bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical characterization of shallow arsenic profiles using SRP2
Authors: Subrahmanyan Ravi , Berkowitz H. , Heddleson J. , Rai-Choudhury P.
Published: July 2002

The accurate measurement of shallow (<0.2 μm) electrically active profiles is complicated by the effects of carrier diffusion which in some cases causes the carrier concentration profile calculated from spreading resistance (SR) data to be different from the impurity profile. This article describes analysis of SR data collected on shallow As profiles using the new analysis program srp2. srp2 is an analysis process which compares the measured SR data with SR data calculated from an assumed impurity profile. This assumed impurity profile is adjusted until the calculated SR profile matches the measured one. The srp2-calculated electrical profiles agree well with independently simulated electrical profiles obtained using models which were calibrated to secondary ion mass spectrometry (i.e., nonelectrical profiles) and sheet resistance data. The distribution of the calculated SR data beyond the junction is found to be strongly dependent upon the assumed tail of the impurity distribution, and therefore provides a means of characterizing the electrically active low-concentration tail (below 1×1016). The variation of the calculated spreading resistance with the assumed shape of the tail is illustrated and compared with measured SR data.
Shallow junctions for 0.1 μm n-type metal–oxide semiconductor devices
Authors: Watts R. K. , Luftman H. S. , Baiocchi F. A.
Published: July 2002

The n+/p junctions for 0.1-μm-gate n-type metal–oxide semiconductor must be no deeper than about 30 nm in order to preserve long-channel behavior in the enhancement mode metal–oxide semiconductor field-effect transistor. We report junctions formed by implantation of antimony or arsenic of depth 16–64 nm. They have been characterized by secondary ion mass spectroscopy, Rutherford backscattering spectroscopy lattice location studies, transmission electron microscopy, and electrical measurements.
Structural considerations in the optimal design of surface-emitting laser diodes
Authors: Gamelin J. , Hong M. , Fischer R. J. , Lin J. , Wang Y. H. , Mannaerts J. P. , Cho A. Y. , Wang S.
Published: July 2002

Growth and design techniques for performance optimization of all-epitaxial surface-emitting lasers are presented. Combined interperiod and intraperiod grading of the p-type doping is shown to minimize free-carrier absorption losses while simultaneously lowering the series resistance. Bulk GaAs lasers employing these grading schemes exhibited specific series resistances below 1.5×10−4 Ω cm2 with low thresholds of 10–20 mA for 20 μm diam devices. Simulations based on a comprehensive model for GaAs/InGaAs/AlGaAs lasers predict that proper choice of the number of multilayer pairs in the output reflector can increase the continuous wave output power from 1 to 7 mW, slope efficiency from 25% to 70%, and reduce the operating current for 3 mW output by 30%.
Effect of barrier thickness asymmetries on the electrical characteristics of AlAs/GaAs double barrier resonant tunneling diodes
Authors: Tsao A. J. , Reddy V. K. , Miller D. R. , Gullapalli K. K. , Neikirk D. P.
Published: July 2002

We report the impact of small barrier thickness asymmetry on the dc I–V characteristics of AlAs/GaAs double barrier resonant tunneling diodes. With a bottom AlAs barrier 6 ML thick and GaAs well 18 ML thick, the effects of varying the top AlAs barrier thickness from 5 to 8 ML produced significant changes in peak current density, peak voltage, and peak-to-valley current ratio (PVCR). PVCRs of 5.6 were obtained on a 7/18/6 monolayer structure, the highest reported to date for an AlAs/GaAs DBRTD structure.
Scanning tunneling characterization of the atomic and electronic structure of nanometer thick carbon films grown by pulsed laser vaporization of graphite
Authors: Vazquez L. , Martin-Gago J. A. , Comin F. , Ferrer S.
Published: July 2002

The authors have characterized in air, carbon films of thickness around 1 nm on Si (100) grown in ultrahigh vacuum conditions by pulsed laser vaporization of a graphite target. The substrate preparation procedure was chosen on the basis of minimizing surface roughness as viewed from scanning tunneling microscope topographic images. Atomic resolution images taken in the constant height mode revealed different atomic ordered configurations. A hexagonal structure was preferentially observed with a lattice parameter of 2.4 Å±0.2 Å and extending up to 140×140 Å2. Also, a square lattice, 2.0 Å±0.2 Å side, was imaged coexisting with the hexagonal one. Other structures were found which could be related with the substrate. I-V spectroscopy was performed in these films showing a p-type rectifying behavior and an electronic band gap.
Large area silicon on insulator by double-merged epitaxial lateral overgrowth
Authors: Subramanian Chitra K. , Neudeck Gerold W.
Published: July 2002

The process and feasibility verification for a full wafer silicon-on-insulator (SOI) process by using two merged epitaxial lateral overgrowths has been achieved. This process can be used to produce SOI material with a wide range of silicon thicknesses from 0.1 μm to several microns thick and is compatible with three-dimensional circuit integration. Formation of local area SOI islands, formation of vertical wall seed windows, and epitaxial lateral overgrowth from these narrow vertical seeds have been demonstrated. This SOI process has the potential to reduce the defect density and cost of SOI substrates.
A study of the anneal technique to recover the electrical characteristics of the packaged metal–oxide semiconductor field effect transistors damaged by Co-60 irradiation
Authors: Chang-Liao Kuei-Shu , Hwu Jenn-Gwo
Published: July 2002

Radiation-induced degradation in packaged metal–oxide semiconductor field effect transistors (MOSFETs) can be efficiently removed by an anneal treatment carried out at 350 °C for 10 min in N2. The electrical characteristics of the MOSFETs including threshold voltage Vth, transconductance Gm, and drain current Id were examined in the recovery of device performance. The irradiation was performed by a Co-60 (γ-ray) source with the irradiation total doses ranging from 10 K rads to 10 M rads. Experimental results show that the anneal treatment can be repeatedly performed on a sample after receiving multiple irradiation and the recovery behavior is quite good for each anneal treatment. The determination of the temperature and the anneal time are also discussed.
1/f noise in HgCdTe metal–insulator–semiconductor infrared detectors
Authors: He Wenmu , Çelik-Butler Zeynep
Published: July 2002

We measured 1/f noise on Hg0.71Cd0.29Te metal–insulator–semiconductor (MIS) infrared detectors in dark and subjected to infrared (IR) background radiation of 300 K. The devices were operated in the correlated double sampling mode where the voltage across the MIS capacitor was sampled when the charge well is empty and right after the accumulation of minority carriers due to IR radiation generation. The noise magnitude as well as the spectral form were investigated as a function of integrated charge, integration time, and dark current. The normalized charge noise magnitude when compared for two different integration times was found to disprove bulk originated Hooge’s theory. The charge noise spectral density was also independent of dark current. Charge fluctuations due to interface state trapping and detrapping were explored. The k–p theory was utilized to compute the position of the quasi-Fermi level during the integration of charge in dark. Then the effective trap state density was extracted from the noise data using the McWhorter Theory. Within 40 meV around the valence band edge, the effective trap density was found to vary between 3.3×1019 and 3.3×1018 cm−3 eV−1, monotonically increasing towards EV. The results are compared to interface trap densities reported on other HgCdTe MIS structures obtained by noise, conductance, and capacitance methods.
Doping of polycrystalline silicon films using an arsenic spin-on-glass source and surface smoothness
Authors: Bashir R. , Venkatesan S. , Yen H. , Neudeck G. W. , Kvam E. P.
Published: July 2002

In this brief, the doping of polycrystalline silicon from a commercially available arsenic spin-on glass (SOG) source is described for the first time. It is shown that the arsenic SOG source provides low sheet resistivities in thin polycrystalline silicon films which can be used as gates and contacts. In addition, the polycrystalline silicon films doped with arsenic SOG and exposed to an oxidation step exhibit reduced top surface roughness when compared to films doped with phosphorus from a POCl3 source. The minimization of the top surface roughness of the polyoxide is important for its use as a gate insulator in advanced three-dimensional complementary metal–oxide–semiconductor (CMOS) and as a sidewall contact in BiCMOS bipolar junction transistor devices.
Spectroscopic differential reflectance as an analytical probe for microelectronic processing
Authors: Burns T. M. , Irene E. A. , Chevacharoenkul S. , McGuire G. E.
Published: July 2002

It is important in microelectronics to be able to measure damage and monitor processing during or following the many different processes. To this end, a simple and universal technique is desirable. In this article, differential reflectance (DR) is examined as a tool for studying several processes including implantation, preamorphization, solid phase epitaxy, and rapid thermal annealing. DR is found to be able to measure small differences between samples, and the amount of damage is qualitatively assessed by the intensity and broadening of the silicon interband transitions. More quantitative information about damage layer thickness can be obtained if interference bands are present. DR results were in good agreement with transmission electron microscope (TEM) findings, and in some cases DR spectra suggested residual damage where TEM found annealing to be complete. Preamorphized samples had different interband transition peak broadening and responded differently to annealing compared to their nonpreamorphized counterparts. Distinctive DR spectral features were also obtained for heavily doped silicon samples, and the features were related to dopant species size.
Temperature formation of structural defects in the interface of GaAs Schottky barrier
Authors: Popov A. , Yakimova R.
Published: July 2002

Possible defects originating in the interface of GaAs Schottky barriers have been considered. Three types of imperfections, such as clusters, metal microphases, and extended dislocation defects, have been recognized after intentional thermal treatment of the samples. It has been shown that those defects may affect strongly the Schottky barrier height, and thus, the idea of an effective work function [J. M. Woodall and J. L. Freeout, J. Vac. Sci. Technol. 21, 578 (1982)] has been supported. By deep-level transient spectroscopy spectra simulation, characteristic broadening and shifting of the experimental spectra have been explained to be due to dislocation defects. A model has been proposed of defect formation which may act as a possible limit of metal–insulator semiconductor field effect transistor operation at high temperatures.
Growth and properties of AlInAs–GaInAs alloys and quantum wells on (110) InP
Authors: Brown A. S. , Metzger R. A. , Henige J. A.
Published: July 2002

GaInAs and AlInAs structures have been grown on on-axis and misoriented [4°-(111) In-plane] (110) InP substrates. In general, the growth on the on-axis substrates shows a high density of defects; while the surface morphology using misoriented substrates is smooth. A smooth morphology is obtained on on-axis (110) InP, however, with a low substrate temperature and high V/III ratio. The photoluminescence properties of the individual alloys grown on (110) show high intensities, similar to that which can be obtained on (100) substrates, but the peaks are significantly broadened and shifted in energy. The interface quality of the GaInAs–AlInAs (110) heterojunction, inferred from the linewidths of quantum well emissions, is improved by growing at higher temperature.
Fabrication and performance of GaAs metal–semiconductor field effect transistors with step-graded striped focused ion beam doping in the channel regions
Authors: Hussain T. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

Finely focused beams of silicon ions have been used to produce novel three-dimensional doping profiles in GaAs metal–semiconductor field effect transistor channels. The structure studied is a GaAs field effect transistor in which the channel consists of conducting stripes in a semi-insulating substrate, with the doping profile graded to give a step change in the doping density under the gate. The striped channel has the effect of increasing the device transconductance, while the longitudinal dopant grading increases the gate breakdown voltage. Striped and stepped-channel devices are compared with devices with uniform channels and with striped nonstepped channels; improved performance is demonstrated.
Combined scanning tunneling microscopy/spectroscopy study on the surface electronic structure of GaAs(100) with spatially resolved scanning tunneling spectroscopy spectra
Authors: Li Nan , Qian Shengfa , Fu Chunsheng , Xie Sishen
Published: July 2002

A combined scanning tunneling microscopy/scanning tunneling spectroscopy (STS) system has been developed by which the spatially resolved electronic structure of a surface can be measured step by step consecutively. With this system, etched GaAs(100) surfaces have been studied in ambient with experimental measurements of the (d ln I/d ln V) vs V curves along a line on the surfaces. The curves exhibit the basic band structure of GaAs. Specific band energies from the curves are plotted versus the surface position at which each of the corresponding STS spectra is measured. The plots show a correlative variation of the surface electronic structure with the surface corrugations. The results present the possibility of investigating the spatial variation of the surface electronic states with surface structures. Based on the correlative variation of the surface electronic structure, a way of imaging the surface corrugation more sensitively is proposed.
Study on the stick-slip phenomenon on a cleaved surface of the Muscovite mica using an atomic force/lateral force microscope
Authors: Fujisawa S. , Sugawara Y. , Morita S. , Ito S. , Mishima S. , Okada T.
Published: July 2002

Study was performed on the stick-slip phenomenon between the Muscovite mica and a cantilever tip. An atomic force/lateral force microscope with an optical lever deflection method was used, which detects the deflection and the torsion of the cantilever simultaneously. We observed the square-wave behavior across the scan direction, but the well-known sawtooth behavior due to the stick-slip motion of the tip along the scan direction. It is found that the square-wave and sawtooth behaviors were synchronized with each other. To explain these behaviors, we propose two-dimensional stick-slip model. In this model, the periodicity of the stick point is the same of that of the lattice structure of the mica surface, so that the tip apex takes a zig–zag walk along the scan.
Plasma immersion ion implantation doping experiments for microelectronics
Authors: Qin Shu , Chan Chung
Published: July 2002

Using plasma immersion ion implantation (PIII), silicon has been doped with boron in a high voltage pulsed microwave multipolar bucket plasma system. In order to optimize the system design and predict the doping results, a collisional dynamic sheath model has been developed, which has been verified by measurements as well as simulations. Silicon devices, including diode, metal–oxide–semiconductor (MOS) capacitor, and PMOS transistor, were fabricated by PIII doping technique. B2H6 diluted in helium (1%) was used as the gas source. The reasonable contamination levels involved from PIII process were observed by the measurements of secondary ion mass spectrometry and characteristics of fabricated devices. Good quality of devices has been demonstrated including low reverse current of diode and reasonable lifetimes of the minority carrier.
Mechanical properties of Si-diamondlike carbon films formed by ion beam assisted deposition
Authors: Fountzoulas C. G. , Kattamis T. Z. , Demaree J. D. , Kosik W. E. , Franzen W. , Hirvonen J. K.
Published: July 2002

This article reports on the composition, microhardness, cohesion, adhesion, and friction coefficients of Si-diamondlike carbon coatings on M50 steel and silicon substrates prepared at room temperature by the ion beam assisted deposition process, using energetic Ar+ ions and tetraphenyl-tetramethyl-trisiloxane (Type 704 Dow–Corning silicone oil) as a precursor material. The thickness, microhardness, and friction coefficients of these films were investigated. The cohesion and adhesion failure loads of the films were also evaluated by automatic scratch testing in combination with optical and scanning electron microscopy observation of the scratch. Rutherford backscattering spectroscopy analysis showed that film stoichiometry is insensitive to deposition parameters including the relative arrival ratios of Ar+ ions and deposited silicon-hydrocarbon molecules. Knoop microhardness values (at 25-g load) were found to vary from 800 to 1600 kg/mm2, and the unlubricated friction coefficients ranged from 0.21 to 0.27, depending on deposition parameters.
Simulations of fabricated field emitter structures
Authors: Hong D. , Aslam M. , Feldmann M. , Olinger M.
Published: July 2002

Five different single field emitters and emitter arrays with flat or nonflat collector structures were selected from the literature to simulate the actual emitting area of the tip. The Poisson’s equation was solved under two different assumptions of emitting behavior; uniform electron emission from the whole tip area, and electron emission from only small part of the tip area. It was observed that the geometry factor β of an array is larger than that of a single emitter, which is believed to be partly responsible for exceedingly small computed value of emitting area α for multiemitter structures. Finite element analysis of single and multiemitter structures indicates that the large β values are due to the interemitter interactions in an array.
Evaluation of Zr/O/W Schottky emitters for microcolumn applications
Authors: Kim H. S. , Kratschmer E. , Yu M. L. , Thomson M. G. R. , Chang T. H. P.
Published: July 2002

Schottky emission tips have been evaluated with microlenses for applications in scanning tunneling microscope aligned field emission microcolumns. Operation of Zr/O/W 〈100〉 Schottky emission tips at 1800 K with an axial separation of 50–100 μm between the tip and a microlens has been successfully tested. The microlens consists of an extraction electrode with a 5-μm-diam hole in a 1-μm-thick silicon membrane. The preliminary results of this study show that thermal field emission tips can be operated continuously in close proximity to a microlens over a long period of time, and that good emission stability of less than 1% noise fluctuation over 10 h is achieved with emission currents up to at least 100 μA.
Tenth micrometer trench fabrication by aperture narrowing of 0.6 μm starting mask structures using chemical-beam deposition and ion-beam redeposition
Authors: Hsu David S. Y.
Published: July 2002

We demonstrated the proof of principle for the fabrication of trenches with widths down to 0.1 μm on a silicon substrate using photolithographically prefabricated starting mask structures having a spacing of 0.6 μm. The corresponding trench width of 0.15 μm was achieved using starting mask structures having a spacing of 1.0 μm. Chemical-beam deposition of metals was used to coat the starting mask structures and to narrow the aperture openings. Metal redeposition by ion-beam sputtering directed perpendicular to the substrate further narrowed the spacing between the sidewalls of the mask structures. The subsequent chemically assisted ion-beam etching of the underlying substrate through the constricted mask apertures produced the trenches with greatly reduced widths.
Nanofabrication and rapid imaging with a scanning tunneling microscope
Authors: Rubel S. , Trochet M. , Ehrichs E. E. , Smith W. F. , de Lozanne A. L.
Published: July 2002

Nanowires have been made by decomposing organometallic gases in a UHV scanning tunneling microscope (STM); this process is a form of chemical vapor deposition (CVD). Our STM is coupled to a commercial scanning electron microscope (SEM), which allows us to align the tip with pre-existing contact pads for electrical measurements of the nanowires. Thus four-contact measurements on two wires have been performed, a first for STM-fabricated structures. The resistivity of the first wire made from a nickel carbonyl precursor gas is 34±10 μΩ cm at room temperature. This is remarkably close to the bulk value of 7.8 μΩ cm, since the wire is only 5 nm thick, 190 nm wide and 3.7 μm long. This indicates that the nickel deposits are fairly pure, and is consistent with Auger analysis made on micron-size deposits: there is at least 95% nickel in these deposits. This is a substantial improvement over previous results from our group and the few other groups using this technique. The second wire is 1.45 μm long and 100 nm wide; its thickness is estimated at 5 nm. It has substantially higher resistivity: 1.1±0.45 mΩ cm, which is attributed to minute near discontinuities in the wire. Finally, lines have been written 4 nm thick, 35 nm wide, and 2μm long, which are unfortunately not long enough to allow resistivity measurements. Reliability problems of this complex STM/SEM system are discussed and new designs for a more dependable system are described. A new technique for rapid imaging of large areas (10–20 μm square) with the STM is being developed and preliminary results are presented here.
Ge/Si heterostructures grown by Sn-surfactant-mediated molecular beam epitaxy
Authors: Lin X. W. , Liliental-Weber Z. , Washburn J. , Weber E. R. , Sasaki A. , Wakahara A. , Hasegawa T.
Published: July 2002

Ge/Si heterostructures were grown on Si (001) by Sn-submonolayer-mediated molecular beam epitaxy (MBE) and characterized by a variety of techniques, in order to study the behavior of Sn surfactant during Ge and Si growth and its influence on Ge/Si interface quality. It was found that Sn strongly segregates to the growing surface of both Ge and Si and that the presence of Sn surfactant can effectively suppress Ge segregation into a Si overlayer and enhance the surface mobility of adatoms. These results suggest that Sn-mediated epitaxy can be used as a viable method to produce Ge/Si superlattices, with an interface quality superior to those grown either by conventional MBE or with other types of surfactants.
Processes of microwave generation and amplification in structures with medium electron transit angles
Authors: Galdetskiy A. V. , Solntsev V. A. , Stepanchuk V. V.
Published: July 2002

The possibility of microwave generation and amplification in vacuum electron devices with the intermediate electron transit angles (about 2π) is shown. These devices are between the conventional microwave tubes with the long-time electron-field interaction (TWT and BWO) and low-frequency triodes with short interaction time. They have a number of advantages in their characteristics and structure. The authors have considered a model for analysis and simulation of this class of devices based on the negative electron beam conductance and modulation of electron emission.
Gold nanocomposites
Authors: Maya L. , Allen W. R. , Glover A. L. , Mabon J. C.
Published: July 2002

A series of nanocomposites, finely divided gold dispersions in solid ceramic matrices, were generated by reactive sputtering of gold alloys in a nitrogen plasma. Gold alloys examined were different compositions of Au–Ga, Au–Al, and Au–Si. The average size of the gold particles was in the range of 3–8 nm. These nanocomposites show interesting chemical characteristics as well as optoelectronic properties. The gold/gallium nitride composite is particularly interesting since GaN is a wide band semiconductor. The gallium nitride composite is also interesting because upon heating at 800 °C the material releases nitrogen and produces a gold–gallium alloy. This property was exploited to generate microscopic metal lines by maskless laser writing and its use explored for brazing ceramic and metal components. The resistivity of the Au/GaN nanocomposite films varied several orders of magnitude depending on the gold loading.
Focused-ion-beam implantation of Ga in elemental and compound semiconductors
Authors: Gnaser H. , Kallmayer C. , Oechsner H.
Published: July 2002

Small-area [∼(50 μm)2], focused-ion-beam implantation of 25 keV Ga+ in Si, Ge, InP, InSb, and ZnSe was investigated by experiments and by computer simulations. Specifically, the Ga concentration was determined for implantation fluences Φ ranging from 1×1014 to 3×1017 Ga+ ions/cm2 by means of secondary-ion mass spectrometry. In all materials the Ga peak concentration exhibits an essentially linear increase with fluence up to some 1016 cm−2; for higher values of Φ the Ga concentration tends to saturate. The saturation content of Ga at the surface c∞ ranges from ∼2 at % for ZnSe to ∼40 at % for Si. These values appear roughly inversely correlated with the specimens’ sputtering yields and agree thus with the predictions of a model of ion retention in the presence of concurrent sputter erosion. The computer simulations with the dynamic binary-collision-approximation code t-dyn produce a fluence-dependent evolution of the Ga concentrations in the examined semiconductors which is in qualitative agreement with the experiments. Furthermore, partial sputtering yields and the most probable ranges for 25 keV Ga+ impact on the different materials have been determined both experimentally and from the simulation output.
Monolayer resolved monitoring of AlAs growth with metalorganic molecular beam epitaxy by reflectance anisotropy spectroscopy
Authors: Rumberg J. , Reinhardt F. , Richter W. , Farrell T. , Armstrong J.
Published: July 2002

Metalorganic molecular beam epitaxy (MOMBE) growth is studied here for the first time in situ with reflectance anisotropy spectroscopy (RAS). Growth of AlAs on GaAs(001) and optical monitoring was performed in a standard MOMBE system. Triisopropylgallium, dimethyl- ethylaminoalane, and precracked arsine were used as precursors. RAS spectra obtained are similar to the ones observed under molecular beam epitaxy or metalorganic vapor phase epitaxy conditions and correspond to the GaAs(001) and AlAs(001) c(4×4) surface reconstructions. Initiating AlAs growth from an arsenic stabilized c(4×4) GaAs(001) or AlAs (001) surface, the RAS signal shows oscillations with a period corresponding to the growth of one AlAs monolayer, as verified by thickness determination on thicker layers. As opposed to growth on an AlAs surface, when growing on GaAs the growth rate was not found to be constant right from the start, but was increasing slightly until it stabilized after several monolayers had been deposited.
Lithography and fabrication processes for sub-100 nm scale complementary metal–oxide semiconductor
Authors: Wind S. J. , Taur Y. , Lee Y. H. , Mii Y. , Viswanathan R. G. , Bucchignano J. J. , Pomerene A. T. , Sicina R. M. , Milkove K. R. , Stiebritz J. W. , Roy R. A. , Hu C. K. , Manny M. P. , Cohen S. , Chen W.
Published: July 2002

We explore the fabrication of complementary metal–oxide–semiconductor (CMOS) devices and circuits with a critical dimension of 100 nm and below using a variety of lithographic, processing, materials, and device design innovations. Device design parameters tailored for high performance at low operating power include the use of bulk and silicon-on-insulator substrates, a steep retrograde channel doping scheme, ultrathin (∼3 nm) gate dielectric, shallow source, and drain extensions, and a metal-over-gate structure. Mix-and-match lithography, including the use of electron-beam lithography for all critical levels, x-ray lithography for gate level definition, and optical (deep ultraviolet) lithography for noncritical levels, is used in an effort to exploit the strongest features of each of these lithography technologies. New reactive ion etching processes for CMOS gate definition as well as for device and circuit metallization have been developed in conjunction with the lithographic processes in an effort to facilitate the scaling of silicon devices toward their ultimate limits.
Ultrasound effects on the tribological properties of synthesized diamond films
Authors: Snitka V. , Trava-Airoldi V. J. , Baranauskas V.
Published: July 2002

The friction and wear behavior of chemical vapor deposition grown diamond films has been investigated under strong ultrasound conditions at the friction interface. Experiments were performed on an alternating ‘‘pin-on-plate’’ tribometer constructed as an ultrasonic motor with excited bimodal mechanical vibrations at the frequency of 20 kHz. Ultrasound sliding of the films was done against alumina ceramics and with the diamond film itself. We have shown that chemical vapor deposition diamond films can be fast polished mechanically without significant graphitization by ultrasonic treatment. The initial film roughness was reduced from an average Ra ≊3000 nm to Ra ≊10 nm. The polishing decreased the static coefficient of friction of the diamond film from about 0.53 to about 0.12. The operative mechanism for the polishing in the case of initially rough diamond samples appears to be asperity fracture. For smooth diamond samples it is suggested that tribochemical oxidation is also a polishing mechanism.
Electrical characteristics of metal/n-InSb contacts with InSb annealed rapidly prior to metal evaporation
Authors: Eftekhari G.
Published: July 2002

It has been reported that rapid thermal annealing of implanted (Be and Si) InSb at a temperature range of 300–450 °C for 20 s is sufficient to activate the implanted dopants. To investigate the effect of such annealing on the unimplanted parts of InSb, the electrical properties of Al and Ag/n-InSb in which InSb is rapidly annealed (using proximity method) prior to Al and Ag evaporation are analyzed. It was determined that annealing at 300 and 350 °C does not degrade contact properties. The parameters of contacts considered here were barrier height (determined using capacitance–voltage method and current–voltage method) and ideality factor. For unannealed contacts the value of barrier height and ideality factor were found to vary in the range 0.14–0.17 eV and 1.12–1.31, respectively, depending on the metal type. Annealing at 400 °C slightly degraded the contact properties while annealing at 450 °C caused a significant degradation. The barrier height and ideality factor decreased to 0.1 eV and 1.41–1.52, respectively, when contacts are annealed at 450 °C. Creation of nonstoichiometric InSb surface layer and injection of charges into native oxide layer are likely causes for the contact degradation.
Ion sputtering of GaAs(110): From individual bombardment events to multilayer removal
Authors: Wang X.-S. , Pechman R. J. , Weaver J. H.
Published: July 2002

We have investigated the effects of ion mass (Ar+, Xe+), energy (0.3–5 keV), trajectory, and sample temperature on the ion sputtering processes for GaAs(110). Scanning tunneling microscopy images reveal that most ion bombardment events at 300 K create pits that are 1–5 unit cells in size, indicating that direct knock-on collisions dominate. The average pit size increases moderately with ion energy but shows a significant variation with the incident angle. Vacancies are sufficiently mobile at 625–775 K that vacancy islands form and the yield can be determined directly. The sputtering yields for these nearly ideal surfaces exhibit structure that can be related to the nuclear stopping power and ion channeling, showing the influence of such geometric factors as surface path length, ion radius, and projected atom column density. Temperature dependent results for monolayer and multilayer sputtering show that adatoms ejected onto the surface refill vacancies but that the surface roughness, as measured by surface width, increases with ion fluence. While interlayer atomic transport is measurable at 625 K and increases with temperature, it is not sufficient to achieve layer-by-layer removal because Asx desorption competes with interlayer transport above ∼800 K.
Algorithm method of correlation position for automatic alignment in microcircuit fabrication
Authors: Xiangdong Wang , Bingchu Du , Ling Wang , Guowei Wu , Huang Ge
Published: July 2002

A new algorithm method used to determine the correlation position between two marks for automatic alignment in microcircuit fabrication has been developed. This algorithm maintains the correlation technique advantage such as its high immunity to noise and poor contrast in the mark signal. The alignment overlay precision achieved is better than one pixel. By using this algorithm method, the 486-33PC computer takes about 4 s to determine the correlation position without any special hardware. This article describes the method along with giving experimental results.
Improvements in the wavelength stability of evaporated TiO2/SiO2 anti-reflection coatings by ion assistance*
Authors: Bhumbra B. S. , Thomas D. J. , Goodchild D. P.
Published: July 2002

We report the deposition of highly stable two-layer TiO2/SiO2 anti-reflection (AR) coatings deposited using ion-assisted deposition (IAD). We have measured the variation of refractive index with ion energy and beam current and found that this increases with the ion energy. This result, in conjunction with Auger electron spectroscopy measurements, implies that the IAD process densifies the deposited films without changing their stoichiometry. Wet etch rate measurements have confirmed that film porosity is correspondingly reduced. Anti-reflection coatings have been deposited on InP substrates and reflectivities less than 0.1% have been obtained. The long-term stability has been monitored over several hundred days and large improvements have been observed when IAD is used. We have also measured the changes in refractive index of single layer films immediately after deposition when the vacuum chamber is vented to atmosphere and no changes are evident in the IAD films. All the evidence implies that changes in non-IAD anti-reflection coatings are a result of a slow moisture ingression into the uppermost SiO2 layer. We could not however simulate this by attempts to accelerate water ingression into non-IAD AR coatings.
In situ diode laser absorption measurements of plasma species in a gaseous electronics conference reference cell reactor
Authors: Oh Daniel B. , Stanton Alan C. , Anderson Harold M. , Splichal Michael P.
Published: July 2002

A major objective of the microelectronics industry is to perfect methods for controlling dimensional accuracy during plasma etching of submicron features in wafer substrates. Optical sensors as monitors of gas phase etch chemistry are attractive because they offer the potential of nonintrusive in situ measurements for use as real time inputs to process control. In this study, infrared lead-salt diode lasers are used to probe fluorocarbon-based plasmas used for etching of silicon and silicon dioxide in a gaseous electronics conference reference cell reactor. The diode laser sensor is used for in situ measurements of neutral CF2 reactive intermediates and CF2O etch product. Possible correlations between etch process outcomes and parameters measured by diode laser absorption are identified. The diode laser measurement of CF2 concentration is found to be possibly useful as an indicator of etch rates or selectivity. In addition, diode laser monitoring of CF2O during etching of SiO2 is potentially useful as an end point monitor. Further research and development based on these results are expected to lead to new process control strategies for improved reliability and product yield in plasma etching.
Atomic force microscopy investigations of loaded crack tips in NiAl
Authors: Göken M. , Vehoff H. , Neumann P.
Published: July 2002

Scanning probe microscopy has great advantages over other high-resolution techniques like transmission electron microscopy in that no extensive specimen preparation, such as thinning, is required. This is important for examinations of crack tips, since thin film effects obscure the deformation behavior of cracks. For the first time, the concurrent processes of crack tip blunting by dislocation emission and unstable crack propagation were studied systematically with the atomic force microscope. Brittle cracks were initiated in NiAl single crystals. NiAl serves as a model alloy for the mechanical behavior of intermetallic compounds. A small bending device was constructed in which the specimens were loaded stepwise to measure the displacement fields of the crack tip in situ at different load levels. With this loading device, cracks were propagated in small steps of a few micrometers. From the atomic force microscope images, dislocation distributions were obtained as functions of the applied load. Nearly radial symmetric elastic deformation fields were observed at the crack tip with a maximum depth of 46 nm. In addition, material parameters such as the fracture toughness KIC were calculated from the crack tip opening at the onset of brittle crack growth. The measured value of 1.5 MPa√m compares favorably with results from standard fracture tests.
Domain structure of Co/Pt multilayers studied by magnetic force microscopy
Authors: Löhndorf M. , Wadas A. , Wiesendanger R. , van Kesteren H. W.
Published: July 2002

We applied magnetic force microscopy to study the domain structure of Co/Pt multilayers [15×Co(3.5 Å)/Pt (6 Å)]. The Co/Pt multilayers were deposited on glass substrates and demag- netized either by lowering the external field or by using an oscillating field. We found that both techniques used to demagnetize our samples led to different domain structure. In the first case, domains had different widths in the range from 0.5 to 5 μm. The other technique (an oscillating field) led to domains more uniform in size with a much smaller width of 70–130 nm. We also studied the stability of the domain structure of Co/Pt multilayers while an external field was applied.
Etching and boron diffusion of high aspect ratio Si trenches for released resonators
Authors: Weigold J. W. , Juan W. H. , Pang S. W.
Published: July 2002

This article discusses etching and boron diffusion in Si for the purpose of fabricating micromachined devices with high aspect ratio features. The etch rate of Si under various doping conditions in a Cl2 plasma generated by an electron cyclotron resonance (ECR) source was measured. It was found that lightly boron and phosphorus doped Si were etched at rates of 0.17 μm/min, whereas heavily boron doped Si had a similar etch rate of 0.16 μm/min. Si doped with high phosphorus concentrations had a faster etch rate of 0.31 μm/min. These etch rates were measured for Si etched at 100 W microwave power, 100 W rf power, 3 mTorr, with 20 sccm of Cl2 flow, and an ECR source to sample distance of 8 cm. The difference between the p++ and n++Si etch rates was more significant when etched at higher microwave power, higher rf power, or higher temperature. The depth of a heavily doped boron diffusion layer was measured for different feature sizes, trench openings, and aspect ratios. The diffusion layer thickness was found to decrease from 2.9 μm at the bottom of 50-μm-wide trenches, to 1.5 μm at the bottom of 2-μm-wide trenches. Diffusion thickness at the bottom of trenches near narrow features was found to increase to 3 μm compared to 2.5 μm for trenches near large features. The diffusion layer on the sides of the trenches for a 30 min boron diffusion at 1175 °C was 3.25 μm thick and was found to be independent of the trench opening and the trench aspect ratio. A deep etch-shallow diffusion process was used to fabricate thick released resonators with a short boron diffusion time. The second dry etch in the deep etch-shallow diffusion process, which is used to etch the p++ layer at the bottom of adjacent features, was studied. It was found that this etch successfully removed the p++ layer at the bottom of Si trenches in addition to widening the slightly tapered profile near the bottom of the trenches. This process has been applied to the fabrication of micromachined comb drive resonators and micromirrors successfully.
Time evolution of nanocontact structure between macroscopic metallic wires leading to nanowire formation
Authors: Correia A. , Marqués M. I. , Garcı́a N.
Published: July 2002

Connections between two macroscopic metallic (gold, copper, silver, platinum, and tungsten) wires have been investigated by transmission and scanning electron microscopy. The results show that metallic contacts exist but do not break cleanly. They are stretched into many filaments or threads of nanometer size leading to nanowire formation as time passes.
Low temperature reactive ion etching of silicon with SF6/O2 plasmas
Authors: Wells T. , El-Gomati M. M. , Wood J.
Published: July 2002

An investigation of low temperature reactive ion etching of silicon to produce ultrasmall structures is presented. Etching was performed between 10–100 mTorr with SF6/O2 plasmas. The silicon samples were cooled using liquid nitrogen, allowing the temperature to be controlled over the range of +25 to −120 °C. With a flow rate of 1 sccm of SF6 and sample temperatures below −85 °C the etch produces nearly anisotropic etching in agreement with predictions of the reactive spot model. At higher flow rates etching produced facetted features indicating higher chemical reactivity of the plasma with the silicon. With the addition of O2 to the plasma the facetting became even more pronounced.
Study on photoelectric properties of a TiO2 nanoparticle
Authors: Chen Yongmei , Cao Yaan , Bai Yubai , Yang Wensheng , Yang Jihua , Jin Haiyan , Li Tiejin
Published: July 2002

Here we report a study of surface states in nanometer-sized TiO2 particles (P1) prepared in our lab with the aid of surface photovoltage spectroscopy, electric field-induced photovoltage spectroscopy (EFISPS), and fluorescence spectrum. The diameter determined by x-ray diffraction is 3.5 nm. The EFISPS of P1 shows several subband gap absorption bands at 350, 375, and 460 nm, respectively. The fluorescence peaks of dry powder and an aqueous suspension of P1 at 361, 391, and 469 nm were detected. The above results are concluded to be relative with the located surface states within the band gap. The surface states were deduced to be oxygen vacancies, i.e., Ti3+, Ti2+, Ti+, whose maximum densities lie at 0.32, 0.50, and 1.02 eV below the maximum density of states in the conduction band, respectively.
Uniform low stress oxynitride films for application as hardmasks on x-ray masks
Authors: Dauksher W. J. , Resnick D. J. , Smith S. M. , Pendharkar S. V. , Tompkins H. G. , Cummings K. D. , Seese P. A. , Mangat P. J. S. , Chan J. A.
Published: July 2002

A low stress silicon oxynitride deposition process has been developed in which the average stress level can be tailored by adjusting silane flow in the plasma enhanced chemical vapor deposition reactor. Stress gradients, as might be caused by nonuniform heating or gas distribution, were not found to exist. By volume, the SiON films were found to be approximately 81% silicon dioxide and 19% silicon nitride. Because the films are easily removed in hydrofluoric acid, this composition is ideally suited for use as a hardmask patterning layer on x-ray masks. A reactive ion etch process employing CHF3, O2, and Ar gases has demonstrated selectivity to Shipley SNR 200 resist of better than 3:1. Smooth pattern transfer into TaSi and TaSiN absorber layers of test features as small as 0.1 μm has been achieved using SiON as the hardmask layer. Image placement distortions on the order of 15 nm (3σ) occur from etching the SiON films on 64 Mbit SRAM x-ray test masks.
Increasing plasma etch resistance of resists using fullerene additives
Authors: Dentinger Paul M. , Taylor James W.
Published: July 2002

We utilize a new class of additive, Fullerenes, which appear to impart superior plasma etch resistance to resist films compared to other additives reported in the literature. [R. R. Kunz, S. C. Palmateer, A. R. Forte, R. D. Allen, G. M. Wallraff, R. A. DiPietro, and D. C. Hofer, Proc. SPIE 2724, 365 (1996).] The plasma etch resistance of PMMA impregnated with [60]Fullerenes was compared directly to pure PMMA; adamantane- and 1-chloroadamantane-impregnated PMMA; the novolac-based, e-beam/x-ray photoresist SAL 605 (The Shipley Co.); APEX-E (IBM Corp.); and an experimental, 193 nm resist, XP96545-7A (The Shipley Co.). These comparison experiments were done under CF4 and Cl2 reactive ion etch conditions. The plasma etch rate of PMMA decreased linearly with concentration of [60]Fullerenes in the film up to at least 11 wt %. When 10.8 wt % C60 (≈7.3 vol %) versus total solids were added to PMMA, the etch rate ratio to SAL 605 dropped from 1.80 to 1.38 in CF4 and from 2.5 to 1.55 in Cl2. Improvements in etch resistance with Fullerenes added to PMMA were similar for both Cl2 plasmas and CF4 plasmas, which was contrary to the results of the unmodified XP96545-7A resist and that reported for alicyclic additives, [R. R. Kunz, S. C. Palmateer, A. R. Forte, R. D. Allen, G. M. Wallraff, R. A. DiPietro, and D. C. Hofer, Proc. SPIE 2724, 365 (1996)]. [60]Fullerenes were also successful at improving the plasma etch durability of pure polystyrene films, showing that these additives have the potential to improve etch resistance of films to better than novolac, provided solubility limitations can be overcome. The absorptivity of [60]Fullerenes at 193 nm can be reduced by derivatizing the C60 to C60H36, C60F40, or C60F48. The fluorinated Fullerenes show high solubility in propylene glycol methyl ether acetate and 1-methoxy-2-propanol. On a mole basis, fluorinated Fullerenes improve the etch resistance of PMMA as well as [60]Fullerenes showing the potential of derivatized Fullerenes for various photoresist applications, including 193 nm imaging materials.
Electron and ion optical design software for integrated circuit manufacturing equipment
Authors: Munro Eric
Published: July 2002

This article describes methods for the computer aided design of electron and ion beam columns for the integrated circuit (IC) manufacturing industry. The techniques described include computation of field distributions in electron lenses and deflectors, electron trajectories and aberrations, dynamic corrections, effects of discrete Coulomb interactions, design of electron guns, treatment of diffraction effects, optimization, and tolerancing of complete columns. These techniques are illustrated with examples relevant to the IC manufacturing industry, including systems for high-throughput electron beam lithography, nanolithography systems, and electron beam systems for inspection, metrology, and voltage testing.
Process optimization for production of sub-20 nm soft x-ray zone plates
Authors: Spector S. J. , Jacobsen C. J. , Tennant D. M.
Published: July 2002

We report here the optimization of processes for producing sub-20 nm soft x-ray zone plates, using a general purpose electron beam lithography system and commercial resist technologies. We have critically evaluated the failure point of the various process steps and where possible chosen alternate methods, materials, or otherwise modified the process. Advances have been made in most steps of the process, including the imaging resist, pattern conversion for electron beam exposure, and pattern transfer. Two phase shifting absorber materials, germanium and nickel, were compared. Zone plates with 30 nm outer zones have been fabricated in both germanium and nickel with excellent quality using polymethyl methyl accrylate and zones as small as 20 nm have been fabricated in nickel using the calixarene resist. The total efficiency as well as the efficiency of different regions of the zone plates were measured. All zone plates have demonstrated good efficiencies, with nickel zone plates performing better than germanium zone plates.