bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron-beam induced deposition for fabrication of vacuum field emitter devices
Authors: Weber M. , Rudolph M. , Kretz J. , Koops H. W. P.
Published: July 2002

Electron-beam induced deposition has been shown to be capable of creating structures of nanometer size in three dimensions without supplementary process steps like lift-off or etching procedures. Tips can be produced with radii of curvature comparable to the beam diameter used for deposition, i.e., some nanometers. By choosing appropriate deposition conditions, vacuum field emitter tips yielding a current of more than one hundred micro amps at 22 V gate voltage have been fabricated. This article will discuss the decomposition process of different organometallic precursor molecules by electron impact. A Monte Carlo simulation is employed to model the scattering of the primary electrons in a tip and to compute the spatial distribution of energy left in the tip. The influence of beam energy, beam current, and precursor material on the morphology and electrical properties of the deposited material are highlighted.
Blue light emission observed in a monolithic thin film edge emission vacuum microelectronic device
Authors: Williams Roger T. , Evatt Steven R. , Legg James D. , Weichold Mark H.
Published: July 2002

A monolithic field emission vacuum microelectronic device has been fabricated which integrates a thin (∼200 Å) metal film edge emitter with a unique thin film phosphor on an electrically inactive (oxidized silicon wafer) substrate. The resulting device has been tested and has been observed to produce blue light (∼488 nm) emission from the thin film phosphor. An asymmetric behavior was observed in which light emission was produced only under the forward bias conditions. The phosphor layer is a multi-layered ZnO based phosphor with a total thickness of 4000–6000 Å having a surface roughness typically measured at 0.1 μm. Further, the phosphor has a sheet resistivity of approximately one half ohms per square making it suitable as an anode material for light emitting devices.
Etching 0.35 μm polysilicon gates on a high-density helicon etcher
Authors: Kraft Robert , Boonstra Tom , Prengle Scott
Published: July 2002

This article describes an evaluation of a helicon high-density plasma etch tool for etching 0.35 μm polysilicon gates. The objective of the evaluation was to establish whether it is possible to etch 0.35 μm lines of both doped and undoped polysilicon (simultaneously) while maintaining straight profiles across the wafer and a very high polysilicon-to-oxide selectivity. Several high-density plasma (HDP) polysilicon etch tools for 0.35 μm technology have been tested at Texas Instruments. It is known that HDP tools operating at low pressures can obtain high polysilicon etch rates and anisotropic etch profiles. Most of the HDP sources utilize two separate radio-frequency (rf) power supplies; one to generate the high-density plasma and a second to bias the chuck. This allows relatively independent control of the ion density and the ion energy. It is possible to attain high polysilicon-to-oxide selectivity in the overetch step by using a high flux (high rf power to the plasma) of low energy (low rf power to the chuck) ions. This high selectivity is particularly important when long overetches are required with thin gate oxides.
Polysilicon gate etching in high density plasmas. I. Process optimization using a chlorine-based chemistry
Authors: Bell F. H. , Joubert O. , Vallier L.
Published: July 2002

High density plasma etching processes using chlorine gas have been developed for 0.25 μm polysilicon etching. Polysilicon films on SiO2-covered 200 mm silicon wafers are masked with photoresist patterns, and then etched downstream using a high density helicon source made by Lucas Labs of Sunnyvale, CA. To enhance the anisotropic etching, ion bombardment is provided by radio frequency (rf) biasing of the sample. Polysilicon trenching can be suppressed by performing a two-step etching process: the first uses a high energy ion bombardment resulting in high etch rate (250 nm/min) and anisotropy and the second a lower ion energy. The second etching step shows a high selectivity (≳80) of Si over SiO2 and therefore ensures the complete removal of the polysilicon during the overetch time. Perfect anisotropic profiles can be obtained without any trenching or other undesirable anomalies. The optimum etch rate nonuniformity is 6.5% (3σ) when operating the source at maximum rf source power (2500 W), 2 mTorr reactor pressure, and adding 30 sccm of helium to a 50 sccm chlorine discharge. Polysilicon and gate oxide etch rates have been measured using a real time in situ HeNe ellipsometer. Etch rates for polysilicon and oxide increase as a function of rf bias power but show no significant pressure or rf source power dependence. After etching, the 200 mm wafers can be transferred (under high vacuum) to an ultra high vacuum analysis chamber equipped with a Fisons ESCALAB 220i x-ray photoelectron spectrometer.
Use of resonance ionization microprobe analysis for characterization of ultrashallow doping profiles in semiconductors
Authors: Arlinghaus H. F. , Joyner C. F.
Published: July 2002

We have built an analytical time-of-flight instrument capable of sputter-initiated resonance ionization microprobe (SIRIMP) measurements. This instrument has the ability to obtain ultrashallow doping profiles with high depth resolution and dynamic range and virtually no matrix effects. The SIRIMP technique is especially valuable for ultratrace element analysis in samples where the complexity of the matrix is frequently a serious source of interferences. We describe the capability of the SIRIMP technique to quantitate with high accuracy and dynamic range dopant and impurity concentrations in silicon and silicon oxide samples at the 1013–1020 level. For example, the depth profile for a Sb implant in silicon shows a dynamic range of greater than 107. Dynamic range and depth resolution, quantitation accuracy, and limitations will be discussed.
Surface analysis, depth profiling, and evaluation of Si cleaning procedures by postionization sputtered neutral mass spectrometry
Authors: Emerson A. B. , Ma Y. , Wise M. L. , Green M. L. , Downey S. W.
Published: July 2002

The characterization of metallic impurities and dopant profiles near or on wafer surfaces is increasingly important as Si device features shrink. Conventional methods of surface analysis are ineffective in the near-surface region. We have used laser postionization sputtered neutral mass spectrometry to determine the efficacy of dry cleaning methods of silicon surfaces and perform shallow doping depth profiling. Unlike secondary ion mass spectrometry, postionization is free of matrix effects in the near-surface region (<100 Å), and permits quantitative analysis. The ability of this technique to track the cleaning of contaminated wafers is demonstrated. Hydrocarbon contamination on the surface limits the determination of Ca. The importance of the ubiquitous hydrocarbon contamination on wafers is also seen in interpreting very shallow depth profiles. Preliminary results demonstrate that ultrahigh intensity (1014 W/cm2) postionization shows promise as a nonselective, but effective means for surface analysis and shallow depth profiling.
Study of electrical measurement techniques for ultra-shallow dopant profiling
Authors: Ishida Emi , Felch Susan B.
Published: July 2002

The evaluation of the doping process requires the ability to measure accurate depth profiles. In this study, the accuracy of electrical measurement techniques is evaluated for the measurement of ultra-shallow dopant profiles. The methods investigated are spreading resistance profiling, electrochemical capacitance–voltage profiling, differential Hall effect profiling, tapered-groove profilometry, and a new method called microwave surface impedance profiling. The focus of this article is the comparative study of the different methods and an evaluation of the accuracy of the profiles. The study points out details of the measurements and analysis which are important in obtaining consistent and accurate measurements of ultra-shallow junctions.
Real-time temperature monitoring using a noncontact thermocouple for the next-generation sputtering system
Authors: Hosokawa Akihiro , Kowaka Masahiko
Published: July 2002

Real-time temperature monitoring of the glass substrate and the shield using noncontact thermocouples has been demonstrated in the Applied Komatsu Technology physical vapor deposition sputtering system. The substrate temperature was monitored in real time within ±5 °C at 250 °C during a pure aluminum deposition. The noncontact thermometry for the glass substrate requires a correction to account for the influence of the susceptor temperature on the sensing element. The equation for the corrected temperature was determined by both experimental and analytical methods, and the correlation between the sensor and the substrate temperature was confirmed to be within ±2%. The shield temperature was monitored and controlled without any correction. The noncontact thermocouple has many practical applications in both high vacuum and high voltage environments.
Application of a reaction-diffusion model for negative chemically amplified resists to determine electron-beam proximity correction parameters
Authors: Glezos N. , Patsis G. P. , Raptis I. , Argitis P. , Gentili M. , Grella L.
Published: July 2002

The method of single pixel exposures is applied for the determination of acid diffusion effects in negative chemically amplified resists. The wide range of crosslink density values contained in a single dot is used to determine nonlinear diffusion parameters. A reaction-diffusion model is developed where the diffusion coefficient D is a function of the crosslink density Θ. This function D(Θ) is evaluated for a given range of postexposure bake parameters in each case and the information obtained is used for proximity correction, also using the e-beam lithography simulation tool LITHOS. In order to test the model under different circumstances, two resists are studied, namely, the commercially available SAL-601 and the experimental epoxy novolac resist EPR. The diffusion coefficient is evaluated for each resist under the best processing conditions. The proximity correction procedure is fully demonstrated in the case of SAL-601.
Controlling sidewall smoothness for micromachined Si mirrors and lenses
Authors: Juan W. H. , Pang S. W.
Published: July 2002

Micromachined vertical mirrors and lenses in Si were fabricated as micro-optical components. A Cl2 plasma generated by an electron cyclotron resonance source was used to etch these mirrors and lenses in Si and the etched Si sidewalls were characterized by atomic force microscopy and scanning electron microscopy. A trilayer resist process has been developed to provide smooth Ni etch mask edges by postbaking the top imaging resist. The resultant Si etched sidewall showed a roughness of 18.69 nm, as compared to the sidewall roughness of 29.95 nm without postbaking. As the plating current density was varied from 5 to 400 mA/cm2, the etched Si sidewall roughness increased from 24.31 to 43.69 nm. Optimized etch conditions were investigated for smooth Si sidewalls. Sidewall was much rougher with a roughness of 98.99 nm when 50 W rf power was applied for dry etching, whereas the roughness was only 29.95 nm when 100 W rf power was used. Additionally, thermal oxidation followed by oxide removal was able to reduce etched Si sidewall roughness. After oxide removal, the sidewall roughness decreased to 5.93 nm after 135 min wet oxidation at 1100 °C. However, oxide grown at 900 °C was less efficient for reducing the sidewall roughness as compared to 1100 °C. The deep etch-shallow diffusion process was applied to fabricate micromirrors and microlenses. It was found that B diffusion at 1175 °C for 2 h decreased the Si sidewall roughness from 29.95 to 10.79 nm and selective wet etch lowered sidewall roughness further to 5.01 nm. Vertical micromirrors that were 40 μm tall and 2 μm wide were bonded onto the glass substrate and released. Microlenses that were 40 μm thick with radius of curvature of 50 μm have also been demonstrated.
Can synthetic aperture techniques be applied to optical lithography?
Authors: Fukuda Hiroshi , von Bunau Rudolf M.
Published: July 2002

This article discusses the theoretical feasibility of applying optical aperture synthesis to lithography. A technique involving the insertion of three phase gratings into a conventional projection system is described. While this approach paraxially yields imaging with doubled spatial bandwidth, aberrations introduced by the gratings are shown to be a serious limitation. Image simulations demonstrated that for very restricted pattern types, resolution down to 0.1 μm is theoretically achievable.
Use of very low energy in situ focused ion beams for three-dimensional dopant patterning during molecular beam epitaxial growth
Authors: Sazio P. J. A. , Thompson J. H. , Jones G. A. C. , Linfield E. H. , Ritchie D. A. , Houlton M. , Smith G. W.
Published: July 2002

In situ focused ion beam doping during molecular beam epitaxial growth allows the fabrication of novel semiconductor structures and devices otherwise unobtainable using standard lithographic, planar processing. In this technique, the thermal dopant effusion cell used in conventional GaAs molecular beam epitaxy (MBE) is replaced by a scanning Si source focused ion beam column. It is therefore possible to write dopant patterns directly into the semiconductor wafer during crystal growth. Precise control over the elemental composition in the growth (z) direction afforded by MBE is thus combined with the high spatial resolution of the focused dopant ion beam in the lateral (xy) plane. High quality bulk doped GaAs was grown with a Si ion landing energy of 100 eV using this technique, attaining a peak mobility of 3400 cm2 V−1 s−1 (185 K) at a carrier concentration of 1.1 ×1017 cm−3. The dependence of free carrier concentration in GaAs as a function of incident ion energy, and the fabrication of GaAs/AlGaAs modulation doped heterostructures will be discussed.
Inductively coupled plasma for polymer etching of 200 mm wafers
Authors: Forgotson N. , Khemka V. , Hopwood J.
Published: July 2002

An inductively coupled plasma etcher has been developed which uses a low aspect ratio, helical coil placed atop a planar vacuum window. The geometry of the inductive coupling element results in strongly peaked radio frequency power absorption around the periphery of the plasma. In addition, capacitive coupling and sputtered contaminants are significantly reduced by electrically grounding the turn of the inductor which is adjacent to the vacuum window. The radially resolved ion saturation current indicates that, in spite of the locally intense induction fields, the uniformity is only marginally better than expected from a discharge with a uniform ionization frequency. This is due to the nonlocal nature of the electron energy distribution. Etching of photoresist from 200 mm wafers using O2 is shown to be 2.5% uniform for operating conditions of 5 mTorr, 50 sccm, and 500 W radio frequency induction power.
Minimized response time of optical emission and mass spectrometric signals for optimized endpoint detection
Authors: Thomas S. , Chen H. H. , Hanish C. K. , Grizzle J. W. , Pang S. W.
Published: July 2002

The response times of optical emission spectroscopy (OES) and mass spectrometry (MS) have been measured for plasma etching of III–V heterostructures. For the Ga optical emission signal at 417.2 nm, a response time as fast as 0.2 s was obtained. The minimum response time of the 145AsCl+2 partial pressure, measured by MS, was found to be 0.9 s. The saturation times of the optical emission signal and the partial pressure signal have been shown to be related to the residence time of etch gases by varying the total gas flow rate and the chamber pressure. Decreasing residence time by reducing the pressure from 6 to 2 mTorr and maintaining a constant flow rate caused the saturation time of the Ga emission signal at 417.2 nm to decrease from 7 to 3 min. The 145AsCl+2 partial pressure signal saturated before the Ga emission signal. Endpoint detection for etching an AlInAs emitter and stopping on a GaInAs base of a heterojunction bipolar transistor was studied. Algorithms which monitor the change in Ga emission intensity have been developed to automatically stop the emitter etch with ∼2 nm of the GaInAs base layer removed. Additionally, etching of GaInAs on an InP substrate was studied and the signal from OES detected the endpoint before the MS signal did due to the faster response time.
New approach to preparing smooth Si(100) surfaces: Characterization by spectroellipsometry and validation of Si/SiO2 interfaces properties in metal-oxide-semiconductor devices
Authors: Schmidt D. , Niimi H. , Hinds B. J. , Aspnes D. E. , Lucovsky G.
Published: July 2002

Wet chemical removal of thermally grown SiO2 layers on Si(100) substrates has been studied as a function of the pH of the etching solutions in the range of −0.32–1.6 by adding controlled amounts of H2SO4 to a 1:30 HF:H2O mixture. Characterization of the stripped Si(100) surfaces by spectroellipsometry showed that the smoothest surfaces were obtained at a 1:0.50:30 HF (49 wt %):H2SO4(98 wt %):H2O etch with a pH of approximately 0.5. Electrical characterization of metal-oxide-semiconductor (MOS) capacitors fabricated on these surfaces with oxide layers prepared by remote plasma enhanced chemical vapor deposition showed (i) the lowest density of interface traps, Dit, (ii) the lowest tunneling currents, J0, and that (iii) the highest breakdown fields, EBD, occurred at the same pH value that produced the smoothest surfaces. In contrast, MOS capacitors fabricated with high-temperature thermally grown oxides were not significantly affected.
Room temperature red light photoluminescence from AlGaAs multiple quantum well structures at very low excitation intensities
Authors: Towner F. J.
Published: July 2002

Red light (700 nm) photoluminescence (PL) was obtained from two AlGaAs multiple quantum well (MQW) structures having 10 nm Al0.22Ga0.78As wells and 5 nm Al0.52Ga0.48As barriers. One sample was undoped and the other was Be doped (p=1×1018 cm−3) in the QWs. The p-doped sample emitted strong PL at low excitation intensities (<0.08 W/cm2) where the undoped sample no longer emitted detectable light. Furthermore, the p-doped sample exhibited room temperature red light emission, easily detectable to the naked eye, when illuminated by white light sources such as a flashlight or microscope light. Excitation-intensity-dependent measurements showed that the undoped sample’s PL intensity increased nearly quadratically while the doped sample’s PL intensity increased nearly linearly with increasing excitation intensity up to about 2 W/cm2. At higher excitation intensities, the luminescence intensities of both samples exhibited the same superlinear dependence; the undoped sample had about 30% higher luminescence intensity.
Investigation of the accuracy of pyrometric interferometry in determining AlxGa1−xAs growth rates and compositions
Authors: Sacks R. N. , Sieg R. M. , Ringel S. A.
Published: July 2002

Pyrometric interferometry (PI) is becoming a widely used method of obtaining in situ growth rates of GaAs and AlAs epitaxial layers grown by molecular beam epitaxy, due to its use of the ubiquitous narrow-band pyrometer and its ability to measure growth rates on rotating substrates. However, the extension of this technique to AlxGa1−xAs has been hindered by the lack of a convenient, detailed oscillation period calibration curve for the technologically important aluminum composition range 0.0<x<0.4. We present such a calibration curve which, although in general agreement with previously published data, resolves an additional structure near x=0.16 which we attribute to the band gap Eg(x) crossing the pyrometer wavelength. In developing the calibration curve, we also studied the effects of apparent surface temperature changes and epilayer absorption on the accuracy of the PI technique. We find that significant error results from apparent surface temperature changes, while epilayer absorption produces no discernable errors. We also investigate PI measurements of short period AlAs/GaAs superlattices, and find that the data has an overall periodic envelope whose frequency is well described by classical optics using bulk AlAs and GaAs optical constants.
All solid source molecular beam epitaxy growth of GaxIn1−xAsyP1−y/InP lasers using phosphorus and arsenic valved cracking cells
Authors: Baillargeon J. N. , Cheng K. Y. , Cho A. Y. , Chu S. N. G.
Published: July 2002

Growth of GaxIn1−xAsyP1−y on (001) InP by molecular beam epitaxy employing solid phosphorus and arsenic sources supplied via valved cracking cells was investigated. For growth temperatures between 430–525 °C, the incorporation of As and P was found to be strongly dependent upon the Ga mole fraction, substrate temperature, and incident As and P fluxes. The relative incorporation of As and P is nonlinearly related to the incident column V fluxes, with P incorporation being enhanced with increasingly higher growth temperatures. The data show that the quaternary could be grown lattice matched to InP across the entire wavelength range 1.15–1.65 μm, with strong photoluminescence emission. Heterojunction laser diodes subsequently fabricated with a broad range of emission wavelengths had threshold current densities as low as 1.7 kA/cm2 with differential quantum efficiencies as high as 28%.
Low interface state density oxide-GaAs structures fabricated by in situ molecular beam epitaxy
Authors: Hong M. , Passlack M. , Mannaerts J. P. , Kwo J. , Chu S. N. G. , Moriya N. , Hou S. Y. , Fratello V. J.
Published: July 2002

Several oxide-GaAs heterostructures were fabricated using in situ multiple-chamber molecular beam epitaxy. The oxides include SiO2, MgO, and Ga2O3(Gd2O3), all evaporated by an electron beam method. The SiO2 and Ga2O3(Gd2O3) films are amorphous while the MgO films are crystalline and part of the films are epitaxially grown on GaAs(100). Among these heterostructures, the Ga2O3(Gd2O3)–GaAs shows a photoluminescence intensity comparable to that of Al0.45Ga0.55As–GaAs, and forms accumulation and inversion layers as measured from capacitance voltage measurement in quasistatic and high frequency modes.
Structural and electronic properties of Sb islands on GaAs (110)
Authors: Magri R. , Manghi F. , Calandra C.
Published: July 2002

We present the results of theoretical calculations of the electronic structure of the Sb/GaAs(110) interface in the submonolayer coverage regime performed in the full ab initio self-consistent pseudopotential scheme. Different structural models for the edges of the extended Sb islands have been considered and their equilibrium geometry has been determined by total energy minimization. The single particle band structure shows interface states arising mainly from the incomplete bonding of the Sb adatoms at the terrace edge to the substrate, which fall within the optical gap. Distinct features are associated to different island terminations. The interface turns out to be metallic in all the considered cases with a partially occupied peak at the Fermi level. We have also studied the effect of including explicitly the on-site Hubbard electron-electron correlation in the calculation of the quasiparticle spectrum, obtaining the observed semiconducting interface when the Coulomb interaction parameter U is larger than 3 eV. The interface states within the optical band gap can be present also at higher coverages when some disorder exists, evidentiating a general mechanism for the Fermi level pinning at this interface.
Study on interface abruptness of InxGa1−xAs/InyGa1−yAszP1−z heterostructures grown by gas-source molecular beam epitaxy
Authors: Bi W. G. , Tu C. W.
Published: July 2002

We report a study of the effect of source switching sequences on the interface abruptness of InGaAs/InGaAsP quantum wells (QWs) grown by gas-source molecular beam epitaxy. Four methods were investigated: i.e., at each interface during growth interruption, (1) introducing a residual group-V source evacuation time (RSE) t where all sources are shut off; (2) no RSE; (3) no RSE but adding a group-III In+Ga prelayer of m monolayers; or (4) using RSE plus the In+Ga prelayer. InGaAs/InGaAsP QWs grown by the different methods were characterized by low-temperature photoluminescence (PL). The results show that by optimizing t or m, both RSE and prelayer methods can improve the heterostructure interface abruptness, which is evidenced by the stronger PL intensity and narrower PL linewidth, and that combining the two with optimized t and m gives the best result. This is due to the minimization of the memory effect by using RSE and of the As/P exchange by using the group-III prelayer.
Electron-beam characteristics of double-gated Si field emitter arrays
Authors: Toma Yasushi , Kanemaru Seigo , Itoh Junji
Published: July 2002

Double-gated Si field emitter arrays were fabricated in order to generate a focused electron beam and their characteristics were measured. These devices were fabricated by reactive ion etching followed by double successive evaporation of insulating layer and electrode. In the present device, the lower gate was used as an extraction electrode and the upper one was used as an electrostatic focusing lens. The device presented here has a 1.2 μm lower gate opening and a 2.2 μm upper gate opening, which are smaller than those reported previously by the authors (2 μm lower gate openings). Beam characteristics such as emission current, focusing properties, spot size, and stability of the focused beam current are reported.
Manufacturing a patternable metallized substrate for tungsten ultralong field emitter array by use of the double ion beam deposition method
Authors: Liu G. Y. , Zhu M. H. , Tang S. W. , Zhu C. C. , Liu J. S.
Published: July 2002

Using Ar ion beam precleaned surface, followed by in situ ion beam sputter deposition of the transition layer and the metal substrate layer sequentially, a double ion beam deposition method was realized. By using the double ion beam deposition method, a metallized substrate with excellent adherence, smooth as a mirror, and able to resist heat, must be grown successfully on the side of a double-polished tungsten ultralong field emitter array (W-UFEA) matrix surface. The substrate film offers not only W-UFEA for fabricating the leads, but also offers the possibility to form a patternable substrate, as well as fabrication of a low capacitive gate electrode for the field emitter array. This article introduces the fabrication and analysis of the metal substrate film, as well as two structure schemes to realize a low capacitive gated field emitter array.
Field-emitter-array development for microwave applications
Authors: Spindt C. A. , Holland C. E. , Schwoebel P. R. , Brodie I.
Published: July 2002

Microfabricated field-emitter arrays are being investigated as a means for gating or prebunching electrons in a microwave amplifier tube. The goals of the program are to demonstrate 10-dB gain at 50 W and 10 GHz in a gated klystrode■ amplifier tube with 50% efficiency. The cathode specifications call for 160-mA peak emission at 10-GHz rates from an annular emitter array having a 600-μm outer diameter and an inner diameter to be determined by cathode capacitance, emitter-tip loading, and transconductance (Gm) considerations. We have shown that an average array capacitance of 6 nF/cm2 and emitter-tip loadings of 10 μA/tip can be routinely achieved with Gm≊1 μS/tip. Calculations based on these results show that an array having 0.4-μm-diam gate apertures on 1-μm centers, a 600-μm outer diameter, and a 560-μm inner diameter would be a reasonable first design to meet the tube specifications. Such an array would have a predicted capacitance of 2.18 pF, a peak Gm of 29.4 mS, and would produce a peak emission of 160 mA with a tip loading of 4.4 μA/tip. The power dissipated in driving the gate at 10-GHz rates would be between 0.1 and 1.0 W.
Field emission from microstructured cesiated surfaces
Authors: Mitterauer J.
Published: July 2002

A comparative analysis of three experiments on field electron emission from microstructured cesiated surfaces is presented. In this context, the term ‘‘cesiated surface’’ implies generally any coverage of cesium on a metallic substrate, while the term ‘‘microstructure’’ includes the intrinsic microstructure of any solid substrate as well as the induced microstructure of the liquid cesium coverage due to electrohydrodynamic effects. These experiments concern a thin-film field-emission microcathode, a single pin-and-tube-type liquid metal electron source, and a large-area microstructured liquid metal electron source. The electron sources are compared by their emission characteristics and the resulting Fowler–Nordheim plots. The existence of both a stable and unstable field-emission mode from microstructured cesiated surfaces had been proven. Whether the first mode is of importance to vacuum microelectronics is a question which needs further investigation; the second mode seems to be of importance for regenerative and indestructible field electron sources with possible applications in pulsed power technology.
Sputtered TaX film properties for x-ray mask absorbers
Authors: Yoshihara Takuya , Kotsuji Setsu , Suzuki Katsumi
Published: July 2002

The characteristics of several elements for binary tantalum alloys, such as crystal structure, x-ray absorption, and dry-etching properties were systematically investigated. As a result, TaGe, TaSi, TaRe, and TaTi were selected as potential candidates for x-ray mask absorbers. We deposited these Ta alloys using conventional magnetron sputtering. The stress in the TaX films was controlled more precisely than in Ta films. It was found that TaGe was one of the most suitable materials based on x-ray absorption, stress control, and fine pattern fabrication.
Ab initio calculations of the reflectance anisotropy spectrum
Authors: Bass J. M. , Matthai C. C.
Published: July 2002

Using an ab initio, nonlocal pseudopotential method, we have calculated the reflectance anisotropy spectrum for a particular model of the GaAs(001) c(4×4) reconstructed surface. Excellent agreement with experiment was obtained, supporting the chosen model. The reflectance anisotropy was found to originate from optical transitions between bulk like valence band states and surface states in the conduction band. The nature and distribution of the electronic states involved is discussed.
Anisotropic optical reflection by stepped surfaces
Authors: de Boeij P. L. , Wijers C. M. J. , Zoethout E.
Published: July 2002

Discrete dipole calculations of the double cell type have been used to study the anisotropic reflection at normal incidence of stepped Si(001̄) 2×1-type surfaces. Only DB-type steps have been used. The maximum of the anisotropy turns out to be in a direction rotated with respect to the principal axes, and the anisotropy itself depends strongly on terrace width. Further the crossed polarizer configuration is interesting for experimental work since it has no offset.
Thin film interference effects in an off-axis illumination system
Authors: Azuma T. , Sato T.
Published: July 2002

Thin film interference effects on process latitude in an off-axis (quadrupole) illumination system are investigated with a bottom antireflective coating (ARC) or without the bottom ARC over SiO2 substrate using an electrical linewidth measurement technique. Experimental results indicate that an off-axis illumination system can improve an increasing disadvantage in maximum depth-of-focus (DOF) range with increasing resist thickness if using a resist thickness corresponding to a top extreme along the swing curve on a sufficient bottom ARC compared with the standard illumination system. But more serious thin film interference such as the case without the bottom ARC provides less advantage in the maximum DOF range even when reducing resist thickness. It is also found that centered focus positions exhibit a trend to offset in the positive defocus direction with increasing resist thickness, even using a combination of the bottom ARC and the smaller incident angle of illumination light in an off-axis illumination system. The centered focus positions without the bottom ARC are found to show more pronounced swing curve-type behavior with an almost horizontal inclination than that with the bottom ARC.
Interface imaging by second-harmonic microscopy
Authors: Flörsheimer M. , Bösch M. , Brillert Ch. , Wierschem M. , Fuchs H.
Published: July 2002

Second-harmonic microscopy (SHM) is a fast noncontact surface specific imaging technique for the quantitative in situ characterization of a large variety of real interfaces including liquid surfaces, surfaces in vacuum, and buried interfaces. The conventional surface second-harmonic generation experiment reveals the surface order and symmetry averaged over the area illuminated with an intense laser beam. In contrast, the SHM experiment probes the interface laterally resolved. Here we show that the optical nonlinearity of any local feature resolved in an image can be measured quantitatively. The nonlinear optical properties can be interpreted in terms of local surface order and symmetry. The lateral resolution limit of the stigmatic microscope is Abbe’s resolution for the generated SH light with a wavelength of, e.g., 532 nm. The contrast mechanism can also be applied to a scanning optical near field microscope.
Atomic force microscope-based data storage using replicated media
Authors: Terris B. D. , Rishton S. A. , Mamin H. J. , Best M. E. , Logan J. A. , Rugar D.
Published: July 2002

We have developed a technique for both mastering and replicating data patterns for potential use in an atomic force microscope (AFM)-based data storage device. The process consists of using electron beam lithography to write data features as small as 50 nm and a photopolymerization process to faithfully replicate the written marks. The replicas can be read using a contact-mode AFM tip on a rotating disk, and no change in the signal is seen after 12 days of continuous reading.
Raman spectra as a measure of interface alloying for IV/IV superlattices
Authors: Zi Jian , Zhang Kaiming , Xie Xide
Published: July 2002

Raman spectra of strained (001)-oriented Si/Ge and α-Sn/Ge superlattices with alloyed interfaces are calculated by a bond-polarizability model with lattice dynamical properties described by using a Keating model. The alloyed interface layers are treated by using a supercell technique. It is found that the Raman peaks around 410 cm−1 of Si/Ge superlattices and 260 cm−1 of α-Sn/Ge superlattices could be used as a measure of interface alloying.
In situ photoemission and reflectance anisotropy spectroscopy studies of CdS grown on InP(001)
Authors: Schultz Ch. , Frisch A. M. , Hinrichs K. , Kinsky J. , Herrmann T. , Rossow U. , Esser N. , Richter W.
Published: July 2002

Structural and electronic properties of the clean InP(001) surface and the CdS/InP(001) interface were investigated by soft x-ray photoemission and reflectance anisotropy spectroscopy (RAS). Clean InP(001) (2×4) surfaces were prepared by desorption of a protective arsenic/phosphorus double capping layer, thereafter, CdS deposited by single source molecular beam epitaxy at a substrate temperature of 200 °C. Core-level and valence-band photoemission spectra, as well as the RAS data, were taken in situ. Core-level spectra show a disappearance of In 4d and P 2p surface core-level shifts and a chemical reaction between indium and sulphur upon CdS deposition. From valence-band spectra, a total valence-band offset of ΔEV=(0.75±0.10) eV is derived, which corresponds to previous results of the CdS/InP(110) interface. After deposition of thin CdS layers, RAS spectra show strong features close to interband critical points of bulk InP due to surface roughening induced by the interface reaction. A feature around 5.3 eV, developing with higher coverage, indicates the formation of the metastable cubic phase of CdS as confirmed by additional Raman spectra.
Interaction of C60 with the (3×3) and (√3×√3) surfaces of 6H-SiC(0001): Adsorption, decomposition, and SiC growth
Authors: Li L. , Hasegawa Y. , Shinohara H. , Sakurai T.
Published: July 2002

Scanning tunneling microscopy was used to study the interaction of C60 with the silicon rich (3×3) and carbon rich (√3×√3) surfaces of 6H-SiC(0001). For both reconstructions, triangular or hexagonal islands commensurate with the substrate structure were observed at submonolayer coverages. The C60 exhibits island growth on these surfaces, with the second layer nucleating on the C60 islands before completion of the first layer. For coverages greater than one monoloyer, a closed-packed face-centered-cubic (111) structure was formed on the (3×3) surface. On the (√3×√3) surface, a disordered layer was observed. A SiC film was also grown using C60 as the carbon source.
Formation of nanocolumn self-assembly by solvent polarity control
Authors: Chai Xiangdong , Yang Wensheng , Cao Yunwei , Jiang Yueshun , Lu Ran , Li Tiejin , He Huixin , Wang Yongqiang , Liu Zhongfan
Published: July 2002

The morphology of self-assembly formed by amphiphilic complementary components, 5-(4-dodecyloxybenzylidene)-2,4,6-(1H,3H)-pyrimidinetrione and 4-amino-2,6-didodecylamino-1,3,5-triazine, was changed from square and rectangle sheets into nanocolumns and helixes corresponding to a recognition pattern change from a linear tape to a cyclic hexamer or a helically grown tape by varying the polarity of the solvent.
Electron beam dot lithography for nanometer-scale tunnel junctions using a double-layered inorganic resist
Authors: Haraichi Satoshi , Wada Toshimi , Gorwadkar Sucheta M. , Ishii Kenichi , Hiroshima Hiroshi
Published: July 2002

We have developed a metal–insulator–metal (MIM) junction fabrication process using top two layers of a separated by implanted oxygen substrate as a double-layered electron beam resist and a dot-exposure method in order to simplify the process sequence and fabricate smaller MIM junctions than those made by the conventional multiple-angle deposition–oxidation–deposition method. The diameter of the dot openings of a suspended mask tends to saturate with an increase in the exposed dose and is independent of the dot interval. We were able to successfully fabricate a series of Ti dots with minimum diameters of about 20 nm and much smaller junctions than the minimum dot size of 20 nm by an inorganic resist lift-off process. A one-dimensional array of six MIM junctions fabricated by this method showed typical current–voltage characteristics of tunnel junctions at room temperature.
Accurate alignment on asymmetrical signals
Authors: Chen Xun , Ghazanfarian Amir A. , McCord Mark , Pease R. Fabian W.
Published: July 2002

Existing alignment algorithms all assume that the alignment signal is symmetrical about the correct center position. When the signal becomes asymmetrical, these algorithms inevitably result in alignment error. We describe a general approach to align accurately on asymmetrical signals. This is achieved by incorporating learning and utilization of a priori information. The proposed algorithm looks at some sample alignment signals with known centers. The latter are provided by metrology data or some other means. The algorithm builds a linear space model of the asymmetry that is present in the sample signals. It then uses the built model to extract the symmetrical part of alignment signals that come from the same, well-controlled process. The extracted nearly symmetrical signal is then used to determine the alignment position. A detailed algorithm is provided for each of the three steps. Computer simulation implementing the algorithms shows that the alignment performance, both in terms of the mean and variance of the alignment error, is significantly improved compared to two examples of alignment algorithm that do not incorporate learning. The two example alignment algorithms used for comparison are phase detection and center of mass detection. A physical interpretation of the linear asymmetry model is provided.
Wall angle measurement with a scanning probe microscope employing a one-dimensional force sensor
Authors: Griffith J. E. , Hopkins L. C. , Bryson C. E. , Berghaus A. , Snyder E. J. , Plombon J. J. , Vasilyev L. A. , Hecht M. , Bindell J. B.
Published: July 2002

To measure the angle of a wall, the probe of a stylus profiler must be able to reach the wall. Sample tilting substantially expands the range of wall angles accessible to a profiler. Tilting also allows flared probe tip characterizers to be used more efficiently. The balance beam force sensor used for this work was designed to permit significant sample tilting.
Pattern placement errors in mask membranes
Authors: Fisher A. H. , Laudon M. F. , Engelstad R. L. , Lovell E. G. , Cerrina F.
Published: July 2002

X-ray and ion-beam lithographic processes require the use of advanced masks with free-standing thin membranes. In the fabrication of these masks, the pattern transfer process involves the deposition or removal of a thin layer of material (or portions of a layer), which can produce relatively large pattern placement errors. The stress-induced distortions of both x-ray and stencil mask membranes (due to the individual fabrication processes) have been simulated by finite-element procedures. For patterned areas of both mask membrane types, equivalent models with uniform characteristics have also been developed and assessed for validity. These models facilitate the calculation of global in-plane distortions needed to perform pattern specific emulation.
Optimal coherent decompositions for radially symmetric optical systems
Authors: von Bünau R. M. , Pati Y. C. , Wang Y.-T. , Pease R. F. W.
Published: July 2002

In this article, we discuss the application of the optimal coherent decompositions introduced by Pati and Kailath [J. Opt. Soc. Am. A 11, 2438 (1994)] to radially symmetric optical systems. We show that for such systems, both the point spread functions and the pupil functions corresponding to each term in the expansion are separable in polar coordinates. We derive analytical expressions for their angular dependence and an integral equation for the radial dependence. Our results reduce the task of computing optimal coherent decompositions from a two-dimensional integral eigenvalue problem to a one-dimensional one.
Nanolithography performances of ultraviolet III chemically amplified positive resist
Authors: Grella L. , Gentili M. , Di Fabrizio E. , Baciocchi M. , Mastrogiacomo L. , Maggiora R. , Scopa L.
Published: July 2002

Devices for future microelectronics shall demand lithographic performance that fall within the nanometer region (100 nm and below). Chemically amplified resists (CARs) offer a substantial gain in speed compared to conventional ones, and thus are attractive for the ultradense layouts of such future devices. However, before they can be selected for advanced microelectronics device production, nanolithography performances have to be proven. Ultraviolet (UV) III is a novel CAR from Shipley Corp. which was reported to possess fine-line lithographic capabilities. In this work, the UV III resist is characterized for the e-beam exposure. A commercial e-beam lithography machine was employed as exposure tool at 50 kV accelerating voltage. A process description for resolution below 100 nm is given, and resist performance was proven on layouts meaningful of actual devices.
Characterization of the radiation-enhanced diffusion of dry-etch damage in n-GaAs
Authors: Chen Ching-Hui , Chiu Yi-Jen , Hu Evelyn L.
Published: July 2002

Radiation-enhanced diffusion of dry-etch damage observed from experiments has been further characterized with Schottky diodes and deep level transient spectroscopy (DLTS) measurements. The use of DLTS spectra to monitor the effects of changes in ion dose rate and the application of laser radiation shows that the ion-induced defects having high diffusivities during ion-assisted processes are basically associated with the components of primary point defects, such as interstitials and vacancies. The properties of ion-induced traps obtained from DLTS measurements may provide us with some information to refine our model on the low-energy ion-induced damage.
Role of defect diffusion in the InP damage profile
Authors: Yu D. G. , Chen C.-H. , Holmes A. L. , DenBaars S. P. , Hu E. L.
Published: July 2002

Channeling of incident ions and radiation-enhanced diffusion of the ion-created defects have been shown to be major components of the ion damage profile. Our earlier results showed a deeper damage profile in InP, compared to GaAs, when subjected to the same ion bombardment conditions. Computer simulations demonstrated that this can partially be attributed to the greater ion channeling range in InP. In this article the role of defect diffusion in InP, through experiments coupled with simulations, is delineated. The multiple quantum well (MQW) probe technique is used to determine the amount of damage by measuring the change in low temperature photoluminescence of quantum wells before and after argon ion bombardment. A blocking superlattice is added to the MQW heterostructure and is proven effective in preventing damage from propagating into the material below it. By correlating the experimental results with computer modeling, an estimate of the defect diffusion constant is obtained and it is found to be in the range of 4×10−15–1×10−14 cm2/s. These high values for diffusion are justified with experimental results that illustrate the presence of radiation-enhanced diffusion mechanisms during ion bombardment.
Electrostatic deflection aberrations revisited: Solution proposed to an old problem
Authors: Retsky Michael
Published: July 2002

The deflection of charged particle beams into large angles is more often done with magnetic fields than with electric fields. One reason is that magnetic deflection aberrations are two to three times lower than electrostatic deflection aberrations. Electrostatic deflection aberrations have been re-examined in an attempt to design a 4 k by 5 k pixel cathode ray tube display suitable for digital mammography workstations. Using a novel ray trace program, it has been determined that electrostatic deflection aberrations can be reduced ten-fold by injecting the electron beam at an optimized offset position into a conventional deflection plate assembly. The surprising result is that the “sweet spot” is not near the center where it would be expected based upon looking at the fringe fields. The optimum injection position is offset almost halfway towards the attracting plate. This result has been confirmed in one test configuration. While the mammography application provided the initial motivation to reduce deflection aberrations, the technology may be useful in electron or ion beam lithography, especially so since the design readily accommodates four discrete beams.