bluuebunny/crossref_metadata_2025 huggingface dataset:
Phonons on reconstructed silicon surfaces
Authors: Mele E. J. , Allan D. C. , Alerhand O. L. , DiVincenzo D. P.
Published: July 2002

A tight-binding theory for structural energies is developed and applied to study the surface reconstructions and the vibrational excitations of the Si(100) and the Si(111) surface. Test calculations for the structural and vibrational properties of FC-2 Si, BC-8 Si, and Si2 are discussed. Phonons are calculated and discussed for the asymmetric dimer model of the Si(100) 2×1 surface and for a hydrogenated model of Si(100) 2×1 with a saturation mononhydride surface layer. Preliminary results for phonons of the π-bonded chain model of Si(111) 2×1 are presented
A computer-aided evaluation system for sectored-type multipole electrostatic deflectors
Authors: Soma T. , Idesawa M. , Goto E. , Sasaki T.
Published: July 2002

An interactive computer aided design and evaluation system for sectored-type electrostatic deflectors has been developed; the geometrical dimensions of a deflector are measured and a computer model is constructed; the wide area deflection properties can be estimated from the computer model and displayed graphically; the evaluation can be made interactively with the graphical outputs. Given focusing and deflection field, the pattern distortion of a shaped beam caused by higher order θ components of the deflection field can also be estimated by the system. Furthermore, an effective modification scheme to improve the deflection properties of a deflector can be found by changing the shape of electrode in the computer model.
Recent developments in the strained layer epitaxy of germanium–silicon alloys
Authors: Bean John C.
Published: July 2002

This paper provides a brief review of recent work on strained layer GexSi1−x including modeling of critical thicknesses for single layers and superlattices; calculations and measurements on strain induced alteration of alloy band gap and heterostructure band alignment; and application to modulation-doped field effect transistors (MODFET) and 1.3 μm photodetector devices.
Kinetics study of initial stage band bending at metal GaAs(110) interfaces
Authors: Cao Renyu , Miyano Ken , Kendelewicz Tom , Chin Ken K. , Lindau Ingolf , Spicer William E.
Published: July 2002

A systematic kinetics study of the initial stage band bending of metal/GaAs(110) has been done. At low temperature, independent of metals, enhanced band bending for p-GaAs and attenuated band bending for n-GaAs as a function of metal coverage has been observed. For p-type GaAs the band bending increases very rapidly to a value larger than that for any coverage at room temperature and then returns to the room temperature position at high coverages. It is found that this excess band bending strongly depends on the work functions of the metal deposited on GaAs. In gives 0.4 eV, Al 0.3 eV, Ag 0.2 eV, and Au only shows small excess band bending. Temperature dependence of GaAs initial stage band bending will also be discussed in this paper. The results strongly suggest that there exists another mechanism which appears to be dominant in the initial stage band bending at low temperature where the defect formation is negligible. The transition from this mechanism to the defect mechanism could be observed by increasing either system temperature or metal coverage, or more generally, disturbance to semiconductor surfaces.
Ultraviolet-assisted growth of GaAs
Authors: Balk P. , Fischer M. , Grundmann D. , Lückerath R. , Lüth H. , Richter W.
Published: July 2002

This paper presents results of a comparative study of the UV-assisted epitaxial growth of GaAs from metal-organic Ga compounds and AsH3 at 0.1 bar total pressure using a low-pressure-Hg lamp (λ=254 nm) or an excimer laser (λ=193 or 351 nm). Since effective stimulation only takes place for reaction-limited growth conditions these were defined first. It is shown that at 0.1 bar only the Ga compound, no AsH3, is involved in the rate-limiting step. The rate increase upon illumination becomes larger with increasing stability of the metal-organic compound, i.e., in the order tri-isobutyl to triethyl to trimethyl gallium. Experiments with UV of 351 nm, a wavelength at which radiation is not absorbed by the reactants, indicate that in this case growth enhancement is absent. Thus, heating effects do not play a significant role in the stimulation process. The other wavelengths are both absorbed by the metal-organic compounds and consequently their use leads to larger growth rates. The attenuation of the incident radiation by absorption in the bulk of the gas phase determines the photon density reaching the substrate surface. Since the absorption depends on the wavelength, the photon energy and wavelength are important factors governing the rate of growth. Although the present data show that the photostimulation takes place very close to the surface, it is not possible to determine whether the stimulation process takes place at the surface, in the gas phase near the surface or in both locations.
Oxygen plasma etching for resist stripping and multilayer lithography
Authors: Hartney M. A. , Hess D. W. , Soane D. S.
Published: July 2002

Oxygen-based plasmas commonly used in resist stripping and multilayer resist patterning are contrasted to highlight the differences involved in these applications. Mechanisms for polymer etching are reviewed, with particular emphasis on silicon-containing resists proposed for bilayer lithography. While silicon-containing materials offer a simpler process than trilayer schemes for improving lithographic resolution, considerable differences in etch behavior among these materials have been observed. Further characterization and fundamental understanding are required before widespread acceptance of silicon-containing resists is achieved.
Growth of epitaxial rare-earth arsenide/(100)GaAs and GaAs/rare-earth arsenide/(100)GaAs structures
Authors: Palmstro/m C. J. , Garrison K. C. , Mounier S. , Sands T. , Schwartz C. L. , Tabatabaie N. , Allen S. J. , Gilchrist H. L. , Miceli P. F.
Published: July 2002

Successful growth of (100)ErAs and (100)LuAs single crystal films on (100)GaAs has been demonstrated. Reflection high-energy electron diffraction, low-energy electron diffraction (LEED), cross-sectional transmission electron microscopy, x-ray diffraction, and Rutherford backscattering with channeling indicate single crystal growth. LEED patterns from the ErAs show a (1×1) structure. The overgrowth of ultrathin GaAs layers on ErAs and LuAs is difficult due to the poor GaAs wetting of the rare-earth arsenide surface, which results in three-dimensional growth. ErAs films thicker than 25 Å are semimetallic with a positive temperature coefficient of resistivity. The resistivity values are in the tens of μΩ cm range. Magnetotransport measurements at low temperature determined the electron and hole concentrations to be ∼1.8×1020 and ∼3.3×1020 cm−3 with mobilities of ∼1100 and ∼540 cm2 /V s, respectively. Electrically continuous buried ErAs films down to ∼7 Å have been made.
A study of electron beam metrology using computer simulation
Authors: Takeuchi S. , Nakamura H. , Watakabe Y. , Mimura R. , Aihara R. , Thompson W. B.
Published: July 2002

For studying the technology of the critical dimension measurement using an electron beam (EB), a computer simulation based on the Monte Carlo and the surface charge methods is carried out, and a wave form of backscattered electrons (BE’s), which hardly suffer from the charging phenomenon, is precisely analyzed using this simulation. First, line widths obtained individually by threshold, maximum slope, and linear approximation methods are examined about various incident-EB conditions such as an accelerating voltage and a beam diameter. The dependencies of pattern structures, such as dimension, side-wall angle, and materials of the patterns, on measured line width are evaluated next. As a result of these calculations, it is found that the variation of the incident-EB conditions doesn’t affect practically the results of the line-width measurement in BE-detection systems, while secondary-electron signals are easily deformed by the charging phenomenon. Although the measured width much depends on the pattern structure, the linear approximation method is comparatively suitable for the purpose of obtaining the width of bottom edges in BE-detection systems.
Electron beam blanker optics
Authors: Gesley Mark , Condran Pat
Published: July 2002

Closed form analytic solutions for electrons interacting with a double-deflection blanker have been developed and implemented as a c-language program. The double-deflection blanker has a transmission line connecting the upper and lower pairs of plates, which can reduce beam positional jitter when the signal propagation time is correctly set. Several proposed design rules for setting the delay time in terms of blanker geometry are evaluated, but these are shown to be insufficient to determine the optimum. A damped cosine function represents the voltage produced by the blanking circuit and models ringing, overshoot, and slew rate. The onset of current transmission is related to blanker voltage and aperture size. The fringe field effect can be accounted for by combining the analysis with an experimental measurement of blanker sensitivity to determine the effective blanker plate length. The design is able to support 160 MHz blanking and 7.5 V/ns slew rate in a 10-kV electron beam lithography system and maintain 0.01-μm positional accuracy over the entire exposure.
The origin of stress in sputter-deposited tungsten films for x-ray masks
Authors: Itoh Masamitsu , Hori Masaru , Nadahara Soichi
Published: July 2002

The mechanism for the cause of stress in a sputter-deposited tungsten (W) film has been clarified. The tensile stress of the film was calculated using the interatomic forces acting on the grain boundary. The average distance of the grain boundary gaps was determined from the measured film density assuming the film had homogeneous size rectangular grains. The calculated and measured stress values were in good agreement in the high working gas pressure region. The difference between these values in the low working gas pressure region has been able to be explained by the compressive stress due to the peening effect of Ar. The low stress in the high pressure region was obtained by large opened grain boundaries which produced low film density. A low film density causes a low x-ray stopping power. The film deposited in the low pressure region is suitable as an x-ray absorber because of its high film density.
Ballistic electron emission microscopy studies of the NiSi2/Si(111) interface
Authors: Fernandez A. , Hallen H. D. , Huang T. , Buhrman R. A. , Silcox J.
Published: July 2002

We have performed ballistic electron emission microscopy measurements on the NiSi2/Si(111) system under UHV conditions. Schottky barrier heights have been measured for types A and B interfaces and are found to be in agreement with other techniques. Through correlations between structural defects in the silicide and local increases in collector currents, we find that elastic scattering in the film can increase ballistic electron transmission rates across the interface.
Initial stage of Au adsorption onto a Si(111) surface studied by scanning tunneling microscopy
Authors: Hasegawa T. , Takata K. , Hosaka S. , Hosoki S.
Published: July 2002

The initial stage of Au adsorption onto a Si(111) surface (<0.2 ML) is studied by scanning tunneling microscopy (STM). Au is deposited at room temperature, and then the sample is annealed at 700 °C. At the very early stage of Au adsorption, a Au-adsorbed 5× structure is found not to break a 7×7 structure. By increasing the amount of adsorbed Au, the Si substrate itself shows a 5× structure. Rows of the Au-adsorbed 5× structure are observed to have grown from the lower side of steps.
Valence band offset in ZnS layers on Si(111) grown by molecular beam epitaxy
Authors: Maierhofer Ch. , Kulkarni S. , Alonso M. , Reich T. , Horn K.
Published: July 2002

The heterojunction between silicon(111) and zinc sulfide was studied using Auger electron spectroscopy, photoelectron spectroscopy, and low-energy electron diffraction. Zinc sulfide layers were deposited onto cleaved Si(111) surfaces as well as Si(111)-(7×7) wafers by molecular beam epitaxy. The overlayers exhibited fair crystalline quality, and the characteristic valence-band spectrum of ZnS. The valence-band offset between the two semiconductors was determined from the core and valence-band spectra (ΔEv=−0.7 eV) and found to be much smaller than predicted. We attribute this disagreement, and the larger than usual scatter in our data, to the influence of interface dipoles in this polar interface, the density of which may partly be influenced by a varying amount of interface reaction.
Submicron Si trench profiling with an electron-beam fabricated atomic force microscope tip
Authors: Lee Kam L. , Abraham David W. , Secord F. , Landstein L.
Published: July 2002

The atomic force microscope (AFM) has the potential for profiling on a nanometer scale. However, for the AFM to be useful as a reliable and accurate metrology tool, the atomic force sensor used (i.e., cantilever and sensor tip) should be highly reproducible in the fabrication process and the tip shape used should be known with high accuracy. Moreover, for profiling and critical dimension measurement of device trenches with submicron openings and trench depth of 1 μm or more, nanometer-scale tip shapes with high aspect ratio will be required. In order to meet the above requirement, a novel high-resolution direct electron-beam deposition process has been developed in which a sharp tip is grown onto an existing Si cantilever structure. In the example to be discussed, sharp tips have been grown directly on the integrated tip of a micromachined Si cantilever by decomposition of a dimethyl-gold organometallic complex. The direct e-beam deposition process provides a unique capability for the controllable fabrication of high aspect ratio, nanometer-scale tip structures. Typical dimensions of the AFM tips achieved are 0.1 μm in column diameter, 1–4 μm high, and 15 nm in tip radius. Recent feasibility experiments of using these e-beam tips in the laser force microscope have demonstrated for the first time that this nano-scale tip can be used for mapping 1-μm-deep Si trenches. Submicron trenches with openings as small as 0.36 μm have been successfully profiled. In this paper, various issues on tip fabrication, deep trench profiling and comparision of AFM and corresponding scanning electron microscopy measurements will be discussed.
Choice of system parameters for projection electron-beam lithography: Accelerating voltage and demagnification factor
Authors: Liddle J. A. , Berger S. D.
Published: July 2002

A lithography system that uses Scattering with Angular Limitation Projection Electron Lithography (SCALPEL) allows us to vary the electron-beam accelerating voltage in a way that was not possible with systems that use absorbing stencil masks. We have discovered that the choice of operating parameters, accelerating voltage, and demagnification factor, as well as many of the subsystem designs, are dominated by the need to control thermal effects within the system. We have derived a model which allows us to find operating parameters that minimize the thermal contribution to the pattern overlay error. This information, when combined with other subsystem constraints, enables us to define a relatively narrow range of possible working conditions. The model is general to high-throughput electron beam lithography systems; we have applied the model to one example of a SCALPEL system.
Low-voltage electron-optical system for the high-speed inspection of integrated circuits
Authors: Meisburger W. D. , Brodie A. D. , Desai A. A.
Published: July 2002

Low-voltage scanning electron microscopes enjoy many advantages over light microscopes for both dimensional measurements and the analysis of small features. Their combination of high-resolution and large depth-of-focus has made them a standard instrument in the semiconductor industry. However, until now, they have been many orders of magnitude too slow to be used for automated wafer inspection. In this article, the authors will determine the optical requirements of high-speed inspection at low voltage and show how this leads to a novel optical system design. This optical system shares similarities with a 20 keV column designed for an x-ray mask inspection system [W. D. Meisburger, A. Desai, and A. D. Brodie, J. Vac. Sci. Technol. B 9, 3010 (1991)]. However, the objective lens and electron detection system are unique. The objective lens combines superimposed electric and magnetic fields to decelerate the primary beam from 20 keV to ∼800 eV, and to effectively collimate and reaccelerate the resulting secondary electrons. Auxiliary electrodes are used to control the electric field on the semiconductor’s surface. A Wien filter is used to separate the secondary electrons from the primary beam. A second Wien filter is used to cancel the transverse chromatic aberration of the first filter. This optical system is capable of producing current densities of 1000 A/cm2 at 800 eV into spots as small as 50 nm. Images are acquired at a rate of 100 million pixels/second. Both theoretical and experimental performance results for this system will be presented.
Reflection high-energy electron diffraction study of Sb incorporation during molecular-beam epitaxy growth of GaSb and AlSb
Authors: Waterman James R. , Shanabrook Benjamin V. , Wagner Robert J.
Published: July 2002

The incorporation of antimony into GaSb and AlSb during molecular-beam epitaxy growth has been investigated using reflection high-energy electron diffraction (RHEED). RHEED intensity oscillations limited by the incorporation rate of Sb were observed. The RHEED oscillation measurements together with beam equivalent pressure measurements demonstrate that four Sb atoms are incorporated for each Sb4 molecule incident on the surfaces of GaSb and AlSb for substrate temperatures ranging from 350 to 530 °C and 420 to 610 °C, respectively. A new Ga stabilized (4×3) surface reconstruction was observed for (100) GaSb.
Strain relaxation and interdiffusion in Si/Si1−xGex strained layer superlattices
Authors: Goorsky M. S. , Kesan V. P. , Ott J. A. , Angilello J.
Published: July 2002

We have investigated the structural properties of Si/Si1−xGex multilayers using x-ray diffraction, x-ray reflection, and cross-sectional transmission electron microscopy. The structures consisted of 14–28 periods of thin (40–70 Å) Si1−xGex layers (0.4≤x≤0.7) with 180–280 Å Si spacers with 1 μm Si cap layers. The sample quality was engineered to range from defect-free to highly defective in order to assess the relative merits of the different analytical techniques. Electron microscopy provides information on layer thicknesses and the presence of extended defects, while the nondestructive x-ray techniques determine composition (χGe±0.005), layer thickness (±1 Å), heterointerface mixing (2.5 Å) roughness, <10 Å grade), and strain relaxation (∼2%) in these structures. We show that multiple characterization techniques are required to study structural issues in Si/Si1−xGex strained layer superlattices.
Embossed grating lead chalcogenide distributed-feedback lasers
Authors: Schlereth K.-H. , Böttner H.
Published: July 2002

The successful preparation of double-heterostructure (DH) distributed-feedback (DFB) PbEuSe lasers using an embossing technique for the DFB sub-micrometer grating is reported here for the first time. The submicrometer grating was performed in (111) oriented silicon wafers by holographic exposure and argon ion milling. Using a hydrostatic press this grating was embossed into a lead chalcogenide wafer, covered by a DH structure grown by molecular beam epitaxy. Lasers made from wafers with grating periodicities of 0.678 and 0.755 μm show DFB characteristics at the corresponding emission wavenumbers around 1420 and 1590 cm−1.
Fabrication of submicron conducting and chemically functionalized structures from poly(3-octylthiophene) by an electron beam
Authors: Cai Sui Xiong , Kanskar Manoj , Nabity J. C. , Keana John F. W. , Wybourne M. N.
Published: July 2002

We present a novel method of using an electron beam to both functionalize and cross-link poly(3-octylthiophene) (P3OT) in a single step to produce submicron scale polymer structures carrying functionalized groups. We have shown P3OT to be a negative electron-beam resist with a sensitivity of 15–30 μC cm−2. The electrical conductivity of doped P3OT wire structures was measured at room temperature and was found to be in the range 4.0–5.9 Ω−1 cm−1. Electron-beam exposure of P3OT films containing 7 wt % of N-hydroxysuccinimide (NHS) functionalized perfluorophenyl azide 2 resulted in the incorporation of the NHS functional groups in the polymer, as well as cross-linking. The functionalized submicron structures were found to be weakly fluorescent under fluorescein excitation (450–490 nm), but after treatment with a solution of 5-(aminoacetamido)fluorescein in ethanol the structures became strongly fluorescent.
Modeling of positive-tone silylation processes for 193-nm lithography
Authors: Hartney Mark A.
Published: July 2002

A modeling approach is presented for positive-tone silylation processes. By reducing the effect of crosslinking on diffusion of the silylating agent to a characteristic curve, the silylation profiles can be determined from aerial images. Comparisons are made to experimental profiles obtained using a scanning electron microscope and selective staining methods. Deviations from the model are observed as a function of both feature size and feature type. These discrepancies are consistent with a swelling limitation imposed by the cross-linking. By combining an anisotropic etching model with the silylation profiles, the final linewidths can be predicted as a function of dose, selectivity, and overetch.
Contributions of scanning probe microscopy and spectroscopy to the investigation and fabrication of nanometer-scale structures*
Authors: Wiesendanger R.
Published: July 2002

Scanning tunneling microscopy and related local probe methods have led to a novel perception of nanometer- and atomic-scale structures and processes. Since the information is obtained directly in real space, the scanning probe techniques offer significant advantages for the investigation of nonperiodic structures at solid surfaces compared with diffraction techniques. Additionally, local probe methods allow the study of a large variety of physical properties of nanometer-scale structures down to atomic resolution and even became useful for the fabrication of artificial nanometer-scale structures. On the other hand, a large number of unresolved scientific and technological issues still remains. In this review, the focus is on two basic questions: what actually has been achieved and which fundamental physics issues need to be addressed further. The discussion will be restricted to topics in solid state physics.
Thermal stability of thin poly-Si/Ta2O5/TiN capacitors for dynamic random access memory applications
Authors: Ishibashi K. , Patnaik B. K. , Parikh N. R. , Sandhu G. S. , Fazan P. C.
Published: July 2002

Capacitors made up of thin films of Ta2O5/TiN on polysilicon have been studied for application to 256 Mbytes dynamic random access memories. In this study, the thermal stability of poly-Si/Ta2O5 films with TiN electrode film deposited by (i) chemical vapor deposition (CVD) with TiCl4 and NH3, (ii) sputtering, and (iii) metalorganic CVD (MOCVD) was compared. These samples were annealed under vacuum at 700, 800, and 900 °C for 30 min. The as-deposited and the annealed samples were analyzed by Rutherford backscattering with 2 MeV He+ ions. The CVD TiN films, which contained a small amount of Cl, provided pathways for the underlying Ta2O5 to out-diffuse during annealing at all temperatures between 700 and 900 °C. The sputtered films were resistant to the diffusion of Ta2O5 up to 800 °C, but relented at 900 °C, with measurable outdiffusion of Ta. There was no noticeable interaction of the Ta2O5 with the TiN layers, deposited by the MOCVD process, at temperatures up to 900 °C. However, the MOCVD TiN films were found to contain light elements such as carbon and oxygen, which were slightly reduced on annealing. Nuclear reaction analysis and secondary ion mass spectroscopy were used to detect the concentrations and depth profiles of light elements. These indicate presence of C and O contents up to at least 20 at. % in these films.
Wavelength dependence of the resist sidewall angle in extreme ultraviolet lithography
Authors: Wood O. R. , Bjorkholm J. E. , Fetter L. , Himel M. D. , Tennant D. M. , MacDowell A. A. , La Fontaine B. , Griffith J. E. , Taylor G. N. , Waskiewicz W. K. , Windt D. L. , Kortright J. B. , Gullikson E. K. , Nguyen K.
Published: July 2002

We report experimental and theoretical studies of the resist sidewall angles produced using extreme ultraviolet lithography at exposure wavelengths of 37.5, 13.9, and 6.8 nm. We show that high resist absorption in this wavelength region leads to a significant degradation in pattern sidewall angle. Because steep resist profiles are needed in semiconductor manufacturing to ensure adequate linewidth control it seems unlikely that a single-layer resist process can be used in extreme ultraviolet lithography except at the shortest wavelength.
Secondary electron line scans over high resolution resist images: Theoretical and experimental investigation of induced local electrical field effects
Authors: Grella Luca , Di Fabrizio Enzo , Gentili Massimo , Baciocchi Marco , Mastrogiacomo Luigi , Maggiora Romano , Capodicci Luigi
Published: July 2002

The effects of the local electric fields generated during the e-beam inspection of high resolution resist features at low voltage are discussed. A theoretical model based on the Monte Carlo technique was developed to simulate the effect of the induced electrical fields on the primary beam and on emitted secondary electrons. It is here proved that reentering secondary electrons act as a negative feedback to the local positive retarding field when at least one of the insulating materials of the sample being inspected has a secondary electron yield bigger than one. Such a recombination mechanism is more important than primary electron absorption, as this last factor takes place far from the escape depth layer. The positive charge compensation prevents the local positive field from growing as the number of line scans increases and allows the local field to reach stability. At the top of resist features, potential values as high as 40 V were found. Although the scanning electron microscope image is highly affected by induced voltage contrast, critical dimension (CD) information is not distorted when the stability conditions are fulfilled; namely, a CD control threshold algorithm can be applied by properly choosing the threshold signal level. The modeling of secondary electron emission and absorption requires a single loop, composed of Monte Carlo simulation, local field computation, and electron ray tracing, to be iterated several times. This computation strategy is applied to feature sizes from 1 μm down to 0.25 μm and to geometries such as line arrays and isolated lines. Two different accelerating voltages are studied, namely 1.2 and 1.5 keV. Probe beam currents of 3 and 10 pA are also considered. In addition, the effect of a sample tilting of 20° is also accounted for. Computation accuracy is proved by comparing theoretical data to experimental data obtained by a cold cathode tungsten field emission microscope.
Fabrication of single-domain magnetic pillar array of 35 nm diameter and 65 Gbits/in.2 density
Authors: Krauss Peter R. , Fischer Paul B. , Chou Stephen Y.
Published: July 2002

Using electron beam nanolithography and electroplating, arrays of Ni pillars on silicon have been fabricated. The effects of plating current and feature size on the plating rate were investigated. The pillar arrays have a period of 100 nm and the pillar diameters are uniform and as small as 35 nm. Because of their nanoscale size, shape anisotropy, and separation from each other, each Ni pillar is single domain with only two quantized perpendicular magnetization states: up and down. If each pillar were to represent one bit of information, the density of the pillar arrays would be 65 Gbits/in.2—over two orders of magnitude greater than the state-of-the-art magnetic storage density. The ultrahigh density, together with the single-domain formation, make these pillar arrays very attractive for high-density magnetic storage devices and fundamental magnetics studies.
Elasticity, wear, and friction properties of thin organic films observed with atomic force microscopy
Authors: Overney R. M. , Bonner T. , Meyer E. , Rüetschi M. , Lüthi R. , Howald L. , Frommer J. , Güntherodt H.-J. , Fujihira M. , Takano H.
Published: July 2002

An atomic force microscopy study is presented on lubricating systems, such as thin organic Langmuir–Blodgett films. Local elastic compliance was measured simultaneously with topography and friction on thin films of mixtures of fluorocarbons and hydrocarbons. On the phase-separated fluorocarbon domains, higher friction and lower Young’s modulus than on the hydrocarbon domains was found. Adhesive wear has been observed to occur randomly on the stiffer hydrocarbon domains if the film is complexed with a counterion polymer of a larger cross-sectional area. A quantitative fractal analysis of the hydrocarbon film remaining areas provided a linear adhesive wear dependence on the scan cycle number.
Direct observation of the atomic force microscopy tip using inverse atomic force microscopy imaging
Authors: Montelius L. , Tegenfeldt J. O. , van Heeren P.
Published: July 2002

It is a well-known fact in scanning probe microscopy that the tip geometry will be convoluted with the shape of the sample. In this study we report on a clear-cut in situ direct observation of the real shape of the atomic force microscopy (AFM) tip using the AFM technique itself, utilizing a specially designed sample. The sample was an array of columns fabricated using aerosol deposition of metal particles and subsequent plasma etching. In this article we report on the so-called inverse AFM mode in which the tip is actually used as the sample and vice versa. We will present results using ordinary AFM tips and ‘‘tapping-mode’’ tips as well as high-aspect-ratio supertips (Nanoprobe). We propose how this method can, with a very high accuracy, be used for studying objects, e.g., biomolecules, that are deliberately attached to the usual AFM cantilever tip. Finally, we discuss how this method can significantly increase the reliability of the obtained AFM images.
Structural and optical properties of self-assembled InGaAs quantum dots
Authors: Leonard D. , Fafard S. , Pond K. , Zhang Y. H. , Merz J. L. , Petroff P. M.
Published: July 2002

A one step method for the production of quantum dots is presented. The method exploits the mismatch strain of molecular beam epitaxy (MBE) deposited InGaAs on GaAs to induce a transition from the two-dimensional growth mode to the three-dimensional (Stranski–Krastanow) growth mode. The cluster size is limited to quantum dimensions by precisely controlling the amount of InGaAs that is deposited in order to cause the growth mode transition. Very narrow lateral size distributions with standard deviations of 14% on the dot area have been obtained. Smooth MBE growth of GaAs over these clusters produces a layer of quantum dots, whose high quality and uniformity has been observed with transmission electron microscopy, atomic force microscopy, and photoluminescence (PL). The quantum dot PL intensity is enhanced compared to a reference quantum well. Resonances in photoluminescence excitation (PLE) spectra suggest that the density of states in these dots has minima close to zero between the quantum states, as expected for a zero-dimensional system .These PLE peaks shift with the detecting energy, showing that by changing the detecting energy, we are sampling different sizes of dots. The temperature dependence of the PL indicates that the onset energy of thermal quenching of quantum dots is enhanced by a factor of 2, as compared to a quantum well, due to the additional confinement. In all samples, there is virtually no overlap between the PL emission and the first PLE peak of the quantum dots.
Atomic force microscope lithography using amorphous silicon as a resist and advances in parallel operation
Authors: Minne S. C. , Flueckiger Ph. , Soh H. T. , Quate C. F.
Published: July 2002

Lithography on (100) single-crystal silicon and amorphous silicon is performed by electric-field-enhanced local oxidation of silicon using an atomic force microscope (AFM). Amorphous silicon is used as a negative resist to pattern silicon oxide, silicon nitride, and selected metals. Amorphous silicon is used in conjunction with chromium to create a robust etch mask, and with titanium to create a positive AFM resist. All lithographies presented here were patterned in parallel by arrays of two piezoresistive silicon or two silicon-nitride cantilevers. Parallel arrays of five piezoresistive cantilevers were fabricated and used in imaging and lithographic applications. A 400 μm×100 μm parallel image is obtained in the time it would normally take to obtain a 100 μm×100 μm image. In our method of parallel operation, it is only possible to image and lithograph in modes that do not require feedback. In imaging, this limits the possible applications of the parallel AFM. During parallel lithography, discrepancies are seen between the tip in the feedback loop and those that are not. To overcome these differences it will be necessary to devise a system where each of the tips in the array are controlled by individual feedback loops.
Initial oxidation of silicon (100): A unified chemical model for thin and thick oxide growth rates and interfacial structure
Authors: Whidden T. K. , Thanikasalam P. , Rack M. J. , Ferry D. K.
Published: July 2002

A model for silicon oxidation that invokes dissociative chemisorption of molecular oxygen at the interface between silicon dioxide and silicon is described. The model accounts for a self-limiting oxide film thickness of 0.5–0.6 nm (for oxidations performed at temperatures sufficient to dissociate surface dimers and permit oxygen penetration of the substrate beyond a single monolayer of suboxide). Detailed examination of the model suggests a mechanism for an inherent oxide/silicon interface roughness of approximately one atomic diameter. Kinetic rate equations developed from the model successfully account for the observed power law dependence of rate on oxygen partial pressure. These relationships were used in the derivation of an expression for the variation of oxide film growth rate with overlying oxide thickness. The relationship is tested against experimental observations reported in the literature and found to give an excellent fit.
Metallurgy of Al–Ni–Ge ohmic contact formation on n-GaAs
Authors: Lin X. W. , Lampert W. V. , Haas T. W. , Holloway P. H. , Liliental-Weber Z. , Swider W. , Washburn J.
Published: July 2002

Al–Ni–Ge ohmic contacts on n-GaAs were prepared by sequential vapor deposition and furnace annealing at 500 °C. The metallurgical properties of the contacts were studied by transmission electron microscopy. It was found that while Al–Ni–Ge as a whole is relatively stable against GaAs, extensive interfacial reactions readily occur within the contact layers, resulting in a very stable layered structure of the type Al3Ni/Ni–Ge/GaAs, with ε′-Ni5Ge3 being the major phase in the Ni–Ge layer. GaAs twins and Ni–As precipitates were found in a thin layer immediately below the metallization, suggesting that the ohmic behavior can be accounted for in terms of a GaAs regrowth mechanism.
Nondestructive characterization of pseudomorphic high-electron-mobility transistor structures using x-ray diffraction and reflectivity
Authors: Rogers T. J. , Ballingall J. M. , Larsen M. , Hall E. L.
Published: July 2002

X-ray diffraction and glancing angle-of-incidence x-ray reflectivity are applied to the analysis of AlGaAs–InGaAs–GaAs pseudomorphic high-electron-mobility transistor structures. Through comparisons between simulations and measured data, we are able to determine the InAs mole fraction and thickness of the InGaAs channel with precisions of ±0.003 and ±3 Å, respectively. The period of the AlGaAs/GaAs superlattice buffer, and the combined thickness of the AlGaAs gate and GaAs contact layers are determined with a precision of ±2%. Thickness values determined with these x-ray techniques agree with those determined by transmission electron microscopy to within 6%.
Enhancement and suppression of the formation of porous silicon
Authors: Duttagupta S. P. , Peng C. , Fauchet P. M. , Kurinec S. K. , Blanton T. N.
Published: July 2002

We present the results of an investigation of various means to enhance or suppress the formation of porous silicon. The first method involves a lithographic process using silicon nitride to produce sub-0.5 μm light emitting porous silicon (LEPSi) lines adjacent to fully protected silicon regions. The second method consists of amorphizing regions of the wafer prior to anodization with high energy/high dose ion implantation, followed by anodization and annealing. In this method, LEPSi is produced in the unimplanted regions only. Using focused ion-beam implantation ∼100 nm patterns have been obtained. The third method utilizes low energy/low dose bombardment (ion milling/reactive ion etching) with argon ions prior to anodization. Under appropriate bombardment conditions, we have observed a strong enhancement of the formation rate of LEPSi, possibly due to the generation of a large number of defects on the wafer surface. Our results demonstrate that porous silicon light emitting diodes (LEDS) and silicon electronic devices can coexist in close proximity (within 1 μm or less) on the same chip.
Layered heavy metal iodides examined by atomic force microscopy
Authors: George M. A. , Chen K.-T. , Collins W. E. , Burger A. , Nason D. , Boatner L.
Published: July 2002

Atomic force microscopy was used to characterize the surface of semi-insulating bismuth tri-iodide, lead iodide, and mercuric iodide crystals. These heavy metal iodides belong to a unique class of materials that provide a wide range of interesting problems that can be studied by atomic force microscopy. They have relatively high vapor pressures and cannot be examined noninvasively in vacuum conditions, such as by electron microscopy. Mercuric, bismuth, and lead iodide are layered materials with van der Waals bonding along the c axis and therefore, like mica, can be easily cleaved to provide fresh atomically flat crystalline surfaces to study. These crystals are soft with a high degree of plasticity and, as a result, the surfaces are easily modified by the cantilever tip. They demonstrate reactivity in ambient air at the surfaces as well as within the van der Waals gap. Freshly cleaved surfaces were examined and it was found that single and multiple atomic layers were easily displaced on the cleaved surfaces in all of the crystals when scanned in both contact and modulated contact mode. The effects of cantilever induced modifications of the surfaces of mercuric, lead, and bismuth iodide were studied by atomic force microscopy and their properties are discussed.
Sensor systems for real-time feedback control of reactive ion etching
Authors: Benson T. E. , Kamlet L. I. , Ruegsegger S. M. , Hanish C. K. , Hanish P. D. , Rashap B. A. , Klimecky P. , Freudenberg J. S. , Grizzle J. W. , Khargonekar P. P. , Terry F. L. , Barney Bryan
Published: July 2002

Previous efforts from our group have shown encouraging initial results in stabilizing etch rates versus time during a run by using real-time, multivariable feedback control (RTC) in an Applied 8300 reactive ion etcher. That work indicated the need for improvements in our sensor systems, both the sensors currently used in feedback control and those monitoring the effects of the control on the wafers being etched. In this article we report on our efforts in the development and improvement of two such sensor systems. The first is an optical emission spectroscopy system which simultaneously measures two emission line intensities for use in actinometry. The second sensor system uses spectral reflectometry data to determine the in situ film thickness, from which we calculate the etch rate. We show examples of RTC using the actinometry sensor system during fluorine-based polycrystalline silicon etching. The results of using these sensors for RTC are presented by comparing open loop signals with those from real-time closed loop etch runs. In situ etch rate accuracies, estimated using our reflectometry system, are discussed. Film thicknesses calculated from in situ measurements are compared with those calculated by ex situ spectroscopic ellipsometry.
Epitaxial growth of Si1−x−yGexCy alloy layers on (100) Si by rapid thermal chemical vapor deposition using methylsilane
Authors: Mi Jian , Warren Patricia , Gailhanou Marc , Ganière Jean-Daniel , Dutoit Michel , Jouneau Pierre-Henri , Houriet Raymond
Published: July 2002

High quality pseudomorphic Si1−yCy and Si1−x−yGexCy layers were grown on (100) Si between 530 and 650 °C by rapid thermal chemical vapor deposition in the SiH4/GeH4/SiH3CH3/H2 system. These layers contained up to 30 at. % Ge and up to 2.2 at. % C. Strain engineering was achieved. The strain could be tailored continuously from compressive (up to 2.2% in Si1−xGex) to tensile (up to −0.8% in Si1−yCy and −0.35% in Si1−x−yGexCy). The relationship between the process parameters and the physical properties of the layers was investigated. A process window for growing high quality layers was defined in terms of the partial pressures of SiH4 and SiH3CH3. It was found to be independent of Ge content, growth temperature, and growth rate. No carbon contamination was observed. No interference between Ge and C incorporation was observed. A model for the incorporation of substitutional C in the films which is based on the chemical reaction of SiH4 and SiH3CH3 on the surface is proposed.
Microstructure control in semiconductor metallization
Authors: Harper J. M. E. , Rodbell K. P.
Published: July 2002

The microstructure of semiconductor metallization is becoming increasingly important as linewidths decrease below 0.5 μm. At these dimensions, reliability and performance are greatly influenced by specific microstructural features rather than only by the average material properties. In this article, we address the prospects for controlling the microstructure of thin film interconnection metals as linewidths are predicted to decrease below 0.1 μm by the year 2010. First, we evaluate the sources of energy available to drive microstructure changes in thin films, both during and after deposition. The internal energy sources considered are grain boundaries, interfaces, surfaces, strain, solidification, crystallization, solute precipitation, and phase transformations, with energy densities ranging from less than 1 meV/atom to greater than 100 meV/atom. The external energy sources considered are particle bombardment during deposition, mechanical deformation, and radiation damage, which may deliver energies greater than 100 eV/atom. Second, we review examples of microstructure changes in terms of these energy sources. These examples include the dependence of Al–Cu and Ti fiber texture on the roughness of SiO2, orientation change and abnormal Cu grain growth coupled to the precipitation of Co in Cu–Co alloys, and in-plane orientation selection during phase transformation of TiSi2 in very narrow lines. A substantial degree of microstructure control is also achieved in films deposited with off-normal incidence energetic particle bombardment, which has been used to produce both in-plane and out-of-plane crystallographic orientations in metals (Mo, Nb), nitrides (AlN), and oxides (ZrO2). Drawing on these examples, we discuss the prospects for microstructure control in future semiconductor metallization with respect to the list of energy sources, the decreasing dimensions, and the changing fabrication processes. One mechanism in particular, discontinuous precipitation of supersaturated solute atoms, is highlighted as having a substantial amount of stored energy available to drive microstructure evolution, and may provide a means to more fully control the microstructure of semiconductor metallization.
Growth and characterization of Si and Ge clusters on ordered C60 overlayers
Authors: Klyachko D. , Chen D. M.
Published: July 2002

We use in situ fabricated ordered C60 overlayers on Si and Ge surfaces as templates to grow isolated Ge and Si clusters, respectively. The growth processes are monitored and characterized by scanning tunneling microscopy, Auger spectroscopy, and low energy electron diffraction. Si and Ge clusters nucleate in the interstices of the C60 layer, and reach a typical lateral size of ∼10 Å before coalescing. Auger spectra of small Si clusters show an enhanced contributions from states of s symmetry, reflecting nontetrahedral coordination of Si atoms in clusters. Room temperature tunneling spectroscopy of isolated clusters reveals an enlarged band gap consistent with the effect of quantum confinement, and a quantized conductance attributable to the Coulomb blockade phenomena in a tip/cluster/substrate double barrier junction.
Reliable 0.28 μm metal contact technology
Authors: Kim J. S. , Kang C. J. , Park J. W. , Chung S. H. , Kim B. C. , Lee J. Y. , Park J. W.
Published: July 2002

A reliable small metal contact (MC) process is developed for the gigabit scaled dynamic random access memories (DRAMs). The high aspect ratio contact etch was accomplished by using a high density inductively coupled plasma reactor. The low contact resistance of the MC for the gigabit scaled DRAMs is realized when the amount of Si consumption at the bottom of the contact holes is minimized (<20 nm). The dopant activation of the source and drain (S/D) regions is also critical to have low contact and sheet resistances (Rc and Rs). Use of the high temperature (>950 °C) rapid thermal annealing enhances the dopant activation and effectively reduces the Rc and Rs. Surface treatment of the bottom of the contact hole after dry etch, becomes a key factor to have low contact resistance in the case of small contacts. The conventional Ar+ in situ sputter cleaning deteriorates the contact resistance of the vertically sloped small MCs. Light etch using CF4 and O2 gases removes damaged layer and improves contact resistance. Rapid thermal nitridation after TiN barrier metal deposition also improves electrical properties of the MCs.
Fabrication and simulation of a gated thin film emitter
Authors: Ko Tae-Young , Chung Bokeon , Lee J. Y. , Jeon D.
Published: July 2002

We have fabricated a gated field emitter using a diamond-like carbon (DLC) film cathode. The process involved the deposition of DLC, insulator, and gate layers followed by backetching to expose a patterned DLC. We also simulated the emission behavior of the gated DLC cathode. The emission sites on the DLC film were simulated by multiple sharp points formed on the DLC surface. The electron trajectory and the emission current were studied as a function of structural parameters such as cathode height, oxide layer thickness, gate hole diameter, and focus electrode.