bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation between surface structure and ordering in GaInP
Authors: Murata H. , Lee S. H. , Ho I. H. , Stringfellow G. B.
Published: July 2002

Ga and In atoms in Ga0.52In0.48P layers spontaneously segregate to form alternating In- and Ga-rich {111} monolayers during organometallic vapor phase epitaxial (OMVPE) growth on (001) oriented GaAs substrates, thus forming the CuPt ordered structure. This ordering phenomenon is believed to be driven by surface processes, although little direct experimental information is available. This work presents evidence, based on surface photoabsorption data, that [1̄10] oriented P dimers are present on the surface during OMVPE growth using trimethylgallium and ethyldimethylindium combined with tertiarybutylphosphine, suggesting a (2×4)-like surface reconstruction. Furthermore, when the growth temperature is increased above 620 °C, with other parameters constant, both the concentration of these P dimers and the degree of order are observed to decrease. A similar correlation of decreased P-dimer concentration with decreased degree of order is observed for decreases in V/III ratio. Thus, the changes in order parameter for variations in temperature and TBP flow rate are found to be closely correlated with the changes in the order parameter. A third parameter studied was the misorientation of the substrate from (001) toward either the {111}A or {111}B planes. The concentration of P dimers decreased as the misorientation increased in either direction. The degree of order was also observed to generally decrease, supporting the connection between surface reconstruction and ordering. However, the difference in order parameter observed for the two misorientation directions suggests the importance of a second parameter, the step structure, itself. For exactly (001) oriented substrates the surface was observed, using high resolution atomic force microscopy, to consist of islands, elongated in the [110] direction, with heights of 30–60 Å. Monolayer steps are observed for some growth conditions, but for most conditions the boundaries are formed exclusively of bilayer (5.7 Å) steps. Predominantly monolayer steps are formed for low V/III ratios and bilayer steps for high V/III ratios.
Atomic structures and growth mechanisms of electrodeposited Ag and Te films as discerned by atomic force microscopy
Authors: Ikemiya Norihito , Yamada Koji , Hara Shigeta
Published: July 2002

We have investigated atomic structures as well as growth morphologies of electrodeposited thin Ag and Te films on Au(100) under an aqueous sulfuric acid solution. The extremely flat Ag films were formed by an ideal Frank–van der Merwe mode even at a high deposition rate [∼7.2 monolayer (ML)/min], which suggests that the surface diffusion process of Ag adatoms is extremely rapid. In the underpotentially deposited Te on Au(100), the (√2×√2)R45°-Te structure (coverage, θ=0.5) for a first monolayer was formed through the (2×2)-Te structure (θ=0.25) under an aqueous H2SO4 solution. In contrast with the Ag films, the bulk deposited Te films were formed by a Stranski–Krastanov mode even at a low deposition rate (∼0.5 ML/min), which suggests that the surface diffusion process of Te adatoms is extremely slow. The Te(101̄0) films (≳80 ML) were grown on Au(100) through the c(√2×3√2)R45° (20–30 ML) and (√2×√2)R45°-Te(<10 ML) structures.
Analysis of Fourier transform infrared spectra and peak shifts in plasma-enhanced chemical vapor deposited fluorinated silica glasses
Authors: Swope Richard , Yoo Woo Sik
Published: July 2002

The use of Fourier transform infrared spectroscopy was investigated to analyze fluorine dopant levels in plasma-enhanced chemical vapor deposited (PECVD) fluorinated silica glasses (FSG). The physical and electrical properties of FSG films are strongly dependent on the fluorine dopant concentrations in the film; however, peak overlaps and film thickness effects can reduce the reliability of fluorine dopant estimates. The relationships between peak positions, peak areas, FSG film thickness, physical properties, and fluorine dopant concentration levels were studied for a large number of PECVD FSG films deposited using a wide variety of process conditions. The position of the Si–F peak was found to be independent of dopant levels or film properties. Shifts of the Si–O peak to higher wave numbers were found to be dependent on the fluorine concentration in the film and on the film thickness. Peak deconvolution and curve fitting can be used to separate the effects of the two interfering peaks that make up the Si–O asymmetrical bond stretch peak. The peak area of the Si–F peak normalized to the peak area of the asymmetrical Si–O peak can give reliable quantitative estimates of fluorine dopant concentration when corrected for the effects of film thickness.
Copper film formation using electron cyclotron resonance plasma sputtering and reflow method
Authors: Shibuki S. , Kanao H. , Akahori T.
Published: July 2002

A subhalf-micron gap filling process for copper (Cu) films was developed by using an electron cyclotron resonance (ECR) plasma sputtering method. The achieved Cu film had a resistivity as low as that of bulk Cu and an excellent, void-free filling property in a 0.5-μm-wide trench. This result is because the distance between the target and wafer was longer than conventional sputtering; the plasma could be generated at low pressure (<1 mTorr); and the ECR plasma sputtering method generates a highly anisotropic particle flux of Cu. Then, a reflow process of the Cu films deposited by using an ECR plasma sputtering method was tried. The reflow phenomenon was observed and the filling property was improved; void-free filling in a 0.4-μm-wide trench was achieved. Moreover, a Cu interconnection of 0.5 μm linewidth was fabricated by a chemical mechanical polishing method without dishing, scratching, and erosion.
Layered structures with delta-doped layers for enhancement of field emission
Authors: Evtukh A. A. , Litovchenko V. G. , Marchenko R. I. , Kydzinovski S. Yu.
Published: July 2002

The electron field emission, from silicon tip arrays with layer structures on their surfaces, was investigated. The main task of the study was to enhance field emission. The n–Si–SiO2, n–Si–Cs–SiO2,n–Si–SiO2–Si*–SiO2,n–Si–Si3N4–Si*–SiO2, etc., were among the different prepared layered structures. The thicknesses of dielectric layers were 1–5 nm and they were prepared both by thermal oxidation and by chemical vapor deposition (CVD). The cesium was deposited on the cathodes with the application of cesium salt (CsCl) in solution. The outer SiO2 layer prevents cesium from evaporating during heating or reaction under exposure to gases. The thin silicon layer (Si*) was formed by CVD. The measurements of electron field emission from layered structures show sufficient enhancement of emission in the case of using the delta-doped cesium layer. The incorporation of cesium is an important way to decrease the threshold voltage of cold cathodes, and in our case the use of a SiO2 layer allows us to stabilize the emission.
Influence of the gas mixture on the reactive ion etching of InP in CH4-H2 plasmas
Authors: Feurprier Y. , Cardinaud Ch. , Turban G.
Published: July 2002

The influence of the CH4-H2 mixture composition on the etching process of InP is investigated by means of plasma diagnostics (optical emission spectroscopy and mass spectrometry) and quasi in situ x-ray photoelectron spectroscopy (XPS) surface analysis. Increasing the mixture composition in methane increases the InP etch rate. For example, it rises from 230 to 380 Å/min when increasing the percentage in CH4 from 2.5% to 75%. In pure methane discharge, at a pressure of 50 mTorr, amorphous carbon is deposited on InP. Quasi in situ XPS reveals major changes in the surface chemistry. In particular P depletion decreases and the mean surface stoichiometry improves as the percentage of methane increases. The mass spectrometry PH3+ signal (m/e=34 amu) corresponding to PH3 molecules and the In* emission line (λ=451.1 nm), which are, respectively, characteristic signals of the individual removal rate of In and P, and the concentration of CH3 radicals in the plasma as measured by the threshold ionization technique display good agreement with the etch rate and surface chemical modifications. These results confirm that the etching mechanism of InP is controlled by the etching mechanism of In, and that the latter is strongly correlated with the concentration of methane in the mixture. Variable photoelectron emission angle measurements are performed to determine precisely the location of the species in the damaged layer. A model for the representation of the surface in the process of etching is then proposed.
Use of interference lithography to pattern arrays of submicron resist structures for field emission flat panel displays
Authors: Fernandez A. , Nguyen H. T. , Britten J. A. , Boyd R. D. , Perry M. D. , Kania D. R. , Hawryluk A. M.
Published: July 2002

We report on the fabrication of square arrays of submicron resist dots and holes using interference lithography—a relatively simple and inexpensive way of generating periodic structures over large areas. The arrays are formed by exposing a layer of resist to a two-beam interference pattern followed by a second exposure after rotating the sample by 90°. Arrays with periods of 0.67–3.2 μm were fabricated. The size of the structures is accurately controlled by varying the exposure dose. The exposure latitude for patterning arrays of dots is ±16% for a ±10% change in structure width when an optimum size-to-period ratio is chosen. Compared to dots, holes are patterned with a smaller process window. We show that arrays of dots with diameters as small as 0.20 μm, sidewall slopes of 88°, and aspect ratios as high as 3:1 can be produced. These structures are well suited for the production of field emission flat panel displays.
Process effects in shallow junction formation by plasma doping
Authors: Matyi R. J. , Felch S. B. , Lee B. S. , Strathman M. R. , Keenan J. A. , Guo Y. , Wang L.
Published: July 2002

We have characterized the effect of implant parameters on the characteristics of boron-implanted silicon prepared by plasma doping. The thickness of the amorphous layer was monitored using Rutherford backscattering spectrometry, transmission electron microscopy, and double crystal x-ray diffraction. At low plasma implant pulse biases (2 kV), both dose rate and pulse repetition rate (10 Hz to 1 kHz) were found to have a negligible effect on the generation of the surface amorphous layer. At higher voltages (5 kV), the thickness of the amorphous layer increased with the pulse repetition rate but was apparently not sensitive to the dose rate. The sheet resistance after annealing correlated strongly with the increasing thickness of the surface amorphous layer formed at 5 kV. From these results, we conclude that an increase in pulse repetition rate has a stronger effect on the formation of the surface amorphous layer than does dose rate.
Epitaxy of Si/Si1−xGex heterostructures with very small roughness using a production-compatible ultrahigh vacuum-chemical vapor deposition reactor
Authors: Lafontaine H. , Mason B. F. , Rolfe S. J. , Perovic D. D. , Bahierathan B.
Published: July 2002

Two different roughening mechanisms are studied using a production-ready epitaxial deposition system to grow various epilayers, including the base layer of bipolar transistors. Surface roughness is measured using atomic force microscopy and transmission electron microscopy is used for cross-sectional analysis. Very smooth surfaces are routinely obtained, with a root mean square roughness of 0.15 nm. However, two possible mechanisms are shown to increase surface roughness under certain conditions. Above a certain critical thickness, for growth temperatures higher than 525 °C and Ge compositions above 25%, strain redistribution results in surface ripples with a typical wavelength of the order of 100 nm. In addition, we find that substrate contamination (C,O) can produce wide depressions, several hundreds of nm wide and on average 10 nm deep in Si epilayers. The addition of a small concentration of Ge (below 15%) seems to produce more planar growth compared to the same thickness (50 nm) of Si only. The origin of the different surface morphologies observed is discussed.
Effects of heat treatment on the field emission property of amorphous carbon nitride
Authors: Chi Eung Joon , Shim Jae Yeob , Choi Dong Jun , Baik Hong Koo
Published: July 2002

As a coating material for silicon field emitters, amorphous carbon nitride (a-C:N) by helical resonator plasma enhanced chemical vapor deposition has been proposed. Thermal annealing in nitrogen ambient up to 600 °C was carried out to investigate the effects of heat treatment on the field emission. The structural and compositional modifications induced by the annealing were followed by several analytical techniques: Fourier transformation infrared (FTIR) spectroscopy, elastic recoil detection analysis (ERDA), and x-ray photoelectron spectroscopy. FTIR and ERDA analyses indicate that hydrogen loss occurs for annealing temperatures higher than 300 °C. Amorphous-C:N films significantly lowered the turn-on voltage and increased the emission current of the silicon emitters. After annealing at 600 °C, the field emission property was further enhanced presumably due to the efficient conduction through the a-C:N films induced by an increase of the number and/or the size of the graphitic domains.
Investigation of process induced defects in SiGe/Si heterojunction bipolar transistors by deep-level transient spectroscopy
Authors: Souifi A. , De Barros O. , Brémond G. , Le Tron B. , Mouis M. , Vincent G. , Ashburn P.
Published: July 2002

Deep-level transient spectroscopy (DLTS) measurements have been performed on SiGe heterojunction bipolar transistors fabricated in a complementary metal–oxide–semiconductor compatible polysilicon self-aligned process. A detailed study of the emitter–base capacitance transient as a function of the filling pulse parameters and transistor geometry has shown that the deep levels are correlated to point defects uniformly distributed along the emitter–base junction periphery and attributed to the reactive ion etching (RIE) process. The observed deep electron traps are located at 0.6 eV below the conduction band with a capture cross section of 10−17 cm2. In order to confirm that the observed defects were not correlated to the SiGe base material, a similar investigation was carried out on mesa devices grown in the same reactor with the same intrinsic structure but whose emitter–base active zone did not suffer RIE. In these devices, a new electron trap with an activation energy of 0.38 eV and a capture cross section of 10−19 cm2 is detected. This trap is sensitive to the electric field as in the case of the self-aligned structure, but a detailed study has shown that it has a different origin. Finally, the first peripheral electron trap at Ec−0.6 eV is not observed in mesa devices in good agreement with our first hypothesis.
Low energy ion beam etching of InP using methane chemistry
Authors: Carlström C. F. , Landgren G. , Anand S.
Published: July 2002

Reactive ion beam etching (RIBE) and chemically assisted ion beam etching (CAIBE) of InP at room temperature have been performed, using an inductively coupled plasma source. Two types of chemistries were used: N2/CH4/H2 and Ar/CH4/H2. The etch rate, surface roughness and anisotropy were investigated for different process parameters. In hydrocarbon chemistry polymer buildup is a commonly encountered problem and therefore efforts were also devoted to minimize the polymer growth. Comparing the two chemistries it was found that the Ar based processes always lead to rougher surfaces, while the N2 based chemistry at low ion energies (<100 eV) results in very smooth surfaces for both types of ion beam processes. However, the CAIBE process not only provides smooth surfaces, but also generates much less polymers than its RIBE counterpart. CAIBE, using N2/CH4/H2 chemistry, is then identified as a promising candidate for fabrication of nanometer sized structures. In addition, the low polymer growth is also advantageous from an equipment service point of view.
Structural, optical, and electrical properties of nanocrystalline silicon films deposited by hydrogen plasma sputtering
Authors: Garrido B. , Pérez-Rodrı́guez A. , Morante J. R. , Achiq A. , Gourbilleau F. , Madelon R. , Rizk R.
Published: July 2002

Nanocrystalline silicon films were deposited by radio frequency sputtering in a pure H2 plasma on glass and monocrystalline 〈100〉 silicon at various substrate temperatures, Ts. The detailed structural, optical, and electrical analysis of the films has been performed by transmission electron microscopy, Raman scattering, infrared spectroscopy, x-ray diffraction, optical absorption, photoluminescence and electrical measurements. The data obtained show that, to a significant extent, control of the structure and hence of the optical and electrical properties of the films can be achieved by changing Ts. Increasing Ts from 50 to 250 °C leads to an increase of the average grain size (from a few nm to a few tens of nm) and crystalline fraction (from 37% to 74%) and the optical band gap decreases from 2.40 to 1.95 eV. Hydrogen incorporation, together with Ts, are thought to be at the origin of the resulting microstructure and consequently determine the optical and transport properties. Moreover, hydrogen content was found to be associated with void formation which induces structure relaxation with very low residual stress. Finally, electrical conductivity in the layers increases by more than six orders of magnitude with Ts. The high dark conductivity measured from the sample deposited at the highest Ts (>10−3 Ω−1 cm−1) and its low activation energy (0.13 eV) are in agreement with the high crystalline fraction of this layer, where tunneling of carriers between the crystallites likely occurs.
Integration of chemical vapor deposition titanium nitride for 0.25 μm contacts and vias
Authors: Westerheim A. C. , Bulger J. M. , Whelan C. S. , Sriram T. S. , Elliott L. J. , Maziarz J. J.
Published: July 2002

A chemical vapor deposition (CVD) TiN liner process was developed and integrated into 0.25 μm contact and via process modules as an adhesion layer and barrier for tungsten plug deposition. The previous physical vapor deposition (PVD) TiN process used for 0.35 μm contacts and vias was found to be inadequate for the next generation 0.25 μm technology due to poor conformality. Three major advantages were achieved for CVD over the previous PVD technology: (1) the CVD TiN liner is able to fill higher aspect ratio contacts resulting in high yield and low contact resistance, (2) the CVD TiN liner produces a conformal adhesion layer that was found to prevent against WF6 attack of underlying silicide for unlanded contacts, and (3) via electromigration resistance was greatly improved through the elimination of early fails. The final process incorporates deposition of a collimated PVD Ti/TiN underlayer which was found to improve contact resistance. Details of the process and supporting electrical and reliability results are presented.
Sputtering rate change and surface roughening during oblique and normal incidence O2+ bombardment of silicon, with and without oxygen flooding
Authors: Magee Charles W. , Mount Gary R. , Smith Stephen P. , Herner Brad , Gossmann Hans-J.
Published: July 2002

A sample of low-temperature epitaxial Si grown with five B delta-doped layers 5.4 nm apart has been profiled using secondary ion mass spectrometry under a variety of O2 bombardment conditions. Energies from 400 eV to 1.5 keV were used with angles of incidence from 0° to 70°. Analyses were performed using oxygen flooding of the sample surface during analysis, as well as without using oxygen flooding. The apparent spacing between the B delta layers was used to determine the magnitude and extent of increased sputtering rate at the beginning of an analysis. Changes in depth resolution due to sputter-induced surface roughening are reflected in variations in the apparent width of the B delta layers. It was found that sputtering with 500 eV O2 at an angle of 50° while flooding with oxygen produced no measurable change in sputtering rate and resulted in no unexpected shift towards the surface of the B delta layers. These analysis conditions also resulted in a depth resolution which was as good as that obtained using 400 eV O2 bombardment at 0° incidence without oxygen flooding. The 0° method of analysis, however, resulted in a 1.1 nm shift of the topmost B delta layer toward the surface, and the 0° method had a sputtering rate only 1/5 that of the 50° method of analysis.
Metallization-induced damage in III–V semiconductors
Authors: Chen Ching-Hui , Hu Evelyn L. , Schoenfeld Winston V. , Petroff Pierre M.
Published: July 2002

Damage introduced from sputtering deposition, electron-beam evaporation, and thermal evaporation were investigated with an InGaAs/GaAs strained quantum well structure. This strained quantum well structure was found to be a more sensitive probe of damage, revealing metallization-induced damage where none was found using comparable lattice-matched quantum wells. The damage was found to vary with deposition method, deposition rates, or even different metal sources used. Noticeable degradation of the photoluminescence of the strained quantum well was observed after a thin layer (∼100 Å) of metal was deposited.
Modification of YBa2Cu3O7−δ wires using a scanning tunneling microscope: Process and electrical transport effects
Authors: Bertsche G. , Clauss W. , Prins F. E. , Kern D. P.
Published: July 2002

Wires of the high temperature superconductor YBa2Cu3O7−δ (YBCO) were fabricated by electron beam lithography and were subsequently modified further on a sub-100 nm scale using the scanning tunneling microscope (STM). The process responsible for this modification has been shown to be field enhanced corrosion of the YBCO surface in the presence of CO2 and H2O. The intention of this work is to investigate the effect of the STM induced modifications on the electrical transport behavior of the YBCO wires with current–voltage characteristics (CVCs) measured at 77 and 4.2 K. Different types of CVCs can be distinguished, depending on the size of the cut into the wire generated by the STM. The measured characteristics will be explained by thermal self-heating at locations of the wire induced by the STM. Thus, the STM modifications initiate thermal domains in the wire where the Joule heat emission generated at sufficient high current values raise the temperature of the wire above its critical temperature. Furthermore, a steplike structure in the CVC of a STM fabricated nanobridge is detected, which we attribute to an increase of the number of vortex trajectories as the transport current through the wire is increased.
Surface photochemistry induced by x-ray irradiation
Authors: Rosenberg Richard A. , Ma Qing , Lai Barry , Mancini Derrick C.
Published: July 2002

The high-intensity, high-energy x rays produced by third-generation synchrotron radiation sources have made possible many new applications, such as deep x-ray lithography, that take advantage of the long penetration lengths of the x rays in lower-Z materials. Recently, we have initiated a program to evaluate the prospects for using x rays for materials processing by performing surface photochemistry induced by x-ray irradiation (SPIXI). The x rays induce reactions on the surfaces of solids immersed in potentially reactive liquids or gases. In this article we present results that demonstrate the feasibility of the SPIXI approach for both etching and deposition. Using a fluorochlorocarbon-based solvent and a Mo substrate we find indications of an etching-type reaction. Au and Ag films and nanocrystalline particles were produced from the irradiation of a Mo substrate immersed in their respective salt solutions. A Au film was also deposited on Kapton by back irradiation. These preliminary results indicate that this approach has great potential for room-temperature, atmospheric, patterned, materials processing.
Time-of-flight secondary ion mass spectrometry depth profiling of multiple quantum well II–VI semiconductors using negative cluster ions
Authors: Zhao Jin , Na Myunghee , McKeown Patrick J. , Chang Huicheng , Lee Eunhwa , Luo Hong , Chen Jiaxing , Wood Troy D. , Gardella Joseph A.
Published: July 2002

II–VI semiconductor heterostructures have been studied using time-of-flight secondary ion mass spectrometry (TOF-SIMS) depth profiling. We demonstrate the use of binary negative cluster ions, such as CdSe− and CdSe2−, to simultaneously monitor the Cl doping and Cd growth profiles of n-type modulation-doped ZnSe:Cl/ZnxCd1−xSe multiple quantum well (MQW) structures in negative ion TOF-SIMS depth profiling. Zn and Cd profiles of MQW structure ZnTe/CdSe are monitored by ZnTe2− and CdSe2− with Te− and Se− simultaneously in negative ion TOF-SIMS depth profiling, so as to avoid the mass interference of ZnTe− and CdSe−. Sputtering rates of numerous II–VI semiconductor epilayers and depth resolution of interface abruptness have been determined. The substitution of either element in ZnSe epilayer by Cd or Te gives a lower sputtering rate. This trend is illustrated by the decrease of sputtering rate on the order of ZnSe, ZnTe, to CdSe, where ZnTe and CdSe have relatively the same sputtering rate. Depth profiling of n-type modulation-doped ZnSe:Cl/ZnxCd1−xSe MQW structure yields a broadening effect due to cascade mixing, which is strongly sputtered-depth dependent. However, the knock-on effect is unrelated to the sputtered depth.
Application of scanning tunneling microscopy to aluminum nanocluster deposition on silicon
Authors: Hu Xiaoming , von Blanckenhagen P.
Published: July 2002

As a substitution material for gold, aluminum and especially its nanocluster form deposited on a clean silicon surface are important for the electronic industry. In this article, a scanning tunneling microscope has been used to deposit nanoscale aluminum clusters on a clean stepped Si(111) surface by applying bias pulses to the tip–sample tunneling junction. It has been found that thresholds for the bias pulses exist for the deposition of aluminum nanoclusters for both positive and negative voltages. By operating around these thresholds, rather small (down to 3 nm) aluminum clusters can be generated. However, positive and negative bias pulses tend to give different nanocluster types, and this can be explained in terms of field evaporation mechanism by considering the evaporation field intensity changes during the deposition process.
Electrochemical microprocess by scanning ion-conductance microscopy
Authors: Zhang Haijun , Wu Lan , Huang Feng
Published: July 2002

An electrochemical microprocess method by scanning ion-conductance microscopy (SICM) has been developed to process microcircuits and microstructures on sample surfaces. A metal electrode inside an electrolyte-filled micropipette and an electrolyte-covered conducting surface are employed as the anode and the cathode, respectively. As the pipette approaches the surface, the flow of ions through the opening of the pipette tip is blocked by the surface at short distances, thus the ion conductance decreases. A feedback system is then used to obtain a given ion conductance, and in turn to maintain a constant tip–surface gap. Due to the mechanism of electrolysis, when a dc voltage is applied between the two electrodes, microstructures such as dots, lines and squares can be processed (electroplated) on the surface as the tip scans laterally over it. Similar to the resolution of SICM, the linewidth of the processed microstructures is approximately on the same order of the inner diameter (ID) of the tip. Using the micropipette with a tip of 1.5 μm ID, we successfully processed some lines of 2.0 μm width on an In2O3+SnO2 surface. As a future aim, the electrochemical microprocess method provides the possibility of fabricating microcircuits and microstructures with linewidth on the order of 0.1–1 μm by using the micropipettes which have IDs of order 0.1 μm.
Properties of titanium nitride film deposited by ionized metal plasma source
Authors: Tanaka Yoichiro , Kim Edwin , Forster John , Xu Zheng
Published: July 2002

Ionized metal plasma (IMP) deposition utilizes an inductively coupled plasma to ionize sputtered metal atoms. The resulting metal ions are then accelerated towards the substrate by applying bias to the substrate. The flux and energy of these ions can be controlled independently. Thus, formation of titanium nitride (TiN) with an IMP source allows for better control of TiN film properties than with conventional dc magnetron sputtering. Ion bombardment energy at substrate has a significant effect on grain size and on the crystallographic orientation. The variation of TiN resistivity with substrate bias can be explained in terms of grain size, film density, and randomness of the crystal structure. Also, ion flux to Ti flux at the substrate is calculated which has an impact on the crystal orientation. Diffusion tests between TiN and Al/Cu alloy are consistent with film density and crystallographic properties. The resistivity nonuniformity of the TiN film can be correlated with the ion flux nonuniformity as measured by a Langmuir probe.
Micro-Raman study of free-standing porous silicon samples
Authors: Trusso Sebastiano , Vasi Cirino , Allegrini Maria , Fuso Francesco , Pennelli Giovanni
Published: July 2002

Micro-Raman spectroscopy has been employed for the characterization of a set of free-standing porous silicon samples with different degrees of porosity, fabricated by electrical anodization of n+ Si wafers. A broadening and a shift toward lower energy of the transverse optical silicon phonon mode have been clearly observed, indicating the presence of nanometer-sized crystalline structures. In particular, higher porosity samples reveal an inhomogeneous structure characterized by a spread of the nanocrystal size as a function of the region under investigation. The photoluminescence properties of samples produced with similar fabrication parameters, displaying both a blue and a red band, seem to be in agreement with the nanocrystal dimensions derived through micro-Raman spectroscopy.
Reaction and thermal stability of cobalt disilicide on polysilicon resulting from a Si/Ti/Co multilayer system
Authors: Alberti A. , La Via F. , Rimini F.
Published: July 2002

The formation and thermal stability of CoSi2 has been investigated using a poly-Si/Ti/Co multilayer structure. The presence of the Ti layer allows the phase formation by a single step with an optimum reaction temperature in the range between 750 and 850 °C. The layer agglomerates at temperatures higher than 950 °C. Sheet resistance measurements have been used to monitor the kinetics of the agglomeration process. The dependence of both the sheet resistance and the thermal stability on the film thickness has been studied in detail. The agglomeration process is thermally activated with an energy of ∼3.9 eV, lower than the value 5.6 eV measured in CoSi2 layers formed by direct reaction of Co with polycrystalline silicon. These activation energies have been correlated to the different layer structures. In the silicide formed without the Ti thin film, the grains are columnar, while the presence of Ti causes a random distribution in the grain shape and smaller size. The low thermal stability of the CoSi2 layer on polysilicon can be a problem to use the Ti/Co bilayer process in self-aligned complementary metal–oxide–semiconductor technology.
Spin relaxation of conduction electrons
Authors: Fabian J. , Sarma S. Das
Published: July 2002

Prospect of building electronic devices in which electron spins store and transport information has revived interest in the spin relaxation of conduction electrons. Since spin-polarized currents cannot flow indefinitely, basic spin-electronic devices must be smaller than the distance electrons diffuse without losing its spin memory. Some recent experimental and theoretical effort has been devoted to the issue of modulating the spin relaxation. It has been shown, for example, that in certain materials doping, alloying, or changing dimensionality can reduce or enhance the spin relaxation by several orders of magnitude. This brief review presents these efforts in the perspective of the current understanding of the spin relaxation of conduction electrons in nonmagnetic semiconductors and metals.
Piezoelectric fields in nitride devices
Authors: Beach R. A. , McGill T. C.
Published: July 2002

We have calculated the piezoelectric field and charge distribution for various III-nitride heterostructures. Our calculations include strain energy minimization and doping effects, and are presented to show the magnitude of piezoelectric effects in strained layers. We compare our calculated results to device results where available. These include the two-dimensional electron gas in heterojunction field effect transistors, Schottky diodes with strained layers for Schottky height engineering, and III-nitride single quantum wells. Calculations that included energy considerations resulted in good agreement between predicted and observed field and charge distributions for the heterojunction fields-effect transistors structure.
Growth and postgrowth rapid thermal annealing of InAsN/InGaAs single quantum well on InP grown by gas source molecular beam epitaxy
Authors: Wang Jyh-Shyang , Lin Hao-Hsiung
Published: July 2002

InAsN/InGaAs single quantum wells (SQWs) with different nitrogen concentration have been successfully grown on InP substrates by gas source molecular beam epitaxy used rf plasma nitrogen source. Photoluminescence (PL) results of the as-grown samples show red-shifted PL peak energy and rapidly degraded intensity as the nitrogen concentration increases. The roughly estimated maximum nitrogen mole fraction in these samples is 0.4%. Both the PL intensity and linewith of these InAsN/InGaAs SQWs were significantly improved after postgrowth rapid thermal annealing with the optimum temperature at 525–550 °C for samples with different nitrogen content. The improvement on 10 K PL intensity can be as high as 230 times, and the room temperature PL intensities of the annealed InAsN SQWs have been comparable to those of InAs SQWs used for laser diodes. Quantum well intermixing (QWI) induced blue-shifted PL spectra were also observed in these samples. The QWI threshold temperature decreases as the nitrogen concentration increases, which indicates that defects created by nitrogen incorporation may enhance the QWI.
Use of atomic layer epitaxy for fabrication of Si/TiN/Cu structures
Authors: Mårtensson Per , Juppo Marika , Ritala Mikko , Leskelä Markku , Carlsson Jan-Otto
Published: July 2002

The properties of titanium nitride deposited by atomic layer epitaxy (ALE) using three different deposition processes, i.e., TiI4+NH3, TiCl4+NH3 and TiCl4+Zn+NH3, as a diffusion barrier between copper and silicon were investigated. After deposition and annealing in Ar/H2, the samples were studied by means of x-ray photoelectron spectroscopy, scanning electron microscopy, x-ray diffraction, sheet resistance measurements and by defect delineating etching of the silicon substrate. ALE TiN deposited by means of the TiCl4/Zn/NH3 process showed the best barrier properties since it was stable at 700 °C, whereas TiN barriers deposited by the two alternative processes started to break down after a 75 min anneal at 650–750 °C. Even though the TiN barriers deposited by the TiI4/NH3 and TiCl4/NH3 processes were not completely comparable to the TiCl4/Zn/NH3 TiN, they were stable for a 15 min anneal at 700 °C which is comparable to or better than previously reported for chemically vapor deposited and physically vapor deposited TiN. Finally, the TiN and copper were of high purity and the deposition on patterned substrates showed good step coverage.
Development of chemically assisted dry etching methods for magnetic device structures
Authors: Jung K. B. , Cho H. , Lee K. P. , Marburger J. , Sharifi F. , Singh R. K. , Kumar D. , Dahmen K. H. , Pearton S. J.
Published: July 2002

There is a strong need for advanced pattern transfer methods for magnetic devices such as magnetic random access memories, sensors for avionics and mine detection, and read/write heads for high density information storage. As the critical dimensions in these devices are decreased, the use of ion milling for pattern transfer presents major obstacles, including sidewall redeposition (which degrades magnetic performance) and poor mask selectivity. Most magnetic materials do not form volatile etch products in conventional reactive ion etching. We have recently found that high density plasmas provide efficient ion-assisted desorption of metal chloride etch products, provided that the etch production formation and removal are balanced by correct choice of ion/neutral ratio. We have completed the survey of plasma chemistries for etching of giant magnetoresistance (GMR) (NiFe, NiMnSb) and collossal magnetoresistance (CMR) (LaCaMnO3,LaSrMnO3,PrBaCaMnO3) materials. The optimum choices are Cl2/Ar for CMR oxides, SF6/Ar for NiMnSb Heusler alloys and either Cl2/Ar or CO/NH3 for GMR multilayers. We have also addressed the issue of postetch cleaning for corrosion prevention, by combining simple water rinsing with in situ plasma cleans involving H2, O2, or F2. Under optimized conditions, there is excellent long-term stability of both the mechanical and magnetic properties of the multilayer structures.
Atomic force microscopy of the topochemical photopolymerization of diolefin crystals
Authors: Zeng Qingdao , Wang Chen , Bai Chunli , Li Yan , Yan Xinjian
Published: July 2002

The formation of regular nanostructures by photopolymerization of three diolefin derivative crystals, P2VB, DSP, and p-CPAEt, is investigated using atomic force microscopy (AFM) and known crystal packing data. AFM reveals that the crystal face (100) and (010) of P2VB exhibit volcanoes, whereas (100) and (010) of DSP give floelike structures. The main face and long side face of p-CPAEt give rise to volcanoes. All of those are guided by the crystal structure. Molecular interpretations of the AFM features of P2VB and DSP are given.
Electromagnetic transmission of nanometric circular aperture on top of a metal coated optical fiber tip: Theory
Authors: Alvarez Lydia , Xiao Mufei
Published: July 2002

Within the framework of the direct moment method, a theory for calculating the optical transmission of nanometric circular aperture on top of a metal coated optical fiber tip is developed. The primary purpose of the study is to estimate transmission efficiency of near field probes widely used in near field scanning optical microscopy. Field distributions immediately after the aperture in the core and cladding of the fiber tip can be accurately calculated in three dimensions. It turns out that the transmission is a function of many variables, such as the radii of the aperture and fiber core, the thickness of the metallic coat, the material responses in the core and cladding area of the fiber, and finally the light frequency.
Dielectric anisotropy and molecular orientation of fluorinated polymers confined in submicron trenches
Authors: Cho T. H. , Lee J. K. , Ho Paul S. , Ryan E. Todd , Pellerin John G.
Published: July 2002

Dielectric anisotropy of polymers with low dielectric constant is an important property to consider for developing interlevel dielectrics for advanced on-chip interconnects. The effect of molecular structure on dielectric anisotropy has been investigated for two low dielectric-constant polymers: a fluorinated polyimide, FPI-136M and a fluorinated poly(aryl ether), FLARE-1.51. Optical and electrical measurements have been carried out to determine the dielectric anisotropy in blanket thin films and trench line structures. Results from optical measurements show that the FPI-136M film has a larger birefringence than the FLARE-1.51 film, indicating a larger dielectric anisotropy. This reflects a higher degree of in-plane molecular orientation for the rigid rod-like fluorinated polyimide, while the fluorinated poly(aryl ether) has an ether linkage that allows greater chain flexibility. Electrical measurement of the dielectric anisotropy has been performed using a metal–insulator–metal structure to determine the out-of-plane dielectric constant and an interdigitated submicron metal line structure coupled with a two-dimension computer model to determine the in-plane dielectric constant. Results show that the rigid rod-like FPI-136M has a smaller dielectric anisotropy compared with that measured from the optical birefringence. In contrast, the dielectric anisotropy of the more flexible FLARE-1.51 is found to be similar to that obtained from the optical birefringence measurement. Fourier transform infrared (FTIR) spectroscopy has been used to examine the molecular structures in the blanket films and the trench line structures. The FTIR spectra of FPI-136M show that its molecular structure in submicron trenches is significantly different to that in spin-coated blanket film. This is in contrast to FLARE-1.51, which has similar molecular orientation for the blanket film and the trench structure. Thus, the molecular orientation of the rigid rod-like FPI-136M seems to be more affected by the confinement in submicron trenches, giving rise to a lesser degree of dielectric anisotropy than that observed in blanket films.
Microprocess for fabricating carbon-nanotube probes of a scanning probe microscope
Authors: Nakayama Yoshikazu , Nishijima Hidehiro , Akita Seiji , Hohmura Ken I. , Yoshimura Shige H. , Takeyasu Kunio
Published: July 2002

We have developed microprocesses to make carbon-nanotube probes for a scanning probe microscope. The processes contain electric-field induced transportation, welding and fixation by electron-beam carbon deposition and are performed in a scanning electron microscope equipped with two individual manipulable stages. Using the nanotube probes produced, a fine structure of helical and twinned deoxyribonucleic acid and an abrupt height transition with high fidelity in a 4.7 GB digital versatile disk are imaged with tapping-mode atomic force microscopy in air.
Optical active gallium arsenide cantilever probes for combined scanning near-field optical microscopy and scanning force microscopy
Authors: Heisig S. , Rudow O. , Oesterschulze E.
Published: July 2002

The fabrication process of a GaAs cantilever probe with an integrated vertical cavity surface emitting laser (VCSEL) for scanning near-field optical microscopy applications is described. The VCSEL illuminates an aperture in a thin Au/Ge metallization layer at the tip apex. The light emitting aperture serves as a subwavelength light source and thus can be used to reduce the lateral resolution in transmission imaging beyond the far-field diffraction limit. The light beam of the VCSEL emitted to the opposite side is exploited for the detection of the mechanical deflection of the cantilever that additionally facilitates the scanning force microscopy setup.
Process damage assessment of a low energy inductively coupled plasma-based neutral source
Authors: Tang Xianmin , Wang Qi , Manos D. M.
Published: July 2002

In this article, we report process damage studies using a low energy inductively coupled plasma-based neutral stream source. Low energy neutrals are generated by the surface reflection neutralization method. Quasistatic capacitance-voltage measurement results of this work demonstrate that this low energy neutral source, which provides controllable fast neutrals for cleaning applications, induces much less damage than a pulsed inductively coupled plasma source. Most of the neutral process damage is caused by ultraviolet photons escaping from the plasma source zone. The process-induced damage by fast neutrals increases as the reflector bias is lowered. The fast neutral process damage also increases with the rf power. Unlike the neutral process-induced damage, the damage induced by pulsed plasmas is found to be a function of both the gas composition and rf pulsed frequencies.
GaAsSb/InGaAs type-II quantum wells for long-wavelength lasers on GaAs substrates
Authors: Klem J. F. , Blum O. , Kurtz S. R. , Fritz I. J. , Choquette K. D.
Published: July 2002

We have investigated the properties of GaAsSb/InGaAs type-II bilayer quantum-well structures grown by molecular-beam epitaxy for use in long-wavelength lasers on GaAs substrates. Structures with layer strains and thicknesses designed to be thermodynamically stable against dislocation formation exhibit room-temperature photoluminescence at wavelengths as long as 1.43 μm. The photoluminescence emission wavelength is significantly affected by growth temperature and the sequence of layer growth (InGaAs/GaAsSb versus GaAsSb/InGaAs), suggesting that Sb and/or In segregation results in nonideal interfaces under certain growth conditions. At low-injection currents, double-heterostructure lasers with GaAsSb/InGaAs bilayer quantum-well active regions display electroluminescence at wavelengths comparable to those obtained in photoluminescence, but at higher currents the electroluminescence shifts to shorter wavelengths. Lasers have been obtained with threshold current densities of 120 A/cm2 at 1.17 μm, and 2.1 kA/cm2 at 1.21 μm.
Interface-controlled Si/SiGe-heterostructure growth and its device application
Authors: Sugii N. , Nakagawa K. , Yamaguchi S. , Miyao M.
Published: July 2002

Si/SiGe heterostructures were grown by molecular-beam epitaxy. With atomic-hydrogen irradiation during the growth of the heterostructure, characteristics of modulation-doped field-effect transistors (MODFETs) were improved. A Hall effect measurement and a device simulation revealed that carrier density capable of being confined in the Si channel is limited in the MODFETs. Surface-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) with strained-Si channel on various buffer layers were fabricated. Effective electron mobility in strained-Si MOSFETs with a SiGe compositionally graded buffer layer was 60% higher than that of an unstrained-Si MOSFET. The enhancement of mobility varied with the types of the buffer layers. This variation may be attributed to the amplitude of surface roughness of the strained-Si layer.
Monolithic integration of resonant interband tunneling diodes and high electron mobility transistors in the InAs/GaSb/AlSb material system
Authors: Bennett B. R. , Bracker A. S. , Magno R. , Boos J. B. , Bass R. , Park D.
Published: July 2002

InAs/AlSb high electron mobility transistors (HEMTs) and resonant interband tunneling diodes (RITDs) with AlSb barriers and GaSb wells were grown in a single heterostructure by molecular beam epitaxy. The resulting HEMTs exhibit excellent dc and microwave performance at low drain voltages, with an intrinsic unity-current-gain cutoff frequency of 220 GHz. The RITD performance is comparable to RITDs grown directly on InAs substrates, with peak current densities above 104 A/cm2 and peak-to-valley ratios near 11 for 15 Å AlSb barriers. The results represent an important step toward the fabrication of high-speed, low-power logic circuits in this material system.
Production of Refractory Dissolved Organic Matter by Bacteria
Authors: Ogawa Hiroshi , Amagai Yukio , Koike Isao , Kaiser Karl , Benner Ronald
Published: July 2002

Most of the oceanic reservoir of dissolved organic matter (DOM) is of marine origin and is resistant to microbial oxidation, but little is known about the mechanisms of its formation. In a laboratory study, natural assemblages of marine bacteria rapidly (in <48 hours) utilized labile compounds (glucose, glutamate) and produced refractory DOM that persisted for more than a year. Only 10 to 15% of the bacterially derived DOM was identified as hydrolyzable amino acids and sugars, a feature consistent with marine DOM. These results suggest that microbial processes alter the molecular structure of DOM, making it resistant to further degradation and thereby preserving fixed carbon in the ocean.