bluuebunny/crossref_metadata_2025 huggingface dataset:
Further Measurements on Physical Factors Influencing Accommodation Pumps
Authors: Baker B. G. , Hobson J. P. , Pye A. W.
Published: July 2002

Measurements similar in concept to those already reported have been continued. New experimental results on accommodation pumps will be given for six classes of measurements: (1) dynamic measurements for the gases Ne and Ar; (2) variations in the rough arm of the pump including surfaces of Pyrex leached in various ways; (3) variations in the smooth arm including surfaces of nickel (deposited under various conditions), aluminum, mica, sodium chloride, fused silica, fused silica etched in hydrofluoric acid; (4) the effect of the introduction of large quantities of Xe, O2, H2O on the pump surfaces; (5) the variation of the cold temperature between 77 and 195 °K for the gases He, Ne, Ar; (6) the pump ratio as a function of the position of the temperature gradient for four new designs of asymmetric pump.
Theory of Aberration Mixing in Electron-Optical Systems
Authors: Harte K. J.
Published: July 2002

In order to analyze the imaging properties of an electron-optical system, it is necessary to know how various sources of aberration combine to increase the size of the final image or spot. Either linear mixing, or else quadratic mixing (based on the assumption that the aberration produces a Gaussian distribution), have been commonly used. In this paper a theory of aberration mixing is developed, starting from the assumption of a circularly symmetric current-density distribution, each point on which is subjected to a circularly symmetric aberration. If the effective radius of the spot (and of each contribution) is defined as the square root of the normalized second moment of the current-density distribution, then the following theorem is shown to hold: when a spot with a circularly symmetric current-density distribution suffers any circularly symmetric aberration, the effective radius of the resultant spot is the square root of the sum of the squares of the effective radii of the original spot and the aberration disk. If several sources of aberration are present, it follows that the effective radii all add quadratically. For a Gaussian distribution, it is shown that the effective radius is just the 1/e point on the current-density distribution. For a rectangular distribution (e.g., defocusing or, to first approximation, astigmatism) and the distribution resulting from the spherical aberration of a lens, numerical constants are derived which relate the effective radius to the more usual and often more convenient outer diameter of the aberration disk.
Depth of field at high magnifications of scanning electron microscopes
Authors: Sato Mitsugu , Mizuno Fumio
Published: July 2002

Depth of field (DoF) in scanning electron microscopes is evaluated at high magnifications where the image resolution is limited by the probe size. The calculation of DoF is made in terms of the information passing capacity of an optical system or entropy of the image estimated along the optical axis near focus. Electron diffraction, source brightness (or source size), and signal-to-noise ratio are taken into account in the calculations of the DoF. The DoF at high magnifications is proportional to Rmin2 where Rmin is resolution of the system, and degrades due to the lack of brightness and aberrations. The DoF in semiconductor applications is also estimated.
Anomalies in kinetics of hydrogen evolution from austenitic stainless steel from 300 to 1000 °C
Authors: Nemanič Vincenc , Zajec Bojan , Šetina Janez
Published: July 2002

The rate of rise method was arranged for monitoring the kinetics of hydrogen evolution from austenitic stainless steel (AISI 304) samples, inductively heated in the range from 300 to 1000 °C. After each heating cycle, the accumulated gases were analyzed by quadrupole mass spectroscopy and quantity of evolved hydrogen was determined. Three sample types were studied: “only cleaned,” hydrogen annealed (1050 °C), and vacuum annealed (950 °C). Below 800 °C, the effect of pretreatment was manifested very differently in kinetics. Fast release of approximately 2×1019 atoms H cm−3 from hydrogen annealed samples was recorded which was close to published data of solubility. By increasing the temperature above 800 °C for a prolonged time, much more hydrogen evolved from all sample types. The equivalent concentration change varied from 4 to 9×1019 atoms H cm−3, but the measurements were ceased before the “totally outgassed state” was reached. By repeated annealing of two samples in high vacuum, the rest of the hydrogen was again partially extracted and partially redistributed to the sites, from which it was easily released after intermediate cooling down. There is a lack of data in the literature about the amount and evolution kinetics of the trapped or tightly bound hydrogen. The present findings differ from existing theoretical models of outgassing and may explain the reason for the inefficiency of thermal treatment methods to prepare stainless steel for extreme high vacuum application.
Thin Ta2O5 Films on Si by XPS
Authors: Atanassova Elena , Spassov Dencho
Published: July 2002

X-ray photoelectron spectra (XPS) for thermally grown (oxidation temperature 673 K) thin (13 nm) tantalum pentoxide films on Si are presented. The peak decomposition technique was employed to identify the composition and the chemical state throughout the film. It is established that stoichiometric Ta2O5 detected at the surface of the layer is reduced to tantalum suboxides in its depth, which amount increases in the depth of Ta2O5 film. The films have a two-layer structure (i.e., silicon dioxide at the interface with Si and tantalum oxide above it) suggesting oxidation of silicon substrate in addition to oxidation of the tantalum film on Si. The interface between Si and this ultra thin SiO2 is not abrupt and the coexistence of Si–O and Ta–O bonding states in close proximity to the interface is found. The thicknesses of both the tantalum oxide and the SiO2, as well as the width of the Si–SiO2 interface transition region are evaluated.
Submicron structure and acoustic properties of ZnO films deposited on (100) InP by pulsed laser deposition
Authors: Vasco E. , Rubio-Zuazo J. , Vázquez L. , Prieto C. , Zaldo C.
Published: July 2002

Highly textured (001) ZnO films have been deposited on (100) InP by pulsed laser deposition without substrate degradation. For this, growth starts in high vacuum, 8×10−7 mbar, with the substrate heated to 350 °C and later the oxygen pressure is increased up to 10−1 mbar, at which optimum crystallinity is achieved. Using a KrF laser at a fluence of 4 J/cm2, a repetition rate of 10 Hz and a target to substrate distance of 6 cm, the film growth rate is 0.08 Å/pulse. The film bulk has a columnar structure. The typical x-ray diffraction full width at half maximum (FWHM) is 0.2°–0.24°, while the ω-rocking curve FWHM is in the 1°–3° range. The surface shows two growth regimes: for thickness below 200 nm a granular film surface is obtained, and above this thickness the film surface exhibits submicron sized hexagonal pyramids. The tops of the pyramids have steps with heights of about 10 Å. The ZnO grains are randomly oriented about the [100] InP direction. The phase velocity of the acoustic bulk phonons of the ZnO films is about 6100 m/s.
Study of x-ray phase-shifting masks for sub-70 nm patterning
Authors: Yang Lei , Taylor James W.
Published: July 2002

One of the major challenges for x-ray lithography as a contender for next generation lithography lies in patterning small features—below 100 nm—with a mask-to-wafer gap greater than 20 μm. X-ray phase masks (XPM) provide an opportunity to alleviate this constraint, if the XPM can be constructed with good radiation and thermal stability for practical applications. In this article, we examine a robust silicon nitride based XPM with improved thermal and radiation stability for sub-70 nm imaging. The impact of various factors, such as exposure dose, phase-shifter thickness, sidewall slope, and mask-to-wafer gap, were studied. Phase-shifter slope and mask-to-wafer gap appeared to have a substantial impact on the printability of the XPMs. However, patterning sub-70 nm features could be achieved at a gap of 20 μm. Phase-shifter thickness variation within 10% appeared to have negligible impact on the linewidth with a synchrotron source. Extensive simulations and exposures were conducted to study the dose and gap dependency of different photoresists. Experimental results for Shipley UV-6 and UVN-30 confirmed the simulation results.
Low voltage, blue phosphor for highly efficient field emission display screens
Authors: Bolchouchine V. A. , Goldburt E. T. , Levonovitch B. N. , Litchmanova V. N. , Sochtine N. P.
Published: July 2002

Ce-doped yttrium orthosilicate, P47, is a blue phosphor used in a nonsulfur containing phosphor triad for field emission display (FED) displays. Its low luminous efficiency does not allow one to achieve the necessary light output. For the first time, a modified yttrium orthosilicate, nonsulfur containing blue phosphor has been synthesized and 4 in. phosphor screens with superior performance have been fabricated. This performance, 1.4 lm/W intrinsic luminous efficiency at 400 V and 5 μA/cm2, is significantly better than that of Nichia 1047 phosphor, which is 0.5 lm/W. Based on this blue phosphor and phosphor screen performance, a white light output of 4.5–5 lm/W is now possible in low-voltage FED displays. This performance is dramatically higher than that of compatible active matrix liquid crystal displays.
Determination of residual casting solvent concentration gradients in resist films by a “halt development” technique
Authors: Gardiner Allen B. , Burns Sean , Qin Anwei , Willson C. Grant
Published: July 2002

The resolution of the microlithography process used to manufacture semiconductor devices is a function of many variables. One interesting and important contributor to resolution is the “surface induction” phenomenon that occurs during development of many photoresist materials. This phenomenon is manifested by a change in dissolution rate as a function of thickness. The top or surface regions of these films dissolve more slowly than the bulk of the film for reasons that are not understood. One popular theory for surface induction is that the variation in rate is caused by a gradient in the concentration of residual casting solvent. However, no study has been performed that directly measured the concentration gradient in residual casting solvent and related that gradient to the extent of surface induction. A “halt development ” procedure has been developed that allows isolation and analysis of thin layers (slices) from resist films. The analysis for concentration of residual casting solvent was accomplished by radiolabeling the solvent and analyzing the layers by scintillation counting. The dissolution rate data was acquired by a multiwavelength interferometry technique. Two resists systems were studied, one with a large extent of surface inhibition and one with a nearly constant dissolution rate. Neither formulation has a significant concentration gradient of residual casting solvent over a range of bake temperatures (70–110 °C). Therefore, it can be concluded that concentration gradients in the residual casting solvent alone cannot account for the surface induction observed in this particular resist system.
Characterization of atomic-size metal ion sources
Authors: Purcell S. T. , Binh Vu Thien
Published: July 2002

The emission by field desorption of a beam of ions from the atomic scale apex of a Au nanotip formed on the axis of a W base tip was extensively analyzed. Emission patterns, currents versus time, voltage and temperature, and energy distributions of the ion beams from the atomic size apex were measured. The data were analyzed using known theories of field desorption. We discuss the formation of the nanotip, the supply function, and the ionization process in order to have a qualitative model of the characteristics of the source.
High density diffusion barrier of ionized metal plasma deposited Ti in Al–0.5%Cu/Ti/SiO2/Si structure
Authors: Li S. , Lee Y. K. , Gao W. , White T. , Dong Z. L. , Latt K. Maung
Published: July 2002

The Ti layer deposited by ionized metal plasma deposition technique and the reacted region between Ti and Al–0.5%Cu, in Al–0.5%Cu/Ti/SiO2/Si structure, were characterized by scanning transmission electron microscopy (STEM) and Rutherford backscattering spectroscopy (RBS). The results indicate that the Ti layer with a column-like structure grew epitaxially in the close-packed [001] direction. This growth mechanism resulted in a high-density Ti layer in Al–0.5%Cu/Ti/SiO2/Si structure. This epitaxially grown Ti layer has anisotropic diffusion properties that can retard the diffusion of Al across the Ti layer in the initial stage of high temperature Al sputtering or reflow processes. But the column-like Ti crystals recrystallized during further processing, altered the [001] alignment of the crystals to cause the interdiffusion of Ti and Al. The reactions between Ti and Al took place subsequently and formed the intemetallic Al3Ti, Al5Ti2, TiAl, and Ti3Al layers from the surface inwards. As the diffusion of Al in Ti, Ti3Al, and TiAl decreased in order, the formation of Ti3Al and TiAl layers further retarded the diffusion of Al into the SiO2 layer. It can be concluded that the intermetallic layers play an important role of diffusion barrier that impede the migration of Al across the films.
Low temperature aluminum nitride deposition on aluminum by rf reactive sputtering
Authors: Tait R. N. , Mirfazli A.
Published: July 2002

Thin film bulk acoustic resonators formed by sputter deposition of piezoelectric films of aluminum nitride on silicon substrates offer an attractive approach to monolithic integration of high Q passive circuit elements with active devices. Such resonators could provide low cost, high performance filters for the steadily growing number of consumer wireless communication devices. Fabrication of these resonators requires a well-characterized low temperature deposition process for aluminum nitride. This material has been studied for use in sensors and actuators, as well as acoustic wave devices. Radio frequency reactive magnetron sputtering produces high quality films, and provides reasonable deposition rates for fabricating high frequency resonators. This work describes aluminum nitride films deposited by radio frequency reactive magnetron sputtering with power varied from 2 to 6 W/cm2, pressure from 0.5 to 1.5 Pa, and N2 flow from 50% to 100% of the total flow. Measured results include x-ray diffraction spectra and measurements of piezoelectric coefficients. X-ray diffraction measurements indicate highly (002) c-axis oriented films. Piezoelectric coefficients e31 were measured by depositing aluminum nitride capacitors on silicon beams and measuring charge generation as each beam was deflected a known distance. Film quality was found to depend strongly on deposition power, with a smaller dependence on pressure and gas mixture. Deposition at higher pressures is preferred for resonator fabrication due to reduction in stress when compared with low pressure deposition.
Influence of the microchannel plate and anode gap parameters on the spatial resolution of an image intensifier
Authors: Hoenderken T. H. , Hagen C. W. , Barth J. E. , Kruit P. , Nützel G. O.
Published: July 2002

The spatial resolution that can be obtained with image intensifiers depends largely on the spatial resolution of the microchannel plate (MCP)-anode assembly. Existing models on MCPs never include the nonuniform anode field penetration into the channels. The objective of this article is to show that this field penetration leads to a lens effect which has a crucial influence on the electron trajectories and the spatial resolution that can be obtained. From a simple model the relevant parameters determining the spatial resolution are identified as the anode gap, the anode field, the end-spoiling penetration depth, and the channel diameter. These parameters are varied in a Monte-Carlo simulation in which 20 000 electrons are traced through a channel, the end-spoiling, and the anode gap. The spatial resolution as obtained from these simulations is shown to depend heavily on the nonuniform field at the end spoiling. Especially low-energy electrons generated at the end spoiling deteriorate the spatial resolution. The best resolution is obtained for a small anode gap (300 μm) and small anode voltage (3 kV). This indicates that, above a certain value of the electric field in the anode gap, the effect of the lens is dominant. Doubling the end-spoiling penetration depth from 10 to 20 μm increases the resolution especially at high spatial frequencies. Furthermore, the resolution is enhanced considerably by decreasing the channel diameter. These results can be fully understood from the simple model presented. In addition, results are presented from experiments in which the spatial resolution is measured for various anode gaps and anode voltages. The dependencies of the spatial resolution on these parameters are in good qualitative agreement with the simulation results.
Microstructure characterization of sol-gel prepared MoO3–TiO2 thin films for oxygen gas sensors
Authors: Li Yongxiang , Galatsis Kosmas , Wlodarski Wojtek , Ghantasala Muralihdar , Russo Salvy , Gorman John , Santucci Sandra , Passacantando Maurizio
Published: July 2002

Binary metal–oxide MoO3–TiO2 films have been prepared using the sol-gel technique. The thin films were annealed at several temperatures including 400, 450, 500, 550, and 600 °C for 1 h. The morphology, crystalline structure, and chemical composition of the films have been analyzed using scanning electron microscopy (SEM) and atomic force microscopy, x-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and x-ray photoelectron spectroscopy (XPS) techniques. The SEM analysis showed that there are two different sizes of grains in the films annealed at temperatures of 400, 450, 500, and 550 °C. One grain type is small with 20–100 nm; the other is a large grain type several micrometers in length. The XRD analysis revealed that the films annealed at 400 °C were a mixture of orthorhombic and hexagonal MoO3 phases. The films annealed at 450 °C showed an increase in the hexagonal phase. A preferential orientation growth along the (100) plane of the hexagonal phase and the (010) plane of the orthorhombic phase has been found in both samples. RBS and XPS analysis showed that the films were stoichiometric. When the annealing temperature was increased beyond 500 °C, the concentration ratio of MoO3–TiO2 decreased due to the evaporation of MoO3. For the study of the electrical and gas sensing properties, the films were deposited on sapphire substrates with interdigital electrodes on the frontside and a Pt heater on the backside. The MoO3–TiO2 thin films are sensitive to oxygen gas. The film has exhibited the O2 response (S=Rg/Rb) of 2.1, 8.1, and 80 for 120, 1000, and 10 000 ppm concentration of O2, respectively.
Nanowearing property of a fatigued polycarbonate surface studied by atomic force microscopy
Authors: Iwata Futoshi , Suzuki Yuichiro , Moriki Yoshitaka , Koike Syunsuke , Sasaki Akira
Published: July 2002

The nanometer-scale wearing property of the fatigued polycarbonate (PC) surface was studied using an atomic force microscope (AFM). The PC sample was fatigued mechanically by applying cyclic compressive strain using a piezoactuator device that could be fixed on the sample stage of the AFM. The direction of the compressive strain in the thin sample was parallel to the surface observed with the AFM. The surface morphology changed and became rougher under the fatigue process. Before the PC sample was fatigued, the formation of a periodic bundle structure was observed at the scan-scratched area. However, after the repetitive strain was applied to the PC sample, the fatigued surface was worn down easily by scan scratching without the formation of bundles. The elasticity of the PC surface was observed using ultrasonic force microscopy. After the fatigue progress, the elasticity of the PC surface decreased entirely due to many microcracks generated by applying repetitive strain. However, the elasticity of the scratched worn-down area was almost the same as that of an unworn surface.
Time-dependent Si etch behavior and its effect on oxide/Si selectivity in CF4+D2 electron cyclotron resonance plasma etching
Authors: Min Kyungjin , Lamb H. Henry , Hauser John R.
Published: July 2002

Transient poly-Si etching behavior in CF4+D2 electron cyclotron resonance plasmas containing different D2 proportions was investigated. Higher D2 proportions resulted in lower atomic F and higher CF2 concentration in the plasma, as evidenced by optical emission spectroscopy (OES), and in greater oxide-to-Si etch selectivity. A high initial poly-Si etch rate that declined very rapidly to a finite-steady-state value was observed for plasma etching under conditions giving low (3:1) oxide-to-Si etch selectivity. In contrast, a lower initial etch rate that declined to approximately zero over a longer (∼45 s) period was observed for poly-Si etching under plasma conditions giving (∼15:1) selectivity. In the latter case, Si consumption during overetching would be significantly underestimated if calculated on the basis of the conventional 60 s selectivity ration. X-ray photoelectron spectroscopy analysis indicated that a thick, more F-deficient fluorocarbon film was deposited on Si under the high-selectivity etching conditions. Real-time SiF4 and atomic F signals, which were measured during SiO2 etching using OES and mass spectroscopy, respectively, evidenced significantly different end-point trends for the high- and low-selectivity etching conditions. These trends are interpreted in light of the transient etching behavior observed for poly-Si under equivalent plasma conditions.
Field-based scanning tunneling microscope manipulation of antimony dimers on Si(001)
Authors: Rogge S. , Timmerman R. H. , Scholte P. M. L. O. , Geerligs L. J. , Salemink H. W. M.
Published: July 2002

The manipulation of antimony dimers, Sb2, on the silicon (001) surface by means of a scanning tunneling microscope (STM) has been experimentally investigated. Directed hopping of the Sb2 dimers due the STM tip can dominate over the thermal motion at temperatures between 300 and 500 K. Statistics on the enhanced hopping are reported and possible tip–adsorbate models are discussed focusing on a field-based interaction. The low yield of directed hopping is believed to be due to the low gradient in the interaction energy intrinsic to a field-based mechanism. Ultimate resolution and limiting factors of this manipulation technique are discussed.
Effect of growth rate on surface morphology of heavily carbon-doped InGaAs
Authors: Kuhl A. G. , Arès R. , Streater R. W.
Published: July 2002

Carbon-doped InGaAs was grown at two growth rates by chemical beam epitaxy using carbon tetrabromide as the dopant precursor. Surface roughness was measured using atomic force microscopy. Step-flow growth was observed for undoped InGaAs but a roughening of the surface and loss of step-flow growth occurred at high carbon-doping levels, possibly due to etching effects. The point at which the surface grew rough also corresponded to an increase in the variability of carbon, as reported by secondary ion mass spectrometry. Increasing the growth rate allowed the surface to remain smooth at higher carbon concentrations. The hole concentration saturated for samples grown at both growth rates. Carrier activation was slightly better in samples grown at a high growth rate. The ability to maintain good surface morphology at elevated carbon concentrations is critical for the fabrication of high frequency heterojunction bipolar transistors.
Very-low-temperature molecular beam epitaxial growth of GaP/AlAs heterostructures for distributed Bragg reflector applications
Authors: Pickrell G. W. , Chang K. L. , Lin H. C. , Hsieh K. C. , Cheng K. Y.
Published: July 2002

Using very-low-temperature (VLT) molecular beam epitaxy (MBE), (Ga,P)/(Al,As) heterostructures were grown for use in a distributed Bragg reflector (DBR). Through the use of VLT MBE and control of the group-V overpressure, the microstructure can be controlled resulting in either amorphous or polycrystalline material for both materials. Also, the growth rate is highly dependent on the group-V overpressure due to the high sticking coefficients of both As and P at these low growth temperatures. Using lateral oxidation, the amorphous AlAs was converted to its oxide for use in a visible wavelength DBR. Variabilities within layer thickness, especially the amorphous AlAs layers, were investigated to determine their effect on the DBR reflectivities. Different DBR designs were employed resulting in a double passband DBR which is highly reflective at wavelengths of both 550 and 1100 nm.
Combined silicon, beryllium, and carbon tetrabromide single-port dopant source for molecular-beam epitaxy
Authors: Moshegov N. T. , Nordquist C. D. , Cai W. Z. , Mayer T. S. , Lubyshev D. I. , Miller D. L.
Published: July 2002

We report the design and the performance of a compact dopant source that combines silicon, beryllium, and carbon tetrabromide in a single port of a molecular-beam-epitaxy system. This design relies on the rapid thermal response of the silicon and beryllium source materials and the rapid response to valve operation of the carbon tetrabromide flux to form abrupt junctions, rather than on shuttering. It features disks of silicon and beryllium without crucibles for low thermal mass and rapid radiative heating and cooling, thermocouples riveted directly to the disks for accurate temperature tracking, and a water-cooled molybdenum baffle to isolate the silicon and beryllium cells. Secondary ion mass spectroscopy analysis of dopant profiles and the I–V characteristics of GaAs p–n junction diodes indicate negligible dopant overlap in Be/Si p–n junctions made without the use of a shutter. Doping density for silicon and beryllium in GaAs varied less than 3% across the central 56 mm diam of a 76 mm (3 in.) wafer. We have used this source in our Gen II molecular-beam-epitaxy system over the past year for the growth of abrupt doping profiles, p–n junctions, high electron mobility transistors, and heterojunction bipolar transistors in arsenide and phosphide materials.
Choice of boron–carbon–nitrogen coating material for electron emission based on photoelectric yield measurements during x-ray absorption studies
Authors: Jiménez I. , Gago R. , Garcı́a M. M. , Albella J. M.
Published: July 2002

Boron–carbon–nitrogen films with different composition and bonding structures are grown by ion-beam-assisted deposition. The photoelectric yield from these films is used to characterize their potential use as coatings to enhance electron emission. As excitation light we used soft x rays in the course of x ray absorption experiments. In this way, we combine a detailed chemical and compositional characterization of the films with their photoelectric yield. Our results indicate that the main parameter affecting the electron emission is the proportion of sp3 hybrids in the film.
Application of dichroic mirror for improvement of luminance and luminous efficacy in an alternating current plasma display cell
Authors: Song Byung Moo , Kim Joong Kyun , Hwang Man-Soo , Yang Jin Ho , Whang Ki-Woong
Published: July 2002

An alternate application of dichroic mirror for the improvement of luminance and luminous efficacy in an ac plasma display panel (PDP) is suggested. Since only part of the vacuum ultraviolet (VUV) generated in the PDP cell is used to excite the phosphor, we propose deploying a dichroic mirror that increases luminance and efficiency by reflecting part of the VUV toward the phosphor. The optical constants of the dielectric layers of the dichroic mirror and a protecting layer of a PDP were determined from the measurements of reflectance and transmittance of the corresponding films and they were used to design the dichroic mirror including the protecting layer. The 147 nm xenon resonance line is usually used to activate the phosphor in the PDP cell. Thus, we designed the dichroic mirror to have a high reflectance for the VUV centered around 147 nm and a high transmittance for the visible light. We investigated the usefulness of the dichroic mirror by comparing the luminance and luminous efficacy of test panels with and without the dichroic mirror and found it could increase the luminance by 20%–31% and the luminous efficacy by 25%–34%.
Silicon V grooves fabricated using Ta2O5 etch mask prepared by room-temperature magnetron sputtering
Authors: Chu A. K. , Lee K. M. , Lan I. J.
Published: July 2002

A tantalum pentoxide (Ta2O5) etch mask process has been developed in the fabrication of silicon V grooves for precision positioning of optical fibers. The relationship between the Ta2O5 etch mask undercutting and the etching temperature of a mixture of ethylenediamine, pyrocatechol, and water (EDP) was studied. The Ta2O5 etch mask with a thickness of 500 nm was deposited by radio-frequency magnetron sputtering at room temperature on both sides of a 4 in. (100) Si substrate. Desired patterns were formed on the substrate using a dielectric lift-off technique. Etching temperatures of EDP ranging from 90 to 120 °C have been tested for the process. The undercut was found to decrease with the increasing etching temperature of EDP. At the etching temperature of 120 °C, an undercut of 1.61±0.13 μm using the Ta2O5 etch mask was achieved.
Improvement of substrate temperature uniformity by using a dual-zone substrate heater in a commercial 4 in. GEN-III molecular beam epitaxy single-wafer reactor
Authors: Fang X. M. , Yurasits T. R. , Loubychev D. , Wu Y. , Liu W. K. , DeBruzzi M. , Priddy S. , Schiprett C.
Published: July 2002

Substrate temperature uniformity on an Applied EPI 4 in. GEN-III single-wafer reactor has been improved with the use of a two-zone substrate heater. Varying the outer filament temperature can effectively change the temperature profile across wafers. The best uniformity in sheet resistance, source-to-drain saturation current in pseudomorphic high electron mobility transistor, photoluminescence peak wavelength and intensity for growth on 4 in. wafers was obtained by setting the inner and outer filaments at the same temperature. The source-to-drain saturation current and photoluminescence intensity uniformity for 4 in. pseudomorphic high electron mobility transistor grown on the GEN-III reactor compared very favorably with those grown on multiwafer production reactors. A total wavelength variation of less than 2 nm across 4 in. AlGaAs calibration wafers grown at 680 °C has been achieved using the dual-zone heater. Improved uniformity was also demonstrated with lattice-matched growth on 4 in. InP substrates.
Fundamental connection between hydrogen/deuterium desorption at silicon surfaces in ultrahigh vacuum and at oxide/silicon interfaces in metal–oxide–semiconductor devices
Authors: Cheng Kangguo , Lee Jinju , Chen Zhi , Shah Samir A. , Hess Karl , Leburton Jean-Pierre , Lyding Joseph W.
Published: July 2002

The fundamental connection between electron stimulated desorption (ESD) of hydrogen (H)/deuterium (D) at silicon surfaces in ultrahigh vacuum and hot-carrier-stimulated desorption of H/D at the oxide/silicon interfaces in complementary metal–oxide–semiconductor (CMOS) devices is presented. The dependences of device degradation on carrier energy and current density were studied on two generations of CMOS devices. The results suggest that the interface degradation in long channel devices is primarily due to the desorption of H/D by high energy electrons through the direct electronic desorption mechanism, while the multiple vibrational heating mechanism becomes important for ESD of H/D in deep submicron devices. By measuring interface trap generation at various stressing conditions in large time scales, we also provide experimental evidence to show that, unlike the uniform energy distribution of Si–H on silicon surfaces, the disordered interface environment introduces a variation of Si–H bond strength at the interface.
Sticking coefficient of boron and phosphorus on silicon during vapor-phase doping
Authors: Kiyota Yukihiro , Inada Taroh
Published: July 2002

A surface reaction model for boron and phosphorus atoms on silicon during vapor-phase doping is proposed by calculating their sticking coefficients. In boron doping, two sticking configurations are found: a low B2H6-concentration case, and a high B2H6-concentration case. In the low B2H6- concentration case, a low sticking coefficient is maintained during doping, and in which hydrogen desorption from the surface opens more sites for boron chemisorption. In the high B2H6-concentration case, excessively chemisorbed boron atoms react with each other, causing boron segregation. A low sticking coefficient is preferred in order to avoid boron segregation and to control the concentration. In the phosphorus doping, the sticking coefficient was much lower than that of boron, and phosphorus does not segregate on silicon.
New plasma display panel packaging technology using electrostatic bonding method
Authors: Lee Duck-Jung , Jeong Jin-Wook , Kim Young-Cho , Lee Yun-Hi , Ju Byeong-Kwon , Cho Tae-Seung , Choi Eun-Ha , Jang Jin
Published: July 2002

In this work, we have developed a plasma display panel (PDP) packaging technology, replacing the tip off tube with an indirect glass-to-glass electrostatic bond with intermediate layers of indium tin oxide and amorphous silicon. The glass-to-glass bonding for the packaging was performed at a low temperature of 180 °C while applying a bias of 250 Vdc in an environment of three mixed gases: He–Ne(27%)–Xe(3%). The 3.6 in. color alternating current-PDP with 8 mm thickness was successfully fabricated, with full white color brightness at a firing voltage of 190 V. Additionally, the luminance during the sustained period was 900–1000 cd/m2. To investigate the capability of applying the glass bonding technology, the hermetic sealing test of the packaged panel was examined by a spinning rotor gauge for time variation. The leak rate test was performed with a helium detector. Since there is very low leakage through the bonded interface during 160 h, we can propose that it is highly possible to apply this technology to any vacuum packaged device.
Flat-panel structure for field-emission displays with carbon nanotube cathode
Authors: Zhu Chang-chun , Liu Weihua , Huangfu Lujiang
Published: July 2002

A flat-panel structure for field-emission displays (FEDs) is proposed, in which an aligned carbon-nanotube film cathode of direct growth is mounted directly on the base plate with elastic assembling technology. The vacuum package is fabricated with some vacuum-fluorescence-display- like process technologies. This structure and the corresponding technologies are stable and reliable at a modest cost. The FED sample of a pixel display of this structure was made to verify the display structure and to analyze characteristics.
Low damage and low surface roughness GaInP etching in Cl2/Ar electron cyclotron resonance process
Authors: Yoon S. F. , Ng T. K. , Zheng H. Q.
Published: July 2002

Electron cyclotron resonance Cl2/Ar plasma etching characterization was performed to obtain low damage and low surface roughness conditions for GaInP lattice matched to GaAs. Micro-Raman spectroscopy, atomic force microscopy (AFM) and surface profiling were used to characterize the near-surface quality and etch rate of GaInP. The results show that near-surface damage increases with dc self-bias voltage in both Ar and Cl2/Ar plasmas. Etching in pure Ar plasma results in significant increase in the transverse-optic (TO) intensity at high dc self-bias voltage of 50 and 70 V, with the longitudinal-optic (LO) peaks downshifted in frequency. A normalized LO/TO intensity was quantified in this study to represent the combined effect of increase in TO intensity and slight decrease in LO intensity. In the case of Cl2/Ar plasma, substantial shifting of the GaP-like LO peak position to lower frequency was observed at dc self-bias voltage of 70 V at 120 °C with increase in the TO peak intensity. In addition, the decreasing trend of the normalized LO/TO intensity of GaP-like LO and InP-like LO peak was observed for samples etched under dc self-bias voltages of 40–70 V. Both observations from Cl2/Ar plasma etching indicate the alteration of the GaInP near-surface region by etch induced damage within the dc self-bias voltage range of 40 to 70 V. AFM studies showed surface damage consistent with the change in Raman spectrum. The damaged layer was caused by enhanced physical etching, which may result in InClx formation and therefore etch rate fluctuation at 70 V. The Raman spectrum of the sample etched at 30 V dc self-bias voltage was similar to that of the reference spectrum with normalized LO/TO intensity values comparable to that of the reference values, indicating a low damage process with root-mean-square (rms) surface roughness of 5.5 nm. Substrate temperature dependence of the surface roughness was studied at 20 V dc self-bias voltage. At 110 °C and 20 V dc self-bias voltage, desorption of volatile products results in low rms surface roughness of 1.28 nm and slow etch rate of 0.4 nm/s. The 20 V dry etch process was compared favorably to a HCl-based wet etch process. The low damage, low surface roughness and low etch rate process has excellent potential in compound semiconductor device processing, such as for GaInP emitter layer etching in heterojunction bipolar transistors fabrication.
Impression of high voltage pulses on substrate in pulsed laser deposition
Authors: Ikegami T. , Nakao M. , Ohsima T. , Ebihara K. , Aoqui S.
Published: July 2002

We report deposition of diamondlike carbon (DLC) films on silicon substrates in vacuum by ablating a graphite target using KrF excimer laser. High voltage pulses synchronous with the ablating laser pulse were applied to substrates to improve the hardness and adhesion of the DLC film. Ions accelerated in the carbon plasma plume resulted in an increase of ion flux and energy that modified the film properties. The effect of high voltage pulses on the laser ablated plasma plume was investigated by the laser induced fluorescence method, and their effect on DLC films was examined using Fourier transform infrared atomic force microscopy, and nanoindentation. High voltage pulse applied to the substrate increased the sp3 constituent in the DLC film and enhanced the smoothness and hardness of the film.
Breakdown characteristics of ultrathin gate oxides (<4 nm) in metal–oxide–semiconductor structure subjected to substrate injection
Authors: Huang Chia-Hong , Hwu Jenn-Gwo
Published: July 2002

Thin oxide property in a metal–oxide–semiconductor structure subjected to substrate injection from semiconductor into oxide is investigated by means of ramp-up and ramp-down current–voltage (I–V) measurements. Generally, gate injection causes catastrophic dielectric breakdown, and the damaged oxide suffers from permanent destruction which exhibits resistorlike behavior in the I–V curve. For substrate injection, however, there are three distinct modes existing in I–V characteristics. They are resistorlike, hysteresislike, and saturation, i.e., no breakdown. Their occurrence frequencies are dependent on the oxide thickness. For oxides thinner than 2.4 nm, in general, the gate current nearly saturates due to the limitation of minority carriers. For 3.9 nm oxide, the minority carrier generation rate increases due to trap generation near the Si surface. Thus the oxide sustains higher field and larger carrier injection causing destructive damage, i.e., resistorlike mode. For 3 nm oxide, sometimes a hysteresislike mode appears due to light damage in the oxide. The related characteristics of these three modes are studied and exhibit oxide thickness dependence. These phenomena are important to recent studies on devices with ultrathin gate oxides.
Atomic models of (∛×∛)R30° reconstruction on hexagonal 6H–SiC(0001) surface
Authors: Han Y. , Aoyama T. , Ichimiya A. , Hisada Y. , Mukainakano S.
Published: July 2002

By using reflection high-energy electron diffraction (RHEED) and RHEED multislice dynamical calculations, the atomic structures of the (∛×∛)R30° reconstruction on 6H–SiC(0001) surface were solved. Both the simple adatom structure with a Si coverage of one-third monolayer occupying the threefold-symmetric T4 or H3 sites and a bit complex structure with Si trimers centered on the T4 positions with 1 monolayer coverage are all compatible with our results.
Metamorphic In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistors on GaAs with InxGa1−xP graded buffer
Authors: Yuan K. , Radhakrishnan K. , Zheng H. Q. , Ng G. I.
Published: July 2002

A new metamorphic In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistor (HEMT) structure was grown on a GaAs substrate with a InxGa1−xP graded buffer layer by solid-source molecular beam epitaxy. The In0.53Ga0.47As channel layer was grown on the InGaP buffer layer directly without an InAlAs buffer as in the conventional design. High-resolution x-ray diffraction reveals that the whole layer structure is nearly fully relaxed. Hall measurement showed that this new layer design exhibits higher electron mobility and carrier concentration as well as lower light sensitivity compared to the reference sample with the conventional design. The promising device performance demonstrates the potential of using this metamorphic HEMT device in high speed and high frequency applications.
Deposition of silicon nitride films by pulsed laser ablation of the Si target in nitrogen gas
Authors: Umezu Ikurou , Kohno Kiminori , Yamaguchi Tomohiro , Sugimura Akira , Inada Mitsuru
Published: July 2002

We prepared SiNx film by pulsed laser ablation from Si target and nitrogen gas. We found that control of gas pressure is important to prepare stable and near stoichiometric film. The nitrogen content in the film increased with increasing nitrogen pressure up to 10 Pa. On the other hand, the film prepared at above 15 Pa easily oxidized in the atmosphere. The nitrogen molecule was decomposed to radicals by plume and reactions between Si and nitrogen take place up to 10 Pa. At higher pressure, formation of SiNx cluster in the plume prevent the production of high quality SiNx film.
Automated Xe adsorption technique to measure small Brunauer–Emmett–Teller surface area of several square centimeters
Authors: Yanazawa Hiroshi , Furukawa Ryoichi , Yamamoto Satoshi , Suzuki Isao , Miura Kazuhisa
Published: July 2002

An automated Xe adsorption apparatus has been developed that enables the measurement of a Brunauer–Emmett–Teller (BET) surface area of several cm2 with a repeatability of 4% (standard deviation). The apparatus is equipped with a differential type capacitance manometer, each hand of which is connected to a sample and reference adsorption cell having a symmetrical design, that is the temperature-compensated volumetric system which was reported by one of the authors [I. Suzuki, Rev. Sci. Instrum. 53, 1061 (1982); ibid., 66, 5070 (1995); ibid., 68, 4531 (1998)]. All procedures for measuring gas adsorption are computer controlled, and the coolant meniscus height is also computer controlled to keep the adsorption cell volume constant. A specially polished Si crystal rod was adopted as the standard sample. The BET surface area of the standard sample was measured by both the original temperature-compensated system and the newly developed automated system. Obtained results are fully consistent. We propose the adsorption cross section of Xe to be 0.25 nm2 based on our measurements. In addition, we demonstrate a series of experimental results which show a quantitative correlation between the capacitance and surface microroughness of a capacitor with rugged surface electrode.
Structure analysis of Ba2In2O5 and related compounds by electron microscopy
Authors: Mitome M. , Okamoto M. , Bando Y. , Yamamura H.
Published: July 2002

Crystal structures of Ba2In2O5: (Ba1−xLax)2In2O5+x (x=0.1, 0.2, 0.3, and 0.5), and Ba2(In1−xGax)2O5 (x=0.1, 0.2 and 0.5) are analyzed by transmission electron microscopy and electron diffraction. Ba2In2O5 has an orthorhombic brownmillerite structure and belongs to space group Ibm2. (Ba1−xLax)2In2O5+x has a tetragonal brownmillerite structure while Ba2(In1−xGax)2O5 has an orthorhombic brownmillerite structure. These compounds consist of small domains that are at 90° orientation to each other. The domain size gets small with increasing La or Ga content. The oxygen vacancies are distributed randomly in the compounds with high La or Ga content, and consequently, the structure approximates as a cubic perovskite structure.
Scanning probe microscopy of domains and domain walls in sol–gel PbTiO3 thin films
Authors: Chen Xiaofeng , Zhu Weiguang , Liu Weiguo , Wang Zhihong
Published: July 2002

We report results on ferroelectric domain and domain-wall observation in sol–gel PbTiO3 thin films using scanning probe microscopy. By taking the phase and amplitude image of the local domain piezovibration separately, more information is given to interpret the domain contrast owing to the a domain and different crystallographic orientations. Particularly, the a–c and c–c domain walls appear as a transition region and a dark region in the amplitude image, respectively, and the corresponding thickness is estimated to be 70 and 8 nm. A torsion vibration model is proposed to describe the tip vibration at the c–c domain wall, which results in the dark contrast correspondingly.
Reduction of residual gas in a sputtering system by auxiliary sputter of rare-earth metal
Authors: Li Dejie
Published: July 2002

In film deposition by sputtering, the oxidation and nitrification of the sputtered material lead to degradation of film quality, particularly with respect to metal sulfide films. We propose to use auxiliary sputtering as a method to produce a fresh film of rare-earth metal, usually dysprosium (Dy), that absorbs the active gases in a sputtering system, greatly reducing the background pressure and protecting the film from oxidation and nitrification effectively. The influence of the auxiliary sputtering power consumption, sputtering time, and medium gas pressure on the background pressure in the vacuum chamber is investigated in detail. If the auxiliary sputtering power exceeds 120 W and the sputtering time is more than 4 min, the background pressure is only one fourth of the ultimate pressure pumped by an oil diffusion pump. The absorption activity of the sputtered Dy film continues at least an hour after completion of the auxiliary sputter. Applied to film deposition of Ti and ZnS, this technique has been proven to be effective. For the Ti film, the total content of N and O is reduced from 45% to 20% when the auxiliary sputtering power of Dy is 120 W, and the sputtering time is 20 min. In the case of ZnS, the content of O is reduced from 8% to 2%.
Morphological transitions of Si1−xGex films growing on Si(100). I. Gas-source molecular-beam epitaxy: From two-dimensional growth to growth in the Stranski–Krastanov mode
Authors: Akazawa Housei
Published: July 2002

Morphological evolution in the growth of thin films of Si1−xGex on Si(100) by gas-source molecular beam epitaxy has been investigated by in situ spectroscopic ellipsometry. When the ellipsometric trajectories are monitored at 3.4 eV and depicted in the plane of (Ψ,Δ) angles, two-dimensional (2D) growth is seen to produce a short one-turn spiral. The onset of three-dimensional nucleation can be detected by the smooth connection of one initial spiral to another small branch before convergence at the destination point of 2D growth or by deviation toward the region of lower Δ. These features correspond to the development of surface undulations that form a sinusoidal-like ripple structure. The second-stage transition from the ripple to coherent pyramidal islands occurs with the appearance of the cusp-shaped inflection point between the first and second branch, which is due to the engraving of troughs between islands. With yet higher content of Ge in the film and at high growth temperatures, the trajectory curve is shifted rapidly toward the lower Δ region after moving along the 2D growth spiral for a while, and this observation reflects the nucleation of isolated dome-shaped islands.