bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence of stress dependence in SiO2/Si3N4 encapsulation-based layer disordering of GaAs/AlGaAs quantum well heterostructures
Authors: Pépin A. , Vieu C. , Schneider M. , Launois H. , Nissim Y.
Published: July 2002

Spatial selectivity of layer disordering induced in GaAs/AlGaAs quantum well heterostructures using SiO2 and Si3N4 capping and annealing was investigated using low temperature photoluminescence in conjunction with cross-sectional transmission electron microscopy. Comparative study reveals opposite behaviors for patterned Si3N4 covered with SiO2 and patterned SiO2 covered with Si3N4. In the former, layer disordering occurs in the regions located under the SiO2 strips and in the latter, layer disordering surprisingly occurs under the Si3N4 strips while it is inhibited in the SiO2-capped areas. These results are in agreement with a proposed interdiffusion model based on the effect on Ga vacancy diffusion of the stress distribution generated in the heterostructure during annealing by the capping layers. This work clearly demonstrates that the diffusion of point defects, such as the Ga vacancies, which are responsible for the layer disordering, can be piloted by the stress field imposed to the semiconductor and opens new perspectives for defect engineering.
Deposition and atomic force microscopy of individual phthalocyanine polymers between nanofabricated electrodes
Authors: Tans S. J. , Geerligs L. J. , Dekker C. , Wu J. , Wegner G.
Published: July 2002

Individual chains of the rigid-rod polymer phthalocyaninepolysiloxane (PcPS) have been deposited and immobilized on top of nanofabricated metal electrodes. This is realized by embedding sparsely distributed PcPS polymers in a monolayer of cellulose using the Langmuir–Blodgett deposition technique. Atomic force microscopy was used to study the resulting spatial arrangement of these one-dimensional conducting polymers. Images of the polymer chains were obtained with a lateral resolution of better than 1 nm. Inspection of the polymers near the edges of the electrodes demonstrates that the monolayer structure is not perturbed by the 15 nm high electrodes. With this procedure, it appears to be possible to bridge two closely spaced electrodes with individual PcPS polymer chains.
Two-dimensional stage self-calibration: Role of symmetry and invariant sets of points
Authors: Raugh Michael R.
Published: July 2002

The National Technology Roadmap for Semiconductors has set a goal of 0.1–0.07 μm features for the end of the decade. Improved calibration methods will be required to achieve this goal. A rigorous method for using an electron (e)-beam stage to calibrate itself, known as stage self-calibration, was published in 1985 and has since been refined in various ways and shown to be capable of accuracy throughout the workspace in the range of the machine’s repeatability. This article presents symmetry and invariant sets as the governing features of self-calibration, using classical reversal methods as illustrations. The term symmetry is used in a dual sense; it refers both to the symmetry of a pattern of points and to the rigid motions that characterize the symmetry of the pattern. The geometric perspective gained in this way can be exploited to derive techniques and explicit error bounds for high-accuracy self-calibration. The article will be of interest to process engineers and metrologists seeking insights and methods for improving the accuracy of high-precision stages.
Optical properties of semiconductor nanostructures
Authors: Reinecke T. L. , Knipp P. A. , Walck S. N.
Published: July 2002

Boundary element methods for calculating the single-particle electron and photon states of semiconductor quantum wires and quantum dots are discussed, and variational treatments for calculating exciton properties are given. Calculations of single-particle carrier states, of exciton binding energies and of confined photon states are compared with experimental data obtained on lithographically formed semiconductor wires and dots.
Reflectance-difference studies of interface-formation and initial-growth processes in ZnSe/GaAs(001) heteroepitaxy
Authors: Yasuda T. , Kimura K. , Miwa S. , Kuo L. H. , Ohtake A. , Jin C. G. , Tanaka K. , Yao T.
Published: July 2002

In situ reflectance-difference studies of initial stages of ZnSe growth on GaAs(001) surfaces are reported. ZnSe layers with thicknesses less than 4 nm were grown by molecular beam epitaxy in both layer-by-layer and island-growth modes. It is found that the reflectance-difference spectra for this thickness range are clearly dependent on ZnSe thickness as well as on the growth mode. This observation indicates that the surface electronic structure develops with thickness and in a manner sensitive to the mid- or long-range order of the surface. The interface-induced peak at 2.8 eV, intensity of which is correlated with the extent of the interfacial Ga–Se bond formation, is pinned during the course of growth, which indicates that atomic rearrangement or mixing at the interface is minimal once several monolayers of ZnSe are deposited on GaAs.
Fabrication, characterization, and the photoelectric conversion of the nanostructured TiO2 electrode
Authors: Deng Huihua , Lu Zuhong , Mao Haifang , Xu Huijun
Published: July 2002

High-surface-area TiO2 film has been deposited on an ITO conducting glass substrate from colloidal suspension. Electronic contact between particles is produced by sintering at 450 °C. Atomic force microscope and scanning electron microscope analyses show that the TiO2 electrode is made up of nanometer-sized and interconnected TiO2 particles and pores. The specific surface area of the TiO2 electrode is determined by the size of particles and the thickness of the film and can be measured to be 150 by the absorption spectrum study of the TiO2 electrode sensitized with zinc tetrasulfonated phthalocyanine (ZnTsPc). A liquid junction cell based on the ZnTsPc/nanostructured TiO2 electrode has been fabricated and harvests 20% of the incident solar energy flux. Under monochromatic illumination at λ=700 nm, the incident-photon-to-current conversion efficiency is about 2.1% and the quantum efficiency, considering the actual absorption of the incident light, is 7%. The conversion efficiency reaches 1.7% under an illumination of 35 mW cm−2, which presents one of the highest values reported for phthalocyanine photovoltaic devices.
Fabrication of a Si scanning probe microscopy tip with an ultrahigh vacuum-scanning tunneling microscope/atomic force microscope
Authors: Ono Takahito , Saitoh Hiroaki , Esashi Masayoshi
Published: July 2002

Fabrication techniques for a sharp Si tip on a cantilever have been developed by using an ultrahigh vacuum-scanning tunneling microscope/atomic force microscope. The Si tip growth was performed by applying a voltage at a constant current between a Si substrate and the cantilever. It is considered that Si atoms were field evaporated on the substrate, and deposited onto the cantilever with this procedure. The sharp Si tip was successfully grown when a 3000 Å gold coated cantilever was used, and not grown when the gold film was absent. The cantilever that formed the tip may have applications in scanning probe microscopy.
Linewidth dependence of stress relaxation and microstructural change in passivated Al(Cu) lines
Authors: Yeo I.-S. , Ho P. S. , Anderson S. G. H. , Kawasaki H.
Published: July 2002

Relaxation of thermally induced stresses in passivated line structures can lead to void formation, and its rate is strongly correlated with microstructural change in the lines. A bending beam technique was used to measure the thermal stress relaxation behavior of passivated Al (1 wt % Cu) line structures with 3, 1, and 0.5 μm linewidths as a function of temperature up to 15 h. Our data indicate that stress relaxation in Al(Cu) lines depends on line geometry and temperature, and exhibits log (time) kinetics, which is consistent with a thermally activated dislocation glide mechanism. The observed behavior can be explained by a combined result of the driving force due to the effective shear stress and kinetics due to thermally activated mass transport. Scanning electron microscope and transmission electron microscope techniques were used to study stress-induced voiding as a function of aging time and temperature. A strong correlation between stress relaxation rate and void density was observed for 1 μm wide lines, but not for 0.5 μm wide lines. A lower void density of 0.5 μm wide lines suggests that the bamboo grain structure may influence the mass transport and retard void formation.
Formation and mechanism of dimple/pit on Si substrate during WSix/poly-Si gate stack etch
Authors: Pan Paihung , Liu Louie
Published: July 2002

The formation of dimple/pit on gate oxide and Si substrate was observed after WSix/poly-Si gate stack etch. The effects of process step on the formation of dimple/pit have been studied. The key process steps causing the dimple/pit problem are the WSix anneal and the low pressure chemical vapor deposition nitride deposition. The mechanism of dimple/pit has been proposed. The rough WSix/poly interface is the main cause of dimple formation, and the presence of Si clusters in the annealed WSix layer is the key contributor for pits in the Si substrate. A low temperature process (before gate stack etch) was found to be effective to reduce and/or eliminate the dimple/pit problem.
Tensor low energy electron diffraction study for the structure of a Cr(001)-p-(1×1)-N surface
Authors: Ri Chang-Seop , Cho Yong-Phil , Park Jong-Bo , Kang Jeong-Soo , Kim Se-Hoon , Lee Kyung-Hee
Published: July 2002

The structure of the Cr(001)-p-(1×1)-N surface was studied by use of the tensor low energy electron diffraction (LEED) current-voltage (I–V) analysis. From the LEED diffraction pattern observed in the process of cleaning of the Cr(001) surface, N was found to form a (1×1) structure on the Cr(001) surface. Experimental I–V characteristic curves for the Cr(001)-p-(1×1)-N structure were generated by Video LEED System and these experimental results were compared with that obtained through theoretical calculations via the TLEED program to analyze surface structure. As a result, we found that N is adsorbed in the hollow site on the Cr(001) surface. The interlayer distances of dN1, d12, and d23 are found to be 0.251, 1.814, and 1.410 Å, respectively.
Air-bridges, air-ramps, planarization, and encapsulation using pyrolytic photoresist in the fabrication of three-dimensional microstructures
Authors: Porkolab G. A. , Chen Y. J. , Tabatabaei Seyed Ahmad , Agarwala Sambhu , Johnson F. G. , King Oliver , Dagenais M. , Frizzell Russell E. , Beard W. T. , Stone D. R.
Published: July 2002

Pyrolyzation of photolithographically patterned photoresist on semiconductor substrates such as silicon, gallium arsenide, and indium phosphide, results in a convex-shaped, chemically inert, temporary form that functions as a mold upon which to lift-off evaporated thin films such as metals. The pyrolyzation process is simply a bake on a standard laboratory hot-plate that is ramped from room temperature to 300 °C air. The pyrolytic-photoresist form is subsequently removed in an oxygen plasma stripper leaving behind the three-dimensional lifted off thin films of free-standing, convex-shaped, full-arch air-bridges or half-arch air-bridges that we call air-ramps. Some applications are interconnects for high-speed devices; inter-level interconnects; out-of-plane coils for out-of-plane inductors; microdomes for eletromagnetic shielding; electrodes for field-emitter tips; and microelectromechanical structures. Pyrolyzing photoresist does not alter the good planarization capabilities of photoresist. Because pyrolytic photoresist is a version of the earliest form of synthetic thermoset resin called Bakelite, it can also be used as a reasonably good encapsulation material.
Effect of the in situ thermal treatments on Ir/n-type Si (111) Schottky contacts
Authors: Jiménez-Leube F. J. , Clement M. , Sanz-Maudes J. , Blanco J. M. , Serrano J. J.
Published: July 2002

In this article we analyze the effect of the in situ thermal treatments on the properties of the Ir/ n-type Si (111) Schottky contacts. The samples were annealed in the evaporation system at 400 °C for 15 min and at 450 °C for 15 min or 2 h. Rutherford backscattering spectroscopy spectra and secondary ion mass spectroscopy compositional profiles indicate that as result of the different thermal treatments performed in the samples there is a clear diffusion of silicon into the iridium layer but the composition of the metal–semiconductor interface cannot be determined. It has been shown previously that a small quantity of IrSi can be formed at an Ir–Si interface when Ir layers are deposited on Si. The current-voltage-temperature (I-V-T) behavior of these diodes indicates that it is dominated by the effect of spatial fluctuations of the surface barrier. After the thermal treatment at 400 °C for 15 min the diodes show I-V characteristics that can be perfectly justified by the unidimensional model of the thermionic emission theory. The Schottky barrier value at 0 K (0.92 eV) and the temperature coefficient of the barrier (3⋅10−4 V/K) corresponds with that previously reported for the IrSi. When the annealing temperature is raised to 450 °C, the resulting devices show a nonhomogeneous barrier with similar values to those found at room temperature. Increasing the annealing time to 2 h leads to devices showing an increase in the ideality factor value (1.12), along with a barrier height value at room temperature (0.86 eV) which coincides with that previously reported for the IrSi1.75. The 0 K barrier height (0.72 eV) indicates that a phase transformation at the interface has taken place.
Influence of AlSiTi grain boundaries on the plasma etch rate
Authors: Schönbächler Edgar , Lecohier Baudouin , Fichtner Wolfgang
Published: July 2002

The influence of the microstructure of an AlSiTi alloy on plasma etch rate is presented in this work. Metal films were individually sputtered onto silicon wafer substrates using different deposition conditions based on a design-of-experiments approach. The grain structure was analyzed for each metal film extracting the average grain size and the grain-size standard deviation. It was found that the etch rate increases with increasing average grain size and grain size standard deviation. Although grain size and standard deviation are dependent on each other in this experiment, we could show that the etch rate varies independently for each grain structure parameter. The physical mechanism at the base of this phenomenon deals with the different composition of grains and grain boundaries. Impurities and minority alloying materials segregate in grain boundaries, which are etched more slowly. A general approach to model the etch rate was performed calculating a factor which includes the total grain boundary length per surface unit. This factor can be expressed using average grain size and grain size standard deviation. We found that the etch rate decreases for increasing values of this factor, thus confirming the grain boundary model.
Dose, shape, and hybrid modifications for PYRAMID in electron beam proximity effect correction
Authors: Cook Brian D. , Lee Soo-Young
Published: July 2002

As the dimensions of circuit primitives are reduced, the proximity effect becomes an increasingly important limiting factor in the fabrication of high density integrated circuits using electron beam (e-beam) lithography. In the past, proximity effect correction schemes have in general utilized one of two different approaches: dose or shape modification. Previously, PYRAMID, a hierarchical, rule-based proximity effect correction scheme which has been demonstrated to be able to correct circuit patterns with a minimum feature size of 0.1 μm was successfully presented. Although PYRAMID has been implemented with a pattern shape modification technique, its correction algorithms are not limited to this approach. In this article, the two approaches are compared in details in terms of CD error (edge placement error) and edge contrast, using the two corresponding versions of PYRAMID. A hybrid approach, i.e., combination of dose and shape modifications, is also considered.
Development of a high brightness gas field ion source
Authors: Edinger Klaus , Yun Victor , Melngailis John , Orloff Jon , Magera Gerald
Published: July 2002

We have investigated the emission properties of gas field ionization emitters built up from electrochemically dc-etched W〈111〉 and W〈100〉 single crystal wires. A standard thermal field method was used to confine the ion emission to a single spot at the apex of the emitter. The angular current density obtained for these kinds of tips with a small end radius (100–200 nm) is in the range of 5 μA/sr. For H2 and Ne, maximum ion current was observed in the temperature range between 18 and 21 K. We have measured the ion current density for different gases (H2, He, and Ne) as a function of extraction voltage and gas pressure. The linear dependence of the angular current density on the gas pressure shows that current densities of 10 μA/sr and above can be expected with this type of emitter.
Photolithography at 0.10 and 0.13 μm using ArF excimer laser lithography in combination with resolution enhancement techniques
Authors: Chan M. , Kunz R. R. , Doran S. P. , Rothschild M.
Published: July 2002

ArF (193 nm) excimer laser lithography was evaluated for production of 0.10- to 0.15-μm-size line widths. For near-term (0.13- to 0.15-μm line widths) work, an emphasis was placed on resolution enhancement strategies not requiring new mask processes or materials and was limited to consideration of binary masks in combination with annular (σi=0.4, σ0=0.6) illumination. Using a 0.5 numerical aperture lens, silylation resist, and a binary mask, a 0.8-μm depth of focus was obtained for 0.14-μm dense lines and 1.0 μm for 0.15-μm lines. However, the lack of resist linearity required almost 50% lower dose for the isolated lines, suggesting the need for optical proximity correction. For smaller features (0.10- to 0.12-μm line widths), chromeless phase-shifting masks were used. Using a partial coherence of 0.6, a 1.8-μm depth of focus and ∼3% exposure latitude was achieved for 0.11-μm isolated lines at spatial periods as small as 0.24 μm. However, aerial image modelling suggests a limitation in this approach is focus-dependent image distortion as a result of lens aberrations. These aberration-induced effects may limit the practical depth of focus for this approach and must be considered for extension of optical lithography to near the Rayleigh resolution limit.
Towards 280 nm i-line random logic lithography with off-axis illumination and optical proximity correction
Authors: Grodnensky I. , Watson G. P. , Garofalo J. , Castro D. , Zych L. , Lee W.
Published: July 2002

The feasibility of imaging 280 nm features for random logic using i-line technology is examined. Theoretical and experimental studies are carried out to evaluate the effects of subresolution assist lines on the printing of an isolated 280 nm line. Optical proximity effect bias corrections for the 280 nm gaps were investigated as well. Simulations and experiments are conducted to study the exposure field nonuniformity and to evaluate the capability of modern i-line high numerical aperture (NA) exposure tools for 280 nm patterning. It is found that for NA=0.63, independent of illumination conditions, the optimum position and width of assist lines are in the range of 260–320 and 140–160 nm, respectively. The 2/3 annular off-axis illumination shows good performance and provides a greater than 1.6 μm depth of focus (DOF) for the assisted 280 nm isolated line. For the 280 nm gap, with the appropriate mask correction features (“hammerheads”), the 2/3 annular illumination also offers more than 1 μm DOF. The image uniformity studies show that the level of variations of the spatial partial coherence factor σ and the coma aberration in modern tools have practically no effect on the across field linewidth variation (AFLV) under the 2/3 annular condition. For the isolated 280 nm assisted line, an AFLV as small as 10 nm was observed over a 17×17 mm2 exposure field.
Investigation of the notching effect for single layer deep ultraviolet resist processing
Authors: Yoshino Hiroshi , Itani Toshiro , Hashimoto Shuichi , Yamana Mitsuharu , Yoshii Tsuyoshi , Samoto Norihiko , Kasama Kunihiko
Published: July 2002

In order to extend the application limit of single layer resist processing to 0.25 μm pattern formation, the influence of resist thickness on reflective notching effects was investigated, using a two-dimensional resist profile simulator with the vector model. As the resist thickness increased, the reflective notching was varied periodically. Resist profile degradation due to reflective notching was maximum at the resist thickness where resist sensitivity was maximum (Emax), and was minimum at the resist thickness where resist sensitivity was minimum (Emin). The reflective notching was strongly dependent on the effective exposure dose Eeff at the bottom of the resist film, defined as the product of resist transmittance and optimum exposure dose Eopt. These simulation results were verified experimentally. It was concluded that the resist thickness should be set to minimize exposure dose for the reduction of reflective notching effects.
Developer temperature effect on negative deep ultraviolet resists: Characterization, modeling, and simulation
Authors: Hagouel Paul Isaac , Karafyllidis Ioannis , Neureuther Andrew R.
Published: July 2002

We consider the effect of developer (solvent) temperature in the dissolution of both the exposed and unexposed parts of the resist. The spin-formatted resist film tends to have macromolecules oriented parallel to the substrate surface. The orientation of the resist macromolecules introduces an anisotropic component to the etch rate: higher in the direction parallel to the substrate surface and lower in the perpendicular one. We performed a series of experiments on resist-coated Si wafers using a stepper and a deep ultraviolet source at 248 nm using SNR-248 negative resist. We obtained scanning electron micrographs for various developer temperatures. The variation of the lateral etch rate manifested itself in sidewall profile slopes and is compatible with the entropy directional flow. Simulation using the Cellular Automata model predicted identical results.
High reflectivity micromirrors fabricated by coating high aspect ratio Si sidewalls
Authors: Juan W. H. , Kao Y. H. , Pang S. W.
Published: July 2002

Micromachined Si vertical structures were sputter coated with Au onto sidewalls as reflective mirrors. These vertical micromirrors were integrated with comb drives as optical switching arrays. The micromirrors were first etched in a Cl2 plasma generated by an electron cyclotron resonance source, followed by a short B diffusion and a wet etch with ethylenediamine pyrocatechol to reduce sidewall roughness and to separate the mirrors from the substrate. The sputter-deposited Au films have nearly uniform thickness along the sidewalls of the micromirrors. There was only a 6% thickness variation from the top to the bottom of the mirror sidewalls. Reducing the sputtering pressure from 30 to 4 mTorr improved the coating uniformity for high aspect ratio, closely spaced mirrors. For 30-μm-tall micromirrors with 6 μm spacing, the Au thickness close to the bottom of the sidewalls decreased by 52% compared to the top of the sidewalls when sputtered at 4 mTorr. The roughness along the micromirror sidewalls was found to change from 7.7 to 16.1 nm as the pressure during sputtering was varied from 4 to 30 mTorr. The resultant reflectivity for these vertical micromirrors decreased from 85% to 70% at a wavelength of 1.55 μm. For high reflectivity micromirrors with smooth sidewalls and uniform thickness, sputter deposition of 400-nm-thick Au at 4 mTorr should be used.
Compact electrostatic lithography column for nanoscale exposure
Authors: Chisholm Tom , Liu Haoning , Munro Eric , Rouse John , Zhu Xieqing
Published: July 2002

This article introduces an all-electrostatic electron-beam column which uses conventional electrode assemblies, resulting in a system which is very much smaller than a magnetic lens column. Computer modeling of the electron-optical performance of the column has shown that the concept has promise as a lithography tool. Beam broadening due to electron–electron interactions and aberrations of the final accelerating lens are both small enough to give a resolution which matches that of present-day magnetic columns.
Micromachined single-crystal silicon electron lenses
Authors: Hofmann Wolfgang , MacDonald Noel C.
Published: July 2002

We report on the design, simulation, and fabrication of micromachined single-crystal silicon electrostatic lenses and lens arrays. The lenses consist of two or three high-aspect-ratio silicon tubes, which are fabricated from a single silicon substrate using a self-aligned process. The tubes are isolated from each other and the substrate by long (>20 μm) thermal silicon oxide spacers. Single microlenses, multipole lens elements, and microlens arrays have been fabricated with tube diameters ranging from 5 to 50 μm and lengths from 5 to 240 μm. After a brief review of scaling considerations for electron microsource and microlenses, a detailed description of the fabrication process is presented. This process is also applicable to a wide variety of other multiple level (array) structures. The electron-optical properties of the microlenses are discussed. Numerical simulation results are used to predict the spherical and chromatic aberration coefficients and to investigate the effects of mechanical tolerances (misalignment, tilt, ellipticity).
Micro-extraction spectrometer structures for voltage contrast in the scanning electron microscope
Authors: Dinnis A. R.
Published: July 2002

This work aims at the achievement of efficient extraction of secondary electrons from the surface of the specimen, with the least possible corruption of the information which they contain. The method adopted is to use a system of microelectrodes very close to the conductor under investigation to extract the electrons and to act as a retarding-field spectrometer system. In the present case, the first extraction electrode structure was added to the integrated circuit specimen at an appropriate point by the use of focused ion beam technology.
Novel objective lens for low voltage electron beam imaging
Authors: Liu W. , McCord M. , Pease R. F.
Published: July 2002

Low energy electron beams are increasingly being used in semiconductor manufacturing for wafer and mask inspection because of their low level of damage to the sample, and the reduced charging effects when the electron energy is close to EII where secondary electron yield is unity. Also due to the short range of the electrons with the sample and the reduced proximity effect, electron beams with even lower energies are attractive for a variety of other applications such as surface studies, thin film microscopy, and lithography. However, achieving high resolution and high secondary electron detection efficiency at 100 eV landing energy and below meets serious electron optical challenges. To address this issue, we describe a low aberration objective lens that is combined with an efficient secondary electron detector. The objective lens has a final electrode just in front of the sample to minimize the electric field at the sample surface. We have optimized the design for minimum beam diameter and high secondary electron collection efficiency, subject to constraints imposed by practical concerns, such as arcing. The lens was fabricated using a combination of conventional machining and silicon micromachining. By inserting the lens into the sample chamber of a traditional scanning electron microscope (SEM), we obtained images of many kinds of samples at landing energies as low as 20 eV. Resolution of better than 30 nm is achieved at 100 eV landing energy. The degradation from the expected resolution (17 nm) is in part due to limitations imposed by the SEM resulting in a nonoptimal convergence angle. At these very low energies the image is seen to be very sensitive to contamination on the sample surface; this illustrates its possible application for viewing ultrathin films. We have calibrated the magnification versus landing energy relationship for the lens and carried out detailed signal and noise analyses for the electronics system.
Ultralow energy secondary ion mass spectrometry and transient yields at the silicon surface
Authors: Dowsett M. G. , Ormsby T. J. , Cooke G. A. , Chu D. P.
Published: July 2002

The use of a normal incidence sub-keV O2+ beam in secondary ion mass spectrometry (SIMS) depth profiling minimizes the widths of the transient regions at the surface of a shallow profile in addition to providing a very high depth resolution. At 300 eV we show that the transient width in silicon is <1 nm, and that the ion yields are relatively insensitive to the presence of native oxide. This suggests that ideal conditions for the profiling of very shallow implants are available at 300 eV and below. Nevertheless, the transient signals reflect differences in the thickness of native oxide, as well as differences in primary beam energy, and could, in principle, be used to measure process and wafer age related differences in the top few nm. We present one of the earliest attempts to accurately calibrate the depth in the pre-equilibrium region of a SIMS profile, taking account of the variation in erosion rate.
Investigation of GaAs/AlGaAs multiple quantum well waveguides involving unconfined energy states
Authors: Chen Y. H. , Chan C. H. , Jan G. J.
Published: July 2002

Photoreflectance (PR) spectra of GaAs/AlGaAs multiple quantum well waveguides at room temperature were investigated. In addition to the allowed and symmetry forbidden transitions between confined states, a number of transitions involving the unconfined states were also observed. The coupling between the multiple wells (miniband dispersion) of both confined states and unconfined states (above barrier band gap) were reported. By using the propagation-matrix method, the energies for both confined transitions and unconfined transitions were calculated and shown to agree with the experimental values determined by fitting the PR spectra to the theoretical line shape expression.
Resonant Fowler–Nordheim tunneling emission from metal-oxide-semiconductor cathodes
Authors: Mimura H. , Abe Y. , Ikeda J. , Tahara K. , Neo Y. , Shimawaki H. , Yokoo K.
Published: July 2002

A metal-oxide-semiconductor tunneling cathode was fabricated with an ultrathin oxide layer and an abrupt interface between the oxide layer and the polycrystalline Si gate electrode. The emission current shows periodic deviations on the Fowler–Nordheim plot estimated by the Wentzel–Kramers–Brillouin (WKB) approximation. The peaks in the oscillations are confirmed to arise from the resonant effect of electron tunneling by comparing the experimental results with the theoretical calculations. This article describes the first experiment of resonant tunneling emission.
Method of a numerical golden rule calculation for single electron transistor simulations
Authors: Nakashima H. , Uozumi K.
Published: July 2002

We present a method of a numerical golden rule calculation for single electron transistor (SET) simulations. This golden rule calculation is, in principle, accurate within the semiclassical framework and is easy to implement. The usefulness of the calculation is demonstrated through the comparison of the current–voltage (I–V) curves for a SET simulated using results of this numerical golden rule calculation with the I–V curve simulated using results of the so-called basic golden rule calculation.
Trends in aluminum etch rate uniformity in a commercial inductively coupled plasma etch system
Authors: Beale Dan , Siu Stanley , Patrick Roger
Published: July 2002

The effects of process conditions and chamber geometry on the uniformity of Al etched by Cl2 were measured in a Lam TCP™ 9600 SE etch reactor. A computer simulation accurately predicted etch uniformity and aided in the explanation of uniformity trends. Parameters used in the experimental matrix included pressures between 6 and 24 mT, flow between 25 and 100 sccm, power supplied to the plasma between 0 and 350 W, and chamber heights ranging from 6 to 12 cm. The distinctive features of this study include the large number of input parameters studied in a commercial reactor and the accurate predictions obtained from a self-consistent simulation without free parameters. Reducing residence time in the experiments by adjusting chamber height or flow rate produces a more center-fast etch, as expected. The flow simulations were useful in corroborating intuitive arguments and in explaining anomalous results such as the effect of pressure on etch uniformity. More specifically, comparison of simulations and measurements demonstrated the quantitative connection between the Peclet number, the residence time, and the edge uniformity over a large range of process conditions. In addition to explaining general trends with residence time, Peclet number considerations also clarify the differing effects of pressure, flow rate, and chamber height change on uniformity. No attempt was made to impose plasma effects in the flow simulation because measurements of the neutral temperature and dissociation fraction were not available. Plasma power was observed experimentally to slightly improve uniformity without changing the average etch rate.
Surface cleaning of copper by thermal and plasma treatment in reducing and inert ambients
Authors: Hymes S. , Kumar K. S. , Murarka S. P. , Wang W. , Lanford W. A.
Published: July 2002

The effects of surface cleaning procedures on the subsequent reactivity of a pure copper thin film to silane was investigated. Ex situ, wet etching and in situ dry, plasma etching using inert and reducing chemistries were employed. A few seconds low power (50 W) plasma exposure using a 3 vol% hydrogen in argon gas mixture was found to be the most beneficial technique for subsequent silicide formation by the silane exposure technique.
Thermal stability of thin CoSi2 layers on polysilicon implanted with As, BF2, and Si
Authors: La Via F. , Alberti A. , Raineri V. , Ravesi S. , Rimini E.
Published: July 2002

The thermal stability of thin cobalt silicide layers grown on preamorphized chemical vapor deposited silicon layers has been studied in the temperature range between 950 and 1100 °C. The morphology of the starting layers and their evolution during the thermal processes was analyzed by transmission electron microscopy, atomic force microscopy and Rutherford backscattering spectroscopy. The observed increase in sheet resistance with the annealing time has been correlated to the agglomeration process taking into account the dependence of the resistivity on film thickness and carrier mean free path. Sheet resistance measurements have been used to study the agglomeration process of CoSi2 by varying temperature and substrate doping (As, BF2, and Si implants). The process is thermally activated with an activation energy of 4.3 eV for the Si implanted samples. The BF2 implanted substrate show a higher activation energy (∼5.4 eV), while the arsenic implanted a lower one (∼3.6 eV). This difference is attributed to the weakening of the Co–Si bonds by arsenic atoms and to the presence of some fluorine precipitates at the CoSi2/Si interface that increase the energy needed for the reaction at the silicide/silicon interface.
Absorption and emission spectroscopy of intersubband transitions in Si1−xGex/Si quantum wells
Authors: Boucaud P. , Gauthier-Lafaye O. , Lourtioz J.-M. , Julien F. H. , Dekel E. , Ehrenfreund E. , Gershoni D. , Sagnes I. , Campidelli Y.
Published: July 2002

An experimental study of the infrared properties of pseudomorphically grown Si1−xGex quantum wells is presented. Undoped quantum wells grown by ultrahigh vacuum chemical vapor deposition are investigated by photoinduced absorption and emission spectroscopies. The 2 nm thick Si0.7Ge0.3 quantum wells exhibit infrared absorption around 10 μm wavelength which is associated with bound-to-continuum intersubband transitions. We show that the study of photoinduced intersubband absorption gives valuable information on the dynamics of photocarriers. An average lifetime τ≈2.5 μs is deduced from the frequency dependence of the photoinduced infrared absorption. We show that the temperature dependence of the photoinduced absorption is governed by the thermal excitation of the carriers above the barriers. The infrared emission of the quantum wells is studied in a second part. In III–V quantum wells, intersubband transitions around 10 μm wavelength are clearly evidenced by room temperature infrared emission spectroscopy. In the case of Si-SiGe quantum wells, only blackbody and defect-related emissions have been observed in the mid-infrared spectral range. The vanishing room-temperature emission is correlated with the weak photoinduced room-temperature absorption.
Iodine and carbon tetrabromide use in solid source molecular beam epitaxy
Authors: Miller D. L. , Micovic M. , Lubyshev D. I. , Cai Weizhong , Hwang Wen-Yen , Zhang Kai
Published: July 2002

We have studied CBr4 doping of GaAs and In0.53Ga0.47As up to 2×1020/cm3, of InxGa1−xAs across the composition range from x=0 to x=1, and of GaAs and In0.53Ga0.47As on the (211)A, (311)A, (511)A, (511)B, (311)B, and (211)B planes. These data show little evidence of self-compensation in C-doped GaAs, although carbon incorporation is more efficient on the Ga-rich (n11)A surfaces. In0.53Ga0.47As shows a similar dependence of carbon incorporation on surface orientation, and also exhibits self-compensation on the As-rich (n11)B surfaces and at In molar fractions x greater than about 0.7. We have made heterojunction bipolar transistors (HBTs) with abrupt emitter-base junctions and GaAs base layers doped to 1×1020/cm3 which have useful dc current gains, and have also used in situ iodine etching for regrowth over patterned subcollectors to make operating HBTs designed for reduced base-collector capacitance. Despite using CBr4 nearly exclusively as our p-type dopant in solid-source molecular beam epitaxy for more than five years and iodine for more than two years, we have observed no persistant degradation in doped or undoped material quality as measured by photoluminescence intensity, carrier mobility, or npn heterojunction bipolar transistor HBT current gain. Photoluminescence intensity and 77 K carrier mobility have gradually improved coincident with the introduction and continued use of iodine in our system, although there is no direct evidence of causality.
Germanium etching in high density plasmas for 0.18 μm complementary metal–oxide–semiconductor gate patterning applications
Authors: Monget C. , Schiltz A. , Joubert O. , Vallier L. , Guillermet M. , Tormen B.
Published: July 2002

Oxide masked polysilicon/polygermanium 0.18 μm gates were etched in high density plasma sources. Using gas mixtures of Cl2 and HBr with O2 which are commonly used for polysilicon, we observed strong deformation of the poly-Si/poly-Ge gate profiles, whereas perfectly anisotropic etching profiles were obtained for poly-Si gates. A multistep etching recipe was developed allowing anisotropic etching profiles to be obtained while maintaining a good selectivity to the gate oxide when using a Cl2/N2 gas mixture. The chemical constituents present on the tops, sidewalls, and bottoms of the etched features were determined by x-ray photoelectron spectroscopy (XPS). XPS analyses have shown that when using a Cl2/N2 gas mixture, a thin GeNx passivation layer is formed on the sidewalls of the poly-Ge features.
Abrupt reduction in poly-Si etch rate in HBr/O2 plasma
Authors: Kuroda Shinji , Iwakuro Hiroaki
Published: July 2002

The effect of oxygen on polycrystalline-Si (poly-Si) and SiO2 etching in hydrogen bromide (HBr) reactive ion etching plasmas has been studied by measuring etch rates and using x-ray photoelectron spectroscopy (XPS) to study compositional changes in the surface layer. The etch rate of the poly-Si increases dramatically from 30 to 235 nm/min as the O2 concentration increases from 0% to 25%, whereas the SiO2 etch rate gradually decreases from 3 to 1 nm/min. Above 30% O2 in HBr, the poly-Si etch rate abruptly decreases by a factor of 16 compared with that at 25%. From XPS analysis, it is found that the abrupt decrease of the poly-Si etch rate at O2 concentrations of more than 30% is closely related with the composition and thickness of an SiBrxOy layer formed during the HBr/O2 plasma exposure. The SiBrxOy layer has a composition of nearly SiO2. Br ions cannot permeate the SiBrxOy layer formed in plasmas containing 30% O2 in HBr (or greater), and therefore, the poly-Si etch terminates.
Cathodoluminescence measurements of suboxide band-tail and Si dangling bond states at ultrathin Si–SiO2 interfaces
Authors: Young A. P. , Schäfer J. , Jessen G. H. , Bandhu R. , Brillson L. J. , Lucovsky G. , Niimi H.
Published: July 2002

We have directly observed cathodoluminescence (CL) in ultrahigh vacuum over a broad spectral range (0.7–4.0 eV) from ultrathin 5 nm layers of remote plasma enhanced chemical vapor deposition grown a-SiO2:H deposited on silicon substrates. In the infrared regime, luminescence is observed at 0.8 eV, consistent with the presence in the as-deposited film of Si dangling bond localized states, as well as at 1.1 eV due to band edge emission. In the optical regime, three peaks (1.9, 2.7, and 3.4 eV) are observed showing evidence for band tail state emission from an amorphous silicon–oxygen bonded suboxide region in the film, with smaller contributions from either substrate related c-Si or defect containing, stoichiometric SiO2. CL spectra with a range of beam voltages indicate that the stoichiometric SiO2 is very close to the free surface of the film, possibly due to oxidation of the air-exposed wafer or due to a nonuniformity in the film. When the films are annealed in situ in stages up to 500 °C, we observe no change in the shape of the a-SiOx:H peak at 1.9 eV, showing the stability of this suboxide to such temperatures. These observations are consistent with CL measurements of thicker films of a-SiO2:H and a-SiOx, and demonstrate the utility of CL spectroscopy for the study of ultrathin dielectric studies.
Atomic-scale compositional structure of InAsP/InP and InNAsP/InP heterostructures grown by molecular-beam epitaxy
Authors: Zuo S. L. , Bi W. G. , Tu C. W. , Yu E. T.
Published: July 2002

Cross-sectional scanning tunneling microscopy (STM) has been used to characterize the atomic-scale structure of InAs0.35P0.65/InP and InN0.01As0.35P0.64/InP strained-layer multiple quantum well structures grown by gas-source molecular-beam epitaxy. Atomically resolved STM images of the (110) cross-sectional plane reveal nanoscale clustering within the InAsxP1−x alloy layers, with the boundaries between As-rich and P-rich regions in the alloy layers appearing to be preferentially oriented along the [1̄12] and [11̄2] directions in the (110) plane. (11̄0) cross-sectional images reveal that considerably less compositional variation appears within the (11̄0) plane; features elongated along the [110] direction are observed, but few 〈112〉 boundaries are seen. These observations suggest that the boundaries between As-rich and P-rich clusters may form preferentially within the (11̄1) and (1̄11) planes. Comparisons of filled-state images of InAsxP1−x/InP and InNxAsyP1−x−y/InP heterostructures suggest that N incorporation increases the valence-band offset in InNxAsyP1−x−y/InP compared to that in InAsxP1−x/InP.
Equilibrium critical thickness for strained-layer growth
Authors: Khor K. E. , Das Sarma S.
Published: July 2002

The critical thickness for two-dimensional layer growth of Si1−xGex on Si and InxGa1−xAs on GaAs is about 1–3 monolayers (ML) for x=1, beyond which islanding begins. Under certain growth conditions, this thickness t would increase as some power of 1/x. The reason for this is not clear; Snyder et al. argue that, under equilibrium conditions, this critical Stranski–Krastanov (SK) thickness tc is independent of x and should remain at 1–3 ML, but that, under nonequilibrium growth conditions, t∼x−4. However, Osten et al. showed, experimentally, that even under equilibrium conditions there is an increase of SK thickness with 1/x. We carry out calculations of energetics of large three-dimensional (3D) islands on substrates with varying thicknesses t of the epilayer and different coverages θ. We show that at low θ or when islands are small (or both) then the SK thickness is small ∼1–3 ML, in agreement with the results of Snyder et al. At increasing coverages, when interisland separation l decreases to the point where l∼s (island size), we observe ΔE to decrease for the lower thicknesses t=3,4,5,…8…; until thicknesses t>3 become more favorable. There is considerable tension going deep into the substrate directly below islands. The larger an island becomes, the more favorable it is for a thicker layer beneath it to be of the same material as the island. It is known that the critical size sc at which 3D islands first become favorable varies as x−2. We argue from this that, at equilibrium, the average 3D island size increases with x−p, p some exponent, and at high enough coverages, when interisland separation is small, SK thickness tc increases. The experimental results of Osten et al. are consistent with exponents 2⩽p⩽4.
Focused ion beam optical column design and consideration on minimum attainable beam size
Authors: Sakaguchi Kiyoshi , Sekine Tetsu
Published: July 2002

We discussed a two lens optical system focused ion beam (FIB) employing a Ga-emitter (LMIS), whose acceleration voltage Vacc is ranged 30–100 kV, which will be used for milling and secondary ion microscope observation purposes. On such an optical system, we investigated the relation between minimum obtainable beam diameter and chromatic aberration coefficient against Vacc, and studied the possibility of improving FIB resolution by increasing the Vacc. The beam diameter is mainly determined by the size of a Gaussian image and the chromatic aberration, especially that of objective lens, if the beam current is very low. From this fact, we showed that the magnification optimization method which is one of the optical optimization methods can be greatly simplified at a lower beam current region. Using this simplified method, we summarized a guide line for evaluating an Vacc value from the standpoint of realizing a finer beam. Also given is information useful for designing a FIB column in consideration of optimized optical column design for realizing the optimized magnification. Finally, calculating the attainable minimum beam diameter and optimum column length against Vacc values, we discussed the limitation of beam diameter by increasing the Vacc.
Analysis of lattice distortions in high-quality InGaAsP epitaxial overgrowth of rectangular-patterned InP gratings
Authors: U’Ren G. D. , Goorsky M. S. , Koontz E. M. , Lim M. H. , Petrich G. S. , Kolodziejski L. A. , Wong V. V. , Smith H. I. , Matney K. M. , Wormington M.
Published: July 2002

The crystalline quality of InGaAsP deposited via gas-source molecular beam epitaxy on rectangular-patterned InP substrates has been investigated. Triple axis x-ray diffractometry measurements of InGaAsP deposited on planar InP substrates confirm that the pseudomorphic epilayer composition is uniform and of high-crystalline quality. Triple axis x-ray diffraction analysis of InGaAsP deposited on rectangular-patterned substrates reveals that the crystalline quality of the epilayer is not compromised by the presence of the grating. Symmetric [(004)] and asymmetric [(224)] reciprocal space maps of overgrown rectangular gratings indicate that both the InP and InGaAsP within the grating region exhibit an overall orthorhombic lattice distortion. Comparison of (004) diffraction scans with dynamical computer simulations suggests that the distortions are not related to detectable compositional grating. The magnitude of the orthorhombic strain, introduced by the rectangular-patterned grating, will alter the refractive index of both materials by amounts that are not expected to compromise the operation of optical devices.