bluuebunny/crossref_metadata_2025 huggingface dataset:
Helium sticking coefficient on cryopanels coated by activated carbon
Authors: Özdemir I. , Perinic D.
Published: July 2002

In the International Thermonuclear Experimental Reactor the plasma exhaust gas contains hydrogen isotopes, helium and impurities which can be pumped off by means of cryopumps. Within the European Fusion Technology Programme, the Karlsruhe Research Center has been charged with the development of cryosorption panels for such pumps. For this purpose, various material combinations (sorbent/bonding/substrate) have been selected by small-scale experiments. A sorbent coating technique was developed which enables uniform and reproducible coating of large panels using activated carbon panels which have been manufactured with coated layer (bonding+sorbent) thicknesses between 0.1 and 3 mm. Three selected circular, plane cryopanels of 43 cm diam coated by different types of activated carbon bonded to metal by inorganic cement were tested at the TITAN cryopump. The measurements have been performed in the two-stage (copumping) as well as three-stage (compound pumping) cryopump configurations. The helium sticking coefficient was determined as a function of gas load and panel temperature. A maximum helium sticking coefficient of 0.25 was determined for copumping and of 0.51 for compound pumping modes. The helium sticking coefficient is higher than 0.1 in the copumping mode up to a gas load of 0.6 mbar l/cm2 and in the compound pumping mode up to a gas load of 5 mbar l/cm2.
Ballistic electron emission microscopy studies on Au/CaF2/n-Si(111) heterostructures
Authors: Sumiya Touru , Miura Tadao , Tanaka Shun-ichiro
Published: July 2002

Electron transport phenomena across Au/CaF2/n-Si (111) heterostructures, in which calcium fluoride (CaF2) [about two monolayers (ML)] was introduced into the interface at room temperature (RT), 550 °C, and 700 °C, have been studied by ballistic electron emission microscopy (BEEM) and ballistic electron emission spectroscopy (BEES). Not only the Au growth but also the electron transport properties strongly depend upon the growth temperatures of CaF2 intralayers. In the case of CaF2 growth at RT, CaF2 molecules will exist on the surface of the 50 ML Au/2 ML CaF2(RT)/n-Si (111) sample. BEES clearly shows that the Schottky barrier of the intermixed layer on Si (111) is about 1.06 V which is higher than the value of 0.73 V for Au/Si (111). At 550 and 700 °C, thin, flat Au islands, each about 0.15 nm thick, grow in stacks on the CaF2 layer. The threshold voltage of the BEEM current for an insulating CaF2 intralayer, which is about 3.58 V, is obtained only in the sample in which CaF2 was deposited at 700 °C. Furthermore, it was found that an inhomogeneous coverage of CaF2 exists on the sample. By using the CaF2 intralayer formed at 700 °C, we modified the electronic potential barrier on the nanometer scale.
Mapping local susceptibility using a scanning coaxial write/read head
Authors: Ström Valter , Rao K. V.
Published: July 2002

A technique to study local susceptibility of magnetic material is introduced. We describe a unique probe based on a pair of write/read heads, to measure and model both the susceptibility components at any point on a surface. With this approach it is possible to map the strength and direction of the local in-plane uniaxial susceptibility at surfaces. The usefulness of our technique is validated by measurements on oriented γ-Fe2O3 in a credit card. In addition, we present studies on an amorphous soft ferromagnet containing different defect structures to reveal the micromagnetic structural details around defects on a surface. Our approach has the distinct advantage of determining the local susceptibility and anisotropy on a length scale not possible by using other techniques available today.
Collision cell containment of dense gas targets for high vacuum applications
Authors: Ketsdever Andrew D. , Muntz E. P.
Published: July 2002

The efficient containment of molecular and atomic target gases within a geometrically augmented, inertially tethered collision cell was studied. The collision cell incorporates opposed containment jets whose gas flows act as collisional barriers to the escape of a relatively dense target gas in the central region of the cell. For molecular nitrogen and argon gas flows, gains of a factor of 10 have been observed in reducing target gas loss to the high vacuum system over conventional collision cells. Target gas pressures on the order of tens of mT have been contained within the collision cell with acceptable loss to the high vacuum system. Pressure probe measurements have been used to determine the most efficient placement of the containment jet sources with respect to the openings in the collision cell for molecular nitrogen and argon gas containment.
Rapid thermal annealing of reactive sputtered tantalum oxide films on GaAs in N2O atmosphere
Authors: Eftekhari G.
Published: July 2002

The electrical properties of composite oxide (anodized oxide and tantalum oxide deposited by reactive sputtering) on GaAs annealed in N2O were studied. The leakage current was decreased and at moderate electric field strengths it is governed by Schottky emission. The breakdown electric field of the samples and the dielectric constant of tantalum oxide were increased after annealing.
Selective SiO2-to-Si3N4 etching in inductively coupled fluorocarbon plasmas: Angular dependence of SiO2 and Si3N4 etching rates
Authors: Schaepkens Marc , Oehrlein Gottlieb S. , Hedlund Christer , Jonsson Lars B. , Blom Hans-Olof
Published: July 2002

In the fabrication of microstructures in SiO2, etch selectivity of SiO2 to masking, etch stop, and underlayer materials need to be maintained at corners and inclined surfaces. The angular dependence of the SiO2-to-Si3N4 etch selectivity mechanism in a high density fluorocarbon plasma has been studied using V-groove structures. The SiO2 etch rate on 54.7° inclined surfaces is lower than on flat surfaces, while the SiO2 etch yield (atoms/ion) is a factor of 1.33 higher. The results are consistent with a chemical sputtering mechanism. The Si3N4 etch yield is greater by a factor of 2.8 for 54.7° inclined surfaces than for flat surfaces. This large enhancement is explained by a fluorocarbon surface passivation mechanism that controls Si3N4 etching. The fluorocarbon deposition is decreased at 54.7° whereas the fluorocarbon etching rate is increased at 54.7°. This produces a thinner steady-state fluorocarbon film on the inclined Si3N4 surface, and results in a large enhancement of the Si3N4 etch yield.
Optical properties of Ge:Sb:Te ternary alloys
Authors: Garcı́a-Garcı́a E. , Mendoza-Galván A. , Vorobiev Y. , Morales-Sánchez E. , González-Hernández J. , Martı́nez G. , Chao B. S.
Published: July 2002

The complex dielectric function of the three stoichiometric compositions GeSb4Te7, GeSb2Te4, and Ge2Sb2Te5 has been measured by spectroscopic ellipsometry in the energy range of 1.4–5.1 eV. Each composition was measured in the amorphous and in the two crystalline states, the metastable face-centered-cubic and the stable hexagonal phases. The complex dielectric function shows strong differences between the amorphous and the crystalline samples, these differences are responsible for the drastic contrast in the reflectivity spectra. The ellipsometric spectra are fitted with models which fulfilling the Kramers–Kronig relations. Thus the Forouhi–Bloomer model was used for the amorphous samples and the Lorentz harmonic oscillator model for the crystalline samples. The temperatures at which the phase transformations are achieved were determined by measuring the ac electrical resistance at 100 Hz while the samples were heated. The temperature derivative of the electrical conductivity shows two well defined peaks at critical temperatures where the phase transformation occurs as is revealed by the x-ray data.
Mechanical properties and residual stress in AlN/Al mixed films prepared by ion-beam-assisted deposition
Authors: Watanabe Yoshihisa , Uchiyama Shingo , Nakamura Yoshikazu , Li Chunlang , Sekino Tohru , Niihara Koichi
Published: July 2002

Mixed films composed of aluminum and aluminum nitride (AlN) were prepared on a silicon substrate by evaporation of aluminum and simultaneous irradiation with a nitrogen ion beam, ion-beam-assisted deposition, where the nitrogen ion beam current was changed so as to obtain different compositional films. The composition of the films and chemical states of aluminum and nitrogen were analyzed by x-ray photoelectron spectroscopy (XPS). Mechanical properties of the films were characterized by a nano-indentation method. Residual stresses in the films were evaluated by film curvature measured with an optical cantilever system. The XPS studies show that the chemical state of aluminum changes from metallic to nitride with increasing the ion beam current density during synthesis. The nano-indentation tests reveal that the film hardness increases and the recovery behavior changes from plastic to elastic as the ion beam current density increases. From both results, it is proposed that the films change from mainly metallic films of Al to ceramic films of AlN via the mixed states of Al and AlN. The residual stresses were found to be compressive and increase with increasing the ion beam current density. Furthermore, it is found that AlN films added by a small amount of Al show the similar hardness to crystalline AlN together with low residual stress.
Diagnostics by optical absorption of sputtered atom density in magnetron discharges
Authors: Dony M. F. , Dauchot J. P. , Wautelet M. , Hecq M. , Ricard A.
Published: July 2002

Densities of sputtered atoms in Ar rf magnetron discharges have been measured by optical absorption. The resonant and self-absorption methods have been used. The first one has given Al and Mg atom densities with an uncertainty of 40% and the second one the order of magnitude of Si atom densities. The Al atom densities are strongly decreasing from 93.7% Al alloy target: (1–5)×1011 cm−3–10.3% Al aluminosilicate glass: (1–2)×109 cm−3. The Si atom density is in the range (3–9)×1010 cm−3 in the aluminosilicate glasses. The Al and Si sputtered atom densities follow the sputtering yields of Al metal and Al, Si oxide targets.
Mechanical properties and residual stress in AlN films prepared by ion beam assisted deposition
Authors: Watanabe Yoshihisa , Kitazawa Nobuaki , Nakamura Yoshikazu , Li Chunliang , Sekino Tohru , Niihara Koichi
Published: July 2002

Aluminum nitride (AlN) thin films were prepared by the ion beam assisted deposition method. The effect of the nitrogen ion beam energy on mechanical properties and residual stresses was studied by changing the ion beam energy from 0.2 to 1.5 keV, resulting in a different film microstructure. Mechanical properties were examined by a nano-indentation method and residual stresses were evaluated from the film curvature measured by an optical cantilever system. All of the films were found to be in a compressive stress state, the value of the stress decreasing with the ion beam energy. It was also observed that the films became soft and plastic with increasing ion beam energy. To study the effect of thermal treatment on the relaxation of residual stresses, films prepared with the ion beam energies of 0.2 and 1.5 keV, which show a columnar and a granular structure, respectively, were annealed in nitrogen at 500 °C. It was found that the granular structure film is relaxed more easily than the columnar structure film.
Temperature dependence of the I–V characteristics of modulation-doped FETs
Authors: Valois A. J. , Robinson G. Y. , Lee K. , Shur M. S.
Published: July 2002

Both normally on and normally off modulation-doped FETs have been fabricated from MBE grown AlGaAs/GaAs heterojunction structures. The static I–V characteristics of recessed-gate FETs were measured over the temperature range 77–400 K. A large change in the threshold voltage Vt with temperature T was observed. The observed Vt(T) data are explained, in part, in terms of a simple model based on the temperature-dependent occupation of deep donor traps in the AlGaAs layer. The traps were characterized by different energies for emission and capture. The transient capacitance of large area modulation-doped Schottky diodes was also measured. The capacitance data is explained by the time-dependent occupation of the same donor traps. The value of the activation energy for carrier emission was estimated to be 450 mV while the donor level was found to be about 42 mV below the conduction band.
Formation of silicon nitride layers on crystalline silicon by ion implantation as revealed by internal friction and infrared transmission measurements
Authors: Ogale A. S. , Bhoraskar V. N. , Ghaisas S. V. , Godbole V. P. , Ogale S. B. , Raye B. S.
Published: July 2002

Structurally integrated silicon nitride layers have been formed on the surface of crystalline silicon, using the process of nitrogen ion implantation. The as-implanted as well as thermally regrown samples have been examined using a thin layer sensitive internal friction technique and infrared transmission measurements. The types of defects formed due to the implantation process and their activation energies have been obtained, along with the information regarding the recovery of the defective as-implanted state during thermal annealing. The internal friction apparatus used in the mechanical measurements on thin silicon reeds is based on the design of Berry et al., wherein one essentially looks for the damping of a resonant flexural mode of oscillation of the reed sample as a function of temperature in a vacuum of 10−6 Torr. This allows one to obtain the information regarding the defect induced anelasticity in thin crystalline samples at an atomic level. In the present case, we have identified defects having activation energies of 0.5 and 0.65 eV produced due to implantation and their transformation into another defect state of activation energy 0.8 eV during thermal treatment. It has been established that the ion-bombardment process leaves the silicon layers with a large percentage of self-interstitials in a strain field. The thermal annealing leads to a release of the structural strain and a development of the silicon–nitride phase. The possibility and importance of using the internal friction technique in studying the interface defects in metastable and modulated semiconductor structures are discussed.
Planarizing of phosphosilicate glass films on patterned silicon wafers
Authors: Johnson L. F. , Ingersoll K. A. , Dalton J. V.
Published: July 2002

Patterned silicon wafers covered with both flowed and nonflowed phosphosilicate glass films have been planarized by argon ion-beam etching. At the optimum planarizing angle of 50°, the nonflowed PSG surface, with 1 μm high topography, is transformed to a flat surface with maximum deviations from planarity of <500 Å. The technique should alleviate resolution, linewidth control, and metallization coverage problems in very large scale integrated circuit fabrication.
A new submicron ion probe system
Authors: Tsumagari T. , Ohiwa H. , Okutani T. , Noda T.
Published: July 2002

An ion optical system for use with EHD ion sources was designed using a cad program and constructed based on the design. This system is composed of six-cylinder electrodes of 10 mm diam where the two middle electrodes function as octopole deflectors. The design goal was to produce a submicron ion probe capable of scanning a 2×2 mm square field under the condition that ion beam energy, the energy spread and acceptance half-angle are 30 keV, 20 eV and 2 mrad, respectively. Preliminary experiments using an electron gun showed that the optical characteristics such as focusing voltage, deflection efficiency and deflection distortion were in good agreement with the results of computer simulation. Deflection characteristics using an EHD Ga ion source showed that an undeflected probe size of 1.5 μm in diameter increased only by 0.4 μm for 0.87 mm deflection even if no dynamic correction is made.
Reactive ion etching of GaAs using CCl2F2 and the effect of Ar addition
Authors: Chaplart J. , Fay B. , Linh Nuyen T.
Published: July 2002

GaAs etching rate performed by RIE in CCl2F2 gas has been shown to depend on many parameters: pressure, rf power and flow rate. Moreover addition of Ar in CCl2F2 has been found to increase the etch rate. This observation and the AES study of etched GaAs surfaces has led to the conclusion that volatile chloride species contribute to the etching mechanism, while fluoride species which are less volatile inhibit etching. Schottky diodes presenting an ideality factor of 1.02 have been fabricated on CCl2F2 etched GaAs surface.
Conventional novolak resists for storage ring x-ray lithography
Authors: Lane J. G. , Maldonado J. R. , Cleland A. N. , Haelbich R. P. , Silverman J. P. , Warlaumont J. M.
Published: July 2002

This paper describes the lithographic processing of several positive novolak-based resists exposed on the IBM x-ray lithography system at the Brookhaven National Laboratory 750 MeV storage ring. One of the advantages of the storage ring exposure system has been the ability to use resist development processes which are the same as the corresponding optical or e-beam processes. The exposure system and the x-ray mask used for resist evaluation are described elsewhere in this symposium. Determining the best process conditions requires consideration of mask contrast as well as the desired linewidth and profile control, particularly in the presence of topography. Data will be presented and compared with results obtained using other lithographic systems (i.e., e-beam and conventional source x-ray). In particular, the relationship of mask absorber thickness to process window will be presented using a simple model of the development process. Using the process window defined by this model, we have exposed test patterns and typical device patterns in 1 to 2 μm thick conventional positive novolak resists. Linewidth control data as a function of dose and development time were determined for one resist at doses in the 100–200 mJ/cm2 range and compared with corresponding results using electron beam exposure. The x-ray exposures compared favorably with the electron beam exposures in the dosage ranges considered.
Electron beam tool/resist interdependence
Authors: Eib Nicholas K. , Jones Fletcher
Published: July 2002

The contribution of an electron beam exposure tool to positive resist profiles has been investigated experimentally and with two- and three-dimensional modelling. Listed in decreasing importance are: spot placement error > beam defocus > beam tilt (trapezoidal energy distribution across and/or down the length of a line in the resist) > beam noise (variation of energy from spot to spot down the length of a resist line, as well as Gaussian noise within the same spot). These tool contributions to resist profile have been characterized in two resists: a linear PMMA derivative and a highly nonlinear novolac resist that exhibits a long induction time before developing.
Economics of processing thin-film solar cells
Authors: Russell T. W. F. , Baron B. N. , Rocheleau R. E.
Published: July 2002

The commercial-scale processing potential for photovoltaic devices based on polycrystalline and amorphous silicon thin films is evaluated by analyzing in detail the semiconductor deposition process for the following material layers: (CdZn)S/CuInSe2, CdS/CdTe, (CdZn)S/Cu2S, and amorphous silicon. The current status of both laboratory-scale and unit-operations-scale experiments is tabulated and the goals required for reasonable commercial-scale production detailed. The costs of manufacture are estimated and it is shown that all thin-film materials which have achieved 10% efficiency in the laboratory can be manufactured at a cost well below one dollar per watt, provided the manufacturing facilities can be designed to produce between 100 000 and 1 000 000 square meters per year. The critical thin-film research areas are identified for each of the materials listed above.
Insulated gate depletion mode and accumulation mode field effect transistors on InP fabricated by electron beam lithography
Authors: Scheps Richard
Published: July 2002

An electron-beam-lithography-compatible process for the fabrication of depletion mode and accumulation mode insulated gate field effect transisitors on InP has been developed and is reported in detail. The exposure system uses an unmodified scanning electron microscope interfaced with a minicomputer. Transistor gate length dimensions for the completed devices range from several microns to submicron, and the smallest gate length for the depletion mode device measures 0.25 μm. Device operation is presented and discussed, and device performance is shown to compare well with long gate devices made by optical lithography.
Angular dependence of etching yield of single crystal Si in Cl2 reactive ion beam etching
Authors: Krueger E. Eric , Ruoff Arthur L.
Published: July 2002

Reactive ion beam etching yield for lightly doped Si(100) using Cl2 gas in the ion source was measured as a function of current density and angle of incidence. Experiments were performed such that the ion flux delivered to the sample was held constant at each angle. At normal ion incidence etching yield decreased linearly with current density. With constant ion flux to the sample surface the yield remained constant from 0° to 70° angle of incidence.
Raman characterization of catalysts
Authors: Wokaun A. , Baiker A. , Fluhr W. , Meier M. , Miller S. K.
Published: July 2002

The use of surface-enhanced Raman scattering as a tool for the elucidation of reaction mechanisms in heterogeneous catalysis is investigated. Following a short survey of surface analytical techniques, the advantages of surface Raman spectroscopy are discussed. Submonolayer sensitivity is achieved by making use of the surface enhancement effect. Adsorption and desorption phenomena of amines, which are of importance for catalytic dehydroamination reactions on copper surfaces, are studied using enhanced Raman scattering. Two models for the bonding of the amine to the surface are tested, by comparing the surface spectra with those of model compounds. Experiments are carried out on copper foils roughened by chemical etching, which exhibit strong surface enhancement. The design of the substrates is guided by advances in modeling the electromagnetic enhancement contribution. In particular the influences of particle size and of dipolar interactions between the particles on a surface must be taken into account.
Binding energies of hydrogenic-impurity states in triangular quantum wells
Authors: Lee Johnson , Vassell M. O. , Spector Harold N.
Published: July 2002

We have calculated the binding energy of hydrogenic impurity states in a GaAs–GaAlAs heterojunction in which the electrons are confined in a triangular potential well formed by charge transfer from the GaAlAs side of the heterojunction to the GaAs side. The binding energy of the impurity is calculated as a function of the position of the impurity in the quantum well and as a function of the electric field which arises in the heterojunction because of the charge transfer. A variational method was used and screening effects were neglected. We find that the peak value of the binding energy of the hydrogenic impurity as a function of distance of the impurity from the boundary of the heterojunction increases with electric field and has a value in strong electric fields which exceeds that predicted for the confinement of hydrogenic impurities in a strictly two-dimensional quantum well. With increasing electric field, the location of that peak is found to move toward the heterojunction.
Electron beam prober for VLSI diagnosis
Authors: Furukawa Y. , Goto Y. , Ito A. , Ishizuka T. , Ozaki K. , Inagaki T.
Published: July 2002

An electron beam (EB) prober for VLSI internal diagnosis has been developed. The essential requirements for an EB prober are quantitative voltage measurement, waveform observation with high time resolution, and a diagnostic function for locating faults easily. The newly developed EB prober satisfies these requirements. It has an improved energy analyzer for quantitative voltage measurement, a stroboscopic function with 1 ns time resolution, and a unique diagnostic function wherein voltage images of LSIs are compared. This voltage image comparison provides easy detection of faulty areas by comparing voltage images of both faulty and normal LSIs. In this respect this EB prober is the first machine which considers locating faults easily in a large VLSI chip.
Pattern width of negative resists in x-ray lithography
Authors: Suzuki Yoshiki
Published: July 2002

In x-ray lithography with divergent x rays, the relationships between the fine line pattern widths of negative resists and exposure parameters were investigated in order to quantitatively analyze the factors to cause the deviations of pattern widths. It was demonstrated that the resist pattern width can be determined by an equation consisting of five variables; that is, pattern width of fine line on mask, size of effective penumbral shadow, mask contrast, resist contrast, and normalized resist thickness. It was confirmed that the theoretical resist pattern widths calculated with the equation agree well with the experimental results. The simulation method developed in this work could be effectively used to determine the exposure parameters in high resolution lithography with divergent x rays.
Growth and device characteristics of short wavelength GaAs multiple quantum well lasers
Authors: Woodbridge K. , Blood P. , Fletcher E. D. , Hulyer P. J.
Published: July 2002

There is widespread interest in the use of the quantum size effect to modify the operating wavelength of semiconductor lasers, particularly in the AlGaAs/GaAs system where there is the possibility of producing short wavelength devices suitable for optical information systems. High quality current injection quantum well lasers grown by molecular beam epitaxy (MBE) have been reported with well widths as thin as 60 Å producing emission down to about 820 nm. Further reductions in wavelength have only been achieved by the addition of Al to relatively wide wells in which the wavelength shortening due to the quantum size effect is small. In this paper we report on the growth and characteristics of AlGaAs/GaAs multiple quantum well (MQW) injection lasers with thin (≤55 Å) GaAs wells utilizing the quantum size effect alone to obtain emission in the visible region of the spectrum. Growth of these multiple layer structures was carried out in a laboratory designed MBE system with rapid automatic beam shuttering in order to obtain abrupt interfaces and good periodicity. High speed substrate rotation was used to ensure uniformity across the wafer. Accurate determination of well widths is essential for meaningful comparisons between calculated and measured wavelengths, especially when well widths are reduced to a few monolayers. The well widths were determined both from growth rate, calibrated by RHEED oscillations, and by electrochemical profiling of the cladding layers. The structures were processed into oxide stripe lasers to study 300 K emission wavelengths and threshold currents as a function of well width. Laser operation at 300 K has been obtained in all devices, and a device with 13 Å wells gave the shortest wavelength (704 nm) reported for an MQW injection device with GaAs wells. The 300 K emission spectra were compared with both the calculated n=1(e-hh) transition for each device and the wavelength of this transition obtained directly by photovoltage spectra on some devices. We have found that the lasing wavelength differs from both the calculated and measured n=1(e-hh) transition wavelengths by about 20 nm over the whole range of well widths studied. A strong dependence of threshold currents on number of wells has been observed.
A gate-controlled planar-doped barrier switch
Authors: Szubert J. M. , Singer K. E.
Published: July 2002

A three-terminal GaAs switch is demonstrated which utilizes the previously reported regenerative switching mechanism shown in a combined planar-doped barrier (PDB) and p-n junction. This latter, two-terminal switch relies on a mechanism by which holes injected into the PDB reduce the net charge in the p plane, and thus leads to a lowering of the barrier for electrons. The resultant increase in thermionic emission of electrons over the barrier in turn leads to more hole injection from the p-n junction. As bias is increased, a point is reached where the internal gain exceeds unity, the PDB collapses, and the device switches to its ‘‘on’’ state. The addition of a third terminal to the n region of the p-n junction allows hole injection within the PDB region to be controlled independently of the total bias across the device. This, in turn, enables the switching threshold voltage to be varied over the full operating range of the device. The device is also demonstrated to function as a reversible, gate-controlled switch. In many respects the characteristics of the switch resemble those of the metal-insulation silicon switch (MIS), but in this case the device is made entirely within the bulk of the semiconductor by MBE and does not rely on a tunneling oxide. The small dimensions in the direction of carrier transport should lead to fast switching speeds, and preliminary measurements have shown a switching-on transition time of 2 ns, and off times of around 10 ns. These times correspond closely to the measured capacitance and resistance of the device and should be capable of substantial improvement in a more optimized structure. The device has possible applications as a high-speed logic element.
PMIPK–azide dry-developable resist in electron beam lithography
Authors: Tsuda Minoru , Oikawa Setsuko , Yabuta Mitsuo , Yakota Akira , Nakane Hisashi , Yamashita Kazuhiro , Gamo Kenji , Namba Susumu
Published: July 2002

Dry development of fine resist patterns in e-beam lithography is described. The best resolution obtained is 100 nm in the monolayer process. The electron sattering effects are essential in the limitation of the resolution. The possible application of dry development in e-beam lithography which overcomes the backscattering limitations is a multilayer resist which gives 100-nm line and 200-nm space dry developed patterns by a conventional e-beam exposure apparatus.
Impurity effects in magnetron sputter deposited tungsten films
Authors: Wickersham C. E. , Poole J. E. , Palmer K. E.
Published: July 2002

This paper describes the effect of metallic and nonmetallic impurities on the electrical and metallurgical properties of tungsten films sputter deposited onto oxidized silicon wafers. Tungsten films, 200-nm-thick, sputter deposited using a 99.996% pure tungsten target and a deposition rate of 6 nm/s with a substrate temperature of 400 °C had an as-deposited resistivity of 13.5 μΩ cm. This value is within experimental error equal to the lowest values reported for electron-beam evaporated and chemical vapor deposited films. Metallic impurities in the target increase the electrical resistivity of the tungsten films. Use of a 99.98% pure (3N8) tungsten target under identical conditions as those reported above produced films with resistivities of 17.3 μΩ cm or a 28% increase in resistivity due to an increase of less than 160 ppmw in the concentration of metallic impurities. Intentional addition of iron and copper to the tungsten film increased the film resistivity by factors of 5 and 1 nΩ cm/ppmw of impurity, respectively. Air leak rate into the sputtering chamber was also evaluated and found to significantly affect tungsten film resistivity. An air leak rate of 0.001 25  Torr 1/s increased the film resistivity from 16 to 21.8 μΩ cm or an average rate of 4640 μΩ cm/(Torr 1/s).
High performance very large scale integrated photomask with a silicide film
Authors: Watakabe Y. , Matsuda S. , Shigetomi A. , Hirosue M. , Kato T. , Nakata H.
Published: July 2002

A molybdenum silicide (Mo-silicide) film deposited on a quartz glass substrate offers major advantages as a high performance photomask material for very large scale integrated (VLSI) fabrication. There is no pattern missing due to exfoliation after ultrasonic cleaning with frequency of 28 kHz and 300 W of power, and after being scrubbed over 10 cycles with a high pressure water jet. Reflectivity and optical density of the Mo-silicide film are not affected by acidic chemicals. Moreover, dry etching can be done at a rate of 50 nm/min; more than five times as fast as etching of a chromium (Cr) mask.
Dependence of minimum linewidth on electron-beam properties in submicron lithography using a rectangular beam
Authors: Okubo Tsuneo , Saito Kenichi , Takamoto Kiichi
Published: July 2002

The relation between beam properties and minimum linewidth for a rectangular electron beam for submicron lithography is obtained through experiments and electron scattering simulation. Patterns are exposed in a 0.5-μm-thick PMMA resist film on a silicon wafer. The result gives a guiding principle in designing an electron-optical column of a rectangular electron-beam exposure system. A minimum linewidth of 0.5 μm can be obtained using a beam with a beam edge width δ=0. 18 μm at a beam voltage Va=25 kV and 0.2-μm minimum linewidth using a beam with δ=0.08 μm at Va=30 kV.
Pulsed-laser atom-probe and field-ion microscope study of solid surfaces
Authors: Tsong T. T. , Liu H. M. , Gao Q. J. , Ren D. M. , Liou Y.
Published: July 2002

The atomic structure of a solid surface can be imaged with the field-ion microscope and the chemical species of surface atoms can be identified by time-of-flight atom probe. By incorporating a pulsed-laser technique to field-ion miscroscopy, atomic structures and atomic steps in a surface reconstruction can be studied with a spatial resolution of ∼2.5 Å and a time resolution of a few nanoseconds. The mass resolution and material applicability of a pulsed-laser atom probe are greatly improved, and it is also an ion energy analyzer of 5 parts in 105 accuracy and resolution, and an ion reaction and dissociation time analyzer of 20 fs time resolution. Some interesting phenomena such as formation of multiple charge cluster ions and dissociation of compound ions by atomic tunneling can be studied with excellent mass, energy, and time resolution for the first time.
Reactive interface formation—Pt/Si〈111〉: Nucleation and morphology
Authors: Nemanich R. J. , Doland C. M. , Ponce F. A.
Published: July 2002

The focus of the study is to determine how the initial interactions affect epitaxial-film formation for Pt deposited on Si〈111〉. The reactions at the interface of Pt and clean-Si〈111〉 surfaces are studied with in situ Auger, low-energy electron diffraction (LEED), and Raman spectroscopy. The epitaxial alignment is determined from high-resolution transmission electron microscopy (TEM). The results confirm that a disorder-intermixed phase precedes silicide formation. For relatively thick films (>3.0 nm) silicide nucleation is observed for substrate temperatures >200 °C. For deposition onto clean-Si〈111〉 at temperatures above the nucleation temperature, a critical thickness of Pt is observed for the formation of silicide clusters. This thickness is related to the critical stable clusters which become growth nuclei. The competition between formation of more nuclei and cluster growth is examined. Nucleation conditions for subcritical films are explored, and it is found that these conditions yield epitaxial alignment over large areas.
Behavior and characteristics of radiationally heated GaAs substrates
Authors: Hoke W. E. , Lyman P. S. , Labossier W. H.
Published: July 2002

Molybdenum substrate holders, which secure GaAs substrates without indium bonding, have been fabricated and tested. The holder design permits quick substrate loading and is compatible for reflection high-energy electron diffraction measurements. The substrate surface temperature is determined pyrometrically and the methodology is discussed in detail. The substrate temperature is stably controlled by regulating the substrate heater voltage as opposed to conventional thermocouple control. Using voltage regulation the temperature of the radiationally heated substrates can be rapidly changed with excellent control. The temperature uniformity for 2 in. diam substrates is ±5 °C at typical molecular-beam epitaxial growth temperatures. Quantitative differences caused by free-carrier absorption are observed in the heating behavior of undoped and N-type substrates. After epitaxial growth has been initiated, negligible substrate temperature droop is observed. The substrates exhibit insignificant backside erosion and wafer flatness is excellent for high resolution lithography.
Investigation of minority carrier retention behind AlAs barriers
Authors: Melloch M. R. , Cooper J. A. , Qian Q-D.
Published: July 2002

Using a transient capacitance–voltage technique we have investigated the dynamic storage of minority carrier holes at an AlAs/GaAs and a superlattice/GaAs interface. Results of hole retention, an avalanche technique for supplying minority carriers, and other characteristics of our devices will be presented.
Ultraviolet photoelectron spectroscopic studies of valence band structures in Si-doped GaAs grown by molecular-beam epitaxy
Authors: Fuwa K. , Osaka T. , Makita Y. , Ihara H. , Uda M.
Published: July 2002

The electronic structure of Si-doped GaAs layers grown by molecular-beam epitaxy was investigated by ultraviolet photoelectron spectroscopy (UPS). It was for the first time demonstrated where the intensities of the photoelectron energy distribution curves (EDC’s) for the conduction band increase with increasing Si dose, and become saturated at a certain critical Si dose where a specific peak appears at the energy corresponding to the acceptor level of Si–GaAs. The results indicate that Si atoms act as acceptors as well as donors at a high Si dose. An observation of an increasing inelastic peak height in the UPS spectrum with the Si dose also gave us an important piece of information on a degree of the crystallinity of Si–GaAs which was degraded with the Si dose.
Dopant diffusion from ion-implanted TaSi2 into Si
Authors: Gierisch H. , Neppl F. , Frenzel E. , Eichinger P. , Hieber K.
Published: July 2002

A secondary ion mass spectrometry analysis of As, B, and P diffusion across the TaSi2/Si interface into mono- and polycrystalline Si was carried out together with an electrical characterization of the resulting structures. In the temperature range 900≤T≤1000 °C, all three types of dopants readily diffused into Si without drastic segregation effects when appropriate interface cleaning was applied. This phenomenon implies a variety of applications in IC technology. In particular, very shallow diffusion regions were obtained in the mono Si underneath the implanted TaSi2 for As as well as for B and P, even at relatively long annealing times sometimes needed for subsequent process steps.
Simple calculation formulas for field and aberrations of resistance box yokes
Authors: Jiang Xinrong
Published: July 2002

Simple calculation formulas for the deflection field and aberrations of resistance box yokes are presented. The field distribution model of the yokes is the same as that of multipole electrostatic deflectors for which adjusting parameters are chosen appropriately. After being simplified, there are only nine integrals in 16 aberration coefficient formulas, and there are no second-order derivatives of the electric field on the optical axis. An approximate formula for the electric field on the optical axis is given. Thus the field distribution of the yokes can be expressed by an analytical function, and the computation of the aberration coefficients is simpler and more convenient.
Au–Zn–Si liquid-metal ion source emitting multiple p- and n-type ion species for compositional disordering of GaAs–AlGaAs multiquantum wells
Authors: Arimoto Hiroshi , Miyauchi Eizo , Furuya Akira , Ishida Koji , Takamori Takeshi , Nakashima Hisao , Hashimoto Hisao
Published: July 2002

We developed a new type of alloyed liquid-metal ion source (LMIS) for maskless ion implantation in III–V compound semiconductors. This ion source, consisting of alloys of Au65Zn11Si24 is capable of emitting Zn (p-type dopant) and Si (n-type dopant). The lifetime of this ion source was restricted to about 50 h due to a selective evaporation of Zn atoms from the liquid alloy surface. However, the vapor pressure of Zn in the alloy at 410 °C was estimated to be 2.3×10−3 Pa (1.7×10−5 Torr). This value is four orders of magnitude smaller than the elemental Zn. Using this ion source, intermixing of GaAs and AlGaAs layers was selectively performed in an undoped GaAs–AlGaAs multiquantum well structure by alternate implantation with 100-keV Zn and 80-keV Si focused ion beams. This disordering technique using focused p- and n-type ion beams offers the possibility of creating a variety of novel structure devices.
Degradation of poly(methylmethacrylate) by deep ultraviolet, x-ray, electron beam, and proton beam irradiations
Authors: Choi J. O. , Moore J. A. , Corelli J. C. , Silverman J. P. , Bakhru H.
Published: July 2002

The chemical changes in poly(methylmethacrylate) (PMMA) caused by irradiation with deep ultraviolet (UV), x-ray, electron, and proton beams were studied by gel permeation chromatography, Fourier-transform infrared, and UV spectroscopy. The quantitative analysis of spectroscopic changes (Beer’s law) demonstrated a 1:1 correspondence between the disappearance of ester groups and the generation of double bonds in the polymer chain by all types of radiation. The ratio of main chain scission to changes in the number of ester groups and unsaturated bonds was compared to determine the characteristics of degradation of PMMA by the different types of radiation. This ratio for deep UV data was very close to the quantum yield of main chain scission of PMMA as reported in the literature. High-energy radiation was ∼10× more efficient than deep UV in causing main chain scission with removal of fewer ester groups. Protons induced more main chain scission than electrons. X-ray irradiation was the most efficient at causing main chain scission of the four different types of radiation.
Optimization of the proximity parameters for the electron beam exposure of nanometer gate-length GaAs metal–semiconductor field effect transistors
Authors: Patrick W. , Vettiger P.
Published: July 2002

Proximity parameters are determined for the electron beam exposure of high-resolution poly(methylmethacrylate) resist for the particular application of defining submicron gate lengths for GaAs metal–semiconductor field effect transistor (MESFET) structures. A ring-shaped exposure cell is used to determine the various parameters of the popularly used double Gaussian approximation of the proximity function. The results are shown to be accurate for gate lengths in the range 0.1–0.5 μm. Using this technique for gate delineation, it is shown that very high performance GaAs MESFET devices and circuits can be achieved at sub-0.5-μm dimensions.
Electron beam fabrication of high-performance InGaAs/InAlAs heterojunction insulated gate field effect transistors with submicron refractory airbridge gates
Authors: Tennant D. M. , Shunk S. C. , Feuer M. D. , Kuo J-M. , Tell B. , Behringer R. E. , Chang T. Y.
Published: July 2002

Self-aligned heterojunction insulated gate field effect transistors devices with gate lengths as short as 0.125 μm (nominal) have been fabricated on molecular-beam epitaxially grown InAlAs/InGaAs/InP heterostructures using electron beam lithography. A bilevel resist comprising poly(methylmethacrylate) (PMMA) and P(MMA/MAA) is exposed in a 50-kV e-beam lithography system and is used to liftoff a removable etch mask material. Reactive ion etching is used to define a tungsten gate, followed by implantation of Si+ to form the self-aligned source and drain contact regions. Tungsten air bridges are formed during the mesa isolation step to provide the lowest gate leakage current and capacitance. Results from preliminary microwave electrical measurements are presented for devices with gate lengths as short as 0.25 μm.
Characterization of etching of silicon dioxide and photoresist in a fluorocarbon plasma
Authors: Karulkar Pramod C. , Wirzbicki Mark A.
Published: July 2002

Reactive ion etching of silicon dioxide and positive photoresist in CHF3–C2F6–O2–He plasma in a parallel-plate etcher is studied using the response surface experimental design procedure. The experimental results are reproducible within 5%. Analytical expression for the dependence of the etch rates on the plasma parameters (oxygen concentration, pressure, rf power) are obtained. Detailed contour maps of the behavior of the etch rates as functions of the plasma parameters are prepared from the analytic expressions. Calculated etch rates are within 10% of the measured value at a large number of points in the range of the parameters explored. Using the results of this study it has been possible to etch contact holes with a variety of sidewall slopes. Predictability of the etch rates from the analytical expressions for resist and silicon dioxide also provided great flexiblity while planarizing a dielectric over patterned aluminum and etching of vias in the planarized but unevenly thick dielectric.
Adsorption of cesium from sulphide solutions on II–VI compounds
Authors: Peisach M. , Rabe C. A. , Pineda C. A. , Mahalu D. , Tenne R.
Published: July 2002

The adsorption of cesium ions from aqueous sulphide solutions on semiconductors belonging to the II–VI family of compounds was investigated using Rutherford backscattering in the random and channeling direction, and proton-induced x-ray emission, with computer simulation of the spectra. Whereas CdSe and CdS are stable against surface exhange (in the dark) ZnSe is unstable in such solutions and extensive O/Se and S/Se exchange occurs after relatively short periods of immersion. Furthermore, while cesium ions are chemisorbed mostly on the semiconductor surface of CdSe and CdS with some penetration into the crystal matrix, extensive indiffusion of cesium occurs in ZnSe. These results may explain the difference in the behavior of these two kinds of materials in sulphide electrolyte under illumination. They can also explain the fact that in ZnSe the work function of the semiconductor does not vary appreciably upon immersion in cesium containing solution while for CdSe and CdS the work function decreases by 150–200 mV and consequently the open circuit potential increases by that amount in cesium sulphide solutions.
Silicon transport in sputter-deposited tantalum layers grown under ion bombardment
Authors: Gallais P. , Hantzpergue J. J. , Remy J. C. , Roptin D.
Published: July 2002

Tantalum was sputter deposited on (111) Si substrate under low-energy ion bombardment in order to study the effects of the ion energy on the silicon transport into the Ta layer. The Si substrate was heated up to 500 °C during growth. For ion energies up to 180 eV silicon is not transported into tantalum and the growth temperature has no effect. An ion bombardment energy of 280 eV enhances the transport of silicon throughout the tantalum layer. Growth temperatures up to 300 °C have no effect on the silicon transport which is mainly enhanced by the ion bombardment. For growth temperatures between 300 and 500 °C, the silicon transport is also enhanced by the thermal diffusion. The experimental depth distribution of silicon is similar to the theoretical depth distribution calculated for the case of an interdiffusion. The ion-enhanced process of silicon transport is characterized by an activation energy of 0.4 eV. Silicon into the layers as-grown at 500 °C is in both states, amorphous silicide and microcrystalline cubic silicon.