bluuebunny/crossref_metadata_2025 huggingface dataset:
Pit-free electropolishing of aluminum and its application for process chamber
Authors: Tajiri K. , Saito Y. , Yamanaka Y. , Kabeya Z.
Published: July 2002

Aluminum is one of the candidate materials of the vacuum chamber and components in the ultra-large scale integration device production facilities, because of high thermal conductivity and minimizing weight. For that purpose, their surface must be smooth and passivated so as to have a low outgassing rate. An electropolishing method to obtain a mirror-finish and pit-free smooth surface has been developed by controlling the flow of the electrolytic fluid during polishing. The polished surface, which shows an average roughness of 0.03 μm was found to be covered with an oxide film of 200 nm thick as determined by Auger electron spectroscopy, indicating a chemically stable surface. The outgassing rate measurement using a conduction-modulation method shows the value of 10−10 Pa m3 s−1 m−2, after baking treatment at 150 °C.
Determining thickness of thin metal films with spectroscopic ellipsometry for applications in magnetic random-access memory
Authors: Tompkins Harland G. , Zhu Theodore , Chen Eugene
Published: July 2002

Metal thicknesses can be determined using optical methods such as spectroscopic ellipsometry when the thickness of the film is small enough that the light penetrates to the bottom of the film. In order to use ellipsometry, it is necessary to determine the optical constants of the film material accurately. In this work, we describe the determination of the optical constants and thicknesses of single metal layers of NiFe, Cu, Co, Ta, FeMn deposited with two different deposition methods. The thicknesses range from about 6 to about 20 nm thick. We have also investigated the ex situ measurement of multiple metal layers, and discuss the conditions where the thicknesses of the individual layers can be determined and the conditions where they cannot be distinguished from each other.
Carbon nitride thin-film growth by pulsed laser deposition
Authors: Chen Ming Y. , Murray P. Terrence
Published: July 2002

Thin films of carbon nitride were deposited using pulsed laser deposition techniques both with and without an atomic nitrogen source. In situ characterization of chemical composition and atomic bonding were studied using scanning Auger, x-ray photoelectron spectroscopy, and electron energy-loss spectroscopy. The influence of growth parameters including substrate temperature, substrate bias, nitrogen partial pressure, and atomic nitrogen on the film composition were studied. Nitrogen content x for CNx films ranged from 0.3 to 0.6 (25–40 at. % nitrogen). Time-of-flight mass spectrometry of the species ejecting from a nitrided carbon target was performed. Neutrals of CN4 and C3N4 clusters and positive ions of CxNy clusters were observed in addition to carbon neutral and positive ion clusters.
Role of the bias voltage during the deposition of thin tin oxide films by plasma assisted chemical vapor deposition
Authors: Arefi-Khonsari F. , Hellegouarc’h F. , Amouroux J.
Published: July 2002

Nonstoichiometric thin tin oxide films have been deposited from an Ar-tetramethyltin-O2 mixture in an rf glow discharge diode reactor at low pressure (15 Pa) and at low temperature (25–100 °C). These films are amorphous and present a high transmittance (95%) in the visible region. The conductivity of the films have been increased considerably (10−2 to 102 Ω−1 cm−1) in a triode system (substrate electrode biased by another rf generator), for treatment times as short as 10 min with a deposition rate of 30 nm/min. This increase of the conductivity leads to a decrease of the gap energy from 3.5 to 2.5 eV accompanied with a slight decrease of the transmittance (from 95% to 89%±2%) and of the grain size (95 to 43 nm). The tin oxide-substrate interface analyzed by Rutherford backscattering has shown to be an abrupt one.
Electronic structure of hydrogenated carbon nitride films
Authors: Hammer P. , Victoria N. M. , Alvarez F.
Published: July 2002

Hydrogen-induced changes on the electronic and structural properties of amorphous carbon nitride (a-CNx:H) prepared by ion beam assisted deposition are investigated by x-ray photoelectron, ultraviolet photoelectron, infrared, and Raman spectroscopies. Two series of specimen are studied: films with a constant nitrogen content (C/N=26%) grown at 150 °C using different hydrogen partial pressures between 0% and 70% and samples deposited at different substrate temperatures (150–500 °C) with fixed H2 partial pressure of 60%. The pronounced changes of the N 1s and C 1s core level spectra on increasing hydrogen incorporation (up to 17 at. %) are interpreted as due to the formation of terminating NH and CH bonds accompanied by modifications of the local C–N bonding structure. Corresponding changes are observed in the He II valence band spectra showing a recession of the leading edge of more than 0.9 eV while the optical band gap widens from 0 to more than 1 eV. Consistent with these results, the information obtained from the infrared and Raman spectra suggests a hydrogen induced transformation of the disordered sp2/sp3 network into a polymerlike structure. With increasing substrate temperature a reversed process takes place. At 700 °C an increasing graphitization of the films is observed, but the effect of hydrogen on the structure influencing the growth kinetics is still present at this temperature. The nitrogen concentration (N/C) of about 30% indicates high thermal stability of the CN material.
Photon stimulated desorption of an unbaked stainless steel chamber by 3.75 keV critical energy photons
Authors: Herbeaux C. , Marin P. , Baglin V. , Gröbner O.
Published: July 2002

A stainless steel vacuum chamber, which had been going through a usual laboratory ultrahigh vacuum process, was exposed to a white synchrotron radiation photon beam, 3.75 keV critical energy, 70 W power at DCI. The vessel was however not baked “in situ” in order to test the necessity of this intermediate step. This is an issue with far reaching consequences for new synchrotron radiation sources. Beam scrubbing from a photon beam dose of 2.3×1023 photons m−1 was found to decrease the molecular yields from an initial value of 10−2 molecules per photon to below 10−5 for the main species CO and CO2. The cleaning effect of the secondaries was clearly demonstrated, thus justifying the definition of the photon beam dose. It also explains the strong reduction of the static pressure. Wall pumping developed by the irradiation of the 3.6 m long tube was found to develop a pumping speed of, respectively, 750 and 1900 l s−1 for CO and CO2 and nil for H2, CH4, and N2. The resulting pumping capacity amounts to an equivalent of 10−4 monolayer for both CO and CO2 to be compared to a total of 2 monolayers removed by beam scrubbing. These results are finally applied to predict the gas beam lifetime for a new synchrotron radiation source SOLEIL. It appears that a reasonable lifetime can be reached in a short time in the absence of in situ bakeout.
High-quality LaNiO3 thin-film electrode grown by pulsed laser deposition
Authors: Guo Xiangxin , Li Chunling , Zhou Yueliang , Chen Zhenghao
Published: July 2002

Epitaxial LaNiO3 (LNO) thin films with a pseudocubic perovskite structure were fabricated by pulsed laser deposition. The effects of processing the substrate temperature as well as oxygen pressure on the structure and surface electrical resistivity were analyzed. In the range of the substrate temperatures from 550 to 800 °C and oxygen pressure from 25 to 50 Pa studied in our experiments, all the films showed good orientation. The LNO thin film deposited at 700 °C in 35 Pa O2 exhibited the best quality of those films deposited in our conditions. Its average roughness is less than 10 nm and the surface electrical resistivity is about 5×10−5Ω cm, better than previously reported values. In addition, the surface morphology and resistivity versus temperature were also investigated. The present LNO films have good epitaxial structure, a smooth surface, and good electrical properties.
Thermal outgassing of vacuum glazing
Authors: Lenzen M. , Turner G. M. , Collins R. E.
Published: July 2002

Vacuum glazing consists of two sheets of glass separated by a narrow evacuated space. In this article we describe investigations of the causes of thermally induced degradation of vacuum glazing. It is shown that the rate of increase of pressure within the glazing during high temperature aging is mainly determined by the diffusion of water out of near-surface regions in the glass. In addition, adsorption of water molecules onto the internal surfaces influences the temperature dependence of the pressure in a degraded glazing. A prediction is made of the likely upper limit of the thermally induced degradation of vacuum glazing, and hence its properties as a thermal insulator, for a given production schedule and under conditions representative of practical applications.
Annealing of copper electrodeposits
Authors: Seah C. H. , Mridha S. , Chan L. H.
Published: July 2002

The properties of electroplated copper film have been investigated as a function of annealing temperatures together with the diffusion barrier performance. Electroplated copper films on copper and tungsten seed materials were annealed from 300 to 700 °C in N2 atmosphere for grain growth study. The average grain size of the as-deposited copper films was found to be different; larger copper grains (0.6 μm) were formed on the W seed layer compared to those formed on Cu (0.2 μm). The copper films also started to recrystallize at 300 °C and grain growth occurred from 400 °C onward. Regardless of the initial grain size of the electroplated copper films, the final grain size was found to be similar on both seed materials. After 600 and 700 °C annealing, the average grain sizes became 1.00 and 1.20 μm, respectively. The driving force for grain growth is from the elimination of grain boundaries where the surface energy is being released to achieve the equilibrium state. The annealed films produced a layered microstructure, together with the presence of pinholes and cavities. The average grain size of the electroplated copper increased in proportion to the square root of the annealing time and increasing temperature. The activation energies of grain growth were 0.31 eV from 400 to 700 °C on the W seed material and 0.62 eV from 400 to 500 °C and 0.28 eV from 500 to 700 °C on the Cu seed material. With annealing, the tensile stress decreased from 202 to 105–149 MPa while the strain at break increased from 7.6% to 17.7%–20.7%. The resistivity of the electroplated copper films was reduced from 2.25 to 1.87 μΩ cm after high temperature annealing. X-ray diffraction results show that only the ionized metal plasma (IMP) TaN survived as the diffusion barrier between copper and silicon up to 700 °C while chemically vapor deposited TiN, physically vapor deposited TiN and IMP Ta failed at lower temperature.
Laminated plastic microfluidic components for biological and chemical systems
Authors: Martin P. M. , Matson D. W. , Bennett W. D. , Lin Y. , Hammerstrom D. J.
Published: July 2002

Laminated plastic microfluidic components are being developed for biological testing systems and chemical sensors. Applications include a DNA thermal cycler, DNA analytical systems, electrophoretic flow systems, dialysis systems, and metal sensors for ground water. This article describes fabrication processes developed for these plastic microfluidic components, and the fabrication of a chromium metal sensor and a microdialysis device. Most of the components have a stacked architecture. Using this architecture, the fluid flows, or is pumped through, as many as nine laminated functional levels. Functions include pumping, mixing, reaction, detection, reservoirs, separations, and electronics. Polyimide, poly(methylmethacrylate) (PMMA), and polycarbonate materials with thicknesses between 25 and 125 μm are used to construct the components. This makes the components low cost, inert to many biological fluids and chemicals, and disposable. The components are fabricated by excimer laser micromachining the microchannel patterns and microstructures in the various laminates. In some cases, micropumps are integrated into these components to move the fluids. Vias and interconnects are also cut by the laser and integrated with micropumps. The laminates are sealed and bonded by adhesive and thermal processes and are leak tight. The parts withstand pressures as high as 790 kPa. Typical channel widths are 50 to 100 μm, with aspect ratios near 5.
INA-X: A novel instrument for electron-gas secondary neutral mass spectrometry with optional in situ x-ray photoelectron spectroscopy
Authors: Oechsner Hans , Müller Matthias
Published: July 2002

A novel instrument for electron-gas secondary neutral mass spectrometry (SNMS) is described which is designed to enable in situ x-ray photoelectron spectroscopy measurements as an option. By operating the postionizing SNMS plasma inside an UHV chamber, residual gas signals are reduced to the mass-independent background in the order of a few 10−1 cps. A comparison between SNMS spectra taken with the existing INA-3 and the novel INA-X instrument reveal an increased detection power down to some 100 ppb. C and O as examples of analytically difficult elements become detectable down to the 10 ppm regime.
The oxidation of GaAs(110): A reevaluation
Authors: Landgren G. , Ludeke R. , Jugnet Y. , Morar J. F. , Himpsel F. J.
Published: July 2002

Photoemission spectra of 3d core levels excited with synchrotron radiation reveal a multicomponent substructure which increases in complexity with oxygen exposures over the range 106–1014L (langmuir). Spectral changes are already evident for Ga at 104 L, and for As near 106 L. Two oxide components shifted by 0.45 and 1 eV relative to the bulk Ga-3d core level are evident throughout the exposure range, but shift to 0.8 and 1.4 eV for 1014 L. With increasing exposure the As-3d core level develops a sequential set of shifted components at 0.8, 2.3, 3.2, and 4.2 eV relative to the bulk position in GaAs, which are attributed to single through fourfold coordinated bond formation to oxygen. Both surface and bulk-sensitive core spectra reveal a nearly equally intense oxide substructure, which indicates that contrary to previous notions subsurface oxidation is the dominant mechanism throughout the exposure range. The core spectra furthermore indicate preferential Ga oxidation—which suggests that separate Ga and As oxide phases form. Thus the oxidation of GaAs(110) is both spatially and chemically inhomogeneous. Changes in the position of the Fermi energy at the surface correlate well with the initial oxidation of surface sites and the onset of subsurface oxidation near 106 L. A final pinning position of the Fermi energy was not observed.
Epitaxial growth of lanthanide trifluorides by MBE
Authors: Sinharoy S. , Hoffman R. A. , Rieger J. H. , Takei W. J. , Farrow R. F. C.
Published: July 2002

The first epitaxial growth of a hexagonal structure lanthanide trifluoride on a semiconductor is reported: LaF3 on Si (111). LEED, RHEED, and x-ray diffraction studies show that the c-axis of LaF3 is normal to the Si(111) plane. A similar epitaxial relation is expected for other members of the lanthanide trifluoride family: CeF3, PrF3, and NdF3 which are isomorphous with LaF3 and have a closer (basal plane) lattice parameter match to Si(111). The hard, water insoluble nature of these materials makes them more practicable than group II fluorides as exploratory films for semiconductor passivation, gate insulator, and epitaxial interlayers.
High speed flat guide ceramic stage for electron-beam lithography system
Authors: Tsuyuzaki Haruo , Shimazu Nobuo , Fujinami Minpei
Published: July 2002

A high speed precision ceramic x–y stage has been developed for a high throughput submicron e-beam lithography system. This stage gives beam exposure during high speed continuous stage movement and shortens the step-and-repeat overhead time. In this exposure method the eddy current on the stage surface caused by high speed stage movement in a magnetic leakage field from the objective lens deteriorates the patterning accuracy. To reduce the eddy current, the stage has no metal bulk parts and the major components are made of a fine ceramic material which is of light weight and low thermal expansion. In order to prevent charge-up phenomenon, electric conductivity of the ceramic has been controlled by adding a small amount of nonmagnetic metal and the nonconductive parts are coated with a thin metal layer. A plate structure with flat guide is used to lighten the stage for achieving both constant velocity movement and high speed step-and-repeat performance. A unique separation mechanism between stage and drive bar with piezoelectric elements has been developed for x–y independent movements avoiding vibration from the driving mechanism. The major stage components and specimen chamber are designed by using dynamic vibration simulation. The stage drive mechanism, which is comprised of roller screws and dc motors, operates with a velocity and position controller. The maximum velocity of 160 mm/s, positioning time of 150 ms/10 mm, and yawing accuracy of ±3 μrad, is achieved. This stage has a direct wafer holding mechanism, operating with an automated wafer loader system which can handle 100 wafers/h.
Integrated circuit repair using focused ion beam milling
Authors: Harriott L. R. , Wagner A. , Fritz F.
Published: July 2002

A method of repairing short circuit defects in integrated circuits using a submicron focused ion beam is described. The technique is applicable to cutting conductive lines in fully processed wafers, whether or not they have been encapsulated. In a manner analogous to scanning electron microscopy, images of the integrated circuit features and defects are produced. Material is removed by slowly rastering the ion beam over the defect area, under computer control. Examples of focused ion beam repair applied during the testing phase of new chip designs are presented.
Sub-100-nm channel-length transistors fabricated using x-ray lithography
Authors: Chou S. Y. , Smith Henry I. , Antoniadis D. A.
Published: July 2002

Enhancement-mode n-channel Si field-effect transistors with channel lengths ranging from 60 nm to 5 μm have been fabricated using combined optical and x-ray lithographies, and were characterized from room temperature to 4.2 K. At room temperature, the 80 nm channel-length device showed quasi-long-channel behavior with high transconductance. At 4.2 K, a significant increase in transconductance was observed which may indicate velocity overshoot.
Laser chemical vapor deposition of gold: Part II
Authors: Baum Thomas H. , Jones Carol R.
Published: July 2002

The laser-induced pyrolytic deposition (LCVD) of high purity gold metal is discussed. The effects of laser flux and cell temperature are examined for the deposition process. Rates of deposition, resistivities, and deposit quality are highlighted.
Channeling transmission of protons through thin silicon membranes
Authors: Parma E. J. , Hart R. R. , Bartelt J. L.
Published: July 2002

The emergent angular and energy distributions of 80–200 keV protons transmitted through thin (<1 μm) single-crystal silicon membranes were measured using a scanning surface barrier detector which had an energy resolution of 7 keV and an acceptance angle of less than 0.1°. Various crystal orientations, thicknesses, and membrane processing methods were examined to determine the appropriate parameters for use in masked ion beam lithography. The crystal alignment, surface disorder, and overall channeling quality of the crystal membranes were determined using proton backscattering. Membrane thickness measurements were made by determining the average energy loss of protons transmitted in a random equivalent direction and using available stopping power data. For a typical 〈100〉 oriented silicon membrane of 0.6 μm thickness, the half-width angle of the near Gaussian emergent particle distribution was 0.43° for an incident proton energy of 200 keV. The average energy loss of these particles was 10% less than for protons transmitted in random equivalent directions. Half-width angle measurements of the emergent distributions for the high-, intermediate-, and low-energy-loss components, as well as for the neutral component of the transmitted beam, are presented as functions of incident proton energy and film thickness for the major crystalline axes.
Requirements on resist layers in deep-etch synchrotron radiation lithography
Authors: Mohr J. , Ehrfeld W. , Münchmeyer D.
Published: July 2002

To fabricate microstructures with heights of several hundred micrometers and great aspect ratios by the LIGA (German acronym for LIthographie, Galvanoformung, Abformtechnik) process thick poly(methylmethacrylate) (PMMA) resist layers are produced on a metallic base plate. The requirements these resist layers must fulfill are reported. It is shown that it is possible to achieve defect-free structuring with high accuracy using cross-linked PMMA with little content of residual monomer. Good adherence of microstructures with extremely small diameters, even on polished surfaces, is achieved by using an internal coupling agent which establishes a chemical bond between the substrate surface and the PMMA layer. By modifying the resist composition requirements dependent on product specifications can be fulfilled.
Process control with chemical amplification resists using deep ultraviolet and x-ray radiation
Authors: Seligson Daniel , Das Siddhartha , Gaw Henry , Pianetta Piero
Published: July 2002

Resists for optical electron beam, and x-ray lithographies that operate on the principles of chemical amplification are entering into widespread use in laboratories. They offer an attractive alternative to conventional positive Novolac photoresists and we may soon see similar use in manufacturing environments. One class of resists within this family is based on acid-hardening chemistry. We have characterized one such resist (Shipley ECX-1033) for illumination by excimer laser deep ultraviolet sources and also by x-ray radiation. A matrix of postexposure bake (PEB) conditions and development conditions was used to examine resist sensitivity and contrast. For all exposure sources we found that contrast is independent of PEB processing and that sensitivity obeys an Arrhenius dependence. Contrast increases with increasing development time while exposed resist loss is minor. A simple kinetic model was developed to explain the observed variations of apparent resist sensitivity with PEB time and temperature. The generality of this model suggests that it is widely applicable to other chemical amplification resists that require a postexposure bake. Together with aerial image calculations for different light sources, the model makes it possible to predict the dependence of linewidth on PEB conditions. In other words, we can anticipate the PEB process control required to achieve a specified critical dimension control. Electrical linewidth measurements of submicron features and their temperature dependence are compared with the predictions of the model.
Fabrication of submicrometer freestanding single-crystal gallium arsenide and silicon structures for quantum transport studies
Authors: Hasko D. G. , Potts A. , Cleaver J. R. A. , Smith C. G. , Ahmed H.
Published: July 2002

Freestanding wires of submicrometer width and with lengths up to 40 μm have been fabricated from single-crystal GaAs and Si for studies of quantum transport. Fabrication techniques are described, and the low-temperature properties for semiconductors and metals such as AuPd are compared. Fabrication of three-terminal freestanding GaAs metal–semiconductor field effect transistor structures is demonstrated.
Direct deposition of 10-nm metallic features with the scanning tunneling microscope
Authors: McCord M. A. , Kern D. P. , Chang T. H. P.
Published: July 2002

In this preliminary study we have used a modified scanning tunneling microscope (STM) to directly deposit metallic features as small as 10 nm by decomposing organometallic gases containing tungsten and gold. Dots as well as lines have been formed. Tungsen deposits analyzed by Auger electron spectroscopy contained 48% tungsten, 40% carbon, and 12% oxygen. A resistivity of 0.01 Ω/cm for the deposits was measured by aligning the STM to a metal contact pattern. This is the first reported combination of STM lithography with conventional lithography. A discussion of several interesting physical and chemical mechanisms involved in the deposition process is also presented.
Problems related to the formation of lateral p–n junctions on channeled substrate (100) GaAs for lasers
Authors: Meier H. P. , Broom R. F. , Epperlein P. W. , van Gieson E. , Harder Ch. , Jäckel H. , Walter W. , Webb D. J.
Published: July 2002

We shall describe the main steps required for molecular-beam epitaxial (MBE) growth on structured GaAs substrates for lasers, in particular, a reproducible etching process develolped for GaAs which yields well-defined and controllable tilt angles. The main parameters determining morphology and doping behavior on a facet are tilt angle Θ, substrate temperature, and the V:III ratio. The limiting values of these three parameters for obtaining good quality n- and p-type films, using Si as a dopant, will be determined. We conclude that a (311A) facet is best suited to obtain plane selective doping without generating a detrimental (111A) plane. As a result of this study, lateral p–n junctions with light emission will be demonstrated showing promise for new device structures such as lasers.
Selective dry etching of GaAs over AlGaAs in SF6/SiCl4 mixtures
Authors: Salimian S. , Cooper C. B.
Published: July 2002

Reactive ion etching of GaAs with high selectivity over Al0.29Ga0.71As in SF6/SiCl4 mixtures was studied. Selectivity, surface morphology, and anisotropy were investigated over a wide range of pressures (15–100 mTorr), dc bias values (−20 to −300 V), and SF6-to-SiCl4 ratios (0–0.5). Higher pressures, lower dc biases, and higher SF6/SiCl4 ratios increase the GaAs-to-AlGaAs selectivity. Electron spectroscopy for chemical analysis indicates that the formation of nonvolatile aluminum fluoride on AlGaAs is responsible for the selective etch process.
Barrier height modification of metal/germanium Schottky diodes
Authors: Han C. C. , Marshall E. D. , Fang F. , Wang L. C. , Lau S. S. , Voreades D.
Published: July 2002

Germanium is experiencing a resurgence of interest due to superior intrinsic properties and recently overcome technological limitations. This paper addresses the problem of Schottky barrier height control. The Fermi level of metal/Ge contacts is pinned at between 0.54 and 0.61 eV below the conduction-band edge, independent of the contacting metallization. We compare the modulation of effective barrier height by means of shallow ion implantation, epitaxial growth, and diffusion from a doped level to create a thin, highly doped interfacial region. Lowering of n-type contacts from 0.54 to 0.4 eV, at room temperature, and enhancement of p-type contacts from 0.09 to 0.23 eV, at 77 K, have been achieved. Experimental results are compared to computer model calculations.
Classification of etching mechanism in reactive ion beam etch
Authors: Tadokoro Takashi , Koyama Fumio , Iga Kenichi
Published: July 2002

Etching characteristics for GaAs and InP using an ultrahigh vacuum reactive ion beam etching (UHV-RIBE) system have been classified. Using a horizontal electron cyclotron resonance (ECR) ion source, a uniform ion beam covering a large area is obtained, and etching at low pressure (≂10−5 Torr) has become possible. The etching gas Cl2, is ionized at a gas pressure of 6×10−4 Torr, and typical applied microwave power is 300 W. We have classified the etching behavior into three categories as a function of extraction voltage and tried to clarify the change of the edge profile and surface condition. It is possible to obtain a vertical mesa. The maximum etch rates for InP and GaAs are 2.0 μm/min and 1.2 μm/min at high temperature and high applied voltage. Under appropriate conditions almost comparable etch rates for GaAs and InP have been obtained.
Initial stages of GaAs and AlAs growth on Si substrates: Atomic-layer epitaxy
Authors: Kitahara K. , Ohtsuka N. , Ozeki M.
Published: July 2002

We report on the initial stages of GaAs and AlAs growth on Si substrates, focusing on that done using atomic-layer epitaxy (ALE). ALE was performed on 3° off (100) substrates at 500 °C using an arsine and metalorganic gas source. Thin layers (5–350 monolayers) were examined using Auger electron spectroscopy, Raman scattering, transmission electron microscopy (TEM), and several other techniques. Measurements showed that ALE on Si substrates starts from three-dimensional growth but changes to layer by layer growth at an early stage. Coverage is remarkably improved by initiating the growth from AlAs instead of GaAs. TEM images for AlAs indicate a relatively smooth surface and regular lattice arrangement on Si substrates. The coverage improvement is attributed to the selective-adsorption and self-limiting effects of ALE and proper arrangement of Al atoms on Si.
A computer program for electron gun design using second-order finite elements
Authors: Zhu Xieqing , Munro Eric
Published: July 2002

A computer program has been developed for the analysis and design of electron guns. The program uses second-order, curved, isoparametric finite elements to obtain very accurate potential and field computation. Special features of the program include fast solution of the second-order finite element equations with a specially written incomplete Choleski conjugate gradient (ICCG) algorithm, accurate field computation using biquartic interpolation, and direct ray tracing with a third-order power series method. Space charge effects are taken into account, with an iterative solution of Poisson’s equation. The brightness is also computed. The second-order finite elements permit accurate simulation of curved cathodes and very large changes in geometrical scale factor. This allows the program to handle all types of electron guns, ranging from field emission guns with submicron radius cathodes, to high current Pierce-type guns. The computational techniques used are described and illustrated with typical examples.
Growth of InxGa1−xAs on patterned GaAs(100) substrates
Authors: Guha S. , Madhukar A. , Kaviani K. , Kapre R.
Published: July 2002

The influence of finite substrate size on misfit dislocation densities in strained systems is examined through the growth of InxGa1−xAs on nonplanar patterned (100) GaAs substrates consisting of parallel mesas of widths between 6500 Å and 1.3 μm and of macroscopic length. Cross-sectional transmission electron microscopy (XTEM) studies on In0.11Ga0.89As films reveal that while the mean misfit dislocation spacing for the growth in the nonpatterned region was ∼1500 Å, for the growth on the mesas no misfit dislocations running parallel to the mesa length were observed. This is likely due to strain relief at the mesa edges, possibly brought about by the ability to transfer strain energy from cluster coalescence boundaries to the mesa edges and/or reduced cluster coalescence boundaries when the mesa size becomes comparable to or less than the effective migration length.
An investigation of CH4/H2 reactive ion etching damage to thin heavily doped GaAs metal–semiconductor field effect transistor layers during gate recessing
Authors: Cameron N. I. , Beaumont S. P. , Wilkinson C. D. W. , Johnson N. P. , Kean A. H. , Stanley C. R.
Published: July 2002

Damage during the reactive ion etching in CH4/H2 of thin, heavily silicon doped, molecular beam epitaxy grown GaAs layers has been investigated. Hall effect and CV measurements showed near complete loss of the free carrier concentration on etching due to passivation by hydrogen of the silicon donor activity. Annealing for a few minutes at 400 °C was sufficient to recover the sheet concentration of the material, measured by Hall effect, but only to a limit determined by the dc bias employed during etching. At 800 V only 5% of the carriers were restored, while reducing the dc bias to 80 V allowed 70% to 80% recovery. CV measurements showed that increased surface depletion accounted for the loss of sheet concentration, while the doping profile in the undepleted channel was unaffected. At 80 V dc bias, the increased surface depletion was only 2.6 nm. Additionally Hall mobility was restored by annealing, to close to the original value of the unetched material, indicating minimal reactive ion etching damage to the depassivated material. Etching of the gate recess of 120-nm gate length metal–semiconductor field effect transistors, at low dc bias, allowed devices with excellent dc and rf performance to be fabricated; dc transconductance of gm=400 mS/mm and unity current gain cutoff frequency of fT=70 GHz were achieved.
Positive photoresist process simulation over nonplanar substrates
Authors: Barouch Eytan , Bradie Brian , Hollerbach Uwe , Orszag Steven A.
Published: July 2002

A three-dimensional computational simulator of nonplanar substrates coated with positive photoresists is presented. The model includes four major steps: projection printing, exposure, post-exposure baking (PEB), and dissolution. Projection printing is based on Hopkins’ classical work. The exposure model employs the full nonlinear wave equation coupled with the photoactive compound (PAC) bleaching rate equation. These equations are solved using a spectral element iterative scheme. The PEB is treated as a material diffusion equation employing ideas introduced by Mack and the dissolution algorithm is our LEAD (least action dissolution) algorithm modified for nonplanar substrates. Several realistic examples are presented displaying final profiles at various dissolution times.
Silylation processes based on ultraviolet laser-induced crosslinking
Authors: Hartney M. A. , Rothschild M. , Kunz R. R. , Ehrlich D. J. , Shaver D. C.
Published: July 2002

This report describes a positive-tone silylation process which results from crosslinking by exposure of novolac-based resists to deep-UV excimer laser irradiation. Comparison of 193 and 248 nm irradiation shows that the former leads to more efficient crosslinking. The dependence of silylation on time, temperature and pressure was studied in order to investigate the mechanism of the diffusion process. Evidence of both standard diffusion and non-Fickian behavior was found. Additionally, diffusion of the silylating agent in patterned resist was determined to be anisotropic.
A method for imaging E. c
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l
i. RNA polymerase holoenzyme with the scanning tunneling microscope in an aqueous environment
Authors: Keller Rebecca W. , Bear David , Bustamante Carlos
Published: July 2002

An electodeposition method has been developed for depositing E. coli. RNA polymerase onto a monoatomically flat gold surface. The scanning tunneling microscope has been used to image this enzyme in a high-humidity or water/glycerol environment, which allows direct observation without metal coating. The deposition technique is reproducible enough to allow optimization of the deposition parameters for controlled electrodeposition. Time-dependence studies were conducted to help determine the binding mechanism of the protein. The enzyme molecules appear as ordered arrays, amorphous features, or ‘‘jaw-shaped’’ molecules depending on the deposition conditions used. The ‘‘jaw-shaped’’ molecules closely resemble those observed by electron microscopy. In some of these a groove 22 Å wide can be seen.
Phase-shifting mask and top-imaging resist for subhalf-micron i-line and deep-ultraviolet lithography
Authors: Tedesco S. , Picard B. , Chevalier M. , Dal’zotto B.
Published: July 2002

Combination of both phase-shifting mask and single layer top-imaging resist will allow i-line and deep-ultraviolet (UV) lithography to meet, respectively, 64 and 256 Mbit requirements and beyond. Using phase-shifting mask in conjunction with DESIRE process, 0.25 μm lines and spaces have been resolved with an ASM-L PAS 5000/50 i-line stepper (365 nm, NA=0.48), on 1 μm thick PLASMASK 200G. With an ASM-L PAS 5000/70 deep-UV (248 nm, NA=0.42) 0.2 μm lines and spaces have been resolved on 0.35 μm thick PLASMASK 200 G using PRIME process. A simulation software package was developed allowing us to optimize phase shifting structures. Moreover, using existing computer aided design (CAD) tools we automatically generate ‘‘edge emphasis’’ structures on contact holes and on 0.3 μm gate level and subsequently expose this data base demonstrating the ability, using this simple technique, to process 64 Mbit DRAM with i-line lithography.
Reflective mask technologies and imaging results in soft x-ray projection lithography
Authors: Tennant D. M. , Bjorkholm J. E. , D’Souza R. M. , Eichner L. , Freeman R. R. , Pastalan J.Z. , Szeto L. H. , Wood O. R. , Jewell T. E. , Mansfield W. M. , Waskiewicz W. K. , White D. L. , Windt D. L. , MacDowell A. A.
Published: July 2002

In this work we investigate and compare a variety of technologies for patterning high resolution Mo/Si multilayer reflective x-ray masks for use at wavelengths near 13 nm. The patterning methods investigated include: absorbing layers deposited on top of multilayer reflectors, reflective coating removal by reactive ion etching and ion damage of multilayer regions to form a planar mask structure. Large area samples were prepared by each of the above methods and reflectivity measurements made to determine the expected mask contrast. The reflectivity data are compared with simulation for the absorber overlayer and etched multilayer measurements. Our results indicate that reflectivity changes between 5 and 300 were effected. Fine patterning tests show that mask features as fine as 0.1 μm can be achieved in each technology. The advantages, process complexity, and limits of each method are discussed. We also report the first use of an x-ray reflectance mask to print 0.1 μm features in resist. The developed resist images obtained using reflection masks in a 20:1 Schwarzschild projection camera compare favorably with transmission mask results obtained using the same optical system.
A scanning tunneling microscopy study of clean and Cs-covered InSb(110)
Authors: Whitman L. J. , Stroscio Joseph A. , Dragoset R. A. , Celotta R. J.
Published: July 2002

Scanning tunneling microscopy has been employed to study clean and Cs-covered InSb(110) surfaces. Atomic-resolution images of both the filled and empty electronic state densities have been obtained. The surface relaxation determined from these images is in good agreement with that predicted by structure calculations. A variety of surface defects have been observed, with the most common appearing to be simple Sb vacancies. Adjacent In and Sb vacancies (Schottky defects) have also been observed. The perturbation of the surface surrounding these defects is asymmetrical along [001], as might be expected due to the asymmetry in the surface. Surprisingly, the perturbation is also asymmetrical along [11̄0], where symmetry is expected. Cs adsorbed on room-temperature InSb(110) forms one-dimensional zig–zag chains along [11̄0], similar to those previously observed on GaAs(110).
Reconstruction at the Ga2Se3/GaAs epitaxial interface
Authors: Li D. , Nakamura Y. , Otsuka N. , Qiu J. , Kobayashi M. , Gunshor R. L.
Published: July 2002

A highly developed two dimensional superstructure was found at the Ga2Se3/GaAs epitaxial interface by transmission electron microscope observations. The atomic arrangement of the superstructure was determined by the analysis of electron diffraction patterns and high resolution transmission electron microscope images. The structure is described as a c(2×2) ordered arrangement of vacancies on the interfacial Ga plane. A possible role of the mismatch of electronic configurations at the Ga2Se3/GaAs interface in the formation of the vacancy ordering is discussed.
Electrical properties of modulation-doped HgTe–CdTe superlattices
Authors: Hwang S. , Lansari Y. , Yang Z. , Cook J. W. , Schetzina J. F.
Published: July 2002

Growth of modulation-doped HgTe–CdTe superlattices (SLs) at very low temperatures (140 °C) by photoassisted molecular beam epitaxy is reported. SL layer thicknesses were intentionally chosen such that most of the SLs studied are inverted-band semimetals or inverted-band semiconductors. Both p- and n-type samples were successfully prepared and studied. The doped superlattices exhibit excellent electrical properties. Lack of carrier freeze-out at low temperatures provides convincing evidence that modulation-doping has been achieved.
Calculation of a proximity resist heating in variably shaped electron beam lithography
Authors: Nakajima Ken , Aizaki Naoaki
Published: July 2002

In variably shaped electron beam (EB) lithography, the horizontal thermal diffusion in a resist cannot be neglected when, high-current density, a high-speed deflector amplifier, and a multiple-layer resist system are used. These cause a horizontal-mode resist heating (labeled ‘‘proximity resist heating’’). Calculation of proximity resist heating is accomplished by a finite element method, using ansys (Ver.4.4A) program. The calculation results suggest that the proximity resist heating is caused by the horizontal thermal flux from previous EB shot through a top layer resist. Especially, in case a high-current acceleration voltage is used, the thermal effect is not caused by the vertical-mode resist heating, but by the horizontal-mode resist heating. It is also shown that the shorter settling time, which is the interval between shots, results in a higher resist temperature and a closer position of maximum resist temperature to the previous EB shot position, and that a high-acceleration voltage in case of using a fixed current density brings out the reduction in resist heating.
Gas source molecular-beam epitaxial growth of normal incidence GaAs/AlGaAs quantum well infrared photodetectors
Authors: Kuo J. M. , Pei S. S. , Hui S. , Gunapala S. D. , Levine B. F.
Published: July 2002

Normal incidence illumination of long wavelength quantum well infrared photodetectors is demonstrated for the first time by using hole intersubband absorption in the GaAs valence band without diffraction gratings. The strong mixing between the heavy and light holes at k≠0 allows the desirable normal incidence illumination geometry to be used. Grown by gas source molecular beam epitaxy, a normal incidence quantum efficiency of η=28% and detectivity of D*λ = 3.1 × 1010 cm√Hz/W at 77 K for a cutoff wavelength λc = 7.9 μm have been achieved.
Acceptor level energies as a probe for the effect of strain on valence band structure in molecular-beam epitaxy grown strained semiconductors
Authors: Loehr J. P. , Chen Y. C. , Rhee J. , Bhattacharya P. K. , Singh J.
Published: July 2002

The acceptor energies for strained SiGe (on Si) and InGaAs (on GaAs) quantum wells are calculated from a 4×4 k⋅p band structure that includes the effects of strain and electric fields. Both center-doped and edge-doped cases are examined. The theory shows marked changes in the acceptor energies with both strain and electric field. The wide variation in binding energy with applied field for the edge-doped quantum wells may provide a mechanism for tunable far-infrared detectors. Photoluminescence measurements are performed on (In,Ga)As/(In,Ga,Al)As quantum wells to determine the acceptor level energy, and the results confirm that biaxial strain has a strong influence on the acceptor energies.
Study of strained epitaxial layers by Raman techniques
Authors: Brafman O.
Published: July 2002

We used phonon frequency shift measured by Raman scattering to determine the strain depth profile within an epitaxial layer of a mismatched heterolayer as its thickness increases beyond the critical one. Three different modes of operation were examined to confirm the results: (i) low penetration laser used to probe strained layers of different thicknesses; (ii) changing the laser wavelength and thereby the light penetration depth inside a given thick strained layer; (iii) disorder induced Raman scattering in a forbidden polarization configuration. It is found that in the case of In0.40Ga0.60As/GaAs, a relaxation of strain is taken place in quantized thickness steps, preserving the higher strain of layers closer to the interface. It is inferred that the structural defects formed as thickness exceeds the critical one, are generated at the surface, are localized there and affect the strain and thereby the lattice parameter of the successive growth. This procedure repeats itself in steps, these steps are even better viewed at the forbidden configuration, where the scattering is disorder induced. We show the advantage gained in cleaving the sample and microprobing it parallel to the interface, a method by which one measures directly the phonon frequency versus the distance from the interface. In addition, the interface can be studied with much greater detail through a second order Raman scattering steming from zone boundary, for which the phonon wavelength is of the order of 1 nm. This is demonstrated on ZnSe/GaAs, where small islands of extremely high strain were found. These could not be detected by first order scattering because the phonon wavelength is very large.
Growth of high-quality p-type GaAs epitaxial layers using carbon tetrabromide by gas source molecular-beam epitaxy and molecular-beam epitaxy
Authors: Houng Yu-Min , Lester S. D. , Mars D. E. , Miller J. N.
Published: July 2002

Heavily C-doped p-type GaAs epitaxial films have been grown using carbon tetrabromide (CBr4) as a dopant source in both gas source molecular-beam epitaxy (GSMBE) and molecular-beam epitaxy (MBE). It was found that CBr4 has a great potential as a p-type dopant source for use in a conventional MBE chamber without any major modification of its pumping system because of its high-doping efficiency and low gas load. Hole concentrations in excess of 1×1020 cm−3 have been measured in CBr4-doped GaAs grown from both the MBE or GSMBE techniques, using As4 or AsH3, respectively. A Hall mobility of ≳80 cm2/V s was measured in layers with doping level of 5×1019 cm−3, which is comparable to that from chemical beam exitaxially (CBE) grown TMGa-doped GaAs. Under GSMBE and MBE modes, the doping memory effect in AlGaAs was greatly reduced using CBr4 as compared to TMGa doping source. GSMBE grown heterojunction bipolar transistors with a CBr4-doped base layer have a current gain as high as 79 and a base sheet resistance as low as 225 Ω/⧠.
Physical basis for applying the Fowler–Nordheim J–E relationship to experimental I–V data
Authors: Nicolaescu Dan
Published: July 2002

The purpose of this work is to show that the Fowler–Nordheim (FN) current–voltage (I–V) plot [log(I/V2) as a function of 1/V] must be treated, on principle, as nonlinear. The cause of this behavior is outlined to be the fact that the electric field and current density are not constant over the emitter’s surface. Traditional approach of the FN I–V plot as being linear may lead to physical contradictions. These contradictions are brought into light. A field emitter model is then developed, which allows to express in closed analytical equations the above statements. Expressions for field enhancement factor, area factor and also for the I–V relationship are obtained. The FN I–V plot nonlinearities are shown to be greater for smaller voltages. Within this model, the FN I–V plot can be taken as quasilinear, under some assumptions. Suggestions for technological parameter extraction from I–V data through nonlinear or linear least-squares optimization techniques are done.
Buried heterostructure laser diodes fabricated using in situ processing
Authors: Hong M. , Vakhshoori D. , Grober L. H. , Mannaerts J. P. , Asom M. T. , Wynn J. D. , Thiel F. A. , Freund R. S.
Published: July 2002

An in situ process which includes electron cyclotron resonance plasma etching and molecular beam epitaxial regrowth is applied to the fabrication of buried heterostructure vertical cavity surface-emitting laser (SEL) diodes and edge-emitting laser (EEL) diodes. The buried SEL with a 7.5 μm diameter has a pulsed laser threshold current of 1 mA, and a threshold voltage of 4 V with a peak power of 0.9 mW. The buried EEL with 2.5 μm stripe width and 800 μm cavity length has a threshold current density of 500 A/cm2.