bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanometer fabrication using selective thermal desorption of SiO2 induced by focused electron beams and electron beam interference fringes
Authors: Fujita S. , Maruno S. , Watanabe H. , Ichikawa M.
Published: July 2002

Based on our earlier works, 10 nm open windows in the SiO2, Si nanowires, and Ge nanowires were fabricated using electron beam induced selective thermal desorption (EB-STD) of SiO2 on Si substrates. In this article, we show that selective etching can be performed with oxygen gas using an SiO2 mask which includes approximately 10-nm-wide open windows formed by STD using focused EB. We also demonstrate the formation of an approximately 10 nm periodic surface structure of Si and SiO2 by STD after irradiation with EB interference fringes. The mechanisms related to these techniques are also discussed. These various methods indicate that EB-STD will be useful for fabricating Si structures of the order of 10 nm.
Molecular beam epitaxial growth of InAs/AlGaAsSb deep quantum well structures on GaAs substrates
Authors: Kuze N. , Goto H. , Matsui M. , Shibasaki I.
Published: July 2002

We investigated InAs deep quantum well structures (InAs QWs) made from InAs/AlGaAsSb materials on GaAs substrates by molecular beam epitaxy. In the InAs QWs, AlGaAsSb layers were lattice matched to InAs. Using reflection high-energy electron diffraction (RHEED) linescan images analysis, we show that AlGaAsSb on GaAs surfaces quickly relaxes within 3–7 monolayers (MLs). The initial stages of AlGaAsSb growth on GaAs(100) substrates and InAs growth on AlGaAsSb layers have been investigated by atomic force microscopy (AFM) and RHEED image analysis. A new growth mode, exhibiting ridgeline shapes during the initial stages of GaAsSb and AlGaAsSb growth on GaAs surfaces, was observed. At the interface of the InAs/AlGaAsSb, the two-dimensional growth of InAs was observed. The roughness at the InAs/AlGaAsSb interface was 3–4 MLs from AFM, high-resolution transmission electron microscopy and grazing incidence x-ray reflectivity analyses. We achieved very high electron mobilities of 32 000 cm2/V s at room temperature using a thin buffer layer of 600 nm AlGaAsSb.
Contact resistance degradation of Pd/Ge ohmic contact on pseudomorphic high electron mobility transistor
Authors: Lee Jong-Lam , Kim Yi-Tae
Published: July 2002

The contact resistance degradation mechanism of the Pd/Ge ohmic contact on a pseudomorphic high electron mobility transistor was interpreted. The contact resistance continuously degrades at temperatures higher than 300 °C although no microstructural changes were observed. Meanwhile, elemental Ga atoms were preferentially outdiffused to the PdGe layer and Ge atoms were indiffused to the GaAs during annealing. The indiffused Ge converts the interfacial GaAs layer into n-GaAs, in which Ga vacancies are produced to maintain the charge neutrality condition. The Ga vacancy concentration further increases with annealing temperature, which plays a role in degrading the contact resistance as a result of the recombination of electrons with the Ga vacancies.
Patterned regrowth of n-GaAs by molecular beam epitaxy using arsenic passivation
Authors: Heinlein Christian , Fimland Bjørn-Ove , Grepstad Jostein K. , Berge Torunn
Published: July 2002

Patterned regrowth of n-GaAs through a Si3N4 mask prepared on molecular beam epitaxy (MBE) grown n-GaAs layers has been explored. An arsenic capping layer was deposited in the MBE growth chamber prior to mask definition, in order to protect the GaAs surface during ex situ processing. Removal of this cap from the lithographically defined mask area was accomplished by hydrogen plasma etching prior to Si3N4 deposition. After in situ thermal desorption of the As cap and phase selective regrowth, the samples were inspected with scanning electron and atomic force microscopy to establish the growth selectivity and examine the surface morphology. Electrolytic carrier profiling and secondary ion mass spectrometry measurements were carried out to characterize the growth-interrupted GaAs–GaAs interface. We find that the surface morphology and defect density of regrown GaAs epilayers are comparable to those of continuously grown epilayers of the same overall thickness. Structuring of the arsenic cap with hydrogen plasma etching and subsequent selective regrowth after decapping can both be achieved on a micrometer length scale. Moreover, this arsenic passivation of the epilayer surface significantly reduces the built-in potential barrier at the regrowth interface (from 0.45 to 0.07 V) and the incorporation of interfacial carbon impurities, compared to regrowth on nonpassivated GaAs surfaces.
Optimized cleaning and conditioning of a five station tetrakis diethylamido titanium chemical vapor deposition TiN chamber
Authors: Whelan C. S. , Bulger J. M. , Dumont A. , Clark J. , Kuhn M.
Published: July 2002

A sequence of running a short plasma clean followed by an optimized chamber conditioning and finally chemical vapor deposition (CVD) TiN deposition has been developed that minimizes contamination particles, wafer to wafer uniformity, and wet clean downtime on a five station CVD TiN tool. This run sequence simultaneously maintains high yield and throughput, and it has been demonstrated over a 1500 wafer marathon. This sequence of short cleans, conditionings and depositions offers considerable advantages over the accepted sequence of a long clean, long conditioning, and extended wafer running. Following a clean, a 70% reduction in deposition rate ramp and thickness non-uniformity has been demonstrated.
Fabrication technology of ultrafine SiO2 masks and Si nanowires using oxidation of vertical sidewalls of a poly-Si layer
Authors: Tsutsumi Toshiyuki , Tomizawa Kazutaka , Ishii Kenichi , Kanemaru Seigo , Maeda Tatsuro , Suzuki Eiichi
Published: July 2002

A fabrication technology of the vertical ultrafine SiO2 wall masks using oxidation of sidewalls of a polycrystalline silicon (poly-Si) layer and Si nanowires utilizing the SiO2 wall masks have been developed. To obtain the vertical SiO2 wall mask, an optimum electron cyclotron resonance (ECR) plasma etching and a suitable wet etching of the poly-Si layer after the sidewall oxidation has been achieved. The vertical ultrafine SiO2 wall masks 10 nm wide and 90 nm high with 33 nm in space have been successfully fabricated for the first time. The dimensions of width and space become essentially smaller than the size of an electron beam resist pattern. The height is sufficient for ECR plasma etching. Si nanowires 10 nm wide and 18 nm thick have been precisely obtained by the ECR plasma etching of the thinned silicon-on-insulator layer using the vertical ultrafine SiO2 wall masks. The fabrication technology using the vertical ultrafine SiO2 wall masks has remarkable merits of fineness, scalability, and wide applicability. It can be utilized for fabricating various designed nanostructures.
Field emission microscopy study of cesium adsorbed on ZrB2 and TiB2
Authors: Hansen Marie , Hinrichs C. H.
Published: July 2002

Field emission microscopy was used to investigate the thermal desorption of cesium from ZrB2 and TiB2 surfaces. Described is a method of extracting the work function and effective emitting area from the Fowler–Nordheim data with minimum assumptions. Work functions were measured after heating at successively higher desorption temperatures, assuming a value of 2.2 eV for the cesium saturated surface. The minimum value of the work function for the cesium coated ZrB2 surface was 2.04±0.1 eV, while that of the TiB2 surface was 1.74±0.05 eV. Average work functions of the thermally cleaned ZrB2 and TiB2 surfaces were found to be 3.78 eV and 5.44 eV, respectively. Activation energies for thermal desorption of cesium from ZrB2 and TiB2 were found to be 1.1±0.1 and 0.71±0.2 eV, respectively.
Effect of Coulomb interaction and pKa on acid diffusion in chemically amplified resists
Authors: Shi Xuelong
Published: July 2002

Acid diffusion plays an important role in chemically amplified resists. Acids are generated from acid generators upon deep ultraviolet light (DUV) irradiation. Physically, what the DUV illumination creates is an electrolyte solution in a nonequilibrium state. In addition to the force due to the concentration gradient, a charged particle undergoing diffusion motion experiences a dielectric friction force from the medium and the Coulomb force created by the surrounding charged particles. The Coulomb force between charged particles can be very important in a medium with a low dielectric constant. In such a case, the diffusivity of the counter ion can have a great impact on the “effective diffusivity” of the acid. The diffusion of acid and its counter ion are correlated strongly. Besides the Coulomb interaction, the acid-base chemical equilibrium also affects acid diffusion. In this article, a simple model of acid diffusion including the effects of acid-base equilibrium and Coulomb interaction is proposed. The theory proposed here shows that the “effective” acid diffusivity is mainly determined by the diffusivity of its counter ion, which can account for the acid generator size effect on acid diffusion observed in experiments.
High barrier iridium silicide Schottky contacts on Si fabricated by rapid thermal annealing
Authors: Sanz-Maudes J. , Jiménez-Leube F. J. , Clement M.
Published: July 2002

The silicidation of iridium layers by rapid thermal annealing as a function of temperature and processing time is studied for both vacuum and argon atmosphere. The electrical properties of the resulting IrSi/n-type Si diodes are determined and related to the interface properties. I–V–T spectroscopy allows us to detect interface modifications even in the case where other diagnostics cannot be employed. Rapid thermal annealing (RTA) vacuum annealed diodes show inhomogeneous potential distribution at the metal–semiconductor interface. This is related with the coexistence of different metallurgical phases (Ir, IrSi, and IrSi1.75) at the interface as a consequence of the thermal treatments. The estimated value for the Schottky barrier height of the IrSi1.75 is 0.7 eV. In contrast, RTA argon annealed diodes show more reproducible characteristics. The main effect of the reaction atmosphere is to slow down the reaction rate as well as to inhibit the IrSi1.75 formation. This could be related with the residual oxygen contents of the reaction atmosphere. RTA argon annealing at 500 °C during 5 min is a reliable procedure for homogeneous IrSi infrared Schottky barrier detectors fabrication that can be employed in an industrial environment.
Emission stability of a diamond-like carbon coated metal-tip field emitter array
Authors: Jung Jae Hoon , Ju Byeong Kwon , Lee Yun Hi , Jang Jin , Oh Myung Hwan
Published: July 2002

The emission stability of Mo-tip field emitter arrays (FEAs) has been improved. The effect of diamond-like carbon (DLC) films deposited using a layer-by-layer technique using plasma enhanced chemical vapor deposition on the electron emission characteristics of Mo-tip FEAs was examined. The turn-on voltage was lowered from 80 V for Mo-tip FEAs to 65 V for DLC-coated Mo-tip FEAs, and the maximum emission current increased from 140 μA for Mo-tip FEAs to 320 μA for DLC-coated Mo-tip FEAs composed of 900 emitters. An anode current for DLC-coated Mo-tip FEAs and Mo tip of 0.1 μA per emitter was measured at gate voltages of about 87 and 107 V, respectively. The emission current of DLC-coated Mo-tip FEAs is more stable than that of Mo-tip FEAs.
Performance of electrophoretic deposited low voltage phosphors for full color field emission display devices
Authors: Jin Y. W. , Jang J. E. , Yi W. K. , Jung J. E. , Lee N. S. , Kim J. M. , Jeon D. Y. , Hong J. P.
Published: July 2002

Electrophoretic deposition of low voltage phosphors was successfully carried out on patterned indium–tin–oxide glass in order to develop prototype full color field emission display devices. The optimized suspension consisted of 2–3 μm size color phosphors in isopropyl alcohol, and mixed La(NO3)2 and Al(NO3)2 salts for the best display panel images. The ZnS:Cu, Al, ZnS:Ag, Cl, and Y2O2S:Eu phosphors were used to produce primary green, blue, and red colors, respectively. The compositional and structural analysis of the phosphors was performed and basic deposition parameters, such as deposition time and applied voltages, were systematically investigated in order to obtain the desirable brightness in real panels. A uniform thickness of about 4–9 μm was achieved over a whole 4 in. glass plate, depending on the electrical properties of each phosphor. Finally, the deposited phosphors were extensively characterized by a scanning electron microscopy, three-dimensional surface analysis.
Modeling of field emission microtriodes with Si semiconductor emitters
Authors: Nicolaescu Dan , Filip Valeriu , Itoh Junji , Okuyama Fumio
Published: July 2002

Field emission arrays using Si semiconductor emitters have been developed using different technologies and configurations, including the field emission microtriode (FEMT). Previously reported modeling results for FEMT structures considered metallic tips and, accordingly, used the Fowler–Nordheim (FN) current density–electric field J(E) relationship. In this article, modified JSi(E) equations for Si semiconductor emitters are used. The FEMT model takes into account a volcano-shaped gate with an emitter protruding through the gate opening. The electric field distribution in the device is numerically computed solving the two-dimensional Laplace equation for the electrical potential using a lattice with a varying grid size. The field emission current is obtained through integration of JSi(E) over the emitter surface. No field enhancement and area factors are used. The FEMT field emission current is computed as function of the device parameters, and is compared to “standard” results derived using the FN J(E) relationship. Similar modeling trends are obtained for the cases of FEMTs with metal and Si emitters.
Theoretical study of thermal instability of Mo tips with and without diamond coatings
Authors: Yu Z. X. , Wu S. S. , Xu N. S.
Published: July 2002

Thermal effects in molybdenum tips with and without diamond coatings are analyzed. An attempt is made to identify “intrinsic” mechanisms that might trigger catastrophic vacuum breakdown. A new theoretical treatment is employed to study the thermal response of tip emitters which takes into account the correlative effect between field emission and its resultant temperature rise at the tip. In both uncoated and chemically vapor deposited diamond coated Mo tip emission regimes, the location of the hot spot is found to be at the tip apex. It is also shown that higher emission current densities can be obtained from a coated tip before the melting temperature of Mo is reached compared to that of an uncoated tip for the same geometry and dimension.
Fabrication of tungsten-coated silicon-based gated emitters
Authors: Chen L. , El-Gomati M. M.
Published: July 2002

The present work reports on the fabrication of tungsten-coated silicon-based gated emitters. The main fabrication procedures include: forming silicon tips by way of reactive ion etching without thermal oxidation sharpening, tungsten coating and dielectric layer coating though plasma-enhanced chemical vapor deposition, metal layer coating by evaporation, and gate aperture opening by wet chemical etching processes. Scanning electron microscopy in combination with energy dispersive x-ray analysis were employed to study the emitters during the fabrication. The radii of the tungsten-coated tips were about 30 nm. The gated emitters have a volcano shape with gate aperture diameter of less than 3 μm and a silicon dioxide insulating layer 1 μm thick. The gated field emitters exhibited a low turn-on voltage of about 60 V. Emission current above 15 μA from a single emitter was observed. Fowler–Nordheim plots of the emitted current from these emitters confirmed the field emission behavior.
Novel nanoscale field emission structures: Fabrication technology, experimental, and calculated characteristics
Authors: Tatarenko N. I. , Solntsev V. A. , Rodionov A. N.
Published: July 2002

The experimental and calculation characteristics for nanoscale field emission arrays (FEAs) fabricated on the basis of a new technology and with the tip packaging density of up to 4×1010 tips/cm2 have been given. The process of fabricating these structures is described. The I–V characteristics of the nanoscale FEAs, measured both in vacuum with the 300 μm between electrode distance and in air at atmospheric pressure in the thin-film two-electrode device with the 150 nm between electrode distance, are given. By means of a modified computer program based on the method of nets and the “zooming” algorithm the electric field gain, the tip field, and the structure capacitance have been calculated. Their values correspond well to the experimental data obtained by measuring the structure capacitance and I–V characteristics. The calculation of the field has been done for two field emission arrays with the different typical geometry. The data experimentally obtained and calculated by us illustrate that further development of the new field emission nanostructure electronics seem to be very promising.
Study of instability in the field electron emission from amorphous diamond films
Authors: Chen J. , Deng S. Z. , Zhen X. G. , Xu N. S.
Published: July 2002

Details are given of an experimental study of the current–voltage characteristics and instability of the field electron emission from amorphous diamond films prepared using a magnetic field-filtered ion deposition technique. A switch-on phenomenon is observed, and two types of instability are found, i.e., fluctuation at low currents and an abrupt change in emission associated with local breakdown events at high currents. Finally, it is found that, in order to establish stable emission with a current density approaching 50 mA/cm2, it is necessary to undergo the switch-on and local breakdown processes. These phenomena are characterized, and the physical mechanisms responsible for them are proposed.
High field characteristics of thin-film metal electrodes
Authors: Ma Xianyun , Muzykov P. G. , Sudarshan T. S.
Published: July 2002

In order to investigate prebreakdown and breakdown characteristics of micrometric vacuum gaps relevant to field emission displays, a specially designed thin film electrode structure, easy to fabricate, was developed to closely simulate electrode gaps in field emission displays (FEDs). An extra-low light detection three-dimensional-imaging system using an intensified charge-coupled device camera was used to diagnose and record the different prebreakdown phases and the breakdown between planar metal film electrodes. Experimental results showed that the prebreakdown activity occurred mostly along the edge of the smaller diameter electrode and obeyed Fowler–Nordheim behavior. Breakdown of the gap at relatively larger gap distances (750 μm) caused damage to the thin-film electrodes; there was no significant damage for small gap distances (250 μm). The extent of electrode damage strongly depended on the film deposition temperature and was believed to be caused by the high-energy electron bombardment. The hold-off voltage of thin-film vacuum gaps was relatively high (>18.0 kV for a Ni/Cr 750 μm gap) which could be improved significantly by direct current glow discharge treatment. The insulation capability of such a vacuum gap was mainly limited by the edge effect and the thin-film quality. The high field characteristics of micrometric thin-film gaps, relevant to FEDs, are reported for the first time in the literature. These results can be used to define the theoretical limits to which actual gaps can be stressed in vacuum microelectronic devices and provide a basis for the design of the phosphor anode and the gate edges of the FEAs.
Analysis of a field-emission magnetic sensor with compensated electron-beam deviation
Authors: Marqués M. I. , Serena P. A. , Nicolaescu D. , Itoh J.
Published: July 2002

A new concept magnetic sensor is proposed and its operation is analyzed using a numerical model. The sensor comprises an array of integrated electron emitters, each one with the tip at potential Vt, and two deflection electrodes at potentials +Vd/2 and −Vd/2. The deflection of the beam due to the Lorentz force can be compensated by a suitable choice of the electric field formed between the electrodes. In this way, a correlation Vd(B) between the electron deflection compensating voltage Vd and the magnetic-field B to be measured is obtained. A linear relationship Vd(B) has been outlined, its slope depending on both the tip–anode difference of potential and the geometrical parameters of the system.
Plasma-based Ion Implantation Facility and Research at the National Accelerator Centre, Faure
Authors: Prozesky V. M. , Meyer K. , Alport M. , Comrie C.
Published: July 2002

A new plasma-based ion implantation (PBII) facility consisting of a dedicated PBII chamber plus characterization equipment has been established at the Van de Graaff Group, National Accelerator Centre, Faure. The implantation unit has an aluminum vacuum chamber with a volume of 1 m3, and it incorporates conventional plasma generation capability for gas plasmas, such as a set of multifilaments. The implantation power supply is capable of delivering 30 kV, with a pulse duration of up to 1000 μs, and a repetition rate of 1 kHz. This allows a maximum average load of 12 J to the target. The facility is being used at the outset for the fundamental study of plasmas, time-dependent x-ray generation during the implantation pulse, and plasma immersion implantation. The facility is supported by a 6 MV Van de Graaff accelerator equipped with the ion-beam analytical tools necessary for characterization of modified surfaces.
Amorphous carbon films for use as both variable-transmission apertures and attenuated phase shift masks for deep ultraviolet lithography
Authors: Windt David L. , Cirelli Raymond A.
Published: July 2002

We describe the development of amorphous carbon (a-C) films grown by magnetron sputtering for use in optical elements for sub-0.25-μm deep ultraviolet (DUV) lithography. We have measured the transmittance of a-C films deposited onto quartz substrates as a function of film thickness, and find that the films are ideally suited for use in variable-transmission apertures that can be used to improve DUV process latitude: we can achieve essentially any transmittance (T) desired in the range 0<T<100% by controlling the film thickness (t) in the range 200>t>0 nm with subnanometer precision. We also find that the transmittance remains stable after prolonged exposure to high intensity DUV radiation. We describe a masked deposition technique to produce variable-transmission apertures using a-C films of various thicknesses, and also discuss the use of these films in attenuated phase shift masks, given that we can simultaneously achieve ∼6%–8% transmittance and a phase shift of 180° at either λ=248 nm or 193 nm.
Role of film conformality in charging damage during plasma-assisted interlevel dielectric deposition
Authors: Hwang Gyeong S. , Giapis Konstantinos P.
Published: July 2002

While observations of charging damage during plasma-assisted deposition have been erratic thus far, concern abounds that it may worsen as aspect ratios increase and high-density plasmas are used more frequently. Simulations of pattern-dependent charging during interlevel dielectric deposition reveal that the initial conformality of the dielectric film plays a crucial role in metal line charge up and the subsequent degradation to the buried gate oxide, to which the metal line is connected. For moderate aspect ratios, significant charging damage occurs for nonconformal step coverage.
Formation of W underlayer by switching bias sputtering to plug 0.25 μm contact holes
Authors: Onuki Jin , Nihei Masayasu , Suwa Masateru , Goshima Hidekazu
Published: July 2002

Physical vapor deposion by a newly developed switching bias sputtering method for the formation of both adhesion and barrier metal underlayers on 0.25 μm contact/via holes with sufficient step coverage has been investigated as a hole filling process. The method features alternating operation of sputtering to deposit and resputtering of the film to enhance step coverages of the side walls by resputtering of the bottom. It was found that W films formed for holes with aspect ratios of 3.0–3.5 gave step coverages of 17%–23% for the side wall and 30%–33% for the bottom. The resistivity of W films deposited on planar surfaces was 10.5 μΩ cm, similar to values for W films deposited by conventional direct current (dc) sputtering. The deposition rate of the sputtering was 50%–80% of the rate of conventional dc sputtering.
Novel lateral field emission device fabricated on silicon-on-insulator material
Authors: Yun Minhee , Turner Anthony , Roedel Ronald J. , Kozicki Michael N.
Published: July 2002

A field emission device which shows very low turn-on voltage with large electrode spacing has been fabricated by applying KOH orientation-dependent etching to single crystal silicon. Aqueous KOH solutions create sharp angular structures bounded by (111) planes at an angle 54.74° from the (100) surface. Using this technique, “self-sharpening” tips were formed on silicon-on-insulator wafers. This process can be used to form lateral sharp edges that can act as both the cathode and the anode in a field emission device. The shapes of the tips were determined using transmission electron microscopy and the smallest emitter tip radius in this study was estimated to be 3 nm. These sharp emitters enable significant electron emission at low turn-on voltage even for large spacing between the emitter and the collector. The lowest turn-on voltage was found to be 27 V with emission currents of 10 μA at 1 μm spacing. Electron emission was observed even at an electrode spacing larger than 2 μm. The field enhancement factor (β) and field emission area (α) have been calculated using the Fowler-Nordheim equation. As expected, the field enhancement factor decreases with increasing electrode spacing. Failure mechanisms for the devices associated with high electric field are also discussed in this article.
Studies on the interfacial etching reaction of development-free vapor photolithography
Authors: Hong Xiaoyin , Lu Jianping , Duan Shengquan , Chen Qidao , Wang Peiqing
Published: July 2002

Development-free vapor photolithography (DFVP) is an all-dry pattern transfer technique, which is based on the reaction of SiO2 with HF vapor under a polymer film in the presence of catalysts, called accelerators, at a temperature above 100 °C. This article reports that both organic bases and superacids can catalyze this interfacial etching reaction. When organic bases are used as the accelerator, the etching mechanism is bimolecular nucleophilic substitution (SN2), while the superacid-catalyzed etching reaction undergoes a unimolecular nucleophilic substitution (SN1) mechanism. Insight gained from this study provides guidance for the development of more sensitive accelerator systems. Now, this novel microlithographic technique is being successfully applied to the manufacture of power electronic devices.
Damage generation and removal in the Ga+ focused ion beam micromachining of GaN for photonic applications
Authors: Chyr Irving , Lee Boon , Chao L. C. , Steckl A. J.
Published: July 2002

We have investigated focused ion beam (FIB) micromachining of GaN films with the goal of fabricating distributed Bragg reflection air/GaN gratings for short cavity lasers. The FIB micromachining process creates damage in the GaN film. To reduce the damage evidenced in the GaN photoluminescence (PL) spectrum, we utilized both furnace annealing for 1 h and rapid thermal annealing (RTA) from 10 to 50 s at 1050 °C. Pulsed nitrogen and He–Cd lasers have been utilized as excitation sources to study differences in the PL spectra from the FIB-milled distributed Bragg reflector (DBR) gratings and the nonmilled GaN film. Surface roughness does not change with increasing annealing time of RTA. The threshold pumping condition has been investigated to compare the DBR grating area with as grown GaN film. We found that the threshold pumping intensity for these two conditions are almost the same, i.e., FIB micromachining followed by thermal anneal would not degrade the PL spectrum performance of GaN film.
Extension of deep-ultraviolet lithography for patterning logic gates using alternating phase shifting masks
Authors: Kuo Chen-Cheng , Lin Chia-Hui , Lin Hua-Tai , Yen Anthony
Published: July 2002

We present the combination of alternating phase-shifting masks and rule-based optical proximity correction (OPC) for the patterning of 0.13 μm polysilicon gate lines. Using the optimal process condition, a process window with 1.2 μm of depth of focus (DOF) and 15% exposure latitude is obtained for 0.13 μm isolated lines in resist. In addition, with the application of rule-based OPC, the common DOF for 0.13 μm lines of various line-to-space ratios can be improved from 0 to 0.6 μm.
Measuring electron-beam landing angle in real time
Authors: Sturans M. A. , Hartley J. G. , Kendall R. A.
Published: July 2002

With the ever increasing need for higher resolution and placement accuracy in mask making, the requirement for eliminating position shifts due to target height variations is becoming a critical factor in the overall image placement error budget. In theory this problem has been eliminated with the IBM patented variable axis immersion lens which can achieve perpendicular landing in all parts of the major magnetic field as well as in the electrostatically deflected subfield. The initial setup and periodic checks, however, require very high accuracy measurements. In the past we have relied on a tedious method which involves exposure and detection of registration marks at various heights, in conjunction with a very accurately calibrated laser stage, followed by position measurements with a state-of-the-art metrology tool. In this article we describe a method which makes this measurement with high accuracy, in real time, using a standard oscilloscope display.
Round-off of trench corner by post-cylindrical molecular pump sidewall oxidation for 0.25 μm and beyond technologies
Authors: Chung Y. S. , Jeon C. W. , Kim J. H. , Han S. K. , Hwang J. W. , Kim S. Y. , Lee J. G. , Hyun I. S.
Published: July 2002

A post-cylindrical molecular pump (CMP) sidewall oxidation (PCSWO) has been developed for the shallow trench isolation (STI) process of 0.25 μm and beyond complementary metal–oxide–semiconductor technologies. One of the most important factors of STI is a round-off of trench top corners without the loss of active area. The conventional STI process usually requires a wall oxidation after trench etch to round off and also an annealing to densify a gap-filled oxide. But PCSWO simplifies the STI process by applying sidewall oxidation and annealing simultaneously. The trench was filled with HDP oxide without the conventional wall oxidation after trench etch. After CMP, post-CMP wall oxide was thermally grown to round off the trench corner at the high temperature of 1100 °C. The high temperature wall oxidation has an annealing effect for HDP oxide, which releases a residual film stress. The anomalous subthreshold conduction of the shallow trench isolated metal–oxide–semiconductor field effect transistors as the so called “kink effect” due to field crowding at the active edge, was successfully eliminated even at the back bias of ±5 V. Isolation and diode characteristics of PCSWO-STI were comparable to those of the conventional STI. Gate oxide reliabilities of PCSWO-STI were similar to those of the conventional STI.
Process interactions between low-energy ion implantation and rapid-thermal annealing for optimized ultrashallow junction formation
Authors: Murrell A. J. , Collart E. J. H. , Foad M. A. , Jennings D.
Published: July 2002

The shallow doping requirements for the next 2–3 device generations can be satisfied by a combination of low-energy ion implantation and rapid-thermal anneal. However, the differing requirements of distinct types of devices preclude the definition of a single optimized process. To tailor the junction properties according to device type and geometry, requires an understanding of the effects of process parameters in both implant and anneal steps. In describing the interactions and mechanisms behind this optimization, a number of tradeoffs are highlighted: (i) The choice of implant energy and dose may be traded off against the anneal time–temperature profile. (ii) The benefits of preamorphization to reduce ion channeling are offset by the detrimental increase in transient-enhanced diffusion and dopant segregation. (iii) The use of oxygen in the anneal ambient is discussed in terms of its effects on diffusion versus dopant loss at the surface.
Field emitter array fabricated using focused ion and electron beam induced reaction
Authors: Yavas O. , Ochiai C. , Takai M. , Park Y. K. , Lehrer C. , Lipp S. , Frey L. , Ryssel H. , Hosono A. , Okuda S.
Published: July 2002

A dual beam system consisting of focused ion and electron beams was used for manufacturing of Nb-gated silicon field emitter arrays. Gate opening was produced either by reactive focused ion beam etching of both the niobium and the silicon dioxide layer or by physical sputtering of the niobium layer by focused ion beam and subsequent wet etching of the underlying silicon dioxide layer. Platinum tips were deposited into the gate opening using an electron beam induced chemical reaction. Prototype devices, which exhibit field emission, were produced successfully. Several process parameters such as ion dose, beam diameter, and etch duration were systematically varied to identify the optimum condition for the fabrication of field emitter arrays.
SiC field emitter arrays fabricated by transfer mold technique
Authors: Górecka-Drzazga A. , Dziuban J. , Prociów E.
Published: July 2002

The field emission arrays of SiC sharp emitter tips have been produced for the first time by use of the transfer mold technique. The test structures of active gun, containing approximately 3×104 of emitters, were prepared. The field emission current and work function calculations for SiC emitter arrays have been presented.
Bond strain, chemical induction, and OH incorporation in low-temperature (350–100 °C) plasma deposited silicon dioxide films
Authors: Gupta A. , Parsons G. N.
Published: July 2002

New device concepts are being considered with very demanding requirements for low-temperature processing. In this article, infrared transmission and ellipsometry is used to compare silicon oxide films formed by plasma chemical vapor deposition using SiH4, N2O, and either He or H2 dilution gas between 350 and 100 °C. The Si–O asymmetric stretching mode is affected by bond strain and chemical induction, and monitoring the Si–O peak position gives insight into the effect of process conditions on local bond structure. Hydrogen is expected to affect surface processes during growth, for instance, to enable the removal of surface SiOH bonds through H-mediated abstraction, leading to improved bonding structure at low temperature. We find that exposing the surface to hydrogen atoms during growth helps eliminate isolated SiOH bonds, leading to Si–Si bond formation. However, an increase in associated SiOH bonding groups, stabilized by hydrogen bonding, is also observed. The density of associated SiOH groups is larger at low temperature where the rate of water desorption is reduced, suggesting that the associated OH is formed by physisorbed water produced during OH removal. Films deposited with hydrogen dilution show somewhat improved electrical performance at <200 °C, but further work is required to produce high quality films at very low temperatures.
Phase-Coherent Optical Pulse Synthesis from Separate Femtosecond Lasers
Authors: Shelton Robert K. , Ma Long-Sheng , Kapteyn Henry C. , Murnane Margaret M. , Hall John L. , Ye Jun
Published: July 2002

We generated a coherently synthesized optical pulse from two independent mode-locked femtosecond lasers, providing a route to extend the coherent bandwidth available for ultrafast science. The two separate lasers (one centered at 760 nanometers wavelength, the other at 810 nanometers) are tightly synchronized and phase-locked. Coherence between the two lasers is demonstrated via spectral interferometry and second-order field cross-correlation. Measurements reveal a coherently synthesized pulse that has a temporally narrower second-order autocorrelation width and that exhibits a larger amplitude than the individual laser outputs. This work represents a new and flexible approach to the synthesis of coherent light.
Delineation of mRNA Export Pathways by the Use of Cell-Permeable Peptides
Authors: Gallouzi Imed-Eddine , Steitz Joan A.
Published: July 2002

The transport of messenger RNAs (mRNAs) from the nucleus to the cytoplasm involves adapter proteins that bind the mRNA as well as receptor proteins that interact with the nuclear pore complex. We demonstrate the utility of cell-permeable peptides designed to interfere with interactions between potential adapter and receptor proteins to define the pathways accessed by particular mRNAs. We show that HuR, a protein implicated in the stabilization of short-lived mRNAs containing AU-rich elements (AREs), serves as an adapter for
c-fos
mRNA export through two pathways. One involves the HuR shuttling domain, HNS, which exhibits a heat shock–sensitive interaction with transportin 2 (Trn2); the other involves two protein ligands of HuR—pp32 and APRIL—which contain leucine-rich nuclear export signals (NES) recognized by the export receptor CRM1. Heterokaryon and in situ hybridization experiments reveal that the peptides selectively block the nucleocytoplasmic shuttling of their respective adapter proteins without perturbing the overall cellular distribution of polyadenylated mRNAs.
A Microphysical Connection Among Biomass Burning, Cumulus Clouds, and Stratospheric Moisture
Authors: Sherwood Steven
Published: July 2002

A likely causal chain is established here that connects humidity in the stratosphere, relative humidity near the tropical tropopause, ice crystal size in towering cumulus clouds, and aerosols associated with tropical biomass burning. The connections are revealed in satellite-observed fluctuations of each quantity on monthly to yearly time scales. More aerosols lead to smaller ice crystals and more water vapor entering the stratosphere. The connections are consistent with physical reasoning, probably hold on longer time scales, and may help to explain why stratospheric water vapor appears to have been increasing for the past five decades.
Alternative Splicing and Neuritic mRNA Translocation Under Long-Term Neuronal Hypersensitivity
Authors: Meshorer Eran , Erb Christina , Gazit Roi , Pavlovsky Lev , Kaufer Daniela , Friedman Alon , Glick David , Ben-Arie Nissim , Soreq Hermona
Published: July 2002

To explore neuronal mechanisms underlying long-term consequences of stress, we studied stress-induced changes in the neuritic translocation of acetylcholinesterase (AChE) splice variants. Under normal conditions, we found the synaptic AChE-S mRNA and protein in neurites. Corticosterone, anticholinesterases, and forced swim, each facilitated a rapid (minutes), yet long-lasting (weeks), shift from AChE-S to the normally rare AChE-R mRNA, promoted AChE-R mRNA translocation into neurites, and induced enzyme secretion. Weeks after stress, electrophysiological measurements in hippocampus slices displayed apparently normal evoked synaptic responses but extreme hypersensitivity to both anticholinesterases and atropine. Our findings suggest that neuronal hypersensitivity under stress involves neuritic replacement of AChE-S with AChE-R.
A Long Pollen Record from Lowland Amazonia: Forest and Cooling in Glacial Times
Authors: Colinvaux P. A. , De Oliveira P. E. , Moreno J. E. , Miller M. C. , Bush M. B.
Published: July 2002

A continuous pollen history of more than 40,000 years was obtained from a lake in the lowland Amazon rain forest. Pollen spectra demonstrate that tropical rain forest occupied the region continuously and that savannas or grasslands were not present during the last glacial maximum. The data suggest that the western Amazon forest was not fragmented into refugia in glacial times and that the lowlands were not a source of dust. Glacial age forests were comparable to modern forests but also included species now restricted to higher elevations by temperature, suggesting a cooling of the order of 5° to 6°C.
Germanyl and Silyl Cations--Free at Last
Authors: von Ragué Schleyer Paul
Published: July 2002

Chemists have long sought to duplicate the rich chemistry of carbon compounds with the related elements silicon and germanium. In his Perspective, Schleyer discusses work published in the same issue by Sekiguchi
et al
. (
p. 60
) in which free cations containing germanium, an elusive target of organic chemists, have been synthesized.
Functional Specificity Among Hsp70 Molecular Chaperones
Authors: James Philip , Pfund Christine , Craig Elizabeth A.
Published: July 2002

Molecular chaperones of the 70-kilodalton heat shock protein (Hsp70) class bind to partially unfolded polypeptide substrates and participate in a wide variety of cellular processes. Differences in peptide-binding specificity among Hsp70s have led to the hypothesis that peptide binding determines specific Hsp70 functions. Protein domains were identified that were required for two separate functions of a yeast Hsp70 family. The peptide-binding domain was not required for either of these specific Hsp70 functions, which suggests that peptide-binding specificity plays little or no role in determining Hsp70 functions in vivo.
El Niño and Infectious Disease
Authors: Yang X. B. , Scherm Harald
Published: July 2002

The idea that climatic cycles such as the El Niño/Southern Oscillation significantly affect infectious disease, raised by Rita R. Colwell (Association Affairs, 20 Dec., p
2025
) in the context of cholera outbreaks, is supported by recent findings from veterinary, entomological, and botanical epidemiology (
1
,
2
).

Botanical epidemiologists have found that plant systems have unique advantages for macro-scale, long-term epidemiological studies. Weather and climate are important driving forces affecting plant disease development. For example, the U.S. Department of Agriculture's annual cereal rust survey, a program started in 1917 to monitor rust outbreaks over North America, accumulates time series of disease intensity, yield loss, and races of rust fungi in cereal crops (
3
). With these data, consistent and significant coherence patterns between El Niño and wheat rust intensity have been found in both the Eastern and Western hemispheres (
2
).

Studies of El Niño-disease associations and their underlying mechanisms could lead to the development of early warning systems. Colwell advocates the use of satellite surveillance for predicting cholera outbreaks, while others propose using El Niño forecasts for malaria alerts (4). Outbreaks of wheat scab in eastern China can be predicted successfully 4 months in advance by measuring sea surface temperatures in the central Pacific (R2 = 0.86; P < 0.001) (5); the mechanism for this association is thought to be the El Niño-dependent advance of the summer monsoon through East Asia, whereby increased precipitation causes increased infection by the scab pathogen. El Niño-disease studies are important also in the context of climate change research: infectious diseases driven by multiyear climatic cycles are likely to respond to slow, decadal changes in climate as well.
Measurement of Parity Nonconservation and an Anapole Moment in Cesium
Authors: Wood C. S. , Bennett S. C. , Cho D. , Masterson B. P. , Roberts J. L. , Tanner C. E. , Wieman C. E.
Published: July 2002

The amplitude of the parity-nonconserving transition between the 6
S
and 7
S
states of cesium was precisely measured with the use of a spin-polarized atomic beam. This measurement gives Im(E1
pnc
)/β = −1.5935(56) millivolts per centimeter and provides an improved test of the standard model at low energy, including a value for the
S
parameter of −1.3(3)
exp
(11)
theory
. The nuclear spin-dependent contribution was 0.077(11) millivolts per centimeter; this contribution is a manifestation of parity violation in atomic nuclei and is a measurement of the long-sought anapole moment.
Amphibian Limb Regeneration: Rebuilding a Complex Structure
Authors: Brockes Jeremy P.
Published: July 2002

The ability to regenerate complex structures is widespread in metazoan phylogeny, but among vertebrates the urodele amphibians are exceptional. Adult urodeles can regenerate their limbs by local formation of a mesenchymal growth zone or blastema. The generation of blastemal cells depends not only on the local extracellular environment after amputation or wounding but also on the ability to reenter the cell cycle from the differentiated state. The blastema replaces structures appropriate to its proximodistal position. Axial identity is probably encoded as a graded property that controls cellular growth and movement through local cell interactions. The molecular basis is not understood, but proximodistal identity in newt blastemal cells may be respecified by signaling through a retinoic acid receptor isoform. The possibility of inducing a blastema on a mammalian limb cannot be discounted, although the molecular constraints are becoming clearer as we understand more about the mechanisms of urodele regeneration.
Nucleosome Mobility and the Maintenance of Nucleosome Positioning
Authors: Pazin Michael J. , Bhargava Purnima , Geiduschek E. Peter , Kadonaga James T.
Published: July 2002

To study nucleosome mobility and positioning, the R3
lac
repressor was used with an adenosine triphosphate (ATP)–dependent chromatin assembly system to establish the positioning of five nucleosomes, with one nucleosome located between two R3
lac
operators. When R3 protein was dissociated from DNA with isopropyl β-
d
-thiogalactopyranoside, the R3-induced nucleosome positions remained unchanged for at least 60 minutes in the absence of ATP but rearranged within 15 minutes in the presence of ATP. These results suggest that nucleosomes are dynamic and mobile rather than static and that a DNA binding factor is continuously required for the maintenance of nucleosome positioning.
Essential Role of Growth Hormone in Ischemia-Induced Retinal Neovascularization
Authors: Smith Lois E. H. , Kopchick John J. , Chen Wen , Knapp Joanne , Kinose Fumi , Daley Douglas , Foley Eliot , Smith Roy G. , Schaeffer James M.
Published: July 2002

Retinal neovascularization is the major cause of untreatable blindness. The role of growth hormone (GH) in ischemia-associated retinal neovascularization was studied in transgenic mice expressing a GH antagonist gene and in normal mice given an inhibitor of GH secretion (MK678). Retinal neovascularization was inhibited in these mice in inverse proportion to serum levels of GH and a downstream effector, insulin-like growth factor–I (IGF-I). Inhibition was reversed with exogenous IGF-I administration. GH inhibition did not diminish hypoxia-stimulated retinal vascular endothelial growth factor (VEGF) or VEGF receptor expression. These data suggest that systemic inhibition of GH or IGF-I, or both, may have therapeutic potential in preventing some forms of retinopathy.
Water on the Sun: Line Assignments Based on Variational Calculations
Authors: Polyansky Oleg L. , Zobov Nikolai F. , Viti Serena , Tennyson Jonathan , Bernath Peter F. , Wallace Lloyd
Published: July 2002

The infrared spectrum of hot water observed in a sunspot has been assigned. The high temperature of the sunspot (3200 K) gave rise to a highly congested pure rotational spectrum in the 10-micrometer region that involved energy levels at least halfway to dissociation. Traditional spectroscopy, based on perturbation theory, is inadequate for this problem. Instead, accurate variational solutions of the vibration-rotation Schrödinger equation were used to make assignments, revealing unexpected features, including rotational difference bands and fewer degeneracies than anticipated. These results indicate that a shift away from perturbation theory to first principles calculations is necessary in order to assign spectra of hot polyatomic molecules such as water.