bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopant profile control and metrology requirements for sub-0.5 μm metal–oxide–semiconductor field-effect transistors
Authors: Duane Michael , Nunan Peter , ter Beek Marcel , Subrahmanyan Ravi
Published: July 2002

Simulation is used to explore the sensitivity of device characteristics to variations in dopant profiles for modern metal–oxide–semiconductor field-effect transistors. These sensitivities place stringent requirements on the allowable variation in dopant profiles and on their metrology. The role of profile characterization and simulation in technology development is also discussed.
Nonlinear optical spectroscopy of Si–heterostructure interfaces
Authors: Meyer C. , Lüpke G. , Lü Z. G. , Gölz A. , Kurz H. , Lucovsky G.
Published: July 2002

Strain, dislocations, and electrically active defects at and near the interface of Si/SiO2 and Si/GaP heterostructures are analyzed by optical second-harmonic spectroscopy. For plasma oxides deposited on Si(001) and Si(111), time-dependent second-harmonic experiments reveal that near-interface oxide defects trap charge by the tunneling of photoexcited electrons from the Si conduction band. The space-charge field-induced second-harmonic transients are resonantly enhanced by two-photon E1 transitions in silicon. In GaP epilayers grown on Si(001) the bulk dipole-allowed electro-optical effect is suppressed by the formation of antiphase domains. In contrast, in GaP films grown on Si(111) and vicinal Si(001) the density of antiphase domains is considerably reduced yielding an enhancement of the second-order nonlinear optical response by two orders of magnitude.
Ultrahigh density data storage on Ag–TDCN thin films by scanning tunneling microscopy
Authors: Gao H. J. , Wang D. W. , Liu N. , Xue Z. Q. , Pang S. J.
Published: July 2002

We present the fabrication of Ag–toluylene 2, 4-dicarbamidonitrite (TDCN) organometallic composite thin films using an ionized cluster beam deposition method. The realization of high density data storage in the composite thin films by scanning tunneling microscopy (STM) is reported. By applying a proper voltage pulse between the STM tip and the surface of the highly oriented pyrolytic graphite substrate on which the Ag–TDCN thin film was previously deposited, marks on the thin films can be formed. The size of the marks is about 50 nm and the corresponding data storage density is larger than 1010 bits/cm2. The thickness of the thin films in the experiment was about 100 nm. The preliminary theoretical analysis of the mechanism of the mark formation in the organometallic functional composite thin films is suggested.
Molecular beam epitaxy growth of Iny2Al1−y2As/In0.73Ga0.27As/Iny1Al1−y1As/ InP P-HEMTs with enhancement conductivity using an intentional nonlattice-matched buffer layer
Authors: Jiang C. , Xu B. , Li H. X. , Liu F. Q. , Gong Q. , Zhou W. , Zhu D. H. , Liang J. B. , Wang Z. G.
Published: July 2002

Pseudomorphic Iny2Al1−y2As/In0.73Ga0.27As/Iny1Al1−y1As (y1⩾0.52) modulation-doped heterostructures with an intentional nonlattice-matched buffer layer were successfully grown by molecular beam epitaxy on (100)InP substrates. Fourier transform photoluminescence and double crystal x-ray diffraction measurements show a superior crystalline quality in the high In content channel, when In mole fraction increases from y1=0.52 to 0.55 in the Iny1Al1−y1As buffer layer. In this case, an increasing of 16.3% and 23.5% for conductivity (μ×ns) and mobility, related to the strain compensation in the In0.73Ga0.27As channel, was achieved, respectively, comparing to the structure containing a well-lattice matched buffer layer. With increasing the mismatch further (y1=0.58), a morphology with cross-hatched pattern was observed due to the onset of a large amount of misfit dislocations, and the electronic characterization is not able to be improved continuously. Because we can realize high quality strained P-HEMTs in a relative wide range of equivalent beam flux (EBF) ratios, the stringent control over the constant EBF is not indispensable on this In-based material system.
Electrical and structural characterization of PtSi/p-Si1−xGex low Schottky barrier junctions prepared by co-sputtering
Authors: Nur O. , Willander M. , Turan R. , Sardela M. R. , Radamson H. H. , Hansson G. V.
Published: July 2002

Schottky barrier junctions of PtSi/Si1−xGex were produced; the silicide was deposited by co-sputtering on defect-free well-calibrated strained-Si1−xGex (0⩽x⩽0.242) layers. This work is motivated by the fact that it is very difficult to control the formation of well-defined and well-controlled PtSi/Si1−xGex junctions by reacting Pt/Si1−xGex or by using a silicon cap layer. The Schottky barrier heights of these junctions were substantially lower than those of PtSi/Si junctions. Different characterization tools were employed for structural characterization. High-resolution multicrystal x-ray diffraction (HR-MCXRD) was used to investigate the sample quality and strain state of the molecular beam epitaxy (MBE) grown Si1−xGex layers and to accurately determine the Ge fraction in the fabricated junctions. Cross-sectional transmission electron microscopy (XTEM) was applied to investigate the interface roughness. The possible interlayer diffusion was investigated by secondary ion mass spectrometry (SIMS). The variation of the barrier height of the junctions with the Ge fraction x was studied, and it was found to follow the same change as the band gap of strained-Si1−xGex. Also, and for comparison, Pt/p-Si1−xGex junctions were produced, and the effect of annealing on electrical characteristics was investigated.
Using a new kind of organic complex system of electrical bistability for ultrahigh density data storage
Authors: Gao H. J. , Ma L. P. , Zhang H. X. , Chen H. Y. , Xue Z. Q. , Pang S. J.
Published: July 2002

We present a new kind of organic complex system of electrical bistability, m-nitrobenzal malononitrile and diamine benzene (mNBMN-DAB), which can be employed as ultrahigh density data storage devices by scanning tunneling microscopy (STM). The mNBMN-DAB thin film was prepared on highly oriented pyrolitic graphite (HOPG) substrates using physical vacuum deposition method. A critical voltage pulse between the STM tip and the surface of the HOPG substrate can make marks on the thin films. The size of the marks is about 1.3 nm and the corresponding data storage density is larger than 1013 bits/cm2. A new mechanism of the charge transfer in the system for the data storage is suggested. These results show a great potential of this type of organic composite systems in the application of the ultrahigh density data storage.
Interfacial reaction behavior of Pt, Pd, and Ni on ZnSe
Authors: Duxstad K. J. , Haller E. E. , Yu K. M. , Bourret E. D. , Lin X. W. , Ruvimov S. , Liliental-Weber Z. , Washburn J.
Published: July 2002

The solid-state reactions of Pt, Pd, and Ni thin film contacts on ZnSe were studied. Pd has been observed to react at 200 °C to form a ternary, epitaxial phase, Pd5+xZnSe. This phase is stable up to 450 °C, when Pd begins to diffuse through the ZnSe into the GaAs substrate. Pt begins to react at 575 °C and forms a layer of Pt5Se4 at the Pt/ZnSe interface. Above the interfacial layer there is a Pt–Zn solid solution, but no Pt–Zn phases were observed. After annealing at 675 °C, the Pt5Se4 phase is no longer observed and Pt–Zn phases form. A small amount of interdiffusion at the Ni/ZnSe interface has been observed by transmission electron microscopy after annealing at 300 °C. Annealing at 425 °C results in the formation of laterally separated grains of a metastable NixSe phase. After annealing at 450 °C, grains of NiSe are observed. The similarities between these reactions and the near-noble metal reactions on Si and GaAs are discussed as well as the possibility of using these reactions for forming electrical contacts to ZnSe.
Nanolithography by displacement of catalytic metal clusters using an atomic force microscope tip
Authors: Brandow S. L. , Dressick W. J. , Dulcey C. S. , Koloski T. S. , Shirey L. M. , Schmidt J. , Calvert J. M.
Published: July 2002

The use of catalytically active nanoclusters as a novel material for atomic force microscope (AFM) nanolithography is demonstrated. Films were prepared from colloidal Au nanoparticles and giant Pd clusters. Lithographic patterns were generated using the contact area of the AFM tip to physically displace nanoclusters, forming two-dimensional patterns on silicon oxide and functionalized silicon surfaces. Linewidth was found to depend on the force applied to the nanoparticles and the number of tip passes used to generate the pattern. Conditions were optimized to clear scanned areas using minimum applied force. Patterned films were used as templates for the selective deposition of electroless metal, which served as a robust plasma etch mask for pattern transfer into the underlying substrate to a depth of 200 nm. Minimum linewidths of approximately 35 nm were achieved in etched samples.
Expression for the growth rate of selective epitaxial growth of silicon using dichlorosilane, hydrogen chloride, and hydrogen in a low pressure chemical vapor deposition pancake reactor
Authors: Kongetira Poonacha , Neudeck Gerold W. , Takoudis Christos G.
Published: July 2002

A semiempirical expression was developed for the growth rate of selective epitaxial growth (SEG) and epitaxial lateral overgrowth of silicon in a rf heated cold-wall low pressure chemical vapor deposition pancake reactor for the dichlorosilane-HCl–H2 system. The model was obtained for temperatures ranging from 920 to 1020 °C, system pressures from 40 to 150 Torr, and over a range of HCl and dichlorosilane gas flows. The growth rate expression is the sum of a growth term which is a function of the partial pressures of dichlorosilane (SiCl2H2) and hydrogen, and an etch term that varies with the partial pressure of HCl. The growth and etch terms have a temperature Arrhenius relation with activation energies of Egr=2.266 and Eet=1.349 eV, respectively. Included is a term to account for the SEG growth rate dependence on the ratio of SiO2 area coverage to silicon wafer area. A methodology was developed for obtaining the coefficients for the semiempirical growth rate expression from several sets of experiments.
Physical characterization of diamond pyramidal microtip emitters
Authors: Kang W. P. , Davidson J. L. , George M. A. , Milosavljevic I. , Li Q. , Xu J. F. , Kerns D. V.
Published: July 2002

Micropatterned diamond pyramidal tips have been demonstrated to have high emission current. This article presents in great detail the physical characterizations that have proceeded to characterize the topology, morphology, and microstructure of these diamond microtips using transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning tunneling microscopy (STM), and Raman spectroscopy. The results show that the diamond microtips are indeed a polycrystalline diamond structure as evidenced by Raman spectroscopy and diffraction analysis of the TEM. AFM and STM results provide detail information as to the surface and tip shape of the diamond emitters. AFM/STM observations suggest a nucleation and growth process whereby the matter in which chemical vapor deposition diamond nucleates on the planar top surface of the tip substrate is distinct and different from the way the diamond grows in the cavity “mold.” Likewise, the TEM results contrast the diamond microstructure in the field area with that of the tip where distinct differences are observed.
Deep submicron resist profile simulation and characterization of electron beam lithography system for cell projection and direct writing
Authors: Ham Young-Mog , Lee Changbuhm , Kim Soo-Hwan , Chun Kukjin
Published: July 2002

In this article we report the experimental data of chemically amplified resists (CARs) used in fabrication of deep submicron pattern delineation using electron beam lithography, and propose a reliable simulation method that fits the experiment results well. CAR is proven to have high resolutions of 150 nm for a 70 nm diameter Gaussian beam at 30 keV, and 125 nm for various shaped beams at 50 keV. The sensitivity to process parameters of CAR can be reduced by finding the optimum experiment condition for the best resist profiles. To make the simulation results more realistic, we applied the ray tracing method to the development simulator especially appropriate for CAR. Also, we modified the conventional hybrid scattering model to include the inelastic scattering and to take the low energy lithography into account.
Layer-by-layer sputtering of Si(111) and (001) surfaces mediated by surface vacancy diffusion: Surface physics and application for nanofabrication
Authors: Watanabe Heiji , Ichikawa Masakazu
Published: July 2002

Layer-by-layer sputtering of Si surfaces by low-energy Ar ions is studied by using scanning reflection electron microscopy. Two types of layer-by-layer etching (reversal of step-flow growth and two-dimensional vacancy-island nucleation) are observed. These results imply that vacancies created by ion impact can diffuse on the surface, and are annihilated at step edges. The diffusion length of vacancies are estimated from the denuded zone width of vacancy islands formed along steps by thermal heating after the vacancy introduction. The obtained activation energies of vacancy diffusion are 3.0±0.2 and 2.3±0.2 eV for Si(111) and (001) surfaces, respectively. We also propose an application of vacancy islands in nanofabrication, where vacancy islands are used as a self-organized template to provide nucleation sites of quantum dots.
Fabrication and near-room temperature transport of patterned gold cluster structures
Authors: Clarke L. , Wybourne M. N. , Yan Mingdi , Cai S. X. , Brown L. O. , Hutchison J. , Keana J. F. W.
Published: July 2002

Ligand stabilized metal clusters are becoming of considerable interest for possible nanoscale electronics applications. In this article, we report the fabrication and near-room temperature electrical transport properties of structures made from the gold-cluster material Au55[P(C6H5)3]12Cl6. While other strategies to produce cluster arrays have been reported, this work is the first to use electron-beam lithography to laterally define the structures. We compare the current–voltage characteristics of nonpatterned and patterned structures, and show that in both cases the nonlinear behavior observed is consistent with Coulomb blockade dominated transport. We argue that charging of individual Au55 cores is responsible for the effects observed.
Characterization of III nitride materials and devices by secondary ion mass spectrometry
Authors: Chu Paul K. , Gao Yumin , Erickson John W.
Published: July 2002

Secondary ion mass spectrometry (SIMS) is an excellent technique to characterize III nitride materials and devices (dopants, impurities, and composition). Using empirical standards, the ion yield trends are derived for III nitride matrices to enable quantitative and high precision characterization of both major and impurity elements. The technique can be employed to investigate the control of purity and doping, determine growth rate and composition, as well as reveal the structure of finished optoelectronic and electronic devices. SIMS is thus a powerful tool for failure analysis, reverse engineering, and concurrent engineering.
Metal–oxide–semiconductor field-effect transistor junction requirements
Authors: Duane Michael , Lynch William
Published: July 2002

The detailed requirements for shallow junctions for deep sub-micron metal–oxide–semiconductor field-effect transistors are reviewed and explained. The National Technology Roadmap for Semiconductors lists the concentration and depth requirements for the next several generations of technology, but does not provide detailed explanation of the electrical requirements that drive these physical junction characteristics. There are actually many more constraints on junction formation in an integrated complimentary metal–oxide–semiconductor flow, e.g., the effect of the junction formation on the channel region, which can include poly depletion, boron penetration, and reverse short channel effects. The guidelines presented here should be useful to researchers developing ultrashallow junction processes or measurement techniques.
Quantification of nanospreading resistance profiling data
Authors: De Wolf P. , Clarysse T. , Vandervorst W.
Published: July 2002

In nanospreading resistance, the resistance measured at a particular position on the sample cross section is not exclusively determined by the carrier concentration at this position, but by the entire surrounding carrier profile. The correct evaluation of this spreading effect requires a detailed calculation, leading to a deconvolution algorithm, which recovers the charge-carrier profile from the measured resistance profile. In this work, a general scheme for transforming a wide range of profiles is proposed. The scheme is based upon finite-element calculations of the potential distribution and the current spreading of a circular flat contact current source on a semi-infinite semiconductor sample with known carrier distribution. A correction factor database is formed as a function of typical profile characteristics such as (i) the distance to perfectly isolating or conducting boundaries, (ii) carrier gradient, and (iii) carrier curvature. In routine operation the transformation of resistance data into the carrier-concentration profile is done by interpolation of the database, hereby avoiding the time-consuming finite-element calculations. The latter results in a very fast calculation of the carrier profile data with an accuracy better than 10%, without any loss in spatial resolution. Examples are given that illustrate the accuracy of the method.
Electron-beam lithography with metal colloids: Direct writing of metallic nanostructures
Authors: Lohau J. , Friedrichowski S. , Dumpich G. , Wassermann E. F. , Winter M. , Reetz M. T.
Published: July 2002

We report on the fabrication of metallic nanostructures in the sub-100 nm region by means of electron-beam lithography with metal colloids. A thin organometallic film consisting of surfactant stabilized Pd-colloids (⩽3 nm) is directly patterned by electron-beam irradiation. Non-exposed colloids are easily removed by rinsing the sample with appropriate dissolvers. The metallic character of the nanostructures is checked by resistance measurements. We find the morphology and the resistance behavior of the present nanostructured Pd-colloids to be similar to those of granular thin Pd/C films. Accordingly, the metal content of the nanostructures fabricated with Pd-colloids can be estimated.
Arsenic incorporation in HgCdTe grown by molecular beam epitaxy*
Authors: Aqariden F. , Wijewarnasuriya P. S. , Sivananthan S.
Published: July 2002

We report the results of in situ doping of HgCdTe by molecular beam epitaxy (MBE) using an elemental arsenic source. Arsenic was successfully incorporated as an acceptor during the MBE growth using either a conventional or planar doping approach. Hall effect measurements and secondary ion mass spectroscopy (SIMS) were used to investigate arsenic activity before and after different Hg anneals. Close to 100% acceptor doping efficiency with arsenic was obtained on these MBE grown layers after annealing. This corresponds to a total arsenic concentration of approximately 2×1018 cm−3 which is more than sufficient for a wide range of infrared devices. At much higher total arsenic concentration, electrical activity falls off drastically.
Electron energy distribution of diamond-coated field emitters
Authors: Choi W. B. , Schlesser R. , Wojak G. , Cuomo J. J. , Sitar Z. , Hren J. J.
Published: July 2002

The influence of metal/diamond interfacial nanostructure and diamond surface treatment on electron emission from diamond-coated Mo emitters is presented. Diamond coatings are known to enhance electron emissivity but may do so at the interfacial barrier and/or the surface barrier, since both influence the magnitude of the current. Prior to annealing the energy distribution of the emitted electrons exhibits a linear displacement in peak position with applied voltage. After annealing in a hydrogen plasma at 600 °C, emission is further enhanced and the magnitude of the peak shift with applied voltage is reduced. A further oxygen plasma treatment yields an intermediate dependence of peak shift with voltage. The effects of hydrogen plasma annealing appear closely related to changes in the nanostructure at the Mo/diamond interface. During annealing Mo2C particles are formed while both molybdenum oxides and an amorphous layer present on the original diamond particles are removed. The smaller voltage drop after the oxygen plasma treatment is thought to be due to the removal of passivating hydrogen as well as to a change in the surface barrier of the diamond. The energy barrier of the diamond/vacuum interface plays only a minor role in the voltage drop.
Effect of laser irradiation on electron emission from Si field emitter arrays
Authors: Takai M. , Suzuki N. , Morimoto H. , Hosono A. , Kawabuchi S.
Published: July 2002

Ultraviolet (UV) laser lights were irradiated on Si field emitter arrays before and during electron emission to investigate the surface cleaning effect of laser light irradiation. UV light irradiation for 2–10 min before electron emission in a vacuum resulted in enhanced electron emission by 50%, which gradually decreased after further aging. Laser light irradiation during electron emission could induce enhanced electron emission by a factor of 2.4 due to photoinduced carrier generation and surface cleaning, and higher electron emission by a factor of 2 than the initial emission was observed even after laser light irradiation and prolonged aging for 20 h.
Tunneling emission from valence band of Si-metal–oxide–semiconductor electron tunneling cathode
Authors: Ikeda Junji , Yamada Atsushi , Okamoto Kazuya , Abe Yoshiaki , Tahara Kaoru , Mimura Hidenori , Yokoo Kuniyoshi
Published: July 2002

A metal–oxide–semiconductor (MOS) electron tunneling cathode using n- and heavily doped p-type Si substrates were fabricated and their characteristics were measured. Two energy peaks in the energy distributions of emitted electrons from the n-type cathode with the gate oxide thickness of 8.5 nm and the p-type cathode with the gate oxide thickness of 8.9 nm were observed. This article discusses the experimental results to make a conduction mechanism clear and shows that a part of electrons tunnel through the oxide barrier from the valence band of Si substrate and are emitted into vacuum in the MOS electron tunneling cathode.
X-ray absorption at Ge L3 edges as a tool to investigate Ge/Si(001) interfaces and heterostructures
Authors: Castrucci P. , Gunnella R. , De Crescenzi M. , Sacchi M. , Dufour G. , Rochet F.
Published: July 2002

The Ge L3 edge x-ray absorption spectra of a series of Ge/Si heterostructures grown on Si(001) substrates were investigated using linearly polarized synchrotron radiation. By making use of a multiple scattering approach we reproduced the experimental spectra for different structural models and several degrees of strain and intermixing. Evidences of interfacial intermixing processes were found even at room temperature. Such an intermixing is strongly inhibited by Sb assisted growth.
Improved quality GaN films grown by molecular beam epitaxy on sapphire
Authors: Reifsnider J. M. , Gotthold D. W. , Holmes A. L. , Streetman B. G.
Published: July 2002

We report on the epitaxial growth and characterization of gallium nitride by molecular beam epitaxy (MBE). The samples were grown on (0002) sapphire using solid metal group III sources and an EPI UniBulb™ rf plasma source to produce atomic neutral nitrogen species. The films were characterized optically using reflectance and photoluminescence, van der Pauw Hall effect measurements, and x-ray rocking curves for the (0002), (101̄4), and (22̄04) directions. Nominally undoped films were grown with a (0002) rocking curve (ω) full width at half maximum (FWHM) from 700 to 125 arcsec, electron mobilities of up to 180 cm2/V s, and background carrier concentrations from the mid- 1017–2×1016/cm3. The room temperature photoluminescence FWHM for these films ranged from 38 up to 62 meV, with peak to yellow ratios from 7 to 70. These values represent an improvement in the quality of nominally undoped heteroepitaxially grown GaN by MBE.
X-ray photoelectron spectroscopy analyses of silicon dioxide contact holes etched in a magnetically enhanced reactive ion etching reactor
Authors: Czuprynski P. , Joubert O.
Published: July 2002

High aspect ratio SiO2 contacts are etched with a C4F8/CO/O2/Ar chemistry using a magnetically enhanced reactive ion etching (MERIE) plasma source with a good selectivity to the underlying silicon. X-ray photoelectron spectroscopy (XPS) studies allow chemical analysis of high aspect ratio SiO2 contact holes. Using the charging effect, a complete separation of the XPS peaks originating from the resist mask and from the bottom of the contact holes is possible. XPS analyses show that the fluorination of the polymer on the bottom of the contact is low (F/C around 0.2) and independent of the aspect ratio of contact holes. Furthermore, XPS spectra also show that the full width at half maximum of the Si 2p doublet measured at the bottom of contact holes strongly increases, showing that the highly energetic ion bombardment induced by the MERIE source lead to a severe amorphization of the silicon surface. Finally, comparisons between MERIE and high density plasma are discussed.
Substitutional carbon impurities in thin silicon films: Equilibrium structure and properties
Authors: Kelires Pantelis C. , Kaxiras Efthimios
Published: July 2002

We discuss a set of atomistic calculations of the structure of Si geometries with substitutional carbon atoms, involving the (100) surface or bulk features related to thin films grown in the (100) direction. We use both quantum mechanical density functional theory and empirical potential calculations at finite temperature and constant pressure to study the local structure, bonding characteristics and overall distribution of the carbon atoms in the host silicon lattice. These calculations reveal a strong nearest neighbor repulsion between substitutional carbon atoms, to the point where these atoms prefer to have fewer bonds than normally in order to avoid each other. This effect still holds for high temperatures and high carbon concentrations. As a result, bulk ordering of the type observed in Si–Ge alloys is unlikely to occur.
Electrical properties of InSb quantum wells remotely doped with Si
Authors: Goldammer K. J. , Liu W. K. , Khodaparast G. A. , Lindstrom S. C. , Johnson M. B. , Doezema R. E. , Santos M. B.
Published: July 2002

Two-dimensional electron systems were realized in InSb quantum wells with AlxIn1−xSb barrier layers δ-doped with Si. Measured electron mobilities in multiple-quantum-well structures were as high as 41 000 cm2/V s at room temperature and 209 000 cm2/V s at 77 K. Simple models can be used to explain the observed dependencies of the electron density on the quantum-well-to-dopant distance and on the number of quantum wells. Characterization by atomic force microscopy indicates that layer morphology may be a factor limiting electron mobility.
Secondary ion mass spectrometry and atomic force spectroscopy studies of surface roughening, erosion rate change and depth resolution in Si during 1 keV 60° O2+ bombardment with oxygen flooding
Authors: Jiang Z. X. , Alkemade P. F. A.
Published: July 2002

Oxygen flooding during secondary ion mass spectrometry (SIMS) depth profiling is often used to achieve very short surface transients. However, for low-energy and obliquely incident O2+ primary beams, oxygen flooding can be detrimental. In this work we have measured as a function of depth the erosion rates, surface topographies and depth resolution for B and Ge in Si bombarded by 1 keV 60° O2+ with and without oxygen flooding. Using B and Ge deltas we showed that the erosion rate under oxygen flooding was not constant. The effect was most pronounced at intermediate flooding pressures; at saturation pressures, a drop of 25%–30% was found within ∼25 nm below the surface. Atomic force microscopy measurements revealed that the erosion rate change was related to the onset of surface roughening. Oxygen flooding influenced the depth resolution in terms of the decay length for B and Ge in different ways. With oxygen flooding, the Ge decay length was larger than without flooding due to oxide-enhanced segregation; while the B decay length was smaller, due to swelling of the sample. In terms of the delta peak width, best depth resolution was always obtained without flooding. This study showed that oxygen flooding impedes accurate ultrashallow SIMS depth profiling.
Focused ion beam direct deposition and its applications
Authors: Nagamachi Shinji , Ueda Masahiro , Ishikawa Junzo
Published: July 2002

We developed focused ion beam direct deposition as a new method for fabricating patterned metal films directly on substrates. We designed and constructed a focused ion beam apparatus which satisfied demanded capabilities for direct deposition such as low energy and fine focused beam, high beam current density, high vacuum condition, changeability of ion species, precise and wide range patterning, sample observation by an optical microscope, and quick sample exchange. We also developed liquid alloy–metal ion sources for conductive materials, superconductive material and magnetic material. We tried to apply the focused ion beam direct deposition method to IC modification, surface acoustic wave (SAW) devices, SQUIDs, multilayers, and probing on small crystals. In SAW devices, SQUIDs, and multilayers, fabricated devices had comparable performance to devices fabricated by ordinary photolithographic processes. In IC modification and probing on small crystals, a low resistant and flexible connection was confirmed. We proved that focused ion beam direct deposition method is a useful tool for research and development such as prototyping.
GaAs microcrystal growth on semiconductor surfaces by low energy focused ion beam
Authors: Chikyow Toyohiro , Koguchi Nobuyuki
Published: July 2002

A position controlled or density controlled GaAs microcrystal growth from Ga droplets was attempted using a low energy focused ion beam system. Ga ions from a liquid Ga ion source were accelerated up to 10 kV to produce a focused ion beam. Subsequently the ions were given a positive bias to reduce their kinetic energy by a four-element retarding lens system. The Ga ions with a 30 eV kinetic energy softly landed on a S-terminated GaAs surface and formed a series of Ga droplets or Ga droplets matrix. After initiating the As molecule supply, GaAs microcrystals were found to grow from these Ga droplets. The low energy focused ion beam was also applied to create nucleation sites of Ga droplets on an As-terminated Si (001) surface at 100 eV. Ga droplets with high density were formed on a region where As atoms were removed partially on the Si surface. From these results, the low energy focused ion beam was found useful for position control or density control of GaAs microcrystals on semiconductor materials.
Formation of GaAs/AlGaAs constricted-channel field-effect transistor structures by focused Ga implantation and transport of electrons via focused ion beam induced localized states
Authors: Kim H. , Noda T. , Sakaki H.
Published: July 2002

We report on the fabrication of n-AlGaAs/GaAs constricted-channel field-effect transistor (FET) structures by focused ion beam (FIB) implantation, and study transport properties of low-dimensional electrons via FIB induced localized states. In this work, quantum wire FET samples with in-plane gates and top gate were formed by using a focused Ga ion beam by which Ga ions of a high dose density (>1015 cm−2) are introduced in the vicinity of a conductive channel at room temperature. The drain conductance Gd was studied in constricted channels with various nominal widths, W. It is found that Gd of a narrow channel (W∼1 μm) becomes quite small and nonlinear at low temperatures. When Gd is measured as a function of gate voltage, Vg, periodic oscillations are clearly observed at 15 K with a typical spacing of Vg∼60 mV, whereas the oscillation weakens and transforms to steplike structures at higher temperature (250 K). This oscillatory characteristic may possibly result from single electron transport through quantum dots associated with FIB-induced random potentials in the channel.
Investigation of the modification mechanism induced by a scanning tunneling microscope on YBa2Cu3O7−δ
Authors: Bertsche G. , Clauss W. , Prins F. E. , Kern D. P.
Published: July 2002

The scanning tunneling microscope (STM) was used to modify wires of the high temperature superconductor YBa2Cu3O7−δ (YBCO) which had been fabricated by electron beam lithography in order to simulate realistic conditions of a fabrication process. The linewidth of the structures generated with the STM was well below 50 nm. For a deeper understanding of the mechanism responsible for the STM-induced modifications, the experiments were performed under ambient conditions, in ultrahigh vacuum, carbon dioxide atmosphere, and nitrogen atmosphere. Results indicate that both water and carbon dioxide are essential for the modification process on the YBCO wires. This suggests that the modification mechanism is based on a water-mediated electrochemical decomposition of YBCO in the field of the STM tip.
Atomistic study of nickel silicide structures on Si(100) by tunneling microscopy
Authors: Ono Izumi , Yoshimura Masamichi , Ueda Kazuyuki
Published: July 2002

Surface structures of Ni-deposited Si(100) have been investigated using scanning tunneling microscopy (STM). After heating at 670 °C, NiSi2 islands consisting of patch features grow on the (2×n) substrate. We have proposed a new structure model for NiSi2 island by taking account of the correlation of heights and lateral positions between top-layer atoms in the NiSi2 and Si dimers in the substrate. In the model, the top-layer atoms, with a nearest neighbor distance of 0.38 nm, are located at bridge sites on the Ni layer of NiSi2. Patch features consist of two equivalent anti-phase sites shifted by half the unit length of 1×1 along both [011] and [01̄1] directions. In addition, it is found in the empty-state STM images that the center atoms make pairs two by two.
Masked ion beam lithography with highly charged ions
Authors: Gillaspy J. D. , Parks D. C. , Ratliff L. P.
Published: July 2002

Masked ion beam lithography using highly charged ions is demonstrated for the first time by producing an array of hundreds of ordered micrometer wide dots using Xe44+ on poly(methylmethacrylate) resist. At low dose, exposure of the resist is incomplete and isolated single-ion impact sites can be seen within the exposed areas. Atomic force microscope images of the single-ion impact sites show craters with a width of 24 nm. At high dose, the exposure is complete and the dot morphology is consistent with limitations from the mask. Scanning electron microscope images indicate that the sidewall slope is steeper than four.
Ion projection lithography: Status of the MEDEA project and United States/European cooperation
Authors: Gross Gerhard , Kaesmaier Rainer , Löschner Hans , Stengl Gerhard
Published: July 2002

Structure and targets of the European MEDEA project on ion projection lithography as well as related U.S./European cooperation are explained. By assuming 10 μm virtual source size and 1 eV (full width half maximum) energy spread calculations for a multielectrode electrostatic ion–optical system (1.25 m between ion source and stencil mask, ≈1.8 m between mask and wafer) we realize the possibility of 100 nm resolution (line and space) over an exposure field of 22×22 mm2 even when using the MONTEC model for calculating the stochastic blur and when running 3.3 μA He+ ion beam current through the ion–optical column, thus more than twice exceeding target specifications. Thus, for 100 nm resolution and 50% pattern density the raw throughput is ≈12 cm2/s corresponding to >75 WPH (pattern within 80% of 300 mm wafer area).
Edge diffraction enhanced printability in x-ray nanolithography
Authors: Chen Y. , Simon G. , Haghiri-Gosnet A. M. , Carcenac F. , Decanini D. , Rousseaux F. , Launois H.
Published: July 2002

We study the edge diffraction enhanced printability in x-ray nanolithography under both proximity and soft-contact printing conditions. Theoretical modeling shows that the gap dependence of the edge diffraction is closely related to that of the minimum linewidth described by the common Fresnel formula and that the edge diffraction can significantly enhance the image contrast of nanometer scale features. Experimental results are also presented to show high resolution and high aspect ratio printability. Furthermore, a method for fabricating ultrahigh resolution and dense structure is discussed based on edge diffraction enhanced printability with very thin absorber masks.
Atomic force microscope observation of plasmid deoxyribose nucleic acid with restriction enzyme
Authors: Nakamura T. , Maeda Y. , Oka T. , Tabata H. , Futai M. , Kawai T.
Published: July 2002

We have observed plasmid deoxyribose nucleic acid (DNA), in real space images, before and after treating with restriction enzyme (Pvu II or Hinc II) using an atomic force microscope (AFM). The enzyme is recognized on DNA even in the absence of Mg2+ ions. In the presence of Mg2+, on the other hand, direct evidence was obtained that the enzyme could bind to circular plasmid DNA without cutting and cleaved it at the site corresponding to the specificity. Lengths of the DNA fragments observed by AFM were consistent with the values estimated by agarose gel electrophoresis. In addition, as substrates for the AFM observation, rutile TiO2(110) single crystal surface was found to be effective in expanding and fixing the DNA molecules as straight chains along the stepped surface.
Investigation of the formation mechanism of Spindt-type cathode by simulation and experiments
Authors: Lee Hangwoo , Park Youngjun , Kim Jaewan , Choi Junhee , Kim Jongmin
Published: July 2002

The formation mechanism of Spindt-type metal emitter is investigated by the simulation and the fabrication. There are several factors in this mechanism. The aspect ratio (emitter height/bottom diameter of emitter) is the major factor determined mainly by the physical properties of evaporation materials and process conditions. On the emitter tip, the emission current depends on the aspect ratio that affects the suitable current density for field emission display. In the fabrication of metal emitter by electron beam evaporator, the dependence of the aspect ratio on materials and process conditions is analyzed by the particle simulation using the modified ballistic deposition model. From these results, the formation mechanism of the metal field emitter is analyzed with experimental data, therefore the optimized process condition is obtained for a suitable aspect ratio.
Simulation of room temperature thermionic emission from AlxGa1−xN negative electron affinity cathodes
Authors: Hatfield C. W. , Bilbro G. L.
Published: July 2002

A cathode consisting of AlxGa1−xN is theoretically investigated. Spatial variations of Al fraction are used to provide a structure which transports electrons from n-type GaN material to Al0.75Ga0.25N material which exhibits negative electron affinity. The simulations indicate the emitted electron current density corresponding to various applied fields. The results for structures in which a 75-nm-thick layer of compositionally graded AlxGa1−xN sits upon a 100-nm-thick layer of GaN indicate that at room temperature a thermionic emission current density on the order of 100 A/cm2 can be expected for an applied field of about 75 V/μm. These new results indicate that AlxGa1−xN compositionally graded cathodes should be useful for vacuum microelectronic devices.
New concept of lateral GaAs field emitter for sensor applications
Authors: Arslan D. , Dehé A. , Hartnagel H. L.
Published: July 2002

We present a novel lateral field emitter structure for sensing applications, which is based on GaAs. According to the Fowler–Nordheim theory, the emitted current depends exponentially on the distance between the cathode and the anode. Hence, this effect is predestined for sensing of vibration, acceleration, and pressure. We have designed and fabricated a lateral field emitter structure consisting of two wedges vis-à-vis. They are etched anisotropically in n+-doped epitaxial GaAs. One of the wedges is released by front side bulk micromachining to form a flexible cantilever. This cantilever contains the seismic mass of the accelerometer. The sensing principle is based on the following effect. The electrical field strength at the cathode is already very strong at relatively low cathode–anode voltages due to the geometrical parameters: (i) the low radius of the emission wedge, its radius of curvature is much smaller than 50 nm and (ii) very small distance between the cathode and the anode. Acceleration or vibration causes the cantilever to bend, so that the distance between the two wedges varies accordingly. This causes a modulation of the electrical field strength at the cathode and leads to a modulation of the emission current. The proposed sensor has the advantage of high sensitivity combined with a good temperature insensitivity. Classical beam theory was applied to define the geometrical parameters and the corresponding deflection of the cantilever.
High resolution organic resists for charged particle lithography
Authors: Ochiai Yukinori , Manako Shoko , Fujita Jun-ichi , Nomura Eiichi
Published: July 2002

Exposure of resist with electron or ion beams is a common nanolithography technology which is used to fabricate electronic devices and microstructures. The resolution mainly depends on the beam size and the resolution of the resist. We have developed two new high resolution organic resists, which are calixarene derivatives. 50 keV electron beams and 260 keV Be2+ ion beams were used to expose the resist, and 10 nm resolution was achieved with the Gaussian electron beam. The electron beam sensitivities of the two resists were 7 and 0.7 mC/cm2. By using them, we produced 10-nm-order resolution patterns, which we exposed with a Gaussian electron beam. We also achieved 10-nm-level resolution by using a low molecular weight (Mw=1100) polystyrene resist, almost the same Mw as that of the calixarene. The resolution of the polystyrene resist improved as lower molecular weights were used. Therefore, the resist resolution depends on the molecular weight or molecular size.
Formation and growth of CoSi2 on (001)Si inside 0.2–2 μm oxide openings prepared by electron-beam lithography
Authors: Yew J. Y. , Chen L. J. , Wu W. F.
Published: July 2002

The formation and growth of CoSi2 inside 0.2–2 μm linear oxide openings and contact holes prepared by electron-beam lithography have been investigated. A thin, uniform epitaxial CoSi2 was grown inside 0.5 μm or smaller linear openings and 0.7 μm or smaller contact holes by both one- and two-step rapid thermal annealing processes. On the other hand, epitaxial and polycrystalline CoSi2 were found to form on silicon near the edge and central region, respectively, inside 0.6 μm or larger linear openings. The size effect of the oxide openings is correlated to the distribution of local stress induced at the oxide edge. The formation of CoSi at low temperature appeared to be retarded by the local compressive stress near the edge of the linear oxide openings. The relative ease in the epitaxial growth of CoSi2 near the oxide edge of the linear openings and of 0.7 μm and smaller contact holes is attributed to the thinness of the CoSi layer.
Molecular beam epitaxy of periodic BaF2 /PbEuSe layers on Si(111)
Authors: Fang X. M. , Wu H. Z. , Shi Z. , McCann P. J. , Dai N.
Published: July 2002

Bragg reflector structures consisting of BaF2/PbEuSe stacks have been epitaxially grown on CaF2/Si (111) substrates. The reflectors are centered at a wavelength of 4.0 μm with a bandwidth of about 3.0 μm. Reflectivity as high as 95% at the center wavelength has been achieved in three-stack reflectors. Cracks were visible under an optical Normarski microscope in two-stack reflectors. The formation of cracks is probably due to the accumulation of the residual thermal strain in thick layers or the hindrance of dislocation glide at the BaF2/PbEuSe interfaces.
Influence of active nitrogen species on high temperature limitations for (0001_) GaN growth by rf plasma-assisted molecular beam epitaxy
Authors: Myers T. H. , Millecchia M. R. , Ptak A. J. , Ziemer K. S. , Stinespring C. D.
Published: July 2002

A reduced growth rate for plasma-assisted molecular beam epitaxy GaN growth often limits growth to temperatures less than 750 °C. The growth rate reduction is significantly larger than expected based on thermal decomposition. Characterization of various rf plasma source configurations indicated that a flux consisting predominantly of either atomic nitrogen or nitrogen metastables can be produced. The use of atomic nitrogen, possibly coupled with the presence of low energy ions, is associated with the premature decrease in growth rate. When the active nitrogen flux consists primarily of nitrogen metastables, the temperature dependence of the decrease is more consistent with decomposition rates. A significant improvement in electrical properties is observed for growth with molecular nitrogen metastables. In addition, atomic hydrogen stabilizes the growing surface of (0001_) GaN.
Role of embedded titanium nanoparticles for enhanced chemical vapor deposition diamond formation on silicon
Authors: Shima R. , Chakk Y. , Folman M. , Hoffman A. , Lai F. , Prawer S.
Published: July 2002

The influence of titanium nanoparticles embedded in the surface of silicon substrates by ultrasonic agitation on diamond chemical vapor deposition was studied. The deposited diamond particle density (DPD) was found to be substantially enhanced by using a mixed slurry (Di/Ti) compared to abrasion with a diamond slurry solely. It was also determined that, under the ultrasonic agitation conditions used in this work, the addition of titanium particles to the abrasive suspension does not affect the quantity of embedded diamond growth centers, nor does it alter their chemical character. Rather, the Ti particle additives are active during the initial stages of deposition. Ion implantation experiments show that diamond homoepitaxially grows on diamond residues, and that Ti residues do not serve as nucleation centers. The annihilation of diamond growth centers prior to stable substrate formation is attributed to hydrogen etching, while the effect of thermal annealing is negligible. These experiments show that Ti residues do not prevent the etching of diamond debris. We therefore conclude that the increase in DPD is related to an enhancement in diamond growth that is induced by the Ti additives. We suggest that the enhanced growth is the result of Ti catalyzed surface reactions.