bluuebunny/crossref_metadata_2025 huggingface dataset:
Giant enhancement of magneto-optical response and increase in perpendicular magnetic anisotropy of ultrathin Co/Pt(111) films upon thermal annealing
Authors: Lin M.-T. , Kuo C. C. , Her H. Y. , Wu Y. E. , Tsay J. S. , Shern C. S.
Published: July 2002

The annealing effects on the magnetic properties, crystallographic structure, and alloy formation, were studied for Co/Pt (111) ultrathin films at coverages up to 6.6 ML, using in situ magneto-optical Kerr effect, low energy electron diffraction, Auger electron spectroscopy, and ultraviolet photoelectron spectroscopy. After the postdeposition annealing in the temperature range of 500–800 K, a significant increase in perpendicular magnetic anisotropy at high coverages and a large enhancement of magneto-optical response with the value about 200%–300% of that before annealing for all coverages investigated are observed. Both findings are shown to be correlated to the formation of a kind of Co–Pt interface (surface) alloy. This is expected to be mainly attributed to the transfer of strong spin-orbit coupling of the Pt into the Co magnetic orbital due to the hybridization during interface alloy formation.
Clean aluminum oxide formation on surface of aluminum cylinder in an ultraclean gas-sampling system
Authors: Ishihara Yoshio , Itou Noriko , Kimijima Tetsuya , Hirano Takashi
Published: July 2002

Because it is difficult to obtain enough space for a gas-analysis system in semiconductor manufacturing lines, gas purity is usually confirmed by an ex situ analysis of gas sampled inside the gas-sampling cylinders (samplers). In order to analyze trace impurities, it is necessary to significantly suppress contaminants generation in samplers and to fabricate surfaces and/or materials with extremely low outgasing rates. We have produced a sampler made of pure aluminum (Al) carried out plasma oxidation in 3% oxygen (O2)/argon (Ar) after the extrusion-lathing process. Nevertheless, the hydrogen (H2) concentration in nitrogen (N2) or Ar sealed at 0.58 MPa in the sampler increased from below 1 to 8 ppb after 168 h. The carbon monoxide (CO) and carbon dioxide (CO2) concentration in O2 also increased. Wet cleaning was carried out in the sampler by deionized water for 72 h at a flow rate of 2 L/min. After wet cleaning, the sampler was annealed at 423 K for 72 h in N2 without exposure to air. We have observed that the H2 concentration in N2 was maintained below 1 ppb, the detection limit of the gas chromatograph for 168 h. The CO and CO2 concentrations in O2 were also sufficiently low. We have confirmed that amorphous γ-aluminum oxide (Al2O3) film with a thickness over 0.5 μm was formed on the inner surface of the sampler using cross-sectional transmission electron microscopy observation. These results suggest that the amorphous γ-Al2O3 film formed by a series of treatments mentioned above functions as a gas-barrier film with an anticatalytic property.
Influence of second phases on the ferroelectric properties of SrBi2TaNbO9 thin films fabricated by radio-frequency magnetron sputtering
Authors: Park Yoon-Baek , Jang Se-Myeong , Lee Jeon-Kook , Park Jong-Wan
Published: July 2002

Ferroelectric properties of SrBi2Ta2−xNbxO9 (SBTN) thin films were affected by the amount of Bi content in SBTN. The addition of Bi into the SBTN films could be accomplished by heat treating the SBTN/Bi2O3/SBTN heterostructure fabricated by the rf magnetron sputtering method. The Bi content was controlled by changing the thickness of the sandwiched Bi2O3 from 100 to 400 Å in the SBTN/Bi2O3/SBTN heterostructure. A Bi2Pt phase was formed as a second phase in the SBTN films inserted with 400 Å Bi2O3 layers, resulting in poor ferroelectric properties. A Bi2Pt phase was formed by the reaction between the bottom Pt layer and the SBTN layer. It is found that the Bi2Pt phase formation depends on the annealing temperature and Bi concentration. By inserting the Bi2O3 layers between the SBTN films, the crystallization temperature and the grain growth temperature was also reduced.
Use of neural networks to model low-temperature tungsten etch characteristics in high density SF6 plasma
Authors: Kim Byungwhan , Sun Jun Hyup , Choi Chang Ju , Lee Dong Duk , Seol Yeo Song
Published: July 2002

A tungsten (W) etch process in a SF6 helicon plasma has been modeled using neural networks. The process was characterized by a 24−1 fractional factorial experimental design. The design factors that were varied include source power, bias power, chuck holder temperature, and SF6 flow rate. The responses modeled include etch rate, selectivity, anisotropy, and nonuniformity. With optical emission spectroscopy, spectra of radical F intensity were collected to investigate the etch mechanisms. High prediction accuracy was achieved in the etch models. The root mean-square prediction errors were 249 Å/min, and 0.41, 0.16 and 0.83 for the etch rate, selectivity, anisotropy, and uniformity models, respectively. While exerting little impact on the selectivity, the temperature greatly affected the etch rate and anisotropy. In particular, the etch nonuniformity was improved at low temperature. Both the selectivity and nonuniformity were predominantly determined by the bias power. The anisotropy was inversely related to the F intensity. Consequently, W etching at temperatures ranging from −50 to −40 °C offers advantages in anisotropy and uniformity, without much sacrifice of the selectivity.
Excimer laser processing for a-Si and poly-Si thin film transistors for imager applications
Authors: Lu J. P. , Mei P. , Fulks R. T. , Rahn J. , Ho J. , Wang Y. , Boyce J. B. , Street R. A.
Published: July 2002

Pulsed excimer laser annealing (ELA) has become an important technology by which to produce high performance thin film transistors (TFTs) for large area electronics. The applications of these advanced TFTs in flat-panel displays and flat-panel imagers for two-dimensional x-ray imaging have attracted much interest. TFTs made from excimer laser crystallized poly-Si thin films with mobilities higher than 100 cm2/V s and off-state leakage currents lower than 2 fA/μm at drain voltage VD=5 V have recently been achieved. The improved off-state leakage current enables one to consider making flat-panel imagers based on poly-Si TFT technology. Laser doping or dopant activation is another important application of the ELA process. Using a laser doping process, we have fabricated a-Si TFTs with self-aligned poly-Si source/drain contacts. These new devices have reduced source/drain parasitic capacitance and their channel length can easily be scaled down. In this article, we will review the excimer laser processing technology for both the poly-Si TFT technology and self-aligned a-Si:H TFT technology and report the current status of developing flat-panel imagers using these new TFT technologies.
Thermal oxidation and anodic film–substrate reactions on Inx Ga1−x Asy P1−y
Authors: Schwartz G. P. , Dutt B. V. , Malyj M. , Griffiths J. E. , Gualtieri G. J.
Published: July 2002

Optically absorbing deposits have been detected by Raman scattering in native oxides on In0.76 Ga0.24 As0.56 P0.44 which were formed by thermal oxidation or by annealing electrochemically anodized films. For air oxidation at 560 °C, the Raman line shape of the absorbing deposit could represent either a two phase mixture of As and an alloy of Asx P1−x with x∼0.7 or pure Asx P1−x with a somewhat larger value of x. The latter possibility seems the more likely at this time. Analysis of the Raman band shapes for air oxidation at 730 °C suggests a mixture of two immiscible Asx P1−x solid solutions, both with x≥0.7. In no case is a simple two phase mixture of crystalline elemental arsenic and red phosphorus detected. Oxidation of the quaternary in As2O3 leads to the detection of hexagonal elemental As, Asx P1−x (x>0.7), and InPO4. The detection of InPO4 provides an explanation of why the detected Asx P1−x alloys are phosphorus depleted relative to the bulk substrate composition, i.e., the formation of orthophosphates such as InPO4 and GaPO4 deplete the potential source of elemental phosphorus. No absorbing deposits were detected in as-grown anodic films on the quaternary, but annealing the anodic films leads to the formation of an optically absorbing layer. The Raman band shape associated with this deposit is broad and has been tentatively assigned as an Asx P1−x alloy. There is insufficient structure, however, to provide an accurate estimate of x or to exclude the possibility that it contains some admixture of amorphous arsenic.
Characterization of GaAs:O–Ge and ZnSe:O–Ge heterointerfaces grown on oxygen-exposed GaAs and ZnSe substrates
Authors: Jain F. C.
Published: July 2002

The electronic behavior of p–n and isotype heterojunctions is shown to be significantly different when a chemisorbed oxygen/oxide layer is present at the heterointerface. Specifically, the characteristics of nGaAs:O–nGe and nZnSe:O–pGe devices are described. In nGaAs:O–nGe devices we have observed under dark and illuminated conditions a polarity inversion in V–I characteristics not normally expected of conventional nGaAs–nGe heterojunctions. The polarity inversion and other aspects of V–I and C–V characteristics of GaAs:O–Ge devices are consistently explained by a new band model involving the presence of localized inversion and/or accumulation layers at the heterointerface. The novel features in the V–I and C–V characteristics of nZnSe–pGe heterojunctions resulting from the presence of interfacial oxygen are also presented.
Study of the GaAs–Au and Si–SiO2 interface formation by the Kelvin method
Authors: Lassabatère L. , Palau J. M. , Vieujot-Testemale E. , Ismail A. , Raisin C. , Bonnet J. , Soonckindt L.
Published: July 2002

In this paper we describe typical and simple results concerning the deposition of metal on GaAs surfaces and the first steps of Si oxidation. In the case of GaAs/metal, typical results illustrating the barrier formation, the electron affinity modification, the contribution of initial surface defects, and metal induced defects are presented and discussed, using the unified model of Spicer, Lindau et al. In the case of Si/SiO2, we focus on illustrating the method of the growth of the oxide and the resulting work function modifications.
Persistent red shift of the photoluminscence from the semi-insulating GaAs substrate in an AlxGa1−xAs/GaAs modulation-doped structure
Authors: Fischer Bernhard , Collins Douglas M.
Published: July 2002

The photoluminescence (PL) spectra of undoped GaAs substrates which are partly covered by a modulation-doped AlxGa1−xAs/GaAs structure show a remarkable new effect at low temperature (T<100 K). When a voltage is applied between two Ohmic contacts to the modulation-doped structure such that a current flows parallel to the interface, the near band edge PL spectra shift slowly toward lower energies with an accompanying reduction in intensity. After removing the bias, the spectra gradually recover to their original position and intensity. The time constants for this behavior vary from sample to sample and range from between a few minutes to more than an hour. The asymptotically approached magnitude of the spectral shift is a monotonic function of the applied voltage. Its value is approximately 18 meV for an 8 V applied bias. The direction and magnitude of shift are independent of the sign of the bias and are uniform over the total area of the sample. The modulation-doped structure can be reduced in lateral dimensions to a small area containing the two Ohmic contacts, and the spectra of the substrate measured several millimeters away from the modulation-doped area still show the described effect. Optical absorption measurements through the substrate show a corresponding shift of the band gap absorption edge toward lower energies thus confirming that the effect occurs throughout the bulk.
Submicrometer-gate GaAs FET fabrication using masked ion beam/optical hybrid lithography
Authors: Adesida I. , Zhang M. , Sadler R. , Tiberio R. , Wolf E. D.
Published: July 2002

A masked ion beam/optical hybrid lithography process for fabricating GaAs MESFETs is described. Techniques for eliminating the damage caused by the ions penetrating through the resist into the GaAs substrate are discussed. Submicrometer gate GaAs FET fabricated using the hybrid lithography is shown and the electrical characteristics of the depletion-mode device presented.
Some investigations on anodic oxide films on gallium arsenide
Authors: Ghosh C. , Polhamus W.
Published: July 2002

The anodic oxides on metal-organically grown GaAs have been investigated by Auger and secondary ion mass spectroscopy (SIMS). The surface of the oxide was found to contain carbon contamination amounting to ∼7 at.%. The carbon contamination was no longer detectable after Auger sputter profiling for 0.6 min (at a rate of 40 Å/min for Ta2O5). Carbon contamination to similar depth on the surface was also observed on freshly etched GaAs. Auger analysis results show a Ga to As atomic ratio of 6:1 for the oxide. As the oxide/GaAs interface is approached, the As concentration increases sharply. The SIMS spectra of the surface and the bulk of the oxide does not show the presence of Ga2O3 and As2O3, believed to be the main constituents of anodic oxides, but peaks corresponding to GaO and AsO and elemental Ga and As are observed. This is probably due to decomposition of Ga2O3 and As2O3 because of argon ion bombardment.
A new probe of the optical properties of surfaces
Authors: Olmstead Marjorie A. , Amer Nabil M.
Published: July 2002

We have developed a new technique, photothermal displacement spectroscopy, for studying the optical and thermal properties of surfaces. The ability to distinguish surface and bulk optical absorptions is demonstrated. The signal is directly proportional to the surface absorption coefficient and is insensitive to variations in the real part of the dielectric constant.
A large angle electrostatic deflection, variable shaped, electron beam exposure system
Authors: Moriya Shigeru , Komatsu Kazuhiko , Harada Katsuhiro , Kitayama Toyoki
Published: July 2002

In electron beam direct writing, a capability of ‘‘one chip within one deflection field’’ can reduce time wasted in stage moving, and eliminate field stitching errors in a chip. These advantages lead to high throughput and high overlay accuracy for successful VLSI fabrications. A large angle electrostatic deflection, variable shaped, electron beam exposure system (EB57) has been developed to achieve this capability. The key EB57 technologies are a large angle electrostatic deflection and high speed deflection control. Newly developed multiple electrostatic deflectors were designed using an in-lens, dual channel deflection method. In this method, two types of field and subfield deflectors are equipped inside a projection lens. Deflectors free of third and fifth θ components can provide a large angle of deflection with a 10 mm2 field. 18-bit digital-to-analog converters, and ±800 V amplifiers effect this large field deflection. The high breakdown voltage for the amplifiers is attained by connecting vertical power MOSFETs in series. The settling time of the amplifiers is less than 10 μs at 1/64 full scale. Amplifiers for subfield scanning and beam shaping have a 250 ns settling time at full scale. To correct chip distortions, deflection distortions, and stage positioning errors, a new data correction method that takes rounding off errors into consideration has been applied to a high speed arithmetic unit. This EB57 system can write from 7 to 10 4-in. wafers per hour with 0.5 μm lithography.
Design aspects of the optics of the VLS-1000 electron-beam direct-write lithography system
Authors: Petric P. F. , Taylor N. J. , Utlaut M.
Published: July 2002

Some of the basic considerations in the design of the electron optics of a variable line scanning (VLS) system, a particular form of variable-shape electron-beam lithography system, are discussed. In the VLS system, the electron beam is projected on the resist-coated wafer in the form of a narrow line whose length and position can be varied simultaneously as it is scanned. The writing is done as the stage is moved in a serpentine fashion under laser control with the pattern features placed using both raster and vectorial placement techniques. The line can be produced in either of two orthogonal directions in order to maximize the exposure rate. In general, the required source brightness is greater than that of a more conventional-shaped-beam system, however, this can be achieved readily with LaB6 at a desirable operating temperature. Exposed and developed patterns demonstrate the resolution capabilities of the optics.
Effects of deposition parameters on the growth of thermal oxide on silicides over single crystal silicon
Authors: Chu Wileen , Bhandia Aloke S. , Stimmell James B.
Published: July 2002

A crucial criterion for utilizing silicide in MOS technologies is the ability to grow good thermal oxide. Silicides that are deposited or oxidized under nonoptimal conditions produce hazy or nonadherent oxides. The effects of three deposition parameters on subsequent oxide quality of planar magnetron cosputtered films were investigated. These variables are: (1) stoichiometry, (2) substrate bias, and (3) substrate rotation speed. The films were oxidized in steam at 920 °C for various time intervals. The appearances were determined visually. Oxide thicknesses were obtained. Substrate bias was observed to play a more critical role in oxide quality than the rotational speed. Changes in stoichiometry produced barely noticeable variations in oxide quality unless the films were too metal rich. Voids were not found to be an intrinsic characteristic of the oxide growth.
Application of titanium polycide interconnects in a silicon-gate process
Authors: Gilfillan Celia D. , Spinella Sal
Published: July 2002

Devices which use titanium polycide to replace polysilicon in a silicon-gate process have been processed and evaluated. The circuit used was designed for standard N-channel Si-gate processing, and was a standard production part. Working devices were obtained and life tested. Electrical characteristics of polycide wafers were compared with electrical characteristics of devices made from the same mask set using polysilicon interconnects. The titanium polycide wafers successfully completed life testing (1000 h of dynamic life testing at 125 °C) showing no degradation.
Direct transfer of resist grating patterns onto InP by reactive-ion etching using CCl4/O2
Authors: Hirata Kazuo , Mikami Osamu , Saitoh Tadashi
Published: July 2002

A reactive-ion-etching technique for direct transfer of resist grating patterns onto InP surfaces was developed. A mixture of CCl4 and O2 at a pressure of 1–5×10−3 Torr enabled a high etching rate of about 850 Å/min for InP. The etch rate ratio of InP to AZ-1350 resist was 3.5-1. Fine grating patterns with periodicity of 4700 Å were successfully transferred to InP and a corrugation depth of about 2000 Å was obtained.
The common anion rule: An electrochemical contribution
Authors: Gautron Jacques , Sculfort Jean-Lou
Published: July 2002

The electrochemical behavior of III–V ternary GaxIn1-xP alloys (with 0≤x≤1) is studied in aqueous and nonaqueous media (sodium iodide liquid ammoniate). The energy position, referenced through an electrochemical scale, of the maximum level of the valence band for each of these compounds is nearly constant. These results still show that this position depends mainly on the anion P, through its electronegativity, in accordance with the so-called common anion rule found with semiconductor–metal junctions.
Mass spectroscopy in ion implantation
Authors: Matteson S.
Published: July 2002

The principles of mass spectrometry are discussed and applied to the problem of assuring the purity of ion beam species in ion implantation. Experimental confirmation of various ion dissociation and charge exchange phenomena is presented for the case of a SiF4 plasma used to produce Si ions for doping GaAs. Techniques for recognizing spurious ion species are explained.
A simple semiquantitative model for classifying metal–compound semiconductor interface reactivity
Authors: McGilp J. F. , McGovern I. T.
Published: July 2002

A scheme for classifying the interfacial reactivity of metal–compound semiconductor systems is presented. The scheme uses a simple bulk model to calculate a ‘‘heat of reaction,’’ which includes the effects of metal–semiconductor anion compound formation and metal–semiconductor cation alloying. The scheme is applied to the layered semiconductors GaSe and MoS2, III–V semiconductor InP, and the II–VI semiconductor CdTe, for a wide range of metals. The resulting classification compares favorably with published experimental data on ultrahigh vacuum cleaved surfaces. For the majority of these interfaces, the reactivity classification is the same as that obtained by considering only metal–semiconductor anion compound formation. However, for the combinations Au–InP, Ni–CdTe, Ni–GaSe, Cu–CdTe, and Cu–GaSe, it is only by including alloying that the combination is classified as reactive, in agreement with experimental data.
Capacitance–voltage characterization of silicide–GaAs Schottky contacts
Authors: Jackson T. N. , DeGelormo J. F.
Published: July 2002

Capacitance–voltage carrier concentration profiling has been used to investigate the high temperature stability of refractory metal silicide films on GaAs. This technique is more sensitive to silicide–semiconductor interactions than is forward I–V characterization since tenacious surface Fermi level pinning of GaAs can yield stable diode barrier height and ideality factor measurements even for some cases of gross silicide–semiconductor interaction. Using C–V characterization we have found tungsten silicide film compositions that exhibit excellent high temperature stability on GaAs and have suggested failure mechanisms for other less stable film compositions.
Large modification of the surface-enhanced Raman scattering of pyridine on Ag surfaces by Pd submonolayers
Authors: Lopez-Rios T. , Gao Y.
Published: July 2002

We report on a large decrease of surface-enhanced Raman scattering (SERS) of pyridine on cold and island Ag films due to Pd submonolayers. In contradistinction, it is shown that very thin (∼1 monolayer) Ag deposits give rise to SERS unobserved before the Ag deposition. Auger and reflectivity measurements are also presented.
Photodesorption and adsorbate–surface interactions stimulated by laser radiation
Authors: Chuang T. J.
Published: July 2002

Laser photons can interact with a gas-solid system to promote heterogeneous reactions and to stimulate desorption. In this paper, a review is given on desorption processes induced by photon radiation. This includes laser-induced thermal desorption and photodesorption by ultraviolet, visible, and infrared lasers. Relevant theories and recent experimental results are discussed with particular emphases on surface molecular dynamics and on assessing the quantum and the thermally assisted radiation effects.
Lattice distortions and energies of atomic substitution
Authors: Kraut Edgar A. , Harrison Walter A.
Published: July 2002

The energies of atomic substitution and the associated excess enthalpies of mixing have been calculated with and without lattice relaxation for both isovalent and heterovalent substitutional impurities in tetrahedrally coordinated semiconductors by using the universal parameter tight binding theory of Harrison. For isovalent substitutional impurities, where experimental data and other theoretical predictions are available, agreement is good. Distortions around isovalent impurities such as indium in gallium arsenide can be readily calculated using the known natural bond lengths for indium arsenide and gallium arsenide. We define corresponding natural bond lengths for heterovalent substitutional impurities (those which come from a different column from that of the atom they replace) by minimizing the total bond energy with respect to interatomic separation. We have used the natural bond lengths calculated in this way to estimate the displacement of the neighbors to a number of impurity systems, and the corresponding reductions in the energy to substitute a free atom for a host atom. When two atoms are exchanged across an interface, relaxation around both atoms must be included and can be large. Such interchanges for heterovalent atoms affect heterojunction band lineups and are therefore of particular interest.
n
+ InGaAs/nGaAs heterojunction Schottky diodes with low barriers controlled by band offset and doping level
Authors: Kleinsasser A. W. , Woodall J. M. , Pettit G. D. , Jackson T. N. , Tang J. Y.-F. , Kirchner P. D.
Published: July 2002

We have fabricated and measured low barrier (30–150 meV) Schottky diodes using n+InGaAs/nGaAs pseudomorphic structures with up to 1.5% lattice mismatch. The I-V measurements at temperatures from 4 to 200 K show rectifying behavior and indicate transport mechanisms which range from tunneling to thermionic emission. The transport properties and barrier height determinations indicate that the band offset is predominantly in the conduction band. The barrier height increases with In concentration, which is consistent with band calculations based on previous experimental data.
Absorption spectra of modulation-doped semiconductor quantum wells
Authors: Sanders G. D. , Chang Y. C.
Published: July 2002

Absorption spectra of modulation-doped GaAs–Ga1−xAlxAs semiconductor quantum wells are studied with the use of a multiband effective mass theory in which coupling of the heavy and light hole valence bands is taken into account. We consider the case in which the (GaAl)As barrier is doped with acceptors and the quantum well is populated with holes. Interband optical absorption for vertical transitions are obtained using Fermi’s golden rule in the envelope function approximation explicitly taking into account the variation of the optical matrix elements with k. Two dimensional excitonic effects are also included in a model similar to that of Shinada and Sugano but including the k dependence of the optical matrix elements. We find that the mixing of heavy and light hole states of both symmetric and antisymmetric envelope functions gives rise to direct optical transitions between all pairs of valence and conduction subbands in violation of the Δn=0 selection rule.
Theory of Si/NiSi2 interface states
Authors: Lim Hunhwa , Allen Roland E.
Published: July 2002

We report calculations of the intrinsic interface states for the Si/NiSi2(111)-type A interface. All of these states are resonances, since NiSi2 is a metal, but one band is found to have a relatively narrow width throughout most of the surface Brillouin zone. This band, whose density of states peaks about 1–2 eV below the Si valence band maximum Ev, should be observable in photoemission experiments. It is associated primarily with Si p and Ni p orbitals in the NiSi2, but also has some Si p amplitude on the Si side of the interface. Resonances associated primarily with Ni d orbitals are found about 3–4 eV below Ev.
Wide band antireflection coatings for semiconductors grown by MBE
Authors: Truscott W. S. , Fleischer S. , Singer K. E.
Published: July 2002

The performance of any optoelectronic system and of infrared windows made from semiconductors is reduced by the large coefficient of reflection at each semiconductor-free space surface, which has a typical value of about 30%. This paper reports the successful growth of multilayer antireflection coatings on GaAs using alternating layers of AlAs and GaAs. Bandwidths of 14% for a reflectivity of less than 13%, and 6% for a reflectivity of less than 7% were achieved, together with a minimum reflectivity of 1.3%. Model calculations suggest that these two structures can have reflectivities less than 10%, and 1% for these bandwidths under ideal conditions; the reasons for these discrepancies are explained. The results show that molecular beam epitaxy (MBE) has the potential for reproducible growth of antireflection coatings giving signal gains of 1.5 dB per surface at a given design wavelength.
The role of length scale in the competition between localization and interaction effects in MBE grown modulation doped GaAs–GaAlAs heterojunctions
Authors: McFadden C. , Long A. P. , Myron H. W. , Pepper M. , Andrews D. , Davies G. J.
Published: July 2002

We report further investigations on the enhancement of fractional quantization obtained by increasing the frequency of measurement and thus decreasing the length scale of the system. The effect is observed in higher order Landau levels than has been previously reported. We also present evidence for the frequency induced removal of the integer quantized Hall effect.
Effects of ion species and adsorbed gas on dry etching induced damage in GaAs
Authors: Pang S. W. , Geis M. W. , Efremow N. N. , Lincoln G. A.
Published: July 2002

Dry etching techniques which induce minimum damage on the etched surfaces are essential for submicrometer device fabrication. In this study, damage induced in GaAs by ion-beam etching and ion-beam-assisted etching was found to be affected by ion energy, ion mass, and adsorbed gas on the sample surfaces during etching. The etching characteristics of Ne, Ar, and Xe ions with energies ranging from 250 to 2000 eV were studied. The effect of gas adsorption was investigated by using Cl2 (reactive gas for GaAs) and NO2 (nonreactive gas for GaAs) with gas fluxes equivalent to pressures between 2 and 50×10−4 Torr. Dry etching induced damage was evaluated by measuring electrical characteristics of Schottky diodes fabricated on the etched GaAs surfaces. Our results indicated that damage in GaAs can be minimized by reducing the ion penetration distance into the substrate by using low ion energy and heavy ion species, and by introducing adsorbed gas, such as Cl2 or NO2, on the sample surface as a protective layer.
Oxygen ion etching mechanism investigation by surface enhanced Raman scattering
Authors: Asada Susumu , Mori Katsumi
Published: July 2002

Reaction products on the surface of an etched polymethylmethacrylate (PMMA) film during O2 reactive ion etching (RIE) have been studied for clarifying RIE processes. Surface enhanced Raman scattering, due to sputtered silver particles on the surface of the etched PMMA film, is used for the surface analysis. The measured Ar laser Raman spectrum for etched PMMA film exhibits double peaks at 1350 and 1580 cm−1 with a subpeak at 1780 cm−1. Judging from the observed graphite and molecular spectra, the double peaks are interpreted as being due to carbon with fused ring structure on the etched PMMA surface. The subpeak is attributed to oxidized carbon structure with C=O bond. The presence of these carbon reaction products is expected to dominate organic film etching mechanisms.
Comparison of N
P
N transistors fabricated with broad beam and spatial profiling using focused beam ion implantation
Authors: Chu S. D. , Corelli J. C. , Steckl A. J. , Reuss R. H. , Clark W. M. , Rensch D. B. , Morris W. G.
Published: July 2002

The base region of NPN transistors was fabricated using a 0.2 μm beam diameter (maskless) of 75 keV B focused ion beam (FIB), and on the same wafer a broad beam (with mask) of 75 keV B ions with conventional ion implantation. Transistor properties were compared using electrical characteristics, microbeam Rutherford backscattering spectroscopy (RBS), and scanning Auger microscopy (SAM). No significant differences were found between the transistors fabricated with FIB and with conventional ion implantation. Lateral doping profiles were implanted using the FIB system. Bipolar transistors with lateral active base profiles implanted with FIB were shown to have normal device characteristics. While the main intent was to assess the feasibility of fabricating the devices, the expected relationships between lateral profile and base resistance and current gain were observed. The results indicate that FIB can be used to study the impact of lateral profiles on device performance.
Early stages in thin film metal–silicon and metal–SiO2 reactions under rapid thermal annealing conditions: The rapid thermal annealing/transmission electron microscopy technique
Authors: Natan Menachem
Published: July 2002

A simple and fast structural characterization technique for thin film solid-phase reactions has been developed, based on a combination of rapid thermal annealing and transmission electron microscopy (the ‘‘RTA/TEM technique’’). The technique is used to investigate fast interfacial reactions in layered Si/Ni/Si, Si/Co/Si, Si/Ti/Si, and SiO2/Ti/SiO2 films. In contradiction to first-phase rules, all three metal–Si systems exhibit nucleation of multiple ‘‘first’’ silicides; under certain conditions, an amorphous (metal+Si) mixture exists prior to this nucleation. The simultaneous study of Si–Ti and SiO2–Ti reactions with RTA/TEM can quickly determine processing ‘‘windows’’ when selective silicidation is required.
Mechanical properties and diffusion of metallic superlattices
Authors: Tsakalakos T.
Published: July 2002

An enhanced modulus effect has been observed in several composition modulated thin films systems containing short wavelength modulations 0.8–1.0 nm. The foils were produced by vapor deposition using two or three source evaporators. As compared with homogeneous foils of the same average composition, the modulated foils exhibited an appreciable increase (up to 300%) in modulus. The plastic behavior, breaking and microhardness of these foils are also presented as a function of the modulation parameters. Current theories based on electronic and strain effects on the elastic constants of metals are also presented to explain the origin of the supermodulus effect. Interdiffusivities of binary and ternary modulated alloys have been measured from the decay of the x-ray diffraction satellite intensities produced by the modulation. The stability of concentration waves at various temperatures is also discussed and examples of the determination of spinodal temperatures are given. The effect of loss of coherency and the appearance of screening singularities in the diffusivities are also considered.
Spatially resolved x-ray photoelectron spectroscopy studies for device-type applications
Authors: Boland John J.
Published: July 2002

A novel scheme is introduced which allows spatially resolved x-ray photoelectron spectroscopy (XPS) studies to be performed in device applications by taking advantage of the ability to bias the various components of the device. The application of a bias voltage produces a shift in the Fermi level of the biased component and there is a corresponding shift in the binding energy of electrons emitted from this component. In this manner it is possible to discriminate between the XPS signals that are due to a given element but which originate from different regions of the sample. By analogy with the corresponding biasing scheme employed in SEM studies, this technique has been called voltage contrast XPS.
Method for measuring contact resistance immediately after metal deposition
Authors: Faith T. J. , O’Neill J. J. , Irven R. S.
Published: July 2002

Modifications have been made on a contact-resistance-monitor (CRM) process which permit measurements to be made immediately after metal deposition, i.e., without photolithographic metal patterning. The modified or prepatterned CRM has been calibrated versus the standard CRM, and shown to have equal sensitivity to sputter-deposition system cleanliness. The sensitivity of the CRM method for monitoring system cleanliness has been shown to be approximately the cube of the sensitivity of residual-gas-analyzer methods.
Chemical reaction at the Al–GaSb interface
Authors: Susnow R. G. , Schwartz G. P. , Gualtieri G. J. , Sunder W. A.
Published: July 2002

Surface reflection Raman scattering has been used to examine interfacial chemical reactions which occur at the Al–GaSb interface during thermal aging. The chemical composition of the interfacial layer has been determined and reactions have been identified at temperatures as low as 300 °C. Under thermal aging conditions where the Al overlayer is not fully reacted, the primary reaction product is AlSb. Depletion of the aluminum overlayer followed by continued reaction leads to an interdiffused layer of AlxGa1−xSb which exhibits a concentration gradient normal to the interface. Both amorphous and crystalline AlSb have been identified depending on the thermal aging conditions.
Orientation dependence of crystal defects formation in Si molecular beam epitaxy
Authors: Hirofuji Yuichi , Matsuo Naoto
Published: July 2002

The origin of crystal defect in epitaxial Si film grown by the molecular beam epitaxial (MBE) method has been studied. Examination went down to the detail of crystal defect density, unintentionally doped carrier concentration, and carbon contaminations of the epitaxial film with both substrate orientations of (100) and (111). The crystal defect originated from the epitaxial interface has been affected by the excessive carbon content formed at the interface during the substrate cleaning process, because both the defect and the amount of carbon with (100) are statistically much lower than those with (111). Both unintentionally doped hole concentration which has a run number dependence and the crystal defect formed during the epitaxial growth have been much smaller with (100) than with (111). A similar trend in the run number has also been observed in terms of the residual gases of CO and CO2 in the vacuum chamber. From these facts, it has been concluded that characteristics of the MBE film grown on the (111) surface are much more sensitive to the carbon contamination than those on the (100).
A photoemission study of the Si(111)/Gd interface: A comparison with the bulk silicides
Authors: Puppin E. , Nogami J. , Carbone C. , Shen Z. X. , Lindau I. , Pate B. B. , Abbati I. , Braicovich L.
Published: July 2002

Synchrotron-radiation photoemission data from the Si(111)/Gd interface (Si 2p/Gd 4 f core levels and valence states) are compared with those from all of the silicides in the Si–Gd phase diagram (Gd3Si5, GdSi, Gd5Si3) measured in strictly comparable conditions. It is shown that the first silicide-like reaction product is formed for a Gd coverage of about 2 monolayers and that this interface silicide-like product is correlated with GdSi. These results are also discussed in connection with the Si(111)/Yb interface where the same experimental approach shows a correlation between the first silicide-like interface product and the metal-rich silicide.
Two-dimensional electron transport in InP surface layers
Authors: Bailey G. R. , Owens R. E. , Wilmsen C. W. , Goodnick S. M.
Published: July 2002

An Ensemble Monte Carlo (EMC) approach to simulate electron transport in InP surface layers. The EMC includes scattering caused by surface roughness, ionized impurities, defects, and polar optic and acoustic phonons. The EMC has been used to analyze two different ranges experiment mobility measurements reported in the literature. Low mobility samples with weak temperature dependence are dominated by surface roughness and ionized impurity scattering. Polar optic scattering at moderate electrical fields is shown to have a strong influence on high mobility samples.
Auger electron spectroscopy and low-energy electron diffraction investigation of the InSb(110)+Ag system at 10–300 K with θ=0–20 monolayers
Authors: Aristov V. Yu. , Bolotin I. L. , Grazhulis V. A.
Published: July 2002

The Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) methods have been employed to study the film growth processes of the high-vacuum-cleaved InSb(110) surface at 10 and 300 K in the coverage interval from 0 to 20 monolayers (ML). The sample evolution in the process of heating up to room temperature after the Ag deposition at 8 K, and in the process of cooling down to 10 K after the deposition at 300 K has been investigated. A comparison of the Auger signals obtained in the process of deposition at 10 and 300 K, and in the process of heating of low-temperature-deposited samples has shown that at 10 K the depth distribution of the Ag atoms has a statistic character, and at room temperature the film growth is accompanied by the island formation. The conclusion on the In-atom diffusion through the silver film is suggested by the interpretation of the Auger spectra, especially of those taken in the process of heating the samples. It is found that the deposition at 300 K leads only to an increase of homogeneous (θ≲10–12) or inhomogeneous (θ≳10–12) backgrounds, the InSb(110)-1×1 spots being conserved. A reversible ordering in the film is observed at cooling. The 10-K deposition, with θ≊1, leads to the appearance of a strong background and to the disappearance of all the diffraction spots. With θ≳4.5 the structure appears that is conserved at heating up to 300 K and corresponds to a (100) plane of the Ag body centered cubic (bcc) structure. In this case (110)Agbcc//(110)InSb, and the analogous crystallographic directions in a (110) plane of either structure are coincident. The process of heating up to room temperature of the samples with θ=1–4.5, obtained at 10 K, gives rise to both the substrate diffraction spots and complementary ones, caused by the adsorbed silver.
Focused ion beam etching of nitrocellulose
Authors: Yasuoka Y. , Harakawa K. , Gamo K. , Namba S.
Published: July 2002

The self-developing and processing properties of nitrocellulose, especially the influence of the thickness of nitrocellulose on the self-developing properties, were studied experimentally. The results show that approximately 500 nm is the optimal thickness for the nitrocellulose film used as the self-developing resist in microfabrication processes using a focused ion beam. Using this film with a finely focused ion beam, aluminum lines having widths of 200–300 nm were obtained.
A practical interferometric technique for mask/wafer alignment during proximity printing
Authors: Bartelt John L. , Olney Ross D.
Published: July 2002

A new automated technique for sensing translational and rotational mask-to-wafer alignment will be presented that is useful with proximity printing processes such as masked ion beam or x-ray lithography. The technique is based on computer interpretation of fringe patterns created by laser beams diffracted from unique grating structures on both the mask and the wafer. It requires no moving parts and features a simple optical configuration that uses a dielectric cube beamsplitter to recombine the diffracted beams. Being an interferometric technique, precision better than 20 nm is easily achieved, while the novel grating structure and fringe analysis provide a capture range in excess of 20 μm. Additional key features of the technique are that it is insensitive to variations in the gap between mask and wafer and that its performance does not degrade with changes in surface reflectivity or topography as device wafers are processed. A single channel of the grating alignment technique has been implemented and tested in a laboratory bench fixture. The results of these experiments will be discussed.
Imaging zone plates for x-ray microscopy fabricated by electron-beam lithography
Authors: Unger P. , Bögli V. , Beneking H. , Niemann B. , Guttmann P.
Published: July 2002

Fresnel zone plates have been fabricated by electron-beam lithography using a modified scanning transmission electron microscope. These microzone plates are designed to work as imaging elements in an x-ray microscope. To achieve zone plates that are free of distortions, the deflection field of the lithography system has been calibrated by the aid of externally generated reference marks. Microzone plates with a minimum linewidth of 20 nm have been written into polymethylmethacrylate and etched into a 15-nm-thick titanium layer. Two methods of transfer into a gold absorber layer have been used, namely sputter etching of the gold layer with a reactively ion etched titanium mask, and electroplating of gold using a suitable trilevel resist system. By these techniques, Fresnel zone plates with 100 zones, a width of the outermost zones of 50 nm, and a thickness of the gold absorber layer of 80 nm have been fabricated. Imaging experiments have been performed at the electron storage ring BESSY in Berlin, and the results have been compared with images obtained by holographically fabricated zone plates.
A new contrast enhancement technique for electron-beam lithography
Authors: Suga Osamu , Aoki Emiko , Okazaki Shinji , Murai Fumio , Shiraishi Hiroshi , Nonogaki Saburo
Published: July 2002

A new electron-beam process technique is proposed to improve resolution and aspect ratio in negative resist patterns. With this technique a modified surface layer, which acts as a dissolution barrier to the developer solution, is introduced on top of the negative resist film. The relationship between development rate and time is varied, and therefore, it becomes a nonlinear relationship. By exploiting this nonlinear development characteristic, resist film thickness loss during development in the electron exposed area can be suppressed significantly. This concept of contrast enhancement is confirmed using an electron-beam resist profile simulator prior to experiment. Since negative resist microresist for shorter wavelengths (MRS) show strong absorption at deep UV, deep-UV flood exposure on MRS provides ideally modified surface layers. The new process, combined deep-UV and electron-beam exposure, realizes 0.3–0.4-μm line and space patterns delineated with very little film thickness loss. This technique is also an efficient way of enhancing the resist sensitivity.
A study of time and angle correlations in the ion emission from gallium liquid metal ion sources
Authors: Barr D. L. , Thomson D. J. , Brown W. L.
Published: July 2002

An ion streak camera has been constructed for measurement of time and angle correlations in ion emission from liquid-metal ion sources. Emission events are detected with a chevron microchannel plate multiplier (MCP) as a fan of the ion beam is electrostatically deflected across the plate. The intensified images on the phosphor of the MCP are recorded in a digital video camera synchronized with the sweep. The images are then digitized and Fourier transformed to obtain two-dimensional power spectra in frequency and angular wave number. Experiments have been performed using sweep times of 100 ns to 10 μs. The time behavior of the emission has been examined for low-current direct current beams and for beams for which the extractor of the source has been driven at 2 MHz. Preliminary results for the power spectra are presented and discussed for these different cases.
Screening and delocalization effects in Schottky barrier formation
Authors: Ludeke R. , Jezequel G. , Taleb-Ibrahimi A.
Published: July 2002

In order to assess the role of metallic screening at the metal–semiconductor interface, we have investigated the effects of Ag deposition on the band bending of GaAs(110) surfaces previously ‘‘pinned’’ with vanadium atoms. Their coverages ranged from 0.05 to 1.5 monolayers (ML), which positioned the surface Fermi level (EF)∼0.85–0.6 eV above the valence band maximum (VBM). For subsequent depositions of Ag additional changes in EF of up to 200 meV towards the VBM were observed on both n- and p-type GaAs. The onset of these changes, which occurs for mean Ag coverages of ∼0.1 ML, coincides with the appearance of metallic characteristics in the Ag clusters. These changes in EF can be explained in terms of a new model in which the interface impurity levels in the band gap of the semiconductor become delocalized through interaction with states of the metal overlayer. A functional expression is developed which relates the Fermi level to the metal and semiconductor parameters, and to an effective charge in each delocalized level. These levels, actually broadened resonances of the impurity-metal system, accommodate the charge densities required to equalize EF throughout the system. In analogy to a partially filled band, EF is determined by the average effective charge residing in each resonance. The resonances are nearly neutral and can accept or donate electronic charge as needed to compensate for the conductivity type of the semiconductor. Calculated changes of EF based on this model agree well with the experimental observations.