bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of helicon wave plasma designed for direct current sputtering
Authors: Zhang J. Q. , Setsuhara Y. , Ariyasu T. , Miyake S.
Published: July 2002

The rf plasma produced in a helicon wave frequency range was studied using helical antennas and its application to dc sputtering at low Ar pressures was reported. A dense plasma of the order of 1012–1013 cm−3 could be obtained at a pressure around 0.1 Pa by using the antennas with azimuthal mode number of m=±1 or m=0. The measurement of the axial magnetic component Bz of the rf field in the plasma showed evidence of the excitation of helicon wave. A sputtering apparatus has been developed by means of the helicon wave plasma excited with a m=0 mode two-turn antenna. It was found that the characteristics of the rf plasma enhanced sputtering discharge were dominated by the properties of the rf plasma sustained at pressures as low as 3×10−2 Pa. A target current as high as 2 A at a pressure of 0.4 Pa was achieved, and sputtering of the Al target indicated that a deposition rate of 1 μm/min could be obtained under this condition.
Probe for measuring ion beam angular distribution
Authors: Kahn J. R. , Kaufman H. R. , Phillips C. A. , Robinson R. S.
Published: July 2002

A new type of ion beam probe is described that measures the angular distribution of energetic ions and, through their sputtering effects, energetic neutrals as well. This probe does not require either complicated motion actuators or very sensitive electrical measurements in the adverse environment of an ion beam, but instead performs the measurement through the sputter etching of a multilayer sample with contrasting metal colors. This probe was tested and found to provide a half-width at half-maximum reproducibility of about ±0.3 deg. After use, the probe sample provides a permanent record of the angular distribution of the ion beam at the target location tested. Because no electrical contacts are required, the probe can even be attached to a moving stage to measure the effective angular distribution of an ion beam while being carried through a complicated planetary pattern. Using this probe, the low divergence and paraxial beam from an ion source with 30 cm flat graphite grids were documented. This probe, in conjunction with profiles obtained with a Faraday probe, allows full global and internal ion beam characterization. It is significant that the minimum divergences obtained in this investigation were 40–60 percent lower than the minimum divergences obtained from earlier tests with small arrays of apertures.
Artificial neural network exponentially weighted moving average controller for semiconductor processes
Authors: Smith Taber H. , Boning Duane S.
Published: July 2002

The linear exponentially weighted moving average (EWMA) controller has been shown to improve run-by-run process control for approximately linear processes that are subject to shifts or persistent drifts in the presence of noise. This work addresses the inability of the linear EWMA controller to adequately control processes that are poorly represented by such models. This issue is important to the success of the EWMA controller in semiconductor manufacturing where processes may be poorly approximated with linear process models. We address this issue by outlining an extension of the EWMA controller that utilizes an artificial neural network (ANN) process model. The ANN model is dynamically updated using an EWMA of the biases in the ANN output layer. Recipe generation takes place by optimizing around the dynamic ANN model. We show that this framework improves on the linear EWMA controller for controlling higher order processes. Simulations show that this controller provides stable control for higher order processes that cause the linear EWMA controller to become unstable. In addition, we suggest that this architecture is robust in the face of model error and noise. This system allows the basic property of the EWMA controller, improved control with minimal added process noise, to be extended for use in higher order semiconductor processes.
Highly oriented rutile-type TiO2 films synthesized by ion beam enhanced deposition
Authors: Zhang Feng , Zheng Zhihong , Ding Xingzhao , Mao Yingjun , Chen Yu , Zhou Zhuyao , Yang Shiqi , Liu Xianghuai
Published: July 2002

Ion beam enhanced deposition was adopted to synthesize titanium dioxide (TiO2) films. The films were prepared by Ti evaporation and Xe+ ion beam bombardment in an O2 environment. The xenon ion energy varied from 40 to 80 keV. The compositions of the TiO2 films were studied by Rutherford backscattering analysis. All the films were close to stoichiometric. The structure of the films were researched by x-ray diffraction. The results showed that the titanium oxide films exhibit a rutile phase structure with high (200) orientation. The optical properties were also studied using ultraviolet–visible transmission spectrometry.
Investigation of stored energy in plasma deposited TiNx films
Authors: Wulff H. , Eggs C.
Published: July 2002

Thin TiNx films were deposited using a hollow cathode arc evaporation device (HCAED) for studying the influence of low energy ion bombardment on film growth and film properties. Films were deposited at various nitrogen gas flows and negative substrate voltages and investigated by x-ray photoelectron spectroscopy (XPS) and thin film x-ray diffraction. The plasma was analyzed by Langmuir probe measurements and energy resolved mass spectrometry. From both the results of nitrogen flow experiments and the negative substrate voltage experiments it can be concluded that the ion concentration as well as the ion energy determine the film properties. The data obtained from plasma monitoring and Langmuir probe measurements were used to calculate the energy flux to the growing film in relation to the deposition parameters. XPS provides information about the chemical composition. From shifting and broadening of x-ray line profiles concentrations of interstitials, dislocation densities, and domain sizes in the films were calculated. The stored energy in the films induced by low energy ion bombardment was calculated using the energy of individual interstices and dislocations and from the fraction of atoms associated with grain boundaries. The estimation of stored energy in grain boundaries was based on a simple model concerning domain sizes and melting heat. These results were compared with investigations of the energy transfer to the substrate during the film deposition in a HCAED. The stored energy is four orders of magnitude smaller than the total ion energy flux.
Near edge x-ray absorption fine structure study of benzene adsorbed on metal surfaces: Comparison to benzene cluster complexes
Authors: Weiss K. , Gebert S. , Wühn M. , Wadepohl H. , Wöll Ch.
Published: July 2002

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy has been used to study benzene adsorbed on several close-packed metal surfaces [Au(111), Rh(111), Pt(111), and Ru(0001)] under the same experimental conditions. The NEXAFS spectra reveal significant differences with regard to the shapes and positions of resonances and the dichroism observed for the resonance intensities. These differences correlate directly with the binding energy and can be attributed to differences in the electronic coupling of the benzene molecule to the substrate and to adsorption in- duced changes in the molecular structure of the benzene molecule. A comparison to the NEXAFS spectra recorded for the benzene metal cluster complexes [Ru(η6–C6H6)(CH3CN)3]2+ and Ru3(CO)9(μ3:η2:η2:η2–C6H6) indicates that the μ3-arene complex, where the benzene ring is bonded to three metal atoms, can be regarded as a reasonable cluster analog for the adsorption of benzene on the Ru(0001) transition metal surface.
Surface studies of plasma source ion implantation treated polystyrene
Authors: Lee Yeonhee , Han Seunghee , Lee Jung-Hye , Yoon Jung-Hyeon , Lim Hyun Eui , Kim Kang-Jin
Published: July 2002

The plasma source ion implantation (PSII) was utilized to improve the wettability and the stability of surface layer formed in the modification of polymeric materials. Polystyrene was treated with different kinds of plasma ions to render the surface more hydrophilic or hydrophobic. Hydrophobic recovery of PSII-treated polystyrene was also observed as a function of aging time, aging temperature, and treatment parameters. Treatment parameters involve kinds of gases, pressure, plasma power, pulse frequency, pulse voltage, etc. To study the effect of inert gas on hydrophobic recovery, polystyrene samples were prepared by helium, argon, or gas-mixture treatment. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been used to interpret the PSII-treated polystyrene surface and its hydrophobic recovery, with the assistance of x-ray photoelectron spectroscopy and water contact angle measurements. TOF-SIMS spectra of O218 PSII-treated samples showed the presence of O18-containing peaks from the modified surfaces. PSII modifications provide more stable surfaces of polystyrene as a function of aging time than plasma treatments. The comparison of aging behavior data allowed for examination of the differences in the stability of the functionality introduced by the two different treatment techniques.
Defect-associated photoluminescence and rapid thermal annealing effect on SiO2 films grown in the plasma phase
Authors: Kim Keunjoo
Published: July 2002

Room temperature visible photoluminescence was observed in amorphous silicon oxides deposited by an electron cyclotron resonance plasma source and also in Corning glass (7059). The intrinsic group of luminescence bands in the Corning glass was consistent with the stoichiometric oxide film. Bands at 2.25 (550), 2.84 (437), and 3.40 eV (365 nm) were observed in both the as-deposited oxide film and the Corning glass. The 3.40 eV band strongly correlates to the 2.84 eV band, implying an original affinity with the origin of the neutral oxygen vacancy and the hole trapped E′ center. The origin of the 2.25 eV band is not clear, however, although it appears to correlate with the Frenkel-type defect structure in amorphous oxides. The deposited oxide film was annealed and highly split luminescence spectra were observed. Furthermore, the Si-enriched sample showed multiple peaks in both the as-deposited and post-annealed samples. This indicates that luminescences may be related to the condensate of Si particles in oxides.
Room-temperature growth of ZrO2 thin films using a novel hyperthermal oxygen-atom source
Authors: Wisotzki Elmar , Balogh Adam G. , Hahn Horst , Wolan John T. , Hoflund Gar B.
Published: July 2002

Thin ZrO2 films have been grown on Si(100) and on glassy carbon substrates using a novel atomic oxygen source in a standard molecular beam epitaxy system. The oxygen source produces a flux of hyperthermal oxygen atoms with an ion/atom-ratio ≪0.001 through electron stimulated desorption from a Ag alloy surface at an operating pressure <10−8 Torr. The films were grown at room temperature and analyzed using Rutherford backscattering spectroscopy, x-ray diffraction (XRD), x-ray photoelectron spectroscopy and transmission electron microscopy (TEM). The results show the successful growth of fully stoichiometric ZrO2 films on nonheated Si(100) and on amorphous glassy carbon substrates at a rate of 0.58 μm/hr. The XRD and TEM investigations indicate the formation of a mixed amorphous/orthorhombic film structure. Based on the film growth rate, the O flux produced by the electron stimulated desorption atom source is estimated to be 8×1014 atoms/cm2 s. This flux value is consistent with other determinations using ion scattering spectroscopy and pyromellitic dianhydride-oxydianiline polyimide (Kapton®) erosion experiments.
Diagnostics of the diamond depositing inductively coupled plasma by electrostatic probes and optical emission spectroscopy
Authors: Teii Kungen
Published: July 2002

Electrostatic probe methods and optical emission spectroscopy have been used for diagnostics of the low-pressure inductively coupled radio frequency plasma at pressures between 5 and 80 mTorr under real environments of diamond deposition. The single, triple, and emissive probe methods were used alone or combined to obtain electron temperature (Te) and electron density (ne). The single or triple probe method combined with the emissive probe method allowed the determination of ne with high reliability as confirmed by cross-checking. Comparison with the grown deposits suggested the existence of a critical ne value of around 2×1010 cm−3, which was responsible for the drastic decrease in diamond growth rate observed below 10 mTorr and the resulting no growth at around 5 mTorr. The energy distribution of excitation levels of the H atom Balmer series was almost constant and the distribution equilibrium was not established except the case of 5 mTorr, which was ascribed to the difference in the excitation process of H atoms.
GaCl molecular beam cell for surface dynamics studies
Authors: Ohashi Masafumi , Ozeki Masashi
Published: July 2002

To study the surface reaction dynamics between GaCl molecules and the GaAs surface, we developed a GaCl molecular cell in which a high-purity GaCl molecular beam was produced by a direct reaction between Ga metal and Cl2 gas. We optimized the Cl2 gas flow gas for producing the GaCl molecular beam and the cell temperature from 920 to 1230 K. The GaCl3 byproduct, which is stable and forms large particles at lower temperature, was observed under an excess supply of Cl2. At 0.25 sccm, GaCl alone was produced and no Cl2 was observed. The flux density at the sample surface, whose radius was 2 mm and which was placed 40 cm away from a cell nozzle, was estimated to be 1.4×1012 molecules⋅cm−2⋅s−1.
Silicon oxide selective etching process keeping harmony with environment by using radical injection technique
Authors: Fujita Kazushi , Ito Masafumi , Hori Masaru , Goto Toshio
Published: July 2002

A novel radical control method using a radical injection technique was proposed for preventing global warming. This system consists of a new fluorocarbon radical source where the polytetrafluoroethylene was ablated by a CO2 laser resulting in producing fluorocarbon radicals working as etching species and a radical filter set in front of the radical source which controls radicals generated from the radical source. Therefore, this system does not employ any fluorocarbon feed gases causing the global warming. The system was successfully applied to SiO2 over Si selective etching process employing an electron cyclotron resonance plasma. CFx (x=1–3) radical densities, F atom densities and higher species were successfully controlled by using the radical filter, which was confirmed by an infrared diode laser absorption spectroscopy and an actinometric optical emission spectroscopy. From these results, it was found that this technique was applicable to SiO2 over Si selective etching process keeping harmony with the environment, particularly for preventing global warming.
Copper electroplating for future ultralarge scale integration interconnection
Authors: Gau W. C. , Chang T. C. , Lin Y. S. , Hu J. C. , Chen L. J. , Chang C. Y. , Cheng C. L.
Published: July 2002

Copper has received considerable attention during the past few years because of its low electrical resistivity, high melting temperature, and high electromigration resistance. Since electrochemical plating has several advantages compared to physical vapor deposition and chemical vapor deposition due to its low cost and low processing temperature, it becomes the most attractive technique for the implementation of Cu metallization. In this article, we report an electroplating scheme for Cu deposition and study aspects of copper electroplating related to chemical additives effected on Cu deposition. A low resistivity Cu film (∼2 μΩ cm) could be obtained when metallic ion concentration is decreased or current density is increased. The detailed correlation between film resistivity, electrolyte concentration, current density, and film morphology is given in this study. In addition, chemical additives in electrolyte solutions also play important roles in copper electroplating. In this report, thiourea and polyethylene glycol, which are usually added in printing circuit board electroplating to influence nucleation, have been used as gap filling promoters to help Cu filling. The results show that addition of thiourea and polyethylene glycol could help in forming smooth Cu film but does not promote Cu filling ability. Hydroxyl amine sulfate, which has both amino and sulfate groups, is proposed for use as a gap filling promoter in helping Cu electroplating. In this work, we demonstrate that Cu could be electroplated into fine trenches (at 0.3 μm dimension with aspect ratio of 3) when hydroxyl amine sulfate is present and no voids are formed.
Effect of nondiamond carbon on electron transport path of field-emitted electrons from undoped polycrystalline diamond films
Authors: Shim Jae Yeob , Baik Hong Koo , Song Kie Moon
Published: July 2002

The transport paths of field-emitted electrons from undoped polycrystalline diamond films with different amounts of nondiamond carbon have been investigated by a transparent anode imaging technique and an electrolytic decoration technique. It is confirmed that for the films with a large amount of nondiamond carbon, electron transport occurs mainly through conductive grain boundaries while for the films with a small amount of nondiamond carbon, electron tunneling at triple junctions transports preferentially through the diamond surface. It was found that applying a hydrogen treatment to the films mainly consisting of nondiamond carbon component leads to a significant improvement of emission uniformity as well as a substantial increase of emission sites. The reason for this has been explained by optimization of triple junction effect at the surface.
How to fabricate a defect free Si(001) surface
Authors: Hata K. , Kimura T. , Ozawa S. , Shigekawa H.
Published: July 2002

We demonstrate the successful fabrication of an almost defect free Si(001) surface by refining the standard annealing and flashing surface preparation method. On any desired samples, we can routinely fabricate a surface with defect densities lower than 0.1%, significantly reducing the defect density compared to surfaces fabricated by standard methodology.
Selective Si and Be implantation in GaAs using a 100 kV mass-separating focused ion beam system with an Au–Si–Be liquid metal ion source
Authors: Miyauchi Eizo , Arimoto Hiroshi , Hashimoto Hisao , Utsumi Takao
Published: July 2002

Submicron Si and Be ion beams have been implanted into GaAs using a 100 kV maskless ion implantation system with a liquid metal ion source which is capable of emitting double ion species (Si++ and Be++). Both ion beams are implanted at 160 keV with the dose of 1013 to 1014 cm−2. The feasibility of the focusing column was demonstrated by forming the submicron width of line patterns of alternative Si and Be doping in GaAs including a pn junction array. The linewidth of the ion implanted area has been evaluated by SEM, after selective etching of the annealed sample. It has been found that high dose implantation results in considerable lateral impurity spread of more than 1 μm even with the focused ion beams with a diameter of 0.1 μm. However, submicron width implantation turns out to be possible with relatively low doses or with shallow dopings.
A high performance electron energy loss spectrometer for use with a dedicated STEM
Authors: Isaacson M. , Scheinfein M.
Published: July 2002

A uniform magnetic field spectrometer corrected for some second order aberrations has been designed and constructed. We demonstrate practical elimination of the focal plane tilt and two of the second order aperture aberrations. The spectrometer is capable of accepting absolute entrance semiangles of up to 7.8 mrad with a resolution better than 1/2 eV at 100 keV incident electron energies. With the addition of a weak octupole coil at the magnet entrance, a reduction in the limiting third order aberrations has been displayed.
Energy broadening in electron beams: A comparison of existing theories and Monte Carlo simulation
Authors: Jansen G. H. , Groves T. R. , Stickel W.
Published: July 2002

Different theories on the Boersch effect are applied to a simple beam geometry with one crossover in drift space.The results are compared with each other, with Monte Carlo simulations, and with the experiment. The most complete and accurate theory is given by van Leeuwen and Jansen. This theory predicts energy spreads within 10% of the Monte Carlo results for operating conditions usually given in systems with thermionic emission sources. No comprehensive theory, however, of energy broadening in electron guns has yet been presented. Nevertheless, the theory of van Leeuwen and Jansen was found to predict the experimental values by trend and within a factor of 2.
Performance of silicon cold cathodes
Authors: van Gorkom G. G. P. , Hoeberechts A. M. E.
Published: July 2002

The emission properties of cesiated silicon cold cathodes are described and the factors which ultimately limit the performance of such cathodes are discussed. It is tentatively concluded that the maximum available current density and brightness are limited by cesium migration and desorption, these maximum values (for emitters with 1 μm diam and with an efficiency of 1.5%) being jvac,max≂1500 A/cm2 and Bmax≂9×106 A/cm2 sr (at V=10 kV). The long term stability of the emission is surprisingly good, in spite of adsorption of oxidizing gases from the vacuum. This indicates that there is a desorption of such gases too, probably due to the outgoing electrons at high current densities.
Maskless ion beam writing of precise doping patterns with Be and Si for molecular beam epitaxially grown multilayer GaAs
Authors: Miyauchi Eizo , Morita Tetsuo , Takamori Akira , Arimoto Hiroshi , Bamba Yasuo , Hashimoto Hisao
Published: July 2002

We have developed a computer-controlled ion beam writing system with 14-bit resolution to operate a 100 kV maskless ion implanter combined with an MBE growth chamber for patterned impurity-doped GaAs/AlGaAs multilayer growth. Performances of various functions of this new computer-controlled, crystal growth system have been tested. (1) Ion species (Si++, Si+, Be++, Be+) are rapidly selected with minimum astigmatism. (2) Depth impurity doping geometry can easily be controlled by automatically selecting ion charges or semiautomatically changing accelerating voltage. (3) Ion beam diameter and position are precisely monitored and controlled. (4) Ion beam mark detection can be performed with submicron resolution over double layers. (5) Ion beam writing for maskless implantation can be done in arbitrary shapes over the 400 μm square field with assigned impurity, ion dose, and energy, while monitoring ion current and beam diameter. Using this system, we have demonstrated arbitrary pattern implantation and GaAs growth with a finely doped structure in three dimensions.
The properties and exposure chemistry of a soluble polydiacetylene (P4BCMU) used as a negative electron-beam resist
Authors: Colton R. J. , Marrian C. R. K. , Snow A. , Dilella D.
Published: July 2002

The behavior of the polydiacetylene with urethane substituents (P4BCMU) has been investigated under electron-beam (e-beam) irradiation. A thin, O(100 nm), coating can be applied to a silicon wafer by spin coating from a solution in chloroform. E-beam exposure of around 20 μC/cm2 renders the polymer insoluble and resistant to both a CF4/O2 plasma etch and a reactive ion etch (RIE) with freon 112. Features down to 0.2 μm in width have been drawn and replicated into silicon in this way. Thus, the material has been demonstrated to act as a negative resist in standard e-beam lithographic procedures without recourse to an image reversal step. X-ray photoelectron spectroscopy (XPS) indicates only a slight change in stoichiometry after e-beam exposure and suggests the irradiated polymer has tertiary amide characteristics. Fourier transform infrared (FTIR) and Raman spectroscopies indicate that the unsaturated carbon bonds in the backbone of the polymer are not destroyed by e-beam irradiation. Rather the main changes occur in the N–H and the C–O (carbonyl) bonds of the urethane group.
Ultrathin polymer films for microlithography
Authors: Kuan S. W. J. , Frank C. W. , Fu C. C. , Allee D. R. , Maccagno P. , Pease R. F. W.
Published: July 2002

Ultrathin (14–22 nm) poly(methylmethacrylate) (PMMA) films prepared by both spin casting and Langmuir–Blodgett (LB) techniques and novolac films prepared by spin casting have been explored as high-resolution electron beam resists. One-eighth micron lines-and-spaces patterns (equal to the smallest beam diameter available) have been achieved by using a Perkin Elmer MEBES I pattern generation system as the exposure tool, and the definition of 45-nm features has recently been achieved by using a high-resolution electron beam lithography system. [J. H. Newman, K. E. Williams, and R. F. W. Pease, J. Vac. Sci. Technol. B 5, 88 (1987)]. The etch resistance of such films is sufficiently good to allow patterning of a chromium film suitable for photomask fabrication. The most surprising result has been that the pinhole densities in 14.3-nm LB PMMA film and 22-nm spin-cast novolac film are only a few per cm2, considerably lower than the density in spin-cast PMMA films of comparable thicknesses.
High-resolution electron beam lithography with negative organic and inorganic resists
Authors: Bernstein G. H. , Liu W. P. , Khawaja Y. N. , Kozicki M. N. , Ferry D. K. , Blum L.
Published: July 2002

In this paper, we report the achievement of high-resolution exposures in the organic negative resist SAL 601-ER7 (Shipley Co. designation), and also in an optimized inorganic As–S:Ag negative resist system, suitable for in situ processing. Sensitivity curves are presented for the organic material, showing the particularly high sensitivity and contrast of this material at exposure voltages ranging from 10 to 40 keV. High aspect ratio (15:1) patterns were formed with the organic resist but mechanical stability was lacking in these structures. A discussion of optimization of material composition is also given for an inorganic resist system based on As–S chalcogenide. The ultimate resolution attained during this study was 50-nm lines on a 100-nm pitch for the organic material and 35-nm lines on a 70-nm pitch for the inorganic resist system.
Reactive plasticizers in negative electron beam resists
Authors: Namaste Y. M. N. , Obendorf S. K. , Rodriguez F.
Published: July 2002

Negative electron resists generally exhibit excellent sensitivity, but suffer from swelling during development which results in poor resolution. A new approach to this problem is presented, in which reactive monomers are blended with host polymers to provide sensitive negative resists with improved resolution. Polychloromethylstyrene (PCMS) and VMCH (a terpolymer containing 86% vinyl chloride, 13% vinyl acetate, and 1% maleic acid) were both found to be compatible with two reactive monomers, trimethylolpropanetrimethacrylate and dipentaerythritolpentaacrylate (DPEPA). Addition of 20 wt. % of either monomer to PCMS or VMCH resulted in approximately tenfold increases in sensitivity. Sensitivity increases dramatically with increasing monomer content, with a 1:1 blend of VMCH and DPEPA exhibiting a sensitivity of ∼0.15 μC/cm2. This represents a more than 100-fold increase in sensitivity over that of VMCH alone. These blends exhibit resolution of 0.5 μm. Blends of the reactive monomers with fractionated base polymers possessing low molecular weight and low polydispersities are promising. Low molecular weight PCMS and VMCH exhibit good contrast and resolution, but suffer from poor sensitivity. Addition of reactive monomers to these base polymers increases their sensitivity, while maintaining contrast and resolution that is superior to the high molecular weight unfractionated polymer alone. These blends exhibit less swelling than the host polymers.
Photoreflectance surface Fermi level measurements of GaAs subjected to various chemical treatments
Authors: Gaskill D. K. , Bottka N. , Sillmon R. S.
Published: July 2002

Electroreflectance (ER), and its contactless form photoreflectance (PR), are optical characterization techniques that can be used to directly measure the surface electric field, and hence, the surface Fermi level, of GaAs films via the Franz–Keldysh effect and the Schottky relation. Photoreflectance was used to measure the surface electric field of an as-grown Si-doped GaAs film before and after exposure to a photochemical wash of low-conductivity water or an Na2S ⋅ 9H2O treatment at 295 K. As reported recently by various authors, these treatments are claimed to reduce the GaAs surface state density and unpin the surface Fermi level. Calibration ER experiments were performed on a separate n-GaAs Ni Schottky barrier and found barrier heights of about 0.80 eV at 82 and 295 K. For the calibration sample, the surface Fermi level of an air exposed surface was determined to be 0.73 eV below the conduction band at 295 K based on the PR measurements. For the as-grown films, after treatment, the surface Fermi levels were found to be about 0.63 eV. The measurements imply that the treatments affect a minority of the surface states and leave the surface Fermi level essentially pinned. Furthermore, these states have a large influence on the photoluminescence intensity and surface recombination velocity of the GaAs surface. The results of the treatments are not inconsistent with the unified defect model.
Surface structure and bonding of the cleavage faces of tetrahedrally coordinated II–VI compounds
Authors: Duke C. B. , Wang Y. R.
Published: July 2002

New sp3 tight-binding models for ZnO, ZnS, ZnSe, CdS, and CdSe are utilized to calculate the atomic geometries and surface-state eigenvalue spectra of the (110) surfaces of zinc-blende allotropes and the (101̄0) and (112̄0) cleavage faces of the wurtzite allotropes. The models predict that each cleavage face [i.e., zinc-blende (110), wurtzite (101̄0), and wurtzite (112̄0)] exhibits a characteristic relaxation in which the anion relaxes outward and the cation inward. The details of these relaxations depend on the local atomic connectivity and hence vary from one cleavage face to another. The dependence of all three classes of relaxed structure on the specific material considered is shown to be described by a linear scaling of the independent surface structural parameters with the bulk lattice constant. All of these structures are shown to result from a rehybridization of surface bonds created by the movement of a dangling-bond surface state from the energy gap into the top of the valence band as it becomes modified to contain some back bonding and/or surface bonding character. The relaxed cleavage face geometries correspond to new types of epitaxially constrained chemical bonding which exhibit no bulk or molecular analogs.
Reflection high-energy electron diffraction pattern calculations for Si(111)-7×7 surface
Authors: Wu Z.-C. , Schowalter L. J.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) pattern intensity calculations were performed within the kinematical approximation for the Si(111)-7×7 reconstructed surface using a structure model containing dimers, adatoms, and stacking faults (DAS) in the surface layers as proposed by Takayanagi et al. By fitting experimental RHEED pattern intensities taken with incident electron energies of 30 and 20 keV along the [1̄1̄2] azimuth, we found that the lateral and vertical positions of atoms in the first two surface layers (i.e., adatom layer and stacking fault layer) are in good agreement with that of an energy minimization calculation (EMC). The best fit to the low-order diffraction spots was obtained when all adatoms were moved out toward vacuum around 0.45 Å from bulk positions, and the average spacing between adatom layer and stacking fault layer was set at (1.23±0.04)Å. If we include the dimer layer in the calculation, using the dimer spacing given by EMC, we found that the relative calculated RHEED pattern intensities slightly deviated from the experimental RHEED patterns. This slight disagreement may be due to incorrect lateral positioning of the dimer atoms by EMC or the kinematical approximation. Also, the calculated relative RHEED pattern intensity is not very sensitive to variations in the spacing between the stacking fault and dimer layers. Finally, our results imply that the kinematical approximation can be used for analyzing the intensities of superlattice RHEED spots in some suitable RHEED patterns.
Mechanisms of Schottky-barrier formation in metal–semiconductor contacts
Authors: Mönch Winfried
Published: July 2002

During the formation of metal–semiconductor contacts two principally different types of electronic states are effective in determining the surface position of the Fermi level within the semiconductor band gap. These are, first, adatom-related surface states of donor character and, second, the continuum of adsorbate-induced interface states which result from the tailing of the metal wave functions into the virtual gap states of the semiconductor band structure. The first type of state is observed at submonolayer coverages either after depositions at low temperatures or even at room temperature when a cation exchange occurs. Each metal adatom contributes one of those surface donors and their energy levels are linearly correlated with the first ionization energies of the metal atoms. The second type of state exists at interfaces under metallic islands and continuous metallic films. The charge transferred across the interface by these tails of the metal wave functions is explained by the difference in electronegativities of metal and semiconductor in analogy to the concept of the partial ionic character of covalent bonds.
High-mobility inverted selectively doped heterojunctions
Authors: Shtrikman Hadas , Heiblum M. , Seo K. , Galbi D. E. , Osterling L.
Published: July 2002

We have used reflection high-energy electron diffraction (RHEED) to study the surface recovery of AlGaAs under different conditions. A modified process for growth interruptions was then introduced, where a GaAs monolayer was grown at each growth stop, and the arsenic flux was turned off during the low-temperature phase of growth interruptions. Selectively doped inverted heterojunctions were grown using the modified growth interruptions together with low-growth temperature (to avoid Si and impurity segregation). This combined process gave reproducible electron mobilities as high as 460 000 cm2/V s with sheet carrier concentration of 2×1011 cm−2 at 4.2 K.
Sub-100-nm x-ray mask technology using focused-ion-beam lithography
Authors: Chu W. , Yen A. , Ismail K. , Shepard M. I. , Lezec H. J. , Musil C. R. , Melngailis J. , Ku Y.-C. , Carter J. M. , Smith Henry I.
Published: July 2002

In the past, nearly all x-ray nanolithography (i.e., sub-100-nm linewidths) employed the CK x-ray line at 4.5 nm. This, in turn, necessitated near-zero gaps (to avoid diffraction) and carbonaceous masks (e.g., polyimide, which is subject to distortion). In order to use x-ray replication in the fabrication of multilevel devices and circuits that cover large areas (∼a few cm2) and have feature sizes well below 100 nm, we have turned to the CuL line at 1.3 nm. Masks consist of 1–1.5 μm thick Si or Si3N4 membranes and Au absorber patterns, 200 nm thick, which provide 10 db contrast. Focused-ion-beam-lithography (FIBL) with Be++ ions at 280 keV was used to produce quantum-effect-device patterns with minimum linewidths of ∼50 nm. These were replicated using the CuL line, indicating that photoelectrons are not a serious problem. The FIBL process [exposure of 300 nm-thick polymethylmethacrylate (PMMA), followed by Au electroplating] is high yield and much simpler than a trilevel electron-beam-lithography process designed to give comparable results. This is the first time FIBL has been used to make x-ray masks at sub-100-nm linewidths. Along with the device patterns, linear-zone-plate alignment marks were also written on the masks, to be aligned to corresponding marks on the substrate via an optical alignment scheme.
Strain and critical thickness in GaSb(001)/AlSb
Authors: Gossmann H.-J. , Schwartz G. P. , Davidson B. A. , Gualtieri G. J.
Published: July 2002

Measurements of critical layer thicknesses and strain relaxation have been made for AlSb on GaSb(001) using ion scattering/particle induced x-ray techniques. The maximum strain in the films agrees well with that calculated from bulk elasticity data. The critical thickness as measured by the ion channeling experiment is ≊140±30 Å. Films exceeding the critical thickness do not relieve the strain immediately but rather show a gradual relaxation up to ≊1000 Å. The results are compared with theoretical models of strain relief and critical thickness. Issues related to the protection of the AlSb films from oxidation, beam damage, and the use of particle-induced x-ray emission have been addressed. A protective cap of ≊200 Å of Be was found to give the best performance.
A JEOL 100 CXII converted for use as an electron-beam lithography system
Authors: Thoms S. , Beaumont S. P. , Wilkinson C. D. W.
Published: July 2002

A JEOL 100 CXII transmission electron microscope with a scanning attachment has been modified for electron-beam writing. A fully software controllable scan generator has been developed which includes a facility for digital rotation, necessary since the modified stage cannot provide rotation. Gold palladium dots have been fabricated on GaAs with dimensions down to 20 nm, and 60 nm pitch gratings with a 30 nm linewidth.
A multichannel time-dispersion voltage contrast detector
Authors: Khursheed A. , Dinnis A. R.
Published: July 2002

This paper analyzes the feasibility of using a new type of voltage contrast detector. Voltage contrast measurements are made by recording transit times of secondary electrons as they are emitted from a specimen and collected above the final lens of a scanning electron microscope. The study shows that such a voltage contrast detector can be designed to combine a high spatial resolution with a large field of view: a spot radius of less than 0.15 μm can be maintained over a 6×6 mm2 region. The detector also requires 16–20 times less electrons to attain the same voltage resolution performance as conventional retarding-field-type voltage contrast detectors. The new detector is thus expected to speed up current data acquisition times by a factor of 16–20.
Dynamics of arsenic diffusion in metalorganic chemical vapor deposition HgCdTe on GaAs/Si substrates
Authors: Bubulac L. O. , Edwall D. D. , Viswanathan C. R.
Published: July 2002

This paper describes the behavior of arsenic when diffused from an ion implanted source in Hg1−xCdxTe (x≂0.19–0.23) grown by metalorganic chemical vapor deposition (MOCVD) on GaAs/Si substrates. The results are compared with the diffusion of arsenic from a grown source in the same material. Diffusion mechanisms of arsenic were studied from chemical analysis (secondary ion mass spectroscopy) and theoretical modeling, combined with techniques for radiation damage study [transmission electron microscopy (TEM)] for revealing the defect structure of material [chemical defect etching-etch pit density (EPD), TEM], and for electrical junction determination (electron beam induced current). The main experimental observation was that arsenic redistributes during thermal anneal by a multicomponent mechanism in which the tail-components differ depending on the EPD of the material. We propose a model that explains the four components observed: (1) a surface retarded diffusion component; (2) an atomic vacancy-based component in which arsenic starts on Te sublattice, well described by the theoretical Gaussian solution to Fick’s second law of diffusion with a constant diffusion coefficient (D(400 °C)≂3×10−14 cm2/s and D(450 °C)≂2×10−13 cm2/s ); (3) an atomic vacancy-based component in which arsenic starts on metal sublattice and undergoes a diffusion process enhanced by a chemical nonequilibrium dependent on EPD of the material; and (4) a short circuit diffusion component. The same model applies to diffusion from a grown source. To control the electrical junction of a photovoltaic device, the concentration of arsenic in the tail components should be reduced to values lower than the n-type background. We show that the primary requirement to obtain this control is reducing the dislocation density of the material. Proper choice of implant/anneal conditions helps in reducing the tail of the arsenic profiles for a given EPD in the material. No diffusion tails were observed in MOCVD material with EPD in the low 106/cm2 range.
Theory of van der Waals microscopy
Authors: Hartmann U.
Published: July 2002

The ability of scanning force microscopy to detect minute forces at high spatial resolution offers the possibility to systematically map the ever-present van der Waals (VDW) forces between probe and sample. Rigorously based on macroscopic quantum field theory the presented analysis involves an ab initio calculation of VDW forces in close relation to the experimental situation. It is shown that VDW forces directly reflect surface dielectric properties of the sample under investigation. Highly polar immersion liquids present between probe and sample are shown to significantly reduce VDW forces in magnitude. Additionally, some immersion media are found to cause a transition from attractive to repulsive interactions. The lateral resolution of VDW microscopy is estimated to be in the sub-100 nm range. First experimental aspects concerning VDW force detection are presented.
High quantum efficiency InGaAs/GaAs quantum wires defined by selective wet etching
Authors: Gréus Ch. , Forchel A. , Straka J. , Pieger K. , Emmerling M.
Published: July 2002

A technology is reported for the fabrication of buried InGaAs/GaAs quantum wires. For the pattern transfer of the nanometer structures a sensitive high resolution negative e-beam resist is used as a direct etch mask. The essential step of the approach is a selective wet etch process by which only the top barrier layer of a quantum well structure is removed between masked regions. Due to the high energy barrier of the etched surface quantum wells compared to the masked regions a lateral potential well is formed. Investigating the width dependence of the photoluminescence efficiency a high intensity is found, even for narrow wires and a significant shift of the emission to high energies for the smallest wires with widths of 35 nm.
A method of beam size approximation for field emission systems
Authors: Sato M.
Published: July 2002

An approximate method is presented for estimating a focused beam size, based on wave optics including the effects of arbitrary spherical and chromatic aberrations, which yields the contrast performance of an optical system. In order to estimate the contrast performance of an optical system, several beam sizes which correspond to the reciprocal of the spatial frequencies resulting from different amplitudes of the optical transfer function (OTF) are defined. The focus position for estimating a beam size is found at the point where the highest quality image is obtained. This new method, which involves fitting the OTF values by means of functional approximations, can be applied with minimal computational effort.
Photoexcited hot electron relaxation processes in n-HgCdTe through impact ionization into traps
Authors: Seiler D. G. , Lowney J. R. , Littler C. L. , Yoon I. T. , Loloee M. R.
Published: July 2002

In this article we report on a new type of spectroscopy for impurity and/or defect levels in the energy gap of narrow-gap semiconductors using the near-band-gap photon energies from a laser. This spectroscopy is done under the conditions of intense laser photoexcitation and is associated with the Auger relaxation processes of hot electrons involving impact ionization of valence electrons into impurity or defect levels. Wavelength-independent structure in the photoconductive response versus magnetic field is observed at high intensities in samples of Hg1−xCdxTe with x≊0.22 and 0.24. This structure arises from hot electrons photoexcited high into the conduction band by sequential absorption of CO2 laser radiation. The hot electrons lose their energy by impact ionizing valence electrons into impurity/defect levels in the gap. For the sample with x≊0.22 and an energy gap of 95 meV, three levels are found at 15, 45, and 59 meV above the valence band. A level at 61 meV is found for the sample with x≊0.24 and a gap of 122 meV.
Atomic layer epitaxy on (001) GaAs: Real-time spectroscopy
Authors: Aspnes D. E. , Kamiya I. , Tanaka H. , Bhat R.
Published: July 2002

Using reflectance-difference spectroscopy, we perform the first real-time spectroscopic investigation of the evolution of the (001) GaAs surface to cyclic and noncyclic exposures to atmospheric pressure H2, H2 and trimethylgallium, and H2 and AsH3 that simulate growth by atomic layer epitaxy. None of our observations are consistent with any previously proposed simple model. The results emphasize the necessity of real-time measurements for the analysis of complex surface reactions.
Characterization of AZ PN114 resist for high resolution using electron-beam and soft-x-ray projection lithographies
Authors: Early K. , Tennant D. M. , Jeon D. Y. , Mulgrew P. P. , MacDowell A. A. , Wood O. R.
Published: July 2002

We report on resolution experiments with the negative chemically amplified resist AZ PN114. Using soft-x-ray projection lithography at λ=14 nm, we imaged 0.1-μm lines and spaces in film thicknesses ranging from 50 to 200 nm with both a 20× reduction Schwarzschild camera and a 1× Offner ring-field optical system at doses of ∼10 mJ/cm2. High-resolution electron-beam lithography was used to study the effect of postexposure bake temperature on resist resolution and to characterize a trilayer structure. We found that at temperatures higher than 105 °C 0.1-μm features could not be resolved and patterns were distorted. Using e-beam, we resolved 0.075-μm lines and spaces in AZ PN114 and transferred the pattern to the underlying levels of the trilayer. We measured feature edge-noise for 0.1- and 0.2-μm critical dimensions (CDs) over a wide range of doses. We compared the edge noise and linewidth variation with those measured on samples written in poly(methyl methacrylate) (PMMA). We found 3σ values of 24 nm for AZ PN114 and 9 nm for PMMA. These results suggest that AZ PN114, or a resist of similar sensitivity, may be useful for CDs as small as 0.25 μm. To maintain sufficient linewidth control at smaller CDs in manufacturing, less sensitive resists will probably be required.
Incremental sheet resistance and spreading resistance: A comparison
Authors: Queirolo G. , Polignano M. L.
Published: July 2002

Spreading resistance measurements are widely used to obtain carrier depth profiles in shallow silicon diffused layers. The transformation of the raw spreading resistance data into concentration data relies on the calibration of the system against standards of known resistivity. This procedure implies that, for a given carrier concentration, the analyzed sample and the standards have the same carrier mobility. However, this hypothesis is not verified when other carrier scattering centers, in addition to those active in a perfect silicon single crystal (lattice and ionized impurities), are present in the sample. In this case spreading resistance cannot give the correct carrier concentration and an independent measurement of carrier mobility must be performed. In addition, uniform standards are not easily available at the very high doping levels used, for instance, for the source and drain diffusion of complementary metal–oxide semiconductor devices, or for the emitter diffusion in bipolar devices. In this paper we compare the results obtained with incremental sheet resistance and sheet Hall coefficient, secondary ion mass spectrometry, and spreading resistance measurements on samples implanted with BF2 at high fluence and annealed at low temperatures, and on high fluence arsenic implanted layers. Rapid thermal annealed samples, implanted with As, As and P, and BF2 have been also studied, due to the present interest in this low thermal budget method for dopant activation.