bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical response from the ultraviolet to the far infrared and atomic force microscopy of Au implanted in CaF2
Authors: Henderson D. O. , Tung Y. S. , Ueda A. , Mu R. , Xue Y. , Hall C. , Collins W. E. , White C. W. , Zuhr R. A. , Zhu Jane G. , Wang Paul W.
Published: July 2002

Gold was implanted into randomly oriented single-crystal CaF2 hosts at doses of 1, 3, 6, and 10×1016 ions/cm2. The modifications of the host resulting from the ion implantation were characterized by measuring the optical response in the 0.0062–6.70 eV range and the changes in surface topography were investigated by atomic force microscopy (AFM). The implantation depth profiles were obtained by Rutherford backscattering measurements. In the as-implanted samples, a peak is observed at 2.33 eV in the electronic spectra which we attribute to the surface plasmon resonance of gold nanocrystals. The 1.24–0.099 eV range shows no significant difference compared to the spectra of the virgin host. However, the far-infrared spectra show a splitting in the longitudinal optical phonon and a decrease in the reflectivity of the transverse optical phonon as the ion dose increases. The surface topography changes from one where the scratch and dig features of the virgin substrate are clearly revealed in the constant force AFM measurements to one where the surface appears to be mottled by the ion implantation. Annealing the samples at 773 K brings about an increase in the surface plasmon intensity and a partial recovery of the intensity of the longitudinal optical phonon. Annealing the ion-implanted samples at temperatures significantly greater than 773 K leads to the development of craters on the CaF2 surface. The crater formation is expected to arise from a strain induced in the host by the growth of gold nanocrystals. Apparently, when the nanocrystals reach a certain size, a critical strain is induced in the crystal such that the primary channel for relaxation is spallation that leads to crater formation.
Nanometer scale lithography of silicon(100) surfaces using tapping mode atomic force microscopy
Authors: Servat J. , Gorostiza P. , Sanz F. , Pérez-Murano F. , Barniol N. , Abadal G. , Aymerich X.
Published: July 2002

Si(100) surfaces have been successfully oxidized at nanometer scale using an atomic force microscope working in tapping mode (TMAFM). To modify the surface, gold coated tips and chromium–gold coated tips have been used in order to apply a positive voltage to the sample against the grounded tip. A silicon oxide line of ∼10 nm lateral dimensions can be routinely grown on Si(100) surfaces by TMAFM, at a tip velocity as high as 0.1 mm/s. Pattern dimensions have been measured for different tip velocities and applied voltages and a tip velocity of up to 10 mm/s has been predicted. The patterns have been successfully used as a lithographic mask for a wet chemical etching.
Use of sputtering and negative carbon ion sources to prepare carbon nitride films
Authors: Murzin Ivan H. , Tompa Gary S. , Forsythe Eric W. , Wei Jianjun , Muratov Victor , Fischer Traugott
Published: July 2002

Carbon nitride may have many different uses as wear and corrosion resistant coatings, electrical insulators, and optical coatings. We report the results of using sputtering and negative carbon ion sources to prepare thin films of carbon nitride. In this work, we compare the tribological properties of the carbon nitride films that were prepared by two separate ion-beam assisted techniques. The first approach used an ONYX-2 magnetron to sputter deposit carbon in a nitrogen atmosphere with and without simultaneous bombardment of the growing film with low-energy (∼50–200 eV) nitrogen ions. The second method utilized a beam of negatively charged carbon ions of 1–5 mA/cm2 current density impinging the substrate at the same time with a positive nitrogen ion beam produced by an “Ion Tech” Kaufman source. We were able to produce microscopically smooth, continuous coatings that are harder than silicon. These films possess wear rates lower than 5×10−7 mm3/Nm and friction coefficients in the range of 0.16–0.6. These data compare favorably with the results obtained by other authors. Raman spectroscopy revealed that the magnetron sputtered films are more structurally disordered than those formed with the negative carbon ion gun. Fourier transform infrared spectroscopy showed the presence of C≡N stretching mode in both types of films.
Ion-assisted etching and profile development of silicon in molecular chlorine
Authors: Levinson Joshua A. , Shaqfeh Eric S. G. , Balooch Mehdi , Hamza Alex V.
Published: July 2002

An ion beam etching study designed to characterize the kinetic and transport processes important in the ion-assisted etching of silicon in molecular chlorine was performed. Monoenergetic argon ion beams were directed normal to a silicon wafer that was simultaneously exposed to a background of molecular chlorine, thereby simulating a low temperature rf plasma etching process. The ion-induced etching yield scaled with the square root of the ion energy for a surface saturated with adsorbed chlorine. Moreover, the yield was found to depend strongly on the ion to neutral flux ratio which was varied over two orders of magnitude. A kinetic model in which the dissociative sticking probability and the yield scale linearly with surface coverage was developed and was found to be consistent with the yield data in the ion energy range of 90–300 eV. Its applicability to etching topography was tested with additional experiments where patterned silicon wafers (with oxide masks and with a range of features and linewidths) were etched at saturation in the apparatus. Minimal lag effects and some microtrenching and sidewall sloping were encountered. The etching selectivity of silicon over oxide at 100 eV was greater than 30. Computer simulations of the etching process and profile development were performed using the kinetic model and a line-of-sight re-emission model for the chlorine transport. Knudsen diffusion was found to be important in the transport of neutrals to the base of the feature, with the aspect ratio dependence of the etch rate becoming significant only at high values of the ion to neutral flux ratio. The agreement between simulation and experiment was good, with the initial sticking probability on a clean surface and the average product stoichiometry as parameters comparing favorably to published results. However, the observed microtrenching and sidewall sloping were not predicted by these simulations.
Effects of bias frequency on reactive ion etching lag in an electron cyclotron resonance plasma etching system
Authors: Doh Hyun-Ho , Yeon Chung-Kyu , Whang Ki-Woong
Published: July 2002

We examined the etch characteristics of SiO2 contact holes which have the sizes of 0.3–1.2 μm in a C4F8+H2 electron cyclotron resonance plasma etching system. We varied the chamber pressure (3–7.5 mTorr), microwave power (300–800 W), gas mixing ratio, bias voltage (100–300 V) and bias frequency (100 –800 kHz) as the experimental parameters to investigate the reactive ion etching (RIE) lag. The RIE lag improved, as the bias voltage increased and this RIE lag improvement was thought to be due to the increase of ion energy incident on the substrate. The RIE lag also improved as the chamber pressure decreased and this improvement is due to the increase of ion current density as the chamber pressure decreases. When we increased the bias frequency from 100 to 800 kHz maintaining the same bias voltage, the RIE lag improved considerably. We calculated energy distribution of ions striking the rf biased substrate using Monte Carlo particle-in-cell method to understand this phenomenon. The ion energy distributions are bimodal when the bias frequencies are below 1 MHz, but as the bias frequency increases from 100 kHz to 1 MHz, the low energy part decreases and the high energy part increases, and it is suggested that this change of ion energy distribution is responsible for the RIE lag improvement with the bias frequency increase.
Fabrication of excess PbO-doped Pb(Zr0.52Ti0.48)O3 thin films using radio frequency magnetron sputtering method
Authors: Kim Tae Song , Kim Dong Joo , Lee Jeon Kook , Jung Hyung Jin
Published: July 2002

As a method for lowering deposition temperature, the effect of 50% excess Pb addition in Pb(Zr0.52T0.48)O3 ceramic target on Pb(Zr0.52T0.48)O3 thin films (4000–5000 Å thickness) was studied. The PZT thin films were grown on Pt/Ti/SiO2/Si(100) substrates by using radio frequency magnetron sputtering method. The existing phase of PZT thin films was confirmed with x-ray diffraction analysis, and growth morphologies were studied with scanning electron microscopy. At the substrate temperature of 440 °C, only the pyrochlore phase existed, and as the substrate temperature was increased, the amount of perovskite phase also increased. It was finally found that the PZT thin films without pyrochlore phase could be fabricated at the temperature as low as 520 °C. It was also observed that the quality of the final phases after the postannealing process severely depends on the initial perovskite phase purity during deposition. The electrical properties of PZT thin films were characterized through P–E hysteresis curves, dielectric constant and loss, and fatigue measurements. It was confirmed that the electrical properties of PZT thin films were closely related to the crystallographic microstructure of PZT thin films.
Effects of Al, Ag, and Ca on luminescence of organic materials
Authors: Choong V.-E. , Park Y. , Gao Y. , Wehrmeister T. , Müllen K. , Hsieh B. R. , Tang C. W.
Published: July 2002

Organic materials have been demonstrated to have the necessary attributes for display applications. In typical organic light emitting devices, metallic electrodes are used to inject charged carriers into the organic electroluminescent (EL) medium. We report severe photoluminescence (PL) quenching of organic thin films comprising the most useful materials, namely 1,4-bis[4-(3,5-di-tert-butylstyryl)styryl]benzene (4PV), upon sub-monolayer deposition of Al, Ag, and Ca in an ultrahigh vacuum environment. The severity of the luminescence quenching, which depends on the type of metal used, can greatly affect the EL device performance. For example, a sub-monolayer coverage of the various metals on a 300 Å 4PV thin film can reduce the PL by as much as 50%. Depositing the 4PV layer onto a metal substrate also exhibits PL quenching. An exciton diffusion length of 200 Å can be estimated from the quenching data.
Sharing of Auger electron spectroscopy and x-ray photoelectron spectroscopy spectral data through the Internet
Authors: Yoshihara Kazuhiro , Yoshitake Michiko
Published: July 2002

In 1994 the Science and Technology Agency of the Japanese Government launched a project to interconnect networks under various ministries and agencies. The project is called the Inter-Ministry Computer Network System (IMNet). As a site of IMNet we are implementing a network-oriented database for surface chemical analysis such as Auger electron spectroscopy and x-ray photoelectron spectroscopy spectra. To create a network-oriented database, the stored spectral data must be shared by the client’s computers. Therefore, spectral data must have a common format, and the energy and intensity scales should be calibrated. To achieve these objectives, the software named the “Common Data Processing System” has been created and is provided via the Internet. A workstation has been installed to store the spectral data acquired on different analysis machines via computer networks. In the future we hope that all computers used with surface analysis machines can be connected to the system so that every surface analyst worldwide can share the spectral data to better characterize surfaces of materials.
Getters and gettering in plasma display panels
Authors: Caloi R. M. , Carretti C.
Published: July 2002

In this article, starting from a calculation of the internal conductance inside AC and DC plasma display panels (PDPs), a simple theoretical model is used to estimate the pressure evolution inside a display during the exhausting process and the lifetime. All the values obtained are then compared to the results of specific measurements carried out on real PDPs. Based on these data, the role of a getter inside PDPs and possible getter configurations are discussed. According to the model proposed, the placement of nonevaporable getters (NEGs) inside the panel in a suitable arrangement is shown to improve the quality of the devices. A NEG can, in fact, act as an in situ pump during the production process (reducing the exhausting time) as well as a gas purifier during the life of the PDP (sorbing the outgassed species).
Growth and characterization of potassium-doped superfulleride thin films
Authors: Swami Nathan , You Yujian , Thompson Mark E. , Koel Bruce E.
Published: July 2002

Growth conditions for the formation of thin films (100–300 Å) of potassium-doped superfullerides (KxC60, x>6) are examined. Thin films of these compounds are formed by depositing C60 onto a potassium precovered single crystal quartz substrate maintained at 200 K or lower, in a proportion of K:C60>12:1, followed by annealing the surface to the K-sublimation temperature (300 K). In situ measurements of electrical and optical properties are used to identify the compounds. The formation of superfullerides is confirmed by C60 doping of these phases to check for the formation of insulating K6C60 with a characteristic absorption spectrum. The absorption spectrum of the superfullerides shows distinct features corresponding to the filling of the t1g band. The presence of two superfulleride phases is suggested, a near-metallic superfulleride KxC60 (x≈11.2) and a more insulating KxC60 (x≈8–9).
Water dissociation and selective absorption in the Zr[V0.5Fe0.5]2 gettering alloy: An x-ray photoemission spectroscopy investigation
Authors: Narducci E. , Kovac J. , Ghezzi F. , Venkataramani N. , Sancrotti M.
Published: July 2002

We report a study, based on x-ray photoemission spectroscopy, on the effects of element-specific selective absorption of the nonevaporable [Zr(V0.5Fe0.5)2] gettering alloy after massive exposure to water vapor (3×103 Pa for ≈2000 h at 400 °C). The specimens have been analyzed both after scraping and along a prolonged Ar+ sputtering in order to comparatively discriminate intergranular versus intragranular properties. Oxygen is found to diffuse into the bulk of the alloy grains giving a distribution of Zr oxides where ZrO2 is the major component. After removal of the outermost atomic layers, Fe and V show a major metallic character in the alloy volume. Traces of Zr hydroxides are also seen. The virgin (nonwater treated) [Zr(V0.5Fe0.5)2] alloy has also been comparatively measured.
High temperature platinum etching using Ti mask layer
Authors: Kim Hyoun-woo , Ju Byong-Sun , Nam Byeong-Yun , Yoo Won-Jong , Kang Chang-Jin , Ahn Tae-Hyuk , Moon Joo-Tae , Lee Moon-Yong
Published: July 2002

Platinum is a strong candidate for an electrode material of the high dielectric capacitors in highly integrated dynamic random access memory devices. However, it is extremely difficult to etch the fine patterns of Pt due to an inherently low etch slope. This characteristic comes from the physical sputtering nature of the Pt etching process. This article reveals that the Pt etching profile depends on the change of the Ti mask layer caused by the increase of wafer temperature during etching. The Pt etching slope of 80° in 0.40 μm pitch was attained by heating the wafer substrate up to 220° with plasma-on. From the transmission electron microscopy analysis the Ti mask is considered to be deformed to TiOx layer in oxygen plasma at high wafer temperature, elevated either by high electrode temperature or plasma irradiation.
Mechanism of C4F8 dissociation in parallel-plate-type plasma
Authors: Hayashi Hisataka , Morishita Satoshi , Tatsumi Tetsuya , Hikosaka Yukinobu , Noda Shuichi , Nakagawa Hideo , Kobayashi Shoji , Inoue Masami , Hoshino Tyuji
Published: July 2002

To investigate the mechanism of C4F8 dissociation in parallel-plate-type plasma, we used several of the latest diagnostic tools and made extensive measurements of electrons, radicals, and ions under conditions that greatly suppressed the effects of plasma-surface interaction. These measurements showed that the amount of light fluorocarbon radicals and ions increased with increasing electron density. The dissociation of C4F8 was analyzed by using rate equations, after confirming the stability and uniformity of the plasma. The total dissociation rate coefficient of C4F8 was 1×10−8 cm3/s, and CF2 radicals were mainly generated from products of C4F8 dissociation. F was mainly generated from CF2 by electron-impact dissociation and lost by pumping. We could estimate that the C2F4 density was roughly comparable to the densities of CF and CF3, and that the surface loss probability of C2F4 increased with increasing electron density. C2F4 might play an important role in the etching because of its rich polymerization characteristics.
Design and performance of InP/GaAsSb/InP double heterojunction bipolar transistors
Authors: Dvorak M. W. , Matine N. , Bolognesi C. R. , Xu X. G. , Watkins S. P.
Published: July 2002

We report a fabrication technique for 1 μm wide emitter finger InP/GaAs0.51Sb0.49/InP double heterojunction bipolar transistors (DHBTs). In this technology, we use a wet-etched undercut airbridge technique to provide device isolation while minimizing parasitics and avoiding damage to semiconductor layers by dry etching. The metalorganic chemical vapor deposition-grown InP/GaAs0.51Sb0.49/InP NpN structure takes advantage of a staggered (“type II”) band lineup at InP/GaAs0.51Sb0.49 interfaces: in this material system the GaAs0.51Sb0.49 base conduction band edge lies 0.18 eV above the InP collector conduction band, thus enabling the implementation of InP collectors free of the collector current blocking effect encountered in conventional Ga0.47In0.53As base DHBTs. The structure results in very low collector current offset voltages, low emitter-base turn-on voltages, and very nearly ideal base and collector current characteristics with junction ideality factors of nB=1.05 and nC=1.00 and DHBTs with cutoff frequencies as high as 106 GHz and breakdown voltages of BVceo=8 V have been implemented, and represent the highest performance ever achieved in this material system. The low turn-on and offset voltages make InP/GaAs0.51Sb0.49/InP DHBTs attractive for long talk-time wireless communication systems, yet these devices can also be adapted to power applications by virtue of their InP collector. Excellent performances are obtained without the need for complex and critical optimizations thanks to the favorable band lineups: all junctions are abrupt and no grading was performed in doping or in material composition.
CdS/CdTe interface analysis by transmission electron microscopy
Authors: Dhere R. G. , Al-Jassim M. M. , Yan Y. , Jones K. M. , Moutinho H. R. , Gessert T. A. , Sheldon P. , Kazmerski L. L.
Published: July 2002

CdTe-based polycrystalline solar cells are leading candidates for terrestrial photovoltaic applications. High efficiency devices have been obtained despite large lattice mismatch between hexagonal CdS and cubic CdTe. In the present work, CdS was deposited by chemical bath deposition on Si substrates, and CdTe was deposited by close spaced sublimation. The chemical nature of the CdS/CdTe interface, structural properties, and their dependence on the fabrication parameters, e.g., substrate temperature (475–600 °C) and postdeposition CdCl2 heat treatment, were analyzed. In addition, the effects of crystallinity of CdS on the interface structural defects were examined. Small spot energy dispersive spectroscopy of the interface revealed a considerable amount of sulfur in CdTe. The concentration of sulfur, in general, was higher in the grains with higher density of structural defects and at the grain boundaries. The planar defect density in CdTe films increased with substrate temperature, whereas the threading dislocation density decreased. Interface analysis showed that the majority of the crystalline defects in the CdTe films deposited on CdS were generated at the interface. The crystallinity of CdS did not have a major influence on the interface defect generation.
Reactive ion etching of Ta–silicide/polysilicon double layers for the fabrication of integrated circuits
Authors: Mattausch H. J. , Hasler B. , Beinvogl W.
Published: July 2002

Polysilicides currently find great interest as low resistivity gate and interconnect materials for integrated MOS circuits. We report on detailed investigations of the dry etching characteristics of Ta–silicide/n+-poly-Si double layers in fluorine and chlorine containing gases. A batch-type parallel plate reactor operated in RIE mode is used. We find a sensitive dependence of the etching results on various process parameters, such as gas mixtures, pressure, and rf power. Possible mechanisms for these findings are discussed. Anisotropic etching of the double layer has been achieved using a two stage process. In addition, we analyze the influence of the layer preparation technique on etching profiles.
Bonding geometries of Cl on Si{111} and Ge{111}
Authors: Bachelet G. B. , Schluter M.
Published: July 2002

We determine the chemisorption geometry of Ci–Si{111} and Cl–Ge{111} by total energy minimization. The calculations are done within the local-density-functional framework using normconserving pseudopotentials. Among the three bonding sites investigated, Cl is found to be most stable in the onefold atop position on both Si{100} and Ge{111}. The calculations confirm the site geometries obtained in recent surface extended x-ray absorption fine structure (SEXAFS) measurements on annealed surfaces. The calculated substrate–Cl bond lengths are in quantitative agreement with the SEXAFS results. We also predict vibrational frequencies for the Cl–substrate modes which, because of the highly ionic character of the bond, should be easily observable by infrared or energy loss spectroscopy.
Binding energies of acceptors in GaAs–AlxGa1−xAs quantum wells
Authors: Masselink W. T. , Chang Yia-Chung , Morkoç H.
Published: July 2002

We have used the variational method to calculate the acceptor binding energies in GaAs–AlxGa1−xAs quantum wells. The calculation includes the coupling of the top four valence bands of both materials in the multiband effective mass approximation. To ensure the convergence of the calculation, a large number of basis functions which are made up of the s-like or d-like spatial states multiplied by j=3/2 spinors are used for the expansion of the acceptor wave function. Because the quantum well potential reduces the symmetry from Td to D2d, the bulk Γ8 acceptor ground state splits into Γ6 and Γ7 states. The Γ6 state is predominantly derived from the heavy-hole subband and the Γ7 state is predominantly derived from the light-hole subband. We have calculated the binding energies of the Γ6 state (measured from the top of the heavy-hole subband) and the Γ7 state (measured from the top of the light-hole subband) for both center doped and edged doped quantum wells for various barrier heights as functions of well width. Except for well widths smaller than ≊40 Å, the Γ7 binding energy is greater than the Γ6 binding energy. In recent studies, the photoluminescence resulting from the acceptor levels to conduction band transition in MBE grown GaAs–AlGaAs superlattices has been measured. Our theoretical results are in excellent agreement with these experimental data.
Laser-stimulated vibrational excitation of an adspecies studied by a generalized master equation: Neutral atomic hydrogen on hydrated KCl(001)
Authors: Beri A. C. , George Thomas F.
Published: July 2002

Vibrational energy transfer between an IR laser, a solid surface, and an adatom is studied by a genralized master equation which includes memory effects. Numerical problems associated with the temporally delocalized memory kernel are overcome by introducing the isomnesic approximation. Results obtained for time scales ranging from 2 ps to 2 μs for H(H20)/KCl(001) show that effective vibrational excitation is possible with low-power lasers (1 W/cm2) in spite of fast phonon relaxation. Detailed time evolution of the system is seen to differ radically from that predicted by Markovian theories, even for fairly long time scales.
Chemical etching of GaAs and InP by chlorine: The thermodynamically predicted dependence on Cl2 pressure and temperature
Authors: McNevin S. C.
Published: July 2002

This paper reports a detailed thermodynamic analysis of the GaAs/Cl and InP/Cl chemical systems, which are of interest in the technological processing of these III–V materials. The thermodynamically predicted dependence of the steady state chemical etching on both Cl2 pressure and temperature is derived assuming Langmuir free evaporation from the surface. The chemical potential data base used in this thermodynamic analysis has been checked for accuracy against all available vapor pressure measurements in the literature. The thermodynamically predicted chemical etching is compared to the etching observed in a Cl2 plasma. This approach shows promise in semiquantitative modeling of the dependence of these reactions on both the temperature and Cl2 pressure. In addition, changes in the surface morphologies resulting from plasma etching appear to be correlated with the thermodynamically predicted transitions of various compounds on the surface.
Interface structure and optical properties of quantum wells and quantum boxes
Authors: Petroff P. M. , Cibert J. , Gossard A. C. , Dolan G. J. , Tu C. W.
Published: July 2002

We investigate two types of GaAs–GaAlAs interfaces in single quantum wells: (a) The abrupt interface produced by growth interruption during molecular-beam epitaxy; (b) the interdiffused interface produced by Ga+ ion implantation and annealing. The abrupt interfaces are shown to contain islands with sizes ≲1.5 μm. The ion implanted and interdiffused interfaces are characterized by an error function Al concentration profile. The Ga and Al interdiffusion is found to be markedly enhanced (up to ≊100 times at 900 °C) following the ion implantation and annealing. Quantum well boxes (QWB) are produced using the implantation enhanced interdiffusion (IEI) process. The new cathodoluminescence spectral lines observed in the analysis of QWB’s are attributed to three-dimensional carrier confinement in the potential wells induced by locally enhanced interdiffusion.
The experimental test of a microwave ion beam source in oxygen
Authors: Asmussen J. , Dahimene M.
Published: July 2002

Recent experiments have demonstrated a microwave (2.45 GHz) plasma disk ion source operating with inert gases both with and without an applied static magnetic field. Earlier results were reported using a preliminary, multicusp static magnetic field configuration produced by alternating pole, small, ∼2.5 kG rare earth magnets surrounding the microwave discharge zone. This electrodeless ion source has been rebuilt incorporating several improvements and has been experimentally tested with different discharge diffusion lengths. The improvements include removing the rare earth magnets from the inside of the microwave cavity and embedding them in the cavity walls. The placement and strength of the magnets allows electron cyclotron resonant surfaces (∼875 G) to lie entirely within the discharge zone. Discharges with different diffusion lengths were created by varying the thickness of the disk-shaped discharge zone. The experimental performance with and without a static magnetic field is discussed at the low flow rates of 2–10 sccm and using a 2.5 cm diam double grid set. Experimental test results are compared to similar ion beam sources in oxygen that employ a dc discharge. The expected lifetime, startup, and shutdown problems and maintenance are also reviewed.
Progress in deep-etch synchrotron radiation lithography
Authors: Ehrfeld W. , Bley P. , Götz F. , Mohr J. , Münchmeyer D. , Schelb W. , Baving H. J. , Beets D.
Published: July 2002

The recent progress in the development of the lithographic processes within the LIGA technique is reported, which is based on deep-etch synchrotron radiation lithography, electroforming, and molding processes (in German: lithografie, galvanoformung, abformung). Mask blanks for high-contrast x-ray masks for 0.2 nm wavelength are fabricated from titanium and beryllium membranes produced by physical vapor deposition techniques. Absorber patterns on these masks can be produced by 50-keV electron-beam pattern generation in 3–5-μm-thick polymethylmethacrylate (PMMA) resists, because the use of beryllium strongly reduces the otherwise marked influence of electrons backscattered from the substrates on the resist profiles. To comply with the requirements of deep-etch lithography cross-linked PMMA resists and suitable multicomponent developers have been formulated. The casting resin-based resists are polymerized directly on the substrate which results in extremely low internal stresses to prevent stress corrosion of the resist structure during development.
Structure and dynamics of strong chemisorption on Si(111) as measured with atomic helium scattering
Authors: Doak R. B.
Published: July 2002

Atomic helium scattering has been used to systematically study strongly chemisorbed overlayers on Si(111) with the principal goal of measuring complete surface phonon dispersion curves for these reconstructed surfaces. The diversity of surface structures and surface lattice dynamics is illustrated with results for As, Cu, Ga, and B chemisorption.
Structure and stability of passivating arsenic sulfide phases on GaAs surfaces
Authors: Sandroff C. J. , Hegde M. S. , Chang C. C.
Published: July 2002

Passivating AsxSy phases that form on GaAs after reactions with aqueous sulfides [Na2S⋅9H2O and (NH4)2S] decompose in the presence of oxygen and light, producing a surface composed primarily of As2O3. X-ray photoelectron spectroscopy (XPS) shows that (NH4)2 S-treated surfaces degrade in two steps with the initial AsxSy (present as a disulfide) degrading by S–S bond cleavage to yield As2O3 and an As2S3 phase like the one that forms on GaAs after Na2S⋅9H2O reactions. XPS reveals little decomposition of surface sulfides in the presence of light or oxygen alone, showing that GaAs passivation could be made long-lived if either is rigorously excluded.
Electromagnetic calculation of soft x-ray diffraction from 0.1-μm scale gold structures
Authors: Schattenburg M. L. , Li K. , Shin R. T. , Kong J. A. , Olster D. B. , Smith Henry I.
Published: July 2002

Because the effects of diffraction during proximity-print x-ray lithography are of critical importance, a number of previous researchers have attempted to calculate the diffraction patterns and minimum achievable feature sizes as a function of wavelength and gap. Work to date has assumed that scalar diffraction theory is applicable—as calculated, e.g., by the Rayleigh–Sommerfeld formulation—and that Kirchhoff boundary conditions (KBC) can be applied. KBC assume that the fields (amplitude and phase) are constant in the open regions between absorbers, and a different constant in regions just under the absorbers (i.e., that there are no fringing fields). An x-ray absorber is, however, best described as a lossy dielectric that is tens or hundreds of wavelengths tall, and hence KBC are unsuitable. In this report we use two numerical techniques to calculate (on a Cray 2 supercomputer) accurate diffracted fields from gold absorbers for two cases: a 30-nm-wide line at λ=4.5 nm, and a 100-nm-wide line at λ=1.3 nm. We show that the use of KBC introduces unphysically high spatial frequencies into the diffracted fields. The suppression of these frequencies—which occurs naturally without the need to introduce an extended source or broad spectrum—tremendously improves exposure latitude for mask features near 0.1 μm and below. In particular, we show that KBC should not be applied to 0.1-μm features and wavelengths near 1.3 nm for gaps below 11 μm.
Azide–novolak resin negative photoresist for i-line phase-shifting lithography
Authors: Uchino Shou-ichi , Tanaka Toshihiko , Ueno Takumi , Iwayanagi Takao , Hayashi Nobuaki
Published: July 2002

A negative photoresist consisting of 4,4′-diazido-3,3′-dimethoxybiphenyl and a novolak resin, called micro resist for i-line (MRI), has been prepared and evaluated for i-line phase-shifting lithography. MRI has a high transmittance (80%/μm) and a high resist contrast (γ) at i line (365 nm). Line-and-space patterns of 0.30 μm were achieved using MRI in conjunction with an i-line phase-shifting lithography. The insolubilization mechanism of MRI is attributed to a secondary amine formed by the reaction of nitrene with novolak resin.
Observation of the temporal evolution of the (1×2) reconstructed Au(110) surface using scanning tunneling microscopy
Authors: Gimzewski J. K. , Berndt R. , Schlittler R. R.
Published: July 2002

We present scanning tunneling microscopy (STM) observations of the Au(110) (1×2) reconstructed surface under ultrahigh vacuum conditions at room temperature. Selected pictures from sequences of STM images taken over several hours are discussed using basic building blocks consisting of steps and domain walls. The temporal evolution of surface structures is clearly observed. Our results unravel the important influence of domain boundaries on the kinetics of the surface in stabilizing energetically unfavorable geometries, such as steps along the [001] direction or steps exposing (331) minifacets.
Tapered etching of aluminum with CHF3/Cl2/BCl3 and its impact on step coverage of plasma-deposited silicon oxide from tetraethoxysilane
Authors: Selamoglu N. , Bredbenner C. N. , Giniecki T. A. , Stocker H. J.
Published: July 2002

The tapered etching of aluminum CHF3/Cl2/BCl3 gas mixtures in a hexode reactive ion etching reactor is reported. The process involves sidewall polymer deposition during etching; Auger analysis of the deposit showed mainly carbon and chlorine. The metal sidewall angle (taper angle) was studied as a function of processing conditions, the spacing between Al lines, and photoresist thickness. The extent of taper increased with increasing CHF3 flow rates, saturating at high flow rates, and decreased with increasing Cl2 flow rates. The extent of taper increased with bias in the range −190 to −230 V, and decreased in the range −230 to −260 V. In addition, the extent of taper increased with increasing spacing and with decreasing photoresist thickness. The taper angle for a given spacing can be tailored in the range 60°–90° by adjusting processing conditions. As expected, the step coverage of plasma-enhanced TEOS oxide on taper-etched aluminum lines showed a marked improvement over that of vertical aluminum lines.
Optical studies of direct modulation doping and quantum wire formation by focused Si on beam implantation
Authors: Li Y. J. , Sasa S. , Beinstingl W. , Miller M. S. , Xu Z. , Snider G. , Petroff P. M.
Published: July 2002

The two-dimensional electron gas (2DEG) produced by a Si++ focused ion beam implantation into GaAs–AlGaAs quantum well structures grown by molecular beam epitaxy (MBE) has been studied by low temperature (15 K) cathodoluminescence (CL), photoluminescence (PL), and photoluminescence excitation (PLE) spectroscopy. Ion channeling effects were used and the Si ion activation was optimized during the rapid thermal annealing following the implantation. PL and PLE measurements were first performed in situ the electron microscope together with the CL to evaluate the 2DEG formation in a uniformly implanted pattern. The localized 2DEG created by linear modulation doping (line dose 1.5×108 ions/cm) was imaged, and a local band bending of ∼25 meV was determined from the monochromatic CL line scanning.
Masks for x-ray lithography with a point source stepper
Authors: Celler G. K. , Biddick C. , Frackoviak J. , Jurgensen C. W. , Kola R. R. , Novembre A. E. , Trimble L. E. , Tennant D. M.
Published: July 2002

We describe some key aspects of proximity x-ray technology currently being developed at AT&T, from mask fabrication to wafer patterning. The masks are primarily based on polycrystalline Si membranes, 1 μm thick, which are formed directly on optically flat glass disks. A tungsten absorber layer is deposited on the membranes by radio-frequency diode sputtering, with in situ stress control in the deposition chamber so that stresses ≤10 MPa are routinely achieved. Patterns are defined in an organosilicon negative resist, P(SI-CMS), using an electron beam writing tool and a neural network based proximity correction algorithm. The patterns are transferred into metallic absorber layers by reactive ion etching in a parallel plate plasma system. Using the above procedure, we have fabricated masks with 0.25 μm features and also some test patterns with lines and spaces as small as 0.1 μm. X-ray exposures were done with a Hampshire 5000P point source stepper, using AZ PF-114 resist from Hoechst–Celanese.
Arsenic precipitate accumulation and depletion zones at AlGaAs/GaAs heterojunctions grown at low substrate temperature by molecular beam epitaxy
Authors: Mahalingam K. , Otsuka N. , Melloch M. R. , Woodall J. M. , Warren A. C.
Published: July 2002

AlxGa1−xAs/GaAs heterojunctions were grown by molecular beam epitaxy under normal growth conditions except that the substrate temperature was 250 °C. After a 1 h anneal at 600 °C, a narrow precipitate depletion (PD) zone was observed on the AlxGa1−xAs sides of the heterojunctions, while a high density precipitate accumulation (PA) zone was observed on the GaAs sides. The formation of these PD and PA zones is explained as a result of diffusion of excess As atoms across the interface from the AlxGa1−xAs layer to the GaAs layer. No significant difference in PD and PA zones was found at interfaces between AlxGa1−xAs grown on GaAs and GaAs grown on AlxGa1−xAs, indicating a negligible effect due to the growth sequence. Widths of PDs were about 250 Å, exhibiting a weak dependence on the Al concentration of the AlxGa1−xAs layers.
How does the chemical nature of the interface modify the band offset?
Authors: Foulon Y. , Priester C. , Allan G. , Garcia J. C. , Landesman J. P.
Published: July 2002

Without the introduction of any external atom, the heterojunction band offsets can be modified by the interface configuration. This phenomenon has been studied, for III–V (100) heterojunctions, from both theoretical and experimental points of view (experiments refer to the lattice-matched GaInAs/InP and GaInP/GaAs systems). The modulation of the band offset is of the range of about 100 meV and only appears when the constituents share neither common anion nor common cation. From a theoretical point of view, the variation of the band offset is related to the modification of interface dipoles due to the chemical rearrangement and to the strain redistribution around the interface.
Trilevel reactive ion etching processes for fabrication of 60 nm germanium structures with high aspect ratio
Authors: Matthies T. , David C. , Thieme J.
Published: July 2002

We investigated the influence of different parameters in reactive ion etching (RIE) on the anisotropy of 60 nm test structures in a 360-nm-thick layer of germanium. Structures of similar dimensions are required for zone plates in x-ray microscopy. A simple optical setup for the holographic exposure of gratings with a period of 120 nm is presented. The gratings cover an area of several mm2. This allows for splitting of the structures perpendicular to the grating lines and successive examination of the etch profiles in a scanning electron microscope. Two different trilevel systems were developed for structuring germanium in a CBrF3 plasma. Both trilevel systems use AZ 1350 photoresist on an intermediate layer of titanium. The bottom layer is either polyimide, which is structured by RIE in an oxygen plasma, or nickel, which is etched in a hydrogen plasma highly selective to titanium. The anisotropy of the germanium etch process has been found to increase with the ratio R of self-bias to gas pressure, whereas the selectivity decreases. The higher stability of the nickel mask allows us to choose higher values of R resulting in etch profiles with nearly vertical sidewalls.
Energy exchange processes in field emission from atomically sharp metallic emitters
Authors: Miskovsky N. M. , Park Sookyung H. , He Jun , Cutler P. H.
Published: July 2002

Resistive heating, thermoelectric, and emission heating or cooling (e.g., the Nottingham effect) are examples of energy exchange processes which are fundamental in determining the thermal stability of electron emitters in high fields and temperatures. In this article, the studies of these energy exchange processes as a function of electrical and geometric properties of the emitter are reported. Specifically, Joule heating and associated thermoelectric effects have been calculated for an irradiated planar diode and a model point-contact diode with a conical tip. For a cone angle of 15°, significant temperature increases (T≥800 K) occur when the induced current densities are ≥108 A/cm2. The temperature rise is confined to the apex region and falls off rapidly beyond about 100 nm. The Nottingham energy exchange process was studied as a function of tip geometry. The inversion temperature, Ti, was calculated for a W tip modeled as a hyperboloid of revolution with a 10 nm radius of curvature. Ti was found to be significantly lower (≥100 K) for sharp emitters (for the same field at the apex) compared to a planar emitter. This can be explained by the relative increase in emission from higher energy states leading to cooling of the cathode emitter. Most significantly, the calculations show that for a given current density, the tip with the sharp geometry will operate at a lower inversion temperature relative to the planar emitter, a result which can be generalized to other pointed geometries.
Fabrication of nanostructures with multilevel architecture
Authors: Taylor R. P. , Adams J. A. , Davies M. , Marshall P. A. , Barber R.
Published: July 2002

The fabrication of a submicron-sized dot, defined by surface gates on a GaAs/AlGaAs heterostructure, is described. Within the dot, a voltage applied to a 200 nm diam central electrode changes the geometry to that of a ring. Contact to the central electrode was achieved using a layer of silicon nitride as an interlevel insulator. This multilayer architecture is presented as a demonstration of an interconnect technique, featuring alignment to within 10 nm, which may be used to link similar discrete nanostructures to form a circuit.
Epitaxial rare earth fluoride insulating layers on semiconductors: Structure, phase transitions, and interface reactions
Authors: Jenkins L. C. , Griffiths C. L. , Hughes A. , Richards J. , Williams R. H.
Published: July 2002

Layers of GdF3 were deposited on Ge(111) and GaAs(111)B surfaces, and the measurements compared with similar ones for HoF3 on Si(111) [C. L. Griffiths, J. E. Macdonald, and R. H. Williams, J. Appl. Phys. 70, 1858 (1991)]. It is shown that the trigonal structure normally only stable at higher temperatures is stable in all cases at room temperature, for thin layers. For thicker films a transition to the orthorhombic phase has been observed and studied by low-energy electron diffraction. Some interesting patterns are observed, and are interpreted in terms of a multidomain orthorhombic structure for HoF3 on Si(111) [C. L. Griffiths, J. E. Macdonald, and R. H. Williams, J. Appl. Phys. 70, 1858 (1991)], with the additional complexity of mirror planes for GdF3 on Ge(111). Interface reactions have also been studied in some detail, using x-ray photoelectron spectroscopy and soft x-ray photoemission spectroscopy. In all cases, except GdF3 on Ge, strong reactions are observed with rare earth silicide formation for HoF3 on Si and more complex products for GdF3 on GaAs. These reactions may be substantially reduced by the incorporation of a passivating interlayer. This is illustrated by the use of an ordered arsenic layer at the LaF3–Si interface.
Materials and failure analysis methods and systems used in the development and manufacture of silicon integrated circuits
Authors: Diebold Alain C.
Published: July 2002

The trends within the electronic industry toward decreasing device dimension and increasing integrated circuit device density are driving developments in analytical technology. The lateral resolution and sensitivity of present generation analytical equipment are challenged by device feature dimensions. In addition, acceptable contamination levels are decreasing. Some of the analysis methods facing this challenge are total reflection x-ray fluorescence, ellipsometry, Auger microprobe, and secondary-ion-mass spectrometry. Networked analytical systems are presently used to improve cycle time for analysis. This type of system allows a focused ion beam tool or a scanning electron microscope to quickly move to previously located electrically active defect. The focus of this presentation will be on the challenges facing materials characterization and failure analysis methods. The discussion will include the effect of networked analytical systems on both problem solving methodology and the potential role of new characterization methods such as heavy-ion backscattering spectrometry and post-ionization of sputtered neutrals.
Improved scanning tunneling microscope feedback performance by means of separate actuators
Authors: Tapson J. , Greene J. R. , Ball A.
Published: July 2002

Scanning tunneling microscopes (STMs) are usually operated in current-feedback mode when scanning over wide areas or rough surfaces. The speed of image acquisition is determined by the scanning rate, which (in this mode) is limited by the bandwidth of the feedback control loop. The control loop bandwidth is usually restricted to frequencies lower than the lowest mechanical resonant frequency (fr) of the STM scanner and tip. This resonant frequency is typically in the range 5–15 kHz and is generally ascribed to mechanical resonance of the piezoelectric scanner tube or scanner tripod. In this article we describe some measured sources of mechanical resonance in STMs, and present a design which eliminates the need to control the scanner at high frequencies. We have established that the lowest mechanical resonance mode may be ascribed to the base mounting structure (in addition to the scanning actuator), depending on the specific design. The complex origins of this mode prevent the use of conventional control techniques at frequencies above fr. We have developed an STM design in which a separate feedback actuator is used to modulate the z position of the sample, independently to the scanning (x and y) actuator. The effective resonance frequency of this actuator is extremely high (in excess of 100 kHz) and the control bandwidth is correspondingly improved.
Arrays of gated field-emitter cones having 0.32 μm tip-to-tip spacing
Authors: Bozler Carl O. , Harris Christopher T. , Rabe Steven , Rathman Dennis D. , Hollis Mark A. , Smith Henry I.
Published: July 2002

We have reduced the gate voltage required to achieve a given emission current density in field-emitter arrays by scaling down the gate-to-tip and tip-to-tip spacing to the unprecedented levels of 0.08 and 0.32 μm, respectively. The submicrometer features of our arrays are patterned using interferometric lithography. Electrical tests of arrays we have fabricated have shown a record low turn-on voltage of 8 V for cesiated molybdenum emitters. Emission current densities of 1600 A/cm2 have been obtained, which is also a record for such structures. These arrays provide large advantages for applications such as flat panel displays and microwave devices.