bluuebunny/crossref_metadata_2025 huggingface dataset:
Field emission from amorphous diamond coated Mo tip emitters by pulsed laser deposition
Authors: Ding M. Q. , Myers A. F. , Choi W. B. , Vispute R. D. , Camphausen S. M. , Narayan J. , Cuomo J. J. , Hren J. J. , Bruley J.
Published: July 2002

Previous studies have shown that carbon films deposited on needle-shaped Si emitters by filtered cathodic arc are amorphous with a high sp2 content. These results can be ascribed to the poor thermal conductivity inherent to this geometry. Our present studies overcome this difficulty by depositing amorphous diamond films on Mo tip emitters by pulsed laser deposition. Monitoring films were grown on sapphire substrates and appeared transparent with a resistivity greater than 1×106 Ω cm, showing a typical amorphous diamond nature. Electron energy loss spectroscopy showed that the sp3 content of the film was 50% at the apex of the tip and 30% at the shank, which was lower than on planar substrates. High resolution transmission electron microscopy images revealed that the film at the apex was much denser than that at the shank, but both film showed a nano-columnar microstructure. Selected area electron diffraction confirmed that the films were amorphous in nature. Field emission from coated Mo tip emitters showed a considerable improvement in both turn-on voltage and emission current, compared with the same emitter before deposition. It has been demonstrated for the first time, that a-D films can be deposited on Mo tip emitters by pulsed laser deposition to achieve a better emission performance and the observation of this in the as-deposited structure.
Base metallization stability in InP/InGaAs heterojunction bipolar transistors and its influence on leakage currents
Authors: Caffin D. , Besombes C. , Bresse J. F. , Legay P. , Roux G. Le , Patriarche G. , Launay P.
Published: July 2002

For InP/InGaAs heterojunction bipolar transistors (HBTs), base–collector leakage current can be quite impairing by restricting their operational conditions to a very narrow emitter–collector voltage range. Results of a study on morphological degradations of various p-type metallizations to InGaAs and their effect on base–collector leakage current of InP/InGaAs double HBTs are reported here. Two kinds of base contacts were investigated. Mn/Au/Ti/Au induces high leakage current after contact annealing at temperatures as low as 300 °C. This is due to important interdiffusion of the species, and precipitation inside the base layer. Ti/Pt/Au is a good alternative, provided that the platinum layer is not too thick, and the contact annealing temperature not too high. Leakage current was found to be related to the strain induced by metal deposition, or to the morphological degradation taking place during annealings at high temperatures (metal precipitates formation inside the base layer inducing strain, and III–V elements exodiffusion). However, HBTs with Ti/Pt/Au base contacts annealed at 300 °C showed no excess leakage current and almost no morphological alteration, and contact resistances below 10−5 Ω cm2 were obtained for base doping levels above 1019 cm−3.
Study of the complex of the Schiff-base polymer with sulfate iron by magnetic force microscopy
Authors: Tian F. , Wang C. , Bai C. L. , Li W. G. , Wan M. X.
Published: July 2002

The micromagnetic distribution of the clusters of the PPH–FeSO4 complex (Schiff-base polymer with sulfate iron) was investigated by magnetic force microscopy (MFM). MFM results exhibited that magnetites (Fe3O4) were irregularly included in PPH–FeSO4 complexes. Some nanocrystalline Fe3O4 magnetites aggregated and formed magnetic clusters of 50–140 nm length. The ferromagnetic properties of the PPH–FeSO4 complex were associated with the existence of Fe3O4 magnetites. Moreover, the influence of the distance between tip and sample surface on the MFM images was also discussed. The observation suggested that MFM was a very useful tool for studying the micromagnetic structure of organic ferromagnets.
Observation of modification and recovery of local properties of polyethylene oxide
Authors: Nie H.-Y. , Motomatsu M. , Mizutani W. , Tokumoto H.
Published: July 2002

By applying large forces to the surface during an atomic force microscopy scanning, crystallized polyethylene oxide (PEO) films were modified and showed a new structure in which there are the formation of a nanometer-scale bundle structure and an increase of elastic stiffness. The modified part was removed by dropping benzene onto a rotating surface through a peeling process for the case of thin modified layers, while for thick layers, the local properties were recovered by absorbing benzene into the modified parts. In the course of these measurements, the thickness of the modified layers was estimated.
Scanning thermal microscope tip-induced chemical reaction on solid organometallic compound thin films
Authors: Zhou L. , Xu G. Q. , Ng H. T. , Li S. F. Y.
Published: July 2002

This article has successfully demonstrated for the first time a chemical reaction induced by a resistive thermal tip. The resulting structures were subsequently imaged by scanning thermal microscopy (SThM) and atomic force microscopy. The thermal conductivity contrast in SThM images suggested that palladium acetate thin film could be decomposed to palladium metal. The resulting palladium metallic features can form down to the substrate and adhere well on the substrate by using thinner precursor palladium acetate film. The effect of control resistance and tip scan rate on resulting features has also been studied. The results obtained indicate the potential application of SThM tip induced chemical reaction in device fabrication.
Automatic mask generation in x-ray lithography
Authors: Bollepalli B. S. , Khan M. , Cerrina F.
Published: July 2002

It is well known that diffraction plays an important role in image formation in any photon-based lithographic system. Some of the consequences of diffraction are reduction in contrast of the aerial image and phenomenon such as line-end shortening. In this article we explore some computational schemes which modify the mask pattern so as to minimize the diffractional effects. Several papers have been written on this problem for the case of optical lithography. Here, we consider the case of x-ray lithography only.
Practical approach to separating the pattern generator-induced mask CD errors from the blank/process-induced mask CD errors using conventional market measurements
Authors: Han Liqun , Wang Weidong , McCord Mark A. , Berglund C. N. , Pease R. F. W. , Weaver L. Suzanne
Published: July 2002

With the continuing reduction of minimum feature sizes for semiconductor wafers, the manufacturing tolerances for photomask CD errors were reduced proportionately. As a result, it has become increasingly important to separate the major sources of mask CD errors so that they can be quantified and appropriately addressed. In this article we describe a reliable, convenient and inexpensive technique for separating the blank, and process CD errors from the pattern generator CD errors using conventional market measurements on cross arrays and two-dimensional spatial frequency Fourier analyses. By taking advantage of the fact that the blank/process-induced CD error spatial distributions are known to be fixed relative to the mask blank, while the pattern generator CD error distributions are known to be fixed relative to the pattern generator, a spatial frequency domain analysis of multiple sets of CD measurements on the masks, each set printed by displacing the mask relative to the previous set, is shown to allow a simple and unambiguous separation of the two types of CD errors. These measurements also directly verify the expected result that the blank/process CD error contributors tend to have mainly low-spatial-frequency components, while the pattern generator tends to mainly have higher-spatial-frequency components. Furthermore, by utilizing this result, it is shown that a simple low-pass filter applied to a single set of market measurements provides a surprisingly accurate estimate of the relative sizes of these two error contributors. Results are presented from masks printed on two commercial mask-making systems, one optical and one e-beam.
Fresnel diffraction mask for optical projection lithography
Authors: Watanabe Hisashi , Okuda Yoshimitsu
Published: July 2002

A photomask technology, Fresnel diffraction mask (FDM) is developed in order to extend the usable depth of focus (DOF) in optical lithography on topographic substrates. By using FDM, a focal plane can be controlled. The Fresnel diffraction image near the photomask is reconstructed on a wafer through a projection lens. The ring-shaped aperture is used as a FDM to form a bright spot. The focal plane of the spot images can be successfully shifted more than 1 μm from the nominal focal plane of the optical system. The FDM produces two light intensity maxima at both sides of the nominal focal plane in the optical axis. By replacing the mask patterns on the highest and/or lowest wafer topography with FDM, the usable DOF on a topographic substrate can be extended because the original mask and FDM have different optimum focal planes.
Investigation into excimer laser radiation damage of deep ultraviolet optical phase masking films
Authors: Smith B. W. , Zavyalova L. , Bourov A. , Butt S. , Fonseca C.
Published: July 2002

A variety of materials based on various oxides, nitrides, fluorides, and composites have been found to be potentially suitable for use as attenuated phase masking materials for use at excimer laser wavelengths. Presented here are results from the investigation into 193 nm excimer laser radiation of zirconium–nitride-based, aluminum–nitride-based, chrome–fluoride, amorphous-carbon, and tantalum–silicon–nitride (TaN/Si3N4) attenuated phase-shift mask materials at fluence levels mask materials experience during wafer exposure. Spectroscopic photometric and ellipsometric methods were utilized to quantify damage through measurement of transmission and reflection properties and extraction of optical constants. Results show that understoichiometric zirconium– and aluminum–nitride materials are susceptible to radiation-induced modification through oxidation effects while tantalum–silicon–nitride and chrome–fluoride films are able to withstand exposure to several thousand J/cm2 without significant degradation.
Resist design concepts for 193 nm lithography: Opportunities for innovation and invention
Authors: Reichmanis E. , Nalamasu O. , Houlihan F. M. , Wallow T. I. , Timko A. G. , Cirelli R. , Dabbagh G. , Hutton R. S. , Novembre A. E. , Smith B. W.
Published: July 2002

Photolithography using 193 nm radiation is the leading candidate for the manufacture of 0.18–0.13 μm design rule devices. The optical absorption of materials such as novolacs, and functionalized poly(hydroxystyrenes) and styrene-acrylate copolymers which are the matrix materials of choice for G line, I line, and 248 nm lithography is significantly higher than one at 193 nm making them too opaque to be useful at this shorter wavelength. The opacity of the current photoresists at 193 nm requires innovation in designing alternative materials and processes to realize the full potential of 193 nm (ArF) lithography. From a materials standpoint, this challenge must be addressed by new chemistries and process schemes capable of providing resists with the aqueous base solubility, etching resistance, resolution, photospeed, and process latitude required for large-scale manufacturing. In addition, regulatory constraints on volatile organic chemical emissions have spurred efforts to design revolutionary resist platforms that address these concerns while providing the performance required for sub-0.18 μm device manufacture.
Optimizing the resist to the aerial image in a chemically amplified system
Authors: Fedynyshyn T. H. , Szmanda C. R. , Cernigliaro G. J.
Published: July 2002

For KrF based lithographic systems, resist design philosophy focuses on methods to maximize resist performance while providing both a reliable and cost effective lithographic process. Such systems will, out of necessity, be high sensitivity and high contrast. A key evaluation criterion for resists is the lithographic process window, as defined by the focus and exposure latitudes of the resist. As the process window is dependent on the type of feature being printed, the overlap of resist process windows between isolated and dense lines is often employed to define the overall resist process window. Two general methods can be employed to manipulate the lithographic performance. One way is to manipulate the image through the numerical aperture of the lens, coherence of the source and bias of the mask. The second is to manipulate the latent image by changing the relative response of the resist to changes in the energy dose. Both methods will directly influence the lithographic performance of the resist and will be feature dependent.
Filter design methodology for defect detection in wafer inspection
Authors: Socha Robert J. , Neureuther Andrew R.
Published: July 2002

A methodology for the design of a filter to image the bottom of a contact is developed through simulation. Without a filter, the topography of the hole causes normally incident light to refract out of the hole. By conditioning the light with a filter, however, light is launched into the hole that is capable of propagating down the hole and imaging the bottom. When using this filter, the reflected aerial image differs by as much as 10% when the contact hole is under etched by 0.05 μm. Although, this initial success shows that the filter is capable of imaging the bottom of the hole, the introduction of process variations such as a larger hole diameter or a thinner oxide cause large deviations in the aerial image.
Self-aligned subchannel implant complementary metal–oxide semiconductor devices fabrication
Authors: Wang W. , Chang C. , Ma D. , Peckerar M. , Berry I. , Goldsman N. , Melngailis J.
Published: July 2002

High-speed and low-power complementary metal–oxide semiconductor devices with subchannel implants have been proposed and demonstrated recently. In subchannel implant devices, the alignment of the gate and the buried implant region is a critical issue. In this article, a fully self-aligned gate and subchannel implant fabrication method is proposed using either focused-ion-beam or conventional ion implantation. This method defines the gate and produces the subchannel implant in the same step. By doing this, the buried implant region and gate are automatically aligned. By exposing the resist with a B+ ion beam, we verified that the dose needed to produce the subchannel implant matches the dose needed to expose the resist (1013 ion/cm2). We have simulated the implant profile and the expected device performance. The subthreshold current was found to be decreased by 1–2 orders of magnitude. Since the process requires implantation through the gate oxide, capacitors were built over the gate oxide for C–V measurement and implanted over a range of doses. Proper postimplantation treatment has been developed to prevent increasing of the interface state density.
Nonselective wet chemical etching of GaAs and AlGaInP for device applications
Authors: Zaknoune M. , Schuler O. , Mollot F. , Théron D. , Crosnier Y.
Published: July 2002

The nonselective wet chemical etching of AlGaInP and GaAs in pure iodic (HIO3) acid and in hydrochloric acid (HCl) associated different oxidant agents has been evaluated. The pure iodic acid is nonselective between III–V phosphides and arsenides. Unfortunately, the etch of GaAs results in a very rough morphology and an etch rate 10 times greater than on AlGaInP. The mixing of HCl with different oxidants such as H2O2 gives a nonselective etchant. However H2O2 dissociates HC1 to form chlorine which produces a wide evolution of the etch rate with time incompatible with the reproducibility necessary for device technology. This phenomenon is easily explained and solved using oxidant agents such as KIO3, K2Cr2O7. Added to HCl, they give chemically stable solutions but unfortunately they give rise to a strong undercut of the AlGaInP under the GaAs. The iodic acid is also a strong oxidant. Therefore a diluted solution of (HCl, HIO3, H2O) is proposed which gives an evolution of the etch rate between 300 and 3000 Å/min with water dilution, a good stability in the time, and similar etch rates on the two materials with very good morphologies. Applied to heterostructure no undercut of the AlGaInP is observed.
Two-dimensional profiling in silicon using conventional and electrochemical selective etching
Authors: Trenkler T. , Vandervorst W. , Hellemans L.
Published: July 2002

One of the methods to delineate a two-dimensional dopant profile in Si devices is the selective etching technique combined with imaging of the doping dependent topography by atomic force microscopy. A major problem of the etching procedures reported so far is the critical control of the etch duration of only a few seconds as well as a limited sensitivity and dynamic range. We report further improvements of the conventional technique and compare it to an alternative approach. Etching experiments were carried out in an electrolytic cell, whereby the etching is controlled potentiostatically. Better control of the dissolved volume is achieved through current integration. Buffered HF as the electrolyte replaces the difficult nitrogen related chemistry of the classical approach. The etch rates thereby decrease by a factor of 10–100 thus allowing for a longer etch duration. The basic mechanisms, the sensitivity, and the dynamic range of the two techniques have been studied by using homogeneous samples and special test structures for calibration and ultrashallow profiling. Two-dimensional profiling has been carried out on cross sections of 0.25 μm complementary metal–oxide–semiconductor devices with the classical and the electrochemical approaches. Problems of preparation, etching procedure, and imaging techniques are discussed in order to improve the quantification of the selective etching technique.
Comparison of secondary ion mass spectrometry profiling of sub-100 nm ultrashallow junctions using NO2+ and O2+ sputtering
Authors: Ronsheim P. A. , Lee K. L.
Published: July 2002

Secondary ion mass spectrometry (SIMS) with low energy sputtering is used to characterize ultrashallow dopant profiles. Molecular ion sputtering species help reduce the mixing depth of the sputtering process and the broadening of the measured dopant distributions. The depth resolution of NO2+ and O2+ primary beams at 2 keV net acceleration and 55° incidence angle to the sample are compared by the measurement of low energy ion implanted dopant distributions. The sputtering conditions result in a 380 eV/sputtering particle (normal to the sample surface) for NO2+, and a 570 eV/sputtering particle for O2+. Measurements of 1 and 2 keV BF2, as well as 5 keV As implants show trailing edge slopes of 2.6 nm/dec for the 1 keV BF2, and 5.5 nm/dec for arsenic. The pre-equilibrium region at the near-surface of the sample is shown to be similar for NO2 and O2, indicating that chemical segregation effects of the nitrogen in the sample are not detrimental to the profile accuracy.
Verification of “lateral secondary ion mass spectrometry” as a method for measuring lateral dopant dose distributions in microelectronics test structures
Authors: von Criegern Rolf , Jahnel Franz , Lange-Gieseler Rosa , Pearson Peter , Hobler Gerhard , Simionescu Alexander
Published: July 2002

“Lateral secondary ion mass spectrometry (SIMS)” has been demonstrated to be capable, within certain limits, of measuring the lateral straggle and diffusion of dopants under mask edges. In the present work measurements of lateral dose distributions of arsenic and boron in silicon are presented and discussed, and information on the error margins of the method derived. It is shown that the lateral dose distribution of arsenic and boron can be measured down to dose levels of 5×1012 cm−2 and 2.6×1013 cm−2, respectively. In repeated measurements, the profile shapes have been reproduced to within a few nanometers, and the profile position relative to the mask edge determined with about ±10 nm error. It is this rather high degree of accuracy that allows Lateral SIMS data to be of value in the calibration and validation of two-dimensional process simulators. An example is given showing the correlation between IMSIL (Technical University Vienna) simulation and experimental data for an as-implanted sample. By comparing experimental data from samples after dopant diffusion and at several topography variants with TMA SUPREM4 simulation, it is shown that an accurate determination of the topography of the implant window in the vicinity of the mask edge is an essential prerequisite of any simulator calibration.
Preparation of ultrasharp diamond tip emitters by ion-beam etching
Authors: Stepanova A. N. , Givargizov E. I. , Bormatova L. V. , Zhirnov V. V. , Mashkova E. S. , Molchanov A. V.
Published: July 2002

Ion-beam milling was used for sharpening of diamond particles on ends of silicon tips. The sharpened diamond samples were used as field-electron emitters. I–V characteristics of the emitters were measured. An effect of conditioning of the emitters was observed: After an emitter worked at least several hours, its current increased for several orders of magnitude and became stabilized.
Propagation characteristics of a premodulated electron beam
Authors: Jin Jeong-Gu , Park Gun-Sik
Published: July 2002

The propagation properties of an electron beam whose energy and current are simultaneously premodulated at the cathode are investigated by computer simulation using the two-dimensional particle-in-cell code, MAGIC. The simulation is carried out to investigate the influence of the initial energy modulation and phase difference between current and energy modulation. With appropriate initial energy modulation, amplitude of the downstream current modulation can be kept as high as the initial modulation level. Appreciable growth of high harmonic components is observed as the electron beam debunches. The maximum amplitude of the fundamental mode (m=1) occurs at the propagation distance, where all the other modes vanish or have a very small amplitude.
Metal–insulator–semiconductor emitter with an epitaxial CaF2 layer as the insulator
Authors: Miyamoto Y. , Yamaguchi A. , Oshima K. , Saitoh W. , Asada M.
Published: July 2002

An 8-nm-thick epitaxial CaF2 layer grown on an n+-Si substrate was used as the insulator in a metal–insulator–semiconductor cathode with a 10 μm2 emitter region. The fabricated cathodes exhibited two different types of I–V characteristics. The first type showed conventional tunnel emission current of 22 pA at an emitter current of 2.4 mA and an emitter voltage of 7 V. The emitter with the other type of characteristics showed an emission current of 5.6 nA at an emitter current of 2.2 mA and an emitter voltage of 4.5 V but it showed current instability.
Defect structure, distribution, and dynamics in diamond-on-silicon optoelectronic devices
Authors: Rossi M. C. , Salvatori S. , Galluzzi F.
Published: July 2002

The role of localized defect centers and continuous gap states distribution in photoluminescence, photoconductivity, and photoresponse time dependence of diamond films have been analyzed for different film morphology and grain orientations. Sharp spectroscopic features related to impurity centers or broad components associated with continuous distribution of gap states prevail in the spectra depending on film microstructure and deposition technique. It is shown that defects, either localized or continuously distributed, reduce carrier lifetimes and slow down carrier transport by trapping effects. The observation of metastability effects after UV illumination giving an increase of subgap photoresponse is also reported.
Electrical characteristics of heterostructure-emitter bipolar transistors using spacer layers
Authors: Lin Y. S. , Shieh H. M. , Hsu W. C. , Su J. S. , Huang J. Z. , Wu Y. H. , Ho S. D. , Lin W.
Published: July 2002

We propose an improved In0.5Ga0.5P/GaAs heterostructure-emitter bipolar transistor (HEBT) grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The recombination at p-n interface can be significantly reduced at low collector current using 100 Å undoped GaAs spacers. Meanwhile, the emitter edge thinning technique is used to reduce the surface recombination current. The passivated device reveals a current gain as high as 360, along with an offset voltage as low as 80 mV. Moreover, the measured results indicate that the current gains vary slowly with temperature. In order to demonstrate that the emitter edge-thinning technique can effectively reduce the surface recombination current, the emitter size effect on current gain is also investigated.
Pattern transfer on mask membranes
Authors: Fisher A. H. , Engelstad R. L. , Lovell E. G. , Puisto D. M.
Published: July 2002

Pattern specific emulation is facilitated by the prediction of the distortions due to pattern transfer. Using finite element (FE) methods along with equivalent modeling techniques, it is possible to determine the distortions due to the fabrication of actual mask patterns. This article presents the results of the FE simulation on x-ray lithography masks. Employing the IBM Talon mask design as an example case, the distortions in the pattern area due to the fabrication of the absorbers on the mask membrane were determined. Results are presented for both a uniformly stressed absorber layer and an absorber layer with a unidirectional linear stress gradient.
Dynamic analysis of a SCALPEL mask during electron-beam exposure
Authors: Semke W. H. , Engelstad R. L. , Lovell E. G. , Liddle J. A.
Published: July 2002

Projection electron-beam lithography, specifically the scattering with angular limitation projection electron lithography (SCALPEL) system, is a viable technology for the production of semiconductor devices with feature sizes in the sub-0.13 μm regime. A step-and-scan approach is used to expose the patterned membrane areas within the grillage structure on the SCALPEL mask. Finite element methods were employed to determine the dynamic distortions caused by an acceleration duty cycle and by various mounting techniques. The transient response of a SCALPEL mask with and without a support ring has been analyzed. Results for both an electrostatic chuck and a “3-2-1” kinematic mount are presented. They show the electrostatic mount produces significantly lower distortions than the 3-2-1 kinematic mount with a support ring.
Endpoint uniformity sensing and analysis in silicon dioxide plasma etching using in situ mass spectrometry
Authors: Chambers J. J. , Min K. , Parsons G. N.
Published: July 2002

Mass spectroscopy is used to characterize the endpoint uniformity of silicon dioxide etching in an electron cyclotron resonance (ECR) plasma etch process. Etch products are observed using a two stage differentially pumped mass spectrometry system attached to the ECR process chamber. Specifically, using CF4 and D2 etch gases, the partial pressure of CO-containing etch products decays near the endpoint, and the rate of signal decay is directly correlated with the uniformity determined from optical interferometry thickness measurements. To correlate the mass spectrometer signal with the etch rate variation across the wafer, etch uniformity is altered by changing the ECR electromagnet geometry and by modifying the initial oxide uniformity. A COF2 etch product material balance is developed to model the observed concentration versus time data, resulting in a quantitative correlation between change in endpoint slope and uniformity. The ability to utilize a process-state sensor, such as a mass spectrometer, for wafer-state information will result in new approaches for sensing, optimizing, and controlling integrated circuit fabrication processes.
Rigorous simulation of statistical electron–electron interactions with fast multipole acceleration and a network of workstations
Authors: Wen Victor S. H. , Carmichael Owen T. , Yamashita Hiroshi , Neureuther Andrew R.
Published: July 2002

Rigorous simulation, which in concept is nearly linear in CPU time with microampere beam currents, has been developed for analyzing statistical electron–electron interactions in lens free regions joined by ideal lenses and apertures. The simulation method is based on combining fast multipole acceleration (FMA) with modifications to a message passing interface for use on a multiprocessor and on a network of workstations. As test cases, the distribution of scattered electrons versus deviation from focus is given as well as results for the interaction between simultaneously imaged spots. The performance improvement per level of spatial division was only about a factor of 2 instead of the expected factor of 8 due to the pencil shape nature of the beam. A FMA method that is adaptable to beam density and geometry is needed. It is projected that it will be possible to simulate a 30 μA beam current on a quad-Pentium Pro machine in half a day and in matter of hour on a network of workstations.
Design study of compact beam lines for x-ray lithography
Authors: Toyota Eijiro
Published: July 2002

This article presents a design study of compact and high-performance beam lines for synchrotron-radiation-based x-ray lithography. The optical system is composed of a single toroidal scanning mirror and a movable beryllium window synchronized with the mirror motion. Usually the use of a toroidal scanning mirror tends to cause excessive deformation of beam shape and degradation of the focusing property of the mirror. This problem has been improved by placing the oscillating center of the mirror near the light source. The arc-shaped beam forms a concave dose distribution along the scanning centerline. A beryllium window foil with a specified curvature is used to create a uniform dose distribution. A series of analytical studies and computer simulations have been carried out to define the curvature. For example, the design study shows a compact beam line of 7 m length with a brightness of 159 mW/(cm2 A) within ±1% of dose uniformity at an exposure field of 50×50 mm.
Copolymer approach to charge-dissipating electron-beam resists
Authors: Hupcey Maggie A. Z. , Ober Christopher K.
Published: July 2002

During electron-beam lithographic exposure on insulating substrates, pattern distortions and displacements are observed due to charging of the surface. To alleviate these displacements, conducting polymers have been investigated in the past decade as negative-tone resists and as unimageable top or bottom layers in a multilayer stack. Our approach uses a graft copolymer: an acrylic backbone for the imaging performance of the resist and a conducting polymer grafted onto the backbone for the charge-dissipating performance. By using this system, the respective properties of the two components can be individually optimized for such properties as speed, etch resistance, solubility, and conductivity. This system also permits positive-tone single-layer imaging, which has not been achievable previously. High-resolution features (<0.10 μm), minimal pattern distortions, and no change in the clearing dose, were observed for graft copolymers containing <1% of the charge-dissipating component that were processed identically to commercially available PMMA resist.
Absorptive masks of light: A useful tool for spatial probing in atom optics
Authors: Keller Claudia , Abfalterer Roland , Bernet Stefan , Oberthaler Markus K. , Schmiedmayer Jörg , Zeilinger Anton
Published: July 2002

We demonstrate periodic localization of neutral atoms of better than 65 nm behind amplitude, i.e., absorptive masks made of light. With these masks, produced by a standing on resonant light wave, it is possible to create and to probe spatially well-defined atomic distributions. Applications of such absorptive masks range from atom lithography to fundamental atom optical experiments. As two examples we show how to use these gratings as a tool to measure the evolution of an atomic wave field behind a static Bragg crystal and its dependence on the incidence angle of the atomic beam and how to demonstrate the frequency shift of atoms diffracted at a modulated Bragg crystal in a beating experiment.
Atomic beam holography for nanofabrication
Authors: Fujita J. , Kisimoto T. , Morinaga M. , Matsui S. , Shimizu F.
Published: July 2002

Atomic beam holography is a unique technique by which to fabricate a nanoscale object by using the interference of matter waves of ultracold atoms. The atomic de Broglie wave coming through a hologram interferes with and reconstructs a desired structure on a substrate. We first demonstrated holographic manipulation of metastable Ne atoms of 7 nm wavelength, where we showed the reconstruction of an “F” pattern and improvement of it. In this article, we propose and show techniques to manipulate three-dimensionally cooled Ne atoms. Atomic beam holography has the potential to make atomic-size objects, and the freedom in designing the hologram enables us to make not only a binary pattern but also an analog (gray scale) pattern. The resolution demonstrated in this experiment was about 60μ, but the minimum feature size expected is theoretically the same as the wavelength, i.e., several nanometers.
Characteristics of focused beam spots using negative ion beams from a compact surface plasma source and merits for new applications
Authors: Guharay S. K. , Sokolovsky E. , Orloff J.
Published: July 2002

The characteristics of H− beams from a compact Penning-type surface plasma source have been studied with the goal of evaluating their merits for improved focused ion beam (FIB) systems. As a proof-of-the principles experiment to demonstrate the beam quality a simple, prototype source was developed without any special cooling arrangement of the electrodes. The source is operated in a pulsed mode with a maximum duty factor of 1%; and the operation can be extended to the dc mode by using water cooling. The beam brightness is estimated to be ∼0.5×105 A cm2 sr−1 at a beam energy of 7 kV, and the energy spread of the beam for angular beam intensity of ∼40 mA/sr is ⩽3 eV. The beam at an energy of 7 keV has been focused by a lens with a magnification factor of M∼0.1, and the spot size is determined by scanning a Si knife edge over the beam as well as by poly(methylmethacrylate) resist exposures. A focused spot, with diameter of ∼6 μm and current density of ∼10 mA/cm2, has been achieved. The dependence of the spot characteristics with the beam intensity from the source has been studied. The results suggest that a submicron size spot with a current density of ⩾1 A/cm2 can be generated using these beams for M∼0.01. The source, with its simple, robust technology, seems an attractive choice for FIB applications.
Thermal–mechanical performance of extreme ultraviolet lithographic reticles
Authors: Gianoulakis Steven E. , Ray-Chaudhuri Avijit K.
Published: July 2002

Thermal deformation of reticles will likely become an important consideration for all advanced lithography techniques targeting 130 nm features and below. Such effects can contribute to image placement errors and blur. These issues necessitate the need to quantify the reticle distortion, induced by the absorption of illumination power, for candidate substrate and coating materials. To study the impact of various substrate and coating materials on reticle performance, detailed three-dimensional transient thermal and solid mechanical models have been developed and extensively applied to predict total placement errors, residual placement errors, and blur on an extreme ultraviolet lithography (EUVL) reticle during scanning. The thermal model includes a bidirectional scanning heat source representative of the illumination incident on the reticle. The heat loads on the reticle are characteristic of an EUVL engineering test stand with a wafer throughput of twenty 200 mm wafers per hour (assuming 80% die coverage and 68% exposure time). This article includes the results which describe the impact of (1) different substrate materials, (2) various degrees of contact conductance between the reticle and chuck, (3) pattern density and arrangement, and (4) temperature variations across the chuck.
130 nm and 150 nm line-and-space critical-dimension control evaluation using XS-1 x-ray stepper
Authors: Tanaka Y. , Taguchi T. , Fujii K. , Tsuboi S. , Yamabe M. , Suzuki K. , Gomei Y. , Hisatsugu T. , Fukuda M. , Morita H.
Published: July 2002

Critical-dimension (CD) control for 130 and 150 nm line-and-space (L/S) patterns printed with the XS-1 x-ray stepper was evaluated using two kinds of resists: SAL606 and TDUR-N908. The largest factor in the CD variation was the nonuniformity of the x-ray dose, which was ±4.4% in a 20 mm×20 mm field. In replicated resist patterns, the CD variation due to mask-CD variation dropped to less than half the mask-CD variation because of Fresnel diffraction. For 130 nm L/S patterns, the CD variation for an 8-in.-diam wafer was 7.9 nm (3σ) for SAL606, and 12.0 nm (3σ) for TDUR-N908. For 150 nm L/S patterns, the values were 10.5 nm (3σ) and 14.6 nm (3σ), respectively. Although the major factors causing CD variation are dose nonuniformity and mask-CD variation, different resist materials reflect the effects of these factors to different degrees. The CD variation of 150 nm L/S patterns among seven wafers exposed on the same day was ±2.8 nm for SAL606 and ±3.7 nm for TDUR-N908, which is most likely due to fluctuations in the exposure dose of ±2.7%. The total CD variation for SAL606 was roughly estimated to be 9.0 nm (3σ) for 130 nm L/S patterns and 11.9 nm (3σ) for 150 nm L/S patterns. These values are within ±10% of the design rule.
Enhanced adhesion buffer layer for deep x-ray lithography using hard x rays
Authors: De Carlo Francesco , Song Joshua J. , Mancini Derrick C.
Published: July 2002

The first step in the fabrication of microstructures using deep x-ray lithography (DXRL) is the irradiation of an x-ray sensitive resist like polymethylmethacrylate (PMMA) by hard x rays. At the Advanced Photon Source, a dedicated beamline allows the proper exposure of very thick (several mm) resists. To fabricate electroformed metal microstructures with heights of several mm, a PMMA sheet is glued onto a metallic plating base. An important requirement is that the PMMA layer must adhere well to the plating base. The adhesion is greatly reduced by the penetration of even a small fraction of hard x rays through the mask absorber into the substrate. In this work we will show a novel technique to improve the adhesion of PMMA onto high-Z substrates for DXRL. Results of the improved adhesion are shown for different exposure/substrate conditions.
Adhesion promotion between poly(methylmethacrylate) and metallic surfaces for LiGA evaluated by shear stress measurements
Authors: Malek C. G. Khan , Das S. S.
Published: July 2002

The fabrication of high-aspect-ratio microelectromechanical structures (HI-MEMS) using the LiGA process [German acronym for Lithography, Galvanoplasty, and molding (Abformung)] requires both sufficient lithographic and mechanical adhesion of thick microstructures to the substrate. The interfacial bond strength between poly(methylmethacrylate) and various metal surfaces (Ti, Cu, and Au), in the preliminary stages of the LiGA process, was evaluated by shear stress measurement. In addition, adhesion promotion processes have been investigated. A mechanical type of adhesion was promoted by modifying the morphology of surfaces. Ti or Cu were microroughened by chemical oxidation and acrylic resist sheets thermally processed. The largest increase in adhesion was obtained with a combination of both substrate and resist treatments. The use of Novolak resists as interfacial layers enhanced adhesion, independently of the nature of the substrates. Severalfold increases in bond strengths were also obtained using various primers, such as 3-aminopropyl-triethoxysilane on Au and Cu substrates.
Field emission properties of BN coated Si tips by pulsed ArF laser deposition
Authors: Jayatissa A. H. , Sato F. , Saito N. , Sawada K. , Masuda T. , Nakanishi Y.
Published: July 2002

Thin films of boron nitride (BN) were deposited by pulsed ArF laser ablation of a pyrolitic BN target in an N2 ambient with and without substrate bias and also in a nitrogen plasma. The structural property studies with infrared and reflection high-energy electron diffraction show that the films possess cubic BN and hexagonal or amorphous phase of BN. Deposition of cubic BN is enhanced by application of substrate bias whereas crystallinity is degraded by the introduction of nitrogen plasma. The field emission of electrons was tested for BN coated Si tips, and it was found that the field emission of electrons enhanced when the cubic BN was coated.
Area evaluation of microscopically rough surfaces
Authors: Lai L. , Irene E. A.
Published: July 2002

In this article, a novel roughness function is developed which enables the assessment of the area of a microscopically rough surface measured by atomic force microscopy (AFM). A reliable area of a surface with microscopic roughness has proven to be difficult to compute due to the small vertical and large spatial differences which cause significant round off error in the computation. Instead of the usual procedure of computing the area of a surface directly from the data set, we utilized the fact that surface area increases with roughness. Two roughness parameters, root mean square (rms) and fractal dimension (DF) yielding vertical and horizontal information, respectively, are employed to provide a reasonably complete description of surface roughness. We show that the area of a microscopically rough surface is exponentially related to DF and quadratically to rms, and these relationships are the basis of a novel roughness function. This function is shown to be both sensitive to the changes in surface topography, and reliable in providing the area of a surface with microscopic roughness.
Application of advanced micromachining techniques for the characterization and debug of high performance microprocessors
Authors: Livengood Richard H. , Winer Paul , Rao Valluri R.
Published: July 2002

Micromachining techniques such as focused ion beam milling have become an integral part of the design debug cycle at many companies for providing fast verification of bug fixes in silicon. With flip chip packaging becoming more prevalent for future high performance processors, it is necessary to perform circuit edits and bug fixes on the silicon while the chip is packaged in the flip chip package. With this technology, however, conventional frontside probing and traditional circuit rewiring of packaged devices are not practical. We have developed a combination of new micromachining techniques for directly accessing metal signals from the backside of the chip. Here we will describe this new process, the technologies used, and some basic applications.
Reflection high-energy electron diffraction oscillations on rotating substrates
Authors: Braun W. , Möller H. , Johnson S. R. , Zhang Y.-H.
Published: July 2002

We compare different methods to measure reflection high-energy electron diffraction oscillations on rotating substrates. The best signal-to-noise ratio as well as the highest accuracy is obtained by measuring the full width at half maximum of the specular spot perpendicular to the surface. The accuracy of the method is well within 1% and offers a practical way to accurately determine growth rates for device fabrication.
GaAs/GaAs
0.8
P
0.2
quantum wells grown on (n11)A GaAs substrates by molecular beam epitaxy
Authors: Tatsuoka Yasuaki , Kamimoto Hitoshi , Kitano Yoshiaki , Kitada Takahiro , Shimomura Satoshi , Hiyamizu Satoshi
Published: July 2002

We investigated optical properties of GaAs/GaAs1−xPx(x≃0.2) quantum wells (QWs) with each well width (Lw) of 2.7–10.0 nm grown on (100) and (n11)A GaAs substrates (n=3, 4, 5) by molecular beam epitaxy with the use of P2 and As4 molecular beams generated from polycrystalline GaP chunk and solid As sources. It was found that the P contents (x) in GaAs1−xPx layers strongly depend on both the substrate orientation and substrate temperature (Ts). In the whole range of the Ts (535–640 °C), the largest P contents (x=0.19–0.23) were observed in the (411)A GaAs1−xPx layers, and the (100) GaAs1−xPx layers showed the smallest x (0.08–0.18). The full width at half maximum of photoluminescence (PL) peak (λ=758 nm) from the (411)A GaAs/GaAsP QW with Lw=2.7 nm was as small as 5 meV which is only 66% of that of the (100) QW probably due to improved interface flatness of the (411)A QW. Furthermore, the PL intensities of the (411)A and (311)A QWs were more than one order of magnitude larger in intensity than that of the (100) QWs.
Analysis of excitonic absorption properties and their electric field dependence in chemical beam epitaxy-grown InAsP/InP multiple quantum wells
Authors: Monier C. , Serdiukova I. , Aguilar L. , Newman F. , Vilela M. F. , Freundlich A.
Published: July 2002

The oscillator strength of heavy-hole excitons is investigated in InAsxP1−x/InP multiquantum well (MQW) p-i-n structures grown by chemical beam epitaxy, for different arsenic contents (0.26<x<0.52) and various well widths. Room temperature photocurrent measurements have been performed under saturation conditions in which the electric field becomes strong enough for the photogenerated carriers to be collected without recombination in the MQW region. A line-shape analysis is carried out within a classic transport model from which the integrated absorption intensity of heavy-hole excitons can be extracted. Preliminary experimental oscillator strengths are in good agreement with results derived from a two variational parameter calculation.
Comparison of strained channel InGaAs high electron mobility structures grown on InP and GaAs
Authors: Sandhu R. S. , Bhasin G. , Moore C. D. , U’Ren G. D. , Goorsky M. S. , Chin T. P. , Wojtowicz M. , Block T. R. , Streit D. C.
Published: July 2002

The carrier transport properties of strained In0.75Ga0.25As channels grown on (001) InP by molecular beam epitaxy in high electron mobility structures differ markedly from similarly strained (Δd/d=1.5×10−2) In0.22Ga0.78As channels grown on (001) GaAs substrates. Hall sheet concentrations for the InP-based structures do not change significantly as the thickness of the channel increases although the mobility does decrease by about 10%–15% as the channel thickness increases to about 35 nm. GaAs-based structures show much more significant decreases in both sheet concentration and mobility at these higher channel thicknesses. 〈110〉 60° misfit dislocations are observed in both sets of samples. The density of misfits in the InP structures is only slightly lower than the density in the GaAs-based structures for a given channel thickness. The InP-based structures also show the presence of edge dislocations and surface roughness undulations along the 〈100〉 directions. It appears that misfit dislocations at the channel interfaces are less important for the transport properties of InP-based structures than for GaAs-based structures.