bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance of a wide-field flux delivery system for synchrotron x-ray lithography
Authors: Silverman J. P. , Archie C. N. , Oberschmidt J. M. , Rippstein R. P.
Published: July 2002

An x-ray flux delivery system consisting of a compact storage ring and dedicated beamlines is now in routine use in the IBM Advanced Lithography Facility in East Fishkill, New York. The beamlines have been designed for use with a stepper that scans the mask and wafer vertically through a stationary beam. The performance of the system from a lithographic standpoint is reported. The measured size and stability of the synchrotron x-ray source will be presented, and the design and performance of the beamlines will be discussed. The beamlines have been designed to provide high intensity, uniform illumination over a wide field. The overall performance of the system has been evaluated by measuring the flux at the mask plane in the stepper. A horizontal uniformity of better than ±2% over a field more than 50 mm wide has been achieved; the vertical uniformity is limited by the uniformity of the stepper scanning mechanism. The delivered mask-incident flux per milliampere of stored beam current has been found to be 1.5 mW/(mA cm), approximately four times greater than obtained with a simple planar mirror. A 100 mJ/cm2 resist with a mask transmission of 50% therefore requires a less than 2 s exposure (plus overscan overhead) for a 2.5 cm high field at a typical stored current of 200 mA, independent of the field width (up to the maximum of more than 50 mm). In addition, the source has proved itself to be highly reliable, with beam available for 99% of the scheduled time over the most recent seven month period.
Edge location errors in Cr-less and rim-type phase-shifting lithography
Authors: Weiss M. , Henke W. , Ronse K.
Published: July 2002

When weak phase-shifting concepts, like the Cr-less or rim-type scheme, are applied, the images of feature edges are usually shifted by some amount with respect to their nominal position on the mask. This effect can be compensated by adding a certain bias to feature edges. This article describes some of the results of an investigation that was performed in order to develop design rules for rim-type and Cr-less phase-shifting masks.
Optical projection system for gigabit dynamic random access memories
Authors: Jeong H. , Markle D. A. , Owen G. , Pease R. F. W. , Grenville A.
Published: July 2002

Containing the cost of new generations of optical lithography, while maintaining improvements in performance, is a major challenge because every three years tends to see a requirement for a three-fold increase in the number of resolvable pixels and a substantial improvement in resolution. Here an optical approach is reported that promises to ameliorate the rapidly increasing cost of optical systems through the means of 1×, mostly reflecting optics. Only three projective components are required and the spectral range is 1000× larger than that of corresponding refractive systems. Such a system appears capable of meeting the lithography requirements of the 256 Mbit dynamic random access memory (DRAM) and, with evolutionary improvements, the 1 Gbit DRAM.
Two methods of experimental evaluation of long-range proximity function components in electron-beam lithography
Authors: Bogdanov Alexei L. , Polyakov Andrei
Published: July 2002

Long range components of a proximity function in electron-beam lithography are of great importance when high accelerating voltage (V∼50 kV or higher) is used. An additional exposure, provided by long-range backscattered electrons, can strongly affect linewidth in a nanometer scale lithography. Proximity correction procedures require proximity functions in an analytical or tabular form. The proximity function can be estimated with a certain degree of accuracy using a Monte Carlo simulation of electron scattering in a given set of layers and materials. In the present work, two rather inexpensive and fast methods of experimental long-range proximity function evaluation are suggested. Comparison of their output and Monte Carlo data produced using standard scattering calculation algorithms has been made. Results obtained show that these methods can be useful for rapid and almost effortless experimental proximity function determination. First of the reported methods makes it possible to obtain quantitative data on the backscattered exposure that is especially useful for the Monte Carlo algorithms verification.
High performance sub-0.1 μm silicon n-metal–oxide–semiconductor transistors with composite metal/polysilicon gates
Authors: Rishton S. A. , Mii Y. J. , Kern D. P. , Taur Y. , Lee K. Y. , Lii T. , Jenkins K. , Quinlan D. , Brown T. , Danner D. , Sewell F. , Polcari M.
Published: July 2002

A new fabrication process for sub-0.1 μm silicon n-metal–oxide–semiconductor field effect transistors with composite metal/polysilicon gates is described. Gate resistance is reduced below that of plain polysilicon or silicided gates, so that higher speed performance is obtained from shorter gate length devices. The process has resulted in 0.08 μm channel length ring oscillators with record per stage delays of 10.5 ps at 85 K and 13 ps at room temperature, and unity-current-gain cutoff frequencies of 119 GHz at 85 K and 93 GHz at 300 K. Record high transconductances of 1040 mS/mm at 85 K and 740 mS/mm at 300 K have been measured in 0.05 μm channel length devices.
Metrology for phase-shifting masks
Authors: Marchman H. M. , Vaidya S. , Pierrat C. , Griffith J.
Published: July 2002

Metrology test reticles that include a wide variety of structures typically encountered on phase-shifting masks were fabricated using a subtractive process. The test masks have been used to assess the ability of metrology instruments to measure linewidth, height, edge slope, roughness, critical dimension uniformity, and placement of the various submicron chromium and quartz features. Results demonstrating the resolution, accuracy, and repeatability of each instrument are presented for different types of phase-shifting mask features.
Role of fluorine atoms in the oxidation-hydrolysis process of plasma assisted chemical vapor deposition fluorinated silicon nitride film
Authors: Sánchez O. , Gómez-Aleixandre C. , Palacio C.
Published: July 2002

The oxidation and/or hydrolysis of a plasma assisted chemical vapor deposition fluorinated silicon nitride film in a moisture atmosphere has been studied. The film presents fluorine atoms incorporated as –SiF, –SiF2, –SiF3, and [–SiF2–]n groups. The open structure of the film, due to the high fluorine content as [–SiF2–]n, favors the penetration of oxygen and water molecules in the network. The evolution of the film has been explained by the different reactivity of the silicon atoms depending on their chemical environment. The role of fluorine atoms incorporated into the film has been established.
Low growth temperature AlGaAs current blocking layers for use in surface normal optoelectronic devices
Authors: Rogers T. J. , Lei C. , Streetman B. G. , Deppe D. G.
Published: July 2002

The application of thin (∼1000–5000 Å) layers of low-temperature (LT) molecular beam epitaxially (MBE) grown AlGaAs as current blocking layers is investigated. Data are presented regarding the current–voltage characteristics of resistors incorporating such layers, and it is shown that layers as thin as 1000 Å are highly resistive when biased to less than 8 V. Lateral current confinement is demonstrated for both surface-emitting light-emitting diodes and vertical-cavity surface-emitting laser (VCSEL) diodes through the use of MBE regrowth over a patterned layer of LT AlGaAs. The VCSEL devices exhibit low series resistance with only 1.8 V at a threshold current of 1.9 mA for 10-μm-diam devices.
Molecular-beam epitaxial growth and characterization of modulation-doped field-effect transistor heterostructures using InAs/GaAs superlattice channels
Authors: Baeta Moreira M. V. , Py M. A. , Ilegems M.
Published: July 2002

The molecular-beam epitaxial growth conditions of (N+1)(InAs)m/N(GaAs)n short period superlattices (SPSs) on GaAs substrates have been optimized. Hall electrical properties measured by the van der Pauw method were compared to low-temperature photoluminescence (77 K PL) spectra of GaAs/SPS/AlGaAs modulation-doped field-effect transistor-type heterostructures. By using these two characterization methods, the influences of the growth temperature Ts, of the SPS channel thickness dch and of its average indium composition ym were studied. Interesting correlations were established between their optical and their transport properties measured at 77 K either in the dark or under white-light illumination. The thickness m of the InAs layers was varied in the range 0.57 to 1.7 and sharp optimum properties were obtained slightly above m=1 monolayer. The PL spectra exhibit one or two bands which are attributed to transitions from electronic states belonging to the first or to the second subband formed in the conduction quantum well, the second transition at higher energy being observed only when the two-dimensional (2D) concentration exceeds a critical value nc which, in the dark, is of the order of 1.85×1012 cm−2 (i.e., dch≊119 Å) for our pulse-doped SPS heterostructures with ym=0.13. The electrical properties in the dark for modulation-doped structures having a (N+1)(InAs)1.14/N(GaAs)n SPS channel have been compared with those obtained on InGaAs alloy channels and it can be observed that the mobilities at 77 K are slightly lower than the mobilities of InGaAs alloys of equivalent In compositions, but the 2D electron gas concentration nso,d seems to be slightly higher in the SPSs.
Comparison of optical pyrometry and infrared transmission measurements on indium-free mounted substrates during molecular-beam epitaxial growth
Authors: Katzer D. S. , Shanabrook B. V.
Published: July 2002

Detailed comparisons have been made of temperatures measured by an infrared transmission (IRT) technique and traditional optical pyrometry during the molecular-beam epitaxial growth of GaAs, AlSb, GaSb, and InAs on undoped semi-insulating (SI) GaAs, blackened SI GaAs, and heavily silicon-doped N+ GaAs substrates in indium-free mounts. These comparisons indicate that IRT and optical pyrometry measurements show excellent agreement (±7 °C at most) over the 400–600 °C temperature range, if extreme care is taken to minimize pyrometer errors caused by stray light and coating of the pyrometer window.
Semiconductor substrate temperature measurement by diffuse reflectance spectroscopy in molecular beam epitaxy
Authors: Johnson S. R. , Lavoie C. , Tiedje T. , Mackenzie J. A.
Published: July 2002

The temperature of semiconductor substrates used in molecular beam epitaxy is determined from the diffuse reflection spectrum (DRS) of the substrates, measured with an external light source. The relative sensitivity of the technique is better than 1 °C. The absolute calibration of the DRS technique for substrates of different thickness, conductivity and back surface texture, is described. The DRS technique is also sensitive to changes in front surface roughness as demonstrated by the increase in the diffuse reflectance at short wavelengths when the oxide desorbs.
Etching on silicon membranes for sub-0.25-μm x-ray mask manufacturing
Authors: Muller K. Paul , Eib Nicholas K. , Faure Thomas B.
Published: July 2002

A multilayer resist (MLR) scheme for the manufacturing of sub-0.25-μm x-ray masks has been developed. MLR facilitates the generation of high-aspect ratio patterns by electron beam lithography and dry etching. The top three layers are standard MLR structures: a thin imaging resist layer, a thin intermediate layer, and a thick organic underlayer. Previously, others have used spin-on-glass or silicon nitride for the intermediate layer [R. Viswanathan, R. Acosta, D. Seeger, H. Voelker, A. D. Wilson, I. Babich, J. Maldonado, J. Warlaumont, O. Vlad’imirsky, F. Hohn, D. Crockatt, and R. Fair, Microelectron. Eng. 9, 93 (1989). A. Huberger, Microelectron. Eng. 5, 3 (1986)]. Sufficiently, thin low-stress tantalum or tungsten was utilized to provide oxygen reactive-ion etching resistance. The following layers are utilized under the MLR stack: another thin tantalum or tungsten etch stop layer; a thin gold plating base; and finally a 2.5-μm silicon membrane. Low image size bias dry etch processes that were successfully developed and performed on the thin x-ray mask membranes using a specially modified Plasma-Therm model 720 etch tool capable of automatically handling x-ray masks are described. Also, studies of membrane surface temperature as a function of plasma conditions are presented. Other dry etch processing issues that are driven by the uniqueness of processing on a membrane substrate and by the uniqueness of the x-ray mask fabrication process are discussed. Lastly, mask pattern distortion issues associated with MLR processing are examined.
Effect of beam condition in variable-shaped electron-beam direct writing for 0.25 μm and below
Authors: Hirasawa Satomi , Nakajima Ken , Tamura Takao , Aizaki Naoaki
Published: July 2002

The effect of incident electron-beam conditions, which are acceleration voltage and beam blur of variable-shaped electron-beam direct writing, is investigated using the deposited energy distribution to realize a fine pattern of ≤0.25 μm in trilayer resist process. The deposited energy distribution is calculated using a three-dimensional Monte Carlo method. In a trilayer resist system, a thin bottom resist layer can be used, because the contrast value derived from the Monte Carlo calculation is independent of the bottom layer thickness. The beam blur of 0.05 μm does not degrade 0.25 μm line-and-space (L/S) patterns, but seriously degrades 0.1 μm L/S patterns. Higher acceleration voltage is effective for improving the contrast. At lower acceleration voltage, the slope of the deposited energy profile defined at the resist bottom is mainly influenced by electron scattering. On the other hand, at higher acceleration voltage, the slope of deposited energy profile mainly depends on the beam blur. The 0.1 μm L/S patterns are expected to be resolved at 30 kV when there is less than 0.02 μm beam blur with trilayer resist system. The possibility of using a single layer resist process for 0.1 μm L/S pattern will be barely realized at the conditions of 50 kV and 0.02 μm beam blur.
Polarization study of the p(1×1)- and p(1×2)-phases of Bi/GaSb(110) using linearly polarized synchrotron radiation
Authors: McIlroy D. N. , Heskett D. , McLean A. B. , Ludeke R. , Munekata H. , DiNardo N. J.
Published: July 2002

The polarization dependence of the surface state bands of the ordered p(1×1)- and p(1×2)-phases of Bi/GaSb(110) at monolayer coverages has been studied with the technique of angle-resolved ultraviolet photoemission spectroscopy. Four new Bi-induced surface state bands (S′, S″, S‴, and SIV) have been observed. The polarization dependence of these states have been probed at the high symmetry points of the surface Brillouin zone and compared with the polarization dependence of corresponding surface state bands of other group-V semimetals on III–V(110) compound semiconductors. For the (1×1)-phase, the states S″, S‴, and SIV all exhibited pz-like dependence at all of the high symmetry points. The polarization dependence of S′ was observed to evolve from pxy-like at the X̄′ point of the surface Brillouin zone to pz-like character at the other high symmetry points. The polarization dependence of S″, S‴, and SIV were relatively unaffected by the phase transition of the overlayer from the (1×1)-phase to the (1×2)-phase.
Na adsorption on Si(111)-(7×7) studied by scanning tunneling microscopy and photoemission
Authors: Paggel J. J. , Haak H. , Theis W. , Horn K.
Published: July 2002

The Na-induced (3×1) reconstruction is investigated by core and valence level photoemission, as well as scanning tunneling microscopy. It is demonstrated that the conversion of the (7×7) into the (3×1) reconstruction involves a large amount of mass transport. The (3×1)-Na reconstruction is semiconducting. We observe a (7×7)/(3×1)-Na coexistence that can be interpreted as metal-semiconductor contact. The density of Na atoms in the (3×1) unit cell is determined to one atom per unit cell.
Electron-beam direct writing system EX-8D employing character projection exposure method
Authors: Hattori K. , Yoshikawa R. , Wada H. , Kusakabe H. , Yamaguchi T. , Magoshi S. , Miyagaki A. , Yamasaki S. , Takigawa T. , Kanoh M. , Nishimura S. , Housai H. , Hashimoto S.
Published: July 2002

An electron-beam direct writing system which adopts character projection methods in addition to conventional variable-shaped beam methods, has been constructed for 0.15 μm class ultra-large scale integration pattern fabrication. This system is a modified version of our variable-shaped beam machine. The electron optical system adopts a three stage octapole deflector for a 2 mm field and installs an aperture plate exchange mechanism for character projection. The objective lens system was designed so that the beam resolution is 0.04 μm. An optimization study to write a 1G-dynamic random access memory pattern with 0.15 μm design rules showed that a preferable character size and number are 2.5 μm and 48, respectively. The writing speed of this system is designed to be 110 s a chip, using the characters for memory cells as well as peripheral circuits. An advanced beam calibration method has been developed for beam current density and for character size, direction, and position. This method effectively adjusts the current density for each character to be the same on wafers. The beam position is accurately corrected by analyzing the obtained beam intensity distribution.
Electrodynamics of fast beam blankers
Authors: Gesley M. , Colby D. , Raymond F. , McClure D. , Abboud F.
Published: July 2002

Performance characteristics of an advanced electron beam blanker for lithography are presented. Various electrodynamic effects are discussed, which must be eliminated to achieve high beam placement accuracy during and after blanking. These electric and magnetic field effects have been measured over six orders of magnitude in time. The fast beam jitter characteristic of transit time effects in a double-deflection blanker is captured with nanosecond time resolution. Eddy current effects measured in the micro- to millisecond time domain are shown to be an inherent problem in earlier double-deflection blanker designs. A consequence is beam misplacement after the unblank transition, which can be 0.05 μm even after 500 μs. Several examples of pattern artifacts in purposely underdeveloped resist are given to illustrate graphically the lithographic consequences of the eddy current effect. All of these electrodynamic effects have been addressed with a new ‘‘virtual ground’’ blanker design. The MEBES IV-TFE maskmaker has been upgraded with this new blanker to meet its accuracy requirements throughout the nano- to millisecond time scale. This enables pattern generation at 160 MHz with 30 nm (3σ) critical dimension (CD) control for 2.0 μm features with addresses up to 0.25 μm. The CD control is tested with patterns that are fractured with a single pixel placed across the scan boundary. This situation provides the most extreme test of blanker accuracy at the nanosecond time scale. Blanker eddy current effects are eliminated from all exposures, including those in underdeveloped resist. The blanker design upgrade has facilitated the fabrication of reticles for production 64 Mbit DRAMs and developmental 256 Mbit DRAMs.
Chemical beam epitaxy of InP-based solar cells and tunnel junctions
Authors: Vilela M. F. , Rossignol V. , Bensaoula A. , Medelci N. , Freundlich A.
Published: July 2002

Chemical beam epitaxy has been utilized to demonstrate high efficiency InGaAs/InP tandem solar cells on InP substrates. The key development in achieving such tandems is the growth of high peak current density InGaAs tunnel junctions for use as interconnect between the top and bottom cells. The growth and performance of the InGaAs bottom cell, the InGaAs tunnel junction, and the InP top cell are first independently presented in the paper. Then the growth of an InP-based tandem cell is described followed by a discussion of its performance.
Stabilized α-Sn grown at high temperature by molecular beam epitaxy
Authors: Kimata M. , Suzuki T. , Saino K. , Kawamura K. , Hobbs A.
Published: July 2002

The first observation of lattice images of stabilized α-Sn grown at 150 °C by high-resolution transmission electron microscopy is reported here. A structure of CdTe/α-Sn/InSb has been grown on an InSb buffer layer, which was grown on an InSb(100) substrate by molecular beam epitaxy at 220 °C. During the growth, cross doping was carefully avoided. In addition, by the energy-dispersive x-ray spectroscopy, it was found that the interdiffusion of In and Te, which usually occurs across the interface of CdTe/InSb, is prevented by the α-Sn layer inserted at the interface.
Molecular beam epitaxy grown AlAsSb/GaAsSb distributed Bragg reflector on InP substrate operating near 1.55 μm
Authors: Blum O. , Fritz I. J. , Dawson L. R. , Howard A. J. , Headley T. J. , Olsen J. A. , Klem J. F. , Drummond T. J.
Published: July 2002

Surface normal optoelectronic devices operating in the 1.3–1.5 μm wavelength range require distributed Bragg reflectors (DBRs) with a practical number (≤50) of mirror layers. This requirement implies a large refractive index difference between the mirror layers, which is difficult to achieve in the traditionally used phosphide compounds. For the first time, an AlAsSb/GaAsSb DBR grown nominally lattice matched to an InP substrate by molecular beam epitaxy is demonstrated. Reflectivity measurements indicate a stop band centered at 1.53 μm, which is well fitted by these theoretical predictions. Atomic force microscopy and transmission electron microscopy indicate reasonable crystal quality with some defects due to an unintentional lattice mismatch to the substrate.
In situ nonalloyed ohmic contacts to p-GaAs
Authors: Hong M. , Vakhshoori D. , Mannaerts J. P. , Thiel F. A. , Wynn J. D.
Published: July 2002

Very low resistivity, nonalloyed ohmic contacts to p-GaAs are realized by in situ molecular beam epitaxy (MBE). Heavily Be-doped GaAs either in a uniform doping or with a δ-doping scheme was grown using MBE. Three different metals of Au, Ag, and Nb were in situ deposited on p-GaAs, yielding contact resistance RC less than (1–4)×10−7 Ω cm2.
Formation of Si–SiO2 stacked-gate structures by plasma-assisted and rapid-thermal processing: Improved device performance through process integration
Authors: Lucovsky G. , Wortman J. J. , Yasuda T. , Xu X-L , Misra V. , Hattangady S. V. , Ma Yi , Hornung B.
Published: July 2002

Formation of Si–SiO2 stacked-gate heterostructures requires (i) preparation of Si surfaces prior to interface formation and oxide deposition, (ii) oxide deposition, (iii) polysilicon gate electrode deposition, and generally (iv) post-deposition doping of the gate electrode. Mid- and/or end-process rapid thermal annealing performed in inert or oxidizing ambients may also be necessary to optimize device performance. Four phases in the development of an integrated processing protocol for stacked-gate structures are described in which these steps have been modified, and continuously improved. Process tools have evolved from (i) single-function chambers for (a) surface cleaning/passivation, and (b) thin film deposition, to (ii) dual-function/single process plasma chambers for (a) in-situ surface cleaning and interface formation and (b) oxide deposition, and finally to (iii) multi-function/dual process chambers in which all of the above process steps are done in situ, but by more than one processing technique. This last approach has culminated in chambers which can accommodate (i) low-temperature plasma-assisted interface formation at ∼300 °C, (ii) intermediate-temperature rapid thermal dielectric and polysilicon depositions at 600–800 °C, and (iii) higher-temperature rapid thermal annealing at 900–1000 °C.
Charge deposition and imaging on a fluoride thin film using the scanning force microscope
Authors: Umeda N. , Makino K. , Takahashi T. , Takayanagi A.
Published: July 2002

This paper describes a localized charge deposition and imaging on a fluoride thin film with a contact mode scanning force microscope (SFM). The charge was deposited by contacting a tip of the SFM to a sample surface and by applying voltage pulses between the tip and back electrode of the sample. After applying a voltage pulse of 300 V and a pulse width of 1 ms, the attractive force image of 250×700 nm2 was obtained corresponding to the charge deposited region. Also, the stored charge was imaged over a period of 8 h. The cause for charge images to occur in elliptical patterns was estimated to be due to the deformation of the tip apex from contact to the sample surface.
Atomic force detection system with a differential heterodyne interferometer using an optical fiber array
Authors: Nakatani Noboru , Oshio Takanori
Published: July 2002

This paper describes an atomic force microscope (AFM) using an optical fiber heterodyne interferometer free from external disturbances in optical paths of two fibers used for measuring small displacement of a microcantilever. An array of two fibers is used for superimposing interference beams easily and obtaining two closely spaced spots on a microcantilever. For eliminating the disturbances, the phase of the two fibers and the two spots of measurement beat signal and the phase of the two fibers of reference beat signal are differentiated. The noise level of this interferometer is 1.1×10−3 nm/√Hz and is limited by the phase noise of the phasemeter used. It is confirmed, by measuring thickness of a thin Au film, that the interferometer has a suitable performance for measuring the displacement of the microcantilever. By observing a surface of an optical disk, it is demonstrated that this AFM is a powerful tool for measuring a surface in the order of nanometer.
Observation of lattice defects using scanning tunneling microscopy/spectroscopy at low temperatures
Authors: Endo T. , Yamada H. , Sumomogi T. , Kino T. , Kusunoki N. , Morita S.
Published: July 2002

In a previous conference, STM’91, we reported the several kinds of lattice defects on microcrystalline graphite. For a further investigation of electronic structure around lattice defects, spectroscopic measurements at low temperatures are desired. A scanning tunneling microscope/spectroscope (STM/STS) workable at low temperatures and in ultrahigh vacuum has been constructed. The system has a surface-cleaning apparatus for removing contamination by pulse laser beam. In order to select a view area, an optical microscope and a movable sample stage are also equipped. At present, atomic STM images on HOPG, microcrystalline graphite, and bulk gold are observed at room temperature. At low temperatures near 60 K, irregular atomic structures of microcrystalline graphite are also observed. These results indicate the STM/STS system is appropriate for the STM/STS measurements at low temperatures.
Direct observation of human liver ferritin by scanning tunneling microscopy
Authors: Mosca A. , Paleari R. , Arosio P. , Cricenti A. , Scarselli M. A. , Generosi R. , Selci S. , Rovida E.
Published: July 2002

We report here on some scanning tunneling microscopy (STM) observations on iron-loaded (1200 atoms/molecule) human liver ferritin (HLF) chemically bound to gold surfaces activated with 4,4′-dipyridil disulfide. The samples were prepared by immersing the activated gold foils in 10–500 μg/mL ferritin solutions in 0.3 mmol/L tris(hydroxymethyl)-aminomethan (TRIS), pH 7.4. After a 30 min incubation period the foils were washed first in water, then in ethanol, air dried, and analyzed with a STM microscope. Individual ferritin molecules were resolved under the STM as spheroidal objects of approximately 10 nm diameter. The HLF molecules appeared as positive bumps above the bare substrates both in constant current and gap-modulated images, with a nonrandom internal structure possibly related to their quaternary structure. After the observation the HLF was extracted and quantified by an immunoenzymatic test. In conclusion, the results obtained by the STM analysis were found to concur with the information provided by x-ray crystallography.
Investigation of C-phycocyanin from blue-green alga spirulina platensis with scanning tunneling microscope*
Authors: Zhang Yuzhong , Ma Zili , Chu Xing , Hu Tianmiao , Zhou Baicheng , Pang Shijin , Tseng C. K.
Published: July 2002

C-phycocyanin (C-PC) was isolated from blue-green alga spirulina platensis. A scanning tunneling microscope (STM) has been used to investigate its three-dimensional structure. The samples were dialyzed before the STM experiment, and then deposited on highly oriented pyrolytic graphite (HOPG). The measurement was carried out in ambient condition at room temperature. STM images showed that C-phycocyanin was uniformly distributed on solid-state substrate HOPG. The shape of C-phycocyanin is disklike with a channel in the center. It is concluded that STM has great potential to observe the structure of biliproteins and phycobilisomes.
Fabrication of a multilevel structure for nanophysics in two-dimensional electron gases
Authors: Soh Yeong-Ah , Snider Gregory L. , Rooks Michael J. , Craighead Harold G. , Parpia Jeevak
Published: July 2002

The fabrication process of a multilevel structure with a central electrode isolated from the outer gates is presented. Polymethylmethacrylate is used as the dielectric material that provides the electrical isolation. Dot gates with a diameter as small as 30 nm aligned in the middle of 0.10 μm split gates have been fabricated. The operation of the dot gates has been tested by conductance measurements through the constriction formed by the split gates.
Anneal technique to recover the electrical characteristics of the packaged bipolar junction transistors damaged by Co-60 radiation
Authors: Chang-Liao Kuei-Shu , Huang Ching-Ju
Published: July 2002

Radiation-induced degradation in packaged bipolar junction transistors (BJT) can be efficiently removed by an anneal treatment carried out at 400 °C for 12 min in N2. The electrical characteristics of BJTs including current gain β, base current IB, and collector current IC were examined in the recovery of device performance. The radiation was performed by a Co-60 (γ-ray) source with the total doses ranging from 10 K rad to 10 M rad. The determinations of anneal temperature and anneal time were also discussed. It was shown that this anneal treatment did not degrade the radiation and hot-carrier hardnesses of devices.
Imaging of neurons by atomic force microscopy
Authors: Umemura Kazuo , Arakawa Hideo , Ikai Atsushi
Published: July 2002

We imaged neurons which were prepared by different methods using the contact mode and the tapping mode atomic force microscope (AFM) in air. The contact mode AFM resolved cells with very thin dendrites from the substrate, and sharpened pyramidal tips gave sharper images of the cells than pyramidal tips. Over the cell surface, the tapping mode AFM gave a higher resolution than the contact AFM. We could resolve particles several nanometers in width using the tapping mode AFM. Our results suggest that the resolution on the cell surface depended not only on the tip shape but also on the physical properties of the cell surface.
Exploring intermediate filament structure with the scanning force microscope: Comparison with transmission electron microscopy data
Authors: Karrasch Simone , Heins Susanne , Aebi Ueli , Engel Andreas
Published: July 2002

We have compared the structures of the filamentous assembly products of different recombinant NF–L polypeptides as seen by the scanning force microscope (SFM) in buffer solution with those obtained by transmission electron microscopy (TEM) of dehydrated specimens. For SFM the filaments were immobilized on a glass surface by photocrosslinking, whereas for TEM the filaments were negatively stained and air-dried. Regarding their length and overall shapes, there is an excellent agreement between the SFM and the TEM data. However, the significant discrepancy of the filament width measured by these two microscopies illustrates the effect of the tip shape with the SFM on width measurements.
Selective deposition of metals on submicron resist patterns
Authors: Petermann J. , Hoffmann T. , Martinez-Salazar J.
Published: July 2002

A process to coat submicron structures in paraffin resists, selectively with metals in a single vacuum cycle (all-dry process), is demonstrated. The process includes the evaporation of paraffin on to a support, the generating of crosslinked areas by irradiation with electrons, the developing of the structure by heating the resist film, and finally a selective coating with metal. The degree of crosslinking of the paraffin film has a remarkably influence on the nucleation density of the metal and allows us to control on a very fine scale the area on which the metal is deposited.
Printability of sub-150 nm features in x-ray lithography: Theory and experiments
Authors: Hector Scott D. , Wong Vincent V. , Smith Henry I. , McCord M. A. , Rhee K. W.
Published: July 2002

Image formation in x-ray lithography has been studied extensively. A previous theoretical study predicted that 0.1 μm features can be printed at large gaps (≳10 μm) with absorbers attenuating less than 10 dB. This study seeks to verify rigorous electromagnetic simulations of image formation by directly measuring the aerial image. Exposures of features with linewidths ranging from 0.15 to 0.075 μm were performed on the Helios synchrotron. Pedestal-style x-ray masks, consisting of SiNx membranes and a Au absorber, were patterned with e-beam lithography at 100 and 50 kV. By careful dose control and inspection of the resulting features, one can directly determine the aerial image (the image at the resist surface). This is verified using a string model of the resist development. Aerial image measurements correlate reasonably well with modeling results.
Evaluation of temperature rise and thermal distortions of x-ray mask for synchrotron radiation lithography
Authors: Yamazaki K. , Satoh F. , Fujii K. , Tanaka Y. , Yoshihara T.
Published: July 2002

This article presents experimental results on the temperature rise in x-ray masks and the temperature-induced distortions printed on wafers during scanning synchrotron radiation exposure. It also presents theoretical analyses confirming the validity of the experiments. The temperature rise was measured with an infrared camera and the resultant thermal distortions were quantified by measuring the displacements of patterns printed on wafers. The theoretical simulations were performed using the finite element method. Results of experiments and simulations agree and indicate that even for exposures in air the temperature-induced distortions are rather small.
Quantitative study of metal–oxide semiconductor field effect transistor damage induced by scanning tunneling microscope lithography
Authors: Fayfield Ty , Higman T. K.
Published: July 2002

The channel areas of n-channel silicon metal–oxide semiconductor field effect transistor (MOSFET) devices have been patterned with an air-operated scanning tunneling microscope (STM) and processed to completion. Gate oxide thickness modulations greater than 80 Å have been achieved with this technique. The impact of the STM process step on the silicon/insulator interface has been characterized with two-level charge pumping. The number of interface traps attributable to the STM lithography process is roughly 7×1010/cm2 eV. Additionally, transistor parameters from the STM FETs are compared with those from virgin FETs to assess any possible leakage current and mobility degradation induced by the STM process.
Fabrication and characterization of InAlAs/InGaAs striped-channel modulation-doped field effect transistors
Authors: Grundbacher R. , Fay P. , Adesida I.
Published: July 2002

Striped-channel modulation-doped field effect transistors (MODFETs), in which the transport of electrons from source to drain is restricted to multiple parallel channels, have been fabricated on a lattice-matched InAlAs/InGaAs heterostructure and characterized at dc and rf frequencies. dc performance of the striped-channel devices shows increased transconductance when normalized with the actual width of the striped channels. This may be attributed to improved control of electron concentrations in the channels since the depletion layer induced by the controlling gate is not only from above, but from below and in lateral directions as well, resulting in improved electron confinement. A reduction of output conductance of the striped-channel device is observed when compared to a conventional MODFET. This is interpreted to be a result of an enhanced barrier between the buffer and channel layers of the striped-channel device, which reduces the injection of hot electrons into the buffer. rf characteristics of the devices show a reduction of cutoff frequency for devices having smaller channels. dc measurements at cryogenic temperatures were performed to investigate the possibility of mobility enhancement in the striped-channel devices.
Extending the limits of optical lithography for arbitrary mask layouts using attenuated phase-shifting masks with optimized illumination
Authors: Ronse Kurt , Pforr Rainer , Baik Ki-Ho , Jonckheere Rik , Van den hove Luc
Published: July 2002

Optical lithography is still the technology of choice for the production of integrated circuits. The continuous need to shrink device geometry was originally made possible by reducing the wavelength and increasing the numerical aperture of the projection steppers. For the past half decade, various resolution and process latitude enhancement techniques, such as phase shifting masks (PSM) and off-axis illumination techniques have received a lot of attention. Although very promising lithographic results have been demonstrated with each of those, their application in real device manufacturing with arbitrary mask layouts has been hampered for various reasons (PSM manufacturing, limited applicability...). World-wide attention is directed more and more towards attenuated (embedded) PSM and annular illumination in order to overcome the limitations. In this article, both attenuated PSM design and illumination have been optimized to provide global improvements on critical random logic gate and contact levels. The optimized results, predicted by simulations, are verified experimentally using top surface imaging processes on a 0.42 NA deep-ultraviolet stepper, focusing on quarter-micrometer design rules. For contact levels, the best results are obtained with highly coherent conventional illumination. Gate levels require the combination of attenuated PSM with annular illumination.
Quarter-micron lithography with a gapped Markle–Dyson system
Authors: Owen G. , Borkholder D. , Knorr C. , Markle D. A. , Pease R. F. W.
Published: July 2002

0.25-μm lithography has previously been demonstrated using an ungapped prototype Markle–Dyson system, in which the wafer was held in soft contact with the mask. However, such an in-contact scheme would be inappropriate for semiconductor fabrication, and so a second prototype has been designed and constructed, in which a gap of 25 μm is introduced between the mask and the wafer. The two major technical problems to be overcome in implementing the gap are the measurement and setting of the gap itself, and correction for the spherical aberration which it introduces. In the new prototype, the gap is set by a piezo-electric actuator and measured using a capacitance gauge, and the spherical aberration is corrected by using a mirror which deviates slightly (by 0.33 μm) from sphericity. The system has been tested lithographically, using chromium reflective masks. It has demonstrated a resolution of 0.25 μm in Shipley XP89131 photoresist.
Co-planar multiple-ring electrostatic particle-beam lenses
Authors: Moran Michael J.
Published: July 2002

Electrostatic particle-beam lenses using a concentric co-planar array of independently biased rings can be advantageous for some applications. Traditional electrostatic lenses often consist of axial series of biased rings, apertures, or tubes. The science of lens design has devoted much attention to finding axial arrangements that compensate for the substantial optical aberrations of the individual elements. Thus, as with multielement lenses for light, a multielement charged-particle lens can have optical behavior that is far superior to that of the individual elements. This article discusses the possibility that transverse multiple-concentric-ring lenses can achieve high performance, while also having advantages in terms of compactness and optical versatility.
Inspection of optical phase-shifting masks with an automated electron-beam system
Authors: Brodie Alan D. , Chen Zhong-Wei , Jau Jack , Meisburger Dan , Grenon Brian
Published: July 2002

There has been great interest lately in using optical masks that contain phase-shifting structures in order to print smaller features than is possible with a standard binary mask. Because of the many varieties under investigation and the complexity of the phase interactions, no definitive experimental work concerning the effects of various types of defects yet exists. However, it is known that, under some circumstances, defects in a phase-shifting mask (PSM) will cause a larger deviation in the printed linewidth than a defect of equal size on a binary mask. For 0.25 μm lithography done with a 248 nm stepper using an ‘‘etched Levinson’’ or alternating PSM, it is thought that phase defects as small as 80 nm need to be detected. At present, the only inspection system capable of meeting the size requirements is based on electron optics (KLA SEMSpec). However, this type of system, which was designed to inspect x-ray masks, requires that the defects exhibit either a topographical or material anomaly in order to be visible and that the mask be conductive. While some types of phase-shifting masks satisfy the contrast formation requirements, none are conductive. This can be remedied by depositing a metallic layer over the surface. However, in order for inspection to proceed at high speed, the defect contrast and signal level must be high. In this article we elucidate the physics of electron-beam image formation of conductively coated phase-shifting masks for various types and thicknesses of coatings. Both theoretical and experimental results are presented. Since adding and removing the conductive coating must be done without damaging the mask, only certain types of coatings and processes are allowable. A list of the most promising coatings is presented along with the supporting experimental evidence. By inspecting a phase-shifting mask that has intentionally written defects of various types, it is shown that defects as small as 0.1 μm can be reliably found.
Evaluation of overlay accuracy for the x-ray stepper TOXS-1
Authors: Hirano Ryoichi , Higashiki Tatsuhiko , Nomura Hiroshi , Kuwabara Osamu , Nishizaka Takeshi , Uchida Norio
Published: July 2002

This article presents the overlay accuracy for the newly developed prototype x-ray stepper TOXS-1. Checkerboard gratings on a mask and wafer were used for an optical-heterodyne interferometry alignment system so that the alignment signals from the mask and wafer gratings can be detected independently without mutual interference. The alignment signal varied slightly with the mask-to-wafer gap due to multiple reflection of the alignment beams between the mask and wafer, which deteriorates the alignment accuracy. To reduce the multiple reflection, the mask grating and the mask alignment window were coated with opaque film and antireflecting film, respectively. A 0.025 μm (mean+3σ) overlay accuracy has been achieved for SiO2 processed wafers. The overlay accuracy was further measured for four different kinds of processed wafers, and a 0.035 μm (mean+3σ) accuracy has been obtained except for an aluminum processed wafer.
Design and test of a through-the-mask alignment sensor for a vertical stage x-ray aligner
Authors: Nelson M. , Kreuzer J. L. , Gallatin G.
Published: July 2002

SVG Lithography is building a production-ready, vertical stage x-ray proximity aligner. For aligner-to-itself overlays, the aligner overlay specification is a mean 3σ value of 33 nm. As part of this aligner specification, each through-the-mask (TTM) alignment sensor has a wafer-to-mask position measurement accuracy specification with a mean value of 7.1 nm and a 3σ value of 9.2 nm. This article presents a summary of the operation, design, and breadboard testing of the TTM sensor. Breadboard testing with silicon membrane x-ray masks and process wafers confirms that the design satisfies the specification. Test data to date show position-sensing repeatability 3σ values that range from 8 to 10 nm. Resist-induced mean alignment offsets, measured as the separation of bare and resist-coated wafer marks, were within the acceptable range of 5 to 8 nm.
Effects of etch chemistry on SF6-based tungsten etching by electron cyclotron resonance reactive ion etching
Authors: Eddy C. R. , Kosakowski J. , Shirey L. M. , Dobisz E. A. , Rhee K. W. , Chu W. , Foster K. W. , Marrian C. R. K. , Peckerar M. C.
Published: July 2002

Studies of etch chemistry effects on SF6-based tungsten etching have been performed in an electron cyclotron resonance microwave reactive ion etching system. The etch chemistry and, therefore, reactive species concentrations were varied in several ways and the effect of these variations on etch rate and anisotropy of etched features were evaluated. Reactive species concentrations were altered by varying the residence time in a pure SF6 plasma or by introducing argon or nitrogen in the SF6 plasma under constant residence time. For pure SF6 and under conditions similar to those in a parallel plate radio frequency system, the tungsten etch rate was more than three times greater—presumably the results of higher dissociation efficiencies. As residence time was increased from 1 to 30 s the etch rate was decreased by greater than a factor of 2 and linewidth loss was reduced from better than 50 to 5%. Addition of argon to the plasma reduced the etch rate while maintaining short residence times. The addition of nitrogen to SF6 resulted in a complex behavior that provided optimum etch rate with minimum linewidth loss for a 50/50 mixture. In evaluating the behavior, sidewall passivation processes and competitive reactions in the gas phase are discussed.
Electron-beam lithography of curved structures with an enhanced vector-scan pattern generator supporting conic-based primitives
Authors: Vasey F. , Prongúê D. , Rothuizen H. , Vettiger P.
Published: July 2002

An IBM vector-scan machine is adapted to the generation of curved patterns by adding a new primitive to its basic set. Quadratic polynomials characterize the curved boundaries of this new primitive, allowing the construction of any conic section in the beam-stepping plane. The implementation is based on a digital signal processor running in tandem with the existing microcontroller and maintains full compatibility with existing hardware and software. The conic sections are approached to the best possible accuracy (better than 1/2 beam step), and the dose is uniformly distributed throughout the area of the primitive as the exposed points remain on a cartesian grid. The successful exposure of an elliptical diffractive optical element with chirped periodicity demonstrates the functionality of the upgraded machine.