bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of indium desorption activation energy from InP layers by laser induced fluorescence
Authors: Kuo Chau-Hong , Choi Calvin , Maracas George N. , Steimle Timothy C.
Published: July 2002

The first measurement of indium desorption activation energy (DAE) from InP layers in gas-source molecular-beam epitaxy is being reported. A thick layer of InP (1.5 μm) was grown on GaAs to relax the strain induced from the lattice mismatch. Temperature programmed desorption (TPD) and laser induced fluorescence (LIF) were used to monitor the temperature dependent indium desorption rate from phosphorus stabilized InP surface. From the TPD experiment, Arrhenius plots of the indium LIF signal versus 1000/Tsub, show that the indium DAE was 4.49±0.15 eV. This value is 1.4 eV higher than our previous measurement of indium DAE from InAs.
Optimum growth temperature determination for GaInSb/InAs strained layer superlattices
Authors: Davis J. L. , Wagner R. J. , Waterman J. R. , Shanabrook B. V. , Omaggio J. P.
Published: July 2002

To determine the optimum growth temperature for GaInSb/InAs strained layer superlattices (SLS) a series of SLS was grown over the temperature range 357–433 °C. Temperatures were estimated by determining the absorption spectrum of the GaAs substrate, hence its band gap, and thus its temperature. SLS were evaluated by single crystal x-ray diffraction and interband magnetoabsorption (IMA) measurements. X-ray spectra showed as many as eight peaks due to the superlattice. The quality of the superlattices as indicated by the x-ray data had a well defined maximum between 390 and 410 °C. IMA measurements indicated band gaps from 85 to 154 meV.
Gravity Probe B Gyroscope charge control using field-emission cathodes
Authors: Buchman Saps , Quinn Theodore , Keiser G. M. , Gill Dale
Published: July 2002

We propose and test a method for controlling the charging of the Gravity Probe B(GP-B) electrostatically suspended gyroscopes using electrons generated by field emission cathodes. The GP-B Gyroscope Experiment is designed to measure for the first time the geodetic and the frame-dragging effects predicted by Einstein’s general theory of relativity. The expected accuracy of ∼0.3 marcsec/yr (10−11 deg/h) will allow for a 0.01% measurement of the geodetic effect and a 1% measurement of the frame-dragging effect. Gyroscope charging is caused by cosmic radiation, by field emission, and by the separation of dissimilar metals. The expected charging rate for the gyroscopes is ∼1 nC/yr and consequently above the 50 pC limit dictated by disturbing torque considerations. The present charge control technique is based on ultraviolet photoemission of electrons from both the gyroscope and an auxiliary electrode. Experiments have shown this method to be effective at room temperature in ground testing, and calculations indicate that it is suitable for charge control in orbit. As an alternative we demonstrate the use of Spindt-type field emission cathodes for the control of the positive charges on the gyroscopes, by using a 10 000 tip emitter array produced by SRI International. The device requirements are (a) stable and reliable operation over two years at 2 K and 1.5×10−9 Pa, (b) average power dissipation in the device of less than 50 μW, (c) peak emission current of 1–100 pA, (d) dimensions less than 2 mm, (e) magnetization less than 10−8 G, (f) electric field at the gyroscope less than 104 V/m. The control of negative charges on the gyroscope is achievable by operating in a regime in which the secondary electron emission coefficient is greater than unity.
Ion-space-charge initiation of gated field emitter failure
Authors: McGruer N. E. , Browning J. , Meassick S. , Gilmore M. , Bintz W. J. , Chan C.
Published: July 2002

Failures of individual micron-scale gated field emitters are observed to be similar in many respects to cathodic arcs. The initiation of a failure event at elevated pressures by ion-space-charge enhancement of the electric field at the emitter tip is simulated and compared with experimental results. The experimental results show a significantly lower pressure failure threshold than that predicted by the simulation. This discrepancy may indicate the presence of additional processes.
Control of deposition rate in remote plasma enhanced chemical vapor deposition of GexSi1−x/Si heteroepitaxial films
Authors: Kinosky D. , Qian R. , Mahajan A. , Thomas S. , Banerjee S. , Tasch A. , Magee C.
Published: July 2002

The addition of germane and dopant gases significantly alter the growth kinetics of low temperature Si epitaxy. Germane, phosphine, and diborane have been reported to both enhance and retard film growth rate in various processes. The growth kinetics of remote plasma enhanced chemical vapor deposition are largely unaffected by the addition of GeH4 or by in situ doping. Adsorption sites are created by low energy ion bombardment and are only minimally dependent on temperature for activation. Ion-induced gas phase reactions also play an important role in the deposition via formation of precursors which have greater sticking probabilities and insertion rates into the hydrogenated surface than for the direct reactions of SiH4 and GeH4 with the Si surface in thermal chemical vapor deposition.
Use of a variable shaped beam electron lithography system for diffractive optics components manufacturing
Authors: Trotel Jacques
Published: July 2002

Binary diffractive optical components using 1–3 mask levels are being manufactured with a variable shaped electron beam system with ‘‘write on the fly’’ writing mode, which is also used for conventional microelectronic applications. Two examples of components are described.
In situ thickness monitoring and control for highly reproducible growth of distributed Bragg reflectors
Authors: Houng Y. M. , Tan M. R. T. , Liang B. W. , Wang S. Y. , Mars D. E.
Published: July 2002

A theoretical model was developed to simulate the apparent substrate temperature oscillation during the growth of AlAs/AlxGa1−xAs, x=0 and 0.25, distributed Bragg reflectors (DBR) for 980- and 780-nm vertical cavity surface emitting lasers, respectively. The simulated data were then used for in situ monitoring and feedback control of layer thickness by a simple pyrometric interferometry technique to obtain a highly reproducible DBR. These measurements can be performed with continuous substrate rotation and without any growth interruption. The reproducibility of the center wavelength and full width at half-maximum of the reflectivity stop band with a variation of <±0.2% and <±0.4% for the AlAs/GaAs and AlAs/AlGaAs mirror stacks, respectively, were achieved.
Knife-edge thin film field emission cathodes on (110) silicon wafers
Authors: Lee Bo , Elliott T. S. , Mazumdar T. K. , McIntyre P. M. , Pang Y. , Trost H. J.
Published: July 2002

In the effort to develop a high performance field emission cathode for application in microwave amplifiers, it is clear that the emitter structure should have a sharp emitter surface, a large emitter height, a small gate opening size, and a small emitter angle. We have developed a technique that fabricates knife-edge field emission arrays (KEFEA) on (110) silicon wafers. KEFEA has an optimized structure meeting the requirements mentioned above. The emitter edge radius is about 250 Å or less, the emitter height is 8 μm, and the gate gap is ∼0.2 μm. Experiments have exhibited Fowler–Nordheim type field emission with gate-to-substrate bias voltage less than 50 V.
Fabrication of 150-nm gate-length high electron mobility transistors using x-ray lithography
Authors: Haghiri-Gosnet A. M. , Lafontaine H. , Jin Y. , Rousseaux F. , Chaker M. , Pépin H. , Launois H.
Published: July 2002

Functional 150-nm gate-length high electron mobility transistors (HEMTs) have been successfully fabricated using storage ring x-ray lithography (XRL) for all process levels. This article describes the L2M XRL exposure system including x-ray masks, the planar-doped GaAlAs/GaAs HEMT fabrication process, and the characteristics of the resulting devices. The gate length, a key device performance parameter, was minimized down to 150 nm using an optimized chemically amplified SAL601 negative resist process at small proximity gap (≤20 μm). This optimization process indicates that process latitude and resolution are primarily limited by the post-exposure bake (PEB) step which has been adjusted to 95 °C. The fabricated HEMTs have excellent dc characteristics with a peak extrinsic transconductance as high as 400 mS/mm.
Parametric modeling at resist–substrate interfaces
Authors: Ocola L. E. , Cerrina F.
Published: July 2002

In the energy range of interest for x-ray lithography, absorption of x rays by atoms results in the emission of photoelectrons and Auger secondary electrons, as well as a shower of low energy electrons. The development of accurate image formation models in x-ray lithography requires that these mechanisms be included. The photoelectron processes produce a redistribution of the x-ray energy over a finite volume. The interaction of the electrons with the medium is complex and can be treated in the framework of a response theory (dielectric function). A simulation code, based on the Monte Carlo method (lesis), has been developed to study the photon energy redistribution in resists, in the vicinity of resist–substrate interfaces and overlayers. The low computational efficiency of the Monte Carlo method motivates the need to parametrize the energy redistribution results of the simulation. This parametrization was performed for a polymethyl-methacrylate/Si interface, as a function of the photon energy. The parametrization can be interpreted as the weighted sum of individual electron responses. The effects on the resist of photoelectrons generated in the substrate are discussed. These effects have been incorporated in an effective dose model that can be used to compute complex interface geometries. The results are particularly relevant for the nanolithography domain (< 100 nm).
Effect of brightener concentration on the thermal distortion of gold plated x-ray masks
Authors: Dauksher W. J. , Resnick D. J. , Seese P. A. , Cummings K. D. , Yanof A. W. , Johnson W. A.
Published: July 2002

In-plane distortion of a fiducial array was used as a metric to compare the relative responses to heat treatments of x-ray masks doped with different brightener levels. Samples plated from gold-sulfite baths containing 0, 2, and 75 ppm Tl all distorted by more than 50 nm after annealing at 100 °C. Quenching in liquid nitrogen fully relieved the stress of the undoped sample only. Room temperature stress relaxation behavior after storage of the gold samples for 2.5 years is detailed. Gold samples doped to any level with a thallium-based brightener gradually relax, if initially stressed, and remain at a zero stress state. Behavior is explained in terms of room temperature grain growth and plastic deformation.
Defocus asymmetry in projection printing
Authors: Barouch Eytan , Hollerbach Uwe , Orszag Steven A.
Published: July 2002

The effect of defocus asymmetry in photolithography has been modeled by modifying FAIM to incorporate the phases of all partial fields emanating from the illuminator. Each partial field exposes the resist independently, and the integration over the illuminator takes place inside the resist, thus accounting for the correct physics of partially coherent light projection. Linewidth versus defocus is obtained as an asymmetric function around zero defocus as found experimentally.
Fabrication of diffractive optical components for an extreme ultraviolet shearing interferometer
Authors: Spector S. J. , Tennant D. M. , Tan Z. , Bjorkholm J. E.
Published: July 2002

We have constructed four optical components for use in an extreme ultraviolet shearing interferometer which will operate at a wavelength of 13.4 nm. The components that have been constructed include transmission diffractive optical components such as a Fresnel zone plate, angled gratings, and two-frequency gratings, as well as pinhole apertures. All the components are fabricated in 110 nm of Ge, which is supported by a 0.5–0.7-μm-thick membrane of Si. The patterns were fabricated by first evaporating Ge and then spinning 100 nm polymethylmethacrylate (PMMA) onto the Si membranes. The desired patterns were exposed in the PMMA resist using electron beam lithography. Custom interative computer programs generated the patterns used to control the exposure. After developing the PMMA resist the Ge layer was etched using a reactive ion etching technique. Electron microscopy of the finished components show that the smallest features in our components are cleanly constructed, and the linewidths and placement of the features meet the desired accuracy.
Negative-tone deep-ultraviolet resists containing benzylic crosslinkers: Experimental and simulation studies of the crosslinking process
Authors: Zenk A. M. , Neureuther A. R. , Lee S. M. , Fréchet J. M. J.
Published: July 2002

Dissolution rate and resolution measurements are used to show that a novel acid-hardened deep-ultraviolet photoresist ML93, based on a benzylic crosslinker, has excellent dissolution and reasonable resolution characteristics. Experimentally, we have observed that ML93 resist is about 20 times more sensitive than Shipley SNR248. While the high sensitivity is a promising result, it has made experimental reproducibility more difficult. In addition, the effect of the crosslinker structure on dissolution is examined with three more resists, ML239, ML240, and ML241, all analogous to ML93 except for variations in the structure of the crosslinker. A kinetic model describing negative resist lithography is applied to ML93 and ML239, and some profile cross sections are simulated using sample. The kinetic model has provided a reasonable fit to the dissolution characteristics of ML93 and ML239 separately, but comparison indicates that the basic role played by the active sites in the dissolution process needs further investigation.
Contrast of ion beam proximity printing with nonideal masks
Authors: Stumbo D. P. , Wolfe J. C.
Published: July 2002

In ion beam proximity printing, a broad, collimated beam of light ions is directed through a stencil mask. For this process, aerial image contrast is limited primarily by scattering near the edges of the mask openings. Previous work by Karapiperis et al. [J. Vac. Sci. Technol. 19, 1259 (1981)] considered the energy deposited in resist (and resist profiles) for ideal incident ion beams. Randall, Stern, and Donnelly [J. Vac. Sci. Technol. B 4, 201 (1986)] have calculated mask contrast as a function of pattern density and mask thickness for grid support masks with smooth vertical sidewalls, showing that contrast is a function of mask aspect ratio. We present simulations from a modified version of TRIM85 including the effects of mask wall angle, roughness and thickness, ion incident angle, resist scattering, and pattern spatial frequency for infinite line and space patterns. Contrast of the deposited energy density and estimated process sensitivity are shown, as well as a simulated resist profile derived using a string development model. A histogram of the angular dependence of ion scattering shows that the effect is a diffuse exposure at reasonable mask-to-wafer gaps. It is also shown that for reentrant mask profiles the contrast increases with mask thickness. Our simulations show that 0.25 μm line and space patterns in 2 μm thick masks with reasonable parameters can have a contrast of 12, a contrast of 8 is attainable for 0.125 μm line and space patterns, and the stringent linewidth control required by surface acoustic wave devices can be achieved with ±5% dose control.
Silicon point contacts: Nanofabrication, molecular beam epitaxial growth, and transport measurements
Authors: Maes J. W. H. , Caro J. , Werner K. , Radelaar S. , Kozub V. I. , Zandbergen H. W.
Published: July 2002

We describe a fabrication process for three-dimensional Si point contacts. The process is based on molecular beam epitaxy to grow electrodes of the devices and on electron-beam lithography and wet etching to produce holes in the insulator. From scanning electron microscopy and transmission electron microscopy analysis we find that the lower electrode has a perfect crystalline structure, while the upper electrode has a composite structure consisting of a single-crystalline column grown out of the hole in the insulator and a poly-crystalline environment. The smallest holes realized have a diameter of 40 nm. I–V curves of point contacts with a boron concentration of about 5×1018 cm−3 and with diameters in the range 200–2000 nm are linear at 300 K and indicate behavior according to the Maxwell resistance, as expected for diffusive transport. Below 40 K variable-range hopping is the transport mechanism. In this temperature range quadratic I–V curves develop, which can be understood from electric field activated hopping in the point-contact geometry.
Surface oxidation of selenium treated GaAs(100)
Authors: Scimeca T. , Watanabe Y. , Maeda F. , Berrigan R. , Oshima M.
Published: July 2002

The surface oxidation of Se treated GaAs(100) has been investigated in order to understand in greater detail the degradation of the Se passivated GaAs surface upon exposure to atmosphere. An increase in band bending is initially observed at relatively low exposure times, which corresponds to an increase in the O 2p intensity in the valence band. At this stage, oxygen is thought to weakly physisorb at the Ga vacancy sites. At intermediate exposure levels, the other unadsorbed oxygen atom of O2 attacks the nearest Ga atom. The bond between the nearest Ga atom and Se is then severed, resulting in the formation of Se, which closely resembles amorphous Se. Ultimately, both Se states are converted to this amorphouslike state and at longer exposure times are oxidized. At longer exposure times, the oxidation of Se is also accompanied by As oxidation. In contrast to S treated GaAs, Se/GaAs is relatively resistant to oxidation where only about 10% of the As is oxidized (As2O3) after 180 min of exposure versus oxidation of 35% of the As atoms for S/GaAs after only 20 min of atmosphere exposure. This relative oxidation resistance is attributed to greater penetration of Se into GaAs relative to S into GaAs.
Deflector and correction coil calibrations in an electron beam block exposure system
Authors: Yamada A. , Sakamoto K. , Yamazaki S. , Kobayashi K. , Sago S. , Oono M. , Watanabe H. , Yasuda H.
Published: July 2002

Mask deflectors and correction coils in an electron beam block exposure system are calibrated to expose 48 mask patterns in a deflection area with the same current density and at the same position on a wafer. The calibration has six measurement steps. When a mask stage changes area positions on a mask, only the last step needs to be executed during exposure. This last step takes about 2 s for measurement. Calibration results show that the current density through each mask pattern differs less than 1.6% from the mean value. Exposed position errors on a wafer are below 0.04 μm for 48 mask patterns. These position errors are corrected by additional deflections with an electrostatic minor deflector. To improve stitching accuracies between exposed patterns, we discuss another routine to adjust beam sizes and rotations of spots on a wafer.
Interior area removal method for p
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Authors: Lee Soo-Young , Cook Brian D.
Published: July 2002

In previous years, pyramid, a hierarchical rule-based scheme for proximity effect correction in electron-beam lithography was presented. pyramid has produced good experimental results for large circuit patterns (up to 80 μm × 80 μm) with a minimum feature size of 0.1 μm in 200 and 500 nm poly(methylmethacrylate) (PMMA) on silicon. Although the circuits used to test pyramid in the past have contained a rapidly varying pattern density, they did not contain very large features (e.g., 10 μm × 10 μm) next to small (0.1 μm) elements. The previous method for performing circuit correction (edge adjustment) has been found to be inadequate when correcting such occurrences. In order to overcome this problem, a new correction technique has been added to the overall pyramid hierarchy. Previously, pyramid performed its correction by adjusting only the locations of the edges of circuit elements. This new correction technique expands upon the previous edge adjustment method by allowing pyramid to remove area from circuit elements not only from the edges, but also from the interior as well. This interior area removal technique substantially improves the correction in cases when small circuit elements are placed near very large features. This article motivates the use of interior area removal both through simulation and experimental results. Experimental results indicating the usefulness of interior area removal are provided.
CH4/H2/Ar/Cl2 electron cyclotron resonance plasma etching of via holes for InP-based microwave devices
Authors: Khare R. , Brown J. , Hu M. , Pierson D. , Melendes M. , Constantine C.
Published: July 2002

We report on a dry etch process for backside through-wafer via hole fabrication in InP-based transistors which addresses many manufacturing issues including wafer mounting schemes, degradation of the frontside ohmic metal pads, yield across two-inch wafers, and reliability issues. Low pressure electron cyclotron resonance plasma etching using a CH4/H2/Ar/Cl2 gas chemistry is investigated and compared to other InP via etching techniques. A photoresist mask was used to define 54 μm×54 μm backside vias in substrates thinned to ∼50 μm. Post-baking the resist served both to strengthen the mask against the plasma, and to control the profile of the through-via. The etching was performed at a temperature of 130 °C to enhance etch product volatility while allowing a reliable wax-mounting scheme for the thinned wafers. Etch rates of ∼1 μm/min were obtained for 950 W microwave power and 250 W rf power (−260 V). After ∼95% of the etched depth was achieved, the rf bias was reduced to minimize sputtering of the frontside metal pad on which the etch terminates. After the residual resist mask was removed, the samples were metalized, de-mounted, and tested for electrical connection, resulting in high yield via etching across the wafer.
Updated system model for x-ray lithography
Authors: Khan M. , Mohammad L. , Xiao J. , Ocola L. , Cerrina F.
Published: July 2002

We present an updated global model for x-ray lithography based on realistic models for image formation, demonstrating how the extendibility of x-ray lithography is well in the nanometer range. We apply these models to define the most convenient spectral range for x-ray lithography manufacturing and the parameters of mirrors and filters to be used in an optimized beam line.
Luminescence spectroscopy of dry etched single dots and wires
Authors: Hübner B. , Jacobs B. , Gréus Ch. , Zengerle R. , Forchel A.
Published: July 2002

Using spatially resolved luminescence spectroscopy we have measured the luminescence properties of single dry etched InP/InGaAs wires and dots. For fabrication of the test structures single quantum well samples grown by metalorganic vapor phase epitaxy were structured by e-beam lithography and subsequent dry etched with CH4, H2, and Ar at different bias voltages. The lateral dimensions of the wires and dots ranged from 10 μm down to 70 nm. The smallest structures that could be measured at room temperature and without surface passivation were 70 nm for wires and 100 nm for dots. By spatially resolved intensity scanning of mesa structures a characteristic intensity profile could be observed. Due to the inhomogeneous excitation and diffusion effects, a significant enhancement of the luminescence on the edges and corners of the structures can be seen even for nonovergrown samples.
Fabrication of arrays of nanometer size test structures for scanning probe microscope tips characterization*
Authors: Bogdanov A. L. , Erts D. , Nilsson B. , Olin H.
Published: July 2002

A problem in scanning probe microscopy (SPM) is the unknown shape of the probing tip. Generally, the image is a convolution between the shape of the tip and the surface. Information of the shape of the probe may be gained by imaging very sharp tips. Here we present a method for making two-dimensional arrays of very sharp tips. The tip arrays were made of silicon using electron beam lithography with subsequent ion-beam etching. To achieve the best possible resolution, ultrasonic excitation was used during development of the bilayered PMMA resist. Thus, openings in the resist with size nearly equal to the spot size of the writing e-beam have been obtained. A further decrease of the radius of the tips was obtained by the choice of appropriate thickness for the masking NiCr layer. The tips were conical with a height up to 100 nm with a radius of the tip down to 10 nm. The tips were suitable for study of the shape of AFM probe tips, under condition that the tip array samples were rinsed in water prior to the measurement. Without the rinsing procedure, strong sticking forces between the probe and the sample would have eroded both of them. The regularity of the array provided an easy way to calibrate the lateral motion of the scanner.
In situ GaAs/AlGaAs patterning using a thin epitaxial InGaAs layer mask as a negative-type electron-beam resist in Cl2 gas
Authors: Kohmoto S. , Sugimoto Y. , Takado N. , Asakawa K.
Published: July 2002

A very thin (50-Å) epitaxial In0.2Ga0.8As layer is used as a Cl2 etching mask for in situ electron-beam (EB) induced GaAs/AlGaAs patterning. Simultaneous EB/Cl2 exposure makes the In0.2Ga0.8As mask layer resistant to Cl2 etching, while the parts of the mask only exposed to Cl2 are easily etched off, resulting in negative-type pattern formation. The resistance of the EB/Cl2-exposed area depends on the In content in the InGaAs mask. Possible causes of this are discussed. Using this patterning technique, a GaAs/AlGaAs quantum well is fabricated into a dot-matrix pattern and the pattern is characterized by a cathodoluminescence measurement.
Synchrotron radiation x-ray photoelectron spectroscopy study of hydrogen-terminated Si surfaces and their oxidation mechanism
Authors: Yamamoto Ken-ichi , Hasegawa Masaki
Published: July 2002

The H-termination process on a Si(100) surface and the oxidation-inhibiting effects were investigated quantitatively by x-ray photoelectron spectroscopy using synchrotron radiation. The H-terminated Si(100) surface has two hydrogen-adsorption components (monohydride and dihydride). This article reports on the oxidation-inhibiting effects of each phase. The H termination of Si(100) surfaces (flat and tilted by 10°) was performed by supplying H atoms that were generated by the exposure of H2 gas to a heated tungsten filament. After that, the surface was exposed to O2 gas (1000 L) at room temperature. The magnitude change of two H-adsorption components in the Si 2p spectra and their peak shifts show a two-stage hydrogen adsorption process on the Si(100) surface. Oxidation of the monohydride phase (2×1-H) is reduced to less than 1/3 of that of a clean Si(100) surface, while that of the dihydride phase (1×1-2H) is reduced to below 1/9. Oxidation occurs more easily for the monohydride phase than for the dihydride phase. Further, the H-terminated Si(100) surface tilted by 10° was not more oxidized than the flat Si(100) surface. This suggests that atomic steps have little effect on oxidation.
Hot electron transport through metal–oxide–semiconductor structures studied by ballistic electron emission spectroscopy
Authors: Ludeke R. , Bauer A. , Cartier E.
Published: July 2002

The tip of a scanning tunneling microscope (STM) was used to inject electrons into thin Pt layers of metal–oxide–semiconductor (MOS) structures. The collector currents emanating from the n-type Si(100) substrates were measured as a function of the electron energy, determined by the STM tip bias VT, for different oxide biases Vox applied independently across the oxide layers. The SiO2 layers were thermally grown in a device processing line and ranged from 27 to 62 Å in thickness. A current threshold near VT=3.90 V is interpreted in terms of current transport through the SiO2 conduction band. The current transport through the MOS structure was modeled in a single band description for zero oxide thickness, and fitted to the collector currents that had been corrected for impact ionization effects in the Si. Deviations between the two curves represent the influence of the transmission probability Tox through the SiO2 film of finite thickness. Tox can thus be determined from the experimental data. Within an eV of threshold the magnitude of Tox was observed to be particularly sensitive to small changes in oxide bias in the range 0.3 V≳Vox≳−0.1 V. The transmission probabilities were also calculated by integrating the Boltzmann equation using Monte Carlo techniques that incorporate energy dependent effective masses and electron phonon scattering rates. Agreement between the two approaches is quite good, including the observed sensitivity on oxide bias in the threshold region, which is a direct consequence of the strong electron-optical phonon scattering in the oxide. The 27 Å thick oxide structures exhibited in the ballistic electron emission microscopy images scattered patches of high transmittance of only 1–2 nm in extent. The collector currents arising from injection at these patches indicated thresholds as low as 1.1 eV, but the observed modest currents above that threshold argue against local shorts that would arise from pinholes in the oxide.
Na/carbon-rich β-SiC(100) surface: Initial interface formation and metallization
Authors: Semond F. , Soukiassian P. , Mangat P. S. , di Cioccio L.
Published: July 2002

We investigate the room temperature interface formation of the Na/carbon-rich β-SiC(100) surface by core level and valence band photoemission spectroscopy using synchrotron radiation. The deposition of a Na layer at saturation coverage results in surface metallization as evident from the presence of plasmon loss features at core levels, and from a Fermi edge building-up in the valence band. Furthermore, large chemical shifts at both C 1s and Si 2p core level indicate reactive interface formation and surface disruption with significant adsorbate–substrate charge transfer. The Na–Si bond establishment leads to subsequent breaking of the C–Si bonds leaving additional C atoms on the surface as carbon/graphite clusters. Exposure of the Na/β-SiC(100) interface to a small amount of oxygen results in the removal of surface metallization.
Stability of CaF2/Si(111) and Al/CaF2/Si(111) interface systems studied with photoelectron spectroscopy and scanning-tunneling microscopy
Authors: Wen H. J. , Dähne-Prietsch M. , Bauer A. , Manke I. , Kaindl G.
Published: July 2002

The stability of CaF2/Si(111) and Al/CaF2/Si(111) interfaces under irradiation by light or electrons and upon thermal annealing was investigated by photoelectron spectroscopy and scanning-tunneling microscopy. Deposition of CaF2 on Si(111)7×7 at 700 °C leads to a shift of the Fermi-level position (EF) towards the Si valence-band maximum (VBM), while subsequent light irradiation results in a back-shift of EF towards its initial value. Upon flashing the irradiated surface at 700 °C, it shifts again towards the VBM. The variation of EF is assigned to a competition of interface states with surface states related to irradiation-induced fluorine vacancies. These surface defects are observed as localized surface charges in the scanning tunneling microscopy images. A thin epitaxial Al layer on top of the CaF2 surface strongly reduces the irradiation-induced effects and leads to a stabilization of EF at 0.30 eV above the VBM.
Formation of the CeSix/Si(111) interface
Authors: Manke I. , Wen H. J. , Höhr A. , Bauer A. , Dähne-Prietsch M. , Kaindl G.
Published: July 2002

The deposition of thin Ce films on Si(111) and subsequent or simultaneous annealing leads to the formation of various structurally, electronically, and chemically different CeSix phases, as revealed by scanning-tunneling microscopy, low-energy electron diffraction, and photoelectron spectroscopy. Several phases can coexist on the same sample, and with increasing annealing temperatures larger homogeneous domains are observed. This behavior is assigned to a mismatch of the lattices of the Si-rich CeSix bulk compounds with that of the Si(111) substrate surface, resulting at temperatures above 700 °C in the formation of a thin film of hexagonal CeSi1.67, which does not exist as a bulk compound.
Low temperature scanning tunneling microscopy studies of granular metal films
Authors: Bar-Sadeh E. , Goldstein Y. , Wolovelsky M. , Porath D. , Zhang C. , Deng H. , Abeles B. , Millo O.
Published: July 2002

Cryogenic scanning tunneling microscopy is used to study local electrical transport properties of thin granular Au/Al2O3 films in the vicinity of the percolation threshold. The current–voltage characteristics are found to vary dramatically from one tip position to another over distances of the order of a few nanometers. The characteristics often exhibit single electron tunneling effects such as the Coulomb blockade and the Coulomb staircase. This behavior is similar to that observed for tunneling into a single isolated nanometer size metallic particle which was explained in terms of a double-barrier tunnel junction model. Some of the characteristics show, however, novel Coulomb-staircase structures having unusual variations in step widths and heights due to complex tunneling paths. A triple-barrier tunnel junction model, where the electron tunnels through two metallic particles along its path, accounts quantitatively for the experimental results.
Surfactant assisted growth of 850 nm light modulators
Authors: Cunningham J. E. , Goossen K. W. , Jan W. , Williams M. D.
Published: July 2002

We compare growth of multiple quantum well modulators atop a p-type or n-type AlGaAs layer. We find the excitonic absorption edge of the quantum wells broadens 30% less under applied field when grown on a p-down AlGaAs layer compared to the n-down case. Auger spectroscopy shows Be surface concentration builds up to 0.3 ML on the p-type AlGaAs layer whereas Si is smaller than 0.07 ML on an n-type AlGaAs layer. X-ray diffraction reveals quantum well crystallinity and interfacial roughness to be improved when grown on p-down AlGaAs layer. We conclude Be is a surfactant that assists AlGaAs epitaxy.
Performance enhancements on IBM’s EL-4 electron-beam lithography system
Authors: Butsch R. , Enichen W. A. , Gordon M. S. , Groves T. R. , Hartley J. G. , Pavick J. W. , Pfeiffer H. C. , Quickle R. J. , Rockrohr J. D. , Stickel W.
Published: July 2002

IBM’s latest electron-beam mask maker, EL-4, is installed at IBM’s Advanced Mask Facility in Essex Junction, Vermont. The EL-4 system is a 75 kV variable-shaped-beam lithography system designed to produce 1X or NX masks for 0.25 μm lithography ground rules, extendable to 0.13 μm. It is currently producing NIST-style x-ray membrane masks with pattern sizes up to 50×50 mm2. After a brief description of the EL-4 tool and its operating features, the article describes the recently implemented new writing subsystem, provides an overview of the tool software structure, and presents measurement data from masks recently produced on the tool.
Nanoscale layer removal of metal surfaces by scanning probe microscope scratching
Authors: Sumomogi T. , Endo T. , Kuwahara K. , Kaneko R.
Published: July 2002

This paper describes micromachining of metal surfaces in air by a scanning probe microscope (SPM) which has a very sharp diamond tip mounted on the end of the cantilever beam. The sample surface of Ni is prepared by mechanical polishing from commercially available pure metal bulks. The sample surface is scanning scratched by a diamond tip with a scan width of 0.5–3 μm and a loading force of 0.5–10 μN, and topographies of the scratched area are observed by the same SPM with a loading force of less than 0.1 μN. Flat square hollows of nanometer-scale depth are obtained. The scratched depth is increased with increasing loading force and repetition numbers of scratching. The scratched depth is also strongly dependent on numbers of x direction scan line, but scarcely on x direction scan rate and x–y direction scan width. Results obtained indicate that the nanoscale thickness material removal can be controlled.
Effect of absorber thickness on image shortening in x-ray lithography
Authors: Maldonado J. R. , DellaGuardia R. , Hector S. , McCord M. , Liebmann L. , Oertel H. K.
Published: July 2002

Image shortening effects have been shown to be a problem for pattern replication using current optical tools. However, a previous study [R. DellaGuardia, J. R. Maldonado, and H. Oertel, J. Vac. Sci. Technol. B 12, 3936 (1994)] indicated that image shortening is less pronounced when pattern replication is performed using x-ray lithography. This article describes the effect of absorber thickness on the image shortening observed in x-ray lithography. The goal is to determine the optimum absorber thickness that minimizes image shortening when replicating complex patterns with the x-ray spectrum from the HELIOS storage ring installed at the IBM Advanced Lithography Facility. To study these effects, an x-ray mask with four quadrants, each having different gold thickness, was fabricated using the IBM vector scan (VS-5) electron-beam system. The mask contains challenging patterns used in IBM devices with ground rules from 0.4 μm down to 0.15 μm. The image shortening effects for different mask/wafer gaps, various line shapes, and feature sizes will be presented in this article. In addition, experimental results with conventional and chemically amplified resists will be presented to shed light on the role of resist in image shortening.
Collimated sputter deposition, a novel method for large area deposition of Spindt type field emission tips
Authors: van Veen G. N. A. , Theunissen B. , van de Heuvel K. , Horne R. , Burgmans A. L. J.
Published: July 2002

A new technique has been developed to manufacture Spindt type field emission (FE) cathodes. It is called collimated sputter deposition (CSD). A standard sputter deposition machine can be utilized to which a direction selecting filter is added. The particles passing the collimator are incident on the integrated field emission structure. As a result the holes in the gate are closed and tips are formed. A number of collimator configurations has been considered. The influence of the dominating process parameters is investigated. Several tip materials have been tested. FE results on tips manufactured by means of CSD are presented.
Simulation of time-dependent quantum transport in field emission from semiconductors: Complications due to scattering, surface density, and temperature
Authors: Jensen K. L.
Published: July 2002

The prediction of electron emission characteristics from semiconductors is difficult due to the extreme conditions (e.g., band-bending effects, high field, etc.) under which field emitting arrays (FEAs) operate in vacuum microelectronics applications. A fundamental quantum transport theory that incorporates semiconductor properties is needed for understanding of limitations of semiconductor FEA device performance, as the assumptions inherent in the low-field transmission-coefficient based approach are not adequate. Here, the Wigner distribution function (WDF) approach to quantum transport has been used to successfully determine the self-consistent potential, density, and current characteristics in a time-dependent simulation. The self-consistent potential is affected by the temperature- and electron density-dependent scattering operator. The field in vacuum was determined solely by the boundary conditions, and was not fixed a priori. The behavior of the WDF is shown to be compatible with the needs of a hybrid scheme in which the supply function in a transmission coefficient-based approach is supplied by the WDF, thereby allowing for a computationally tractable and robust method for estimating emission behavior from semiconductors.
Error budget analysis of the SCALPEL(R) mask for sub-0.2 μm lithography
Authors: Liddle J. Alexander , Huggins Harold A. , Watson G. Patrick
Published: July 2002

In this article we derive the design constraints, and hence the fabrication requirements, for the SCALPEL(R) mask for sub-0.2 μm design rules. These are determined by the Semiconductor Industry Association (SIA) advanced mask specifications, in combination with the likely error budget of an advanced pattern generator. Further constraints are imposed by the overall SCALPEL system error budget. We demonstrate that the mask is not only technically feasible to construct, but also that it can be fabricated at an acceptable cost.
Real time statistical process control for improved etch tool performances
Authors: Smith Gene , Highberg Ivar
Published: July 2002

Through the use of a commercially available computer integrated manufacturing software package, it has been shown that the efficiency of a batch reactive ion etch reactor has increased dramatically. Standard statistical process control methodology has been applied to process input parameters in eliminating the need to run periodic ‘‘process qualification tests,’’ identify lot-to-lot variations, and to improve the scheduling of preventative maintenance functions. These techniques have shown an increase in the first pass yield, by reducing scrap, and have proven invaluable in both process development and optimization. This has in turn increased the capacity and extended the capability of the tool. These techniques are straightforward and can be applied to other tools with potentially similar results.
Metal contamination of silicon wafers induced by reactive ion etching plasmas and its behavior upon subsequent cleaning procedures
Authors: Verdonck Patrick , Hasenack Claus Martin , Mansano Ronaldo Domingues
Published: July 2002

Reactive ion etching (RIE) causes several types of damage in fabrication of integrated circuits. In this article the metallic contamination content of silicon wafer surfaces after performing RIE plasmas has been measured by total reflection x-ray fluorescence. The dependence of the contamination content on different electrode materials was investigated and could be shown to be mainly a function of the electrode material, not as much as of the rest of the material of which the reactor is built. In order to remove the metals found on the wafer surface after RIE, different cleaning cycles were applied to the wafers and it could be shown that the standard RCA cleaning, followed by a HF dip, works well for most contaminants, with the exception of Cu and Ni. In particular, it was found that Ni deposited onto a silicon surface as a consequence of a RIE type plasma cannot be removed by a standard RCA clean. There are strong indications that Ni is not deposited in the form of atoms, but that a stable nickel silicide is formed.
Effect of molecular weight on poly(methyl methacrylate) resolution
Authors: Khoury Maroun , Ferry David K.
Published: July 2002

Electron-beam lithography’s resolution limit is greater than the beam diameter due to resist limitations as well as electron interaction with solids. We examine the effect of molecular weight on the resolution of poly(methyl methacrylate) (PMMA). The experimental procedure uses thin Si3N4 in order to reduce the backscattered electron contribution to the exposure, and the resist contrast standard deviation σ was determined. Molecular weights of 950×103, 120×103, and 15×103 amu were used. It is found that relatively equivalent exposure and resolution are found in each case, and that the entanglement threshold is either lower than thought, or is not a factor in the resolution of PMMA. Lines as small as 7 nm are found in the highest molecular weight.
Experimental investigation of the increase in depth resolution obtained through the use of maximum entropy deconvolution of secondary ion mass spectrometry depth profiles
Authors: Cooke G. A. , Dowsett M. G. , Phillips P.
Published: July 2002

Depth profiling using secondary ion mass spectrometry (SIMS) provides profiles of high sensitivity and depth resolution. To obtain the greatest depth resolution, low energy probes must be employed to minimize the redistribution of the sample. However, there is a lower limit beyond which further reduction in energy causes a decrease in ion and sputter yields to a point where sensitive SIMS is no longer possible. Also, with most ion guns, a reduction in energy brings a dramatic loss of current leading to unrealistically long analysis times. To overcome these problems a deconvolution method may be employed to extract the maximum amount of information from data acquired at a higher energy. In this article we experimentally investigate the extent to which the maximum entropy deconvolution method may enhance the depth resolution, by studying its effect on a sample containing closely spaced delta layers near the conventional SIMS depth resolution limit.
Scanning tunneling microscopy studies and computer simulations of annealing of gold films
Authors: Porath D. , Millo O. , Gersten J. I.
Published: July 2002

The effect of thermal annealing on the surface morphology of thin gold films is studied using a scanning tunneling microscope (STM) and computer simulations. The gold films were thermally evaporated onto glass substrates, and were then measured with the STM at room temperature before and after annealing. The annealing treatments were done at temperatures between 200 and 500 °C and for periods ranging from 1 to 200 h. We present data showing the evolution of the average surface-grain size and root-mean-square roughness amplitude of the gold films as a function of annealing temperature and duration. Our data suggest that surface diffusion is the main process active at low annealing temperatures of 300 °C and below. At higher annealing temperatures grain coarsening, which can be explained by recovery and recrystallization (secondary grain growth), is the dominant process contributing to large scale morphology changes. Computer simulations based on these processes account well for the experimental results, with activation energies of about 1.0 and 1.4 eV, for surface self-diffusion of gold and grain coarsening, respectively.
One- and two-dimensional carrier profiling in semiconductors by nanospreading resistance profiling
Authors: De Wolf P. , Clarysse T. , Vandervorst W. , Snauwaert J. , Hellemans L.
Published: July 2002

Measurement of the carrier concentrations in silicon with lateral and in-depth resolution on the sub-100 nm scale has been demonstrated with an atomic force microscope (AFM) using conducting tips. The technique determines the local spreading resistance and hence inherits the attractive features of the conventional spreading resistance profiling (SRP) technique and will be referred to as nano-SRP. For instance, the calibration curve established by measuring homogeneously doped substrates indicates a dynamic range of concentrations between 1014 and 1019 cm−3 and a monotonic relation between resistance and resistivity, similar to a conventional SRP calibration curve. In the present study, W-coated diamond tips are used at a precisely controlled force of 70 μN, leading to a contact radius of 50 nm as determined from AFM analysis of the resulting imprints. The drastic reduction of the contact size implies that one can measure directly on a vertical cross section of the structure and overcome some limitations created by the beveling step. Moreover, the applicability to a cross section implies that one can determine with high resolution the in-depth as well as the lateral carrier distributions, which is not feasible with conventional SRP. The nano-SRP technique has been applied to measure the carrier distribution in several types of submicron structures: pn junctions, two-dimensional implanted and diffused layers. A comparison shows that the different measurement geometries (bevel versus cross section) lead to the expected differences in carrier spilling.