bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy exchange processes in electron emission at high fields and temperatures
Authors: Chung M. S. , Cutler P. H. , Miskovsky N. M. , Sullivan T. E.
Published: July 2002

A new more complete theory for energy exchange processes in electron emission is formulated. It is found that the tunneling contribution to the availability of vacant states is necessary to explain the replacement process occurring in the emitter region. The introduction of the tunneling states now makes it possible to obtain both the average energies of the emitted and replacement electrons using the same formalism. At T=0 K, the average energy of replacement electrons, 〈εr〉, is the same as the average energy of the emitted electrons, 〈εe〉. As T increases, 〈εr〉 increases rapidly until it reaches a maximum and then decreases slowly, while 〈εe〉 increases monotonically. When T equals the inversion temperature Ti, 〈εe〉=〈εr〉 and the energy exchange Δε=0. We have also calculated both Δε and Ti as a function of field F. For high temperature and fields, the value of Ti differs considerably from that obtained without the tunneling state contribution and Ti exhibits nonlinear behavior as a function of field. Tunneling state contributions are essential for explaining the steady state condition in the conduction process, especially at very low temperatures. These results are crucial for resolving the controversial problem of the replacement process in electron emission. Contrary to the assertion of Nottingham [Phys. Rev. 59, 907 (1941)] that the replacement energy is the Fermi energy, the current results indicate that the average value can be 10–102 meV less than the Fermi energy in agreement with Fleming and Henderson [Phys. Rev. 58, 887 (1940)]. Nonequilibrium effects evaluated within the relaxation time approximation are significant only for large fields.
Technological parameters distribution effects on the current–voltage characteristics of field emitter arrays
Authors: Nicolaescu Dan
Published: July 2002

Different applications require the development of field emitters arrays (FEA). The uniformity of the emitters is an important feature of FEA. The array technological parameters distribution effects on the FEA Fowler–Nordheim (FN) current–voltage I(V) plot has been investigated based on the ideal field emitter floating sphere model. The model parameters are emitter height h, radius R, work function φ, and anode–cathode planes distance d. The array FN I(V) plot is shown to be modified in a specific way when the parameters R and h vary according to a Gaussian distribution function (DF). The array representative emitter is defined and its parameters are obtained through a parameter extraction procedure. Several analytical results are presented for parabolic DF on R. Further modeling suggestions are given.
SiC microcomponents via reaction of C60 with silicon
Authors: Balooch M. , Hamza A. V.
Published: July 2002

Free silicon carbide microcomponents are produced on silicon wafers. Silicon carbide is selectively grown on silicon by reaction of C60 with the substrate at surface temperatures between 900 and 1200 K. Because of the large lattice mismatch (∼20%), the adhesion of the silicon carbide film is weak after growth of 1–1.5 μm thickness. An atomic force microscope tip can subsequently maneuver the microcomponent to a desired location on the wafer.
Fabrication of self-aligned GaAs/AlGaAs and GaAs/InGaP microwave power heterojunction bipolar transistors
Authors: Ren F. , Lothian J. R. , Pearton S. J. , Abernathy C. R. , Wisk P. W. , Fullowan T. R. , Tseng B. , Chu S. N. G. , Chen Y. K. , Yang L. W. , Fu S. T. , Brozovich R. S. , Lin H. H. , Henning C. L. , Henry T.
Published: July 2002

Self-aligned processing of high efficiency power heterojunction bipolar transistors (HBTs) using implant isolation, selective wet and dry etching for mesa formation, plasma-enhanced chemical vapor deposited SiNx for sidewall spacers and through-wafer via connections is reported. GaAs/AlGaAs and GaAs/InGaP HBTs grown by metalorganic molecular beam epitaxy utilizing carbon for high, well-confined base doping produced power-added efficiencies of 63%, power gain of 10 dB and output power of 1.7 W at 4 GHz for twelve 2×15 μm2 double-emitter finger devices (GaAs/AlGaAs) and 57% power-added efficiency, power gain of 11.3 dB and output power of 0.6 W at 4 GHz (GaAs/InGaP), respectively.
Spiral growth of GaAs by metalorganic vapor phase epitaxy
Authors: Hsu C. C. , Lu Y. C. , Xu J. B. , Wong T. K. S. , Wilson I. H.
Published: July 2002

Growth spirals are observed on metalorganic vapor phase epitaxy grown GaAs surfaces by atomic force microscopy. The growth mechanism is according to the classical Burton–Cabrera–Frank theory. Spirals originate from screw dislocations. Successive turns of the steps are sent out by the dislocations. These steps are of monolayer height (0.28 nm) and the interstep distance is around 150 nm.
Reactive ion etching for microelectrical mechanical system fabrication
Authors: Rangelow Ivaylo W. , Löschner Hans
Published: July 2002

The suitability of reactive ion etching for the fabrication of microelectro mechanical systems (MEMS) has been evaluated by characterizing the change of lateral dimensions versus depth in etching deep structures in silicon. Fluorine, chlorine, and bromine containing gases have provided the basis for this investigation. A conventional planar RIE (reactive ion etching) reactor has been used, in some cases with magnetic field enhancement or an inductive coupled plasma source and low substrate temperature. For RIE based on Cl2 or Cl2/HBr plasma a slightly ‘‘positive’’ (top wider than bottom) slope is achieved when etching structures with a depth of several 10 μm, whereas a ‘‘negative’’ slope is obtained when etching with an SF6 /CCl2F2-based plasma. A pattern transfer with vertical walls is obtained for RIE based on SF6 (with O2 added) when maintaining the substrate at low temperature (≊−70 °C). Further optimization of plasma chemistries and RIE procedures should result in runouts on the order of 0.1/100 μm depth in Si as well as in organic materials.
Charging effects in plasma immersion ion implantation for microelectronics
Authors: Qin Shu , Bernstein James D. , Zhao Zhuofan , Liu Wei , Chan Chung , Shao Jiqun , Denholm Stuart
Published: July 2002

The charging effects of plasma immersion ion implantation (PIII) doping experiments have been investigated using a dynamic sheath model and PDP1 plasma simulation code. When the target has a dielectric film, charge accumulation during PIII can have a profound impact on doping results. Under certain process conditions, it can significantly reduce implant energy and dose and thereby alter the implant profile. In addition, it may degrade device reliability, especially for ultralarge-scale integrated circuit devices. In order to minimize charging effects, shorter pulse widths along with moderate values of plasma density and pulse potential should be used.
Fabrication of sub-10-nm silicon lines with minimum fluctuation
Authors: Namatsu H. , Nagase M. , Kurihara K. , Iwadate K. , Furuta T. , Murase K.
Published: July 2002

This article reports the fabrication of sub-10-nm Si lines by e-beam lithography and aqueous potassium hydroxide (KOH)-based etching. The fabrication technique provides both the high resolution and minimum linewidth fluctuation necessary for fabricating nano-scale Si structures. In e-beam lithography, the combination of high-resolution posi-type resist and hexyl acetate developer is effective in improving the resolution and in reducing pattern fluctuation. Resist lines less than 20 nm wide with a fluctuation less than 3 nm are obtained. When these lines, aligned in the 〈112〉 direction on a (110) Si wafer, are transferred to Si by KOH etching, Si lines with a rectangular cross section are obtained and linewidth fluctuation is reduced further because (111) planes are exposed as the sidewalls. In addition, 6–9 nm wide lines can be formed by additional etching using an alcohol/KOH solution. Photoluminescence spectra are obtained for sub-10-nm Si lines after slight oxidation.
Novel method for producing nanostructures in silicon inversion layers
Authors: Campbell B. E. , Huang X. , Bernstein G. H.
Published: July 2002

A novel method for fabricating nanostructures based on the interaction of an electron beam with the metal–oxide–semiconductor material system has been demonstrated. The electron beam produces a stable charge near the oxide–semiconductor interface which modulates the surface potential creating a quasi-one-dimensional potential valley. Electrical transport measurements conducted on the post-irradiated silicon metal–oxide–semiconductor field-effect transistors (MOSFETs) reveal structure in the conductance which is not present in an unexposed device, indicating that quasi-one-dimensional structures can be created directly in the gate of a silicon MOSFET.
Fabrication of silicon nanostructures with a poly(methylmethacrylate) single-layer process
Authors: Tada Tetsuya , Kanayama Toshihiko
Published: July 2002

Poly(methylmethacrylate) has been found to act as a high resolution negative electron beam resist with sufficient dry-etch durability if acetone is used as a developer. We fabricated 10 nm silicon structures using the poly(methylmethacrylate) single-layer process and low temperature electron cyclotron resonance-type microwave-plasma etching without any additional complex processes.
Modeling of oxide charging effects in plasma processing
Authors: En William , Linder Barry P. , Cheung Nathan W.
Published: July 2002

An analytical model of oxide charging in plasma processing is presented. The model simulates the interactions of the plasma with semiconductor device structures on the wafer and the substrate bias to determine the charging induced in thin gate oxides. This model agrees well with experimental data for pulsed substrate bias. The simulation shows that a lower plasma electron temperature can reduce the charging damage. Well structures modulate the charging damage, with p wells charging more negatively and n wells charging more positively than an identical case without a well structure. Two-dimensional charging effects such as plasma nonuniformities and antenna structures have also been successfully modeled. Antenna-type device structures are shown to enhance the charging damage in both capacitor and well structures.
Verification of models for the simulation of boron implantation into crystalline silicon
Authors: Hobler G. , Simionescu A. , Palmetshofer L. , Jahnel F. , von Criegern R. , Tian C. , Stingeder G.
Published: July 2002

A comprehensive study of 20 keV B implantations into crystalline Si is presented. B has been implanted with doses between 1013 and 1016 cm−2 along the three channeling directions [110], [100], and [211] and parallel to (111) planes. In addition, implantations into (100)- and (110)-Si have been performed with tilt angles of 7° and 38°, respectively. The doping profiles have been measured with secondary ion mass spectroscopy. The experimental results are analyzed by Monte Carlo simulations using different models of lattice damage, thermal vibrations, and interatomic potentials. It is found that both the random interstitial and the split 〈110〉 interstitial model are adequate to describe the experimental dopant profiles, but not the tetrahedral interstitial model. Debye temperatures of 450 and 490 K both yield good results, but not 645 K. Finally, using the specific B–Si Ziegler–Biersack–Littmark (ZBL) potential or the universal ZBL potential makes little difference in most cases, but the specific B–Si clearly has to be preferred to obtain accurate [110] channeling profiles.
Characteristics of photon scanning tunneling microscope read-out
Authors: Kobayashi Kiyoshi , Watanuki Osaaki
Published: July 2002

A semimicroscopic approach based on linear response theory is applied to analysis of the near-field-reading process, both for an isolated recording bit and for bits periodically arranged by means of photon scanning tunneling microscopy (PSTM). The polarization effects and typical characteristics of super-resolution are shown by simulation. The results are valid not only for the read-out process in optical storage, but also for sensing of local indices of refraction or absorption in samples observed with PSTM, in general. Some theoretical results are compared with experimental data in terms of the resolving power.
Molecular-beam epitaxy growth of strontium thiogallate
Authors: Yang T. , Wagner B. K. , Chaichimansour M. , Park W. , Wang Z. L. , Summers C. J.
Published: July 2002

The molecular-beam epitaxy growth and characterization of cerium doped strontium thiogallate (SrGa2S4:Ce) thin film phosphors are reported. The layers were grown on GaAs, and glass/indium tin oxide/dielectric stack substrates for device fabrication. Ga2S3/Sr beam equivalent pressure ratios of 20–100 and CeCl3/Sr flux (molecules cm−2 s−1) ratios of 1/20–1/10 were investigated in this study. The substrate temperature was varied between 530 and 575 °C. A typical SrGa2S4:Ce film growth rate of 0.5 μm/h was obtained with Sr, Ga2S3, and CeCl3 beam equivalent pressures of 2.0×10−7, 1.0×10−5, and 3.5×10−8 Torr, respectively. Characterization of the layers’ structural and optical properties by x-ray diffraction, transmission electron microscopy, energy dispersive x-ray spectroscopy, and photoluminescence spectroscopy is presented.
Zn preadsorption on GaAs(100)2×4 prior to ZnSe growth
Authors: Heun S. , Paggel J. J. , Rubini S. , Franciosi A.
Published: July 2002

We report here a systematic study of the adsorption of Zn on GaAs(100)2×4 prior to ZnSe growth. At the typical ZnSe growth temperature of 290 °C, the Zn coverage was found to increase only logarithmically with increasing exposure time, so that only submonolayer coverages of Zn can be absorbed and remain stable on the GaAs substrates. At room temperature, and in general at temperatures below 150–200 °C, a drastic increase in the Zn sticking coefficient makes monolayer and multilayer adsorption possible. However, subsequent annealing at the ZnSe growth temperature removes most of the Zn atoms from the surface, so that only submonolayer coverages are found on the initial growth surface. We discuss the possible role of Zn as an interface control layer between ZnSe and GaAs in the light of our results.
Current imaging tunneling spectroscopy of an alkyl cyanobiphenyl liquid crystal
Authors: Rivera M. , Williamson R. L. , Miles M. J.
Published: July 2002

An adsorbed ordered monolayer of the liquid crystal molecule 4-n-octyl-4′-cyanobiphenyl (8CB) on a highly ordered pyrolitic graphite substrate was imaged both in the constant-current mode and in the current imaging tunneling spectroscopy (CITS) mode of the scanning tunneling microscope. The constant–current images showed the well-known banded smecticlike structure. CITS images were collected over a range of CITS voltages (350–1200 mV) and also a range of constant currents (0.008–0.100 nA) and voltages (500–900 mV) used to control the tip-specimen separation. CITS images at higher constant currents showed little variation in contrast over the range of voltages selected. They exhibited higher resolution than CITS images collected using lower constant current. However, the contrast in these CITS images collected at lower constant current showed a strong dependence on voltage. The general trends observed in these images are discussed in terms of the tip-specimen separation and the relationship between the ‘‘uncertainty principle’’ and energy resolution in scanning tunneling spectroscopy. The chemical-group specific contrast is discussed in terms of different di/dV for the groups.
(2×4)/c(2×8) to (4×2)/c(8×2) transition on GaAs(001) surfaces
Authors: Moriarty P. , Beton P. H. , Ma Y.-R. , Dunn A. W. , Henini M. , Woolf D. A.
Published: July 2002

We present scanning tunneling microscopy data illustrating the evolution of the decapped GaAs(001) surface following annealing in stages from 450 to 540 °C. After annealing at 450 °C a (2×4) reconstruction is formed by kinked rows of two As dimer unit cells. Following annealing in the 475–500 °C range small isolated regions of (4×2) reconstruction are visible, with a considerable increase in disorder of the remaining (2×4) reconstructed areas. Annealing at higher temperatures causes the (4×2) structure to become increasingly dominant. We have noted significant differences in the surface morphology as a function of annealing time. Our images of the (4×2) surface are similar to those recently reported by other groups but we propose a new structural model.
Submicron air-bridge interconnection process for complex gate geometries
Authors: Persson Magnus , Pettersson Joakim
Published: July 2002

A one-step electron-beam lithography process for fabrication of submicron air bridges is described. The fabrication principle is based on differing sensitivities of three layers of resist. By modulating the exposure dose it is possible to develop through all layers, the top layers only, or the center layer only (tunnels). We have fabricated the gate structure for making a quantum ring of 1 μm diameter on GaAs material, with five separate Ti/Au Schottky gates around and in the center of the ring, including an air-bridge connection to the center gate.
High rate CH4:H2 plasma etch processes for InP
Authors: Whelan Colin S. , Kazior Thomas E. , Hur Katerina Y.
Published: July 2002

High rate plasma etch processes for InP with smooth etched surfaces and highly anisotropic sidewall profiles were developed. A CH4:H2-based process using an electron cyclotron resonance (ECR) etcher and a reactive ion etcher (RIE) was investigated. Etch rates in excess of 120 nm/min in an ECR etcher using CH4:H2:Ar plasma and 135 nm/min in a RIE using CH4:H2:O2 were achieved in InP and produced minimal surface roughness. These etch rates are significantly faster than those previously reported.
Fabrication of hybrid superconductor–semiconductor nanostructures by integrated ultraviolet-atomic force microscope lithography
Authors: Pingue Pasqualantonio , Lazzarino Marco , Beltram Fabio , Cecconi Ciro , Baschieri Paolo , Frediani Carlo , Ascoli Cesare
Published: July 2002

Hybrid superconductor–semiconductor (S–Sm) nanostructures were fabricated by integrating standard ultraviolet photolithography and direct patterning of photoresist with an atomic force microscope (AFM). This novel technology was used to fabricate Nb–InAs–Nb weak links comparable in length to the coherence length. These structures exhibit high critical currents up to 10 μA/μm in planar geometry at 0.3 K. The fabrication protocol is based on the modification of photolithographically defined patterns by AFM static ploughing of the photoresist. Wet chemical etching is subsequently used for the definition of nanoscale S–Sm–S bridges. Additionally Lift-off procedures allowed the fabrication of submicron superconducting bridges. Successful fabrication of the nanostructures was verified by electrical characterization and by AFM and scanning electron microscope structural characterization.
Evaluation of diamond-ground beveled surfaces with Hg gate capacitance–voltage and current–voltage
Authors: Hillard R. J. , Sherbondy J. C. , Hartford C. L. , Weinzierl S. R. , Mazur R. G.
Published: July 2002

The spreading resistance profiling (SRP) method has undergone significant improvements over the last five years, enhancing the techniques’ capability for profiling sub-100 nm junctions. Newly developed procedures for conditioning probes, preparing beveled surfaces, and processing the raw data now yield a high degree of success. We believe that the sample preparation technique determines the quality of the bevel surface and thus plays a key role in the repeatability and sensitivity of SRP measurements. Although some previous work has suggested that the diamond ground beveled surfaces used for these measurements involve significant surface damage and hence, a high surface state density, little work has been done to quantify bevel surface quality. In this article, Hg gate capacitance–voltage (C–V) and current–voltage (I–V) have been used for the first time to determine the electrical properties of the diamond-beveled surfaces. Diamond particle sizes ranging from 0.05 to 0.25 μm were used to bevel p silicon samples. Measurements were made on both the diamond-ground bevels and on the original top surface of the sample chips using a mercury probe and several defect sensitive C–V and I–V measurements such as Schottky C–V and forward and reverse I–V. The three major surface quality factors that are investigated are surface leakage, interface and near surface bulk trap density, and surface roughness.
Diffusion from polymer spin-on films: Measurements and simulations
Authors: Ber B. Ya. , Guk E. G. , Kamanin A. V. , Kudryavtsev Yu. A. , Mokina L. A. , Shmidt N. M. , Shuman V. B. , Busygina L. A. , Yurre T. A.
Published: July 2002

The possibilities of diffusion from polymer spin-on films have been investigated for the purpose of obtaining shallow junctions in Si, GaAs, InP, and InGaAs. Compared to the conventional diffusion techniques, diffusion from polymer spin-on films is simpler and more controllable. The peculiarities of the method are associated with a uniform distribution of the dopant atoms in the three-dimensional network of the polymer chains. The possibilities have been demonstrated for control of the atomic concentration of B in silicon and of Zn in III–V compounds (from 1021 to 1017 cm−3) and for obtaining shallow p-n junctions; for example, a junction depth of 40 nm has been obtained in silicon. Diffusion conditions have been analyzed which provide a near-entire activation of the impurity. Moreover, gettering the defects and the background impurities by the spin-on film in the near-surface region of the semiconductor has been investigated.
Physically based modeling of two-dimensional and three-dimensional implantation profiles: Influence of damage accumulation
Authors: Murthy C. S. , Posselt M. , Feudel T.
Published: July 2002

The alteration of the shape of one-dimensional, two-dimensional (2D), and three-dimensional (3D) range distributions with growing dose as well as the extension of amorphous zones formed at high doses is studied for 15 keV BF2+ and 30 keV P+ implantations into (100)Si using the dynamic binary collision code Crystal-TRIM. The range and damage profiles are calculated for the area 97.74 (parallel to [010])×97.74 (parallel to [001]) nm2 at the target surface irradiated by the ion beam and surrounded by impenetrable masks. The change of the shape of the 2D and 3D distributions in the lateral direction is less pronounced than in the depth direction. At low doses the lateral profile branches are determined by rechanneled particles, at high doses the enhanced dechanneling is the reason for the increased lateral straggling. The latter effect is responsible for the relatively large lateral extension of the amorphous zone beneath the masks. The simulated depth profiles of boron and phosphorus and the predicted thickness of the amorphous layer are in good agreement with experimental data.
Strong effect of dopant concentration gradient on etching rate
Authors: Ukraintsev V. A. , McGlothlin R. , Gribelyuk M. A. , Edwards Hal
Published: July 2002

Dopant concentration sensitive etching of silicon in HF:HNO3:CH3COOH solution was studied using epitaxially grown silicon samples. The study has shown the unstable character of the process, significant time and structure size dependencies of the etching rate, as well as the dependence of the rate on the dopant concentration gradient. The data may be rationalized on the basis of the electrochemical and autocatalytic nature of the reaction. The influence of the dopant gradient and overall device geometry on the etching rate may cause significant inaccuracy of the dopant distribution measurements.
Fabrication and photoluminescence investigation of silicon nanowires on silicon-on-insulator material
Authors: Gotza M. , Dutoit M. , Ilegems M.
Published: July 2002

A process compatible with very large scale integrated technology for preparing high densities (up to 500 μm−2) of well-passivated sub-5 nm diam silicon nanowires is presented. The nanowire formation consists of the deposition of a fine-grained natural mask and the subsequent transfer of the pattern into the silicon substrate by reactive ion etching. To isolate the nanowires from the bulk and from each other, this process was applied on silicon-on-insulator material, where the buried oxide layer acts as an etch stop. The nanowire diameter distribution was then shifted below 5 nm by self-limiting oxidation. Finally, hydrogen-rich amorphous silicon nitride (a-SiNx:H), prepared by plasma enhanced chemical vapor deposition, was deposited onto the structures to act as a source of hydrogen. After annealing in forming gas, visible photoluminescence (PL) is detected under 325 nm excitation. The a-SiNx:H was found to emit broad PL, where peak position and intensity depend on the layer composition. Buried silicon oxide, covered by a-SiNx:H and annealed in forming gas emits yellow (480 nm), blue (560 nm), and red (650 nm) PL. After subtraction of the PL originating from both silicon oxide and silicon nitride, no light could be attributed to the nanowires, possibly due to insufficient passivation of the wires.
Effect of N doping on the electron emission properties of diamondlike carbon film on a 2-in. Mo field emitter array panel
Authors: Jung Jae Hoon , Ju Byeong Kwon , Kim Hoon , Oh Myung Hwan , Chung Suk Jae , Jang Jin
Published: July 2002

We have studied the enhancement of field-emission characteristics by hydrogen-free nitrogen-doped diamondlike carbon (DLC) coating on Mo-tip field emitter arrays by a layer-by-layer technique using plasma-enhanced chemical vapor deposition. The Spindt-type molybdenum tip is used as an emission source without a resistive layer on the silicon substrate. The maximum emission current for each pixel was increased from 160 to 1520 μA by a 20 nm N-doped DLC coating. Furthermore, the emission current from DLC-coated field emitter arrays (FEAs) is more stable than that of noncoated FEAs.
Fabrication of self-aligned silicon field emission devices and effects of surface passivation on emission current
Authors: Rakhshandehroo M. R. , Pang S. W.
Published: July 2002

Arrays of uniform gated Si field emitters with small gate-tip spacing and sharp tips were fabricated using a newly developed self-aligned process. Emitter tips with 80 nm gate-tip spacing were fabricated and low temperature plasma oxidation was used to sharpen the emitter tips. The enhancement factor of the field emitters increased by a factor of 2.6 after the emitter tips radius was reduced from 67 to 8 nm by plasma oxidation. Effects of surface passivation on the emission current of gated Si field emitters were investigated by exposing emitter tips to Cl2 and H2 plasmas prior to testing. Considerable improvements in the emission characteristics were observed after plasma passivation. The emission current was enhanced and the turn-on voltage was reduced after Cl2 and H2 plasma passivation, which corresponds to a work function reduction of 0.5 and 0.9 eV, respectively.
Polycrystalline silicon field emitter arrays by silicidation-sharpening technique at low temperature
Authors: Lee Jin Ho , Song Yoon-Ho , Kang Seung-Youl , Cho Kyoung Ik , Lee Sang Yun , Yoo Hyung Joun
Published: July 2002

Gated polysilicon field emitter tip arrays have been fabricated by a method consisting of dry etching and silicidation-sharpening techniques instead of high-temperature thermal oxidation. The silicidation process of titanium was adopted for the tip sharpening process. After dry etching of amorphous silicon, a titanium layer was deposited and silicide was formed by a low-temperature (450–550 °C) annealing process. After the formation of titanium silicide, the silicide layer was removed by a buffered HF solution and sharply formed amorphous silicon tips were converted to polysilicon tips by low-temperature (600 °C) annealing. The gate aperture was formed by a spin-on-glass etch-back process. The obtained polysilicon tips were very sharp, comparable with those by the conventional oxidation process. All processes were done below 600 °C, so that the technology could be applied to a glass-based polysilicon field-emission display.
Fabrication and characterization of gated porous silicon cathode field emission arrays
Authors: Jessing J. R. , Kim H. R. , Parker D. L. , Weichold M. H.
Published: July 2002

Gated porous silicon cathode field emission arrays have been fabricated. The devices were fabricated by using a simple self-aligning gate process which results in reproducible physical characteristics across the entire array. In addition, an anodization process has been developed to form porous silicon in a localized region on the substrate. The resulting device structure consists of a conical porous silicon tip that is self-aligned with respect to a concentric metal gate electrode. Small arrays exhibited Fowler–Nordheim characteristics over several decades of anode current. The porous silicon tip has been shown to produce a large submicroscopic field enhancement which leads to an improvement in emission characteristics.
Electron emission from gated silicide field emitter arrays
Authors: Takai M. , Iriguchi T. , Morimoto H. , Hosono A. , Kawabuchi S.
Published: July 2002

Silicidation of the top surface of Si tips with a Nb gate structure has been carried out to improve the emission behavior of Si field emitter arrays (FEAs). A Pt layer with a thickness of 5–10 nm was deposited through the gate opening and annealed at 850 °C. The electron emission was enhanced by a factor of 10 and the average emission per tip was 3.5 μA for a 10×10 FEA. Fowler–Nordheim plots indicated the decrease in work function after silicidation.
Effect of gas ambient on improvement in emission behavior of Si field emitter arrays
Authors: Takai Mikio , Morimoto Hiroji , Hosono Akihiko , Kawabuchi Shinji
Published: July 2002

Gated Si field emitter arrays (FEAs) have been operated in various gas atmospheres such as air, H2, O2, and Ar at 10−7 Torr to improve the emission behavior. The electron emission from the FEAs was enhanced by a factor of up to 10 during or after gas ambient emission with H2, O2, and Ar, while the improvement was not observed by a process with air. Fowler–Nordheim plots indicated a drastic change in slope only for H2 processes, in which hydrogen atoms would adsorb to Si tip surfaces. An emission pattern with a fourfold symmetry was observed for a single-tip emitter after hydrogen ambient emission, indicating the tip surface crystallinity after gas ambient emission.
Surface application of molybdenum silicide onto gated poly-Si emitters for enhanced field emission performance
Authors: Uh Hyung Soo , Park Byung Gook , Lee Jong Duk
Published: July 2002

This article investigates the merits of molybdenum (Mo) silicide formation on gated polycrystalline silicon (poly-Si) field emitters. Metal silicides are promising materials for field emission cathode due to their high electrical and thermal conductivity and high-temperature stability. In our experiment, Mo silicide was produced by direct metallurgical reaction, that is, deposition of Mo and subsequent rapid thermal annealing. The surface morphologies and field emission properties of Mo-silicided poly-Si (Mo-polycide) emitters have been examined and compared with those of pure poly-Si emitters. Field emission from these Mo-polycide emitters exhibited significant enhancement compared with pure poly-Si emitters in both total emission current and stability. The reason for this improved electron emission efficiency and stability could be explained by the smaller work function and better surface inertness of Mo-polycide emitters than those of poly-Si emitters.
Emission stability analysis of cone-shaped metal-insulator-semiconductor cathode by Monte Carlo simulation
Authors: Ishikawa J. , Gotoh Y. , Sadakane S. , Inoue K. , Nagao M. , Tsuji H.
Published: July 2002

We have proposed a cone-shaped metal-insulator-semiconductor cathode (COSMISC) to improve the emission efficiency of the conventional metal-insulator-semiconductor cathode. This cathode is also recognized as the field emitter with prior electron acceleration mechanism. Since the COSMISC emits the electrons with higher energy than those at the Fermi level of the metal electrode, it is expected that the current fluctuation due to the change in work function of the metal electrode is less significant than that of a conventional field emitter. In this article, we analyzed the emission characteristics of the COSMISC in detail by Monte Carlo simulation, especially from the viewpoint of the emission stability against the change in work function of the upper metal electrode. The calculation procedure is as follows: electrons are generated according to their energy distribution at the semiconductor-insulator surface, and the scattering processes in the insulator and in the metal electrode were simulated with random numbers. Emission of electrons into vacuum was judged also according to the transmission probability at the surface barrier of the metal electrode. The obtained results are arranged with respect to the work function and also to the external field at the apex of the metal electrode. It was shown that the fluctuation of the emission current in COSMISC due to the change in work function is lower than that of the conventional field emitter.
Empirical implantation damage model and its effect on reverse short channel effect for 0.35 μm complementary metal–oxide–semiconductor technology
Authors: Kim Jongmin , Yang Kwangsun , Kim Hyunchul , Baek Junho , Kim Choonkyung
Published: July 2002

This study presents an empirical implantation damage model on the basis of the “+1” model, describing the defect profile as a function of implantation energy, dose, and species. The model implies that the defect profile generated by ion implantation is very sensitive to the implantation condition especially at low doses and energies. This sensitivity is not accounted sufficiently for by the existing model, and that it can be effectively argumented by the proposed dependencies of D.PLUS. To validate the model, the extracted dependencies were applied to process and device simulations for our 0.35 μm complementary metal–oxide–semiconductor technology. An excellent agreement between simulation and measurement was obtained in the reverse short channel effect as well as in the drain induced barrier lowering and the body effect, which indicates that both vertical and lateral profiles are accurately described by this model.
Chemical beam epitaxial growth of GaAs1−xPx on GaAs (100) substrates
Authors: Wildt D. , Garcı́a B. J. , Castaño J. L. , Piqueras J. , Pastor C. J.
Published: July 2002

Phosphorus incorporation during chemical beam epitaxial (CBE) growth of GaAs1−xPx from triethylgallium, tertiarybutylarsine, and tertiarybutylphosphine is investigated. Reflection high-energy electron diffraction intensity oscillations are used to measure the phosphorus incorporation during the As-limited and the (As+P)-limited growth on a Ga-rich surface. The resulting phosphorus mole fraction is compared with the phosphorus composition measured by x-ray rocking curves on the strained GaAs1−xPx layers grown by conventional CBE with a simultaneous supply of group V and group III elements. The phosphorus incorporation rate during CBE growth is lower than that measured during the group V controlled growth but is still much higher than the incorporation rate reported for molecular beam epitaxy growth using elemental sources.
Low temperature scanning tunneling microscope-induced luminescence of GaN
Authors: Evoy S. , Harnett C. K. , Craighead H. G. , Eustis T. J. , Davis W. A. , Murphy M. J. , Schaff W. J. , Eastman L. F.
Published: July 2002

We report the low temperature scanning tunneling microscope-induced luminescence of molecular beam epitaxy grown α-GaN. Semiquantitative spectroscopic analysis suggests near band edge emission, as well as emission covering the rest of the visible range. The relative intensity of band edge emission increases by one order of magnitude under liquid helium cooling. We also report the first photon emission images of GaN obtained with this technique. These images reveal stronger band edge emission at the center of crystallites. This study is complemented with a scanning electron microscope-induced cathodoluminescence analysis. Cathodoluminescence is dominated by the hexagonal (D°, X) transition and reveals evidence of small quantities of the cubic phase.
Investigation of growth mode behavior and surface morphology evolution of metalorganic vapor phase epitaxy grown ZnTe layers on (001) GaAs
Authors: Longo M. , Lovergine N. , Mancini A. M. , Leo G. , Berti M.
Published: July 2002

A systematic investigation on the mechanisms of nucleation and surface morphology evolution was performed on ZnTe epilayers, deposited on chemically etched GaAs(001) by metalorganic vapor phase epitaxy. A 2D–3D growth mode transition was observed at around two ZnTe equivalent monolyers (ML), which was ascribed to a Stransky–Krastanow growth mode. The 3D growth behavior was correlated to the development of {n11}-type planes, leading to a surface ridging effect along the [11̄0] direction for 4000-ML-thick ZnTe epilayers. The use of a solid-on- solid kinetic roughening model allowed the identification of a mechanism that limits the self- organization of ZnTe nanosized islands, namely, the high density of kink sites found in non- atomically flat GaAs substrates.
Interaction of H2O with active Spindt-type molybdenum field emitter arrays
Authors: Chalamala Babu R. , Wallace Robert M. , Gnade Bruce E.
Published: July 2002

Electron emission from molybdenum field emission microcathode arrays is sensitive to the contamination of the emitters by the residual gases. We studied the effects of H2O exposures on the emission properties of several Spindt-type molybdenum field emitter arrays. Exposure of the field emitters to H2O resulted in emission degradation ranging from (13.8±5.7)% for 50 L to 90.7% for a 4000 L exposure.
Metal–Ge-Si heterostructures for near-infrared light detection
Authors: Colace L. , Masini G. , Galluzzi F. , Assanto G. , Capellini G. , Di Gaspare L. , Palange E. , Evangelisti F.
Published: July 2002

We report on Ge Schottky photodiodes epitaxially grown on Si (100) exhibiting a good responsivity in the near infrared up to 1.55 μm. The Ge epitaxial layers, grown by ultrahigh vacuum chemical vapor deposition, were deposited in two steps differing by the substrate temperature. With this procedure it was possible to obtain films thicknesses comparable with light penetration depth in the 1.3–1.6 μm range. The photodiodes have a photocurrent which increases as a function of voltage bias, reaching a maximum responsivity of 0.12 A/W at 1.3 μm under a reverse bias of 4 V. The leakage current density at the saturation voltage is 1 nA/μm2. The results show that the proposed approach is promising for the fabrication of 1.3–1.55 μm near-infrared photodetectors integrated on silicon chips.
Transition metal carbide field emitters for field-emitter array devices and high current applications
Authors: Mackie W. A. , Xie Tianbao , Davis P. R.
Published: July 2002

We report on the use of transition metal carbides, primarily zirconium carbide, for field emission cathodes. This work encompasses three areas first, the use of carbide films as overcoatings on molybdenum field-emitter cathodes, second, the deposition of thick carbide films to form field-emitter cones directly in field-emitter arrays, and third, the use of single emitters formed from macroscopoic, single crystal carbide for use at high currents and in adverse vacuum conditions. Recent work with ZrC film overcoatings on Mo field emitters has focused on the processing steps required to obtain stable, low work function surfaces. Clean substrates are found to be essential. Emission degradation sometimes noted after exposure to air has been successfully reversed through operation in 10−5 Torr pressure of hydrogen. The most promising results applicable for use with arrays have been achieved with the direct deposition of zirconium carbide cones in blank field-emitter arrays. Thick films were deposited by physical vapor deposition from refined, crystalline carbide sources. Operation of single and multitip arrays has resulted in high currents (>1 μA) per tip and relatively low turn-on voltages given the gate geometry. These improvements are primarily attributed to the lower work function associated with these carbide materials. We also report on the use of etched transition metal carbides as single emitters for applications including high-current, small-spot sources for accelerators and free electron lasers, and cold cathodes for operation in poor vacuum environments. Stable, single emitter currents in the mA range have been demonstrated. A brief discussion is given regarding the ability to extract information from I(V) data using the Fowler–Nordheim equation and log(I/V2) vs 1/V plots. From this we propose a method to determine if nanoprotrusions account for a large fraction of the emission current measured.
Bonding constraint-induced defect formation at Si-dielectric interfaces and internal interfaces in dual-layer gate dielectrics
Authors: Lucovsky G. , Wu Y. , Niimi H. , Misra V. , Phillips J. C.
Published: July 2002

As aggressive scaling of integrated circuits continues into the next century, insulators with dielectric constants higher than SiO2 with different local bonding arrangements will be required to increase gate dielectric capacitance in field effect transistor devices. An important issue in semiconductor device physics is determining whether differences between the bonding at (i) Si–SiO2 interfaces and (ii) interfaces between crystalline Si and alternative gate dielectric materials will result in increased densities of electrically active defects at the alternative dielectric interfaces, thereby limiting targeted levels of performance and reliability. In particular, it is important to understand from a chemical bonding perspective why Si–SiO2 interfaces display both low defect densities and high reliability, while other interfaces such as Si–Si3N4 with similar bonding chemistry, display defect densities that are at least two orders of magnitude higher. Building on previously established criteria for formation of low defect density glasses and thin films, constraint theory is extended to crystalline Si-dielectric interfaces that go beyond Si–SiO2 through development of a model that is based on the average bonding coordination at these interfaces. This approach identifies quantitative bonding criteria that distinguish between device-quality and highly defective interfaces. This extension of constraint theory is validated by its application to interfaces between Si and stacked silicon oxide/nitride dielectrics which demonstrates that as in bulk glasses and thin films an average coordination, Nav>3 yields increasingly defective interfaces. Finally, the universality of this application of constraint theory is demonstrated by showing that defect densities scale with overcoordination in the same way in thin films and at interfaces.
Patterning curved surfaces: Template generation by ion beam proximity lithography and relief transfer by step and flash imprint lithography
Authors: Ruchhoeft P. , Colburn M. , Choi B. , Nounu H. , Johnson S. , Bailey T. , Damle S. , Stewart M. , Ekerdt J. , Sreenivasan S. V. , Wolfe J. C. , Willson C. G.
Published: July 2002

Submicron patterning of 1 in. diameter curved surfaces with a 46 mm radius of curvature has been demonstrated with step and flash imprint lithography (SFIL) using templates patterned by ion beam proximity printing (IBP). Concave and convex spherical quartz templates were coated with 700-nm-thick poly(methylmethacrylate) (PMMA) and patterned by step-and-repeat IBP. The developed resist features were etched into the quartz template and the remaining PMMA stripped. During SFIL, a low viscosity, photopolymerizable formulation containing organosilicon precursors was introduced into the gap between the etched template and a substrate coated with an organic transfer layer and exposed to ultraviolet illumination. The smallest features on the templates were faithfully replicated in the silylated layer.
Outgassing of organic vapors from 193 nm photoresists: Impact on atmospheric purity near the lens optics
Authors: Kunz R. R. , Downs D. K.
Published: July 2002

Fourteen different 193 nm photoresists were tested for organic vapor outgassing after exposure and their outgassing rates were measured to be between 1011 and 1013 molecules cm−2 s−1, with the primary compounds being isobutene and benzylic photoacid generator fragments. Rough estimates indicate that for an outgassing rate of 1011 molecules cm−2 s−1 and a well purged tool, organic vapor partial pressures between 10 ppb and 1 ppm are likely, depending on the lens working distance. Higher levels of outgassing combined with poor ventilation can result in partial pressures in excess of 1 Torr. These values exceed the residual ambient levels expected in a fab and hence constitute an increased risk of contamination to the final optical element of 193 nm exposure tools.
Practicalities and limitations of scanning capacitance microscopy for routine integrated circuit characterization
Authors: Stephenson Robert , De Wolf Peter , Trenkler Thomas , Hantschel Thomas , Clarysse Trudo , Jansen Philippe , Vandervorst Wilfried
Published: July 2002

We have imaged several n-type metal-oxide-semiconductor transistors with different source and drain architectures to assess the feasibility of extracting useful figures of merit, such as the effective channel length of a device, from the data. By varying the dc bias on the sample we observe a shift of the junction position in the image and consider how best to interpret a set of voltage dependent images produced for a single sample. Careful attention is paid to the effects of surface variation from sample preparation and tip wear during an experiment by considering the scanning capacitance microscopy signal in the substrate as a function of applied dc bias.
Experimentation and modeling of organic photocontamination on lithographic optics
Authors: Kunz R. R. , Liberman V. , Downs D. K.
Published: July 2002

Photodeposition of organic films on transparent substrates irradiated in the presence of trace levels (ppb to ppm) of hydrocarbons has been experimentally investigated and a model is presented that describes the film growth behavior. The efficacy of a given organic precursor at forming a deposit is proportional to the product of its surface coverage (as governed by its partial pressure relative to its saturation partial pressure) and by its photon absorption cross section. These measurements are important in predicting the transmission characteristics of lithographic optics operating at 157, 193, and 248 nm wavelength. For example, a lens element irradiated continuously for 1 yr (1 kHz, 0.1 mJ/cm2/pulse) in the presence of 1 ppb of t-butyl benzene would exhibit a transmission of ∼87% at 193 nm. The effects of oxygen-containing ambients are also documented, and methods for elimination and/or prevention of organic contamination are suggested.
Choice Behavior of
Drosophila
Facing Contradictory Visual Cues
Authors: Tang Shiming , Guo Aike
Published: July 2002

We studied the underlying neural mechanism of a simple choice behavior between competing alternatives in
Drosophila
. In a flight simulator, individual flies were conditioned to choose one of two flight paths in response to color and shape cues; after the training, they were tested with contradictory cues. Wild-type flies made a discrete choice that switched from one alternative to the other as the relative salience of color and shape cues gradually changed, but this ability was greatly diminished in mutant (

mbm
1

) flies with miniature mushroom bodies or with hydroxyurea ablation of mushroom bodies. Thus,
Drosophila
genetics may be useful for elucidating the neural basis of choice behavior.