bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion beam assisted growth of β-FeSi2*
Authors: Terrasi A. , Ravesi S. , Grimaldi M. G. , Spinella C.
Published: July 2002

This article reports the structural and morphological characterization of β-FeSi2 films, about 120 nm thick, grown by ion beam assisted deposition (IBAD). The silicide layers were obtained by Fe evaporations onto (001) Si substrates maintained at T=600 °C, while an Ar+ beam bombarded the sample surface at an energy ranging between 100 and 650 eV. Beta-FeSi2 films were even grown at several ion current densities and, in one case, the beam bombardment was limited to the early stage of the silicide formation. We have found that IBAD process reduces the crystalline grain size and improves the film morphology. Moreover, the relationship between ion beam process and grain nucleation at the silicide/silicon interface shows that when the number of Ar+ reaching the silicide/Si interface is about 1/3 of the Si substrate surface atomic density, the nucleation mechanism tends to saturate.
Characterization of SiO2 layers on Si wafers using atomic force microscopy
Authors: Zúñiga-Segundo A. , Ruiz F. , Vázquez-López C. , González-Hernández J. , Torres-Delgado G. , Tsu D. V.
Published: July 2002

The surface roughness, infrared absorption, and index of refraction characteristics of SiO2 films prepared with various commonly used techniques are discussed. According to the atomic force microscopy images, thin oxides (100 Å or less) have smooth surfaces with an rms surface roughness of about 4 Å. The roughness increases slightly with the increase of the film thickness to about 1000 Å. Oxide films prepared by low-pressure chemical vapor deposition pyrolytic decomposition of SiH4/O2 mixtures, electron-beam (e-beam) evaporation, and microwave plasma decomposition of SiH4/O2 gas mixtures exhibit rougher surfaces with an rms surface roughness exceeding 20 Å. In particular, the atomic force microscopy images obtained in films prepared by e-beam evaporation and microwave plasma decomposition reveal the presence of microvoids and pinholes which probably facilitate the diffusion of water vapor into the oxide after film deposition. This later aspect was inferred from infrared absorption data which show absorption bands associated with atomic motions of Si–OH and H–O–H groups.
Study of tunneling current oscillation dependence on SiO2 thickness and Si roughness at the Si/SiO2 interface
Authors: Zafar S. , Liu Q. , Irene E. A.
Published: July 2002

The tunneling current through tin (∼50 Å) silicon dioxide films is observed to have a small oscillatory component at high electric fields. Three main results involving the oscillatory component of the tunneling current are reported. First, a new and improved analysis for obtaining the oscillatory component from the current measurements is described. Then, using this analysis, the dependence of the oscillatory component on oxide thickness and SiO2/Si interface roughness is studied. The thickness study shows that the oscillation amplitude decreases exponentially as the distance traveled by the electron in the conduction band of SiO2 increases. This decrease is attributed to the scattering effects and the mean free path of the electron in SiO2 is estimated to be 6 Å, in agreement with previous reports. The roughness study is performed on thermally oxidized purposely roughened Si surfaces, and the roughness is characterized by the atomic force microscopy. The oscillations in the tunneling currents show no dependence on the interface roughness, indicating that the roughness at the Si surface has little effect on the thickness uniformity of thermally grown thin oxide films and that oxide films grow uniformly over the roughened Si surfaces for at least the first 50 Å or so.
Crystallization of Pb(Zr,Ti)O3 films prepared by radio frequency magnetron sputtering with a stoichiometric oxide target
Authors: Basit Nasir Abdul , Kim Hong Koo
Published: July 2002

Highly oriented and ferroelectric Pb(Zr,Ti)O3 (or PZT) thin films were obtained by radio frequency magnetron sputtering of a stoichiometric oxide target (Zr/Ti ratio of 53/47). No excess lead was used either during sputtering or during postdeposition annealing. Films deposited at 200 °C or below crystallize into a perovskite phase upon receiving anneal treatment at 590 °C or above. The annealing study, carried out using a conventional furnace, also revealed that the perovskite formation is completed during the first 5 min of annealing. The annealed films are highly (100) oriented on (111)-Pt coated oxidized Si substrates. Maximum polarization of 36 μC/cm2, remanent polarization of 20 μC/cm2, and coercive field of 22 kV/cm were obtained with excellent fatigue resistance. This suggests that the low thermal-budget process (i.e., low-temperature deposition and short-time anneal in a conventional furnace) with a stoichiometric oxide target may be appropriate as a reliable, simple, and economical method of preparing PZT films. Depositions at 500 °C or higher, however, resulted in TixOy or ZrTiO4 films, suggesting that lead was significantly lost during deposition.
Development of Cu-doped ZnTe as a back-contact interface layer for thin-film CdS/CdTe solar cells
Authors: Gessert T. A. , Mason A. R. , Sheldon P. , Swartzlander A. B. , Niles D. , Coutts T. J.
Published: July 2002

The full potential of thin-film, CdS/CdTe photovoltaic solar cells will not be realized until issues relating to the fabrication of environmentally stable, low-resistance, and easily manufactured contacts to the p-CdTe layer are addressed. One alternative that provides the required contact parameters employs a Cu-doped ZnTe(ZnTe:Cu) interface layer between the p-CdTe and the outer metal contact. Thin films of ZnTe:Cu containing various concentrations of metallic Cu are produced by rf-magnetron sputtering. Additionally, the effect of incorporating small amounts of excess Zn into the sputtering target is studied. We find that the electrical resistivity of ZnTe:Cu films deposited at 300 °C, and prepared with Cu concentrations of ∼0.45 at. %, is much higher than would be expected from studies of films doped with higher Cu concentrations (∼6 at. % Cu). We also find that postdeposition heat treatment significantly reduces the electrical resistivity of the films containing ∼0.45 at. % Cu. However, compositional analysis indicates that the surface of the films become increasingly enriched in Zn at annealing temperatures ≳350 °C. Analysis of the hole effective mass (mh) for films containing ∼6 at. % Cu indicates a value for mh of 0.35 me, and a high-frequency dielectric constant (ε∞) of 8.2.
Deconvolution of the Gaussian-convoluted profiles of mercury ions implanted into nickel
Authors: Shi Bo-Rong , Cue N. , Wang Ke-Ming
Published: July 2002

Based on a nonlinear least squares optimisation, a deconvolution method is proposed to remove the system resolution from the ion implantation profiles measured. The method is applied to the range distributions of 200 keV Hg ions implanted into nickel at various tilt angles. The results show that the range straggling is markedly reduced after the deconvolution, the skewness and kurtosis are slightly larger than those of the experimental measured profiles, and they all can be represented by a Pearson IV distribution that is different from the Pearson I distribution predicted by TRIM. The longitudinal and lateral range straggling for normal incidence could be deduced from the angular dependence of the deconvoluted range straggling.
Deposition polymerization of polyurea thin films by ionization-assisted method
Authors: Usui H. , Kikuchi H. , Tanaka K. , Miyata S. , Watanabe T.
Published: July 2002

Polyurea thin films were prepared by ionization-assisted codeposition of 1,3-di(4-piperidyl)propane, and 4,4′-diphenylmethane-diisocyanate, and their optical nonlinearity was investigated in connection with the bias voltage applied on the substrate in the course of deposition. The formation of polyurea was confirmed by IR absorption spectra. At the optimum evaporation temperature for each monomer, the birefringence of the film was the largest. The film had high optical transparency in the visible range, and the absorption in the UV range was influenced by the substrate bias voltage. The film showed optical nonlinearity even without the poling process after the deposition. The Maker fringe measurement indicated that the deposited films have a peculiar dipole orientation, unlike the normal poled polymer films. The second harmonic generation characteristic was influenced by the substrate bias and also by the material of the substrate holder. These results revealed the importance of the electric field on the substrate during the deposition in determining the dipole orientation.
Stability of Si-O-F low-K dielectrics: Attack by water molecules as function of near-neighbor Si-F bonding arrangements
Authors: Yang H. , Lucovsky G.
Published: July 2002

Ab initio configuration interaction calculations have been previously used to account for the relatively large decreases in the static dielectric constant of Si-O-F alloys with low alloy concentrations of F atoms, ∼22% for F concentrations of ∼10 at. %. The present study addresses the stability of these alloy films with respect to attack of Si-F bonds by water molecules. The present calculations show that the reaction: H2O+2Si-F→2HF+Si-O-Si is exothermic by about 0.7 eV. Our calculations focus on the reaction energetics and geometries as a function of the distance between the F atoms of the Si-F groups and water molecules. Combining these calculations for interactions with H2O with a statistical model of bonding in the alloy films as presented in our previous article, an upper limit for chemically stable F corporation has been determined to be ∼10–12 at. % F, which corresponds to static dielectric constant of 3.2–3.4.
Graphite growth influenced by crystallographic faces of Ni films
Authors: Yudasaka Masako , Kikuchi Rie , Ohki Yoshimasa , Yoshimura Susumu
Published: July 2002

We grew graphite by chemical vapor deposition at 700 °C on a Ni thin film having a Ni(100), Ni(111) or Ni(110) face parallel to the Ni thin-film surface. We found that the growth rate of graphite on the Ni(100) face is faster than that on the Ni(111) or Ni(110) face.
Spectroellipsometric characterization of plasma-deposited Au/fluoropolymer nanocomposite films
Authors: Dalacu Dan , Martinu Ludvik
Published: July 2002

Nanocomposite thin film structures are presently being studied because of their interesting nonlinear optical properties. The microstructure of plasma-deposited nanocomposite films consisting of gold particles embedded in a plasma-polymerized fluorocarbon matrix was fully characterized using a generalized Maxwell–Garnett effective medium approach applied to ellipsometric data. The particle size dependence of the dielectric properties of gold was treated classically using a broadening parameter, A, equal to 0.25, as determined from transmission electron microscopy analysis. In general, the model predicted correctly the dependence of microstructural characteristics on glow discharge parameters and post-deposition thermal treatments. However, careful interpretation of the model fit parameters is necessary in both the high gold volume fraction limit and small particle size limit. For the former, misleading results with respect to particle size and shape may be obtained due to aggregation effects, the onset of which was determined to occur at a gold volume fraction of about 30%. For the latter, deviations from the classical description of the permittivity of gold nanoparticles (occurring for particles smaller than 7 nm) can lead to misleading results with respect to particle shape.
Butanethiol on Au{100}-(5×20) using a simple retractable doser
Authors: Dixon-Warren St. J. , Bondzie V. , Burson N. , Lucchesi L. , Yu Y. , Zhang L.
Published: July 2002

A design for a simple gas doser, which incorporates a movable shutter, is presented. The operation of this doser is demonstrated using the dosing and subsequent temperature programmed desorption of butanethiol on Au{100}-(5×20). The sticking probability for adsorption of the butanethiol at 100 K was measured to be s=0.85±0.05. The butanethiol desorption showed two features corresponding to the desorption of the chemisorbed monolayer at 500 K, and physisorbed multilayers at 140 K. The chemisorbed monolayer feature was not observed in the desorption of the parent molecular ion at 90 amu, but was observed at 56 amu, suggesting that desorption was accompanied by decomposition of the chemisorbed butanethiolate species. The primary gas phase product appears to be 1-butene. Auger electron spectroscopy showed that the thiolate sulfur remained on the surface until above 700 K.
Ferromagnetic semiconductor heterostructures based on (GaMn)As
Authors: Tanaka M. , Shimizu H. , Hayashi T. , Shimada H. , Ando K.
Published: July 2002

Growth, transport, magnetic, magneto-optical, and magnetotunneling properties of ferromagnetic semiconductor (GaMn)As and its quantum heterostructures, including superlattices and tunnel junctions, are presented. Spin-related phenomena in such III–V based ferromagnetic quantum heterostructures are shown to give a new degree of freedom in the band-gap engineering and wave function engineering for semiconductor electronics and photonics.
Fabrication of metal nanowire using carbon nanotube as a mask
Authors: Yun Wan Soo , Kim Jinhee , Park Kang-Ho , Ha Jeong Sook , Ko Young-Jo , Park Kyoungwan , Kim Seong Keun , Doh Yong-Joo , Lee Hu-Jong , Salvetat Jean-Paul , Forró László
Published: July 2002

We report on the fabrication of metal nanowires on an insulating substrate using carbon nanotubes as a new kind of mask material. By irradiating Ar+ ions of 300 eV energy on a nanotube-coated Au/Ti thin layer on a SiO2 substrate, Au/Ti nanowires were successfully formed just underneath the nanotube, indicating that the carbon nanotubes had acted as a good mask against the argon ion bombardment. The Au/Ti wire of a few nanometers in width was frequently observed among the wires of various widths. After the formation of the Au/Ti nanowires, the carbon nanotube on the metal nanowire could be removed by atomic force microscope.
Origin of electrical property distribution on the surface of ZnO:Al films prepared by magnetron sputtering
Authors: Minami Tadatsugu , Miyata Toshihiro , Yamamoto Takashi , Toda Hidenobu
Published: July 2002

The origin of electrical property distribution on the substrate surface of Al-doped ZnO (AZO) films prepared by magnetron sputtering is reported. When the films were prepared on substrates at the same temperature with the same deposition rate under optimized sputter deposition and target preparation conditions, the minimum obtained resistivity found in AZO films prepared by either dc or rf magnetron sputtering was roughly the same: 3–4×10−4 Ω cm on substrates at 200 °C. However, the AZO films prepared by dc sputtering exhibited a larger increase of resistivity at locations on the substrate corresponding to the target erosion area than that found in films prepared by rf sputtering. The resistivity distribution of AZO films prepared by rf magnetron sputtering under an applied external magnetic field which focused the rf plasma was similar to that of films prepared by dc magnetron sputtering. Thus, the electrical property distribution found in films prepared by either dc or rf magnetron sputtering is mainly related to the activity and the amount of oxygen reaching the substrate surface as well as its spatial distribution.
Chemical vapor deposition of alpha aluminum oxide for high-temperature aerospace sensors
Authors: Niska Raymond H. , Constant Alan P. , Witt Tony , Gregory Otto J.
Published: July 2002

Thin-film thermocouples and strain gages are being developed for high-temperature application on aerospace propulsion hardware for both development test purposes and as active control sensors. The critical technology necessary in the fabrication of the sensor is an adherent, dense, and homogeneous dielectric to provide electrical isolation at engine operating temperatures. Techniques are being developed to create a crystalline aluminum oxide dielectric formed by a combination of a thermally grown oxide (TGO) from a NiCoCrAlY hardcoating, which is then enhanced with the addition of a chemical vapor deposited (CVD) crystalline aluminum oxide layer. This article will focus on the process development used to deposit the α alumina layer on the TGO using CVD in a coldwall reactor at 1100 °C. The chemistry employed in this process is the pyrolitic decomposition of aluminum tri-isopropoxide. The hexagonal (HCP) α phase is achieved at deposition temperatures of 1000–1100 °C, as confirmed by x-ray diffraction analysis. By eliminating gas phase and hot wall decomposition, this approach minimizes precursor depletion effects, yielding a more dense and uniform film morphology. Conformal coatings up to 10 μm thick with high resistivity and good adhesion and hardness have been observed on complex airfoil geometries. Growth rates up to 10 μm/h are possible, although low growth rates lead to more desirable film properties. The kinetics of the deposition indicate that the reaction proceeds by a mass transport limited mechanism. Uniform temperature control over highly complex geometry is desirable, but not essential for uniform film growth. Results indicate that the gas flow uniformity and the precursor transport rate are the critical variables.
Lead–rare-earth chalcogenides grown by molecular beam epitaxy
Authors: Partin Dale L.
Published: July 2002

The development of wide band gap alloys of lead–telluride (PbTe) would extend the total wavelength range covered by lead–tin–telluride (Pb1−xSnxTe) diode lasers. The advantages of alloys of PbTe with ytterbium (Yb) or europium (Eu) over those of cadmium, manganese, and germanium grown by molecular beam epitaxy (MBE) are discussed. Experimentally, it was found that Yb atoms bond strongly to a PbTe surface and have a small diffusion coefficient (<3×10−17 cm2/s at 370 °C). The lattice constant (in Å) of Pb1−xYbxTe is 6.460–0.015 x for 0≤x≤0.42. Yb introduces a donor level into PbTe near the valence band edge which is caused by the Yb+2=Yb+3+e− transition. The level appears to move into the valence band in (Pb0.85Sn0.15)1−xYbxTe for x≲0.07, making it possible to dope the material p-type as well as n-type for diode laser applications.
Basic chemistry and mechanisms of plasma etching
Authors: Flamm Daniel L. , Donnelly Vincent M. , Ibbotson Dale E.
Published: July 2002

A recent review of plasma etching is extended with discussions of similarity variables governing discharges, anisotropic oxide etching in fluorine and unsaturate-rich plasmas, surface texture, the loading effect, and gas-surface reactions.
Reactive ion etching of GaAs and InP using SiCl4
Authors: Stern M. B. , Liao P. F.
Published: July 2002

High resolution reactive ion etching of GaAs and InP is achieved using SiCl4 as the etching gas. Etching rates and profiles are examined at pressures between 1 and 10 mTorr and power densities from 0.2 to 0.9 W/cm2. Under the proper conditions, it is possible to obtain extremely vertical etch profiles and etch ratios of GaAs relative to masking materials such as Si3N4 and NiCr which exceed 10 to 1.
Native oxide formation and electrical instabilities at the insulator/InP interface
Authors: Wager J. F. , Geib K. M. , Wilmsen C. W. , Kazmerski L. L.
Published: July 2002

A variety of surface analytical techniques have been employed in an attempt to correlate the chemistry of InP native oxides with electrical interface instabilities observed in InP MIS devices. The native oxides examined were predominantly InPO4 but upon closer examination had small amounts of In2O3 incorporated into the outer oxide surface. The band gap of InPO4 was estimated to be about 4.5 eV, although several observations indicate that this may be only a lower limit. It is suggested that tunneling of electrons from InP through the InPO4 into In2O3 may account for electrical interface instabilities observed in InP MIS devices.
High resolution patterning with Ag2S/As2S3 inorganic electron-beam resist and reactive ion etching
Authors: Singh B. , Beaumont S. P. , Webb A. , Bower P. G. , Wilkinson C. D. W.
Published: July 2002

A new two-step development process has been devised which considerably improves edge smoothness and linewidth resolution in the Ag2S/As2S3 inorganic resist system. Using this process, smooth-edged 30 nm wide lines have been patterned by electron-beam lithography and transferred into an underlying polyimide film by oxygen reactive ion etching. This high resolution bilayer process exploits the exceptional etch resistance of the silver-doped chalcogenide glass.
A low temperature process for vapor etching of indium phosphide
Authors: Chang H. L. , Meiners L. G.
Published: July 2002

The vapor of the organic halide, ethylene dibromide (EDB), was used for InP in situ etching. The etching process was carried out in a low pressure (≂50 Pa) flowing system. A two-zone resistance-heated furnace was employed such that EDB molecules were decomposed to yield a more reactive form of bromine in the high temperature zone, whereas the substrate was placed in the low temperature zone to avoid thermal degradation of the InP. Surfaces as specular as before etching were obtained by using this technique. The process was studied for substrate temperatures between 120 and 540 °C and for hot zone temperatures between 600 and 900 °C. The etch rate varied between 0.002 and 1.0 μm/min depending on the furnace temperature and the EDB flow rate.
Block copolymers as bilevel resists
Authors: Hartney M. A. , Novembre A. E. , Bates F. S.
Published: July 2002

A bilayer resist system is demonstrated using chlorinated polymethylstyrene-polydimethylsiloxane (CPMS/DMS) block copolymers. The copolymers are prepared using anionic polymerization techniques and are subsequently sensitized to electron beam, and 250–300 nm radiation by preferential chlorination of the polymethylstyrene block. The electron lithographic performance of a block copolymer containing 15.5 wt. % silicon, 0.58 chlorines per methylstyrene unit (total M̄w=8.7×104) and polydispersity=1.3 was determined to exhibit a sensitivity (D0.5g)=0.9 μC/cm2, and contrast=1.3. The etch ratio compared to the HPR-204 planarizing layer was 13.5 : 1 with an observed resolution range of 0.75 to 1.0 μm. These results derive from the intrinsic behavior of block copolymers, which provides for the synergistic combination of inherently distinct polymer species while avoiding macroscopic phase separation prevalent in homopolymer blends. The concept of utilizing block copolymers as resists is general and may be extended to positive tone resists as well.
X-ray zone plates fabricated using electron beam lithography and reactive ion etching
Authors: Aritome H. , Aoki H. , Namba S.
Published: July 2002

A Fresnel zone plate, a focusing element that operates using diffraction, is a promising candidate for x-ray optical elements since the index of refraction of all materials in this region is slightly less than unity. In this report, a new fabrication method for zone plates using electron beam lithography and reactive ion etching is described. By this method, it is possible to obtain a high resolution zone plate with a large aspect ratio. Focusing characteristics of fabricated zone plates are measured by synchrotron radiation. At the wavelength of 9 nm, the spot size of 2 μm is obtained at the focal point of 100 mm.
Methacrylated silicone-based negative photoresist for high resolution bilayer resist systems
Authors: Morita Masao , Tanaka Akinobu , Onose Katsuhide
Published: July 2002

We propose a new photoresist (MSNR: methacrylated silicone-based negative resist) for high resolution bilayer resist systems. This photoresist shows high sensitivity to near-UV light (350–450 nm), D0.5n =40 mJ/cm2, and excellent resistance to reactive ion etching with oxygen. A submicron (0.5 μm) pattern with a high aspect ratio can be easily fabricated with MSNR/AZ bilayer resist systems using near-UV lithography.
Organometallic materials in lithography: A review
Authors: Hatzakis M. , Shaw J. , Babich E. , Paraszczak J.
Published: July 2002

Organosilicon polymers have found many uses in the electronics industry in the last 25 years due to their low-dielectric constant and water-repelling properties. These uses include insulators and encapsulating materials (RTV) for electronic parts. More recently, siloxanes have been incorporated into polyimides for the purpose of increasing the water resistance, improving mechanical properties, and preventing atomic oxygen attack of polyimides [R. H. Bott, J. D. Summers, C. A. Arnold, L. T. Taylor, T. C. Ward, and J. E. McGrath, J. Adhes. 23, 67 (1987)]. In only the last few years, some uses of organosilicon polymers in lithography have been reported. In this paper, a review of these uses will be presented and the requirements for organosilicon materials in lithographic applications will be outlined.
Coulomb interactions in particle beams
Authors: Jansen G. H.
Published: July 2002

A comprehensive theory has been developed to describe all manifestations of Coulomb interactions between charged particles in low- and medium-density nonrelativistic beams, e.g., as found in electron beam pattern generators and scanning electron microscopes. A survey is given of the analytical prescriptions for the calculation of the Boersch effect, trajectory displacement effect, and space-charge effect occurring in the drift space of a column. The theory is applied to the IBM EL3 and the Perkin–Elmer aeble 150 shaped spot lithography machines. The results are in close agreement with Monte Carlo simulations as well as the available experimental data.
Interface and growth studies of α-Sn/CdTe(110) superlattices
Authors: Höchst Hartmut , Niles David W. , Hernández-Calderón Isaac
Published: July 2002

Angular-resolved synchrotron radiation photoemission spectroscopy and reflection high-energy electron diffraction (RHEED) are used to study the molecular-beam epitaxy of CdTe/ α-Sn(110) interfaces and superlattices. Core level photoemission spectra indicate that both sides of the interface are stable, nonreactive, and abrupt for growth temperatures up to 100 °C. At the α-Sn/CdTe interface, the valence band maximum at Γ is at EV=1.1 eV below the Fermi level. This gives a valence band offset of ΔEV=1.1 eV, assuming zero band gap for the Sn. Stable superlattices of α-Sn/CdTe(110) have been grown at 100 °C. The surface quality of the superstructure degrades after the growth of several α-Sn/CdTe periods. After the growth of ten periods each 50-Å thick, the RHEED pattern shows mainly three-dimensional bulk diffraction, indicating increased surface, and interface roughness.
Electrical properties of thermal oxides grown over doped polysilicon thin films
Authors: Suryanarayana P. , Dixit B. B. , Joshi B. C. , Runthala D. P. , Vyas P. D. , Khokle W. S.
Published: July 2002

Thermal oxides were grown on different doped polysilicon thin films: (i) as-grown polysilicon at 620 °C, (ii) as-grown polysilicon and annealed at 1000 and 1100 °C in nitrogen, and (iii) as-grown amorphous silicon films at 570 °C subsequently converted into polycrystalline form during doping. These films are qualitatively characterized by studying electrical properties, such as leakage current, breakdown field, the temperature dependence of current, and the time dependence of current. The electrical measurements of oxides grown on polysilicon converted from amorphous form show lower leakage current and higher dielectric breakdown than oxides grown on as-deposited polysilicon films. The results were interpreted in terms of interface texture of polysilicon/polyoxide using the Fowler–Nordheim tunneling mechanism. The temperature dependence of current through the oxides shows little variation at low temperatures, but it increases exponentially at high temperatures. The oxides also exhibit a time-dependent current. This dependence could be ascribed to ionic–Ohmic conduction of charge carriers in the polyoxide, at low fields and high temperatures.
Direct observation of B-form and Z-form DNA by scanning tunneling microscopy
Authors: Li Min-Qian , Zhu Jin-de , Zhu Jie-Qing , Hu Jun , Gu Ming-Min , Xu Yao-Liang , Zhang Lan-Ping , Huang Ze-Qi , Xu Liu-Zhong , Yao Xiao-Wei
Published: July 2002

Using a scanning tunneling microscope (STM) of atomic resolution, we have directly observed variant comformations of DNA, including normal B-form and Z-form DNA, with a modified working condition. STM images of natural fish sperm and calf thymus B-form DNA and poly (dG-me5 dC) and bromized poly dCG Z-form DNA have been obtained at a subnatural environment. These results have provided some new evidence that images characteristic of DNA molecules can be obtained with STM.
Electrochemical deposition of nucleic acid polymers for scanning probe microscopy
Authors: DeRose J. A. , Lindsay S. M. , Nagahara L. A. , Oden P. I. , Thundat T. , Rill R. L.
Published: July 2002

We have studied gold and graphite as substrates for electrochemical deposition of DNA fragments for scanning tunneling microscope imaging. We obtain the most reproducible results with gold grown epitaxially onto mica. Gold can react with chlorine ions, and with the tris(hydroxymethyl) aminomethane buffer salt we use. However, under potentiostatic or galvanostatic control, the surface is modified in quite characteristic ways when DNA fragments are present. We present results for positive electrodes where DNA appears to react predictably only in the presence of salts which co-adsorb with it. Although very reproducible coverage of the electrode is possible, the salt complicates interpretation of the images.
Variable temperature scanning tunneling microscopy studies of the charge density wave phases in tantalum disulfide
Authors: Wu Xian Liang , Lieber Charles M.
Published: July 2002

Variable temperature scanning tunneling microscopy has been used to elucidate details of the nearly commensurate charge density wave (CDW) phase in 1T-TaS2. Large-area images show that the nearly commensurate phase has a hexagonal domain structure, and that the domain period exhibits a strong temperature dependence. Real-space and two-dimensional Fourier transform analyses of atomic resolution images further demonstrate that within the domains the CDW is approximately commensurate with the atomic lattice, and that between domains the CDW amplitude decreases and the CDW phase changes. In addition, disorder observed in the hexagonal domain structure at low temperatures is suggested to be due to domain wall pinning.
Electrochemistry on a gold surface observed with the atomic force microscope
Authors: Manne S. , Massie J. , Elings V. B. , Hansma P. K. , Gewirth A. A.
Published: July 2002

We present atomic force microscope images of hydroxide and oxide formation on a gold surface obtained in perchloric acid electrolyte and under potential control. We find that the oxide is disordered over the Au(111) surface. Further, these images show that oxide formation on rough gold surfaces is accompanied by rapid annealing, most likely due to place exchange.
Fabrication of encapsulated silicon-vacuum field-emission transistors and diodes
Authors: Sune C. T. , Jones G. W. , Vellenga D.
Published: July 2002

We have succeeded in developing encapsulated silicon-vacuum field-emission transistors by using integrated circuit technology. This success will accelerate the development of integrated circuit of silicon-vacuum field-emission devices. Preliminary electrical characteristics of these encapsulated silicon-vacuum field-emission transistors show very similar characteristics to the gated field-emitter diode. However, the turn-on voltage and the transconductance are lower compared to the open gated field emitters.
Electron-beam cell-projection lithography system
Authors: Sakitani Y. , Yoda H. , Todokoro H. , Shibata Y. , Yamazaki T. , Ohbitu K. , Saitou N. , Moriyama S. , Okazaki S. , Matuoka G. , Murai F. , Okumura M.
Published: July 2002

An electron-beam exposure system HL-800D has been developed for the mass production of both quarter micron large-scale integrated memories and application specific integrated circuits (ASICs). To achieve a productive level of throughput, the system utilizes a cell-projection method combined with variable shaped method and a continuously moving stage at variable speed depending on the pattern density. The system is operated at a 50 kV acceleration voltage and a 1 μC/cm2 dosage. Three stage deflectors have been developed to assure high-speed deflection and highly accurate positioning. A fast pattern controller generates patern data at 200 ns shot-cycle-time with the positioning error correction and proximity effect correction. A high-speed ceramic XY stage and an automatic wafer loder have been developed. The system is operated by a workstation which also provides data conversion. The estimated throughput of the system is 11 wafers/h for 0.3 μm ASICs and 20 wafers/h for quarter micron memories.
Observation of quantum dot levels produced by strain modulation of GaAs–AlGaAs quantum wells
Authors: Kash K. , Mahoney Derek D. , Van der Gaag B. P. , Gozdz A. S. , Harbison J. P. , Florez L. T.
Published: July 2002

We present the first observation of resolved quantum dot levels produced by strain modulation of a semiconductor. Excitons are confined in lateral potential wells of up to 60 meV, the largest yet reported for strain-induced quantum wire or dot structures. The dependence of the quantum dot level separation on dot size is in agreement with calculations of the strain-induced band edge modulation. For 200 nm wide carbon dot stressors the level separations are approximately 2 meV. Frustration of acceptor recombination by three-dimensional localization of carriers in the strain-induced potential wells is clearly observed. Finally, we detect luminescence from a single quantum dot at low excitation intensity, a result of the frustration of nonradiative recombination by localization.
Fluorescence behavior of diazonaphthoquinone-type photoresist materials
Authors: Vleggaar J. J. M. , Huizer A. H. , Varma C. A. G. O. , Kraakman P. A. , Nijssen W. P. N. , Visser R. J.
Published: July 2002

Photolysis of substituted diazo-naphthoquinones (DNQs) in the presence of H2O, yields the corresponding indene carboxylic acids as main products. HPLC analysis reveals that, depending on the matrix or the solvent, up to 20% of the DNQ may be converted into other photoproducts. Their nature and the mechanism involved in their formation is discussed. The side products are strongly fluorescent, and their fluorescence bands overlap with the first UV absorption band of the DNQ. Photolysis of DNQs by this fluorescence may affect the spatial resolution in photolithographic applications based on these photoactive compounds. Numerical calculations are presented, in which the spatial dependence of the magnitude of this effect is simulated. The calculations show that the conversion of DNQ in a photoresist layer, due to fluorescence, is in the order of a few percent of the total at most. In practice the fluorescence will have a negligible effect on the resolution.
Solid source diffusion from agglomerating silicide sources. II. Experimental results and analysis
Authors: Tsai J. Y. , Osburn C. M. , Canovai C. A.
Published: July 2002

The interface roughness and dopant diffusion behavior of CoSi2 silicide-as-a-diffusion-source (SADS) samples annealed at different temperatures and for different periods of time were examined using secondary ion mass spectrometry, with conditions optimized to characterize the solid source diffusion profile. A convolution/deconvolution methodology was applied to derive the root-mean-square silicide/silicon interface roughness and to correct the dopant profiles. The model which was developed to relate the interface roughness and the sheet resistance increase of the agglomerated silicide films worked quite well over the temperature and time range of interest. The measured activation energies confirmed that silicide roughening and its resistance increase share the same kinetic mechanism. Arsenic implanted CoSi2 samples exhibited a better thermal stability than those implanted with BF2. No obvious enhancement or retardation of boron diffusion was seen, while a transient enhancement of arsenic diffusion was observed, but not as pronounced as previously reported. Furthermore, in cases where dopant is strongly segregated or exhibits a marked step at the silicide/silicon interface, even the convolution/deconvolution technique was not able to adequately determine the actual dopant diffusion.
Ion beam modification and patterning of organosilane self-assembled monolayers
Authors: Ada Earl T. , Hanley Luke , Etchin Sergei , Melngailis John , Dressick Walter J. , Chen Mu-San , Calvert Jeffrey M.
Published: July 2002

The patterning and modification of organosilane self-assembled monolayers on Si native oxide surfaces by low- and high-energy ion beams were investigated. The nature and extent of low-energy (50–140 eV) Ar+ ion-induced modification of a 2-(trimethoxysilyl) ethyl-2-pyridine monolayer was studied by x-ray photoelectron spectroscopy and by the quality of the electroless Ni patterns obtained. C(1s) and N(1s) core level x-ray photoelectron spectroscopy indicated that the ion-induced modification of the monolayer involved loss of the ethylpyridyl chain by sputtering and/or decomposition. The type of modification was independent of the ion energy and fluence, but the extent of modification depended on both parameters. The modification of the pyridine monolayer was monitored by the percent loss in the N(1s) peak area; modification commenced at a fluence of 5×1014 ions/cm2 and was observed for all ion energies studied. However, selective electroless metallization occurred only for monolayers that suffered ≳50% loss in the N(1s) x-ray photoelectron spectroscopy signal. A damage saturation level of 80% N(1s) loss was indicated at an ion fluence of 9×1015 ions/cm2. A high-energy focused ion beam lithography system was also used to evaluate the high resolution patterning of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, (aminoethylaminomethyl) phenethyltrimethoxysilane, and pyridine monolayers by Ga+, Si++, Au+, and Au++ ions at energies ranging from 50 to 280 keV. The highest resolution metal features obtained were 0.3-μm-wide gaps on phenethyltrimethoxysilane and pyridine monolayers using Ga+ and Si++ ions. Aminopropyltrimethoxysilane monolayers were found to require ten times higher ion fluences to achieve comparable results with the phenethyltrimethoxysilane and pyridine monolayers for all ions investigated.
Mechanisms of surface anodization produced by scanning probe microscopes
Authors: Gordon A. E. , Fayfield R. T. , Litfin D. D. , Higman T. K.
Published: July 2002

The direct modification of silicon and other semiconductor and metal surfaces by the process of anodization using the electric field from a scanning probe microscope in conjunction with the absorbed water from the atmosphere as the electrolyte is one promising method of accomplishing direct write lithography for the electron device fabrication using scanning probe microscopes. Both scanning tunneling microscopes and conductive-tip atomic force microscopes have been used for anodization with the work reported here primarily accomplished with a conductive-tip atomic force microscope. We have found that the terminating thickness of the scanning probe microscope induced oxide is governed by the diffusion limited electric field at the surface (which in this case is a function of the scanning probe microscope tip potential), with many similarities to liquid electrolyte anodization process. In particular, when using atmospheric water as the electrolyte on a silicon substrate and a conductive-tip atomic force microscope with a −7 to −10 V tip potential, the terminating electric field that is reached as the silicon dioxide thickness increases is to its final value of 80 Å is ∼1×107 V/cm. This is consistent with the diffusion limited electric field that is observed in many other anodization processes and the native oxidation of silicon (Mott–Cabrera process).
Illumination system for extreme ultraviolet lithography
Authors: Haga Tsuneyuki , Kinoshita Hiroo
Published: July 2002

We have designed and built a four-mirror grazing incidence, illumination system for extreme ultraviolet lithography that is applicable to a two-aspherical-mirror reduction system. It was designed for a synchrotron radiation source, and it provides uniform illumination (size: 100×125 mm) and proper numerical aperture for incoherent illumination of the demagnifying optics. A large illumination area was achieved by an oscillating mirror and synchronous movement of the mask and wafer stages. Experimental results have demonstrated that, with a reduction ratio of 1/5, this system is capable of replicating chips of practical size (20×25 mm).
Three-dimensional design in electron-beam lithography
Authors: Aristov V. V. , Dubonos S. V. , Dyachenko R. Ya. , Gaifullin B. N. , Matveev V. N. , Raith H. , Svintsov A. A. , Zaitsev S. I.
Published: July 2002

A technology for micro/nanostructuring of surfaces based on one-step direct electron-beam lithography, plasma-chemical etching, and electrochemical deposition is developed. The key operation for three-dimensional (3D) design is 3D dose correction. It allows one to create structures in organic resist on a substrate with a predefined profile with vertical sizes in the range of 50 nm–5 μm and with 50–1 mm dimensions in the lateral direction. Metal replicas were created by electrochemical deposition. The replicas were used then as a stamp for fast transferring of the relief into a soft material (polymer). We expect the application of this process in optoelectronics, optical processing, creation of zone plates, and other diffractive optical elements (calculated holograms).
Submonolayer Pb deposition on Si(100) studied by scanning tunneling microscopy
Authors: Veuillen J.-Y. , Gómez-Rodríguez J.-M. , Cinti R. C.
Published: July 2002

Initial stages of Pb deposition on Si(100) 2×1 surfaces have been studied by means of scanning tunneling microscopy. Scanning tunneling microscopy results show that, at room temperature and low coverage, long quasi-one-dimensional Pb chains can be formed on this substrate. These chains, composed of Pb dimers, run in a direction perpendicular to the underlying Si dimer rows. The chain length suggests that Pb diffusion on the Si surface is a relevant effect even at room temperature. Some indications of Pb dimers movements are presented.
Parameters of the tip arrays covered by low work function layers
Authors: Evtukh A. A. , Litovchenko V. G. , Marchenko R. I. , Klyui N. I. , Semenovich V. , Nelep C.
Published: July 2002

Silicon field emitter arrays have been fabricated and investigated. Four different field emission enhancement layers were studied: (1) porous silicon layers, (2) carbon films, (3) hydrogen implanted layers, (4) Cs-enriched layers. Scanning electron microscopy was used to study the morphology of the tips. Comparison of the above arrays was accomplished by obtaining effective work functions, field enhancement factors, and effective emission areas from Fowler–Nordheim plots.
ω-functionalized self-assembled monolayers chemisorbed on ultraflat Au(111) surfaces for biological scanning probe microscopy in aqueous buffers
Authors: Wagner Peter , Zaugg Frank , Kernen Peter , Hegner Martin , Semenza Giorgio
Published: July 2002

Two immobilization procedures for ultimately carrying out scanning probe microscopy of native biological macromolecules in buffer solution are presented. They are based on the preparation of ultraflat template-stripped gold surfaces and subsequent chemisorption of bioreactive ω-functionalized self-assembled monolayers. Immobilization was achieved either via amide bond formation or diazo linkage. The first was carried out using a long-chain N-hydroxysuccinimide-ester functionalized disulfide, which binds amino-group-containing biomacromolecules under mild conditions. The latter was performed via chemisorption of a nitrobenzylalkylthiol, followed by in situ transformation to the active diazo intermediate. Typical targets were activated aromatic hydrogens, such as phenolic or imidazole groups. The preparation of these monolayers, their characterization by scanning tunneling microscopy and radiolabeling, and as an example the in situ atomic force microscopy study of clathrin cages under native conditions in appropriate buffers are presented.
Selective epitaxial growth of Si1−xGex/Si strained-layers in a tubular hot-wall low pressure chemical vapor deposition system
Authors: Wang Wei-Chung , Denton John P. , Neudeck Gerold W. , Lee I-Ming , Takoudis Christos G. , Koh Michael T. K. , Kvam Eric P.
Published: July 2002

Selective epitaxial growth (SEG) of SiGe on patterned-oxide silicon substrates, using a tubular hot-wall low pressure chemical vapor deposition (LPCVD) system, has been demonstrated. This conventional LPCVD system was proposed as a low cost alternative for SiGe epitaxial growth. Dichlorosilane (SiH2Cl2) and germane (GeH4) were used as the reactant gases with hydrogen as a carrier gas, with no addition of HCl needed to achieve selectivity in quality epitaxial growth of SiGe. Nomarski microscopy showed good selectivity with no nucleation occurring on the SiO2 areas. A low defect silicon buffer layer grown under SEG conditions was key in obtaining high-quality growth. Cross-sectional transmission electron microscopy showed that the SiGe strained layers grown at 700 °C, 750 °C, and 800 °C were of high quality.
Micromechanical thermal sensors: Comparison of experimental results and simulations
Authors: Moulin A. M. , Stephenson R. J. , Welland M. E.
Published: July 2002

In this article the results of a numerical simulation of the thermal and mechanical properties of micromechanical sensors are described. Finite element analysis is used to model the response of the composite cantilever to temperature variations. The simulations consider triangular shaped cantilevers in air and water environments and under different configurations of thermal loading. The models utilize conditions from actual experiments which are conducted in parallel. Good agreement between numerical and experimental results studied so far allows us to use our numerical simulation to confidently predict the performance of the sensor under novel operating conditions and to optimize the sensor design for specific applications.
Improved cold electron emission characteristics of electroluminescent porous silicon diodes
Authors: Sheng Xia , Koyama Hideki , Koshida Nobuyoshi , Iwasaki Shingo , Negishi Nobuyasu , Chuman Takashi , Yoshikawa Takamasa , Ogasawara Kiyohide
Published: July 2002

The property of electroluminescent porous silicon (PS) diodes as surface-emitting cold cathodes were investigated. The experimental PS diodes consist of thin Au films, PS, n+-type Si substrates, and ohmic back contacts. When a positive bias voltage VPS is applied to the Au electrode with respect to the substrate, electrons are uniformly emitted through the Au contact as well as photons. The cold electron emission characteristics are presented here in terms of the PS layer thickness dependence, effects of rapid thermal oxidation (RTO), and electroluminescence (EL) characteristics. It was demonstrated that both the decrease in the PS layer thickness (dPS) and the introduction of RTO treatment are useful for a significant improvement in the emission characteristics, and that the emission current and efficiency for a RTO-treated diode with dPS=3 μm reach 450 μA/cm2 and 0.2%, respectively, at VPS=27 V. It is also shown that in every case, the Fowler–Nordheim scheme holds in the bias voltage dependence of the emission current. The emission mechanism based on the high-field effect near the outer surface of PS layer, is discussed in relation to the visible EL emission.