bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic and microstructural properties of disorder-induced gap states at compound semiconductor–insulator interfaces
Authors: Hasegawa Hideki , He Li , Ohno Hideo , Sawada Takayuki , Haga Tetsuya , Abe Yutaka , Takahashi Heishichirou
Published: July 2002

In order to clarify the structure and properties of the disordered semiconductor layer which forms the basis of the recently proposed disorder-induced gap state (DIGS) model, the electronic and microstructural properties of the compound semiconductor insulator–semiconductor interfaces (InP, GaAs, AlGaAs, InGaAs) are studied using C–V, isothermal capacitance transient spectroscopy, photocapacitance transient spectroscopy, cross-sectional transmission electron microscopy, Rutherford backscattering spectrometry, and x-ray and ultraviolet photoemission spectroscopy techniques. Based on the experimental results, a detailed model of the disordered layer which consists of a disordered crystal region and a graded amorphous region is presented. In these two regions, DIGS are distributed both in energy and space. The model can reproduce the observed hysteresis behavior remarkably well, and can explain the observed anomalous thermal and optical transient behavior. The measured location of the charge neutrality point EHO of DIGS continuum with respect to the valence-band maximum agrees well with the theoretical locations of the hybrid orbital energy based on sp3s* tight binding theory for various semiconductors.
Laser probing of gallium atom interactions with silicon(100) surfaces
Authors: Carleton Karen L. , Leone Stephen R.
Published: July 2002

The interactions of gallium atoms with silicon (100) surfaces are studied with laser probing. Laser-induced fluorescence is used to interrogate either the Ga 2P1/2 or 2P3/2 state following desorption from a 2×1 reconstructed Si(100) surface. From isothermal desorption measurements, the desorption energy of Ga on silicon is determined to be 277±7.5 kJ/mol (66±2 kcal/mol or 2.9 eV) with a frequency factor of 6×1014±1 s−1. Temperature programmed desorption heating rate studies give slightly larger values for the desorption energy and preexponential factor, but these results appear to be less reliable because of thermal lags in the temperature measurement. The strong gallium–silicon bond is consistent with the unity sticking coefficient observed here and the fact that the scattering is dominated by a trapping desorption mechanism. The value of the preexponential factor is suggestive of a one-dimensional mobility of the Ga atoms on the 2×1 silicon (100) surface.
Ga2O3 and particulates: The origins of oval defects in GaAs-related molecular-beam epitaxy
Authors: Weng Shang-Lin
Published: July 2002

Based on micrographic evidence, thermodynamic data, and quantitative analysis, we show that the predominant origins of oval defects in GaAs-related molecular-beam epitaxy are particulates on the wafer surface and Ga2O3 in the Ga melt. Both sources can be traced to contamination in the wafer preparation environment and in the Ga melt used, respectively. Substrate defects are also found to induce the formation of oval defects under improper growth conditions. We propose a thermodynamic mechanism, which explains how Ga2O3 in the Ga melt can lead to the formation of oval defects on the epilayer surface.
Lift-off metallization using poly(methyl methacrylate) exposed with a scanning tunneling microscope
Authors: McCord M. A. , Pease R. F. W.
Published: July 2002

The scanning tunneling microscope (STM) is a unique tool for ultrahigh resolution, ultralow voltage electron beam lithography. In a previous paper we described the formation of metallic patterns by a ‘‘contamination’’ process followed by sputter etching. Here we report the formation of 22-nm-wide metal lines by STM exposure of poly(methyl methacrylate) (PMMA) resist followed by liftoff. Resist exposure and liftoff have also been achieved with reverse polarity, where the electrons are emitted from the resist sample and accelerated towards the tip. Results include the first working device made with a STM, a thin-film resistor 2 μ long and 120 nm in width. In addition to lithographic applications, studying resists in this regime may offer new insights on the chemical process of resist exposure and the role played by secondary electrons in exposing resist. Our results indicate that PMMA only works as a negative resist for energies above 25 eV; below this value it appears that the electrons cannot cause sufficient crosslinking to render the resist insoluble in the usual solvents.
(AlAs)1/2(GaAs)1/2 fractional-layer superlattices grown on (001) vicinal GaAs substrates by metal–organic chemical vapor deposition
Authors: Fukui Takashi , Saito Hisao
Published: July 2002

(AlAs)1/2(GaAs)1/2 fractional-layer superlattices with a new periodicity perpendicular to the growth direction are successfully grown, by metal–organic chemical vapor deposition on (001) GaAs substrates, slightly misoriented towards [1̄10]. The periodic structure in the lateral [1̄10] direction is analyzed by x-ray superlattice satellite diffraction and high-resolution transmission electron microscopy(TEM). Superlattice width along [1̄10] direction are exactly the same as the mean distance of each monolayer step on the (001) vicinal surface. The satellite peak intensity increases with increasing AsH3 partial pressure, and is stronger for substrates misoriented towards [1̄10] than those misoriented towards [110]. The result can be explained using the lateral growth model, taking into account the dangling bond at the step edge. The superlattice image is clearly observed by TEM, which shows that the superlattice periods are almost uniform everywhere.
Finite difference programs for computing tolerances for electrostatic lenses
Authors: Munro E.
Published: July 2002

A set of programs has been developed for computing aberrations caused by small imperfections in the construction and alignment of electrostatic lenses. The programs predict the beam displacement and coma caused by misalignments and tilts, and the astigmatism caused by ellipticities, of each electrode. Any number of electrodes can be handled, and they can be of any shape. The finite difference method is used to compute first the potential distribution in the ideal rotationally symmetric lens, and then the perturbations in the potential distribution caused by small changes in the position and shape of each electrode. Finally, the asymmetry aberrations are calculated using aberration integrals. Computed results are presented for three typical electrostatic lenses, to illustrate the calculation of tolerances for electrostatic lenses for focused ion beam systems. The programs are very simple to use and can all be run in a few minutes on a personal computer.
Characterization of single step-edge defects using He atom scattering
Authors: Hinch B. J. , Lock A. , Toennies J. P. , Zhang G.
Published: July 2002

He atom scattering (HAS) has been used to study surface step-edge defects. The diffuse elastic scattering from steps show characteristic intensity oscillations with scattering angles along certain azimuths. The form of these oscillations has been compared with Eikonal calculations to find the effective step-edge shapes. The shape parameters of steps on the Pt(111), Al(111), Ni(001), and Cu(111) surfaces have been determined. In addition, diffuse intensities of Cu(111) have been measured showing annealing of step edges. The thermal behavior of step edges is dependent on the exact means of step preparation and exhibits a memory effect.
Energy dependence and depth distribution of dry etching-induced damage in III/V semiconductor heterostructures
Authors: Germann R. , Forchel A. , Bresch M. , Meier H. P.
Published: July 2002

We have investigated the depth distribution, energy dependence, and the effect of the angle of incidence of ion beam etching (IBE) induced damage. Our technique is based on the partial etching of the upper GaAlAs barrier of a GaAs single quantum well (SQW) layer. The optical emission of the SQW at low temperatures is used as a local probe for the created damage. The dependence of the quantum efficiency on the etch depth can be described by a Gaussian depth distribution with a typical decay length of 5.6 nm and a non-Gaussian long range tail. Our measurements show a strong dependence of the dry etch damage on the angle of incidence of the ion beam and on the sample orientation.
The sulfurized InP surface
Authors: Wilmsen C. W. , Geib K. M. , Shin J. , Iyer R. , Lile D. L. , Pouch John J.
Published: July 2002

Sulfur treatments have previously been shown to improve the electrical characteristics of InP and GaAs devices. This paper reports the results of an Auger/x-ray photoelectron spectroscopy investigation of the InP surface after sulfur treatment. It is shown that the sulfur remains on the surface bonded to indium. There is no indication of elemental sulfur or sulfur bonded to phosphorus. This suggests that the sulfur has replaced phosphorus on the surface and has filled the phosphorus vacancies.
Ultrashallow Si p+–n junction fabrication by low energy Ga+ focused ion beam implantation
Authors: Steckl A. J. , Mogul H. C. , Mogren S. M.
Published: July 2002

The fabrication of ultrashallow Si p+–n junctions by low energy Ga+ focused ion beam implantation has been investigated at energies ranging from 5 to 15 keV. Post-implantation rapid thermal annealing was performed at 600 °C for 30 s to activate the implanted Ga and to regrow the implanted layer. Secondary ion mass spectroscopy (SIMS), spreading resistance profile (SRP), and cross-sectional transmission electron microscopy (TEM) have been employed to characterize the resulting Ga atomic concentration depth profile and the structure of the implanted layer. For 5 keV Ga+ implantation, the cross-sectional TEM (xTEM) measurement yielded an amorphous layer thickness of 9 nm and a line of end-of-range defects 16 nm below the surface [after rapid thermal annealing (RTA)]. The SIMS profiles indicate that only minor Ga channeling occurred during implantation. The SRP measurements give a junction depth of only 20 nm for the 5-keV Ga implants. Leakage current density of 20 nA/cm2 has been measured at 5 V reverse bias.
A unified line-of-sight model of deposition in rectangular trenches
Authors: Cale T. S. , Raupp G. B.
Published: July 2002

The integro-differential equations which describe free molecular flow in long rectangular trenches in the absence of deposition and to both low pressure chemical vapor deposition (LPCVD) and physical vapor deposition (PVD) are derived. A pseudosteady state assumption is implicit in the formulation, i.e., the feature dimensions change slowly relative to the time required for the flux to redistribute in response to the changes. Numerical solution of the governing equations provides film and deposition rate profiles as a function of deposition time until the trench is completely filled. Solutions are discussed for selected values of the sticking coefficient from zero to unity. The calculated film profiles are consistent with empirical results which typically show poor uniformity in PVD and step coverage increasing with decreasing sticking coefficient in LPCVD. Film profiles compare well with Monte Carlo based simulations of deposition processes.
Perfect selective and highly anisotropic electron cyclotron resonance plasma etching for WSix/poly-Si at electron cyclotron resonance position
Authors: Samukawa Seiji , Sasaki Masami , Suzuki Yasuhiro
Published: July 2002

Perfect selective and highly anisotropic etching for tungsten polycide (WSix/poly-Si) structure without sidewall protection is achieved at the electron cyclotron resonance (ECR) position in a newly developed ECR plasma etching system. The etching selectivity ratio of WSix/poly-Si structure etching to SiO2 etching is infinite by using Cl2/SF6/O2 gas mixture under 5×10−4 Torr. The etching rate is more than 2000 Å/min with no radio frequency bias above selectivity conditions. The addition of a small amount of SF6 is efficient for removing tungsten residue. The perfect etching selectivity is caused by low ion energy at the ECR position and the effect of O2 gas addition. The high etching rate is achieved by high ion current density at the ECR position. Furthermore, a highly anisotropic etching profile is realized at the substrate temperature of 60 °C.
Electronic and geometric structure of clean InP(001) and of the CaF2/InP(001) interface
Authors: Weiss W. , Hornstein R. , Schmeisser D. , Göpel W.
Published: July 2002

In low-energy electron diffraction (LEED), we find two different reconstructions of the technologically important InP(001) surface, the well known (4×2) structure and a high temperature (4×2) structure with streaks at the half order spot positions which is interpreted as a disordered c(8×2) structure. The corresponding electronic structures were investigated by ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS). For both types of reconstructions, we observe a surface state emission at the valence-band maximum and a strong fermi-level pinning. CaF2 was deposited onto these surfaces, and the interface formation was studied by LEED, UPS, and XPS. The overlayer grows epitaxially with (001) orientation of its bulk fluorite structure inspite of the large lattice mismatch of 7.5%. The electronic interface scheme with its valence-band discontinuity was deduced from photoemission measurements as a function of overlayer coverage. Band bending at the interface results from p-type defects.
Achievement of exceptionally high mobilities in modulation-doped Ga1−xInxAs on InP using a stress compensated structure
Authors: Chin Albert , Chang T. Y.
Published: July 2002

We report in this paper the achievement of unprecedented high mobilities of 15 200 and 123 000 cm2/V s with carrier concentrations of 1.84×1012 and 1.81×1012 cm−2 at 300 and 77 K, respectively, through the use of a novel channel design utilizing oppositely strained layers with x=0.25 and 0.80 in Ga1−xInxAs. We have shown experimentally that the critical layer thickness for highly strained Ga1−xInxAs can be effectively enhanced by using such stress compensated structure. This novel modulation-doped heterostructure with very high electron mobility should find important implications in very high speed electronics.
Comparison of exposure, bake, and dissolution characteristics of electron beam and optically exposed chemically amplified resists
Authors: Tam N. N. , Ferguson R. A. , Titus A. , Hutchinson J. M. , Spence C. A. , Neureuther A. R.
Published: July 2002

Fourier-transform infrared (FTIR) spectrometry and dissolution rate measurements are used to compare chemical–physical mechanisms in electron beam and deep-ultraviolet (UV) optical exposure of a chemically amplified negative crosslinking resist, Shipley XP-8843 (SNR-248). In contrast to optical exposure, up to 20% of the maximum extent of reaction by the melamine crosslinking agent, as measured by the change in peak-to-peak absorbance of the infrared (IR) spectrum at 990–1070 cm−1, was observed after electron beam exposure at nominal exposure doses of 0.5–3 μC/cm2. For both electron-beam and optical exposure, the kinetics of the acid-catalyzed crosslinking reactions during the postexposure bake (PEB) were similar and the saturation value of the crosslinking reaction measured by the FTIR was identical. A plot of the dissolution rate versus the degree of crosslinking for normal lithographic doses was single-valued and tended to follow comparable data for optical exposure. When doses >5 μC/cm2 are used without a PEB, the slowing of the dissolution rate is less than expected from IR spectral change. Contrary to typical electron beam exposed negative resists, slightly underexposing small features produced a reentrant profile apparently owing to the high contrast of this resist.
Integrated silicon grid ion extraction system for O2 processes
Authors: Korzec D. , Engemann J. , Bansky J. , Keller H. M.
Published: July 2002

A novel multibeamlet very low energy ion extraction optic technology avoiding cumbersome grid readjustment and thermal degradation of beam properties during a reactive process has been developed. In this approach anisotropically etched silicon grids ([100]-oriented Si wafers) are permanently integrated into a holder made of layered ceramics or micromachined AlN. The performance of such extraction systems having 300, 600, and 900 μm grid separation was tested in a 3 cm capacitively coupled rf-ion source. Stable system operation with use of oxygen has been achieved for an extended period of time (>100 h) for a total extraction voltage of 140 V which represents the maximum voltage to be applied for a grid separation of 0.3 mm. Additionally detailed Faraday-cup measurements of the extracted ion beam have been carried out for a total voltage range of 0–600 V, a vacuum chamber pressure of 1×10−4–1×10−3 mbar, rf-power levels of 10–170 W, a net-to-total voltage ratio of 0.5–1.0 and an axial magnetic field of up to 22 mT. For O2 an ion current density of 1.3 mA/cm2 could be extracted with ions having a mean energy of 60 eV. Even for energies as low as 50-eV current densities of 0.8 mA/cm2 could be achieved. In combination with the filamentless capacitively coupled rf source used, this approach has promise in various fields of materials research and processing such as ion beam assisted deposition of high-Tc YBaCuO layers and etching/modification of diamondlike, diamond and polymer thin films.
Ring structures on natural molybdenum disulfide investigated by scanning tunneling and scanning force microscopy
Authors: Heckl Wolfgang M. , Ohnesorge Frank , Binnig Gerd , Specht Martin , Hashmi M.
Published: July 2002

Ring-like structures of two different sizes on a nanometer scale have been found on natural molybdenum disulfide (MoS2). Investigation by scanning tunneling and scanning force microscopy as well as secondary-ion mass spectroscopy indicate that these rings might originate from included molecules. Synthetic compared to natural MoS2 shows characteristic differences. The origin of these striking structures could be the morphology of organic or even remnants of biological material included at the geological time when the mineral was formed and could therefore be regarded as a result of a molecular fossilization process. The alternative explanation that the ring structure is a nonmorphological and purely electronic effect caused by a point defect like a dopant is also discussed.
Modeling and characterization of a 0.5 μm deep ultraviolet process
Authors: Mack Chris A. , Capsuto Elliott , Sethi Satyendra , Witowski Joyce
Published: July 2002

A half-micron semiconductor manufacturing process using excimer laser lithography, single-layer chemically amplified resist on antireflective coating (ARC), and dry etch processes with in situ ARC development is discussed. Process window characterization experiments, long-term process stability/repeatability data, and initial defect test results are presented. Results show that the complexities added to the process by the incorporation of the ARC are outweighed by the improvement in linewidth control. Additionally, modeling of the lithography process is shown to accurately predict the process window and other lithographic effects.
A scanning tunneling microscope using dual-axes inchworms for the observation of a cleaved semiconductor surface
Authors: Kato T. , Osaka F. , Tanaka I. , Ohkouchi S.
Published: July 2002

We have constructed a new scanning tunneling microscope (STM) that uses x and z inchworms for micropositioning in an ultrahigh vacuum environment. One (z inchworm) is for approaching the tip to the sample surface and the other (x inchworm) is for both cleaving the sample and moving the sample to positions of interest. We have demonstrated that this STM is very useful for observing the cross section of a thin epitaxial layer, such as the cleaved (110) surface of a Ga0.47In0.53As/InP multiquantum well (MQW) structure. The STM image of GaInAs well layers and InP barrier layers has been shown to reflect the feature of the MQW potential. Moreover, we have obtained images of the filled states on the group-V anions in the GaInAs and InP layers.
Scanning tunneling microscopy: Critical dimension and surface roughness analysis
Authors: Files-Sesler Leigh Ann , Randall John N. , Harkness David
Published: July 2002

Applications of a scanning tunneling microscope combined with an optical microscope for metrology are reported. The ability to perform critical linewidth measurements on device structures is demonstrated. The need for such a high-resolution metrology tool is illustrated by comparing scanning electron microscope and scanning tunneling microscope images of metal contacts for quantum devices which were fabricated by e-beam lithography and metal lift-off. These contacts are typically 100 nm in diameter and vary between 30 and 100 nm in height. Another topic being addressed is the effectiveness of annealing and electropolishing on the topography of stainless-steel tubing interior surfaces. This study was initiated to reduce particle entrapment in liquid and gas supply lines being designed for our new fabrication facilities at Texas Instruments.
Theoretical interpretation of scanning tunneling microscopy images: Application to the molybdenum disulfide family of transition metal dichalcogenides
Authors: Coley Terry R. , Goddard William A. , Baldeschwieler John D.
Published: July 2002

We have performed ab initio quantum mechanical calculations to describe scanning tunneling microscopy (STM) images of MoS2 and MoTe2. These results indicate that the interpretation of the STM images of these and related materials depends sensitively on experimental conditions. For example, determining whether the maximum tunneling current correlates to the top atom (S or Te) or to the second-layer atom (Mo) requires information on the tip-sample separation. Based on these results we discuss some STM experimental procedures which would allow assignment of the chemical identity of STM spots with greater certainty.
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u overgrowth on GaAs patterned by focused-ion-beam-assisted Cl2 etching
Authors: Sugimoto Y. , Taneya M. , Akita K.
Published: July 2002

I n situ pattern formation of GaAs by focused-ion-beam (FIB)-assisted Cl2 etching followed by overgrowth by molecular-beam epitaxy (MBE) has been studied. In situ Auger electron spectroscopy (AES) measurements of the etched samples showed that preferential sputtering of As, which was observed on a GaAs surface processed by ion sputtering, did not take place on a GaAs surface processed by FIB-assisted Cl2 etching. The surface morphology of the overgrown AlGaAs layer on the in situ patterned substrates were excellent. Observations of the cross-sectional view in the etched region of an overgrowth sample showed that the interface between the etched surface and the overgrown layer was flat, and that no undulations caused by etching were observed. A 1-μm linewidth with a 2-μm pitch line-and-space pattern of GaAs covered with an AlGaAs layer was obtained by a combination of FIB-assisted Cl2 etching and subsequent MBE overgrowth.
The effect of submonolayer Sn δ-doping layers on the growth of InGaAs and GaAs
Authors: Petrich G. S. , Dabiran A. M. , Macdonald J. E. , Cohen P. I.
Published: July 2002

We have studied the effect of Sn coverage on the growth of GaAs and strained InGaAs on GaAs(001) by reflection high-energy electron diffraction (RHEED). Upon deposition of fractional monolayer (ML) amounts of Sn on the GaAs(001) surface, the (2×4) reconstruction disappeared and the diffracted beam intensities decreased. However, there was no change in the width of the beams nor was there an increase in the diffuse scattering—indicating an epitaxial Sn or tin—arsenide formation. This submonolayer coverage was found to enhance the layer-by-layer growth of GaAs and was found to remain at the surface longer than previously predicted. Most dramatically, strong beats in the RHEED intensity oscillations during GaAs growth were observed at a Sn coverage of ∼0.3 ML. The growth of GaAs on a vicinal (001) surface after the deposition of Sn, was found to order the step terrace lengths and to reduce the meandering of the steps. The vicinal (001) surface oriented toward [11̄0] ultimately ordered more than the one oriented toward [110]. For InxGa1−xAs with x=0.36 or 0.54, the transition between the two-dimensional and three-dimensional growth modes was found to be independent of the Sn coverage. This last result indicates that at these mole fractions and under the growth conditions used here, Sn does not appear to act as a surfactant for the growth of InGaAs.
Mercury cadmium telluride material requirements for infrared systems
Authors: Balcerak Raymond , Brown Lynette
Published: July 2002

High-quality semiconductor material is essential to the production of high performance, affordable semiconductor components. With infrared (IR) components, the maturity and quality of the material has an increased significance, affecting not only component characteristics, but also system performance and cost. The criteria for selection of the focal plane material involves consideration of the system cooling requirements, spectral band, nonuniformity correction, and even system reliability. Each of these system parameters has a direct relationship to the IR material. The system requirements place demands on the quality and cost of the starting material and help to define the appropriate material growth technique, wafer size, the requirements for on-chip signal processing, and relevant material figures-of-merit. A concurrent engineering approach to IR material development is necessary, taking into account both the material limitations and the demands of the infrared imaging system for the proposed application. In addition to the material performance figures-of-merit, the impact of the material on device fabrication and system cost must be taken into account. Ideally, a quantitative assessment of the effect of IR material characteristics on detector module cost and on system complexity should guide this process. Mercury cadmium telluride (MCT) has been the dominant IR material for a broad range of system applications. However, the cost and availability of the MCT are major considerations in the production of affordable IR local plane arrays. This article discusses these general issues relative to the state-of-the-art of this IR material, and provides generic guidelines for the selection of material for IR imaging applications.
Submicron modulation-doped field-effect transistor/metal–semiconductor–metal-based optoelectronic integrated circuit receiver fabricated by direct-write electron-beam lithography
Authors: Ketterson A. , Tong M. , Seo J.-W. , Nummila K. , Cheng K. Y. , Morikuni J. , Kang S. , Adesida I.
Published: July 2002

An all direct-write electron-beam fabrication process has been developed for the fabrication of monolithic optoelectronic integrated circuits (OEICs). Various electron-beam resist technologies are investigated including image reversed AZ5214, PMMA/P[MMA−MAA] bilayer, and PMMA/P[MMA−MAA]/PMMA trilayer. A novel single-step air-bridge formation process utilizing selective development is described. These processes are demonstrated in the fabrication of a 0.85-μm sensitive OEIC receiver comprised of a metal–semiconductor–metal (MSM) detector integrated with a submicron GaAs/InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistor based transimpedance amplifier. A 3-dB transimpedance bandwidth of 5.6 GHz and a transimpedance bandwidth product of 4.8 THz Ω are measured for the amplifier. Discrete high-resolution MSM photodetectors with finger/gap spacings ranging from 0.1 to 1.0 μm have been fabricated and characterized.
Investigation of high-quantum efficiency InGaAs/InP and InGaAs/GaAs quantum dots
Authors: Schmidt A. , Forchel A. , Straka J. , Gyuro I. , Speier P. , Zielinski E.
Published: July 2002

Using selective wet-chemical etching of the top barrier material of a quantum well, we have fabricated effectively buried quantum dots in the material systems InGaAs/InP and InGaAs/GaAs. The patterning is carried out on InGaAs quantum well samples masked by a high-resolution negative e-beam resist which is used as etch mask. A lateral potential well is formed due to the change of the energy barrier between the original quantum well and the surface quantum well regions. The photoluminescence shows a high efficiency as well as a shift of the luminescence signal to higher energy as the structure size is decreased. For InGaAs/InP single quantum well samples the emission of the open surface quantum well is detected. The emission of the lateral barrier regions is blue-shifted by about 24 meV compared to an unetched reference.
Ion projector wafer exposure results at 5× ion-optical reduction obtained with nickel and silicon stencil masks
Authors: Stengl G. , Bösch G. , Chalupka A. , Fegerl J. , Fischer R. , Lammer G. , Löschner H. , Malek L. , Nowak R. , Traher C. , Wolf P. , Mauger P. , Shimkunas A. , Sen S. , Wolfe J. C.
Published: July 2002

A detailed study of the resolution performance of an advanced research type ‘‘Alpha Ion Projector’’ with 5× ion-optical reduction has been performed. One part of the study was done with a nickel open stencil test mask with an active field of 40 mm×40 mm with smallest line pattern openings of ≊0.7 μm width (2.0 μm periodicity). The other part was done with a silicon stencil test mask (120 mm diam, 2.5 μm thickness, 60 mm×60 mm design field) with smallest line patterns of ≊0.4 μm width (1.0 μm periodicity). The Alpha Ion Projector exposures were performed in positive (PMMA: OEBR-1000) and negative (SNR-M4, RAY-PN) resist materials with subsequent wet chemical development. The 0.15-μm resolution was obtained in the case of wafer exposures with the nickel stencil mask within the 8 mm×8 mm exposure field whereas in the case of wafer exposures with the silicon stencil mask sub-0.1-μm resolution could be achieved near the center of the exposure field at 5.2× ion-optical reduction.
High-quality materials and heterostructures on (111)B GaAs
Authors: Chin Albert , Martin Paul , Das U. , Ballingall Jim , Yu Tan-hua
Published: July 2002

We report the successful growth of high-quality molecular-beam epitaxy (MBE) GaAs, AlGaAs, AlGaAs/GaAs modulation-doped heterostructures, GaAs/InGaAs/GaAs quantum well, and AlGaAs/InGaAs multiple quantum wells (NQW) on GaAs (111)B substrates. Modulation-doped heterostructures show a 77-K mobility of 145 500 cm2/V s with a sheet density of 5.0×1011 cm−2. Photoluminescence of (111)B GaAs indicates a lower carbon incorporation than achieved on (100) substrates. The high material quality obtainable at low growth temperatures for (111)B growth will be advantageous for laser diode and heterostructure field-effect transistor applications. AlGaAs/InGaAs MQW on (111)B are comparable in the photoluminescence linewidths to those on (100) GaAs.
Migration-enhanced epitaxy of doped GaAs on (111)B and (100)GaAs substrates
Authors: Fu Jianming , Zhang Kai , Miller D. L.
Published: July 2002

Si-doped n-type GaAs and Be-doped p-type GaAs have been grown on (111)B oriented GaAs substrates using the migration-enhanced epitaxy (MEE) technique, in which arsenic and gallium are deposited separately. The mobilities and carrier densities have been compared with GaAs grown by MEE and conventional epitaxy on GaAs (100) substrates. Under migration enhanced conditions, the range of substrate temperatures and arsenic fluxes to obtain smooth surfaces and good mobilities is wider than for conventional molecular-beam epitaxy, for both substrate orientations. High-quality doped GaAs material was obtained at substrate temperature as low as 400–450 °C on (111)B substrates.
Near-surface atom imaging using multiple-energy photoelectron holography
Authors: Terminello L. J. , Barton J. J. , Lapiano-Smith D. A.
Published: July 2002

Copper atoms near a (100) single crystal face were imaged using multiple-energy photoelectron holography. Experimental holograms were extracted from Cu 3p photoelectron angular distributions that were measured at nine kinetic energies from 268 to 477 eV. Synchrotron radiation was used to excite the 3p core electrons to these energies. Each hologram was Fourier transformed and then multiple-energy phase summed to produce higher fidelity atom images. With this demonstration of the multiple-energy method substantial resolution improvement, twin image suppression, and artifact removal was achieved.
Fabrication of micromachined silicon tip transducer for tactile sensing
Authors: Jiang J. C. , Faynberg V. , White R. C. , Allen P. K.
Published: July 2002

The tunneling vacuum diode was employed to construct a novel displacement transducer for tactile sensing. High sensitivity of the emission current to variations of cathode–anode separation is the most important feature. The device was fabricated on a silicon wafer. The device components are a single tip or an array of tips made by wet etching, and a metal anode diaphragm. Nitric acid-ammonium fluoride etchant is used at room temperature to etch the silicon tips, with an easily controlled etch rate and excellent uniformity. A unique sacrificial layer technique creates and controls the spacing between cathode tip and anode diaphragm. Highly sensitive responses of the device current to different force loads on the anode diaphragm are presented.
Luminescence from Si1−xGex/Si quantum wells grown by Si molecular-beam epitaxy
Authors: Fukatsu S. , Usami N. , Shiraki Y.
Published: July 2002

Luminescence from strained Si1−xGex/Si quantum wells (QWs) grown on Si substrates by Si molecular-beam epitaxy was studied. Influenece of the crystal quality on the luminescence efficiency was investigated by excitation dependence of luminescence intensity. Electroluminescence (EL) from coupled double QWs for the material system and the associated peak red shift is presented for the first time. Transverse-electric-polarized EL was observed from cleaved edge samples for the first time, showing that the optical transition in QW luminescence is due to electron–heavy hole recombination.
Molecular-beam epitaxial growth of boron-doped GaAs films
Authors: Hoke W. E. , Lemonias P. J. , Weir D. G. , Hendriks H. T.
Published: July 2002

GaAs films doped with boron in the 1020 cm−3 range were grown by solid source molecular-beam epitaxy. Lattice contractions were observed in x-ray double crystal spectra. Substitutional boron concentrations up to 1.7×1020 cm−3 were obtained with narrow x-ray linewidths and specular surface morphology. For a given boron flux, the substitutional concentration was dependent on growth temperature. P-type conductivity due to boron incorporation was measured in the films with hole concentration reaching 1×1019 cm−3. The lattice contractions exhibited good thermal stability for rapid thermal anneals.
Influence of substrate temperature on the growth of InGaAs layers on (111)B GaAs
Authors: Yoo H. M. , Ohuchi F. S. , Stoebe T. G.
Published: July 2002

The influence of substrate temperature on the growth of InGaAs layers on (111)B GaAs, has been studied. Photoluminescence (PL) spectra obtained from GaAs/InGaAs single quantum well structures show strong dependence on InGaAs growth temperature. As the growth temperature increases, PL peaks shift to a higher energy, which is attributed to reevaporation of indium from the InGaAs layer during the growth at higher substrate temperatures. An activation energy of 3.1±0.2 eV for indium desorption from the (111)B GaAs substrate was obtained. InGaAs layers grown below 530 °C, where reflection high-energy electron diffraction shows (2×2) reconstruction, exhibit a wider PL linewidth than those grown above 530 °C. The optimum temperature for growth of InGaAs on (111)B GaAs substrates is the lowest possible temperature where one can maintain a (√19×√19)R23.4 reconstruction; this varies with the group V/III beam equivalent pressure ratio.
Surface morphology and quality of strained InGaAs grown by molecular-beam epitaxy on GaAs
Authors: Yoon Soon Fatt
Published: July 2002

InGaAs layers of varying epilayer thickness grown at different temperatures on GaAs substrates by molecular-beam epitaxy are analyzed by atomic force microscopy. The surface roughness and morphology of InGaAs grown at substrate temperatures ranging from 450 to 530 °C are analyzed as the epilayer thickness is increased from 100 to 800 Å. Over an area of 100 μm2, an abrupt increase in the surface roughness probably indicates an acceleration of surface roughening mechanisms related to the process of strain relaxation. At higher InGaAs thicknesses, surface corrugations were observed. The results indicate that thicker pseudomorphic InGaAs films on GaAs substrates can be grown at lower temperatures. Raman spectroscopy data of strain-induced shifts in the GaAs-like mode longitudinal optic phonon indicate that the GaAs has tensile strain along the interface. The strain calculated from the observed frequency shift agrees with the lattice-mismatch strain given by the elasticity theory.
Limits of low-energy electron optics
Authors: Hordon Laurence S. , Huang Zhirong , Maluf Nadim , Browning Ray , Pease R. Fabian W.
Published: July 2002

High-resolution beams of low-energy (20–2000 eV) electrons are obviously attractive because of the very compact volume of interaction between the beam and sample, and because the associated high secondary emission coefficient minimizes charging of insulating samples. Previous work showed that values of aberration coefficients can be scaled down with voltage and minimum values are achieved by maximizing the focusing field. Here we derive some very simple expressions for the minimum beam diameter and show some experimental results. For a magnetic lens with a constant field of 1 T operating at a large demagnification, the limiting beam diameter is set by chromatic aberration (with an energy spread of 1 eV) and diffraction, and is approximately dm=126 V−1/2 nm, where V is the electron energy in eV; the dependence on magnetic field strength B is B−1/2. For a retarding field lens operating at a large demagnification and with the final landing voltage V much less than the accelerating potential, the limiting value of beam diameter is given by de=17 V−1/4 nm; the dependence on electric field strength E is E−1/2. Experimentally, preliminary results were obtained with a small, (permanent) magnetic lens that approximates the constant field case and can be inserted into the work chamber of a conventional scanning electron microscope (SEM). This added immersion lens effectively extends the range of operation of an ordinary SEM down to low energy, and has so far achieved 40 nm resolution at 300 V.
Atomic arrangement at the CuBr(100) surface and CuBr/GaAs(100) interface: Application of the electron counting method
Authors: Dassanayake U. M. , Chen W. , Kahn A.
Published: July 2002

The composition and structure of the CuBr(100) surface and CuBr/GaAs(100) interface are studied with low-energy electron diffraction, ultraviolet photoemission spectroscopy, x-ray photoemission spectroscopy, and Auger electron spectroscopy. The CuBr(100) surface exhibits a c-(2×2) superstructure. Assuming that the surface is semiconducting and that all anion and cation surface dangling bonds are, respectively, full and empty, we show with electron counting that the c-(2×2) structure is due to a half-monolayer of anion or cation vacancies instead of the usual dimerization of (100) surface atoms. The interface composition, however, does not appear to follow the electron matching requirement and seems to be dominated by chemistry.
Active neutral network control of wafer attributes in a plasma etch process
Authors: Rietman Edward A. , Frye Robert C. , Lory Earl R. , Harry Thomas R.
Published: July 2002

We have investigated the use of a neural network to compute plasma etch end point times based on in situ monitoring of the optical-emission trace. The network was trained using data from a complementary metal–oxide semiconductor production facility. In some cases, even though an end-point system is used, the overetch that follows has to be adjusted continuously to reflect machine conditions as it ages after a clean. This can be done manually by measuring wafers after the etch and adjusting the overetch time for the next run. At its present level of training, the neural network shows equivalent performance without the need for such intervention. As the network’s learning database grows, we can expect its performance to improve.
Scanning tunneling microscopy of doping and compositional III–V homo- and heterostructures
Authors: Gwo S. , Chao K.-J. , Smith A. R. , Shih C. K. , Sadra K. , Streetman B. G.
Published: July 2002

Scanning tunneling microscopy (STM) was used to study the (110) cross-sectional surfaces of molecular-beam epitaxially grown III–V homo- and heterostructures, which include GaAs multiple p–n junctions, (InGa)As/GaAs strained-layer multiple quantum wells, and (AlGa)As/GaAs heterojunctions. Both doping and compositional effects can be resolved by the topographic contrasts of constant-current STM images. The samples were prepared by either cleaving in ultrahigh vacuum or cleaving ex situ followed by sulfide [(NH4)2S] passivation. Sulfide passivated samples have been found to be advantageous for the measurements of scanning tunneling spectroscopy.
Diffusive and inelastic scattering in ballistic-electron-emission spectroscopy and ballistic-electron-emission microscopy
Authors: Lee E. Y. , Turner B. R. , Schowalter L. J. , Jimenez J. R.
Published: July 2002

Ballistic-electron-emission microscopy (BEEM) of Au/Si(001) n type was done to study whether elastic scattering in the Au overlayer is dominant. It was found that there is no dependence of the BEEM current on the relative gradient of the Au surface with respect to the Si interface, and this demonstrates that significant elastic scattering must occur in the Au overlayer. Ballistic-electron-emission spectroscopy (BEES) was also done, and, rather than using the conventional direct-current BEES, alternating-current (ac) BEES was done on Au/Si and also on Au/PtSi/Si(001) n type. The technique of ac BEES was found to give linear threshold for the Schottky barrier, and it also clearly showed the onset of electron–hole pair creation and other inelastic scattering events. The study of device quality PtSi in Au/PtSi/Si(001) yielded an attenuation length of 4 nm for electrons of energy 1 eV above the PtSi Fermi energy.
Optimization of high mobility two-dimensional hole gases
Authors: Simmons M. Y. , Ritchie D. A. , Zailer I. , Churchill A. C. , Jones G. A. C.
Published: July 2002

Modulation-doped (Al,Ga)As two-dimensional hole gas (2DHG) structures have been grown by molecular-beam epitaxy (MBE) on the (311)A surface of GaAs using silicon as a p-type dopant. Systematic variations of carrier density ps and mobility μ with undoped spacer thickness were observed at 1.7 K, with a peak mobility of 4.95×105 cm2 V−1 s−1 at a sheet carrier density of 2.2×1011 cm−2 occurring at a spacer thickness of 200 Å. The mobility and carrier density of all samples were also measured over the temperature range 300 mK to 4.2 K. These results lead to the conclusion that for samples with spacer thicknesses greater than 400 Å, acoustic phonon scattering limits the mobility at low temperatures, whereas for samples with spacer thicknesses less than this value, ionized impurity scattering was observed to be the dominant scattering mechanism. As observed with electron gases, an increase in mobility was achieved by using a thicker region of lightly doped (Al,Ga)As, giving a sample with a mobility of 7.2×105 cm2 V−1 s−1, at a carrier density of 8.7×1010 cm−2 measured at 300 mK. This value constitutes the highest mobility so far reported, at carrier densities below 1×1011 cm−2.
Electrical characteristics of InP grown by molecular beam epitaxy using a valved phosphorus cracking cell
Authors: Baillargeon J. N. , Cho A. Y. , Fischer R. J. , Pearah P. J. , Cheng K. Y.
Published: July 2002

The electrical characteristics of InP grown by molecular beam epitaxy (MBE) using a valved phosphorus cracking cell are presented. Stoichiometric growth of InP was achieved with a beam equivalent pressure as low as 5×10−7 Torr and 1 μm/h InP growth rate. The efficiency of the solid source is high, consuming on average only ∼0.09 g of phosphorus per μm of InP growth with the beam equivalent pressure ∼1.5×10−6 Torr. The conductivity of the unintentionally doped layers is n-type, with the electrical background concentration primarily dependent upon the valved cell cracking zone temperature. Electrical carrier concentrations at 300 K ranged from 2.9×1015 cm−3 to 3.3×1016 cm−3. The lowest backgrounds were achieved with the lowest cracking zone temperatures. Low temperature photoluminescence shows impurity related emission at 1.383 eV.
Extremely high uniformity of interfaces in GaAs/AlGaAs quantum wells grown on (411)A GaAs substrates by molecular beam epitaxy
Authors: Hiyamizu S. , Shimomura S. , Wakejima A. , Kaneko S. , Adachi A. , Okamoto Y. , Sano N. , Murase K.
Published: July 2002

GaAs/AlGaAs quantum wells (QWs) were grown on (411)A-oriented GaAs substrates by molecular beam epitaxy (MBE). Photoluminescence linewidths at 4.2 K are almost the same as the narrowest linewidths reported so far for GaAs/AlGaAs QWs grown on (100)-oriented GaAs substrates with the growth interruption at the heterointerfaces. Furthermore, only one sharp peak was observed for each QW on the (411) substrate over the whole area of the wafer (10 mm×10 mm), in contrast with three splitted luminescence peaks for one kind of GaAs/AlGaAs QW grown on the (100) substrates by MBE with growth interruption. This result implies that effectively atomically flat interfaces over a macroscopic area (about 10 mm×10 mm) has been realized for the first time in GaAs/Al0.3Ga0.7As QWs grown on (411)A GaAs substrates by MBE. This is possibly due to the large migration of Ga and Al atoms on the (411)A plane during MBE growth and the step-flow growth mode on the atomically corrugated (411)A plane.
Dielectric thin film deposition by electron cyclotron resonance plasma chemical vapor deposition for optoelectronics
Authors: Dzioba Steven , Rousina R.
Published: July 2002

An ultrahigh vacuum electron cyclotron resonance (ECR) plasma source has been used to deposit a:Si, Si3N4, SiNx, SiOxNy, and SiO2 dielectric thin films on InP and related compound semiconductors for optoelectronic applications. Films are deposited without substrate heating using mixtures of SiH4, N2, O2, and Ar. Following deposition, thermomechanical properties have been studied by annealing to 450 °C in N2. High temperature film stability is strongly influenced by the addition of Ar to the gas mixture, indicating an important role of ion bombardment during film growth by ECR plasma chemical vapor deposition. In addition, for applications as optical coatings for photonic devices, film refractive index can be accurately controlled by the N2/O2/Ar flow rate ratios.
High-speed spectral ellipsometry for in situ diagnostics and process control
Authors: Duncan W. M. , Henck S. A. , Kuehne J. W. , Loewenstein L. M. , Maung S.
Published: July 2002

Real-time sensors are key for flexible manufacturing environments where variable layer structures are processed concurrently. We have developed a high speed spectral ellipsometer capable of precisely measuring thicknesses and compositions of multilayer structures in situ and in real-time (i.e., the time frame of process changes or about one second). This spectral ellipsometer has been integrated into several vacuum chambers of a flexible process flow. Utilizing phase modulation, multichannel detection, and digital signal processing techniques, less than 0.5 s is required for acquisition of 46 spectral points. Fast numerical algorithms and processor are used for reducing measured spectral ellipsometric data to physical parameters (i.e., thicknesses and compositions), in real time based on a ‘‘standard model’’ approach. Implementations of spectral ellipsometric sensing in rapid thermal oxidation and remote plasma etch are described. For thermally activated processes such as oxidation, temperature dependent dielectric functions have been employed for analyzing samples at process temperatures as high as 1100 °C. Multilayer combinations of Si3N4, SiO2, Si3N4 plus SiO2 mixtures, and polycrystalline Si have been monitored and thicknesses controlled.