bluuebunny/crossref_metadata_2025 huggingface dataset:
100 kV thermal field emission electron beam lithography tool for high-resolution x-ray mask patterning
Authors: McCord M. A. , Viswanathan R. , Hohn F. J. , Wilson A. D. , Naumann R. , Newman T. H.
Published: July 2002

High-voltage (≥50 kV) electron beam lithography (EBL) is the preferred technique for fabrication of additive-process x-ray masks, because the high-voltage minimizes scattering in the resist and membrane, resulting in better resolution, straighter sidewalls, and reduced proximity effect. We have designed and built a new 100 kV column for a vector scan EBL machine for the purpose of writing high-resolution, high-precision x-ray masks in order to explore the technological and fundamental limits of x-ray lithography. The column features a 100 kV thermal field emission gun with an electrostatic condenser lens, conjugate blanking, and a liquid-cooled magnetic final lens with high-precision double magnetic deflection. The two-lens optics provides a beam diameter of 30 nm at a current of 5 nA, sufficient to expose moderately sensitive resists at pixel rates approaching the maximum deflection speed of 10 MHz. Results obtained include proximity corrected, complex patterns in thin resist with feature sizes down to 50 nm. Comparisons of proximity effects, exposure parameters, and actual resist profiles, show that 100 kV is clearly superior to 50 kV and even 75 kV for feature sizes below 0.25 μm in thick (0.75 μm) resist. Excellent linewidth control has been obtained on plated gold x-ray masks with feature sizes as small as 75 nm. Problems of patterning nanometer features with aspect ratios as high as 10:1, which include forward scattering, development effects, and plating effects, are discussed.
Coulomb interactions in a shaped ion beam pattern generator
Authors: Vijgen L. J. , Kruit P.
Published: July 2002

The statistical Coulomb interactions between the particles of a focused ion beam can severely reduce the quality of a system. The interactions in the source region of a liquid metal ion source have been studied extensively and lead to the well-known virtual source diameter of 50 nm and energy width of 5 eV in a Ga source. In this report, the interactions are described in the rest of the column of the Delft ion beam pattern generator, a system using a shaped beam with Köhler illumination. The simulations have been done with the Interac and Montec programs developed by Jansen [G. H. Jansen, Coulomb Interactions in Particle Beams (Academic, San Diego, 1990), Suppl. 22; G. H. Jansen, Montec, and Interac Programs, information obtainable from, Particle Optics Foundation, Lorentzweg 1, 2628 CJ Delft, The Netherlands]. The results show that the Coulomb interactions are a limiting factor for the beam quality, not only in the source region but also in the rest of the column. In particular, long segments with small opening angles cause deterioration of the beam. In these segments, the beam can even tend to thermodynamic relaxation. For the case of a square shape with size 100 nm and edge sharpness 25 nm, for which the normal probe current should be about 1 nA, interactions cause the edge sharpness to deteriorate by a factor of two at 100 pA while for more than 200 pA the square shape is not recognizable anymore.
Fabrication of deep submicron patterns with high aspect ratio using magnetron reactive ion etching and sidewall process
Authors: Shiping Gao , Mengzhen Chen
Published: July 2002

A method for fabrication of fine patterns by conventional technologies is described. Using the sidewall process for fine pattern transfer and magnetron reactive ion etching, deep submicron and nanometer patterns with high aspect ratio have been prepared.
Adsorption and reaction of diethylzinc on GaAs(100)
Authors: Rueter M. A. , Vohs J. M.
Published: July 2002

The reactions of diethylzinc (DEZ) on the GaAs(100) surface have been studied using temperature programmed desorption, x-ray photoelectron spectroscopy (XPS), and high-resolution electron energy-loss spectroscopy. DEZ dissociated on the GaAs(100) surface below room temperature forming adsorbed zinc atoms and ethyl groups. The adsorbed zinc metal interacted weakly with the GaAs(100) surface and desorbed near 530 K. The ethyl species formed via DEZ dissociation bond to surface Ga atoms. The resulting surface ethyl-Ga complexes were stable to approximately 500 K at which point they reacted to form ethylene, hydrogen, and smaller amounts of ethyl radicals and ethane. At high surface ethyl coverages a fraction of the ethyl-Ga species reacted between 300 and 500 K to form gaseous galliumalkyls. XPS results demonstrate that the decomposition of the adsorbed ethyl groups did not result in carbon deposition onto the surface.
Comparison of mobility-limiting mechanisms in high-mobility Si1−xGex heterostructures
Authors: Monroe Don , Xie Y. H. , Fitzgerald E. A. , Silverman P. J. , Watson G. P.
Published: July 2002

Relaxed Si1−xGex buffers on Si have yielded record low-temperature mobilities for both electrons and holes in the Si–Ge system. We analyze various limitations on this mobility, including scattering from remote dopants, background impurities, interface roughness, alloy fluctuations, and the specific strain, morphology, and threading dislocations expected for relaxed alloy buffers. Comparison with experiments eliminates all but the first four as potential limitations on the mobility.
Performance of 0.2 μm optical lithography using KrF and ArF excimer laser sources
Authors: Yamashita Kazuhiro , Endo Masayuki , Sasago Masaru , Nomura Noboru , Nagano Hiroyuki , Mizuguchi Shinichi , Ono Takuhiro , Sato Takeo
Published: July 2002

KrF and ArF excimer laser lithography are considered to be candidates for a next lithography tool to achieve a miniaturization below quarter micron. To improve the focus latitude and overlay accuracy, an in-house KrF excimer laser stepper with off-axis illumination has been developed. This developed system can successfully resolve 0.2 μm features using off-axis illumination combined with an in-house developed positive chemically amplified resist and can also attain overlay accuracy of better than 60 nm using heterodyne holographic alignment. Reducing the optical absorption of the resist and the lens material at 193 nm was a challenge. The newly developed 193 nm resist contains no aromatic groups, and the designed projection lens has aspherical elements to establish ArF excimer laser lithography.
Relationship between resist performance and reaction order in a chemically amplified resist system
Authors: Fedynyshyn Theodore H. , Szmanda Charles R. , Blacksmith Robert F. , Houck William E. , Root Jonathan C.
Published: July 2002

The threshold cross-link density model describes the effect of cross-link density (Θ) on image formation and the relationship of the cross-link density to acid concentration in the resist. This method was used to determine experimentally the reaction order of acid in the cross-linking reaction of negative acid catalyzed resists. The order of the cross-linking reaction in acid effectively modulates the aerial image of the resist by transforming the initial acid concentration defined by the aerial image by a power equal to the reaction order of the acid. The reaction order of the acid catalyzed cross-linking reaction is also determined via the measurement of bulk resist properties. Determining the reaction order by bulk methods generates a quantity that is independent of the effects of acid diffusion in the resist and is similar to that obtained by the threshold cross-link density model. Also described is the effect acid diffusion will have on mitigating the enhancement of the image obtained with large reaction orders. Finally, the effect of developer selectivity is addressed and a method to determine developer selectivity is presented. The effect on the modulation of the initial energy distribution which is defined by the aerial image from diffusion, reaction order, and developer selectivity is described.
Real-time latent image monitoring during holographic fabrication of submicron diffraction gratings
Authors: Gregus Jeffrey A. , Green Christian A. , Yoon Euijoon , Ostermayer Fred W. , Hayes Todd R. , Pawelek Richard , Gottscho Richard A. , Naqvi S. Sohail H.
Published: July 2002

Real-time monitoring of latent images in photoresist during the holographic exposure of submicron period diffraction gratings is reported. The first-order diffraction efficiency is recorded as a function of time for different resist thicknesses and polarizations. By monitoring the diffraction efficiency in real time, the process can be controlled to compensate for variations in exposure dose, resist thickness, and the optical properties of underlying materials. It is demonstrated that latent image monitoring (LIM) can be performed in real time and that the diffraction efficiency correlates well with the linewidth. To interpret diffraction efficiencies with changes in resist thickness and polarization, rigorous coupled wave analysis combined with a commercial software package to simulate the real-time data was used. However, the data show evidence for slow changes in the composition of the resist during exposure that are consistent with chemical intermediates reacting with water in the film. The commercial exposure simulation tool cannot account for these phenomena, which complicate the application of LIM to real-time exposure control.
Silane reduced chemical vapor deposition tungsten as a nucleating step in blanket W
Authors: McInerney E. J. , Mountsier T. W. , Chin B. L. , Broadbent E. K.
Published: July 2002

The SiH4–WF6 nucleation step of chemical vapor deposition blanket tungsten has been studied in the 10–100 Torr pressure range. The deposition rate, particle generation rate, and step coverage were studied as a function of the process parameters. The deposition rate was found to be mass transfer limited over the entire range of process conditions. Deposition rates from 300 to over 70 000 Å/min were observed. An in situ detector was used to measure gas phase particle levels. Particle generation rates were found to range from 0 to 108 particles/s over the parameter range studied. The strongest dependence seen was on the SiH4/WF6 flow ratio. At ratios of less than one, no detectable particles were produced. The particle generation rate increases rapidly at ratios above one. The particle rate also increases with increasing temperature and pressure. The step coverage was found to be ∼85% for 1000 Å films in 3:1 aspect ratio trenches. Overall, the results indicate that SiH4 nucleation in the 10–100 Torr range is an attractive alternative to the ≤1 Torr processes commonly in use today.
Ultrasharp tips for field emission applications prepared by the vapor–liquid–solid growth technique
Authors: Givargizov E. I.
Published: July 2002

A technique for preparation of ultrasharp tips, preferentially of silicon, useful for field-emission research and applications is described. Regular arrays of tips, as well as triodelike microstructures (‘‘Spindt cathodes’’), can be prepared in such a way. In addition, high-aspect-ratio tips suitable for field-ion microscopy and field-electron microscopy can be prepared by this technique. Finally, a version of the technique allowing to prepare special-shape probes for scanning tunneling microscopes and related instruments is given.
Scanning tunneling microscopy of flat and vicinal molecular-beam epitaxy grown GaAs(001)-(2×4) surfaces: The effect of growth rate
Authors: Pond K. , Maboudian R. , Bressler-Hill V. , Leonard D. , Wang X.-S. , Self K. , Weinberg W. H. , Petroff P. M.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to investigate the effect of the deposition rate on the resulting morphology of nominally flat and vicinal GaAs(001)-(2×4) surfaces grown by molecular-beam epitaxy. On the nominally flat surfaces, low deposition rates are found to create smooth surfaces and lead to anisotropic islanding with an A-type step (Ga terminated, parallel to the [1̄10] direction) to B-type step (As terminated, parallel to the [110] direction) average aspect ratio which is larger than that produced by standard deposition rates. The results suggest that the increase in the island anisotropy at low growth rates reflects the energetics of the step edges. In contrast, the growth rates investigated are found not to have any obvious effect on the resultant morphology of the 2° A-type vicinal surfaces. In particular, no islanding on the terraces is observed at either deposition rate. However, detailed statistical analyses of the STM images indicate that there is a larger spread in the terrace width and a greater probability for forming kinks with increasing growth rate. This observation suggests that the probability of a Ga adatom incorporating at an A-type step (rather than at a B-type kink) is greater for standard growth rates than for low growth rates.
Structure of Sb monolayers on Ge(111)2×1: A combined study using core-level photoemission, x-ray standing waves, and surface extended x-ray absorption fine structure
Authors: Kendelewicz T. , Woicik J. C. , Miyano K. E. , Herrera-Gomez A. , Cowan P. L. , Pianetta P. , Spicer W. E.
Published: July 2002

The atomic stucture of an annealed monolayer of Sb on the Ge(111)-(2×1) surface has been studied with core-level photoemission, x-ray standing waves (XSW), and surface extended x-ray absorption fine structure (SEXAFS). Phase analysis of the SEXAFS data taken over the Sb L3 edge using bulk Sb and GaSb as standards determines the bond lengths within the first Sb shell to be 2.87±0.03 Å and 2.67±0.03 Å for the Sb–Sb and Sb–Ge bonds, respectively. The XSW data for (111) planes, taken in the backreflection diffraction geometry, place the Sb layer 2.60±0.05 Å above the Ge(111) surface. A relatively high coherent fraction (0.85) indicates small disorder or buckling in the Sb overlayer. The Sb overlayer is found to quench the clean surface shifted components of the Ge 3d core-level spectrum, which indicates an ideal termination of the Ge(111) surface with all dangling bonds saturated by the Sb adatoms. Lack of chemically shifted components in both the Ge 3d and the Sb 4d core level spectra indicates a single bonding site for the Sb atoms. Although it is not possible to differentiate between Sb trimers [as found for the Sb/Si(111) interface] or zigzag chains (common for Sb/III–V interfaces) on the Ge surface, substitutional geometries, in which Sb replaces the topmost layer of the Ge surface bilayer [as found for As/Ge(111)], can be ruled out.
Interfacial atomic composition and Schottky barrier heights at the Al/GaAs(001) interface
Authors: Dandrea R. G. , Duke C. B.
Published: July 2002

The influence of different interfacial chemical compositions on the Schottky barrier heights across the Al/GaAs(001) interface is studied using first-principles local density functional calculations. The barrier heights are calculated for seven different interfacial chemical compositions, including the chemically abrupt As-terminated and Ga-terminated interfaces, and also several other interfaces related by Al↔Ga place exchange or containing As antisites. We find p-type barrier heights φp that vary by 0.4 eV, demonstrating a significant influence of the interface composition on the resulting barrier heights. The barrier height variation is explained by the different chemical bonding at the interface in the various cases. The metal induced gap states (MIGS) of two structures with different barrier heights are compared in order to demonstrate why such states do not result in barrier heights independent of interfacial chemical composition. It is thus suggested that the reason an experimental value of φp=0.65 eV is generally found for Al/GaAs is not due to several possible interfacial structures all having their Fermi level pinned by MIGS at the same value, but rather due to the thermodynamic preference for certain structures over others with significantly different barriers. This proposal offers a potential explanation for recent photoemission experiments that find the Fermi level position in the gap varying by several tenths of a volt as a function of the initial surface structure of the GaAs substrate: some of the samples are likely to have interfacial compositions which are metastable with respect to structures that give the standard barrier heights.
Relaxation of GaAs surface band bending by atomic layer passivation
Authors: Wada Yoshinori , Wada Kazumi
Published: July 2002

GaAs surface passivation by several atomic layers of InP is presented. The deposition of an atomically thin InP layer on n- and p-type (100) GaAs by chemical vapor deposition shows very strong enhancement in photoluminescence intensity and a remarkable reduction in surface band bending determined by Hall effect measurements. The surface modification effect is very stable, and evidence suggests that the oxidation of InP plays an important role in this passivation mechanism. These results indicates that atomically thin InP layer is very effective for the surface passivation of GaAs.
Repeated compressive stress increase with 400 °C thermal cycling in tantalum thin films due to increases in the oxygen content
Authors: Cabral C. , Clevenger L. A. , Schad R. G.
Published: July 2002

Stresses which build up in thin films such as tantalum, during thermal processing, can cause major reliability problems in electronic and x-ray optics applications. We demonstrate that 50–200 nm thick sputtered β-Ta thin films undergo repeated compressive stress increases when thermally cycled to 400 °C (at a rate of 10 °C/min) and back in a purified He ambient because of small amounts of oxygen gettered by the tantalum. The oxygen contamination results from the poor quality of the atmospheric seal on the quartz annealing chamber. As-deposited Ta thin films have a compressive stress ranging from −1 to −4 GPa. The compressive stress buildup was monitored in situ and was shown to increase −0.5 GPa on average after each thermal cycle for a final value from −6 to −7 GPa after seven cycles. After being cycled thermally seven times any perturbation of the film such as a four-point probe resistivity measurement can cause the film to instantaneously crack in a serpentine pattern, relieving the large compressive stress. Auger electron spectroscopy depth profiling analysis was used to determine that the as-deposited film contained 1 at. % oxygen which increased to 8%–12% after seven thermal cycles with an approximate doubling in resistivity. The −0.5 GPa average compressive stress increase in Ta thin films when cycled to 400 °C is attributed to a 1.3% increase in oxygen concentration leading to a Ta unit cell expansion of 0.6%.
Do manufacturing technologies need federal policies?
Authors: Schmitt R. W.
Published: July 2002

U.S. manufacturing capabilities are a key component of our global economic competitveness. Because the U.S. fell behind in several important manufacturing industries—especially in competition with the Japanese—federal attention to the health of these industries has grown. The Japanese cut into U.S. leadership through their attention to quality and continuous improvement. Current challenges in the field include reaping productivity benefits from computerization, developing environmentally friendly manufacturing methods, and shifting the federal research and development (R&D) emphasis from military defense to industrial R&D, including manufacturing technologies. Current federal proposals to increase federal support of manufacturing technologies may play an important role in future competitiveness of U.S. industry. The challenge is to grow these programs fast enough to meet the goals of defense conversion, yet not so fast that we do them poorly. Recommendations are offered on practical ways to target, adjust and apply these proposals.
Novel technique for the separation of mechanical properties and intrinsic stress of pre- and post-irradiated membranes
Authors: Chen H. T. H. , Engelstad R. L. , Cerrina F.
Published: July 2002

The focus of this paper is to introduce and describe a new technique for the determination of x-ray lithography mask distortions for pre- and post-irradiated membranes using a combination of numerical, analytical, and experimental methods. At the heart of this technique is a new test structure and fixture that allow for the accurate determination of material properties so that changes due to radiation exposure can then be incorporated into a finite element model to predict distortions. In addition, due to the size of the membranes used for the test structure, larger accumulated doses can be delivered in shorter periods of time. Once the material property and stress changes have been incorporated into numerical models, calculations can then be performed to simulate the effect of radiation on various membrane pattern areas and geometries.
Experimental determination of the effective lithographic contrast for x-ray masks
Authors: Maldonado Juan R.
Published: July 2002

A new technique for measuring effective lithographic contrast based on its definition is presented. Results obtained at the IBM Advanced Lithography Facility using the Helios storage ring are compared with conventional ways of determining mask contrast. In addition, a method to decrease the effects of multiple exposures in adjacent fields during the step and repeat operation of an x-ray lithography stepper is presented.
Synchrotron radiation x-ray lithography beamline optics alignment using the Hartmann method
Authors: Chen G. , Yamazaki K. , Waldo W. , Welnak J. , Wells G. M. , Cerrina F.
Published: July 2002

This article studies the effect of mirror misalignment on run-out overlay errors in a synchrotron radiation based x-ray lithography system. Using the ES-5 beam-line installation at the CXrL as an example, we found that the current beamline mirror alignment method, which relies on the final beam shape and orientation at the mask-wafer plane, is insensitive to the mirror grazing incident angle alignment. Simulations using the ray-tracing program shadow indicate that a smaller than ±0.5-mrad mirror grazing angle misalignment consumes the required run-out overlay error budget of the beamline. A direct beamline run-out overlay measurement technique based on the Hartmann method was developed for the beamline mirror alignment. This measurement technique was applied to our ES-5 beamline mirror alignment procedure. The measurement results show that the beamline induced run-out error of the installed ES-5 beamline is less than 0.014 μm in both horizontal and vertical direction for a 25-mm exposure field with a mask-wafer gap of 40 μm. The across field run-out error distribution is also compared with shadow simulation results. The good agreement between measurement and simulation data indicates that our measurement technique provides a sensitive, practical, and accurate method for x-ray lithography beamline mirror alignment and evaluation.
Temperature uniformity across an x-ray mask membrane during resist baking
Authors: Resnick D. J. , Cummings K. D. , Johnson W. A. , Chen H. T. H. , Choi B. , Engelstad R. L.
Published: July 2002

We have studied temperature uniformity during the post-exposure bake process across a 40 mm diameter of an x-ray mask membrane. Membrane temperature was determined by measuring line size as a function of position across the membrane. A two-dimensional finite element model (FEM) was used to analyze the results and optimize the design of a new bake chuck. The 3σ variation across the diameter of the mask was reduced to 27 nm. The FEM was also used to examine issues associated with resist baking on the ARPA-NIST X-ray Mask Standard and the initial results are discussed.
Wavelength dependence of exposure window and resist profile in x-ray lithography
Authors: Guo Jerry Z. Y. , Celler George K. , Maldonado Juan R. , Hector Scott D.
Published: July 2002

In proximity x-ray lithography, wavelengths in the range of 4–20 Å are used. The choice of wavelength is a complicated system issue, which depends on many lithographic aspects. Shorter wavelength x rays offer aerial image diffraction advantages. However, they may also give rise to spurious photoelectron effects. Longer wavelength x rays make mask patterning easier since the absorber can have a smaller aspect ratio for the required contrast, but a thinner, less robust membrane is needed to give the same x-ray transmission. Softer x rays are also better absorbed in resist, reducing the exposure time, but higher absorption can have an adverse effect on the resist sidewall profile. A study is conducted to address the wavelength issue in x-ray lithography using the exposure window, resist profiles, power efficiency, and the mask contrast as merit/cost functions. Results show that a compromise among these factors is needed to achieve best performance.
Application of a high-throughput electron-beam system for 0.3 μm large scale integration
Authors: Mizuno F. , Kato M. , Hayakawa H. , Sato K. , Hasegawa K. , Sakitani Y. , Saitou N. , Murai F. , Shiraishi H. , Uchino S.-i.
Published: July 2002

A high-throughput electron-beam direct writing technology has been developed. The new technology enables the manufacture of 0.3 μm large scale integration with a maximum throughput of 15 wafers/h, and the application of electron-beam lithography for high-volume large scale integrations. The throughput attained with this technology is 4–20 times higher than that of conventional technologies (e-beam direct writing system: Hitachi HL-700D; e-beam resist: Hitachi RE-5000P). This technology has been realized by utilizing a combination of the new e-beam direct writing system HL-800D and the new e-beam resists RE-4200N/PSR.
Application of real time infrared spectroscopy to monitoring the kinetics of chemically amplified resists
Authors: Howes Glenn R. , Gamsky Christopher J. , Taylor James W.
Published: July 2002

Currently, the major approach to improving the performance of chemically amplified resists is by means of statistical design methods. These methods do not make use of information about the underlying chemical processes, information which could be useful in expediting the optimization process. We have developed techniques and equipment to monitor changes in resist chemistry during the bake steps using in situ using real time Fourier transform infrared spectrometry (RT-FTIR). Using the Shipley SAL 605 negative chemically amplified resist, we monitored exposed resist as it was being baked at 110 °C; we were thus able to see several peaks change, including the growth of a peak at 982 cm−1 which we associate with the formation of an ether linkage during cross-linking. When the height of this peak is plotted over time from the start of the bake, it shows several things, among them (a) the reaction being monitored takes much longer to reach its final level of completion (≳300 s) than the statistically derived optimum (∼60 s), (b) as expected, the reaction rate is a function of dose, and (c) the results are reproducible between identically treated wafers. We speculate that the reason we see peak growth long after the resist is cross-linked enough for processing is due to the multiple available sites on the cross-linker molecule which allow continued bond formation after enough have formed to make the resist sufficiently insoluble. With chemically amplified resists there has been concern over residual solvent which can interfere with the catalytic mechanism of the photogenerated acid. The same RT-FTIR techniques were also shown to be effective in monitoring the loss of solvent from the resist during the preexposure bake, giving the time at which the solvent can be assumed to have been removed—in the case of Shipley SAL 605, approx 30 s. Finally, the RT-FTIR technique can be used to follow the individual contributions of the components of the resist formulation as their concentrations are changed to affect different resist properties. The monitoring is directly on the resist-coated wafer, and special handling techniques, to be described in the text, are necessary to make these measurements directly applicable to resist processing.
Positive-tone silylated, dry-developed, deep ultraviolet resist with 0.2 μm resolution
Authors: Hutton R. S. , Stein S. M. , Boyce C. H. , Cirelli R. A. , Taylor G. N. , Baiocchi F. A. , Kovalchick J. , Wheeler D. R.
Published: July 2002

This paper describes the development of a surface-imaging process for a positive-tone silylated, dry-developed bilayer resist which has 0.2 μm resolution and an aspect ratio of 4.5 using deep-UV (248 nm) exposure. The many processing variables such as thermal treatment parameters, silylation conditions, and etching conditions were examined to determine their effects on lithographic performance in terms of resolution, feature size linearity, focus latitude, and sensitivity. Critical to the success of the process are: the bilayer structure which restricts diffusion of the Si, the use of a disilane reagent to increase the Si content of the masking layer, limiting migration of photogenerated acid by the appropriate choice of softbake and post-exposure bake temperatures, initial etching with an Ar/Cl2 mixture to remove the thin layer of silylated resist in the exposed areas, and employing CO2 instead of O2 as the etching gas to eliminate lateral etching of the features. With this process we have obtained good critical dimension linearity down to 0.25 μm for bright-field and dark-field lines and spaces as well as isolated lines and isolated spaces. The dose required is ∼75 mJ/cm2 and the dose latitude is ±6%. Focus latitude is at least ±0.4 μm. We also observe no environmental effects on sensitivity or resolution.
Comparison of image shortening effects in x-ray and optical lithography
Authors: Dellaguardia R. , Maldonado J. R. , Prein F. , Zell T. , Kluwe A. , Oertel H. K.
Published: July 2002

Data on image shortening effects with patterns replicated with x-ray and optical lithography are presented. The x-ray exposures were performed at the IBM Advanced Lithography Facility using the Helios superconducting storage ring and a SUSS stepper. The optical exposures were performed using SVGL Micrascan 1 and 2 tools and biased optical masks. The results indicate that the image shortening effects using x-ray lithography (XRL) are considerably less pronounced than the effects observed with the optical tools. In addition, modeling of the image shortening effects for XRL using the xmas three-dimensional program for resist patterns is presented and compared with experimental results.
Writing strategies of circular gratings for surface-emitting lasers using focused ion-beam (x–y coordinate) and electron-beam (polar coordinate) lithography
Authors: Fallahi M. , Templeton I. M. , Chatenoud F. , Champion G. , Dion M. , Barber R.
Published: July 2002

In this article the fabrication of circular gratings by electron-beam lithography (r-θ coordinates) and by focused ion-beam lithography (x-y coordinate) is presented. The differences between the two techniques, relevant to the fabrication of circular patterns, are described. The optimum writing strategies and the quality of circular gratings are compared. Electrically pumped circular-grating surface-emitting distributed Bragg reflector (DBR) lasers were fabricated by the two techniques. Room temperature cw operation of a circular-grating surface-emitting DBR laser is demonstrated.
Sub-0.1-μm T-shaped gate fabrication technology using mixing-layer sidewalls in a double-layer resist system
Authors: Samoto N. , Miura I. , Makino Y. , Yamanoguchi K.
Published: July 2002

In this paper, we report on a novel fabrication technique for sub-0.1-μm T-shaped gates for ultrahigh frequency field effect transistors using the mixing layer generated in a double-layer resist system. The typical resist layer structure in this work consists of a 1.1-μm ultraviolet (UV) resist, PFI-15A, and a 0.15-μm electron-beam (EB) resist, polymethylmethacrylate (PMMA). First the PMMA layer is spin-coated, exposed by EB, and developed to define the gate footprint. Next the PFI-15A layer is spin-coated and exposed with i-line stepper for the gate top, then developed using an image reversal method to obtain an undercut opening. A mixing layer is created at the interface between the resists by the method. This layer acts as a sidewall which reduces the initial PMMA pattern size by 30–40 nm. A T-shaped gate of a 70-nm footprint is fabricated from a 0.1-μm initial linewidth in PMMA using a lift-off process.
Calculation of current contrasts in two-terminals atomic switches
Authors: Vigneron J. P. , Derycke I.
Published: July 2002

Scanning tunneling microscope images of xenon atoms lying at various sites of a nickel surface are calculated using a Laue representation of the electron scattering states. The simulation program views the tip and the adsorbate as discrete atomic clusters attached to the planar surface of facing Sommerfeld metallic half spaces. It is shown that the elastic electron scattering provides an adequate description of the Xe images: rows of Xe atoms are resolved with a shape in good agreement with experiment. The same model is applied to the study of the recently described one-atom switch of Eigler et al. [Nature 352, 600 (1991)]. The computed current contrast, which adequately compares to observed values, shows significant variations for different Xe adsorption sites on the tip.
Electric field influence on the observation of molecules with a scanning tunneling microscope
Authors: Hörber J. K. H. , Häberle W. , Ruppersberg P. , Niksch M. , Smith D. P. E. , Binnig G.
Published: July 2002

With a specially developed double-tip scanning tunneling microscope the influence of a lateral electric field on the ordering of the liquid-crystal molecules (10CB) was observed. In this setup two independent scanning units could work on a common substrate with different tunneling voltages and currents. No interference between the two tunneling currents was observed down to tip distances of 2 μm. This result means that it is unlikely that surface currents are a major contribution to the imaging mechanism on nonconducting molecules. The additional electric field was observed to alter the alignment of the molecules on the substrate. Modified scanning tunneling spectroscopy by tip voltage modulation was used to characterize the conductivity of the phenyl and alkyl parts of the molecules at tip potentials between 0 and 1.2 V.
Temperature dependence of photoluminescence linewidth in GaAs/GaAsP strained-layer quantum well structures
Authors: Zhang Xiong , Shiraki Yasuhiro , Yaguchi Hiroyuki , Onabe Kentaro , Ito Ryoichi
Published: July 2002

The temperature dependence of photoluminescence (PL) spectra for the GaAs/GaAsP strained-layer single quantum well structures has been investigated in detail. For temperatures below 77 K, the PL linewidth was found to first decrease and then to increase slowly as the temperature was enhanced. This phenomenon was clearly seen for the GaAs/GaAsP strained-barrier quantum wells exhibiting higher dislocation densities than the GaAs/GaAsP strained-well quantum wells. This fact strongly suggests that beside the unintentionally introduced impurities, the misfit dislocations may also play an important role in determining the temperature-dependent PL linewidth.
Radiation stability of SiO2-antireflective film coated SiN and SiC x-ray mask membranes
Authors: Arakawa T. , Okuyama H. , Yamashita Y. , Syoki T. , Nagasawa H. , Yamaguchi Y. , Matsuo T. , Noguchi F.
Published: July 2002

Radiation stability of SiO2 antireflective film coated SiN and SiC x-ray mask membranes was studied. Although the transmission at 633 nm of the SiO2-coated SiN was reduced by about 8% after synchrotron radiation (SR) exposure with an absorber dose of 100 MJ/cm3, the oscillation of the transmission due to interference was considerably suppressed even after the SR absorption. Furthermore, the optical transmission spectrum of the SiO2-coated SiC was nearly equal to that of uncoated SiC after the SR absorption of 100 MJ/cm3. The pattern displacement induced by the SR absorption of 10 MJ/cm3 for the SiO2-coated SiN and for the SiO2-coated SiC was σx=6 nm, σy=7 nm and σx=8 nm, σy=6 nm on the 25-mm-square area, respectively, the values of which were within the reproducibility of the displacement measurement. Electron spin resonance analysis indicated that no significant difference of spin density between the SiO2-coated and uncoated SiN membranes was recognized before and after the SR absorption.
Sodium contamination free ashing process using O2+H2O plasma downstream
Authors: Fujimura Shuzo , Suzuki Miki T. , Shinagawa Keisuke , Nakamura Moritaka
Published: July 2002

The effect of O2+H2O plasma downstream ashing on sodium contamination from resists has been studied through measurement of flatband voltage shifts of metal–oxide–semiconductor (MOS) diodes after bias-stress treatment and measurement by atomic absorption spectroscopy of the amount of sodium in the SiO2 layer after resist stripping. The flatband voltage shift of the MOS diodes on which a resist layer was stripped by the O2+H2O plasma downstream was almost the same as that treated by the O2+H2O plasma downstream without resist and smaller than that where the resist was removed by other dry ashing methods such as O2 plasma and O2 plasma downstream. In addition, the amount of sodium that existed in the SiO2 layer after resist ashing by the O2+H2O plasma downstream was also nearly the same as that in the SiO2 layer as grown. This sodium passivation by the O2+H2O plasma downstream was most effective at the H2O percentage of 40%–60%, and did not depend on wafer temperature below 200 °C or over-ashing time. These results support our original idea of sodium passivation, i.e., OH radicals generated in the O2+H2O plasma and its downstream react with sodium to prevent sodium invasion into the SiO2layer.
Annealing-induced near-surface ordering in disordered Ga0.5In0.5P
Authors: Luo J. S. , Olson J. M. , Wu Meng-Chyi
Published: July 2002

Most samples of Ga0.5In0.5P grown by metalorganic chemical vapor deposition (MOCVD) on (001)-like surfaces are partially ordered and exhibit distinctive reflectance difference spectral (RDS) features associated with the anisotropic properties of the ordered bulk structure. It is known that the ordering is not a ground-state property of the bulk but is surface-induced during growth. On the other hand, Ga0.5In0.5P grown by liquid-phase epitaxy (LPE) is completely disordered, and it has been shown that its RD spectrum is essentially featureless. In this article, we present a study of the effects of annealing (in a PH3/H2 atmosphere) on LPE-grown Ga0.5In0.5P using ex situ and in situ RDS. The annealing temperatures and times used in this study (650°C and tens of minutes) have virtually no effect on the bulk optical or structural properties of MOCVD-grown Ga0.5In0.5P. For LPE-grown Ga0.5In0.5P, we find that annealing induces bulk-like RDS features at both E0 and E1 with line shapes similar to those observed for MOCVD-grown ordered Ga0.5In0.5P. These bulk-like spectral features are, however, due to near-surface reconstruction of Ga and In because they are effectively quenched by exposure to air. Also, the E0 feature becomes sharper and both the E0 and the E1 features red-shift as the annealing process is prolonged. This indicates that this reconstruction is kinetically limited, presumably by the slow interdiffusion of Ga and In necessary to achieve the ordered bulk-like structure.
Surface roughness and pattern formation during homoepitaxial growth of Ge(001) at low temperatures
Authors: Van Nostrand Joseph E. , Chey S. Jay , Cahill David G.
Published: July 2002

The evolution of surface roughness during growth of Ge(001) by molecular beam epitaxy at 155°C is characterized using in situ scanning tunneling microscopy. The range of film thickness studied spans more than three orders of magnitude, 0.1–200 nm. Beginning at a film thickness near 100 nm, a periodic pattern of growth mounds is observed. The average in-plane separation of growth features d evolves continuously with film thickness t, following a power law d=t0.42. The vertical roughness of the film does not follow a single power-law behavior over this range of film thickness.
Nanolithographic patterning of Au films with a scanning tunneling microscope
Authors: Van Haesendonck C. , Stockman L. , Neuttiens G. , Strunk C. , Bruynseraede Y.
Published: July 2002

We present a new lithographic technique with a scannning tunneling microscope (STM), allowing us to pattern thin evaporated Au films at the nanometer scale. The electron beam produced by the STM tip is used to expose a very thin layer of ω-tricosenoic acid. Only four monolayers of the acid, which acts as an electron sensitive, negative resist, are deposited on top of the Au films using the Langmuir–Blodgett technique. We have verified the influence of the exposure conditions on the quality of the fabricated fine-line structures with a linewidth down to 15 nm. We can also measure the electrical properties of narrow Au lines which interconnect large predefined contact pads. As expected, the low-temperature magnetoresistance is strongly influenced by quantum interference effects.
Surface ordering on GaAs(100) by indium-termination
Authors: Resch-Esser U. , Esser N. , Springer C. , Zegenhagen J. , Richter W. , Cardona M. , Fimland B. O.
Published: July 2002

The growth of indium-layers in the monolayer regime on As-rich (2×4)/c(2×8)- and Ga-rich (4×2)/c(8×2)-GaAs(100) surfaces has been investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and reflectance anisotropy spectroscopy (RAS). Clean (2×4)- and (4×2)-reconstructed surfaces were prepared in UHV by thermal desorption of a protective arsenic layer deposited on top of GaAs(100) surfaces grown in a molecular beam epitaxy (MBE)-system. For the (2×4) reconstruction, the STM images show As-dimer rows consisting mostly of two dimers per unit cell in the outermost layer. Besides a large number of kinks in the dimer rows, a surface roughness corresponding to about three bilayer steps (8.4 Å) is observed due to multiple layer nucleation during MBE growth. After deposition of indium and subsequent annealing to approximately 450 °C a well ordered reconstruction with c(8×2)-symmetry is established. The STM images show a pattern consisting of kink free, alternating straight and broken rows oriented along the [110]-direction attributed to In-dimer rows. Remarkably, the surface roughness of these In-terminated surfaces is strongly reduced. For the Ga-terminated (4×2) surface reconstruction, STM results show a surface terminated with Ga-dimer rows, free of kinks, which appears flat over large areas similar to the In-terminated surface. After deposition of indium and annealing to 450 °C, LEED, RAS and STM reveal a surface structure very similar to that formed on the (2×4)-surface. Thus we conclude that in both cases a structure with In-dimer-rows on top of an As-layer (second layer) is formed. The smoothing of the surface roughness is a consequence of the larger mobility of the group III surface atoms, following the As desorption.
Pilot experiments on microstructured liquid metal ion and electron sources
Authors: Mitterauer J.
Published: July 2002

Ion or electron beams can be emitted from liquid metal wetted needles, or from capillaries or slits into which the liquid metal is allowed to flow. Large-area liquid metal field emission sources have been proposed recently, using either two-dimensional, regular arrays of cones or capillaries, or even a substrate with an intrinsically microstructured surface covered by a liquid metal film. Now this latter concept has been realized in a pilot experiment by in situ wicking and wetting of a porous sintered metal disk. A similar concept has been applied formerly on a mercury-film cathode supporting a low pressure arc discharge. Microstructured liquid metal ion or electron sources are capable to operate in a pulsed mode at a current level which is orders of magnitude above that for steady-state operation.
Selective-area epitaxy of carbon-doped (Al)GaAs by chemical beam epitaxy
Authors: Li N. Y. , Dong H. K. , Hsin Y. M. , Nakamura T. , Asbeck P. M. , Tu C. W.
Published: July 2002

Selective-area epitaxy (SAE) of carbon-doped (Al)GaAs by chemical beam epitaxy (CBE) using tris-dimethylaminoarsenic is investigated. Orientation of the growth front can significantly affect the growth rate of the regrown layers, resulting in facet formation around the mask. Moreover, the facets can be varied by adjusting the V/III ratio. For stripes along the [011̄] direction, the growth rate of (110) and (111)A planes is lowest when the V/III ratio is close to 1, resulting in lateral growth. This lateral growth has been exploited to fabricate heterojunction bipolar transistors (HBTs) with selectively regrown GaAs/AlGaAs:C external base layers. These HBTs exhibit a 62% reduction in the base sheet resistance and a higher current gain, compared to the original HBT strcuture. No degradation of the current gain is found after regrowth, demonstrating the great potential of SAE by CBE.
Study of space-charge devices for focused ion beam systems
Authors: Wang Li , Orloff Jon , Tang Tiantong
Published: July 2002

Axisymmetric and nonaxisymmetric electron space-charge lenses and spherical aberration correctors are studied theoretically. Many interesting features of the space-charge devices are revealed by considering some simple, but physically reasonable models. It is shown that a number of simple space-charge distributions can compensate for a large range of positive spherical aberrations. Several numerical examples are presented in some detail.
Coulomb effect in cell projection lithography
Authors: Sohda Yasunari , Someda Yasuhiro , Saitou Norio , Itoh Hiroyuki
Published: July 2002

Beam blurring due to Coulomb effects is very important in cell projection lithography. This article reports on Coulomb effects in cell projection lithography by simulation and experiment, and shows some important results. First, the Coulomb effect in a single cell is substantially uniform in conventional cell projection optics. Second, refocusing is effective in reducing the space charge effect even in Koehler illumination with a Gaussian crossover. Third, the optimum cell size in the case of a large aperture percentage depends on the ratio of the total exposure time in the peripheral circuit to the total settling time in the memory cell mat. In addition, a modified mask technique is proposed to decrease the influence of Coulomb effects on throughput.
Fabrication of integrated micromachined electron guns
Authors: Hofmann Wolfgang , Chen Liang-Yuh , MacDonald Noel C.
Published: July 2002

We present a novel process for the fabrication of silicon tip emitters with self-aligned planar tungsten gate electrodes formed by low-temperature selective chemical vapor deposition. Emitters with tip radii of less than 20 nm and gate apertures with diameters of 0.5 μm have been fabricated using this process. The planar nature of the process allows the integration of multiple additional planar tungsten electrodes to produce an entire micromachined electron gun on a single silicon substrate. The gate electrode is self-aligned. Misalignment of the lens electrodes, typically less than 0.25 μm, can be corrected using integrated microelectromechanical actuators or multipole electrodes. Fabrication of multiple levels of complex suspended tungsten microstructures is demonstrated using a multiple level planar tungsten process. Test structures consisting of three levels of suspended tungsten honeycomb microstructures (1.5 μm tungsten beam width, 5 μm aperture diameter) and suspended microstages with integrated actuators are shown.
AlAsSb/InAsSb heterojunction diodes grown on Si by molecular-beam epitaxy
Authors: Du Q. , Wang W. I.
Published: July 2002

We report for the first time AlAs0.08Sb0.92/InAs0.91Sb0.09 heterostructure diodes grown on Si substrates by molecular-beam epitaxy. Strained InSb/GaSb buffer layers were employed to improve the crystalline quality of the active epitaxial layers. Heterostructure p-n junction diodes have been fabricated showing excellent current–voltage characteristics at room temperature.