bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray phosphor deposition technology for co-integration with amorphous silicon imaging arrays
Authors: Gu Z. H. , Tao S. , Chan I. , Nathan A.
Published: July 2002

X-ray phosphor films based on composite materials, for conversion of x rays into visible light, have been synthesized for large area imaging applications. Here the major components are gadolinium oxysulfide doped with terbium (Gd2O2S:Tb), polyvinyl alcohol and water. A small amount of additives (ethylene glycol and sulfonated type agents) were incorporated to disintegrate aggregated phosphor powders and to minimize coating defects. The films, with thicknesses ranging from 380 to 1100 μm and phosphor grain size of 10 μm, were deposited onto glass substrates. The coating quality of the films was evaluated via confocal laser beam scanning microscopy. The x-ray absorption efficiency and the green light emission intensity of the films were measured as functions of film thickness and x-ray source voltage.
Intrinsic thin film stresses in multilayered imaging pixels
Authors: Park B. , Karim K. S. , Nathan A.
Published: July 2002

When thin film devices are integrated in display or imaging arrays, the intrinsic mechanical stresses in the films can be severe enough to cause the films to either crack or even peel off the underlying substrate layer. This is a particular concern in large area x-ray imaging applications based on molybdenum/amorphous silicon (Mo/a-Si:H) Schottky diodes. This family of image sensors can be used for direct detection of x rays without the need for a phosphor layer [W. Zhao and J. A. Rowlands, Med. Phys. 22, 1595 (1995)]. In these sensors, the interaction of x-ray photons with Mo leads to injections of high energy electrons into a reverse-biased a-Si:H depletion layer, thereby producing an amplified output signal due to charge multiplication. The generated charge is read out by a thin film transistor (TFT) which is composed of intrinsic amorphous silicon (i-a-Si:H) as the active channel layer, silicon nitride (a-SiNx) as the insulating layer, and highly doped microcrystalline silicon (n+μc-Si:H) as the contact layer. For example, the i-a-Si:H layer is in compressive stress with a magnitude of 0.116 GPa, whereas low temperature, low resistivity n+μc-Si:H layer is in compressive stress of 1.47 GPa. The a-SiNx layer is in tensile stress of 0.222 GPa. The heavy metals used in the x-ray detector, such as Mo and chromium (Cr) (deposited at 5 mTorr), are found to be in tensile stress of 0.807 and 0.575 GPa, respectively. This article presents the internal mechanical stresses in thin film devices used in x-ray imaging, and more importantly, how the total film stress can be reduced without undermining device performance.
Monte Carlo simulation of vapor transport in physical vapor deposition of titanium
Authors: Balakrishnan Jitendra , Boyd Iain D. , Braun David G.
Published: July 2002

In this work, the direct simulation Monte Carlo (DSMC) method is used to model the physical vapor deposition of titanium using electron-beam evaporation. Titanium atoms are vaporized from a molten pool at a very high temperature and are accelerated collisionally to the deposition surface. The electronic excitation of the vapor is significant at the temperatures of interest. Energy transfer between the electronic and translational modes of energy affects the flow significantly. The electronic energy is modeled in the DSMC method and comparisons are made between simulations in which electronic energy is excluded from and included among the energy modes of particles. The experimentally measured deposition profile is also compared to the results of the simulations. It is concluded that electronic energy is an important factor to consider in the modeling of flows of this nature. The simulation results show good agreement with experimental data.
Reactions of gas-phase atomic hydrogen and deuterium with chemically modified Ir(111) surfaces
Authors: Hagedorn Christopher J. , Weiss Michael J. , Weinberg W. Henry
Published: July 2002

The reactions of gas-phase atomic hydrogen (H(g)) and deuterium (D(g)) with the chemically modified Ir(111)–p(1×2)-O, and deuterium (D(a)) and hydrogen (H(a)) adatom precovered Ir(111) surfaces at 100 K have been studied using thermal desorption mass spectrometry. Although the Ir(111)–p(1×2)-O surface at a temperature of 100 K is passivated with respect to adsorption of gas-phase H2 and D2, the interaction of H(g) and D(g) with this surface at 100 K results in the subsequent desorption of water in thermal desorption spectra. These results suggest that while the dissociative chemisorption of molecular hydrogen on Ir(111) is precluded by the presence of the (1×2)-O oxygen overlayer, energetically “hot” H(g) reacts readily with this oxygen-modified surface. Moreover, a strong kinetic isotope effect has been observed in the interaction of H(g) and D(g) with D(a) and H(a) precovered Ir(111) surfaces at 100 K. We find that H(a) is more readily replaced by D(g) (abstraction cross section of σD(g)=4.7±0.4×10−16 cm2) than is D(a) by H(g) (σH(g)=2.6±0.2×10−16 cm2). These calculated cross sections assume a unity probability for reaction of H(g) and D(g) with the Ir(111)–p(1×2)-O surface. This observed isotopic difference in abstraction cross sections is consistent with the differences associated with the expected zero point energy of the transition state for the abstraction reaction and differences associated with the zero point energy between H and D adatoms.
Organic films prepared by polymer sputtering
Authors: Biederman Hynek
Published: July 2002

Deposition of organic films by means of radio frequency (rf) sputtering of conventional polymers became the center of attention in the 1970s. The interest was particularly in polytetrafluoroethylene (PTFE) and recently it has been renewed. In addition to PTFE, polyimide and polyethylene (PE) sputtering has also been studied. Findings from these studies are briefly reviewed. Our results of the kinetics of rf magnetron sputtering of PTFE by energy resolved mass spectrometry are shown in more detail. Various CXFY species were detected in the discharge, with the composition affected by the discharge parameters. It is assumed that CF, CF2, and CF3 fragments from the sputter process are the most important for film growth. The morphology of fluorocarbon plasma polymer films deposited on Si substrates at various temperatures was observed by means of scanning electron microscopy. It was concluded that below +23 °C, a columnar structure appears. The structure and basic properties of hydrocarbon plasma polymer films prepared by rf sputtering of PE are concisely presented. Composite metal/plasma polymer films prepared by polymer and metal cosputtering are briefly discussed.
Dry vacuum pumps for semiconductor processes: Guidelines for primary pump selection
Authors: Lessard Philip A.
Published: July 2002

Each of the many processes used for the production of ultralarge scale integrated devices or flat panel displays has its own chemical and physical requirements. Many require a vacuum environment that may range from slightly below atmospheric pressure to ultrahigh vacuum. Requirements for system cleanliness often dictate an oil-free pumping system. This article discusses each of the process classes which require a dry primary vacuum pump and offers guidelines for the selection of the proper pump type. There are three classes of pump needed depending on the severity of the process—clean, moderate, and harsh—with escalating complexity and cost for pumps made for the harsher environments. In addition to reviewing some of the latest developments in materials and vacuum design, particular attention is paid to operating experience with the very harshest processes—dielectric deposition and metal etch.
Pinhole decoration in magnetic tunnel junctions
Authors: Allen D. , Schad R. , Zangari G. , Zana I. , Yang D. , Tondra M. C. , Wang D.
Published: July 2002

Magnetic tunnel junctions may experience failure due to local shortcuts in the insulating layers of such devices. To further develop magnetic tunnel junctions, the areal density of pinholes must be analyzed. By electrodepositing copper, we have developed a method to image pinholes and analyze the density of pinholes. Copper selectively nucleates at particular sites, forming structures that can be visualized using an optical microscope. Using this method, we examined the change in size of grown copper structures over time and the increase in the areal density of defects as a function of the applied electrodeposition potential.
Oxidation of Ni3Al(111) at 600, 800, and 1050 K investigated by scanning tunneling microscopy
Authors: Rosenhahn A. , Schneider J. , Becker C. , Wandelt K.
Published: July 2002

The oxidation of Ni3Al(111) at 600, 800, and 1050 K was investigated using scanning tunneling microscopy. Exposing the alloy crystal to oxygen at 600 K results in triangular shaped oxidic nuclei at low coverage. At higher coverage a rather disordered oxide layer can be observed. At 800 K, highly ordered O/Al single layer islands with a triangular shape are formed throughout the coverage range. The islands show a Moiré structure, which is unrotated with respect to the substrate. Oxidation at 1050 K leads to highly ordered Al2O3 thin films that exist in two rotational domains. In conjunction with previous measurements [Rosenhahn et al., Appl. Surf. Sci. 142, 169 (1999); Surf. Sci. 433–435, 705 (1999); C. Becker et al., J. Vac. Sci. Technol. A 16, 1000 (1998)] it can be clearly be seen that the temperature strongly controls the chemical composition and the structure of the oxides.
Gas-phase chemistry in up-scaled plasma enhanced metal-organic chemical-vapor deposition of TiN and Ti(C, N) on tool steel
Authors: Driessen J. P. A. M. , Kuypers A. D. , Schoonman J.
Published: July 2002

In this article, the deposition of TiN and Ti(C, N) in a relatively large scale reactor vessel is discussed. Tetrakis(diethylamine)titanium (TDEAT) was used for the deposition of TiN and Ti(C, N) at low temperatures. Favorable gas-phase conditions for deposition of Ti(C, N) in a pulsed direct current plasma have been determined, making use of mass and optical spectroscopy. Decomposition of TDEAT in a pure hydrogen plasma resulted in the favorable cleavage of diethylamine from the precursor but prevents the formation of Ti(C, N) due to the lack of nitrogen and carbon. Addition of N2 to the hydrogen plasma results in the formation of NHx (1⩽x⩽4), opening transamination pathways. Seemingly high quality Ti(C, N) coatings (Hv=1600) were deposited on WN 1.2370 tool steel.
Electronic properties of MO–CVD grown InGaAs–InP heterojunctions and superlattices
Authors: Voos M.
Published: July 2002

We present optical and magnetotransport experiments performed in InGaAs–InP heterojunctions and superlattices grown by metalorganic chemical vapor deposition. These investigations give evidence of the two-dimensional nature of these new structures, and also some information on their electronic properties.
Damped oscillations in reflection high energy electron diffraction during GaAs MBE
Authors: Van Hove J. M. , Lent C. S. , Pukite P. R. , Cohen P. I.
Published: July 2002

Oscillations in the time evolution of electron diffraction during MBE growth of GaAs are shown to be related to periodic variations in the step distributions on GaAs surfaces during epitaxial growth. Unintentionally doped GaAs surfaces were first prepared by MBE. Then the Ga flux is interrupted until an instrument limited diffraction pattern was obtained. During this process the angular width of the specular beam was measured versus time. When the Ga flux there are intensity oscillations that are weak near the Bragg angle. At the Bragg angle, where the diffraction is insensitive to surface steps, the length of the specular RHEED streak does not change. At angles between the Bragg angles, where steps lengthen the streaks, there are periodic variations in the streak length. We interpret the results in terms of a model in which a partially completed surface has a step distribution with smaller average terrace lengths than a completed surface.
Investigation of localized annealing by electron beams
Authors: Sun H. T. , McMahon R. A. , Ahmed H.
Published: July 2002

An improved method of localized annealing with electron beams,—selective repeat electron beam scanning (SREBS) is described. The annealed region is better delineated than with single scan localized annealing. Three characteristic types of cross sections, perpendicular to an annealed line have been investigated to determine the extent of e-beam induced damage in the ion implanted layer and the substrate. The resolution of the annealed region is limited by edge phenomena caused by the local temperature gradient.
Schottky barrier heights of single crystal silicides on Si(111)
Authors: Tung R. T.
Published: July 2002

Capacitance–voltage and current–voltage characteristics at single crystal silicide–silicon interfaces are studied. Schottky barrier heights are determined for epitaxial NiSi2 and CoSi2 layers grown under ultrahigh vacuum conditions on Si(111). These results demonstrate that there is an influence of interface structure on Schottky barrier height. This dependence suggests a reassessment of many previous interpretations or models of Schottky barriers. It also shows that experimentally measured barrier heights of metal–semiconductor systems with inhomogeneous interface structure are likely to be the averages from those associated with different regions of the interface. Homogeneous metal–semiconductor interfaces are therefore the simplest and most desirable systems for the study of Schottky barrier mechanisms. In particular, the present epitaxial silicide–silicon interfaces represent ideal candidates for detailed theoretical investigations based on experimentally obtained atomic structures.
Theoretical study of Si/Ge interfaces
Authors: Van de Walle Chris G. , Martin Richard M.
Published: July 2002

We present a theoretical study of the structural and electronic properties of pseudomorphic Si/Ge interfaces, in which the layers are strained such that the lattice spacing parallel to the interface is equal on both sides. The self-consistent calculations, based on the local density functional and ab initio pseudopotentials, determine the minimum energy configurations, and the relative position of the Si and Ge bands. The presence of the strains influences the interface dipole, and also causes significant shifts and splittings of the bulk bands. For (001) interfaces we find for the top of the valence bands: Ev, Ge−Ev, Si=0.74 and 0.21 eV, respectively, for the cases corresponding to Ge strained to match a Si substrate and vice versa. A discussion of these results and comparison with experiment is presented.
Transient capacitance study of epitaxial CoSi2/Si〈111〉 Schottky barriers
Authors: Rosencher E. , Delage S. , D’Avitaya F. Arnaud
Published: July 2002

Epitaxial CoSi2/Si structures, grown under ultrahigh vacuum conditions by annealing of room temperature deposited Co layers, are studied by transient capacitance spectroscopy. No electron traps associated to Co diffusion have been detected in the Si bulk within the DLTS detection limit of 1011 cm−3. Nearly ideal Schottky diodes may thus be obtained for annealing temperature below 700 °C and CoSi2 film thickness up to 200 Å. In samples presenting carbon surface contamination prior to Co evaporation, a continuum of states is found, highly localized in the vicinity of the CoSi2/Si interface. The influence of annealing temperature and CoSi2 layer thickness on the defect concentration profile is also studied. The physical origin of such extended defects is briefly discussed.
Application of a focused ion beam system to defect repair of VLSI masks
Authors: Heard P. J. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

A scanning ion beam lithography system has been used for the rework of chromium-on-glass mask plates to repair defects in the VLSI circuit pattern. By using submicrometer diameter beams of gallium and of gold ions to sputter selected areas of the mask, both clear and opaque areas have been generated on the substrate.
Integrated circuit diagnosis using focused ion beams
Authors: Shaver D. C. , Ward B. W.
Published: July 2002

The application of a focused ion beam to voltage-contrast probing and repair of integrated circuits is demonstrated. Holes have been opened through passivation layers and waveforms have been acquired using voltage contrast. Voltage-coding techniques have been used to trace signals and confirm repairs. A complementary metal-oxide semiconductor (CMOS) programmable logic array (PLA) with a design error has been successfully repaired using ion beam milling to disconnect metal lines buried under thick passivation.
Tunneling spectroscopy of the GaAs(110) surface
Authors: Feenstra R. M. , Stroscio Joseph A.
Published: July 2002

The scanning tunneling microscope is used to study the spectroscopy of p-type, n-type, and oxygen-covered GaAs(110) surfaces. On the clean surface, three components of the current are identified—tunneling out of valence-band states, tunneling into conduction-band states, and tunneling through dopant-induced states in the semiconductor. The results are compared with a theoretical computation of the tunneling current, including band bending in the semiconductor. Good agreement between theory and experiment is obtained only when tunneling through the space-charge region of the semiconductor is included. On the oxygen-covered surface, the spectroscopic results show evidence of band bending due to the oxygen adsorbates.
Resist heating effect in direct electron beam writing
Authors: Abe Takayuki , Ohta Kenji , Wada Hirotsugu , Takigawa Tadahiro
Published: July 2002

A new model for the analysis of resist heating is proposed and applied to the direct electron beam writing method using a variably-shaped electron beam system and a single-layer resist. From calculations based on the present model and experiment, it was found that the resist heating effect leads to resist ablation, difference in resist sensitivity between single exposure and multiple exposures, and depth dependence and beam size dependence of resist sensitivity. It also explains the degradation of shaped beam stitching accuracy as well as pattern size error. The resist heating effect is more serious for direct writing than the estimation obtained from a conventional model. In order to realize submicron patterns below 0.5 μm with considerable high throughput, the use of a highly sensitive resist is essential for overcoming the resist heating effect.
Oxidation study by Auger electron spectroscopy and electron energy-loss spectroscopy of GaSb(001) surfaces grown by molecular-beam epitaxy
Authors: Raisin C. , Da Silva F. W. O. , Lassabatere L.
Published: July 2002

GaSb (001) surfaces were prepared by molecular-beam epitaxy. Auger electron spectroscopy (AES) and electron energy-loss spectroscopy (EELS) are reported for clean surfaces exposed to oxygen, and during the process the ionization gauge of the vacuum system is turned on. Successive stages of chemisorption can be distinguished. For oxygen coverage up to 0.5 monolayer, the surface states are saturated by bonding of the oxygen with Ga and Sb atoms. Sb atoms desorb causing significant Sb depletion in the first layer. Larger exposures further increase the coverage and induce, in the EELS spectra, losses related to O(2p) and O(2s) atomic states and new plasmon excitations. In the AES spectra the shift of Auger emission lines which are characteristic of Sb and Ga oxide forms appear; at coverages of about one monolayer back bonds break forming Sb2 O3 and Ga2 O3 . Further exposures to oxygen result in thicker oxide layers of Ga and Sb.
High aspect ratio asymmetric gate structures employed in novel self-aligned high electron mobility transistor technology
Authors: Thompson M. A. , Jelloian L. M. , Nguyen L. D. , Mishra U. K.
Published: July 2002

We report on the development and fabrication of high aspect ratio asymmetric gate structures defined by electron beam lithography. The asymmetric gate or ‘‘gamma’’ gate, as it is referred to, has substantially lower resistance compared to gates fabricated by more conventional techniques. The improved gate resistance is achieved by having an increased cross section (∼3×) over conventional T-shaped gates, which is provided by the asymmetric fabrication scheme. Concurrently, the gamma gate has been incorporated into a self-aligned high electron mobility transistor process, in which its asymmetric shape can be used to define the gate to source and gate to drain spacings independently. The unique tailoring capabilities of this fabrication technique, enables specific gate to source (Lgs), gate to drain (Lgd), and source to drain (Lsd) dimensions independent of the gate length (Lg). Devices fabricated using this technique, had an Lg of 0.10 μm, an Lgs of 0.20 μm, and an Lgd of 0.90 μm. The total Lsd self-aligned dimension was 1.20 μm, with a resultant aspect ratio of 12:1 for a given Lg of 0.10 μm.
Inductive reactances and excess capacitances at WNx/n-GaAs Schottky gate contacts
Authors: Steiner Klaus , Uchitomi Naotaka , Toyoda Nobuyuki
Published: July 2002

Minority carrier injection at forward-biased WNx/n-GaAs Schottky gates lead to diffusion capacitances in excess to the space charge capacitance and inductive reactances in certain frequency ranges. p-buffer layers act as a minority carrier sink which enhances the minority carrier injection. This finally gives stronger excess capacitances and inductive reactances. Furthermore, excess diffusion capacitances can be observed at higher frequencies. The frequency dependent admittance behavior of forward biased WNx/n-GaAs gates is studied in the temperature range between 77 K and room temperature.
Molecular tip arrays for molecular imaging and nanofabrication
Authors: Drexler K. Eric
Published: July 2002

A class of devices based on the atomic force microscope [Phys. Rev. Lett. 56, 930 (1986)] is proposed that would enable imaging with tips of atomically defined structure. These molecular tip array (MTA) systems would enable sequential application of tips with differing structures to a single sample, limited to a small substrate area. MTAs with suitable binding sites can enable nanofabrication via positional chemical synthesis exploiting local effective concentration enhancements of ∼108. A method for canceling or inverting the net van der Waals attraction between a tip and a substrate in a fluid medium is suggested, and a new analysis of imaging forces for proteins is presented.
Scanning tunneling microscopy observation of local damages induced on graphite surface by ion implantation
Authors: Porte L. , de Villeneuve C. H. , Phaner M.
Published: July 2002

Highly oriented pyrolitic graphite was implanted with 50 keV argon ions. Low ion doses were deposited in order to observe, with the scanning tunneling microscope, surface damages due to single-ion impacts. Ion impacts were revealed by the formation of hillocks on the graphite surface. The raising of the surface is attributed to internal stresses which develop in the volume surrounding the ion track as damages and lattice defects are created by the collision cascade process. Structural transformations are induced by ion implantation: On the hillock the graphite structure was lost and no atomic organization of the surface was evidenced. Surface reconstructions and superstructures were also imaged next to some hillocks.
Dynamic in-plane thermal distortion analysis of an x-ray mask membrane for synchrotron radiation lithography
Authors: Chiba Akira , Okada Koichi
Published: July 2002

Dynamic in-plane thermal distortion (IPTD) in an SiN x-ray mask membrane during repetitive scanning x-ray exposure for synchrotron radiation (SR) lithography has been exactly calculated using a model which is close to realistic physical conditions. In order to decide the heating model, a flow regime in the mask-to-wafer proximity gap filled with a 760-Torr helium gas is examined by using the value of the Knudsen number. Heat generated in the mask membrane, a helium gas, and a resist coated on a wafer during x-ray exposure is taken into consideration for the thermal balance equations. The effects of the proximity gap, scanning frequency, and membrane window size on the dynamic IPTD are simulated. The dynamic IPTD indicates a constant value depending on a scanning frequency within the region of the 10–100-μm gap. According to the scanning frequency dependence, the dynamic behavior of the IPTD is divided into three regions: quasistatic, transient, and saturated regions. Using >10-Hz scanning frequencies (saturated region), the dynamic IPTD appears to converge to an equivalent value obtained by a uniform exposure. In the region of >10-mm window size, the dynamic IPTD, not proportional to the window size, seems to be saturated.
Low-temperature heteroepitaxy of Ge on Si by GeH4 gas low-pressure chemical vapor deposition
Authors: Fujinaga Kiyohisa
Published: July 2002

The crystalline quality of Ge grown epitaxially on Si can be improved by using GeH4/H2 gas low-pressure chemical vapor deposition at a low temperature of 410 °C and surface-cleaning processing with a purified-H2 flow prior to GeH4 introduction into a CVD reactor. H2 flow processing is carried out at growth temperature. The dislocation density of a 1.3-μm thick Ge film is nearly 2×108 cm−2, which is as low as that of molecular-beam epitaxy (MBE)-grown Ge films. Stacking faults commonly generated in the CVD-grown Ge films at temperatures higher than 700 °C are not observed. The 700 °C heat treatment of the Ge film reduces dislocation density to 2×107 cm−2 and causes no interface reaction between Ge and Si. This technique is superior to conventional chemical vapor deposition (CVD) techniques for Ge epitaxial growth.
Scanning tunneling microscopy of single platinum atoms and small platinum clusters on highly oriented pyrolytic graphite
Authors: Müller U. , Sattler K. , Xhie J. , Venkateswaran N. , Raina G.
Published: July 2002

We did a topographic study of single platinum atoms, platinum dimers and trimers on highly oriented pyrolytic graphite using a scanning tunneling microscope in air. The particles were produced by evaporation of platinum onto the surface. The platinum atoms and the small clusters could be imaged on the graphite surface without changes for many scans. We show the adsorption site distribution for the monomers. The average bond length of a Pt-dimer on graphite is 2.45 Å. We found only two kinds of Pt-trimers, as a linear chain or as an equilateral triangle. The average bond length is 2.66 Å.
Focused-ion-beam ‘‘cutter’’ and ‘‘attacher’’ for micromachining and device transplantation
Authors: Ishitani T. , Ohnishi T. , Madokoro Y. , Kawanami Y.
Published: July 2002

In focused-ion-beam (FIB) applications of micromachining and device transplantation, four kinds of FIB processes, namely FIB sputtering, FIB-induced etching, redeposition, and FIB-induced deposition, are well utilized. The first and second processes play the role of ‘‘cutter’’ and the third and last processes play the role of ‘‘attacher’’. In this paper, the characteristics of FIB ‘‘cutter’’ and ‘‘attacher’’ are discussed using previously obtained feasibility experimental data and simple simulations.
Surface imaging of focused ion-beam exposed resists
Authors: Hartney M. A. , Shaver D. C. , Shepard M. I. , Melngailis J. , Medvedev V. , Robinson W. P.
Published: July 2002

Silylation processes have previously been applied to optical lithography to overcome deleterious substrate effects and to achieve smaller linewidths. We have applied silylation to focused ion-beam (FIB) lithography, thereby eliminating the need for exposure throughout the entire resist thickness. This approach permits the use of Ga+ ions which have a limited range in the resist but are available from high brightness sources. Thus FIB lithography writing speed can be dramatically improved. Sensitivity of 8×1011 ions/cm2 was found with 30-keV Ga+ using SAL 601 resist, and linewidths below 100 nm have been demonstrated.
Noise (1/f) and dark currents in midwavelength infrared PACE-I HgCdTe photodiodes
Authors: Bajaj J. , Blazejewski E. R. , Williams G. M. , DeWames R. E. , Brown M.
Published: July 2002

A detailed and systematic study of excess (1/f) noise currents and their associated dark currents in midwavelength infrared HgCdTe/CdTe/sapphire (PACE-I) n+/p photodiodes is presented. Variable area diodes ranging in size from 9.0×10−6 to 2.5×10−3 cm2 were examined to determine bulk and surface contributions. Variable temperature measurements ranging from 77 to 250 K were performed to isolate limiting current and noise mechanisms. Two temperature regions, 115–120 and 180–200 K, are emphasized. Both bare surface diodes with only a thin native oxide at the surface and electron-beam deposited CdTe passivated diodes were studied. The measured diodes exhibited high performance with R0A products ≳105 Ω cm2 at 120 K for 4.5 μm cutoff wavelength. Data from a large number of devices are reported. Experimental data at diffusion-current-limited temperatures do not support a proportionality between the noise and dark currents. For these temperatures, the dependence of noise current on temperature yields an activation energy of 0.75Eg which does not support generation–recombination centers located in the midgap. At low temperatures, the analysis of data is complex because of a large scatter in data indicating influence of localized defects. The differences between present results and theoretical model calculations of Kleinpenning are addressed.
Electrostatic force microscope imaging analyzed by the surface charge method
Authors: Watanabe S. , Hane K. , Ohye T. , Ito M. , Goto T.
Published: July 2002

The electrostatic force acting between the probe of the force microscope and the sample surface is theoretically investigated by using the surface charge method. The actual shapes of the probe (an etched tungsten wire) and the sample (gratinglike electrodes) which are used in the experiments are considered to calculate the electrostatic forces quantitatively. It is shown that the macroscopic probe has to be taken into account for the force measurement. However, only the top part of the probe is responsive for the measurement of the force gradient. The imaging properties through the detection of the electrostatic force are also investigated experimentally by using the dynamic (ac) mode force microscope. The potentiometric and topographic effects on the imaging are discussed on the basis of theoretical calculations and the experimental results.
Transmission electron microscopy specimen preparation technique using focused ion beam fabrication: Application to GaAs metal–semiconductor field effect transistors
Authors: Yamaguchi Akira , Shibata Masahiro , Hashinaga Tatsuya
Published: July 2002

A specimen preparation technique using a focused ion beam to generate cross-sectional transmission electron microscopy (TEM) samples of GaAs integrated circuits (ICs) was studied. Using a two axes tilting technique it was possible to prepare sample with minimal thickness (∼10 nm) to enhance spatial resolution in TEM and x-ray spectrometer analysis. This method was applied for failure analysis of degraded GaAs ICs. The interfacial microstructure between the gate metallization and the GaAs substrate, caused by high temperature operation, was also investigated
Synchrotron radiation beamline for x-ray lithography
Authors: Goto Shunji , Taguchi Takao , Osada Toshihiko , Okamura Shigeru , Hisatsugu Tokushige
Published: July 2002

We designed a synchrotron radiation (SR) beamline for x-ray lithography and optimized the beamline based on ray-tracing calculations. For a beamline with a single toroidal mirror, the intensity uniformity in the horizontal direction can be improved by making the meridian radius different from that of the general focal condition. We used this method to determine beamline parameters. Converging the SR beam gave an intensity gain of about 4, and we reduced the nonuniformity of intensity distribution to less than 3%. We also estimated the overlay error due to incorrect mirror parameters to be a maximum of 14 nm with a gap of 20 μm. We calculated an exposure-gap diagram using simulation codes; the calculation accounted for absorbed energy distribution due to Fresnel diffraction, penumbral blur, electron ranges of the secondary electrons in the resist, and development properties. We found that there is a dose margin of at least ±5% to achieve ±10% linewidth control for 0.15 μm feature size for gaps below 20 μm. We made preliminary measurements of spectra and intensity distributions for the constructed beamline, and showed that the performance is as predicted by our calculations.
Capacitance–voltage measurement and modeling on a nanometer scale by scanning C–V microscopy
Authors: Huang Y. , Williams C. C.
Published: July 2002

Presently, a nanometer scale capacitance–voltage (C–V) method for the quantitative measurement of the lateral dopant distribution near a semiconductor surface is being established. An atomic force microscope is used to position a nanometer scale tip at a semiconductor surface, and local C–V measurements are performed. Experimental C–V curves have been performed with tips of sub-50 nm radius on a series of silicon wafers of known dopant density. It is shown that repeatable C–V measurements can be performed with nanometer scale tips, and that the capacitance change from accumulation to depletion varies monotonically with local dopant density. The C–V measurements are compared with the theoretical predictions of a simple analytical model. The experimental measurements will be described and the results will be discussed.
Comparison of surface recombination velocities in InGaP and AlGaAs mesa diodes
Authors: Pearton S. J. , Ren F. , Hobson W. S. , Abernathy C. R. , Chakrabarti U. K.
Published: July 2002

The diode diameter dependence of current density in mesa p–n junctions was used to measure surface recombination velocities (S) for both InGaP and AlGaAs. For InGaP, S values of 4–5×104 cm s−1 were obtained for both wet- and dry-etched mesas, and the surface was relatively insensitive to changes resulting from annealing or plasma exposure. Surface passivation by (NH4)2Sx treatment reduced the recombination velocity by a factor of 2. By contrast, AlGaAs displayed a strong sensitivity to the type of processing steps used in photonic and electronic device fabrication, with values of S as high as 9×105 cm s−1 after low temperature annealing, and as low as 3.7×104 cm s−1 after sulphide passivation.
Calibration, drift elimination, and molecular structure analysis
Authors: Jo/rgensen J. F. , Madsen L. L. , Garnaes J. , Carneiro K. , Schaumburg K.
Published: July 2002

A new automated technique for the estimation of the lateral calibration factors and for the drift in the fast scanning direction of SXM instruments is introduced. It is based on the detection of the reciprocal unit cell in Fourier space. The estimated calibration and drift factors are used for the restoration of distorted images containing self-assembled didodecylbenzene (DDB) molecules physisorbed on graphite. From the corrected images, the DDB unit cells are calculated in the Fourier domain. The long unit cell vector of the DDB molecules is calculated more accurately from images showing the graphite unit cells and the DDB lamellas simultaneously. By use of a correlation averaging technique, the structures of the DDB molecules within the unit cells are furthermore analyzed. The benzene ring and the C2H4 groups are thereby identified in the alkyl chains.
Novel single mirror condenser for x-ray lithography beam lines
Authors: Xiao Jiabei , Cerrina Franco , Rippstein Robert P.
Published: July 2002

In proximity x-ray lithography (XRL), two types of illumination are used: full field and scanning. We describe a single mirror condenser for XRL beam lines which provides a high flux of soft x rays. The surface is generally aspheric, designed using numerical methods, and described by polynomials. The flexible design approach can be used to find a result with specific imaging characteristics according to the various requirements of the beam line, and thus is of more general application. The performance of the designed condenser is verified with ray tracing. For advanced submicron applications, mirror scanning is preferred because of its higher scanning speed. However, with figured mirrors, a small change of grazing angle may cause a large variation of image shape, so that to provide a uniform beam, the scanning of the mirror is compensated by a lateral shift. A uniform exposure of 50×50 mm2 field can be achieved.
Atomic force microscope tip radius needed for accurate imaging of thin film surfaces
Authors: Westra K. L. , Thomson D. J.
Published: July 2002

This article discusses the distortion of atomic force microscope (AFM) images of columnar thin films caused by the finite size of the AFM tip. The amount of distortion in an image depends on the relative sharpness of the tip and the surface features. Two-dimensional numerical simulations were used to predict the effect of this distortion on the accuracy of AFM images. We propose that the ratio of the radius of the curvature of the features in an AFM image to the radius of the tip (RAFM/Rtip) provides an effective measure of the degree of tip induced distortion in AFM images of columnar thin films. Using simulations, we show that, for the distortion in an AFM image of columnar thin films to be undetectable by eye, the radius of the curvature of the features in the AFM image must be 10 times larger than the radius of the tip. At the other extreme, if the radius of the curvature features in the AFM image is less than twice the radius of the AFM tip, the images are severely distorted and not representative of the surface of the thin film. From a study of 23 different thin films we found that for only 6 (26%) thin films did the AFM images have distortion undetectable by eye. For 7 (30%) of the thin films, the AFM images were sufficiently distorted to be nonrepresentative of the surface of the thin film.
Overlay accuracy of a synchrotron radiation stepper evaluated by two-mask double exposure
Authors: Fukuda M. , Suzuki M. , Kanai M. , Tsuyuzaki H. , Shibayama A. , Ishihara S.
Published: July 2002

The overlay accuracy of a synchrotron radiation stepper has been evaluated when different masks are used as in actual exposure. Using several masks requires both high repeatability and accurate offset controllability to perform the proper alignment of the stepper. To this end, a two-mask double-exposure method that considers mask error has been devised. It yields a 3σ deviation of 25 nm for the overlay repeatability of our SS-1 stepper. This is almost the same as in the one-mask double-exposure method, which means that the stepper effectively has an alignment repeatability of less than 25 nm. In addition, a mask stage is developed to improve the offset controllability and enlarge the stroke. The resolution and stroke of the stage are 20 nm and ±1000 μm, respectively, for x and y directions, and 0.5 and ±800 μrad, respectively, for theta. This stepper facilitates the reduction of alignment offset deviations to less than ±10 nm in the x and y directions and less than ±1.0 μrad for rotation.
100 kV electron beam lithography using a Schottky field emission source
Authors: Koek B. H. , Chisholm T. , Somers J. , Davey J. , Romijn J. , Run A. J. v.
Published: July 2002

We have investigated the usage of high energy (100 kV) electron beam lithography for various applications. Exposures with high energy electrons are less susceptible to resist thickness variations. Additional exposures from adjacent pixels and shapes can be corrected relatively easily compared to medium energy exposures (20–50 kV). The 100 kV performance of the Leica Cambridge EBPG5-FE system is described. A beam stability of better than 10 nm and a drift of less than 20 nm/h are combined with a Schottky field emission source for high current density. Spot sizes of 7–165 nm with corresponding currents between 0.7 and 120 nA can be selected to enable both very high resolution and accurate mask making.
Study of silicon etching in CF4/O2 plasmas to establish surface re-emission as the dominant transport mechanism
Authors: Singh Vivek K. , Shaqfeh Eric S. G. , McVittie James P.
Published: July 2002

This article describes an investigation of the etching of polysilicon in a CF4/O2 plasma. The ‘‘undercut’’ observed in etch profiles is related to the surface transport of reaction precursors. The possible mechanisms for this transport include surface re-emission and surface diffusion of the precursors. Simulations of profile evolution, conducted with both mechanisms, are compared with experimental results. The surface reemission simulations are found to predict experimental profile evolution accurately, whereas surface diffusion simulations require unphysical values for the surface diffusion length. Novel test structures have been fabricated and etched under the same conditions as used for trench etching. Surface re-emission simulations accurately predict the etch rate deep inside the shadowed cavity of different structures. On the other hand, simulations assuming surface diffusion to be dominant do not capture even the qualitative trends in test structure etching. This is strong evidence that surface re-emission is the dominant mechanism for transport of etch precursors in CF4/O2 plasmas.
Growth mechanism of GaAs on (110) GaAs studied by high-energy electron diffraction and atomic force microscopy
Authors: Wassermeier M. , Yang H. , Tournié E. , Däweritz L. , Ploog K.
Published: July 2002

Using in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM) we have studied the homoepitaxial growth on the (110) surface of GaAs. RHEED intensity oscillations indicate a layer-by-layer growth mode. The RHEED intensity oscillation frequency, however, decreases at a constant Ga flux with increasing substrate temperature and decreasing As flux, resulting in a lower apparent growth rate. AFM images of the surfaces reveal that at low As pressures large triangular shaped islands that ultimately lead to a rough surface are formed. The size and height of the islands increase and their density decreases with decreasing As pressures. In the area between the islands up to 1 μm large islands and terraces of monolayer height are found. The AFM images indicate that growth via step-propagation on the islands and the monolayer stepped areas between the islands, not contributing to RHEED intensity oscillations, can account for the decrease in the apparent growth rate. For very low growth rates surface roughening due to island formation during growth is completely suppressed, resulting in a well ordered terraced surface with monolayer high steps and up to 0.5 μm large terraces that are due only to the unintentional 0.04° misorientation of the substrates. The formation of these large terrace sizes is due to the surprisingly large diffusion length of the Ga on the (110) surface.
Surface-science aspects of vacuum microelectronics
Authors: Schwoebel P. R. , Brodie I.
Published: July 2002

Vacuum microelectronics (VME) concerns the design and manufacture of vacuum devices and components built to sizes and tolerances similar to those found in solid state microelectronic devices. This technology is well suited for use in electron devices of commercial importance, particularly flat-panel displays. The flat-panel display industry is projected to have annual revenues measured in the tens of billions of dollars by the turn of the century. As opposed to conventional electron tubes that utilize cathodes based on thermionic emission, vacuum microelectronic devices principally utilize cold cathodes based on field-electron emission. The introduction of field-electron emission cathodes can yield unique device performance; however, attaining the level of reliability required for commercial applications requires addressing a host of challenging surface physics and chemistry problems. In this review we outline the surface-science-related issues of importance in VME. These issues cover a large realm of surface science ranging from adsorption/desorption phenomena, surface diffusion, surface passivation, and the deposition of overlayers to cathode bombardment, field-electron current density limits, emission noise, low-voltage phosphors, thin-film growth, and voltage breakdown. As the field of VME is relatively new, many of these surface aspects have not been thoroughly investigated and many more remain to be identified.
Oxidation behavior of aluminum nanopowders
Authors: Aumann C. E. , Skofronick G. L. , Martin J. A.
Published: July 2002

Rutherford backscattering spectrometry, thermogravimetric analysis, and high-resolution transmission electron microscopy were used to investigate the oxidation behavior of ultrafine grain aluminum powder. Fractional change in mass of Al powder samples were obtained as a function of temperature and exposure time for samples with different particle size distributions. As expected from surface energy considerations, the activation energy for oxidation of ultrafine grain particles is less than that for nominally flat surfaces. Activation energy for oxidation of powder samples with average particle diameters from 240 to 650 Å was determined to be 0.5 eV, which is smaller than the value of 1.7 eV known for flat Al samples.
Two-dimensional scanning capacitance microscopy measurements of cross-sectioned very large scale integration test structures
Authors: Neubauer Gabi , Erickson Andrew , Williams Clayton C. , Kopanski Joseph J. , Rodgers Mark , Adderton Dennis
Published: July 2002

Scanning probe technology, with its inherent two-dimensionality, offers unique capabilities for the measurement of electrical properties on a nanoscale. We have developed a setup which uses scanning capacitance microscopy (SCM) to obtain electrical information of cross-sectioned samples while simultaneously acquiring conventional topographical atomic force microscopy (AFM) data. In an extension of our work on very large scale integration cross sections, we have now obtained one-dimensional and two-dimensional SCM data of cross sections of blanket-implanted, annealed Si wafers as well as special test structures on Si. We find excellent agreement of total implant depth obtained from SCM signals of these cross-sectioned samples with conventional secondary ion mass spectrometry (SIMS) profiles of the same samples. Although no modeling for a direct correlation between signal output and absolute concentration has yet been attempted, we have inferred quantitative dopant concentrations from correlation to SIMS depth profiles obtained on the same sample. By these means of indirect modeling, we have found that our SCM technique is sensitive to carrier density concentrations varying over several orders of magnitude, i.e., <1×1015 to 1×1020 atoms/cm3, with a lateral resolution of 20–150 nm, depending on tip and dopant level.
Vacuum emission of hot and ballistic electrons from GaAs
Authors: Fitting H.-J , Hingst Th. , Schreiber E. , Geib E.
Published: July 2002

Intrinsic GaAs layers of 1 and 3 μm thickness on a highly doped n++-substrate, were covered with very thin Au layers (10 nm) in order to manufacture planar field emission cathodes. At nearly the tenfold Gunn field of about 50 kV/cm we observe the beginning of hot and ballistic electron emission into vacuum. The energy distributions span several eV, exceeding even 10 eV for thick samples. We have started to describe this high energy transport by means of Monte Carlo calculations including acoustic and optical phonon interaction of electrons, intervalley scattering, and impact ionization of valence band electrons. In earlier work we have done vacuum emission experiments, electron beam induced conductivity and Monte Carlo calculations to examine and analyze high field transport in ZnS and SiO2.