bluuebunny/crossref_metadata_2025 huggingface dataset:
Local Swirl Chamber Heat Transfer and Flow Structure at Different Reynolds Numbers
Authors: Hedlund C. R. , Ligrani P. M.
Published: July 2002

Local flow behavior and heat transfer results are presented from two swirl chambers, which model passages used to cool the leading edges of turbine blades in gas turbine engines. Flow results are obtained in an isothermal swirl chamber. Surface Nusselt number distributions are measured in a second swirl chamber (with a constant wall heat flux boundary condition) using infrared thermography in conjunction with thermocouples, energy balances, and in situ calibration procedures. In both cases, Reynolds numbers Re based on inlet duct characteristics range from 6000 to about 20,000. Bulk helical flow is produced in each chamber by two inlets, which are tangent to the swirl chamber circumference. Important changes to local and globally averaged surface Nusselt numbers, instantaneous flow structure from flow visualizations, and distributions of static pressure, total pressure, and circumferential velocity are observed throughout the swirl chambers as the Reynolds number increases. Of particular importance are increases of local surface Nusselt numbers (as well as ones globally averaged over the entire swirl chamber surface) with increasing Reynolds number. These are tied to increased advection, as well as important changes to vortex characteristics near the concave surfaces of the swirl chambers. Higher Re also give larger axial components of velocity, and increased turning of the flow from each inlet, which gives Go¨rtler vortex pair trajectories greater skewness as they are advected downstream of each inlet. [S0889-504X(00)00502-X]
Strip Yield Analysis of Plastic Zone Coalescence for Collinear Edge Crack and Internal Crack in a Semi-Infinite Sheet
Authors: Nishimura Toshihiko
Published: July 2002

The coalescence conditions of plastic zones are calculated for an edge crack and an internal crack in a semi-infinite sheet. The cracks and their plastic zones are treated as a fictitious crack, and integral equations are formulated on equilibrium of surface traction, no stress singularity at the crack tip, and zero crack face displacement at the coalesced point of plastic zones. The integral equations are iteratively solved, and critical values of remote stress, plastic zone sizes, and crack tip opening displacements are determined. Numerical results for an edge crack and an internal crack due to remote stress are presented. [S0094-9930(00)00301-2]
Welding Residual Stresses and Effects on Fracture in Pressure Vessel and Piping Components: A Millennium Review and Beyond
Authors: Dong P. , Brust F. W.
Published: July 2002

In this paper, the recent advances in weld residual stress modeling procedures are first reviewed within the context of pressure vessel and piping applications. A typical pipe girth weld was then used as an example to highlight some of the critical issues in weld residual stress prediction, measurement, and residual stress effects on various aspects of fracture behaviors from stress intensity factor solutions for a growing crack to crack-opening displacement calculations for leak-before-break assessment. Finally, the future needs in improved fracture mechanics procedures by incorporating the rapidly expanding knowledge on weld residual stresses are summarized with respect to pressure vessel and piping applications. [S0094-9930(00)02103-X]
Core Level and Valence Band XPS Spectra of E-120 Pitch-based Carbon Fiber Potentiostatically Oxidized in (NH4)2CO3 Solution
Authors: Xie Yaoming , Wang Tiejun , Sherwood Peter M. A.
Published: July 2002

Du Pont E-120 high modulus pitch-based carbon fiber was potentiostatically oxidized in (NH4)2CO3 solution and analyzed with both core level and valence band XPS. Compared to the untreated E-120 fiber, this electrochemically oxidized fiber had a much higher oxygen content on its surface. Nitrogen was also found on this carbon fiber sample after the treatment in (NH4)2CO3 solution, but no nitrogen was found either before or after the treatment in HNO3 solution. Our previously reported work [see Y. Xie and P. M. A. Sherwood, Chem. Mater. 1, 427 (1989); 2, 293 (1990); Appl. Spectrosc. 44, 797 (1990); Chem. Mater. 3, 164 (1991); Appl. Spectrosc. 44, 1621 (1990); 45, 1158 (1991); Y. Xie, T. Wang, O. Franklin, and P. M. A. Sherwood, ibid. 46, 645 (1992)] showed that XPS valence band spectra were more sensitive to chemical environment on the carbon fiber surface than core level spectra and could be well interpreted by X–α calculations with model compounds. In this work, the valence band spectrum shows that there were three different types of oxygen-containing functional groups formed on the fiber surface when the fiber was electrochemically oxidized in (NH4)2CO3 solution, but only one type of oxygen-containing functionality formed after the electrochemical treatment in HNO3 solution. We also reported [see Y. Xie and P. M. A. Sherwood, Appl. Spectrosc. 46, 1158 (1991)] that the reproducibility of the potentiostatic treatment was not as good as that of the galvanostatic treatment, although the results from potentiostatic oxidation and galvanostatic oxidation were very similar.
Relativistic corrections in displacement measuring interferometry
Authors: Heilmann Ralf K. , Konkola Paul T. , Chen Carl G. , Schattenburg Mark L.
Published: July 2002

Displacement measuring interferometry is based on measuring the Doppler frequency shift that a beam of radiation undergoes upon reflection off a mirror connected to a moving stage. Usually the velocity of the reflecting stage is very small compared to the speed of light and is therefore deduced using the classical expression for the Doppler shift. We calculate relativistic corrections to the Doppler frequency shift, considering arbitrary stage motion in two dimensions and multiple passes through the moving interferometer arm. Changes in optical path lengths due to the varying stage displacement are explicitly taken into account. For stage velocities on the order of only 1 m/s the resulting corrections to the classically derived stage displacement can amount to nanometers. We discuss model velocity profiles similar to those currently employed in industrial step-and-scan systems for integrated circuit manufacturing, and for recently proposed scanning-beam interference lithography schemes. Expected future increases in stage speed and wafer sizes will necessitate the inclusion of relativistic corrections to the Doppler shift to maintain pattern placement accuracy at the nanometer level.
Membrane-mask distortion correction: Analytical and experimental results
Authors: Murooka Ken-ichi , Lim Michael H. , Smith Henry I.
Published: July 2002

We describe a strategy for eliminating distortion in x-ray masks. Prior to patterning the x-ray absorber, the mask membrane is patterned with a shallow, fine-period fiducial grid, made by interference lithography. After patterning the absorber, the grid is measured using a holographic-phase-shifting interferometer (HPSI) to determine the distortion, i.e., the distribution of displacements from the original grid caused by stress in the absorber. Using an analytical technique we developed, the stress distribution that caused the distortion is calculated from the HPSI measurements using a rapid algorithm. To correct the distortion we follow the proposal of Feldman [J. Vac. Sci. Technol. B 17, 3407 (1999)] and apply a heat distribution such that taking into account thermal diffusion and heat loss the resulting thermal expansion produces a compensating stress distribution. This adaptive x-ray mask should enable real-time distortion correction. We show first-stage experimental results which support its feasibility.
Evolutionary optimization of the electron-beam lithography process for gate fabrication of high electron mobility transistors
Authors: Robin Franck , Orzati Andrea , Homan Otte J. , Bächtold Werner
Published: July 2002

An electron-beam lithography simulation tool was realized. This tool models the development of multilayered poly(methylmethacrylate) resist structures after exposure with an electron beam. A development front propagates inside the resist stack as a function of time and the local solubility. The local solubility was experimentally measured versus the electron dose for different types of resist. The efficiency of incident and backscattered electrons was determined using doughnut-shaped structures. The ratio of the backscattered to incident electron efficiencies η was found to be 1.35 for an acceleration voltage of 30 kV on InP substrates. We used genetic algorithms to optimize the electron dose necessary for the realization of a given resist profile. This tool was applied to fabricate T-gates and asymmetric gate recesses.
Fabrication technique for nanometer-scale InAs quantum devices: Observation of quantum interference in Aharonov–Bohm rings and Coulomb blockade in quantum dots
Authors: Chang T. H. , Chen K. A. , Yang C. H. , Yang M. J. , Park D.
Published: July 2002

We report an approach to the lateral confinement of electrons in InAs/AlSb single quantum wells. Using electron-beam lithography and reactive ion etching, we have fabricated conducting wires, rings, and dots with lateral dimensions ⩾50 nm. Characterization on narrow wires and rings indicates that the electron transport is in the quasiballistic regime at 4.2 K. The current–voltage characteristics of 70-nm-diam dots in single-electron transistor structures show the Coulomb gap and the Coulomb staircase features. These artificially patterned devices have an ultimate lateral dimension of a few nanometers, limited by the resolution of electron-beam lithography.
Implementing advanced lithography technology: A 100 MHz, 1 V digital signal processor fabricated with phase shifted gates
Authors: Watson G. P. , Kizilyalli I. C. , Nalamasu O. , Cirelli R. A. , Miller M. , Wang Y. , Pati B. , Radosevich J. , Kohler R. , Freyman R. , Klemens F. , Mansfield W. , Vaidya H. , Timko A. , Trimble L. , Frackoviak J.
Published: July 2002

To demonstrate the effectiveness of alternating aperture phase shift lithography for integrated circuit manufacturing, a demonstration device was designed and processed. A 2 million transistor integrated circuit was processed with a phase shifted gate level using 248 nm wavelength lithography. The lithographic results were confirmed by careful feature size measurements throughout the process sequence and finally by the performance of the devices themselves. Gate lengths were reduced from 240 to 120 nm, resulting in fully functional chips with 100 MHz circuit speed at 1.0 V operation, more than a two-fold speed improvement and a record for communication circuits of this type at a low supply voltage.
Process development for small-area GaN/AlGaN heterojunction bipolar transistors
Authors: Lee K. P. , Zhang A. P. , Dang G. , Ren F. , Han J. , Hobson W. S. , Lopata J. , Abenathy C. R. , Pearton S. J. , Lee J. W.
Published: July 2002

A self-aligned fabrication process for small emitter contact area (2×4 μm2) GaN/AlGaN heterojunction bipolar transistor is described. The process features dielectric-spacer sidewalls, low damage dry etching, and selected-area regrowth of GaAs(C) on the base contact. The junction current–voltage (I–V) characteristics were evaluated at various stages of the process sequence and provided an excellent diagnostic for monitoring the effect of plasma processes such as chemical vapor deposition or etching. A comparison is given with large emitter-area (1.96×103 μm2) devices fabricated on the same material. The small-area devices are attractive for microwave power switching applications provided a high-yield process can be developed.
Thermal imidization of fluorinated poly(amic acid) precursors on a glycidyl methacrylate graft-polymerized Si(100) surface
Authors: Zhang Yan , Tan K. L. , Liaw B. Y. , Liaw D. J. , Kang E. T. , Neoh K. G.
Published: July 2002

A novel method was developed to achieve good adhesion of fluorinated polyimides (FPIs) on a Si(100) surface via thermal imidization of the fluorinated poly(amic acid) precursors (FPAAs) onto an argon plasma-pretreated and glycidyl methacrylate (GMA) graft-polymerized Si(100) (GMA-g-Si) surface. The FPI/GMA-g-Si laminates exhibited 180°-peel adhesion strengths as high as 8.0 N/cm, compared to negligible adhesion strength for the laminates prepared from thermal imidization of the FPAAs on pristine and argon plasma-treated Si(100) substrates. The high-adhesion strength was attributed to the synergistic effect of coupling the curing of epoxide functional groups of the grafted GMA chains with the imidization process of the FPAAs, and the fact that the GMA chains were covalently tethered on the Si(100) surface. The adhesion strength of the thermally imidized poly(amic acid) precursor of polyimide (PI, Kapton HN®) on the present graft-modified Si(100) surface was also investigated for comparison purpose. It was found that the presence of fluorine-containing groups, such as CF3, had negligible effect on the adhesion of the FPIs to the present graft-modified silicon substrates. The plasma-activated and graft-modified silicon surfaces were characterized by x-ray photoelectron spectroscopy (XPS) and atomic-force microscopy. The reaction and composition at the polymer–Si interphase were investigated by Fourier transform infrared spectroscopy and XPS. XPS results also revealed that the FPI/GMA-g-Si assembly delaminated by cohesive failure inside the polymer film.
Novel technique to enhance etch selectivity of carbon antireflective coating over photoresist based on O2/CHF3/Ar gas chemistry
Authors: Hong J. , Jeon J. S. , Kim Y. B. , Min G. J. , Ahn T. H.
Published: July 2002

A new antireflective coating (ARC), amorphous carbon (C-ARC), substituted for inorganic ARC (SiON) is gaining attention in dynamic random access memory processing as devices scale down, requiring more fine control of submicron (<0.13μ) patterning. A parametric study of enhancing etch selectivity of C-ARC over photoresist was performed based on O2/CHF3/Ar gas chemistry in a capacitively coupled plasma tool. The etch rate of C-ARC is found to be strongly dependent on the formation of hydrogen radicals in the plasma, heat treatment, and deposition temperature of the amorphous carbon. Fourier transform infrared data revealed that a bonding transformation occurred in the C-ARC from sp3 tetrahedral structure to sp2 graphite structure when amorphous carbon is subjected to heat treatment in a furnace at 600 °C for 15 min, leading to a boost in the etch rate of C-ARC. An etch selectivity of ∼0.8 of C-ARC over the photoresist was achieved with annealing of the amorphous carbon. The presence of hydrogen radicals in the plasma produced a similar result, with C-ARC phase transition from sp3 to sp2 bonding. The deposition temperature of C-ARC determined the hydrogen content on the surface. The hydrogen behavior on the surface appeared to be the dominant factor in controlling etch selectivity. The surface reaction mechanism of amorphous carbon is also discussed.
Sidewall passivation of GaAs in BCl3-containing atmospheres
Authors: Franz Gerhard , Hösler Wolfgang , Treichler Rolf
Published: July 2002

The sidewall passivation of GaAs in atmospheres containing the chain-building molecule BCl3 has been investigated employing Auger electron spectroscopy and time-of-flight secondary ion mass spectrometry. It could be proven that the film that protects the sidewalls from further chemical attack is composed mainly of (B2Cl4)∞ rather than polymers of B2O3.
Enhancement of isopropanol-based photoresist removal by the addition of aqueous alkaline solutions
Authors: Kamal T. , Hess D. W.
Published: July 2002

Removal of photoresist films along with underlying hexamethyldisilazane (HMDS) layers from SiO2 surfaces was studied using isopropanol (IPA) and IPA/NH4OH/H2O mixtures. Although IPA removed photoresist layers, pure IPA was unable to remove the HMDS layer, even at temperatures above 60 °C and pressures above 50 psi. Addition of NH4OH/H2O to IPA resulted in attack of the Si–O–Si bonds at the Si/HMDS interface. Residual carbon concentrations as low as 2.5 at. % on the posttreated surfaces were observed. IPA/NH4OH/H2O surfaces exhibited hydrophilic contact angles (15°–20°) indicating removal of both photoresist and the adhesion promoter layer from silicon dioxide surfaces. Atomic force microscopy analyses indicated no increase in the SiO2 surface root-mean-square roughness.
Novel method for the formation of an aluminum parting layer in the fabrication of field emitter arrays
Authors: Kang Seung-Youl , Jung Moon Youn , Hwang Chi-Sun , Cho Young-Rae , Song Yoon-Ho , Lee Sang-Kyun , Lee Jin Ho , Cho Kyoung-Ik
Published: July 2002

We proposed a method for the formation of an aluminum parting layer in the fabrication of field emitter arrays, in which we used a reflow property of aluminum at a lower temperature than the softening point of glass. In contrast to a conventional Spindt-type method, an aluminum layer was successively deposited on gate metal/dielectric layers by the usual sputter method and all the layers including the aluminum layer were etched together for the formation of gate holes. By a rapid thermal annealing process, the aluminum slightly diffused into the gate hole. This reflowed aluminum was used as a parting layer and emitter arrays were easily fabricated.
Corrosion behavior of Co–Sm based magnetic media
Authors: Zana Iulica , Zangari Giovanni
Published: July 2002

In this article the long term stability of Co–Sm thin films, both with no overcoat and covered with silicon nitride layers of varying thickness, has been investigated by means of accelerated corrosion tests in vacuum, air, and in a humidity chamber. Bare Co–Sm films exhibit an accelerated decrease in magnetization with respect to reference Co–Pt films, dependent in part on the effective surface area of the magnetic film. X-ray photoelectron spectroscopy depth profiling and corrosion tests demonstrate that silicon nitride layers of about 8 nm should provide adequate protection against degradation of the magnetic properties of Co–Sm thin films.
Aspect ratio dependent plasma-induced charging damage in rf precleaning of a metal contact
Authors: Kim J. , Shin K. S. , Park W. J. , Kim Y. J. , Kang C. J. , Ahn T. H. , Moon J. T.
Published: July 2002

As the packing density increases in the fabrication of semiconductor chips, the aspect ratio and the critical dimension (CD) of a metal contact are exponentially aggravated in dry etch processing. The aspect ratio dependency of plasma-induced charging damage during the rf precleaning of a metal contact has been evaluated with a two-dimensional Monte Carlo simulation and with related experiments. From the simulation of a metal contact opened on a gate metal, it is found that the potential on a metal contact bottom, which is directly related to plasma-induced charging damage, is saturated near an aspect ratio of 4 after initially linearly increasing with the aspect ratio. However, the linear decrease of CD of a metal contact exponentially increases the potential stress on the gate oxide. These simulation results are confirmed with the two different experiments, an in situ charge-up monitoring and the electrical test of fully fabricated complementary metal–oxide–semiconductor wafers. A phase controlled inductively coupled plasma is newly proposed to suppress the plasma-induced charging damage. With this system, the plasma-induced damage is strongly suppressed when the phase delay of the bias power to the source power is near 180°.
ZnO:Zn phosphor thin films prepared by filtered arc deposition
Authors: Li Wei , Mao Dongsheng , Zhang Fumin , Wang Xi , Liu Xianghuai , Zou Shichang , Zhu Yukun , Li Qiong , Xu Jingfang
Published: July 2002

ZnO:Zn phosphor thin films, which can be used in field emission displays, were prepared by filtered arc deposition. Depositing parameters, including bias and temperature of the substrates, duct current and partial pressure of O2 in the depositing chamber, were varied to synthesize the films. Both dc and rf bias were utilized in the process. The structure, thickness, luminescent intensity, and morphology of the films were investigated. Most of the as-deposited films contained both crystalline and amorphous phases. It was found that lower bias, lower substrate temperature, rf bias, and lower duct current tended to obtain thicker films. Neither lower nor higher O2 concentration in the chamber obtained thicker films. There are two categories of luminescent peaks, the UV/violet emission (370–420 nm) and the blue/green light (470–530 nm), in the deposited ZnO:Zn films. An interesting relation between PL intensity and morphology was found. Some samples with a special type of individual tip-like structures showed stronger luminescence in a magnitude than others. The forming of the tip structures may be due to the bombarding effect of the plasma with high energy during the deposition and that there were less boundaries or defects between the individual tips may account for the stronger luminescence.
Effect of interlayer on thermal stability of nickel silicide
Authors: Maa Jer-shen , Ono Yoshi , Tweet Douglas J. , Zhang Fengyan , Hsu Sheng Teng
Published: July 2002

The thermal stability of nickel silicide is improved significantly by adding a thin layer of Ir or Co at the Ni/Si interface. The sheet resistance remains low after 850 °C annealing. The thermal stability was evaluated by measuring the junction leakage of an ultra-shallow junction with a 40 nm junction depth. With Ir, the film was stable and the reverse leakage of both N+/P and P+/N junctions remained in the picoampere range at 3 V on 100 μm×100 μm feature after 850 °C annealing. With Co, the leakage from P+/N junctions was low when the temperature was as high as 850 °C; leakage from N+/P junction was in the picoampere range up to 750 °C. These films were characterized by x-ray diffraction. The improved stability and low junction leakage is attributed to a very smooth interface.
Heterojunction based on polyacetylene and its photocurrent density
Authors: Pengyi Liu , Hai Ye
Published: July 2002

A heterojunction based on polyacetylene is fabricated through directly synthesizing (CH)x on the surface of n-SnO2. The relationship of photocurrent density Jph versus incident power for the heterojunction is obtained by using argon–ion laser. Only considering the absorption of polyacetylene, the formula of the photocurrent density of the heterojunction based on polyacetylene has been deduced.
Ultraviolet photoemission spectroscopy study of ultrahigh-vacuum-fractured CaVO3 surface
Authors: Aiura Y. , Kawanaka H. , Bando H. , Yasue T.
Published: July 2002

The effect of surface defects on the electronic structure of CaVO3 has been studied by ultraviolet photoemission spectroscopy (UPS). We used flat surfaces obtained by in situ fracturing of single-crystalline samples in an ultrahigh vacuum, and rough surfaces obtained by scraping, which are presumed to contain many surface defects. It is shown that the UPS spectra of CaVO3 are very sensitive to the surface structures, which depend on the cleaning procedure. In addition, the oxygen-exposure dependence of the UPS spectra was investigated in order to evaluate the influence of those surface defects on the UPS spectra. We conclude that the UPS spectra observed on the CaVO3 surfaces (both fractured and scraped) are strongly influenced by the electronic structure characteristic of the surface.
Applications of atomic force microscopy/scanning capacitance microscopy in imaging implant structures of semiconductor devices
Authors: Chao Kuo-Jen , Kingsley Jeffrey R. , Plano Robert J. , Lu Xing , Ward Ian
Published: July 2002

Atomic force microscopy [G. Binnig et al., Phys. Rev. Lett. 56, 930 (1986)] and scanning capacitance microscopy [C. C. Williams et al., Appl. Phys. Lett. 55, 203 (1989)] (AFM/SCM) have been widely used to investigate the two-dimensional carrier profile of semiconductor devices. In this work, AFM/SCM was applied to both process control and failure analysis. Several different cases were studied. First, a commercially available integrated circuit device was cross sectioned and polished for the AFM/SCM investigation using standard scanning electron microscopy sample preparation techniques. Implant structures near the gate were clearly resolved. Second, a GaAs device with Zn thermally diffused through the opening of a Si3N4 mask was studied. The lateral diffusion length of Zn was determined. Third, two semiconductor devices, one good and one that had failed, were prepared by cross sectioning, followed by polishing. Implant profiles of similar structures on both devices were imaged. The thickness of the N-well structure was found to be thinner in the failed device by about 0.4 μm. These cases demonstrate applications of AFM/SCM in process control and device failure analysis.
Writing, repairing, and inspecting of extreme ultraviolet lithography reticles considering the impact of the materials
Authors: Wasson J. R. , Lu B. , Mangat P. J. S. , Nordquist K. , Resnick D. J.
Published: July 2002

Extreme ultraviolet lithography (EUVL) is the leading candidate for next generation lithography with the potential for extendibility beyond the 50 nm node. Selecting the proper materials for the absorber stack directly impacts one’s ability to conduct effective electron beam patterning, focused ion beam repair, and inspection of an EUVL reticle. An attempt to define the optimal absorber stack based on the interaction of electrons, ions, and photons with the absorber stack is studied from the perspective of patterning, repair, and inspection of EUVL reticles, respectively.
Control of dielectric cap induced band-gap shift in 1.55 μm laser structures
Authors: Wojcik J. , Robinson B. J. , Thompson D. A. , Mascher P.
Published: July 2002

Silicon oxynitride (SiOxNy) thin films, deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition, have been used to induce blueshifting of the emission wavelength of 1.55 μm partial three quantum well laser structures after an annealing treatment. The SiOxNy caps had thicknesses of about 1000 Å and refractive indices ranging from 1.45 to 1.85. Room temperature photoluminescence was used to measure the magnitude of the cap-induced blueshift. It was found that the maximum blueshift occurs for an index of refraction of 1.63. Rapid thermal annealing was applied after the deposition and the importance of accurate temperature control is discussed. Finally, the role of the microwave power is analyzed and its impact on the blueshift is discussed.
Improving resist resolution and sensitivity via electric-field enhanced postexposure baking
Authors: Cheng Mosong , Yuan Lei , Croffie Ebo , Neureuther Andrew
Published: July 2002

This article explores a methodology for enhancing the resist resolution and improving resist profile based on confining the photoacid drift/diffusion by an external electric field. A properly offset alternating electric field applied to the resist film during postexposure bake (PEB) can enhance the photoacid drift in the vertical direction, drive acid to the desired direction, and thereby confine the lateral acid diffusion. The experiments were conducted on UVIIHS resist with JEOL electron-beam exposure tool and UVII-10 resist on ASML KrF stepper, respectively. The scanning electron microscopy pictures show that electric-field enhanced PEB can control the resist profiles and increase the verticality of resist sidewalls. Electric-field-enhanced PEB also significantly improves the tolerance of over and underexposure and provides better critical dimension control. It is estimated that it reduces the lateral acid diffusion length by about 70–90 nm in KrF lithography.
Crystallization transformations in vacuum-deposited amorphous aluminum fluoride self-developing thin-film resists induced by electron-beam irradiation
Authors: Chen G. S. , Lee P. Y. , Boothroyd C. B. , Humphreys C. J.
Published: July 2002

Conventional transmission electron microscopy is employed to investigate in situ electron-beam-induced phase transformations in vacuum-deposited amorphous aluminum fluoride (a-AlF3) self-developing thin-film resists. The a-AlF3 resists exhibit a very complex sequence of crystallization transitions with three crystalline materials (Al, AlF3, and Al2O3) formed sequentially as the electron dose increases from 105 to 107 Cm−2. Thermally evaporated “dry” a-AlF3 is dissociated into Al crystalline colloids at a threshold dose of ∼1×105 Cm−2, and begins to transform into crystalline AlF3 (c-AlF3) at a dose of ∼1×106 Cm−2. However, water contained in the “wet” films accelerates the transition of a-AlF3 to c-AlF3 at a reduced threshold dose of ∼2×105 Cm−2. Moreover, a-AlF3 films prepared by electron-beam deposition require a markedly different dose for each substance to crystallize, attributed to a microstructure variation. For all of the a-AlF3 films, textured Al2O3 is formed at doses of ⩾1×107 Cm−2, also with the aid of H2O absorbed from the microscope vacuum and by the following chemical reaction: 2AlF3(s)+3H2O(g)→Al2O3(s)+6HF(g).
Ultrafast high-field carrier transport in a GaAs photoconductive switch
Authors: Cummings M. D. , Holzman J. F. , Elezzabi A. Y.
Published: July 2002

Utilizing 18 fs optical pulses, field screening, and carrier dynamics which occur in the high-field region of an edge-illuminated coplanar transmission line are investigated. It is found, through the use of transient pump-probe reflectivity measurements, that the ballistic acceleration of carriers and subsequent field screening dominate the ultrashort electrical pulse generation for an edge-illuminated photoconductive switch. The formation of an instantaneous macroscopic polarization and phonon-plasmon modes are also observed. In addition, lattice and plasmon contributions to the field screening are found to be highly dependent on the excitation position within the gap. The measurements suggest that sub-100 fs electrical pulses can be generated.
Ion energy distributions at rf-biased wafer surfaces
Authors: Woodworth J. R. , Abraham I. C. , Riley M. E. , Miller P. A. , Hamilton T. W. , Aragon B. P. , Shul R. J. , Willison C. G.
Published: July 2002

We report the measurement of ion energy distributions at a radio frequency (rf)-biased electrode in inductively driven discharges in argon. We compare measurements made with a gridded energy analyzer and a commercial analyzer that contains a mass spectrometer and energy analyzer in tandem. The inductive drive and the rf bias in our Gaseous Electronics Conference reference cell were both at 13.56 MHz. By varying the plasma density, we were able to examine the transition region between the “low frequency limit” for rf bias and the intermediate frequency region where, at fixed bias frequency, the ion energy distribution width varies with the plasma density. We find that the experimental ion energy distributions become narrower as the time for ion transit through the sheath approaches the rf period, but that the ion distributions still have widths which are ∼90% of their low frequency limit when the ion transit time is 40% of the rf period. Space-charge-induced beam broadening inside our analyzers appears to significantly affect our measurements of ion angular distributions, especially at low ion energies.
Growth and characterization of InAs on (100) InP ultrathin single quantum wells using tertiarybutylarsine and tertiarybutylphosphine
Authors: Frankland D. , Masut R. A. , Leonelli R.
Published: July 2002

Ultrathin InAs/InP single quantum wells were grown by low-pressure metalorganic vapor phase epitaxy using tertiarybutylphosphine and tertiarybutylarsine, with nominal thicknesses between 2 and 3 ML. Characterization of a large number of samples by high-resolution x-ray diffraction (HR-XRD) and photoluminescence (PL) indicates an average InAs thickness very close to the nominal one. Photoluminescence excitation and absorption spectra of selected samples contain excitonic resonances associated with electron-hole transitions in 2 or 3 ML of InAs buried in InP. Only one set of these resonances appears in a given sample, thereby corroborating HR-XRD and PL measurements. Thus, our measurements indicate an absence of significant As–P intermixing.
High-Reflectance Multilayer Dielectric Mirrors
Authors: Behrndt K. H. , Doughty D. W.
Published: July 2002

Mirror reflectances of close to 100% are needed for numerous applications in gas lasers. Since the transmittance of multilayer dielectric films can be reduced to almost zero by increasing the number of layers, the limiting factor is loss introduced by scattering centers. The causes for the formation of the latter are found to be excessive surface roughness or improper cleaning of the substrate in the residual-gas atmosprere of the bell jar and “spitting” of the evaporation source. Techniques for minimizing these effects are described. Mirrors of 6 in. diameter with a reflectance of 99.89% and scattering losses of 0.09% were fabricated for ZnS/ThOF2. The reflectance was found to vary with the number of layers displaying a maximum at N = 21.
Electron-beam melting of Ti–6Al–4V
Authors: Landig T. , McKoon R. , Young M.
Published: July 2002

A program to recycle Ti–6Al–4V machine chip scrap by electron-beam (EB) melting is described. The advantages of utilizing EB melting are described in terms of the selection of raw materials, the unique characteristics of the EB hearth furnace, the alloying and refining reactions that are promoted, and the unique character of the solidification process. Experimental results are presented on a manufacturing technology program sponsored by the Air Force Materials Laboratory in which machined chips, sponge, and alloy elements are recycled into specification grade Ti–6Al–4V bar stock.
High-precision automatic alignment procedure for vector scan e-beam lithography
Authors: Stephani D. , Fröschle E.
Published: July 2002

The described automatic alignment procedure permits an alignment of two successive exposure levels of better than ±50 nm in a deflection field of 600 μm at a beam current of 5×10−10 A within an average time of 3 s even without using a laser interferometer controlled stage.
Self-modulating ion gauge
Authors: Edwards D. , Lanni C.
Published: July 2002

A Bayard–Alpert ionization pressure gauge has been modified by shortening the collector wire thereby reducing the x-ray limit from ∠2.5×10−11 to ∠0.6×10−11 Torr. In addition it has proven possible to modulate this gauge and thus make an in situ determination of the x-ray limit without the introduction of a modulation electrode. Thus a self-modulating, low x-ray limit ion gauge has been developed at reasonably low cost and seems particularly suited to the ISABELLE ultrahigh vacuum system.
Influence of residual gases on the properties of dc magnetron-sputtered aluminum–silicon
Authors: Nowicki R. S.
Published: July 2002

The influence of trace residual gases on the film specularity, grain size, and resistivity of aluminum–1.5% silicon alloy was investigated. Oxygen and nitrogen are shown to be the major contributors to loss of film specularity. The reflectance is decreased from ca. 90% to 10%–20% when oxygen or nitrogen are present in the sputtering system at about 5×10−3 Pa above the vacuum system residual pressure (8×10−5 Pa in this case). Hydrogen is shown to have no significant effect on reflectance at this level of contamination. The resultant grain size variations show only small changes when correlated with each contaminant. However, there appears to be a separate, crystalline phase which appears with hydrogen and nitrogen. Additionally, film analysis by nuclear reaction techniques shows some direct correlation between loss of reflectance and carbon content. The results are discussed with regard to microelectronic device processing.
Transient getter scheme for the Tokamak Fusion Test Reactor
Authors: Cecchi J. L. , Cohen S. A. , Sredniawski J. J.
Published: July 2002

The ability of the Tokamak Fusion Test Reactor (TFTR) to attain the largest fusion power gain depends critically on minimizing plasma contamination and controlling the densities of the reacting deuterium and tritium. Experiments on a number of tokamaks have demonstrated that gettering over an appreciable surface area (? 10%) of the vacuum vessel greatly facilitates both of these objectives. One particular problem in implementing a surface pumping system in TFTR, however, is a restriction on the maximum allowable tritium content of the getter. This restriction could require regeneration of the absorbed tritium after as few as 50 machine pulses. We have developed a scheme utilizing SAES Zr/Al getter modules which obviates the need for such frequent interruptions of machine operation by taking advantage of the pulsed operation of TFTR. With the Zr/Al getter at temperatures between 500°–600°C it is possible to achieve a quasisteady state in the tritium loading where the quantity of tritium desorbed between pulses is equal to the quantity which is absorbed during a pulse. Since frequent thermal cycling is not required, this scheme also reduces the possibility of Zr/Al getter material fatigue.
Aims and recent accomplishments of surface theory
Authors: Feibelman Peter J.
Published: July 2002

The goals of surface science include the understanding of surface bonding, structure, transport, and chemistry. However, our present activities are mainly focused on the most basic problem, viz., what are the constituents of a given surface, where are they located and how are they bonded? Theorists are approaching this surface characterization problem from two sides. To make better use of the data available from the many experimental surface probes, we are developing an understanding of the force laws which govern the motion of probe particles near surfaces, and we are studying intensively the relation between the excitation and ground state spectra of a solid. In order to develop a predictive capability regarding surface structure, we are studying a variety of intrinsic surface properties including the nature of bonds at transition metal surfaces, the meaning of bond locality in extended systems, and generally the electronic factors underlying the forces which govern surface geometry. These studies often raise technical issues such as the validity of using local exchange correlation potentials and the applicability of cluster calculations to the analysis of extended surface situations, which, however, should not obscure the main thrust of current work — empirical and predictive surface structure determination. These points will be illustrated with examples from recent research and ways in which experimental surface work might assist theoretical efforts will be indicated.
Frontiers in microelectronics and thin film components
Authors: Duke C. B.
Published: July 2002

This paper is the text of an address delivered by the outgoing president of the American Vacuum Society at the Society’s annual meeting in 1979. Following a brief outline of the mission, functions, and organization of the Society, a discussion of trends in the fabrication of modern microelectronics is presented together with an outline of the Society’s activities which contribute toward these trends. The address concludes with a consideration of the consequences of these trends for the American Vacuum Society and an indication of the unique roles of a multidisciplinary organization like the American Vacuum Society in the American Institute of Physics.
Mixed valent ytterbium-aluminium thin films
Authors: Tibbetts G. G. , Egelhoff W. F.
Published: July 2002

The criteria for the formation of thin mixed valent films have been studied by depositing thin layers of Yb on an Al(100) substrate and carefully controlling the interdiffusion. X-ray photoemission (XPS) of pure Yb surface layers shows only the divalent character of the filled f14 shell. Formation of a mixed valent state begins when interdiffusion becomes substantial above 150°C. Further heating above 350°C causes the Yb to revert to the divalent state despite the fact that a charge transfer mechanism would predict the presence of a substantial trivalent component. It is clear that the divalent component is not predominant on the surface of our mixed valent film since low intensity ion sputtering converts the trivalent component to the divalent. Finally, we observe an increase in the divalent character of an alloy of stochiometry YbAl3 at low temperatures smaller than that predicted by theory.
Microfabrication at the University of Cincinnati
Authors: Naumaan A. , Roenker K. P. , Boyd J. T.
Published: July 2002

This paper outlines a two quarter laboratory course in integrated circuit design and fabrication offered by the Department of Electrical and Computer Engineering at the University of Cincinnati. Included in this course is an introduction to the operation and use of a wide range of vacuum system technology. The course also covers integrated circuit device design and layout, computerized mask generation, hands-on processing, and evaluation of the finished IC chips. Traditional instruction is supplemented by video tapes of both lectures and demonstrations of the use of various pieces of equipment. Labortory facilities include high-vacuum systems containing diffusion, ion and turbomolecular pumps used in several chemical vapor deposition systems, sputtering systems, and in an ion implantation system. The laboratory also features leak detection equipment, diffusion furnaces, photolithographic equipment, and a scanning electron microscope. Senior graduate students are given responsibility for routine maintenance of laboratory equipment including vacuum systems.
Microgravimetric/infrared studies: a review
Authors: Low M. J. D.
Published: July 2002

Infrared spectroscopic techniques are widely used to study solid surfaces and the changes occurring upon them. Similarly, microgravimetric methods are widely used for analogous purposes. However, the two techniques are only rarely employed simultaneously with the same sample; common practice is to use one sample for infrared and another sample for gravimetric study. The various factors leading to the lack of easy compatibility of the two techniques are outlined and examples of combined gravimetric/infrared experiments are reviewed.
Development of variable capacitance pressure transducers for vacuum applications
Authors: Sullivan John J.
Published: July 2002

The development of variable capacitance diaphragm-type pressure transducer systems for vacuum applications is described in detail. This technology area is an interesting and challenging problem of design and manufacturing engineering and incorporates an interdisciplinary mixture of material science, and state-of-the-art techniques in electronics. Since the measurement system must be usable for a wide variety of applications in vacuum science ranging from very high accuracy metrology transfer standards to general-purpose vacuum measurements under very demanding environmental conditions, many conflicting factors must be considered in the design. For all practical purposes, this technology has evolved over a 35 yr period from 1949 to 1984 within which there have been several distinct developmental time periods; 1949–1969, 1970–1975, 1975–1980, 1981–1984. This paper will review the technology, considering the chronological development of sensors, signal conditioners, and overall transducer systems. Some very recent advances will be discussed as well as projections for the future.
Coaxial helium leak detection probe
Authors: Fowler G. L.
Published: July 2002

A coaxial device has been developed which makes it possible to pinpoint a leak in a piece of vacuum hardware or tubing within a space of one-sixteenth of an inch. The device consists of a delivery tube which directs the helium to a precise spot and a coaxial outer tube which pumps away the excess helium. This arrangement prevents diffusion or drift to a real leak in close proximity of the test area.
Spherical oscillator gauge with field emission cold cathode
Authors: Li Wangkui , Zhang Dixin
Published: July 2002

The spherical oscillator gauge with field emission cold cathode has been successfully developed on the basis of many experiments and theoretical calculations with a computer. It basically keeps the advantage of the high sensitivity (K=15 Pa−1) of an oscillator gauge. The incident electrons move in oscillatory mode and effectively restrain their trajectory. The resulting ion beam is focused and collected. Successfully applying the field emission code cathode to the spherical oscillator gauge is the key step of solving the problem in extremely high-vacuum measurement.
Occupied and empty surface states of monocrystalline (100) aluminum studied by low electron energy-loss spectroscopy and inverse photoemission
Authors: Gautier M. , Marteaux E. , Duraud J. P. , Baptist R. , Brénac A. , Spanjaard D.
Published: July 2002

Using low electron energy-loss spectroscopy, we showed previously the existence, on monocrystalline Al(111), of an electronic transition involving surface states. This work is extended to another crystallographic orientation Al(100). Main results show that the transition energy depends both on the surface orientation and on the primary energy. Its dispersion has been followed for primary energies ranging from 10 to 100 eV. In order to better characterize the location of these states in the surface band structure E(k∥), experiments have been combined with UV inverse photoemission spectroscopy, which gives direct access to the unoccupied states above the Fermi level. The results are discussed in the frame of surface band calculations.
Study of the vibrational modes of subsurface oxygen on Al(111) using diode laser infrared reflection–absorption spectroscopy
Authors: Bermudez V. M. , Rubinovitz R. L. , Butler J. E.
Published: July 2002

Infrared reflection–absorption spectroscopy, using polarization modulation and tunable diode laser excitation, has been applied to the study of the vibrational modes of subsurface oxygen on Al(111). The dependence of the spectra on O2 exposure and on annealing has been investigated at a resolution of ∼10 to 20 cm−1 (1.2–2.5 meV) and correlated with Auger data. The absorption band (∼780–920 cm−1) consists of overlapping bands at ∼835 and 862 cm−1 associated, respectively, with isolated sites and with clusters of such sites resembling Al2O3. The apparent shift of this band to higher energy with increasing coverage, observed at lower resolution (but higher sensitivity) in electron energy-loss spectroscopy, is found to result from the change in relative intensity of the two modes.
High-selectivity plasma etching of silicon dioxide on single-wafer etchers
Authors: Yin Gerald Z. , Ben-Dor Monique , Chang Mark S. , Yep Tom O.
Published: July 2002

Etching of silicon dioxide with CHF3 /CF4 chemistry has been investigated on single-wafer etchers with both high-frequency and low-frequency plasma discharge. A simple kinetic model emphasizing surface reaction and desorption is proposed to explain the selectivity mechanism, polymer control, and process trends. A reproducible single-step plasma etch process with a high selectivity of thermal oxide to polysilicon is then developed employing effective temperature controls on both electrodes as well as the wafers being etched. It is demonstrated that the plasma etching mode is capable of etching submicron geometries.