bluuebunny/crossref_metadata_2025 huggingface dataset:
Velocity distribution of organic molecules emitted from effusion cells measured by time-of-flight technique
Authors: Shimada Toshihiro , Koide Jun , Cho Kyoung Ah , Koma Atsushi
Published: July 2002

Velocity distribution of the molecules emitted from effusion cells commonly used in molecular beam epitaxy was measured by using time-of-flight technique. The result for organic molecular phthalocyanine can be fitted by a shifted Maxwellian distribution. The effects of the temperature and the aspect ratios of the sources are discussed.
Low-temperature plasma deposition of dielectric coatings from organosilicon precursors
Authors: Lin C.-T. , Li F. , Mantei T. D.
Published: July 2002

Silicon dioxide coatings have been grown with deposition rates up to 0.7 μm/min and substrate temperatures from 80 to 140 °C in a high-density microwave electron cyclotron resonance discharge. The deposition precursors were tetraethoxysilane (TEOS), hexamethyldisiloxane (HMDSO), and hexamethylcyclotrisiloxane (HMCTSO), with oxygen as an additive gas. The O2/precursor flow ratios ranged from 2:1 to 8:1 and the total gas pressure prior to plasma ignition was 1–10 mTorr. The deposited films for all precursors were hard, colorless, and transparent. Maximum deposition growth rates were 0.25 μm/min for TEOS, 0.65 μm/min for HMDSO, and 0.68 μm/min for HMCTSO; final film thicknesses were 3–10 μm. Deposition growth rates increased with increasing precursor gas flow, increasing input power, and decreasing O2/precursor flow ratio. The coatings exhibit Si–O elemental bonding with a small Si–CH3 component. The oxygen-to-silicon ratios are approximately 2:1 with some incorporated carbon.
Characterization of sol-gel prepared WO3 thin films as a gas sensor
Authors: Cantalini C. , Atashbar M. Z. , Li Y. , Ghantasala M. K. , Santucci S. , Wlodarski W. , Passacantando M.
Published: July 2002

Tungsten trioxide (WO3) thin films have been prepared by the sol-gel process and annealed at different temperatures of 400, 500, 600, and 700 °C for 1 h. The morphology, microstructure, crystalline structure, and composition of the films have been analyzed using scanning electron microscopy (SEM), x-ray diffraction, Rutherford backscattering spectroscopy (RBS), and x-ray photoelectron spectroscopy (XPS) techniques. The SEM analysis showed that the films annealed at 400 °C are smooth and uniform. However, these evolved as granular at an annealing temperature of 500 °C. The films annealed at still higher temperatures have two distinct grains of different shapes and sizes. The films annealed below 400 °C are amorphous. Annealing at 500 °C resulted in the films having polycrystalline structure. RBS and XPS characterization have revealed that the films annealed at 400 °C are stoichiometric. Annealing above this temperature resulted in the films becoming off-stoichiometric. The electrical resistance of the films annealed at 500 °C increased 18 times when exposed to 175 ppb O3 gas compared to the air exposure, with the response time being as short as 1–2 min.
Thin-film gas sensors based on high-temperature-operated metal oxides
Authors: Fleischer M. , Meixner H.
Published: July 2002

Research into the characteristics of semiconducting metal-oxide films that are stable at high temperatures intensified with the aim of providing reproducible and reliable gas detection in various ambients. First, there is a discussion of the specifics relating to these materials, for example, the effect of grain-boundary barriers on the sensing mechanism, the influence of humidity, and the temperature dependence of the sensing mechanism. Then, the technology for the preparation of the gas sensors will be described. Examples that have already been implemented like λ detection, oxygen and NOx measurements in exhaust gases, detection of explosive and toxic gases in air, as well as hydrogen leakage detection are discussed.
Mass spectrometric measurements on inductively coupled fluorocarbon plasmas: Positive ions, radicals and endpoint detection
Authors: Li Xi , Schaepkens Marc , Oehrlein Gottlieb S. , Ellefson Robert E. , Frees Louis C. , Mueller Norbert , Korner Norman
Published: July 2002

Positive ions and radicals in C2F6 and CHF3 high density discharges were measured using a direct-line-of-sight mass spectrometer. The ion energy distributions of the dominant ions were measured as a function of process conditions. Appearance potential mass spectrometry was performed to measure trends of the radical densities. For C2F6 plasmas CF3 and CF3+are the most abundant neutral and ionic species, respectively. CF3 is the most abundant neutral species for a CHF3 plasma, whereas CHF2+ and CF+ are the most abundant ionic species at 600–1000 and 1400 W, respectively. Erosion of the quartz coupling window is an important contaminant source for our inductively coupled plasma system. For comparison, downstream mass spectrometry was also applied using a closed ion source system since this approach is of interest for real-time monitoring and control. Endpoint detection for Si and SiO2 film etching in a CHF3 plasma was investigated using the downstream mass spectrometer system and compared with data obtained simultaneously using the direct-line-of-sight mass spectrometer and optical emission spectroscopy. It was found that the downstream mass spectrometer system can be used for endpoint detection during SiO2 over Si selective etching. The signal changes of different species measured by these techniques for different SiO2 and Si etching processes as a function of time are reported and compared.
Bistable microelectrothermal actuator in a standard complementary metal-oxide-semiconductor process
Authors: Ressejac I. C. , Landsberger L. M. , Currie J. F.
Published: July 2002

A new kind of bistable microelectrothermal actuator is designed and fabricated in a standard complementary metal-oxide-semiconductor technology. This actuator is designed to be the basic element of an N by N switching matrix that enables the connection of an input signal among N outputs. A microelectronic addressing circuit integrated on the same substrate can control this matrix. Bulk micromachining processes release SiO2 and Al cantilever beams, each having two bilayer actuators. When the Al is resistance heated, stresses are generated leading to deflections of the cantilever. By proper sequencing of heating and cooling of the heaters, complex motion of the beam is possible, including two stable positions. A combination of anisotropic and isotropic etching techniques using tetramethyl ammonium hydroxide and XeF2 are used to realize these structures.
Microstructural and morphological analysis of ultrathin YBa2Cu3O7−x films grown by modulated magnetron sputtering on SrTiO3 substrates
Authors: Del Vecchio A. , De Riccardis M. F. , Tapfer L. , Camerlingo C. , Russo M.
Published: July 2002

The defect structure, the degree of crystalline perfection and the surface roughness of HTc superconductor films are affected by the initial layer configuration at the early stage of growth. In this work we report on structural and morphological investigations of ultrathin YBa2Cu3O7−x films grown on SrTiO3 substrate. The films are fabricated by inverted cylindrical magnetron sputtering with a modified deposition process based on the modulation of sputtering power. The modulated sputtering deposition promotes a higher in-plane grain connectivity and allows us to fabricate films with a lower defect density. The structural analyses of very thin films (thickness <25 nm) are performed by using low-angle x-ray specular reflectivity, double crystal diffraction, reciprocal space mapping and atomic force microscopy. The results indicate that a total relaxation of our films occurs at layer thickness larger than 25 nm. For thinner layers a tetragonal distortion of the unit cell and no twinning are observed. The low-angle measurements show distinct Kiessig fringes revealing a smooth surface and film/substrate interface. The off-specular reflectivity measurements indicate that the surface and interface roughness across the YBa2Cu3O7−x layer are uncorrelated.
Epitaxial growth structure and physical properties of Fe film biased dc-plasma sputter deposited on MgO(001)
Authors: Chen Chang Chuan , Yang Jiping , Nakai Hisashi , Hashimoto Mituru
Published: July 2002

One hundred-nm-thick Fe film has been deposited on MgO(001) substrate at 250 °C by biased dc-plasma sputtering at 2.9 kV in Ar gas. A dc bias voltage Vs between 0 and −160 V was applied to the substrate during deposition. Reflection high energy electron diffraction, x-ray diffraction, cross sectional transmission electron microscopy (XTEM) and high resolution XTEM were used to investigate the structure of the films. Electrical resistivity at room temperature was measured by four-point probe method. Saturation magnetization of the films at room temperature was measured using a vibration sample magnetometer. As a result, when Vs=−140 V the Fe film could be epitaxially grown with Fe(001)[110]//MgO(001)[100] while the film retained a polycrystalline structure when Vs was higher or lower than −140 V. The minimum electrical resistivity and the maximum saturation magnetization were achieved at Vs=−140 V consistent with the result of the growth structure. In conclusion, when Vs=−140 V the Fe film can be epitaxially grown with the lower defect density under the bombardment of energetic Ar particles accelerated by Vs to increase the mobility of Fe adatoms and to resputter impurity species during the film formation.
Low noise bipolar complementary metal–oxide–semiconductor mixer for radio frequency applications
Authors: Colomines S. , Parra T. , Graffeuil J. , Plana R.
Published: July 2002

This article presents a low IF mixer featuring metal–oxide–semiconductor devices in the rf and the active load stages for DCS applications which have been optimized with respect to the supply voltage (2.2 V), current consumption (<10 mA), gain (10 dB), linearity (IIP3=8.5 dBm), and noise (DSB Nf=13 dB at 100 kHz). Special attention has been paid to the identification of the noise mechanisms.
Low-temperature gaseous nitriding and subsequent oxidation of epitaxial Ni/Fe bilayers
Authors: Mijiritskii A. V. , Boerma D. O.
Published: July 2002

Low-temperature gaseous nitriding was applied to epitaxial Ni/Fe bilayers deposited onto a MgO(001) substrate. The pore-free nitride layers produced were subsequently oxidized in oxygen. The samples were analyzed by conversion electron Mössbauer spectroscopy (CEMS), x-ray diffraction (XRD), and Rutherford backscattering spectroscopy in combination with channeling techniques. Nitriding in pure NH3 gas at 300 °C led to the formation of a textured ε-Fe–nitride layer with a predominant composition of Fe2.07N. The epitaxial relationship of the ε-Fe–nitride layer with the MgO substrate was found to be ε-Fe2.07N{203}〈010〉‖MgO{001}〈110〉. The nitride layer produced was subsequently oxidized in p(O2)=100 mbar at 275 °C. While the XRD spectra acquired on the oxidized samples revealed the formation of a Fe–oxide phase with a spinel structure, the CEMS spectral lines could not be interpreted in terms of any Fe–oxide or Fe–hydroxide phase know. It is suggested that the peculiarities in the CEMS data are caused by N atoms incorporated into the oxide lattice.
Surface-sensitive, element-specific magnetometry with x-ray linear dichroism
Authors: Schumann F. O. , Willis R. F. , Tobin J. G.
Published: July 2002

It is shown that the x-ray magnetic linear dichroism (XMLD) in x-ray photoemission signal can be used to monitor the element specific magnetic moments in ultra thin alloy films. Comparison with recent superconducting quantum interference device data provides a quantitative check that demonstrates that the total magnetization derived from summing the constituent elemental moments changes with the composition of the alloy. This is illustrated by the contrasting behavior of FeNi and CoNi alloys.
Fabrication of a nanosize metal aperture for a near field scanning optical microscopy sensor using photoresist removal and sputtering techniques
Authors: Jung M. Y. , Lyo I. W. , Kim D. W. , Choi S. S.
Published: July 2002

Micromachining of a nanoscale Si3N4 tip for near field scanning optical microscopy (NSOM) and scanning force microscopy (SFM) has been described. The tapered optical metal-coated fiber is generally used to provide a subwavelength sized aperture on the tip. Several micromachining methods have been performed in order to have a metal aperture with a radius less than λ/2. Apertures provided with less than λ/2 and hollow tips would provide a suitable probe for both NSOM and SFM. A Si3N4 tip coated with a thin metal film will meet these requirements. The Si tip has been initially fabricated using reactive ion etching. The SiO2 etch masks with 10 and 2 μm were patterned followed by Si etching. The etched Si post was at least 3 μm tall and the radii of the tips were found to be 30 and 10 nm depending on the fabrication methods. A Si3N4 thin film was deposited on the fabricated Si tip using a low pressure chemical vapor deposition technique in order to provide a capability for an atomic force microscope. A 30 or 60 nm Cr metal film was deposited using an electron beam evaporator. The thick photoresist (PR) film was coated using a two-stage method in order to cover the tall Si tip. The PR film was carefully etched to have a metal aperture size with less than λ/2. The removal of the Cr metal at the top of the Si tip has been performed using a Ne sputtering technique. The radius of the sputtered tip has been observed to be ∼80 nm after 2 h sputter etching.
Roles of N2 gas in etching of platinum by inductively coupled Ar/Cl2/N2 plasmas
Authors: Ryu Jae-Heung , Kim Nam-Hoon , Kim Hyeon-Soo , Yeom Geun-Young , Chang Eui-Goo , Kim Chang-Il
Published: July 2002

Recently, much effort has been expended on etching platinum film, which is the candidate electrode material for the capacitor structure of future dynamic random access memory and ferroelectric random access memory. One of the most critical problems in the etching of platinum was generally considered to be the gradual character of the etch slope. Therefore, the addition of N2 gas into the Ar/Cl2 gas mixture, which had been proposed as the optimized platinum etching gas combination in our previous article, was performed. The selectivity of platinum to oxide as an etch mask increased with the addition of N2 gas, and a steeper etch slope, over 75°, could be obtained. These phenomena were interpreted as the result of a blocking layer, such as Si–N or Si–O–N, on the oxide mask. Compositional analysis was carried out by x-ray photoelectron spectroscopy and secondary ion mass spectrometry. Moreover, the higher etch rate of the Pt film and a steeper profile without residues (such as Pt–Cl and Pt–Pt) could be obtained by the addition of 20% N2 gas in the Ar(90)/Cl2(10) plasma. The plasma characteristics were extracted from optical emission spectroscopy.
Origin, symmetry, and temperature dependence of the perturbation induced by Si extrinsic defects on the Sn/Si(111) α surface: A scanning tunneling microscopy study
Authors: Ottaviano L. , Crivellari M. , Profeta G. , Continenza A. , Lozzi L. , Santucci S.
Published: July 2002

We have studied with variable temperature scanning tunneling microscopy (STM) experiments the local structure of substitutional Si defects of the 1/3 ML Sn/Si(111) α surface. Empty state images show that most substitutional Si defects drift toward H3 sites leaving an unsaturated dangling bond from the first layer Si atoms. Consequently there is a charge transfer toward the Sn first neighbors of the defect. Filled state images show defect centered perturbations having 3×3 symmetry, which locally modifies the surface into a honeycomb pattern. Low temperature (120 K) STM images show undoubtedly the increase of the decay length of such perturbation, indicating the possibility of an overall phase transition at much lower temperatures.
Effects of interface mixing on adhesion of amorphous carbon films synthesized by variable-energy direct carbon ion beam deposition
Authors: Sohn M. H. , Kim S. I.
Published: July 2002

Using a variable-energy direct carbon ion beam deposition technique, thin amorphous carbon films were grown on a silicon substrate. Interface modification was performed using C− energies in the range of 300–500 eV prior to the growth of the film to enhance adhesion of the film. By lowering the energy of the C− beam to 150 eV, amorphous carbon film was continuously grown after the interface modification. High-resolution electron microscopy illustrated that the silicon surface was severely damaged by 500 eV C− beam and the thickness of damage layer was about 15 nm. The carbon concentration profile in silicon as determined by electron energy loss spectroscopy showed that 500 eV C− beam implanted carbon into silicon up to 30 nm in depth and carbon was mixed with silicon in this implanted region. Silicon L-edge study at the C/Si mixed region found C–Si bonding formation only at the surface of silicon over 2–3-nm-thick layers. The damage layer or C/Si mixing was not observed at 300 eV C− beam modification. Wear testing found that strong adhesion occurred in samples modified at 500 eV, which indicated complete mixing at the interface. At 300 eV, modified samples exhibited delamination failure, which indicated inferior adhesion of the films.
Temperature profiles in solid targets irradiated with finely focused beams
Authors: Iranmanesh Ali A. , Pease R. F. W.
Published: July 2002

The quantitative understanding of the processes involving focused beams, such as recrystallization of semiconductors or thermal annealing and recording, requires a detailed knowledge of the temperature profiles within the target. We have derived first a normalized analytical representation for the distribution of power dissipation in targets bombarded with electron beams. This representation has then been combined with the Green’s function approach and Kirchoff transformation to predict the steady state and transient temperature profiles in targets with linear and nonlinear thermal conductivities. This calculation for the case of transient heating when thermal conductivity changes with temperature is not strictly accurate and, therefore, a numerical technique was developed involving successive over relaxation. Considerable care was needed in choosing the distribution of mesh size because of the great difference between beam radius (down to 2 μm) and target dimensions (250–500 μm). Numerical calculations for silicon (a nonlinear conductor) agreed well with transient analytical calculations using Kirchoff transformation.
Band offsets, defects, and dipole layers in semiconductor heterojunctions
Authors: Zur A. , McGill T. C.
Published: July 2002

The role of defects in heterojunctions was investigated. The density of such defects required to pin the Fermi level or to affect the band offset was estimated using simple electrostatic considerations. We conclude that it is very unlikely that defects play any role in determining the band offsets, but they might affect the Fermi-level position at the interface.
X-ray lithography for sub-100-nm-channel-length transistors using masks fabricated with conventional photolithography, anisotropic etching, and oblique shadowing
Authors: Chou S. Y. , Smith Henry I. , Antoniadis D. A.
Published: July 2002

In order to fabricate submicrometer-channel-length MOSFET’s using x-ray lithography, a novel mask fabrication technique was developed. The mask enabled PMMA lines with widths of 100, 160, 250, 270, and 5000 nm to be exposed simultaneously on the same substrate. The mask consists of a polyimide membrane with narrow absorber lines on the front side (facing the substrate) and coarse absorber patterns on the back side (facing the x-ray source). The narrow absorber lines are formed by oblique shadowing of gold onto sidewalls of rectangular mesas molded on the polyimide from wells anisotropically etched in (110)Si. As a result, exposed lines are straight, controlled in width to ∼10%, and have very small edge ripple. Source and drain pattern areas are formed in gold on the back surface of the membrane by conventional photolithography and ion beam etching. PMMA lines exposed with the x-ray mask were used for channel masking during source–drain ion implantation. Operating MOSFET’s were fabricated with minimum channel length estimated to be 75 nm.
Silicide formation of thin vanadium layers in ultrahigh vacuum studied by ion scattering, Auger electron spectroscopy, low energy electron diffraction, and secondary ion mass spectrometry
Authors: Achete C. , Niehus H. , Losch W.
Published: July 2002

Vanadium silicide formation has been monitored by low energy noble gas ion scattering (IS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS). Vanadium deposited at 300 K shows no silicide formation. The topmost layer is composed of V atoms only. Annealing leads to a chemical reaction of vanadium and silicon to a vanadium silicide. Upon annealing at T=830 K the top layer consists of a Si layer. The silicide formation could be monitored by the VSi+2 SIMS line. At 830 K a complete reaction of a 5000-Å-thick V film into a VSi2 silicide occurs.
Monte Carlo simulation of line edge profiles and linewidth control in x-ray lithography
Authors: Semenzato L. , Eaton S. , Neukermans A. , Jaeger R. P.
Published: July 2002

X-ray lithography exposures of PMMA on silicon have been simulated with a Monte–Carlo method including the energy backscattering from the substrate. The line-edge acuity of the resist image has been modeled with experimentally determined x-ray spectra of various sources (aluminum, tungsten, and palladium) and various source diameters (0.1, 1.5, and 3 mm). The intrinsic line-edge degradation due to secondary electron exposure is derived from the point source images while the finite-source effect (penumbra) is extracted from the additional degradation at finite source diameters. The penumbra effect is found to be rather small in PMMA. Depth profiles of the energy absorbed in PMMA demonstrate the significance of the energy backscattering from the substrate for energetic x rays. This effect can be significantly reduced by an organic spacer layer. The extent of the geometric projection effect has been modeled with the aluminum source. The results show that a finite angle of incidence of the x rays causes a sizable enlargement of the mask shadow due to the finite absorber thickness ultimately restricting the usable field size. The resultant linewidth variation is more pronounced for a mask with vertical profiles than for one with 20° wall angle. It can be reduced by thinning the absorber although at the expense of the mask contrast. The angle of incidence is replicated in the resist profiles causing an increasing tilt of the lines further away from the center of the wafer. This also restricts the field size but can be controlled to some extent by the thickness of the imaging resist layer.
Excimer-laser etching of diamond and hard carbon films by direct writing and optical projection
Authors: Rothschild M. , Arnone C. , Ehrlich D. J.
Published: July 2002

Excimer-laser patterning of monocrystalline diamond was performed in the direct writing and in the optical projection modes. The etching mechanism employs combined photochemical/thermal transformation of the initial crystal to graphite followed by sublimation or reaction of the transformed solid. In optical projection, linewidths as narrow as 0.13 μm were etched with patterning possible using single 0.193 μm (wavelength) laser pulses. Etch rates of 2000 Å/pulse were achieved. The morphology of the etched features was optimized by introducing gases which reacted chemically with the hot graphitic layer generated in the process of etching. Patterning of diamond-like carbon thin films was accomplished and the effectiveness of these films as resists for submicrometer-resolution lithography of semiconductors was demonstrated.
Lithography with the scanning tunneling microscope
Authors: McCord M. A. , Pease R. F. W.
Published: July 2002

In a recent paper [McCord and Pease, J. Vac. Sci. Technol. B 3, 198 (1985)] we described how it should be possible to generate, for lithography and other materials processing, an electron beam with an extraordinary combination of high current (>1 mA), low voltage (<100 V) and small diameter (<0.1 μm) using a modified scanning tunneling microscope (STM) operating in the field emission mode. To test this prediction we have built a modified STM onto the stage of a scanning electron microscope (SEM) so that we can monitor system geometry. The tip, an etched tungsten wire, can be manually moved in the z direction (normal to the target) for coarse motion and three PZT piezoelectric transducers allow 10 μm travel in the x, y, and z directions. A feedback system stabilizes the field emission current (and hence the tip-to-target spacing). We have obtained beams with currents from 1 nA to several microamps at voltages from 1 to 1000 V. We have used the beam to produce lines of contamination on a gold film; the contamination was then used as a mask against sputter etching to produce gold lines. In addition we have exposed a Langmuir–Blodgett resist film. In both cases we have produced sub-tenth-micron lines.
The residue phenomenon in the anisotropic dry etching of conductive films deposited on topographic steps
Authors: Maa Jer-shen , Halon Bernard
Published: July 2002

In the anisotropic dry etching of conductive films deposited on topographic steps, it is difficult to remove the residue even with extended overetch. The resistances of the residues from aluminum and silicide etching are found not to depend on film thickness or step coverage but to depend on bias voltage and pressure. The etch profiles observed by SEM are discussed in terms of native oxide film and polymer film formation. A simple model is proposed to reveal the residue formation process and to explain the problem encountered during the removal of the etched residue. A simple method is presented to determine the minimum requirement of a reliable etch process associated with surface topology.
Capacitance transient analysis of molecular-beam epitaxial n-In0.53Ga0.47As and n-In0.52Al0.48 As
Authors: Whitney Peter S. , Lee Wai , Fonstad Clifton G.
Published: July 2002

A deep level capacitance transient analysis of n-In0.53Ga0.47As and n-In0.52Al0.48 As epitaxial layers grown by molecular-beam epitaxy is reported. The In0.53Ga0.47As layers exhibited very low deep level concentrations. The principle deep level was an electron trap located near mid gap at a concentration of 1.5×1013 cm−3. The In0.52Al0.48As layers showed high concentrations of deep electron traps. The observed capacitance transients in In0.52Al0.48As samples exhibited nonexponential behavior caused by the similarities in time constants of different deep levels. By using an analysis of stored capacitance transients based on fitting to multiple exponentials, the activation energies and concentrations of six electron traps have been identified. The activation energies of the two traps with highest concentrations are 0.58 and 0.61 eV.
Masked ion beam lithography for submicrometer-gate-length transistors
Authors: Pang S. W. , Lyszczarz T. M. , Chen C. L. , Donnelly J. P. , Randall J. N.
Published: July 2002

GaAs metal-semiconductor field-effect transistors (MESFETs) with 0.3-μm gate length were fabricated using masked ion beam lithography (MIBL). Since MIBL allows submicrometer features to be patterned in thick layers of polymethylmethacrylate (PMMA), a new self-aligned technique was developed. The submicrometer gate as well as the source and drain patterns were defined in PMMA by MIBL and were transferred to the underlying SiO2 film by reactive ion etching. The high aspect ratio structure, formed in the combined PMMA and SiO2 layers used to define the submicrometer gate, allows Ohmic metals to be deposited only in the source and drain regions and not in the gate region via shadow evaporation. The rest of the patterning for contact pads, device isolation, and T-gate overlay was done by optical lithography. The device fabrication process for GaAs MESFETs is presented and the electrical characteristics of these devices are analyzed. The fabricated devices have 0.3-μm gate length and a transconductance of 150 mS/mm. The effects of ion radiation on the device performance is studied. With a 150-nm SiO2 layer between the PMMA and the GaAs substrates, proton induced damage can be removed by thermal annealing at 450 °C for 5 s or by wet etching 50 nm of the top GaAs surface.
Contrast improvement of alignment signals from resist coated patterns
Authors: Kuniyoshi Shinji , Terasawa Tsuneo , Kurosaki Toshiei , Kimura Takeshi
Published: July 2002

A method of enhancing the contrast of alignment signals for use in step-and-repeat projection aligners is described. In conventional through-the-lens alignment, signals are greatly influenced by interference phenomena between the resist surface and the wafer surface. Factors such as resist thickness, step depth, and alignment wavelength are examined to determine their effect on signal contrast. Based on the results, two wavelengths (i line/e line) are used for alignment and an alignment accuracy of 0.13 μm is obtained.
Microstructures for particle beam control
Authors: Jones G. W. , Jones S. K. , Walters M. , Dudley B.
Published: July 2002

Submicron lithography presents significant challenges to the fabrication of high-density complex devices. Resolution, speed, critical dimension precision, variable design sets, and registration generally are conflicting goals for a lithography system. In this paper, we will present a new concept in electron or ion beam lithography with the potential to write far submicrometer patterns at speeds well beyond those of single beam systems currently available. This structure serves as a combined multiple aperture and beam deflection structure in a high-speed multibeam raster scan writing system. The principle device structure to be discussed consists of an array of apertures micromachined into a portion of a silicon substrate with electrostatic deflection lines connected to each aperture. This structure is a key part of a lithography system with targeted 0.1-μm-pixel resolution. Apertures of 0.08 μm2 diameter with 10% dimensional control have been fabricated along with multiple multipole lenses using various microfabrication techniques. The paper will focus on the fabrication of these novel structures and will discuss potential system applications.
Patterned wafer inspection using laser holography and spatial frequency filtering
Authors: Cavan D. L. , Lin L. H. , Howe R. B. , Graves R. E. , Fusek R. L.
Published: July 2002

An automatic patterned wafer inspection system for use in integrated circuit fabrication is described. The system is based on the techniques of optical spatial frequency filtering and laser holography. The system can locate defects as small as 0.5 μm over a 150 mm patterned silicon wafer in ∼30 min. The wafer under inspection is placed in front of a lens and is flood illuminated through beam splitting optics with a collimated laser beam. The light reflected and diffracted from the wafer is collected by the lens through the beam splitter. In the back focal plane of the lens, the Fourier transform (spatial frequency) pattern of the wafer circuit is formed. A spatial filter placed in this plane effectively blocks the transmission of the light from the repetitive circuit features of all dies of the wafer. The wave front transmitted through the filter is then recorded in a hologram. The conjugate to the recorded wave front is later reconstructed from the hologram. The reconstructed wave front thus reverse ray traces the filter and the lens, forming a real image of the wafer. In this image, the defects are greatly intensified relative to the filtered circuit features. An analysis of the optical wave fronts in the system is provided. The defect information is obtained by scanning a two-dimensional photodetector array through the holographic image and recording the size and location of each point of light above a predetermined threshold. Test wafers containing electron beam programmed defects in a trilevel resist structure were prepared and inspected. Performance results are described.
High-resolution deposition and etching of metals with a scanning electrochemical microscope
Authors: Hüsser Oskar E. , Craston Derek H. , Bard Allen J.
Published: July 2002

A novel method is described which can be used for both the electrochemical deposition of metals in polymer films and the etching of metals with very high resolution. These faradaic processes are controlled using a scanning electrochemical microscope (similar to the scanning tunneling microscope). Patterns of silver and gold deposited in Nafion and poly(4-vinylpyridine), respectively, with a linewidth smaller than 0.5 μm, and high-resolution etching patterns in copper are shown. Extensions of this methodology to depositions of other materials, the use of other conducting polymer films, and possible applications for submicron devices are discussed.
Electronic structure of small coverages of column III metals on silicon [100]
Authors: Klepeis John E. , Harrison Walter A.
Published: July 2002

We calculate the electronic structure of geometrically ideal interfaces between column III metals and silicon. For a single neutral adatom the associated metallic Fermi energy must lie between the energy (0,+), for the removal of an electron, and the energy (0,−), for adding an electron, but is otherwise unrestricted. This circumstance also holds for many uncoupled adatoms and will produce pinning if the (0,+) and (0,−) levels are in the gap and the semiconductor Fermi energy is outside this range. At still larger coverages the occupied (0,+) levels and the (0,−) levels shift and broaden in energy until the gap between them disappears, pinning n-type and p-type semiconductors at the same energy. We find that the (0,+) level for a single aluminum adatom is in the silicon gap and that the (0,−) level is in the conduction band. In addition, the (0,+) level moves towards the valence band maximum as the metal coverage is increased.
Ultraviolet photoetching of copper
Authors: Brannon James H. , Brannon Karen W.
Published: July 2002

Excimer laser etching of copper using CCl4 and CF2Br2 vapors is described. These gases, unlike pure halogen gas, are inert toward copper in the absence of light. For pressures of 2–10 Torr, 248-nm dissociation of CCl4 or CF2Br2 results in etching that is linear in pressure, and is approximately the same for both gases. At 351 nm, only CCl4 causes etching. This wavelength variability, examined together with the gas-phase absorption spectra, suggests that gas-phase photolysis occurs prior to etching for CF2Br2 at 248 nm, but that a surface mediated dissociation likely occurs for CCl4 at 248 and 351 nm. A numerical solution of the one-dimensional heat flow equation was used to obtain the laser-induced surface temperature-time profile for the case of a bare copper surface, and copper covered with differing thicknesses of CuCl. CuCl is the reaction layer assumed to form when CCl4 dissociates on copper. Surface melting is not indicated, implying that etching occurs either by transient evaporation (solid→vapor) or by a quantum (nonthermal) process. Numerical solution of an etching model based upon transient evaporation of the CuCl reaction layer gives calculated etch rates that are many orders of magnitude smaller than the experimental rates. It is thus argued that nonthermal photophysical processes are responsible for material removal from the surface. The implications of these results for excimer laser etching of copper in Cl2 or Br2 gases are discussed.
Thermal distribution and the effect on resist sensitivity in electron-beam direct write
Authors: Eib Nicholas K. , Kvitek Richard J.
Published: July 2002

Thermal sensitivity measurements of diazoquinone/novolac (DQN), poly-olefin sulfone/novolac (SNS), and an acid catalyzed/proprietary resin (XPR) were made by gently exposing coated wafers at 10−9 amp/cm2 on a cooled/heated stage in our e-beam exposure tool. The results were characterized by the influence of exposure temperature on blanket-exposure-dissolution rates and developed image profiles. Three-dimensional Monte Carlo absorbed-energy-density calculations have been combined with ANSYS finite-element-thermal analysis to estimate the time evolution of temperature profiles on silicon wafers, silicon membranes, and SiO2 wafers at 50 keV. Lithographic modeling system (LMS) has then combined the predicted thermal fronts with the experimentally measured resist response to predict the effects on image profiles. Thermal proximity effects in 2 μm wide lines are negligible on Si wafers, 3–5% on Si membranes, and two to three times worse on SiO2 substrates.
A program for Monte Carlo simulation of electron energy loss in nanostructures
Authors: Johnson S. , MacDonald N. C.
Published: July 2002

A Monte Carlo program named simulation of electron energy loss (SEEL) has been developed to simulate electron trajectories in submicron scale electronic structures. The accuracy of the program at low energies is investigated, and the simulation techniques described. The backscattered electron energy spectra have been taken for Au and Al using an Auger electron spectrometer with a cylindrical mirror energy analyzer. For a beam energy of 1.5 keV, simulated electron energy distributions follow the experimental distributions down to 0.1 keV, showing relatively good agreement with experimental results at low electron energies.
Electron beam induced selective etching and deposition technology
Authors: Matsui Shinji , Ichihashi Toshinari , Mito Masanobu
Published: July 2002

W deposition, using a WF6 source by electron beam induced surface reaction, has been studied by Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). The initial growth process has been observed in situ by AES and TEM. As a result, it became clear that a growth rate for W is ∼1 Å/min at 2×10−7 Torr and β-W clusters are formed by electron beam irradiation of the WF6 adlayer. Moreover, it has been observed that W layers are formed by coalescing the W clusters by electron beam irradiation at 5×10−7 Torr WF6 gas pressure. Furthermore, a nanostructure involving a W rod with a 15-nm diameter has been demonstrated by using electron beam induced surface reaction. Direct writing onto Si, GaAs, and poly(methylmethacrylate) (PMMA) resist have been demonstrated by electron beam induced surface reaction using XeF2, Cl2, and ClF3 sources. The electron beam stimulated etched depth is proportional to the electron dose. A 0.5-μm linewidth Si and PMMA resist patterns have been fabricated at 4×10−3 and 2×10−3 C/cm2 doses, respectively. The PMMA resist etched depth profile control has been demonstrated by changing doses. GaAs etching has been achieved by heating the substrate.
Practical optimization of electrostatic lenses
Authors: Adriaanse J. P. , van der Steen H. W. G. , Barth J. E.
Published: July 2002

A method for the optimization of electrostatic lenses is presented. It is applied to optimize several three-electrode lens designs for particular applications. The free parameters of the optimization are the physical quantities describing the shape of the lens: the electrode thicknesses, the gaps between the electrodes, and the electrode radii at a number of axial points for each electrode. With these parameters a cubic spline approximation to the axial potential is found by solving a system of linear equations. The method has been named the second-order electrode method. Constraints for the optimization are the working distance on object and image side, a breakdown limit on off-axis field strength, a limit to electrode potentials and minimum and maximum values for all parameters. No constraints are used to keep the object and image at their specified position. Before each merit function evaluation the middle electrode excitation is adjusted in order to satisfy the specified first-order optical properties, so this construction keeps the first-order properties out of the optimization. The figure of merit is application dependent and is a function of the chromatic and spherical aberration coefficients. The optimization method is based on a nonlinear optimization algorithm.
Molecular-beam epitaxy growth of ZnSe using a cracked selenium source
Authors: Cheng H. , DePuydt J. M. , Haase M. A. , Potts J. E.
Published: July 2002

A double-oven cracking furnace has been used to produce a flux composed of smaller selenium molecular species for the molecular-beam epitaxy (MBE) growth of ZnSe on (100) GaAs substrates. Mass spectrometric analysis of fluxes from a conventional effusion cell and the cracking oven showed a significant difference in the number of large selenium molecules Sen (n>2) in their mass spectra. This new selenium source was found to be reactive with GaAs and its oxides, therefore its reaction with the substrate reduced the effectiveness in desorbing the oxide layer by heat treatment. Using the cracked selenium source, unintentionally doped ZnSe films have been grown on GaAs substrates desorbed in a separate ultrahigh vacuum (UHV) chamber linked to the MBE system. These undoped layers were highly resistive at room temperature and had low-temperature photoluminescence spectra dominated by emission from the recombination of free excitons, comparable to the best layers grown using an uncracked selenium source.
Electrical and structural properties of Pt/Ti/p+–InAs ohmic contacts
Authors: Katz A. , Chu S. N. G. , Weir B. E. , Savin W. , Harris D. W. , Dautremont-Smith W. C. , Tanbun-Ek T. , Logan R. A.
Published: July 2002

The thermally stable Pt/Ti metallization scheme was applied to Zn doped InAs layers in order to evaluate the influence of the outstanding electrical properties of the latter, such as the narrow band gap and the fact that the surface Fermi level pins in the conduction band, on the ohmic contact performance. These contacts applied to 1×1018, 5×1018, and 1×1019 cm−3 Zn doped InAs layers, grown directly on InP(Fe) substrates, were already ohmic as-deposited with a specific resistance values of 3.0×10−5, 9.8×10−6, and 7.5×10−6 Ω cm−2, respectively. Rapid thermal processing for 30 s at elevated temperatures yielded even a further reduction of the specific contact resistances, with a minimum value of less than 6×10−7 Ω cm2, for a 450 °C anneal. This heat treatment enhanced limited reactions in both the Pt/Ti and Ti/InAs interfaces, but, however, did not lead to the degradation of the stable microstructure.
Adsorption controlled molecular beam epitaxy of rubidium barium bismuth oxide
Authors: Hellman E. S. , Hartford E. H.
Published: July 2002

Measurements of the sticking coefficients for rubidium, barium, and bismuth have been made during molecular beam epitaxy of (Rb,Ba)BiO3 on MgO. This simple cubic perovskite is a high temperature superconductor for Rb fractions between 0.4 and 0.5. The dependence of the sticking coefficients on substrate temperature, oxygen plasma conditions, and on incident flux composition indicate that in a narrow region of flux compositions, adsorption, and desorption rates of bismuth and rubidium will control the stoichiometry of the film.
An advanced electron beam lithography system for sub-half-micron ultra-large-scale production: The distortion corrector technology
Authors: Nakamura K. , Okino T. , Nakanoda S. , Kawamura I. , Goto N. , Nakagawa Y. , Thompson W. , Shearer M. Hassel
Published: July 2002

The manufacture of the critical layers of production of ultra-large-scale integration (ULSI) devices requires resolution beyond the capability of today’s photolithography equipment. JEOL has developed a high precision electron beam lithography system, the JBX-8600DV, which satisfies the demands of these new device designs. The 8600DV employs advanced calibration algorithms to ensure accurate feature placement and linewidth control. This paper discusses a real time distortion and aberration correction system which compensates for stepper lens distortions, wafer warpage, and deflector anomalies. The system incorporates novel dynamic focus, astigmatism, and distortion corrector technologies to reduce distortion and aberration. The corrector system utilizes a two-dimensional spline fitting technique to produce the proper correction coefficients. This technology reduces linewidth dimensional errors to 0.03 μm(3σ) within a 2 mm deflection field and main field placement errors to <0.04 μm.
Ion beam assisted etching of GaAs by low energy focused ion beam
Authors: Kosugi T. , Gamo K. , Namba S. , Aihara R.
Published: July 2002

We have been investigating the characteristics of the ion beam assisted etching (IBAE) of GaAs performed using a Ga low energy focused ion beam (FIB) and Cl2 gas. The etch yield increased monotonously with increasing the Cl2 flow rate and showed a tendency to saturate at a high Cl2 flow rate. At a flow rate of 7×1018 molecules/cm2 s and an ion current density of about 5 mA/cm2, etch yields of 18–52 atoms/ion were obtained for 0.2–15 keV Ga+ beams. The IBAE to physical sputter etching ratio was about 14 at 1 keV and above and became larger for lower energy. The etch yield of IBAE varied in proportion to the deposited energy at the surface. Residual chlorine was below the detection limit after IBAE by Auger electron spectroscopy. The radiation damage was estimated by photoluminescence (PL) measurements. After 600 °C annealing, full recovery of PL intensity was observed for IBAE at the energy of 0.2 keV.
Fabrication of parallel quasi-one-dimensional wires using a novel conformable x-ray mask technology
Authors: Ghanbari R. A. , Chu W. , Moon E. E. , Burkhardt M. , Yee K. , Antoniadis D. A. , Smith Henry I. , Schattenburg M. L. , Rhee K. W. , Bass R. , Peckerar M. C. , Melloch M. R.
Published: July 2002

We report on the fabrication of quasi-one-dimensional wires on modulation-doped GaAs/AlGaAs using a novel conformable x-ray mask technology which allows us to expose arbitrary sized samples, including samples much smaller than the membrane area, using our laboratory’s standard 31 mm-diam silicon-nitride x-ray mask. After optical alignment, the sample and mask are brought into contact electrically, and then loaded into a specially designed cartridge which allows a vacuum to be pulled between mask and substrate. The vacuum causes the x-ray mask to conform around the sample. We find that a vacuum hold down is necessary to allow easy separation of the sample from the mask with minimal risk to both.
High performance optical lithography using a separated light source
Authors: Asai Satoru , Hanyu Isamu , Hikosaka Kohki
Published: July 2002

In projection lithography systems with fly’s-eye elements, a virtual source is created as an array of approximately mutually incoherent point sources. This article describes light amplitude and phase simulations for an image of a mask illuminated by a point source. This article discusses the dependence on the point-source location for a plane perpendicular to the optical axis. An image projected by a separated light source, rather than a ring-shaped light source, improves due to interference effects between multiple apertures is shown. Resolution of 0.25 μm equal lines and spaces was improved experimentally at a wavelength of 365 nm and a numerical aperture of 0.54. Also, how an isolated pattern image can be improved theoretically using an optimally separated light source is shown.