bluuebunny/crossref_metadata_2025 huggingface dataset:
Galvanomagnetic study of p-Hg1−xCdxTe passivated surfaces
Authors: Höschl P. , Moravec P. , Franc J. , Grill R. , Milev P. , Belas E.
Published: July 2002

Three types of passivated surfaces were measured with a method of low temperature measurement of conductivity and the Hall coefficient—electrochemically prepared native sulfides, e-gun evaporated ZnS, and a combination of both these layers. From the obtained RH(T) and σ(T) curves (300 K≳T≳4.2 K), it is obvious that galvanomagnetic properties of all three types of passivated surfaces are strongly dependent on the storage time. Several surface parameters are calculated by a solution of the Poisson equation—surface field ℰs, surface potential ψs, and band bending ψ(x).
Ellipsometric monitoring and control of the rapid thermal oxidation of silicon
Authors: Conrad K. A. , Sampson R. K. , Massoud H. Z. , Irene E. A.
Published: July 2002

Single wavelength ellipsometry is demonstrated for in situ process monitoring and control in a rapid thermal processing system. Simultaneous in situ ellipsometric measurements of the temperature and oxide film thickness allow closed-loop feedback control during film growth. Data are presented for the rapid thermal oxidation of silicon under computer control for oxide thickness ranging from 60 to 175 Å and temperatures from 850 to 1000 °C.
Soft x-ray photochemistry of chemisorbed self-assembled monolayers
Authors: Suh D. , Simons J. K. , Taylor J. W. , Koloski T. S. , Calvert J. M.
Published: July 2002

The first results of the effect of monochromatic soft x-ray exposure of self-assembled monolayers (SAMs) of iodomethylphenylsilyl groups chemisorbed on the native oxide surface of a Si substrate are presented. The SAMs, combined with a subsequent selective metallization process, have already been shown to be an effective resist system for projection x-ray lithography and show great promise as an e-beam resist. The first conclusive evidence is presented for the loss of iodine from the SAM during soft x-ray exposure. The loss of iodine in the exposed areas allows the selective deposition of an etch resistant metal in the unexposed areas. The SAMs also provide a model system for the study of resists at the molecular level, and the role of photogenerated electrons in determining sensitivity and resolution. The concentration of iodine left on the surface during monochromatic exposure was monitored using photoemission. The loss of iodine with exposure was then fit with a double exponential. The photon energy dependence of the decay rates are measured and presented for photon energies 75–108 eV. The SAM sensitivity is shown to correlate with photoelectrons generated from the Si native oxide surface.
Ultrahigh resolution magnetic force microscope tip fabricated using electron beam lithography
Authors: Fischer Paul B. , Wei Mark S. , Chou Stephen Y.
Published: July 2002

A novel magnetic force microscope tip has been proposed and fabricated that consists of a ∼30 nm thick ferromagnetic film coated on one side of a nonmagnetic pillar which is ∼150 nm wide and over 1.5 μm long. The pillar was fabricated on the apex of a commercial scanning force microscope tip using high-resolution electron beam lithography. The ferromagnetic film was evaporated on the pillar from an angle so that only the pillar, not the rest of the tip, was coated. The coated ferromagnetic film has a trough shape and a tapered end with a tip radius of ∼10 nm. The film is single domain because of the nanoscale size and shape anisotropy. Compared to conventional Ni wire tips, the new tips have a much smaller, magnetic cross section at the end of the tip, thus offering better imaging resolution and they have lower stray field, thus making them well suited to measuring soft magnetic materials.
Mechanism of Si etching reaction in aqueous solutions
Authors: Seo Young Hun , Yun Min Hee , Nahm Kee Suk , Lee Kee Bang
Published: July 2002

The mechanism of Si(100) etching reaction in HF-oxidizing agent–H2O mixed solutions was investigated using the redox potential of etching solution and the band theory of semiconductors. The experimental data of the etching reaction were taken in etching solutions of various compositions over the temperature range of 273–323 K. The etch rates were almost the same for both n- and p-type Si(100). The higher the energy difference between the valence band of Si and the solution potential of etchant, the lower the activation energy and the faster the etch rate of Si. In He/Ne laser-induced etching of Si with frequency of 632.8 nm, the etch rate for n-Si was drastically increased, while p-Si was not responsive to laser illumination. Experimental results showed that the rate determining step of the silicon etching reaction was the formation of holes at the surface.
Remote plasma etching reactors: Modeling and experiment
Authors: Deshmukh Shashank C. , Economou Demetre J.
Published: July 2002

A combined theoretical–experimental analysis of a remote plasma etching reactor was undertaken. Chlorine plasma etching of polysilicon was chosen as a case study to illustrate the approach. A model of the plasma (radical source) and of the transport and reaction of radicals through the downstream section was developed. The effect of tube dimensions, gas pressure, flow rate, and wall recombination probability was examined. In the parameter range investigated, low pressure, high flow rate, short downstream section, and low wall recombination probability favor higher radical fluxes at the substrate. A conflict arises in choosing the tube radius. A tubular reactor with different radii for the source and downstream sections is proposed to optimize the radical flux. Model predictions were tested in a radical beam reactor. Actinometry was used to monitor the Cl-atom density in the source and to verify the predictions of the plasma model. Using the wall recombination probability as the only adjustable parameter, reasonable agreement between predicted and measured atom flux at the reactor exit was also obtained.
High-resolution reactive ion etching of SiGe alloys
Authors: Couillard J. G. , Craighead H. G.
Published: July 2002

Epitaxial Si1−xGex (x=0.08–0.12) films were reactive ion etched in fluorine- and chlorine-based plasmas. The etch characteristics are similar to those for pure Si. By studying the effects of the etch parameters, such as power, pressure, and gas composition a statistical model of the etch process for SiGe in CF4/H2 plasmas has been produced. This etching method has been successfully applied to the fabrication of features in SiGe below 0.1 μm, smaller than any yet reported. This result encourages further progress in the development of SiGe-based submicron devices.
Photoluminescence and Hall characterization of pseudomorphic GaAs/InGaAs/AlGaAs heterostructures grown by molecular-beam epitaxy
Authors: Baeta Moreira M. V. , Py M. A. , Ilegems M.
Published: July 2002

Hall electrical properties measured by the van der Pauw method and low-temperature photoluminescence (77 K PL) spectra of pseudomorphic GaAs/InyGa1−yAs/AlGaAs modulation-doped field-effect transistor-type heterostructures grown by molecular-beam epitaxy were compared. By using these two characterization methods, the influences of the growth temperature Ts , the InGaAs quantum-well channel thickness dch , and its indium composition y were studied. Interesting correlations were established between their 77 K PL spectra and their transport properties measured either in the dark or under white-light illumination. The PL spectra exhibit one or two bands which are attributed to transitions from electronic states belonging to the first or to the second subband formed in the conduction quantum well, the second transition at higher energy being observed only when the two-dimensional concentration exceeds a critical value nc which, in the dark, is ∼2.4×1012 cm−2 (i.e., dch≊108 Å) for the homogeneously doped heterostructures with y=0.25.
Evidence of phonon-absorption-assisted electron resonant tunneling in Si/Si1−xGex diodes
Authors: Matutinović-Krstelj Ž. , Liu C. W. , Xiao X. , Sturm J. C.
Published: July 2002

We report a study of temperature dependence of electron resonant tunneling diodes in an Si/Si1−xGex material system grown by rapid thermal chemical vapor deposition. Up to four highly symmetric resonances were observed, but the lowest energy resonance has an anomalous temperature behavior, decreasing in strength with decreasing temperature below 140 K and entirely disappearing below 50 K. The temperature behavior and bias position of the resonance are consistent with a model of phonon-absorption-assisted tunneling with a phonon energy of 14±2 meV. The phonon is thought to be an acoustic phonon which promotes Umklapp scattering between the conduction band minima in the emitter and quantum well states.
Sensitivity of the focusing property of optimized electrostatic lenses
Authors: Bodrogi P. , Szép J.
Published: July 2002

The optical properties of a given axially symmetric electrostatic multielectrode lens were examined by changing its external parameters (source parameters, object-side and image-side potentials, and working distances, etc.) and optimizing the electrode potentials of the lens for each considered value of an external parameter. Our main result is the discovery of the tendencies how the optimal total beam radius depends on the external parameters, i.e., the sensitivity of the optimum related to the change of the external parameters. We established that the external parameters can be distinguished clearly from each other on the basis of the scale of the sensitivity of the optimum related to them.
Thin film properties of low-pressure chemical vapor deposition TiN barrier for ultra-large-scale integration applications
Authors: Hegde Rama I. , Fiordalice Robert W. , Travis Edward O. , Tobin Philip J.
Published: July 2002

Titanium nitride films deposited by low-pressure chemical vapor deposition (LPCVD) on Si(100) using TiCl4 and NH3 as reactants, were investigated as a function of deposition temperature between 400 and 700 °C. LPCVD TiN depositions were carried out in a rapid thermal chemical vapor deposition system with a total deposition pressure of 155 mTorr. Stoichiometric TiN films were formed regardless of the deposition temperature and composition was uniform across the entire film. Depending on deposition temperature, varying amounts of chlorine (Cl) and oxygen (O) impurities are found in the TiN films. Films deposited at lower temperatures (400 and 550 °C) contained more than 5 at. % Cl, while the films produced at 700 °C contained as little as 1 at. % Cl. For the films deposited at 650 and 700 °C, the bulk of the TiN films is oxygen-free. LPCVD TiN deposition rates of 400 Å/min with no appreciable incubation time were routinely achieved. The LPCVD TiN deposition process is surface reaction controlled with an activation energy of 35 kJ/mol. Excellent TiN film conformality was observed. Electrical resistivity of the TiN films was found to decrease with increasing deposition temperature. Resistivity in the range of 85 μΩ cm was observed. Polycrystalline ∂-TiN phase with a preferred orientation of (200) was observed at all deposition temperatures. These TiN films have columnar grain structure. The TiN/Si interface is smooth, and no voids are observed at the silicon substrate interface, a prerequisite for good adhesion. An increase in the average grain size and lattice parameter was observed with increasing deposition temperature. While increasing the deposition temperature increases the TiN film growth rate, it also produces larger TiN grains and rougher surface morphology. The reliability of the TiN films as a diffusion barrier between aluminum and silicon was evaluated by diode leakage current measurements, which remained low after being thermally stressed up to 550 °C.
Low-voltage field emitter array cathode for high frequency applications
Authors: Hill D. N. , Ohlinger W. L. , Cochran J. K. , Feeney R. K. , Carter W. B. , Harris H. M.
Published: July 2002

The composite-based low voltage field emitter cathode offers distinct advantages for high-frequency applications. It is based on a directionally solidified ZrO2⋅Y2O3–W eutectic composite containing aligned, single-crystal tungsten fibers, ≊500 nm in diameter, with spatial densities of 2–50×106/cm2. The composite can be etched to form fibers of virtually any length with tip radii of 5–10 nm. A gridded structure can be formed around the fibers using a line-of-sight vapor deposition process. Because of the thickness of the composite chips used as the substrate (0.5 mm) and the high resistivity of the oxide matrix, the insulator film can be made extremely thin, thereby reducing the extractor aperture radius. Emission tests have verified this configuration results in measurably higher field enhancement values for the arrays.
Effects of focused ion beam reticle repair on optical lithography at i-line and deep ultraviolet wavelengths
Authors: Prewett P. D. , Martin B. , Eastwood A. W. , Watson J. G.
Published: July 2002

The repair of opaque defects in photomasks and reticles using focused ion beams (FIBs) can give rise to staining of the quartz substrate. A purpose built system is used to measure the transmission properties of stained regions and reveals relative fractional transmission of 60% at i line, falling to 25% in the deep ultraviolet (DUV). A series of printability trials using commercial steppers and processes at i line and DUV wavelengths shows the effects in resist images due to these stains in comparison with the original defects. The negative resist process used at DUV affords some protection against the printability of stained areas. However, the results confirm that antistain processes must be used with FIB repair which can be counter productive without them.
Low damage etching of InGaAs/AlGaAs by the electron cyclotron resonance plasma with Cl2/He mixture for heterojunction bipolar transistors
Authors: Miyakuni S. , Sakai M. , Hattori R. , Izumi S. , Shimura T. , Sato K. , Takano H. , Otsubo M.
Published: July 2002

Low damage InGaAs/AlGaAs etching was realized by electron cyclotron resonance (ECR) plasma with a Cl2/He mixture for heterojunction bipolar transistors (HBTs) emitter mesa formation. By optimizing the etching pressure and the Cl2/He ratio, n-InGaAs cap layer and n-AlGaAs emitter layer are successively etched and the smooth surface morphology was obtained. An optical emission measurement reveals that the enhancement of the ionized Cl etching plays the essential role for etching of InGaAs. Raman scattering spectra and the base contact resistance measurements indicate that the etching induced damage is extremely low. Moreover, it was found that the etching rate of p-AlGaAs base layer decreased down to two-thirds of that for n-AlGaAs emitter layer under the optimized etching condition. These results demonstrate the potentiality of ECR plasma etching with Cl2/He discharge providing degradation-free dry etching for AlGaAs/GaAs HBTs.
Pyrometric interferometry for real time molecular beam epitaxy process monitoring
Authors: Böbel F. G. , Möller H. , Wowchak A. , Hertl B. , Van Hove J. , Chow L. A. , Chow P. P.
Published: July 2002

Pyrometric interferometry (PI) has recently been demonstrated for simultaneous real time wafer temperature and thickness measurement during the molecular beam epitaxy process. Both parameters of the thin film layer can be determined from the changing interference conditions in the layer. We used a reflection assisted version of PI to follow the thermal history of the wafer under different conditions and were able to resolve temperature to less than 1 °C. For thickness measurements, a parabolic fitting algorithm was used to accurately determine the endpoints of the GaAs/AlAs quarter wave stacks. Compared to other noncontact methods this technique can be used for very thick layers and is unaffected by the layer absorption and optical effects.
Fabrication of a nanoscale, in-plane gated quantum wire by low energy ion exposure
Authors: Andrews C. C. , Spencer G. F. , Li F. , Weichold M. H. , Kirk W. P.
Published: July 2002

The fabrication of a nanoscale gated quantum wire in a GaAs modulation doped field effect transistor substrate is described. Both the wire conduction channel, with a 110 nm physical width, and the gates were patterned into the two-dimensional electron gas of the substrate. This scheme produced in-plane gated devices with 110 nm gate lengths and 75 nm separations between the active areas. Electron-beam lithography was used to define masks for a subsequent flood exposure step with low energy argon ions (150 eV). This ion exposure technique produced very high gate-to-wire isolation, typically greater than 1014 Ω at 4.2 K. The in-plane design employed here drastically reduces gate capacitance compared with metal top-gate designs, and promises ultrafast switching times. These devices showed no short channel punch-through effects, exhibited low gate leakage, and had sufficient gain to permit integration of several such devices into more complex circuits such as logic gates.
Macroscopic electronic behavior and atomic arrangements of GaAs surfaces immersed in HCl solution
Authors: Ishikawa Y. , Ishii H. , Hasegawa H. , Fukui T.
Published: July 2002

The macroscopic electronic behavior and atomic arrangements of the GaAs surfaces immersed in HCl solution were studied by surface current transport (SCT), band-edge photoluminescence (PL), atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS). SCT measurements indicated reduction of the surface band bending on immersion into HCl solution for both n- and p-type materials. A remarkable increase of the band-edge PL intensity was also observed. In the AFM image taken in HCl solution, the (001) surface showed an array of atoms along [110] and [1̄10] direction with the spacing of 4.1 Å, indicating presence of a (1×1) structure. Similarly, (1×1) images with threefold symmetry were observed on the (111)A and (111)B surfaces. The XPS analysis of the GaAs surfaces after immersion into HCl solution detected a monolayer level presence of gallium chloride. These results indicate that bond termination on the GaAs surface by adsorption of Cl atoms to surface Ga atoms realizes a nonstrained regular (1×1) passivation structure which removes surface states from the band-gap region.
Ion-matrix sheath around a square bar
Authors: Sheridan T. E. , Alport M. J.
Published: July 2002

The structure of the ion-matrix sheath surrounding a square bar is calculated. Equipotentials and field lines are presented, and the sheath width and eccentricity are calculated as a function of the bar width.
Tungsten trench etching in a magnetically enhanced triode reactor
Authors: Pendharkar S. V. , Wolfe J. C.
Published: July 2002

The problem of polymer contamination in W trench etching is studied for fluorocarbon plasmas. Polymer contamination of narrow trenches has been observed on samples where isolated positive-relief structures (mesas) are clean. This effect is linked to sidewall sputtering by ions backscattered at low angles from the substrate: the sidewalls of a mesa are bombarded by reflected ions originating over a larger area of the substrate than the sidewalls of a trench. The presence of a blast of backscattered ions is confirmed (in an SF6/Br2 plasma) by images where sidewalls adjacent to large substrate areas etch isotropically while those in the shadow of an adjacent feature etch anisotropically. Finally, it is shown that ultrathin, durable polymer coatings which protect mesa sidewalls without contaminating nanometer-scale trenches can be formed in a magnetically enhanced, triode etching system using a CF4/O2 source gas: 40 nm wide, 300 nm deep trenches are shown.
Silicon surface electrical properties after low-temperature in situ cleaning using an electron cyclotron resonance plasma
Authors: Nam C. W. , Ashok S. , Tsai W. , Day M. E.
Published: July 2002

Electron cyclotron resonance hydrogen plasma and argon plasma was used to clean Si surface without additional heating within 4 min and 30 s, respectively. Changes in the electrical properties after plasma treatment with different exposure times have been studied and compared using a Schottky diode structure. The reverse saturation current of the Schottky diodes changes less in the case of the hydrogen plasma cleaned samples than the argon plasma cleaned samples. After hydrogen plasma exposure, residual hydrogen introduced into the Si was found to enhance greatly the formation of thermal donors which induces considerable changes in the defect states after annealing. After annealing at ∼450 °C in N2, new defects, caused by thermal donors, appear and these defects decrease significantly at 750 °C. Defects in the argon plasma treated samples annihilate after annealing at 1000 °C for 1 h.
Atomic force microscopy study of Pd clusters on graphite and mica
Authors: Nie H. Y. , Shimizu T. , Tokumoto H.
Published: July 2002

We report on a growth of single crystals of Pd clusters on highly oriented pyrolytic graphite (HOPG) and mica. On HOPG, edges of the clusters were parallel to the imaged substrate atom rows. On mica, both clusters with edges parallel to and 30° off from the imaged atom rows were observed. The atomic resolution with a separation of 0.28 nm on Pd clusters on mica was obtained with atomic force microscopy (AFM). We propose structural models for the epitaxial nature of Pd on HOPG and mica.
Microscopic picture of Si(113): A novel surface reconstruction, the origin of defects, and the process of adsorption. Theoretical and experimental study
Authors: Da̧browski J. , Müssig H.-J. , Wolff G.
Published: July 2002

We report results of scanning tunneling microscope measurements and ab initio calculations for Si(113). This surface is of general interest: Ge islands on Si(001) and Si(111) have (113) facets, Si(113) is thermally stable despite its high index, and it has properties of a good substrate. We bring into focus the peculiar atomic structure of Si(113) which contains a novel structural unit built around a subsurface interstitial atom. Such interstitials may be present also at other surfaces, particularly at steps, and may play an important role in atomic diffusion in the subsurface layer. The interstitials are sixfold coordinated; this unexpected result disturbs the simple picture of reconstruction driven by rebonding of dangling bonds. Our calculations indicate that the interstitials are released when the surface dangling orbitals rebond, e.g., as the result of adsorption of atomic hydrogen or during epitaxial growth.
Nonuniform distribution of strain in InGaAs/GaAs quantum wires
Authors: Chen Yu-Pei , Reed Jason D. , Schaff William J. , Eastman Lester F.
Published: July 2002

Nonuniform strain distribution in In0.2Ga0.8As/GaAs strained quantum wire (QWR) has been observed by measuring the lattice spacing from the high-resolution transmission electron microscopic lattice image of the cross section of the wire. It was found that in the wire, the region near the wire sidewall was under a larger compressive strain in the growth direction (vertical strain) than the center of the wire. In the barrier, near the wire sidewall, GaAs was under a vertical tensile strain by the In0.2Ga0.8As wire. This observation explains experimental observation of quantum confinement in strained InGaAs/GaAs quantum wires where the possibility of nonconfining band offsets was previously hypothesized. This phenomenon of nonuniform vertical strain distribution in the wire is essential for the application of these strained material systems to the fabrication of strained QWR lasers, and the result presented here is important for the further modeling and design of these strained QWR structures.
Surface morphology of epitaxial CaF2/Si(111) and its influence on subsequent GaAs epitaxy
Authors: Li Weidan , Thundat Thomas , Anan Takayoshi , Schowalter Leo J.
Published: July 2002

Atomic force microscopy (AFM) has been intensively used to investigate the surface morphology of CaF2 films. The atomic steps of CaF2 grown on tilted Si substrates are observed to bunch up during growth, which leads to the formation of large, atomically flat plateaus separated by polyatomic steps. Both the shape and the size of those steps strongly depend upon the misorientation direction of the Si substrate. Quantitative AFM analysis indicates that the size of the plateaus on the CaF2 surface grown on Si substrates tilted towards the [1̄1̄2] azimuth is about eight times smaller than the size of those grown on a Si substrate tilted towards the opposite direction (the [112̄] azimuth). Smaller plateaus on the CaF2 surface are observed to result in smaller twins which are more easily suppressed if proper growth conditions are chosen. High resolution scanning electron microscopy has also been employed to study the surface of GaAs films grown on CaF2/Si(111) substrates with different misorientation directions. The GaAs films have a layer-by-layer growth mode when grown under optimal growth conditions.
Ultrasonic atomization of the DNA solution for atomic force microscopy
Authors: Sasaki Minoru , Okuma Shigeru , Miyata Keizou , Hane Kazuhiro , Takeda Yutaka
Published: July 2002

We have investigated the ultrasonic atomization of the deoxyribonucleic acid (DNA) solution as a simple preparation technique to image circular DNA molecules with the atomic force microscope. The DNA solution with a relatively high concentration (∼25 μg/ml) is ultrasonically atomized at the exciting frequency of 2.4 MHz. Preliminary results show that this technique allows an even distribution of unaggregated strands.
Evaluation of the performance and operating characteristics of a solid phosphorus source valved cracking cell for molecular beam epitaxy growth of III–V compounds
Authors: Baillargeon J. N. , Cho A. Y. , Fischer R. J.
Published: July 2002

We studied the performance of a new type of valved cracking cell which contains a separate condensing reservoir and is intended for molecular beam epitaxy of phosphide compounds. The cell was designed to operate with a white phosphorus source, derived in situ by sublimation and subsequent condensation of red phosphorus vapor. The parameters investigated were stability of the beam flux, switching transients, and growth chamber recovery time. The data show that a properly constructed valved cell, which incorporates a valve where shut-off and metering are independently controllable, provides for a rapidly switched, stable beam flux with a minimum chamber recovery time. An in situ generated white phosphorus source was found to reduce the P4 burst accompanying the use of a red phosphorus source by over 300%.
Passivation of GaAs surfaces and AlGaAs/GaAs heterojunction bipolar transistors using sulfide solutions and SiNx overlayer
Authors: Kapila A. , Malhotra V. , Camnitz L. H. , Seaward K. L. , Mars D.
Published: July 2002

Stable passivation of GaAs surfaces and AlGaAs/GaAs heterojunction bipolar transistors has been achieved using sulfide solutions and SiNx overlayers. The SiNx layers are deposited at ∼200 °C using electron cyclotron resonance plasma-enhanced chemical vapor deposition technique. The capacitance–voltage measurements indicate a substantial reduction in the density of electronic defects at the SiNx/S–GaAs interface as a result of annealing in N2 ambient. The base current of a 36×36 μm2 AlGaAs/GaAs heterojunction bipolar transistor is reduced by approximately two orders of magnitude in the low collector current regime by using sulfide treatment, SiNx deposition, and anneal. Both the Al/SiNx/S–GaAs capacitors and transistors are stable for several months with no noticeable degradation in their electrical characteristics.
Role of ions in electron cyclotron resonance plasma-enhanced chemical vapor deposition of silicon dioxide
Authors: Seaward K. L. , Turner J. E. , Nauka K. , Nel A. M. E.
Published: July 2002

Silicon dioxide films were deposited in an electron cyclotron resonance plasma onto substrates at temperatures ranging from 65 to 200 °C. In order to determine the effect of ions on the deposition, both ion flux and ion energy were investigated. The ratio of ion flux to deposition flux was found to be a significant parameter and this ‘‘flux ratio’’ was varied between 8 and 100. Mean ion energy was investigated at 10, 50, and 75 eV. The silicon dioxide films were characterized by measurement of wet etch rate, density, composition, and stress, and by infrared spectroscopy. It was found that above a flux ratio of about 20, high-quality SiO2 was deposited whether or not the substrate was thermally floating or at 65–200 °C, indicating that the flux ratio was dominant over the temperature. Use of radio-frequency bias to increase the mean ion energy to 50 eV or above was effective in producing high-quality SiO2 when the flux ratio was below 20, but not as effective as using a high flux ratio. Thus high ion flux and low ion energy were found to be useful in producing SiO2 at temperatures as low as 65 °C with properties close to that of thermal silicon dioxide. The role of ions in the deposition process was found to be densification, removal of –OH (or hydrogen) and alteration of Si–O bonding.
Implant isolation of InxAl1−xN and InxGa1−xN
Authors: Vartuli C. B. , Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Zolper J. C.
Published: July 2002

N-type layers of InxAl1−xN and InxGa1−xN were implanted with multiple energy N+, F+, or O+ ions at doses in the range 5×1012–5×1014 cm−2, and subsequently annealed up to 900 °C. Increases in sheet resistance of up to factors of ∼104 were achieved in In0.75Al0.25N after implantation at the higher doses, followed by annealing at 600–700 °C. The behavior for InxGa1−xN followed the same trend, with somewhat lower increases in sheet resistance. The implantation creates deep acceptor states in the upper part of the band gap of both types of material, rather than at midgap, which is the optimum situation for implant isolation.
Field emitter array mask patterning using laser interference lithography
Authors: Spallas J. P. , Hawryluk A. M. , Kania D. R.
Published: July 2002

We have fabricated uniform arrays of 120-nm-diam dot masks on 300 nm centers using laser interference lithography. Chrome, cobalt, nickel, and germanium dot arrays have been fabricated. The density of these arrays is ≳109 dots/cm2. The standard deviation of the average dot diameter is 7.4% over a 5-cm-diam silicon substrate. The center-to-center spacing of the dot mask is determined by the laser wavelength and interference angle. Some control over the dot diameter is possible by varying the angle of the substrate during the metal deposition prior to liftoff. We have used a reactive ion etch with these metal dot masks to form single crystal silicon pedestals demonstrating that these structures are suitable for self-aligned gated field emitter array fabrication.
Synthesis of electrostatic multielectrode deflectors
Authors: Cho H. , Szilagyi M.
Published: July 2002

Synthesis of electrostatic deflectors with given source parameters, first-order properties, and minimum aberrations can be realized by using the cubic spline method or the a priori given multielectrode approach. Synthesis of electrostatic deflectors was successfully achieved previously by using the cubic spline method. In this paper we present synthesis of electrostatic deflectors based on the a priori given multielectrode approach for the purpose of obtaining the minimum beam spot size through a sequential optimization technique. Our calculations show that the third-order geometrical deflection aberrations can be reduced by about two to three orders of magnitude using a multielectrode deflector with three units or five units, each having short cylindrical segments with geometrically octupole symmetry.
Charge build-up reduction during biased electron cyclotron resonance plasma deposition
Authors: Machida K. , Itsumi M. , Minegishi K. , Arai E.
Published: July 2002

A technique to reduce charge buildup causing gate-oxide deterioration during biased electron cyclotron resonance (ECR) plasma deposition has been developed. For SiO2 planarization and filling techniques, it is necessary to resolve the charge build-up phenomenon with the biased ECR plasma system. The deterioration is reduced by adjusting the magnet-coil position in the ECR plasma system which means minimizing the magnetic-flux density at the specimen surface.
Novel fabrication process utilizing thermal stress for uniform ultrafine SiO2 gaps with perfectly vertical sidewalls
Authors: Nishibe Tohru
Published: July 2002

A novel fabrication process for uniform ultrafine SiO2 gaps with perfectly vertical sidewalls is proposed and experimentally demonstrated. The gaps without undulation were successfully fabricated by splitting the SiO2 layer along the guidelines established beforehand, utilizing thermal stress between the SiO2 layer and the InP substrate. High uniformity of the gap width of less than 5% along 200 μm has been obtained. Minimum gap width of 20 nm has been realized. Moreover, this ‘‘split mask’’ was found to be applicable as a selective regrowth mask and a dry etching mask.
Characterization of sidewall defects in selective epitaxial growth of silicon
Authors: Bashir R. , Neudeck G. W. , Haw Y. , Kvam E. P. , Denton J. P.
Published: July 2002

The sidewall defects in high quality selective epitaxial growth (SEG) of silicon were characterized. Three different SEG diode structures were fabricated and the bulk and perimeter defects were characterized through electrical measurements and transmission electron microscopy (TEM). The structures investigated were SEG grown in a 1.2 μm thick wet-etched field oxide, SEG grown in 1.2 μm thick reactive-ion etched field oxide, and SEG grown in a 1.2 μm high and 0.3 μm wide sidewall oxide cavity. The thin sidewall oxide cavity SEG diode showed the best ideality factors and minimum saturation current densities for diodes intersecting the sidewall, indicating the least thermal stress generated at the SEG/oxide sidewall interface during the cool-down period. Cross-sectional TEM micrographs showed no defects in the bulk SEG or at the sidewall, indicating that the thermal stress in all the processes was not high enough to cause plastic deformation, dislocations, or stacking faults.
Fabrication of diffractive optical elements using a single optical exposure with a gray level mask
Authors: Däschner Walter , Long Pin , Larsson Michael , Lee S. H.
Published: July 2002

A method for mass fabrication of environmentally rugged monolithic diffractive optical elements (DOEs) is demonstrated. A one-step optical exposure, with a gray level mask, was used to produce analog resist profiles that were transferred into their substrates using chemically assisted ion beam etching in a single etching step. The described procedure allows mass fabrication of DOEs without the tedious multiple exposure and etching steps commonly used in multilevel DOE fabrication. To generate a multilevel DOE in an optical substrate, only a single exposure using a gray level mask and a single etching step are necessary. The fabrication method presented will reduce processing time and increase manufacturability, which will result in a general cost reduction per element.
Ambient scanning tunneling lithography of Langmuir–Blodgett and self-assembled monolayers
Authors: Xu L. S. , Allee D. R.
Published: July 2002

Ultrathin resist films have been prepared by both Langmuir–Blodgett (LB) and self-assembly (SA) techniques. The LB films include both monomer films (stearic alcohol) and polymer films (polymethyl-methacrylate). Nanometer scale patterning of these thin films have been performed on different substrates (GaAs, Au, and Pt) by using the scanning tunneling microscope (STM) as the exposing tool. Both carbon deposit buildup and chain breakdown underneath the STM tip are observed. The STM-generated patterns are transferred into metal films and semiconductor substrates by chemical etching. Using an atomic force microscope for imaging, lines with 25 nm width have been observed.
Electron-beam-heated solid source for carbon doping in GaAs and AlGaAs alloys grown by molecular-beam epitaxy
Authors: Walker John F. , Sorba Lucia , De Franceschi Silvano , Beltram Fabio
Published: July 2002

A wide range of carbon doping in molecular-beam-epitaxy-grown GaAs and AlGaAs alloys was obtained by means of a new electron-beam heated solid source. Free hole concentrations from low 1015 cm−3 to over 1×1020 cm−3 were reproducibly obtained in GaAs and in direct-gap AlxGa1−xAs while maintaining good surface morphology. These results extend the doping range in both directions with respect to commercial solid carbon sources. High activation percentage, negligible memory effects and diffusion were demonstrated via secondary ion mass spectrometer and photoluminescence measurements.
Process kit and wafer temperature effects on dielectric etch rate and uniformity of electrostatic chuck
Authors: Shan Hongching , Pu Bryan Y. , Gao Hua , Ke Kuang-Han , Lewis Jenny , Welch Michael , Deshpandey Chandra
Published: July 2002

Etch rate and uniformity are two basic indicators of how rf power is coupled into the wafer. In reactive ion etch of dielectric layers, wafer temperature also appears as a key parameter, due to the innate deposition. When electrostatic chuck is introduced, we have to study and control both rf coupling and wafer temperature to maximize etch rate and minimize nonuniformity. We first review the basics of the electrostatic chuck (e-chuck) design and operation, and check them against Applied Materials’ polyimide monopolar e-chuck. Then a simple circuit model is developed and fitted to the experimental results. The model says to have higher etch rate, one needs to couple more energy through the wafer center. This is achieved by using a thicker insulating process kit with low dielectric constant. The uniformity study shows for a given wafer, its etch rate variation across the wafer can be divided into three sections—center, B-field corner, and very edge of the wafer, and each section is controlled by a key parameter. By optimizing these parameters, we are able to increase the etch rate and decrease its nonuniformity to 1.5% (1σ, 3 mm edge exclusion). Finally, wafer temperatures of both center and edge are studied and the delta between center and edge is reduced to ∼6 °C, and spin-on-glass etch rate nonuniformity is reduced to 1σ of 1.88%.
Growth structure of Fe on the Cu(001) surface
Authors: Noh H. P. , Choi Y. J. , Park J. Y. , Jeong I. C. , Suh Y. D. , Kuk Y.
Published: July 2002

Initial stage of Fe growth on Cu(001) surface has been studied using scanning tunneling microscopy. Growth can be characterized predominantly by a layer-by-layer scheme up to 5 ML. The island size distributions are scaled to different curves at the submonolayer regime, suggesting atomic mixing at the first layer. Interdiffusion may occur through the atomic defects or impurities on the Cu surface. Annealing the grown Fe film results in change of the surface morphology.
Scanning tunneling spectroscopy on low- and high-T
c superconductors
Authors: Mielke F. , Memmert U. , Golubov A. A. , Hartmann U.
Published: July 2002

Using some sophisticated modes of scanning tunneling spectroscopy the local density of states on two superconducting compounds in the superconductive state at 4.2 K were analyzed. On NbSe2 which is a type-II low-Tc material, the Abrikosov flux line lattice was imaged for various external magnetic fields up to BC2. The field-induced decrease of the vortex core radius for increasing magnetic field, which was recently predicted by a microscopic theory, could be clearly verified. On sputtered YBa2Cu3O7−δ films the measurements yielded some distinct types of the surface density of states involving gaps, being in accordance to the Bardeen–Cooper–Schrieffer theory, unexpectedly large gaps, Coulomb staircases, and zero-bias peaks.
Effects of low-temperature-grown GaAs and AlGaAs on the current of a metal–insulator–semiconductor structure
Authors: Chen C. L. , Mahoney L. J. , Nichols K. B. , Manfra M. J. , Brown E. R. , Nitishin P. M. , Molvar K. M. , Gramstorff B. F. , Murphy R. A.
Published: July 2002

GaAs and AlGaAs layers grown by molecular beam epitaxy at low temperatures were used as the insulator in a metal–insulator–semiconductor diode simulating the gate structure of a GaAs metal–insulator–semiconductor field-effect transistor (MISFET). The diode current increases after the high-temperature annealing at 800 °C for 10 s, a schedule commonly used for ion-implantation activation, and the amount of the increase depends strongly on the insulator material and the growth temperature. It appears that the low-temperature-grown (LTG) GaAs grown at 200 °C and the LTG Al0.43Ga0.57As grown at 300 °C, both embedded between AlAs barrier layers grown at a normal temperature, are the two best gate insulators when the high-temperature annealing is a required process for the MISFET. For a diode with a 300-Å-thick Al0.43Ga0.57As insulator and 100-Å-thick AlAs barriers, 1.42 V forward bias results in a leakage current of 1 nA/μm2. This low diode current proves that the LTG insulator is suitable for the gate of MISFETs.
Thin, high atomic weight refractory film deposition for diffusion barrier, adhesion layer, and seed layer applications
Authors: Rossnagel S. M. , Nichols C. , Hamaguchi S. , Ruzic D. , Turkot R.
Published: July 2002

Thin, nearly conformal films are required for semiconductor applications to function as diffusion barriers, adhesion layers and seed layers within trenches and vias. The deposition of high mass refractory films with conventional, noncollimated magnetron sputtering at low pressures shows better-than-expected conformality which is dependent on the degree of directionality of the depositing atoms: the conformality increases as the directionality increases. The primary cause appears to be a strongly angle-dependent reflection coefficient for the depositing metal atoms. As the deposition is made more directional by increasing the cathode-to-sample distance, the depositing atoms are more likely to reflect from the steep sidewalls, leading to better conformality as well as a less columnar film structure.
Comment on ‘‘Optimization of electrostatic deflectors’’ [J. Vac. Sci. Technol. B 13, 142 (1995)]
Authors: Lencová Bohumila
Published: July 2002

It is contended that contrarily to the claim of Szilagyi and Cho (Ref. 1), thecoma of deflection as well as field curvature can not be eliminated in the optimized electrostatic deflectors. (AIP)
A study of acid diffusion in chemically amplified deep ultraviolet resist
Authors: Itani Toshiro , Yoshino Hiroshi , Hashimoto Shuichi , Yamana Mitsuharu , Samoto Norihiko , Kasama Kunihiko
Published: July 2002

Postexposure bake (PEB) dependence of photogenerated acid diffusion was investigated in a chemically amplified deep ultraviolet positive resist. The resist consisted of a tert-butoxycarbonyl protected polystyrene as base resin and 2,4-dimethylbenzenesulfonic acid derivative as photoacid generator. The diffusion length of photoacid increased with increasing PEB temperature or its time. Moreover, the activation energy of acid diffusion reaction within the resist film became smaller, with increased exposure dose. It is considered that hydrophilic OH sites of the base resin generated by the deprotection of hydrophobic protecting groups has a role as one of the diffusion paths in the polymer matrix. Furthermore, it was found that the diffusion coefficient under high PEB conditions was affected by the acid reduction. Based on the analysis of diffusion characteristics, clear correlation between acid diffusion in the resist film and PEB conditions was obtained. These results are useful for improving both resolution capability and pattern profiles.
Fabrication and performance of thin amorphous Si subwavelength transmission grating for controlling vertical cavity surface emitting laser polarization
Authors: Zhuang Lei , Schablitsky Steve , Shi Rick C. , Chou Stephen Y.
Published: July 2002

Amorphous Si subwavelength transmission gratings (SWTGs) with a thickness of 240 nm and a period ranging from 50 to 900 nm were fabricated on a fused silica substrate using electron beam lithography, lift-off, and reactive ion etching. At certain grating periods, the SWTGs exhibit polarization dependent reflectance and transmittance due to the polarization dependent coupling of the eigenmodes inside the grating. By putting the SWTG in front of the output window of a vertical cavity surface emitting laser (VCSEL), a polarization dependent optical feedback can be achieved. Using this feedback, we demonstrated the locking, switching, and enhancement of the VCSEL’s polarization. A polarization ratio as high as 200:1 was achieved.
Effects of compaction on 193 nm lithographic system performance
Authors: Schenker Richard , Oldham William
Published: July 2002

Ultraviolet radiation induces compaction in fused silica. Using stress-induced birefringence as a dosimeter, we are able to measure refractive index changes over the range of 20 ppb–1.5 ppm and have found a general description of compaction versus 193 nm dose valid for a wide range of intensities, pulse rates, and fused silicas. Using the experimental data, we evaluate the effect of compaction damage on a model 193 nm optic. Zernike phase aberration terms from compaction in elements near the pupil plane of the system are calculated using Fourier optics while aberrations from other elements are estimated using ray-tracing. Aerial image simulations show significant distortion and focal shifts occur at the edge of the image field for only a 0.05λ total rms compaction-induced wave front aberration. The useful life of the model system depends strongly on the throughput, resist sensitivity, and partial coherence. For a system operating at 10 million pulses per day with a 70% clear field mask and sigma of 0.5, we predict a life range of 6 months to 12 years for resist sensitivities ranging from 50 mJ/cm2 to 10 mJ/cm2. This life prediction increases by over factor of 2 for sigma of 0.7.
Normal and lateral force images, sub-angstrom height resolution, and midlevel lateral resolution with a phonograph cartridge as scanning force sensor
Authors: Mariani Tullio , Frediani Carlo , Ascoli Cesare
Published: July 2002

The similarity of the operating principles of the atomic force microscope and the phonograph has suggested testing of a phonograph cartridge as a force sensor for scanning force microscopy (SFM). The results were surprisingly good. A stereophonic piezoelectric cartridge showed a height resolution limit of 0.01 Å, and was used, with the original stylus, to take SFM images in both normal and lateral force modes. The device works in constant height mode on a height range of more than 106, from less than 1 Å to about 100 μm, but its high capacitance sensors also allow the feedback mode operation. A model of the lateral resolution of an exploring stylus that allows a direct comparison with the resolution of optical instruments is discussed.
Reticle fabrication by high acceleration voltage electron beam: Representative figure method for proximity effect correction [VI]
Authors: Abe Takayuki
Published: July 2002

Proximity effect correction for reticle making by the dose correction method is discussed. A new algorithm for calculating the optimum dose is proposed, which is based on the dose formula method and the representative figure method. Its main feature is that dose evaluation points are fixed at individual small regions whose size is sufficiently small compared with the backscattering range. The calculation speed of the computer is evaluated which is sufficient to suppress the correction time to less than the writing time. The required calculation speed is 500 MIPS×4 CPU at most for a minimum feature size greater than 0.2 μm on the reticle. This result suggests that the real-time proximity effect correction is possible for making reticles. Furthermore, when the algorithm is applied to x-ray mask fabrication and direct writing process, the calculation time can be suppressed to less than the writing time.