bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the Si evaporation source on the incorporation of In during Si molecular-beam epitaxy growth: A comparative study of magnetically and electrostatically-focused electron-gun evaporators
Authors: Knall J. , Sundgren J.-E. , Markert L. C. , Rockett A. , Greene J. E.
Published: July 2002

The incorporation behavior of thermally evaporated In during the growth of Si(100) by molecular-beam epitaxy has been observed to depend critically on whether a magnetically focused electron gun (MFG) or electrostatically focused electron gun (EFG) evaporation source was used for Si evaporation. When a MFG source was used, the incorporation probability σ was found to be very low during growth on grounded substrates, but could be increased considerably by the application of a negative substrate bias between 100 and 2000 V. This increase was due to Si+ ion bombardment of the In surface overlayer resulting in secondary implantation during growth. For deposition on electrically grounded substrates, σ was found to be much higher during growth with the EFG source than with the MFG source. This was primarily due to bombardment of the In overlayer by energetic neutral Si atoms emitted from the EFG source.
Epitaxial growth of high-temperature superconducting thin films
Authors: Eckstein J. N. , Schlom D. G. , Hellman E. S. , von Dessonneck K. E. , Chen Z. J. , Webb C. , Turner F. , Harris J. S. , Beasley M. R. , Geballe T. H.
Published: July 2002

We report the development of molecular-beam epitaxy (MBE) techniques for the growth of high-temperature, perovskite-like superconductors. The use of a plasma source of active oxygen allows the in situ growth of such layers. Some of the films grown this way were superconducting as grown. Smooth films exhibiting streaked reflection high-energy electron diffraction (RHEED) patterns, were obtained by using shuttering to kinetically control the growth process. We also report initial results of experiments in which kinetic control is used to layer metastable, nonequilibrium structures in the bismuthstrontium–calcium–copper–oxide system.
Growth of InGaP on GaAs using gas-source molecular-beam epitaxy
Authors: Quigley J. H. , Hafich M. J. , Lee H. Y. , Stave R. E. , Robinson G. Y.
Published: July 2002

The growth of high-quality InGaP films lattice matched to (100) GaAs substrates by gas-source molecular-beam epitaxy is reported. InxGa1−x P alloys were grown using a P2 molecular-beam produced by thermal decomposition of PH3 at 900 °C in a low-pressure cracking oven, and the composition x was varied from 0.48 to 0.61 using conventional effusion ovens for the In and Ga sources. Sharp (2×1) reflection high-energy electron diffraction patterns were observed during InGaP growth, and smooth surface morphology and a lattice mismatch of <1×10−4 was obtained. Using the optimum growth conditions of a PH3 flow rate of 7.6 standard cm3/min (sccm) and a substrate temperature of ∼490 °C at a growth rate of 0.5 μm/h, InGaP films were found to exhibit low-temperature photoluminesence linewidths as small as 11 meV, x-ray rocking curve linewidths as narrow as 20 arcsec, and electron mobilities similar to that reported for other epitaxial growth techniques.
X-ray studies of heat treated SiGe/Si strained-layer superlattices
Authors: Prokes S. M. , Fatemi M. , Wang K. L.
Published: July 2002

An x-ray study of annealing effects in Si0.65 Ge0.35 /Si strained-layer superlattices grown by molecular-beam epitaxy (MBE) at 500 °C is reported. The samples were subjected to thermal treatments between 600 and 698 °C, and the superlattice peaks and Si(004) peak were monitored at both low and high angles using powder and double crystal diffractometries. The interdiffusion coefficient of the average composition, obtained from the decay in intensity of the first superlattice peak about (000), was found to be similar to the results obtained from satellites about (004). This leads to the important conclusion that the diffusion coefficient can be obtained using the high-angle technique, which is generally faster and less susceptible to experimental errors. The comparison between the two groups of measurements further emphasizes the fact that the critical slopes of the intensity plots should be excluded from the calculation of the diffusion coefficient.
The removal of hydrocarbons and silicone grease stains from silicon wafers
Authors: Sherman Robert , Whitlock Walter
Published: July 2002

A relatively new method of removing hydrocarbon and silicone grease stains from silicon wafer surfaces is discussed. In this technique, high purity liquid or gaseous CO2 is expanded in a special nozzle to form a high speed jet. The jet contains numerous small diameter particles of solid CO2. The CO2 particles, referred to as snow, strike the surface and remove adherent particles (even submicron sizes), hydrocarbon stains such as fingerprints and noseprints, and silicone grease. Indeed, CO2 snow cleaning of clean wafer surfaces has led to sizable reductions in the adventitious hydrocarbons; in one case, the reduction was about 60%. Surface analysis of clean and contaminated silicon wafers indicates that CO2 snow cleaning causes no apparent chemical interactions and leaves no detectable residues.
Plasma etching of III–V semiconductors in CH4/H2/Ar electron cyclotron resonance discharges
Authors: Constantine C. , Johnson D. , Pearton S. J. , Chakrabarti U. K. , Emerson A. B. , Hobson W. S. , Kinsella A. P.
Published: July 2002

We have investigated the etch rates, residual lattice damage, surface morphologies, and chemistries of InP, InGaAs, AlInAs, and GaAs plasma etched in electron cyclotron resonance (ECR) CH4/H2/Ar discharges. The etch rates of InP and InGaAs increase linearly with additional rf biasing of the substrate, and are approximately a factor of 2 faster than for GaAs. Under our conditions the etch rate of Al0.52Ga0.48As is very low (∼25 Å min−1) even for the addition of 100 V rf bias. In all of these materials the residual damage layer remaining after dry etching is very shallow (∼20 Å) as evidenced from Schottky barrier height and photoluminescence measurements combined with wet chemical etching. InP shows significant P depletion with the addition of rf biasing during the ECR etching while GaAs retains a near-stoichiometric surface. Hydrogen passivation of shallow donors in n-type GaAs occurs to a depth of ∼3000 Å during exposure to the CH4/H2/Ar discharge for long periods (60 min). The surface morphologies in the In-based materials become roughened for etching with the addition of rf biasing while GaAs displays smooth, residue-free surfaces under these conditions.
Spatial period division with synchrotron radiation bandwidth control by W/Be multilayer mirror
Authors: Utsumi Yuichi , Kyuragi Hakaru , Urisu Tsuneo
Published: July 2002

Submicrometer periodic patterns were fabricated by spatial period division (SPD) using synchrotron radiation. The spectrum bandwidth was controlled to nearly the optimum width by using a W/Be multilayer mirror. This reduces the influence of gap variations between the x-ray mask and the Si wafer.
Optical techniques for composition measurement of bulk and thin-film Cd1−yZnyTe
Authors: Johnson S. M. , Sen S. , Konkel W. H. , Kalisher M. H.
Published: July 2002

The composition of high-quality single-crystal bulk-grown Cd1−yZnyTe (0≤y≤0.2) was determined from precision lattice constant measurements for a total of 22 data points. These samples were used to develop calibration curves for an accurate, contactless, nondestructive optical determination of composition using either 300 K transmission measurements or 77 K photoluminescence measurements. The 300 K transmission technique is useful for bulk CdZnTe wafers while the 77 K PL technique is applicable to both bulk and thin-film CdZnTe. Both techniques are useful in determining Cd1−yZnyTe composition in the range (0≤y≤0.2) which covers the range needed for lattice-matching to Hg1−xCdxTe and Hg1−xZnxTe epitaxial layers. The ability to map sample composition with high precision is available with both techniques.
Characterization of selective chemical vapor deposited tungsten using SiH4 reduction
Authors: Colgan E. G. , Chapple-Sokol J. D.
Published: July 2002

The growth rate, resistivity, and selectivity of selective chemical vapor deposition of tungsten using SiH4 reduction of WF6 has been examined as a function of SiH4 partial pressure (PP), WF6 PP, growth temperature, total pressure, average residence time, and fraction of exposed area. The growth rate is proportional to the SiH4 PP, decreases with increased temperature, and decreases with increased exposed area. The deposition rate also decreases slightly as the WF6 to SiH4 ratio increases. With a constant SiH4 PP, the growth rate decreases as the total pressure increases (the SiH4 flow rate is decreased at higher total pressures). The SiH4 conversion efficiency increases as the residence time and fraction of exposed area increase. The resistivity decreases as the growth temperature increases or the deposition rate decreases. The resistance increases with increasing Si and F concentrations in the films. Low temperature residual resistance measurements indicated that the increase in resistance is due to impurity scattering. The selectivity is better at lower temperatures, low growth rates, high WF6 to SiH4 ratios, and intermediate pressures (25–100 mTorr). A mechanistic model of the deposition process is presented which explains much of the observed phenomenology.
Investigation of single sideband optical lithography using oblique incidence illumination
Authors: Tamechika Emi , Matsuo Seitaro , Komatsu Kazuhiko , Takeuchi Yoshinobu , Mimura Yoshiaki , Harada Katsuhiro
Published: July 2002

We propose a new method for enhancing the image contrast in oblique illumination lithography. In this article, we analyze the modulation transfer function to clarify the cause of poor contrast in oblique illumination systems. A unique optimization procedure is also proposed. It is carried out for the oblique illumination systems, including single sideband optical lithography. It is found that the contrast enhancing method and optimization can improve the resolution for annular source and four-point-type sources. These improvements open up the possibility of 0.25-μm resolution with i-line lithography.
Study of the lithographic process in deposited silicon dioxide
Authors: Pan Xiaodan , Broers A. N. , Jeynes C.
Published: July 2002

The lithographic process induced by electron beam irradiation in SiO2 deposited by low-temperature plasma-enhanced chemical vapor deposition is studied. It is found that the as-deposited SiO2 acts as a negative resist when the p-etch system (15:10:300 HF:HNO3:H2O in volume unit) is used as a developer, but the process is not suitable for lithographic applications because of nonuniform linewidth and relatively poor resolution. Modification of the as-deposited oxide by 50 keV oxygen ion implantation with a dose of 1×1016/cm2 did not improve the resolution much, but could offer slightly denser structures. However, the linewidth was still inhomogeneous. Annealing the as-deposited SiO2∼600 °C turned the resist process positive, but again failed to improve the nonuniformity in linewidth and the resolution. A high-resolution lithographic process was only achieved in the modified oxide films by oxygen ion implantation and subsequent annealing at ∼600 °C. Using this modified oxide as a positive electron beam resist, we have fabricated trenches with feature sizes as small as 10 nm and periods down to 15 nm which are comparable to those previously achieved in thermally grown SiO2.
Electron beam lithography using MEBES IV
Authors: Abboud F. , Gesley M. , Colby D. , Comendant K. , Dean R. , Eckes W. , McClure D. , Pearce-Percy H. , Prior R. , Watson S.
Published: July 2002

The lithographic performance of the MEBESR IV maskmaker is described. This raster-scan electron beam lithography system automates the thermal field emission (TFE) column and makes a number of advances in the electronics and software control subsystems to achieve the stability and accuracy sufficient for 64-Mbit production and 256-Mbit development. Key module developments are highlighted, including TFE column vibration reduction, column setup automation, 160 MHz blanking at a high slew rate, low noise, and increased linearity of the deflection control electronics, and multipoint system temperature control. Data on lithographic quality is presented, as well as ghostTM proximity correction results for 1× maskmaking applications with 0.2 μm minimum feature sizes.
Photoluminescence from pseudomorphic Si1−xGex quantum wells grown by molecular beam epitaxy: Variation of the band gap with high pressure
Authors: Northrop G. A. , Morar J. F. , Wolford D. J. , Bradley J. A.
Published: July 2002

We report the first observation of truly near-edge photoluminescence (PL) from molecular beam epitaxy (MBE) prepared, narrow, strained-epitaxial Si/Si1−xGex quantum wells. Indeed, PL intensity from just two 25-Å wells is comparable to that from the free exciton in high-quality Si−thus reflecting the achievement of excellent MBE-epilayer quality. As importantly, we also report the first measurement of the variation of quantum-well emissions with applied hydrostatic pressure. A clear no-phonon emission line is found in the low-temperature (6 K) PL which displays, versus pressure, a strictly linear dependence in emission energy, with a slope virtually identical to that of the Si free exciton. This result is strong evidence that this quantum-well emission process is indeed ‘‘shallow’’ in origin, and is associated with the lowest, indirect X1-gap transition in these strained (unrelaxed) structures. Furthermore, these results provide circumstantial evidence that the band alignment in this system is effectively type I.
Influence of the desorption and growth temperatures on the crystalline quality of molecular-beam epitaxy InAlAs layers
Authors: Peiró F. , Cornet A. , Herms A. , Morante J. R. , Georgakilas A. , Halkias G.
Published: July 2002

The influence of molecular-beam epitaxy growth conditions, especially oxide desorption and growth temperature, on the final quality of InAlAs layers grown on (100) InP substrates, has been analyzed by conventional and high-resolution transmission electron microscopy observations. InP thermal cleaning prior growth at 500 °C has been found to produce rough interfaces and extended defects which propagate up to the surface, while thermal cleaning at 530 °C results in abrupt interfaces and improved epilayer structure. The increase of growth temperature up to 530 °C, also improves the crystalline quality of InAlAs.
Identification of the facet planes of phase I TiO2(001) rutile by scanning tunneling microscopy and low energy electron diffraction
Authors: Poirier G. E. , Hance B. K. , White J. M.
Published: July 2002

The thermal faceting of TiO2(001) rutile was studied in ultrahigh vacuum using scanning tunneling microscopy (STM), Auger electron spectroscopy, and low energy electron diffraction (LEED). The predominant facet planes observed by STM after annealing to 510 °C were (011) and stepped (011), in agreement with the LEED work of Firment. The step structure on (011) planes is indicative of facet growth by surface migration. A smaller number of (114) and (111) planes were observed, in agreement with the work of Firment and Tait and Kasowski. Facet structures resembling those proposed by Kurtz, based on electron simulated desorption ion angular distribution results, were observed for the (011) planes.
Temperature measurement for scanning tunnel microscope samples using a detachable thermocouple
Authors: John Kevin D. , Wan K. J. , Yates John T.
Published: July 2002

A detachable thermocouple contact for the measurement of sample temperature in ultrahigh vacuum was constructed and tested. The thermocouple was demonstrated to be accurate to within 1.2 K from 77 to 373 K. The thermocouple was also compared against a reference thermocouple of conventional design up to 1300 K (during ohmic heating) and the agreement was within 20 K throughout this temperature range.
Simultaneous optimization of spectrum, spatial coherence, gap, feature bias, and absorber thickness in synchrotron-based x-ray lithography
Authors: Hector Scott D. , Smith Henry I. , Schattenburg M. L.
Published: July 2002

Of the many factors affecting the x-ray intensity distribution, the variables that can be controlled are the source spectrum, the proximity gap, the source spatial coherence, the mask linewidth bias, and the absorber thickness. To obtain the highest quality aerial image, all of these parameters must be optimized simultaneously. An optimization of the spectrum of the synchrotron Helios, located at IBM’s Advanced Lithography Facility is described. The optimum parameter space for proximity x-ray lithography at 0.1 μm minimum linewidth is then determined using the optimized spectrum by adjusting the free parameters. For maximum accuracy, a rigorous electromagnetic model that accounts for the dielectric properties of the absorber, the source partial coherence, and diffraction in the proximity gap is used to calculate the x-ray aerial image at the wafer. Descriptive figures-of-merit (FOMs) of the aerial image are the image contrast [(Imax−Imin)/(Imax+Imin)] and the exposure latitude. These two FOMs are maximized with respect to source spectrum, gap, source spatial coherence, feature size and bias, and mask absorber thickness. The global maximum of these FOMs is coarsely located in parameter space by determining the dependence of the FOMs on two variables at a time. The feature bias is then determined so that all feature types (gratings, lines, spaces) can be printed at the same dose with maximum average contrast and exposure latitude.
Field emission from structures with quantum wells
Authors: Litovchenko V. G. , Kryuchenko Yu. V.
Published: July 2002

Computer simulation studies of the properties of some novel types of field emitters have been carried out in the framework of the theory of quantum disc effects. The following cases have been analyzed in detail. (1) Emission from the field surface states (SS) exhibiting both discrete and continuous energy spectra. This case resembles the known effect of the work-function deterioration ΔW∼(Ec−ESS), yet, here, prior to the emission into vacuum, the SS electrons must be excited the conductivity band via the Pool–Frenkel mechanism: ne≂C exp(aEs1/2/kT), or some other. (2) Emission from the δ-doped structures via the internal field ionization of filled states, deposited near to surface in semiconductor or in super-thin insulator layer. (3) Emission from the two-dimensional (2D) quantum well (QW) surface space charge regions. In this case, the bottom of a subsurface c band is shifted by the quantization value E=Ec−Ei with Ei=(ℏ2/2m*)1/3 [3/2πeEs(i+3/4)]2/3∼Es2/3. Here Es=4π/2eNs is the strength of the surface electric field and i stands for the number of a quantum well (or a 2D subband). In contrast with the three-dimensional (3D) case, the electron concentration in the ith 2D degenerate subband is given bt a step function Ns=(m*/πℏ2)kT ln{1+exp[(Ec−Ei)/kT]}. With m*=0.01 me, the difference E=(Ei−Ec) greatly increases in pretty high applied fields (Es∼10 V cm−1) and, thus, may give rise to a pronounced increase of the field emission current. Moreover, with growing Es, subsequent bands are being filed and, due to the steplike dependence of NSS, an additional growth of the emission current may occur, together with emerging collisions on the Fowler–Nordheim differential curve. (4) Emission from very sharp tips containing 2D-conducting layer (QW space charge), when τ tip is comparable to the low thickness of QW layer.

Here we have so-called zero-size (zero-dimensional) systems, when the dependence ΔW on ES becomes even sharper. (%) emission from the tips covered by very thin films with quantized conducting electrons. For these, narrow-band or semimetallic materials (such as Bi) with very low effective mass (HgCdTe, InSb, PbSTe, etc.) may be used. Discrete Q levels Ei govern the current oscillations with the increasing Es, when Ei is filled by the applied field. For the transversal current (in the direction of the electron localization) to appear, necessary determine or ionization 2D quasilocalized electron to more high, 3D subbands, or due to different scattering processes (including oscillation in QW).
Integration of microstructures onto negative electron affinity cathodes: Fabrication and operation of an addressable negative electron affinity cathode
Authors: Santos Edval J. P. , MacDonald Noel C.
Published: July 2002

A new cathode technology which integrates isolated multilayer structures onto negative electron affinity (NEA) cathodes has been developed. The process is designed to have the emission areas protected throughout the processing steps. With this process, a three-metal layer structure has been integrated onto a GaAs chip to fabricate an addressable-array NEA cathode. The metal layers are sputter-deposited TiW, the topmost layer is SiN. The addressable-array NEA cathodes were tested in an ultrahigh vacuum chamber, where they were coated with cesium and oxygen to achieve the NEA condition on the lithographically selected areas. Electron emission from the addressable cathodes has been projected onto a phosphorous screen. The photocurrent was modulated by applying a voltage to each control electrode. Pictures demonstrating the addressing capability are presented. The addressable-array NEA cathode technology offers the possibility of new projection electron-beam architectures for high throughput electron-beam lithography.
First-wafer effect in remote plasma processing: The stripping of photoresist, silicon nitride, and polysilicon
Authors: Loewenstein Lee M. , Stefani Jerry A. , Watts Butler Stephanie
Published: July 2002

We have identified a first-wafer effect for photoresist ashing and silicon nitride-polysilicon stripping in remote plasma reactors. The first-wafer effect consists of the first wafer etching differently from the subsequent wafers in a lot. For photoresist ashing, the first wafer ashes faster than subsequent wafers. For silicon nitride and polysilicon stripping, first wafers show higher etch rates of silicon nitride and polysilicon, while silicon dioxide first wafers etch faster for the polysilicon strip process, and slower for the silicon nitride strip process. We have modeled the first-wafer effect for photoresist ashing. We found an inverse relationship between the percentage change in the time to clear the photoresist from the wafer and the time delay between processing sequential wafers. We have included this first-wafer effect in the on-line statistical process control strategy for the photoresist asher in our laboratory. Examination of this first-wafer effect suggests that it may be caused by the generation of species in the discharge in the first few seconds of operation that alter the reactivity of the chamber walls. While these species are quick to adsorb on the walls, they only desorb slowly. Pumping on the chamber in the absence of a microwave discharge returns the chamber to its original state.
Molybdenum silicide based attenuated phase-shift masks
Authors: Jonckheere Rik , Ronse Kurt , Popa Ovidiu , Van den hove Luc
Published: July 2002

The use of phase shifting masks (PSMs) causes revolutionary improvements of the performance of existing wafer steppers. Nowadays the attenuated PSM, also referred to as halftone, is found to be most attractive, as the technique is self-aligned. Moreover, the number of additional process steps in mask fabrication is limited to a dry etching step. Typically, both focus and exposure latitudes for contact holes of 0.35 μm are improved by a factor of 1.5–2 over a conventional mask. As linewidths on mask shrink towards 1 μm (a critical dimension of 0.25 μm, at 4× magnification) and below, the required critical dimension control becomes much tighter. It becomes more and more clear that the accuracy cannot be met anymore with wet etching of chrome. Sputtered molybdenum silicide (MoSi) is easier to dry etch than chrome and is therefore an important candidate as alternative opaque material on masks. The use of MoSi for attenuated PSMs is discussed. This approach has the advantage over the use of an SOG/Cr combination in that only a single dry etch process is required to etch the stack, since both materials can be etched using fluorine based plasmas. This is in contrast to chrome/shifter attenuated masks where chrome and shifter are etched separately, either wet/dry or both dry but in different chemistries. Recently published work describes the application of a single layer of a MoSiO or MoSiON with the required opacity and phase shift, by careful tuning of the refractive index and extinction coefficient. A comparison to these so-called embedded PSMs is included. For the latter an important disadvantage is the lack of conductivity of the layer, such that an extra (sacrificial) layer is required for charge dissipation during electron-beam exposure. An intermediate solution, referred to as partially embedded, is suggested as a compromise.
Experimental investigation of stochastic space charge effects on pattern resolution in ion projection lithography systems
Authors: Hammel E. , Chalupka A. , Fegerl J. , Fischer R. , Lammer G. , Löschner H. , Malek L. , Nowak R. , Stengl G. , Vonach H. , Wolf P. , Brünger W. H. , Buchmann L.-M. , Torkler M. , Cekan E. , Fallmann W. , Paschke F. , Stangl G. , Thalinger F. , Berry I. L. , Harriott L. R. , Finkelstein W. , Hill R. W.
Published: July 2002

Coulomb interactions in charged particle beams are known to blur beam profiles as the total current is increased. While this has been studied in single ion beam columns, similar studies have not been published, so far, for masked ion beam projection systems. Experiments were performed using highly transparent stencil grid masks of 40 mm×40 mm area with resolution test patterns in central and peripheral positions. Such grid test masks have been inserted into the ion projection lithography machine IPLM-02 and into the ‘‘Alpha ion projector’’ operated at 5× ion–optical reduction (Alpha-5×). A standard duoplasmatron ion source was used for both ion projectors. Operating the IPLM-02 at 8.7× demagnification with He+ ions of 73 keV ion energy at the wafer plane (about 50 keV at the crossover), no significant degradation in resolution was found changing the ion beam current through the column from 300 nA to 2 μA. Using the Alpha-5×, the total current through the column was changed either by varying the ion source emission or by blanking parts of the mask, using appropriate apertures. The special design of the Alpha ion projector with an ion energy of 5–7 keV at the crossover region between the imaging lenses is a sort of worst case scenario for space charge effects. Thus, the influence of stochastic space charge effects on resolution could be clearly identified. Using helium ions with 7 keV at the crossover the exposure latitude (change of linewidth in nm with 10% change of exposure dose) increased by 60 nm when changing the current through the column from 3 to 120 nA. Based on this experimental result with the Alpha ion projector and on well-known scaling laws, it can be stated that a newly designed ion projector (ALG-1000) with 200 keV ion energy at the crossover will allow sub-0.15-μm resolution for total ion beam currents through the column of 3 μA, as needed for future high volume production of dense patterns within ≥20 mm×20 mm exposure fields. Furthermore, improved designs of ion optical columns will allow a reduction of system length, thus reducing the influence of stochastic space charge effects. Consequently, ion projection lithography can be extended to the high volume fabrication of sub-0.10-μm feature patterns in large exposure fields.
Nanometer-scale dimensional metrology for advanced lithography
Authors: Marchman H. M. , Griffith J. E. , Guo J. Z. Y. , Frackoviak J. , Celler G. K.
Published: July 2002

Increased performance of lithographic process techniques has been the key enabler for the continued reduction of minimum device feature sizes down to 0.25 μm and beyond. However, this increase in performance has been accompanied by the added fabrication complexity of the various types of lithographic reticles. Theoretical simulations have revealed that metrological requirements for the fabrication of devices having subhalf micrometer dimensions are indeed on the nanometer scale. A comparison of available metrology tools is presented as well as improvements to current techniques. Direct correlations between top-down critical dimension cleanroom scanning electron microscopy (SEM), cross-sectional analytical SEM, and various atomic force microscopy (AFM) techniques (scanning techniques and probe shapes) are described as well as the use of AFM to nondestructively characterize features on x-ray membrane masks is described. Finally, the use of novel optical fiber probes to image subresolution quartz features on optical phase-shifting masks is presented.
Microfabrication of arrays of scanning electron microscopes
Authors: Feinerman A. D. , Crewe D. A. , Crewe A. V.
Published: July 2002

Arrays of miniature scanning electron microscopes (MSEMs) can conceivably solve the low throughput rates traditionally associated with direct write lithography. An inexpensive and accurate method for fabricating arrays of electron beam columns has been proposed: horizontal surface mounted electrode sectioning (slicing). This method combines the precision of semiconductor processing and fiber optic technology to fabricate macroscopic structures consisting of charged particle sources, deflecting and focusing electrodes, and detectors. Slicing can be used to miniaturize columns operating at 10–50 kV. Voltages in this range are required to produce characteristic x rays for elemental analysis. Slicing should allow the SEM to be considerably reduced in size while preserving performance and also can be adapted to produce arrays of MSEMs. The performance of the proposed sliced columns is discussed and initial results indicate that a 15 kV sliced MSEM 8.5 mm long will have 2.2 nm resolution.
Emission characteristics of ultrasharp cold field emitters
Authors: Yu Ming L. , Hussey Brian W. , Kim Ho-Seob , Chang T. H. Philip
Published: July 2002

We have examined the field emission characteristics of oxygen-processed and thermal-field buildup W 〈111〉 tips. Good emission angular confinement was found to correlate with the global geometry of the tip. Emission stability was related to the atomic arrangement at the apex. This phenomenon is described by the different driving forces for atomic surface diffusion. We also showed that tip apexes can be engineered to form flat (111) facets at the tip end for improved stability.
Measurement and manipulation of van der Waals forces in atomic-force microscopy
Authors: Hutter Jeffrey L. , Bechhoefer John
Published: July 2002

An understanding of the interaction between tip and sample in atomic-force microscopy is needed to interpret atomic-force-microscope (AFM) images. In contact mode, the strength of the van der Waals (vdW) force sets image resolution; in noncontact mode, local gradients in the vdW force are imaged. By immersing tip and sample in an appropriate fluid, we can decrease the vdW forces and even change their sign. Selecting a fluid that leads to a small repulsive vdW force can greatly improve image resolution and eliminates problems caused by the well-known tip-snapping instability. To measure the vdW interactions produced by different fluids, we have developed ways to calibrate the spring constant and sharpness of AFM tips and to measure accurately the Hamaker constant of vdW interactions. These techniques show that the AFM can be used for local force measurements with an accuracy approaching that of surface-force apparatuses. As an example, we have observed the crossover from nonretarded to retarded vdW forces between a silicon nitride tip and a mica sample in air.
Microfabrication by ion milling: The lathe technique
Authors: Vasile Michael J. , Biddick Christopher , Schwalm Stephanie A.
Published: July 2002

Several novel and unusual microstructures were made by focused ion beam milling. These microstructures include needles, hooks, forks, and similar shapes resulting from 360° access afforded to the ion beam by a rotation mounting device. The lengths of the microstructures are in the 10 μm range, and the thicknesses all in the 1–2 μm range. Similar procedures were used to make prototype stylus geometries for scanning probe microscopy applications. Resolution limits to the fabrication process come mainly from the grain structure of the material being sputtered. The ion beam is 0.3 μm in diameter, and 0.08 μm pixel resolution for ion beam location was used to generate the objects. Start-to-finish fabrication time for most of the objects made was ∼2 h without any effort to streamline the process.
Generation of degradation defects, stacking faults, and misfit dislocations in ZnSe-based films grown on GaAs
Authors: Kuo L. H. , Salamanca-Riba L. , Wu B. J. , Haugen G. M. , DePuydt J. M. , Hofler G. , Cheng H.
Published: July 2002

Transmission electron microscopy is used to investigate the structure of the crystalline defects in degraded and undegraded ZnSe-based films/GaAs heterostructures. In degraded areas, dark line defects (DLDs) originate from the preexisting or grown-in defects (i.e., stacking faults and misfit dislocations) during device operation and make the laser diode fail. From our observation, the nucleation of DLDs is based on the initial emission of a mobile faulted defect from the preexisting grown-in defects. Along the trace of the faulted defects, [100] dark line defects form. We also investigated the origins and mechanisms for the generation of stacking faults and misfit dislocations. The generation of stacking faults is strongly related to the doping concentration, substrate surface stoichiometry, and growth mode of the films. The vacancy contained Ga–Se interfacial layers are thought to be sources for the generation of Frank-type stacking faults. In addition, Shockley partial dislocations form due to island coalescence of the ZnSxSe1−x/ZnSe epilayers on GaAs substrates. In situ electron beam heating studies were carried out to realize the mechanism of strain relaxation and formation of 60°-type misfit dislocations in the II–VI/GaAs interface from the dissociation of Frank-type partial dislocations. The generation of screw-type interfacial dislocations was also observed. This takes place by gliding the threading segments of the Shockley partial dislocations toward the ZnSxSe1−x/GaAs interface on {111}-type planes.
New type of metal ion source: Surface diffusion Li+ ion source
Authors: Medvedev V. K. , Suchorski Yu. , Block J. H.
Published: July 2002

A surface diffusion metal ion source, a new type of metal ion source, is explored. In this device a field desorption process is used to achieve an almost monoenergetic continuous flux of Li+ ions from a [111]-oriented W field emitter. Earlier difficulties with the continuous supply of adatoms, required to produce measurable desorption rates, were overcome by making use of solid state surface diffusion from the Li multilayer reservoir at the shank of the field emitter. The high density of the ion beam (an ion current of 10−12 A was achieved from a W trimer), the extremely narrow energy distribution (full width at half-maximum of 0.25 eV) and the stable geometric form of the emitter itself during the operation are advantages of the new ion source which may be important in different areas of nanotechnology.
Extremely low specific contact resistivities for p-type GaSb, grown by molecular beam epitaxy
Authors: Tadayon Bijan , Kyono Carl S. , Fatemi Mohammad , Tadayon Saied , Mittereder Jeffrey A.
Published: July 2002

We have investigated different metal contacts (Cr/Au, Ti/Pt/Au, and Au) on p-type GaSb, grown by the molecular beam epitaxy. For Au contacts, specific contact resistivities in the range of 1.4×10−8–7.8×10−8 Ω cm2 have been obtained. These are the lowest values ever reported for p-type GaSb. A simple procedure for surface preparation is also reported.
Resolution analysis in electron-beam cell projection lithography system
Authors: Yamashita Hiroshi , Tokunaga Kenichi , Kojima Yoshikatu , Nozue Hiroshi , Nomura Eiichi
Published: July 2002

We have experimentally analyzed the resolution in electron-beam cell projection lithography systems. The results indicated that the Coulomb interaction effect and the proximity effect are critical issues for resolution because of the larger beam current compared with the conventional variable-shaped beam. We achieved a practical resolution of 0.18 μm, which is enough for 1 Gbit dynamic random access memory (DRAM) fabrication, by adjusting the beam current. We have also found that there is some interaction between the individual line beams (streams). Also, the beam profile degradation in cell projection lithography systems depends not only on the beam current but also on the distance between the streams. Therefore, in order to obtain higher resolution, these effects must be considered more carefully than in the case of conventional variable-shaped beam lithography systems. A resolution of less than 0.15 μm, which is required for Gbit level DRAM fabrication, can then be available in cell projection lithography systems.
Comment on ‘‘Domain structure and polarization reversal in ferroelectrics studied by atomic force microscopy’’ [J. Vac. Sci. Technol. B 13, 1095 (1995)]
Authors: Takata Keiji
Published: July 2002

Ferroelectric domain observation by static piezoelectric deformation has been described by Gruverman et al. If the observed protrusions are caused by piezoelectric deformation induced by depolarization fields of domains, as suggested in the article, serious questions arise. The author believes that the protrusions are not ferroelectric domains. In imaging static deformation, it is difficult to distinguish corrugation due to piezoelectric deformation from those of the other possible causes.
The electrostatic moving objective lens and optimized deflection systems for microcolumns
Authors: Thomson M. G. R.
Published: July 2002

The designs of the deflector and the final focusing lens in microcolumns are constrained by the extremely small physical size, and by the low energy of the beam. Because the overall column size and working distance are much smaller, the diameter of the deflection field that can be used without excessive increase in the probe diameter is also smaller. This field size can be improved by incorporating deflectors within the focusing lens. The theory of the ‘‘moving objective lens’’ can be extended to apply to electrostatic lenses and deflectors, and this can lead to greatly increased deflection field sizes when a vertical landing beam is required. The implementation of the moving objective lens requires a pre-deflector, as well as an electrostatic deflecting field proportional to the second derivative of the axial potential inside the focusing lens. The curvature of field and third order astigmatism must also be dynamically corrected by additional fields, and these can be provided outside the lens. The in-lens deflecting fields can be obtained by segmenting the lens electrodes so that they can provide both focusing and deflecting fields, and adding shields to shape the fields correctly. In the absence of dynamic correction, the relative magnitudes of the deflecting fields can be optimized to maximize the deflection field size both with and without vertical landing. In the cases that have been analyzed theoretically, the addition of in-lens deflectors offers increased field size in comparison with optimized prelens double deflectors. The importance of increasing the field size will determine the degree of complexity of the configuration that must be used.
Focused ion beam biased repair of conventional and phase shift masks
Authors: Cui Zheng , Prewett Philip D. , Watson John G.
Published: July 2002

A novel technique, focused ion beam biased sputtering, is used to repair opaque defects in both conventional binary intensity masks and phase shift masks without leaving post-repair residual defects caused by gallium ion staining. The biased repair involves sputter removal of a defect to an area larger than its original size. The reduction of light transmission due to gallium stain is then effectively compensated by the enlarged repair. Results are presented on the repair of both conventional and attenuated phase shift masks using the biased method in comparison with conventional (no bias) repair. Optimum bias is determined by computer simulation of optical imaging and resist development. Unlike other anti-staining techniques which require additional equipment and process steps, the biased repair method involves only a change of sputtering strategy and can be implemented in any existing focused ion beam mask repair tools.
Dry etching damage in III–V semiconductors
Authors: Murad S. , Rahman M. , Johnson N. , Thoms S. , Beaumont S. P. , Wilkinson C. D. W.
Published: July 2002

Dry etching using ions can cause damage to the underlying semiconductor. This paper discusses damage in III–V semiconductors and presents examples of etching conditions under which it can be effectively eliminated. A distinction between surface and sidewall damage is made and methods of measuring both parameters are reviewed. It is noted that the noble gases cause relatively deep damage, while under the correct circumstances, etchants that have a marked chemical effect can cause much less damage. The present state of understanding of the mechanisms for the damage is discussed.
Metal stack etching using a helical resonator plasma
Authors: Labelle C. B. , Maynard H. L. , Lee J. T. C.
Published: July 2002

A low-pressure etching process for advanced aluminum metallization stacks was developed using a high-density helical resonator plasma source (Prototech model ESRF 600) mounted on a Lucas Labs cluster tool. The metallization stacks consisted of a 300 Å TiN antireflection layer on 6000 Å of Al (1% Cu) with a 1000 Å TiN diffusion barrier and a 100 Å Ti film to enhance adhesion to the underlying SiO2. The features widths were as small as 0.45 μm. The films were etched using gas mixtures of Cl2/BCl3. The BCl3 proved to be an important additive to reduce notching of the Al film at the interface between the Al and the top layer of TiN. Best feature profiles were obtained using 80–90 sccm Cl2 and 10–20 sccm BCl3 at the following reactor conditions: 2.0 mTorr, wafer platen temperature T=0 °C, 100 W rf bias power, and 1500 W source power. More anisotropic profiles are obtained by either decreasing the wafer platen temperature or increasing the rf-bias power. The photoresist is also stripped in the same process chamber using an oxygen plasma at 5 mTorr, 50 W rf-bias power, and 1500 W source power at a chuck temperature of 25 °C. Extensive application of real-time process diagnostics, including optical emission spectroscopy and full wafer interferometry, aided process development by identifying end points, etching rates, and etching rate uniformities.
Atomic antimony for molecular beam epitaxy of high quality III–V semiconductor alloys
Authors: Brewer P. D. , Chow D. H. , Miles R. H.
Published: July 2002

The product distribution of an antimony cracking effusion cell has been characterized using a time-of-flight mass spectrometer employing resonance-enhanced laser ionization. Source operating conditions have been identified under which predominately tetramers, dimers, and monomers of antimony are produced. Molecular beam epitaxy experiments employing the characterized antimony source for the growth of antimonide/arsenide superlattices and GaSb epilayers show that significant improvements in material quality can be obtained using monomeric antimony over that using molecular antimony species. A comparison of the surface chemistry of atomic and diatomic antimony species in the growth of several Sb-containing semiconductors will be presented.
Emission characteristics of metal–insulator–metal tunnel cathodes
Authors: Adachi Hiroshi
Published: July 2002

The tunnel cathode is one type of cold cathode. A very thin insulating film is sandwiched between two metal electrodes. The upper electrode is so thin that the electrons that tunnel through the insulating film can penetrate through it and emit to the vacuum. Emission characteristics are experimentally examined, especially the energy distribution of the emitted electrons and the emission uniformity over the active area.
Self-assembled InSb and GaSb quantum dots on GaAs(001)
Authors: Bennett B. R. , Thibado P. M. , Twigg M. E. , Glaser E. R. , Magno R. , Shanabrook B. V. , Whitman L. J.
Published: July 2002

Quantum dots of InSb and GaSb were grown on GaAs(001) by molecular-beam epitaxy. In situ scanning tunneling microscopy measurements taken after 1–2 monolayers of InSb or GaSb growth reveal the surface is a network of anisotropic ribbon-like platelets. These platelets are a precursor to quantum dot growth. Transmission electron microscopy measurements indicate that the quantum dots are coherently strained. Quantum dots of InSb and GaSb capped by GaAs exhibit strong luminescence near 1.1 eV.
Influence of external factors on electron field emission from thin-film nanofilament carbon structures
Authors: Chernozatonskii L. A. , Kosakovskaya Z. Ya. , Gulyaev Yu. V. , Sinitsyn N. I. , Torgashov G. V. , Zakharchenko Yu. F.
Published: July 2002

The influence of temperature and residual gas pressure on the field emission of thin-film nanotube carbon structures has been studied. These structures are shown to exhibit low work functions. They are promising for fabrication of effective low-voltage field emitters and low-temperature thermal emitters.
Automated calibration of the sample image using crystalline lattice for scale reference in scanning tunneling microscopy
Authors: Kawakatsu Hideki , Kougami Hiroshi
Published: July 2002

This article describes the configuration and application of an image processing software developed for extracting periodic atomic features from scanning tunneling microscopy (STM) images. This was done with a view to calibrating the lateral and/or vertical scale of images acquired by a STM with two tunneling units, where a crystal can be used as the scale reference with one of the tunneling units. The image processing software was applied to consecutively acquired images of graphite with a size of 150×5 nm. The number of lattices automatically counted in a line scan of 150 nm, scanned in 400 ms, showed a matching of 99.95% from one image to the other. On the other hand, the matching in the feed direction, where image width was only 5 nm, but took 240 s, was 95%. As an example of application of the developed software, nonlinear movement of piezoscanners were readily monitored in the 100 nm order.