bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron-beam cell projection lithography: A new high-throughput electron-beam direct-writing technology using a specially tailored Si aperture
Authors: Nakayama Y. , Okazaki S. , Saitou N. , Wakabayashi H.
Published: July 2002

Electron-beam cell projection lithography realizes a high throughput capability suitable for ultra-large-scale integration (ULSI) manufacturing. This method makes it possible to drastically reduce the number of electron-beam exposure shots by utilizing a specially shaped beam. This shaped beam is created by an Si aperture which forms various shapes, coinciding with the array of each unit cell of an ULSI pattern. The aperture also forms a rectangular shape for conventional variable-shaped method in order to create random patterns. An aperture made of a single crystal of Si is fabricated using ULSI process techniques. As the reduction ratio of electron optics is larger than that of an optical stepper, pattern size errors caused by aperture inaccuracies can be reduced significantly.
Proximity correction using computer aided proximity correction (CAPROX): Evaluation and application
Authors: Hintermaier M. , Hofmann U. , Hübner B. , Kalus C. K. , Knapek E. , Koops H. W. P. , Schlager R. , Seebald E. , Weber M.
Published: July 2002

Direct write electron beam lithography requires proximity effect correction to achieve high fidelity. CAPROX (computer aided proximity correction) serves this purpose. It preserves hierarchy as far as possible, thus reducing memory and CPU time. The program guides the evaluation of the correction parameters. The need for and the result of correction is judged evaluating exposures written at a reduced dose in optical white light interference contrast microscopy. If the color observed in large and small structures is equal, no poximity effect correction is necessary. We applied CAPROX to correct structures written in positive and negative resists using the Philips EBPG-4 and the JEOL JBX-5D11 beam writer. The proximity effect correction is indispensable for the fabrication of an ACMOS-ASIC with 1 μm minimum features written in 1.8 μm thick negative resist.
Scanning probe tip geometry optimized for metrology by focused ion beam ion milling
Authors: Vasile M. J. , Grigg D. , Griffith J. E. , Fitzgerald E. , Russell P. E.
Published: July 2002

We have developed a novel technique for producing tips for scanning probe microscopy. The shape of the tip is optimized for applications where high aspect ratio surface topography is the norm, as with integrated circuit structures. The technique involves focused ion beam (FIB) milling of a tip which was previously shaped to a nominal geometry by electrochemical etching. The ion milling pattern is annular, and the ion beam is collinear with the axis of the tip. The process allows control of the ion milling dose using 20 keV Ga+ with submicron control of the annular patterns. The result is a narrow, tapered structure approximately 20 μm in length which ends in a point with a radius of curvature between 30 and 50 nm when grains dominate the sputter process, and radii of about 3–4 nm when there is no evidence of grain structure effects. This microstructure is 3 μm in diameter at the base and it protrudes from a portion of the shank of the macrostructure where the diameter is about 15 μm. We have sufficient control over the sputter process to yield the final tip length, taper, and radius. Cone angles between 12° and 15° over the first two microns from the apex can be achieved routinely, by the correct choice of annulus and ion dose. Sputter simulations predict the correct shape of the final tip profile, and show the effect of varying the ion beam focus, dose, and inner and outer annulus radii. Tips with the desired geometry have been produced in polycrystalline tungsten, iridium, and platinum-iridium. Significant improvements in scanning tip microscopy (STM) images have been consistently observed with these FIB milled tips.
Projection x-ray lithography using computer-generated holograms: A study of compatibility with proximity lithography
Authors: Jacobsen Chris , Howells Malcolm
Published: July 2002

X-ray projection lithography has recently been explored as a method for the manufacture of ≤200 nm linewidth integrated circuits. A method was previously described [J. Appl. Phys. 71, 2993 (1992)] whereby projected lithographic images can be formed with x rays by means of a transmission hologram. The form of the hologram is computed by an algorithm which eliminates the unwanted signals normally present as systematic errors in in-line holographic images. Such an approach to projection x-ray lithography requires an x-ray beam with very little coherence and is thus compatible with high wafer throughput schemes; in addition, image fidelity remains high even when moderately small contaminant particles block the light from small regions of the hologram. Previous example calculations involved using 5 nm x rays to illuminate a 0–1 μm thick carbon hologram located 200 μm from the wafer to produce simulated 0.06 μm linewidth images with good fidelity and with 6 μm depth of field. Presented here are simulations involving holographic masks made of 0–1 μm of tungsten operating at 1 nm wavelength with 50 μm mask-to-wafer gap. Such a configuration can be viewed as a future extension of the existing technology of proximity x-ray lithography to linewidths as small as 0.02 μm.
Low voltage, high resolution studies of electron beam resist exposure and proximity effect
Authors: McCord M. A. , Newman T. H.
Published: July 2002

Resist exposure characteristics have been studied over a voltage range from 1 to 10 kV in order to demonstrate the feasibility of using low voltage electron beam lithography (EBL) to pattern submicron features without the proximity effect problems seen at higher voltages. The exposures were done by modifying a 25 kV thermal field emission EBL machine to run in a retarding field configuration where the sample is biased at a large negative potential, thus reducing the final beam landing energy. After analyzing the linewidths of various proximity test patterns with features as small as 0.15 μm, we conclude that at these dimensions the proximity effect on silicon substrates, compared to 10 kV, is greatly reduced at 5 kV and almost negligible at 3 kV. In order to maintain resolution at these low voltages, it is normally necessary to reduce the beam current due to increased aberrations and reduced source brightness. However, calculations and experiments show that these problems are much less severe in the retarding field configuration, where the electron beam is accelerated to a high potential through most of the optical path length and then reduced to the working voltage just before striking the workpiece. In addition, the reduced beam current is compensated by an almost corresponding increase in the resist sensitivity. Thus, low voltage is shown to be an effective means of avoiding the proximity effect, and a tool using the combination of a thermal field emission electron source and a retarding field final lens is shown to have the resolution and beam current required to expose patterns at the required voltage with reasonable throughput.
In situ ellipsometry and reflectometry during etching of patterned surfaces: Experiments and simulations
Authors: Haverlag M. , Oehrlein G. S.
Published: July 2002

To address the question whether it is possible to perform in situ end point detection during etching using ellipsometry on patterned wafers, a number of experiments were performed on wafers that were covered with a photoresist line pattern on an oxide-covered silicon substrate. Two situations were investigated, one in which the probe beam was directed parallel to the line pattern, and one in which the probe beam was perpendicular to the lines. For each situation, a separate ellipsometric model was developed. Employing photoresist and SiO2 etch rates measured with blanket wafers, a good fit between the experimental curves and the simulations was obtained. Though the agreement between modeling and experiment is good, it is shown that the applicability of ellipsometry for end point detection on patterned wafers depends on the aspect ratio of etched holes, the selectivity of the etching process, and the pattern factor (the unmasked area fraction of the wafer). For comparison, experiments and simulations were also performed with a laser interferometer at normal incidence. In this case, only the selectivity and the pattern factor are important. It has been shown that the selectivity of the process becomes less important if the derivative of the reflectivity is used as an end point signal instead of the reflectivity itself. To optimize the end point signal for this method the wavelength can be used to maximize the change in the reflectivity slope at the end point of the process.
Etching of photoresist using oxygen plasma generated by a multipolar electron cyclotron resonance source
Authors: Pang S. W. , Sung K. T. , Ko K. K.
Published: July 2002

Etching of photoresist in an O2 plasma generated by an electron cyclotron resonance source (ECR) was investigated. The ECR source was a microwave multipolar reactor at 2.45 GHz, and the stage was connected to a rf power supply at 13.56 MHz. Effects of microwave power, rf power, ECR source to sample distance, and pressure on photoresist etch rate were characterized. It has been found that the photoresist etch rate increases with microwave and rf power, but decreases with source to sample distance. With microwave power at 1000 W and rf power at 300 W, smooth morphology and fast etch rate at 1.61 μm/min were obtained. Self-induced dc bias voltage increases with rf power and source to sample distance, but decreases with microwave power. Etch rate uniformity better than 0.5% was obtained across 7.5 cm diam wafer even with a very close source to sample distance of 3 cm. Etch profile can be varied depending on the etch conditions. Vertical profile in polyimide has been obtained using a trilayer resist scheme.
Growth and properties of high mobility strained inverted AlInAs–GaInAs modulation doped structures
Authors: Brown A. S. , Nguyen L. D. , Metzger R. A. , Schmitz A. E. , Henige J. A.
Published: July 2002

GaInAs–AlInAs inverted modulation-doped structures exhibit degraded two-dimensional electron gas (2DEG) transport properties when grown under standard conditions. This results from the surface segregation of Si from the donor layer into the GaInAs channel layer. Consequently, the 2DEG has poor mobility due to increased ionized impurity scattering. We have obtained high mobility inverted structures through the inhibition of this surface segregation by growing the spacer layer at a greatly reduced substrate temperature. Inverted modulation doped structures optimized for high frequency device applications require the use of thin channel layers. In order to obtain a large charge density (≳ 2.3 × 1012 cm−2) with high quality transport characteristics, In-rich, strained channels are required. This paper presents the results of an investigation of the electronic and optical properties of strained, inverted, thin-channel modulation doped structures. Channel thicknesses of 50–200 Å and In compositions of 53% to 80% were investigated. A 300 K electron mobility of 13 000 cm2/V s was obtained with a sheet charge density of 2.4 × 1012 cm−2 for a 75 Å thick Ga0.27In0.73As channel.
Measurement of AlP/GaP (001) heterojunction band offsets by x-ray photoemission spectroscopy
Authors: Waldrop J. R. , Grant R. W. , Kraut E. A.
Published: July 2002

X-ray photoemission spectroscopy has been used to measure the valence band offset ΔEυ for the AlP/GaP (001) heterojunction interface. The heterojunction samples were prepared by molecular-beam epitaxy. A value of ΔEυ=0.43 eV is obtained (staggered band alignment, with AlP valence band below that of GaP).
Parametric modeling of photoelectron effects in x-ray lithography
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 secondaries, as well as the generation of a shower of low-energy electrons. The development of accurate models for the image formation in x-ray lithography requires that this mechanism be included. The electronic 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 simplified model can be obtained by separating elastic and inelastic interactions. The elastic interactions are treated with atomic Mott cross sections, and the inelastic interactions by a continuous slowing down approximation based on the dielectric response function. The model accounts for all the physical interactions of interest, and includes tabulated values for ε from published data. These models were incorporated in a Monte Carlo simulation code and have successfully benchmarked it with published results of Murata et al. [Optik 84, 163 (1990)]. The low efficiency of the Monte Carlo method motivates the need to parameterize the energy redistribution results from the simulation. This parameterization was performed, for a given material, in two steps: First, as a function of the photoelectron initial kinetic energy and then as a function of the photon energy. Parameterization as a function of the photoelectron initial kinetic energy is interpreted as a response of the medium to a particular electron. The parameterization as a function of the photon energy is the weighted sum of individual electron responses, according to the electrons emitted. Both can be used as point-spread functions as appropriate.
Fabrication of sub-10 nm structures by lift-off and by etching after electron-beam exposure of poly(methylmethacrylate) resist on solid substrates
Authors: Chen Wei , Ahmed Haroon
Published: July 2002

Sub-10 nm structures were fabricated by lift-off and by etching following electron-beam exposure of poly(methylmethacrylate) (PMMA) resist on solid semiconductor substrates. Electron beam lithography at 80 kV with a beam diameter smaller than 5 nm was used to expose PMMA resist on either Si or GaAs substrates. The exposed resist was developed with a 3:7 cellosolve:methanol mixture in an ultrasonic bath for 5 s followed by rinsing in IPA and blown dry with pure nitrogen. Ultrasonic agitation during development was found to be essential for forming sub-10 nm structures in PMMA. The patterned PMMA resist was used either as a lift-off mask or an etching mask and successful transfer of the pattern to the substrates was achieved. For lift-off an ionized beam deposition method, which gives smaller grain size and better adhesion of the metal film to the substrate, was used to deposit a layer of AuPd. Metal dots with sub-10 nm diam and metal structures with sub-10 nm gaps were fabricated. For sub-10 nm etched structures reactive ion etching was used to transfer either the PMMA pattern or the lift-off metal pattern to either Si or GaAs substrates. Etched lines and pillars with dimensions smaller than 10 nm were obtained.
Via hole process for GaAs monolithic microwave integrated circuit using two-step dry etching
Authors: Chung M. S. , Kim H. R. , Lee J. E. , Kang B. K. , Kim B. M.
Published: July 2002

A fast, reproducible, and reliable via hole dry etching process for GaAs monolithic microwave integrated circuit (MMIC) fabrication is described. The etching process consists of two steps. During the first etching step, BCl3/Cl2/Ar gas mixture is used to achieve a high etch rate and small lateral etching. In the second etching step, CCl2F2 gas is used to achieve a selective etching of the GaAs substrate with respect to the front side metal layer, which is 500 Å thick chromium. Via holes are formed from the back side of a 100 μm thick GaAs substrate and are electroplated with gold (∼20 μm thick). The resulting via hole profile and surface morphology are satisfactory for reproducible and reliable MMIC via groundings.
External photoluminescence efficiency and minority carrier lifetime of (Al,Ga)As/GaAs multi-quantum-well samples grown by molecular beam epitaxy using both As2 and As4
Authors: Foxon C. T. , Cheng T. S. , Dawson P. , Lacklison D. E. , Orton J. W. , Van der Vleuten W. , Hughes O. H. , Henini M.
Published: July 2002

We report the results of measurement of the external photoluminescence efficiency and minority carrier lifetime of a series of n- and p-type (AlGa)As–GaAs multi-quantum-well samples grown by molecular beam epitaxy, as a function of growth temperature in the range 600 to 700 °C, using both As2 and As4. For equivalent growth conditions (substrate temperature and arsenic species) the minority carrier lifetimes in n- and p-type samples are found to be the same. We suggest that the lifetimes are determined by recombination via deep centers (possibly oxygen-related) close to the (AlGa)As/GaAs interface. For an individual sample there is a good correlation between the variations in lifetime and external efficiency across a wafer, the variation being ascribed to temperature differences resulting from poor wetting with In. A much weaker correlation is observed from sample to sample, suggesting that there are factors other than the internal photoluminescence efficiency that determine the light emitted from the surface. We tentatively suggest that morphology may be a factor.
Tunneling microscopy verification of an x-ray scattering-derived molecular model of tyrosine-based melanin
Authors: Zajac G. W. , Gallas J. M. , Alvarado-Swaisgood A. E.
Published: July 2002

The molecular structure of melanins has been a focus of study for many years and only recently has a molecular model (MM) been proposed based upon x-ray scattering results. In order to test the validity of the model, scanning tunneling microscopy (STM) and spectroscopy have been performed on the same tyrosine-derived melanin, which has been characterized in the x-ray scattering studies and has been shown to exhibit characteristics of natural melanins. The STM measurements of the lateral and vertical dimensions provide a characteristic fundamental size which agree well with the x-ray scattering-derived MM. We find that the compact three-dimensional structure is best described as a planar morphology of finite lateral extent (≊2 nm) with a vertical extent (<1 nm) which is believed to consist of stacks of a basic two-dimensional amorphous polymer of 5,6 indolequinone units. Molecular mechanics and orbital calculations of representative amorphous models support the x-ray scattering and STM results.
Fabrication of noble-metal nanoconstrictions and observation of conductance fluctuations
Authors: Scheer E. , Löhneysen H. v. , Hein H.
Published: July 2002

We describe the fabrication of planar metallic nanostructures with lateral dimensions down to about 80 nm and thicknesses varying from 15 to 50 nm. We use a lift-off process with a polymethylmethacerylate bilayer resist on silicon substrate and an electron beam writer system for microfabrication. The noble-metal layers are deposited by thermal evaporation. The geometries are point contacts, rings, and wires in two-lead configuration. We discuss measurements of the magnetoconductance at very low temperatures and in magnetic fields up to 4 T in dependence of the width of the samples. Here the electron transport is in the diffusive regime and the width dependence of the universal conductance fluctuations is investigated.
Scanning tunneling microscopy investigation of bainite in steel
Authors: Yan Jun-jue , Yu Hong-bin , Ge Zheng , Huang Yun , Fang Hong-sheng , Wang Jia-jun , Yang Zhi-gang , Deng Xu-rui
Published: July 2002

In the present work, scanning tunneling microscopy has been used to study Bainite steel surfaces prepared by polishing and etching, and then covered with a layer of glycerol. The success of sample preparation method of this work offers a general way of studying easy-oxidized metal surfaces in an ambient environment. It is found that Bainitic ferrite is composed of structural units much smaller than subunits that are generally accepted as the smallest building block of Bainitic ferrite and that the structural units at different levels have certain self-similarity, an important characteristic of fractals. Two kinds of fractal dimension calculations have been carried out. The straight line in the ln–ln plot of scan size versus the number of ‘‘boxes’’, as well as the obtained fractal dimension, DB = 2.74, indicate that Bainitic ferrite is a sort of self-embedded fractal, at least in the scale range of the images.
Subatmospheric chemical vapor deposition ozone/TEOS process for SiO2 trench filling
Authors: Shareef I. A. , Rubloff G. W. , Anderle M. , Gill W. N. , Cotte J. , Kim D. H.
Published: July 2002

Ozone/TEOS thermal chemical vapor deposition (CVD) has been investigated for SiO2 deposition on Si, using a cold-wall research reactor equipped to determine the effects of precursor concentration, deposition temperature (300–500 °C), and pressure (30–200 Torr) on deposition rates, etch rates, and step coverage in the regime of subatmospheric CVD (SACVD). Deposition rates first increase with substrate temperature then reach a maximum and finally decrease distinctly at higher temperatures, with the latter reflective of reactant depletion in the gas phase. Wet etch rates decrease at higher deposition temperature and higher ozone/TEOS ratio, indicating improved film quality under these conditions. Elevated deposition temperatures significantly improves step coverage in high-aspect-ratio trenches, but decreases deposition rates. Deposition rates increase and then saturate with TEOS concentration, suggesting rate-limited behavior associated with lack of ozone.
Fabrication of photonic band-gap crystals
Authors: Cheng C. C. , Scherer A.
Published: July 2002

We describe the fabrication of three-dimensional photonic crystals using a reproducible and reliable procedure consisting of electron beam lithography followed by a sequence of dry etching steps. Careful fabrication has enabled us to define photonic crystals with 280 nm holes defined with 350 nm center to center spacings in GaAsP and GaAs epilayers. We construct these photonic crystals by transferring a submicron pattern of holes from 70-nm-thick polymethylmethacrylate resist layers into 300-nm-thick silicon dioxide ion etch masks, and then anisotropically angle etching the III-V semiconductor material using this mask. Here, we show the procedure used to generate photonic crystals with up to four lattice periods depth.
Electron microscopy characterization of GaN films grown by molecular-beam epitaxy on sapphire and SiC
Authors: Liliental-Weber Zuzanna , Sohn Hyunchul , Newman Nathan , Washburn Jack
Published: July 2002

Transmission electron microscopy was used for the characterization of GaN epitaxial layers grown by molecular-beam epitaxy on two different substrates: sapphire (Al2O3) and 6H-SiC. GaN layers grown on both substrates crystallize with the wurtzite structure. Despite the very different lattice mismatch associated with their two substrates, similar types of defects were formed in the GaN layer; only their density differed. In addition to small-angle subgrain boundaries two other types of defects were seen in cross-sectioned samples: defects parallel to the growth surface and microtwins with a width of about 8–10 nm perpendicular to the growth surface. The parallel defects were identified as stacking faults leading to a local fcc atom arrangement in the layer and are believed to be growth defects. The density of these faults decreased with layer thickness. However, the density of the vertical microtwins remained constant through the layer. Slight local lattice twists between the microtwins and surrounding areas or differences of stoichiometry are suggested as an explanation for the observed contrast of the high-resolution images.
Correlation between contact-electrified charge groups on a thin silicon oxide
Authors: Uchihashi Takayuki , Okusako Takahiro , Sugawara Yasuhiro , Yamanishi Yoshiki , Oasa Takahiko , Morita Seizo
Published: July 2002

Proximity effects of charge groups deposited by contact electrification on thin silicon oxide in air were investigated using a modified atomic force microscope. For initial separations L of L∼3.0 μm, oppositely charged groups recede from each other in distance with time after contact electrification. On the other hand, a couple of negative (unipolar) charge groups approach each other with time. These features are contrary to the expected approach or recession due to the Coulomb attractive or repulsive force, respectively. Furthermore, the critical time tc of a stable–unstable phase transition of negative charges becomes shorter or longer due to the proximity effects by the opposite or same charge groups, respectively. These proximity effects seem to be induced by the interplay of the Coulomb force and the surface charge diffusion.
Spatial and energy variation of the local density of states in the charge density wave phase of 2H–NbSe2
Authors: Mallet P. , Sacks W. , Roditchev D. , Défourneau D. , Klein J.
Published: July 2002

Using low-temperature scanning tunneling microscopy, detailed aspects of the charge density wave state in 2H–NbSe2 have been investigated by exploiting both the spectroscopic and topographic mode. The images are examined as a function of bias voltage and tip-to-surface distance. It is shown that the local density of states in the charge density wave phase is sensitive to the bias voltage, and especially to its sign, revealing the complexity of the electronic structure near the Fermi energy. In particular, for the first time a bias-dependent contrast in the charge density wave phase of 2H–NbSe2 was observed. This contrast must come from the spatial separation between the occupied and unoccupied electronic states responsible for the charge density wave.
Analysis of ultrashallow doping profiles obtained by low energy ion implantation
Authors: Parab K. B. , Yang S.-H. , Morris S. J. , Tian S. , Tasch A. F. , Kamenitsa D. , Simonton R. , Magee C.
Published: July 2002

Deep submicron (<0.35 mm) devices in future generations of integrated circuit technology will require ultrashallow source/drain junctions. Ion implantation has long been used extensively in junction formation and will be a vitally important process for the fabrication of ultrashallow junctions. However, implant channeling needs to be understood and minimized. This article presents the results of a detailed experimental analysis of the dependence of low energy boron, BF2, and arsenic as-implanted profiles on the implant tilt angle and rotation angle. The dopant impurities were implanted at very low energies of 5 and 10 keV into crystalline silicon directly. The resultant impurity profiles were measured by secondary ion mass spectroscopy using low energy primary ions. The behavior of the impurity profiles has been analyzed in terms of their dependence on tilt angle (0°–10°) and rotation angle (0°–360°). The profiles exhibit a strong dependence on tilt angle while the dependence on rotation angle is less pronounced for boron and arsenic. The rotation angle dependence of the profiles is almost negligible for BF2 at these very low implant energies. It is found that the dependence of the impurity doping profiles on rotation angle decreases with decreasing implant energy. This information on ultrashallow implanted profiles is important for the development of low energy implantation models for process simulators, for the development of scaled devices with ultrashallow junctions, and for a better understanding of process control requirements in manufacturing.
Scanning Hall probe microscopy of superconductors and magnetic materials
Authors: Oral A. , Bending S. J. , Henini M.
Published: July 2002

We describe results from a scanning Hall probe microscope operating in a broad temperature range, 4–300 K. A submicron Hall probe manufactured in a GaAs/AlGaAs two-dimensional electron gas is scanned over the sample to measure the surface magnetic fields using conventional scanning tunneling microscopy positioning techniques. The magnetic field structure of the sample together with the topography can be obtained simultaneously. The technique is noninvasive with an extremely low self-field of <10−2 G and yields a quantitative measurement of the surface magnetic field in contrast to magnetic force microscopy. In addition the microscope has an outstanding magnetic field resolution (∼1.1×10−3 G/√Hz at 77 K) and high spatial resolution, ∼0.85 μm. Images of individual vortices in a high-Tc Y1Ba2Cu3O7−δ thin film at low temperatures and magnetic domains in an Fe-garnet crystal at room temperature are presented.
Smooth etching of various III/V and II/VI semiconductors by Cl2 reactive ion beam etching
Authors: Yoshikawa T. , Sugimoto Y. , Sakata Y. , Takeuchi T. , Yamamoto M. , Hotta H. , Kohmoto S. , Asakawa K.
Published: July 2002

Smooth etching by Cl2 reactive ion beam etching is performed on various III/V or II/VI compound semiconductors, such as InP, GaAs, ZnSe, and ZnTe. These can be properly etched only under one set of conditions: high substrate temperature (∼200 °C), high ion energy (∼1 keV), and low gas pressure (∼3×10−5 Torr). The smoothness of a 1 μm etched surface was estimated by surface tunneling microscopy to be only 1.4 nm, comparable to its smoothness before etching, 0.9 nm. The etched surface was clean and without C or O contamination as estimated by in situ Auger electron spectroscopy. Although etching damage from high ion energy was a concern, maximum damage depth was found to be less than 150 nm, and damage to the etched sidewall was negligible. Laser diodes and photodetectors were fabricated using this etching technique, and these had reliability and other characteristics comparable to conventional devices.
Effect of fluorine concentration on the etch characteristics of fluorinated tetraethylorthosilicate films
Authors: Allen Lynn R.
Published: July 2002

Fluorinated silicon dioxide films have generated much interest as potential low dielectric constant materials for use in back end interconnect technologies in microelectronics manufacturing. A recent article from this group reported on the reliability and stability of fluorinated oxide films. These films were prepared in a conventional parallel plate dual frequency plasma-enhanced chemical-vapor deposition reactor. The concentration of the fluorine in the film was varied by changing the deposition parameters. The highest fluorine concentration obtained was 15% in that study. The fluorine included in the film is expected to affect the results obtained during plasma etch of the film. The effect of the incorporated fluorine on the etch rate of the film and microloading and the profile of contact structures are examined.
Effects of native oxide removal from silicon substrate and annealing on SiO2 films deposited at 120 °C by plasma enhanced chemical vapor deposition using disilane and nitrous oxide
Authors: Song Juho , Ajmera P. K. , Lee G. S.
Published: July 2002

The effects of native oxide removal from the Si substrate surface and annealing on SiO2 films deposited by plasma enhanced chemical vapor deposition at 120 °C using Si2H6 and N2O are investigated. The effective oxide charge and the interface trap densities for the as-deposited films with the native oxide etched off the substrate surface prior to the film deposition were nearly five times higher than for the as-deposited films without the removal of the native oxide. Postdeposition annealing in N2 reduced the effective oxide charges for the films deposited on substrates without the native oxide. However, a 30 min postmetallization anneal at 400 °C in 5% H2 in N2 ambient reduced both the effective oxide charge density and the interface trap density much more effectively. The values for both these charge densities and the dielectric breakdown field were comparable after this postmetallization annealing regardless of the substrate cleaning procedure and the postdeposition annealing cycle in N2.
Growth of copper nanocrystallites on copper seed cones: Evidence for the presence of a liquid phase on an ion-impacting cone surface
Authors: Okuyama F.
Published: July 2002

The Ar+-sputter-induced ‘‘cone evolution’’ on Mo-seeded Cu is known to entail the growth of hillocklike crystallites on the cone surface. Such crystallites have now been identified as Cu, by means of high-resolution energy dispersive x-ray analysis. The Cu crystallites grew selectively on the Mo lattice of seed layers, and sometimes at the seed-layer apex which suffered from head-on ion impact during sputtering. The crystallite growth was thus not a direct consequence of ion impact, leading to a hypothesis that a viscous overlayer of Cu on the growing Mo lattice condensed into dewdroplike crystallites upon switching off the ion beam.
The effect of the Ti glue layer in an integrated Ti/TiN/Ti/AlSiCu/TiN contact metallization process
Authors: Ouellet L. , Tremblay Y. , Gagnon G. , Caron M. , Currie J. F. , Gujrathi S. C. , Biberger M.
Published: July 2002

A Ti/TiN bilayer deposited under an Ti/AlSiCu/TiN interconnect is generally used at the contact level to stabilize the contact resistance of small diameter contacts as well as to prevent junction spiking during postdeposition anneals. An air break followed by a furnace or a RTP anneal is generally required after the deposition of the Ti/TiN bilayer to improve the barrier stability. This three step interconnect scheme results in a low net effective throughput process if the same metallization system is used twice or, alternatively, in a high cost-of-ownership process if two metallization systems are used, a first for the Ti/TiN barrier and a second for the Ti/AlSiCu/TiN interconnect. In this article, it is shown that collimation permits the deposition of very thick TiN barriers at the bottom of high aspect ratio contacts which allows contact metallization integration in a single metallization system. In addition, it is found that the use of a Ti glue layer between the barrier and the AlSiCu contact interconnect to promote the filling of these high aspect ratio contacts with Al alloys results in a yield loss of n+ and p+ contact chains and therefore should be avoided. Finally, it is demonstrated that an integrated Ti/TiN/AlSiCu/TiN contact metallization with excellent electrical properties is possible with collimated TiN barriers.
Blind reconstruction of scanning probe image data
Authors: Williams P. M. , Shakesheff K. M. , Davies M. C. , Jackson D. E. , Roberts C. J. , Tendler S. J. B.
Published: July 2002

Scanning probe microscopy has proven to be an invaluable tool for the investigation of surface topography; however, the finite geometry of the imaging tip can often distort image data and complicate metrological investigations of surface features. Here, the derivation of a computational procedure for the estimation of the geometry of the scanning probe from the topographic image data alone is presented. The properties of the tip function extracted from such data permit an assessment of the sample-related information content of an image. The technique is demonstrated by its application to simulated scanning probe microscopy image data, where its performance can be assessed, and by its application to experimental image data obtained from the scanning force microscope.
Application of phase-sensitive photoreflectance spectroscopy to a study of undoped AlGaAs/GaAs quantum well structures
Authors: Hughes P. J. , Weiss B. L.
Published: July 2002

Phase-sensitive photoreflectance (PR) has been used here to study undoped AlGaAs/GaAs single and multiple quantum well structures. The PR features of these structures exhibited a phase detection angle dependence as a function of spectral energy at the output of the lock-in amplifier, which was attributed to the differences in temporal behavior of the PR features from different layers within these structures.
Optical properties of reactive-ion-etched Si/Si1−xGex heterostructures
Authors: Köster T. , Gondermann J. , Hadam B. , Spangenberg B. , Schütze M. , Roskos H. G. , Kurz H. , Brunner J. , Abstreiter G.
Published: July 2002

A patterning technology for fabrication of nanometer structures in Si/SiGe heterosystems is developed. The method pursued here combines high-resolution electron-beam lithography with reactive-ion-etching pattern transfer. A modified SF6/O2 dry-etching process is optimized by varying the gas mixture to achieve the required anisotropy. Photoluminescence measurements are carried out on uniformly etched samples to determine the influence of the reactive-ion-etching process on the optical properties. Etch process induced surface modifications drastically alter the electrical surface potentials. They are identified by laser desorption. These modifications are partially removed by low-temperature postannealing steps. A qualitative model is presented to explain the observed effects. With this optimized technology, SiGe wires with lateral widths from 4 μm down to 25 nm are fabricated. Photoluminescence has been detected for structures as small as 600 nm.
Scanning tunneling microscopy investigation of the dimer vacancy–dimer vacancy interaction on the Si(001) 2×n surface
Authors: Smith A. R. , Men F. K. , Chao K.-J. , Zhang Zhenyu , Shih C. K.
Published: July 2002

Scanning tunneling microscopy has been used to investigate the formation of the 2×n vacancy line structure on Si(001). We find that quenching the surface from high temperatures results in the formation of vacancies. After further quenching, these vacancies nucleate into chains running perpendicular to the dimer rows. Finally, the vacancy chains connect and develop into vacancy lines which extend for many thousands of Å’s. Each vacancy line consists of mainly two types of dimer vacancies: (1) a di-vacancy and (2) a combination of a single vacancy and a di-vacancy separated by an isolated dimer. All the vacancy lines together with the dimer rows form a 2×n structure with 6≤n≤12. Calculations using the Stillinger–Weber potential support the view that the formation of the vacancy line structure is due to the interaction between vacancies.
On the origin of the notching effect during etching in uniform high density plasmas
Authors: Hwang Gyeong S. , Giapis Konstantinos P.
Published: July 2002

We present a two-dimensional Monte Carlo simulation of profile evolution during the overetching step of polysilicon-on-insulator structures, which considers explicitly (a) electric field effects during the charging transient, (b) etching reactions of energetic ions impinging on the poly-Si, and (c) forward inelastic scattering effects. Realistic energy and angular distributions for ions and electrons are used in trajectory calculations through local electric fields near and in the microstructure. Transient charging of exposed insulator surfaces is found to profoundly affect local sidewall etching (notching). Ion scattering contributions are small but important in matching experimental notch profiles. The model is validated by capturing quantitatively the notch characteristics and also the effects of the line connectivity and open area width on the notch depth, which have been observed experimentally by Nozawa et al. [Jpn. J. Appl. Phys. 34, 2107 (1995)]. Elucidation of the mechanisms responsible for the effect facilitates the prediction of ways to minimize or eliminate notching.
Analyses of the chemical topography of silicon dioxide contact holes etched in a high density plasma source
Authors: Joubert O. , Czuprynski P. , Bell F. H. , Berruyer P. , Blanc R.
Published: July 2002

High aspect ratio sub-half-micron contacts were etched in SiO2 using a high density C2F6 plasma generated by an inductively coupled, low pressure reactor. Process development studies have shown that high aspect ratio contact holes can be open in thick dielectric layers with a good selectivity to the underlying silicon. Minimization of reactive ion etching lag is obtained by using high bias power conditions, which on the other hand induce a degradation of the photoresist, described as a graphitization of the resist. The degradation induces considerable roughness at the edges of the resist structures which leads to the creation of striations in the silicon dioxide as the pattern transfer in the SiO2 proceeds. X-ray photoelectron spectroscopy (XPS) studies have allowed analysis of high aspect ratio SiO2 contact holes. Using appropriate flood gun conditions, a complete separation of the XPS peaks originating from the resist mask and from the fluorocarbon polymer deposited on the bottom of the contact holes is possible. The XPS analyses show, in particular, that the fluorination of the polymers on the bottom of the contact holes strongly increases with the aspect ratio of the contact hole, and that the fluorination of the polymers deposited on the contact hole sidewalls is even greater.
Quantitative measurement of the resist heating in a variable shaped electron lithography
Authors: Babin Sergey , Hudek Peter , Kostic Ivan
Published: July 2002

Experiments investigating resist heating were performed in a variable shaped electron lithography system. The temperature rise and associated change in resist sensitivity were related to the current density and size of flashes. The experiment avoids other contributing factors allowing the pure heating effect to be isolated. The response of the resist to temperature rise was determined by direct heating of the substrate using an exposure that causes no additional heating. The resist temperature rise under electron beam of variable size was also determined as a function of flash size and of throughput of lithography system. Applying multiple exposure with a delay between the successive shots, the time dependence on the heating effect was determined.
Growth and characterization of light emitting ZnS/GaN heterostructures
Authors: Piquette E. C. , Bandić Z. Z. , McCaldin J. O. , McGill T. C.
Published: July 2002

Heterostructures involving ZnS/GaN show promise for the injection of holes from p-GaN into n-ZnS. Utilizing knowledge obtained from ZnS phosphor technology, this combination could result in a new type of multi-color electroluminescent display. Further, this combination provides a very interesting interface. Both ZnS and GaN are very ionic materials. Hence, it is desirable that the interface will be relatively benign, and that charge injection can occur despite the large lattice mismatch and resulting misfit defects that form near the interface. The highly lattice mismatched structures ZnS/GaN and ZnS/Al2O3 were grown by molecular beam epitaxy using elemental sources. Growth rates of up to 0.4 μm ph were observed for the lower growth temperatures, with rapidly diminishing rates for temperatures above 350 °C. The GaN substrate consisted of a 3 μm epilayer grown on sapphire (0001) by metalorganic chemical vapor deposition. Reflection high energy electron diffraction observations indicate that the zincblende ZnS layers commonly contain (111) twins, although films with no visible twin spots could be grown at a high substrate temperature. The sulfide layers were characterized using photoluminescence, x-ray diffraction, and scanning electron microscopy (SEM). X-ray peaks typically had widths of 400 arcsec for ω/2θ scans, and somewhat worse for ω scans, indicating mosaic tilt. Photoluminescence spectra of the ZnS films doped with Ag and Al demonstrated the characteristic blue transition near 440 nm. SEM electron channeling patterns indicated that the ZnS films lie at a 30° rotated orientation to the Al2O3 (0001) substrate, as does GaN. p-GaN/n-ZnS devices were fabricated using standard photolithography techniques. The current voltage characteristics are reported and preliminary electroluminescence results are discussed for this heterojunction system.
Schottky contacts on reactive-ion etched InGaP
Authors: Kuzmı́k Ján , Darmo Juraj , Kúdela Robert , Haščı́k Štefan , Mozolová Želmı́ra
Published: July 2002

We report on the technology and properties of Schottky contacts on reactive-ion etched n-In0.49Ga0.51P (n=7.5×1017 cm−3). A mixture of CH4/H2 was used for a controllable smooth dry etching of InGaP while a CCl2F2-based plasma was shown to enable a highly selective etching of GaAs over InGaP. Current–voltage (I–V), capacitance–voltage (C–V) methods and deep-level transient spectroscopy (DLTS) were used for diode characterization. CCl2F2-based reactive-ion etching (RIE) led to diodes with barrier heights of 0.67 eV (from I–V measurements) and ideality factors of 1.24, which are parameters that are very close to those of the reference (not dry etched) sample. Additional C–V and DLTS characterization has confirmed no detectable damage for CCl2F2-based RIE. On the other hand, hydrogenation after CH4/H2 plasma led to substantial passivation of donors which were successfully reactivated after 430–470 °C rapid thermal annealing (RTA). For this type of processing we measured barrier heights of 0.70–0.75 eV and ideality factors of 1.25–1.27, depending on the temperature of the RTA. DLTS on CH4/H2-RIE based diodes has shown that, in contrast to the reference sample, no bulk deep traps are generated with RTA. We point out that thermal treatment also led to changes in the interface states density which may be responsible for the diode barrier height increase.
Energy dependence of proximity parameters investigated by fitting before measurement tests
Authors: Aparshina L. I. , Dubonos S. V. , Maksimov S. V. , Svintsov A. A. , Zaitsev S. I.
Published: July 2002

Some years ago a method for fast and accurate experimental evaluation of the proximity parameters α, β, η was suggested [S. V. Dubonos et al., Microelectron. Eng. 21, 293 (1993)]. The method, called the fitting before measurement procedure, is used for regular measurements of β and η in a wide energy range for different bulk substrates (Si, SiO2, mica, ZrO2, Al2O3, InAs, GaAs) and of α as function of resist thickness and energy. An empirical relation from the fitting procedure allows one to extrapolate the β and η values to other substrates and energies. It is demonstrated that a resist of micron thickness can remarkably reduce the resolution of e-beam lithography. It is important that the reducing could not be improved by accurate focusing of the beam but could be overcome only by using a higher accelerating voltage. A phenomenological relation helps to predict resolution as function of resist thickness and electron energy.
Miniature electron beam column with a silicon micro field emitter
Authors: Honjo Ichiro , Endo Yasuhiro , Goto Shunji
Published: July 2002

Silicon micro field emitters (Si-MFEs) are expected to be promising as electron sources for their high brightness and ease in making arrayed microcolumns due to small physical size. We have developed a Si-MFE electron gun assembly that produces an electron beam of 1 keV. All components including the Si acceleration electrode are mounted on an integrated circuit (IC) package stem (TO-8) by anodic and eutectic bonding. A high brightness (75 μA/sr) and a long lifetime (>1000 h) have been observed. To overcome the intrinsic emission instability of Si-MFEs, we developed a simple feedback circuit which controls an extraction voltage. The source position shift and the aberration coefficient change caused by stabilization were evaluated analytically and found to be negligible due to the scaling law as applied to micron size. We confirmed that the total emission fluctuation could be stabilized to less than 1% by detecting the absorption current but also found that this detection should be done in the electron beam column to stabilize the probe current due to the instability of the emission angle. Using the Si-MFE electron gun along with a miniature electron beam column 5 cm in length, we evaluated the electron optical properties and succeeded in demonstrating a scanning electron microscope operation with a resolution less than 0.5 μm.