bluuebunny/crossref_metadata_2025 huggingface dataset:
Behavior of thin Ta-based films in the Cu/barrier/Si system
Authors: Stavrev Momtchil , Fischer Dirk , Praessler Frank , Wenzel Christian , Drescher Kurt
Published: July 2002

This work concentrates on the diffusion barrier stability of very thin (10 or 20 nm) α- or β-Ta, TaN, Ta(O) and Ta(N,O) films in the Cu/barrier/Si system. Based on the classical theory of the thin film growth and know how of material transport in thin films, the various Ta-based films were classified according to their density of free short-circuit paths. Using scanning electron microscopy, transmission electron microscopy, glow discharge optical emission spectroscopy and secondary ion mass spectrometry, the 20 nm thin polycrystalline columnar-structured β-Ta films were found to be stable up to 500 °C for 1 h. After 1 h at 600 °C Cu3Si was formed due to short-circuit diffusion of Cu throughout the β-Ta films. The 20 nm thin giant-grained α-Ta films show equivalent performance to the β-Ta films. On the other hand, the 10 nm thin stuffed nanocrystalline face-centered-cubic (fcc) TaN films were able to protect the Si from Cu diffusion up to at least 600 °C/1 h. Ten nm thin amorphous-like Ta(N,O) and Ta(O) films also show barrier stability that is comparable to fcc TaN. While Ta(N,O) tends to recrystallize mainly into hexagonal-close-packed Ta2N above 500 °C, the Ta(O) remains amorphous even at 600 °C. Besides the amorphous-like microstructure, the high recrystallization temperature of Ta(O) is the reason why the introduction of 5 nm thin Ta(O) film into the Cu/5 nm Ta(O)/5 nm β-Ta/Si structure leads to a stability increase up to at least 600 °C for 1 h.
Using pulsed direct current power for reactive sputtering of Al2O3
Authors: Belkind A. , Freilich A. , Scholl R.
Published: July 2002

Application of steady direct current (DC) power to the reactive sputtering of dielectrics such as Al2O3 is seriously hampered by arcing. This arcing can be alleviated to a great extent when pulsed dc power is applied. By pulsed dc power we mean that the power is applied for a short “on” period, and then removed for a short “off” period. During the “off” period the plasma can discharge the surfaces, provided certain conditions are met. The dependence of adequate discharging, and thus arc prevention, on the duration of the “on” and “off” periods is examined. In addition, the dynamics of plasma density loss in the “off” period and its reestablishment in the initial part of the “on” period are discussed. Reactive sputtering takes place only during the “on” period, and part of this period is lost for effective sputtering due to the time required for full plasma reestablishment. This produces a dependence of the deposition rate on both the duty cycle and the frequency of pulsing, but not on the power consumed. This dependence is examined and the power efficiencies of alternating current and pulsed power dc reactive sputtering are compared and the differences between single and dual cathode systems in published results is discussed.
Structure of ultrathin SiO2/Si(111) interfaces studied by photoelectron spectroscopy
Authors: Keister J. W. , Rowe J. E. , Kolodziej J. J. , Niimi H. , Tao H.-S. , Madey T. E. , Lucovsky G.
Published: July 2002

Device-grade ultrathin (9–22 Å) films of silicon dioxide, prepared from crystalline silicon by remote-plasma oxidation, are studied by soft x-ray photoelectron spectroscopy (SXPS). The 2p core-level spectra for silicon show evidence of five distinct states of Si, attributable to the five oxidation states of silicon between Si0 (the Si substrate) and Si4+ (the thin SiO2 film). The relative binding energy shifts for peaks Si1+ through Si4+ (with respect to Si0) are in agreement with earlier work. The relatively weaker signals found for the three intermediate states (I1, I2, and I3) are attributed to silicon atoms at the abrupt interface between the thin SiO2 film and substrate. Estimates of the interface state density from these interface signals agree with the values reported earlier of ∼2 monolayers (ML). The position and intensity of the five peaks are measured as a function of post-growth annealing temperature, crystal orientation, and exposure to He/N2 plasma. We find that annealing produces more abrupt interfaces (by reducing the suboxide interface state density), but never more abrupt than ∼1.5 monolayers. We observe a 15%–20% drop in the interface thickness (in particular the “Si2+” peak intensity) with increasing annealing temperature. Somewhat different behavior is observed with small amounts of nitrogen in the SiO2 film where an apparent increase in interface state density is seen. A quantitative analysis is presented which explores the effects of these sample preparation parameters in terms of relative interface state density and modeling of the SXPS data.
Growth of Mg films on H-terminated Si (111)
Authors: Saiki Koichiro , Nishita Kouichi , Ariga Yasuo , Koma Atsushi
Published: July 2002

The growth of Mg has been examined on H-terminated Si (111) and the grown film was characterized by reflection high-energy electron diffraction, Auger electron spectroscopy, and electron energy loss spectroscopy. Mg grows epitaxially on H–Si (111) in island form with an epitaxial orientation of Mg (0001) [112̄0]//Si (111)[11̄0]. At the very initial stages of growth a contraction of the Mg lattice is observed, which might cause a shift in plasmon energy of the initial Mg aggregate.
Pulsed bias magnetron sputtering of thin films on insulators
Authors: Barnat Edward , Lu T.-M.
Published: July 2002

It is shown that a pulsed direct current (dc) bias is capable of discharging insulating surfaces and providing a good means of controlling the energy of the ions extracted from the sputter magnetron plasma. Numerical calculations were made for surface potentials of an insulating thin film exposed to a plasma, placed on a conductor with a pulsed dc bias. Surface potentials are calculated as a function of time for pulses of variable frequency and duty. Average ion energy is shown to converge to applied dc biases at higher frequencies. Thin aluminum films were deposited on SiO2 substrates as a function of pulse frequency. Atomic force microscopy scans of the surface show that increasing the frequency of the pulses produces drastic changes in resulting film surface morphology.
Ion-enhanced etching of Si(100) with molecular chlorine: Reaction mechanisms and product yields
Authors: Goodman Rory S. , Materer N. , Leone Stephen R.
Published: July 2002

Laser single-photon ionization time-of-flight mass spectrometry is used to measure silicon etch products that evolve during argon ion-enhanced etching of room temperature Si(100) with molecular chlorine over an ion energy range of 275–975 eV. The etch products are examined as a function of ion energy, ion flux, and molecular chlorine flux. The neutral Si atom, SiCl, and SiCl2 are the only product species observed with the 118 nm ionization and are detected directly without fragmentation. The Si and SiCl species are the main products, with the latter having much greater yield. The yield of each product increases with increasing ion energy. The SiCl/Si yield ratio increases with decreasing ion kinetic energy, indicating an increase in the chlorine surface coverage at lower ion energies. A simple kinetic model, including chlorine adsorption and sputtering of the resulting silicon chloride surface moieties, is proposed to describe the formation of Si and SiCl etch products. A model describing the chlorine pressure dependence of Si atom sputtering is developed in which the sputtering of Si atoms occurs from two different precursor states, one from an unchlorinated site and another from a partially chlorinated site. Using this kinetic model, the sputtering yield for SiCl per Ar+ is estimated from the molecular chlorine flux dependence of the SiCl signals and ranges from 3.2±0.8 to 4.9±0.9.
Reaction layer dynamics in ion-assisted Si/XeF2 etching: Ion flux dependence
Authors: Sebel P. G. M. , Hermans L. J. F. , Beijerinck H. C. W.
Published: July 2002

The etch rate of Si by XeF2 can be enhanced by more than a factor of 8 by ion bombardment. This enhancement is studied in a multiple-beam setup by looking at the response of reaction product signals upon ion pulses on time scales of 1–100 s in a multiple-beam setup. On a time scale of 100 s, it is found that ion bombardment causes fluorine depletion of the reaction layer and changes the structure of the reaction layer. This lower fluorine content results in a lower contribution of the spontaneous SiF4 production during ion bombardment. For the enhanced SiF4 production two processes are found from pulse measurements on the time scale of 1–10 s. First, ion bombardment creates weakly bound surface species, e.g., SiF2, that can react in the reaction layer to SiF4. Second, XeF2 reacts with these species with a higher reaction probability, thus enhancing the SiF4 production. The relative importance of both mechanisms is determined. Further, the limiting steps during spontaneous and ion-assisted etching are discussed, revealing that the creation of dangling bonds is the reason for the higher sticking probability of XeF2 during ion-assisted etching.
High quality low roughness niobium thin films made by electron cyclotron resonance technique
Authors: Esposito Antonio , Nakagawa Hiroshi , Akoh Hiroshi , Takada Susumu
Published: July 2002

We performed growth of body-centered-cubic Nb thin films using an electron cyclotron resonance (ECR) technique on {100} Si substrates. We deposited Nb films using both Ar and Xe plasmas. Reflection high-energy electron diffraction and atomic force microscopy analyses have been performed in order to observe the surface topography. We found that the surface roughness of films deposited by ECR is 4–5 times smoother than films deposited by magnetron sputtering systems. We obtained this result even at room temperature deposition conditions.
Monitoring plasma impedance match characteristics in a multipole inductively coupled plasma for process control
Authors: Kim Byungwhan , Lee ChangKeun
Published: July 2002

A real-time system is presented to monitor impedance match characteristics of a recently manufactured etch system, where a low pressure planar plasma is provided using multipole magnetic cores. Apart from typical radio-frequency (rf) parameters, the system particularly monitors match positions for the diagnosis of plasma impedance. Sensitivities of match positions to factor variations were examined. Statistical analysis was performed over transient match data to extract further diagnostic clues. Using a real-time rf sensor, meanwhile, match positions were correlated to plasma impedance. The process factors that were varied in the experiments include source power, pressure, Ar, and O2 flow rates. A sublinear relationship was found between each position and source power with much lessened match sensitivity in Ar or O2 flows. Phase match position demonstrated an enhanced sensitivity over impedance match position. Statistical mean analysis of transient match data enabled further detection of shifts in plasma impedance. A catastrophic mismatch fault was correctly identified, while being illustrated as an inadequacy of reflected rf power as a diagnostic variable. Revealed further with the sensor is that plasma impedance is a strong function of reactance, which was most significant in Ar or O2 variations. As a result, monitoring match positions in conjunction with statistical transient analysis is an effective alternative to diagnosing plasma impedance.
Low-temperature growth of epitaxial LaNiO3/Pb(Zr0.52Ti0.48)O3/LaNiO3 on Si(001) by pulsed-laser deposition
Authors: Wu Wenbin , Wong K. H. , Choy C. L.
Published: July 2002

Epitaxial ferroelectric thin-film capacitors, LaNiO3/Pb(Zr0.52Ti0.48)O3/LaNiO3, have been grown on Si(001) substrates using SrTiO3/TiN as the buffer layer. The whole capacitor and the buffer layer stack were in situ deposited at 540 °C by the pulsed-laser deposition method. Structural characterization using three-axis x-ray diffraction (θ–2θ scan, ω-scan rocking curve, and φ scan) reveals a cube-on-cube epitaxial growth for all layers. High-resolution scanning electron micrographs show that the epitaxial heterostructures have a smooth and crack-free surface. The sharp characteristic optical absorption bands of the SrTiO3 and Pb(Zr0.52Ti0.48)O3 layers also imply good crystallinity in the as-grown films. Resistivity versus temperature measurements show that both the bottom and top LaNiO3 electrodes are metallic and highly conductive with resistivity of 210 and 150 μΩ cm, respectively, at 300 K. Remnant polarization of about 26 μC/cm2, coercive field of 33 kV/cm, and no visible fatigue after 108 cycles indicate good electrical performance of the integrated capacitor structure.
Measuring the electrical characteristics of thin polymeric films
Authors: Gladys M. , Greig P. , Dastoor P.
Published: July 2002

A new simple device for measuring the insulating properties of thin polymer films as a function of applied load has been designed, developed, and tested. This new apparatus, which is based on a commercially available and inexpensive pressure sensor, is very sensitive to small changes in applied pressure. The pressure sensitivity of the apparatus is better than ±20 Pa over a nominal pressure range of 0–200 kPa. Experimental results of the insulating properties of ultrathin propyltrimethoxysilane polymeric films adsorbed onto iron oxide substrates are presented and illustrate the implementation of the new apparatus.
Biased target deposition
Authors: Zhurin V. V. , Kaufman H. R. , Kahn J. R. , Hylton T. L.
Published: July 2002

The biased target deposition apparatus described herein uses a low energy ion source. The ions are generated at energies for which the sputter yield is negligible for typical construction materials, so that there is no need for expensive optics to focus the ions on the target. The bias of the target provides the energy for sputtering the target material, in addition to restricting the sputtering to the target. Using the biased target technique, copper films were deposited with an average resistivity of about 2.5 μΩ cm at a thickness of 1000 Å. This apparatus is well suited to the deposition of very thin (⩽1000 Å) high quality films, such as used in recent magnetoresistive devices. It is also well suited for use in compact and reliable multitarget systems to deposit such films.
Characterization of plasma enhanced chemical vapor deposited SiC and its application in advanced reticle technology–scattering with angular limitation in projection electron beam lithography membrane
Authors: Han S.-I. , Mangat P. J. S. , Smith S. M. , Dauksher W. J. , Convey D. , Gregory R. B.
Published: July 2002

In scattering with angular limitation in projection electron beam lithography (SCALPEL) mask technology, the choice of membrane material is an important issue from the perspective of mask performance and manufacturing. Low-pressure chemical vapor deposition SiN has been widely employed for SCALPEL membranes because of its excellent manufacturability and other material properties. However, amorphous plasma enhanced chemical vapor deposition SiC:H has a good potential for the membrane material, and we have developed an optimized process to deposit the SiC films for mask fabrication.
Diagnostic of rf discharge plasma by Thomson scattering with gated intensified charge coupled device detectors
Authors: Moshkalyov S. A. , Thompson C. , Morrow T. , Graham W. G.
Published: July 2002

A Thomson scattering diagnostic, using an intensified gated charged coupled device detector and a high-repetition rate yttrium aluminum garnet laser, was utilized to measure electron parameters in a radio-frequency discharge. Both inductively and capacitively coupled plasmas in argon and argon–oxygen mixtures were studied, with electron densities as low as ∼5×109 cm−3. Different modes of detection (direct accumulation and photon counting) have been compared. The photon counting technique has been used to provide better accuracy at low light level (i.e., low electron densities). The results are compared with Langmuir probe measurements performed under the same plasma conditions, and good agreement is found between the two diagnostics.
Alternative procedure for the fabrication of close-spaced sublimated CdTe solar cells
Authors: Moutinho H. R. , Dhere R. G. , Ballif C. , Al-Jassim M. M. , Kazmerski L. L.
Published: July 2002

We deposited CdTe thin films by close-spaced sublimtation using an alternative procedure, with temperatures about 170 °C lower than the ones used in the standard procedure. These films were used in the fabrication of all thin-film CdTe/CdS solar cells. We treated the cells using the well-established CdCl2 dipping process as well as a new vapor treatment. The vapor process was more reproducible and easier to control, and it produced the best devices. This process was also much more effective in the recrystallization of the CdTe films. The best device that we produced had an efficiently of 11.6%, close to the 12.3% efficiency of the best device fabricated using the standard process. These results show that the new process has good potential, and besides being an alternative for lower-cost solar cell production, it can also produce high-efficiency devices.
Influence of copper phthalocynanine on the charge injection and growth modes for organic light emitting diodes
Authors: Forsythe E. W. , Abkowitz M. A. , Gao Yongli , Tang C. W.
Published: July 2002

The stability and efficiency for organic light emitting diodes (OLEDs) based on tris-8-(hydroxyquinoline) aluminum and N,N′-bis-(1-naphthyl)-N,N′-diphenyl1-1, 1-biphenyl1-4,4′-diamine (NPB) are enhanced with the use of a copper phthalocynanine (CuPc) layer between the indium tin oxide (ITO) anode and the NPB hole transport layer. In the following, we have investigated two fundamental properties of the CuPc buffer that contribute to improved stability. Using time of flight and dark current as a function of applied field, we show that the CuPc interlayer influences the hole injection from the ITO to the NPB transport layer. Because NPB is trap free, a direct and self-consistent measure of the hole injection efficiency can be determined from the measured drift mobility and dark current at the same applied field. By this means we have been able to demonstrate that the hole transport from the ITO anode to the NPB is injection limited and the hole injection efficiency is further reduced with a 15.0 nm CuPc interlayer. Using atomic force microscopy, we have determined that NPB organic molecules grow in island-like modes on ITO compared to a layer by layer growth for the CuPc organic molecules. With CuPc as the substrate, NPB also grows in apparent layers. The combined electrical and structural characteristics of the CuPc layer are important to the overall performance of OLEDs.
Sputtered coatings for microfluidic applications
Authors: Matson Dean W. , Martin Peter M. , Bennett Wendy D. , Johnston John W. , Stewart Donald C. , Bonham Charles C.
Published: July 2002

Magnetron sputter-deposited features and coatings are finding a broad range of uses in microfluidic devices being developed at the Pacific Northwest National Laboratory. Such features are routinely incorporated into multilayer laminated microfluidic components where specific functionality is required, and where other methods for producing these features have been deemed unacceptable. Applications include electrochemical sensors, heaters and temperature probes, electrical leads and insulation layers, piezoelectric actuators and transducers, and chemical modification of surfaces. Small features, such as those required for the production of microsensor electrodes or miniature resistive heaters on microfluidic chips, were patterned using standard lithographic methods, or with masks produced by laser micromachining processes. Thin-film piezoelectric materials such as aluminum nitride have been deposited at low temperatures for use with temperature sensitive materials. Use of the coating technology and its application in the fabrication of specific microfluidic devices, including a groundwater sensor, miniature piezoelectric ultrasonic transducers and actuators, a polymerase chain reaction thermal cycler, and a microchannel flow diagnostic device, are discussed. Technical issues associated with these coatings, such as adhesion, chemical resistance, and surface defects are also addressed.
Liquid phase epitaxy of unstable alloys: Substrate-induced stabilization and connected effects
Authors: Quillec M. , Launois H. , Joncour M. C.
Published: July 2002

It is now well admitted that most quaternary III–V compounds show unstable regions in the temperature range commonly used in epitaxy. For instance, according to these authors, the InGaAsP alloy, lattice matched to InP and with emitting wavelength 1.3 μm should be unstable at temperatures below 700 °C. Liquid phase epitaxy, however, is commonly performed down to 600 °C. As this growth technique occurs close to thermodynamical equilibrium, such growth should not take place. It was clearly demonstrated that the substrate stabilizing effect is responsible for this paradoxical behavior. Another LPE substrate effect pointed out by Stringfellow is known as the ‘‘pulling effect.’’ Results will be presented showing the connection between these effects in the system InGaAsP/InP and particularly InGaAs/InP. ‘‘Stabilized’’ GaAsSb was also successfully epitaxially grown on InP, in the immiscibility region, from the liquid phase. Microscopic compositional periodical modulations are observed in standard InGaAsP epilayers, if growths are performed below a critical temperature. This phenomena, also related to solid instability, can be interpreted in terms of liquid–solid interfacial spinodal decomposition.
Heterostructure bipolar transistors: What should we build?
Authors: Kroemer Herbert
Published: July 2002

The paper discusses likely future developments in heterostructure bipolar technology, especially by MBE. This written version concentrates on two new conceptual developments extending earlier concepts. One of these pertains to the problem of emitter/base junction grading. A grading scheme is proposed that extends the grading through the base region and creates a graded-gap base. The other proposes an extension of permeable base transistor technology to bipolar transistors in what is called a gridded-base bipolar transistor. Both promise a further increase in device speed, largely by addressing themselves to the persistent problem of base resistance reduction. Several other topics, already contained in the author’s January 1982 review paper and presented orally at the Workshop, have been omitted from this printed version.
Interfacial studies of deposited thin films of refractory metals on gallium arsenide substrates. Mo–GaAs
Authors: Suh K. , Park H. K. , Moazed K. L.
Published: July 2002

A study of the temperature dependence of interfacial reactions and electrical characteristics of vacuum-deposited thin films of molybdenum on gallium arsenide single-crystal substrates was conducted and the data analyzed. The molybdenum films, which were deposited by utilizing an electron beam evaporation source, were observed to have (110) preferred orientation. Gallium outdiffusion to the exterior surface of molybdenum was detected by means of surface profiling in conjunction with Auger electron spectrometry and secondary-ion mass spectrometry analyses. The formation of binary compounds Mo5As4, Mo2As3, and Mo3Ga and the formation of a ternary compound with the tentative composition of Mo3GaAs2 were detected by x-ray diffraction techniques. The compound formation was found to be temperature dependent.
Exposure and development simulations for nanometer electron beam lithography
Authors: Samoto N. , Shimizu R. , Hashimoto H. , Adesida I. , Wolf E. , Namba S.
Published: July 2002

A new Monte Carlo simulation including generation of secondary electrons combined with development process was applied to study ultimate resolution of electron beam lithography. With respect to the simulation of inelastic scattering processes of the primary electrons we used Gryzinski’s excitation function for single electron excitation processes, and for generating secondary electrons, while the inelastic mean free path proposed by Seah and Dench for organic materials, and the energy loss spectrum obtained by Ritsko were used for simulating the inelastic scattering processes of the secondaries. The etching process which we used is the time evolution development proposed by Neureuther et al., using the model of Hatzakis et al. for polymethylmethacrylate (PMMA). The calculations were made to assess the line-profile resist development of 30 nm-thick films of PMMA on 60 nm-thick silicon substrate for line exposure by a parallel electron beam 6 nm wide at 50 keV. The result shows a developed profile given by the contour representing the shortest evolution time which intersects the substrate is ∼18 nm wide at the surface. The theoretical result was compared with the experimental study of ultimate resolution of electron beam lithography, done by Broers.
The growth and characterization of nominally undoped Al1−xInxAs grown by molecular beam epitaxy
Authors: Davies G. J. , Kerr T. , Tuppen C. G. , Wakefield B. , Andrews D. A.
Published: July 2002

Al1−xInxAs films have been grown by molecular beam epitaxy (MBE) on InP substrates. Unintentionally doped material had a free electron concentration of the order of 1×1016 cm−3 when grown above 560 °C but was semi-insulating when grown below 520 °C. The effects of substrate temperature and the group V to group III flux ratio during growth on the electrical properties and on the 4 K cathodoluminescence are reported. The Auger electron spectroscopy (AES) profiles through the films show that loss of indium is detectable only at temperatures in excess of 600 °C for As4/group III flux ratios of 15–20:1. The optimum MBE growth temperature for Al1−xInxAs on InP is 580 °C. Cathodoluminescence spectroscopy was used to measure the band gap of the epitaxial layers as a function of In content for values of x between 0.46 and 0.55. Over this range, at room temperature the band gap energy was found to vary as Eg(300 K)=1.450+2.29(0.523−x) eV, while at 4 K the relation was measured to be Eg(4 K)=1.508+2.22(0.523−x) eV. The effect of strain on the band gap due to lattice mismatch between the epilayer and substrate is also considered.
Dangling bonds and Schottky barriers
Authors: Sankey Otto F. , Allen Roland E. , Ren Shang-Fen , Dow John D.
Published: July 2002

We review theoretical interpretations of Schottky barriers and Fermi-level pinning, which result when metals and other chemical species are deposited on semiconductor surfaces. Experiments indicate that these two phenomena are closely connected, so a theory of Schottky barriers must also explain Fermi-level pinning for submonolayer coverages of both metallic and nonmetallic species. Proposed mechanisms include the following: (a) Intrinsic surface states. For GaAs and several other materials, there are no intrinsic surface states within the band gap; GaP, e.g., does have surface states in the gap, but they are not at the correct energy to explain Schottky barrier formation. (b)

M e t a l-induced gap states. These states, which require a thick metal overlayer, cannot explain Fermi-level pinning at submonolayer metallic coverages. They also cannot explain why a single semiconductor (n-type InP) exhibits two distinct Schottky barrier heights. Furthermore, they cannot explain why the Schottky barrier persists when there is an oxide layer between semiconductor and metal. Metal-induced states can in principle give rise to Schottky barriers at defect-free interfaces, but they fail to explain much of the existing experimental data for III–V semiconductors and Si. (c) The classic Schottky model. This model is not in agreement with experiment for III–V and Group IV semiconductors, but does appear to account for the measurements involving nonreactive metals on GaSe−a layered material expected to be relatively free of defects. (d) The Spicer defect model. This phenomenological model, now supported by microscopic theoretical studies, appears to account for many of the observations regarding Schottky barrier and Fermi-level pinning. We review our theoretical investigations within the framework of the defect model, which provide a satisfactory explanation of the principal observations for both III–V and Group IV semiconductors. We conclude that the levels responsible for Schottky barriers and Fermi-level pinning arise from two sources: (1) bulk-derived deep levels (e.g., the deep donor level for the antisite defect AsGa, which persists when this defect is present at the surface, but which is shifted in energy), and (2) dangling-bond deep levels (which are also shifted in energy according to the environment of the dangling bond). Most of the observed Schottky barriers—for both III–V and Group IV semiconductors—are attributed to dangling bonds.
A combined high-resolution electron microscopy, x-ray photoemission spectroscopy, and electrical properties study of the InP–SiO2 interface
Authors: Krivanek O. L. , Liliental Z. , Wager J. F. , Gan R. G. , Goodnick S. M. , Wilmsen C. W.
Published: July 2002

The InP-native oxide-SiO2 interface system has been studied by cross sectional high-resolution electron microscopy (HREM), x-ray photoemission spectroscopy (XPS) depth profiling, and C-V and G-V measurements. The devices were prepared on InP treated in several different ways, including InP oxidized in air at about 350 °C for 68 h. HREM shows that the interface roughness varies, depending on the InP surface treatment, from <5 Å for InP treated in a solution of KOH in methanol to >100 Å for InP etched in iodic acid. Ellipsometry measurements on as-cleaned InP indicate a native oxide of 9 to 15 Å thickness, but no such oxide is clearly evident in HREM images. For the thermal oxide ellipsometry gives a thickness of 107 Å, and HREM shows an oxide of ∼110 Å thickness between the InP and the SiO2. HREM further shows that the thermal oxide consists of an inner layer (next to InP) about 50 Å thick and an outer layer about 60 Å thick, and that the oxidation roughens the InP substrate to a depth of 30–50 Å. XPS suggests that the inner oxide layer is primarily InPO4, while the outer layer is rich in In2O3. Finally, some correlations are established with the electrical properties: thin native oxides lead to lower interface state densities than the thick thermal one, but the roughness of the interface does not, at present, appear to adversely affect the electrical results.
Proximity effect correction in variably shaped electron-beam lithography
Authors: Chen A. S. , Neureuther A. R. , Pavkovich J. M.
Published: July 2002

Proximity effect in electron-beam lithography is studied with an emphasis on physical understanding. Computer simulation is used to explore correction schemes which specifically include the resist behavior and yet are theoretically manageable in formulating the pattern correction for mathematical analysis. Both energy density part way through the resist and relative importance of background on critical edge are investigated. It is shown that one-third of the resist thickness from the substrate appears to be where the process parameters should be characterized, and that the total effective deposited energy at the nominal edge must be reduced as the background contribution increases. A mathematical model and design graphs are developed so that the impact of the background on the edge control is directly related to fundamental physics through the Monte Carlo calculation. The nominal edge is used as the critical aspect to be controlled and the constraint of constant bias can be applied.
High resolution electron beam and dry etch based process for self-aligned 200 nm Si FET’s
Authors: Nulman J. , Krusius J. P.
Published: July 2002

A high resolution fabrication process for integrated semiconductor structures with 100 nm minimum feature sizes, based on electron beam lithography and reactive ion etching, will be described. This process has been used in the fabrication of self-aligned Si FET’s. Both single and multilayer resist structures have been employed. SiO2 sidewall spacers and As+ ion implantation allows for minimum source-to-gate and drain-to-gate spacings of 100 nm. Channel depths between 40 and 80 nm have been reached with double ion implantation and low temperature-time cycles. Si MESFET and buried channel MOSFET devices and circuits have been fabricated in order to evaluate the capabilities of this process. The obtained switching speed for normally-off Si MESFET logic is superior to any previously reported result for Si MESFET’s. Ultimate limits of this process and its implications on device performance are also addressed.
Modeling and exposure of three-dimensional shaped beam profiles in electron resist
Authors: Augur R. A. , Jones G. A. C. , Ahmed H.
Published: July 2002

A computer program has been developed to calculate the three-dimensional energy density distribution deposited by a shaped electron beam exposure. The program is applicable to both direct-write and cathode-projection systems. Simulations have been carried out for a range of beam voltages up to 40 kV and compared with experimental results from a direct writing system operating in the range 23–36 kV. The results show that the magnitude of inside and outside corner radii of patterns are different, resulting from the interproximity effect, and tend to smaller values with increasing voltage. In addition, pattern fidelity improves generally as the beam voltage is increased.
Formation of submicron isolation in GaAs by implanting a focused boron ion beam emitted from a Pd–Ni–Si–Be–B LM ion source
Authors: Arimoto H. , Takamori A. , Miyauchi E. , Hashimoto H.
Published: July 2002

We have developed a new type of alloyed liquid metal ion source for maskless ion implantation in III–V compound semiconductors. This ion source with alloys consisting of Pd (50), Ni (26), Si (5), Be (6), and B (13) is capable of emitting Si (n-type dopant), Be (p-type dopant), and B (device isolation) ions. Using this ion source, active regions (n-type GaAs, 2×1017/cm3) were isolated by single line implantation with a 100 keV focused B+ ion beam of 0.1 μm diam. A good isolation of submicron width (less than 0.5 μm) has been obtained. The resistivity of these isolated regions implanted with 2×1014 to 2×1015 ions/cm2 is found to be 104 to 105 Ω cm with breakdown voltages of 4 to 10 V after a heat treatment at 800 °C for 20 min. This result indicates that the submicron isolation using this technology can be maintained through the high-temperature device fabrication process.
A high speed, high precision electron beam lithography system (system design)
Authors: Nakamura K. , Sakitani Y. , Konishi T. , Komoda T. , Saitou N. , Sugawara K.
Published: July 2002

A variably shaped electron beam lithography system HL-600 has been developed for use in a semiconductor factory. HL-600 was for high throughput. It is capable of direct wafer writing at high speed and also capable of mask writing at high accuracy. A very high speed beam control circuit has been developed. The pattern data were decomposed through the pipeline digital circuit. The settling time of the DA converter was shortened to 100 ns at full scale. An automated loader and wafer prealigner have been developed minimizing operator intervention. The specially designed computer and software system allow background processing pattern data during exposure. One of the most distinctive features of HL-600 is the mode changing function. The large deflection mode guarantees writing of ten 4-in. wafers per hour and the small deflection mode can accurately write submicron patterns. The mode change can be carried out immediately without special adjustment. This paper describes the system configuration in detail.
Virtual gap states and Fermi level pinning by adsorbates at semiconductor surfaces
Authors: Mönch W.
Published: July 2002

The pinning positions of the Fermi level observed after the deposition of metal or semiconductor atoms and the adsorption of oxygen or hydrogen on clean (110) surfaces of III–V compound semiconductors are compared with the charge-neutrality levels of the virtual gap states of these compounds. Close agreement is found for GaAs, GaSb, and InAs independent of the adsorbate while both GaP and InP give deviations of up to 0.3 eV depending on the adsorbates. The latter differences are explained by additional defects of donor type which may be phosphorous vacancies. It is concluded that the virtual gap states, which were first discussed in this context by Heine, are predominantly determining the position of the Fermi level at adsorbate-covered semiconductor surfaces.
The characterization and optimization of masked ion beam lithography with 〈100〉 silicon channeling masks
Authors: Atkinson G. M. , Bartelt J. L. , Neureuther A. R. , Cheung N. W.
Published: July 2002

Surface response methodology is used to optimize the masked ion beam lithography (MIBL) mask structure and exposure process. The effects of beam energy, dose, membrane thickness, absorber thickness, resist thickness, contrast, sensitivity, and development time are examined and the MIBL exposure process is optimized with high throughput and low mask distortion as constraints. The resolution and process latitude of MIBL using silicon channeling masks are predicted to be 0.50±0.1 μm in single level resists and 0.25±0.05 μm in bilevel resist imaging layers.
EB60: An advanced direct wafer exposure electron-beam lithography system for high-throughput, high-precision, submicron pattern writing
Authors: Fujinami Minpei , Shimazu Nobuo , Hosokawa Teruo , Shibayama Akinori
Published: July 2002

A high-throughput, high-precision e-beam direct writing system, the EB60, has been developed for both submicron VLSI memories and application specific integrated circuits (ASICs). The throughput is twenty and eighty 4-in. wafers per hour for 0.5 μm VLSI memories and 0.8 μm ASICs, respectively, with ±0.1 μm overlay accuracy. To achieve this performance, a novel drawing method and the following key subsystems were developed: (1) Vector beam scanning during continuous stage movement with an advanced three dimensional registration method, which has reduced overhead time and results in a well balanced system design. (2) Variable shaped beam electron optical column with 0.2 μm beam edge resolution at 2.0×1.5 (1.5×2.0) μm maximum beam size and a current density of up to 70 A/cm2. (3) High-speed beam deflection and dynamic focus system, including high-speed analog circuits, all-electrostatic deflectors, and an electrostatic dynamic focus lens. (4) Fast pattern controller, which executes 16 Mshot/s pattern data generation, and several data calculations for beam positioning error corrections and pattern writing during continuous stage movement. (5) High-speed precision ceramic XY stage and high-speed wafer handling mechanism which enables automatic exposure of 50 wafers. (6) Control software which is friendly to both operators and LSI designers. Through the coordination of the above subsystems, a lithography system with a high throughput and a wide range of applications has been developed.
Production of focused, low-energy, hydrogen-ion beams using a Colutron ion source
Authors: Cain Bruce L. , Ruzic David N. , Bastasz Robert
Published: July 2002

An ion beam decelerator for energies down to 5 eV is described. The decelerator is a Menzinger retardation system that has been modified according to the results of calculations using a ray tracing model to optimize lens geometry. Performance tests of the decelerator demonstrate that H+2 beams with currents ≥20 nA can be obtained with a spot size adjustable from 0.5 to 10 mm using a beam raster system.
Electron optical characteristics of negative electron affinity cathodes
Authors: Sanford Colin A. , MacDonald Noel C.
Published: July 2002

Stable continuous electron emission has been obtained from GaAs electron cathodes which have been activated to a negative electron affinity condition. Negative electron affinity (NEA) photocathodes offer one means of producing very short electron pulses with a high peak brightness necessary for time-resolved metrology. Despite concerns regarding the stability of such cathodes, we have demonstrated a high degree of short-term stability through the ability to take scanning electron microscope photographs and Auger spectra using a NEA cathode. We have also demonstrated an effective brightness measured at the sample of 1×105 A/cm2 sr at 3 kV using our prototype electron gun. Room-temperature operation and laser excitation of this cathode make it particularly well-suited for low-voltage time-resolved electron probe and electron spectroscopy applications.
Focused ion beam induced optical emission spectroscopy
Authors: Ward B. W. , Ward M. , Edwards D. , Economou N. P.
Published: July 2002

We describe a focused ion beam system and a spectroscopic technique that utilize photons emitted from electronically excited sputtered neutrals for surface element identification and end-point detection. When a target is bombarded by a focused ion beam, some of the sputtered atoms (as much as 0.2%) leave the surface in electronically excited states and then quickly decay (10−6–10−8 s) by emitting photons of characteristic energies. A sputter-induced optical emission spectrometer and elemental imaging system were constructed using a focused ion beam in conjunction with a wavelength-selectable photon detector. Count rates as high as 104/s have been achieved for Al and Si with a 25-keV, 1.5-nA Ga+ beam. For these materials, an unambiguous elemental identification and/or end point can be determined by spectral analysis of the emitted photons. Details of the system and its performance will be discussed. In addition, the increase in yield of electronically excited neutrals from oxides or oxidized surfaces is discussed and the utility of a small gas jet to provide oxygen to the target surface is described. Effects of redeposition are considered as they relate to end-point detection.
Implantation enhanced interdiffusion in GaAs/GaAlAs quantum structures
Authors: Laruelle F. , Hu P. , Simes R. , Kubena R. , Robinson W. , Merz J. , Petroff P. M.
Published: July 2002

A high-energy (up to 150 keV) Ga+ focused ion beam is used to implant quantum well structures and interdiffuse GaAs/GaAlAs heterojunctions thus creating quantum wires and boxes. We investigate the optical properties of these structures using low-temperature cathodoluminescence. Wires as wide as 800 Å have been observed 2000 Å below the surface. We study the optical damage and the interdiffusion process as a function of the implantation parameters (ion energy ion dose) and as a function of the rapid thermal annealing time. A universal correlation between the optical damage and the interdiffusion length has been found. The optimum process conditions are proposed.
The growth of titanium silicides in thin film Ti/Si structures
Authors: Lakshmikumar S. T. , Rastogi A. C.
Published: July 2002

Microstructural changes and the evolution of silicide phases initiating at the interface between thin films of Si and Ti have been investigated by transmission electron microscopy and diffraction. This configuration allows an unambiguous interpretation of the results since the reactions are not mediated by SiO2. Spontaneous formation of the TiSi phase of nominal thickness occurs at room temperature, which is however not the actual growth phase at intermediate annealing temperature (500<T<600 °C). At these temperatures, mixed phases of Ti5Si3, Ti5Si4, and TiSi occur. Subsequent annealing at 600 °C leads to the orthorhombic TiSi phase with a heavily defective microstructure. On direct annealing at 600 °C, a well crystallized TiSi phase evolves in the early stages. Progressive growth of this phase does not occur and later a transformation to the C54 TiSi2 phase with a heavily defected microstructure occurs.
Observation of large Stark shift in GexSi1−x/Si multiple quantum wells
Authors: Park J. S. , Karunasiri R. P. G. , Wang K. L.
Published: July 2002

Large quantum-confined Stark shift is observed in a type II GeSi/Si multiple quantum well structure for the first time. In this experiment, we have employed the photocurrent measurement using reverse biased p-i-n diodes with multiple quantum wells in the i-region. The photocurrent as a function of bias is carried out at 77 and 300 K. The results show large red shift of the absorption edge which is about 0.75 meV kV−1 cm. This suggests the application of GeSi/Si type II structure for nonlinear electro-optics devices near the 1.3 μm range.
Fabrication technologies for advanced 5X reticles for 16M-bit dynamic random access memory
Authors: Shigetomi Akira , Matsuda Shuichi , Moriizumi Koichi , Kusunose Haruhiko , Onoda Hiroshi , Imai Tadayoshi , Watakabe Yaichiro
Published: July 2002

Fabrication technologies for advanced photomasks with a molybdenum silicide (MoSi) film have been developed by using a variable-shaped electron-beam (e-beam) system. These technologies were applied to the fabrication of 5X reticles for 16M-bit DRAMs. The variable-shaped e-beam system is very effective in increasing the throughput for writing reticles which have a great number of figures, such as 16M-bit DRAMs. The average writing time was 100 min, which was ∼ (1)/(3) of the time when using a conventional raster-scan e-beam system. Photomasks with the MoSi film have advantages in comparison with those with conventional chromium (Cr) film. Pattern defects did not appear during the photomask cleaning because of strong adhesion of the MoSi film to the quartz substrate. Moreover, an accurate feature size on the photomasks was obtained, because the MoSi film was easily dry etched. The feature size accuracy obtained was 0.03 μm in 3σ all over the 5 in. blanks.
Suppression of Be diffusion in molecular-beam epitaxy AlGaAs by the incorporation of In for heterojunction bipolar transistor applications
Authors: Fujii T. , Tomioka T. , Ishikawa H. , Sasa S. , Endoh A. , Bamba Y. , Ishii K. , Kataoka Y.
Published: July 2002

We report for the first time on the suppression of Be diffusion in molecular-beam epitaxy Al0.1Ga0.9As by incorporating In into the epilayer. The minimum diffusion coefficient of Be-doped Iny(Al0.1Ga0.9)1−yAs layers with a carrier concentration of 7×1019 cm−3 and an InAs mole fraction of 0.07 grown at 600 °C was about 2×10−15 cm2/s, which is five times smaller than that without In incorporation. The photoluminescence intensity of the layers drastically decreased above a value of y of 0.05, probably due to crystal degradation resulting from misfit dislocations. A heterojunction bipolar transistor with a 100 nm-thick p+In0.055 (AlxGa1−x)0.945As base layer (Al graded composition x: 0 to 0.1, emitter area: 4×5 μm2) yielded a dc current gain of 27 at a collector current of 8 mA.
Synchrotron radiation assisted metalorganic layer epitaxy
Authors: Höchst Hartmut , Engelhardt Mike A.
Published: July 2002

Experiments of the photodissociation of tetramethyltin by synchrotron radiation and the epitaxial atomic layer growth of diamond structured α-Sn films are reported. We used surface sensitive core and valence band photoemission spectroscopy to study the temperature dependence of the condensation and desorption behavior of tetramethyltin on CdTe(100). A quantitative analysis of the deposition and photodissociation of tetramethyltin including the work function change and the evolution of the substrate Te 4d and overlayer Sn 4d intensities during the overlayer deposition suggests that individual monolayers can be grown by the technique of synchrotron radiation assisted metal organic layer epitaxy. The photofragmentation process does not cause a significant carbon build up in the overlayer film. The photodissociated hydrocarbons seem to recombine and desorb from the surface.