bluuebunny/crossref_metadata_2025 huggingface dataset:
Moderately in situ phosphorus-doped polycrystalline silicon by single wafer reduced pressure chemical vapor deposition
Authors: Violette Katherine E. , Wise Rick L.
Published: July 2002

A study of moderately in situ doped polycrystalline silicon deposition from SiH4, PH3, and H2 by single-wafer reduced pressure chemical vapor deposition has been carried out. The process window which yielded P concentrations on the order of 1019 cm−3 was a pressure of 80 Torr in a hydrogen carrier with a PH3/SiH4 mole fraction range of 0.1×10−4–1×10−4, and temperatures of 600–700 °C. It was found that the PH3/SiH4 mole fraction in this process window has little effect on the deposition rate unlike the rate reduction caused by PH3 in a saturation-doped polysilicon process with doping levels in excess of 1020 cm−3. The activation energy of the process, 48 kCal mol−1, over this temperature range approaches one of a hydrogen desorption limited process, 49 kCal mol−1, suggesting that the deposition rate is dominated by the high H2 pressure. The transition of the as-deposited film structure from predominately amorphous to completely polycrystalline occurs at about 675 °C, about 100 °C higher than in typical low-pressure chemical vapor deposition and is likely due to a combination of high H2 pressure and high deposition rates. To a first order, the post-anneal film resistivity appears to be dominated by the grain structure and not by the P incorporation rate in the moderately doped concentration regime.
Investigation of Ge on Si(100) quantum wells by photoelectron spectroscopies
Authors: Di Gaspare L. , Capellini G. , Cianci E. , Evangelisti F.
Published: July 2002

In the present work we report on the evolution of the electronic states as a function of Ge overlayer thickness ranging from a fraction of a monolayer to few tens of monolayers. The Ge states above the Si valence band top could be clearly detected at every overlayer thickness d. For d<∼6 Å, the Ge state density exhibits a double linear edge. Upon increasing the overlayer thickness the split between the two edges decreases and the double edge structure disappears for d>∼6 Å, i.e., at the critical thickness for the transition from strained to unstrained overlayers. For these larger thicknesses, the Ge edge becomes broad and featureless. The energy separation between the Ge onset and the Si valence top increases up to 0.70 eV at larger overlayer thicknesses.
Thick pure Ge films for photodetectors
Authors: Scarinci F. , Fiordelisi M. , Calarco R. , Lagomarsino S. , Colace L. , Masini G. , Barucca G. , Coffa S. , Spinella S.
Published: July 2002

Pure Ge/Si heterostructures were epitaxially grown on Si in order to obtain Si-integrated photodetectors in the near-infrared region. Samples grown with different procedures are compared. Graded buffer layers of Si1−xGex with x variable as a function of depth were grown in order to relax the stress. On top of these, pure Ge layers were grown. The mechanism of strain relaxation has been investigated by transmission electron microscopy and the surface morphology by scanning electron microscopy. The results on different samples are discussed and compared in terms of structural properties and photoresponse, in an attempt to correlate structural defects to photodetector efficiency.
Bromine ion-beam-assisted etching of InP and GaAs
Authors: Rossler J. M. , Royter Y. , Mull D. E. , Goodhue W. D. , Fonstad C. G.
Published: July 2002

Bromine ion-beam-assisted etching produces smooth vertical sidewalls in GaAs wafers with substrate temperatures in the range of 20–200 °C and smooth vertical sidewalls in InP wafers with substrate temperatures in the range of 150–200 °C. Etch rates can be varied from several nm/min to 0.16 μm/min through the bromine flow rate, Ar+ ion beam density and energy, and the substrate temperature. The etching rate ratios of bromine-only etching (no Ar+ ion beam) to argon ion-beam-assisted bromine etching to argon ion etching (no bromine) with an ion beam density of 40 μA/cm2 and ion beam energy of 500 V were measured to be 11.5:23:1 and 16:125:1 at a substrate temperature of 200 °C and 2:42:1 and 1:40:1 at a substrate temperature of 100 °C for GaAs and InP, respectively. Such rate enhancements were found to be typical with these materials. Bromine ion-beam-assisted etching also appears to have an advantage over chlorine ion-beam-assisted etching in that high anisotropy can be achieved with bromine in both the GaAs and the InP materials systems at substrate temperatures as high as 200 °C as compared to chlorine where the etching of GaAs is spontaneous and isotropic at temperatures above 150 °C.
Optimization of In0.53Ga0.47As reactive ion etching with CH4/H2 using design of experiment methods
Authors: Zavieh L. , Nordquist C. D. , Mayer T. S.
Published: July 2002

Optimization of etch depth and anisotropy of In0.53Ga0.47As by CH4/H2 reactive ion etching is investigated using a central composite experimental design. Etching characteristics are examined by considering the general trends and main effects of pressure, flow rate, and CH4 concentration factors on etch depth and sidewall profile responses. Predictive models are developed using regression analysis for etch depth and sidewall profile responses. These models can be used to predict with 95% confidence etch depth and sidewall profile within approximately 56 nm and 0.16 rad.
Layer by layer growth mode stabilization and step-edge smoothing of cation-stabilized In1−xGaxAs strained layers grown on InP
Authors: Robach Y. , Solére A. , Gendry M. , Porte L.
Published: July 2002

Scanning tunneling microscopy has been used to study the surface morphology of strained In1−xGaxAs layers (either 2% compressively or 2% tensilely strained for x=0.18 or x=0.75, respectively) grown by molecular beam epitaxy on (001) InP substrate under cation-stabilized conditions. Under such growing conditions a smooth two-dimensional (2D) surface morphology is well preserved until the onset of plastic relaxation. This behavior is completely unlike the 2D/3D growth mode transition observed under As-stabilized conditions of growth. Along with the 2D growth mode stabilization, a step-edge smoothing is also observed. These results are assigned to a high value of step formation free energy on (4×2) reconstructed surfaces. The resultant increase in surface tension delays the onset of coherent 3D island formation beyond the onset of plastic relaxation and stabilizes 2D growth.
Thermal stability of selective chemical vapor deposited tungsten contact and effects of in situ N2 plasma treatment
Authors: Wang M. T. , Wang P. C. , Chuang M. C. , Chen L. J. , Chen M. C.
Published: July 2002

This work investigates the thermal stability of Al/W/p+-n junction diodes, in which the W contact was filled using selective chemical vapor deposition to a thickness of about 450 nm and served as diffusion barrier between the Al and the Si substrate. The effects of in situ N2 plasma treatment on the barrier effectiveness were also investigated. The Al/W(450 nm)/p+-n junction diodes can sustain a 30 min furnace annealing up to 575 °C. With an in situ N2 plasma treatment on the W surface caused a thin layer of WNx to form on the W surface, and the nitrified layer of WNx/W acting as barrier between the Al and the Si substrate effectively suppressed WAl12 formation at elevated temperatures, resulting in a significant barrier improvement. N2 plasma treatment at 100 W for 300 s enabled the Al/WNx/W(450 nm)/p+-n junction diodes to sustain thermal annealing at temperatures up to 625 °C without degradation of electrical characteristics.
Aligned pipe arrays formation by silicon anodic etching
Authors: dos Santos M. C. , Teschke O.
Published: July 2002

A simple technique is described here that produces aligned curved or straight arrays of pipes. This opens the way to produce complete systems (electronic, photonic and fiber optic connectors) from silicon with large scale fabrication techniques. Our strategy in creating parallel pipes is to use high current densities (∼100 mA/cm2) silicon anodization in HF solutions, in a cell where the current direction and the preferential etching directions are not coincident in (111) silicon substrates. The etched structure in a nanoscale range was observed using atomic force microscopy, which shows steps. In a macroscopic scale steps were observed in the walls of arrays of tenths of millimeters diameter pipes. Pores arrays were obtained forming a ∼90° angle with the current direction. Molecular mechanics simulations of the pipe wall structure show that a preferential etching along the 〈100〉 direction and passivation of the (111) planes are the mechanisms responsible for the formation of pore arrays structure.
Perturbation solution for the interfacial oxidation of silicon
Authors: Mhetar Vijay R. , Archer L. A.
Published: July 2002

A new perturbation solution for the oxidation of silicon that properly accounts for diffusion of molecular oxygen and reaction kinetics at the silicon–silicon dioxide interface is presented. The perturbation treatment is based on the assumption of a dilute solution of O2 in SiO2 phase. We show that the solution obtained by Deal and Grove [J. Appl. Phys. 36, 3770 (1965)] is the zeroth perturbation solution and formally prove that it is a quasi-steady-state solution. In the limiting case of instantaneous reaction, the perturbation solution is shown to be equivalent to the result obtained by Peng, Wang, and Slattery [J. Vac. Sci. Technol B 14, 3316 (1996)]. The proposed perturbation scheme is developed here for first-order reaction kinetics, but can easily be extended to other rate expressions. The higher order corrections offered to Deal and Grove model predictions might provide a needed method for assessing the error incurred when these predictions are used to estimate oxide film thickness in practical situations.
Interface states induced in GaAs by growth interruption during an in situ process
Authors: Wakaya F. , Matsubara T. , Nakayama M. , Yanagisawa J. , Yuba Y. , Takaoka S. , Murase K. , Gamo K.
Published: July 2002

Density and level of interface states are accompanied by growth interruption, which is inevitable in an in situ process using molecular beam epitaxy (MBE). This MBE process coupled with focused ion beam systems is investigated by means of the Hall measurements and capacitance–voltage measurements. The experimental results are compared to those of the self-consistent calculation. These results suggest that interface states are located at a shallow level from the conduction band edge.
Microwave modulated photoluminescence used to measure surface recombination velocities
Authors: Inglefield C. E. , DeLong M. C. , Taylor P. C. , Harrison W. A.
Published: July 2002

Microwave modulated photoluminescence (MMPL) is a characterization technique in which a semiconducting sample is subjected to continuous optical pumping and chopped microwave electric fields. The signal normally detected in an MMPL experiment is the change in the photoluminescence (PL) spectrum due to the presence of the microwave electric field, which increases the kinetic energy of the free carriers. We have previously correlated the quenching of the PL signal, as induced by the microwaves, with nonradiative recombination at a surface/interface of the photoexcited volume. In this work, we determine quantitatively surface recombination velocities through a combined measurement of microwave induced changes in photoconductivity and in PL. From the change in the photoconductivity we infer a change in the diffusion constant of free carriers in the material. The change in diffusion constant, along with the change in luminescent intensity, uniquely determines the surface recombination velocity of the layer. Results for GaAs layers with bare surfaces are presented and the potential usefulness of the technique to other material systems, including the measurement of properties of buried interfaces, is discussed.
Interpretation of reflectance anisotropy spectroscopy spectra of ZnSe(001) grown on GaAs(001) in terms of bulk, interface, and surface contributions
Authors: Frisch A. M. , Schultz Ch. , Herrmann T. , Emiliani V. , Wolfframm D. , Evans D. A. , Korn M. , Rossow U. , Esser N. , Richter W.
Published: July 2002

We combine reflectance anisotropy spectroscopy (RAS) with low energy electron diffraction, Auger electron spectroscopy, and soft x-ray photoemission spectra to analyze the surface optical anisotropy of ZnSe(001). Clean surfaces were prepared by thermal desorption of a protective Se cap from ZnSe layers of different thicknesses grown by molecular beam epitaxy on GaAs(001). Two surface reconstructions have been prepared by subsequent annealing, the Se-rich (2×1) reconstruction and the Zn-rich c(2×2) reconstruction. By modifying the surfaces either through submonolayer deposition of Sb or a short exposure to atmosphere it was possible to distinguish between surface and bulk/interface contributions to the optical anisotropy. Only on disordered, very Se-rich ZnSe(001) surfaces prepared at low annealing temperatures RAS features possibly related to electronic surface states are found. RAS spectra of the (2×1) and the c(2×2) surfaces are correlated with surface morphology and ordering rather than surface reconstruction and show features near the critical points of the bulk ZnSe band structure.
Chemical bonding features for faultily stacked interfaces of GaAs{111}
Authors: Nakamura Jun , Mishima Tetsuya , Masui Moto-hisa , Sawayanagi Mineo , Cho Sung-Pyo , Nishizawa Masayasu , Eguchi Toyoaki , Osaka Toshiaki
Published: July 2002

The electronic states for normally stacked and faultily stacked layers on the GaAs{111} A, B surfaces are calculated by use of the discrete variational X α cluster method and the plane wave nonlocal pseudopotential method. The results show that chemical bondings between atoms are not as ionic in the faultily stacked layer of (111) B as they are in the (111) A case, and that on the (111) A surface more attractive Coulomb interaction energy is gained in the faulty stacking layer than in the normal stacking one. These results explain well the more frequent emergence of in-plane faults in the (111) A surface, which is well known in GaAs{111} A, B growth experiments. The total energy calculations also provide quantitative interpretation of such growth features.
AlGaAs/GaAs heterostructures grown on a focused-Be-ion-beam written backgate
Authors: Hirayama Y. , Saku T.
Published: July 2002

Novel structures, in which an AlGaAs/GaAs modulation doped structure is overgrown on an underlying Be-implanted p-type region, are successfully fabricated using a system in which focused-ion-beam (FIB) implantation and molecular-beam epitaxy chambers are connected through a high vacuum tunnel. The two-dimensional electron gas (2DEG) at the heterointerface is well controlled by a voltage applied to the Be-FIB written backgate. Though Be out diffusion into the overgrown layer is observed, the sharp front of the out diffusion enables us to fabricate devices with a small separation between the 2DEG and p-type backgate. The three-dimensional hole gas (3DHG) formed by the Be-FIB implantation is used not only as a backgate but also for measuring the interaction between 2DEG and 3DHG.
Effect of a deep-level trap on hole transport in In0.5Al0.5As/In0.5Ga0.5As metal–semiconductor–metal photodetectors
Authors: Lee Kun-Jing , Johnson F. G. , Johnson W. B. , Kim Junghwan , Lee Chi H.
Published: July 2002

The photoresponse of In0.5Ga0.5As metal–semiconductor–metal photodetectors is related to the presence of a hole trap. Detectors made from material grown with an In0.5Al0.5As buffer layer had no measurable trap density when examined using deep-level transient spectroscopy, and the full width half maximum (FWHM) of the photoresponse was 80 ps at 5 V bias for 3 μm interdigitated fingers and spacings. Detectors made from material grown without an In0.5Al0.5As buffer layer had a hole trap and a FWHM photoresponse of 220 ps. This deep hole trap is likely related to impurities that diffused upward from an interface of an InP substrate and an InGaAs epilayer.
Effects of interface roughness and conducting filaments in metal–oxide–semiconductor tunnel structures
Authors: Ting D. Z.-Y. , McGill T. C.
Published: July 2002

The current–voltage characteristics of n+ poly-Si/SiO2/p-Si tunnel structures containing nonuniform ultrathin oxide layers are studied using three-dimensional quantum mechanical scattering calculations. We find that, in general, roughness at the Si/SiO2 interface renders the oxide layer more permeable. In the direct-tunneling regime, interface roughness induces lateral localization of wave functions, which leads to preferential current paths. But in the Fowler–Nordheim tunneling regime it affects transport primarily through scattering. These two distinct mechanisms lead to opposite current density dependencies on island size. We have also examined oxide-embedded conducting filaments, and found that they act as highly efficient localized conduction paths and lead to dramatic increases in current densities. Depending on the filament length, our model can mimic experimental current voltage for ultrathin oxides having undergone either quasibreakdown or breakdown. We also found that the lower bias current densities in the structure with long filaments are greatly enhanced by resonant tunneling through states identified as quantum dots, and that this current enhancement is highly temperature dependent. We also report on the dependence of current–voltage characteristics on filament diameter size and filament density.
Simple lithographic technique for chip repairing using a light microscope
Authors: Carelli P. , Castellano M. G. , Leoni R. , Torrioli G.
Published: July 2002

We have developed a simple lithographic technique for repairing damaged chips, even after the end of the whole fabrication process, by using simply a light microscope for lithographic definition. In the usual laboratory practice, it can happen that the fabricated chips present defects which make them useless, such as broken metallic lines, or unwanted contacts between close elements on the same layer. Repairing these defects requires that the damaged area is lithographically defined in the photoresist, so that a subsequent step of film deposition (for broken lines) or etching (for unwanted contacts) can be performed. The white illumination of a usual light microscope with a reduced field (by means of a diaphragm already present in the microscope optical path) can provide the necessary light source to expose the resist. Both spots and narrow lines (several microns wide) can be defined in the resist; we give the details of operation and show some examples from our devices.
On the atomic arrangement on the ZrO/W(100) cathode surface: Models for low-energy electron diffraction
Authors: Nakane Hideaki , Kawata Satoru , Oka Masayoshi , Takami Taichi , Mizuno Seigi , Adachi Hiroshi
Published: July 2002

A low-energy electron diffraction examination of the ZrO/W(100) surface, which has a remarkably low work function and is practically applied to a thermal-field emission cathode for an electron microscope, showed a peculiar pattern. Assuming that reduction of the work function should occur due to a dipole effect of the Zr-O pair at the surface, I–V (intensity versus voltage) analysis was done for the pattern. It is revealed that no model, for which a perpendicular dipole effect on the surface can be expected, gives a small enough R factor to conclude that the model exhibits a real atomic arrangement. The results suggest that it is necessary to consider the parallel dipole effect on the surface.
Microwave amplification in structures with field and secondary emission
Authors: Galdetskiy A.
Published: July 2002

A new design of a microwave distributed amplifier is considered in which rf voltage is applied to the anode electrode, the field effect cathode emits an unmodulated electron flow, and wide band amplification can be achieved due to secondary emission modulation. As an example, an amplifier design is considered that has a cutoff frequency 24.7 GHz, a gain of 2.1 dB/cm, efficiency of 33%, and pulse output power of 49 W.
Research and development in plasma-based ion implantation in Europe. I. Apparatus and projects
Authors: Ensinger W.
Published: July 2002

More than a decade ago the first results on plasma-based ion implantation were presented by groups in the U.S. and Australia in the metallurgical field, and by groups in Japan for semiconductor processing. In the meantime, this technology has found widespread interest and is nearing commercialization. In Europe, the first reports in the literature appeared in the beginning of the 1990s. The present review discusses the research and development in plasma-based ion implantation in Europe, both the historical development and the present status, including the development of apparatus and projects which have been carried out.
Fabrication and characteristics of an emitter-sharpened double-gate racetrack-shaped field emitter structure
Authors: Wang Baoping , Tang Yongming , Wang Chen , Huang Zhongping , Sin Johnny K. O. , Xue Kunxing , Tong Linsu
Published: July 2002

In this article, numerical and experimental characterizations of an emitter-sharpened double-gate racetrack-shaped field emitter structure are reported. The racetrack-shaped edge emission with double-gate control is used to provide good uniformity, large field emission current density, and small turn-on voltage. In order to improve the performance of this structure further, an emitter-sharpened structure is used to minimize gate current. Experimental results show that the gate current of the emitter-sharpened double-gate structure is 7 times and 15 times smaller than that of the nonemitter-sharpened double-gate structure and the single-gate structure, respectively. Simulated results also show that the gate current of the emitter-sharpened double-gate structure can almost be eliminated.
Semianalytical model of electron source potential barriers
Authors: Jensen K. L.
Published: July 2002

Potential barrier profiles are developed for the study of field and thermionic emission electron sources. The model consists of the exchange and correlation potential, an ionic core potential to correct the “jellium” model, a triangular representation of the barrier, and a numerical integration of Poisson’s equation to evaluate the dipole potential. As a test, evaluations of the work function of various metals are made which rely on “effective” ionic radii which are often close to the actual ionic radii, and a good correspondence is found between the potential profiles and an “analytic” image charge potential. Modifications to the parameters inherent in the Richardson–Laue–Dushman and Fowler–Nordheim equations, so as to obtain current density estimates, are described. The method is suggested to be suitable for the analysis of more complex potential barrier profiles which are encountered in actual (realistic) thermionic and field emission electron sources, in that it captures the behavior of the exchange–correlation potential near the surface and includes those effects in the image charge potential.
Characterization of bending in single crystal Si beams and resonators
Authors: Weigold J. W. , Juan W. H. , Pang S. W. , Borenstein J. T.
Published: July 2002

Optical interferometry has been applied to determine the displacement of p++ Si beams. Clamped-clamped Si beams and cantilevered beams were fabricated with short and long B diffusion processes and characterized. Measurements of beam bending for released Si structures with length varying from 50 to 1000 μm, width varying from 5 to 15 μm, and thickness varying from 6 to 37 μm were obtained. By taking advantage of an etch-diffusion process, thicker beams can be fabricated which have less bending due to stress gradients. A 6.0-μm-thick cantilevered beam had a deflection of 11.2 μm due to stress gradients, while a 36.7-μm-thick beam had a deflection of only 0.3 μm. Beams fabricated using a dissolved wafer process with a 12 h B diffusion were found to bend the same amount as those fabricated with a 4 h diffusion. This indicates that bending in doped Si beams not only depends on the gradients in the B concentrations, it could also be related to the distribution of dislocations. Using the deep-etch shallow-diffusion process, resonating elements that are 20 μm long, 4 μm wide, and 28 μm thick were found to be perfectly flat without any bending.
Relations between the solubility speed and the electrical conductivity of phenol novolak polymer solutions
Authors: Takeda T. , Saka M.
Published: July 2002

Relations between the solubility speed of phenol novolak resins which are typical photoresist base polymers, with the ac-electrical conductivity of their polymer solutions were studied. Strong correlations between these quantities were found. These relations were found to be affected by the concentration of the solution and the measured temperature. It is suggested to use such relations to predict the solubility speed of photosensitive novolak polymers by measuring their ac-electrical conductivity instead of measuring the solubility speed directly.
Generalization of electrostatic lens characteristics using the Picht ray trajectories
Authors: Kawanami Yoshimi , Ishitani Tohru
Published: July 2002

Paraxial electron/ion trajectories in rotationally symmetric fields are analyzed in the Picht space to derive analytical forms of thin lens characteristics such as focal length F, magnification M, and chromatic and spherical aberration coefficients Cc and Cs. Dimensionless forms of T/F, {(Cc/T)/(T/F)}/(Lo/T)2, and {(Cs/T)/(T/F)}/(Lo/T)4, which are determined only by the normalized lens-potential distribution, are derived to evaluate the lens. Here, T is the lens thickness and Lo is the distance from the object to the lens. As to bipotential or unipotential lenses composed of electrodes facing each other symmetrically, it is found that the accelerating mode at V2/V1=a(>1) and the decelerating mode at V2/V1=1/a(<1) have relationships of Faccel=Fdecel, Cc,accel=Cc,decel/a, and Cs,accel=Cs,decel/a1/2, where V1 and V2 are the 1st and 2nd electrode potentials, respectively. Under constant lens fields, the known M-dependent Cc and Cs expressions, i.e., Cc=Cc,∞(1−1/M)2 and Cs=Cs,∞(1−1/M)4, are analytically derived also in the present approach.
Superlatticed negative differential-resistance heterojunction bipolar transistor
Authors: Cheng Shiou-Ying , Tsai Jung-Hui , Lin Po-Hung , Liu Wen-Chau
Published: July 2002

In this article, we report the fabrication of a new superlatticed negative-differential-resistance heterojunction bipolar transistor (SNDR-HBT) based on a lattice-matched Al0.48In0.52As/Ga0.47In0.53As material system. A 20-period AlInAs/GaInAs superlattice is used to serve the resonant tunneling route and the confinement barrier for minority carriers. From experimental results, an extremely low offset voltage of 61 mV and a common-emitter current gain of about 25 has been obtained at room temperature for the non-optimized device, simultaneously. In addition, we also observe the interesting N-shape negative-differential-resistance (NDR) phenomena in both two- and three-terminal operations at 77 K. It is believed that the N-shaped NDR results mainly from resonant tunneling within the 20-period AlInAs/GaInAs superlattice.
Mechanism of highly preferred (002) texture of Ti films sputter deposited on water-absorbed borophosphosilicate glass films
Authors: Yoshida Tomoyuki , Aoki Koyu , Mitsushima Yasuichi
Published: July 2002

The texture of Ti films sputter deposited at 350 °C on water-immersed borophosphosilicate glass (BPSG) films were investigated as a function of the boron content and immersion time of the BPSG films. The Ti film texture was the most strongly (002) preferred for the BPSG films that absorbed a certain amount of water, regardless of their boron content and immersion time. The following mechanism is proposed for the improved texture. The water-absorbed BPSG films increase H2O partial pressure near the BPSG surface during the heating up to 350 °C prior to Ti sputtering; the increased H2O pressure increases the density of silanol groups on the BPSG surface to reduce surface free energy; this results in Ti film growth toward highly preferred (002) texture by self-assembly of Ti atoms.
Deliberately designed interfaces for monolithic integration in optoelectronics
Authors: Wang Tairan , Moll N. , Cho Kyeongjae , Joannopoulos J. D.
Published: July 2002

A novel class of semiconductors is introduced, based on computational design, to solve the long-standing problem of lattice and polarity mismatch in heteroepitaxial growth of III–V alloys on silicon substrates. Ab initio total-energy calculations and quasiparticle GW calculations are used to investigate the physical properties of these new semiconductors. One particular configuration is designed to match lattice constant and polarity with the Si(100) surface and to possess a direct band gap of 1.59 μm, which is close to the canonical frequency used by the optoelectronics industry. These results could pave the way for eventual monolithic integration of optical materials on silicon.
Analysis of buried (Al,Ga)As interfaces after molecular-beam epitaxy overgrowth
Authors: Wassermeier M. , Hey R. , Höricke M. , Wiebicke E. , Kostial H.
Published: July 2002

The buried interface (IF) formed by molecular-beam epitaxy overgrowth on differently prepared (Al,Ga)As templates has been analyzed by secondary ion mass spectrometry and capacitance/voltage profiling. For the regrowth of GaAs on GaAs the lowest IF contamination is achieved by a H-assisted oxide desorption at 450 °C. This process retains atomically flat surfaces and is highly efficient in reducing the carbon contamination and the interfacial carrier depletion compared to thermal oxide desorption at 580 °C. For the regrowth on AlxGa1−xAs templates, due to the high reactivity of Al, the carbon and oxygen contaminations increase with increasing Al-mole fraction. An efficient reduction of the IF contamination can be accomplished by reevaporating a sacrificial GaAs cap layer. Carrier deficits as low as 7×1011 cm−2 for the H-assisted oxide-desorbed GaAs homointerface and 7.5×1011 cm−2 for AlxGa1−xAs on Al0.5Ga0.5As after reevaporating the sacrificial GaAs cap could be achieved. The carrier deficit can be compensated by a tailored doping profile around the IF.
Maskless extreme ultraviolet lithography
Authors: Choksi Neha , Pickard D. S. , McCord Mark , Pease R. F. W. , Shroff Yashesh , Chen Yijian , Oldham William , Markle David
Published: July 2002

Masks have been identified as the high risk, high cost issue for extreme ultraviolet (EUV) lithography. Challenges in EUV mask technology such as providing a pellicle and correcting defects have prompted the search for a maskless technique. Here we describe two approaches in which the mask of a current EUV system is replaced by an array of micron-sized mirrors. Patterns are achieved by modulating individual mirrors to create selected bright and dark spots. In one approach, individual mirrors can be lowered by λ/4 to yield locally dark regions because of destructive interference. In another approach, each mirror is mounted on a cantilever. Selected cantilevers can be tilted such that incident light from those mirrors is out of the pupil of the imaging objective. The wafer is mechanically scanned and the object is electronically scrolled across the array of mirrors in order to build up the required pattern. We have simulated the mechanical properties of the micron-sized mirrors and some aerial images showing that sub-100 nm features appear feasible.
Thin oxides on passivated silicon irradiated by focused ion beams
Authors: Fuhrmann H. , Döbeli M. , Kötz R. , Mühle R. , Schnyder B.
Published: July 2002

When a hydrogen-terminated Si (100) surface is irradiated with a focused ion beam, the irradiated areas are not affected by a subsequent KOH etch. We discuss the influence of irradiation-induced doping, amorphization, defect doping, and surface oxidation on this effect. Point defects and amorphization were measured by thermal wave analysis. X-ray photoelectron spectroscopy was used for surface analysis. We show that both damage and oxidation can lead to the observed etch stop in KOH, but can be controlled independently from each other.
Combined focused ion beam deposition system and scanning probe microscope for metal nanostructure fabrication and characterization
Authors: Woodham R. G. , Ahmed H.
Published: July 2002

We have developed a combined focused ion beam deposition machine and scanning probe microscope which has been used to fabricate and characterize metal nanoparticles entirely within a high-vacuum environment. The focused ion beam section is fitted with a retarding-field stage which allows the landing energy of ions to be adjusted from ∼20 to over 400 eV. The microscope has been adapted to enable the probe to be directed to the localized deposits so that the physical structure of the deposits and the electrical properties can be measured in situ.
Determination of high-order lens aberration using phase/amplitude linear algebra
Authors: Fukuda Hiroshi , Hayano Katsuya , Shirai Seiichiro
Published: July 2002

New approaches to measuring lens aberration of optical exposure tools in semiconductor manufacturing environment are discussed. First, plural image quantities are measured and expressed by linear combinations of contributions from several Zernike aberration terms. Then, the linear problem is solved to find the best combination of each term to explain the experimental results. Using side-lobe intensity near octagonal aperture edges in an attenuated phase-shifting mask as a detector, third-order Coma and trifoil aberrations were successfully measured.
High contrast chemically amplified 193 nm resist for gigabit dynamic random access memory generation
Authors: Itani Toshiro , Yoshino Hiroshi , Yamana Mitsuharu , Takimoto Michiya , Tanabe Hiroyoshi
Published: July 2002

Four Gb dynamic access random memory (DRAM) cell patterns which have a 0.12 μm design rule were demonstrated by using a high contrast chemically amplified 193 nm positive resist and high resolution exposure. All critical layers of 4 Gb DRAM, such as isolation, word line, contact hole, bit line, and storage node, were successfully resolved with suitable focus margin. The dissolution contrast of the resist film and the slope of dissolution rate curve were much higher than those of conventional polyhydroxystyrene based chemically amplified KrF positive resist. Moreover, the dry etch resistance of the resist film for both the polysilicon etch and the oxide etch was better than those of KrF resist. These results indicated that this resist material has enough potential for practical use. Furthermore, the resist profile simulation showed that mass production of 4 Gb DRAMs can be achieved by a combination of a high contrast resist and a higher numerical aperture lens under annular illumination.
Direct epitaxial growth of submicron-patterned SiC structures on Si(001)
Authors: Yi Gyu-Chul , Eres G. , Lowndes D. H.
Published: July 2002

We report on the direct epitaxial growth of submicron-patterned SiC structures on Si(001) substrates using supersonic molecular jet epitaxy and resistless e-beam lithography. Prior to SiC film growth, an electron beam was scanned on hydrogen-passivated Si substrates in order to produce silicon oxide lines with widths ⩾60 nm. The SiC nucleation and growth rates were significantly reduced on the oxidized regions during the subsequent supersonic jet epitaxial growth of SiC, which yielded epitaxial, submicron-patterned SiC films. The effects of the growth temperature and e-beam dose on the SiC growth and pattern linewidth are discussed.
Formation of silicided shallow p+n junctions by BF2+ implantation into thin amorphous-Si or Ni/amorphous-Si films on Si substrates and subsequent Ni silicidation
Authors: Juang M. H. , Hu M. C. , Yang C. J.
Published: July 2002

The process scheme that forms NiSi-silicided shallow p+n junctions by BF2+ implantation into thin amorphous-Si (a-Si) or Ni/a-Si films on Si substrates and subsequent Ni silicidation has been studied. As for the scheme using a-Si as an implantation barrier, an NiSi-silicided junction with a leakage of about 0.7 nA/cm2 at −5 V is obtained by the sample Ni silicided at 700 °C for 30 min. The implantation energy and the crystallinity of the deposited Si films after annealing would greatly affect the junctions formed at various temperatures, attributable to different implantation effects and boron depth profile. However, the junctions formed by rapid thermal processing or high implant energy are considerably degraded at 800 °C, attributable to anomalous Ni penetration into the Si substrate with the further silicidation of NiSi into NiSi2. On the other hand, the specimens with Ni/a-Si as an implantation barrier sustain few defects, thus significantly suppressing the junction degradation at 800 °C. However, the formed junctions are worse than those by the former scheme, mainly due to lower dopant drive-in efficiency.
SiO
2
thickness determination by x-ray photoelectron spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, Rutherford backscattering, transmission electron microscopy, and ellipsometry
Authors: Cole D. A. , Shallenberger J. R. , Novak S. W. , Moore R. L. , Edgell M. J. , Smith S. P. , Hitzman C. J. , Kirchhoff J. F. , Principe E. , Nieveen W. , Huang F. K. , Biswas S. , Bleiler R. J. , Jones K.
Published: July 2002

As the Rp of ion implants steadily decreases an ever-increasing percentage of the implant species lies in the oxide layer and is, therefore, not electrically active. For this reason, it is important to have analytical techniques capable of accurately measuring the thickness of ultrathin oxide layers. A round-robin study was performed on a series of SiO2 films ranging from 0.3 to 20 nm in order to evaluate the advantages and disadvantages of five commonly used analytical techniques. High-resolution cross-section transmission electron microscopy (TEM) offers the only true measurement of oxide thickness because no density assumptions are made. In this study, TEM is used as the standard for all the other techniques. X-ray photoelectron spectroscopy and Auger electron spectroscopy offer precise measurements for ultrathin (<3 nm) films, but are limited for thicker films (>15 nm) due to the exponential decay functions that describe the sampling depth in both techniques. Secondary ion mass spectrometry (SIMS) has historically been used for characterizing relatively thick films (>10 nm) but not for thinner films because of atomic mixing effects. Encapsulating oxides with amorphous silicon prior to performing a SIMS experiment can negate these effects. A comparison of SIMS on encapsulated and as received films is made. Rutherford backscattering is an excellent technique for determining oxide thickness over a wide thickness range by channeling the Si signal from the crystalline substrate and analyzing oxygen from the amorphous oxide. Ellipsometry, being both rapid and low cost, is one of the most widely used techniques capable of accurate measurements on thick films (>10 nm).
Growth of InxGa1−xAs/GaAs heterostructures using Bi as a surfactant
Authors: Pillai M. R. , Kim Seong-Soo , Ho S. T. , Barnett S. A.
Published: July 2002

The effects of a bismuth surfactant layer on the molecular beam epitaxy of GaAs and InxGa1−xAs layers on GaAs (001) were studied. The InxGa1−xAs surface reconstruction changed from arsenic stabilized 2×4 to bismuth stabilized 1×3 for high enough bismuth fluxes and low enough substrate temperatures. Maintaining a bismuth stabilized surface during InxGa1−xAs growth resulted in a larger number of reflection high-energy electron diffraction (RHEED) oscillations. RHEED patterns were also streakier after InxGa1−xAs growth with Bi. Roughness measurements using atomic force microscopy showed reduced root mean square roughness with Bi, e.g., from 3.8 to 2.8 nm, for 4 nm thick In0.3Ga0.7As layers. Simulations of x-ray diffraction results from 10 period In0.5Ga0.5As/GaAs superlattices showed that Bi reduced interface roughness from 1.1 to 0.5 nm and reduced interfacial broadening from 2.8 to 2.1 nm. The latter was attributed to reduced In segregation. InxGa1−xAs/GaAs (x=0.2–0.4) multiple quantum wells grown with Bi exhibited photoluminescence peaks that were more intense than those grown without Bi.
An Antimicrobial Peptide Gene Found in the Male Reproductive System of Rats
Authors: Li Peng , Chan Hsiao Chang , He Bin , So Siu Cheung , Chung Yiu Wa , Shang Quan , Zhang You-Duan , Zhang Yong-Lian
Published: July 2002

Little is known about the innate defense mechanisms of the male reproductive tract. We cloned a 385–base pair complementary DNA and its genomic DNA named Bin1b that is exclusively expressed in the caput region of the rat epididymis and that is responsible for sperm maturation, storage, and protection. Bin1b exhibits structural characteristics and antimicrobial activity similar to that of cationic antimicrobial peptides, β-defensins. Bin1b is maximally expressed when the rats are sexually mature and can be up-regulated by inflammation. Bin1b appears to be a natural epididymis-specific antimicrobial peptide that plays a role in reproductive tract host defense and male fertility.
G Protein Signaling from Activated Rat Frizzled-1 to the β-Catenin-Lef-Tcf Pathway
Authors: Liu Tong , DeCostanzo Anthony J. , Liu Xunxian , Wang Hsien-yu , Hallagan Sarah , Moon Randall T. , Malbon Craig C.
Published: July 2002

The
frizzled
receptors, which mediate development and display seven hydrophobic, membrane-spanning segments, are cell membrane–localized. We constructed a chimeric receptor with the ligand-binding and transmembrane segments from the β
2
-adrenergic receptor (β
2
AR) and the cytoplasmic domains from rat Frizzled-1 (Rfz1). Stimulation of mouse F9 clones expressing the chimera (β
2
AR-Rfz1) with the β-adrenergic agonist isoproterenol stimulated stabilization of β-catenin, activation of a β-catenin–sensitive promoter, and formation of primitive endoderm. The response was blocked by inactivation of pertussis toxin–sensitive, heterotrimeric guanine nucleotide–binding proteins (G proteins) and by depletion of Gαq and Gαo. Thus, G proteins are elements of Wnt/Frizzled-1 signaling to the β-catenin–lymphoid-enhancer factor (LEF)-T cell factor (Tcf) pathway.
Tumor Therapy with Targeted Atomic Nanogenerators
Authors: McDevitt Michael R. , Ma Dangshe , Lai Lawrence T. , Simon Jim , Borchardt Paul , Frank R. Keith , Wu Karen , Pellegrini Virginia , Curcio Michael J. , Miederer Matthias , Bander Neil H. , Scheinberg David A.
Published: July 2002

A single, high linear energy transfer alpha particle can kill a target cell. We have developed methods to target molecular-sized generators of alpha-emitting isotope cascades to the inside of cancer cells using actinium-225 coupled to internalizing monoclonal antibodies. In vitro, these constructs specifically killed leukemia, lymphoma, breast, ovarian, neuroblastoma, and prostate cancer cells at becquerel (picocurie) levels. Injection of single doses of the constructs at kilobecquerel (nanocurie) levels into mice bearing solid prostate carcinoma or disseminated human lymphoma induced tumor regression and prolonged survival, without toxicity, in a substantial fraction of animals. Nanogenerators targeting a wide variety of cancers may be possible.
Magnetic Ordering in an Organic Polymer
Authors: Rajca Andrzej , Wongsriratanakul Jirawat , Rajca Suchada
Published: July 2002

We describe preparation and magnetic properties of an organic π-conjugated polymer with very large magnetic moment and magnetic order at low temperatures. The polymer is designed with a large density of cross-links and alternating connectivity of radical modules with unequal spin quantum numbers (
S
), macrocyclic
S
= 2 and, cross-linking
S
= ½ modules, which permits large net
S
values for either ferromagnetic or antiferromagnetic exchange couplings between the modules. In the highly cross-linked polymer, an effective magnetic moment corresponding to an average
S
of about 5000 and slow reorientation of the magnetization by a small magnetic field (less than or equal to 1 oersted) below a temperature of about 10 kelvin are found. Qualitatively, this magnetic behavior is comparable to that of insulating spin glasses and blocked superparamagnets.
Tunneling Spectroscopy of the Elementary Excitations in a One-Dimensional Wire
Authors: Auslaender O. M. , Yacoby A. , de Picciotto R. , Baldwin K. W. , Pfeiffer L. N. , West K. W.
Published: July 2002

The collective excitation spectrum of interacting electrons in one dimension has been measured by controlling the energy and momentum of electrons tunneling between two closely spaced, parallel quantum wires in a GaAs/AlGaAs heterostructure while measuring the resulting conductance. The excitation spectrum deviates from the noninteracting spectrum, attesting to the importance of Coulomb interactions. An observed 30% enhancement of the excitation velocity relative to noninteracting electrons with the same density, a parameter determined experimentally, is consistent with theories on interacting electrons in one dimension. In short wires, 6 and 2 micrometers long, finite size effects, resulting from the breaking of translational invariance, are observed.
Why Global Warming Is Controversial
Authors: Philander George
Published: July 2002

Changing the Atmosphere
Expert Knowledge and Environmental Governance. Clark A. Miller and Paul N. Edwards, Eds. MIT Press, Cambridge, MA, 2001. 397 pp. $67, £47.95. ISBN 0-262-13387-3. Paper, $26.95, £18.95. ISBN 0-262-63219-5.

The contributors, drawn largely from the field of science and technology studies, discuss the creation of knowledge about climate change and the use of such research in shaping governmental policies.
Flow-Induced Molecular Orientation of a Langmuir Film
Authors: Maruyama Takayuki , Fuller Gerald , Frank Curtis , Robertson Channing
Published: July 2002

The two-dimensional fluid dynamics of the different phases of a fatty acid monolayer (docosanoic acid) were examined. Brewster angle microscopy was used to investigate the polydomain structure of two "liquid condensed" phases (the L
2
and L'
2
phases) and the "solid" (S) phase in situ during an extensional flow. Only the L
2
phase deformed affinely with a liquid-like response. The two other phases experienced flow-induced reorientation of the lattice onto which the molecules were arranged. The reorientation process was accompanied by the appearance of shear bands in the monolayers at an angle of ±45 degrees to the extension axis of the flow.
Galileo Turns Geology Upside Down on Jupiter's Icy Moons
Authors: Kerr Richard A.
Published: July 2002

Galileo's sharp images of the moons Ganymede and Europa turn previous ideas about the moons' icy volcanism and tectonic movements upside down. See the Galileo Orbiter Reports beginning on (page
377
)of this issue.
Winning Incentives for Truthtelling
Authors: Seife Charles
Published: July 2002

Two economists win this year's Nobel Memorial Prize in Economic Science for their contributions to the theory of auctions, tax systems, and other situations in which decision-makers have different information. For more information on this prize, see the
Nobel Foundation Web site
.
Effects of Absorption by Io on Composition of Energetic Heavy Ions
Authors: Garrard T. L. , Stone E. C. , Murphy N.
Published: July 2002

The Galileo heavy ion counter is sensitive to ions with atomic numbers
Z
≥ 6 and energies greater than ∼6 MeV per nucleon. During Galileo's passage through Jupiter's inner magnetosphere, the observed composition of these heavy ions was consistent with the presence of singly ionized iogenic O, Na, and S and highly ionized solar C, O, and Ne. The solar component is absorbed more strongly by Io because its gyroradius is smaller than Io's diameter.