bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear optical properties of InSb1−xAsx-based alloys and superlattices
Authors: Youngdale E. R. , Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Thompson P. E. , Davis J. L.
Published: July 2002

We report the first observation of in-band optical nonlinearities in III–V semiconductors at CO2 wavelengths, obtained from nondegenerate four-wave mixing experiments on both InSb1−xAsx alloy layers and InSb1−xAsx–InSb strained-layer superlattices. An alloy of composition near that for the minimum energy gap (x=0.43) was found to have a large χ(3) at 300 K (≳ 10−5 esu). While the nonlinearity in the alloy saturated at high intensities due to the dynamic Burstein shift, results for an InSb0.83As0.17-InSb superlattice showed no evidence for saturation at intensities up to 5 × 105 W/cm2. Theoretical arguments predict that one should expect type-II superlattices such as InSb1−xAsx–InSb to be superior to previously studied nonlinear materials with regard to combining large χ(3) with small absorption coefficient and large saturation threshold.
Electronic structure of samarium atoms adsorbed on the GaAs(110) surface
Authors: Allan G. , Delerue C.
Published: July 2002

The electronic structure of samarium atoms adsorbed on a GaAs(110) surface is calculated in the tight-binding approximation. It is shown that in the ground state, this adatom is divalent at low coverage when it is adsorbed on Ga surface atoms. The adsorption unrelaxes the surface atoms close to the adatom. Charge transfer from the adatom leads to a strong Coulomb potential and to a bonding state localized close to the conduction band minimum. Comparison is made with surface atom core-level shifts and valence and conduction band states measured by photoemission spectroscopy.
Sublattice orientation dilemma: A reflection high-energy electron diffraction and x-ray photoelectron diffraction study of GaAs growth on vicinal Si(001) surfaces
Authors: Olivier J. , Bartenlian B. , Bisaro R. , Wyczisk F.
Published: July 2002

It is shown by reflection high-energy electron diffraction that the temperature at which As and Si interact is a key factor in surface reconstruction: at low (TS = 400 °C) and high (TS= 600–700 °C) substrate temperature, and at As4 pressure ∼ 10−5 Torr, the dangling bonds of arsenic are, respectively, perpendicular or parallel to the step edges of the vicinal surface. Photoelectron diffraction shows that, from the very first steps of GaAs molecular-beam epitaxial growth on such surfaces, the GaAs lattice (i) exhibits two orientations determined by As initial orientation and related by a 90° rotation, (ii) is without antiphase domains within the sensitivity limit of the method.
Thermodynamics of surface-induced ordering in the Ga1−xInxP alloy
Authors: Osório Roberto , Bernard James E. , Froyen Sverre , Zunger Alex
Published: July 2002

The occurrence of spontaneous CuPt-like ordering in epitaxial Ga1−xInxP alloys is examined by means of a thermodynamic theory. We treat both cation- and anion-terminated surfaces. We find that the order parameter of the observed CuPtB variant is significant for reconstructed cation-terminated surfaces even at preparation temperatures. A possible mechanism for the formation of the three-dimensional CuPtB structure involves partial equilibration of the cation-terminated reconstructed surface followed by freezing of the cations as the surface is buried by newly deposited layers.
TiNxOy transparent electrode material for HgCdTe infrared devices
Authors: Wan C. F. , Sulzbach F. C. , Luttmer J. D.
Published: July 2002

We studied various transparent, conductive thin-film coatings for infrared focal-plane array applications. Films of TiNxOy prepared by reactive direct current magnetron sputtering best satisfied the performance and producibility requirements. The films have robust chemical and mechanical properties, little free-carrier absorptance, and the resistivity can be tailored to requirements. Transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy were used to study the film characteristic, phase equilibria, and reaction mechanisms of film formation. Composition was found to be TiNxOy and Ti oxides. The amount of oxygen in the films controls both its electrical and optical properties. Oxygen content is controlled by film microstructure which is dependent on deposition conditions.
Properties of Cu film under XeCl excimer laser irradiation
Authors: Wang Shi-Qing , Ong Edith
Published: July 2002

Sputter deposited Cu films on top of a substrate were melted and recrystallized by irradiating under a XeCl (308 nm) excimer laser with a 45 ns pulse duration at substrate temperatures of 20, 365, and 440 °C. The properties of the irradiated film, such as sheet resistance, reflectance, grain size, stress, and preferred orientation were characterized as a function of the laser fluence at each of temperatures. The results show a decrease in sheet resistance and specular reflectance, and an increase in grain size after laser irradiation. The net stress of the film stack changes from compressive to tensile with substrate heating and laser irradiation and the polycrystalline orientation of the Cu films changes from (111) for the as-deposited sample to (110) after laser irradiation. The significance of these results is discussed.
Pulsed ultraviolet laser stimulated chlorination mechanisms for Si(111)
Authors: Paulsen-Boaz Carlotta , O’Brien William L. , Rhodin Thor
Published: July 2002

Pulsed ultraviolet laser induced surface reactions of chlorine on silicon were investigated. The predominant chlorination products were SiCl and SiCl2. Laser fluence effects could be clearly divided into three regimes: under ≊150 mJ/cm2 a nonthermal reaction occurred, from 200–400 mJ/cm2 thermal effects play a significant role, and above this vaporization and plasma formation dominate. Wavelength effects were also apparent. Fluence thresholds for the appearance of products varied with 351 nm having the lowest, 308 nm the highest, and 248 nm intermediate values. The effect of wavelength upon product ratios suggests that a competing process of chlorine photodesorption is accessed at 308 nm. Increases in dopant concentration yielded increased production of silicon chlorides. The results of combined variations in dopant concentration and wavelength indicate the presence of at least two distinct mechanisms—one involving initial photon-substrate interactions, the other photon-adsorbate interactions. Under all conditions studied silicon chloride production was linear in chlorine gas pressure.
Scanning tunneling microscopy studies on the growth and structure of thin metallic films on metal substrates
Authors: Hwang R. Q. , Behm R. J.
Published: July 2002

The value and applicability of scanning tunneling microscopy (STM) studies for investigating the structure and growth of thin metal films is demonstrated in model studies on two epitaxial systems, Cu/Ru(0001) and Au/Ru(0001). STM imaging gives direct access to the microscopic features of thin film growth and by following the film morphology with coverage and observing the variations with changes in the growth conditions, information on the kinetics of nucleation, diffusion barriers, and two-dimensional growth mechanisms were obtained. High resolution imaging allowed the atomic structure within the overlayers to be investigated, revealing their characteristic defects, and their mechanisms of stress accommodation between subsequent layers. These data are compared with results of earlier studies using nonlocal, averaging techniques and the often indirect conclusions drawn from those measurements.
Qualification and application of profiling data for model development and characterization
Authors: Wu Sheldon , Chien Ling-Chu
Published: July 2002

This article discusses the utilization of profiling data from an end-user’s viewpoint and emphasizes some requirements of profiling techniques for the modeling of present and future integrated circuit technologies. In the development and characterization of diffusion model, we have to fit both the measured profile shape and integrated dose for each dopant. We will present the evaluation of secondary ion mass spectrometry (SIMS) and spreading resistance (SRP) profiling techniques against this criterion and the selection of SIMS data as the standard for model parameter extraction. We will then discuss the methodology and results of model characterization which is a step-by-step application of SIMS data for the calibration of SUPREM III model parameters. To validate the characterized model for technology development, we will talk about the checking against available SRP, sheet resistance, C–V, and device I–V data. Finally, we want to bring up the need of profiling data for the characterization of two-dimensional shallow junctions and dopant diffusion in polysilicon.
High contrast optically bistable optoelectronic switches based on InGaAs/GaAs(100) conventional and inverted asymmetric Fabry–Pérot modulators grown via molecular-beam epitaxy
Authors: Chen Li , Hu Kezhong , Kapre R. M. , Chen W. , Chen P. , Madhukar A.
Published: July 2002

High contrast ratio InGaAs based asymmetric Fabry–Pérot reflection modulators, realized in both conventional and inverted geometry, were used to obtain high contrast optically bistable switches in various schemes utilizing both ‘‘normally on’’ and ‘‘normally off’’ types of modulators. The flexibility provided by the inverted structure in realizing novel optical and electrical interconnections is demonstrated.
Molecular-beam epitaxial growth of high quality, double channel AlGaAs/InGaAs pulse-doped pseudomorphic high electron mobility transistors
Authors: Hoke W. E. , Lyman P. S. , Labossier W. H. , Hendriks H. T. , Shanfield S. , Aucoin L. , Pan N. , Carter J.
Published: July 2002

Pulse-doped pseudomorphic AlGaAs/InGaAs high electron mobility transistors with two InGaAs channels have been grown by molecular-beam epitaxy. Electrical measurements indicate that the two channels are contributing nearly equally to the conduction. The sheet density is approximately twice that of the single channel structure, and good electron mobilities are obtained. Shubnikov–de Haas measurements confirm the two dimensional transport in the structure. Direct current measurements on device structures exhibit a double peak in the transconductance, low source resistance, and a sharp pinch-off characteristic.
The influence of InAs well thickness on the negative differential resistance behaviors in GaSb/AlSb/InAs/GaSb/AlSb/InAs double barrier structures
Authors: Houng M. P. , Wang Y. H. , Shen C. L. , Liu M. H. , Chen J. F. , Cho A. Y.
Published: July 2002

The peak-to-valley current ratio can be improved by adding a thin InAs layer in the well region of the GaSb/AlSb/GaSb/AlSb/InAs resonant interband tunneling structure. It is found that the ratio rises to more than 20 at room temperature for an InAs layer reaching 30 Å. Increasing the InAs layer beyond 30 Å the ratio gradually goes down. However, we also find as the added InAs layer is further increased to 240 Å, the I–V characteristics change from single negative differential resistance (NDR) to multiple NDR behavior. Such interesting phenomena can be modeled theoretically due to the coupling effect of the electrons from the added InAs layer and the light holes from the GaSb layer in the well region.
Analysis of the mean crystallite size and microstress in titanium silicide thin films
Authors: Morimoto N. I. , Swart J. W. , Gracher Riella H.
Published: July 2002

This paper presents the analysis of the mean crystallite size and microstress in thin titanium silicide films based on the broadening of x-ray diffraction profiles. The titanium silicide specimens were obtained by rapid thermal annealing of thin titanium films deposited on single-crystal silicon substrate. The experimental results have shown either the face centered orthorhombic C54 type TiSi2 structure with mean crystallite size of 50 nm or the base centered orthorhombic C49 type TiSi2 structure with 20 nm mean crystallite size, depending on annealing conditions. A decrease in the microstress has been observed with increasing annealing times at 800 °C, without significant variations of the mean crystallite size.
Quality dependence of Pt–n-GaAs Schottky diodes on the defects introduced during electron beam deposition of Pt
Authors: Auret F. D. , Myburg G. , Kunert H. W. , Barnard W. O.
Published: July 2002

Schottky barrier diodes (SBDs) were fabricated on epitaxially grown n-GaAs by electron beam (e-beam) deposition of Pt at various rates. The quality of the SBDs was evaluated by standard current–voltage (I–V) measurements and the defects introduced during e-beam deposition were characterized by deep level transient spectroscopy (DLTS). The results showed that if the GaAs was shielded from stray electrons originating at the e-beam filament during deposition, then high quality SBDs were formed. However, if the GaAs was not shielded during deposition, then the quality of the devices was poor and the degree to which their characteristics deviated from ideal increased as the deposition rate decreased, i.e., as the total electron dose reaching the substrate during metallization increased. DLTS revealed that several surface and subsurface defects were introduced during metallization without the electron shield and, for the first time, it is shown that these e-beam induced defects result in poor SBD device characteristics.
The effects of substrate bias on microwave plasma etching
Authors: Jin Ming , Kao Kwan C.
Published: July 2002

The effects of substrate bias on microwave plasma etching have been theoretically analyzed, and the potentials at the surface of the semiconducting and the insulating materials being etched under a substrate bias have been derived. The computed results indicate that the etch rate increases with increasing impinging ion energy which depends strongly on the magnitude and the frequency of the substrate bias voltage. The theory correlates well with the experimental results on the electron cyclotron resonance microwave plasma etching of semiconducting Si and insulating Si3N4 films under radio frequency (107 Hz) substrate bias voltages.
Improved barrier layer for high-T
c superconductor on silicon
Authors: Parsons R. , Orfino F. , Osborne N. , Grigg D. , Zindler R.
Published: July 2002

Buffer layer configurations consisting of magnetron sputtered ZrO2, Zr–Si mixed oxide, and SiO2 were investigated for sputter deposition of Bi–Sr–Ca–Cu–O high-Tc superconducting thin films onto silicon wafers. A problem associated with film flaking during postdeposition annealing was overcome by burying the sample in a powder of Bi–Sr–Ca–Cu–O material. Crack growth and buckling in the buffer layers, associated with differential thermal expansions, were eliminated by raising the deposition temperature for the buffer layers. Unfortunately, the improved buffer layers were not good enough to prevent substrate–film interactions over the long annealing times (e.g., 14 h), and the sufficiently high temperature (e.g., 850 °C) needed for the formation of the 2223 high Tc (110 K) phase.
Optical focus and level sensor for wafer steppers
Authors: van der Werf J. E.
Published: July 2002

A new optical focus system for wafer steppers, insensitive to structures on the wafer surface, is presented. It is based on the grazing-incident beam method. In traditionally used monochromatic focus systems, interference effects in the layer stack on the wafer are a severe limitation on the accuracy. In the system presented here, this problem is overcome by using an incandescent lamp as a polychromatic light source. Due to the large spectral range of 300 nm, interference effects in the layer stack on the wafer are averaged. Calculations of the influence of these interference effects on the focus measurement show good agreement with the experimental results. An additional feature of the system is its large measurement spot, which averages effects related to locally varying reflection and topography. Moiré fringe and modulation techniques are used to enhance the signal-to-noise ratio. As a result the dynamic range of the system is increased to 103. The mechanical stability is considerably improved by the addition of a reference branch that measures the position of the projection lens. This enables the accurate and precise measurement of the required distance between lens and wafer. The extra optical features together with the mechanical stability yield a vertical accuracy and precision better than 100 and 20 nm, respectively. The combination of four of these focus systems within one stepper permits the measurement of the local tilt of the wafer.
Photo- and electron-beam lithography sharing common stencil
Authors: Krupenin V. A. , Lotkhov S. V. , Vyshenskii S. V.
Published: July 2002

It is described how photolithography can be employed to pattern large shapes in the Ge stencil simultaneously with electron-beam lithography based on the scanning electron microscopy. This results in the absence of the additional contact between different metals deposited with different lithography processes. This approach was used to fabricate systems of ultrasmall Al tunnel junctions and mesoscopic Al loops.
Metallization of W/Co–Ti/Si and simultaneous formation of diffusion barrier and shallow CoSi2 contact in normal flowing-nitrogen furnace
Authors: Yang Fann-Mei , Peng Jaw-Gi , Huang Tsung-Shiew , Huang Sheng-Liang , Chen Mao-Chieh
Published: July 2002

A structure of W–Ti/CoSi2/Si can be formed from an appropriate metallization system of W(400 Å)/Co63Ti37(360 Å)/Si at temperatures from 620 to 760 °C in a normal flowing-nitrogen ambient. The W–Ti alloy layer is only slightly oxidized on the shallow surface and can be used as a diffusion barrier between the aluminum and silicide. Furthermore, silicide lateral growth does not occur in this silicidation scheme. However, an additional intermediate Ti–silicide and/or Ti–oxide as well as a Ti–oxide layer on the surface will be formed if the content of Ti in the Co–Ti alloy exceeds that required to saturate in the overlying W film, e.g., W(400 Å)/Co63Ti37(840 Å)/Si. The Al/W–Ti/CoSi2/p+n diodes with metallization using this scheme are able to maintain the integrity of I–V characteristics with a post-Al annealing at 550 °C for 20 min. In addition, epitaxy of CoSi2 occurs in this metallization system.
Influence of the frequency of a periodic biasing voltage upon the etching of polymers
Authors: Bounasri F. , Moisan M. , Sauvé G. , Pelletier J.
Published: July 2002

The influence of the amplitude Vb and frequency fb of a plasma-independent sinusoidal biasing voltage Vb sin(2πfbt) upon the etching of a polymer is investigated in both chemically active (O2, O2/CF4, SF6) and chemically inert (argon) discharges. As far as the etch rate is concerned, two regimes have been evidenced in chemically active discharges, namely ion-assisted chemical etching and, as Vb is increased above a certain threshold value, a so-called damage-induced ion-assisted chemical etching. With inert gas discharges, the only etching regime is that resulting from physical sputtering. The chemical etching rate is approximately one order of magnitude larger than the physical etching rate and is practically independent of fb/fpi ( fpi is the ion plasma frequency) in contrast to physical sputtering where the etch rate is larger for fb/fpi≪1. X-ray photoelectron spectroscopy analysis of the polymer surface composition after etching in chemically active discharges shows a dependence on fb/fpi, even though the etch rate does not. In the specific case of an SF6 discharge etching polyimide, the fluorine surface coverage increases with fb/fpi. The results reported show that the chemical etching of polymers can be further controlled via fb and Vb to allow optimizing the etch rate under minimum surface damage conditions.
Ultraviolet-ozone oxidation of GaAs(100) and InP(100)
Authors: Lu Z. H. , Bryskiewicz B. , McCaffrey J. , Wasilewski Z. , Graham M. J.
Published: July 2002

This article reports on a study of the ultraviolet (UV)-ozone oxidation of GaAs(100) and InP(100) using high-resolution x-ray photoelectron spectroscopy (XPS) complemented by transmission electron microscopy (TEM). For GaAs(100), various oxides As2O3, As2O5, and Ga2O3 are observed. The As2O3 core level intensity follows a logarithmic growth, while As2O5 and Ga2O3 exhibit a linear growth as a function of UV-ozone exposure time. Angle-resolved XPS and TEM measurements confirm that the oxide has a layered structure represented schematically as (As2O5, Ga2O3)/(As2O3, Ga2O3)/GaAs(100). Two different oxidation processes likely occur; the first is bulk oxidation at the GaAs(100)/oxide interface, and the second process occurring at the higher oxide/lower oxide interface is conversion of the lower As oxide to the higher As oxidation state. On InP(100), oxides corresponding to In2O3 and POx are observed, and the respective photoelectron intensities follow a logarithmic growth as a function of UV-ozone exposure time. Angle-resolved XPS measurements show that the In2O3 and POx are homogeneously mixed. The total oxide thickness, calculated from the photoelectron intensity ratio, follows a logarithmic growth as a function of exposure time on both GaAs(100) and InP(100).
Tolerance on alignment error in GHOST proximity effect correction
Authors: Moriizumi K. , Broers A. N.
Published: July 2002

The GHOST method is well known proximity effect correction scheme which is simple and accurate, and requires no extensive computer calculations. Although the tolerances on dose and beam diameter of correction exposure have been studied by several researchers, there has been no systematic evaluation of the tolerance on alignment between primary and correction exposure. In this research, the tolerance on alignment has been calculated for a two-dimensional test pattern by using a simple numerical calculation with the double-Gaussian approximation and a threshold energy model. The calculation shows that an alignment error causes much larger deviations in linewidth than in position shift. The tolerance on alignment, therefore, is determined by linewidth deviation. The tolerance has linear dependence on both the range of backscattered energy distributions (Bb) and the ratio of the absorbed energy deposited by the backscattered electrons to the absorbed energy by the forward scattered electrons (η). The larger Bb and lower η values provide greater tolerance to misalignment. The feasibility of applying the GHOST method to electron-beam energies of 10 keV, a range from 20 to 30 and 50 keV is discussed using the calculated results.
Image monitor for Markle–Dyson optics
Authors: Grenville A. , Owen G. , Pease R. F. W.
Published: July 2002

A method for characterizing the performance of a lithographic imaging system has been devised which is independent of resist processing. A scanned grating technique has been adopted for measuring modulation as a function of both spatial frequency and defocus and it has been applied to the Markle–Dyson prototype (λ=248 nm, NA=0.7) previously described. A theoretical model based on Hopkins’ formulation of partially coherent imaging was developed and showed agreement with measurement within experimental uncertainty. This demonstrates that the optics are indeed diffraction limited and are operating to specification.
Single component deep-ultraviolet and x-ray resists: The lithographic behavior of poly[(2-methyl-4-t-butoxycarbonyloxystyrene)sulfone] and poly[(3-chloro-4-t-butoxycarbonyloxystyrene)sulfone]
Authors: Neenan Thomas X. , Kumar Uday , Kometani Janet M. , Novembre Anthony E.
Published: July 2002

A series of styrene monomers was prepared having the structure R-4-t-butoxy- carbonyloxystyrene, (R=2-CH3, 3-Cl). The monomers were copolymerized with sulfur dioxide to give copolymers (PMTBSS and PClTBSS, respectively) with the ratio of styrene to SO2 of ∼2:1. The polymers were evaluated as single component deep-ultraviolet (DUV) and x-ray resists and compared to PTBSS, the copolymer of 4-t-butoxycarbonyloxystyrene and sulfur dioxide. No enhancement in sensitivity was observed for either new material under standard processing conditions for either DUV or x-ray (1.4 nm) radiation. However, the enhanced thermal stability of PMTBSS allowed higher postexposure bake (PEB) temperatures (150 versus 140 °C), and using a PEB of 150 °C, PMBTSS showed an x-ray sensitivity of 8–10 mJ/cm2 as compared to 18 mJ/cm2 for PTBSS.
Self-aligned fabrication of arrays of back-to-back external 45° reflectors integrated with ridge-waveguide lasers for surface-emitting high-power semiconductor laser sources in AlGaAs/GaAs
Authors: Porkolab G. A. , Wolf E. D.
Published: July 2002

A self-aligned fabrication process is presented for making surface-emitting high-power AlGaAs/GaAs GRIN-SCH-SQW semiconductor laser sources designed to produce ≳1 W optical output at the nominal GaAs wavelength of 830 nm. The process uses double-layer masking with photoresist masks used as repeatedly changed selector masks on top of a semimetallic amorphous carbon (SMAC) mask which is an unchanging master mask on top of the AlGaAs/GaAs. The SMAC master mask, defined in one photolithography step, thus assuring the self-alignment, contains all the edges to be etched at all the different angle/depth specifications. Four separate Cl+2/Cl2 chemically assisted ion beam etches of AlGaAs/GaAs at three different angle/depth specifications create the three-dimensional microstructures of vertical ridges, back-to-back external 45° reflectors, and vertical laser facets with current deflection trenches, in large arrays. Final encapsulation is by plasma-enhanced chemical-vapor-deposited (PECVD) amorphous silicon-rich nitro-oxide hydrogenated (a-SiwNyOz:H), thin film having triple use as chemical passivation, optical antireflection coating, and electrical insulation. We propose that PECVD amorphous silicon-rich carbo-nitro-oxide hydrogenated (a-SiwCxNyOz:H), thin film might be an improved triple-use encapsulation thin film.
Fabrication of Y-gate, submicron gate length GaAs metal–semiconductor field effect transistors
Authors: Ren F. , Pearton S. J. , Lothian J. R. , Abernathy C. R.
Published: July 2002

0.1 μm Y-shape metal contacts for use as gates on GaAs metal–semiconductor field effect transistors (MESFETs) are produced using a novel SiNx deposition over features 1–2 μm wide, with subsequent etchback and gate metal deposition. Excellent across-wafer uniformity (≤10%) on 3 in. φ substrates is achieved, yielding a simple technique for extending the resolution of conventional optical lithography tools. One of the key features in this method is the need to have an initial negative resist profile. The SiNx is deposited at low temperature (50 °C) by plasma-enhanced chemical vapor deposition in order to avoid distortion of the resist, and exhibits conformal coverage over the initial resist openings. Submicron gate GaAs MESFETs fabricated by this technique have extrinsic transconductance, gm, value of ∼225 mS mm−1 at −0.5 V gate bias, and have comparable performance to devices fabricated using electron-beam lithography to produce a more conventional T-shape gate.
Integrated approach to quantum dot fabrication
Authors: Rishton S. A. , Lee Y. H. , Milkove K. R. , Hong J. M. , Boegli V. , DeFranza M. , Sivan U. , Kern D. P.
Published: July 2002

A method of fabricating individually contacted quantum dots of dimensions down to 0.14 μm is presented. The dots are defined by electron-beam lithography and electron cyclotron resonance etching. The GaAs/AlGaAs heterostructures include additional layers beneath the defined dots to serve as a spectrometer to analyze the level structure in the dots. The conductance of the dots scales well with area over six orders of magnitude.
Focused ion beam interaction with a shallow two-dimensional electron gas
Authors: Soh Yeong-Ah , Snider Gregory L. , Skvarla Michael J. , Craighead Harold G.
Published: July 2002

It is demonstrated that Be ion implantation using a focused ion beam (FIB) can be used for the fabrication of fine feature size two-dimensional electron gas devices. A careful investigation to reduce the width of the FIB-induced insulating region was performed by varying the dose of the implantation. The narrowest constriction obtained using 200 keV Be2+ was 0.5 μm, smaller than those fabricated using 100 keV Ga+. Numerical simulations of the band diagram and charge distribution of the implanted structure were done to describe this behavior. A comparison with experimental results indicates the presence of channeling for Ga implantation and the existence of a mechanism that is more than compensation of donors for the creation of barriers induced by Be implantation.
Low-loss beamwidth transformers on InP with reduced requirements on lithographic resolution
Authors: Zengerle R. , Brückner H. J. , Hübner B. , Weiershausen W.
Published: July 2002

An optimized waveguide taper structure is investigated for the efficient spot-size transformation of guided waves on InP-based optoelectronically integrated circuits. The simple two-layer structure is suitable for very low-loss chip-fiber interconnections. Using a special layout and process steps, the earlier strong requirements on lithographic resolution can be reduced to values of 200–300 nm, maintaining, however, the low-loss transformation properties. The quality of different process sequences are compared with respect to their loss properties.
Electron optical properties and aberrations of field emission microsources
Authors: Ximen Jiye , Ximen Hongyu , Zhou Li
Published: July 2002

Because of the rapid development of microfabricating and micromachining semiconductor devices, the need to design a miniaturized electron beam system has drawn much attention. In this article, different types of field emission source were investigated by taking space charge effects into consideration and using the second order finite element method. Scaling down the dimensional sizes from the conventional field emission source to the field emission microsource, electron optical properties for these field emission sources have been systematically calculated, including spherical and chromatic aberrations, diameter of crossover, the probe size, and the brightness. The microelectron sources proposed in the present study possess better performances than the conventional ones and thus can be used to develop microscanning electron microscopes and microelectron beam writing/reading devices.
Au(111) 23×√3 surface as a test surface for comparing the atomic force and scanning tunneling microscopes
Authors: Oden P. I. , Tao N. J. , Lindsay S. M.
Published: July 2002

The first observation of a surface reconstruction with an atomic force microscope (AFM) is reported. The Au(111) p×√3(p∼22–30) surface under electrochemical potential control has been studied. Values for the periodicities and corrugation of the reconstruction that are similar to those found with a scanning tunneling microscope (STM) are obtained. This is an important test of instrumental artifacts owing to the high electric field and uncontrolled contact force in the STM. The STM consistantly yields higher resolution of the reconstruction, although both techniques also consistantly show an ‘‘atomic’’ lattice at high magnification. This apparent contradiction suggests that the atomic resolution in the AFM may be caused by atomic-scale periodicity in the tip–substrate interaction rather than by true single atom contact. This cannot be explained by tip geometry because the corrugation of the p×√3 reconstruction is much less (∼0.15 Å) than the height of a single atomic step on the Au(111) surface.
Effect of oxygen ions on filling SiO2 into holes using biased electron cyclotron resonance plasma deposition
Authors: Machida Katsuyuki , Hashimoto Chisato , Oikawa Hideo
Published: July 2002

An SiO2 filling technique is proposed for holes with an aspect ratio (depth/diameter of hole) of over 2.0 left after the metallization process. It is found that the oxygen ions introduced during bias electron cyclotron resonance (ECR) plasma deposition selectively etch the SiO2 at a hole edge, but do not etch the metal. The selective etching prevents the opening part of the hole from closing, and the directionality of the deposition particles with bias ECR plasma deposition makes it possible to deposit SiO2 into the hole bottom. By applying this technique before the interlevel dielectric planarization process using argon gas during bias ECR plasma deposition, 0.3-μm-diam metallized holes are filled with SiO2 film that are void-free and perfectly planarized.
Phosphorus doping in low-pressure silicon selective epitaxial growth
Authors: Wang Wei-Chung , Denton John P. , Neudeck Gerold W.
Published: July 2002

In situ phosphorus doping in silicon selective epitaxial growth (SEG) and epitaxial lateral overgrowth, using a reduced pressure radio-frequency heated pancake reactor, was studied. Phosphorus doping ranging from 1016 to 1018 atoms/cm3 was achieved at 920–1020 °C and pressures of 40–150 Torr. It was observed that phosphorus concentration increased with increasing phosphine dopant flow rate. Lower temperature and pressure, along with a smaller HCl/DCS flow rate ratio, were preferred for larger phosphorus concentrations in SEG. Undoped SEG deposited at 970 °C and 40 Torr was characterized by diodes and bipolar transistors which indicated good material quality.
Patterning of C60 films
Authors: Hamza A. V. , Balooch M. , Tench R. J. , Schildbach M. A. , Hawley-Fedder R. A. , Lee H. W. H. , McConaghy C.
Published: July 2002

Lines of C60 films with widths between 3 and 5 μm and heights of 0.4–0.8 μm have been patterned on a Si(100) substrate using photoresist and liftoff techniques. Smooth 50 Å root mean square roughness films were detected by atomic force microscopy. Auger depth profiling showed no impurities in the film. Fourier transform infrared spectroscopy confirmed the film was composed of C60. An estimate of the C60 sticking probability onto a growing C60 film is ∼0.2.
Lateral straggle of Si and Be focused-ion beam implanted in GaAs
Authors: Vignaud D. , Musil C. R. , Etchin S. , Antoniadis D. A. , Melngailis J.
Published: July 2002

The lateral distribution of focused-ion-beam implanted Si and Be atoms has been studied by measuring the electrical resistivity in grating structures. The gratings which were oriented perpendicular to the direction of the current flow were implanted with silicon and beryllium at 280 and 260 keV, respectively. They were implanted into semi-insulating materials cut on and off axis, and then rapid thermal annealed. The lateral straggle was found to be less than 100 nm for Si and equal to 190 nm for the Be implants. The standard deviation of the lateral distribution was found to increase with the dose. This is attributed to a concentration-dependent diffusion which results in an anomalously high diffusion coefficient. Comparison of the experimental parameters of the implanted distribution with values found in standard tables or calculated by a Monte Carlo trim code seems to indicate that all simulations overestimate the lateral straggle at the expense of the penetration depth.
Highly selective reactive ion etch process for InP-based device fabrication using methane/hydrogen/argon
Authors: Schramm Jeff E. , Hu Evelyn L. , Merz James L. , Brown Julia J. , Melendes Melissa A. , Thompson Mark A. , Brown April S.
Published: July 2002

The etch rates of GaInAs and AlInAs were characterized using a mixture of methane, hydrogen, and argon as a function of self-bias voltage. Effectively infinite etch selectivity between GaInAs and AlInAs was found for voltages below 200 V. This highly selective etch process was applied to the gate recess of a high electron mobility transistor device, and preliminary device measurements were made.
Magnetic microlens with an atomically sharp field emitter
Authors: Terris B. D. , Züǵer O. , Rugar D.
Published: July 2002

The design and performance of a simple magnetic microlens for the focusing of electron beams are described. A chemically etched tungsten field emission tip was placed between the poles of two high strength permanent magnets, and the emitted electrons focused. By in situ sharpening of the tip, an emission angle of 2° was obtained and a 2σ spot size of 80 nm was achieved at a distance of 2 mm. By mechanically scanning a sample through the focused beam, images of a test sample were obtained.
Stepper focus characterization using diffraction from latent images
Authors: Milner Lisa M. , Bishop Ken P. , Naqvi S. Sohail H. , McNeil John R.
Published: July 2002

We present a novel technique for the rapid, nondestructive evaluation of the contrast of the latent image in photoresist. Measurements are made of the intensity of light diffracted from a grating pattern in exposed, undeveloped photoresist, the so-called latent image. Optimum exposure tool parameters such as exposure tool dose and focus can be determined based on the intensity of light diffracted into specific orders. Employing the proposed technique, measurements can be made sufficiently fast to allow rapid control of the exposure conditions, such as focus, which influences image contrast. The measurement can be made after an exposure, and corrections to focus for subsequent exposures may be derived to compensate for changing optical or mechanical properties of the wafer. The technique may be used with a variety of photoresist materials on different substrates.
Silicon spikes and impurity accumulation at interrupted growth interfaces during molecular-beam epitaxy
Authors: SpringThorpe A. J. , Moore W. T. , Majeed A. , Streater R. W.
Published: July 2002

Recent proposals by Wood and Wilson [C. E. C. Wood and R. A. Wilson, J. Vac. Sci. Technol. B 11, 1036 (1993)], to explain the formation of impurity spikes at substrate/epitaxial layer interfaces in GaAs prepared by molecular-beam epitaxy (MBE), have been experimentally investigated. Their suggestion that the spikes form due to suboxide transport via reactions that involve the As2O3 released from the substrate during oxide desorption and hot Knudsen cells, is not supported by the experimental data. The same authors have also speculated that there may be significant flux leakage from nominally closed cells. For this to occur, reflection and scattering of flux by inadequately cooled cryoshroud baffle surfaces are necessary. Secondary ion mass spectrometry analyses of interfaces, at which the growth of GaAs and AlAs was interrupted for times up to 30 min, confirm that this takes place. However, flux leakage is only found to be significant for the high vapor pressure group III elements. For these elements, incorporation levels in the range 0.02%–0.1% are found under normal deposition conditions. These results suggest that careful attention should be given to increasing the internal MBE system baffling in order to eliminate cross contamination problems.
One-dimensional wire formed by molecular-beam epitaxial regrowth on a patterned pnpnp GaAs substrate
Authors: Burroughes J. H. , Grimshaw M. P. , Leadbeater M. L. , Ritchie D. A. , Pepper M. , Jones G. A. C.
Published: July 2002

We have grown high mobility one-dimensional electron gases by molecular-beam epitaxy (MBE) on etched GaAs pnpnp facets. By applying the appropriate bias to the p- and n-GaAs layers which serve as a unique backgate, the electron gas width and mobility may be controlled. The width may be varied between about 400 and 100 nm. We also find that the mobility increases up to about 6×105 cm2/V s, rather than decreases with falling carrier concentration.
High-quality strained quantum wires grown by molecular beam epitaxy on (100) GaAs substrate
Authors: Chen Y.-P. , Reed J. D. , Schaff W. J. , Eastman L. F.
Published: July 2002

High-radiative recombination efficiency arrays of InGaAs/GaAs strained quantum wires have been fabricated by a combination of e-beam lithography, dry and wet etching, sidewall desorption, migration-enhanced epitaxial and molecular beam epitaxial regrowth. The structure was evaluated by reflection high-energy electron diffraction, cross-sectional transmission electron microscopy, and photoluminescence spectroscopy. Transmission electron microscopy study showed that a defect-free regrown layer and excellent sidewall coverage have been attained. From the photoluminescence measurement, the sample showed high-radiative efficiency, and had strong photoluminescence for wire widths down to 190 nm.
Observation of quantum mechanical reflections of electrons at an in situ grown GaAs/aluminum Schottky barrier
Authors: Weckwerth M. V. , van der Wagt Jan P. A. , Harris James S.
Published: July 2002

The room temperature observation of quantum mechanical reflections of electrons at an aluminum/gallium arsenide Schottky barrier is reported here. Molecular-beam epitaxy was used to grow an AlAs/GaAs/AlAs double barrier resonant tunneling diode (RTD) followed by an epitaxial in situ grown aluminum/gallium arsenide Schottky barrier. This RTD was used to inject a nearly monoenergetic beam of electrons towards the Schottky barrier. The measured I–V curves show resonances associated with the reflections of electrons at the Schottky interface. Understanding the transport properties of hot electrons at a Schottky barrier may prove important for understanding the physics of metal base transistors and other device structures that employ the use of epitaxial metals.
Structural and optical characterizations of InAsP/InP strained multiple quantum wells grown on InP (111)B substrates
Authors: Hou H. Q. , Tu C. W. , Shan W. , Hwang S. J. , Song J. J. , Chu S. N. G.
Published: July 2002

InAsP/InP strained multiple quantum wells (MQWs) with specular surfaces were grown on InP (111)B substrates by gas-source molecular beam epitaxy. Cross-sectional transmission electron microscopy and high-resolution x-ray rocking curves show that the InAsP/InP (111)B MQW structures possess sharp and uniform interfaces, excellent periodicity, and crystalline quality. Structural parameters were extracted accurately from a dynamical-theory simulation by considering the anisotropy of the (111) strain tensor. Low-temperature photoluminescence and photoluminescence excitation measurements revealed interband excitonic transitions, and the energies agree with a calculation with an internal piezoelectric field taken into account.
Bonding and migration of 111In atoms on GaAs surfaces studied by perturbed-angular-correlation spectroscopy
Authors: Fu Jianming , Adams James M. , Catchen Gary L. , Miller D. L. , Kim J. , Gallagher M. C. , Willis R. F.
Published: July 2002

The first application of perturbed-angular-correlation (PAC) spectroscopy to study the incorporation and diffusion of In atoms on GaAs surfaces is reported here. A PAC-MBE system has been established to perform in situ PAC measurements on surfaces grown by molecular beam epitaxy. To define the surface conditions that the PAC experiments are based on, scanning tunneling microscopy is used to characterize the topography of similar surfaces grown under identical conditions. To perform the PAC surface experiments, 111In–111Cd radioactive probe nuclei are deposited onto the surface to be studied in trace quantities (10−4 ML). The measured physical quantity is the electric-field-gradient tensor at the probe site. Preliminary results show that In atoms are incorporated into several types of sites on (001) and (111)B surfaces. These surface sites are characterized by well-defined electric-field gradients. These results show that PAC spectroscopy is sensitive to the local atomic arrangement of surface atoms. Moreover, annealing experiments show that changes in electric-field gradients associated with surface-site conversion characterize surface processes on GaAs such as diffusion, desorption, and adsorption.
Interface analysis of dry etched and molecular beam epitaxial regrown AlGaAs
Authors: Grober L. H. , Hong M. , Mannaerts J. P. , Freund R. S. , Luftman H. S. , Chu S. N. G.
Published: July 2002

Many novel optoelectronic devices can be realized by the technique of molecular beam epitaxy regrowth on etched surfaces. A smooth etched surface free from contaminants is necessary as this surface determines the success of the regrowth and the etched/regrown interface affects the performance and reliability of the devices. We have systematically studied the contaminants at the etched and regrown interface of Al0.4Ga0.6As for various steps of our in situ process. Using secondary ion mass spectroscopy, transmission electron microscopy, and mass spectroscopic analysis we have pinpointed what we believe to be the sources of carbon, oxygen, and silicon contamination in the etch chamber and have taken steps to eliminate them.
Advanced electron cyclotron resonance plasma etching technology for precise ultra-large-scale integration patterning
Authors: Samukawa Seiji
Published: July 2002

Ultra-large-scale integration patterning with less than 0.25-μm precision requires the optimization of electron cyclotron resonance (ECR) plasma discharge. This is because ion motion and etching results are affected by magnetohydrodynamic plasma instability and charge accumulation on the substrate in nonuniform plasma. Microloading and unusual notching at the boundary pattern between dense patterns and open spaces are both caused during n+ poly-Si etching in nonuniform plasma. To prevent these problems, optimally uniform ECR plasma generation is necessary. This is accomplished by optimizing both the magnetic field profile and the introduction of microwaves.
Discretization of curved lines and arbitrary areas for ion and electron beam writing on a nonrectangular grid
Authors: de Vries D. K. , Wieck A. D. , Ploog K.
Published: July 2002

A method is presented to discretize almost arbitrary curves and areas on nonrectangular grids. This method can be applied in focused ion and electron beam systems. Distortion of the physical writing grid can be taken into account at the discretization, thus eliminating the need for a correction step afterwards.
Fabrication and characterization of an array of gated avalanche p+–n++ junction as a micro-vacuum triode
Authors: Li Q. , Kang W. P. , Yaun M. Y. , Xu J. F. , Zhang D.
Published: July 2002

An array of 3×4 ultrashallow p+–n++ silicon junctions with gate (grid) structure has been developed for application as a micro-vacuum triode. The device is fabricated by low energy ion implantation in conjunction with a new anode oxidation technique. The final junction depth is estimated to be 150 Å. Device structure and fabrication processes, especially on the formation and monitoring of the ultrashallow junction, are described. The current emission characteristics of the triode are investigated as a function of anode voltage, gate (grid) voltage, anode–emitter distance, and reverse bias current. The typical emission efficiency measured on bare silicon is 7.6×10−5.
Scanning tunneling microscope tip-induced anodization of titanium: Characterization of the modified surface and application to the metal resist process for nanolithography
Authors: Sugimura Hiroyuki , Uchida Tatsuya , Kitamura Noboru , Masuhara Hiroshi
Published: July 2002

Nanometer scale oxide patterns were fabricated on titanium (Ti) surfaces on the basis of scanning tunneling microscope (STM) tip-induced anodization. The spatial resolution of the method was limited to approximately 20 nm, owing to the surface roughness of the Ti film used. Chemical analyses of fabricated patterns by Auger electron spectroscopy proved that the surface chemical composition of the pattern was titanium dioxide (TiO2), and the oxide thickness on the pattern was certainly thicker than that of the native oxide on the unmodified area. A novel Ti-metal resist process for nanolithography based on STM tip-induced anodization was proposed. The Ti film on which anodized patterns were formed could be etched by hydrofluoric acid using the anodic oxide patterns as an etching mask. Ti lines of ∼60 nm in width were successfully fabricated by the present method.