bluuebunny/crossref_metadata_2025 huggingface dataset:
Low pressure chemical vapor deposition of silicon dioxide below 500 °C by the pyrolysis of diethylsilane in oxygen
Authors: Patterson James D. , Öztürk Mehmet C.
Published: July 2002

Low pressure chemical vapor deposition (LPCVD) of SiO2 in a horizontal LPCVD furnace using liquid diethylsilane and oxygen has been studied. A temperature deposition window ranging from 425–500 °C was observed resulting in a maximum deposition rate of ∼275 Å/min. The pressure dependence of the deposition rate revealed a threshold of ≳950 mTorr for gas phase reactions at a deposition temperature of 450 °C. Analysis of the films by Rutherford backscattering spectroscopy has indicated that as-deposited films are stoichiometric SiO2 for deposition temperatures ≤450 °C. Best case across wafer uniformity was ±5% for a caged boat. Wet chemical and reactive ion etch rates were found to be comparable to those of thermal oxides after annealing. Cross-sectional scanning electron microscopy images of the SiO2 films deposited on 2 μm deep 1 μm wide silicon trenches revealed a conformality of ∼80%. The electrical properties of films deposited at 450 °C were studied. The electrical properties of the films were studied as-deposited and after annealing the films in a cold-wall rapid thermal annealing (RTA) system. RTAs were performed at temperatures ranging from 950 to 1100 °C in Ar, N2, or O2 ambients. Current–voltage, current–temperature, and capacitance–voltage measurements were performed for the electrical characterization. Catastrophic breakdown field measurements have shown electric field strengths of 9.5 MV/cm for as-deposited 500 Å films. A study of the leakage current conduction mechanisms has indicated that as-deposited films exhibit trap conduction mechanisms at high electric fields and temperatures. However, if deposition is followed by a RTA in Ar or O2, the leakage current follows closely the Fowler–Nordheim mechanism and yields a leakage-current electric field dependence comparable to a thermal oxide. Results have shown that values as low as 6 × 1010/cm2 for fixed charge density can be obtained if oxide deposition is followed by a RTA in Ar or N2.
Structural analysis of epitaxial GaAs on on-axis (100) Si grown by ionized source beam epitaxy
Authors: Yoo M. C. , Yun S. J. , Kim K. , Rigsbee J. M.
Published: July 2002

In order to understand the effects of ionized source beam epitaxy (ISBE) on defect formation and film growth kinetics, GaAs films grown on on-axis (100) Si with an ionized As source beam were compared with those grown with conventional neutral source beams using results from reflection high-energy electron diffraction and cross-section transmission electron microscopy (XTEM) analysis. Compared to the very irregular surfaces of the films grown with neutral source beams, very flat surfaces, and higher crystal quality of the films were obtained by the As beam ionization and acceleration. The results of defect characterization using XTEM showed that no antiphase domains were present in the ISBE-grown GaAs epilayer and that the nature of the dislocations and stacking faults in the GaAs epilayer was quite different as compared to the neutral source beam case. This evidence strongly suggests that ionization and acceleration of the As source beam not only enhances the As adatom mobility, but also stimulates the Ga adatom migration so as to prevent Ga atoms from aggregating to form three-dimensional islands during the early stages of the film growth. As a result, the enhanced As and Ga mobilities obtained with the ISBE process promote the coalescence process, thus transforming the nucleation dynamics from three-dimensional growth to layer-by-layer growth.
Line profile measurement with a scanning probe microscope
Authors: Griffith J. E. , Marchman H. M. , Miller G. L. , Hopkins L. C. , Vasile M. J. , Schwalm S. A.
Published: July 2002

Profilometry of high-aspect-ratio, submicron lithographic features with a scanning force microscope is possible if the instrument satisfies several requirements. The probe must be slender enough to reach into narrow holes without sacrificing stability. The force sensor must follow the surface without damaging the sample or the probe. Finally, a position monitor must measure the location of the probe. With such an instrument, high-resolution depth measurements are straightforward. Width measurements are more difficult because of the mixing of the probe shape with sidewalls, but this problem can be overcome through careful control of the probe shape. Measurements of high-aspect ratio features with a characteristic size less than 0.5 μm will be shown, and some of the distortions caused by the probe–sample interaction will be discussed.
Electron intersubband normal incidence absorption in InGaAs/GaAs quantum wells*
Authors: Li H. S. , Karunasiri R. P. G. , Chen Y. W. , Wang K. L.
Published: July 2002

Normal incidence electron intersubband transition in InGaAs/GaAs square quantum wells has been observed. With the incident light polarized (x axis) perpendicular to the growth direction (z axis) of the quantum well, a distinct absorption peak was observed. The absorption peak occurs at a different frequency from the peak induced by a mixed yz-polarized light. The latter has a smaller peak strength and is shifted at a lower frequency in the absorption spectrum, and the shift can be interpreted in part as a result of the depolarization effect. The mechanism responsible for the observation of the normal incidence absorption is discussed.
Optimization of molecular beam epitaxy grown pin multiple quantum well electroabsorption modulators for the 1.5-μm wavelength region
Authors: Chang T. Y. , Sauer N. J. , He Y.
Published: July 2002

Comparisons of several molecular beam epitaxy grown GaInAs/AlInAs and GaInAs/Al0.34Ga0.14In0.52As 12-period multiple quantum well structures show that the largest quantum-confined Stark shift (97 nm at −6 V) can be obtained by using the latter structure with the growth temperature set at 500 °C. Deleterious effects of growth interruptions and system contamination are identified in the photocurrent spectra and their physical interpretations are given. The potential benefit of modulating the substrate temperature during growth was found to be negated by the need to introduce growth interruptions.
Low-temperature epitaxial growth of Zn chalcogenides on GaAs(001) by postheated molecular beams
Authors: Yoneta Minoru , Hamasaki Tetsuya , Ohishi Masakazu , Saito Hiroshi
Published: July 2002

Epitaxial layers of ZnSe and ZnS were grown by molecular-beam epitaxy at temperature as low as 150 °C by using postheated molecular beams generated from elemental materials. To obtain postheated molecular beams as well as to control flux intensity for materials with very high vapor pressure, new types of effusion cells are developed. Experiments under the different temperature and molecular-beam conditions clarified that the enhancement of the surface migration of Zn atoms is essential to the lowering of the growth temperature.
Arsenic reflection from GaAs and AlGaAs surfaces during molecular-beam epitaxy
Authors: SpringThorpe A. J. , Arent D. J.
Published: July 2002

An ion gauge with a direct line-of-sight view of the substrate can be used to monitor the reflected pressure of the group V species at all stages in the molecular-beam epitaxial growth sequence. During growth of GaAs on rotating substrates, periodic oscillations in the pressure signal are observed when As2 is used for surface stabilization, but not with As4. These oscillations can be correlated to arrival of reflected As2 from the reconstructed surface of GaAs. Changes in oscillation amplitude as the substrate temperature is varied, or the arsenic flux is changed, are found to correspond with the onset of different surface reconstructions. Additionally, abrupt changes in the pressure and reflection mass spectrometry signals, which occur on initiating epitaxial deposition, are quantifiably proportional to relative growth rates. Thus, following an appropriate calibration, such measurements can be used for both growth rate and alloy composition estimation during normal epitaxial deposition sequences.
On free-exciton behavior in molecular-beam epitaxially grown Si1−xGex quantum wells
Authors: Rowell N. L. , Noël J.-P. , Houghton D. C. , Wang A. , Perovic D. D.
Published: July 2002

Free-exciton phenomena, observed by photoluminescence (PL) at 20 K, have been studied in a coherent Si1−xGex multilayer grown by molecular-beam epitaxy on Si(100) substrates. Phonon-resolved transitions originating from free excitons were observed in addition to a broad band of luminescence. By studying the excitation density, excitation wavelength, and layer-by-layer dependences of the luminescence intensity we have examined a particular Si1−xGex/Si heterostructure exhibiting both types of PL spectra. In such spectra, whether phonon-resolved or broad PL is predominant depends strongly on these PL conditions as well as the position of a quantum well in the structure. The occurrence of the broad PL peak is correlated with the appearance of morphological features, i.e., interstitial platelets, of higher germanium concentration and such platelets were present at low density in the last-grown wells of this sample. The position of the wells responsible for the interstitial platelet luminescence was determined by two methods, i.e., by removing the last-grown layers by etching and by varying the excitation penetration depth. At 20 K, a transition from phonon-resolved PL to the broad PL band as a function of excitation density occurs as the interstitial platelets become saturated with excitons at increasing excitation densities.
Selective SiGe and heavily As doped Si deposited at low temperature by atmospheric pressure chemical vapor deposition
Authors: Sedgwick T. O. , Grützmacher D. A. , Zaslavsky A. , Kesan V. P.
Published: July 2002

Selective epitaxial Si with added As for n-type doping or Ge for band gap modulation can be deposited in an ultraclean atmospheric pressure chemical vapor deposition system down to temperatures as low as 550–750 °C. Depositions are carried out in a hydrogen ambience using dichlorosilane, HCl, and arsine or germane. The additives, arsine and germane enhance the Si deposition rate at low temperatures so that practical deposition rates can be achieved. HCl, which is used to control deposition selectivity with respect to oxide or nitride, decreases the deposition rate so that final growth rates are in the range 1–5 nm/min. Rutherford backscattering spectrometry was used to measure As concentrations as high as 1×1021/cm3 and Ge concentrations as high as 50%. A selective growth process for SiGe has been used to grow p-type metal–oxide–semiconductor field effect transistors and resonant tunneling diodes which display excellent device characteristics.
Role of space charge in field emission cathodes
Authors: Anderson Weston A.
Published: July 2002

Space charge plays an extremely important role in thermionic vacuum tubes. Normally it can be neglected in the operation of field emitter cathodes because the very high electric fields at the cathode negates the formation of space charge. However at very high current densities, it may be evident in field emission cathodes. This article explores the region where space charge affects the potential distribution in field emission cathodes of the type proposed for use in vacuum microelectronics applications. Rectangular, cylindrical, and spherical geometries are considered.
Design, fabrication, and characterization of a hot-electron vacuum transistor
Authors: Klemer David P. , Chen Chun-Yao , Shieh Tsay-Jiu , Pujara Manisha
Published: July 2002

The design and fabrication of a vacuum transistor is described which uses hot-electron emission through a thin Schottky metallization as a source of electrons for current flow. A thin titanium metallization on p-type ion-implanted gallium arsenide is used to form a Schottky contact. Application of a reverse bias greater than the avalanche breakdown voltage results in the generation of hot-electrons which are extracted by a collector metallization suspended above the Schottky metal. The collector is fabricated using a standard air-bridge fabrication process which is compatible with standard GaAs monolithic microwave integrated circuit technology. Measurements on fabricated prototype devices confirm a collector current which can be modulated by varying the potential applied to the Schottky metallization and consequently the resulting hot-electron generation. Small-signal modeling suggests that the device can be used for voltage and power gain, although the required load resistances are high for the first-generation prototype devices. This transistor may find application as a high-speed amplifier or in switching circuits for display applications.
Comparison of pnp and npn InGaAlAs/InGaAs heterojunction bipolar transistors
Authors: Dodabalapur A. , Chang T. Y.
Published: July 2002

The molecular-beam epitaxial growth conditions and characteristics of npn and pnp heterojunction bipolar transistors in the InGaAlAs/InGaAs material system are described. Direct-current current gains of more than 15 000 have been obtained for npn heterojunction bipolar transistors (HBTs). pnp HBTs have a larger breakdown voltage compared to equivalent npn HBTs. A novel pnp HBT structure in which a strained hole filter is placed just above the base to inject light holes preferentially is proposed. The high speed performance of pnp HBTs is at present limited by emitter series resistance.
Interface contamination by suboxide transport
Authors: Wood Colin E. C. , Wilson Richard A.
Published: July 2002

Evidence is presented to suggest that unintentional concentrations of silicon, germanium, and aluminum at gallium arsenide film substrate interfaces are transported as suboxides. A thermodynamic treatment is used to conclude that arsenic oxide, desorbed from substrates, provides the oxygen for suboxide formation in the vicinity of effusion cells. Silicon and germanium suboxides can then be reduced by gallium on substrate surfaces. Reduction of aluminum suboxide is thermodynamically unfavorable, thus, oxygen is incorporated with the aluminum. An approximate value of 68.4 entropy units results from the analysis for the process As4⇔2As2. This value has not been previously reported.
Generation of fast-switching As2 and P2 beams from AsH3 and PH3 for gas-source molecular-beam epitaxial growth of InGaAs/InP multiple quantum well and superlattice structures
Authors: Jackson S. L. , Baillargeon J. N. , Curtis A. P. , Liu X. , Baker J. E. , Malin J. I. , Hsieh K. C. , Bishop S. G. , Cheng K. Y. , Stillman G. E.
Published: July 2002

In an attempt to maximize the cracking and dimerization efficiencies with the use of Ta baffling, a severe memory effect was observed which necessitated excessive growth pause durations for group V beam switching. This memory effect was significantly reduced by the implementation of separate Ta-tube catalytic hydride crackers for each group V source. A comparison of W and Ta tubes revealed that the catalytic effect which was observed for the decomposition of AsH3 and PH3 on a Ta surface was not observed for a W surface. The improved high-conductance design yielded cracking and dimerization efficiencies on the order of 99% and 90%, respectively. Switching characteristics have been studied using time-resolved quadrupole mass spectrometry, and switching times of <1 s have been achieved for As2 and P2 with significantly longer switching times observed for As4. Multiple layer heterostructures have been grown with the baffled/common cracker and the separate open-tube crackers for evaluation of the memory effects by secondary ion mass spectrometry. InGaAs/InP quantum well structures have been grown with the fast-switching crackers. Double crystal x-ray diffraction, transmission electron microscopy, and low temperature photoluminescence (PL) characterization suggest that the interfaces obtained with the fast-switching crackers are abrupt to within ∼5 Å when short growth interuptions (∼10 s) are used. However, low temperature (5 K) PL excitation spectra indicate that an interface asymmetry is present. These data suggest that despite verification of fast As2 and P2 switching using time-resolved quadrupole mass spectrometry, growth pause optimization, and group III flux stabilization are still required in order to obtain optimal interface quality for InGaAs/InP heterostructures.
Characterization of the Si/SiO2 interface morphology from quantum oscillations in Fowler–Nordheim tunneling currents
Authors: Poler J. C. , McKay K. K. , Irene E. A.
Published: July 2002

As design rules shrink to conform with ultra-large-scale integration device dimensions, gate dielectrics for metal–oxide–semiconductor field effect transistor structures are required to be scaled to below ∼60 Å, where some properties of the device, such as interface roughness, that are negligible for thicker films become critical. Microroughness at the interface of ultrathin MOS capacitors has been shown to degrade these devices. The present study focuses on the interfacial region of ∼50 Å SiO2 on Si, using the quantum oscillations in Fowler–Nordheim tunneling currents as a probe. The oscillations are sensitive to the electron potential and abruptness of the film and interfaces. In particular, inelastic scattering of the electrons will reduce the amplitude of the oscillations. The amplitude of the oscillations is used to examine the degree of microroughness at the interface that results from a preoxidation high temperature anneal in an inert ambient containing various amounts of H2O. Atomic force microscopy imaging has shown correlations supporting a microroughness induced change in the quantum oscillation amplitudes.
Accurate determination of shallow doping profiles and interface states for metal–oxide–semiconductor structures from measured capacitance–voltage data
Authors: Osse A. L. M. , Krusius J. P. , Weinzierl S.
Published: July 2002

A numerical method for the determination of ultra-shallow metal–oxide–semiconductor (MOS) doping profiles and the associated interface trap distribution from measured capacitance–voltage (C–V) characteristics is presented. The method is demonstrated via two cases: (a) theoretical analysis to assess the accuracy of the method; and (b) fabricated MOS test structures, with correlations with spreading resistance profiling (SRP) and secondary ion mass spectroscopy (SIMS). Excellent agreement is seen between C–V and SRP. Our method appears so accurate that it should be considered for routine C–V analysis for shallow MOS doping profiles.
Characterization of structure/dopant behavior by electron microscopy
Authors: Maher Dennis M. , Zhang Bojun
Published: July 2002

Transmission electron microscopy analyses that result in a quantitative characterization of structure/dopant behavior at the nanometer scale are the focus of this research activity. Of particular concern is the quantitative characterization of sequential changes in process-dependent material features, which impact on structure/dopant behavior for silicon-based material systems. In order to illustrate the situation, the determination of the vertical and lateral donor distribution is addressed, and the case of diffusion into a 〈100〉 silicon substrate from a patterned structure of arsenic implanted and rapid thermally annealed polysilicon is discussed. The so-called chemical etching technique is used to delineate arsenic by local variations in the crystal thickness. It is demonstrated that a two-dimensional isoconcentration contour that maps the arsenic distribution can be quantitatively characterized at the nanometer scale from cross-sectional transmission electron microscopy data, which are recorded under high-resolution imaging conditions. The evaluation of microstructural features is briefly considered, and it is concluded that the structure/dopant characterizations that are reviewed in this paper define necessary input parameters for two-dimensional process and device simulation at 0.25 μm design rules and below.
Improvement of depth resolution in secondary ion mass spectrometry depth profiling of silicided poly contacts
Authors: Corcoran Sean F. , Soza Dave , Kincaid Nancy , Danielson Don
Published: July 2002

Performing secondary ion mass spectrometry (SIMS) depth profiles with high depth resolution, <10 nm, through silicided polysilicon contacts is made difficult by the inherent roughness of the silicide/poly interface. This interface roughness results in a loss in depth resolution and leads to the subsequent broadening of the dopant profile under the silicide. In some instances, where the junction is less than 100 nm, it is not possible to obtain an accurate and reliable depth profile of the dopant in the poly or the substrate Si. In this article, the practical application of polishing techniques for planarization and subsequent high depth resolution SIMS analyses are presented. This article will focus on the application of this technique to silicided poly contacts over diffusion areas.
On the reduction of carrier spilling effects during resistance measurements with the spreading impedance probe
Authors: Czech I. , Clarysse T. , Vandervorst W.
Published: July 2002

Despite the rapidly increasing capabilities of Poisson deconvolution schemes for spreading resistance (SR) measurements, carrier spilling effects will remain a serious problem for the interpretation of SR profiles for structures involving significant forward spilling such as epilayers. In order to remedy this situation a spreading impedance probe is being developed allowing to influence the internal spilling by an external dc field, while performing an impedance measurement at a small ac bias. Three-dimensional calibration surfaces representing resistance versus resistivity and dc bias determine the probe characteristics. Results for a p well and a p⋅p+ epilayer will be discussed.
Cs-induced highest E
F jump above InAs(110) conduction-band minimum
Authors: Aristov V. Yu , Le Lay G. , Soukiassian P. , Hricovini K. , Bonnet J. E. , Osvald J. , Olsson O.
Published: July 2002

Upon room-temperature deposition of minute amounts of Cs on InAs(110) surfaces, one induces probably the highest Fermi-level pinning position (≊0.6 eV) for a semiconductor above the conduction-band minimum. Synchrotron-radiation core-level photoemission spectroscopy was used to follow the Fermi-level movement from the shift of the In 4d and As 3d core levels as a function of Cs coverages at room temperature. Already at very low coverages the Fermi level reaches an extremely high maximum above the conduction-band minimum. The maximum of the Fermi-level position correlates fairly well with the ionization energy of the individual atoms, as expected in the framework of the theory of donor-type surface states induced by metallic adatoms. We thus consider that individual Cs adatoms produce donor-type surface states placed at ≊0.6 eV above the conduction-band minimum. This induces a very strong downward band bending which suggests the existence of a two-dimensional electron gas at the open, nearly clean InAs(110) surface.
Progress in noncontact dynamic force microscopy
Authors: Lüthi R. , Meyer E. , Howald L. , Haefke H. , Anselmetti D. , Dreier M. , Rüetschi M. , Bonner T. , Overney R. M. , Frommer J. , Güntherodt H.-J.
Published: July 2002

The technique of operating the scanning force microscope in the dynamic noncontact mode (dynamic force microscopy) has been improved. Home-built instruments based on an optical beam deflection scheme in two different environments were used. The two force microscopes were operated in ambient air and in ultrahigh vacuum, respectively. In order to control the oscillating cantilever different methods were applied: slope-detection (lock-in amplifier, RMS-to-DC converter) and frequency modulation (FM) technique as well. The advantages of this nondestructive technique are demonstrated on different samples, such as soft organic matter (hexagonally packed intermediate layer, Langmuir–Blodgett film), layer-structured compounds (CdI2), n-doped Si(111), and ferroelectric crystals [triglycine sulfate (TGS), guanidinium aluminum sulfate hexahydrate (GASH)]. On TGS and GASH cleavage faces, the ferroelectric domains and domain walls could be imaged. From experimental data a spatial resolution of about 1–2 nm in lateral and <0.1 nm in vertical directions could be determined.
Ion-assisted etching of Si with Cl2: The effect of flux ratio
Authors: Coburn J. W.
Published: July 2002

The room-temperature ion-assisted etching of poly-Si with molecular chlorine and 1 keV Ar+ ions has been studied for a wide range of the neutral flux/ion flux ratio. In situ measurements of the etch rate made using quartz crystal microbalance methods are combined with modulated beam mass spectrometric studies of the etch products and the unreacted molecular chlorine reflected from the Si surface. The reaction probability for the incident chlorine is determined in two independent ways and good agreement is obtained. The products are determined to be primarily SiCl2 and SiCl4 with significant amounts of sputtered SiCl at low flux ratios.
Two ion fluid model for plasma source ion implantation
Authors: Thomas K. , Alport M. J. , Sheridan T. E.
Published: July 2002

For plasma source ion implantation in a nitrogen discharge, there is a mixture of atomic and molecular species N+ and N+2, respectively. A time dependent fluid model has been developed, which models a plasma consisting of two species of cold collisionless ion fluids, assuming that the electrons are in thermal equilibrium. Following the application of a large, negative voltage pulse to the metal target, the density and velocity of the two ion species, and the sheath evolution for a range of possible ion mixtures are calculated.
Application of particle-in-cell simulation to plasma source ion implantation
Authors: Faehl Rickey , De Volder Barbara , Wood Blake
Published: July 2002

The powerful numerical technique of particle-in-cell simulation has been used to study sheath formation and dynamics of plasma source ion implantation (PSII). Two-dimensional cylindrical calculations permit us to study the process when sheath dimensions are large compared to feature scales of the implanted object, where conformality is not assured. Plasma chambers as large as the PSII system at Los Alamos have been modeled. Densities of 1014–15 m−3 are initialized in the numerical configuration. Voltages of −50 to −100 kV have been modeled, with rise times on this pulse of 0.1–1.0 μs. Calculations of the ambient electron/N+2 ion plasma are presented. The implantation flux and dose on a variety of different shapes, including long cylinders and bores in flat plates, have been investigated. Finally, magnetic fields have been added to the calculations. The effect of this field on the process is measured with and without the effect of secondary electron emission from the surface.
Transition metal carbides for use as field emission cathodes
Authors: Mackie William A. , Hartman Robert L. , Anderson Mark A. , Davis Paul R.
Published: July 2002

Field emission characteristics of clean ZrC, HfC, and TaC cathodes are reported. High current density emission, greater than 1×108 A/cm2, is discussed, and a method for determining the cathode changes leading to this high current emission condition is proposed. A close-spaced triode designed for testing individual emitters is described, and results are reported. The effective thermionic work functions of clean and partially oxygen covered surfaces of ZrCx specimens of two different bulk compositions are reported and discussed. Clean values of 3.5 and 3.4 eV were observed for ZrC0.92 and ZrC0.86 specimens, respectively, at 1500 K. With adsorbed oxygen, values as low as 3.4 and 3.2 eV, respectively, were observed for these surfaces at 1500 K.
Field emission diode characterization through model parameters extraction from current–voltage experimental data
Authors: Nicolaescu Dan , Avramescu Viorel
Published: July 2002

Standard field emission diode and array modeling is based on the planar Fowler–Nordheim (FN) current density-electric field J(E) relationship and the introduction of the field enhancement a and area b factors to relate E and J to the measurable quantities potential V and current I. This approach is questionable because E is not constant on the emitter and the b factor is V dependent. In this article, while still using the FN J(E) relationship, I(V) is obtained through J integration over the emitter surface, based on the ideal field emitter floating sphere model (FSM). The model parameters are the emitter’s height h, radius R, work function φ, and anode–cathode planes spacing d and the factors a and b are not used. A parameters extraction procedure (PEP) has been developed, in order to obtain the value of the parameters within the model framework ensuring the best fit to the experimental field emission data. The objective function to be minimized is the standard deviation between FSM and experimental field emission I(V) data. The nonlinear minimization routine used in PEP has been chosen after an extensive testing. The best set of searching variables is outlined. The PEP was applied to reported field emission data. An electric field reduction factor ρ was introduced allowing a physical explanation to be derived. Several ways of applying the PEP are suggested.
Effects of substrate temperature and angular position on the properties of ion beam sputter deposited Fe films on (100) GaAs substrates
Authors: Bernstein S. D. , Wong T. Y. , Tustison R. W.
Published: July 2002

The effects of substrate temperature and position on the properties of Fe films deposited onto (100) GaAs substrates by ion beam sputtering were studied. Films were deposited on substrates at angular positions from −20° to 66°, with respect to the target surface normal, at temperatures from 100 to 500 °C. The deposition rate was higher in the forward scattered direction but decreased for angles greater than 45°. The macroscopic film stress was compressive at low temperatures but underwent a compressive to tensile transition between 300 and 500 °C. Furthermore, the stress varied with substrate position. The stress predicted from thermal expansion mismatch is tensile. Both the low temperature compressive stress and the variation of stress with position are qualitatively accounted for by an energetic bombardment or ‘‘atomic peening’’ process. For optimum deposition conditions, the films are highly (200) oriented, with rocking curves as narrow as 0.5°. The resistivity of the films approaches that of bulk Fe, and the variations of resistivity with deposition conditions appear to be associated with the crystallographic perfection of the films.
Scanning tunneling microscopy studies of self-assembled monolayers of alkanethiols on gold
Authors: Stranick S. J. , Kamna M. M. , Krom K. R. , Parikh A. N. , Allara D. L. , Weiss P. S.
Published: July 2002

Scanning tunneling microscopy was used to probe the molecular scale structures of pure and mixed composition self-assembled monolayers of CH3(CH2)15SH and CH3O2C(CH2)15SH on gold. A predominant defect structure is found for both films, and is assigned as a void defect in the thiolate overlayer. The mixed composition films are observed to phase segregate into domains of the pure component thiolates. Time-lapse series of scanning tunneling microscope images reveal kink-driven motion at step edges and exchange of thiolate molecules on terraces.
Dynamic observation of silicon homoepitaxial growth by high-temperature scanning tunneling microscopy
Authors: Hasegawa T. , Kohno M. , Hosaka S. , Hosoki S.
Published: July 2002

The dynamic process of Si crystal growth on a Si(111)7×7 surface was studied in situ using high-temperature scanning tunneling microscopy. Si was evaporated onto a Si(111)7×7 surface, kept at 350 °C, and the crystal growth was observed. Both step-flow growth and island growth were observed. In the step-flow growth, the [112̄] steps became jagged with [2] steps. At the [112̄] steps, new adatoms appeared in rows along the step edges. In the island growth, the multilayer growth was observed. A rearrangement of adatoms in the first layer was observed when the second layer was formed on the first layer.
Electrochemical scanning tunneling microscopy study of the electrochemical behavior of naked and n-alkanethiol-modified Au(111) surfaces in F−- and CN−-containing electrolyte solutions
Authors: Li Yin-Quan , Chailapakul Orawon , Crooks Richard M.
Published: July 2002

We report an electrochemical scanning tunneling microscopy (ECSTM) study of CN−- and F−-induced etching of naked and n-alkanethiol-modified Au(111) surfaces. We use electrochemical methods to activate or deactivate etching of the Au surface, and we monitor changes in surface topography simultaneously using STM. In F−-containing electrolytes we have observed that the STM tip can induce surface–atom diffusion in the electrochemical environment thereby enhancing surface pitting, island growth, and step edge movement. At potentials more negative than −150 mV (vs Ag/AgCl) the tip selectively removes Au atoms from surface defects and enhances growth on terraces. Similarly, we have found that the STM tip can profoundly alter the CN−-induced dissolution rate of Au. On naked Au surfaces held at extreme negative potentials, no CN− etching of the surface occurs. However, at slightly more positive potentials the surface is homogeneously etched. At intermediate potentials the area under the scanning STM tip is selectively etched at positive tip biases, but at slightly more negative biases etching proceeds less rapidly in the scanned region. Finally, when the Au(111) surface is modified with a single self-assembled monolayer (SAM) of organomercaptan molecules, surface etching processes are dramatically attenuated regardless of the substrate potential or tip bias.
Nanofabrication with a scanning tunneling microscope using chemical vapor deposition
Authors: Rubel S. , Wang X.-D. , de Lozanne A. L.
Published: July 2002

For the past few years we have made transport measurements of pure nickel wires made by decomposing nickel carbonyl with the electrons from a scanning tunneling microscope (STM), which is a form of chemical vapor deposition (CVD). The need to align the tip with four micron-size contact pads resulted in a design incorporating a non-UHV scanning electron microscope (SEM), and a concomitant low throughput of samples. Nonetheless, we have continued to reduce our wires’ dimensions and improve their quality; we show these results and discuss the primary factors governing line quality. To improve throughput and reliability further, we have finished a novel design that utilizes a high power optical microscope instead of a SEM. Two key features of this design are a very compact x–y positioner and a custom window welded directly on the side of the chamber. The positioner is built into a standard fine-screw tripod. It provides over 150 μm of orthogonal motion by tilting a 0.25 in. ball bearing that holds a 0.188 in. ball bearing in an off-center position. The 2 in. sapphire window, which protrudes into the vacuum chamber, makes it possible to have the tip as close as 6 mm to the atmosphere side. This gives an excellent view of the whole STM and allows us to use a 40× (or 20×) objective lens with a 14 (or 19) mm working distance. The extra distance is important for viewing the sample from different angles and makes it possible to place the tip over any desired feature on the surface. We present results from the new STM demonstrating this capability.
Silicon field emitter arrays with low capacitance and improved transconductance for microwave amplifier applications
Authors: Palmer D. , Gray H. F. , Mancusi J. , Temple D. , Ball C. , Shaw J. L. , McGuire G. E.
Published: July 2002

We report here on DC and RF measurements of electron field emission current obtained from silicon field emitter arrays (FEAs) containing more than 1000 tips. The field emitters in these FEAs have the form of 4 μm tall cylindrical columns where the tops of the columns were sharpened into points having radii of curvature estimated from TEM analysis of similar devices to be less than 100 Å. With a gate bias voltage of about 120 V DC, emission currents of approximately 2 mA have been collected at the anode. This collector current, corresponding to about 2 μA per tip, is in the acceptable range suggested in the literature for RF amplification in the GHz frequency range. RF modulation of the collected current at 1 GHz has been measured from these structures and the data are presented. As a result of placing the field emitters on tall columns, the parallel-plate capacitance between the cathode and gate electrodes of these FEAs has been decreased to under 2 fF per emitter tip. The magnitude of the input impedance at 1 GHz is about 30 Ω, which is a reasonable match to the commonly used 50 Ω instrument impedance. The RF measurements of collected current, input power, and device input impedance are consistent with the current and voltage measurements at DC, thereby giving credence to the design of vacuum microelectronic microwave amplifiers using this type of silicon FEA. From these results we believe that RF power gain in the GHz regime is attainable with vacuum microelectronic triode and tetrode structures by scaling up the size of these low-capacitance, high-transconductance silicon FEAs.
Smooth reactive ion etching of GaAs using a hydrogen plasma pretreatment
Authors: Choquette Kent D. , Shul R. J. , Howard A. J. , Rieger D. J. , Freund R. S. , Wetzel R. C.
Published: July 2002

Extremely smooth GaAs surfaces are attained after SiCl4 reactive ion etching by preparing the surface before etching with hydrogen plasma exposure to selectively remove the native surface oxides. Using this hydrogen plasma pretreatment, the surface morphology after etching is equivalent to that of the original surface since the etching proceeds uniformly through the GaAs without micromasking effects from a nonuniform surface oxide. The beneficial effects of the hydrogen plasma processing are observed in two different reactors and are found to be independent of the platen temperature during etching. Using atomic force microscopy we find an optimized hydrogen plasma process produces an etched surface morphology with an average surface roughness of 0.9–1.5 nm, as compared to the surface roughness of 0.6 nm before etching or as great as 11.8 nm after etching without the hydrogen plasma pretreatment.
Immunity to signal degradation by overlayers using a novel spatial-phase-matching alignment system
Authors: Moon Euclid E. , Everett Patrick N. , Smith Henry I.
Published: July 2002

We describe improvements to the interferometric broad-band imaging alignment scheme introduced in 1993. Alignment is signified by matching, across the midline of a charge-coupled device, the spatial phase of interference fringes formed by diffraction from complementary marks on mask and substrate. Image contrast is enhanced by back diffraction from hatched alignment marks on the substrate. Overlayers of resist, polysilicon, and aluminum have negligible effect on interferometric broad-band imaging alignment; they alter image contrast but not spatial phase. Novel alignment marks that incorporate four gratings increase the capture range to several tens of micrometers. By spatial filtering in the back focal plane of the alignment microscope, mask-sample gap may be determined from the resulting spatial phase shift. An alignment system for x-ray nanolithography (XLS-4) that incorporates the interferometric broad-band imaging scheme has been constructed.
Selective reactive ion etching of InGaAs and InP over InAlAs in SiCl4/SiF4/HBr plasmas
Authors: Murad S. K. , Beaumont S. P. , Holland M. , Wilkinson C. D. W.
Published: July 2002

A new selective reactive ion etching (RIE) process has been developed for etching InGaAs and InP over InAlAs using a mixture of SiCl4/SiF4/HBr gases. Optical emission spectroscopic (OES) investigation showed that the dominant emitting species in the plasma are HBr+, Br, and Br2, with weaker emission from SiBr and SiHBr. Using a flow rate of SiCl4/HBr of 6/15 SCCM, a pressure of 100 mTorr, and with a dc bias of 180 V, the etch rates of InGaAs and AlInAs can be as high as 200 nm/min at room temperature with good surface morphology. The formation of bromosilanes or chlorosilanes of the form (SiHxBry, SiHxCly) in the plasma is believed to be responsible for the etching In-containing compounds through the formation of indiumbromosilanes and indiumchlorosilanes. The selectivity of etching InGaAs and InP over InAlAs is obtained by the addition of SiF4 to the mixture of SiCl4/HBr, which is thought to be due to the formation of an etch stop layer of AlF3 on the AlInAs layer. Using a flow rate ratio of SiCl4/SiF4/HBr of 5/6/25 SCCM, a dc bias of ≤70 V, and a pressure of 100 mTorr, the selectivity was extraordinary high for this material system a minimum of (600:1). The etching was stopped on a 5-nm-thick AlInAs layer for at least 60 min. These values of selectivity are an order of magnitude higher than the reported values in the literature. Moreover, this RIE process (SiCl4/SiF4/HBr) etches silicon nitride, and NiCr very slowly. Structures in InP have been etched as deep as 6 μm with very little erosion to the mask which was a very thin layer (100 nm thick) of either Si3N4 or NiCr. The dry etch damage was evaluated using Hall effect measurements made on a high electron mobility transistors material structure. This structure had a 7 nm InGaAs capping layer. Etching the 7 nm cap layer had very little effect on the value of the sheet carrier concentration and the mobility even after 7 min of continuous bombardment of the active layers by selective etching of the 7 nm capping layer.
Structural and electronic effects of argon sputtering and reactive ion etching on In0.53Ga0.47As and In0.52Al0.48As studied by inelastic light scattering
Authors: Maslar J. E. , Dorsten J. F. , Bohn P. W. , Agarwala S. , Adesida I. , Caneau C. , Bhat R.
Published: July 2002

The effects of Ar sputtering and HBr reactive ion etching on In0.53Ga0.47As and In0.52Al0.48As epitaxial layers were investigated by Raman spectroscopy. First-order phonon scattering was used as a probe of structural modification, while coupled phonon–plasmon mode scattering was used to investigate electrical modification. Second-order phonon scattering proved insensitive to sputter- and etch-induced structural modification. For both In0.53Ga0.47As and In0.52Al0.48As, Ar sputtering leads to more structural modification than does HBr etching, the difference being greater for In0.53Ga0.47As. In0.52Al0.48As exhibits a greater resistance to sputter-induced structural damage than does In0.53Ga0.47As, and nominally undoped material displays less susceptibility to being disordered structurally than does more highly doped material for both In0.53Ga0.47As and In0.52Al0.48As. HBr etching results in no electrical modification of In0.53Ga0.47As, whereas a decrease in carrier density and/or an increase in plasmon damping is observed in In0.52Al0.48As. Annealing In0.52Al0.48As under conditions known to restore electrical activity of dopants in GaAs and Al0.3Ga0.7As results in no change in the coupled mode spectra, indicating that electrical modification is not due to hydrogen passivation of dopants.
Sub-10 nm lithography and development properties of inorganic resist by scanning electron beams
Authors: Fujita J. , Watanabe H. , Ochiai Y. , Manako S. , Tsai J. S. , Matsui S.
Published: July 2002

We report the self-developing properties of a AlF3-doped LiF inorganic resist under irradiation by a scanning electron beam with an energy of 50 keV. The self-development properties strongly depended on both AlF3 concentration and film thickness. The required dose to complete the development seemed to be proportional to the volume under the irradiation area. To explain this behavior, we presented an exposure model that takes into account a balance between a carbon contamination and a transfer process. By optimizing resist qualities, we were able to delineate 5 nm linewidth patterns with 60 nm periodicity using a 30 kV electron beam, and pattern transfer by liftoff was demonstrated.
Electric field-potential correlation factors for field emission microtriodes
Authors: Nicolaescu Dan
Published: July 2002

The field emission microtriode (FEMT) correlation factors β and γ between the electric field E on the emitter and the gate Vg and anode Va potentials have been numerically studied. It was found that E is linear with Vg and Va for every emitter point, as long as the Laplace equation can be applied for potential. Two FEMT scaling effects were stated. The FEMT model used has parallel cathode, gate and anode planes, the gate having near the emitter a ‘‘volcano’’ shape. The emitter has a conical shape with spherical tip, protruding through the gate circular opening. A set of linear relationships for β and γ was derived. It was found that the γ correlation factor and the transconductance gm can be increased with orders of magnitude in this FEMT collector-assisted mode of operation. Comparison with experimental results is provided.
Studies into the emission uniformity of large silicon field emitter arrays
Authors: Cade N. A. , Johnston R. , Miller A. J. , Patel C.
Published: July 2002

We report the results of three indirect techniques which, together, provide a clear measure of emitter uniformity. First, a study of the Fowler–Nordheim characteristics has allowed limits to be placed on the variability of those tips contributing to the total current. Second, the emission characteristics of arrays are compared with those of neighboring single tips. Finally, these results have been compared with the variability observed in small arrays of close-spaced but individually addressable tips. The results obtained suggest a relatively uniform and narrow distribution of characteristics within emitter arrays produced by GEC–Marconi in which effectively 70% of the tips contribute to the total emission current. This conclusion is discussed in the context of direct emission images formed by beam collimating double-gridded cathodes.
Steady-state damage profiles due to reactive ion etching and ion-assisted etching
Authors: Davis Robert J. , Jha Pankah
Published: July 2002

Ion damage of materials due to reactive ion etching and ion-assisted etching is formulated as a dynamic problem involving the etch rate, damage creation due to ions, diffusion, and ion range effects. The differential equation is solved in the steady-state assuming an exponentially decreasing damage creation function. The ratio D/aε, where D is the damage coefficient, a the inherent depth of ion damage, and ε the etch rate is shown to be an important parameter determining the steady-state damage profile. Results are examined for situations in which the parameter is much less than or much greater than unity, corresponding to range- and diffusion-dominated profiles, respectively. In both situations, steady-state damage profiles will be quite sensitive to the etch rate of the surface. We suggest some experiments which may elucidate the separate contributions of ion channeling and diffusion to observed damage depth profiles.
Vicinal surfaces of Au(110) and Ag(110) investigated by scanning tunneling microscopy
Authors: Li J. T. , Berndt R. , Gaisch R. , Schneider W.-D.
Published: July 2002

We report scanning tunneling microscopy results obtained on nominally (110) oriented, slightly miscut Au and Ag surfaces studied in ultrahigh vacuum at ambient and low temperatures (50 K). On these surfaces extended areas comprised of vicinal planes were observed and they exhibit intriguing step structures. An analysis of these planes in terms of their orientation, atomic structures, and steps is presented.