bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of surface chemical treatment on the formation of metal GaAs interfaces
Authors: Shoji Daisei , Shinohara Masanori , Miura Taka-aki , Niwano Michio , Miyamoto Nobuo
Published: July 2002

We have used synchrotron radiation photoemission spectroscopy to investigate the chemical interactions at metal/GaAs interfaces during deposition of Au and In onto GaAs(100) surfaces that are chemically treated in etching solutions. We determine that there exists a thin native oxide layer on the surface that is treated in H2SO4 solution. Au reacts with the oxide overlayer to generate AuGa alloy, but In does not interact appreciably with the oxide overlayer leading to the island growth of the In overlayer at high In coverages. We confirmed (NH4)2Sx treatment leads to a GaAs surface that is terminated with sulfur. For the Au deposition onto this surface, alloy formation and segregates both at interfacial regions and on metallic overlayers are significantly suppressed, leading to the island growth of the Au overlayer. On the other hand, at initial stages of In deposition, In strongly interacted with the (NH4)2Sx-treated surface to generate a thin layer of InxGa1−xAs alloy on which the In overlayer formed in a layer-by-layer fashion. We also investigate the effects of surface treatments in the Fermi level pinning.
Combined beam profile reflectometry, beam profile ellipsometry and ultraviolet-visible spectrophotometry for the characterization of ultrathin oxide-nitride-oxide films on silicon
Authors: Leng J. M. , Opsal J. , Aspnes D. E.
Published: July 2002

We show that a combination of beam profile reflectometry, beam profile ellipsometry, and deep ultraviolet-visible spectroreflectometry can accurately characterize ultrathin oxide on nitride on oxide films with total thicknesses of less than 200 Å. Beam profile ellipsometry establishes the total thickness, while beam profile reflectometry provides the key data to detect the multilayer structure. Optical absorption of the nitride layer at wavelengths shorter than 270 nm as measured by spectroreflectometry provides additional accuracy in determining the thicknesses of the individual layers. The fit to the data is improved by including a 12 Å interlayer between the Si substrate and the bottom oxide. Determined thicknesses are in excellent agreement with those deduced by cross-sectional transmission electron microscopy.
Passivation of stainless steel by δ-Al2O3 films resistant to ozonized water
Authors: Yoshida M. , Seki A. , Shirai Y. , Ohmi T.
Published: July 2002

Alumina films have been successfully formed on austenitic stainless steels containing 4 and 5 wt % Al by selective oxidation of Al in a H2O/H2 environment. γ-alumina films have been formed by oxidation at 800 °C and δ-alumina films at 900 °C. Satisfactory corrosion resistance performance for ozone gas has been obtained for both γ- and δ-alumina films. For ozonized water, δ-alumina films formed with pH2O/pH2⩽1×10−4 have good corrosion resistance while δ-alumina films formed with pH2O/pH2⩾3×10−4 or γ-alumina films do not. Holes of a characteristic triangular shape are observed on the oxidized surface of stainless steels containing 4 wt % Al, probably caused by the habitual formation of precipitated β-(Fe,Ni)Al. No such hole has been observed on the oxidized surface of stainless steels containing 5 wt % Al.
Polysilicon sealed vacuum cavities for microelectromechanical systems
Authors: Zook J. David , Herb William R. , Ahn Yongchul , Guckel Henry
Published: July 2002

Sealed vacuum cavities are highly useful in silicon-based microelectromechanical systems. Sealed polysilicon cavities serve as reference chambers for commercially available pressure sensors and provide enclosures for high-Q mechanical resonators. They also provide isolation of resonant strain gauges from ambient gases and liquids for use in precision pressure transmitters. The residual pressure in such cavities is less than 10−5 Torr, as evidenced by the polysilicon resonator Q values which can be as high as 300 000. Measured values of Q can be dominated by parasitic electrical resistance losses in the electrical drive circuit. After these losses are accounted for, the dominant loss is due to mechanical radiation of acoustic waves from the supports to the rest of the die and package. The vibration of the beams can be excited and sensed in several different ways for testing purposes. Fiberoptically driven and sensed microbeams operating at up to 510 °C for several hours resulted in no loss of vacuum as evidenced by the restoration of resonator Q upon its return to room temperature. Thus optically resonant microbeams are potentially suitable for fiberoptic-based sensors that withstand harsh environments, including high temperature.
Automated, high precision measurement of critical dimensions using the atomic force microscope
Authors: Chernoff Donald A. , Burkhead David L.
Published: July 2002

We describe a computerized method to analyze the microstructure of optical disks. On digital versatile disks (DVDs), the smallest features are pits or bumps about 400 nm long, 320 nm wide, 120 nm high, with a track pitch of 740 nm. We measured the following parameters: track pitch, bump height, bump width and length (at various threshold levels), and four sidewall slope angles, in each case reporting the mean, standard deviation, and other statistics. In a single 10×10 μm image of a DVD stamper containing about 100 bumps, we tabulated about 1000 values. In a plot of bump width versus bump length, we found that the width at half height increased from 328 nm for the shortest bumps (440 nm long) to about 385 nm for bumps longer than 800 nm; this matches the increase seen for corresponding optical signals produced when a finished disk is played. Where a sidewall angle deviated from the norm, we were able to review the image data to identify the specific nature of the defect. This automated method yields statistically robust results, not only for mean values of structural parameters, but also for the standard deviations so that process windows can be determined. Thus, feature geometry will no longer be a hidden variable in the path between controlling production equipment and observing the good or bad electrical performance of a finished disk.
Nonlinear amplitude evolution during spontaneous patterning of ion-bombarded Si(001)
Authors: Erlebacher Jonah , Aziz Michael J. , Chason Eric , Sinclair Michael B. , Floro Jerrold A.
Published: July 2002

The time evolution of the amplitude of periodic nanoscale ripple patterns formed on Ar+ sputtered Si(001) surfaces was examined using a recently developed in situ spectroscopic technique. At sufficiently long times, we find that the amplitude does not continue to grow exponentially as predicted by the standard Bradley–Harper sputter rippling model. In accounting for this discrepancy, we rule out effects related to the concentration of mobile species, high surface curvature, surface energy anisotropy, and ion-surface interactions. We observe that for all wavelengths the amplitude ceases to grow when the width of the topmost terrace of the ripples is reduced to approximately 25 nm. This observation suggests that a short circuit relaxation mechanism limits amplitude growth. A strategy for influencing the ultimate ripple amplitude is discussed.
Annealing effects on the interfacial reactions of Ni on Si0.76Ge0.24 and Si1−x−yGexCy
Authors: Luo Jian-Shing , Lin Wen-Tai , Chang C. Y. , Shih P. S. , Pan F. M.
Published: July 2002

Interfacial reactions of Ni/Si0.76Ge0.24 and Ni/Si1−x−yGexCy by vacuum annealing and pulsed KrF laser annealing were studied. Upon annealing at a temperature of 200–600 °C Ge segregation occurred with the extent becoming more severe at higher temperatures. The temperatures at which phase transformation and the agglomeration structure occurred were higher for Ni/Si1−x−yGexCy than for Ni/Si0.76Ge0.24. Upon pulsed KrF laser annealing the agglomeration structure was considerably improved, however, the retardation of phase transformation in the Ni/Si1−x−yGexCy system still occurred. C accumulation around the original amorphous/crystal interface formed by C+ implantation played a significant effect on delaying the phase transformation. For the Ni/Si0.76Ge0.24 and Ni/Si1−x−yGexCy samples annealed at 0.2 J/cm2 for 20 and 30 pulses, respectively, smooth Ni(Si0.76Ge0.24)2 and Ni(Si1−x−yGexCy)2 films could be grown, meanwhile Ge segregation and strain relaxation of the unreacted Si0.76Ge0.24 films were effectively suppressed.
Study of doping concentration variation in InGaAs/InP high electron mobility transistor layer structures by Raman scattering
Authors: Radhakrishnan K. , Patrick T. H. K. , Zheng H. Q. , Zhang P. H. , Yoon S. F.
Published: July 2002

The effect of varying the dopant concentration (ND) in the InP donor layer of In0.53Ga0.47As/InP high-electron mobility transistor (HEMT) structure was studied by Raman scattering measurements. The carrier concentration in the InGaAs channel was found to increase when the doping concentration in the donor layer was increased assuming that the donors are fully ionized. The coupled mode between the InGaAs longitudinal optical phonons and the electrons in the InGaAs channel shifts continuously to a lower wave number with the increase in the value of ND in the InP donor layer. The correlation between the observed Raman shift with the carrier concentration in the channel layer can be used to characterize the HEMT structures nondestructively.
Electronic core levels of HgPX3 chalcogenophosphates
Authors: Calareso C. , Curró G. M. , Grasso V. , Silipigni L.
Published: July 2002

X-ray photoelectron spectroscopy and x-ray excited Auger electron spectroscopy have been used to investigate the electronic core levels of mercury chalcogenophosphate HgPS3 and HgPSe3 single crystals. On the basis of the measured chemical shifts relative to the elements information on the bonding state of the compositional atoms has been deduced. Single peak structures have been observed for the analyzed Hg, P, S, and Se core levels. As happens in CdPS3 and ZnPS3 the Hg 5d levels are discrete and well localized. This analogy confirms the validity of the transition-metal weakly interacting model already used satisfactorily for interpreting the optical properties of these chalcogenophosphates.
Investigation of persistent photoconductivity in a Ge-doped ZnSe epilayer
Authors: Zhang L. , Dai N. , Hu G. J. , Chen L. Y. , Tamargo M. C.
Published: July 2002

A persistent photoconductivity (PPC) measurement was made on Ge-doped ZnSe using contact electrodes. It is shown that Ge in ZnSe forms deep levels responsible for the observed PPC effect at a quenching temperature of 210 K. The photogenerated carriers move freely in the ZnSe:Ge epilayer but are confined in the region exposed to light, indicating that it is possible to write an erasable metallic pattern on the epilayer.
Cryogenic ultrahigh vacuum manipulator for angle dependent x-ray photoelectron spectroscopy studies
Authors: Hawkridge Adam M. , Gardella Joseph A. , Sagerman Gary R.
Published: July 2002

A cryogenic ultrahigh vacuum manipulator is described for angle-dependent x-ray photoelectron spectroscopy studies. A commercially available cold finger has been modified with a differentially pumped rotational flange to allow for rotation along the x axis. The described apparatus can be easily adapted to other ultrahigh vacuum systems.
Growth mechanisms and modeling for metalorganic chemical vapor deposition selective-area epitaxy on InP substrates
Authors: Greenspan J. E. , Zhang X. , Puetz N. , Emmerstorfer B.
Published: July 2002

Selective area epitaxy of InP on masked (100) InP substrates is studied. InP layers are deposited between pairs of SiO2 stripes using low-pressure metalorganic chemical vapor deposition. Layer thickness is investigated by surface profiling and scanning electron microscopy. For growth between oxide stripes, the growth velocity is enhanced by lateral diffusion of growth species from the masked region to the exposed region. Two transport mechanisms are known to exist: vapor phase diffusion and surface migration. However, most existing quantitative models focus only on the former. A new computational model, based on the diffusion equation with time dependent boundary conditions, is presented which describes the growth enhancement component due to surface migration. The role played by surface migration is shown to depend on nominal film thickness. The model correctly predicts a super growth enhanced region adjacent to the oxide. Previous quantitative models have not successfully described this aspect of growth near the oxide film.
Optimization of n+μc-Si:H contact layer for low leakage current in a-Si:H thin film transistors
Authors: Murthy R. V. R. , Servati P. , Nathan A. , Chamberlain S. G.
Published: July 2002

The leakage current in a-Si:H thin film transistors (TFTs) at low drain voltages (<5 V) and at low gate voltages (<5 V) is observed to be due to diffusion of phosphorus into the a-Si:H layer from the n+μc-Si:H contact layer, where the phosphorus is used as an n dopant. This diffusion creates a relatively high conductivity path in the a-Si:H layer, near the n+μc-Si:H/a-Si:H interface, as well as defect states in the bulk a-Si:H region. A systematic characterization of the TFT for different deposition temperatures of the contact layer indicates that the optimal deposition temperature for low leakage current (and hence, low phosphorus diffusion) is around 200 °C. A physical model has been developed to predict the dependence of the leakage current on voltage. Simulated and measured characteristics are in reasonable agreement.
Electrodissolution and passivation phenomena in III–V semiconducting compounds
Authors: Menezes S. , Miller B. , Bachmann K. J.
Published: July 2002

Anodic dissolution and passivation characteristics of n- and p-type III-V compounds (III=Ga, In and V=P, As, Sb) have been compared in aqueous electrolytes. A range of interfacial behavior was observed on controlled potential cycling of these semiconductors in acidic, basic, and neutral solutions, the differences being more pronounced in acids. The dissolution of InP on anodization is severely inhibited even in acid medium by the formation of a coherent film removable only by extensive cathodic reduction. GaP, InSb, and GaSb passivate less readily, forming solubility-limited precipitates on the surface at high current densities. Passivation of InAs or GaAs at pH∼0 is virtually unreachable, except at extremes of current densities, with the films formed being quite porous and permitting considerable surface corrosion. The gradation of properties observed in the III–V compound series indicates that both group III and V members are involved in the film formation. Previous observations of the functions of films on InP and GaAs in photoelectrochemical cells, in acid and neutral media, respectively, are consistent with the above results. The formation of indium layers in InP, after reduction in acid media, has been demonstrated by ring–disk electrode techniques.
Adsorption of H, O, and H2O at Si(100) and Si(111) surfaces in the monolayer range: A combined EELS, LEED, and XPS study
Authors: Schaefer J. A. , Stucki F. , Frankel D. J. , Göpel W. , Lapeyre G. J.
Published: July 2002

This paper is a summary of a series of experiments studying the exposure of hydrogen, oxygen, and water, on the (2×1) surfaces of Si(100) and Si(111). While the primary focus has been on high resolution electron energy loss (EELS) results, low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) are also used in the studies. Both the (100) and cleavage (111) surfaces form a monohydride and a dihydride exhibiting a (2×1) and a (1×1) LEED pattern, respectively. These systems exhibit saturation, which is consistent with the model of hydrogen saturation of the dangling bonds. Upon water adsorption the Si–H and Si–OH vibronic modes are observed, indicating that water is decomposed. On the cleavage surface only, there is evidence of a very weak scissor mode, allowing for the possibility of a few percent of molecular water adsorption. Oxygen adsorption is complex. For samples formed at high temperatures (∼1000 K) the observed vibronic features are similar to those known for the Si–O–Si complexes in vitreous glasses. For thin oxide layers (0.5<θ<1.3 monolayers) a linear relationship is observed between oxygen coverage and asymmetric mode frequency. These data are fit with models developed for glasses which, for the monolayer regime, yield an average bond angle of about 130° and a bond distance of 1.65 Å. The results support the model in which the oxygens are envisioned as being inserted into the Si–Si back bonds.
Evaluation of registration performance of IBM EL-3 e-beam mask making system
Authors: Hsia L. C. , Weber E. V.
Published: July 2002

The IBM EL-3 e-beam mask making system is a high performance and high throughput tool designed for lithography pattern exposure in manufacturing. The main system features and architecture, which include a high-current, variable-shaped spot and subfield deflection have been designed primarily for direct wafer exposure. Special engineering efforts have been made to identify and eliminate minor magnetic influences and structure flexures that introduce submicron tool character so that mask patterns can be accurately exposed. This evaluation of the tool overlay performance is the result of a close tool monitor operated to reflect a manufacturing mode. Overlay verification patterns in the kerf area are measured by a Nikon x-y interferometric measurement system. Analysis of the data indicates EL-3 consistently delivers a level-to-level overlay accuracy of the order of 0.1 μm.
E-beam metrology of chromium master masks and of masks for x-ray lithography
Authors: Bruenger W. H. , Betz H. , Heuberger A. , Müller K. P.
Published: July 2002

Mask fabrication is a key technology for x-ray lithography which could limit the size of future step and repeat fields used for x-ray exposure. This paper deals with distortions induced by single process steps during mask fabrication. To control the positional accuracy of the microstructures after different fabrication steps the e-beam metrology tool EBMT-5 has been used. Average distortions as low as 0.12 μm were found in a 40×40 cm field for the thinning process of the Si-wafer to form the 2 μm thick mask membrane on a 3 in. wafer. This result was achieved after stress compensation of the Si membrane.
New, deep UV resist (LMR) for lift-off technique
Authors: Yamashita Yoshio , Kawazu Ryuzi , Kawamura Kazutami , Ohno Seigo , Asano Takateru , Kobayashi Kenji , Nagamatsu Gentaro
Published: July 2002

A new, deep UV resist, LMR (low molecular weight resist) has been developed. LMR is a quinone–diazide ester of a novolak resin whose molecular weight is about 1000. It has strong absorption in the deep UV region (12 μm−1 at 250 nm). LMR is negative working upon irradiation with deep UV light and forms an overhung structure with a single development step. The sensitivity of LMR is 30 mJ/cm2 and 0.3 μm wide spaces are clearly resolved. By use of LMR, a simple and reliable lift-off process is realized. Submicron wide metal patterns having a thickness twice that of the resist can be formed by this process.
A comparison of backscattered electron and optical images for submicron defect detection
Authors: Rosenfield Michael G. , Goodman Douglas S. , Neureuther Andrew R. , Prouty Mark D.
Published: July 2002

A rapid and automated inspection system is a necessity for the detection of defects in x ray and optical lithography masks. Monte Carlo techniques and optical simulation are used to examine the relative qualities of backscattered electron signals and transmitted optical images for use in a mask inspection system. The backscattered electron signals from one and two dimensional submicron structures are examined for different take-off angle ranges and beam sizes and compared to the corresponding optical images for different wavelengths and numerical apertures. It is shown that signal quality in electron-beam inspection systems can improve as defect size decreases while the optical images tend to degrade. An examination of shot noise signal-noise ratio characteristics shows that shot noise alone should not be a fundamental limit in a well designed inspection system.
Modeling highly nonlinear resists
Authors: Eib Nicholas K.
Published: July 2002

A master rate equation based on Bose–Einstein statistics is presented that accurately describes the dissolution characteristics of any highly nonlinear resist. Nonlinear resists exhibit long time delays or induction times before the onset of rapid development rates. The master rate equation requires a maximum of five adjustable fitting parameters, may be used for both optical and electron beam lithography modeling, and avoids problems with local negative development rates, discontinuities, and infinities whenever other dissolution rate equations are used. The least-squares fit of the master rate equation to experimental dissolution data is rapid and stable. The accuracy of the master rate equation has been verified for electron beam modeling by comparison with experimentally determined nonlinear resist profiles.
New trilevel and bilevel resist systems using silyl ethers of novolak and low molecular weight resist
Authors: Kawazu Ryuji , Yamashita Yoshio , Ito Toshio , Kawamura Kazutami , Ohno Seigo , Asano Takateru , Kobayasi Kenji , Nagamatsu Gentaro
Published: July 2002

A new intermediate layer material, silyl ether of novolak (Si–novolak), and a new Si containing resist, silyl ether of a naphthoquinone diazide ester of novolak, Si–LMR (low molecular weight resist), have been developed for trilevel and bilevel resist systems, respectively. Si–novolak has high O2-reactive ion etching (RIE) resistivity and high solubility in nonpolar solvents, such as xylene and chlorobenzene, which cause no damage to the film of novolak. When novolak and Si–novolak are employed as the bottom and intermediate layer materials, respectively, both layers can be formed by successive coatings without baking the bottom layer. Si–novolak is easily hardened by deep UV light. Therefore, a trilevel resist can be formed by one deep UV blanket exposure and one baking step, besides coating steps. The triresist system, LMR/Si–novolak/novolak, provides 0.5 μm resist patterns with steep profiles and good line control over topography. Si–LMR is a negative deep UV resist and its sensitivity is 100 mJ/cm2. The O2-RIE selectivity of Si–LMR to AZ-2400 is larger than 15. The bilevel resist system, Si–LMR/AZ-2400, clearly generates 0.5-μm-wide patterns with an aspect ratio of 4.
Reduced aberrations in an electron matrix lens through the use of offset apertures
Authors: Kurihara Kenji
Published: July 2002

A design method for a low aberration matrix lens is developed. The matrix lens consists of an electrostatic lens array and beam limiting aperture array located outside of the lens array. It is shown that off-axial aberrations, which are dominant in the outer lenses, can be reduced by shifting the aperture from the optical axis of each lens to its optimum position. Using this aperture shift effect, a low aberration matrix lens consisting of einzel lenses is designed for submicron electron beam exposure systems. An aberration of 0.1 μm is predicted for a 40 mm2 matrix lens with a beam half-angle of 5 mrad.
Focus: The critical parameter for submicron lithography
Authors: Levinson Harry J. , Arnold William H.
Published: July 2002

A simple model of the photolithographic process is used to analyze the effects of defocus on resist profiles and process control. An expression is obtained for linewidth variation as a function of exposure and defocus, whereby a process window can be established. The parameters which must be specified in a practical and self-consistent definition of the depth of focus are identified: the resist process, printdown, nominal linewidths, linewidth variability, and profile slope. The model also provides a framework for interpreting empirical results obtained on a new generation of wafer steppers. Measurements of the effects of lens astigmatism and barometric pressure on the depth of focus are presented.
Lithography for ultrashort channel silicon field effect transistor circuits
Authors: Rishton S. A. , Schmid H. , Kern D. P. , Luhn H. E. , Chang T. H. P. , Sai-Halasz G. A. , Wordeman M. R. , Ganin E. , Polcari M.
Published: July 2002

This paper describes techniques suitable for the fabrication of silicon field effect transistor (FET) circuits with gate lengths as small as 0.07 μm, intended for experiments to assess the feasibility of FET technology in the 0.1-μm channel length regime. High-resolution electron-beam lithography using a vector scan system capable of an 8-nm Gaussian spot size has been performed successfully for all levels, with various resist systems tailored to the specific processing requirements. Proximity correction has been found to be a critical issue and was performed using parameters derived from measured point exposure distributions. Metal liftoff using double-layer poly(methyl methacrylate) resist has been performed successfully with complex patterns. Better than 0.1-μm linewidth and 0.05-μm alignment accuracy is achieved over a 250-μm field, using tantalum silicide alignment marks.
High-speed electron beam testing
Authors: Chiu George , Halbout Jean-Marc , May Paul
Published: July 2002

The performance of submicron devices and circuits for the coming decade is advancing at a rapid pace. The emerging requirements to probe the internal nodes of these ultrafast, small and dense circuits give rise to great challenges for high-speed electron beam testing. In this paper, we review the steps of advancing the electron beam testing to achieve simultaneously: 5-ps temporal resolution, 0.1-μm spot size, and 3 mV/Hz1/2 voltage sensitivity. The newly developed instrument, called the picosecond photoelectron scanning electron microscope, is capable of measuring the state-of-the art bipolar and field-effect transistor circuits.
Electron beam induced surface nucleation and low-temperature decomposition of metal carbonyls
Authors: Kunz R. R. , Mayer T. M.
Published: July 2002

The kinetics of low-energy electron beam induced metal film nucleation have been investigated. Experiments performed were the deposition of Fe and Cr from Fe(CO)5 and Cr(CO)6, respectively. It was found that the activation energy for the autocatalytic thermal decomposition of these compounds was lower than the activation energy for decomposition on Si surface. The autocatalytic activation energies were measured as 0.14 eV for Fe(CO)5 and 1.02 eV for Cr(CO)6. The electron beam induced nucleation, together with the rapid autocatalytic decomposition, allowed for selective area metal film growth. A qualitative model based on classical nucleation theory describes well the effect of electron irradiation in inducing film growth. The electron beam induced nucleation step has been modeled in more detail and shows a t4 dependence for the early stages of film growth, in agreement with the observed data.
Emission characteristics and stability of a helium field ion source
Authors: Horiuchi K. , Itakura T. , Ishikawa H.
Published: July 2002

The emission characteristics and stability of a helium field ion source were studied. Detailed measurements of current emitted from the (111) plane of a tungsten emitter revealed a sharp peak in I–V characteristics that shifted toward a higher voltage when the helium pressure increased or the emitter temperature rose. Measurements of the pressure dependence of the ion current showed a decrease in current above the critical pressure, ∼1.3 Pa. To determine why the current decreased, we varied the helium flow rate and the distance between the emitter tip and aperture. The measured characteristics indicated that the decrease in current was not caused by a large flow of warm helium or by a charge exchange of emitted He+ ions with neutral He atoms inside the ion source, so we had to assume the cause lies elsewhere. We recorded ion current versus time characteristics to determine emission stability, which could be improved to ±10% within 60 min by reducing impurities in the helium gas.
Density of states of quasi-two, -one, and -zero dimensional superlattices
Authors: Cho Hung-Sik , Prucnal Paul R.
Published: July 2002

A formalism is developed using the effective mass approximation to evaluate the density of states of quasi-two, -one, and -zero dimensional semiconductor superlattices (QnD SLs). This formalism is applied to GaAs/AlGaAs systems to determine the effect of barrier size on the density of states. The calculated results show that the density of states of QnD SLs evolves from that of QnD structures to that of Q(n+1) D structures with decreasing barrier sizes, where n=0, 1, and 2.
Stoichiometry-related defects in GaAs grown by molecular-beam epitaxy at low temperatures
Authors: Kaminska M. , Weber E. R. , Liliental-Weber Z. , Leon R. , Rek Z. U.
Published: July 2002

GaAs layers grown by molecular-beam epitaxy (MBE) at very low substrate temperatures have gained considerable interest as buffer layers for GaAs metal–semiconductor field effect transistors (MESFET’s) due to high resistivity and excellent device isolation. However, the structure and the electronic properties of such layers have not yet been investigated in detail. We have studied unannealed low temperature (LT) MBE layers grown at 200 °C using transmission electron microscopy (TEM), analytical TEM, x-ray diffraction, the Hall effect, and electron paramagnetic resonance (EPR) techniques. TEM data indicated large arsenic-rich deviations from stoichiometry of ∼1–1.5 at. %. X-ray rocking curves showed a uniform increase of 0.1% in all directions of lattice parameters compared to semi-insulating GaAs substrate. The Hall effect and thermally induced changes of photo-EPR measurements revealed the presence of an acceptor level at an energy of ∼0.3 eV above the valence band. This acceptor level has been tentatively attributed to a gallium vacancy defect.
Mechanism of surface selectivity in aluminum chemical vapor deposition
Authors: Higashi G. S. , Raghavachari Krishnan , Steigerwald M. L.
Published: July 2002

The pyrolysis of triisobutylaluminum occurs much more readily on the surface of Al than on the surface of an oxide. This propensity allows Al to be grown selectively on a wafer and may simplify certain metallization steps in integrated circuit manufacture. In this study, ab initio molecular orbital techniques have been used to elucidate how the transition state energy for beta-hydride elimination of the alkyl ligand varies for Al atoms in different chemical environments. Elementary considerations of the nature of the four-center transition state suggest that the energetics of promoting an electron to the empty pπ-orbital on Al determines the energy of the transition state. Molecular cluster calculations are then used to show that the energy of this electron promotion increases substantially when comparing an Al atom bonded to other Al atoms versus O atoms, explaining the observed surface selectivity.
A study on stress-induced migration in aluminum metallization based on direct stress measurements
Authors: Hinode Kenji , Asano Isamu , Ishiba Tutomu , Homma Yoshio
Published: July 2002

Stress-induced migration is investigated based on direct measurements of average stress in aluminum fine lines. Measured lifetime of the lines is expressed as a power function of the longitudinal tensile stress. The stresses in the fine lines are not directly influenced by the internal stress of the passivation layers, but are caused mainly by thermal expansion mismatch.
A scanning tunneling microscope/scanning electron microscope system for the fabrication of nanostructures
Authors: Ehrichs E. E. , Smith W. F. , de Lozanne A. L.
Published: July 2002

We have developed an ultrahigh vacuum (UHV) scanning tunneling microscope (STM) designed to work in conjunction with a commercial, high-vacuum scanning electron microscope (SEM). The STM resides in its own UHV subchamber which is housed in the JEOL 820 SEM. We have used the SEM to image the STM tip and its location on the sample. This instrument was built to fabricate and study metallic and contamination resist nanostructures and devices on semiconductor surfaces. To create these structures, we use a technique developed in our lab which uses the STM to dissociate organometallic gases or organic residues on semiconductor surfaces. Our system allows precise alignment of the STM-fabricated structures with underlying macroscopic contact pads. The UHV subchamber, which includes standard UHV sample preparation and analysis equipment, is required to prepare atomically flat and clean samples.
Recent advances in an excimer laser source for microlithography
Authors: Elliott D. J. , Pennelli C. P. , Sengupta U. K.
Published: July 2002

This paper describes the advances made in a KrF excimer laser source designed specifically for the deep-UV reduction stepper. Data is presented on key performance aspects that are required for the laser to be used in the next generation of excimer steppers. Major topics discussed will be spectral bandwidth reduction, center wavelength control, pulse-to-pulse energy stability, higher power performance, and the production worthiness of the system. The first generation excimer laser (CX-2LS) for lithography operated at 200 Hz and 3 W, with a spectral bandwidth of 3 pm and a wavelength stability of ±0.5 pm. The new laser (ELS-4000) is designed and engineered to perform at 400 Hz and 4 W with a narrower spectral bandwidth (2 pm) and a wavelength stability of better than ±0.25 pm. In addition, the pulse-to-pulse stability has been improved in stepper-mode operation. The ELS-4000 also employs a new microprocessor controlled gas injection system that permits uninterrupted operation for 10–20 h (7–10 million pulses). This level of performance assures the compatibility of the laser with the requirements of production excimer steppers being developed with higher numerical aperature lenses, larger fields, and higher wafer throughputs.
Developments and trends in the technology of focused ion beams
Authors: Mackenzie Ross A. D.
Published: July 2002

A bibliography has been compiled covering the production, control, and application of high brightness ion beams extracted from liquid metal and gas field ion sources. The development of this research field is studied, from its inception in the 1970’s in United States and United Kingdom research laboratories to its current status as a routine research tool used in the characterization and modification of a wide range of materials in laboratories worldwide. The increasing importance of Japanese research institutions in the development of new source materials and in the use of these beams in semiconductor materials modification is noted.
Bulk and interfacial properties of the compositionally graded InxAl1−xAs (x≤0.52) quasi-insulator and its applications
Authors: Lee P. Z. , Lin C. L. , Chang J. C. P. , Meiners L. G. , Wieder H. H.
Published: July 2002

We have investigated the first in a series of compositionally graded quasi-insulator/semiconductor heterojunction (HJ) capacitors, intended to provide low interface state densities, low dc leakage currents, and high effective surface barriers. Molecular-beam epitaxy (MBE) was used to grow compositionally graded InxAl1−xAs quasi-insulators with x≤0.52 deposited on semiconducting In0.53Ga0.47As layers lattice matched to n+ -InP substrates. Interface states derived from electric field and temperature-dependent capacitance-voltage measurements have densities in the order of ≊1011/cm2 eV and have time constant distributions which are strongly dependent on compositional gradient. The surface barrier height also depends on the compositional gradient and the leakage current is decreased by three orders of magnitude from 10−6 to 10−9 A for a reverse bias of 1 V. Heterojunction insulated gate field-effect transistors (HIGFETs) with an intrinsic transconductance gm=125 mS/mm were obtained on a 5-μm-long gate structure.
Spontaneous change of growth orientation of In0.5Ga0.5P/GaAs superlattices in molecular beam epitaxy
Authors: Nakamura Y. , Mahalingam K. , Otsuka N. , Lee H. Y. , Hafich M. J. , Robinson G. Y.
Published: July 2002

The spontaneous change of growth orientation during the molecular beam epitaxy of In0.5Ga0.5P/GaAs superlattices is investigated as a function of the growth temperature by cross-sectional transmission electron microscopy. It is observed that there exists a critical temperature above which a change in growth orientation from 〈100〉 to 〈311〉 occurs and is characterized by the evolution of V-shaped grooves with {311} facets. Further increase in the temperature enhances the evolution of the {311} facets. It is found that the formation of the V-shaped grooves is along the [01̄1] direction and that the most critical stage for the change in orientation is the interruption after the growth of the GaAs layer with P2 flux. Based on these observations the atomic arrangement on a stable (311) surface resulting from the spontaneous change of the growth orientation is discussed.
Morphology, chemistry, and band bending at Ag– and In–(100)GaSb interfaces
Authors: Chang Y. , Mao D. , Kahn A. , Bonnet J. J. , Soonckindt L. , Le Lay G.
Published: July 2002

In order to extend the comparison of the initial stages of Schottky barrier formation to different surfaces of III–V semiconductors, we present here an investigation with low-energy electron diffraction, Auger electron spectroscopy, and ultraviolet photoemission spectroscopy of In– and Ag–GaSb(100) interfaces at room temperature and after annealing. The initial GaSb surfaces exhibit a (3×2) structure. The low-coverage growth of In and Ag is essentially two dimensional. It is followed by substantial islanding (In) especially after annealing. Band bending measurements show no significant movement of the Fermi level from its initial position near the valence band maximum.
The metal adatom on GaAs(110): A surface negative U center
Authors: Allan G. , Lannoo M.
Published: July 2002

Metallic atom adsorption on the GaAs(110) surface is studied in the tight-binding approximation. By comparison with the experimental results and the lack of As localized states in the band gap, we first show that adsorption cannot occur on a completely unrelaxed surface. The other point concerns the Fermi level position which is located in a minimum density of states. We show that adatom relaxation is quite important and must be considered as it strongly modifies the energy to add or to remove an electron from the crystal. We show that a possible explanation of the observed adatom level energies is the existence of a negative U center.
Optical studies of dry etched GaAs
Authors: Glembocki O. J. , Taylor B. E. , Dobisz E. A.
Published: July 2002

Reactive-ion etching (RIE) and chemically assisted ion-beam etching are routinely used in the fabrication of submicrometer features. Both techniques are known to produce electrical damage. We have used a combination of Raman spectroscopy and photoreflectance to study the effects of dry etching on the depletion layer width and built-in electric field of heavily doped GaAs. We find that RIE reduces the built-in electric field and at the same time increases the depletion layer width. These results can be understood in terms of the formation of a more insulating layer near the surface. Our analysis shows that even though the Fermi-level pinning position can change, the predominant effect of dry etching is to change the carrier density of the near-surface region. We also observe that the use of chlorine-based species in the etch reduces the electrical damage.
Mesa surface recombination current in AlGaAs/GaAs heterojunction bipolar transistors with an emitter–base–emitter structure
Authors: Liu William , Harris James S.
Published: July 2002

An analytical solution for the minority carrier concentration in the base region of an emitter–base–emitter contact topology heterojunction bipolar transistor has been developed. This solution is used to calculate various base current components, including the mesa surface recombination current which is geometry dependent. This mesa surface recombination current affects the efficiency with which the injected carriers from emitter traverse the base and reach the collector. The significance of this mesa surface recombination current is evaluated and the current gain is calculated as a function of device geometry and base doping level. In particular, the effect of this mesa surface recombination is examined for devices specifically designed for high frequency applications. The emitter crowding is also analyzed quantitatively and its effects on device current gain are discussed.
Differences in final state effects for adsorbates on metal and semiconductor surfaces
Authors: Karlsson K. , Kanski J. , Nyqvist O.
Published: July 2002

In a recent article we pointed out the importance of final state effects in the context of Schottky-barrier measurements by core-level photoemission. Using a wave vector-dependent image-screening model, we concluded that final state effects give a substantial contribution to the estimated Schottky-barrier height. In the present comment the list of supporting evidence is extended by new experimental work emphasizing the difference in final state screening at metal and semiconductor surfaces. We find that the measured differences are well reproduced by the screening model with similar parameters as used in our earlier discussion of Schottky barriers.
Remote plasma chemical vapor deposition of copper for applications in microelectronics
Authors: Li Hongwen , Eisenbraun Eric T. , Kaloyeros Alain E.
Published: July 2002

High-quality copper films were deposited from the β-diketonate precursor copper(II) (hexafluoroacetylacetonato), Cu(hfa2), using a remote plasma chemical vapor deposition (RPCVD) process which allows the delivery to the reaction zone of the reactive hydrogen species (mostly atomic and ionic hydrogen) needed for precursor reduction while avoiding plasma-induced substrate damage. The RPCVD process was employed to grow copper films at temperatures in the range 150–250 °C at a reactor pressure and plasma power of, respectively, 0.5–2 Torr and 75–100 W (power density of 1.5–2.2 W/cm2), with an average copper growth rate of 50–75 Å/min. Films thus grown were analyzed by x-ray diffraction, Rutherford backscattering, x-ray photoelectron spectroscopy, four-point resistivity probe, and scanning electron microscopy. The results of these studies showed that the films were pure (impurity levels were below the detection limits of the techniques used), uniform, continuous, and had resistivity values under 2.0 μΩ cm.
Application of x-ray lithography with a single-layer resist process to subquartermicron large scale integrated circuit fabrication
Authors: Deguchi Kimiyoshi , Miyoshi Kazunori , Ban Hiroshi , Kyuragi Hakaru , Konaka Shinsuke , Matsuda Tadahito
Published: July 2002

The applicability of synchrotron radiation x-ray lithography to future ultralarge scale integrated circuit fabrication processes is demonstrated by the test fabrication of subquartermicron bipolar- complementary metaloxide semiconductor devices (SRAM, gate arrays, and several test element groups) with a total size of two-million transistors. Synchrotron radiation lithography is used at four critical levels: gate poly, first metal, via hole, and second metal. Both negative and positive chemically amplified resists are used with a single-layer resist system to simplify the resist process. An overview of the lithography process is presented with emphasis on patterning and overlay performance.
Criteria for use of electron beam charging technique for very large scale integration process inspection
Authors: Jenkins Keith A.
Published: July 2002

A mathematical description of the method of testing by electron beam charging is used to clearly specify its measurement capabilities. The scanning electron microscopy parameters of beam current, frame scan time, and magnification, are used to derive the requirements necessary to distinguish between shorted and isolated structures.
Electrical properties of the thermal induced degradation in TiSi2/TiW/AlSi layered structures
Authors: Nahar R. K. , Vyas P. D.
Published: July 2002

Thermal degradation of TiSi2/TiW/AlSi layered structures is studied by the resistivity measurements on samples annealed in the temperature range of 400–550 °C. The effect of using pure TiW and stuffed TiW(N) as a diffusion barrier on the reaction kinetics of the layered structure is studied. The change in the resistivity is correlated to the rate of formation of intermetallic compound. It is shown that the reaction rate of the compound formation is reduced by about 25% for TiW(N) barrier layer compared to pure TiW annealed at 500 °C.
Chemical modification and characterization of Te-doped n-GaSb (111) single crystals for device application
Authors: Basu S. , Barman P.
Published: July 2002

Ru+3 and Pt+4 modification showed considerable improvement in the surface properties of Te-doped n-GaSb (111) single crystals. The surface carrier concentration (Ns) decreased from 1.24×1017 to 0.42×1017 cm−3 after modification and the surface mobility (μs) increased from 510.86 to 734.56 cm2 V−1 s−1. Au/n-GaSb Schottky diodes prepared after Ru+3 and Pt+4 treatment of GaSb surface showed considerable increase in barrier height (Vs) from 0.55 to 0.68 eV. The dark current density (Jo) decreased from 3.2×10−3 to 8×10−4 A/cm2, and the ideality factor (n) decreased from 3 to 1.54. Although Pt+4 treatment also improved the GaSb surface, treatment with Ru+3 produced superior results. Ru+3 and Pt+4 treatment effectively decreased the etch pit density considerably.
Schottky barrier height and negative electron affinity of titanium on (111) diamond
Authors: van der Weide J. , Nemanich R. J.
Published: July 2002

Titanium was deposited on a natural type IIb diamond surface with a (111) orientation. The titanium-diamond interface was studied with ultraviolet photoemission spectroscopy, using 21.2 eV light. Prior to deposition, the diamond was chemically cleaned, and a sharp (0.5 eV full width at half-maximum) peak was observed at the position of the conduction band, indicating a negative electron affinity surface. After a subsequent argon plasma clean this peak disappeared, while the spectrum shifted 0.5 eV towards higher energies. Upon submonolayer titanium deposition the spectrum shifted 0.5 eV down, while the negative electron affinity peak reappeared. Further titanium depositions caused this titanium induced negative electron affinity peak to be attenuated, indicating that the emission originated from the interface. By determining the relative positions of the diamond valence band edge and the titanium Fermi level, the Schottky barrier height of titanium on diamond (111) was measured and found to be 1.0±0.2 eV. A model for the observed titanium induced negative electron affinity is proposed, based on the Schottky barrier height of titanium on diamond, and the work function of titanium.
Strain and the two-dimensional electronic structure of monolayers of Bi/InAs(110) and Bi/GaAs(110)
Authors: Heskett D. , McIlroy D. , Swanston D. M. , McLean A. B. , DiNardo N. J. , Munekata H. , Ludeke R.
Published: July 2002

The two-dimensional band structure of monolayers of the Bi/InAs(110)(1×1) and Bi/GaAs(110)(1×1) systems have been measured using the technique of angle-resolved photoemission spectroscopy with a synchrotron light source. Measurements of the dispersion and bandwidth of the uppermost occupied electronic state nearest the Fermi level revealed that the bandwidth was significantly smaller for the Bi/InAs(110) system. A comparison to available theoretical calculations of Sb overlayers on III–V semiconductor surfaces implies that the differences between the two Bi systems is greater than would be predicted by a standard theoretical analysis. The authors interpret the results as indicating the importance of strain in these systems.