bluuebunny/crossref_metadata_2025 huggingface dataset:
InAs/Ga1−xInxSb strained-layer superlattices grown by molecular-beam epitaxy
Authors: Chow D. H. , Miles R. H. , Söderström J. R. , McGill T. C.
Published: July 2002

We report the successful growth of InAs/Ga1−xInxSb strained-layer superlattices by molecular-beam epitaxy. The superlattices are grown on thick, strain-relaxed InAs or GaSb buffer layers on (100)-oriented GaAs substrates. A short-period, heavily strained superlattice at the GaAs interface is found to improve the structural quality of the buffer layer. Arsenic incorporation in nominally pure GaSb layers is found to depend strongly on substrate temperature and As-background pressure. Best strained-layer superlattice structural quality is achieved for samples grown at fairly low substrate temperatures (<400 °C). Photoluminescence measurements indicate that the energy gaps of the strained-layer superlattices are smaller than those of InAs/GaSb superlattices with the same layer thicknesses, in agreement with the theoretical predictions of Smith and Mailhiot [J. Appl. Phys. 62, 2545 (1987)]. Far-infrared photoluminescence is observed from a 37/25 Å, InAs/Ga0.75In0.25Sb superlattice, demonstrating that far-infrared cutoff wavelengths are compatible with short superlattice periods in this material system.
Low temperature nonilluminated anodization of n-type silicon
Authors: Montero I. , Gómez-San Roman R. J. , Albella J. M. , Climent A. , Perrière J.
Published: July 2002

The kinetics of the anodic oxidation of crystalline n-type (100) silicon have been studied under room temperature conditions and in darkness. The initial stages of the oxidation process show an island-type growth until the islands coalesce forming the oxide. The resulting films have been characterized by capacitance measurements, Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), and infrared absorption spectroscopy (IR). Relevant parameters of the oxidation process such as the electric field of formation and the current efficiency were obtained. Combined NRA and IR analysis show a correlation between the Si–O bond absorption peak and the oxygen content of the SiO2 films.
Formation of In/GaP(1̄ 1̄ 1̄) interface studied by energy loss spectroscopy, x-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy
Authors: Yu M. R. , Wang P. Q. , Jin X. F. , Wang X.
Published: July 2002

Submonolayer to several monolayers of In were evaporated onto the GaP(1̄ 1̄ 1̄) (1×1) clean surface at room temperature to investigate the formation of In/GaP(1̄ 1̄ 1̄) interface. From the electron energy loss spectra, it has been shown that the surface electronic states related with the Ga dangling bonds are significantly affected by the deposited In atoms even at initial stage. The growth mode of In overlayers on GaP(1̄ 1̄ 1̄) is island like rather than layer-by-layer form. By increasing the amount of deposited In atoms, the In islands become larger and thicker, as evaluated from the relative peak intensities of the bulk and plasmon losses. The core-level photoelectron specrtra show there is no indication of the occurrence of In–Ga interfacial exchange reaction. The valence band ultraviolet photoelecton spectroscopy reveals a new peak structure at the energy of 5.2 eV below Fermi level, which is believed to be attributed by metallic In. In the case of Ga on InP, it has already been verified that the Ga–In interchange reaction does exist and is quite remarkable. It does not seem sufficient to explain the irreversibility of surface interchange reaction between Ga/InP and In/GaP simply by means of thermodynamical consideration. The surface migration coefficient and the stability of metallic clusters may play a complementary role in determining the surface chemical reactivity.
Growth of high quality AlGaAs/GaAs heterostructures by gas source molecular-beam epitaxy
Authors: Houng Yu-Min , Lee Biing-Jye , Low T. S. , Miller J. N.
Published: July 2002

Unintentional p-type doping of GaAs films grown by gas source molecular-beam epitaxy (GSMBE) was reduced to 2×1014 cm−3 with a room-temperature hole mobility of 490 cm2/V s. Intentional Si doping of GaAs films grown by GSMBE, using an elemental Si source, yielded controlled carrier concentrations from 7×1014 to 8×1018 cm−3 with 77 K mobilities from 62 700 to 2 500 cm2/V s. Residual carbon incorporation was reduced in AlGaAs by growing at 560 °C and using tri-isobutylaluminum such that 77 K two-dimensional electron gas mobilities as high as 88 600 cm2/V s were obtained. Our study of using trimethylgallium or a graphite filament as a carbon source for p-type doping indicates that doping levels can be controlled in the range of 5×1016–1.5×1020 cm−3 with good hole mobility and surface morphology. Preliminary results show an undetectable diffusion of carbon in the AlGaAs/GaAs heterojunction bipolar transistor (HBT) structures with a base doping level as high as 1.5×1020 cm−3, using carbon as a p-type dopant, grown at a substrate temperature of 600 °C and annealed at 700 °C for 30 min.
Optical properties of InGaAs/InP semiconductor nanostructures
Authors: Weiner J. S. , Wang Y. L. , Temkin H. , Harriott L. R. , Hamm R. A. , Panish M. B.
Published: July 2002

We have studied the optical properties of buried InGaAs/InP nanostructures fabricated by in situ focused gallium ion beam writing, dry etching, and overgrowth by gas source molecular beam epitaxy. Due to the small size and buried nature of these structures, cathodoluminescence imaging and spectroscopy are the most suitable techniques for studying them. We have determined the dose dependence of their optical properties and have fabricated fully buried quantum wires. We find high quantum efficiency of optical emission from structures as small as 2000 Å in lateral extent. With improvements in the in situ processing it should be possible to fabricate fully buried nanostructures as small as a few hundred angstroms in laterial dimensions.
First order distributed feedback gratings (92.5–105 nm period) for GaInP/AlGaInP lasers emitting in the visible range
Authors: Korn M. , Körfer T. , Forchel A. , Roentgen P.
Published: July 2002

The fabrication of first order gratings for distributed feedback (DFB) GaInP/AlGaInP laser structures with periods in the range of 100 nm will be reported. The laser structures were pumped optically and show single mode emission at 639 and 651 nm with coupling coefficients of 151 cm−1. Due to the principally nonexisting radiation mode loss first order DFB lasers will show lower thresholds than the yet demonstrated third order DFB lasers with three times coarser grating periods. The gratings fabricated by e-beam lithography and dry etching techniques show strong feedback and moderate damaging of the waveguide properties.
The first x-ray lithography beamline at Hefei National Synchrotron Radiation Laboratory
Authors: Qian Shinan , Li Guihe , Liu Zewen , Chen Qianhong , Jiang Dikui , Liu Wanpo , Kan Ya , Su Yonggang
Published: July 2002

An x-ray lithography beamline, the first of six planned at Hefei National Synchrotron Radiation Laboratory (HESYRL), was completed and installed in the summer of 1989. A scanning mirror, the key optical component of the beamline, is used to cut off shorter wavelength light and to expand the vertical dimension of the exposure beam. It is oscillated by a stepping motor, while an in situ Moiré fringe grating system measures the uniformity of the motor speed. Downstream after the front end section of the beamline, a Be window is used to block longer wavelength light. A laser alignment system is used to align the beamline with a He-Ne laser. A special exposure shutter controlled by a second stepping motor can define the exposure time. An exposure chamber in which the vacuum can reach 5×10−7 Torr is located 7 m downstream from the synchrotron radiation source. Since the chamber does not include a vacuum window, a differential pumping system has been installed upstream from the exposure chamber. Test results of simulation experiments are presented and a plan for the first XRL experiments is given in the paper.
Surface imaging lithography at 248 nm
Authors: Misium George R. , Tipton Mike , Garza Cesar M.
Published: July 2002

This paper discusses the use of surface imaging lithography for deep UV step and repeat applications. In particular, results obtained using the DESIRE process are presented. It is shown that surface imaging is a very attractive option for 248 nm lithography given the small depth of focus of steppers working at this wavelength and the lack of standard, commercially available, photoresists able to fulfill the requirements of deep UV lithography. First, the concept of surface imaging lithography and the DESIRE process are reviewed. Next, results obtained using g-line resists exposed at 248 nm are presented. Although the results are acceptable, the exposure requirements are prohibitive. A deep UV formulation of the resist allows for higher silylation temperatures and the consequent reduction in exposure requirements to the 100 mJ/cm2 range. The focus latitude for 0.5 μm lines is ∼1.5 μm, while the uniformity across the wafer, for the same lines, is 5%. The etch is done using a highly selective process in a parallel plate reactor. In addition, results obtained using a commercially available magnetically-enhanced ion etcher are discussed. Other characteristics of the process, as well as its drawbacks, are also presented. Finally, alternate surface imaging processes for deep UV applications are discussed.
Gold deposition from a scanning tunneling microscope tip
Authors: Mamin H. J. , Chiang S. , Birk H. , Guethner P. H. , Rugar D.
Published: July 2002

We have demonstrated that a gold scanning tunneling microscope (STM) tip can be used as a miniature solid-state emission source for directly depositing nanometer-size gold structures. The process has been demonstrated in ultrahigh vacuum on gold substrates, and in air on gold and platinum substrates. Studies made in air suggest that the process is fast, repeatable, and field-induced. The emission mechanism is believed to be field evaporation of tip atoms, which is enhanced by the close proximity of the substrate. The technique has been used to write several thousand features with no apparent degradation of the tip’s ability to write. Elevated and room temperature studies show the written structures to be stable over periods of weeks, in contrast to some previous STM measurements of gold self-diffusion.
An ion counting apparatus for studying the statistics of ion emission from liquid metal ion sources
Authors: Ward J. W. , Kubena R. L. , Joyce R. J.
Published: July 2002

We have constructed a new ion counting apparatus for measuring the noise properties of liquid metal ion sources operating at low extraction currents. With this apparatus we have measured the noise properties of a gallium liquid metal ion source operating at source currents of 2, 5, and 10 μA. We have found that the spectral density of the current fluctuations corresponds to ‘‘white noise,’’ which is flat from dc out to our maximum measured frequency of 400 kHz. We also find that the variance of the current fluctuations is approximately 50% to 100% greater than would be expected for pure shot noise. These results imply that the ions do not arrive at the target at totally random times, but are partially correlated, and therefore exhibit properties of a slightly bunched beam.
Application of e-beam lithography and reactive ion etching to the fabrication of masks for projection x-ray lithography
Authors: Malek C. Khan , Ladan F. R. , Rivoira R. , Moreno T.
Published: July 2002

Mo/Si multilayer mirrors deposited on silicon wafers by triode sputtering were patterned by electron-beam lithography and etched by reactive ion etching in a fluorinated plasma with an intermediate metallic mask made by the lift-off process. The etch rate and etch profile were investigated as a function of the gas mixture, pressure, and plasma rf power. The groove depth was monitored by following the reflectivity of the structure with a helium-neon laser during etching and comparing it with an optical model. Large structures consisting of gratings and Fresnel zone plates with potential applications to high-resolution alignment for projection x-ray lithography were fabricated in Mo/Si. The fabrication feasibility of finer structures such as gratings with 0.3–0.5 μm pitch and linewidths smaller than 100 nm as well as linear and circular Fresnel zone plates with a 0.4-μm-wide outer zones were investigated in the similar Mo/C multilayer system.
Electrochemical approaches to cleaning, reconstruction, passivation, and characterization of the HgCdTe surface
Authors: Menezes S. , McLevige W. V. , Blazejewski E. R. , Tennant W. E. , Ziegler J. P.
Published: July 2002

A novel electrochemical approach based on voltammetric studies of reactions occurring at the HgCdTe/electrolyte interface has been devised to clean and reconstruct the HgCdTe surface prior to passivation. Sequential potential steps, applied to a HgCdTe specimen immersed in an electrolyte, oxidize the surface, remove Hg and leave a thin protective CdTe layer, reconstructed from the lattice atoms. A thick CdTe dielectric can be subsequently electrodeposited on this surface. The electrochemically processed interfaces were characterized by a low (1010 cm−2 V−1) density of fast interface states, negligible concentration of slow traps and unusual stability to prolonged air exposure and to 100 °C air anneal. The electrochemical technique was further developed as a surface characterization tool to assess the quality of Br2 -etched HgCdTe surfaces. Monolayers of Te remaining on Br2 -etched surfaces convert sequentially to TeO2 and then to HgTeO3 on air exposure.
Improvement of adhesion between Si3N4 thin films and polycarbonate substrates by preparation of an interpenetrating layer using microwave plasma enhanced chemical vapor deposition
Authors: Satoh Toshiya , Takahashi Shigeru
Published: July 2002

The adhesion between a silicon nitride layer and polycarbonate substrate was improved by employing a silicon interfacial layer which was deposited by a microwave plasma enhanced chemical vapor deposition technique. The silicon interfacial layer had an interpenetrating layer composed of the two materials, which provided an anchoring effect. In the interpenetrating layer, it was assumed that chemical bonding between carbon of the polycarbonate substrate and the silicon interfacial layer occurred through the oxygen when the radio frequency power was used in the fabrication process. The oxygen originated in the polycarbonate substrate. During the silicon interfacial layer deposition, carbon was sputtered and oxygen reacted with silicon.
Gold/carbon superfine particles produced in pulsed CO2 laser stimulated plasmas
Authors: Colgate S. O. , Simon C. G. , Boggess S. J. , Moini M. , D’Agostino A. T. , Ammons J. M.
Published: July 2002

A new technique for the production of composite nano materials was used to produce carbon coated gold superfine particles in the 100 nm size range. Particles were produced in pulsed CO2 laser (2 J/pulse at 3×109 W/cm2 ) stimulated plasmas using solid Au targets and 1:3 mixtures of CH4, CO, or CO2 with He or H2 gases at 1.3 kPa pressure. The particle production rate was dependent on the presence and type of carbonaceous gas species, and the partial and total gas pressures. Thin films of the black superfine particles were deposited on glass, ceramic and metal substrates. X-ray photoelectron spectroscopic analyses showed that Au was in the metallic state in the particles, both before and after thermal annealing, at an average concentration of 95% by mass. Fourier transform ion cyclotron resonance mass spectrometry of gaseous products emitted during thermal and laser anneals identified the major constituents as carbon dioxide and hydrocarbons. Scanning electron microscopy images of thermally annealed films showed that the particles retained their relatively uniform 100 nm diam size, despite significant changes in optical and electrical properties.

This is attributed to loss of the carbon coating on the exterior of the Au particles. While some of the carbon is catalytically oxidized during thermal annealing, the majority remains in the bulk of the film, presumably concentrated at subsurface grain boundaries. Annealing the films in air produced sharp, permanent color changes to purple at 470 K and red/yellow at 493 K due to the loss of the carbon coating from the basic Au particle. Films deposited at 373 K on glass substrates were ∼5× more reflective in the 450–750 nm portion of the spectrum than films deposited at 300 K due to increased particle packing density. Particle films were also annealed using an unfocused CO2 laser beam and a radio-frequency field. A focused argon ion laser beam was used to anneal lines as narrow as 0.5 μm in particle films on glass substrates. The lowest sheet resistance value measured for an unannealed particle film deposited on glass at 298 K was 5600 Ω/square. Resistance versus temperature (in air) measurements across a 2 mm wide gap of a coated ceramic feedthrough exhibited minima of 9 mΩ at 450 K and 4.47 MΩ at 655 K, and a maximum of >20 MΩ from 493–600 K. The temperature dependent electrical and optical properties of the Au/C particle films, especially their high temperature stability relative to traditional gold blacks, make them potential candidates for applications in infrared optical systems.
AlInAs/InGaAs based heterojunction bipolar transistors fabricated by electron cyclotron resonance etch
Authors: Fullowan T. R. , Pearton S. J. , Kopf K. F. , Smith P. R.
Published: July 2002

A dry etch fabrication technology for high-speed AlInAs/InGaAs heterojunction bipolar transistors (HBTs) utilizing low-damage electron cyclotron resonance (ECR) CH4/H2/Ar plasma etching is detailed. Small-area (2×4 to 3×9 μm2 ) devices demonstrated current gains up to 160, unity gain cutoff frequency ( fT) of 57 GHz and a maximum oscillation frequency ( fmax) of 35 GHz. The dry etch process uses triple self-alignment of the emitter and base metals and the base mesa, minimizing the base-collector capacitance (CBC). These results represent the first report of a truly scalable process for In-based HBTs and demonstrate the ability of ECR plasma etching to provide smooth, degradation-free etching of III–V semiconductors.
Influence of silicon concentration and layering of molybdenum silicide on the reliability of Al–Si–Cu interconnections
Authors: Suwa Motoo , Fukada Shin-ichi , Onuki Jin , Fujii Yuuji , Yamada Kouichiro
Published: July 2002

The influence of Si concentration on the stress induced migration resistance and the electrical resistivity change from silicon precipitates of Al–Si–Cu and Al–Si–Cu/MoSi2 interconnections was investigated. Electromigration of Al–Si–Cu/MoSi2 was examined as a function of MoSi2 thickness. A 1.5 wt. % Si concentration in aluminum alloy prevented grain growth and improved the stress induced migration resistance of the interconnections. However, this amount of Si addition caused resistance increases, because Si precipitates grew to the point that they were the same size as the interconnection linewidth. Layering of the Al–Si–Cu alloy containing 0.7 wt. % Si with MoSi2 improved the stress induced migration resistance of aluminum interconnections and prevented the resistance increases. Furthermore, increasing MoSi2 thickness improved electromigration resistance of layered interconnections. For MoSi2 thickness of >30 nm, electromigration resistance was better than that of single layer Al–Si–Cu interconnections.
Atomic motion and mass transport in the oxygen induced reconstructions of Cu(110)
Authors: Wintterlin J. , Schuster R. , Coulman D. J. , Ertl G. , Behm R. J.
Published: July 2002

The mobility of individual adatoms and of different structural elements in the O/Cu system is analyzed on the basis of scanning tunneling microscopy data. A value of D≊10−14 cm2 s−1 for the coefficient of self-diffusion at 300 K on the bare Cu(110) surface is derived from the motion of steps. Supply of Cu adatoms by ‘‘evaporation’’ from steps rather than the migration of individual O or Cu adatoms on the terraces is rate limiting for the ‘‘added row’’ reconstruction processes, leading to a slowdown of the transformation with increasing conversion. The kinetics for the (1×1)→(2×1) reconstruction is shown to follow that behavior, supporting a supply-controlled rather than a growth-controlled mechanism for (2×1) formation. The role of lateral interactions between neighboring -Cu–O–Cu- strings and of lateral displacements of entire such strings for the stabilization and growth of (2×1) islands and for the removal of antiphase domain boundaries (Ostwald ripening) are discussed. Conversion into the higher coverage c(6×2)O phase, again associated with a change in topmost layer Cu density and thus with mass transport, occurs in the direct vicinity of the location of the activated process, contrary to (2×1)O formation, and can be described as a local solid-solid transformation.
Scanning chemical potential microscope: A new technique for atomic scale surface investigation
Authors: Williams C. C. , Wickramasinghe H. K.
Published: July 2002

A new microscope, the scanning chemical potential microscope (SCPM), has demonstrated the measurement of thermoelectric potential variations with atomic resolution. These measurements can be attributed to atomic scale variations in the surface chemical potential gradient (∂μ/∂T). This capability was experimentally demonstrated by measuring the thermoelectric voltage produced at the tunnel junction between a tip and a heated sample with a modified scanning tunnelling microscope (STM). Registered images of STM current and thermoelectric voltage were acquired by temporally multiplexing current and voltage data from line to line, providing a direct spatial comparison of current and voltage contrast. The results on graphite and molybdenum disulfide demonstrate that the tunnelling and thermoelectric contrast is spatially different on an atomic scale. The experiments are described, and the results of some first order classical calculations are presented.
Etching reactions for silicon with F atoms: Product distributions and ion enhancement mechanisms
Authors: Winters Harold F. , Plumb Ian C.
Published: July 2002

Spontaneous and ion-enhanced etching reactions were investigated for the interaction of F atoms with Si(111) using modulated beam mass spectrometry. The F atoms were generated using a microwave plasma source which was compatible with ultrahigh vacuum. An impurity free surface, which was characterized by x-ray photoelectron spectroscopy (XPS), could be obtained even after long exposures. The atom source and the experimental system are described in detail. It is shown that spontaneous etching at room temperature produces the stable gases SiF4, Si2F6, and Si3F8 with SiF4 being the dominant product. It is suggested that previous mass spectrometric investigations incorrectly ascribed SiF+ and SiF+2 peaks to a significant SiF2 product, whereas these peaks should be assigned to Si2F6 and Si3F8. As the surface temperature is increased, the relative contributions of the etch products SiF4, Si2F6, and Si3F8 decrease while SiF2 increases and eventually becomes the major product. Ion bombardment significantly enhances the production rate for all products. However, the type of mechanisms and magnitude of ion-enhanced etching depend upon the type of product being observed. In contrast to spontaneous etching, ion-induced etching produces a significant amount of SiF2 as well as other products. Evidence is presented that suggests that chemical sputtering and an increased spontaneous etch rate are the primary mechanisms leading to ion-enhanced etching. It will be shown that physical sputtering makes only a minor contribution under the conditions of these experiments.
The electrical properties of metal contact Au and Ti on p-type HgCdTe
Authors: Bahir G. , Adar R. , Fastow R.
Published: July 2002

Schottky barrier photodiodes have been fabricated on p-type Hg1−xCdxTe, composition x=0.22 and carrier concentration from 6×1015 to 5×1016 cm−3, with Au and Ti as contact metals. It has been found that Au barrier height is lower than that of Ti for all carrier concentrations. Low temperature annealing, 75 °C for 24 h, reduces the effective Au barrier height and raises the Ti barrier height. The electrical results are correlated with Auger depth profiling of the difference interfaces, and transport mechanisms are proposed.
Additive tracers for resist plasma etching
Authors: Cheaib M. , Sadeghi N. , Schiltz A.
Published: July 2002

Halogenated organic compounds incorporated into novolac-based resists act as tracers and provide a specific end point detection (EPD) signal which can characterize the transition between resist layers during plasma etching. The EPD signal is supplied by the plasma induced emission intensity of the halogen resonance lines, all located in the VUV spectral region. Two chlorine—and bromine—based tracers have been selected which provide specific and convenient EPD signals to monitor the etching of multilayer systems. The basic criteria for an organic compound tracer to be incorporated into novolac-based resist are discussed.
High-speed, large-scale imaging with the atomic force microscope
Authors: Barrett R. C. , Quate C. F.
Published: July 2002

The atomic force microscope (AFM) can be used to generate both images and height profiles of samples with micron-sized features, combining the resolution and speed of the scanning electron microscope and the height information of the stylus profilometer. We have increased the scan speed of our AFM so that these images may be taken in real time, allowing the operator to interact easily with the microscope parameters. The increased scan speed does not noticeably degrade the images. The resulting images contain complete height information, allowing height profiles to be extracted. In this paper, we present images taken in this manner as well as discuss some of the nonideal characteristics of the AFM, such as tip-shape artifacts, tip contamination, sample damage, and scanner nonlinearities.
Aberrations of electron focusing and deflection systems in the presence of three-dimensional perturbation fields
Authors: Rouse John , Zhu Xieqing , Munro Eric
Published: July 2002

The numerical analysis of the focusing and aberration properties of electron beam columns involves two tasks: computation of the axial fields and computations of the aberrations. Some electron beam columns contain three-dimensional (3-D) perturbation fields that cannot be conveniently computed by two-dimensional numerical methods. In such cases, a fully 3-D field computation and an extension of existing aberration theories are required to compute the effects of these 3-D fields on the primary beam optics. In this paper it is described how a software package for computing 3-D electric and magnetic fields has been interfaced with a new optical properties package, which computes the aberrations and plots spot diagrams in electron focusing and deflection systems with additional 3-D perturbation fields. The new aberration theory is outlined and gives several illustrative examples of the use of the new software.
Silicon films on insulator formation using lateral solid-phase epitaxy induced by focused ion beam
Authors: Kanemaru Seigo , Kanayama Toshihiko , Tanoue Hisao , Komuro Masanori
Published: July 2002

Single-crystalline silicon films on insulator (SOI) were formed by using lateral solid-phase epitaxy (LSPE) induced by irradiation of a focused Si ion beam (beam-induced LSPE). When the irradiation was done with the beam scanned over a few microns width, it was found that the beam-induced LSPE was hindered by the beam-induced polycrystallization in SOI regions. In order to avoid the polycrystallization and to obtain long LSPE, a pseudolinear beam was used so that only the area near the amorphous/crystalline interface was irradiated without unnecessary irradiation to SOI regions. To continue the LSPE, the sweep velocity of the beam should be carefully selected to match with the enhanced LSPE rate, which depends on the dose rate. The maximum LSPE rate obtained was 30 nm/s for the dose rate of 3×1015 cm−2 s−1 at 500 °C and the LSPE has been extended to 20 μm from the seed.
Electrical properties of nanometer-scale Si p+-n junctions fabricated by low energy Ga+ focused ion beam implantation
Authors: Steckl A. J. , Mogul H. C. , Mogren S.
Published: July 2002

Diodes have been fabricated by on-axis Ga+ focused ion beam (FIB) implantation at 4–25 keV into n-Si 〈100〉 wafers doped to 2×1015/cm3. Post-implantation anneal was performed at 600 °C for 30 s to electrically activate the Ga and to regrow the implanted layer. SIMS measurements performed to obtain the Ga concentration depth profile indicate good agreement with trim simulation even at low energies. At 4 keV an electrical junction depth of 15 nm is obtained from spreading resistance profiling (SRP). The junction depth was found to vary linearly with energy over the range explored. The electrical properties of the diodes were obtained from I-V characteristics. The leakage current density of the 5 keV diode was measured to be 1 and 20 nA/cm2 at a reverse bias of 1 and 5 V, respectively. The corresponding leakage current density values for the 10 and 15 keV diodes were between 25% and 50% lower than those reported for 5 keV. The reverse bias breakdown voltage was between 105 and 110 V for all diodes. The combination of nanometer-scale junction depth, low leakage current density, and high breakdown voltage indicate that low energy Ga FIB implantation is a promising technology for ultrashallow p+ -n junction fabrication.
Oxidation sharpening of silicon tips
Authors: Ravi T. S. , Marcus R. B. , Liu D.
Published: July 2002

Sharp microtips of silicon have potential applications as field emitters and as electrical or mechanical microsensors. This study describes a single unified etching/oxidation treatment that results in uniform tips with controlled radii of atomic dimensions or larger. Variations in the etching/oxidation treatment form multiple tips with two or four tips per etched pyramid, which offer the possibility of higher emission current density for field emitter applications, and higher sensitivity for microsensor applications.
Microprobe of helium ions
Authors: Itakura T. , Horiuchi K. , Nakayama N.
Published: July 2002

A helium field ion source emits intense beams from a (111) plane protruding from a tungsten emitter. Gomer’s hopping model was expanded to explain the I–V characteristic of the plane. Our calculations agreed with the experimental results. To make a microprobe of helium ions, we constructed a 100 keV focusing column. It has a gimbal assembly and a phosphor screen with a microchannel plate to adjust the beam axis. Using a measured energy spread of 1 eV, the probe diameter was calculated to be less than 10 nm at a 1 pA probe current. Using scanning ion microscope images obtained with 90 keV helium ions, the actual probe diameter was estimated to be 2 μm. Although some improvements are necessary to focus the beam sharply, we showed the basic design of the focusing column for a helium field ion source.
Long-wavelength infrared detection in a photovoltaic-type superlattice structure
Authors: O Byungsung , Choe J.-W. , Francombe M. H. , Bandara K. M. S. V. , Sorar E. , Coon D. D. , Lin Y. F. , Takei W. J.
Published: July 2002

The first successful demonstration of long wavelength infrared (LWIR) detection with a photovoltaic-type AlGaAs/GaAs superlattice structure is reported. The experimental response band of the detector is centered near 10 μm in good agreement with the theoretical response band provided that electron–electron interactions are taken into account. The detector operates at significantly lower bias voltage than photoconductive multiple quantum well LWIR detectors. This could lead to important advantages in applications to photovoltaic detector arrays. Optimization through the use of termination layers at the ends of superlattices is also discussed. The response at 83 K is about 50% of the response at 24 K which is 5 mA/W. Optimization of the response, operating temperature or bias voltage has not been carried out.
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u ellipsometric measurements of x-ray resists
Authors: Sullivan Monroe , Taylor James W. , Babcock Carl
Published: July 2002

This paper presents the results of in situ ellipsometry of x-ray photoresists during development. PMMA was used to verify the results of previous studies and confirm the validity of the technique and the theoretical models. The technique was then applied to a negative chemically amplified photoresist Microposit XP-90104C (Shipley). Because the chemically amplified resist uses an aqueous-base developer (instead of the alcohol solvents such as in the PMMA system), in situ ellipsometry was employed to test the assumption that the resist does not swell during development. No appreciable swelling of exposed XP-90104C was observed in MF-322 developer for temperatures below 35 °C. At 40 °C, the onset of swelling was detected. The process of dissolution measured by ellipsometry departed slightly from a theoretical model of uniform film dissolution with an abrupt resist-developer interface. Scanning electron microscopy (SEM) images of 0.3 μm lines printed with XP-90104C indicate that surface roughening of the resist may account for the discrepancy of the experimental data from the uniform dissolution model.
Superconducting-normal metal interfaces produced by reactive ion etching
Authors: Lin K. , Kwong Y. K. , Park M. , Parpia J. M. , Isaacson M. S.
Published: July 2002

We have used CHF3/O2 reactive ion etching to reliably change the superconducting transition temperature (Tc) of aluminum thin films by 10–50 mK. Microanalyses using scanning Auger and scanning electron microscopy (SEM) indicate that the etching process results in a surface layer of high fluorine and low oxygen contents. The analyses show that photolithography and etching can produce very sharp interfaces between etched (lowered Tc) and unetched (higher Tc) regions. This technique is applied to study two specific configurations. First, long strips of aluminum thin films are patterned with a periodic structure of alternating regions of high and low Tc. The resistive transition of these films shows a surprisingly long proximity effect with a length scale of more than 50 μm, nearly two orders of magnitude greater than expected from established theory. Second, an aluminum strip with a single S–N–S (high–low–high Tc ) structure possesses a resistive anomaly just above the lower Tc. This anomaly depends on the position of the measurement voltage probes relative to the interfaces and appears to have a length scale of several μm.
Anisotropic etching of submicron silicon features in a 23 cm diameter microwave multicusp electron-cyclotron-resonance plasma reactor
Authors: Musson B. D. , Sze F. C. , Reinhard D. K. , Asmussen J.
Published: July 2002

The performance of a large diameter, 2.45 GHz multicusp electron-cyclotron-resonance (ECR) plasma etching system with regard to etch rate uniformity and submicron pattern definition in silicon is described. Results are compared to earlier work on a similar system operated at 915 MHz. The plasma source utilizes a 23 cm diam discharge and a 12-pole static magnetic field geometry to create multicusp ECR zones in the plasma excitation region. Microwave excitation at 2.45 GHz with power levels up to 600 W is used to excite discharges for etching of single 125 mm diam wafers and multiple 75 mm diam wafers. For single 125 mm wafers with oxide masks the 3σ variation of silicon etch rate uniformity was 2.3% and for multiple 75 mm wafers with aluminum masks the 3σ variation was 8.1% over a 150 mm diam. Vertical anisotropic etching was obtained both at the center of the wafers and the peripheries. Etch profiles were evaluated as a function of position on the substrate and no substantial positional or orientation effects were observed. Microloading effects appear small for both oxide and aluminum masks. Submicron (0.6 μm) trenches and holes were anisotropically etched in silicon and show approximately a 5% lower etch rate than large (>5 μm) features. For the relatively low microwave input power densities used, etch rates ranged from 40 to 140 nm/min as the SF6 ratio ranged from 5% to 15%.
Statistics of pattern placement errors in lithography
Authors: Groves T. R.
Published: July 2002

The placement of pattern features in lithography must be accurate to within some small fraction of the minimum feature size or critical dimension (CD). As CDs decrease over the years, driven by the demand for high density memory, the requirements on pattern placement become accordingly more stringent. A practical problem exists: after a wafer or mask is written, a binary decision must be made, based on a set of measurements, whether the pattern placement is deemed acceptably accurate. Based on this decision, the substrate will either be retained for further processing, or discarded. The large number of pattern features, together with the slowness of present-day metrology, cause the acceptance decision to be based on measurement of a tiny fraction of all features in the pattern. It is a classic problem in sampling statistics. A proper analysis relies on the probability that any feature, were it to be measured, would have a placement error exceeding some predetermined limit. In practice errors contain both systematic and random components. Systematic errors include magnification, orthogonality, and distortion, to name a few. Random errors arise from noise and jitter in the lithography or metrology tool, for example. The purpose of this paper is to derive a criterion for the binary acceptance decision, which is useful in the presence of combined systematic and random errors. The distribution of systematic errors is shown to be proportional to the area between the lines of a contour map of the error. The method is applied to an e-beam written mask for x-ray lithography. It is shown that conventional variance analysis is inadequate for predicting the error rate.
New method for producing sharp atomic protrusions on blunt tungsten tips
Authors: Sharma A. K. , Vispute R. D. , Ogale S. B. , Joag D. S.
Published: July 2002

A new method is reported to produce atomically sharp protrusions by laser-induced reactive quenching of blunt tungsten tips. The field emitter tips made of 1 mm diam tungsten wire were processed in a benzene bath by pulsed Ruby laser (λ=693.4 nm, pulse width=30 ns). Subsequent examination of such tips in field ion and field electron emission microscopes shows very sharp atomic protrusions formed on the tip apex. The glancing angle x-ray diffraction studies of thin tungsten foils laser irradiated under identical conditions reveal the formation of tungsten carbide on the surface. The atomic protrusions on the tip, thought to arise due to carbon atoms, were found to be strongly bound to the surface as judged by the field evaporation voltage required to strip them off the surface. The experimental results are explained on the basis of a laser-induced reactive quenching process at the tungsten/benzene interface.
Low voltage alternative for electron beam lithography
Authors: Lee Y.-H. , Browning R. , Maluf N. , Owen G. , Pease R. F. W.
Published: July 2002

The current trend in electron beam lithography for patterning submicron features is towards the use of higher beam voltages (20–100 keV). Among the problems often perceived to be associated with the use of low voltages are the poorer resolution, the lower brightness, and the greater sensitivity to electric and magnetic interference. Both by simulation and by experiment at 2 kV it is shown: (1) features of less than 100 nm are clearly resolved in resist of about the same thickness; (2) such features are clearly resolved in both sparse and dense pattern; (3) such features in sparse and dense areas are clearly resolved over a twofold range of exposure doses; (4) such delineation is largely independent of substrate material; (5) there is no evidence of alternating-current magnetic interference; (6) the lower beam brightness at low voltages is compensated by the increased sensitivity of resists to lower energy electrons. The remaining concerns about low voltage lithography are the reliability of resist with an imaging layer less than 100 nm thick and the extent and effect of charging of such a resist.
Silicidation using electron cyclotron resonance plasma
Authors: Nagase M. , Ishii H. , Machida K. , Akiya H.
Published: July 2002

A new annealing technique for silicidation using electron cyclotron resonance plasma is proposed, and the method is successfully used to apply self-aligned silicide of molybdenum on a Si substrate. The technique enables the temperature to be rapidly increased above 500 °C independent of substrate materials and a high degree of controllability enables reliable, self-aligned silicidation on Si.
Effect of strain on Si/Si1−xGex valence band structure studied by angle-resolved magnetotunneling spectroscopy
Authors: Gennser Ulf , Kesan V. P. , Syphers D. A. , Ott J. A. , Smith T. P. , Iyer S. S. , Yang E. S.
Published: July 2002

We have studied the effect of strain and strain relaxation on the band structure of Si1−xGex quantum wells. Two differently strained, molecular-beam epitaxy grown Si/Si1−xGex hole resonant tunneling structures were studied: one fully pseudomorphic structure, with the strain in the Si1−xGex well, and the other grown on a thick relaxed Si1−xGex buffer, with the strain in the Si barriers. For the latter structure transmission electron microscopy revealed a large threading dislocation density emanating from the buffer. Using angle-resolved magnetotunneling spectroscopy we found an anisotropy in the hole states in different in-plane 90° directions, that was not present in fully pseudomorphically grown structures. We suggest that this is due to anisotropic strain relaxation in the buffer layer.
Are low temperature molecular-beam epitaxy GaAs buffers good for microwave applications?
Authors: Streit Dwight C. , Hoppe Matthew M. , Chen Chung-Hsu , Liu John K. , Yen Kuo-Hsiung
Published: July 2002

We have compared the effect of three different molecular-beam epitaxy (MBE) buffer layer designs on the dc and microwave characteristics of 0.5 μm GaAs metal–semiconductor field effect transistors (MESFETs). MESFETs grown on regular GaAs buffers or GaAs/AlGaAs superlattice buffers had essentially identical dc and microwave performance. MESFETs grown using high resistivity GaAs buffer layers deposited at low temperature had significantly improved dc output resistance and backgate voltage, but with reduced microwave output resistance, transconductance, and cutoff frequency compared to the other devices. We conclude that while the high resistivity buffer provides better dc isolation, at microwave frequencies it is not as effective as the other types of MBE buffers used here.
Degradation of photoluminescence from quantum wells grown on top of low-temperature buffers
Authors: Srinivasan A. , Shih Y. C. , Streetman B. G.
Published: July 2002

The high-resistivity properties of low-temperature (200–300 °C) molecular-beam-epitaxy-grown GaAs and AlGaAs have great potential for device applications. The purpose of this study is to examine the effect of low-temperature buffers (LTB) on the crystal quality of epilayers grown on top. Photoluminescence (PL) from quantum wells grown at regular growth temperatures (620 °C) is found to be sensitive to changes in crystal quality introduced by the LTB. Limiting LT AlGaAs buffer thicknesses to a critical thickness is found necessary for growing layers with good quantum-well PL.
Influence of resonant defect states on subband structures in Hg1−xCdxTe
Authors: Chu J. H. , Mi Z. Y. , Sizmann R. , Koch F. , Wollrab R. , Ziegler J. , Maier H.
Published: July 2002

A revised C–V fitting model is presented to determine the subband structures of n-type inversion layer in p-type Hg1−xCdxTe with higher native doping concentration by taking into account the influence of a resonant defect level, which is found from the capacitance measurements. By the model the subband structure and its dependence on surface electron concentrations Ns as well as the relationship between the subband structures and doping concentrations for Hg1−xCdxTe with x=0.21 and a wide doping range of NA = 3.6 × 1016–6.95 × 1017 cm−3 are obtained. By the C–V fitting procedure the resonant defect level, which is located at 45 meV above the conduction band edge for the samples of x=0.21, and its density are also obtained. The annealing and Au-doping experiments on the sample as well as the theoretical analysis reveal that the resonant defect states arise from mercury vacancies occupied by oxygen atoms. The way to eliminate the defect states is also discussed.
Rotationally anisotropic second-harmonic generation studies of the structure and thermal stability of Cu(110)
Authors: Hoffbauer Mark A. , McVeigh Victoria J. , Zuerlein Michael J.
Published: July 2002

Rotationally anisotropic surface second-harmonic generation (SHG) has been used to investigate the surface structure and thermal stability of a clean, well-characterized Cu(110) single crystal surface in ultrahigh vacuum. The results show clear evidence of the sensitivity of optical SHG to changes in surface structure. At a fixed Cu(110) sample azimuthal angle, the temperature dependence of the second-harmonic radiation field from the surface was measured at two different wavelengths and found to be in agreement with other experiments performed using very different surface probes that show a sharp change in slope above ∼600 K associated with a possible order–disorder transition. The rotationally anisotropic SH intensity from Cu(110) was found to dramatically decrease as the surface temperature was increased above ∼600 K indicating a loss of surface order and symmetry. A simple model is proposed where thermally induced one-dimensional disordering accounts for all of the experimental observations between ∼600 and ∼800 K, and where the Cu(110) surface has thermally disordered in two-dimensions above ∼800 K.
Measurements of abrupt transitions in III–V compounds and heterostructures
Authors: Streetman B. G. , Shih Y. C.
Published: July 2002

We review measurements of abrupt transitions in III–V compound semiconductors and heterostructures, including abrupt interfaces as found in quantum wells (QWs) and high electron mobility transistors (HEMTs), and abrupt doping profiles such as delta doping. The interface quality of QW and HEMT structures can be studied using photoluminescence (PL). Several methods are employed to characterize the abrupt doping profiles of delta-doped structures. Hall and Shubnikov–de Haas measurements are used to extract the 2D carrier concentrations in detail. C–V profiling is employed to study the carrier profiles normal to the dopant plane. The actual dopant distribution can be obtained by secondary ion mass spectrometry or by combining C–V profiling with theoretical calculations. The resolution of these measuring techniques will be discussed.