bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning tunneling microscopy investigations of the surface structure and electronic properties of ternary graphite intercalation compounds
Authors: Kelty Stephen P. , Lieber Charles M.
Published: July 2002

Scanning tunneling microscopy has been used to characterize the surface structure of the KHgC4 (stage 1) and KHgC8 (stage 2) graphite intercalation compounds. Images of the stage 1 and stage 2 materials exhibit a new commensurate 2×2 superlattice in addition to the centered hexagonal lattice observed in images of pristine graphite. Consideration of the intercalant layer structure and previous studies of stage 1 (MC8) and stage 2 (MC24) alkali metal graphite intercalation compounds (GICs) indicate that the 2×2 superlattice is due to a modulation of the surface carbon layer density of states by the periodic (2×2) potential of the potassium ions. In addition, a new orthorhombic superlattice, a=b=0.89 nm and <a−b≂89°, has been observed in images of the stage 1 KHgC4 material. Possible origins of this novel superstructure are discussed.
Plasma–surface interactions in fluorocarbon etching of silicon dioxide
Authors: Butterbaugh J. W. , Gray D. C. , Sawin H. H.
Published: July 2002

The major species present in a fluorocarbon plasma environment were simulated and independently controlled using radical and ion beams in an ultrahigh-vacuum apparatus. The beams used in this study were chosen to determine the importance of CFx radicals in a CF4 plasma; the beams included F and CF2, with a beam of Ar+ to simulate energetic ion bombardment. Both CF2 and F enhance the etching yield of SiO2 under energetic Ar+ bombardment; however, the enhancement with F is twice that seen with CF2 at similar fluxes. When CF2 and F fluxes are used simultaneously, F dominates and the CF2 flux has little effect on the overall etching yield. Combined with previous work on Si substrates, these results are consistent with qualitative theories for SiO2/Si selectivity in fluorocarbon plasmas. Possible elementary steps in the ion-enhanced etching process are proposed and reduced to a two-parameter model which represents the process as ion-enhanced neutral adsorption followed by ion-induced reaction to form volatile products.
An ultrahigh vacuum-compatible scanning tunneling microscope head mounted on a 2 3/4 in. outer diameter flange
Authors: Schmid A. K. , Kirschner J.
Published: July 2002

A simplified ultra-high-vacuum scanning-tunneling-microscope (UHV-STM) was developed. The UHV-STM can be mounted through a 35-mm i.d. flange in arbitrary spatial orientation. It is thermally well-compensated and highly insensitive to vibrations. The scanner provides atomic resolution capability as well as a large scan range of 7×7 μm. The UHV-STM is driven by unmodified ‘‘Nanoscope 2’’ electronics. Samples as well as tips are exchangeable via an airlock system. Topographic images of the 7×7 reconstruction on Si(111) and of micron-size Au islands on Si(111) are shown.
Characterization of the Au surface structure of Al–I–Au light-emitting tunnel junctions
Authors: Hagan H. P. , Ferguson A. J. L. , Turner R. J. , Smith K. W. , Dawson P. , Walmsley D. G.
Published: July 2002

Visible light is emitted from the Au-air interface of Al–I–Au thin-film tunnel junctions (deposited over a thin layer of CaF2 on glass) as a result of the decay of surface plasmon polaritons (SPPs). We show the surface topography of such a Au film and relate its large-scale features to the outcoupling of fast SPP’s to photons. The absence of short-scale roughness features is explained by their disappearance through surface diffusion. To confirm this a controlled sequence of 5-nm, 20-ms scanning tunneling microscope (STM) W tip crashes has been used to produce indentations 3 nm deep with a lateral dimension of 5–7 nm on a Au crystal in air at room temperature. Four sequences of indentations were drawn in the form of a square box. Right from the start, feature decay is observed and over a period of 2 h a succession of images shows that the structure disappears into the background as a result of surface diffusion. The surface diffusion constant is estimated to be 10−18 cm2 s−1. The lack of light output via slow mode SPPs is an inevitable consequence of surface annealing.
Kinetics and dynamics on Si(100)
Authors: Huang Z.-H. , Gryko J. , Allen R. E.
Published: July 2002

The motion of Si atoms at a Si(100) surface is investigated on both short (∼ 1ps) and long (∼1 s) time scales. It is found that silicon atoms in the surface layer can form dimers within a time of order 1 ps. An interesting ‘‘switching’’ between symmetric and asymmetric dimers is observed in some runs. In others, the coexistence of symmetric and asymmetric dimers is observed. On a long time scale, stochastic modeling is used to simulate adsorption, diffusion, and growth. While deposition of Si atoms continues on vicinal Si(100), there is a tendency toward a one-domain surface with double steps. When deposition is turned off, diffusion leads to a two-domain surface with single steps. These conclusions are consistent with recent scanning tunneling microscopy and reflection high-energy electron diffraction observations.
Scanning tunneling microscopy/scanning tunneling spectroscopy observation of step structures of Si (001) and (111) surfaces
Authors: Iwawaki Fumikazu , Tomitori Masahiko , Nishikawa Osamu
Published: July 2002

The step-edge structures of the Si (001) and (111) surfaces roughened by heating at 1300 °C were studied utilizing the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The bunches of 7–8 double layer steps and the 200–300 Å wide terraces were observed on the Si (111) surface. An unexpected finding is the interminglement of single and double atomic layer steps on the vicinal Si (001) surfaces tilted to any orientation. The double layer steps split into two single layer steps at the kink sites of the step edge. The dimer rows on the lower terraces shift in the direction of the rotation of the vicinal surface around the normal axis of the surface. The tunneling spectra at the single step exhibits several peaks at the sample bias voltages 0.6, −0.6, −1.4, −1.7, −2.1, and −2.4 V. The peaks at −1.4 and −1.7 V are found to be particularly sharp and high at the step edge.
Growth structures of electroless copper films for printed wiring boards
Authors: Moffatt Kennedy R. , Minten Karl , Yang Xiuru , Fennell Evans D.
Published: July 2002

Though a mature process, electroless copper deposition occupies an important economic and technological position in the electronics industry today. Virtually all multilayer circuit boards require the process for through hole connections enabling the miniaturization of the board to keep apace with the total electronics trend to higher densities and smaller components. This trend places more stringent requirements on adhesion of the copper and reliability of the film. The process itself consists of two deposition stages, a surface catalyzation with a palladium colloid followed by deposition of copper. The surface presents a composite substrate of greatly different materials on which adhesion is required: copper, silicate glass, and polymeric resins of diverse compositions. To facilitate study of surface structures, we have used highly oriented pyrolitic graphite as a substrate. Scanning tunneling microscopy (STM) has shown the incipient stages of the palladium catalyst and electroless copper. The results of STM investigations have revealed the nucleation, the microisland formation and the surface growth morphology. The surface composition at each step is identified by scanning tunneling spectroscopy. The surface structures and the defect formation on printed circuit board materials are also investigated by AFM.
Mechanisms controlling growth quality of Si–Ge superlattices in different growth directions
Authors: Khor K. E. , Sarma S. Das
Published: July 2002

We apply an empirical potential-based approach to the study of growth quality of Si–Ge/Si superlattices in various directions. The particular emphasis is on understanding quantitatively the strain energetics at the interface. Recent experimental work by Kuan and Iyer show that the best growth morphology is obtained in the [100] directions, while twin formation substantially affects quality on [110] and [111] surfaces. We show that twins do not relax misfit strain, as originally thought, but that twin surfaces allow growth to switch over to energetically more favorable twin directions. We obtain the relative stability of strained Si–Ge superlattices for different orientations which are consistent with the predictions of harmonic elasticity theory. The results should also be applicable to III–V semiconductor superlattices. KI also showed that long-range ordering ocurred only on thick relaxed SiGe layers grown on [100] surfaces and not on thin strained-layer superlattices. We present some numerical results and discuss the mechanism for this phenomenon.
Anisotropic reactive ion etching of InP in methane/hydrogen based plasmas
Authors: McNabb J. W. , Craighead H. G. , Temkin H. , Logan R. A.
Published: July 2002

Reactive ion etching of InP in CH4/H2 has been studied to assess anisotropy and surface morphology. Empirical models have been developed for etch and polymer deposition rates. Highly anisotropic features characterized by high ratios of etch to polymer formation rates are obtained at low methane concentration and relatively high power density. The inclusion of oxygen in the gas composition reduces polymer deposition but increases surface roughness.
Focused ion beam observation of grain structure and precipitates in aluminum thin films
Authors: Barr D. L. , Harriott L. R. , Brown W. L.
Published: July 2002

Reliability in very large scale integrated circuits is strongly dependent on the grain structure of the aluminum metallization used in interconnection between devices on a chip. Commonly used techniques for grain metrology require the use of time consuming sample preparation. Focused ion beam microscopy is well suited to studying grain size and structure because it needs little or no sample preparation and can give information about grain structure throughout the typical 0.5–1 μm thickness of aluminum films. Measurements of grain size and observations of precipitates in aluminum metallization by using focused ion beam are presented.
Formation of complex features using electron-beam direct-write decomposition of palladium acetate
Authors: Stark T. J. , Mayer T. M. , Griffis D. P. , Russell P. E.
Published: July 2002

A focused electron beam has been used to selectively decompose thin films of palladium acetate, (Pd–Ac), resulting in the formation of ≤50 nm wide conductive Pd-rich features. The formation of features from various film thicknesses of Pd–Ac has been investigated using a wide range of electron energies. Monte Carlo simulations of electron energy loss distributions in Pd–Ac films were calculated over a wide range of film thicknesses and electron energies. The Monte Carlo calculations were used to predict the volume over which the energy of the electron beam is deposited within the films. Thin conductive wires having profiles from high aspect ratio to almost circular cross sections produced by varying the electron beam energy were in agreement with the Monte Carlo predictions. Complex multilayer Pd–Ac features were then fabricated by performing overlapping exposures of Pd–Ac films with differing electron beam energies.
Deep three-dimensional microstructure fabrication for infrared binary optics
Authors: Stern M. B. , Medeiros S. S.
Published: July 2002

Anisotropic reactive ion etching of deep Si structures (≥8 μm), planarization of deeply stepped topographies, and multilayer resist processes have been developed for fabrication of silicon IR binary optics devices. The effect of adding O2 and C2F6 to the SF6 feed gas on sidewall profile and etch selectivity (Si:photoresist) has been determined. Vertical profiles, without mask undercutting or surface texturing, and high etch selectivity (≥5:1) have been obtained with a 74% SF6–26% O2 mixture. We have successfully fabricated 8-μm deep Si optics with 16 phase levels and eight-level structures with a total depth of 14 μm in Si.
In situ transmission electron microscopy measurements of the electrical and structural properties of strained layer GeSi/Si p–n junctions
Authors: Ross F. M. , Hull R. , Bahnck D. , Bean J. C. , Peticolas J. , Hamm R. A. , Huggins H. A.
Published: July 2002

We describe experiments to correlate the dislocation structure and the electrical properties of strained layer p–n junction diodes by examining both structural and electrical characteristics simultaneously in a transmission electron microscope. Device characteristics and structural changes are followed on a single specimen as it is subjected in situ to heat treatment designed to induce relaxation. We describe the nucleation and growth of dislocations at the strained interfaces for different diode geometries and the influence of these dislocations on the electrical properties of the diodes. Our results indicate the dominant role of nucleation sites in the relaxation process. We also describe an enhancement in layer stability after patterning and metallizing strained layer heterostructures.
Growth of InN for ohmic contact formation by electron cyclotron resonance metalorganic molecular-beam epitaxy
Authors: Abernathy C. R. , Pearton S. J. , Ren F. , Wisk P. W.
Published: July 2002

We have investigated the feasibility of depositing InN from nitrogen plasmas by electron cyclotron resonance metalorganic molecular-beam epitaxy (ECR MOMBE) for use in ohmic contact formation. Resistivity, growth rate, and morphology were evaluated as a function of microwave power, growth temperature, and trimethylindium flux. Fine-grained polycrystalline films with N/In ratios of 1.15 and resistivities as low as 190 μΩ cm were obtained under optimized growth conditions and represent the first demonstration of nitride growth by ECR MOMBE. Carbon and oxygen backgrounds were below the detection level of Auger electron spectroscopy. Ti/Pt/Au contacts deposited on InN yielded contact resistances of 5–6×10−7 Ω cm2 and are thermally stable at normal alloying temperatures (∼380 °C).
Effects of As flux on Si δ-doped GaAs
Authors: Shih Y. C. Albert , Neikirk D. P. , Streetman B. G. , Magee C. W.
Published: July 2002

The effects of As flux and As species during growth interruption has been studied for Si δ-doped GaAs. Using a valved As cracker source, all the epitaxial layers were grown under identical conditions and the As flux was changed rapidly before and after the growth interruption. With increasing As flux, the electron density decreases by as much as a factor of two at a doping density of 2.0×1013 cm−2. It is also observed that using As4 has a stronger influence on the resulting electron densities than does As2. However, the As flux has minor effect on the Si incorporation and the sticking coefficient of Si is near unity. The electron density is most directly determined by Si autocompensation ratio, which is found to be significantly affected by the As flux.
Cross-sectional imaging of doped layers in epitaxial gallium arsenide films by scanning tunneling microscopy
Authors: Pinnington T. , Patitsas S. N. , Lavoie C. , Sanderson A. , Tiedje T.
Published: July 2002

Cross sections of epitaxial GaAs/GaAlAs layers have been imaged by scanning tunneling microscopy in air, and individual doped layers with different conductivity type have been resolved for the first time in air. In constant current images acquired with a positive tip bias, the n regions appear to be higher than the p regions, by ∼5 Å depending on the junction bias due to an electronic contrast mechanism. A new imaging method is described which decouples the electronic contrast from the topography. In this method, one obtains an image by repetitively interrupting the feedback loop and sampling the tunneling current at a different tip–sample voltage, selected to yield high conductivity-type contrast.
Strained layer single quantum well double-heterostructure optoelectronic switching laser
Authors: Docter D. P. , Claisse P. R. , Taylor G. W.
Published: July 2002

The double-heterostructure optoelectronic switch (DOES) has been demonstrated as a strained layer single quantum well laser. Broad area laser devices exhibited the lowest threshold currents (77 A/cm2 for a 2000 μm device length) ever reported for DOES devices. The devices had ideal electrical switching characteristics of 7.2 V and 1.0 mA/cm2 at the switching condition and 1.6 V and 0.4 A/cm2 at the holding condition. The switching and holding currents are also the lowest reported for any DOES device. For the lasers, the loss was measured to be 7.5 cm−1 and an external efficiency as high as 0.6 W/A was measured for a 400 μm device length.
Characteristics of modulation-doped quantum well lasers grown by molecular-beam epitaxy
Authors: Shank S. M. , Varriano J. A. , Koch M. W. , Wicks G. W.
Published: July 2002

Single quantum well GaAs/AlGaAs lasers with n-type modulation-doped active regions are investigated. The effects of modulation doping on transparency current density and threshold current density are determined and compared to single quantum well lasers with conventional profiles. Modulation doping reduces transparency current density, thereby also reducing threshold current density. Quantum well lasers with electron sheet concentrations of 6×1011 cm−2 reduce threshold current densities by 30%, to low values of less than 150 A/cm2 for long cavities. Lasers with sheet carrier concentrations of 2.4×1012 cm−2 lase on the second quantized state. No degradation of laser performance is observed due to the location of the electrical junction 1000 Å away from the active region or due to free-carrier absorption loss.
Migration-enhanced epitaxial growth of GaAs on Si using (GaAs)1−x(Si2)x/GaAs strained-layer superlattice buffer layers
Authors: Sudersena Rao T. , Nozawa K. , Horikoshi Y.
Published: July 2002

(GaAs)1−x(Si2)x/GaAs strained-layer superlattices (SLS) have been used as buffer layers to reduce the dislocation density in GaAs grown on Si by migration-enhanced epitaxy. The cross-sectional transmission electron microscopy (TEM) investigations revealed extensive threading dislocation bending at each interface of (GaAs)1−x(Si2)x and GaAs, making the SLS highly efficient. The observed highly effective dislocation bending, it is believed that due to a combined effect of built-in strain in the SLS and the relatively high elastic stiffness constant of  (GaAs)1−x(Si2)x  alloys. Plan-view TEM studies indicated dislocation densities <106 cm−2 at a distance of 0.2 μm from the surface of GaAs on Si.
Characterization of GaAs/GaAsP strained multiple quantum wells grown by gas-source molecular beam epitaxy
Authors: Hou H. Q. , Tu C. W. , Shan W. , Hwang S. J. , Song J. J. , Chu S. N. G.
Published: July 2002

GaAs/GaAs1−xPx strained multiple quantum well (SMQW) structures with x ranging from 0 to 0.5 were prepared by gas-source molecular beam epitaxy. High-resolution x-ray rocking curves and transmission electron microscopy show the multilayered GaAs/GaAsP structures to possess good periodicity and crystalline quality. Photoluminescence and photoluminescence excitation spectra show sharp and distinct peaks that are attributed to the various interband excitonic transitions in quantum wells. An energy-level calculation based on an envelope function model suggests Qv=ΔEv/ΔEg=0.42 for strained GaAs/GaAs0.61P0.39 quantum well structure. Moreover, a 90-meV valence-band offset for a GaAs(76.5 Å)/GaAs0.68P0.32(76 Å) SMQW structure is determined from photoluminescence measurements under hydrostatic pressures.
Molecular-beam epitaxial growth condition dependence of reflection high-energy electron diffraction dampening and quantum well photoluminescence
Authors: Block T. R. , Neikirk D. P. , Streetman B. G.
Published: July 2002

The influence of growth conditions on reflection high-energy electron diffraction (RHEED) dampening and quantum well (QW) photoluminescence (PL) were studied. A set of GaAs/AlGaAs QW samples were grown at substrate temperatures between 580 and 660 °C while a second set of samples was grown at 620 °C as the As/Ga incorporation ratio was varied from 1.2 to 2.5. GaAs and AlGaAs RHEED oscillations were measured under the same growth conditions and fitted with a dampening constant. The As/Ga incorporation ratio study showed a clear correlation as both the RHEED dampening and the PL linewidths were found to increase with an increasing As/Ga ratio. The results for the substrate temperature study were more complex, as the PL linewidths were found to increase as the substrate temperature was decreased while the amount of RHEED dampening was found to be essentially constant.
Multiple quantum wells consisting of InAs/GaAs short-period strained-layer superlattice wells for 1.3–1.55 μm photonic applications
Authors: Hasenberg T. C.
Published: July 2002

Solid source molecular-beam epitaxy has been employed to grow InAs/GaAs short period strained-layer superlattices (SPSLS) on InP substrates, and multiple quantum well samples incorporating these SPSLS as the well regions. Excitons are observed in the room-temperature transmission data at 1.3 μm wavelength, without the use of phosphorous. We discuss our novel shutter sequence which involves a total growth interrupt (all shutters closed), and the growth conditions necessary to obtain high quality SPSLS on InP substrates. Furthermore, data including room-temperature absorbance spectra, low temperature photoluminescence, and x-ray diffraction on various samples with band edges in the 1.3–1.6 μm wavelength range are presented.
Epitaxy and doping of Si and Si1−xGex at low temperature by rapid thermal chemical vapor deposition
Authors: Dutartre D. , Warren P. , Sagnes I. , Badoz P. A. , Perio A. , Dupuis J. C. , Prudon G.
Published: July 2002

Rapid thermal chemical vapor deposition has been applied to the epitaxy and p-type doping of Si and Si1−xGex structure on a 1-nm scale using SiH4, GeH4, and B2H6 in an H2 carrier gas. First, the kinetics of silicon growth is studied between 1000 and 550 °C and the results are shown to be consistent with a model based on the Langmuir–Hinshelwood adsorption mechanism. The growth kinetics of the Si1−xGex alloys is determined down to 525 °C and compared to that of the silicon. Transmission electron microscopy characterizations show that epitaxial structures and short-period (1.7-nm) superlattices without any extended defects are grown at these low temperatures. The boron incorporation in Si and Si1−xGex is then studied. At low temperature, doping levels exceeding 1020 holes cm−3 and delta dopings with a real full width at half-maximum around 1 nm are achieved. In the final part, the growth technique is applied to p-type modulation-doped double heterostructures, and we report a hole mobility value as high as 1800 cm2/V s at 30 K for a sheet density of 4×1012 cm−2.
Scanning tunneling microscopy and spectroscopy of Si-based heterostructures
Authors: Yu E. T. , Johnson M. B. , Powell A. R. , Halbout J.-M. , Iyer S. S.
Published: July 2002

We have used cross-sectional scanning tunneling microscopy (STM) and spectroscopy to study the electronic properties of Si (001) p-n junctions and Si/Si1−xGex (001) strained-layer superlattices grown by molecular-beam epitaxy. Spectroscopic measurements on Si p-n junctions show a clear transition between p- and n-type Si, and variations in the band-edge energies can be detected with a spatial resolution of better than 100 Å. Cross-sectional STM measurements on Si/Si1−xGex superlattices show clear topographic contrast between the Si and Si1−xGex layers, and features such as band-edge discontinuities and band bending arising from doping can be seen in spectroscopic measurements across the superlattice structures.
Microfield emitter array triodes with electron bombarded semiconductor anode
Authors: Kitamura Masayoshi , Tanoue Kenji
Published: July 2002

The Schottky diode with a thin Al barrier layer is examined as an electron bombarded semiconductor (EBS) anode for the microfield emitter array (micro-FEA) triode. The electrons from FEA accelerated to 4 keV can be multiplied over 1000 times at an anode. The high frequency performances of the micro-FEA triode with EBS anode are estimated. It is shown that the planer triode with lateral thin film emitter and EBS anode promises over 100 GHz operation.
Air-bridge field-emission vacuum device fabrication with 0.1 μm spacing
Authors: Chen Chun-Yao , Klemer David P. , Shieh Tsay-Jiu , Shieh Jyun-Li , Pujara Manisha
Published: July 2002

A novel approach for the fabrication of air-bridge field-emission vacuum diodes is described. In order to reduce the device operating voltage, a submicron anode/cathode spacing is required for lateral devices which typically causes difficulties with conventional optical lithography. This article reports on a vertical air-bridge thin-film process which achieves a 0.1 μm anode/cathode spacing while avoiding costly patterning lithography. The vacuum devices are designed to use Mo/Au/Au plating as anode and Mo as cathode. A silicon dioxide spacer layer is used to create a submicron gap-spacer within the air-bridge vacuum diode. The results of dc current-voltage characterization on prototype devices are presented. The devices exhibit a low cut-in voltage (21 V) from dc measurements. This novel fabrication process has the benefits of low-cost and simplicity, and significantly reduces the extraction voltage in vacuum field-emission device applications.
In situ laser light scattering for monitoring III–V semiconductor film growth by molecular-beam epitaxy
Authors: Yang K. , Mirabelli E. , Wu Z.-C. , Schowalter L. J.
Published: July 2002

In situ laser light scattering has been employed to monitor the growth of III–V semiconductor films by molecular-beam epitaxy. By using near-normal incidence and scattering geometry, the system was demonstrated to be extremely sensitive to the surface morphology. The results suggest that the surface begins to roughen after 2 ML of InAs deposition on a GaAs substrate. The development of slip lines during the deposition of InxGa1−xAs(70 Å)/GaAs(140 Å) strained-layer superlattice has also been successfully monitored.
Nonlinear regression technique for parameter extraction from field-emission data
Authors: Barry S. W. , Weichold M. H.
Published: July 2002

The standard method for obtaining field emission parameter estimates from current–voltage data is to transform the Fowler–Nordheim equation [L. W. Nordheim, Proc. R. Soc. London Ser. A 119, 626 (1928)] with approximate elliptical functions such that a linear regression technique can be used to obtain the emission area and enhancement factor estimates for a given work function. We present here a method for obtaining the parameter estimates that avoids bias caused by the functional approximations and the data transformation required for the previous method. The parameter bias due to several nonideal measurement situations is also considered. Finally, the method is applied to experimental data.
Single micromachined emitter characteristics
Authors: Tringides M. C. , Seymour P. , Jacobs K. , Busta H. H. , Pogemiller J. D.
Published: July 2002

The emission from a single, lateral micromachined W protrusion on a silica substrate is examined to identify important factors controlling the emission of commercially interesting field emission arrays (FEAs). From the emission pattern of the single tip obtained on a phosphor screen and the I–V characteristics it was concluded that mini protrusions of a few hundred angstroms are responsible for the emission. Large fluctuations in the emission current are caused by absorption–desorption events from the background gas. Comparison of the I–V characteristics and the fluctuations of the single tip to gated FEAs (under the assumption that similar miniprotrusions are responsible for the emission in other geometries) suggests that only a fraction of the tips is emitting.
Diffusion stability of ellipsoidal field-emitter microcathodes
Authors: Eremchenko D. V. , Makhov V. I.
Published: July 2002

The stability of a single-crystal microcathode under the self-diffusion of surface atoms is considered in the conditions of equilibrium between electrostatic and surface tensions. The corrections to the Dyke et al. formula are found.
Multilayer resist dry etching technology for deep submicron lithography
Authors: Tokashiki Ken , Sato Kiyoyuki , Aoto Nahomi , Ikawa Eiji
Published: July 2002

Using an O2+HBr mixed gas plasma, multilayer resist dry etching under low substrate temperature is applied to the 0.25 μm design-rule 256Mb dynamic random access memory fabrication. Anisotropic etching profiles with a critical dimension (CD) loss less than 0.02 μm are obtained by optimizing the amount of HBr in the plasma. With exceeding amounts of HBr, the pattern width varies with the spacing of the patterned lines due to variations of the thickness of deposited on the resist sidewall, causing a large CD loss. This phenomenon is named ‘‘the pattern-dependent deposition.’’ An increase in the HBr flow rate enhances the pattern-dependent deposition. It is also found that the resist overetching can cause the pattern-dependent deposition. An electron dispersive x-ray spectroscopy analysis reveals that under etching conditions of the pattern-dependent deposition, the characteristics of deposited film are similar to that of an oxidized silicon film. In comparison, the deposited film is close to the silicon-rich film when there is no pattern-dependent deposition. A mechanism of the pattern-dependent deposition is discussed.
Molecular-beam epitaxial growth and characterization of inverted, pulse-doped AlGaAs/InGaAs/GaAs transistor structures
Authors: Hoke W. E. , Lyman P. S. , Brierley S. K. , Hendriks H. T. , Pan N. , Carter J. R.
Published: July 2002

Inverted, pulse-doped AlGaAs/InGaAs pseudomorphic high electron mobility transistor structures were grown by molecular-beam epitaxy. Growth conditions were optimized to improve the quality of the selectively doped AlGaAs layer and to minimize dopant diffusion into the InGaAs channel. The sheet densities and mobilities of the inverted structure were found to be essentially equivalent to those obtained with the normal structure. Shubnikov–de Haas measurements exhibited strong oscillations in the magnetoresistance and plateaus in the Hall resistance. Four optical transitions from the lowest bound electron and hole quantum well states were observed in room-temperature photoluminescence spectra.
Dry etching of GaAs and AlGaAs by Cl2 in molecular beam epitaxy system
Authors: Lee H. G. , Fischer R. J. , Zydzik G. J. , Cho A. Y.
Published: July 2002

We have investigated in situ dry etching of GaAs and AlGaAs utilizing Cl2 gas. At 350 °C substrate temperature, the etch rate was 0.2 and 0.5 μm/min for both GaAs and Al0.3Ga0.7As at a Cl2 flow rate of 1 and 4 sccm, respectively. The Arrhenius plots of the etch rate indicates an activation energy of 10 kcal/mol for GaAs. Within the accuracy of our experiments, the AlGaAs etching behaves similarly to that of GaAs. We found that reproducible etching could only be obtained when great care was taken to assure a clean starting surface. Overgrowth of AlGaAs on etched AlGaAs results in a mirrorlike surface.
Low temperature nitridation of silicon by direct ammonia nitridation in a molecular-beam epitaxy reactor
Authors: Higman T. K. , Fayfield R. T. , Hagedorn M. S. , Lee K. H. , Campbell S. A. , Baillargeon J. N. , Cheng K. Y.
Published: July 2002

The direct thermal nitridation of silicon by ammonia in a molecular-beam epitaxial reactor is being reported. These films, which are subsequently thickened by low-pressure chemical vapor deposition, exhibit extremely low surface state densities (∼1010/eV/cm2), which we attribute to extremely low interfacial oxygen contamination.
Wafer-scale temperature mapping for molecular beam epitaxy and chemical beam epitaxy
Authors: Miner C. J. , Watt B. , Moore W. T. , Majeed A. , SpringThorpe A. J.
Published: July 2002

A technique for the measurement of the variation in surface temperature across GaAs and InP wafers under normal molecular beam epitaxy and chemical beam epitaxy growth conditions is described. It is based on measuring heat treatment induced changes in the thickness of an epitaxial layer. The thickness map of a given slice, generated by scanning reflectance spectrometry, is compared with that obtained after a subsequent heat treatment in the deposition system. The thickness difference map obtained by subtracting the two data files is a measure of the evaporative loss of material due to the additional heat treatment. Since the rate of loss of material is exponentially dependent on the surface temperature (activation energy ∼3.7 eV), small temperature variations (<0.2 °C) can be readily measured. The high spatial resolution (<200 μm point-to-point), the whole wafer mapping capability and the use of a differential technique to eliminate thickness variations due to nonthermal causes, enables the effects of substrate mounting and back surface preparation to be clearly discerned.
Reaching consensus and closure on key questions, a history of success, and failure of GaAs surfaces and interfaces at the Proceedings of the Physics and Chemistry of Semiconductor Interfaces
Authors: Spicer W. E. , Green A. M.
Published: July 2002

It is difficult to make scientific progress without consensus and closure. Periodic and focused meetings such as the Proceedings of the Physics and Chemistry of Semiconductor Interfaces (PCSI) provide perhaps an ideal format for this. Two examples are given and examined. The first involves intrinsic pinning of the Fermi level at the surface of GaAs and other III–V semiconductors. This is explored as an example of successful consensus and closure at PCSI. The mechanism for extrinsic pinning of the Fermi level and Schottky barrier formation is given as a second and unsuccessful example. Rather than surveying all models and experiments related to this, this article focuses on the unified defect model and the advanced defect model in order to give specific examples of this failure and suggest approaches which might avoid these problems in the future. Because it is difficult to define ‘‘consensus and closure,’’ considerable space is allocated to the definition and meaning of these concepts.
Reactions between molten aluminum and pyrolytic boron nitride crucibles
Authors: SpringThorpe A. J. , Majeed A. , Ingrey S. J. , Smith G. M. , Bassignana I. C. , Macquistan D. , Szymanski J. T.
Published: July 2002

Pyrolytic boron nitride crucibles, used for the containment of aluminum in molecular-beam epitaxy systems, are attacked by the molten metal. The reaction appears to be self-limiting, with the formation of a coating of aluminum nitride on the crucible walls. The boron is held in solution, in the aluminum, until the concentration is sufficient to cause crystallization of a mixture of aluminum borides. When this point in the cell’s life cycle is reached, the flux from the cell no longer follows a simple exponential temperature dependence.
Very narrow SiGe/Si quantum wells deposited by low-temperature atmospheric pressure chemical vapor deposition
Authors: Grützmacher D. A. , Sedgwick T. O. , Northrop G. A. , Zaslavsky A. , Powell A. R. , Kesan V. P.
Published: July 2002

The optical, structural, and electrical properties of very narrow SiGe quantum wells grown by ‘‘ultra-clean’’ atmospheric pressure chemical vapor deposition (APCVD) are investigated. X-ray reflectivity data reveal abrupt interfaces with a root-mean-square roughness of not more than 0.2 nm. For the first time narrow (4.3 meV) excitonic photoluminescence (PL) spectra were obtained from APCVD grown samples containing SiGe wells with 12.5% to 32.5% Ge. For the narrowest wells PL doublets are observed which are attributed to atomic steps at the SiGe/Si interfaces. The PL and x-ray diffractometry data show that process deposition control for well and barrier width is within the monolayer range. Resonant tunneling diodes fabricated with 2.5-mm-wide Si0.75Ge0.25 wells show world record peak to valley ratios of 4.2. Magneto-transport measurements performed at high magnetic fields of two-dimensional hole gases exhibit pronounced Hall plateaus and well-defined Shubnikov de Hass oscillations, indicating high material quality. The results give evidence that atmospheric pressure chemical vapor deposition, which relies on gas switching sequences of the reactive gases in a hydrogen ambience, is able to produce interface abruptness comparable if not better than reported by any other technique.
Transmission electron microscopy study of two-dimensional semiconductor device junction delineation by chemical etching
Authors: Liu Jingbao , Dass M. Lawrence A. , Gronsky Ronald
Published: July 2002

Quantitative chemical delineation of both n+ and p+ junctions in silicon-based integrated circuits has been achieved and monitored with respect to etching time, temperature, and ultraviolet illumination, using samples prepared by a new planar polishing technique for uniform initial flatness. Junction depths and dopant profiles obtained from cross-sectional transmission electron microscopy images are compared and cross-calibrated with both secondary ion mass spectrometry and spreading resistance profiling, confirming that dopant concentrations of 1017 cm−3 are detected and laterally mapped with 10 nm spatial resolution.
Sputter-initiated resonance ionization spectroscopy: An analytical technique for quantitative and sensitive measurements of impurities and ultra-shallow doping profiles in semiconductors
Authors: Arlinghaus H. F. , Spaar M. T. , Tanigaki T. , McMahon A. W. , Holloway P. H.
Published: July 2002

Sputter-initiated resonance ionization spectroscopy (SIRIS) is an emerging analytical technique for quantitative and sensitive measurements of impurities and ultra-shallow doping profiles in semiconductors. SIRIS has almost all of the advantages of secondary ion mass spectroscopy (SIMS), while making significant improvements in the following SIMS shortcomings: efficiency, matrix dependence, isobaric and molecular interferences, sensitivity, dynamic range, and quantitation accuracy. In this article, the SIRIS technique is described and shows typical SIRIS depth profiles of boron implanted into silicon with dynamic ranges greater than ∼2×106 as well as SIRIS aluminum depth profiles of layered GaAs/AlGaAs/GaAs samples with depth resolution of up to ∼2 nm at 0.5 keV Ar+ primary ion energy. SIRIS’s dynamic range, sensitivity, depth resolution and its limitations, and quantitation accuracy will be discussed in detail.
Improved analysis of spreading resistance measurements
Authors: Dunham Scott T. , Collins Nat , Jeng Nanseng
Published: July 2002

In this article, a system is described for the analysis of spreading resistance data which includes carrier spilling through the solution of Poisson’s equation. The Poisson equation solution requires boundary conditions for the charge density on the beveled surface, which was modeled by considering the presence of surface states with levels within the band gap. Considering surface states allows the deviation from ideality of both n- and p-type calibration curves to be accounted for consistently without empirical contact resistance or variable radius corrections. In addition, the effects of finite probe penetration and change in energy gap due to probe pressure were considered to account for the reduction in peak resistance near junctions observed experimentally as compared to theoretical calculations. The software (SERAPES) can be used both to calculate simulated resistance profiles from doping profiles for process model characterization, as well as to calculate doping profiles directly from spreading resistance measurements.
Automatic generation of shallow electrically active dopant profiles from spreading resistance measurements
Authors: Clarysse T. , Vandervorst W.
Published: July 2002

The calculation of the electrically active dopant profile from spreading resistance measurements requires not only the calculation of the sampling volume correction factor but also a deconvolution of the carrier spilling effects. A completely automatic Poisson-based correction package has been developed which performs this calculation–deconvolution within 1 min on a 486-based microcomputer and supports all the currently known contact models. The capabilities of the package will be demonstrated on an ultra-shallow opposite type implant, a narrow-base transistor and a submicron source-drain implant. Furthermore, a series of requirements is being proposed for the accurate correction of carrier spilling effects. The currently available Poisson contact models will be reviewed with respect to these requirements starting from secondary ion mass spectrometry measurements and an improved contact model involving the parallel circuit of an elastically deformed stress layer and a plastically deformed metallic phase layer will be proposed.
From InP/GaInAsP interface study to nanometer range heterostructure detection with probe method
Authors: Walachová J. , Šroubek Z. , Zelinka J. , Kot M. , Pittroff W.
Published: July 2002

Results of InP/GaInAsP interface study using the contact probe profiling method are presented. Results of the interface study are given for λ=1.3 μm laser heterostructures. A correlation is shown between the shape of the interface in the heterostructure and the threshold current of lasers produced from such heterostructures. The correlation of the results with secondary ion mass spectroscopy measurements is also demonstrated. An idea is given of how to detect the very close spaced interfaces with the contact probe method. Its realization with the use of Kr+ ion bombardment is shown. In conclusion the ballistic electron emission microscopy is suggested as an attractive new method for characterization of shallow heterostructures.
Secondary ion mass spectrometry measurements of shallow boron profiles in cobalt, silicon, and cobalt disilicide
Authors: Mohadjeri B. , Svensson B. G.
Published: July 2002

Implantations of 49BF+2 ions at 35 and 50 keV have been performed in thin films of cobalt and the resulting 11B+ profiles have been measured by low energy secondary ion mass spectrometry (SIMS). Careful crater depth measurements as a function of sputtering time revealed that under 3.0 keV 32O+2 ion bombardment the erosion rate at the surface was ∼70% higher than that in the ‘‘bulk.’’ A correction procedure was applied for determining the true depth of the measured boron distributions, and values of the projected range and the parallel straggling were extracted from the SIMS profiles. By using measured range data for boron in Si, Bragg’s rule was applied for calculating the corresponding values for boron distributions in CoSi2. The results are compared with measured profiles in CoSi2 thin films and theoretical predictions based on Monte Carlo simulations.
Scanning tunneling microscopy of Cl2-gas etched GaAs (001) surfaces using an ultrahigh vacuum sample transfer system
Authors: Osaka Fukunobu , Ishikawa Tomonori , Tanaka Nobuyuki , López Máximo , Matsuyama Isamu
Published: July 2002

A novel ultrahigh vacuum (UHV) sample transfer system was constructed for the purpose of transferring Cl2-gas etched GaAs samples from an in situ processing UHV multichamber to a scanning tunneling microscopy (STM) chamber. First, the performance of the sample transfer system was confirmed by an UHV-STM observation of an As-stabilized (2×4) structure of a molecular-beam epitaxially (MBE) grown GaAs (001) surface. Next, four kinds of Cl2-gas etched samples were prepared in the UHV multichamber, and an UHV-STM observation of these etched surfaces was carried out. A strong dependence of the surface roughness on the etching temperature was observed; a 200 °C Cl2-gas etched GaAs (001) surface exhibited a corrugation amplitude of several nanometers, which was about 1.5-times smaller than that of a 70 °C etched surface. Through annealing under an arsenic pressure at 600 °C which is a typical temperature for MBE growth, the smoothness of the etched surfaces remarkably improved; the corrugation amplitude of the 70 °C etched surface decreased by a factor of 2, and that of the 200 °C etched surface decreased by a factor of 3–4. As a result, the 200 °C etched surface has become very smooth, being only about 1.5-times rougher than the MBE grown surface. This indicates the usefulness of the in situ fabrication processes, since an interface formed by Cl2-gas etching and following MBE regrowth has been guaranteed to be nearly as smooth as an as-grown surface.
Structural properties of the Na/Si(111)2×1 surface studied by photoemission extended x-ray-absorption fine structures
Authors: Mangat P. S. , Soukiassian P. , Huttel Y. , Hurych Z.
Published: July 2002

We present a coverage dependent structural study of Na adsorption on the Si(111)2×1 surface by photoemission extended x-ray-absorption fine-structure, core-level, and valence-band photo- emission spectroscopies using synchrotron radiation. In the submonolayer coverages, our results indicate the existence of two Na adsorption sites having a large difference in ionicity. Furthermore, a clear ionic to covalent transition is observed when completing the sodium monolayer saturation coverage, which corresponds to the alkali atom adsorbed on a threefold hollow site. These results indicate a very different behavior for the Na adsorption on Si(111)2×1 when compared to the Si(100)2×1 surface, where the Na–Si bond remains covalent in nature, even at low coverages.
Hysteresis correction of scanning tunneling microscope images
Authors: Jo/rgensen J. F. , Carneiro K. , Madsen L. L. , Conradsen Knut
Published: July 2002

The hysteresis of the scanning elements in STM are known to cause geometrically distorted images. By analyzing the traces and retraces of the tip, the hysteresis can be quantified and a general model describing the hysteresis can be constructed. That the use of the inverse model can eliminate the hysteresis distortion in STM images is demonstrated. The method does not require any specific ordering of the image. Another method that can be used only on images of surfaces with ordered patterns is also presented. It is an iterative technique where the highest peak in the Fourier domain is maximized by tuning the hysteresis model.
Auger depth profiles of TiN/Ti films in submicron contact holes: A comparison of collimated and uncollimated deposition processes
Authors: Hoener Carolyn F. , Pylant Eddie , Boden Edward G. , Wang Shi-Qing
Published: July 2002

Auger depth profiles are used to compare sputtered Ti, reactively sputtered TiN, and TiN/Ti bilayer films in submicron (0.8 and 0.4 μm) contact/via holes, deposited with and without a collimator. Samples were cleaved and mounted to minimize difficulties associated with the sputter profiling of and data acquisition from recessed features. The Ti and N concentrations were calculated with a subtract-and-weight routine which uses dN(E)/d(E) peak-to-peak intensities. Transmission electron microscopy film thicknesses measurements were used to confirm that the sputter rates were comparable for the various sample mounting geometries. The thickness of films deposited on the contact base, relative to those on the surrounding oxide was greater when the collimator was used. For 0.8 μm contacts, the film thickness ratio obtained using the collimator was nearly twice that obtained with the uncollimated deposition (0.5 versus 0.25 for TiN; 0.8 versus 0.6 for Ti). The benefits of the collimator, for obtaining good coverage of the base of the hole, are more pronounced in smaller geometries. For films deposited with the collimated on 0.4 μm contacts the film thickness ratio was ten times that for films deposited without the collimator (0.4 versus 0.05 for TiN, 0.35 versus 0.03 for Ti). There was no evidence of variations in the TiN stoichiometry for films deposited in confined geometries versus the surrounding oxide for either deposition configuration. There was an increase in the depth of surface oxidation for the Ti-only film deposited on the sidewalls using the collimator. Shadowing effects cause an increase in film porosity when the direction of collimated metal flux is parallel to the sample surface. On exposure to atmosphere, this porosity allows oxidation below the surface of the film.