bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-dimensional electron gas in AlGaN/GaN heterostructures
Authors: Li J. Z. , Lin J. Y. , Jiang H. X. , Khan M. A. , Chen Q.
Published: July 2002

The formation of a two-dimensional electron gas (2DEG) system by an AlGaN/GaN heterostructure has been further confirmed by measuring its electrical properties. The effect of persistent photoconductivity (PPC) has been observed and its unique features have been utilized to study the properties of 2DEG formed by the AlGaN/GaN heterointerface. Sharp electronic transitions from the first to the second subbands in the 2DEG channel have been observed by monitoring the 2DEG carrier mobility as a function of carrier concentration through the use of PPC. These results are expected to have significant implications on field-effect transistor and high electron mobility transistor applications based on the GaN system.
Molecular patterns by manipulating DNA molecules
Authors: Ouyang Zhen-qian , Hu Jun , Chen Sheng-fu , Sun Jie-lin , Li Min-qian
Published: July 2002

Manipulating DNA molecules to form molecular patterns on a nanometer scale is a subject with wide prospects. By applying a modified “molecular combing” technique and imaging in air with atomic force microscope, we aligned DNA molecules on a mica surface which was chemically modified with a small organic molecule, (3-aminopropyl)-triethanoxysilane. Two-dimensional patterns of DNA molecules were also constructed.
Metrology of scattering with angular limitation projection electron lithography masks
Authors: Liddle J. A. , Blakey M. I. , Saunders T. , Farrow R. C. , Fetter L. A. , Knurek C. S. , Kasica R. , Novembre A. E. , Peabody M. L. , Tennant D. M. , Windt D. L. , Postek M.
Published: July 2002

Mask metrology is a vital part of any lithographic technology, both for control of the mask patterning process and also for ensuring that the contribution of the mask to the system error budget is within acceptable limits. For design rules of 0.13 μm and below, errors arising from metrology must be kept to less than 1 nm. We have examined the potential for achieving this, in the case of scattering with angular limitation projection electron lithography (SCALPEL) masks, by using high-energy (100 keV) electron transmission measurements. We have also performed extensive metrology using conventional scanning electron microscope techniques. These results show that the SCALPEL mask has the potential to meet the specifications necessary for lithography at the 0.13 μm generation and beyond.
Quantification of the extent of reaction in a negative, novolac-based, chemically amplified resist
Authors: Dentinger Paul M. , Taylor James W.
Published: July 2002

A technique for determining the extent of reaction and the molar absorptivity of the Fourier transform infrared (FTIR) peak created during the postexposure bake (PEB) reaction of the negative e-beam/x-ray Shipley resist, SAL 605, is described. Wafers were oven baked within a gas-tight bomb. The product of the linking reaction, methanol, was quantified from the gas in the bomb and within the resist film after the PEB. The ether peak, corresponding to the reaction between hexamethoxymethylmelamine (HMMM) and novolac was measured on the same wafer using FTIR. In addition, the absolute number of HMMM molecules reacted was measured by gel permeation chromatography to yield the number of moles methanol produced/HMMM reacted. The molar absorptivity for the ether peak, resulting from a reaction between an HMMM and a phenolic site on the novolac is 3.14±0.53×105 cm2/mole. Under conditions sufficient for imaging in a 0.5 μm thick film, the average number of reactions/HMMM molecule is 1.27±0.24. From previous work on the acid concentration in this resist [P. M. Dentinger, C. M. Nelson, S. J. Rhyner, J. W. Taylor, T. H. Fedynyshyn, and M. F. Cronin, J. Vac. Sci. Technol. B 14, 4239 (1996)] each acid moiety created was found to catalyze an average of 26±8 events during the PEB process. It appears that no more than 1.5%–2% of the available phenolic sites in the film need to be reacted for the required differential dissolution rate, and that the film does not crosslink. The ramifications of this work on modeling this type of resist will also be discussed.
Ion induced damage in strained CdZnSe/ZnSe quantum well structures
Authors: Sparing L. M. , Wang P. D. , Mintairov A. M. , Lee S. , Bindley U. , Chen C. H. , Shi S. S. , Furdyna J. K. , Merz J. L. , Snider G. L.
Published: July 2002

A study of the effects of reactive ion etching on molecular beam epitaxy grown (CdxZn1−xSe/ZnSe) strained quantum well (QW) samples using low temperature photoluminescence reveals a blue shift in the characteristic peak position of the 8 nm QW when exposed to plasmas of H2, D2, or He. Based on experimental results we suggest that this blue shift is a result of ion induced damage interacting with strain present in the as-grown QW. The QW is compressively strained at the interface with additional local strains in the QW lattice due to its random ternary alloy composition. The shallowest QW samples exhibit a peak in the blue shift as a function of bias voltage, with a reduced blue shift seen at high voltages.
Recoil implantation of boron into silicon for ultrashallow junction formation: Modeling, fabrication, and characterization
Authors: Liu Henley L. , Gearhart Steven S. , Booske John H. , Wang Wei
Published: July 2002

An ion-beam mixing technique is used to fabricate ultrashallow p+/n junctions. In this method, a thin boron layer is first sputter deposited onto the Si wafer surface. Then a 10–40 keV Ge ion beam or −3 kV Ar plasma source ion implantation (PSII) is used to knock the boron atoms into the Si substrate by means of ion-beam mixing. For the thin (0.7 nm) boron layers used in this effort, a selective etch for the removal of boron is unnecessary. Sub-100 nm p+/n junctions have been realized with this method. Numerical simulations, performed to predict the recoiled boron profiles, show good agreement between the simulated and measured data.
Effect of sp2 content and tip treatment on the field emission of micropatterned pyramidal diamond tips
Authors: Kang W. P. , Wisitsora-at A. , Davidson J. L. , Kerns D. V. , Li Q. , Xu J. F. , Kim C. K.
Published: July 2002

Electron field emission characteristics of uniformly constructed micro-pyramids of polycrystalline diamond with varying sp2 content have been systemically investigated. Concurrently, tip surface treatment was performed and emission characteristics of the post-treated tips were evaluated. The experimental results show that the field emission characteristics of the diamond can be enhanced by increasing the sp2 content and performing surface treatment. The emission current is significantly improved and the turn-on electric field is drastically reduced. Hypotheses are proposed for the effect of sp2 content and surface treatment on the field emission enhancement of diamond tips: (i) lowering of the work function due to sp2 defect induced band and impurity desorption, and (ii) increase in field enhancement factor due to sp2-diamond-sp2 microstructures and a field forming process. Analysis of the experimental results indicates that (ii) is the more probable explanation.
Progress toward silicon-based intersubband lasers
Authors: Soref Richard A. , Friedman Lionel , Lew Yan Voon L. C. , Ram-Mohan L. R. , Sun Gregory
Published: July 2002

Design results are presented for the quantum parallel laser (QPL) at 1–20 μm wavelengths and the cryogenic 4–20 μm quantum cascade laser (QCL). For 1–2 μm lasing, the optimum multiple quantum well heterostructures are Si quantum wells (QWs) confined by wide-gap lattice-matched semiconductor layers, especially the Si/ZnS, Si/BeSeTe, Si/γ–Al2O3, Si/CeO2, and Si/SiOx systems (SiOx is a crystalline suboxide). The electrically pumped 300 K unipolar p-i-p. QPL consists of tightly coupled QWs exhibiting coherent transport of carriers on superlattice (SL) minibands. A good QPL candidate is the symmetrically strained Gen–Sin SL grown on relaxed Si0.5Ge0.5. Local-in-k population inversion is engineered between two valence minibands. Our calculations indicate that the p-i-p QCL is feasible in Ge–Si or in lattice-matched Si0.63Ge0.33C0.04/Si. The oscillator strength fz=0.1 calculated for the 8 ML×8 ML Si/ZnS zone-folded SL is insufficient for 1.1 μm band-to-band lasing; however, the in-plane dispersion of Si QWs in Si/ZnS SLs shows valence subbands that are sufficiently nonparabolic for local-in-k lasing in QPLs and QCLs.
Thermal instability of a conduction channel in chemical vapor deposition diamond films
Authors: Yu Z. X. , Xu N. S.
Published: July 2002

Thermal instability of a conduction channel in a nonmetallic field emission regime has been assumed as an origin of cathode-initiated vacuum breakdown process. In this article, details are given of a theoretical study of thermal response of a conduction channel in insulating media to dc fields, which takes into account the effect of temperature rise on field emission from substrates. It is found that this effect can lead to a regenerative process, which will finally cause a thermal runaway. In addition, an analysis was carried out on chemical vapor deposition diamond films, and it reveals that the thermal conductivity of diamond films is a key parameter in deciding the initiating mechanism of thermal instability of a channel in the film.
Photoluminescence from pseudomorphic Si1−yCy layers on Si substrates
Authors: Penn C. , Zerlauth S. , Stangl J. , Bauer G. , Brunthaler G. , Schäffler F.
Published: July 2002

We observe near band edge photoluminescence (PL) from pseudomorphic Si/Si1−yCy multiple quantum wells and thick Si1−yCy epilayers, which were grown by molecular beam epitaxy on Si substrates. Pieces of these structures were annealed at temperatures between 500 and 1000 °C to investigate their thermal stability. While annealing at 900 °C or more leads to a reduction of the amount of substitutionally incorporated carbon and to a quenching of the PL signal, annealing at temperatures between 500 and 700 °C results in increased PL intensities and reduced linewidths. Although no decrease in the carbon content is observed under these conditions, we also observe a blue shift of the PL lines after annealing. In addition, increasing the temperature, at which the PL is recorded, leads to a red shift of the lines. We show that these findings are consistent with a recombination model of excitons bound to alloy fluctuations and a homogenization of not statistically distributed carbon atoms upon annealing.
Strain-induced birefringence in Si1−xGex optical waveguides
Authors: Robillard M. , Jessop P. E. , Bruce D. M. , Janz S. , Williams R. L. , Mailhot S. , Lafontaine H. , Kovacic S. J. , Ojha J. J.
Published: July 2002

For the design of Si1−xGex optical waveguide devices, one of the most important material parameters is the refractive index difference, δn, between the alloy layer and the silicon substrate. We have measured δn for pseudomorphic waveguide layers with germanium fractions between 1% and 9% by fitting measured mode profiles to theoretical mode shapes for a wavelength of 1.3 μm. For transverse electric modes, the measured δn varied with composition as δn=(0.34±0.05)x. Transverse magnetic modes were more tightly confined to the waveguide layer and the index was determined to be δn=(0.55±0.05)x. The large difference between the two polarizations results from strain-induced birefringence. Bulk photoelastic theory, using constants appropriate for pure silicon, predicts strain contributions to the index of −0.080x and +0.095x for light polarized parallel and perpendicular, respectively, to the substrate plane, consistent with experimental observations.
Implanted gallium-ion concentrations of focused-ion-beam prepared cross sections
Authors: Ishitani T. , Koike H. , Yaguchi T. , Kamino T.
Published: July 2002

A gallium (Ga) focused-ion-beam (FIB) has been popularly used to prepare cross-sectional samples for transmission electron microscopes (TEMs) and scanning electron or ion microscopes. However, characteristics of the FIB-prepared cross sections such as ion concentration and radiation damage have been little studied either in theory or in experiment. In the present study, cross sections prepared by 30 keV Ga FIB are modeled using a combination of analytical and Monte Carlo methods to calculate the implanted Ga concentration. It is found that the Si/W layered sample is cross sectioned at grazing angles β≈2.5° and 6° for these layers, respectively. The implanted Ga ions for the cross-sectioned Si and W layers are concentrated very near their surfaces of <10 nm to yield the Ga concentrations CGa of about 4 and 9 at % for these layers, respectively. Although there is some differences in sample materials between the calculations and the experiments, the calculated CGa values for Si and W layers roughly agree with the experimental values for the magneto-optical disk TEM sample. This agreement firmly supports the present modeling of FIB-milled cross sections.
Interface formation and thermal stability of advanced metal gate and ultrathin gate dielectric layers
Authors: Claflin B. , Lucovsky G.
Published: July 2002

The compatibility of metallic titanium nitride (TiNx) films for advanced gate electrodes and remote plasma enhanced chemical vapor deposited silicon oxide (SiO2) or silicon oxide/silicon nitride (Si3N4) advanced gate dielectric layers is investigated by interrupted growth and on-line rapid thermal annealing using on-line Auger electron spectroscopy. Growth of TiNx on SiO2 and Si3N4 occurs uniformly without a titanium seed layer. TiNx/SiO2 and TiNx/Si3N4 interfaces are chemically stable against reaction for rapid thermal annealing treatments below 850 °C. Metal–oxide–semiconductor capacitors using TiNx gate contacts and SiO2 or SiO2/Si3N4 gate dielectrics exhibit excellent C–V characteristics. The measured TiNx/SiO2 barrier height in these devices is Φb=3.7±0.1 eV. The observed difference in fixed charge for SiO2 and SiO2/Si3N4 dielectrics is briefly discussed in terms of a new interface dipole model.
Influence of sulfur interlayers on the Mg/GaAs(100) interface formation
Authors: Hohenecker St. , Kampen T. U. , Zahn D. R. T. , Braun W.
Published: July 2002

The modification of clean GaAs(100) surfaces by in situ deposition of molecular sulfur was investigated by soft x-ray photoemission spectroscopy. Upon S treatment of the clean GaAs(100) sample at 435–455 °C in ultrahigh vacuum the formation of a three monolayer thick gallium sulfide-like compound is observed, which exhibits a (2×1) low-energy electron diffraction pattern. Due to the S modification on n-GaAs a reduction of the band bending by 0.35 eV is achieved, while the band bending on p-GaAs is increased by 0.17 eV. The subsequent Mg evaporation leads to the formation of a metal/semiconductor contact with a reacted magnesium sulfide-like compound at the interface. After 1 nm Mg deposition the Schottky barrier height of the S-modified Mg/n-GaAs(100) contact amounts to 0.44 eV, which is 0.18 eV lower than without S modification, while the Mg/p-GaAs(100) Schottky contact exhibits an increase in the Schottky barrier height by 0.30 eV in comparison to the value of the unmodified Schottky contact (0.55 eV).
Effects of thermal annealing on emission characteristics and emitter surface properties of a Spindt-type field emission cathode
Authors: Ito Fuminori , Konuma Kazuo , Okamoto Akihiko , Yano Akihiro
Published: July 2002

The effects of thermal annealing below 500 °C on Spindt-type molybdenum field emitter arrays were studied through the field emission characteristics and Mo surface analysis. The anode current of the field emitter arrays increases with increasing annealing time and then saturates after a certain period that is shorter for higher-temperature annealing. These phenomena are clearly explained by the molybdenum trioxide (MoO3) desorption revealed by studies using x-ray photoelectron spectroscopy and temperature programmed desorption, and by calculation of MoO3 desorption rates. The MoO3 desorption is the predominant effect for low-temperature annealing and the increase in the anode current is mainly due to lowering of the work function after MoO3 desorption.
AlGaAs/GaAs Npn heterojunction bipolar transistors grown on Si (311) by molecular beam epitaxy
Authors: Jurkovic M. J. , Alperin J. , Du Q. , Wang W. I. , Chang M. F.
Published: July 2002

AlGaAs/GaAs Npn heterojunction bipolar transistors have been grown by molecular beam epitaxy on Si (311) substrates utilizing a GaAs buffer layer as thin as 2 μm and fabricated using a self-aligned base contact process. Reflection high-energy electron diffraction patterns correspond with antiphase domain-free growth. Direct current measurements for a 70×70 μm2 device reveal a small-signal common-emitter current gain of 10 and collector-emitter breakdown of 13 V at a collector current of 1.8 kA/cm2. These results indicate that further optimization in growth technique may render the growth of GaAs-on-Si (311) a viable candidate for application in high-power integration.
Passivation of the GaAs(100) surface with a vapor-deposited GaS film
Authors: Cao Xian-an , Hu Hai-tian , Ding Xun-min , Yuan Ze-liang , Dong Yang , Chen Xi-ying , Lai Bing , Hou Xiao-yuan
Published: July 2002

A vapor-deposited GaS passivating layer is formed on GaAs(100) with α-Ga2S3 powder used as a single-source precursor for the deposition. The films grown show near-single-crystal quality, and are characterized by Auger electron spectroscopy and x-ray diffraction spectroscopy. The band-edge discontinuities of the GaS/GaAs heterojunction are determined to be 1.9 eV for the valence band and 0.3 eV for the conduction band, respectively, by ultraviolet photoelectron spectroscopy and electron-energy-loss spectroscopy. It is also observed that the valence-band structure of the GaS overlayer becomes much sharper after annealing.
Correlation between the early stage of copper metal organic chemical vapor deposition and the material properties of thin film
Authors: Hwang Eui Seong , Lee Jihwa
Published: July 2002

Cu metal organic chemical vapor deposition has been performed on TiN/Si(100) substrates using Cu(I)(hfac)(vtms) at various substrate (110⩽Ts⩽300 °C) and bubbler temperature (0⩽Tb⩽30 °C) conditions, in which the early stage of film formation characterized by scanning electron microscopy and in situ laser beam (λ=6328 Å) reflectance measurement could be well correlated with the surface roughness and the electrical resistivity of the copper films developed in a later stage. All the reflectance versus deposition time curves showed a qualitatively similar shape consisting of three sequential parts: a rapid initial decrease to a minimum, an increase to a maximum, and a gradual decay to almost zero, in which the minimum and maximum roughly correspond to the onset and completion of island coalescence, respectively. As the Ts is raised and/or the Tb is lowered, larger islands were formed in a smaller density at the onset of island coalescence due to a lower nucleation rate. The surface roughness gradually develops with increasing film thickness after forming a continuous film, but it does not saturate at a thickness of ∼2 μm and shows a correlation with the average island size in the earlier coalescence stage, i.e., the smaller islands evolves to a smoother surface. Above the threshold temperature (Ts∼230 for Tb=30 °C) the copper islands begin to show facets and at even higher Ts large truncated polyhedron-shaped copper islands are formed, which upon coalescing leave many interfacial voids to result in a film with a very rough surface and a high electrical resistivity. The copper films deposited at 150⩽Ts⩽200 °C have a very low value of ρ≈2 μΩ cm, which increases by a factor of ∼2 when Ts is lowered to 110 °C. The latter was accompanied by the formation of smaller islands at the onset of coalescence, and therefore the increase in ρ at Ts⩽150 °C was attributed to the electron scattering at the grain boundaries.
Coulomb blockade devices fabricated by liquid metal ion source droplet deposition
Authors: Vieu C. , Pepin A. , Gierak J. , David C. , Jin Y. , Carcenac F. , Launois H.
Published: July 2002

The fabrication of two-dimensional multiple tunnel junction (MTJ) devices by deposition of Au droplets from a liquid metal ion source is reported. By adjusting the emission parameters of the source and the final landing voltage of the droplets we have been able to deposit 1 nm size islands with a good reproducibility and with a sufficient density to allow tunneling between islands. Our devices exhibit a Coulomb gap up to a temperature of 200 K and show nonlinear current–voltage characteristics up to room temperature. The thermal behavior of these devices was investigated and shows the absence of a Kosterlitz–Thouless–Berezenskii transition. The charging energy of the islands is as high as 240 meV opening interesting perspectives for the integration of these MTJ devices in single electron memory cells working at high temperature.
Fabrication of self-aligned metallic Coulomb blockade devices on Si nanowires
Authors: Ford E. M. , Ahmed H.
Published: July 2002

A self-aligned metallic single-electron tunneling transistor was fabricated on a Separated by Implanted Oxygen substrate. An array of 10–50 gold islands of 1–3 nm diameter was isolated between source and drain electrodes on a silicon nanowire. This design reduces the number of transport paths by restricting the number of active nanodots between source and drain. The islands were deposited by a retarding field single ion deposition method, whereby the island sizes and separations could be varied by adjusting landing energy and dose. An undercut beneath the nanowire was used to separate the side gates from the multiple tunnel junction. Coulomb blockade was observed in the source drain characteristics at 77 K.
Multilayer resist methods for nanoimprint lithography on nonflat surfaces
Authors: Sun Xiaoyun , Zhuang Lei , Zhang Wei , Chou Stephen Y.
Published: July 2002

Five multilayer resist methods (three positive tones and two negative tones) have been devised for nanoimprint lithography on nonflat surfaces. Three of the methods have been demonstrated experimentally on a SiO2 surface with 100 nm deep sharp steps. The advantages and disadvantages of each method are discussed. Our results should be applicable to nanoimprint lithography with 10 nm feature size on nonflat surfaces.
Extreme ultraviolet lithography
Authors: Gwyn C. W. , Stulen R. , Sweeney D. , Attwood D.
Published: July 2002

An extreme ultraviolet (EUV) lithography tool using 13.4 nm radiation is being developed by a consortium of integrated circuit (IC) manufacturers to support 100 nm imaging for integrated circuit production. The 4×, 0.1 NA alpha tool has a >1 μm depth of focus, all reflective optics, a xenon laser plasma source, and robust reflective masks. The technology is expected to support feature scaling down to 30 nm.
Optical system for tunneling-electron luminescence spectro/microscopes with conductive-transparent tips in ultrahigh vacuums
Authors: Murashita Tooru
Published: July 2002

A unique optical system has been developed for a tunneling-electron luminescence (TL) spectro/microscope with conductive-transparent (CT) tips operable and changeable in an ultrahigh vacuum (UHV). The optical system consists of two essential elements. The first element is fiber-optics, which effectively guides the luminescence from the CT tips to optical detectors without the need for optical alignment. The fiber-optics features (1) a mechanism to automatically reproduce optical coupling between the CT tip and the fiber every time the tip is changed, (2) a fiber set in a vacuum chamber to prevent steep fiber bending, and (3) a compact fiber-optic vacuum seal that maintains high transmittance and limits low gas leakage to ultimate pressures below 10−10 Torr. The second element is optical detection and processing, which reduce the influence of fluctuations in TL intensities, which is a serious problem in TL measurements. The main structures of this element are a whole spectral detector for spectroscopy and a tip-scan-synchronized photon counter for microscopy. The optical system was characterized through TL measurements on semiconductor nanostructures at low temperatures in an UHV. A TL spectro/microscope with the optical system achieved satisfactory performance.
Properties of gate quality silicon dioxide films deposited on Si–Ge using remote plasma-enhanced chemical vapor deposition with no preoxidation
Authors: Sharma R. , Fretwell J. L. , Ngai T. , Banerjee S.
Published: July 2002

SiO 2 films were deposited on Si–Ge using a low temperature (300 °C) remote plasma-assisted chemical vapor deposition (RPCVD) process. A novel feature of this process is that it does not require a preoxidation step prior to deposition. The electrical properties of the resulting oxide films were analyzed, indicating good interfacial (Dit∼3×1011 cm−2 eV−1) and excellent breakdown properties (Ebd∼10 MV/cm). Electron trapping was determined to be the dominant charge trapping mechanism. Interfacial properties and oxide reliability were seen to improve upon annealing at moderately high (550–650 °C) temperatures.
Larger critical thickness determined by photoluminescence measurements in pseudomorphic In0.25Ga0.75As/Al0.32Ga0.68As quantum well grown on (411)A GaAs substrates by molecular beam epitaxy
Authors: Nii K. , Kuriyama R. , Hiraoka T. , Kitada T. , Shimomura S. , Hiyamizu S.
Published: July 2002

Pseudomorphic In0.25Ga0.75As/Al0.32Ga0.68As quantum wells (QWs) with well widths (Lw) of 13, 15, 17, 19, 21, and 23 nm were grown simultaneously on the (411)A and (100) GaAs substrates at 480 °C by molecular beam epitaxy. The critical thickness of an InGaAs QW layer in the (411)A QW was determined by photoluminescence (PL) measurements at 11 K to be approximately 20 nm, i.e., significant increase in full width at half maximum of PL peaks was observed for Lw⩾20 nm for (411)A QWs. This critical thickness is more than 60% larger than that (around 12 nm) of the (100) QWs.
Substrate preparation and interface grading in InGaAs/InAlAs photodiodes grown on InP by molecular-beam epitaxy
Authors: Lenox C. , Nie H. , Kinsey G. , Hansing C. , Campbell J. C. , Holmes A. L. , Streetman B. G.
Published: July 2002

InAlGaAs alloys grown lattice matched to InP substrates has been shown to be an important material system in fabrication of long-wavelength (1.3–1.55 μm) photodetectors for fiber-optic applications. We report on the growth of InGaAs/InAlAs p-i-n photodiodes by molecular-beam epitaxy utilizing surface preparation under a solid-source phosphorous flux and an InP buffer layer. Characterization of InGaAs/InAlAs p-i-n photodiodes grown with this technique shows improved direct current and transient device response through the use of a superlattice graded region at the absorption region heterojunction.
Electrical characteristics of As-doped p-type HgCdTe epilayers grown on CdZnTe(211)B substrates by molecular beam epitaxy
Authors: Yang B. , Aqariden F. , Grein C. H. , Jandaska A. , Lee T. S. , Nemani A. , Rujirawat S. , Shi X. H. , Sumstine M. , Velicu S. , Sivananthan S.
Published: July 2002

We report here the electrical properties of As-doped HgCdTe(211)B epilayers grown by molecular beam epitaxy (MBE) using As4 as the dopant. It is found that though the as-grown As-doped HgCdTe layers are n type, As can be activated to be a p-type dopant in the HgCdTe(211)B layers after an ex situ annealing process. The As4 sticking coefficient on the growing HgCdTe surface is found to decrease from the order of 10−2–10−4 when the substrate temperature is increased from 165 to 175 °C. The hole mobility in As-doped HgCdTe is calculated by considering seven major scattering mechanisms: ionized impurity, strain field, polar optical phonon, acoustic phonon, alloy disorder, nonpolar optical phonon, and dislocation scattering. The ionization energies of shallow acceptors related to As in MBE HgCdTe layers with different Cd composition have been obtained by fitting variable temperature Hall measurement results to a two-band nonparabolic Kane model.
Surface structure characterization of DNA oligomer on Cu(111) surface using low temperature scanning tunneling microscopy
Authors: Hamai Chiho , Tanaka Hiroyuki , Kawai Tomoji
Published: July 2002

The surface structures of DNA oligomers, pAAAAAAATTTTTTT, deposited on Cu(111) surface have been characterized at liquid nitrogen temperature using a scanning tunneling microscope. Four different types of adsorbed structures have been observed in DNA oligomers; (i) an isolated whole molecule, (ii) a shortened molecule, (iii) a cluster, and (iv) a double helix. The internal structures of the oligomers also have been resolved.
Low voltage electron beam lithography in PMMA
Authors: Olkhovets A. , Craighead H. G.
Published: July 2002

We have studied low voltage (1–2 kV) electron beam lithography processes in PMMA and compared them to conventional high voltage processing. We looked at the deposited metal after liftoff as well as directly imaging resist profiles by atomic force microscopy. As expected, the proximity effects were greatly reduced. The forward scattering was found to increase at low voltage. The study of developed resist profiles showed that linewidth versus dose has a single Gaussian functional form, proving that forward scattering plays the major role in line broadening. The effective Gaussian linewidth is 60 nm at 1 kV in a 50 nm resist layer. Modeling of the lithographic process showed a significant increase in resolution and process latitude for thinner resists.
Interfacial properties of ultrathin pure silicon nitride formed by remote plasma enhanced chemical vapor deposition
Authors: Misra V. , Lazar H. , Wang Z. , Wu Y. , Niimi H. , Lucovsky G. , Wortman J. J. , Hauser J. R.
Published: July 2002

This article addresses the electrical properties of interfaces between n- and p-type Si and remote plasma-deposited Si3N4, which are of interest in aggressively scaled advanced CMOSFETs. The nitride films of this article display excellent electrical properties when implemented into stacked oxide/nitride dielectrics in both NMOSFETs and PMOSFETs with oxide, or nitrided oxide interfaces. The same nitride layers deposited directly onto clean Si surfaces display degraded electrical properties with respect to devices with oxide, or nitrided oxide interfaces. PMOS interfaces are significantly more degraded than n-type metal–oxide semiconductors interfaces indicating a relatively high density of donor-like interface traps that inhibit channel formation.
Via-hole etching for SiC
Authors: Leerungnawarat P. , Hays D. C. , Cho H. , Pearton S. J. , Strong R. M. , Zetterling C.-M. , Östling M.
Published: July 2002

Four different F2-based plasma chemistries for high-rate etching of SiC under inductively coupled plasma (ICP) conditions were examined. Much higher rates (up to 8000 Å min−1) were achieved with NF3 and SF6 compared with BF3 and PF5, in good correlation with their bond energies and their dissociation efficiency in the ICP source. Three different materials (Al, Ni, and indium–tin oxide) were compared as possible masks during deep SiC etching for through-wafer via holes. Al appears to produce the best etch resistance, particularly when O2 is added to the plasma chemistry. With the correct choice of plasma chemistry and mask material, ICP etching appears to be capable of producing via holes in SiC substrates.
High aperture diffractive x-ray and extreme ultraviolet optical elements for microscopy and lithography applications
Authors: Hambach D. , Schneider G.
Published: July 2002

Microscopy and lithography using isotropic plasma x-ray and extreme ultraviolet sources require condenser elements with high numerical aperture. As shown by coupled-wave theory, zone structures with high aspect ratios can diffract a sufficiently large proportion of incident radiation into a single high order. This enables new diffractive optical elements for these applications with significantly increased numerical aperture. Suitable zone plate materials are nickel for water window wavelengths and organic polymers for λ=13 nm radiation. Copolymer and nickel zone structures have been produced with aspect ratios of 15 and 11, respectively. For optimization of the etched zone profile, the reactive ion etching process with O2 was periodically interrupted. In a first experiment at λ=3.4 nm a nickel linear zone plate with 75 nm outermost zone width and 500 nm height showed a diffraction efficiency of 1% in the sixth diffraction order.
Sheath expansion in a drifting, nonuniform plasma
Authors: Keidar M. , Brown I. G.
Published: July 2002

A model is proposed for the sheath expansion into a nonuniform plasma with substantial drift velocity. We refer in particular to the streaming metal plasma produced by a vacuum arc discharge; this kind of plasma is characterized by its spatial nonuniformity and high ion drift velocity. It is shown that for a nonuniform plasma and high substrate bias voltage (>10 kV), the sheath thickness is significantly smaller than in a uniform plasma. High drift velocity also leads to a decrease in sheath thickness. For plasma immersion ion implantation carried out in a nonuniform plasma, the increase in ion implantation current with increasing voltage is different from that of a uniform plasma where the ion current is constant with voltage. This effect was found to be quantitative agreement with experiment. The decrease in sheath thickness with increasing plasma drift velocity can explain qualitatively the experimentally observed existence of a stable high-voltage sheath for a relatively long time.
Prototype negative electron affinity-based multibeam electron gun for lithography and microscopy
Authors: Baum A. , Arcuni P. , Aebi V. , Presley S. , Elder M.
Published: July 2002

Negative electron affinity (NEA) photocathodes offer unprecedented capabilities as electron sources that promise to enable a new generation of microscopy and lithography instruments. Extremely low-energy spread and emission noise, high brightness, ultrafast blankerless switching, changeable emission area, and uniform multibeam emission are some of the advantages that this source offers. Their unique advantages in high-throughput multibeam applications have been discussed elsewhere. The main barrier to their widespread acceptance has been concern about lifetime and stability. A prototype electron gun based on NEA photocathodes has been constructed to demonstrate the performance, including stability, of NEA sources. Initial results, showing over 100 h of excellent stability from a single 2 μm emission area, show the paramount importance of in situ recesiation in attaining long cathode lifetime.
Nanoscale elemental imaging of semiconductor materials using focused ion beam secondary ion mass spectrometry
Authors: Stevie F. A. , Downey S. W. , Brown S. R. , Shofner T. L. , Decker M. A. , Dingle T. , Christman L.
Published: July 2002

The semiconductor industry demands elemental information from ever smaller regions. The sensitivity of secondary ion mass spectrometry, coupled with the lateral resolution of a focused ion beam, can provide nanoscale elemental data that are competitive with that from other analytical techniques. Ion images of the sidewalls in repetitive semiconductor features tilted to present a large surface area have shown boron contamination after an etch process. The boron is removed by a specific cleaning step. Spot defect analysis was enhanced by the use of mass spectra that provide information on a range of elements before the defect is removed by sputtering. Ion implanted samples were analyzed in cross section and the implant shape detected. Summation of the secondary ion counts in the implant cross section over a few micrometers resulted in detection limits below 0.1 at. %. Implantation profiles have been detected for Al, Cr, Na, Li, and K without the aid of secondary ion enhancing species, such as oxygen or cesium.
Improvement of InGaP/GaAs heterointerface quality by controlling AsH3 flow conditions
Authors: Fukai Yoshino K. , Hyuga Fumiaki , Nittono Takumi , Watanabe Kazuo , Sugahara Hirohiko
Published: July 2002

Heterointerfaces between disordered InGaP on GaAs, whose conduction band offset, ΔEc, is 0.2 eV, can be improved and have less interface charges by controlling the AsH3 cover time and flow rate at the growth interval from GaAs to InGaP by metalorganic chemical vapor deposition. A small AsH3 cover of 5 cc (0.05 min with 100 cc/min) creates a low interface charge density, σ, of 6.4×1010 cm−2. Extending the AsH3 cover to only 25 cc increases σ by one order, even though AsH3 is purged by PH3 for a rather long time after being covered. Interface charges are confirmed to be donors whose energy level is near the conduction band edge. These results show that excess As on the GaAs surface enhances the formation of donor-like defects in the InGaP layer. An As-poor GaAs surface is essential in order to achieve high-quality InGaP/GaAs heterointerfaces.
Design and integration considerations for end-of-the roadmap ultrashallow junctions
Authors: Osburn C. M. , De I. , Yee K. F. , Srivastava A.
Published: July 2002

Device simulations and response surface analysis have been used to quantify the trade-offs and issues encountered in designing ultrashallow junctions for the 250–50 nm generations of complimentary metal-oxide-semiconductor ultralarge scale integration technology. The design of contacting and extension junctions is performed to optimize short channel effects, performance, and reliability, while meeting the National Technology Roadmap for Semiconductors off-state leakage specifications. A maxima in saturated drive current is observed for an intermediate extension junction depth (∼20 nm for 100 nm technology): shallower junctions lead to higher series resistance, and deeper junctions result in more severe short channel effects. The gate-to-junction overlap required to preserve drive current was seen to depend on junction abruptness. For a perfectly abrupt junction, it is not necessary for the gate to overlap the junction. Performance depends on many parameters, including: overlap of gate to extension junction, junction capacitance, and parasitic series resistance, which depends on the doping gradient at the junction (spreading resistance), the extension series resistance, and the contact resistance. Extraction of these parameters using I–V or C–V measurements can potentially lead to erroneous conclusions about lateral junction excursion and abruptness.
Qualification of spreading resistance probe operations. I
Authors: Clarysse T. , Vandervorst W.
Published: July 2002

In this article we discuss the final results obtained from an extensive spreading resistance probe (SRP) experimental intercomparison conducted among 21 international laboratories with different levels of expertise both in the U.S. and in eight European countries. Twenty different structures representative of current SRP needs (complementary metal–oxide–semiconductor, bipolar, epi) were used. Specialized structures such as buried oxides with different thicknesses (10–40 nm) and identical implants junction isolated and nonisolated (carrier diffusion) were included. The SRP accuracy was determined according to four point probe sheet resistance mappings and secondary ion mass spectrometry depth profiles. In order for SRP to gain wider credibility an error of less than 10% (std dev) should be routinely achievable on the typical SRP results (e.g., dose, sheet, shape carrier profile) irrespective of where, when, or by whom the measurement is performed. The round robin that was conducted showed that present American Society for Testing and Measurement standards are not detailed enough to obtain this target accuracy. In order to achieve this accuracy, precise quantitative specifications on as many as 14 primary qualification parameters must be satisfied simultaneously. Of these, some of the more important ones are low surface roughness, sharp bevel edge, low probe penetration, stable probe contact, small contact size, accurate bevel angle, accurate starting point, sufficient data point density, low probe separation, good probe alignment, and a standardized contact model. The required specifications will be illustrated with results from the round robin. Also, other topics investigated in the round robin will be discussed briefly such as the on-bevel stepsize reproducibility, the microcontact distribution, the different contact radii involved, the amount of barrier resistance, rectification, and noise.
Accuracy of secondary ion mass spectrometry in determining ion implanted B doses as confirmed by nuclear reaction analysis
Authors: Magee Charles W. , Jacobson Dale , Gossmann Hans-J.
Published: July 2002

The recent need for measuring depth profiles for ultralow-energy B ion implants in Si has pushed the technique of secondary ion mass spectrometry (SIMS) into unprecedented degrees of high depth resolution. For such shallow implant distributions, it remained to be seen if the quantification procedures which have been used for determining deeper B in-depth distributions are accurate for these very shallow profiles. What is more, the B concentrations at the surface can be in the percentage range for implants of 1E15/cm2 at energies below 1 keV. It has not been demonstrated that SIMS can be accurate in this high-concentration regime. In this article, we use the nuclear reaction B11(p,α)8Be to confirm the accuracy of the implanted doses in low-energy B implants in Si. Our results indicate that the doses measured by SIMS are within 5% of those measured using nuclear reaction analysis.
Effective channel length and base width measurements by scanning capacitance microscopy
Authors: Raineri V. , Lombardo S.
Published: July 2002

In this article scanning capacitance measurements (SCM), carried out directly on device sections, are presented. Quantitative SCM have been applied to determine the channel length in an advanced power metal–oxide–semiconductor device and the base width in a heterojunction bipolar transistor. Ion implantation in samples with 45°-edge mask allowed us to demonstrate the SCM capability to image the depletion region and to delineate the junction position. The effective channel length was determined by considering the depletion region. A channel length of less than 200 nm was determined. Measurements on a heterojunction bipolar transistor device allowed us to image a base width of less than 180 nm.
Effect of radio frequency bias power on SiO2 feature etching in inductively coupled fluorocarbon plasmas
Authors: Schaepkens M. , Oehrlein G. S. , Cook J. M.
Published: July 2002

We present and discuss results obtained in studies of the mechanisms underlying various feature size dependencies of SiO2 etching in inductively coupled fluorocarbon plasmas. The variation of the fluorocarbon deposition rate and the SiO2 etch rate with both feature size and rf bias power has been measured in a variety of constant aspect ratio features for both an etch stop (C3F6/H2) and a nonetch stop (CHF3) feedgas chemistry.
Serial process for electron emission from solid-state field controlled emitters
Authors: Binh Vu Thien , Dupin J. P. , Thevenard P. , Purcell S. T. , Semet V.
Published: July 2002

In this work we explore planar cathodes emitting electron currents at room temperature, based on a new concept of electron emission from a serial process. This serial process uses a solid-state Schottky metal–semiconductor barrier to inject electrons into a field-controlled negative electron affinity surface which is an ultrathin semiconductor layer. A model for the electron emission for these planar cathodes is proposed and discussed within the experimental data obtained. Analysis of the emission behavior was performed with different planar cathodes presenting a low Schottky barrier metal–semiconductor junction (∼0.1 eV) with an injection medium having different cathode geometries in order to localize the emission area. The analysis included measurements of the emitted currents versus applied voltages and time, variations of the currents with temperature, energy distribution of the emitted electrons, and numerical simulations of the field distribution over the cathode. Stable electron currents are experimentally obtained from such planar cathodes with small operating electric fields (∼10 V/μm) and with working vacuum as low as 10−7 Torr.
Electron field emission from polycrystalline silicon tips
Authors: Vossough K. K. , Bower R. W.
Published: July 2002

Arrays of 10 polysilicon field emitter tips were fabricated using plasma etch and oxidized to form sharp tips. Phosphorus doped polysilicon tips emit at around 10–15 V regardless of the degree of their sharpness. Similarly, intrinsic polysilicon tips emit at around 50 V (at 2 μm tip to anode spacing). The same turn on voltages have been observed on flat polysilicon surfaces. Field emission data of the diode structures revealed a significant difference between phosphorous doped and intrinsic polysilicon tips and flat surfaces. The φ3/2/β versus applied voltage was obtained from the transconductance data and was used to compare the performance of the doped and intrinsic polysilicon tips. A qualitative comparison of φ3/2/β ratio reveals an increase in the effective work function of the intrinsic polysilicon device which is related to the field penetration inside the emitting surfaces. Furthermore, field emission data reveal the conduction limitation of the intrinsic polysilicon films associated with the single carrier injection mechanism.
Fabrication of volcano-type TiN field emitter arrays
Authors: Lee Dong-Gu , Baik Dong-Ki , Kang Nam-Seok , Cho Won-Ki , Yoon Sang-Jo , Kim Tae-Young , Hwang Hyun-Deog , Ahn Dong-Hoon , Park Myung-Ho
Published: July 2002

A new volcano-type triode field emitter array has been fabricated on a glass substrate using titanium nitride as the emitter material. It is based on the process development for the formation of uniform emitters over large areas using reactive ion etching and the sputtering method. In this study, the effects of the ratio of volcano emitter size to gate hole size on the emission characteristics were investigated with a fixed emitter–gate distance of 1.0 μm and compared with computer simulation results using a finite element method. As the ratio of volcano emitter size to gate hole size decreased, especially from a ratio of around 0.5 to 0.4, the anode current significantly increased. This behavior may result from the increase in the maximum electric field on a tip with a decrease in the ratio as is expected from computer simulation.
Direct patterning of noble metal nanostructures with a scanning tunneling microscope
Authors: Marchi F. , Tonneau D. , Dallaporta H. , Safarov V. , Bouchiat V. , Doppelt P. , Even R. , Beitone L.
Published: July 2002

We demonstrate in this article the controlled deposition of noble metal dots and lines using local chemical vapor deposition in the tip–sample gap of a scanning tunneling microscope. 3 nm diam rhodium dots have been patterned by local decomposition of an inorganic precursor, which was synthesized on purpose. Deposition is obtained on gold surfaces by applying a series of negative voltage pulses on the sample exceeding a voltage threshold of 1.9 V. The influence of kinetics parameters (pulse voltage duration and number, as well as the effect of gas pressure) are presented. In a second step, the deposition process has been applied on hydrogenated silicon (100) surfaces. These samples were previously hydrogen passivated using two different wet etching operations, leading surface dangling bonds saturated by either mono- or di-hydride bonds. The difference in the deposition processes observed in both cases is discussed.
Negative differential resistance of a ridge-type InGaAs quantum wire field-effect transistor
Authors: Sugaya Takeyoshi , Kim Seong-Jin , Nakagawa Tadashi , Sugiyama Yoshinobu , Ogura Mutsuo
Published: July 2002

Negative differential resistance with a high peak to valley ratio and low onset voltage is clearly observed in a quantum wire field-effect transistor (QWR-FET) with a channel width of 100 nm, while it is not observed in a QWR-FET with a channel width of 300 nm. The saturation characteristics of Landau plots indicate that the 100 nm wide QWR has one-dimensional characteristics of electron transport, as opposed to the 300 nm wide QWR that has two-dimensional electrons.