bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved monolithic vacuum field emission diodes
Authors: Legg James D. , Mason Mark E. , Williams Roger T. , Weichold Mark H.
Published: July 2002

Realization of an easily manufacturable field emission device has been widely recognized as one of the keys to the widespread acceptance of vacuum microelectronics technology. Working to achieve this goal, many researchers have investigated edge emission cathodes similar to those developed by Gray et al. These efforts include work in the area of nonplanar edge emission devices reported by Weichold et al. and devices reported by Itoh et al. Based on that concept, this paper describes an improved nonplanar edge emission diode, suitable for monolithic integration. The structure described by Weichold has several interesting qualities, including the ability to easily define, nonphotolithographically, the anode to cathode spacing during the fabrication process. Additionally, the unique device geometry provides several advantages over traditional structures. Unfortunately, this device does not lend itself well to integration, due to the difficulty of making electrical contact to the cathode. An improved nonplanar diode design which addresses this issue has been conceived and manufactured. The new design has the additional advantage of relying only upon standard manufacturing techniques for its construction. Preliminary device testing has shown current–voltage characteristics that follow the Fowler–Nordheim model for cold field emission over several orders of magnitude of current. In this work, various cathode sizes are investigated and several cathode array sizes are tested.
Calculations of capacitance and electric field of a vacuum field effect device
Authors: Huang Z.-H. , Cutler P. H. , Miskovsky N. M. , Sullivan T. E.
Published: July 2002

Capacitance and transconductance are critical parameters determining the limiting operating frequency of a vacuum field effect transistor. We calculate the capacitance and the electric field of a vacuum field effect device using the charge density method. The cathode is modeled as a cone of half angle α with a rounded tip (a section of a sphere) of radius R, and the gate is represented by a thin circular disk of radius R2 with a concentric circular hole of radius R1, and placed a distance d above the tip. It is found that (1) The capacitance C is 0.2 fF for R=0.05 μm, R1=1 μm, R2=3 μm, d=0, and α=15°. (2) For fixed R1, C increases linearly with ΔR=R2−R1. (3) For fixed ΔR and d, C increases with increasing R1. (4) For fixed R1 and R2, C decreases with increasing d. (5) A significant field drop occurs close to the tip, as is expected. This strongly localized gradient focuses a majority of the electrons initially in the direction perpendicular to the plane of the gate.
Photoresist channel-constrained deposition of electroless metallization on ligating self-assembled films
Authors: Calvert Jeffrey M. , Calabrese Gary S. , Bohland John F. , Chen Mu-San , Dressick Walter J. , Dulcey Charles S. , Georger Jacque H. , Kosakowski John , Pavelcheck Edward K. , Rhee Kee W. , Shirey Loretta M.
Published: July 2002

Patterned, selective electroless deposition has been achieved using exposed and developed photoresists, produced with UV and e-beam exposure sources, to create channels for constrained metal growth on ligating self-assembled film surfaces. This process is attractive for the production of high-resolution, etching-resistant features for semiconductor integrated circuit (IC) fabrication, as well as for the fabrication of patterned metal lines for IC-level and (PWB)-level interconnects. Etched metal features with linewidths of 150 nm have been demonstrated.
Electron beam lithography with monolayers of alkylthiols and alkylsiloxanes
Authors: Lercel M. J. , Redinbo G. F. , Pardo F. D. , Rooks M. , Tiberio R. C. , Simpson P. , Craighead H. G. , Sheen C. W. , Parikh A. N. , Allara D. L.
Published: July 2002

Self-assembled monolayers have been modified with focused electron beams of energy 1–50 keV and scanning tunneling microscopy (STM) based lithography with energies of ∼10 eV. Modifications ∼15 nm in size have been formed by STM and ∼25 nm in size by 50 keV beams. The fact that these materials work as self-developing electron beam resists is demonstrated by both atomic force microscopy imaging and pattern transfer using conventional wet etchants. Patterns have been transferred to silicon substrates to a depth of ≳120 nm with a multistep wet etching process. The mechanism of electron beam modification has also been explored to better design future monolayer processes.
Analytic models for plasma-assisted etching of semiconductor trenches
Authors: Abraham-Shrauner Barbara
Published: July 2002

The etching of semiconductor wafers is modeled for etching by radicals (isotropic etching) and etching by both radicals and vertically incident cold ions (anisotropic etching) in a glow-discharge plasma. Explicit analytical expressions for evolving two-dimensional etched surfaces are found by the method of characteristics. These parametric relations are expressed in terms of the position along the initial exposed wafer surface. Exact surface equations are given for the radical etching with two different ansatz for the evolution equation. The superposition of radical etching and etching due to vertically incident, bombarding ions is solved by approximate analytical expressions for the etched surface. Two-dimensional etched surfaces are displayed graphically for various times.
Dimensional metrology with scanning probe microscopes
Authors: Griffith J. E. , Marchman H. M. , Miller G. L. , Hopkins L. C.
Published: July 2002

Dimensional measurement of surface topography with a probe microscope requires surface proximity sensing, probe position measurement, a probe with known shape, and careful analysis of the image generated. Our probe microscope contains some novel features. The proximity detector is a magnetically constrained rocking-beam force sensor stabilized with a capacitance-based force-balance system. This sensor accepts a wide range of probe tips, which are fabricated separately. The probes are either focused-ion-beam etched metal or chemically etched optical fibers. We show measurements of features arising from semiconductor manufacture.
Coarse guidelines in designing focused ion beam optics
Authors: Ishitani Tohru , Kawanami Yoshimi
Published: July 2002

Coarse guidelines for designing a two-lens focused ion beam (FIB) column have been proposed, based on the locus of the characteristic point in the FIB spot versus current (i.e., d–Ip) graph in logarithmic scale. Here, the characteristic point is the intersection of two lines corresponding to d=Gaussian beam spot and d=chromatic aberrations spot in the graph. These guidelines are especially useful for designing the FIB column, which is applied both for the milling using wide range diameter FIBs with high current density and for the scanning ion microscope imaging with high image resolution.
Effect of the duty ratio of line and space in phase-shifting lithography
Authors: Miyazaki J. , Yamaguchi A. , Fujiwara K. , Yoshioka N. , Morimoto H. , Tsukamoto K.
Published: July 2002

This article discusses the impact of the line and space duty ratio and optical coherence on image quality for i-line projection systems used in conjunction with alternated type phase shifters on projection masks. With a negative process, it was found that the alternated phase-shifting method improve the depth of focus (DOF) for space patterns with a width smaller than the linewidth. On the contrary, there was no effect for narrow line patterns when the space width was larger than twice the linewidth. It was also found that the DOF became larger when the coherence became higher using both the alternated and the conventional mask for line patterns with a width smaller than the space width. It is concluded that high degree of optical coherence must be chosen for the phase-shifting method. The alternated phase-shifting method was applied to a bit line layer of 64 Mbit DRAM, and a DOF of 1.2 μm was obtained for both memory cells and peripheral patterns in which the minimum feature size is 0.35 μm. It is suggested that a negative i-line resist with a large focus latitude at a high degree of optical coherence will be indispensable in applying phase-shifting lithography to device fabrication.
Miniature three-axis micropositioner for scanning proximal probe and other applications
Authors: Kleindiek S. , Kim H. S. , Kratschmer E. , Chang T. H. P.
Published: July 2002

A small, 2×2×1.1 cm (height), three-axis micropositioner has been developed. It combines sub-nm positioning capability with a large range of travel of more than 1 mm in each direction. Its applications range from scanning proximal probe instruments to sample stages for electron or light microscopes. Two shear piezos are provided in each direction to facilitate motion. They are located at opposite sides of a moving frame which is guided by V grooves on sapphire balls (or rods). A critical point in designing this kind of positioners is how to generate the ‘‘attachment’’ force that holds the parts of the positioner together. Gravity cannot be used as the stage needs to work in all orientations. Springs, connecting the two parts moving relative to each other, generate a force in the direction of the desired motion that is changing with position, making the stage motion nonlinear. Magnets are not appropriate when low-energy electrons are involved in the vicinity. This problem is solved by especially designed leaf springs coupled to V grooves and balls (or rods). This design allows the attachment force to remain constant and orthogonal to the direction of motion when the stage moves, thus making the motion very linear and independent of the orientation of the positioner. The positioner is exceptionally compact and can be operated in ultrahigh vacuum. These properties make the positioner attractive for atomic scale resolution scanning proximal probe microscopes and a wide range of other applications.
Metal–In80Al20Sb interface formation: An x-ray photoelectron spectroscopy study
Authors: Clark S. A. , Wilks S. P. , Williams R. H. , Johnson A. D. , Whitehouse C. R.
Published: July 2002

The formation of intimate, atomically clean, In–In80Al20Sb interfaces has been investigated using x-ray photoelectron spectroscopy. The attenuation of the substrate (Sb) core levels showed anomalous behavior; increasing for the first few monolayers of In deposited. This is interpreted in terms of a reaction between chemisorbed In on the c(8×2) reconstructed In-rich In80Al20Sb surface and deposited In, to produce clustering, so enhancing the substrate signals emanating from bulk In80Al20Sb. The incremental deposition of In brought about incremental shifts of the In core level binding energies, related to changes in the chemical environment of the In. For the other bulk core levels examined, no further shifts were resolved, indicating that the Fermi level at the In80Al20Sb surface is pinned prior to metallization.
Atomic force microscopy investigations of dry etched gate recesses for InGaAs/InAlAs-based high-electron-mobility transistors using methane–hydrogen reactive ion etching
Authors: Duran Halit C. , Patrick William , Bächtold Werner
Published: July 2002

A methane–hydrogen (CH4/H2) reactive ion etching process has been developed for selective gate recess etching of lattice-matched InGaAs/InAlAs/InP high-electron-mobility transistors without the need for additional ashing or annealing steps after dry etching. An atomic force microscope was used for accurate studies of the morphology of the etched 0.2 μm gate recess. We found that dry etching does not alter the surface roughness significantly for low methane concentrations. Direct current and microwave measurements showed uniform device parameters with a peak transconductance gmmax of 700 mS/mm and a unity current gain frequency ft of 170 GHz.
Synthesis and atomic force microscopy characterization of GeFe nanophase materials
Authors: Eastman Timothy , Shi Jing , Zhu Da-Ming
Published: July 2002

Nanocrystalline GeFe samples with Fe concentration varying from a few percent to about 86% were synthesized using an inert gas condensation method. The samples were compressed into thin disks in vacuum before exposure to air. Magnetization measurements found that the magnetization of the samples cannot be described by a simple Langevin function. Atomic force microscopy has been used to characterize the average size of the nanocrystals in the samples. For samples with a low concentration of Fe, atomic force microscopy images show distinct individual clusters with an average size of about 500 Å in diameter. For samples with a higher concentration of Fe, individual clusters cannot be distinguished, and atomic force microscope images show a mountain-like, rugged morphology on the sample surfaces.
Characterization of zinc sulfide nanoclusters via atomic force and scanning tunneling microscopy
Authors: Coury J. E. , Pitts E. C. , Shorrosh R. , Felton R. H. , Bottomley L. A.
Published: July 2002

II–VI nanocrystals or nanoclusters recently have been the subject of intensive study because of their potential use in high-speed electronics applications. We have prepared and characterized a series of ZnS nanoclusters which vary in size and type of capping groups. Capping of the nanoclusters with alkanethiols possessing charged end groups enabled their electrostatic immobilization to oppositely charged surfaces (e.g., chemically modified gold and mica). Electrostatic immobilization provided reproducible scanned probe imaging of the clusters on these surfaces. Size distributions were obtained by scanning tunneling microscopy (STM) and atomic force microscopy (AFM); mean particle diameters correlated well with values obtained by x-ray diffraction. Compressibility studies were performed and showed that the nanoclusters were relatively incompressible under typical imaging forces. This article describes the reliable and reproducible AFM and STM imaging of semiconductor nanoclusters.
First-order gain-coupled (Ga,In)As/(Al,Ga)As distributed feedback lasers by focused ion beam implantation and in situ overgrowth
Authors: Orth Andreas , Reithmaier Johann Peter , Faller Frank , Forchel Alfred
Published: July 2002

First-order gain-coupled distributed feedback lasers have been fabricated in the (Ga,In)As/(Al,Ga)As material system by maskless patterning with focused ion beam implantation. The laser devices are operating at 77 K and room temperature at emission wavelengths between 1.0 and 0.7 μm. The structures obtained are thermally stable up to annealing temperatures of 800 °C. A full in situ processing of gain-coupled distributed feedback laser structures was for the first time successfully demonstrated. This process includes molecular beam epitaxy, grating patterning by focused ion beam, and epitaxial overgrowth. All processed lasers show single mode emission at all operating conditions as expected for gain-coupled lasers.
Field distortion characterization using linewidth or pitch measurement
Authors: Ye Jun , Berglund C. N. , Pease R. F. W. , Owen G. , Jaeger Rolf , Alexander Katie , Seeger Judith
Published: July 2002

Field distortion in steppers and mask pattern generators can be a serious source of placement errors, which subsequently translate to overlay errors if different steppers/masks (with different distortion) are used in different layers of wafer printing. Such distortion is often determined using an expensive coordinate measuring system (e.g., Leica LMS2020 optical metrology system) which may not be readily available. We describe a simple and inexpensive technique for measuring field distortion using readily available instruments. The essence of the technique is to build up a pattern using multiple exposures with different portions of the field overlapped in the complete pattern, so that the resulting linewidth or pitch variation across the field gives the difference between the field distortion and a shifted field distortion. We can then reconstruct the field distortion by measuring the linewidth/pitch. We have applied this technique to two optical steppers, and have shown that the reconstructed field distortion agrees well with the direct LMS2020 measurement.
Phase-measuring interferometry using extreme ultraviolet radiation
Authors: Bjorkholm J. E. , MacDowell A. A. , Wood O. R. , Tan Z. , LaFontaine B. , Tennant D. M.
Published: July 2002

We describe initial experiments carried out with a phase-measuring, lateral-shearing interferometer that we have developed for use with radiation having a wavelength of about 13 nm. The system was developed for testing the imaging quality of extreme ultraviolet (EUV) lithographic cameras at the wavelength of their intended use. We describe here our initial work in which we measured essentially spherical wave fronts obtained by focusing undulator radiation onto a small pinhole. The interferometer is shown to have a sensitivity of 0.021 waves rms, or better, at an operating wavelength of 13 nm, which is more than sufficient to determine whether or not an EUV imaging system exhibits diffraction-limited performance.
Studies of 1 and 2 keV electron beam lithography using silicon containing P(SI–CMS) resist
Authors: Lo C. W. , Lo W. K. , Rooks M. J. , Isaacson M. , Craighead H. G. , Novembre A. E.
Published: July 2002

We have investigated low voltage electron beam lithography at 1 and 2 keV using P(SI–CMS) resist. With this system, 10:1 aspect ratio, 80-nm-wide polyimide fins, and ≳7:1 aspect ratio, 80-nm-wide Si fins were fabricated using 2 kV exposures. Analysis of our results suggests that observed reductions in the process latitude at 1 kV are not resist specific and can be understood on the basis of electron scattering. Experimental comparisons have been made by exposure of PMMA. In order to describe the results and help guide future development, we have conducted Monte Carlo simulations and experimental studies of the energy deposition in resists by 1 and 2 keV beams.
Fabrication of nanostructures with submicron Schottky and ohmic contacts
Authors: Feng Y. , Sachrajda A. S. , Coleridge P. T. , Taylor R. P. , Davies M. , Marshall P.
Published: July 2002

The deposition of metallic patterns on the surface of a semiconductor is a critical part of today’s very large scale integrated technology, where the patterns are employed in three distinct capacities: as ohmic contacts, as electrostatic gates, and as interconnects. Whereas the feature size of electrostatic gates has been successfully reduced to 20 nm or less, nanostructures have not previously benefited from similar reductions in scale of the ohmic and interconnect technologies. We describe the fabrication and low-temperature investigation of nanostructures defined by submicron-sized gates, interconnections, and ohmic metallization constructed on the surface of AlGaAs/GaAs heterostructures. A two-level metallization is adopted: ohmic and gate surface patterns are linked by patterned interconnects separated by an interlayer insulator. The approach features electron-beam lithography with a ±10 nm alignment accuracy and has been used to interconnect several isolated metal patterns as small as 100 nm allowing a new generation of nanostructure designs to be realized. For ohmic metallization we report data from a gated micron-sized Corbino disk—the first example of a nanostructure defined by ohmic contacts incorporating a Schottky gate.
Enhancing a hierarchical, parallel electron beam data conversion processor toward 1 Gbit memory lithography
Authors: Koyama K. , Watanabe S. , Saito T. , Hara S. , Murakami E. , Magoshi S. , Yano K. , Suzuki H. , Kabeya A. , Ohki S. , Fujii T. , Sakamoto S.
Published: July 2002

A new hierarchical, parallel electron beam (EB) data conversion system has been developed to be used in lithography for the fabrication of memories of 1 Gbit or more. The conversion system has been enhanced not only to meet EB writing requirements but also to cover new data processing capabilities required for critical dimension control and for optical resolution enhancement. The conversion system takes full advantage of the hierarchical, parallel technique and generates patterns for various EB lithography systems, including the EX-8 mask writing system, EX-8D wafer direct writing system, and MC-100 defect inspection system. The interface with computer aided design (CAD) systems has been improved by realizing direct input from CADENCE Opus or Edge and from a design rule checker ENMA in addition to CALMA GDSII format. A design guide has been established to guarantee efficient, problem-free hierarchical data conversion. Also, a new data compaction technique has been employed. The system is equipped with functions for increasing EB writing throughput. Moreover, functions for multipass writing and resize writing are available to improve pattern transfer fidelity in the resist development or chromium etching process. In the EB proximity effect correction, Ghost and dose modulation can be selectably used. For alternating phase shifting mask fabrication, a new CAD software to automatically assign shifter phase has been added. When a model 1 Gbit dynamic random access memory pattern with 0.15 μm minimum features designed following the design guide was scaled up for 4× reticle mask making and converted to the resize writing pattern on a workstation with four central processor units, the maximum conversion time per layer was 7 min 17 s, and an average conversion time was about 5 min. The data volume per mask amounted to 456 Mbytes. Using the compaction technique, the data volume was reduced to 1/7.7 at the maximum, and an average data compaction ratio of 4.5 was obtained.
Equilibrium morphology of Au(111) vicinal surfaces revealed by scanning tunneling microscopy
Authors: Rousset S. , Pourmir F. , Gauthier S. , Lacaze E. , Sotto M. , Klein J. , Lecoeur J.
Published: July 2002

We have investigated the thermal instability of Au(111) vicinal surfaces by scanning tunneling microscopy in ultrahigh vacuum. Above an annealing temperature of 700 K, both the Au(11,9,9) and the Au(4,3,3) surfaces undergo a phase separation into (111) facets and portions of (7,5,5). In addition, the faceted surfaces present a long-range order: the superperiod is 70 Å for Au(11,9,9) and 110 Å for Au(4,3,3). Large scale images show that this structure extends everywhere on the samples. It is demonstrated that the novel periodic morphology is an equilibrium state. Comparison is made with preliminary results of the Au(4,5,5) surface that belongs to the opposite zone. Observations suggest a dramatically different behavior: The surface phase separates into large (2,3,3) portions and a more complicated vicinal surface. The superperiod seems to be greater than 2000 Å.
Imaging integrated circuit dopant profiles with the force-based scanning Kelvin probe microscope
Authors: Hochwitz Todd , Henning Albert K. , Levey Chris , Daghlian Charles , Slinkman James , Never James , Kaszuba Phil , Gluck Robert , Wells Randy , Pekarik John , Finch Robert
Published: July 2002

A force-based scanning Kelvin probe microscope has been used to image dopant profiles in silicon for integrated circuit devices on a submicron scale. By measuring the potential difference which minimizes the electrostatic force between a probe and surface of a sample, an estimate of the work function difference between the probe and surface may be made. To the extent that this work function difference is a consequence of the dopant concentration near the sample surface, doping profiles are inferred from the measurements. An overview of the measurement technique is presented, along with several examples of resulting dopant imaging of integrated circuits.
Antimony doped GaAs: A model of dominant current transport mechanism
Authors: Valcheva E. , Paskova T. , Yakimova R.
Published: July 2002

Schottky barrier structures formed on epitaxial GaAs:Sb have been studied at different Sb concentrations (0–1×1020 cm−3) and different temperatures (80–300 K). Current–voltage (I–V) characteristics have been numerically simulated and compared with the experimental measurements in an attempt to reveal the dominant current transport mechanism. Since Sb is a nonelectrically active dopant in GaAs but efficiently influences defect ensemble, the role of the defects on the electrical characteristics of the device structures could be investigated. Three different regions of Sb doping have been considered in accordance with a previous study of the structural and electronic properties of metal organic vapor phase epitaxy-grown GaAs:Sb. The current transport in the samples containing an optimum amount of Sb (respectively, minimum defects) is dominated by a thermionic field emission in the main operation bias range, although indications of Poole–Frenkel effect are observed, related to the intrinsic near mid-gap electron levels. In the undoped and highly doped samples the current is mainly due to a carrier diffusion mechanism. In addition, the large amount of defects in these samples results in an electron tunneling component which is present in the I–V characteristics.
Effect of gaseous permeability of overcoat layer on KrF chemically amplified positive resists
Authors: Kishimura S. , Sakai J. , Tsujita K. , Matsui Y.
Published: July 2002

The process of removing an overcoat (OC) on the tert-butoxycarbonyl (t-BOC) type chemically amplified positive resists has been studied, and it has been found that in the case of removing the OC after postexposure bake (PEB), or at development, the decrease in the dissolution rate at the exposed region results in the formation of the surface insoluble layer and scum. This reduction in the rate became larger with increasing the OC thickness and the t-BOC ratio in the resist, and it was shown by Fourier transform infrared spectra that the t-BOC group disappeared and a small amount of tert-butoxy moiety appeared in the fully exposed region. When the OC layer remained on the resist film during PEB, isobutene generated by the deprotection of t-BOC was prevented from permeating out of the resist film and then recombined with the OH group in the base polymer. Therefore, it was found and verified that by using the acidic OC material which exhibits a high permeability for gases, the resist performance was improved.
Reliable fabrication of sub-40 nm period gratings using a nanolithography system with interferometric dynamic focus control
Authors: Cumming D. R. S. , Thomas S. , Beaumont S. P. , Weaver J. M. R.
Published: July 2002

Electron beam nanolithography tools readily permit the fabrication of ultra small structures. However, the disadvantage of such a system is that the depth of field is very small, making it difficult to maintain the focus of the system as the sample is moved due to sample topography, tilt, and stage run out. This presents a serious limitation to nanofabrication. To overcome this problem, we have built and installed a two color, heterodyne common path interferometer on a converted JEOL 100 CXII scanning transmission electron microscope. The interferometer compensates for the very small depth of field of the system by detecting variations in the sample working distance with respect to the electron optical objective lens, and dynamically correcting the lens current. The advantage of this system is that optical access to the sample can be made in a microscope with a very small working distance or sample space. To demonstrate this system, we have fabricated 38 nm period gratings on a silicon substrate. The process was a conventional one using a single 30 nm layer of 350 k molecular weight poly methyl methacrylate resist. The grating was exposed with a linear dose of 1.6 nC/cm and developed in 3:1 IPA:MIBK for 30 s at 23 °C. Patterns were transferred by lift off of an evaporated Ni/Au film. The gratings have a 1:1 mark:space ratio and a line-width variation of 5 nm at 4σ. The stage can be moved over large areas and from chip to chip, and the lithography repeated successfully. This system therefore permits reliable state-of-the-art nanolithography.
Modeling of electron elastic and inelastic scattering
Authors: Marrian C. R. K. , Perkins F. K. , Park D. , Dobisz E. A. , Peckerar M. C. , Rhee K.-W. , Bass R.
Published: July 2002

The role of the form of the elastic and inelastic cross section in Monte Carlo simulations of electron–solid scattering has been studied to understand the processes whereby energy is deposited by electrons as they traverse thin films. Specifically we are interested in these phenomena as they relate to proximity effects in electron-beam lithography and the detection of electrons by a Schottky diode with a patterned absorber overlayer. Lithographic point and line spread functions have been measured in three resist materials. We show that the inclusion of discrete inelastic scattering events whereby fast secondaries are generated is essential for matching simulation and experiment. The secondaries are crucial in determining the shape of the spread functions in the 0.1–1 μm regime and must be included to model proximity effects. Further, the fitting of line spread function simulations to experiment allows the accurate prediction of dot spread functions and applied dose thresholds as well as three dimensional resist profiles. The form of the elastic cross section is important in determining the energy loss in, and transmission through, thin metallic films. For electron energies where the film transmission is low, the Mott cross section provides a more accurate simulation than the screened Rutherford cross section.
Rh/n-GaAs contacts with and without sulfur passivation
Authors: Eftekhari G.
Published: July 2002

The Rh/n-GaAs contacts with and without sulfur passivation were examined. It was demonstrated that passivation results in contacts of better quality and improved thermal stability. The passivated contacts had higher barrier height, lower reverse current, and lower ideality factor. The formation of thermally stable S–S, S–Ga, and S–As bonds at the GaAs surface, suppression of thermally generated defects, and possible modification in the charge and structure of native oxide were used to explain the observations.
Distinguishing the close-packed hexagonal and face centered cubic phases of the metallization of diamond by polarization-dependent extended x-ray absorption fine structure
Authors: Kemner K. M. , Elam W. T. , Harris V. G. , Idzerda Y. U. , Wolf J. A.
Published: July 2002

Polarization-dependent extended x-ray absorption fine structure (PD-EXAFS) measurements have been made on a single-crystal 1000-Å-thick Co film deposited on (100) diamond. By comparing the EXAFS signals corresponding to the in-plane and out-of-plane structure relative to the film plane, we clearly determine that the film does establish the face centered cubic (fcc) phase. Distinguishing between the hcp and fcc phases can thus be performed by qualitatively noting the polarization dependence of the Fourier transform peak amplitudes corresponding to the third and fourth coordination shells. This EXAFS study shows that the Co film studied here is unambiguously in the fcc phase. The Fourier transform peaks corresponding to the first nearest neighbors, parallel and perpendicular to the film, have been compared. Results indicate less than a 0.0075 Å difference between in-plane and out-of-plane bondlengths, no significant change in coordination number and less than a 0.001 Å2 difference in EXAFS Debye–Waller factors. All of these results indicate no tetragonal distortion of the fcc Co crystal lattice. This technique should prove valuable in future studies when trying to determine the crystallinity of thin films.
Performance of the trial scanning atom probe: New approach to evaluate the microtip apex
Authors: Nishikawa Osamu , Iwatsuki Masashi , Aoki Susumu , Ishikawa Yuuichi
Published: July 2002

In order to examine the feasibility of realizing the scanning atom probe, a trial instrument was constructed by modifying a low-temperature ultrahigh vacuum scanning tunneling microscope (STM). A scanning electron microscope was mounted on the trial instrument to inspect the relative position of both the open hole at the end of the funnel-shaped extraction electrode and a cusp apex on a specimen surface. In the preliminary experiment, a single sharp W tip of the STM and two extraction electrodes with respective open hole diameters of 10 and 20 μm were employed. The tip was brought near the electrode by employing a microscrew and a piezoactuator as with a conventional STM. The variation of the field emission current with the position of the center of the hole relative to the cusp apex was found to be significant enough to bring the apex precisely to the center of the hole. An interesting finding was that the field emission was observed from a tip with a radius of more than 2 μm at a relatively low voltage, indicating that the field confined to a narrow space between the electrode and the tip apex was high enough to induce field emission.
Simulation of uniformity and lifetime effects in collimated sputtering
Authors: Tait R. N. , Dew S. K. , Tsai W. , Hodul D. , Smy T. , Brett M. J.
Published: July 2002

Collimated sputtering has been successful in providing good contact barriers for sub-half micron contacts with aspect ratios of 3 and greater. This approach does present drawbacks, however, particularly in terms of reduced deposition rates and degraded film uniformity. The deposition rate can be less than 25% relative to uncollimated systems due to the flux collected on the collimator itself. This in turn leads to closing off of the collimator cells by depositing material, which further reduces deposition rate on the wafer and limits the life of the collimator. This article demonstrates simulation of the filling of the collimator with different system configurations and pressures using the SIMSPUD vapor transport and SIMBAD thin-film growth simulators. The model can determine collimator filling uniformity, blanket film uniformity, angular distribution of collimated sputter flux, and lifetime of the collimator. Given the target erosion profile, system geometry, and deposition rate, collimator lifetime can be predicted. The model indicates that for a 300 mm diam source a drop in operating pressure from 0.67 to 0.27 Pa has little effect on collimator life in terms of kW h, while increasing collimator life in terms of wafers by about 50%. The increase in the number of wafers processed comes at the expense of a small loss of uniformity. A universal relationship between via hole aspect ratio and the product of collimator transmission and hole bottom fill is also demonstrated.
Effect of growth conditions on surface roughening of relaxed InGaAs on GaAs
Authors: Pinnington T. , Lavoie C. , Tiedje T.
Published: July 2002

We report elastic light scattering measurements of the surface morphology of strained InxGa1–xAs on GaAs, grown by molecular beam epitaxy at different growth temperatures and In contents. During strain relaxation through formation of interfacial misfit dislocations, the surface of the film roughens in response to inhomogeneous surface strains produced by the interfacial misfit dislocations. The time dependence of this roughening is modeled by an Edwards–Wilkinson equation in which the deposition flux noise is neglected and the inhomogeneous surface stress is the only driving term.
Molecular organization of azobenzene derivatives at the liquid/graphite interface observed with scanning tunneling microscopy
Authors: Grim P. C. M. , Vanoppen P. , Rücker M. , De Feyter S. , Valiyaveettil S. , Moessner G. , Müllen K. , De Schryver F. C.
Published: July 2002

Physisorbed monolayers of azobenzene derivatives were studied with a scanning tunneling microscope at the liquid/graphite interface. Three different compounds, namely, 4,4′-di(dodecyloxy) azobenzene (C12(AZO)C12), 5-[ω-(4′-dodecyloxy-4-azobenzene-oxy)dodecyloxy] isophthalic acid (C12(AZO)C12ISA), and 4,4′-bis(ω-[3,5-bis(carboxylato) phenyl-1-oxy] dodecyloxy) azobenzene (ISAC12(AZO)C12ISA) have been investigated. In all cases monolayers could be observed with submolecular resolution at the liquid/graphite interface, allowing one to identify the azobenzene, as well as the other parts of the molecules. For each monolayer structure a molecular model could be composed with a good correspondence to the experimental data. Differences in the observed monolayer structures could be related to the chemical structure of the investigated compounds. The introduction of an isophthalic acid (ISA) headgroup has a profound influence on the monolayer structure because of its capability of hydrogen bond formation with other ISA groups or with solvent molecules. In addition, for the trans isomer of C12(AZO)C12ISA solvent codeposition was observed. The compound C12(AZO)C12ISA was used to investigate the effect of cis-trans isomerization on the molecular packing of the resulting monolayers. Under the influence of uv light, the azobenzene groups isomerize from the trans isomer to the thermodynamically less stable cis isomer. This isomerization process significantly changes the composition and structure of the observed monolayers.
Ultrathin cobalt silicide layers formed by rapid thermal processing of metal on amorphous silicon
Authors: Kamal A. H. M. , Rack M. J. , Kozicki M. N. , Ferry D. K. , Lützen J. , Hallmark J. A.
Published: July 2002

The formation of thin (<15 nm) cobalt silicide layers on amorphous silicon (a-Si) has been investigated as a part of a program involving the fabrication of poly-Si-based single electron transistors. Rapid thermal annealing was used to promote the reaction between the a-Si and cobalt metal films. The effects of three most important factors on silicide formation during annealing (temperature, temperature ramp rate, and anneal time) were studied using both electrical (sheet resistance) and surface analysis (Auger electron spectroscopy) techniques. In particular, the impact of temperature ramp rate on silicide formation has been addressed. The optimization of the thin silicide process has been achieved by a statistical analysis. Transmission electron microscopy cross-sectional analysis has been performed to determine the thickness of the film.
Electrical characterization of iridium Schottky contacts to silicon: Early stages of silicidation
Authors: Jiménez-Leube F. J. , Clement M. , Sanz Maudes J. , Rodrı́guez T.
Published: July 2002

High-quality Ir/n-Si Schottky diodes have been prepared. The diodes exhibit ideal behavior at room temperature according to thermionic emission theory with linear log (I)–Vcharacteristics over eight current decades. Ideality factors less than 1.02 were obtained. Schottky barrier heights determined by forward I–V and C–V characterization are close to 0.9 eV. Current–voltage characteristics show deviations from the simple thermionic emission law at low temperature. This anomalous behavior is explained in terms of spatial inhomogeneities in the barrier height that result from the presence of a polycrystalline interlayer at the metal–semiconductor interface. The flat-band Schottky barrier height (0.98 eV) at 0 K and the temperature coefficient of the barrier (−3.8×10−4 V K−1) agree with those reported for the IrSi phase implying that some reaction between Ir and Si has taken place.
Focused ion beam sputter yield change as a function of scan speed
Authors: Santamore D. , Edinger K. , Orloff J. , Melngailis J.
Published: July 2002

In many of the applications of focused ion beams, such as integrated circuit sectioning and TEM sample preparation, considerable volume of materials may need to be removed. Thus optimizing the sputter yield is important. For very rapid scan speeds at normal incidence, each pass of the beam removes a thickness of material which is much smaller than the beam diameter. In this case, this milling yield corresponds to the yield at normal incidence. However, if the scan speed is slowed down so that the thickness removed per pass is comparable to the beam diameter, then locally under the beam the ions are not normally incident even though the beam is normal to the surface. The milling yield of Si and SiO2, for example, increases by a factor of seven to eight in going from normal incidence at 0° to 75°–85°. Thus the material removal rate can be significantly increased by reducing the scan speed. We have measured the milling yield of Si and SiO2 as a function of scan speed in one axis by milling boxes, typically 7 μm×9 μm using 30 keV Ga+ ions. In the other axis, the scan speed is many orders of magnitude faster so that the beam can be thought of as a sheet or “blade.” To measure the dependence of yield on scan speed, we milled the boxes with a single scan in the slow direction, and then measured the depth of the boxes with an atomic force microscope. The beam currents used were 1 and 2.9 nA. At the slowest single-axis speeds, the sputter yield increased by a factor of two. The observed dependence on scan speed agrees with existing models, which assume a single local angle of incidence under the beam. We also measured the redeposition on the bottom of the pit and found that it increased as the scan speed was decreased. In many applications, a small amount of redeposition would be unimportant.
At-wavelength interferometry for extreme ultraviolet lithography
Authors: Tejnil Edita , Goldberg Kenneth A. , Lee SangHun , Medecki Hector , Batson Phillip J. , Denham Paul E. , MacDowell Alastair A. , Bokor Jeffrey , Attwood David
Published: July 2002

A phase-shifting point diffraction interferometer is being developed for at-wavelength testing of extreme ultraviolet lithographic optical systems. The interferometer was implemented to characterize the aberrations of a 10× Schwarzschild multilayer-coated reflective optical system at the operational wavelength of 13.4 nm. Chromatic vignetting effects are observed and they demonstrate the influence of multilayer coatings on the wave front. A subaperture of the optic with a numerical aperture of 0.07 was measured as having a wave front error of 0.090 wave (1.21 nm) root mean square (rms) at a 13.4 nm wavelength. The wave front measurements indicate measurement repeatability of ±0.008 wave (±0.11 nm) rms. Image calculations that include the effects of the measured aberrations are consistent with imaging performed with the 10× Schwarzschild optic on an extreme ultraviolet exposure tool.
Specific features of field emission from submicron cathode surface areas at high current densities
Authors: Fursey G. N. , Baskin L. M. , Glazanov D. V. , Yevgen’ev A. O. , Kotcheryzhenkov A. V. , Polezhaev S. A.
Published: July 2002

Using numerical treatment of experimentally obtained Fowler–Nordheim emission plots, radii of nanotips, formed by the build-up process in strong electric fields on the surface of the tungsten base cathode were determined. It was found that the typical size of such structures depended upon the conditions of their forming and was in the range of 10–50 Å. The field emission characteristics of these emitters for extremely high electric fields and current densities J were studied. Studies of the emission current kinetics from a single nanotip show that at J>Jblunting∼3–5×109 A/cm2 an irreversible change of the tip submicrogeometry—“blunting” of the nanoemitter—takes place. Its apex radius increases 3–5 times. The maximum attainable J values from nanotips exceed the values for annealed substrate emitters up to 1 to 2 orders of magnitude. These values range from 1010 to 1011 A/cm2 depending on the size, structure, and geometry of tips. The results are presented of numerical simulation of cathode thermal regime, using the heat-transfer equation approach. It has been shown, that the explosive destruction of emitter and initiation of the vacuum breakdown is due not to heating of nanotips by high-density emission currents but to the energy accumulation in the base emitter bulk. The theoretical approach has been developed to the description of energy extraction accompanying the emission from ultrasmall structures (smaller than the free-path length for electron-phonon scattering). It was found that the maximum value of the total emission current was practically constant for emitting object from ∼10 up to ∼50 Å in size.
Generic scanned-probe microscope sensors by combined micromachining and electron-beam lithography
Authors: Zhou H. , Midha A. , Mills G. , Thoms S. , Murad S. K. , Weaver J. M. R.
Published: July 2002

We present a novel method for the fabrication of generic scanned-probe microscope probes by performing multiple level direct-write electron-beam lithography on the apex of micromachined atomic force microscope tips. Pattern transfer is by conventional etching or liftoff in a wide range of materials. Lithographic resolution is 50 nm or better. The substrates support the use of automatic alignment and allow for the fabrication of 50 probes/in2. The integration of a force-sensing cantilever permits simple height regulation of the probes during operation. The technology is illustrated by the fabrication of thermocouple and near-field optical probes.
Electron mobility in quantized β-SiC inversion layers
Authors: Gámiz F. , Roldán J. B. , López-Villanueva J. A. , Cartujo P.
Published: July 2002

Electron transport properties in β-SiC quantized inversion layers have been studied and the results of electron mobility calculations at room and higher temperatures have been reported. To do so, we have developed a Monte Carlo simulator used in conjunction with the self-consistent solution of the Poisson and Schrödinger equations. We show that for a fixed inversion-charge concentration, β-SiC inversion-layer electrons spread less into the bulk than Si ones as a consequence of the effective mass values. Therefore, the defects of the SiO2/β-SiC (interface roughness, charged centers) will strongly affect electron transport properties.
Transport properties of unintentionally doped iron silicide thin films on silicon(111)
Authors: Muret P. , Ali I.
Published: July 2002

Transport properties of semiconducting β-FeSi2 thin films obtained by co-sputtering of iron and silicon and post-anneal are investigated. In these polycrystalline thin films, majority carriers are electrons and their Hall mobility can reach values of 900 cm2/V s at room temperature. Conductivity, Hall effect and photoconductivity of unintentionally doped silicide thin films are studied. The results obtained in two of them are presented, because they are representative of the extreme values found for the Hall concentration. They turn out to be, respectively, 1.8×1017 and 6×1015 electrons cm−3 at room temperature. In addition to shallow donors present only in the first sample, deeper centers show ionization energy of 0.11 and 0.23 eV, respectively. For the second sample, the substrate contribution has to be considered for extracting values which are relevant for the β-FeSi2 film alone. Photoconductivity takes place in these samples: at 80 K, it shows a maximum value at 0.86–0.87 eV, which correlates well with the direct band gap of β-FeSi2 while at ambient temperature a step still appears at the same energy. Such results are a consequence of the important decrease of residual impurity concentration in comparison to values published previously.
Room-temperature midinfrared type-II quantum-well lasers with high power efficiency
Authors: Lin Chih-Hsiang , Murry S. J. , Yang Rui Q. , Yang B. H. , Pei S. S. , Yan Chi , Gianardi D. M. , McDaniel D. L. , Falcon M.
Published: July 2002

We report the room-temperature operation of optically pumped InAs/InGaSb/InAs/AlSb type-II quantum-well lasers at 4.48 μm with a pulse length of 650 ns and a repetition rate of 2 kHz. The absorbed threshold peak pump intensity was only 0.27 kW/cm2 at 220 K and 1.1 kW/cm2 at 300 K, with a characteristic temperature T0 of 61.6 K for temperatures up to 300 K. At 49 K, the continuous wave output power was 4.2 mW/facet with an absorbed threshold pump power of 31.5 mW and an absorbed pump power of 62 mW, indicating a differential external quantum efficiency of 54% for two facets.