the potential fluctuations in a-Si:H measured by the optical and transport methods
Authors: Sinha A. K. , Agarwal S. C.
Published: July 2002

Hydrogenated amorphous silicon (a-Si:H) has potential fluctuations, which arise from the heterogeneities, variations in the bond angles, bond lengths, and nonuniform distribution of hydrogen and dopants, etc. We have estimated the potential fluctuations present in undoped and doped a-Si:H from the optical as well as from the transport measurements. In the optical measurements, the subgap absorption has been used to estimate the width of the potential fluctuations. In the transport method, the conductivity and the thermopower measured as a function of temperature are used to provide the width of the potential fluctuations, as shown by Overhof and Beyer. We find that in all cases, the width of the potential fluctuations measured by the optical measurements is about 20 times larger than that measured by the transport measurements on the same sample. This is explained by noting that optical absorption is a local process, which is sensitive to the short-range potential fluctuations by the order of 3 Å, whereas the transport measurements are sensitive to the long-range potential fluctuations (≈80 Å) which may have smaller width.
β-AlF3 by Au 4f7/2-referenced XPS and XAES
Authors: Lippitz A. , Boese O. , Kemnitz E. , Unger W. E. S.
Published: July 2002

Powder x-ray diffraction (XRD) defined β-AlF3 has been investigated by x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XAES). The Au 4f7/2 orbital is used for static charge referencing. This feature originates from well-defined and chemically inert 20 nm highly dispersed gold particles deposited on the sample surface. The particles, with a narrow particle size distribution, were obtained from a highly purified colloidal solution (sodium concentration below 1 mg/l). This procedure allows a determination of gold-referenced XPS and XAES data sets.
A Transcriptively Active Complex of APP with Fe65 and Histone Acetyltransferase Tip60
Authors: Cao Xinwei , Südhof Thomas C.
Published: July 2002

Amyloid-β precursor protein (APP), a widely expressed cell-surface protein, is cleaved in the transmembrane region by γ-secretase. γ-Cleavage of APP produces the extracellular amyloid β-peptide of Alzheimer's disease and releases an intracellular tail fragment of unknown physiological function. We now demonstrate that the cytoplasmic tail of APP forms a multimeric complex with the nuclear adaptor protein Fe65 and the histone acetyltransferase Tip60. This complex potently stimulates transcription via heterologous Gal4- or LexA-DNA binding domains, suggesting that release of the cytoplasmic tail of APP by γ-cleavage may function in gene expression.