bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma etch-back planarization coupled to chemical mechanical polishing for sub 0.18 μm shallow trench isolation technology
Authors: Schiltz André , Palatini Laëtitia , Paoli Maryse , Rivoire Maurice , Prola Alain
Published: July 2002

A new plasma etch-back planarization technique is presented with countermasking to preplanarize shallow trench isolation (STI) substrates before chemical mechanical polishing (CMP). A preplanarization step is necessary since CMP alone cannot provide effective planarization for sub 0.18 technology due to the dishing effect. The preplanarization step uses the principle of two layer planarization technique which consists of spin coating a first photoresist layer, using a countermask for the lithographic step, flowing and curing the resist blocks in STI topographies, spin coating a second photoresist layer to planarize the residual topography, and transferring the final flat surface into the substrate using conventional plasma etch back. In difference with previous techniques, we used a special mask with oversizing and exclusion of all STI critical dimensions smaller than 1.55 μm, the zones with the smaller STI dimensions being masked using a special narrow lines grid. Such a masking strategy avoids any misalignment problem, where the resized first photoresist blocks are reflowed in STI topographies, leading to an easy planarization by the second resist layer. Additionally, the lithographic step is a noncritical step using conventional i-line resist. Using appropriate planarization model and simulation, the first layer thickness can be adjusted to get an effectively planarized topography. The final surface is then transferred into the oxide substrate using the plasma etch-back technique. Various gas mixtures were tested using LAM 4520 plasma etching equipment. The (Ar/CF4/O2) gas mixture was observed to fulfill etch-back requirements with better performance. Equality of etch rate in resist and in oxide can be adjusted by the O2/CF4 gas ratio. A design of experiment was used to determine the optimum conditions of plasma transfer of the planarized profile into the substrate. Finally, the preplanarized wafer is polished by CMP, resulting in an effectively planarized topography with residual topography smaller than 50 nm. The technique is a noncritical lithographic technique scaleable for technologies below 0.18 μm.
Fabrication of bismuth nanowires with a silver nanocrystal shadowmask
Authors: Choi S. H. , Wang K. L. , Leung M. S. , Stupian G. W. , Presser N. , Morgan B. A. , Robertson R. E. , Abraham M. , King E. E. , Tueling M. B. , Chung S. W. , Heath J. R. , Cho S. L. , Ketterson J. B.
Published: July 2002

We fabricated bismuth (Bi) nanowires with low energy electron beam lithography using silver (Ag) nanocrystal shadowmasks and a subsequent chlorine reactive ion etching. Submicron-size metal contacts on the single Bi nanowire were successfully prepared by in situ focused ion beam metal deposition for transport measurements. The temperature dependent resistance measurements on the 50 nm wide Bi nanowires showed that the resistance increased with decreasing temperature, which is characteristic of semiconductors and insulators.
Influence of the target-substrate distance on the properties of indium tin oxide films prepared by radio frequency reactive magnetron sputtering
Authors: Meng Li-Jian , dos Santos M. P.
Published: July 2002

Indium tin oxide (ITO) films were deposited onto glass substrates by radio frequency reactive magnetron sputtering. The distance between the target and the substrate were changed from 50 to 100 mm. X-ray diffraction shows that film prepared at the larger target-substrate distance has a strong orientation along the (440) direction, and as the distance decreases, the intensity of the (440) peak decreases and the intensity of the (222) peak increases. The electrical resistivity of the ITO films decreases as the target-substrate distance gets small. This variation could be related to the change of the orientation of the films, since the film which has a strong (222) peak intensity has a low electrical resistivity. The optical transmittance of the ITO films decreases and the optical band gap moves to the low energy direction, as the target-substrate distance decreases. All of these phenomena will be discussed in this work.
Integrated measurement of Ti and TiN thickness and optical constants using reflectance data through a vacuum chamber window
Authors: Tabet Milad F. , Kelkar Umesh , McGahan William A.
Published: July 2002

The thickness and optical constants of titanium and titanium nitride thin films were measured by visible reflectometry through a window of a vacuum deposition system while the wafer was cooling from deposition to room temperature. The measurement system is ultracompact and was designed for integration into semiconductor processing equipment. This integrated metrology tool does not affect the system throughput. The Ti and TiN films were deposited on 300 nm silicon dioxide films on 200 mm diam silicon wafers using an Applied Materials Endura physical vapor deposition system. The system was used to characterize thin metal films with various thicknesses and deposited using conventional dc magnetron sputtering. The optical constants of the Ti and TiN films were modeled through the use of a Lorentz oscillator dispersion model. A variable angle of incidence spectroscopic ellipsometer (VASE)® was used to measure spectroscopic ellipsometric data at multiple angles of incidence and these data were fit to an optical model. The model obtained from the VASE® data analysis was then used to fit the visible reflectance data measurements. This article will compare the integrated measurements with measurements from a production metrology tool that measure both ellipsometric and reflectance data from the same location on the wafer, as well as with measurements from a research grade ellipsometer (VASE®).
Growth and characterization of poly(arylamine) thin films prepared by vapor deposition
Authors: Szulczewski G. J. , Selby T. D. , Kim K.-Y. , Hassenzahl J. D. , Blackstock S. C.
Published: July 2002

Thin films of new organic redox-active arylamine dendrimers have been examined. The thermal properties of the bulk samples have been measured by differential scanning calorimetry and thermogravimetric analysis. In general, these compounds exhibit amorphous phases with glass transition temperatures near 100 °C and are thermally stable up to 400 °C. Thin films (1–100 nm) of these large (1300–2200 amu) molecules were prepared by vapor deposition onto Au and Si(100) surfaces. Nuclear magnetic resonance analysis of redissolved films proved that vapor deposition occurs without molecular decomposition. Ex situ surface characterization was performed by reflection–absorption infrared spectroscopy, x-ray photoelectron spectroscopy, spectroscopic ellipsometry, and atomic-force microscopy to document the chemical integrity and morphology of the films. The analyses show that the vapor deposition produces molecularly smooth dendrimer films at high surface coverages, while at low surface coverage, film growth and morphology depend greatly on the chemical nature of the surface.
Deposition and characterization of highly oriented Mg3(VO4)2 thin film catalysts
Authors: Ruffner Judith A. , Sault Allen G. , Rodriguez Mark A. , Tissot Ralph G.
Published: July 2002

Magnesium vanadates are potentially important catalytic materials for the conversion of alkanes to alkenes via oxidative dehydrogenation. However, little is known about the active sites at which the catalytic reactions take place. It may be possible to obtain a significant increase in the catalytic efficiency if the effects of certain material properties on the surface reactions could be quantified and optimized through the use of appropriate preparation techniques. Given that surface reactivity is often dependent upon surface structure and that the atomic level structure of the active sites in these catalysts is virtually unknown, we desire thin film samples consisting of a single magnesium vanadate phase and a well defined crystallographic orientation in order to reduce the complexity and simplify the study of active sites. We report on the use of reactive rf sputter deposition to fabricate very highly oriented, stoichiometric Mg3(VO4)2 thin films for use in these surface analysis studies. Deposition of samples onto amorphous substrates resulted in very poor crystallinity. However, deposition of Mg3(VO4)2 onto well-oriented, lattice-matched thin film “seed” layers such as Ti(0001), Au(111), or Pt(111) resulted in very strong preferential (042) crystallographic orientation (pseudohexagonal oxygen planes parallel to the substrate). This strong preferential growth of the Mg3(VO4)2 suggests epitaxial (single-crystal) growth of this mixed metal oxide on the underlying metal seed layer. The effects of the seed layer material, deposition temperature, and postdeposition reactive treatments on thin film properties such as stoichiometry, crystallographic orientation, and chemical interactions will be discussed.
Low-temperature polysilicon deposition by ionized magnetron sputtering
Authors: Joo Junghoon
Published: July 2002

Ionized magnetron sputtering was successfully applied to polycrystalline silicon thin-film deposition on glass substrate at temperatures lower than 250 °C maintaining a deposition rate of about 133 Å/min. Hydrogen mixing was effective up to Ar:H2=10:6 by mass flow rate. Prior to deposition, H2 inductively coupled plasma was used for precleaning the substrate with −40 V bias. During Si deposition, the substrate biasing scheme was in two steps; +20 V for an initial stage and +20 to −40 V bipolar pulse bias for the rest of the deposition time. The crystallinity was evaluated by both x-ray diffraction analysis and Raman spectroscopy; the average crystalline fraction was calculated as 70%. Grain size was measured in plan-view scanning-electron micrographs after selective etching of the amorphous phase by chemical solution. In 800-nm-thick samples, grains are 500–700 Å in diameter. Optical emission spectroscopy was used as real-time diagnostics, and ionization of sputtered silicon atoms distinctly increased as the hydrogen partial pressure increased. The successful deposition of polycrystalline silicon was explained as being due to enhanced ionization of sputtered and reflected neutrals and resultant energy control by bipolar substrate bias.
Real-time thickness and compositional control of Ga1−xInxP growth using p-polarized reflectance
Authors: Woods V. , Dietz N. , Ito K. , Lauko I.
Published: July 2002

Advances in the engineering and design of advanced electro-optical materials require sensors and control strategies that allow tight control over thickness and composition of multilayered structures. In response to this demand, we developed and applied p-polarized reflectance (PR) for real-time optical characterization and control of heteroepitaxial GaP/GaInP growth under pulsed chemical beam epitaxy conditions. For closed-loop control, we applied nonlinear control algorithms (based on nonlinear Kalman filtering) that utilizes the PR signals to adjust the source flows involved in the heteroepitaxial growth of Ga1−xInxP on Si(001). A reduced order surface kinetics model has been formulated to establish the linkage between the surface reaction kinetic and its optical response. These data are linked to compute the compositional and thickness change per time unit, utilizing the monitored PR signals for validation. This allows the establishment of feedback control algorithms, able to control both the growth rate and composition of Ga1−xInxP heterostructures.
Absorption properties of the bottom novolac layer in multilayer resist systems
Authors: Namatsu Hideo
Published: July 2002

A novolac resin suitable for the bottom planarizing layer in multilayer resist systems is discussed from the standpoint of exposure wavelength absorption. Absorption by the bottom planarizing layer is crucial to reduce the reflected light from the resist–substrate interface. It was clarified that the absorption of phenol novolac resin was higher than that of the cresol novolac resin under the same baking conditions. From infrared and nuclear magnetic resonance analysis, it was found that carbonyl structures were formed in the novolac resin after baking. In addition, cross-linking was found to occur at the methylene bridges in the phenol novolac resins. These factors seem to cause the absorption maxima to shift to a longer wavelength.
Adhesion enhancement of Ni films on polyimide using ion processing. I. 28Si+ implantation
Authors: Galuska A. A.
Published: July 2002

The influence of 28Si+ ion implantation on the interfacial chemistry and adhesion of 30 nm Ni films on po1y[N,N-(p,p′-oxydiphenylene) pyromellitimide] (PI) substrates was examined. The Ni/PI specimens were held at temperatures below 100 °C, and implanted with 55 keV 28Si+ at doses of either 1×1016 , 5×1016 or 1×1017 Si/cm2 . The 1×1016 Si/cm2 implants had no influence on the surface topography, but the higher dose implants introduced some submicron void formation. Cross-sectional transmission electron microscopy and Auger electron spectroscopy depth profile analyses showed that the as-deposited Ni films formed very sharp interfaces with the polyimide substrates. However, after implantation the interfaces became graded by up to a factor of 2 compared to the as-deposited specimens. Large quantities of C were transferred into the Ni films, resulting in the formation of a C overlayer. The concentration of implanted Si reached a maximum (at approximately 16 at. % for the 1×1017 Si/cm2 implant) in the Ni films and extended deeply into the PI substrates. X-ray photoelectron spectroscopy analysis of the interfaces of the specimens implanted with 1×1017 Si/cm2 showed a mixture of Ni–Si, Si–O, and C–O chemical bonding, consistent with Ni–Si–O–C complex formation. Adhesion testing showed substantial adhesion increases (up to a factor of 20) with 28Si+ dose. The Ni films implanted with 1×1017 Si/cm2 were only removed upon substrate failure. The adhesion increases induced by 28 Si+ implantation are attributed to a combination of substrate toughening, mechanical interlocking, interfacial grading, and chemical bonding across the interfaces.
Proposal for a novel magnetometer
Authors: Witek A. , Onn David G.
Published: July 2002

A tunneling junction is proposed as an amplitude sensor for a vibrating reed magnetometer. Technical details of such a design are proposed and discussed. Due to the strong distance dependence of tunneling current on electrode spacing, tunneling can be used to measure subangstrom amplitudes. The amplitude of vibration of the new vibrating magnetometer is proposed as being measured by the tunneling current both in a constant current mode and in an alternating current mode. The predicted sensitivities are calculated for both modes of working. A compensating mode for a vibrating reed magnetometer technique, with a tunneling junction as a zero displacement detector is also considered. Numerical evaluation suggests that a sensitivity of about 10−10 (A cm2) could be achieved for the magnetic moment. Such a sensitivity would be higher than the sensitivity of any commercially available SQUID magnetometer. Some advantages of the proposed magnetometer are discussed.
Resolution limits in x-ray lithography
Authors: Feldman M. , Sun J.
Published: July 2002

During an x-ray lithography proximity exposure x rays generate electrons in the resist which deposit energy along a finite range. This range combines with diffraction spreading to degrade the image resolution. The component of resolution arising from electron range is often taken as the Grun range of the most copiously generated photoelectrons, about 0.1 μm at an exposure wavelength of 10 Å. Although some experiments have shown much better resolutions, there is a widespread belief that photoelectron range limits resolution to about 0.1 μm. We have analytically modeled the distribution of energy deposited by Auger and photoelectrons. Near an edge the distribution is well-fit by an error function. The standard deviation of this error function, which we define as the ‘‘effective range,’’ is about 0.01 μm at 10 Å in poly(methylmethacrylate) (PMMA) resist. For all energies of interest to x-ray lithography the effective range of the electrons is much smaller than the Grun range, explaining the high-resolution results. It is diffraction which dominates the resolution of conventional x-ray lithography. Consequently, reducing the gap in proximity printing should produce resolutions far below 0.1 μm, while retaining all the latitude inherent in the x-ray lithography process.
Focused ion beam induced deposition and ion milling as a function of angle of ion incidence
Authors: Xu Xin , Della Ratta Anthony D. , Sosonkina Jane , Melngailis John
Published: July 2002

In the repair of integrated circuits, and x-ray masks focused ion beam induced deposition, and ion milling often have to be performed over quite nonplanar topography. Thus, the milling and the deposition as a function of the angle of ion incidence are important. The milling yield of Si, SiO2, Au, and W versus angle of incidence using 25 keV Ga+ ions has been measured. In qualitative agreement with simulations, the yield rises with angle and then falls as grazing incidence is approached. Deposition yield versus angle was measured using dimethylgold hexafluoro-acetylacetonate and W(CO)6 as the precursor gases. The measurements were carried out using cylindrical quartz fibers 30–50 μm in diameter which automatically provide angles of incidence from 0° to 90° or on planar surfaces at various angles. Rippling of the deposited material is observed at angles of incidence greater than 50°.
Focused-ion beam induced deposition of copper
Authors: Della Ratta Anthony D. , Melngailis John , Thompson Carl V.
Published: July 2002

As the dimensions of integrated circuits (ICs) decrease into the submicron range, the problems of circuit delay and interconnect reliability become more urgent. Due to its low resistivity (1.67 μΩ cm) and high electromigration resistance, copper has received attention as a candidate metal for the ICs of the future. In addition, the focused-ion beam (FIB), with its capability for milling and deposition at linewidths of 0.1 μm or below, has proved useful as a tool for integrated IC ‘‘microsurgery.’’ FIB induced deposition of copper from a novel organometallic precursor compound, Cu(hfac)TMVS, has been achieved using 25–35 keV Ga+ ions from a liquid metal ion source. Submicron copper lines deposited at room temperature from this precursor exhibit resistivities as low as 50 μΩ cm; a sharp drop in these values is noted for deposition above 67 °C, and deposition on a substrate heated above ∼100 °C yields resistivities near those of pure bulk copper. Composition analysis by Auger electron spectroscopy shows the high temperature deposition to be nearly pure copper. Deposition yields of 14 copper atoms per incident Ga+ ion have been obtained on both silicon and silicon dioxide substrates, with growth rates of up to 2.2 nm/s at an average ion current density of 200 μA/cm2. The quality and microstructure of the deposited film seems to be inextricably tied to the ability of the carbon-containing by-product molecules to desorb from the growing film. For instance, high-temperature deposition results in a low resistivity film with few impurities, most likely because this condition allows greater by-product desorption. Under the proper conditions, this particular precursor compound shows great promise for use in the FIB induced deposition of low resistivity, submicron interconnects on ICs for repair processes.
Mechanism of ion beam induced deposition of gold
Authors: Ro J. S. , Thompson C. V. , Melngailis J.
Published: July 2002

Ion beam induced deposition is a novel method of thin film growth in which adsorbed, metal-bearing molecules are decomposed by incident energetic ions thus leaving a deposit. In conjunction with finely focused ion beams this process is used in microelectronics for local repair, i.e., deposition of patches of metal film with better than 0.1 μm resolution. Each ion can decompose as many as 40–50 adsorbed molecules. The fundamental aspects of this process, namely how is the energy of the ion transferred to adsorbed molecules over a radius of up to 5 nm, have been studied. The decomposition yield (number of molecules decomposed/ion) was measured for Ne, Ar, Kr, and Xe ions at 50 and 100 keV. A model based on trim calculations was developed. The data correlate with this model confirming the view that collision cascades which can provide energy to surface atoms over a substantial area are responsible for ion beam induced deposition.
Nanofabrication on electron beam resist using scanning tunneling microscopy
Authors: Archer A. , Hetrick J. M. , Nayfeh M. H. , Adesida I.
Published: July 2002

We report the results of nanofabrication using a scanning tunneling microscope on silicon coated with SAL 601 electron beam resist. The process is found to be complex, switching over from producing structures that appear as mounds to structures that appear as grooves as the biasing voltage drops below 6 V. Mound-like structures of width as small as 18 nm with a 2 nm corrugation, and structures like grooves as small as 15 nm in width and 0.5 nm in depth were fabricated. Somewhat narrower but shallower structures can be produced in the resist, but we believe that these results are reaching the practical limit of fabrication.
Newly developed low-temperature scanning tunneling microscope and its application to the study of superconducting materials
Authors: Gao Fan , Dai Changchun , Chen Zengbo , Huang Guizhen , Bai Chunli , Tao Hongjie , Yin Bo , Yang Qiansheng , Zhao Zhongxian
Published: July 2002

A newly developed scanning tunneling microscope (STM) capable of operating at room temperature, 77 K, and 4.2 K is presented. This compact STM has a highly symmetric and rigid tunneling unit designed as an integral frame except the coarse and fine adjustment parts. The tunneling unit is incorporated into a small vacuum chamber that is usually pumped down to 2×10−4 Pa to avoid water contamination. The fine mechanic adjustment makes the tip approach the sample in 5 nm steps. The coarse adjustment not only changes the distance between the tip and the sample, but also adjusts the tip to be normal to the surface of the sample. With this low-temperature STM atomic resolution images of Bi-2212 single-crystal and large-scale topographies of a YBa2Cu3O7 thin film are observed at 77 K.
Luminescence enhancement of InGaAs/InP surface quantum wells by room-temperature ion-gun hydrogenation
Authors: Chang Ying-Lan , Tan I-Hsing , Reaves Casper , Hu Evelyn , Merz James , DenBaars Steve
Published: July 2002

An InGaAs/InP surface quantum well has been used as a very effective probe of surface states before and after room-temperature low-energy ion-gun hydrogenation. We found that the luminescence efficiency from the surface quantum well (QW) does not improve for ion exposures less than 1015 ions/cm2. Above this value, the luminescence efficiency increases monotonically, up to two orders of magnitude at the ion exposure of 1017 ions/cm2. The luminescence efficiency for samples hydrogenated with exposures of 1015 and 1016 ions/cm2 degraded slightly after two months in ambient air; however, a further enhancement of luminescence efficiency by ∼20% was observed for samples hydrogenated with an exposure of 1017 ions/cm2.
Writhing number of supercoiled DNA from its scanning force microscopy imaging
Authors: Zuccheri G. , Ranieri G. A. , Nigro C. , Samorì B.
Published: July 2002

Scanning force microscopy can routinely image supercoiled DNA molecules under liquids or in air and the complete three-dimensional path of the chain can be identified. This makes it possible to evaluate the writhing number (Wr) of the coiled curve described by the chain axis in the imaged conformation of the molecule. Wr is a much better descriptor of supercoiling than the linking deficit (ΔLk) which has been commonly used so far. Wr of the DNA axis curve can be roughly estimated by the signed-intersection approach or calculated as the Gauss integral of the curve itself. We applied both methods to a model closed simple curve and to coiled DNA molecules exhibiting one or two turns of the chain about their superhelical axis.
High speed layer by layer patterning of phthalocyanine Langmuir–Blodgett films by the atomic force microscope
Authors: Bourgoin J. P. , Sudiwala R. V. , Palacin S.
Published: July 2002

Anisotropic Langmuir–Blodgett films of phthalocyanine derivatives have been patterned using an atomic force microscope to scan the surface of the film at high scan rate (≳100 μm/s). The depth of the periodic grooved lines, of width down to 50 nm, formed perpendicular to the fast scan direction can be controlled to the monolayer level through the effect of the load (a few nanonewtons) applied to the tip. It is shown that the patterning results from an oscillation in the feedback loop resulting in a periodic force modulation of a few nanonewtons along each scan line. Using the same principle, we show that the microscope can be modified to write patterns of arbitrary form by the superposition of a given voltage waveform onto the Z piezo voltage.
Calorimetric measurements of optical materials for 193 nm lithography
Authors: Grenville A. , Uttaro R. , Sedlacek J. H. C. , Rothschild M. , Corliss D.
Published: July 2002

We have developed a new calorimetric method to accurately determine the absorption coefficient at 193 nm of optical materials such as fused silica and calcium fluoride. The amount of absorbed radiation is the power consumed by a thermoelectric cooler that maintains the sample at room temperature during exposure with a 193 nm laser. We report initial results from five types of fused silica which indicate that absorption coefficients are still a factor of 3 higher than the target of 0.001 cm−1 and that batch to batch variations remain common. The absorption coefficient for one grade of calcium fluoride has also been obtained. On one fused silica sample, an upper bound has been placed on the two-photon absorption coefficient at a factor of 2 lower than those previously reported. Measurements have been performed under a variety of vacuum conditions yielding anomalous losses in transmission.
Effect of substrate temperature and annealing on the structural properties of ZnO ultrafine particle films
Authors: Dachun Zhao , Zhongkai Qu , Xiaoren Pan , Muji Dai , Minggen Sun
Published: July 2002

ZnO ultrafine particle (UFP) films were deposited on glass and SiO2 substrates by a direct current gas discharge activated reactive evaporation method. The effect of substrate temperature and annealing on the structure and morphology of ZnO UFP films was studied by x-ray diffraction and scanning electron microscope. The results show that the spherical island density decreases with increasing annealing temperature and the structure becomes polycrystalline with a (002) preferential orientation as the substrate temperature increases. In addition, angle resolved x-ray photoelectron spectroscopy was used to study the absorption of water on the ZnO UFP film surface by measuring the two deconvoluted peaks for O 1s. The two deconvoluted peaks for O 1s were located at 533.2 and 534.8 eV. The absorption coefficients of water on the surface were 0.52 and 0.43, respectively, for nonannealed and annealed ZnO UFP films.
Dose modification proximity effect correction scheme with inherent forward scattering corrections
Authors: Watson G. Patrick , Fetter Linus A. , Liddle J. Alexander
Published: July 2002

A new approach to dose modification proximity effect correction (PEC) has been proposed that accounts for both short range and long range scatter in advanced direct-write electron beam lithography systems. This scheme can be applied to device writing and to optical mask making where critical dimension (CD) control is of increasing importance. This technique is unique because detailed knowledge of the short range scatter dose distribution is unnecessary; by correcting only for long range scatter, both short and long range compensation is obtained. The new approach is based on the fact that if the characteristic distance of short range scatter is about one third or less of the smallest feature, and if each feature is at least five addressable pixels in the beam writer, then the feature can be printed at its coded dimension if the resist clearing or threshold dose is at the midpoint of the dose profile. Si wafers coated with a positive tone e-beam resist were exposed to a test pattern using no PEC, conventional dose modification PEC and the new scheme. Results show that CD control is maintained over a larger pattern density variation and over a larger exposure dose range by the new technique when compared to the older method and to the uncorrected patterns.
Overlay performance of 180 nm ground rule generation x-ray lithography aligner
Authors: Chen A. C. , Flamholz A. L. , Rippstein R. , Fair R. H. , Heald D. A. , Amodeo R. J.
Published: July 2002

The 180 nm ground rule production prototype x-ray lithography aligner was developed for the Defense Advanced Lithography Program (DALP) and installed in IBM’s Advanced Lithography Facility (ALF) in 1995. This aligner is designed to satisfy the manufacturing requirement for 250 and 180 nm ground rule electronic devices, such as 256 Mbit and 1 Gbit dynamic random access memories. The acceptance evaluation of this aligner was presented elsewhere (Ref. 12). The aligner uses an innovative x-ray image sensor (XRIS) to align the mask by detecting its x-ray actinic image and uses an off-axis alignment system, similar to the alignment system used in Micrascan-II™ (a trademark of Silicon Valley Group Lithography), to align the wafer. From subsystem testing, the alignment repeatability of XRIS is not a significant contributor to the aligner’s contribution of overlay error. As a result, the x-ray alignment sensor technology can be used for future generations of x-ray lithography aligners. This article will specifically focus on the overlay performance of the aligner. The overlay evaluation consisted of careful wafer stage and alignment system calibration, off-line subsystem testing, and extensive exposure tests. The exposure tests were designed to measure the alignment performance of the aligner across a wide range of wafer structure types. A detailed discussion is given on the test methodology and the aligner contribution to the total overlay error. On the better levels (e.g., etched Si), the tool-to-itself aligner contribution to overlay error is in the range of 35–40 nm (mean+3σ) and approaches the overlay error budget for a 180 nm ground rule generation x-ray aligner. An overlay model was also developed to include the error contributions of the aligner as well as the image placement accuracy of the mask. The modeling results show that the aligner, with image placement errors of current x-ray masks, can satisfy the overlay requirement (mean+3σ<70 nm) for 1 Gbit device demonstration programs.
X-ray photoelectron spectroscopy analyses of metal stacks etched in Cl2/BCl3 high density plasmas
Authors: Czuprynski P. , Joubert O. , Vallier L. , Puttock M. , Heitzmann M.
Published: July 2002

We have used x-ray photoelectron spectroscopy to determine the chemical elements present on the tops, sidewalls, and bottoms of submicron metal features etched in a high density inductively coupled plasma source using Cl2/BCl3 gas mixtures. X-ray photoelectron spectroscopy analyses have shown that aluminum oxide is deposited on all the surfaces of the features exposed to the plasma due to erosion of the alumina liner located in the source region. A chlorine rich carbon film is formed on the sidewalls and at the bottom of the aluminum features during the etching process. At the bottom of the features, chlorine species must diffuse through the carbon layer to etch aluminum whereas spontaneous reactions between chlorine and aluminum are blocked on the sides of the features. On the sidewalls of the features, aluminum oxide species coming from the sputtering of the alumina liner are embedded in the carbon rich film as it grows. This sidewall passivation film enhances anisotropic etching by providing a thin protective layer against spontaneous etching reaction of chlorine with aluminum.
Measurements and calculations of the valence band offsets of SiOx/ZnS(111) and SiOx/CdTe(111) heterojunctions
Authors: Ban Da-yan , Xue Jian-geng , Fang Rong-chuan , Xu Shi-hong , Lu Er-dong , Xu Peng-shou
Published: July 2002

SiO x (x>1.5) overlayers have been in situ grown on ZnS (111) and CdTe (111) substrates. Synchrotron radiation photoemission spectroscopy has been used to measure the electronic structures and band lineups of these two heterojunctions. The valence band offsets of SiOx/ZnS(111) and SiOx/CdTe(111) derived from the measurements are 2.8±0.2 and 4.7±0.2 eV, respectively. Harrison’s “tight binding” theory is extended into the theoretical estimation of the band lineups of SiO2 related heterojunctions. The agreement between the experimental and theoretical results is good. Our result also explains the positive role of SiO2 layers in ZnS-based thin film electroluminescence devices.
In situ scanning tunneling microscope studies of high-energy, focused ion implantation of Ga into GaAs: Direct observation of ion beam profiles
Authors: Jones G. A. C. , Rose P. D. , Brown S.
Published: July 2002

The profile of an ion beam line exposure of Ga+ ions into GaAs(100) was characterized in situ using scanning probe microscopy. Current imaging tunneling spectroscopy was used to characterize the surface defects induced by the high-energy Ga+ ions. Spatially reproducible features, approximately one per ion and 2–3 nm in diameter, were observed on the irradiated surface. Differential conductance spectra of these features indicated that the image contrast was due to acceptor states induced in the surface band gap. The density of these defects was used to form a profile of the ion beam in the semiconductor surface. The resulting profile was in excellent agreement with the two-Gaussian fit reported in previous work.
Nanoscale freestanding gratings for ultraviolet blocking filters
Authors: van Beek J. T. M. , Fleming R. C. , Hindle P. S. , Prentiss J. D. , Schattenburg M. L. , Ritzau S.
Published: July 2002

Ultraviolet (UV) blocking filters are needed for atomic flux imaging in environments where high levels of ultraviolet radiation are present. Freestanding gratings are a promising candidate for UV filtering. They have a high aspect ratio (∼13), narrow (∼40 nm) slots, and effectively block UV radiation. The grating fabrication process makes use of several etching, electroplating, and lithographic steps and includes an optional step to plug pinholes induced by particles during processing. Gratings were successfully manufactured and tested. Measured UV transmissions of ∼10−5 and particle transmissions of ∼10% are in agreement with theoretical predictions.
Study of precursor gases for focused ion beam insulator deposition
Authors: Edinger K. , Melngailis J. , Orloff J.
Published: July 2002

The electrical properties of insulators formed by focused ion beam induced deposition of various siloxane precursor gases have been compared. Leakage current and breakdown field have been measured by forming metal-insulator-metal structures. It was found that the focused ion beam induced deposition of metal on top of the insulator can substantially degrade the quality of the insulator. We found that the resistivity of the insulator material depends on the deposition yield (e.g., the amount of Ga implantation) as well as on the chemical nature of the precursor gas. From the precursor gases studied, the new compound pentamethylcyclopentasiloxane shows the best performance. Compared to the commercially used tetramethylcyclotetrasiloxane compound, an improvement in resistivity by two orders of magnitude (∼8×1011 versus ∼6×109 Ω cm) and a factor of about 1.5 in breakdown field (650 vs 440 V/μm) could be achieved.
Local field emission features of thick diamond films on various silicon substrates
Authors: Göhl A. , Habermann T. , Nau D. , Müller G. , Raiko V. , Theirich D. , Engemann J.
Published: July 2002

The field emission of diamond is promising for high-power applications. According to theoretical analyses, the field emission (FE) of insulating diamond should be governed by the diamond-substrate interface. Therefore, we have investigated the influence of differently p- and n-doped Si(100)-substrate types on the FE properties of thick, oriented, and locally insulating diamond films, grown in a microwave plasma-assisted chemical vapor deposition setup. Local FE measurements were performed by means of a field emission scanning microscope with variable lateral resolution R⩾100 nm. By using anodes of 1 μm tip diameter, very high maximum reproducible local current densities JREP (from μm2-sized areas) up to 8860 A/cm2 could be achieved at vacuum field strengths E of typical 1200–3000 V/μm, corresponding to 20–50 V/μm in the diamond near the substrate. The current I vs E behavior, the reproducibility, and JREP depended strongly on the substrate type. FE mapping over a 10×10 μm2 sized area revealed a uniform emission on a 100 nm scale. In order to realize high currents for power applications, the uniformity of the substrate-diamond interface, as well as of the film smoothness, should be improved.
Fabrication of a metal nanostructure on the Si(111) surface
Authors: Rogers D. , Nejoh H.
Published: July 2002

A metal nanostructure was fabricated on a Si(111) surface in ultrahigh vacuum. The stages in the fabrication were H passivation of the surface, Pb evaporation, depassivation of selected areas with the tip of a scanning tunneling microscope, and heating. Using this procedure, a nanowire and two contact pads to connect it to external probes were fabricated. At each stage of the process, the surface was imaged with scanning tunneling microscopy.
Effects of O2 gas flow ratio and flow rate on the formation of RuO2 thin films by reactive sputtering
Authors: Abe Y. , Kaga Y. , Kawamura M. , Sasaki K.
Published: July 2002

RuO 2 thin films were grown by sputtering a Ru target in Ar and O2 mixed gas, and the effects of O2 gas flow ratio and flow rate on the formation of RuO2 films were studied. Based on changes in the deposition rate and plasma emission spectra observed when the O2 flow ratio was varied, the formation process of RuO2 films is categorized into two classes: (1) oxidation of Ru atoms at the substrate surface (metallic target mode) in a lower O2 flow ratio region and (2) sputtering of the oxidized target (oxide target mode) in a higher O2 flow ratio region. In addition, the supplied O2 flow rate, rather than the O2 flow ratio, is found to be the dominant factor in the formation of RuO2 thin films. At an O2 gas supply at which twice as many oxygen molecules as sputtered Ru atoms are introduced into the sputtering chamber, RuO2 thin films begin to be deposited in the metal target mode.
Communication of the Position of Exon-Exon Junctions to the mRNA Surveillance Machinery by the Protein RNPS1
Authors: Lykke-Andersen Jens , Shu Mei-Di , Steitz Joan A.
Published: July 2002

In mammalian cells, splice junctions play a dual role in mRNA quality control: They mediate selective nuclear export of mature mRNA and they serve as a mark for mRNA surveillance, which subjects aberrant mRNAs with premature termination codons to nonsense-mediated decay (NMD). Here, we demonstrate that the protein RNPS1, a component of the postsplicing complex that is deposited 5′ to exon-exon junctions, interacts with the evolutionarily conserved human Upf complex, a central component of NMD. Significantly, RNPS1 triggers NMD when tethered to the 3′ untranslated region of β-globin mRNA, demonstrating its role as a subunit of the postsplicing complex directly involved in mRNA surveillance.
Anticircumvention Rules: Threat to Science
Authors: Samuelson Pamela
Published: July 2002

Scientists who study encryption or computer security or otherwise reverse engineer technical measures, who make tools enabling them to do this work, and who report the results of their research face new risks of legal liability because of recently adopted rules prohibiting the circumvention of technical measures and manufacture or distribution of circumvention tools. Because all data in digital form can be technically protected, the impact of these rules goes far beyond encryption and computer security research. The scientific community must recognize the harms these rules pose and provide guidance about how to improve the anticircumvention rules.
Defective Antigen Processing in GILT-Free Mice
Authors: Maric Maja , Arunachalam Balasubramanian , Phan Uyen T. , Dong Chen , Garrett Wendy S. , Cannon Kurt S. , Alfonso Christopher , Karlsson Lars , Flavell Richard A. , Cresswell Peter
Published: July 2002

Processing of proteins for major histocompatibility complex (MHC) class II–restricted presentation to CD4-positive T lymphocytes occurs after they are internalized by antigen-presenting cells (APCs). Antigenic proteins frequently contain disulfide bonds, and their reduction in the endocytic pathway facilitates processing. In humans, a gamma interferon–inducible lysosomal thiol reductase (GILT) is constitutively present in late endocytic compartments of APCs. Here, we identified the mouse homolog of GILT and generated a GILT knockout mouse. GILT facilitated the processing and presentation to antigen-specific T cells of protein antigens containing disulfide bonds. The response to hen egg lysozyme, a model antigen with a compact structure containing four disulfide bonds, was examined in detail.
Structural Basis of Transcription Initiation: RNA Polymerase Holoenzyme at 4 Å Resolution
Authors: Murakami Katsuhiko S. , Masuda Shoko , Darst Seth A.
Published: July 2002

The crystal structure of the initiating form of
Thermus aquaticus
RNA polymerase, containing core RNA polymerase (α
2
ββ′ω) and the promoter specificity σ subunit, has been determined at 4 angstrom resolution. Important structural features of the RNA polymerase and their roles in positioning σ within the initiation complex are delineated, as well as the role played by σ in modulating the opening of the RNA polymerase active-site channel. The two carboxyl-terminal domains of σ are separated by 45 angstroms on the surface of the RNA polymerase, but are linked by an extended loop. The loop winds near the RNA polymerase active site, where it may play a role in initiating nucleotide substrate binding, and out through the RNA exit channel. The advancing RNA transcript must displace the loop, leading to abortive initiation and ultimately to σ release.
Latest
Homo erectus
of Java: Potential Contemporaneity with
Homo sapiens
in Southeast Asia
Authors: Swisher C. C. , Rink W. J. , Antón S. C. , Schwarcz H. P. , Curtis G. H. , Suprijo A. , Widiasmoro
Published: July 2002

Hominid fossils from Ngandong and Sambungmacan, Central Java, are considered the most morphologically advanced representatives of
Homo erectus.
Electron spin resonance (ESR) and mass spectrometric U-series dating of fossil bovid teeth collected from the hominid-bearing levels at these sites gave mean ages of 27 ± 2 to 53.3 ± 4 thousand years ago; the range in ages reflects uncertainties in uranium migration histories. These ages are 20,000 to 400,000 years younger than previous age estimates for these hominids and indicate that
H. erectus
may have survived on Java at least 250,000 years longer than on the Asian mainland, and perhaps 1 million years longer than in Africa. The new ages raise the possibility that
H. erectus
overlapped in time with anatomically modern humans
(H. sapiens)
in Southeast Asia.
Activation of the G Protein Gq/11 Through Tyrosine Phosphorylation of the α Subunit
Authors: Umemori Hisashi , Inoue Takafumi , Kume Shoen , Sekiyama Naohiro , Nagao Motoshi , Itoh Hiroshi , Nakanishi Shigetada , Mikoshiba Katsuhiko , Yamamoto Tadashi
Published: July 2002

Various receptors coupled to the heterotrimeric guanine nucleotide-binding protein Gq/11 stimulate formation of inositol-1,4,5-trisphosphate (IP
3
). Activation of these receptors also induces protein tyrosine phosphorylation. Formation of IP
3
in response to stimulated receptors that couple to Gq/11 was blocked by protein tyrosine kinase inhibitors. These inhibitors appeared to act before activation of Gq/11. Moreover, stimulation of receptors coupled to Gq/11 induced phosphorylation on a tyrosine residue (Tyr
356
) of the Gα
q/11
subunit, and this tyrosine phosphorylation event was essential for Gq/11 activation. Tyrosine phosphorylation of Gα
q/11
induced changes in its interaction with receptors. Therefore, tyrosine phosphorylation of Gα
q/11
appears to regulate the activation of Gq/11 protein.
Reversible Tuning of Silver Quantum Dot Monolayers Through the Metal-Insulator Transition
Authors: Collier C. P. , Saykally R. J. , Shiang J. J. , Henrichs S. E. , Heath J. R.
Published: July 2002

The linear and nonlinear (χ
(2)
) optical responses of Langmuir monolayers of organically functionalized silver quantum dots were measured as a continuous function of interparticle separation under near-ambient conditions. As the distance between metal surfaces was decreased from 12 to ∼5 angstroms, both quantum and classical effects were observed in the optical signals. When the separation was less than 5 angstroms, the optical second-harmonic generation (SHG) response exhibited a sharp discontinuity, and the linear reflectance and absorbance began to resemble those of a thin metallic film, indicating that an insulator-to-metal transition occurred. This transition was reversible.
The Theropod Ancestry of Birds: New Evidence from the Late Cretaceous of Madagascar
Authors: Forster Catherine A. , Sampson Scott D. , Chiappe Luis M. , Krause David W.
Published: July 2002

A partial skeleton of a primitive bird,
Rahona ostromi
, gen. et sp. nov., has been discovered from the Late Cretaceous of Madagascar. This specimen, although exhibiting avian features such as a reversed hallux and ulnar papillae, retains characteristics that indicate a theropod ancestry, including a pubic foot and hyposphene-hypantra vertebral articulations.
Rahona
has a robust, hyperextendible second digit on the hind foot that terminates in a sicklelike claw, a unique characteristic of the theropod groups Troodontidae and Dromaeosauridae. A phylogenetic analysis places
Rahona
with
Archaeopteryx
, making
Rahona
one of the most primitive birds yet discovered.
Experimental Demonstration of Guiding and Bending of Electromagnetic Waves in a Photonic Crystal
Authors: Lin Shawn-Yu , Chow Edmund , Hietala Vince , Villeneuve Pierre R. , Joannopoulos J. D.
Published: July 2002

The routing and interconnection of optical signals through narrow channels and around sharp corners are important for large-scale all-optical circuit applications. A recent computational result suggests that photonic crystals may offer a novel way of achieving this goal by providing a mechanism for guiding light that is fundamentally different from traditional index guiding. Waveguiding in a photonic crystal and near 100 percent transmission of electromagnetic waves around sharp 90 degree corners were observed experimentally. Bending radii were made smaller than one wavelength.