bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropic reactive ion etching of titanium
Authors: Blumenstock K. , Stephani D.
Published: July 2002

The reactive ion etching of titanium is described using rf discharges of CCl4 and O2 with additions of fluorine containing gases. Because of these additions the titanium etch rate increases substantially in comparison with the pure CCl4/O2 plasma. This is presumably due to a shift of equilibrium reactions within the discharge towards the production of the volatile etch product. Process parameters are given for which the reactive ion etching of titanium with a photoresist mask is highly anisotropic and an etch end point control by optical emission spectroscopy is possible.
PbEuSeTe buried heterostructure lasers grown by molecular-beam epitaxy
Authors: Feit Z. , Kostyk D. , Woods R. J. , Mak P.
Published: July 2002

The successful preparation of lattice matched buried heterostructure (BH)PbEuSeTe lasers grown by molecular-beam epitaxy (MBE) is reported here for the first time. Lasers with 2–8 μm wide and 0.5 μm thick buried Pb1−xEuxSeyTe1−y active layers, in the composition range of 0≤x≤0.015 and cavity lengths between 200 and 300 μm, were fabricated. Single mode operation was realized in most devices for injection currents 1.2 to 4.5 times the threshold current. A maximum continuous wave (cw) operation temperature of 180 and 176 K was measured for BH diode lasers with PbTe and PbEuSeTe (0.22 at. % Eu) active layer compositions, respectively. Using a high-resolution scanning electron microscope, growth discontinuities were found in the nonplanar regions of the second cladding and capping layers. In most cases, lower threshold current densities were measured for BH lasers in comparison to double heterostructure (DH) lasers with the same active layer composition. It is believed that improvement of growth morphology, and optimizing layer thicknesses and doping profiles will lead to lower threshold currents and higher operation temperatures in BH lasers.
Evaluation of a new high capacity, all-tantalum molecular-beam-epitaxy arsenic cracker furnace
Authors: Sacks R. N. , Eichler D. W. , Pastorello R. A. , Colombo P.
Published: July 2002

A novel effusion furnace for the production of As2 from As4 by combined thermal and catalytic cracking has been evaluated in a Varian GEN II molecular-beam epitaxy (MBE) system. The furnace consists of two temperature zones with a one-piece all-tantalum combined crucible, delivery tube, and cracking zone. Ta baffles are inserted into the cracking zone. Thermal isolation of the ‘‘warm’’ sublimation zone and the ‘‘hot’’ cracking zone is achieved by water or liquid nitrogen cooling of the sublimation zone. With the cracking zone at 1500 °C and no power to the 200 cc capacity sublimator, the sublimation zone rises to only 75 °C. Cracking of As4 begins at about 750 °C and saturates at about 900 °C. The As flux stabilizes in about 1.25 h. Installation of the cracker furnace in a position previously used for the old As effusion furnace resulted in considerable outgassing due to the previous condensation of As and trapped impurities on the cryoshroud around the mouth of the old furnace. Soon after installation, growth of nominally undoped GaAs in the As4 mode (by holding the cracking zone at 400 °C) gave background doping concentrations of p=2×1014/cm3, but the first attempts at growth of nominally undoped GaAs with As2 gave high n-type background doping levels due to the outgassing mentioned above. A combination of secondary ion mass spectroscopy (SIMS) and photoluminescence analysis showed decreased C and increased S in the As2 grown layers. Following mechanical scraping and extended thermal cleaning of the shroud area around the cracking zone, the residual As2 background doping dropped dramatically (to high 1013/cm3) while still remaining n type. Material and device benefits we have observed for As2 grown GaAs and (Al,Ga)As are: slightly improved surface morphology, decreased C incorporation, increased doping efficiency in (Al,Ga)As:Si, greatly improved low-temperature photoluminescence, and excellent heterojunction acoustic charge transport (HACT) device results.
A new perspective on proximity printing: From ultraviolet to x ray
Authors: Lin B. J.
Published: July 2002

Proximity printing is characterized in terms of linewidth variations in the gap–exposure (E–G) space. The usable E–G regions of all feature shapes and sizes on a given mask design have to be superimposed and the common region defines the depth of focus as well as the working distance for a given exposure latitude and linewidth tolerance. In this paper, the E–G diagrams are constructed and studied for 0.25, 0.35, and 0.5 μm x-ray features at mask-to-wafer gaps between 10 and 80 μm, or equivalently, 2.5, 3.5, and 5 μm features for 250-nm-deep-UV light at mask-to-wafer gaps between 4 and 20 μm. The types of illumination include collimated light, finite source size, and ghost line suppression. Linewidth tolerances of ±25 and ±16 nm for perfect and imperfect masks are examined. The effects of 50 nm positive and negative print biases are studied. The depth of focus and working distance are given for five representative lithographic features consisting of equal lines and spaces, isolated line openings, isolated opaque spaces, holes, and islands as well as for only the three long features.
Fabrication and testing of 0.1-μm-linewidth microgap x-ray masks
Authors: Schattenburg M. L. , Early K. , Ku Y.-C. , Chu W. , Shepard M. I. , The S.-C. , Smith Henry I. , Peters D. W. , Frankel R. D. , Kelly D. R. , Drumheller J. P.
Published: July 2002

A technology has been developed for the printing of 0.1-μm-linewidth patterns using a ‘‘microgap,’’ out-of-contact scheme for x-ray nanolithography (as opposed to zero-gap electrostatic contact). Mask-to-wafer gaps of ∼5 μm are maintained by the use of gap-setting aluminum studs fabricated onto the front surface of the mask mesa rim. X-ray mask blanks are fabricated from silicon wafers coated with low-stress, silicon-rich low-pressure chemical vapor deposition SiNx. The resulting 1–2-μm-thick 6×108 dyn/cm2 stress membranes exhibit extreme strength. A novel aluminum-stencil etching procedure—which includes three CF4 RIE and two KOH etching steps—is used to define the mask membrane and ‘‘mesa’’ structure. Mask absorber pattern fabrication is performed by focused-ion-beam lithography (FIBL) and gold electroplating. We present details of the mask fabrication procedure and the results of testing these masks with x rays from a laboratory CuL (λ=1.34 nm) electron bombardment source and a commercial pulsed laser-plasma x-ray source. This marks the first time that FIBL-generated masks have been used with a pulsed laser-plasma source, and also the finest lines that have been printed using a laser plasma. The results of the evaluation of the x-ray resists PMMA, RAY-PF, RAY-PN, and SAL-601 are presented.
Electron emission properties of laser pulsed GaAs negative electron affinity photocathodes
Authors: Sanford Colin A. , MacDonald Noel C.
Published: July 2002

The emitted electron energy distribution of a laser pulsed GaAs negative electron affinity (NEA) photocathode was measured with a retarding grid analyzer. The total electron energy distribution was found to depend strongly on laser intensity and cathode thickness. A model based on the separation of the excess photogenerated carriers within the cathode structure has been developed and tested to explain this behavior. Pulsed electron emission patterns were obtained by directing the emitted electrons to a phosphorous screen. The patterns indicate that uniform emission occurs and that the emission develops uniformly as the cathode is activated to a NEA condition. An extrapolated plot of the angular intensity FWHM versus V1/2B indicates that the pulsed cathode possesses a natural semicone angle of approximately 10°. The angular distribution is narrow because of the electron refraction which occurs upon emission due to differences in the effective mass and vacuum rest mass of the electrons.
Resist heating effects in 25 and 50 kV e-beam lithography on glass masks
Authors: Kratschmer E. , Groves T. R.
Published: July 2002

Electron sensitive resists have been exposed on optical masks in a variably shaped spot electron beam lithography system, EL3, at 25 and 50 kV and beam current densities up to 50 A/cm2 to evaluate the effects of resist heating during electron exposure. Resist heating effects are primarily observed in dense patterns at high electron exposure dose. For the purpose of comparison resist heating effects are quantified in terms of the development rate change that is caused by the temperature rise in the resist during electron beam exposure. From an energy density point of view the maximum temperature rise in the resist during exposure is very similar for both 25 and 50 kV exposures. The area on the mask over which the temperature rise in the resist can change resist properties is significantly larger at 50 kV: up to 20 μm at 50 kV compared to ∼5 μm at 25 kV. Using sensitive electron beam resists requiring 1–5 μC/cm2 exposure dose no resist heating effects are observed at beam current densities up to 50 A/cm2.
Stress and stress relaxation in integrated circuit metals and dielectrics
Authors: Draper Bruce L. , Hill Thomas A.
Published: July 2002

In order to provide data needed in the investigation and modeling of stress voiding in integrated circuit metallizations, stress and stress relaxation in Al/Si/Cu alloys and common dielectrics were studied as a function of storage temperature and deposition conditions. It was found that the room-temperature tensile stress in Al/Si/Cu increases with increasing substrate bias and deposition temperature, and that the isothermal relaxation rate upon cooling from 400 °C is sharply dependent on temperature. The activation energy for the relaxation process was found to be 0.39 eV above 130 °C and about 0.08 eV at lower temperatures. For insulating layers deposited with plasma-enhanced chemical-vapor deposition techniques, strong correlations were found among stress, density, hydrogen content, deposition temperature, and film composition (oxides, nitrides, and several intermediate oxynitrides), with the highest levels of compressive stress (near 1 GPa) being measured in nitride films deposited at 300 °C. These films, as well as phosphorus-doped glasses used as capping/protection layers, were found to undergo structural changes upon post-deposition thermal cycling which affected stress levels.
Alkane based plasma etching of GaAs
Authors: Law V. J. , Tewordt M. , Ingram S. G. , Jones G. A. C.
Published: July 2002

A mechanistic model for the plasma etching of GaAs is compared with experimentally determined kinetic reaction rates and thermodynamic data. The measurements were made on etching characteristics of radio frequency (rf) and electron cyclotron resonance (ECR) plasmas in alkane (CH4, C2H6, and C3H8 ), hydrogen and noble gas mixtures. The model examines the reaction mechanisms on the substrate surface in terms of sequential adsorption and fragmentation of the precursor alkane molecules and the subsequent desorption of volatile reaction products. Experimental results show GaAs etch rates in rf plasmas to be proportional to the initial alkane concentration, and the order of reaction increases with the number of constituent CHx groups within the alkane precursor molecule. By using different noble gas admixtures it has been possible to determine their effect on etch rates with respect to pure hydrogen admixtures, where results show that etch rates scale with the substitution of He<H2<Ar admixtures in CH4 plasmas. GaAs etch rates in ECR/magnetic mirror coupled plasmas show that GaAs etch rates are lower than in rf plasmas, with evidence of enhanced positive photoresist degradation at high microwave powers, and H2 partial pressures.
Characterization of low temperature SiO2 and Si3N4 films deposited by plasma enhanced evaporation
Authors: Lorenz H. , Eisele I. , Ramm J. , Edlinger J. , Bühler M.
Published: July 2002

SiO2 and Si3N4 films have been deposited at low temperatures by a new plasma enhanced evaporation process. The films are stoichiometric and have hydrogen contents below 1 at. %. For the electrical characterization metal–insulator–semiconductor diodes were fabricated and investigated before and after annealing in H2/N2 atmosphere at 430 °C. Ellipsometric and capacitance–voltage measurements yield the dielectric constants which agree well with the theoretical values. From conductance–voltage characteristics the silicon–insulator interface state density Dit was determined. After annealing Dit amounts to 2×1011 eV−1 cm−2 for Si3N4 and to 8×1010 eV−1 cm−2 for SiO2. In addition, the bulk resistivity and the surface resistivity of the deposited films were measured and compared with the values for films grown by conventional high temperature processes.
Graded-index strained multiquantum-well GaInAsP lasers grown by gas-source molecular-beam epitaxy: Growth and characterization
Authors: Keskinen Jari , Asonen Harry , Hovinen Minna , Tappura Kirsi , Näppi Jari , Pessa Markus
Published: July 2002

We have grown graded-index strained multiquantum-well GaInAsP lasers by gas-source molecular-beam epitaxy (GSMBE) for a wavelength of 1.47 μm. The growth of graded layers and quantum wells by GSMBE is reported. X-ray diffraction measurements of the laser structure were made and a simulation by dynamical diffraction theory gave good fitting. The threshold current densities were measured for 400- and 1000-μm-long broad-area lasers, and they were 1350 and 780 A/cm2, respectively. We have also fabricated ridge waveguide lasers from the same sample.
Use of scanning tunneling microscopy and transmission electron microscopy to quantify and characterize CoSi2 roughness
Authors: Chapman R. C. , Smith P. , Adu R. P. , McGuire G. E. , Canovai C. , Osburn C.
Published: July 2002

Scanning tunneling microscopy (STM) and transmission electron microscopy (TEM) were used to quantify and characterize CoSi2 surface roughness and CoSi2/Si interface roughness. Roughness at the CoSi2/Si interface has been reported to be on the order of 20 nm, enough for concern in shallow junction formation in submicron complementary metal–oxide semiconductor devices. Interface roughness is tied to surface roughness by thermal grooving kinetics and by thermodynamics. Hence, a correlation should be seen between roughness at the interface and the surface, yielding information regarding grooving kinetics. This study focused on the processing time dependence of surface and interface roughness. This roughness was quantified using the average roughness measurement technique. The roughness values obtained by TEM were compared to those obtained by STM. Both were fitted to thermal grooving kinetics equations.
Strain-induced dimer adatom stacking fault structures of germanium on Si(111)-(√3×√3)R30°:B observed by scanning tunneling microscopy
Authors: Müller B. , Jusko O. , Pietsch G. J. , Köhler U.
Published: July 2002

The growth and the atomic structure of the Ge on the Si(111)-((3)1/2×(3)1/2)R30° surface are investigated by scanning tunneling microscopy. The coexistence of the ((3)1/2×(3)1/2)R30° and the c(2×4) reconstruction at the Si-substrate is discussed. Germanium on silicon, usually indistinguishable from the silicon is identified on the boron induced ((3)1/2×(3)1/2)R30° surface using the difference in reconstruction of the substrate and epitaxial material. The germanium deposit shows a dimer adatom stacking fault-like structure while the substrate still remains ((3)1/2×(3)1/2)R30° reconstructed. A significant boron diffusion is only observed after annealing at 480 °C, which converts the island surface into a ((3)1/2×(3)1/2)R30° reconstruction.
Wet-developed bilayer resists for 193-nm excimer laser lithography
Authors: Kunz R. R. , Horn M. W. , Bianconi P. A. , Smith D. A. , Eshelman J. R.
Published: July 2002

A high-contrast resist process using polysilynes has been developed for 193-nm excimer laser lithography. Copolymerization allows for control of both polymer molecular weight and the net polymer solubility parameter. Optimal formulations yield sensitivities of 35–60 mJ/cm2 and line-edge roughness of ≤20 nm. Addition of sensitizers into the resist further improves sensitivity and values from 5 to 30 mJ/cm2 have been demonstrated. Use of high-density, low-bias etching sources for the oxygen-plasma pattern transfer improves process windows. For example, etch rate selectivities of 80:1 for the planarizing layer versus the polysilyne imaging layer have been observed even when the planarizing layer etch rate exceeds 1 μm/min. Under these conditions, the exposure latitude is 40% for k1=0.57 and the development latitude is 100% (20±10 s) for 10% linewidth control.
Cascade mixing limitations in sputter profiling
Authors: Hofmann S.
Published: July 2002

The most fundamental physical processes which limit the depth resolution achieved in depth profiling by sputtering and surface analysis techniques are surface microroughening and atomic mixing in the collisional cascade. A survey of theoretical modeling of cascade mixing and its effect on the shape of measured profiles is presented. In particular, diffusion type models show reasonable agreement with recent experimental results of secondary ion mass spectroscopy and Auger electron spectroscopy profiles on delta function marker layers and on multilayer sandwich structures. The mixing range is related to the range of the primary ions and determines the depth resolution. Minimum values obtained under optimized sputtering conditions are of the order of 1 nm. Depending on the gradient of the true in-depth distribution of composition, deconvolution procedures may become necessary to disclose the latter. Because sputtering is based on cascade mixing, the ultimate achievable resolution in depth profiling is limited by this effect.
p-type ZnSe grown by molecular beam epitaxy with remote microwave plasma of N2
Authors: Kawakami Y. , Ohnakado T. , Tsuka M. , Tokudera S. , Ito Y. , Fujita Sz. , Fujita Sg.
Published: July 2002

p-type ZnSe layers have been successfully grown by molecular beam epitaxy using remote microwave plasma of N2. The net acceptor concentration NA−ND in the layer from 1.5×1016 to 1.2×1018 cm−3 has been controlled by adjusting the flow rate of N2, the input microwave power and the substrate temperature. At a doping level of NA−ND=1.5×1016 cm−3, the photoluminescence at 4.2 K was characterized by an acceptor bound exciton at 444.3 nm (2.790 eV), a free electron to acceptor hole (FA) emission with a zero phonon line (ZPL) at 457.3 nm (2.710 eV) and a donor–acceptor pair (DAP) emission with a ZPL at 459.9 nm (2.695 eV). However, if NA−ND exceeds 1017 cm−3, the different series of DAP with a ZPL at 463.0 nm (2.677 eV) dominated the spectra, indicating some compensation occurring in the sample. The deep level transient spectroscopy revealed a deep hole trap level, whose activation energy was determined as 0.67 eV.
Efficiency of electron-beam proximity effect correction
Authors: Groves T. R.
Published: July 2002

The trend of increasing pattern data volume, together with decreasing critical dimensions, causes correction of proximity effect to be continually more time consuming and expensive. A tradeoff exists between speed and accuracy. A given correction method may be judged efficient if the direct computational overhead needed to achieve a predetermined level of accuracy is small. Some basic principles relating to efficiency are derived. An optimal correction algorithm follows naturally from the analysis. Forward and backward scattering have greatly differing ranges, and correspondingly differing computational requirements. The two processes are easily separated analytically. Dose correction is used to offset backscattering, while edge displacement is used to offset forward scattering. The only direct computational overhead is the local pattern density. All other necessary parameters are precomputed, and accessed by memory lookup.
Design and analysis of InAs/AlSb ballistic constrictions for high temperature operation and low gate leakage
Authors: Koester S. J. , Bolognesi C. R. , Hu E. L. , Kroemer H. , Rooks M. J. , Snider G. L.
Published: July 2002

Split-gate ballistic constrictions have been fabricated on two separate InAs/AlSb quantum well heterostructures. Constrictions in the initial material layer structure displayed quantized conductance to temperatures as high as 30 K, but suffered from poor reliability and large gate leakage current. Self-consistent Schrödinger–Poisson calculations indicate that donorlike states at the InAs–AlSb interface may aggravate the problem of gate leakage. Constrictions fabricated on an improved layer structure had gate leakage currents several orders of magnitude lower than in the original layer structure. This allowed measurement of quantized conductance with a dc measurement, up to bias voltages of 8 mV.
Characterization of undoped multiple quantum well structures
Authors: Misra R. , Strong R. , Greve D. W. , Schlesinger T. E.
Published: July 2002

GexSi1−x/Si multiple quantum well structures with varying germanium fraction and well thickness have been grown by ultrahigh vacuum chemical vapor deposition. Photoluminescence, electroluminescence, and photoconductivity measurements have been performed. The no phonon bound exciton recombination line together with phonon replicas are observed in all samples except two with thicker wells. In those samples, only silicon dislocation lines are observed rather than the broad single peak frequently observed in solid-source molecular beam epitaxy grown material. The results are contrasted with previous photoluminescence and electroluminescence studies.
Real-time flux monitoring and feedback control of a valved arsenic source
Authors: Mattord T. J. , Sadra K. , Srinivasan A. , Tang A. , Block T. R. , Shih Y. C. Albert , Neikirk D. P. , Streetman B. G.
Published: July 2002

The design and operation of a valved arsenic source equipped with a real-time flux monitoring apparatus is reported. The ability to monitor the source output during growth is convenient. Furthermore, it allows for feedback control of the flux. In most cases, the feedback mechanism can maintain a constant flux to better than ±1%.
Room temperature photoluminescence from modulation doped AlGaAs/InGaAs/GaAs quantum wells
Authors: Svensson Stefan P. , Gill D. M. , Towner F. J. , Uppal P. N.
Published: July 2002

The photoluminescence (PL) spectral shape and position from single, modulation doped, and undoped AlGaAs/InGaAs/GaAs quantum wells have been studied at room temperature (RT) with the purpose of evaluating the usefulness of the PL technique for verifying device material structures. Starting with a general expression for the line shape, we can qualitatively predict the spectral shape and position by evaluation of the squared overlap integrals of the four possible transitions between the two lowest states in the valence and conduction band wells. A self-consistent calculation is used to determine the equilibrium wave functions and the energies of the bound states in the quantum well. Good agreement is found between the experimental and theoretical peak positions, and the Stark shift in the low-energy spectral onset between doped and undoped structures also can be closely reproduced. The accuracy of the calculations has been verified by comparing structures with varying layer widths and constant In composition, and vice versa. We demonstrate that the doping-induced electric field in the quantum well strongly affects the spectral shape of the PL signal. In fact, the dominant transition is typically from the first excited conduction band state to the valence band ground state. A sensitivity analysis restricted to the square of the overlap integrals and the peak wavelengths shows that changes in the quantum well parameters induced by changing the Ga and In fluxes can be separated for InGaAs mole fractions typically used in devices. This has also been verified by experiment.
Normal and lateral forces in scanning force microscopy
Authors: Ascoli C. , Dinelli F. , Frediani C. , Petracchi D. , Salerno M. , Labardi M. , Allegrini M. , Fuso F.
Published: July 2002

With an atomic force/friction force microscope operating in the constant force mode and with an optical lever technique as a deflection sensor, we have investigated the total force acting on the cantilever tip during the raster scanning of the sample surface. A model including the normal and lateral components of the force has been worked out. The normal force is related to the cantilever loading. The lateral force has two components, dissipative and nondissipative, having opposite symmetry with respect to the scanning direction. Within our model, the nondissipative component, which is related to the topography, can be distinguished from the friction component in two different ways, both leading to ‘‘pure friction’’ images. The first method is based on the comparison of two images acquired in the forward and backward scanning direction, respectively. The second method is based on the comparison of the topographic and lateral force images acquired in the same scanning direction. This latter way does not need correction for the nonlinear behavior of the piezoelectric transducer. Results from various samples are reported.
Photoluminescence of molecular beam epitaxial grown Al0.48In0.52As
Authors: Ferguson I. T. , Cheng T. S. , Torres C. M. Sotomayor , Murray R.
Published: July 2002

This article provides an in-depth study of the photoluminescence (PL) and photoluminescence excitation (PLE) from Al0.48In0.52As grown by molecular beam epitaxy that exhibits linewidths of ∼17 meV, comparable with the best reported to date. When the sample temperature is increased from 2 K the emission energy exhibits an inverted S-shape dependence and this is normally associated with exciton localization. It is suggested that this anomalous temperature dependence occurs because the emission is a convolution of more than one transition from 35 K to 65 K. The 2 K emission intensity quenches with an activation energy of 17.5±2.5 meV. A similar difference in energy of 17–20 meV is also observed between the PL and PLE spectrum and this has been explained by alloy fluctuations and a localization of the exciton. It is suggested that due to the close proximity of the Γ–X crossover that non-Γ contributions to the donor binding energy cannot be dismissed. The large luminescence linewidth observed in Al0.48In0.52As compared to other ternary alloys cannot be attributed to alloy scattering alone. If non-Γ contributions to the donor binding energy are present excitons will be more localized sensing any local fluctuations in the alloy composition. However, we have demonstrated the difficulties in proving any direct correspondence between the luminescence linewidth and clustered regions. The emission from Al0.48In0.52As may not be excitonic as it could also be attributed to a neutral donor to free hole transition (D°,h). Band-edge emission is not observed in the luminescence spectrum until the sample temperature reaches ∼100 K.
Etched profile distortions in high density electron cyclotron resonance plasma
Authors: Yoneda Masahiro , Maruyama Takahiro , Fujiwara Nobuo
Published: July 2002

Recent studies of electron cyclotron resonance plasma etching for fabricating the gate electrode of metal-oxide-semiconductor large-scale integrated circuits indicate a serious problem in the etched profiles. The problem is a local pattern distortion caused by a charge buildup of the patterns. We report basic investigations of the etched profiles and propose the model for local side etch. Plasma parameters are measured by the electrostatic probes. The relationships between the local pattern distortion and the plasma properties are investigated. Lowering the electron temperature perpendicular to the surface normal is one of the most effective techniques for eliminating the local side etch. Lowering the electron temperature is enhanced by setting the wafer at the lower magnetic field. As the large space charge bends the ion trajectories, the lower ion current density is also effective to reduce the local side etch. The smoothly decreasing distribution of plasma potential which accelerates the ions can reduce the local side etch in spite of the higher current density.
Magnetically confined plasma reactive ion etching of GaAs/AlGaAs/AlAs quantum nanostructures
Authors: Song Y. P. , Wang P. D. , Sotomayor Torres C. M. , Wilkinson C. D. W.
Published: July 2002

An electron cyclotron resonance reactive ion etching machine has been successfully run under low magnetic field conditions. We call this the magnetically confined plasma condition. Under this condition, a new process using SiCl4 with a small amount of O2 has been developed for etching nanometer scale structures on GaAs, AlGaAs, and AlAs multilayer materials. The effects of the percentage of O2, the rf power, the microwave power, and the flow rate are described. 100 nm quantum dots have been etched on multiple quantum well materials to a depth of about 1 μm. Vertical and smooth sidewalls were obtained on these nanostructures. Poly-methylmethacrylate (PMMA) electron beam resist can be used directly as a dry etch mask, and the selectivity between GaAs and PMMA can be as high as 28:1. Raman spectroscopic studies showed that the process induced no detectable damage to the surface for an etch depth of 130 nm and only very little damage for deeper etching.
Reaction between diamond and titanium for ohmic contact and metallization adhesion layers
Authors: Viljoen P. E. , Lambers E. S. , Holloway P. H.
Published: July 2002

The reaction of sputter deposited layers of Ti on the (001) surface of a synthetically grown single crystal type IIb boron doped diamond has been investigated using Auger electron spectroscopy with depth profiling, Rutherford backscattering spectroscopy (RBS) and Raman spectroscopy. Electrical characteristics of the contacts were measured using I–V data and separated from substrate electrical effects using Hall measurements of the carrier concentration and mobility. Heat treatments above 425 °C were found necessary to cause the transition from a rectifying to an ohmic contact. Without a protective 150 nm layer of Au, oxidation of the Ti layer was observed at T≥425 °C, even for annealing in forming gas. This was detrimental to the adhesion of the layer and the long term stability of the ohmic contact resistance. With a protective Au film, low resistance, adherent ohmic contacts were observed even after 1 h at 750 °C, even though Ti diffused along Au grain boundaries to form nodules of TiO2 at the Au/ambient interface. Interfacial carbides were detected by both Auger peak shape changes and RBS measurements for annealing temperatures as low as 500 °C, and their appearance correlated with the transition to ohmic contacts. The carbides increased in thickness to about 50 nm after 1 h at 750 °C.
Fabrication of nanostructures in AlGaSb/InAs using electron-beam lithography and chemically assisted ion-beam etching
Authors: Arafa M. , Youtsey C. , Grundbacher R. , Adesida I. , Klem J.
Published: July 2002

Electron-beam patterned wires in InAs/AlGaSb heterostructures were fabricated using chemically assisted ion-beam etching (CAIBE) with Cl2 and an Ar ion beam. The CAIBE process yielded very vertical sidewalls and smooth wire edges. CAIBE was also used to etch deep trenches through the AlGaSb barrier layer which provided isolation for the wires and suppressed the parallel conductance of the AlGaSb barrier. The interdevice leakage current was also decreased by a final CAIBE device isolation step. Wires 1 μm long and having varying widths between 70 and 210 nm have been fabricated.
Atomic structure of Bi on the Si(111) surface
Authors: Bakhtizin R. Z. , Park Ch. , Hashizume T. , Sakurai T.
Published: July 2002

Bi-induced (√3×√3)R30° structures formed on the Si(111) surface are studied using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Three distinct phases are identified depending on the Bi coverage: monomer, trimer, and honeycomb phases. The √3×√3 symmetry is preserved for these phases in the LEED observation. At low coverages, Bi atoms are found to occupy the T4 site. In this adsorption geometry, the monomer phase (α phase) is formed stably up to the ideal coverage of 1/3 ML (ML=monolayer). In the trimer phase (β phase) at the saturation coverage of 1 ML, the individual atoms of the Bi clusters are clearly resolved. Between these two coverages, however, a honeycomb-type √3×√3 reconstruction has also been found by the STM to coexist with the trimer phase. This result reveals a new coverage dependent reconstruction process involving the √3×√3 reconstruction of the Si(111) surface.
Atomic force microscope for chemical sensing
Authors: Nakagawa Tohru , Ogawa Kazufumi , Kurumizawa Toshimitsu
Published: July 2002

A novel atomic force microscope (AFM) having a tip on whose surface sensor molecules were immobilized has been developed for chemical sensing. The AFM tips chemically modified with octadecyltrichlorosilane [CH3(CH)17SiCl3; OTS] or perfluorotrichlorosilane [CF3(CF2)7C2H4SiCl3; FS-17] were more sensitive than the unmodified tips in detecting adhesive force on some monolayers on the silicon substrates. Using OTS modified tip, the hydrocarbon chain length of chemically adsorbed alkyltrichlorosilanes [CH3(CH)nSiCl3, n=1,8,13,17] on the silicon substrates was discriminated in ethanol environment. The origin of the interaction between the chemically modified tips and the sample surfaces, which depend on the monolayers and environmental liquids where the interactions were measured, has been speculated to arise from the entwining of carbon chains in monolayers on the tip and the sample.
X-ray photoelectron spectroscopy and atomic force microscopy surface study of GaAs(100) cleaning procedures
Authors: Song Z. , Shogen S. , Kawasaki M. , Suemune I.
Published: July 2002

The chemical composition of GaAs(100) surfaces after HCl/H2O wet etching sequences has been examined with x-ray photoelectron spectroscopy (XPS). XPS measurements show that oxides and chlorides are removed from the GaAs surface by the HCl solution etching in 10–20 min and subsequent H2O rinse in several seconds. The surface of the GaAs substrate thus prepared has been examined with atomic force microscopy. The surface flatness is so improved by the HCl/H2O treatment that the surface undulation remains within a ±1 monolayer fluctuation over a 1×1 μm surface area.
High rate electron cyclotron resonance etching of GaN, InN, and AlN
Authors: Shul R. J. , Howard A. J. , Pearton S. J. , Abernathy C. R. , Vartuli C. B. , Barnes P. A. , Bozack M. J.
Published: July 2002

Electron cyclotron resonance etch rates of GaN, InN, and AlN are reported as a function of pressure, microwave power, and radio-frequency (rf) power in a Cl2/H2/CH4/Ar plasma at 170 °C. The etch rates for GaN and InN increase as a function of rf power. At 275 W, the etch rates reach maximum values of 2850 and 3840 Å/min, respectively. These are the highest etch rates reported for these materials. As a function of pressure, the etch rates reach a maximum value at 2 mTorr and then decrease as the pressure is increased to 10 mTorr. The GaN and AlN etch rates increase less than a factor of 2 as the microwave power is increased from 125 to 850 W whereas the InN etch rate increases by more than a factor of 3.5. The maximum etch rate for AlN obtained in this study is 1245 Å/min at a microwave power of 850 W, 1 mTorr pressure, and 225 W rf power. Atomic force microscopy is used to determine root-mean-square roughness as a function of etch conditions for GaN and InN and, while very smooth pattern transfer can be obtained for a wide range of plasma conditions for GaN, the smoothness of the etched InN surface is more sensitive to rf power, microwave power, and process pressure. The surface composition of the GaN is characterized using Auger spectroscopy and has shown that the Ga:N ratio increases with increasing rf power or microwave power.
Etching of GaAs/AlGaAs rib waveguide structures using BCl3/Cl2/N2/Ar electron cyclotron resonance
Authors: Constantine C. , Shul R. J. , Sullivan C. T. , Snipes M. B. , McClellan G. B. , Hafich M. , Fuller C. T. , Mileham J. R. , Pearton S. J.
Published: July 2002

An anisotropic nonselective etch for GaAs/AlGaAs rib waveguides has been developed for use under electron cyclotron resonance conditions. The plasma chemistry features BCl3 to minimize AlGaAs oxidation effects and small additions of N2 to induce sidewall protection when using photoresist masks. The fundamental mode attenuation in GaAs/AlGaAs waveguides is sensitive to the choice of both plasma chemistry and masking material, but can be reduced to ≤1 dB cm−1 for channel widths of 4–5 μm.
High-brightness II–VI light-emitting diodes grown by molecular-beam epitaxy on ZnSe substrates
Authors: Yu Z. , Eason D. B. , Boney C. , Ren J. , Hughes W. C. , Rowland W. H. , Cook J. W. , Schetzina J. F. , Cantwell G. , Harsch W. C.
Published: July 2002

High-brightness blue and green light-emitting diodes (LEDs) based on II–VI double heterostructures (DHs) have been successfully grown by molecular-beam epitaxy (MBE) on (100) ZnSe substrates. These LED structures consist of a 500–1000 Å thick active region of undoped blue-emitting Zn0.9Cd0.1Se/ZnSe multiple quantum wells or a green-emitting ZnTe0.1Se0.9 single quantum well sandwiched between a 2–3 μm thick n-type ZnSe:Cl layer and a ∼1 μm thick p-type ZnSe:N layer. Operated at 10 mA (3.0 V), the blue LEDs produce 327 μW of light output sharply peaked at 489 nm, corresponding to an external quantum efficiency of 1.3%. The green LEDs generate 1.3 mW of light peaked at 512 nm with a corresponding external quantum efficiency of 5.3%. In terms of photometric units, the luminous efficiencies for these II–VI blue and green LEDs are 1.7 and 18.0 lm/W, respectively.
Yellow (5735 Å) emission GaInP multiple quantum well lasers grown by gas source molecular-beam epitaxy
Authors: Chen A. C. , Moy A. M. , Cheng K. Y.
Published: July 2002

We report current injected stimulated emission in AlGaInP/Ga0.65In0.35P heterostructures grown on commercially available GaAs0.6P0.4 substrates by gas source molecular-beam epitaxy. Room temperature photoluminescence of bulk GaInP grown on these substrates exhibited a full-width half-maximum of 36 meV, which is equal to the narrowest reported. At 77 K laser devices exhibited yellow stimulated emission near 5735 Å with a current density of 900A/cm2.
Patterning accuracy improvement of the electron beam direct writing system EX-8D
Authors: Yoshikawa R. , Hattori K. , Wada H. , Magoshi S. , Sunaoshi H. , Ando A. , Yamaguchi T. , Mikami S. , Nishimura S. , Housai H. , Hashimoto S. , Takigawa T.
Published: July 2002

To improve patterning accuracy, a feedback compensation technique for the magnetic field was applied to EX-8D. The beam position deviation induced by low-frequency ambient magnetic field changes and 50 Hz magnetic interference has been minimized by using a feedback system for the interference source signals. As the result of the feedback technique and magnetic shielding applied to EX-8D, the subfield position deviation measured on written patterns has been improved to be 22 nm as a 3σ value without room shielding. The main deflection calibration method was also improved by utilizing an axially displaceable mark together with a fixed-height mark. On the fixed mark, the main deflection coefficients were determined with no concern to height sensor outputs. Height-dependent coefficients were then calibrated by evaluating the field size for various heights using the axially displaceable mark. The calibration accuracy was estimated to be 9.7 nm at the main field edge. It was also confirmed that height-dependent coefficients would be calibrated accurately enough by the use of a piezodriven mark. As a result, a stripe stitching error of less than 30 nm has been obtained.
Three-dimensional modeling of low-dose BF+2 implantation into single-crystalline silicon
Authors: Murthy C. S. , Posselt M. , Frei Th.
Published: July 2002

Three-dimensional (3D) simulations of 15 keV BF+2 implantation into (100) Si for an ion dose of 1×1013 cm−2 are performed using the binary collision code Crystal-TRIM. At this relatively low dose, damage accumulation during ion bombardment can be neglected. For a given area at the target surface irradiated by the ion beam and impenetrable masks, 3D range distributions can therefore be calculated by the superposition of ‘‘point response’’ profiles. The influence of channeling effects on the 3D boron range distribution in channeling and tilt-angle implantations are studied in detail. In addition to the simulation of 3D profiles, the depth distributions of boron and fluorine are compared with recently published experimental data.
High voltage electron beam nanolithography on WO3
Authors: Carcenac F. , Vieu C. , Haghiri-Gosnet A. M. , Simon G. , Mejias M. , Launois H.
Published: July 2002

High voltage electron beam lithography experiments on thin films of tungsten trioxide are reported. For linear doses around 10 mC/cm at 200 kV, a negative resist behavior is observed after development in a NaOH solution. Features with dimensions as low as 15 nm with aspect ratios up to 10, exhibiting weak size fluctuations and vertical sidewalls are routinely achieved. Proximity effects are found to be negligible allowing the fabrication of structures with less than 10 nm separation. The exposure mechanism is investigated by transmission electron microscopy and diffraction. A crystallization process induced by the electron bombardment is clearly evidenced. A model based on the amorphous to crystalline phase transition induced by electron irradiation is proposed to account for the experimental observations.
Spatial distribution of the electric field for field emission microtriodes
Authors: Nicolaescu Dan
Published: July 2002

The spatial distribution of the electric field on the emitter is studied for field emission microtriodes (FEMTs). An analytical three-dimensional FEMT model is used to show that the electric field on the emitter as a function of the angular position E(φ) can be written as a sum of an anode field term Ea(φ) and a gate field term Eg(φ). The anode term has a maximal value located on the emitter apex. When the gate is placed far away from the emitter, both terms Eg(φ) and Ea(φ) have maxima on the emitter apex. When the emitter-gate distance is small, Eg(φ) has a lateral maximum. The resulting field distribution E(φ) depends on the relative magnitude of the anode/gate voltages and the geometry of the system. These features are further studied considering a three-dimensional FEMT numerical model. The model involves an emitter with conical body and spherical tip and a plane gate. The emission current is obtained using the standard Fowler–Nordheim relationship and integrating the current density over the emitter surface. The anode Ia and gate Ig currents are computed ignoring space charge effects and assuming that each electron follows between the emitter and the gate a straight line trajectory normal to the tip surface. The spatial field distribution E(φ) and the current ratio Ia/Ig are outlined as functions of model parameters. For usual FEMT structures, with large emitter-gate distances, the field distribution E(φ) has a maximum on the emitter apex and decreases sharply for lateral positions.
Patterned eutectic bonding with Al/Ge thin films for microelectromechanical systems
Authors: Vu Bao , Zavracky Paul M.
Published: July 2002

In this article, we report our results using the aluminum/germanium eutectic to create high quality patterned bonds between two silicon dice. The bonds are formed using thin metal layers and with essentially no pressure applied. We have measured bond strength by fabricating and bonding patterned dice. Pull tests were conducted and the force required to separate the bonds was measured and found to be about 1.6×107 Pa. When bonds break, portions of the substrate are removed. Testing of the hermiticity of the bond demonstrated that leak rates below the detection limit of the leak tester (10−9 sccs) are possible.
A proposal for maskless, zone-plate-array nanolithography
Authors: Smith Henry I.
Published: July 2002

We propose a novel form of x-ray projection lithography that: (1) requires no mask, and hence can be considered an x-ray pattern generator; (2) is, in principle, capable of reaching the limits of the lithographic process. The new scheme utilizes an array of Fresnel zone plates, and matrix-addressed micromechanical shutters to turn individual x-ray beamlets on or off in response to commands from a control computer. Zone plate resolution is approximately equal to the minimum zone width, which can approach 10 nm. Zone plates are narrow-band lensing elements: For a diffraction limited focus, the source bandwidth Δλ/λ should be less than or equal to the reciprocal of the number of zones N. An undulator having Nu magnetic sections emits collimated radiation in a bandwidth Δλ/λ=1/Nu. Nu is usually in the range 35–100. We present a system design based on 25 nm lithographic resolution using λ=4.5 nm. For N=100 the zone-plate diameter is 10 μm. Each zone plate of the array would be responsible only for exposure within its ‘‘unit cell.’’ To fill in a full pattern, the stage holding the sample would be scanned in X and Y while the beamlets are multiplexed on and off. A microundulator designed for installation on a commercial compact synchrotron can provide 87 mW within a 2% bandwidth around 4.5 nm in a divergence cone of 0.28 mrad. The calculated efficiency of first-order focus for a zone plate operating at 4.5 nm is 31%, using 130 nm of spent U as the absorber/phase shifter. An exposure rate of ∼1 cm2/s at 25 nm resolution appears feasible.
Simultaneous optical detection techniques, interferometry, and optical beam deflection for dynamic mode control of scanning force microscopy
Authors: Hoummady M. , Farnault E. , Yahiro T. , Kawakatsu H.
Published: July 2002

In dynamic mode control of scanning force microscopy (SFM), optical beam deflection and interferometry are the techniques most used for detection of force gradients by means of a tip and a microcantilever that usually vibrates at the first resonant mode. In order to increase the sensitivity of these kinds of microscopes, one possible means is to investigate the potential of the highest resonance modes which allow an increase in the operating frequencies. For these two detection techniques, according to the local displacement slope, care must be taken in the choice of an appropriate microcantilever point where the laser beam is focused. In this article, an original technique based on simultaneous detection, interferometry, and the beam deflection method is introduced. These techniques are able to characterize within two degrees of freedom, normal displacement and angular deflection, thus resonating the SFM cantilever.
Wire-channel and wrap-around-gate metal–oxide–semiconductor field-effect transistors with a significant reduction of short channel effects
Authors: Leobandung Effendi , Gu Jian , Guo Lingjie , Chou Stephen Y.
Published: July 2002

Metal–oxide–semiconductor field-effect transistors (MOSFETs) with a wire-channel and wrap-around-gate (WW) structure were fabricated using electron beam lithography and reactive ion etching. The smallest devices have a 35 nm channel width, a 50 nm channel thickness, and a 70 nm channel length. Measurements showed that as the channel width of WW MOSFETs decreased from 75 to 35 nm short channel effects were significantly reduced: the subthreshold slope decreased from 356 to 80 mV/dec and the drain-induced barrier lowering decreased from 988 to 129 mV. Furthermore, the reduction of channel width increases the drive current per unit channel width. A multichannel WW MOSFET with a high current driving capability is discussed.