bluuebunny/crossref_metadata_2025 huggingface dataset:
Test system timing considerations for electron beam microprobing of logic devices
Authors: Lange J. A.
Published: July 2002

Shrinking geometries, increasing vertical density of standard logic devices and faster execution times are forcing circuit designers and analyzers to depend ever more heavily on electron beam microprobing (EBM) to investigate problem cells in very large scale integrated and ultra large scale integrated logic circuits. However, in the present geometries there are also changes occurring which are forcing designers to look at electron (e-)beam probing systems as more than a laboratory fascination. The most current of these changes is vertical integration or the addition of more conductive layers to allow for a more dense design, resulting in a more efficient use of silicon area. Currently designs of two-layer metal and two-layer polycrystalline silicon are used, with the promise of more on the way, possibly including diffused active regions. The attendant close horizontal spacing between upper layers makes the physical microprobing of underlying layers a delicate proposition at best, if not impossible. The market is also pushing for more speed which means that on-chip clocks are going to be ever faster, approaching 100 MHz in the foreseeable future. This forces the use of a system with the fewest distributed constants, capable of resolution in the gigahertz region. Effective use of EBM with random logic circuits requires consideration of the test environment external to the e-beam system itself. Due to the requirement for long patterns of data prior to the particular bit time of interest, very long cycle times are often necessary to allow for internal logic to be setup prior to execution of the offending instruction. In addition, faster clock frequencies require the analyst to be more aware of high-frequency effects in the distributed constants of the test setup interconnects. Current electron beam microprobe systems are capable of dealing with relatively long cycle times and bandwidth limitations do not present a problem. However the test setup itself can introduce errors due to external hardware and/or software being incompatible with the particular sampling technique in use on most current systems. A brief review of this technique, known generically as boxcar averaging is given along with its unique software and hardware timing requirements, and some common errors to be avoided in interconnection of external systems.
Growth and characterization of AlGaAs/InGaAs/GaAs pseudomorphic structures
Authors: Fischer-Colbrie A. , Miller J. N. , Laderman S. S. , Rosner S. J. , Hull R.
Published: July 2002

We have grown pseudomorphic modulation-doped Aly Ga1−y As (0.25≤y≤0.30)/Inx Ga1−xAs (x≤0.50) on GaAs structures by molecular-beam epitaxy and obtained two-dimensional electron gas densities as high as 2.6×1012/cm2 with mobilities of 6600 and 14 900 cm2/V s at 300 and 77 K, respectively. In conjunction with this work, Rutherford backscattering measurements were made to study the substrate temperature dependence of In incorporation. Cross-section transmission electron microscopy (TEM) measurements were made to determine layer morphology (planar versus island growth) as a function of substrate temperature and composition. Dislocation density as a function of InGaAs layer thickness was studied using plan-view TEM. Hall measurements are consistent with the composition, morphology, and structural measurements of the material and indicate that there is a limited composition-dependent thickness and temperature range over which both InGaAs and AlGaAs of high quality can be grown.
A focused ion beam vacuum lithography process compatible with gas source molecular beam epitaxy
Authors: Harriott L. R. , Temkin H. , Hamm R. A. , Weiner J. , Panish M. B.
Published: July 2002

We demonstrate a direct-write lithography process for InP wafers in which a finely focused Ga+ ion beam is used to form the pattern which is then transferred into the substrate by dry etching. The result is a patterned substrate which is suitable for epitaxial growth. We have combined the ion beam writing and dry etching in a common vacuum chamber with a gas source molecular beam epitaxy (GSMBE) system. GaInAs/InP heterostructures grown on the in situ patterned substrates show excellent morphology and high luminescence efficiency. Surface relief on the order of 1000–2000 Å has been produced with this process using a 20 keV Ga+ ion beam. Lateral resolution is limited by the ion beam diameter, 2000 Å.
Micropatterning of surfaces by excimer laser projection
Authors: Brannon James H.
Published: July 2002

In the coming years, excimer lasers will play two important roles in microelectronic fabrication: as new light sources for submicron photolithography, and for direct surface patterning by ablation or etching. Using this latter application, results are presented for 248 nm excimer laser formation of micron-sized patterns in several materials by image projection. Photoablation was used to produce patterning in polyimide and a fluorocarbon polymer, while micropatterning by photoetching is demonstrated in copper and silicon using chlorine vapor. The results are discussed both in terms of the optical characteristics of the projection apparatus, and from the point of material response.
Focused ion beam stimulated deposition of organic compounds
Authors: Vasile M. J. , Harriott L. R.
Published: July 2002

The successful deposition of an opaque organic-based film for a clear defect photomask repair process has been reported. The process relies upon the polymerization of styrene stimulated by a focused ion beam, with subsequent cross-linking and ion implantation. Since that report, a class of compounds has been identified which are all suitable as precursors for film deposition with a focused ion beam. More importantly, this class of compounds defines the key chemical structures necessary for film deposition under focused ion beam conditions (high-current density/high-sputter yield). A necessary requirement for film formation is to supply the precursor to the substrate at a particle current density equivalent to that of the ion beam current density. This condition is not, however, a sufficient one: the chemistry which determines the bonding of the precursor to the substrate is the key to deposition. The combination of an aromatic ring with a pendant double or triply bonded substituent satisfies the chemical criteria. The incident molecules bond with high efficiency through the vinyl bond to radical sites created by ion bombardment. Subsequent ion bombardment at those sites cause the aromatic ring to open, leaving a highly reactive CnHn chain bonded to the surface. Vibrational excitation may cause fragmentation of this chain, but cross-linking will also occur, resulting in net deposition. The aromatic ring thus supplies a sufficient number of carbon atoms per incident precursor molecule to insure net deposition. Successful deposition has been obtained with styrene, phenylacetylene, indene, and benzofuran, all of which have a conjugated, unsaturated bond adjacent to an aromatic ring. No deposition, or net sputtering of the substrate was observed for the analogous class of molecules, benzene, toluene, ethylbenzene, and indane, all of which have an aromatic ring but lack the unsaturated pendant group necessary for efficient bonding to the surface.
Effects of thermal history on stress-related properties of very thin films of thermally grown silicon dioxide
Authors: Fitch J. T. , Lucovsky G. , Kobeda E. , Irene E. A.
Published: July 2002

This paper presents studies of the infrared (IR) absorbance and the intrinsic stress in thermally grown very thin films (60 to 700 Å) of SiO2. These data are combined with previously obtained data for thicker thermally grown films (∼1300 Å) to study the variation in intrinsic growth stress close to the Si/SiO2 interface. The combined data indicate that the intrinsic stress at Si/SiO2 interfaces extrapolates to the same relatively high values for oxides grown at 700 and 1000 °C, and that the distribution of Si–O–Si bond angles close to the Si/SiO2 interface, as deduced from the IR data, is quantitatively different than in the bulk of the oxide film. These two observations are explained in terms of a model based on a temperature dependent viscoelastic relaxation of the oxide stress. This model emphasizes differences in the thermal history of the SiO2 near the Si/SiO2 interface, as compared to the SiO2 that is well removed from that interface and is in the bulk of the film and/or close to the ‘‘top’’ surface of the film. The observed differences between the 700 and 1000 °C bulk oxides, and the associated Si/SiO2 interfaces are explained in terms of a renormalized time scale that is defined by the ratio of the growth time to the viscoelastic relaxation time at the growth temperature.
Formation of S–GaAs surface bonds
Authors: Geib K. M. , Shin J. , Wilmsen C. W.
Published: July 2002

Treating the GaAs surface with Na2S⋅9H2O or (NH4)2S has previously been shown to form a thin layer (∼1 ML) of sulfur bonded to the GaAs surface. The exact nature of this bond is not clear since a number of different bonding energies have been reported. This paper reports the results of an investigation of the formation of S–GaAs bonds using H2S gas as the source of sulfur. The angle resolved x-ray photoelectron spectra show that as the substrate temperature is increased, three different S–GaAs bonding states appear: As–S bonding peaks in the As3d spectra exhibit core level shifts of 1.0 and 1.6 eV, Ga–S bonding causes a core level shift of 0.6 eV. These binding energy shifts (ΔBEs) are approximately the same as those observed for GaAs treated with (NH4)2S or Na2S⋅9H2O although the H2S treated samples yield a much larger amount of S bonding.
A review of simplified photolithographic techniques for image transfer in planarized very large scale integrated circuits technology
Authors: Frieser R. G. , Ashburn S. P. , Tranjan F. M. , DuBois T. D. , Bobbio S. M.
Published: July 2002

This paper reviews recent publications concerned with simplifying photolithographic techniques for image transfer into planarizing polyimide layers in very large scale integrated (VLSI) technology. The primary purpose of the reviewed papers is to reduce the complexity of the more commonly used trilayer technology. To achieve the same results conventionally obtained with a trilayer process, bilayer schemes are discussed, as well as techniques employing photosensitive polyimide. An attempt is made to assess the success of these techniques on the basis of the reported resolution capabilities. Because patterning and etching planarizing layers is still a dynamically growing technology at the present time, only tentative mechanisms can be suggested, and only in some cases.
Gas phase silylation in the diffusion enhanced silylated resist process for application to sub-0.5 μm optical lithography
Authors: Baik Ki-Ho , Van den hove L. , Goethals A. M. , Op de Beeck M. , Roland B.
Published: July 2002

The diffusion enhanced silylated resist (DESIRE) process has been presented as one of the most attractive surface imaging technologies for advanced optical lithography. It has been shown that the silylation step, usually carried out in a hexamethyldisilazane (HMDS) ambient, is one of the more critical steps in the process. In this paper an in-depth study of the silylation is presented. Several alternative mono- and polyfunctional silylating agents are evaluated for application in the DESIRE process. DMSDMA, TMSDMA, and TMDS are promising candidates, showing several advantages over HMDS. For the case of HMDS and TMDS, the kinetics of the silylation are additionally studied using Rutherford backscattering spectroscopy, Auger electron spectroscopy, and infrared measurements for various process conditions. In an earlier study we have reported lateral swelling for silylation with HMDS resulting from volume expansion of the silylated resist. Because of the reduced volume expansion and/or the lower silylation temperature, these alternative silylating agents reduce the swelling and surface roughness. It has been observed that the silylation process window can be greatly increased by optimizing the presilylation bake.
The surface silylating process using chemical amplification resist for electron beam lithography
Authors: Fujino T. , Takeuchi S. , Morimoto H. , Watakabe Y. , Abe H. , Koshiba M. , Murata M. , Kawamura S.
Published: July 2002

This paper describes the surface silylating process for electron beam (EB) lithography. Surface reaction and dry development processes have many advantages for electron beam lithography. The original three components resist named SIMPLE (SIlylating resist using chemical aMPlification for Electron beam) is developed for EB silylating process. High sensitivity is attained by using chemical amplification reaction and the optimization of resist contents. The reaction mechanism is examined using Fourier transform infrared spectrometry and Rutherford backscattering spectroscopy. It is found that the silylation rate in the unexposed area is controlled by the reaction rate at the silylation front, and the silylation is suppressed by the limited diffusion rate of the silylating agent in the exposed area. Submicron resist patterns with a thickness of 1.4 μm are successfully fabricated even in a single layer process.
Ordered arrays of proteins on graphite observed by scanning tunneling microscopy
Authors: Haggerty Lorie , Watson Brian A. , Barteau Mark A. , Lenhoff Abraham M.
Published: July 2002

Two globular proteins, lysozyme and chymotrypsinogen A, were imaged on graphite using a scanning tunneling microscope. In contrast to the isolated molecules typically seen, long-range order was observed in both of these systems when the protein concentration of the solution deposited on the graphite was sufficient for multilayer coverage. For lysozyme, regular two-dimensional arrays of protein molecules were seen, with periodicities ranging from about 40 (the approximate size of a lysozyme molecule) to about 150 Å. These length scales depend on the lysozyme concentration in the initial solution. For chymotrypsinogen A, two-dimensional structures that covered a much smaller area of the graphite were observed. The structural features observed suggest such possibilities as protein structure determination using surface structural techniques and epitaxial growth of protein crystals on these two-dimensional structures.
Scanning tunneling microscopy resolution of surface features on cytokeratin protein is enhanced by prolonged exposure of protein to cold temperatures
Authors: Vernetti L. A. , Nowlin C. L. A. , Hameroff S. R. , Gandolfi A. J. , Lee Y. C. , Sarid D.
Published: July 2002

Scanning tunneling microscopy (STM) is used to image fine surface detail of cytokeratin α-helical protein. Resolution of molecular structure increased with extended exposure of partially purified cytokeratin protein to cold temperatures from 12 to 48 h. Surface of a cytokeratin tetrameric units resolved by STM depicts 2 nm diam wraps of cytokeratin proteins.
Studies and modeling of growth uniformity in molecular beam epitaxy
Authors: Wasilewski Z. R. , Aers G. C. , SpringThorpe A. J. , Miner C. J.
Published: July 2002

We have developed a numerical model for the flux distribution in molecular beam epitaxy over stationary and rotating substrates. The existence of a temperature profile along the crucible and accumulation of material at the crucible orifice is taken into account. The influence of melt level tilt on the flux distribution is discussed in detail, and, in contrast to previous reports, is found to be small for the cases considered. Accurate thickness maps of GaAs wafers grown with two different types of effusion cells on stationary substrates were obtained using a scanning reflectance system. Excellent agreement of these experimental results with predictions of the model is demonstrated. We explain some of the deficiencies of the present arrangement and calculate the optimum system conditions for obtaining uniformity across a wafer to better than ±0.3%.
A mask-to-wafer alignment and gap setting method for x-ray lithography using gratings
Authors: Uchida Norio , Ishibashi Yoriyuki , Hirano Ryoichi
Published: July 2002

A new optical-heterodyne interferometry alignment and gap setting method for x-ray lithography is developed, where the phases of beat signals are used for detection. The fact that the lateral displacement and the gap between mask and wafer can be detected independently is shown, based on the results of analysis and experiments. Two pairs of gratings are arranged as detection marks. One pair forms a window on the mask and a checkerboard grating on the wafer, while another pair forms two linear gratings at right angles to each other. Two He-Ne laser beams with slightly different frequencies illuminate the gratings from the ±1st-order diffraction light directions. The lateral displacement is detected by measuring the beat signal phase difference between the two (0,1)th-order diffraction lights from two pairs of gratings. To detect the gap, the signal phase difference between the (0,1)th- and (1,1)th-order diffraction lights from the pair of linear gratings is used. Better than 0.02 μm (3σ) alignment repeatability and 0.1 μm gap setting accuracy have been achieved.
Metal-free chemically amplified positive resist resolving 0.2 μm in x-ray lithography
Authors: Ban Hiroshi , Nakamura Jiro , Deguchi Kimiyoshi , Tanaka Akinobu
Published: July 2002

A chemically amplified positive resist (EXP) and its processing have been optimized for high resolution in x-ray lithography. EXP is composed of a novolak resin, 2,2-bis(t-butoxycarbonyloxyphenyl)-propane as a dissolution inhibitor, and bis(p-t-butylphenyl)iodonium trifluoromethanesulfonate as an acid generator. Sensitivity and resolution characteristics were greatly influenced by post-exposure baking (PEB) conditions. Applying PEB at 65 °C for 60 s resulted in the successful fabrication of 0.2-μm patterns in a 1.3-μm-thick EXP film. The pattern width remained virtually unchanged during a three-hour holding time between x-ray exposure and PEB. The exposure latitude for ±10% width change for 0.2 μm holes was about 10%.
Development of bilayer resists for deep-ultraviolet and i-line application
Authors: McKean D. R. , Clecak N. J. , Renaldo A. F.
Published: July 2002

Bilayer photoresist schemes have the potential of satisfying the many stringent demands associated with the lithographic exposure step. Because the film thickness for this process is quite small, the aspect ratios are increased relative to single layer lithography and hence increased resolution may be obtained. The planarizing layer used in bilayer schemes can also be dyed to avoid reflectivity problems. In this paper the development of a resist for use as the imaging layer in a bilayer resist scheme incorporating oxygen reactive ion etch for image transfer is described. The resist chemistry is based on the coupling reaction(s) of cyclic polyfunctional silanols. The resist is composed of a cyclic silanol, an acid photogenerator, and a phenolic resin. The catalytic nature of the chemistry involved in the resist resulted in high sensitivity during the exposure process. The observed contrast was greater than four for several of the formulations due in part to the unique ‘‘bimodal’’ characteristics of this resist. With sufficient silanol content, high etch resistance was observed and bilayer resist methodology was carried out without loss of film thickness in the exposed regions. Submicron resolution was demonstrated.
The photon scanning tunneling microscope
Authors: Ferrell T. L. , Goundonnet J. P. , Reddick R. C. , Sharp S. L. , Warmack R. J.
Published: July 2002

The tunneling of photons from an evanescent wave to a sharpened optical fiber probe tip provides the basis for an analogous instrument to the electron scanning tunneling microscope. The transmission and reflection coefficients for s-polarized photons are exactly the same as those for electrons. Imaging at subwavelength resolution is made possible by the exponential character of the tunneling. We have constructed several photon scanning tunneling microscopes (PSTMs) and successfully imaged the topography of a number of samples placed on microscope slides. Each slide is coupled to a prism with an index matching gel and light is internally reflected within the sample. The reflection is frustrated as tunneling sets in when the probe tip is brought close to the surface. The electronics and software used are similar to those used in our electron STMs. Lateral resolution of λ/12 has been obtained and high-resolution spectroscopy has also been accomplished simultaneously. Images of several types of samples, including biological samples will be presented.
0.5 μm GaAs metal semiconductor field effect transistor circuit fabrication using single layer I-line photoresists
Authors: Pomerene Andrew T. S. , Greiner James H. , Connolly John J.
Published: July 2002

This paper describes the implementation of an I-line photoresist process which was used to build 0.5 and 0.4 μm GaAs metal semiconductor field effect transistor (MESFET) devices with good parametric test results. A new PE/Micrastep I-line step and repeat system with enhanced air gauge focus, dark field alignment and laser stage exposed all of the photo levels. AZ 5214, AZ 5209, and KTI 895i resists were used for the liftoff wiring, gate metal, implant, and insulation levels, respectively. Thickness vs exposure and depth of focus curves are shown. The photo process effects upon the surface sensitive GaAs MESFET are discussed. Examination of alignment effects upon the device performance and the photochemistry interaction with the physical and electrical properties are shown. Final device results are shown with good results down to 0.4 μm.
Fabrication of 25 nm gold-bridges and observation of ballistic and quantum interference effects
Authors: Langheinrich W. , Beneking H. , Murek U. , Braden C. , Wohlleben D.
Published: July 2002

This paper is devoted to pure Au quantum wires with a length varied between 50 nm and 1 μm. In order to obtain extremely pure metallic nanometer structures, a liftoff process is preferred. To overcome the problem of grain size limited linewidth control and edge quality, a four-layer resist system for electron beam lithography has been developed, which enables the reproducible fabrication of mesoscopic devices with lateral dimensions down to 25 nm. I–V characteristics and magnetoconductance measurements have been carried out. Especially in the case of short wires, where electron transport is in the quasiballistic regime, universal conductance fluctuations have been observed, which are visible even at temperatures above 30 K.
Application of x-ray diffraction techniques to the structural study of silicon based heterostructures
Authors: Baribeau J.-M. , Houghton D. C.
Published: July 2002

X-ray techniques have been applied to the characterization of various device type Si–Ge heterostructures. Double crystal diffractometry was used to evaluate the crystal perfection and thermal stability of buried Si1−xGex layers used in heterojunction bipolar transistors and of Si1−xGex/Si superlattices used in p-i-n photodetectors. The glancing incidence x-ray technique is more sensitive to the near surface region and better suited to study thin layered structures. This method was used to obtain the structural parameters of SimGen short-period superlattices. Ultrathin buried Ge layers (1–12 monolayers) on (100) Si were also investigated by analyzing intensity oscillations in the reflected x rays arising from interference effects. This technique is sensitive enough to detect Ge layers one atomic layer thick. Comparison of the measured and calculated reflected intensity also provided an estimate of the morphology and interface sharpness of these heterostructures. The same technique was also applied to the study of a very thin heavily erbium-doped Si epilayer.
Stress reduction of gold absorber patterns on x-ray masks
Authors: Johnson W. A. , Acosta R. E. , Berry B. S. , Pritchet W. C. , Resnick D. J. , Dauksher W. J.
Published: July 2002

A resonance frequency measurement technique has been used to measure the stress at temperature of plated gold films on x-ray mask membranes over the temperature range of 90–525 K. Room temperature tensile stress increases are observed after above room temperature anneals. Stress relaxations are measured after liquid nitrogen cools. The tensile stress increases and the stress relaxations depend upon the microstructure of the plated films. Focused ion beam imaging shows that grain growth is the dominant mechanism for the tensile stress increases observed for fine grained as-plated gold films.
Growth studies of GaAsP in gas-source molecular beam epitaxy
Authors: Hou H. Q. , Liang B. W. , Ho M. C. , Chin T. P. , Tu C. W.
Published: July 2002

In this article, we report a study of incorporation behavior of the phosphorus in GaAs1−xPx during gas-source molecular beam epitaxial growth under various experimental conditions. The phosphorus composition in GaAsP was found to be generally different from the phosphine flow-rate fraction in the gas phase, and it is independent of the V/III incorporation ratio. This composition, however, agrees with the group-V-induced reflection high-energy electron diffraction oscillation determination. An increase of the phosphorus composition occurs at the substrate temperature region between 520 and 620 °C, attributable to different desorption kinetics of As and P. The same phosphorus incorporation into GaAsP under different strain states was found when the GaAsP layer was pseudomorphically grown on GaAs and GaP substrates.
Growth of shallow AlGaAs/GaAs quantum wells by gas-source molecular beam epitaxy
Authors: Jan W. Y. , Cunningham J. E. , Goossen K. W. , Knox W.
Published: July 2002

One key factor limiting device performance in multiple quantum well p-i(MQW)-n modulators is photoexcited carrier escape and transport to the contacts. With deep wells, in the AlGaAs/GaAs system, this problem limits the ultimate switching speed of the device. To reduce the impact of this problem, we have grown shallow quantum well structures containing AlxGa1−xAs barriers as low as x=0.01. Several structures have been grown at 600 °C with x=0.01–0.08 which show sharp excitonic features at room temperature, and good quantum confined stark shifts under an applied field. We report room temperature photocurrent, transmission, x-ray, and low temperature photoluminesence data of the x=0.02 device.
Elemental vapor transport epitaxy of GaAs, without oval defects
Authors: Tompa G. S. , Gurary A. , Nelson C. R. , Stall R. A. , Liang S. , Lu Y.
Published: July 2002

A novel, high yield, vacuum growth technique, elemental vapor transport epitaxy (EVTE), is reviewed and materials results are presented. In EVTE, vapors are transported from remote elemental source reservoirs and feed through regulating valves into a common hot manifold which is located directly beneath the inverted wafer. Film uniformity is controlled by the flux distribution from the common manifold. Using the hot flux manifold we have demonstrated oval defect-free growth of specular GaAs films on 2 in. diam (100) and (111) 2° off substrates at growth rates exceeding 1 μm/h to several microns of thickness. Without the flux manifold, under similar growth conditions, the films are observed to have many oval defects. The technique offers the safety of the molecular beam epitaxy process without the oval defects and the flux control of the organometallic vapor phase epitaxy/chemical beam epitaxy processes without the carbon contamination.
Quantum Hall effect in HgTe–CdTe superlattices with strong three-dimensional dispersion
Authors: Hoffman C. A. , Meyer J. R. , Bartoli F. J. , Lansari Y. , Cook J. W. , Schetzina J. F.
Published: July 2002

We have studied the quantum Hall effect in modulation-doped HgTe–CdTe superlattices with electron concentrations in the range 8 × 1015 ≤ n ≤ 3 × 1017 cm−3. Since the quantum Hall phenomenon should in principle be restricted to two-dimensional systems, it is not surprising that the plateaus in the Hall conductivity (at multiples of ≊ 200e2/h in the 200-period superlattices) and minima in the diagonal conductivity are most pronounced in samples with relatively thick barriers, i.e., when the energy bands have little dispersion in the growth direction. However, well-resolved quantum Hall features are also observed in thinner-well superlattices having miniband widths of up to 17 meV. While present phenomenological models can account for this as long as the Landau level spacing is large compared to the miniband width, it is surprising that broad lowest-order plateaus are also evident in data for two superlattices having little or no gap between adjacent levels. Possible implications of this finding are discussed.
Homotype resonant tunneling structures in molecular-beam epitaxially grown delta-doped GaAs
Authors: Wang Y. H. , Houng M. P. , Chen H. H. , Wei H. C.
Published: July 2002

A homotype negative differential resistance (NDR) device in a GaAs delta-doped structure prepared by molecular-beam epitaxy is demonstrated. One Be and two Si delta-doped planes are inserted in the GaAs layer (i.e., n+-δn+-i-δp+-i-δn+-n+), to form the required resonant tunneling structure. Electrons transported from the conduction band of the n+ layer then, can resonantly tunnel through the light hole level of the δp+ induced quantum well. When the device is operated at room temperature, symmetrical NDR characteristics with high peak to valley current ratios of 3:1 are found to be comparable with those of the heterotype AlGaAs/GaAs double barrier structure. The experimentally determined peak voltage and current density are in good agreement with these theoretically calculated from a stationary-state transport model using two-band envelope function approximation. The effects of the delta-doped p plane and device parameters on NDR behavior are discussed.
Low energy boron implantation in isotopically pure silicon by simulation
Authors: Tsatis Demetre E.
Published: July 2002

The range profile for the combination implantation of 10B and 11B into the three stable isotopes of silicon 28Si, 29Si, and 30Si in the energy range between 1 and 50 keV, has been studied by using the Monte Carlo simulation program trim. It is found that for a given boron isotope, the implantation profile depends strongly on the isotopic state of silicon. The presence of the least abundant isotopes 29Si and 30Si, in silicon of natural abundance, influence considerably the range profile.
Direct observation of individual fluorine ions on a SrF2(111) surface by atomic force microscopy
Authors: Dietz Peter , Ramos Carlos A. , Hansma Paul K.
Published: July 2002

Atomic force microscopy (AFM) was used to image the surface of SrF2(111) with resolution of individual fluorine ions. A SrF2 single crystal was cleaved along the (111) plane and imaged under 0.01 M HCl solution to remove contaminants. In some areas the hexagonal arrangement of the ions is clearly visible with interionic spacings of 3.96 Å, which is in good agreement with the crystallographical data. Studies of the epitaxial growth of alkaline earth fluorides on semiconductors may now be possible with AFM.
Y-gate submicron gate length GaAs metal–semiconductor field effect transistors
Authors: Ren F. , Pearton S. J. , Lothian J. R. , Abernathy C. R.
Published: July 2002

Submicron GaAs field effect transistors are demonstrated using a simple low temperature SiNx deposition and etchback process with negative resist profiles produced on an optical stepper. Conformal coverage of the SiNx over the resist openings and subsequent low bias (−75 V) SF6 based plasma dry etching produces reproducible features down to 0.1 μm, from initial openings of 1–2 μm. Subsequent gate etch and lift-off metal deposition produces a Y-shape gate with similar characteristics to the more conventional T-shape gates fabricated with multilevel electron-beam resists. This is a simple technique for extending the resolution of standard optical lithography tools.
Simulated optimum gate and encapsulant properties for a refractory gate GaAs metal–semiconductor field effect transistor during annealing
Authors: Kitajo S. , Kanamori M.
Published: July 2002

The stress distribution in a refractory gate GaAs substrate during annealing was calculated by computer simulation, using the finite element method. Simulations were used to investigate the correlation between the thermal expansion coefficient of the gate and the encapsulant internal stress. The condition in which minimum or no dislocations were induced into the GaAs substrate were studied. It was demonstrate that the best thermal expansion coefficient value of the gate was close to the value that was reported for tungsten. It was concluded that, by controlling the encapsulant thermal stress of SiO2 or SiN encapsulant, during high temperature annealing, a dislocation-free GaAs substrate could be obtained.
Influence of hydrogen evolution from plasma-deposited silicon nitride on underlying aluminum deformations
Authors: Kikkawa Takamaro , Endo Nobuhiro
Published: July 2002

The influence of hydrogen evolution from plasma-enhanced chemical vapor deposited silicon nitride (P-SiN) films on underlying aluminum (Al) film deformations was investigated. Hydrogen molecules evolved from the P-SiN/Al layered structures during heat treatments above 450 °C. The sources of the hydrogen were the decomposition of N–H bonds as well as the desorption of hydrogen molecules from the P-SiN films. The hydrogen evolution caused the plastic deformation of the P-SiN films. The sharp peak in the hydrogen evolution rate for the P-SiN/Al layered structure was attributed to crack formation in P-SiN film blisters, in which hydrogen molecules accumulated. The Al deformations such as voids, depressions, and pileups were formed under the P-SiN film blister. The underlying Al deformation was caused more significantly when the P-SiN film evolved more hydrogen resulting in more stress change.
Gas-source molecular-beam epitaxy of InGaP and GaAs on strained-relaxed GexSi1−x/Si
Authors: Kuo J. M. , Fitzgerald E. A. , Xie Y. H. , Silverman P. J.
Published: July 2002

Lattice-matched GaAs and InGaP structures on strain-relieved Ge/graded GeSi/Si without increasing the threading dislocation density at the III–V/Ge interface have been successfully grown. The results show that exposure of the Ge surface to As2 produces a drastic change in the step structure of the Ge surface. Subsequent exposure to Ga and continuation of growth invariably produces three-dimensional growth and a high threading dislocation density at the GaAs/Ge interface. However, exposure of the Ge surface to Ga does not appear to change the Ge step structure, and subsequent growth of GaAs leads to near two-dimensional growth and no massive increase in threading dislocation density at the GaAs/Ge interface as in the case of As2 exposure. InGaP light-emitting homojunction diodes have been fabricated on the relaxed Ge/graded GeSi/Si. Room-temperature operation was achieved with a surface-emitting output power of ∼10 mW/cm2. The best dislocation density achieved was 5×106–107 cm−2 in the InGaP/GaAs/Ge/graded GeSi/Si structure.
Temperature dependence of I–V characteristics of vacuum triodes from 24 to 300 K
Authors: Busta H. H. , Zimmerman B. J. , Pogemiller J. E. , Tringides M. C. , Spindt C. A.
Published: July 2002

Collector and gate currents as a function of collector voltage have been measured for molybdenum Spindt emitters, for n-type monocrystalline, and for n-type polycrystalline silicon emitters in the temperature range from 24 to 300 K and at a pressure of 1×10−8 Torr. The devices were tested in an as-fabricated mode with a modest in situ bake of 100 °C. The silicon devices which were fabricated in two different laboratories using different processes showed very little temperature dependencies, whereas the molybdenum emitter exhibited an increase in work function with decreasing temperature. It is conjectured that adsorption/desorption events from the background gas onto the emitter tips are responsible for the observed temperature dependency.
Controllable layer-by-layer etching of III–V compound semiconductors with an electron cyclotron resonance source
Authors: Ko K. K. , Pang S. W.
Published: July 2002

A highly controllable etching technique, in which the etching proceeds layer by layer, has been studied using a plasma generated by an electron cyclotron resonance (ECR) source. In this etching technique, the sample is exposed to reactive chlorine radicals and low energy Ar ions separately and repeatedly. For GaAs etching, the chlorine radicals were typically generated with 35 W microwave power and the Ar ions were produced using 50 W microwave power and 6 W rf power, with a self-induced dc bias of −38 V. When there was complete coverage of the surface by reactive chlorine radicals, the etch rate was found to be independent of chlorine radical or Ar ion reaction time. Layer-by-layer etching with the etch rate in the range of 0.5 nm/cycle has been achieved on GaAs. No GaAs etching was observed at −120 °C and the etch rate increased significantly with temperature. The etch rate increased initially with microwave power used in the adsorption step, then decreased at microwave power ≳60 W due to passivation effects. Faster etch rates were obtained on samples etched at higher rf power during the etch product desorption step and/or longer distance from the ECR source. Layer-by-layer etching of GaInAs, AlInAs, and InP has been demonstrated for the first time. For GaInAs and AlInAs, etching was observed at room temperature and rf power level similar to that used for etching of GaAs. For InP, etching was obtained only at higher temperature (150 °C) and rf power (8 W) during the etch product desorption step. Etch-induced damage was minimal since electrical characteristics of Schottky diodes fabricated on the etched surface were similar to an unetched sample.
Raman scattering of α-Sn/Ge superlattices on Ge (001)
Authors: Schorer R. , Wegscheider W. , Abstreiter G.
Published: July 2002

A Raman scattering study on short-period single-crystal α-Sn/Ge superlattices grown by low-temperature molecular beam epitaxy pseudomorphically on Ge (001) substrate is presented herein. The phonon spectra exhibit distinct superlattice effects, such as narrow first, second, and third order folded-acoustic modes showing a doublet splitting, which is evidence for the proper periodic compositional modulation of the structure. A peak at 260 cm−1 is attributed to a Sn–Ge vibrational mode. The Raman cross section resonance of this mode is redshifted compared to that of the Ge optical mode. There are also Ge bulklike contributions from two-phonon scattering and disorder activated modes present in the spectra. Annealing experiments show that, despite the negligible solid solubility of Sn and Ge, layer intermixing occurs up to complete alloying, while the crystal quality is preserved.
Polycrystalline silicon ‘‘slit nanowire’’ for possible quantum devices
Authors: Wada Yasuo , Kure Tokuo , Yoshimura Toshiyuki , Sudou Yoshimi , Kobayashi Takashi , Gotou Yasushi , Kondo Seiichi
Published: July 2002

Polycrystalline silicon (poly-Si) ‘‘slit nanowire’’ was fabricated in a slit formed with 100 nm lithography, microwave dry etching of silicon substrate, conformable filling of the trench by chemical vapor deposition (CVD) SiO2, slit etching of the CVD SiO2, conformable deposition of doped amorphous silicon, followed by etchback and annealing. Observation with transmission electron microscope confirmed that a poly-Si slit nanowire, with a cross section of ∼5–8 nm×20 nm is fabricated. Appropriate annealing of the a-Si layer makes the poly-Si grains grow to more than 2 μm in length. This technique would make it possible to realize silicon quantum devices, and to fabricate conventional integrated circuit devices and light emitting slit nanowire devices on a same silicon chip, which would allow the fabrication of integrated optoelectronic circuits.
Analysis of stoichiometry and oxide growth of HF treated GaAs (100) by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry
Authors: Storm W. , Wolany D. , Schröder F. , Becker G. , Burkhardt B. , Wiedmann L. , Benninghoven A.
Published: July 2002

The influence of HF (5%) on the surface of GaAs (100) and the oxidation of HF treated samples in laboratory air have been investigated by x-ray photoelectron spectroscopy, angle-resolved monochromatized photoelectron spectroscopy, and time-of-flight secondary ion mass spectroscopy. Etching with HF does not only remove the oxide but leads to an increasing loss of Ga from the surface. After some minutes a layer of elemental As is formed which grows linearly with the logarithm of HF storage time. Subsequent oxidation starts with the formation of As2O3 and Ga2O3, with preferential oxidation of As. After some hours, higher oxidized states of As and Ga [As2O5, GaAsO4, Ga(OH)3] are formed under the influence of light. The rate of As oxidation decreases until a state is reached which consists of nearly equal amounts of As and Ga. For storage times less than one week, the oxide thickness increases linearly with the logarithm of storage time, which is consistent with the Cabrera–Mott mechanism found earlier for the oxidation of GaAs.
Characteristics of a plasma doping system for semiconductor device fabrication
Authors: Sheng T. , Felch S. B. , Cooper C. B.
Published: July 2002

A plasma doping system for semiconductor ion implantation is described. The target to be implanted is placed directly in the plasma and then biased to a negative potential to accelerate the positive ions into the target. A wafer bias of up to −5 kV with a BF3 source gas are used to implant boron ions into 150 mm diameter Si wafers. Data are presented showing sub-100 nm shallow p+–n junction with good sheet resistance uniformity and dose control repeatability. A high dose rate of ≳1015 cm−2 per minute at low energy (<5 keV) can be readily achieved. Excellent charging test device performance as well as surface contamination control are discussed. All of these results demonstrate the attractiveness of this unique alternate doping technique.
Identification of ordered and disordered Ga0.51In0.49P domains by spatially resolved luminescence and Raman spectroscopy
Authors: Krost A. , Esser N. , Selber H. , Christen J. , Richter W. , Bimberg D. , Su L. C. , Stringfellow G. B.
Published: July 2002

Ga0.51In0.49P layers were grown by organometallic vapor phase epitaxy on grooved GaAs(001) substrates misoriented by 9°. The formation of adjacent ordered and disordered domains has been observed on such substrates. The combination of both Raman and cathodoluminescence measurements allows for an independent determination of composition by analyzing the frequency positions of the optical phonon modes (with an accuracy of 1%) and of the band gap from the luminescence at the same position on the sample. Furthermore, ordered and disordered domains can be clearly identified from their different polarization selection rules observed in the Raman spectra. The cathodoluminescence spectra show shifts of the luminescence maxima of up to 100 meV for ordered and disordered domains of the same composition.
Novel WSi/Au T-shaped gate GaAs metal–semiconductor field-effect-transistor fabrication process for super low-noise microwave monolithic integrated circuit amplifiers
Authors: Takano H. , Hosogi K. , Kato T. , Oku T. , Kohno Y. , Nakano H. , Sato K. , Funada M. , Ishihara O. , Tsubouchi N.
Published: July 2002

A fully ion-implanted self-aligned T-shaped gate GaAs metal–semiconductor field-effect transistor (MESFET) with high frequency and extremely low-noise performance has been successfully fabricated for super low-noise microwave monolithic integrated circuit (MMIC) amplifiers. A subhalf-micrometer gate structure composed of WSi/Ti/Mo/Au is employed to reduce gate resistance effectively. This multilayer gate structure is formed by newly developed dummy SiON self-alignment technology and a photoresist planarization process. At an operating frequency of 12 GHz, a minimum noise figure of 0.87 dB with an associated gain of 10.62 dB has been obtained. Based on the novel FET process, a low-noise single-stage MMIC amplifier with an excellent low-noise figure of 1.2 dB with an associated gain of 8 dB in the 14 GHz band has been realized. This is the lowest noise figure ever reported at this frequency for low-noise MMICs based on ion-implanted self-aligned gate MESFET technology.
Effect of ultrahigh nucleation density on diamond growth at different growth rates and temperatures
Authors: Yang G. S. , Aslam M. , Kuo K. P. , Reinhard D. K. , Asmussen J.
Published: July 2002

A nucleation density in the range 108–1011 cm−2 is used for diamond film deposition on Si substrates. Diamond films, prepared by hot filament and microwave plasma chemical vapor deposition with deposition rate and temperature in the ranges of 0.05–2.5 μm per hour and 470–950 °C, respectively, were characterized by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. The surface roughness was studied as a function of deposition time, film thickness, grain size, and nucleation density. Films 1 μm thick were obtained with a mean surface roughness of 30 nm. It is found that the surface roughness is strongly dependent on nucleation density at the early stage of deposition.
Mechanisms of copper removal during chemical mechanical polishing
Authors: Steigerwald J. M. , Murarka S. P. , Ho J. , Gutmann R. J. , Duquette D. J.
Published: July 2002

Schemes using chemical mechanical polishing of copper have been proposed for the patterning of interconnections in copper multilevel metallization. In this article, the phenomena involved in the removal of copper during copper chemical mechanical polishing are investigated. The concentration of chemical etchant in the polish slurry is varied to investigate the chemical component, and the applied pressure is varied to investigate the mechanical component. Two slurries, an ammonium hydroxide plus ferricyanide slurry and a nitric acid slurry, are used to polish both copper and Cu2O thin films. Removal of copper or Cu2O is hypothesized to be a result of mechanical abrasion, while the role of the chemical etchant is to dissolve the material abraded from the surface rather than to etch the material directly from the surface.
Conducting atomic force microscopy study of silicon dioxide breakdown
Authors: O’Shea S. J. , Atta R. M. , Murrell M. P. , Welland M. E.
Published: July 2002

A summary is given of an experimental method used to obtain the local dielectric strength of thin insulators using atomic force microscopy with conducting tips. This technique is applied to 7–15 nm thick SiO2 films grown on either crystalline silicon or polysilicon substrates. The dielectric breakdown of the oxides over small areas (∼5×10−16 m2) follows that observed in the intrinsic breakdown of conventional metal–oxide–semiconductor structures, with a maximum breakdown field of 13.2±0.8 MV/cm. On the polycrystalline samples variation in dielectric strength between individual grains can be observed, with the oxide over some grains breaking down entirely. A difficulty when working in air is that sample or tip contamination and induced growth of material under the tip lead to changes in either the effective barrier height or local material thickness which are not related to the SiO2 film. These effects are discussed in detail.
Electrical characterization of single barrier GaAs/GaN/GaAs heterostructures
Authors: Huang X. , Cheng T. S. , Hooper S. E. , Foster T. J. , Jenkins L. C. , Wang J. , Foxon C. T. , Orton J. W. , Eaves L. , Main P. C.
Published: July 2002

A modified molecular beam epitaxy technique has been used to grow single barrier GaAs/GaN/GaAs heterostructures of both n- and p-type. The temperature-dependent I(V) measurements show thermally activated conduction over the barrier above about 200 K. A Type I band alignment is indicated by significant offsets in both the conduction and valence bands at the GaAs/GaN heterointerface.