bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of high order reconstructions of the Si(100) surface
Authors: Ihm J. , Lee D. H. , Joannopoulos J. D. , Berker A. N.
Published: July 2002

The structure of the reconstructed Si(100) surface is studied using the tight-binding energy minimization method combined with a renormalization-group calculation. (2×1), c(2×2), p(2×2), (4×1), c(4×2), and p(4×2) structures are studied and compared. They are classified into two groups which are separated by a large activation barrier. In one group, (2×1), p(2×2), and c(4×2) structures are almost degenerate in energy, which can result in diffuse (2×1) LEED patterns. In the other group, a second-order phase transition can occur from the c(2×2) to the disordered structure at ∼800 K. Domains of different structures may coexist on the actual surface.
Contact resistance monitor for silicon integrated circuits
Authors: Faith T. J. , Irven R. S. , Reed L. H. , O’Neill J. J. , Jones M. C. , Levin B. B.
Published: July 2002

Chronic problems have been experienced in integrated circuit fabrication lines in the formation of Ohmic contacts between Al–Si interconnect metallization and device (bulk or epi) silicon. One of the reasons for such problems has been the absence of a simple and reliable method for predicting, immediately after metal deposition, whether or not the contact resistances in the finished circuits will be satisfactory. This paper describes and demonstrates such a method for (Al–1% Si)/(phosphorus-implanted) n+ Si contacts.
Sputtering of silicon nitride with hydrogen ions
Authors: Zalm P. C. , Beckers L. J.
Published: July 2002

The possibility of using hydrogen as a substitute for halogen gases in dry etching processes is discussed. Etch rates for Si, SiO2, and Si3N4 are compared.(AIP)
Aluminum growth on (100) indium phosphide
Authors: Houzay F. , Moison J. M. , Bensoussan M.
Published: July 2002

The first detailed study of the room temperature growth of Al on the 4×2 (100) InP surface is reported. In the monolayer range, Al strongly reacts with the substrate and an Al–In exchange reaction occurs, leaving AlP clusters and metallic In. Above a coverage of several monolayers, 3D single-crystal islands of Al grow. Their epitaxial relationship with the substrate is (110)Al//(100)InP, with two possible domains. After a few hundred monolayers, the majority domains coalesce, leading to a smooth (110)Al surface. The final structure is formed by a thin AlP interface between bulk InP and the Al film, whose surface is covered with segregated In.
Characterization of defects introduced during dc magnetron sputter deposition of Ti–W on n-Si
Authors: Auret F. D. , Nel M. , Bojarczuk N. A.
Published: July 2002

Schottky barrier diodes were fabricated by sputter depositing Ti–W on n-type Si in a dc magnetron sputtering system at voltages ranging from 460 to 780 V dc. The diode characteristics were determined by current–voltage (I–V) and capacitance–voltage (C–V) methods, while deep level transient spectroscopy (DLTS) served to characterize the sputter induced defects and investigate their dependence on sputtering voltage. Barrier heights of the devices and the concentrations of the sputter induced defects strongly depend on the sputtering voltage. Devices deposited at 660 V dc had the highest barrier height (0.60 eV) and contained the lowest concentration of defects. Several electron traps were measured in the as-deposited devices. Their concentrations varied by a factor of up to 20 and depended upon the sputtering voltage. Isochronal annealing for 10 min up to a temperature of 400 °C increased the barrier height of all devices, except those deposited at 780 V dc, to a value approximately equal to that of the 660 V dc deposited devices. The isochronal annealing showed that some defects could be removed and that others were again introduced. When annealed at temperatures above 400 °C, defects appeared to be distributed deeper into the substrates than before annealing.
Cr/InSb(110): A study of interface development with high-resolution core-level photoemission
Authors: Boscherini F. , Shapira Yoram , Capasso C. , Aldao C. M. , Weaver J. H.
Published: July 2002

We present a study of Cr/InSb(110) interface evolution based on high-resolution core-level photoemission with synchrotron radiation at room temperature. We find that In atoms are segregated in the early stages of interface development and that the photoemission line shape of this segregated species has a metallic character. At a critical coverage ∼22 Å, In atoms are expelled to the surface from the intermixed region and the In 4d emission increases. Indium surface enrichment continues to ∼42 Å when we observe a slow decay of the In 4d intensity. The progressive chemical shift indicates a more Cr-rich environment.
Structure of CdTe/ZnTe superlattices
Authors: Miles R. H. , McGill T. C. , Sivananthan S. , Chu X. , Faurie J. P.
Published: July 2002

The structure of CdTe/ZnTe superlattices has been analyzed through θ/2θ x-ray diffraction, photoluminescence, and in situ reflection high-energy electron diffraction (RHEED) measurements. Samples are found to break away from CdxZn1−xTe buffer layers as a consequence of the 6% lattice mismatch in this system. However, defect densities in these superlattices are seen to drop dramatically away from the buffer layer interface, accounting for the intense photoluminescence and high-average strain fields seen in each of our samples. Observed variations in residual strains suggest that growth conditions play a role in forming misfit defects. This could explain discrepancies with calculated values of critical thickness based on models which neglect growth conditions. Photoluminescence spectra reveal that layer-to-layer growth proceeded with single monolayer uniformity, suggesting highly reproducible growth. Our results give hope for relatively defect-free CdxZn1−xTe/CdyZn1−yTe superlattices with the potential for applications to optoelectronics offered by intense visible light emitters.
Coherence of defect interactions with features in optical imaging
Authors: Neureuther A. R. , Flanner P. , Shen S.
Published: July 2002

For optical projection printing the variation of image intensity due to a defect in proximity to a feature is shown to be far greater than the image intensity produced by the same defect when it is isolated. This large impact is due to a nearly coherent interaction of electric fields of the defect with those of the feature. The effective mutual coherence μeff between a feature and a defect is defined and shown to be closely related to the degree of spatial coherence in the illumination across the mask. An algebraic model for feature variation as a function of defect size and location is derived from knowledge of defect intensity, feature line edge intensity slope, and μeff. It is predicted and confirmed by simulation that a 0.25λ/NA defect which has only a 3% isolated image intensity will create a 12% linewidth variation when adjacent to a 0.8λ/NA minimum feature size line. The linewidth variation perpendicular to the feature edge is directly proportional to the area of the defect. The length of the bulge produced parallel to the feature edge is given by the point spread function for the optical system and is thus independent of feature size. This makes defects appear larger than their actual size in both projection printing and inspection systems.
High-resolution, low-energy beams by means of mirror optics
Authors: Munro E. , Orloff J. , Rutherford R. , Wallmark J.
Published: July 2002

Electron and ion beam systems with low beam landing energies are needed for many important applications, such as microcircuit inspection and charge storage devices. In this paper, therefore, we have analyzed focusing and deflection systems with strong electrostatic retarding fields immediately in front of the final target plane, with beam landing energies as low as 50 eV. A simple theory is presented, which proves that such strong retarding fields dramatically reduce all the aberration coefficients, including the deflection aberration coefficients as well as the on-axis ones. The overall spot size (for given beam current) inevitably increases as the beam is retarded, due to the increased aperture angle and increased fractional energy spread at the image plane. Nevertheless, on account of the great reduction in the aberration coefficients, the degradation of spot size at low beam landing energies turns out to be much less severe than might intuitively be expected. Our electron optical design software has been enhanced to compute accurately the aberrations of such retarding field systems. This software has been used to verify the predictions of our theory. A practical retarding field system with 50-eV beam landing energy has been built and tested, and its experimental performance confirms our computer analysis. The design has been significantly further improved with the aid of our programs. The computed results show that, using a thermal-field emission source with 1-eV energy spread, the proposed final design should be capable of producing a 111-nA beam of <0.3-μm diameter throughout a 10×10 mm2 deflection field, at a final landing energy of 50 eV.
Molecular-beam epitaxy growth of tilted GaAs/AlAs superlattices by deposition of fractional monolayers on vicinal (001) substrates
Authors: Gaines J. M. , Petroff P. M. , Kroemer H. , Simes R. J. , Geels R. S. , English J. H.
Published: July 2002

We report the successful growth of GaAs/AlAs superlattices having interface planes tilted with respect to the substrate surface plane. The amount of tilt and the superlattice period may be controlled by adjusting the growth parameters. The tilted superlattices (TSL’s) were produced by depositing fractional monolayer superlattices (GaAs)m(AlAs)n, with p=m+n≂1, on vicinal (001) substrates. We demonstrate the growth of quantum wirelike structures produced by placing short sections of TSL between horizontal layers of AlAs. Variations of the TSL period and tilt, both on uniform surfaces and on surfaces containing defects, yield insight to the growth kinetics and to the influence of variations in the growth parameters during molecular-beam epitaxy growth.
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u development of ion bombarded poly(methylmethacrylate) resist in a reactive gas ambient
Authors: Gamo Kenji , Hamauzu Hidenori , Xu Zheng , Namba Susumu
Published: July 2002

Self-development of poly(methylmethacrylate) (PMMA) resist was done by irradiating various rare-gas ions at 50 keV in a mixed gas atmosphere of XeF2 and O2 to enhance the self-development rate, and the effects of various exposure parameters, including gas pressure, mixing ratio, dose, current density, pulse repetition period for pulsed beam irradiation, and ion mass, have been investigated. It was observed that the self-developing rate of PMMA for exposure without gas was very low at high doses of ≥1015/cm2, while the rate with the gas increased almost linearly with increasing dose. This is because the irradiated surface is carbonized and has a low sputtering rate after the high-dose exposure, while the ion assisted chemical process also occurs on the carbonized surface, almost independent of the surface state. It was also found that the self-developing rate depends on the current density and pulse repetition rate. This suggests that the reaction process has a decay time of a few ms.
Diffusivity of Al in Ti and the effect of Si doping for very large scale integrated circuit interconnect metallization
Authors: Nahar R. K. , Devashrayee N. M. , Khokle W. S.
Published: July 2002

Interaction between Ti/Al and Ti/AlSi layered structures is studied by the resistivity measurements. The change in the resistivity of the structure is correlated to the rate of formation of an intermetallic transition metal compound due to interaction between Al and Ti. It is found that the presence of Si inhibits the interaction. As the reaction rate of the intermetallic compound formation is reduced the activation energy increases. The diffusion coefficient of Al in Ti reduces to a value 6.6×10−17 from 6×10−14 cm2/s and the amount of Ti consumed is reduced by about two orders of magnitude at 450 °C for Ti/AlSi. The results are discussed and implications for multilevel metallization are pointed out.
Photoemission study on initial stage of GaAs growth on Si
Authors: Okumura H. , Suzuki Y. , Miki K. , Sakamoto K. , Sakamoto T. , Misawa S. , Yoshida S.
Published: July 2002

Initial stages of GaAs growth on Si by molecular-beam epitaxy were investigated by in situ photoemission spectroscopy. The obtained results suggest that the first layer on Si is the As layer, and that the electronic structure of the Si surface exposed to As4 depends on the exposure temperature. The interface structure between GaAs epilayers and Si substrates is discussed in terms of the initial process of the growth.
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u cleaning of silicon substrate surfaces by remote plasma-excited hydrogen
Authors: Anthony B. , Breaux L. , Hsu T. , Banerjee S. , Tasch A.
Published: July 2002

We have demonstrated a low-temperature cleaning technique for removing both carbon and oxygen from a Si surface. It uses a combination of ex situ wet chemical clean and an in situ remote rf plasma-excited hydrogen clean in an ultrahigh vacuum chamber. Since a remote rf plasma is used, there is insignificant plasma damage or other deleterious effects on surface morphology. A combination of in situ Auger and RHEED analysis has been used to confirm the removal of surface contaminants and the reconstruction of the Si surface. From mass spectroscopy studies, we believe that the hydrogen cleaning is due to a chemical etching of the Si by atomic hydrogen produced by the plasma. This clean is compatible with UHV processing and yields Si substrates that can be used for successful very low temperature (220–400 °C) Si homoepitaxy by remote plasma-enhanced chemical vapor deposition.
Ion irradiation effects on graphite with the scanning tunneling microscope
Authors: Shen T. C. , Brockenbrough R. T. , Hubacek J. S. , Tucker J. R. , Lyding J. W.
Published: July 2002

Scanning tunneling microscope is used to create local surface modifications by means of ion impact damage. Graphite has been used as a test case to demonstrate this local surface sputtering. Using a 0.1-μs voltage pulse of −30 to −140 V applied to the sample in a rough vacuum of 10−2 Torr, a confined area of damage (typically about 100 Å in diameter) is usually obtained. The damaged area consists of several layers of terraces. Defects of the size of a few atoms can also be found. Electronic perturbations caused by defects can form superlattices with a spacing three times that of the graphite lattice. From measurements of the threshold voltage for the discharge, the minimum radius of curvature of the tip can be estimated. The potential applications of this technique and comparison with previous results are discussed.
Pattern generation on semiconductor surfaces by a scanning tunneling microscope operating in air
Authors: Dagata J. A. , Schneir J. , Harary H. H. , Bennett J. , Tseng W.
Published: July 2002

Recent results employing scanning tunneling microscope-based techniques for the generation of nanometer-scale patterns on passivated semiconductor surfaces are presented. Preparation and characterization of hydrogen-passivated silicon and sulfur-passivated gallium arsenide surfaces are described and the determination of the chemical and morphological properties of the patterned regions by scanning electron microscopy and time-of-flight secondary ion mass spectrometry are discussed. Our recent demonstration that ultrashallow, oxide features written by scanning tunneling microscope (STM) can serve as an effective mask for selective-area GaAs heteroepitaxy on silicon is used to illustrate key requirements necessary for the realization of a unique, STM-based nanotechnology.
Imaging purple membranes dry and in water with the atomic force microscope
Authors: Butt Hans-Jürgen , Prater C. B. , Hansma Paul K.
Published: July 2002

Purple membranes were imaged dry and in water with the atomic force microscope. Slowly air-dried purple membranes showed large cracks on one side and narrow cracks on the other side. Purple membranes that were imaged in water adsorbed to mica showed no cracks. The hexagonal arrangement of the bacteriorhodopsin molecules could be seen in the two-dimensional Fourier transform from images obtained in water. Often spots to the fifth order corresponding to about 1.1 nm resolution were observed.
Observation of highly ordered, two-dimensional n-alkane and n-alkanol structures on graphite
Authors: McGonigal G. C. , Bernhardt R. H. , Yeo Y. H. , Thomson D. J.
Published: July 2002

We have directly imaged n-alkane and n-alkanol layers at the liquid–graphite interface using a scanning tunneling microscope (STM). The layers possessed a high degree of two-dimensional ordering, and the adsorbate was observed to enhance the tunneling current. The results of this study agree with calorimetric and surface mass measurements, and show that these macroscopic measurements can aid in the selection of systems suitable for imaging with the STM.
SiC membranes for x-ray masks produced by laser ablation deposition
Authors: Boily S. , Chaker M. , Pépin H. , Kerdja T. , Voyer J. , Jean A. , Kieffer J. C. , Leung P. , Cerrina F. , Wells G.
Published: July 2002

Laser ablation deposition is used for the first time to fabricate SiC membranes for x-ray lithography. The process has the unique advantage of producing in a very simple manner purely stoichiometric (1:1) SiC films free of hydrogen. The variation of deposition rate with laser energy and intensity, the uniformity and quality of the films produced as well as an estimate of the energy of the neutrals and of the ions involved in the deposition are presented. SiC membranes of 1 in. diam have been successfully fabricated after anisotropic etching of the silicon substrate in a KOH solution. They present an optical transparency of 40% at 633 nm.
Gas-induced restructuring of palladium model catalysts studied with atomic force microscopy
Authors: Erlandsson R. , Eriksson M. , Olsson L. , Helmersson U. , Lundström I. , Petersson L.-G.
Published: July 2002

The structure of thin Pd films evaporated onto planar SiO2 substrates changes dramatically during oxygen/hydrogen exposures in ultrahigh vacuum. In this work we have used an atomic force microscope (AFM), operated in the attractive mode, to obtain the three-dimensional morphology of the Pd surface for different film thicknesses and treatments, and compared the data with transmission electron microscopy (TEM) micrographs. During restructuring, a 100-Å film changes from being a smooth continuous film with cracks into metal clusters dispersed on the SiO2 support. In the 5-Å case the metal films are already well dispersed as fabricated. Here the gas exposure instead results in a clustering effect resulting in larger particles. The AFM gives results which are consistent with TEM micrographs but also gives additional information on metal particle shape which can lead to a further understanding of the restructuring process.
Scanning tunneling microscope study on mid-desorption stages of native oxides on Si(111)
Authors: Kobayashi Yoshihiro , Sugii Kiyomasa
Published: July 2002

Scanning tunneling microscope images lead us to the conclusion that the thermal desorption of native oxides on Si(111) does not occur layer by layer but through the formation and lateral growth of voids. This conclusion is consistent with results obtained by reflection high-energy electron diffraction, i.e., that in desorption stages, a (7×7) pattern appears with streaky diffraction spots due to small diffraction areas and with a background due to an amorphous oxide film on the surface. It also agrees with Auger electron spectroscopy results, that is, the temperature dependence of the oxide area before and during desorption. Nucleation centers for voids have not been identified.
A system for the study of magnetic materials and magnetic imaging with the scanning tunneling microscope
Authors: First P. N. , Stroscio Joseph A. , Pierce D. T. , Dragoset R. A. , Celotta R. J.
Published: July 2002

A report of work in progress to determine the feasibility of imaging the magnetization of ferromagnetic samples with the scanning tunneling microscope (STM) is presented. A vacuum system was designed to test several different proposals as well as to prepare and characterize thin films of magnetic materials by conventional means, including STM. This was begun with an attempt to detect spatially resolved spin-polarization of secondary electrons emitted from the sample when operating the STM in the scanning field emission mode. Results are currently inconclusive, but encouraging. A weak spin-polarization signal has been observed corresponding to one of the in-plane components of magnetization. However, topographic feedthrough has not been fully eliminated as a possible spurious source of contrast.
Experimental study of electron cyclotron resonance reactive ion beam etching of W and Mo thin film
Authors: Teng Robert K. F. , Yang H. G.
Published: July 2002

A microwave electron cyclotron resonance ion source has been developed and studied for use in a reactive ion-beam system. The system has been tested and fully characterized for thin film etching. The CF4 reactive ion beam etching of W and Mo, have been investigated as a microfabrication technique for integrated semiconductor devices of submicron geometry. The etching rate has been characterized as a function of ion energy, ion-beam current density, and angle of beam incidence. It has been found that the etching rate increase linearly with current density and pressure. The rate also increases with ion energy, but the rate of increase drops as the ion energy increases. The maximum etching occurs at a beam angle of 35°.
A rewiring technique for integrated circuit operation analysis using a silicon oxide film deposited by a focused ion beam
Authors: Komano Haruki , Nakamura Hiroko , Takigawa Tadahiro
Published: July 2002

The silicon oxide deposition technique with a Si focused ion beam was applied to rewiring from the first aluminum line below a wide power line in a 256k CMOS SRAM. The widths of the power line and the first aluminum line were 130 and 1.5 μm, respectively. First, the layer on the first aluminum line was etched for an area of 4.5×4.5 μm by a Ga focused ion beam. Second, silicon oxide was deposited into the hole using a 60-keV Si2+ focused ion beam with a mixed gas of tetramethoxysilane and oxygen, then, the deposited silicon oxide film was etched for an area of 2×2 μm down to the first aluminum line by the Ga focused ion beam. Last, tungsten was deposited for rewiring from the first aluminum line using the conventional focused ion beam method. The leak current measured between the deposited tungsten and the power line was 1×10−8 A at 5 V which is sufficiently small for operation analyses of semiconductor devices.
Surface energies for molecular beam epitaxy growth of HgTe and CdTe
Authors: Berding M. A. , Krishnamurthy Srinivasan , Sher A.
Published: July 2002

We present results for the surface binding energies for HgTe and CdTe that will serve as input for molecular beam epitaxy growth models. We have found that the surface binding energies are surface orientation dependent and are not simply proportional to the number of first-neighbor bonds being made to the underlying layer. Moreover, because of the possibility of charge transfer between cation and anion surface states, one may have large differences between the binding energy for the first and the last atom in a given layer, and these differences will be different for the narrow-gap, less ionic materials than for the wide-gap, ionic materials. We also find that the surface states associated with an isolated surface atom or vacancy are extended in materials with small gaps and small effective masses, and thus call into question the modeling of surface binding by simple pair interactions.
FeGe liquid metal ion source for maskless isolation implants in InP
Authors: Chu C. H. , Barr D. L. , Harriott L. R. , Wade H. H.
Published: July 2002

A Fe–Ge alloy was used to fabricate a liquid metal ion source (LMIS) for our focused ion beam system. The iron ion and germanium ions can be utilized to create semi-insulating regions for device isolation and n-type doping in InP. The properties of the Fe–Ge LMIS were characterized by measuring the ion current-extraction voltage characteristics, the mass spectrum of the ion species in the ion beam, and the stability of the source current. The changes of resistivity in InP before and after Fe++ implant and after thermal annealing were measured in mesa-etched four-terminal test structures. The resistivity of as-implanted samples increases about four orders of magnitude compared with original resistivity. After rapid thermal annealing at 400 °C for 10 s, the resistivity is about two times larger than that of as-implanted sample.
Low-energy electron beam enhanced etching of Si(100)-(2×1) by molecular hydrogen
Authors: Gillis H. P. , Clemons J. L. , Chamberlain J. P.
Published: July 2002

The use of low-energy electrons to enhance the rate of the reaction between H2 and Si to produce SiHx has been investigated. Etching was accomplished by steady-state application of H2 and electrons, with quadrupole mass spectrometer (QMS) detection of etch products. After etching, low-energy electron diffraction (LEED) was used to check for surface damage. Ultraviolet photoelectron spectroscopy and thermally stimulated desorption were used to determine the surface composition after etching. Experiments of this type have been conducted with electron energies from 200–1000 eV, hydrogen flux held constant, and the sample at room temperature. All have shown qualitatively similar results: the QMS detected species do not represent the fragmentation pattern of SiH4, the thermodynamically predicted product, and LEED shows that the surface has not been damaged.
Evidence for an Eley–Rideal mechanism in the addition of hydrogen atoms to unsaturated hydrocarbons on Cu(111)
Authors: Xi Ming , Bent Brian E.
Published: July 2002

The addition of hydrogen atoms to ethylene and benzene on a Cu(111) surface has been studied by temperature-programmed desorption and integrated desorption mass spectrometry. The results show that adsorbed ethylene and benzene react with atomic hydrogen from the gas phase at temperatures as low as 110 K. The reaction intermediates, ethyl groups and partially hydrogenated benzene, can be isolated on the surface at this low temperature. When the surface is heated to above 150 K, hydrogen elimination reactions occur to produce ethylene, benzene, cyclohexadiene, and cyclohexene. Complete hydrogenation to alkanes also occurs for larger H-atom exposures. The absence of these addition reactions when H atoms are adsorbed onto the surface before ethylene or benzene suggests Eley–Rideal mechanisms for these processes.
Electron beam writing of continuous resist profiles for optical applications
Authors: Stauffer J. M. , Oppliger Y. , Regnault P. , Baraldi L. , Gale M. T.
Published: July 2002

This article reports on progress in the fabrication by e-beam lithography of high resolution, continuous-relief microstructures for integrated optical applications in the visible and near infrared. The microstructures are designed for subsequent replications from an electroformed metal shim by embossing into polymer films on glass. The objective of this work is to fabricate complete integrated optical devices and circuits by low-cost embossing or casting replication technology.
Adsorption and thermal desorption of chlorine from GaAs(100) surfaces
Authors: Mokler S. M. , Watson P. R. , Ungier L. , Arthur J. R.
Published: July 2002

The adsorption and thermal desorption of chlorine on GaAs(100) surfaces prepared either As-rich or Ga-rich has been studied using Auger electron spectroscopy, thermal desorption spectroscopy (TDS), and low-energy electron diffraction (LEED). The initial adsorption occurs more rapidly on the Ga-rich surfaces, however saturation coverages appear equal on both As- and Ga-rich surfaces. Monitoring the As and Ga Auger signals during adsorption reveals a consistent drop in the As signal while the Ga signal remains constant, which may be a result of a replacement reaction between Cl and As. Sputter damaged surfaces result in more exposed Ga, and hence, 20% more chlorine can be adsorbed onto this surface. LEED and TDS experiments on clean surfaces reveal that desorption of As2 closely follows observed reconstruction changes. Chlorine saturated surfaces, however, show no noticeable reconstruction change from that of the clean surface, and upon heating the saturated surface, only GaCl and As2 are seen as desorption products. Both the adsorption and desorption behavior of chlorine suggest a preferential formation of a Ga–Cl bond at the GaAs surface.
Spreading resistance:A quantitative tool for process control and development
Authors: Pawlik Marek
Published: July 2002

During the last five years much work has been done in developing the spreading resistance technique. This work has led to a much clearer understanding of the strengths and weaknesses of the technique. It has been shown that it is capable of producing carrier concentration profiles which are accurate enough to be used in process control and development. A review is presented which highlights the three steps necessary to obtain such data. These are the optimization of the acquisition of raw data, the conversion of the raw data to carrier profiles, and finally the interpretation and use of the final profiles. A great emphasis is placed on the need to acquire the most accurate and reproducible data and on the methods which are used to achieve this objective. For the accurate profiling of ultrashallow layers such procedures are shown to be of paramount importance.
Modification of heterojunction band offsets at III–V/IV/III–V interfaces
Authors: Franciosi A. , Sorba L. , Bratina G. , Biasiol G.
Published: July 2002

III–V/IV semiconductor heterojunctions (with IV=Si, Ge, and III–V=GaAs, AlAs) as well as III–V/IV/III–V single and multiple quantum well structures have been synthesized by molecular beam epitaxy and characterized by a variety of in situ and ex situ characterization techniques. The goal was to investigate the composition profile achievable at the interface, the band discontinuities, the charged versus neutral character of the interfaces, and the dependence of the band discontinuities on the local interface environment. Relatively abrupt composition profiles can be achieved through appropriate growth protocols. Large deviations from the commutativity and transitivity rules of heterojunction band offsets in these systems are related to the establishment of inequivalent local interface environments. Such deviations can in principle be exploited to tune the band alignment in heterostructures.
Influences of gases on the field emission
Authors: Itoh S. , Niiyama T. , Yokoyama M.
Published: July 2002

Influences of gases on the field emission were measured using the specimens of Spindt-type Mo field emitter array. Gases were introduced into a vacuum chamber where the specimens were driven with pulse and dc voltages to emit electrons. In case of pulse drive, effects of N2 , H2 , Ar, or CO2 on emitter arrays could hardly be observed until the vacuum level reduced to 5×10−6 Torr. When the vacuum level was recovered to the background level, emission showed the recovery to be almost the same value as that before gas introduction. When pulse driven, a small amount of H2 gas reduced the work function of the emitter surface and increase the emission characteristics of emission array. In case of dc drive, on the other hand, emission began decreasing at 10−7 Torr. The introduction of SO2 led to the decrease of emission to ∼70% of the initial value at 5×10−6 Torr because of the contamination of emitter tips caused by SO2 when pulse driven. It was also clarified that CH4 , H2 , and CO adsorbed to emitters to reduce the work function of emitter tips. Particularly with CH4 , emission was doubled or more the initial value at 5×10−5 Torr.
Luminescence studies of confined excitons in pseudomorphic Si/SiGe quantum wells grown by solid source molecular beam epitaxy
Authors: Brunner J. , Nützel J. , Gail M. , Menczigar U. , Abstreiter G.
Published: July 2002

Band gap luminescence from pseudomorphic Si/Si1−xGex/Si quantum wells grown by solid source molecular beam epitaxy is studied for a composition range from x=0.14 to x=0.28 and well widths from 1.6 to 6.4 nm. All peak energies are in good agreement with recent results on wide wells and are close to theoretical calculations. With decreasing well width, a systematic decrease of the intensity of the no phonon transition with respect to its phonon replica is observed. For the highest Ge contents, confinement energies of more than 130 meV are evaluated. Realistic Ge profiles including segregation effects of Ge during growth are used for calculating confinement energies. The results demonstrate the importance of segregation for the used growth parameters.
Oxygen processed field emission tips for microcolumn applications
Authors: Kim H. S. , Yu M. L. , Staufer U. , Muray L. P. , Kern D. P. , Chang T. H. P.
Published: July 2002

An oxygen induced sharpening process of field emitter tips, W〈111〉, for use in a scanning tunneling microscope aligned field emission microcolumn system has been developed. The sharpening process which depends on processing temperature and oxygen pressure can be used to control tip radius accurately with reliability and reproducibility. The measured tungsten removal rate was ∼13 Å/min at a processing temperature of ≂1650 K and at an oxygen pressure of ≂4×10−5 Torr. The process is primarily intended for more accurate control of the tip radius and hence performance of newly etched tips, although damaged or blunt tips can also be resharpened in situ with this process. Favorable emission characteristics of the oxygen processed tips have been observed with microcolumn operation: (1) reasonably stable emission current, (2) low extraction voltage, (3) reproducible threefold symmetric emission patterns, and (4) small emission angle.
Chemistry of silicon surfaces after wet chemical preparation: A thermodesorption spectroscopy study
Authors: Pietsch G. J. , Köhler U. , Henzler M.
Published: July 2002

Ultraclean wet chemical preparation in air and a fast new load-locking technique opens up a way to characterize real Si(111) surfaces after processing for microelectronic device fabrication with the proven surface-analytical tools available in an ultrahigh vacuum. For the first time thermodesorption spectroscopy can be utilized, without interference from typical artefacts like contamination introduced by the ex situ preparation, to investigate the chemical termination and molecular composition of silicon surfaces after initial wet chemical key processes in semiconductor technology (chemical and UV/ozone-enhanced cleaning, liquid and gaseous phase etching, rinsing with de-ionized water). By multiplexing a mass spectrometer and analyzing thermally desorbed molecules over a wide range of masses simultaneously, we can separate quantitatively between the major surface-terminating molecules that are inherently responsible for the different chemical surface properties (hydrophilic due to –OH groups after wet chemical or UV/ozone-enhanced oxidation; hydrophobic due to termination with hydrides after etching with hydrofluoric acid/ammonium fluoride, HF/NH4F) and minor species characteristic for details of the preparation process (physisorbed residues upon omission of a final rinsing step; contributions from residual carbon–hydride contamination). Furthermore, distinct desorption channels of hydrogen molecules from mono-, di-, and trihydride surface states allow a characterization of the pH-dependent etching by H2O:HF:NH4F [concentrated HF: selective removal of surface oxides; dilute HF: additional slow isotropic attack of bulk silicon; HF/NH4F: anisotropic attack by fast removal of higher hydride defect sites on Si(111)] and a determination of the resulting microroughness of the silicon surface. Slow regrowth of an ultrathin oxide on HF-treated surfaces during final rinsing with water can be monitored by a separation between H2O desorption at high temperature from surface silanol groups and low-temperature desorption of physisorbed water.
Novel electrostatic column for ion projection lithography
Authors: Chalupka A. , Stengl G. , Buschbeck H. , Lammer G. , Vonach H. , Fischer R. , Hammel E. , Löschner H. , Nowak R. , Wolf P. , Finkelstein W. , Hill R. W. , Berry I. L. , Harriott L. R. , Melngailis J. , Randall J. N. , Wolfe J. C. , Stroh H. , Wollnik H. , Mondelli A. A. , Petillo J. J. , Leung K.
Published: July 2002

Ion projection lithography (IPL) is being considered for high volume sub-0.25-μm lithography. A novel ion-optical column has been designed for exposing 20×20 mm2 fields at 3× reduction from stencil mask to wafer substrates. A diverging lens is realized by using the stencil mask as the first electrode of the ion-optical column. The second and third electrode form an accelerating field lens. The aberrations of the first two lenses (diverging lens and field lens) are compensated by an asymmetric Einzel lens projecting an ion image of the stencil mask openings onto the wafer substrate with better than 2 mrad telecentricity. Less than 30 nm intrafield distortion was calculated within 20×20 mm2 exposure fields. The calculation uncertainty is estimated to be about 10 nm. The calculation holds for helium ions with ≊10 keV ion energy at the stencil mask and 150 keV ion energy at the wafer plane. A virtual ion source size of 10 μm has been assumed. The calculated chromatic aberrations are less than 60 nm, assuming 6 eV energy spread of the ions extracted from a duoplasmatron source. Recently a multicusp ion source has been developed for which preliminary results indicate an energy spread of less than 2 eV. Thus, with a multicusp source chromatic aberrations of less than 20 nm are to be expected. The ion energy at the crossover between the field lens and the asymmetric Einzel lens is 200 keV. Therefore, stochastic space charge induced degradations in resolution can be kept sufficiently low. The divergence of the ion image projected to the wafer plane is less than 2 mrad. Thus, the ‘‘usable’’ depth of focus for the novel ion optics is in the order of 10 μm.
Electromigration kinetics of gold on a carbon thin film surface studied by scanning tunneling microscopy and scanning tunneling potentiometry
Authors: Besold J. , Kunze R. , Matz N.
Published: July 2002

The techniques of scanning tunneling microscopy (STM) and scanning tunneling potentiometry (STP) have been used simultaneously to study the electromigration behavior of a gold covering (1–2 nm) on a carbon thin film surface over 200 h. The applied lateral direct-current (dc) voltage gradient corresponded to a mean current density j=1×104 A/cm2. The topography of the surface was measured by alternating-current (ac) tunneling. The spatial variation of the electric potential was determined from the dc component of the tunneling current. The surface was studied continuously without any interruptions of the tunneling contact on an area of about (2.3 μm)2. The topography and the potential distribution are drastically changed during this long-range experiment. In considerations of the local potential drop we were able to characterize the thickness of the Au covering. In the first stage of the experiment (t<60 h) the STM/STP results indicate a flux of Au atoms from the anode to the cathode. After that coalescence and faceting of the Au covering were observed. We assume that the surface is adjusted to a minimum surface energy configuration, involving in most cases (111) facets.
Plasma-immersed oxygen ion implantation of iron-doped glass for nonmetallic magnetic hard disks
Authors: Zhang L. , Booske J. H. , Cooper R. F. , Shohet J. L. , Jacobs J. R. , Anderson F. S. B. , Goeckner M. J. , Wicksberg E. B. , Was G.
Published: July 2002

The object of this work is to develop a fabrication process to produce a nonmetallic magnetic hard disk with a thin magnetic layer that features small magnetic spinel grains suspended in a host nonmetallic medium. Plasma source ion implantation (PSII) of oxygen into iron-doped magnesium aluminosilicate (MAS) glass and simultaneous implantation of iron and oxygen into calcium aluminosilicate (CAS) glass have been investigated. The implant energy used in these experiments was 30 keV and the oxygen dose was estimated to be 1×1017 ions/cm2 for both MAS and CAS glasses. The results showed that PSII of oxygen into MAS glass increased the iron ions’ binding energy, probably due to the valence state conversion of Fe2+ to Fe3+. The post anneal yielded a thin two-phase layer near the surface, consisting of Mg–Fe–Si–O crystals and the glass matrix. A slight segregation of Fe in the implanted region took place during the anneal, because of the out-diffusion of Fe2+ ions from the substrate to the oxygen-rich region. The simultaneous implantation of iron and oxygen into CAS glass resulted in the formation of an iron oxide, Fe2O3.
Scanning tunneling microscopy of alkali metal-induced structures on the Si(111) surface
Authors: Jeon D. , Hashizume T. , Sakurai T.
Published: July 2002

Scanning tunneling microscopy and spectroscopy have been applied to the study of the atomic structure and the insulator–metal transition of the alkali metal-adsorbed Si(111) surfaces. Tunneling images of the Na- and K-induced Si(111)3×1 surface, formed by metal deposition and simultaneous substrate annealing, showed that the 3×1 structure consisted of zigzag chains separated by a single atomic row. The K-induced 3×1 surface contained more vacancy defects, possibly because of the larger lattice mismatch between K and Si. Upon additional deposition onto the 3×1 surface kept at room temperature, a multilayer of Na and K was grown. The Na overlayer was highly ordered whereas the K overlayer was disordered. However, both Na- and K-covered surfaces exhibited a metallic tunneling I–V (current–voltage) curve when a first layer by room temperature deposition was formed. Cs deposition and annealing induced the formation of a zigzag chain in which atoms were arranged in a 2×2 periodicity, but the overall surface was disordered.
Simulations of the interaction of tunneling electrons with optical fields in laser-illuminated field emission
Authors: Hagmann Mark J.
Published: July 2002

The one-dimensional time-dependent Schrödinger equation is solved for a sinusoidally modulated barrier by means of the numerical procedure of shooting methods. Calculations for square barriers, as well as for the Fowler–Nordheim model of the static potential in field emission, show the existence of a new resonance. The increased tunneling current at resonance is primarily in the upper sideband, which consists of particles that have absorbed one quantum from the time-dependent barrier. Using parameters that are typical of laser-illuminated field emission, this resonance is rather broad and is generally centered between 400 and 600 nm. Analyses for illumination by two cw lasers with a small difference in frequency, and by one amplitude-modulated laser, suggest that the emitted current could be modulated efficiently at microwave frequencies by using lasers operating near the new resonance.
Oxygen-associated defects near Si–SiO2 interfaces in porous Si and their role in photoluminescence
Authors: Carlos W. E. , Prokes S. M.
Published: July 2002

Porous is comprised of nanometer-scale crystallites of Si which, on exposure to the atmosphere, become surrounded by thin oxide layers. It has been proposed that the red room temperature luminescence in this material is primarily due to defects at or near the interface between the crystallites and the thin oxide. We report here the observation of two electron spin resonance (ESR) active oxygen-centric defects; one in nominally unoxidized porous Si and the second in material which has been oxidized for a short period of time. The first is a variant of the thermal donors observed in crystalline Si and the second is the EX center observed in thin layers of SiO2 on crystalline Si. These two centers are thought to have similar cores, a Si vacancy surrounded by four Si–O linkages, with the primary difference in the surrounding lattice (Si vs SiO2). The ESR intensity of the EX center is related to the photoluminescence intensity and may be directly involved in the luminescence process.
Comparison of H+ and He+ implant isolation of GaAs-based heterojunction bipolar transistors
Authors: Pearton S. J. , Abernathy C. R. , Lee J. W. , Ren F. , Wu C. S.
Published: July 2002

The use of multiple energy He+ implantation for producing electrical isolation between neighboring GaAs/AlGaAs or GaAs/InGaP heterojunction bipolar transistors is found to alleviate the problem of time-dependent current gain behavior found in H+ isolated devices. This latter phenomenon is ascribed to rapid diffusion of atomic hydrogen into the active base region during the anneal required to maximize the resistance of the implanted areas, and the subsequent reactivation of passivated C acceptors in the base. Replacement of H+ with He+ ions in the implant scheme produces similar high resistance isolation regions (≳108 Ω/cm) without the presence of hydrogen passivation effects.
Control of temperature gradients and distortion of ion projection lithography masks
Authors: Birman Amnon , Levush Baruch , Melngailis John , Löschner Hans , Stengl Gerhard
Published: July 2002

In ion projection lithography a stencil mask is back ‘‘illuminated’’ by a broad beam of ions, and its demagnified image (∼3×) is projected onto a resist covered substrate. The stencil mask that will be used in the next generation systems consists of a 120-mm-diam 2.5-μm-thick single crystal silicon membrane etched in a 150-mm-diam wafer whose edge acts as part of a supporting frame. The main sources of distortion are thought to be stress relief due to the cutting of holes and the thermal expansion due to mask heating by the incident ions. In this paper we calculate the temperature distribution in the mask for the expected heat input by the beam, the resulting mask distortion, and the effect of optimized radiation cooling. The central 100-mm-diam area of an unpatterned membrane is assumed to be irradiated with an energy input of 3.3 mW/cm. The edge of the membrane at the frame is assumed to be at room temperature and held rigidly. Heat is lost by radiation and by conduction. An effective method of reducing temperature gradient in the membrane is to place a cooled cylinder above the mask surrounding the ion beam. The expected temperature profiles for various sample emissivities as well as the corresponding distortion (radial displacement of the mask membrane) are computed with and without the cooled cylinder. These computations are done for various geometries and cylinder temperatures. For example, in a membrane of emissivity 0.55 with a cylinder, 6.5 cm high 13 cm in diameter, placed 3.2 cm above the mask and cooled to 273 K, the temperature is uniform around 300 K to better than ±1.5 K and the expected mask distortion is then less than ±10 nm. Since the ion beam will be incident on the mask continuously, the cooling cylinder will be effective in reducing thermal distortion to well below the permitted limit.