bluuebunny/crossref_metadata_2025 huggingface dataset:
A new approach to high fidelity e-beam and ion-beam lithography based on an i
n s
i
t
u global-fiducial grid
Authors: Smith Henry I. , Hector Scott D. , Schattenburg M. L. , Anderson Erik H.
Published: July 2002

The distortion-free scan field of an electron-beam or ion-beam lithography system is generally quite small (∼104×104 beam addresses) and hence to achieve pattern fidelity over large areas laser-interferometer-controlled stages are employed. Because the laser interferometer monitors the stage, not the electron or ion beam, beam drift of thermal, mechanical, electrostatic, magnetic, or electronic origin is not accounted for, leading to pattern placement error. To overcome this fundamental problem of ‘‘dead reckoning’’ we propose a new approach in which a global-fiducial reference grid, which does not disturb the writing process, is put directly on the substrate. The grid is scanned with sufficiently low areal dose that the subsequent pattern development is not adversely affected. This can be achieved by ‘‘sparse sampling’’ of the grid over the entire scan field in conjunction with phase-locking technqiues in the time domain. In this way one can spatially phase lock the two grids together and thereby ensure pattern placement accuracy. The pattern of interest is then written within the scan field. This method assumes that no drift occurs during the writing of the single field. However, it may also be feasible to do some drift monitoring during the field writing. We consider secondary electrons to be the optimal signal for ‘‘seeing’’ the grid. In addition to providing enhanced pattern integrity (and hence better overlay in 1-to-1 masks), lithography systems based on an in situ global-fiducial grid may prove to be of lower cost than conventional systems since the difficult task of ensuring pattern integrity is thrust upon a computer rather than an advanced electromechanical system.
Projection electron-beam lithography: A new approach
Authors: Berger S. D. , Gibson J. M. , Camarda R. M. , Farrow R. C. , Huggins H. A. , Kraus J. S. , Liddle J. A.
Published: July 2002

Projection electron-beam lithography is potentially one of the most attractive techniques available. It offers high resolution, high throughput, and good overlay and registration characteristics. In this paper we discuss some new approaches which seem to offer solutions to problems associated with earlier systems.
Study of temperature dependent structural changes in molecular-beam epitaxy grown Hg1−xCdxTe by x-ray lattice parameter measurements and extended x-ray absorption fine structure
Authors: Di Marzio D. , Lee M. B. , DeCarlo J. , Gibaud A. , Heald S. M.
Published: July 2002

Infrared detectors fabricated from Hg1−xCdxTe typically operate in the 60 to 160 K range. The temperature dependence of the atomic structure of HgCdTe may influence device performance. We present the first detailed study of the x-ray diffraction lattice parameters of molecular-beam epitaxy grown Hg1−xCdxTe epilayers between 15 and 300 K. The epilayers were grown on (100) oriented CdTe substrates, and varied in thickness (6 to 11-μm) and composition (x=0–0.172). The (400) reflection was measured to determine the lattice parameter a⊥ normal to the film. HgTe (x=0) exhibited normal lattice contraction (α=4.7×10−6±0.3 K−1 at 300 K), with a minimum in a⊥ at 60 K, and an expansion of a⊥ below 60 K. In addition to showing a minimum in a⊥ at 60 K, some of the Hg1−xCdxTe (x≠0) epilayers (10 μm thick) exhibited anomalous behavior with varying degrees of thermal hysteresis in a⊥. The average contraction of a⊥ for these epilayers from 300 to 60 K is 0.006 Å. This is compared with results we have obtained from a temperature dependent extended x-ray absorption fine structure study of these HgCdTe epilayers: whereas HgTe exhibited a normal thermal contraction of the Hg–Te bond length consistent with the lattice parameter results, in the HgCdTe epilayers this bond contracts 0.02 to 0.03 Å on cooling from 300 to 10 K. We also present lattice parameter measurements for a thin cap layer of CdTe on HgCdTe. An increase of 0.0134 Å in a⊥ relative to the bulk was observed for a 1000 Å layer of CdTe on HgCdTe at 300 K.
Atmospheric scanning electron microscopy using silicon nitride thin film windows
Authors: Green E. D. , Kino G. S.
Published: July 2002

We report preliminary results of scanning electron microscopy (SEM) imaging with submicron resolution at atmospheric pressure using silicon nitride windows to separate the atmosphere from the electron optics. The edge response of the current system is 0.25 μm through 75 nm windows at 15 μm air path length. We discuss the merits of windowed atmospheric SEM systems.
The driving force behind the chemistry of hydrogen on the Si(111)-7×7 surface
Authors: Boland John J.
Published: July 2002

A scanning tunneling microscopy and spectroscopy study of the chemistry of H on the Si(111)-7×7 surface is presented. It is shown that the driving force behind the chemistry is the relaxation of the strained bonds formed by the reconstruction. The limited number of such bonds accounts for the apparent saturation of H on this surface. The manner in which this relaxation occurs determines both the nature and the population of different hydrides present on the surface. Models that fail to account for the presence of these strained bonds and their modes of relaxation necessarily provide an inadequate description of the surface chemistry.
Analysis and compensation of thermal effects in laser-assisted scanning tunneling microscopy
Authors: Grafström S. , Kowalski J. , Neumann R. , Probst O. , Wörtge M.
Published: July 2002

As an indispensable step towards detection of selective, resonant light absorption in laser-assisted STM, we analyzed the thermal expansion produced by laser irradiation of the tunneling junction. The expansion as a function of the modulation frequency of the light power could be related to the specific heat and thermal conductivity of the materials involved. A scheme is presented, aiming for detection of small tunneling current changes induced by resonant optical excitation of an adsorbate. It is based on the idea of irradiating the tunneling gap with two laser beams of different wavelengths—only one being in resonance with the adsorbate—and suppressing the thermal contribution to the tunneling current by an amplitude modulation of both beams with a 180° phase shift.
High brightness limited area cathodes
Authors: Broers Alec , Xia Shanhong , Maloney Chris , Zhu Xieqing , Munro Eric
Published: July 2002

In this paper the theoretical description of limited area thermionic cathodes for use in electron microscopes and related equipment is presented. With these cathodes the emitting area is set by the extent of the active cathode surface and not by a control electrode, as is the case for the conventional triode electron microscope gun. This allows the accelerating field at the cathode surface to be greatly increased and the deleterious effects of space charge eliminated. The field can also be increased to the point that the Schottky effect enhances emission without the need to use sharply pointed cathodes. For example, considerable Schottky enhancement can be realized for cathodes with tip radii around 50 μm. The overall effect is that brightness can be increased by more than an order of magnitude over the standard triode gun. Other advantages are that the total beam current can be much higher than it is with field-emission and thermal field-emission cathodes and that the Boersch effect is reduced because no real crossover is formed.
Atomic ordering in III/V semiconductor alloys
Authors: Stringfellow G. B. , Chen G. S.
Published: July 2002

The phenomenon of spontaneous atomic scale ordering was first reported for semiconductor alloys only ∼5 years ago. Since that time, ordering has been observed in nearly all III/V alloy systems. This paper will describe the ordered structures observed, as well as the extent of ordering, in specific III/V alloys. The effects of ordering on the fundamental properties will be described briefly. The paper will emphasize a summary of our current understanding of the phenomenon. Both thermodynamic and kinetic factors play a role in determining the degree of order for specific epitaxial growth parameters and on which planes the compositional modulations occur.
Surface morphology of epitaxial Ge on Si grown by plasma enhanced chemical vapor deposition
Authors: Varhue W. J. , Carulli J. M. , Miller J. A. , Peterson G. G.
Published: July 2002

Heteroepitaxial Ge films have been deposited on (100) Si substrates at low temperature (325 °C) by electron cyclotron resonance plasma enhanced chemical vapor deposition. The substrates were subjected to an in situ hydrogen/argon plasma etch prior to film growth to remove carbon and oxygen. The surface morphology has been observed with optical and scanning electron and scanning tunneling microscopy. Surface roughness due to three dimensional growth is strongly influenced by ion flux and arrival rate of reactive species on the growth surface. Surface roughness has a detrimental effect on the crystallinity of the deposited films as determined by reflection high-energy electron diffraction and x-ray diffraction measurements.
Minority carrier lifetimes of metalorganic chemical vapor deposition long-wavelength infrared HgCdTe on GaAs
Authors: Zucca R. , Edwall D. D. , Chen J. S. , Johnston S. L. , Younger C. R.
Published: July 2002

Metalorganic chemical vapor deposition (MOCVD) growth of HgCdTe on GaAs is a promising technique that overcomes the size and crystal quality limitations of CdTe substrates. An important material parameter is the minority carrier lifetime, which determines the ultimate zero bias impedance and quantum efficiency of a photodiode. We present the first systematic study of the temperature and carrier concentration dependence of minority carrier lifetimes on n-type and p-type layers of MOCVD long-wavelength infrared HgCdTe grown on GaAs substrates. The temperature dependencies of the lifetime are compared with theoretical predictions based on Auger, radiative, and Shockley–Read recombination. Excellent fits are obtained over a broad temperature range, from 20 K to room temperature. The experimental lifetimes of n-type material reach the theoretical limit imposed by Auger+radiative recombination for carrier concentrations higher than 2×1015 cm−3. For lower carrier concentrations, the measured lifetimes are shorter than those predicted from Auger+radiative recombination, and Shockley–Read recombination must be added to the calculations. The lifetimes of arsenic-doped and vacancy-doped p-type material are Shockley-Read limited. They are one order of magnitude longer than those previously observed on vacancy-doped liquid phase epitaxy material.
Lithographic applications of conducting polymers
Authors: Angelopoulos Marie , Shaw Jane M. , Lee Kam-Leung , Huang Wu-Song , Lecorre Marie-Annick , Tissier Michel
Published: July 2002

Electrically conducting polyaniline is found to be suitable for several lithographic applications. Because the polyaniline is not significantly soluble in the conducting state, the material has generally been processed by first applying the soluble, nonconducting version of the material, and in a second step externally doping the polymer film with aqueous acids. We have eliminated the need for this type of external doping by developing methods of inducing the doping in a dry fashion in situ in the polymer. This is accomplished by incorporating onium salts or amine triflate salts in the polyaniline which decompose upon radiation or thermal treatment, respectively, to generate the active dopant species, i.e., protonic acids. The use of these in situ dopants simplifies the processing of the conducting polyaniline and makes the material more convenient for lithographic applications. With the use of onium salts, the polyaniline is made into a high resolution negative conducting resist. 0.25 μm conducting lines have been patterned with e-beam radiation. Polyaniline is found to be an effective discharge layer for e-beam lithography and a removable discharge layer for the high resolution inspection and dimensional measurements of x-ray and optical masks by scanning electron microscopy (SEM). In addition, the polyaniline can be used for both electrolytic and electroless-type metallization processes.
Optical properties of quantum structures fabricated by focused Ga+ ion beam implantation
Authors: Beinstingl W. , Li Y. J. , Weman H. , Merz J. , Petroff P. M.
Published: July 2002

High energy focused ion beam implantation of Ga is used to interdiffuse AlGaAs/GaAs quantum wells. Results from low temperature cathodoluminescence, time-decay photoluminescence measurements and photolumuniscence excitation spectroscopy indicate a good quality of the interdiffused quantum wells. The broadened luminescence peaks are explained by spatial inhomogeneities of the interdiffusion. Quantum boxes were fabricated and studied by cathodoluminescence line scanning. The introduction of a few monolayers of InGaAs close to the quantum well resulted in a remarkable improvement of the homogeneity of the interdiffusion.
1/8 μm optical lithography
Authors: Owen G. , Pease R. F. W. , Markle D. A. , Grenville A. , Hsieh R. L. , von Bünau R. , Maluf N. I.
Published: July 2002

The critical bottleneck to extending optical lithography down to the 1/8 μm level is the performance of the projection optics. The Markle–Dyson configuration is virtually free of all geometric and chromatic aberrations. A prototype system has been constructed and characterized. The system uses 248 nm light from a mercury arc lamp at a numerical aperture of 0.7. 0.25 μm resolution has been demonstrated with non phase shifting masks: using phase shifting Levenson-type masks, a grating consisting of 0.125 μm lines and spaces has been printed. Two possible extensions of the existing design are proposed which would allow general 1/8 μm geometries to be patterned. The first is a 0.7 numerical aperture (NA) system working at a wavelength of 157 nm, and the second is a 1.05 NA immersion system working at 193 nm. At these high NAs the depth-of-focus (DOF) of the image becomes very small if a clear aperture is used. However, if the aperture is apodized, the DOF can be increased considerably, and a procedure for optimizing apodization functions has been devised. This makes it possible to consider high NA optical techniques as candidates worthy of further investigation for 1/8 μm lithography.
Selective order–disorder transition in GaInP/AlGaInP: A new approach for the definition of buried quantum wires
Authors: Hämisch Y. , Steffen R. , Oshinowo J. , Forchel A. , Röntgen P.
Published: July 2002

Buried semiconductor wires have been fabricated using the order/disorder transition in GaInP/AlGaInP due to ion implantation and annealing. The transition has been investigated as a function of annealing temperature and implantation dose. In order to induce this transition locally, gold wires were defined as implantation masks by a lift-off process. After low dose implantation and annealing a lateral potential well is formed, due to the band gap difference between the ordered and the disordered state. The photoluminescence even of the narrowest wire structures shows two sharp and well separated emission bands, due to the recombination in the masked wire areas and in the lateral barrier.
Phase holograms in polymethyl methacrylate
Authors: Maker P. D. , Muller R. E.
Published: July 2002

Complex computer generated phase holograms (CGPHs) have been fabricated in polymethyl methacrylate (PMMA) by partial exposure and subsequent partial development. The CGPH was encoded as a sequence of phase delay pixels and written by e-beam (JEOL JBX-5DII), a different dose being assigned to each value of phase delay. Following carefully controlled, partial development, the pattern appears, rendered in relief, in the PMMA which then acts as the phase-delay medium. The exposure dose was in the range 20–200 μC/cm2, and very aggressive development in pure acetone led to low contrast. This enabled etch depth control to better than ±20 nm corresponding to an optical phase shift in transmission, relative to air, of ±λvis/60. That result was obtained by exposing isolated 50 μm square patches and measuring resist removal over the central area where the proximity effect dose was uniform and related only to the local exposure. For complex CGPHs with pixel size of the order of the proximity radius, the patterns must be corrected for proximity effects. In addition, the isotropic nature of the development process will produce sidewall etching effects. The devices fabricated were designed with 16 equal phase steps per retardation cycle, were up to 3 mm square, and consisted of up to 10 million 0.3–2.0 μm square pixels. Data files were up to 60 Mb long and exposure times ranged to several hours. No sidewall etch corrections were applied to the pattern and proximity effects were only treated approximately. A Fresnel phase lens was fabricated that had diffraction limited optical performance with 83% efficiency.
Temperature-dependent chemical and electronic structure of reconstructed GaAs (100) surfaces
Authors: Vitomirov I. M. , Raisanen A. D. , Finnefrock A. C. , Viturro R. E. , Brillson L. J. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: July 2002

Low-energy electron diffraction, soft x-ray photoemission, cathodoluminescence (CL), and Auger electron spectroscopies have been performed to investigate the geometric, chemical, and electronic properties of GaAs (100) surfaces as a function of annealing temperature and surface reconstruction. These measurements indicate gradual changes in surface geometry, composition, deep level CL features, and Fermi-level (EF) position with increasing temperature of surface preparation. In contrast, it was observed that pronounced changes in the surface ionization potential and work function between different surface reconstructions. For most of the desorption temperatures and surface reconstructions, the secondary electron emission exhibits characteristic double onsets, possibly due to the existence of differently reconstructed patches on the surface. The implications of these variations in the surface chemical and electronic structure of GaAs (100) surfaces on their metal contact properties. It was concluded that (a) unique characterization of these surfaces requires measurements of geometric ordering, chemical composition and bonding, and deep level emission in the band gap, and (b) the correlation of the surface geometry with chemical and electronic surface and interface structure points to the central role of surface preparation in achieving controlled Schottky barrier behavior.
Critical stress of Hg1−xCdxTe solid solutions
Authors: Ekpenuma Sylvester N. , Myles Charles W.
Published: July 2002

The motion of dislocations in crystals is known to be impeded by the addition of isovalent impurities at concentrations of a few percent. By treating the Hg1−xCdxTe alloy as resulting from the addition of Cd impurities into the HgTe lattice, the critical resolved shear stress for solid-solution hardening in this material is calculated at room temperature as a function of Cd composition x. In this solid solution model, the critical stress is derived from the elastic size interaction between the Cd solute atoms and the edge dislocations in a HgTe solvent. The predicted dependence of the critical stress on x at room temperature compares favorably with experimental results for the lower yield stress. Estimates of the critical stress at temperatures up to 440 °C are also made at selected compositions by using the relation for the temperature and strain rate dependence of the lower yield stress.
Diethylsilane on silicon surfaces: Adsorption and decomposition kinetics
Authors: Coon P. A. , Wise M. L. , Dillon A. C. , Robinson M. B. , George S. M.
Published: July 2002

The adsorption and decomposition kinetics of diethylsilane (DES), (CH3CH2)2SiH2, on silicon surfaces were studied using laser-induced thermal desorption (LITD), temperature programmed desorption, and Fourier transform infrared (FTIR) spectroscopic techniques. LITD measurements determined that the initial reactive sticking coefficient of DES on Si(111) 7×7 decreased versus surface temperature from S0≊1.7×10−3 at 200 K to S0≊4×10−5 at 440 K. The temperature-dependent sticking coefficients suggested a precursor-mediated adsorption mechanism. FTIR studies on high surface area porous silicon surfaces indicated that DES adsorbs dissociatively at 300 K and produces SiH and SiC2H5 surface species. Annealing studies also revealed that the hydrogen coverage on porous silicon increased as the SiC2H5 surface species decomposed. CH2=CH2 and H2 were the observed desorption products at 700 and 810 K, respectively, following DES adsorption on Si(111) 7×7. The ethylene desorption and growth of hydrogen coverage during ethyl group decomposition were consistent with a β-hydride elimination mechanism for the SiC2H5 surface species, i.e., SiC2H5→SiH+CH2=CH2. Isothermal LITD studies monitored the decomposition kinetics of SiC2H5 on Si(111) 7×7 as a function of time following DES exposures. The first-order decomposition kinetics were Ed=36 kcal/mol and νd=2.7×109 s−1. These decomposition kinetics suggest that the silicon surface catalyzes the β-hydride elimination reaction.
A new spreading resistance correction scheme combining variable radius and barrier resistance with epilayer matching
Authors: Clarysse T. , Vandervorst W.
Published: July 2002

Laplace based reconstruction of the carrier profile from spreading resistance measurements is adequate in the absence of carrier spilling effects provided the calibration curve is interpreted correctly through an appropriate constant (variable) contact radius and (zero) barrier calibration. It will be shown that serious disagreement between secondary ion mass spectroscopy (SIMS) and SRP profiles can arise solely due to the incorrect choice of these parameters. A universal barrier and radius calibration procedure is described which removes the above discrepancies, is applicable to p- as well as n-type material, for any type of calibration curve and generates accurate profiles in agreement with SIMS (also for p p+ -layers) and correct sheet resistance values.
Identification of volatile products in low pressure hydrocarbon electron cyclotron resonance reactive ion etching of InP and GaAs
Authors: Melville D. L. , Simmons J. G. , Thompson D. A.
Published: July 2002

Volatile species produced during CH4/H2 and CH4/H2/Ar electron cyclotron resonance (ECR) reactive ion etching (RIE) of InP and GaAs at pressures of 2 mTorr have been investigated with secondary ion mass spectrometry diagnostics. A CH4/H2 ECR plasma with −120 V rf bias on the sample stage is found to etch InP but not GaAs. However, etching of GaAs does occur at this bias if the CH4/H2 mixture is diluted with Ar, showing the importance of physical bombardment to ‘‘activate’’ the GaAs surface. Group V hydrides are usually considered the most dominant volatile products in hydrocarbon RIE. In this work, it is shown that Ar dilution of a CH4/H2 mixture significantly increases the proportion of group V organometallic to hydride species in both GaAs and InP etching. More important, the main group III volatile ions from this etching process have been positively identified for the first time as In(CH3)+2 and Ga(CH3)+2 ions in InP and GaAs etching, respectively. Finally, the application of volatile product identification to end-point detection is demonstrated with a depth resolution better than 50 Å.
Fabrication of hard x-ray phase zone plate by x-ray lithography
Authors: Krasnoperova A. A. , Xiao J. , Cerrina F. , Di Fabrizio E. , Luciani L. , Figliomeni M. , Gentili M. , Yun W. , Lai B. , Gluskin E.
Published: July 2002

Fresnel phase zone plates for hard x-ray microfocusing have been fabricated. An original x-ray mask written by e-beam lithography was replicated into thick PMMA by x-ray proximity printing. The pattern was transferred into gold and nickel by electroplating. A smallest linewidth of 0.25 μm with an aspect ratio of 14 in the metal pattern has been achieved. Thickness of fabricated zone plates was dictated by a π-phase shift requirement for focusing of the x rays at 8 and 20 keV energies.
Molecular-beam epitaxial growth of high-mobility n-GaSb
Authors: Turner G. W. , Eglash S. J. , Strauss A. J.
Published: July 2002

The electrical properties of MBE-grown GaSb have been investigated as a step toward obtaining n-AlGaSb epilayers with low carrier concentrations and high mobilities for high-performance photodetectors at 2 μm and beyond. By doping with Te donors provided by a GaTe source, we have obtained n-GaSb layers, on (100) GaAs substrates, with Hall mobilities as high as 7600 and 12 600 cm2/V s at room temperature and 77 K, respectively. These values are ∼50% greater than the highest previously reported values for n-GaSb epilayers grown on similar substrates.
Ion projection lithography for vacuum microelectronics
Authors: Löschner H. , Stengl G. , Chalupka A. , Fegerl J. , Fischer R. , Lammer G. , Malek L. , Nowak R. , Traher C. , Wolf P.
Published: July 2002

Ion projection lithography has the advantage of demagnifying ion-optical mask-to-wafer pattern transfer with sub-0.1 μm resolution and large depth of focus (≥10 μm). There is the possibility of electronic alignment (‘‘pattern lock’’) of the projected ion image on-line during chip exposure with nanometer precision. Potential application areas of ion projection lithography include high volume silicon and GaAs chip fabrication and, implementing exposure field stitching and electrostatic step exposure techniques, the manufacture of flat panel devices based on vacuum microelectronics.
Evaluation of beryllium foils for x-ray lithography beamlines
Authors: Wells G. M. , Brodsky E. L. , Cerrina F. , Waldo W. G.
Published: July 2002

A commonly used exit window material for x-ray lithography beamlines is beryllium, which combines a high degree of transparency to x rays with photon energies greater than 1000 eV, with the material strength that allows the use of thin windows that can support atmospheric pressure. The mechanical and x-ray transmission properties of beryllium foils are dependent on the purity of the initial materials and the fabrication technique used in the foil formation. An evaluation of the strength and x-ray transmission of foils prepared by using different initial materials and different techniques is presented. Improvements in exposure uniformity that are obtained by scanning to average the x-ray transmission variations are discussed.
Heterojunction band discontinuities: A fundamental problem in solid-state science
Authors: Margaritondo Giorgio
Published: July 2002

Heterojunction band lineups have been investigated for over 40 years, and still are one of the most difficult open problems in condensed matter research—with an immediate impact on heterojunction devices. Steady progress has been made at least in understanding the ingredients of the band lineup process since the advent of surface-sensitive techniques in this field. Empirical links with the problem of Schottky barriers were discovered, and for both cases ‘‘extreme’’ models based on only one ingredient had to be abandoned except in very special cases. A whole array of new and advanced instruments such as ultrabright synchrotron sources, photoemission spectromicroscopes, and free electron lasers is now being developed that will allow a rejuvenated attack to this problem, raising questions about old experiments, and opening new perspective in the very definition of interface barriers and band lineups.
Fabrication of independent contacts to two closely spaced two-dimensional electron gases using molecular beam epitaxy regrowth and in situ focused ion beam lithography
Authors: Brown K. M. , Linfield E. H. , Ritchie D. A. , Jones G. A. C. , Grimshaw M. P. , Churchill A. C.
Published: July 2002

Lateral patterning of a buried GaAs epilayer can be achieved during molecular beam epitaxy growth by in situ implantation with a high energy focused ion beam. Applying this technique, 30 keV Ga ions have been used to form small, highly resistive, regions in the backgate layer of a double two-dimensional electron gas (2DEG) structure. Independent contacts to the two 2DEGs were then achieved by selectively depleting out regions of the upper and lower 2DEGs with potentials on patterned front and backgates. In the resulting devices, the magnetoresistance of the two 2DEG layers was measured both together and separately. It was demonstrated that a bias of up to ±50 mV could be applied, across the 20 nm AlGaAs barrier separating the 2DEGs, with leakage currents of <0.01 nA at 4.2 K. Finally, resonant tunneling between the two 2DEGs was observed when the barrier thickness was reduced to 7 nm. These results have demonstrated the success of this novel in situ fabrication route.
Study of interaction between incident silicon and germanium fluxes and SiO2 layer using solid-source molecular beam epitaxy
Authors: Yun Sun Jin , Lee Seung-Chang , Kim Bo-Woo , Kang Sang-Won
Published: July 2002

The dependence on the substrate temperature and the flux rates of the behavior of impinging elemental Si and Ge fluxes on a SiO2 surface, including SiO2 etching and the deposition of polycrystalline Si and SiGe films, was investigated by using the solid source molecular beam epitaxy (MBE). Flux rates of the source beams and a substrate temperature were in the range of 1 to 5×1013 atoms/cm2 s and 710–810 °C, respectively. Under these experimental conditions, the Ge flux was not individually effective to etch the SiO2, but contributed to etching the oxide layer with an accompanying Si flux. The critical flux of Si for SiO2 etching at 740 °C was determined to be about 1×1013 atoms/cm2 s.
Transport and heating of small particles in high density plasma sources
Authors: Kilgore M. D. , Daugherty J. E. , Porteous R. K. , Graves D. B.
Published: July 2002

Calculations of the forces experienced by particles in high density plasma sources such as an electron cyclotron resonance system indicate that particles can accelerate in the plasma and travel through sheaths. This is due primarily to the very high ion fluxes in these systems and relatively low sheath potentials. The net result is less particle trapping and growth in the plasma compared to conventional plasma sources. The temperature of the particles is calculated from an energy balance. The particles heat due to electron-ion recombination on their surface, and they cool by radiation and conduction to the neutral gas. Because of the high plasma density and low neutral pressure, the particles may reach high temperatures (T∼1000 K).
Ponderomotive transport of charge in the induction plasma
Authors: Helmer John C. , Feinstein Joseph
Published: July 2002

The transformer coupled plasma reactor (TCP) is a low frequency, inductively coupled plasma reactor, with a gradient electromagnetic source field, such that electrons experience a secular (time average) force—the ponderomotive force. There are two electric forces and one magnetic force, the latter of which is strongly active in the TCP. The ponderomotive force has previously been explored for confinement in fusion reactors, but has not been discussed in connection with semiconductor processing. In modeling with plasma fluid equations, there is a need to include large-scale particle kinetics. The calculation of the ponderomotive force in laboratory devices is a problem, because the form of the field is often taken as a zero-curl approximation which violates Maxwell’s equations. To clarify this issue we have analyzed the ponderomotive force field in the transverse-electric electromagnetic field of a rectangular waveguide. A specific model of the TCP is analyzed. This shows that the rf-magnetic field of the TCP coil, in the range of a few gauss, creates a significant ponderomotive force at 13 MHz, which is enhanced at lower frequencies such as 1 MHz. This force acts to protect the rf window from erosion and cancel ambipolar diffusion losses, thereby improving the density uniformity of the plasma.
Method for the measurement of the lateral dose distribution of dopants at implantation or diffusion mask edges (‘‘lateral SIMS’’)
Authors: von Criegern R. , Jahnel F. , Bianco M. , Lange-Gieseler R.
Published: July 2002

A method is presented allowing the lateral dopant distribution in the vicinity of the edge of a linear implantation (or diffusion) mask of specific test samples to be measured. Basically, the sample is sectioned perpendicularly to the surface, and parallel to the mask edge. The dopant distribution into the depth of this section (i.e., parallel to the surface of the wafer) is then measured with secondary ion mass spectrometry (SIMS), making use of its excellent depth resolution. The concept of this approach, its requirements, the sample preparation, and first results obtained on ion-implanted arsenic in silicon are presented and discussed. Limiting effects involved in this approach are identified, and a potentially useful extension of the method toward the measurement of the two-dimensional dopant distribution (2D SIMS) is discussed. The results of the measurements on ion-implanted arsenic appear to be sufficiently accurate to provide a valuable input for comparison with computer simulation results.
Analytical modeling of plasma immersion ion implantation target current using the SPICE circuit simulator
Authors: En William , Cheung Nathan W.
Published: July 2002

Plasma immersion ion implantation applies a series of negative high-voltage pulses to a target immersed in a plasma. An analytical model of the currents and potentials induced before, during, and after the negative bias in a planar geometry is presented. The effect of multiple pulses on the results is also studied. The model determines the time-varying ion current, electron current, total current, total dose, and sheath thickness for a piecewise linear voltage pulse. The sheath collapse is found to be important for high repetition rate pulses. Implementation of the model is done in SPICE, a circuit simulator. Comparison with experimental data has demonstrated the accuracy of the model.
Proximal probe study of self-assembled monolayer resist materials
Authors: Perkins F. Keith , Dobisz Elizabeth A. , Brandow Susan L. , Koloski Timothy S. , Calvert Jeffrey M. , Rhee Kee W. , Kosakowski John E. , Marrian Christie R. K.
Published: July 2002

A scanning tunneling microscope (STM) has been used to investigate organosilane self-assembled monolayer films (SAMs) as imaging layers for low voltage e-beam lithography. We have studied three different SAMs [(aminoethylaminomethyl)phenethyltrimethoxysilane (PEDA), 4-chloromethylphenyltrichlorosilane (CMPTS), and n-octadecyltrichlorosilane (OTS)] deposited on the native oxide of Si. We have found OTS to act as a positive resist in wet etch processing upon exposure to 50 keV electrons, in agreement with Lercel [J. Vac. Sci. Technol. B 11, 2823 (1993)]. Identically processed samples patterned with low voltage (−10 to −25 V tip–sample bias) electrons in the STM exhibit a negative tone. STM biases below −10 V were insufficient to expose the film. An improved etch for STM-generated patterns, leading to smoother surfaces, was developed. STM exposure of PEDA and CMPTS SAMs leads to a destruction of ligand functionality. An exposure threshold of −4 V bias for CMPTS and −8 V for PEDA has been established. As an example of post-exposure processing, these latent images were metallized with an aqueous Pd(II) catalyst solution followed by an electroless Ni plating bath. The patterned, thin (25 nm) Ni layers grown in this way are shown to be excellent masks for reactive ion etching (RIE) with SF6, exhibiting at least a 1:200 etch selectivity on Si. Linewidths after metallization of 20 nm and etched (CBrF3/O2 RIE) trench widths of 25 nm are shown.
Continuous ultra-dry process for enhancing the reliability of ultrathin silicon oxide films in metal–oxide semiconductors
Authors: Yamada Hiroshi
Published: July 2002

Time-dependent dielectric breakdown lifetime of 5-nm-thick silicon oxide films in metal–oxide semiconductors (MOSs) fabricated by a new continuous ultra-dry process was investigated. In this process, three fundamental stages in MOS diode fabrication—oxidation, amorphous-Si electrode film formation, and annealing to crystallize the electrode film—are continuously performed in an ultra-dry ambient with less than 100 ppb moisture concentration (humidity). The lifetime for the continuously ultra-dry processed MOS diodes is considerably larger than that of conventional ones produced in an ambient with more than 100–200 ppm humidity. The stress-induced positive charges that affect lifetime are mainly generated and trapped near both oxide interfaces. This indicates that the interface condition is probably improved by the present process.
Scanning tunneling microscopy at low temperatures on the c(4×2)/(2×1) phase transition of Si(100)
Authors: Badt D. , Wengelnik H. , Neddermeyer H.
Published: July 2002

Using scanning tunneling microscopy (STM) at low temperatures, we have studied the transition between the c(4×2) and (2×1) phases of Si(100). The phase transition is resulting from the stabilization and ordering of asymmetric dimers on reconstructed Si(100) at low temperatures. The occurrence of asymmetric dimers already at room temperature in previous STM results has so far been associated with defect structures, which were believed to produce a local buckling in an arrangement of symmetric dimers. By cooling Si(100) we observe growth of c(4×2) domains which, below 200 K, cover the entire surface. The phase transition can be explained by freezing in of the vibration of asymmetric dimers, which is present on defect-free parts of the surface at room temperature.
Restructuring process of the Si(111) surface upon Ag deposition studied by in situ high-temperature scanning tunneling microscopy
Authors: Shibata A. , Kimura Y. , Takayanagi K.
Published: July 2002

Restructuring processes of the Si(111) surface from the 7×7 to the √3×√3 structure upon the deposition of Ag has been observed by a high-temperature in situ STM method. Although the √3×√3 structure is formed at substrate temperatures above 240 °C, Ag islands do not have the √3×√3 structure at the initial stage of the condensation. The restructuring is found to occur after the Ag island has grown larger than the critical size, which is four times as large as the half unit cell of the 7×7 structure. The restructuring starts from the edges of such Ag islands and the area of the √3×√3 structure expands gradually as they grow. The hole-island pairs are formed so as to conserve the number of Si atoms underneath each Ag island.
Measurement of nanomechanical properties of metals using the atomic force microscope
Authors: Hues Steven M. , Draper Charles F. , Colton Richard J.
Published: July 2002

The capability of the atomic force microscope (AFM) to quantitatively measure the nanoscale mechanical properties of metals via nanoindentation is illustrated with three single-crystal metals–chromium, molybdenum, and tungsten. Three distinct regions with differing elastic moduli are found: (1) a low modulus for the outermost surface layer whose thickness scales with the degree of hydrocarbon surface contamination, (2) a much higher modulus at a depth and thickness corresponding to the native oxide layer; and (3) an intermediate modulus at larger depths corresponding to the bulk modulus of the metal. In all cases, the modulus of the oxide is significantly larger than the bulk metal. Furthermore, the AFM can be used to ‘‘depth profile’’ the oxide layer giving new information about the sharpness of the oxide/metal interface.
Comparison of advanced plasma sources for etching applications. I. Etching rate, uniformity, and profile control in a helicon and a multiple electron cyclotron resonance source
Authors: Tepermeister I. , Blayo N. , Klemens F. P. , Ibbotson D. E. , Gottscho R. A. , Lee J. T. C. , Sawin H. H.
Published: July 2002

We have studied the etching performance of two commercially available low pressure, high density plasma sources and their application for the etching of 0.35 μm features in polysilicon films. The two sources are a rf-inductively coupled helicon made by Lucas Labs of Sunnyvale, CA and a multipole electron cyclotron resonance (ECR) source made by Wavemat of Plymouth, MI. The sources are mounted on a dual chamber etching platform to remove platform dependent effects. Performance metrics consist of measuring the polysilicon etching rate, etching rate uniformity, and profile control in HBr gas-phase chemistry. The effect of applied source power, applied rf-bias power, and reactor pressure on the etching rate and uniformity is examined using a response surface experiment. Profile control is determined by examining nested and isolated lines and trenches using oxide mask/polysilicon/oxide structures. In both sources, high uniformity and vertical profiles are obtained at low reactor pressure, high applied source power, and applied rf-bias powers between 50 and 60 W. To decrease the lateral etching rate and increase the anisotropy of the etching process, approximately 3% of O2 is added to the feed-gas. For the helicon, the operating point for best uniformity is at 2.0 mTorr, 2500 W applied source power, and 57 W applied rf-bias power resulting in a measured etching rate of 2340 Å/min and uniformity of ±3.3%(2σ). For the ECR, the operating point for best uniformity is at 2.8 mTorr, 1370 W applied source power, and 60 W applied rf-bias power resulting in a measured etching rate of 2580 Å/min and uniformity of ±1.4%(2σ). Since both sources exhibit remarkably similar performance for the etching of polysilicon films, other factors such as ease of operation, plasma stability, and plasma ignition sequence become relatively more important when deciding which source to use for a particular application.
Long-throw low-pressure sputtering technology for very large-scale integrated devices
Authors: Motegi Nobuhiro , Kashimoto Yuzou , Nagatani Koji , Takahashi Seiichi , Kondo Tomoyasu , Mizusawa Yasushi , Nakayama Izumi
Published: July 2002

For the next generation of semiconductor devices, new metal deposition technologies (such as Cu and Ti chemical vapor deposition) are being developed. As very large-scale integrated fabrication becomes more highly integrated, the size of contact/via holes must shrink, producing higher aspect ratios. These geometries create major difficulties in obtaining acceptable step coverage of the barrier/glue layer within the contact/via holes. A new technology has been developed, called long-throw sputter (LTS), for achieving acceptable step coverage particularly for geometries below 0.5 μm without employing collimators in the system. LTS (patent pending) provides more than 40% bottom coverage of barrier metal films in 0.35 μm contact holes with 3.0 aspect ratio while maintaining a high deposition rate and acceptable film uniformity. Additionally, LTS may facilitate Al alloy flow and/or reflow application.
Physical and magnetic properties of submicron lithographically patterned magnetic islands
Authors: New R. M. H. , Pease R. F. W. , White R. L.
Published: July 2002

We have developed a procedure for high-resolution patterning of magnetic thin films using direct-write electron beam lithography and a multistep sputter etching process [New et al., J. Vac. Sci. Technol. B 12, 3196 (1994)]. Using this patterning procedure we have defined large arrays of 0.2 by 0.4 μm magnetic islands out of a 200-Å-thick polycrystalline film of cobalt. The physical and magnetic structure of these islands has been examined using atomic and magnetic force microscopy, as well as transmission electron microscopy. Hysteresis loop measurements have been taken from large arrays of weakly interacting islands. The particles are not single domain and show considerable nonuniformity of magnetization when they are completely demagnetized. However, after application and removal of a large field along the long axes of the islands, most of the particles do relax into an almost uniform magnetization state.
Transmission electron microscopy study of In0.25Ga0.75As epilayers grown on GaAs (001) by molecular beam epitaxy: The effect of epilayer thickness
Authors: Edirisinghe S. P. , Staton-Bevan A. , Fawcett P. N. , Joyce B. A.
Published: July 2002

Transmission electron microscopy (TEM) has been employed to investigate the epitaxial growth of In0.25Ga0.75As on GaAs (001) by molecular beam epitaxy Plan-view and cross-section TEM has been used to determine the effect of epilayer thickness on the occurrence of misfit dislocations. The critical thickness (hc) has thereby been estimated and compared with the predictions of several theoretical models. The critical thickness for the In0.25Ga0.75As epilayers was between 15 and 25 nm. This value is greater than the hc predicted by the Matthews and Blakeslee model but agrees well with more recent experimental observations reported by other workers. No threading dislocations were observed in any of the epilayers and no misfit dislocations were observed for epilayer thicknesses less than 25 nm. For an epilayer thickness of 25 nm, 60° dislocations were observed lying predominantly along one of the interfacial 〈110〉 directions. For epilayer thicknesses between 50 and 150 nm, 60° dislocations were observed along both 〈110〉 interfacial directions. The residual strain in the epilayer showed a large decrease soon after the critical thickness was reached but thereafter relaxation progresses more slowly. In the thickness range investigated, the experimental data fitted the Tsao et al. model for hc as a function of misfit, with excess stress/shear modulus=0.04. However, comparison with other reported studies suggests that this model is not applicable in all situations.
Fabrication of lateral-type thin-film edge field emitters by focused ion beam technique
Authors: Gotoh Y. , Ohtake T. , Fujita N. , Inoue K. , Tsuji H. , Ishikawa J.
Published: July 2002

Lateral-type, thin-film, edge field emitters have been fabricated with a focused ion beam (FIB) technique. A metal thin film deposited on the thermally oxidized silicon wafer was cut by a 20 keV gallium ion beam with a diameter of 1–2 μm to produce an emitter-collector gap. One of the advantages of the present procedure is such that the edge of the emitter could be sharpened owing to the current density distribution of the FIB. Another advantage is precise controllability of the emitter-gate gap. Nickel, chromium, and platinum emitters were fabricated. It was found that the chromium emitters exhibited superior properties as compared with the other materials. Electron emission characteristics were also investigated for the single emitters and for the arrayed emitters made of chromium. By adding an external collector, the device showed triode characteristics.
Ambient scanning tunneling microscopy and atomic force microscopy on GaAs (110) treated with (NH4)2Sx and SeS2 solutions
Authors: Nozaki Shinji , Tamura Satoshi , Takahashi Kiyoshi
Published: July 2002

The surface of GaAs (110) cleavage faces treated with (NH4)2Sx and SeS2 solutions were studied by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) in air. Sulfur passivation using a (NH4)2Sx solution removes the native oxide and leaves a thin unreactive sulfur layer, while selenium passivation using a SeS2 solution neither removes the native oxide nor produces a selenium-terminated surface. With sulfur passivation, an atomically flat surface of the GaAs (110) cleavage face was obtained in the STM image. The topographic contrast over the p-n junction in the STM image obtained with sulfur passivation shows the n region to be higher than the p region, while there was no height difference seen in the AFM image.