bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of contact resistivity and Schottky diode characteristics on dry etching induced damage of GaInAs
Authors: Thomas S. , Pang S. W.
Published: July 2002

GaInAs was etched in a Cl2 plasma generated with an electron cyclotron resonance source. The effects of changing etch parameters on etch rate, morphology, and surface damage were analyzed. Increased microwave power, rf power, and Cl2 percentage in Ar caused the etch rate to increase monotonically. The etch rate decreased with increasing distance and reached a maximum for a pressure of 1.0 mTorr. The etch conditions were chosen to maintain smooth morphology, which requires a balance between ion energy, ion flux, concentration of reactive species, and pressure. Ohmic contacts for transmission lines and Schottky contacts for diodes were deposited directly on the etched GaInAs surface for the evaluation of etch induced damage. It was found that the transmission line measurements were more sensitive to surface damage than the diode characteristics and the specific contact resistivity (ρc) was a more sensitive measure of the damage than sheet resistivity. Defects generated by dry etching typically caused a reduction in ρc. The contact resistivity decreased with increasing rf power and source distance. More damage was introduced when only rf power was applied, as indicated by the lower ρc compared to when both microwave and rf power were applied. Addition of 10% Cl2 in Ar dramatically reduced the damage when compared to etching only with Ar. Increasing the pressure from 0.5 to 5.0 mTorr caused an increase in ρc but a degradation in surface morphology. The damage depth was estimated to be ∼6 nm at 50 W rf power and increased to ∼18 nm at 200 W rf power. Minimal surface damage was obtained when low rf power was used. For a self-induced dc bias of −68 V (25 W rf power), ρc was 8.3×10−5 Ω cm2, similar to the control sample.
Quarter-micron lithography with a wet-silylated and dry-developed commercial photoresist
Authors: Gogolides Evangelos , Tzevelekis Dimitrios , Tsoi Elizabeth , Hatzakis Michael , Goethals Anne-Marie , Baik Ki-Ho , Van Roey Freida
Published: July 2002

A positive-tone surface imaging process using wet silylation of the commercial photoresist AZ 5214ETM is presented; it is seen as a practical method to extend optical lithography down to 0.25 μm and to increase significantly the resolution limits of available steppers, without adding appreciable process complexity and cost. A comparative study is done using H-line, I-line, and deep ultraviolet at 248 nm lithography on different steppers. The resolution achieved corresponds to a k factor of 0.4 [i.e., 0.4λ/(numerical aperture)]. The importance of the dry-development step and the thermal effects associated with the heating of the wafer during etching are discussed.
Comparative evaluation of chemically amplified resists for electron-beeam top surface imaging use
Authors: Irmscher M. , Höfflinger B. , Springer R.
Published: July 2002

The ultimate lithographic performance of e-beam direct writing can only be achieved if the proximity effect is reduced by a top surface imaging resist technology. The capability of some commercial and experimental chemically amplified resists for an e-beam-sensitive top surface imaging process were evaluated. Analogous to the resist contrast, a silicon contrast was defined, which characterizes the silylation property of the resists very well and enables a comparison of the evaluated resists. The influence of bake and silylation conditions on the silicon contrast was investigated. The patterning results prove that the proximity effect was reduced dramatically. One of the evaluated resists was applied to structuring the metal layers of a 0.8-μm-CMOS technology.
Structure of Au on Ag(110) studied by scanning tunneling microscopy
Authors: Chiang S. , Rousset S. , Fowler D. E. , Chambliss D. D.
Published: July 2002

The epitaxial growth of Au on Ag(110) has been studied by scanning tunneling microscopy up to 8 ML. In the submonolayer range the results show that gold atoms are intermixed with the silver atoms in the top two layers. Above 1 ML a two-dimensional fingerlike growth gives rise to anisotropic three-dimensional islands of gold, which appear to be thermal equilibrium structures. Above 5 ML, the gold overlayer forms a (1×3) reconstruction which is manifested as double rows of atoms growing along [11̄0]. The development of this reconstruction is followed as a function of coverage.
Atomic force microscope study of thin-plate martensites in an Fe–Ni–C alloy
Authors: Yamamoto Masahiko , Nishikawa Kouichi , Noda Yasuo , Saburi Toshio , Hayakawa Motozo , Oka Muneo , Kurumizawa Toshimitsu
Published: July 2002

Morphology and accommodation of thin-plate martensites in an Fe–Ni–C alloy have been investigated with atomic force microscopy (AFM). The quantitative observation of surface relieves made it possible to determine the kinds of thin-plate martensite variants by combining with single-face trace analysis. The martensites keep complementary configuration of variants in order to make the overall strain minimize. Strain distribution induced by the martensite formation in the parent phase was calculated using the height of the surface relief obtained by AFM observation and it was found that a highly strained region exists near the front of the martensite.
Three-dimensional laser direct writing: Applications to multichip modules
Authors: Nassuphis N. , Mathews R. H. , Palmacci S. T. , Ehrlich D. J.
Published: July 2002

Laser direct write deposition and etching have been developed for uses on multichip modules. Instrumentation has been demonstrated for these and other applications on substrates with significant three-dimensional topography.
High efficiency diffractive coupling lenses by three-dimensional profiling with electron-beam lithography and reactive ion etching
Authors: Stemmer A. , Zarschizky H. , Knapek E. , Lefranc G. , Mayerhofer F.
Published: July 2002

Single diffractive lenses with submicrometer feature sizes are realized with binary, multilevel, and blazed reliefs using computer-aided design methods, three-dimensional (3D) profiling algorithms, direct write e-beam lithography, reactive ion etching, antireflection coating, and wafer dicing. Depending on the relief profile, maximum diffraction efficiencies of more than 70% for lenses with a high numerical aperture of 0.5 were measured and aberration-free imaging was observed. In order to enhance the diffraction efficiency we present a method for obtaining Fresnel grating lenses and a flexible 3D shaping of the resist mask for the dry etch process.
Electron-beam lithography for the fabrication of air-bridged, submicron Schottky collectors
Authors: Muller R. E. , Martin S. C. , Smith R. P. , Allen S. A. , Reddy M. , Bhattacharya U. , Rodwell M. J. W.
Published: July 2002

T-gate technology as is commonly used for field-effect transistors and high electron mobility transistors has been adapted for use in Schottky-collector resonant tunneling diodes (SRTDs) devices in which it is necessary for the footprint to be extremely small in both dimensions. By air bridging the contact, GaAs-based RTDs with projected cutoff frequencies of nearly 1 THz have been fabricated. The process is advantageous for the fabrication of terahertz diodes because of the large periphery to area ratio associated with the small footprint (which reduces the parasitic resistance), because small areas provide better impedances, and because the air bridge both reduces parasitic capacitances and provides certain processing advantages. The process is also inherently planar in contrast with other diode implementations for use at submillimeter wave frequencies. In addition to the GaAs-based RTDs, the process is also being used for the fabrication of GaAs Mott diodes, which have cutoff frequencies of 12.5 THz and InGaAs/AlAs RTDs, which appear to have cutoff frequencies of 2.5–3 THz.
Microstructure study by scanning tunneling microscopy of glassy carbons heat treated at different temperatures
Authors: Lei H. N. , Métrot A. , Troyon M.
Published: July 2002

The surface structures obtained by scanning tunneling microscopy studies of two commercial glassy carbon samples, heat treated at 1000 and 2500 °C, respectively, are presented and discussed. These glassy carbons consist of large areas of featureless amorphous regions which coexist with different types of ordered zones. In the glassy carbon treated at 1000 °C, three types of microcrystallites have been observed: a hexagonal ‘‘graphitelike’’ structure with apparent interatomic distances di=2.2±0.1 Å, a structure in form of atom rows distant of 3.6±0.2 Å and a rectangular structure with a periodicity equal to 3.3±0.2 and 2.50±0.15 Å. In the glassy carbon treated at 2500 °C three types of microcrystallites have also been observed: a graphitelike structure with di=2.2±0.1 Å, a hexagonal ‘‘graphitic’’ structure with 2.5±0.15 Å, and a centered rectangular structure (a=6.8±0.4 Å, b=2.3±0.2 Å).
Molecular mechanics calculation and scanning tunneling microscopic research of polyaniline doped with perchlorate
Authors: Bai C. , Zhu C. F. , Zhang P. C. , Yu T. , Wang F. S.
Published: July 2002

On the basis of the molecular mechanics method, using a minimized conformational strain energy calculation, several models have been proposed for chains with six repeat units of aniline. First, a model of a single isolated polyaniline chain is set up. Second, according to the interaction between the two adjacent polyaniline chains, a monolayer film model of parallel chains is presented. Third, a model of double layers of polyaniline chains is presented based on the interaction among three chains located in the different layers. Polyaniline film doped with perchlorate was investigated by a scanning tunneling microscope (STM). STM data are basically in agreement with the above molecular mechanics calculated models.
Scanning probe microscopy and spectroscopy study of the organic salt (ET)2KHg(SCN)4
Authors: Dubois J. G. A. , Gerritsen J. W. , van Kempen H. , Campos C. E. , Tibbitts T. T. , Brooks J. S. , Tokumoto M. , Kinoshita N. , Tanaka Y.
Published: July 2002

The surfaces of cleaved single crystals of (ET)2KHg(SCN)4 [where ET is bis(ethylenedithio)tetrathiafulvalene] were imaged by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Two distinct surfaces are observed with STM: a complete (ET)+2 layer and a complete KHg(SCN)−4 layer. STM images of the cation layer are independent of scanning tip polarity, which is consistent with its metallic character. By contrast, images of the anion layer are strongly dependent upon the polarity of the tip and thus provide information about occupied and unoccupied molecular orbitals in the KHg(SCN)−4 surface. The AFM images were obtained at ambient conditions and correlate well with STM images of the (ET)+2 layer. Preliminary spectroscopy measurements on cleaved crystals at low temperature indicate that the insulating ground state phase contains a 3 meV gap in the density of states, which has a value of 2Δ/kTc=8.
Scanning tunneling microscopy study of the reaction of AlCl3 with the Si(111) surface
Authors: Uesugi K. , Takiguchi T. , Yoshimura M. , Yao T.
Published: July 2002

The initial stage of the reaction of aluminum trichloride (AlCl3) with the Si(111)-(7×7) surface and annealing effects of the adsorbed surface are investigated with a scanning tunneling microscope. Reacted and unreacted sites manifest in the contrast of adatom sites on the AlCl3-exposed surface. An AlCl3 molecule dissociatively adsorbs onto the Si(111)-(7×7) surface at room temperature, which yields chlorine atoms. Preferential adsorption site is found to be the center adatom site rather than the corner adatom site, and the chlorine atom adsorbs onto the top site of the center Si adatom. The migration of adsorbed molecules around the rest atom in the 7×7 unit cell is observed at room temperature. The Si–Clx species desorb from the surface by thermal annealing at 600 °C, leaving vacancies behind, after annealing at 1200 °C. Aluminum deposition occurs in a limited area and the surface shows the √7×√7 reconstruction.
Surface structures of InP and InAs thermally cleaned in an arsenic flux
Authors: Ohkouchi Shunsuke , Ikoma Nobuyuki , Tanaka Ichiro
Published: July 2002

The surface structures of InP and InAs thermally cleaned in an arsenic flux were investigated using an ultrahigh vacuum scanning tunneling microscope multichamber system equipped with a molecular beam epitaxy facility. The InP surfaces thus treated at 510 °C showed In-stabilized (4×2) reconstructions which depended on the time of thermal cleaning. The surface structure of this substrate after thermal cleaning for 3 min comprised one In dimer and three missing dimers. This structure was the same as that of InAs treated under the same conditions. These In-stabilized (4×2) structures formed on both InP and InAs substrates changed to an As-stabilized (2×4) structure when the substrate temperature was lowered to below 480 °C under the same arsenic pressure.
Reconstructed structures in metal/Si(100) surfaces at high temperature observed by scanning tunneling microscopy
Authors: Ichinokawa T. , Itoh H. , Schmid A. , Winau D. , Kirschner J.
Published: July 2002

Reconstructed structures of metal on Si(100)2×1 surfaces annealed at high temperature have been investigated by scanning tunneling microscopy as functions of the type of metal, coverage, and annealing temperature. The reconstruction mechanisms at high temperature depend on the type of metal. In the present paper, the formation mechanisms of reconstruction at high temperature are classified briefly into three categories and are discussed qualitatively.
Fine structure of the GaAs(001) surface
Authors: Haga Y. , Miwa S. , Morita E.
Published: July 2002

The GaAs(001) 2×4 arsenic-stabilized surface and the selenium treated GaAs(001) surface grown by molecular beam epitaxy (MBE) have been investigated by scanning tunneling microscopy (STM). The results showed the differences between the structures of the surface after 30 ML GaAs growth (ML = monolayer) and that after growth of the GaAs layer. The GaAs(001) 2×4 surface unit cell was found to consist of two arsenic dimers and two missing dimers. We also observed the selenium treated GaAs(001) surface with a 2×1 reconstruction.
Gate-controlled modulation of charge transport in long-channel, δ-doped, heterojunction Hall-bar structures
Authors: Wieder H. H. , Goldman R. S. , Chen Jianhui , Young A. P.
Published: July 2002

The charge-transport properties of the two-dimensional electron gas (2DEG) generated by δ-doping lattice-matched InxGa1−xAs/InyAl1−yAs heterojunctions, x≤0.4, grown on GaAs substrates by means of compositionally step-graded, strain-relaxed, InyAl1−yAs buffer layers were investigated. Gate-controlled, long-channel, eight-arm Hall-bridge specimens using Shubnikov–de Haas (SdH) oscillatory magnetoresistance measurements, made at 1.6 K, low-field Hall-effect and resistivity measurements, and field-effect transistor measurements were made on the same specimens at 1.6 and 77 K. Fast Fourier transform analysis of the SdH data indicates that the displacement of the Fermi level produced by a quasistatic applied gate voltage can populate one, two, or three subbands of the 2DEG in its quantum well. The experimental data are in good agreement with theoretical Poisson/Schrödinger simulations of the equilibrium properties of such gate-controlled heterostructures. The effective electron density, mobility, and threshold voltage of the 2DEG are affected strongly by the density, distribution, time constants, and field-effect modulation of the deep-level electron traps present in the InyAl1−yAs charge-supply layer. Low-frequency transistor characteristics are consistent with a simple, long-channel, modulation-doped field-effect transistor model employing the parameters derived from the quasistatic measurements, gradual channel approximation rules, and current saturation affected by electron diffusion.
Electrical and mechanical properties of metallic nanowires: Conductance quantization and localization
Authors: Pascual J. I. , Méndez J. , Gómez-Herrero J. , Baró A. M. , Garcia N. , Landman Uzi , Luedtke W. D. , Bogachek E. N. , Cheng H.-P.
Published: July 2002

Measurements of room-temperature electronic transport in pulled metallic nanowires are presented, demonstrating that the conductance characteristics depend on the length, lateral dimensions, state and degree of disorder, and elongation mechanism of the wire. Conductance during elongation of short wires, l∼50 Å, exhibits periodic quantization steps with characteristic dips, correlating with the order-disorder states of layers of atoms in the wire, predicted via molecular dynamics simulations. The resistance of longer wires, l≳100 Å, exhibits localization characteristics with ln R(l)∼l2. Effects of disorder and variations in wire geometry, exhibited via their influence on the transmittivity of the conductance channels and/or the quantization conditions, are demonstrated.
Influence of substrate electrical bias on the growth of GaN in plasma-assisted epitaxy
Authors: Beresford R. , Ohtani A. , Stevens K. S. , Kinniburgh M.
Published: July 2002

A sample bias on the order of −15 V arises during electron cyclotron resonance plasma-assisted epitaxy of GaN on insulating substrates. In contrast, conducting substrates enable growth under zero or positive bias conditions. Surface morphology of GaN/Si(111) is progressively smoother with increasing bias (−10 to +10 V) for a microwave power of 30 W. Emission spectroscopy of the plasma suggests that both N and N+2 are produced from collisions involving N*2 and that for low power (10 W), the N and N+2 production is limited by the N*2 abundance. In contrast, at higher power (50 W), ion and atom production appears limited by the electron collision frequency. Electrostatic probe measurements near the growth stage indicate that the ion energy has a minimum of about 6 eV, attained at low plasma power or at medium power (30 W) with a positive substrate bias. Mg-doped films produced at 10 W and zero bias are highly resistive. p-n junction diodes formed by Si-doped GaN grown on Mg-doped GaN on p-type Si are operated at relatively low current densities of 100 A cm−2 and emit light near 2.5 eV at room temperature.
Silicon cathodes with array of tips used as pulsed photoemitters
Authors: Aboubacar A. , Chbihi A. , Dupont M. , Gardès J. , Laguna M. , Querrou M.
Published: July 2002

Cathodes with array of tips made from silicon wafer previously tested under continuous laser and high local electric field have produced satisfactory results [Aboubacar et al., Nucl. Instrum. Method B 63, 489 (1992)]. These cathodes have been submitted to a pulsed laser beam in the range of few tens of nanoseconds to 35 ps duration at several optical frequencies. Fast time response, less than 400 ps (limitation of the scope), have been observed. This could be useful in future works for higher-frequency operation, such as the achievement and the development of very high-energy linear accelerators and photoinjectors for free-electron lasers. To enhance photocurrents triggered by laser pulses, photoemission using two colors has been realized. Some preliminary results and discussion are presented.
Modulated reflectivity spectroscopy of electronic states confined in surface quantum wells and above quantum barriers
Authors: Parks C. , Ramdas A. K. , Melloch M. R. , Steblovsky G. , Ram-Mohan L. R. , Luo H.
Published: July 2002

In a surface quantum well, realized by a structure such as vacuum/GaAs/AlxGa1−xAs fabricated by molecular beam epitaxy, electronic states can experience quantum confinement. In the present study the existence of such quantum confined electronic states has been demonstrated with piezo- and electromodulated reflectivity spectroscopy. Equally remarkable signatures appear in the modulated reflectivity spectra which can be traced to electronic levels localized above the AlxGa1−xAs single quantum barrier formed by this structure. The dependence on the barrier thickness and the wave functions of the above barrier states are similar to their bound counterparts in single quantum wells. The finite element method was used to deduce the energy levels of the surface quantum wells and quantum barriers in the empirical two-band model.
Studies of porous silicon field emitters
Authors: Boswell E. , Seong T. Y. , Wilshaw P. R.
Published: July 2002

Recent work on field emitters has shown that a thin layer of porous silicon formed on the surface of pyramidal p-type silicon emitters can dramatically improve their emission characteristics, both in terms of the maximum emission current obtained and also the uniformity of emission between different pyramids [Wilshaw and Boswell, J. Vac. Sci. Technol. B 12, 662 (1994)]. A transmission electron microscope (TEM) study of the emitting surface of such pyramids is presented which shows that they are covered with a high density of surface asperities. TEM studies and electrical characterization are presented for two contrasting porous silicon morphologies.
Photoemission of microrelief semiconductor surfaces with semitransparent Au films
Authors: Dmitruk N. L. , Litovchenko V. G. , Mamikin S. V.
Published: July 2002

In this article the dependence of the photoemission current of microrelief interfaces of Au–GaAs on temperature, intensity of light and bias, and its connection with electrophysical parameters of the structure is analyzed. A detailed analysis of the characteristics of the anomalous photoemission current and the theory of this effect have been carried out.
New fabrication method of silicon field emitter arrays using thermal oxidation
Authors: Uh Hyung Soo , Lee Jong Duk
Published: July 2002

The fabrication and emission characteristics of a silicon field emitter array using pure thermal oxide as a gate insulator are described. Since the thermally grown oxide film has a better stoichiometry and is a better insulator than the evaporated oxide, the fabrication process could be stabilized and the tip-to-tip uniformity improved. In addition, the aspect ratio can be controlled easily by this process free from the shadowing effect that appears in the evaporation process. Fabricated samples have been measured electrically in the vacuum of 1×10−8 Torr. The anode current of 290 nA (37 nA) for a single tip was observed at the gate voltage of 130 V (100 V), and the gate current was less than 1% of the emission current. The emission patterns of a 625-tip array showed a very uniform phosphor luminescence due to the averaging effect resulting from the multiple silicon tips.
Focused ion beam/optical-merged lithographic technique using ladder silicone spin-on glass
Authors: Suzuki Kohei , Kinoshita Takashi , Yamashita Motoji , Kawakami Nobuyuki , Nakaue Akimitsu
Published: July 2002

Focused ion beam (FIB) optical-merged lithography has been developed to improve the throughput in delineating the gate pattern of the metal–oxide–semiconductor field-effect transistor. In this process, only the critical part of the pattern is delineated with FIB and merged with optically printed noncritical parts. Ladder silicone spin-on glass (LS-SOG) has been used as the negative resist for the 200 keV Si2+-focused ion beam. The 100 nm polysilicon gate was successfully fabricated using the single-level resist process. The film characteristics of the LS-SOG were also investigated.
Pattern positioning error of reticle writing induced by reticle clamping
Authors: Hirano Ryoichi , Matsuki Kazuto , Yoshitake Shusuke , Takahashi Yoshihiko , Tamamushi Shuichi , Ogawa Yoji , Tojo Toru
Published: July 2002

This article describes the effect of reticle flexure caused by clamping on pattern positioning accuracy. Reticle flexure causes a pattern shift resulting from stretching or compression of the reticle surface. We focused on the clamping mechanism of the pattern writing system and the measuring machine which held the reticle at four points. By repeating the clamping of the reticle, it was recognized that the surface height distribution deviates. As a result, pattern shift deviation occurs. To improve the repeatability of clamping, a new three-point clamping mechanism was developed for electron-beam writing systems, and also a three-point adapter was employed for the measuring machine. The values parameters related to pattern positioning accuracy, x and y scaling, and orthogonality were calculated for several reticles (5 in. sq., 0.09 in. thick). By clamping the reticle at three points, the deviations of these three values were reduced to less than 53% that of four-point clamping. Moreover, surface shift caused by three-point clamping was precisely compensated by adding a compensation circuit to the electron-beam writing system.
Gate oxide loss at the periphery of a metal–oxide–semiconductor field-effect transistor resulting from a polysilicon gate etch with a helicon etch tool
Authors: Kraft R. , Krishnan S.
Published: July 2002

This article describes a study of gate oxide loss at the gate periphery of a metal–oxide–semiconductor field-effect transistor (MOSFET) resulting from a polysilicon gate etch with a commercially available low pressure, high density plasma helicon etch tool. When the oxide is removed at the periphery of a MOSFET with the gate etch process, it is possible to damage the underlying silicon in the source and drain regions leading to device degradation or failure. Conventional oxide thickness and scanning electron microscope measurements after the gate etch have been shown to be inadequate in detecting microtrenches and microholes in the oxide at the gate periphery. To measure the integrity of the oxide at the gate periphery, a modified MOS (MMOS) capacitor test structure has been developed to measure the electrical field breakdown strength of the oxide at the gate periphery. This article describes a MMOS study of the oxide loss and underlying etch mechanisms encountered in a low pressure, high plasma density helicon etch tool.
Influence of in situ argon cleaning of GaAs on Schottky diodes and metal–semiconductor field-effect transistors
Authors: van Hassel J. G. , Heyker H. C. , Kwaspen J. J. M.
Published: July 2002

The influence of in situ argon cleaning of GaAs on the electrical characteristics of Schottky diodes and metal–semiconductor field-effect transistors (MESFETs) is investigated. The beam energy was varied from 50 to 500 eV and the characteristics were compared to wet chemically cleaned devices. The characteristics of the Schottky diodes showed a significant degradation as a consequence of damage introduced by argon cleaning. Recovery was obtained with an additional annealing step at 300 °C for diodes cleaned at energies below 125 eV. For higher energies, the samples became worse with annealing. MESFETs showed degraded performances for positive gate voltages due to a high gate leakage current. Improvement was also obtained upon annealing.
Photoluminescence of quantum dots fabricated using tungsten stressors
Authors: Yater J. A. , Plaut A. S. , Kash K. , Lin P. S. D. , Florez Leigh T. , Harbison James P. , Das S. R. , Lebrun L.
Published: July 2002

Strain modulation of a semiconductor band gap spatially confines excitons in a near-surface GaAs/AlGaAs quantum well. We report photoluminescence (PL) results of quantum dot arrays fabricated using tungsten stressors. Excitons are confined in a 35 meV potential well under 100 nm dot stressors, which is 2.4 times deeper than that observed using 100 nm carbon stressors. Such a confinement potential corresponds to quantum dot energy level splittings of approximately 7 meV. Arrays of dots are studied, each with individual stressors of a different size ranging from 100 to 800 nm. The lateral potential well depth, as measured by the red shift in PL signal, is dependent on the stressor width and thickness in a well-understood manner. The integrated PL signal from the dots increases with increasing temperature, indicating increased efficiency of trapping of excitons from the quantum well into the quantum dots. Interpretation of excitation spectra, and observation of higher energy levels, are complicated by the details of the strain pattern and the near-field coupling of radiation between the metallic stressors and the quantum well.
Preparation and characterization of epitaxial gold films deposited on mica by direct current magnetron sputtering
Authors: Elbel N. , Behner H. , von Seggern H.
Published: July 2002

The preparation of epitaxial Au(111) films on mica by means of direct current magnetron sputtering is reported. We employed low-energy electron diffraction, scanning electron microscopy, and scanning tunneling microscopy to study the surface structure of sputtered gold films at various deposition temperatures and substrate cleaning procedures. It will be shown that by sputter deposition at 400 °C onto oxygen annealed mica substrates uniformly textured gold films can be obtained which typically exhibit step-free, atomically flat areas of about 150×150 nm2.
New microfabrication technique on a submicrometer scale by synchrotron radiation-excited etching
Authors: Terakado Shingo , Goto Takashi , Ogura Masayoshi , Kaneda Kazuhiro , Kitamura Osamu , Suzuki Shigeo , Nakao Masao , Tanaka Kenichiro
Published: July 2002

Synchrotron radiation-excited etching of Si, SiC, and WO3 has been investigated using a noncontact mask with a pattern of submicrometer scale. The blank pattern of the mask was replicated on the etched surface, and highly area-selective etching was realized at the size of ∼0.4 μm. The spatial distribution of synchrotron radiation intensity on the sample determined the depth profile of the etched region of the sample. Some adsorbate which might be redeposited etching products appeared in the vicinity of the blank pattern of the mask.
Volume increase phenomena in reciprocal scratching of polycarbonate studied by atomic force microscopy
Authors: Khurshudov Andrew , Kato Koji
Published: July 2002

An atomic force microscope (AFM) was used to study the microwear process of polycarbonate (PC). Testing included line scratching of the polymer surface using a microfabricated Si3N4 AFM tip of 10–20 nm radius. Interfacial adhesion, friction, the effect of the number of scratches, and scanning speed were studied. Unlike previous reports, projections as a result of polycarbonate apparent volume increase have been observed after reciprocal scratching on the same track (without an AFM tip lateral feed). In spite of analytically predicted elastic/plastic contact, no plastic deformation was found during the tests. A model, based on the formation of cracks and their growth was suggested to explain these phenomena. No viscoelastic/plastic behavior (scanning speed effect on friction or microwear) was found.
Chemical analysis of a Cl2/BCl3/IBr3 chemically assisted ion-beam etching process for GaAs and InP laser-mirror fabrication under cryo-pumped ultrahigh vacuum conditions
Authors: Daleiden J. , Eisele K. , Sah R. E. , Schmidt K. H. , Ralston J. D.
Published: July 2002

We have investigated the compatibility of Cl2/BCl3/IBr3 etch gas mixtures with a cryo-pumped ultrahigh vacuum chemically assisted ion-beam etching system. The machine was designed for the fabrication of ultrahigh-quality laser facets in monolithically integrated GaAs- and InP-based optoelectronic integrated circuits. The chemical composition of etch byproducts deposited in the vacuum chambers and the pumping system has been examined in particular detail. After 70 h of process time, samples of such deposits were scraped from the chamber walls and the various stages of the cryo-pump and roughing pump; these samples were analyzed using energy-dispersive x-ray measurements. Automated overnight regeneration of the cryopump, the use of integrated external bakeout heaters, and the implementation of a cryo-pumped load-lock chamber allow the deposition of reactive Cl-containing residues to be confined to surfaces and components which can be cleaned or replaced during routinely scheduled yearly maintenance.
Transverse chromatic aberration in a symmetric magnetic doublet with dynamically compensated field aberrations
Authors: Nakasuji Mamoru , Shimizu Hiroyasu
Published: July 2002

Radial and azimuthal transverse chromatic aberrations, which are calculated from the electron trajectories, are much larger than those calculated from the axial magnetic field distribution and its first derivative. The generation mechanism for such large transverse chromatic aberrations is assumed to be that the electron trajectories initiated at the same object position with different beam energies travel through different paths. This assumption is roughly confirmed by studying the crossover position deviation and the magnetic vector potentials as a function of radius along the Z axis and their curvature. When the object side and image side lenses are shifted in the crossover direction by 32 and 8 mm, respectively, the azimuthal and radial transverse chromatic aberrations are 1.9 and 1.3 nm/eV for a field size of 20×0.25 mm2 and a beam energy of 100 keV. The radial and azimuthal distortions in the subfield are much smaller than 10 nm, when the radial subfield size is 250 μm and the target rotation is corrected.
Thermal stability of rapidly annealed indium tin oxide/n-GaAs heterostructures
Authors: Eftekhari G.
Published: July 2002

The effects of rapid thermal annealing on the electrical properties of ITO/n-GaAs are investigated. For as-deposited contacts the current is dominated by recombination at low bias and by thermionic emission at high bias. Annealing at 500 °C for 20 s causes the current to be dominated by thermionic emission for all biases. Annealing at 600 and 700 °C degrades the contact properties. At 700 °C annealing temperature the current is dominated by tunneling. Removal of sputter generated defects at low annealing temperature, diffusion of indium and tin atoms into GaAs and formation of an n+InAs–InxGa1−xAs layer at higher annealing temperature are proposed as mechanisms to explain the observations.
Molecular beam epitaxy growth and properties of GaN films on GaN/SiC substrates
Authors: Hughes W. C. , Rowland W. H. , Johnson M. A. L. , Fujita Shizuo , Cook J. W. , Schetzina J. F. , Ren J. , Edmond J. A.
Published: July 2002

Two types of nitrogen plasma sources, an electron cyclotron resonance (ECR) plasma source and a radio frequency (rf) plasma source, were used for the growth of GaN by molecular beam epitaxy (MBE). GaN film quality was correlated with the optical emission characteristics of each type of nitrogen plasma source employed. The best quality GaN films were those grown using the rf nitrogen plasma source. This source was found to emit a much larger fraction of atomic nitrogen and 1st-positive series excited molecular nitrogen in contrast to the ECR plasma source which mainly produced 2nd-positive series excited molecular nitrogen and nitrogen molecular ions when operated under the same conditions. The benefit of homoepitaxial growth of GaN, using metalorganic vapor phase epitaxy grown GaN layers on basal plane 6H-SiC, was seen by the observation of surface reconstructions before, during, and after GaN film growth by MBE. In addition, the MBE-grown GaN films exhibited remarkably intense photoluminescence dominated by a sharp band-edge peak at 3.409 eV having a full-width at half-maximum (FWHM) of 29.7 meV at room temperature. At lower temperatures, splitting of the near-edge excition peaks was observed. Double-crystal x-ray rocking curve measurements of selected MBE-grown GaN films yielded (0002) diffraction peaks having FWHMs as narrow as 156 arcsec.
Variable shaped electron-beam lithography application to subwavelength and computer generated diffractive optics fabrication
Authors: Babin Sergey , Danilov Victor
Published: July 2002

Electron-beam lithography for generation of diffractive optical elements topology is examined. The formula for the estimation of exposure data volume for variable shaped electron-beam lithography is presented as a function of diffractive optical element parameters and approximation accuracy. Diffractive optical elements with a subwavelength feature size were manufactured. These elements act as optical elements with an artificial refractive index. A Fresnel zone plate with an artificial phase retardation has been manufactured. Based on the proximity function measured for the actual exposure conditions, the proximity correction has been provided and undistorted structures have been fabricated. Experimental results are presented on computer generated optical elements for industrial applications. A computer generated lens which focuses radiation into a ring has been fabricated. A photomask set was manufactured for a reflecting optical element which focuses a high power CO2 laser beam to two points with parameters required for laser welding.
Direct observation of a vacuum tunnel gap in a tunneling microscope using a transmission electron microscope
Authors: Lutwyche M. I. , Wada Y.
Published: July 2002

This article reports the observation of the vacuum tunnel gap between two conductors using a high resolution transmission electron microscope. A 2.5-mm-sq micromachined tunneling microscope chip has been fabricated with a minimum feature size of 0.4 μm. The chip fits into a modified side-entry transmission electron microscope holder. The electrostatic actuators and springs are designed to produce a large force which is linear with applied voltage to overcome the forces between the tip and sample. The tunnel gap is controlled by a purpose-built feedback controller. One-dimensional micromachines work reliably during observation of the tip apex in a transmission electron microscope, allowing the voltage and current to be changed while the tunnel gap is observed. Two-dimensional machines that can scan the tip have also been tested and shown to be functional.
Application of ultraviolet depth lithography for surface micromachining
Authors: Loechel Bernd , Maciossek Andreas , Rothe Martina
Published: July 2002

Very thick photoresist layers were patterned by contact ultraviolet (UV) lithography. In a following microelectrodeposition step the generated resist patterns were molded and three-dimensional (3D) microstructures were fabricated directly onto system surfaces. The new technology, called 3D UV-microforming, consists of an advanced resist preparation process, an UV lithographic step, resist development, a molding procedure by electrodeposition, and finally stripping and cleaning for finishing the structures. It enables the low-cost fabrication of a wide variety of microcomponents for many different uses. During resist preparation, layers up to 200 μm thickness were obtained. By using a standard UV mask aligner as an exposure tool followed by immersion development, thick resist layers up to 100 μm could be patterned in a single step on preprocessed silicon wafers. Repeated exposure and development were successfully used for structuring resist layers of up to 200 μm thickness. Using AZ 4000 series photoresist, the resolution is also limited by mechanical stability. For lines and spaces in 15-μm-thick resist a minimum width of 3 μm for the resist was found to be necessary to overcome the fabrication process. For thicker layers high aspect ratios of more than 10 as well as steep edges of more than 88° could be fabricated. The resist patterns used were molded by pulse or by direct current electroplating. For microsystem applications some metals and alloys were deposited. Three-dimensional microcomponents were fabricated as samples for demonstrating the new technique. The technique allows the use of materials with interesting properties, ones that could not be provided by standard processes.
Application of plasma polymerized methylsilane resist for all-dry 193 nm deep ultraviolet processing
Authors: Kostelak R. L. , Weidman T. W. , Vaidya S. , Joubert O. , Palmateer S. C. , Hibbs M.
Published: July 2002

Preliminary experiments employing plasma polymerized methylsilane (PPMS) as a single and bilayer resist system demonstrated that the resist process developed at 248 nm is extendible for application at 193 nm. PPMS exhibited excellent photosensitivity with efficient photo-oxidative bleaching when exposed to 193 nm radiation in air. PPMS as thick as 200 nm demonstrated complete bleaching throughout the film. A nitrogen atmosphere was found to quench the photo-oxidative bleaching. However, upon switching the gas ambient to air, the photo-oxidative bleaching rapidly proceeded to completion. Both positive- and negative-tone images were achieved with PPMS at 193 nm depending upon the development process. Using negative-tone development in a chlorine plasma, 0.2 μm lines/spaces were resolved in 100 nm films at an exposure dose of 20 mJ/cm2 and with a depth of focus of nearly 1.0 μm.
Printability of substrate and absorber defects on extreme ultraviolet lithographic masks
Authors: Nguyen K. B. , Ray-Chaudhuri A. K. , Stulen R. H. , Krenz K. , Fetter L. A. , Tennant D. M. , Windt D. L.
Published: July 2002

Extreme ultraviolet lithography (EUVL) is a candidate for high-volume production of integrated circuits with 0.1 μm design rules. As a reduction imaging technique with robust mask substrates, EUVL reduces the mask contribution to the critical dimension (CD) error budget. However, the ability to manufacture EUVL mask blanks that are free of printable defects remains an important challenge. Electromagnetic simulations and imaging experiments have suggested that defects in the substrates and reflective coatings, in particular, may be highly printable and difficult to detect. A defect printability study using programmed defects was performed in order to determine the printing behavior of mask defects of different sizes and locations with respect to absorber features. Imaging was performed using a 10× Schwarzschild camera operating at 13.4 nm with a numerical aperture of 0.08, corresponding to a Rayleigh resolution of 0.1 μm. This system has an effective exposure field of 0.4 mm diam. Measurements of the defect-induced linewidth variations on the printed resist lines were performed with scanning electron microscopy and atomic force microscopy. Results show that defects located on the substrate and overcoated by the reflective coating are more printable compared to defects of the same sizes located above the reflective coating. In addition, defects centered in the clear region of lines-and-space (L/S) pattern are more printable compared to those located at the line edge programmed defects located in L/S patterns that are larger than 1/3 of the linewidth caused ≥10% CD variations, while defects that are ≤1/6 of the linewidth did not cause measurable CD variations.
A background dose proximity effect correction technique for scattering with angular limitation projection electron lithography implemented in hardware
Authors: Watson G. Patrick , Berger Steven D. , Liddle J. Alexander , Waskiewicz Warren K.
Published: July 2002

A background dose proximity effect correction procedure is proposed that utilizes the unique way image contrast is formed in scattering with angular limitation projection electron lithography (SCALPEL(R)). An electron beam is selectively scattered by a thin, high atomic number layer patterned on a membrane mask. Some of the scattered radiation, which is normally blocked at an aperture to form contrast at the wafer, is allowed to pass through the system optics. Nominally dark regions of the mask are therefore allowed to expose the resist on a wafer. However, because the scattered radiation enters the projection system at relatively large angles, it is subjected to system aberrations and is improperly focused at the wafer. This dispersed radiation mimics the natural long range backscatter exposure emanating from the intentionally exposed regions, and ideally results in a constant background exposure in the resist—similar to the GHOST background correction technique used in direct-write applications. However, unlike the direct-write correction, both the primary exposure and the correction exposure are achieved at the same time. Throughput is not reduced by the correction. Although the correction dose profile may not resemble the form of the long range backscatter energy deposition in the resist, the deviations of background exposure are small for mask patterns of practical interest, in comparison with the variation of uncorrected exposures of the same pattern.
Precise measurement of the effective backscatter coefficient for 100-keV electron-beam lithography on Si
Authors: Watson G. Patrick , Berger Steven D. , Liddle J. Alex , Fetter Linus A. , Farrow Reginald C. , Tarascon Regine G. , Mkrtchyan Masis , Novembre Anthony E. , Blakey Myrtle I. , Bolan Kevin J. , Poli Louis
Published: July 2002

A technique has been developed to measure the effective backscatter coefficient in resist that is more reliable than conventional techniques since (1) it does not require precise information about the form of the backscatter profile, and (2) it makes use of the complete resist exposure response function. The estimated backscatter coefficient on Si for 100 keV electrons has been found to be 0.38±0.05, significantly lower than other published values determined at this energy. Within the accuracy of the measurement, the backscatter coefficient is the same for tests determined by scattering with angular limitation projection electron lithography and direct write exposures.
The effects of electron- and ion-beam irradiation on the mechanical response of silicon microresonators
Authors: Mihailovich R. E. , MacDonald N. C.
Published: July 2002

We have investigated the mechanical response of silicon microresonators exposed to electron- and ion-beam irradiation. The microresonators were single-crystal silicon structures consisting of beams ∼0.7 μm wide, and having preirradiation frequency of 48 kHz and Q−1 of 2.5×10−5. For the electron-beam experiment, microresonator response was measured after 10 min irradiations with 10 keV electrons, for beam currents ranging from 2 to 20 nA. The frequency shows a monotonic increase with electron dose, while the Q−1 shows a peak versus dose. For the ion-beam experiment, the microresonator was irradiated with 3.5 keV Ar+ ions for timed intervals up to 10 min. The microresonator frequency and Q−1 exhibit extrema versus irradiation time. These mechanical-response changes are significant for both electron- and ion-irradiation experiments, with frequency shifts ∼0.1% and Q−1 changes of a factor ∼3.
Characterization of a GaAs metal–semiconductor–metal low-energy electron detector
Authors: Zolgharnain S. , Lee K. Y. , Rishton S. A. , Kisker D. , Chang T. H. P.
Published: July 2002

In this article we present the preliminary results regarding the performance characterization of a metal–semiconductor–metal low-energy (≤1 keV) electron detector fabricated by electron-beam lithography on metal–oxide chemical vapor deposition grown GaAs. These devices display very low dark currents, ≤3 nA at 1 V and 300 nA at 9 V. Also, under electron-beam irradiation very high gain values (≳1000) have been noted, which could be evidence of avalanche multiplicative effects. In addition, the input/output response of the device shows a high degree of linearity even in the high gain regime. The signal-to-noise response of the devices is well within the acceptable range of operation for low current sensitivity.