bluuebunny/crossref_metadata_2025 huggingface dataset:
Low energy electron microscopy studies of steps on single crystal thin films of refractory metals
Authors: Ondrejcek M. , Swiech W. , Yang G. , Flynn C. P.
Published: December 2002

We describe low energy electron microscopy (LEEM) studies of the behavior at high temperatures of step edges on the close-packed surfaces of refractory metal thin films grown by molecular beam epitaxy. The research includes bcc Mo (011), V (011), Nb (011), and Ta (011), and comparison with bulk single crystals of Nb (011) and fcc Pt (111). Properties observed include faceting of individual steps, step–step interactions, and the interactions of steps with defects such as threading dislocations and with surface reconstructions. Step fluctuations on these surfaces are quantified. For Mo (011) observed by LEEM, the Fourier amplitudes are fit with an attachment model to obtain the step stiffness and its entropy, the step free energy, and its orientation dependence.
Design and prototyping of a micropropulsion system for microsatellites attitude control and orbit correction
Authors: Vaccari L. , Altissimo M. , Di Fabrizio E. , De Grandis F. , Manzoni G. , Santoni F. , Graziani F. , Gerardino A. , Perennes F. , Miotti P.
Published: December 2002

Silicon micromachining is an attractive technique for batch production of a wide class of miniaturized components and systems. In particular, micromachined components can be combined with semiconductor lasers, microlenses, and micromechanics to develop a new class of instruments. A worldwide impulse in micromachining is originated by the space industry. Space exploration in the new millennium will mostly rely on drastically miniaturized spacecraft by today’s standards. It is worth to note that the space community is used to speak about nanosatellites when satellite mass ranges between 1 and 10 kg, while microsatellites range between 10 and 100 kg (ESA/IPC 81 Information Note, Paris, October 2000). A key point for precise micronanosatellites orbit and attitude control is the development of a suitable propulsion system, weighting a few grams and capable of few μN of thrust. A microthruster complying these requirements is under development jointly by our laboratory and Mechatronic, using MEMS technology. The article will show the microthruster design, fabrication processes, and the experimental setup to test in space the micropropulsion system prototype. The experiment will be performed on-board the microsatellite UNISAT-2 of the University of Roma.
Direct measurement of chromatic aberrations induced by SiNx continuous membrane mask
Authors: Yahiro Takehisa , Suzuki Shohei , Irita Takeshi , Kawata Shintaro , Suzuki Kazuaki
Published: December 2002

In this article, we present experimental results that quantify the magnitude of chromatic aberrations induced by a SiNx continuous membrane mask. We used a continuous membrane mask, which consists of a TaSi scatterer layer on a SiNx membrane layer of 100 nm thickness, for the experiments. The beam edge profiles were measured directly by the knife-edge method, which can measure the image blur with the repeatability of 3 nm (3 sigma). The effect of electron energy loss induced by inelastic scattering is clearly shown in the measured beam edge profiles. The magnitude of chromatic aberrations is quantified from the measured beam edge profiles considering lens aberrations and measurement errors. The results show that lower atomic number Z and lower density materials and thinner membrane are required on the mask membrane for a high resolution lithography.
Single-electron transistor structures based on silicon-on-insulator silicon nanowire fabrication by scanning probe lithography and wet etching
Authors: Sheu J. T. , You K. S. , Wu C. H. , Chang K. M.
Published: December 2002

We propose a promising fabrication technology for single-electron transistors based on a silicon-on-insulator (SOI) nanowire fabricated by scanning probe lithography and KOH wet etching. The 10-nm-wide and 10-nm-high silicon nanowire is defined by scanning probe lithography and KOH wet etching process technology. Along the [100] direction on a (100) SOI silicon wafer, local oxidation was performed in ambient using highly doped Si cantilevers with a resistivity of 0.01–0.0025 Ω cm and a commercial atomic force microscope/scanning tunneling microscope instrument. Using the oxide pattern as a Si etching mask, the Si substrate was dipped in aqueous KOH solution, in which unoxidized regions are selectively etched by aqueous KOH orientation-dependent etching. The silicon nanowire was obtained by well-controlled overetching of 34 wt % at 40 °C for 50 s. The top gate, back gates and contact pads were defined by photolithography and dry etching. Statistics showing the reproducibility of this technique are also demonstrated.
Precision fringe metrology using a Fresnel zone plate
Authors: Joo Chulmin , Pati G. S. , Chen Carl G. , Konkola Paul T. , Heilmann Ralf K. , Schattenburg Mark L. , Liddle Alexander , Anderson Erik H.
Published: December 2002

In scanning beam interference lithography, a resist-coated substrate is scanned under phase-locked interfering beams to pattern large gratings or grids with nanometer level distortions. To achieve design goals, it is required to measure the spatial period, phase, and rotation of the interference fringes in real-time with high precision. In this article, we report the use of a Fresnel zone plate to characterize interference fringes. With properly controlled errors, it should enable us to achieve high precision measurement of fringe characteristics for a wide range of fringe periods. The mathematical model, details of the metrological procedure, and experimental results are presented.
Localized and directed lateral growth of carbon nanotubes from a porous template
Authors: Wind S. J. , Martel R. , Avouris Ph.
Published: December 2002

We report on the growth of laterally oriented carbon nanotubes with both positional and directional control. The growth was done by chemical vapor deposition from Fe/Mo catalyst embedded inside a porous silicon medium which was formed electrochemically on the vertical faces of etched posts on a silicon substrate. A solution containing the catalyst was allowed to diffuse into the porous medium only in lithographically defined areas. Nanotubes grew only in the patterned areas with a preferred orientation normal to the edges of the etched posts.
Achieving nanometer-scale, controllable pattern shifts in x-ray lithography using an assembly-tilting technique
Authors: Qi Minghao , Smith Henry I.
Published: December 2002

In x-ray lithography the finite gap between the mask and substrate, and the highly directional nature of the short wavelength radiation, enable one to shift the entire mask image by tilting the mask–substrate assembly relative to the axis of illumination. The amount of image shift depends on the mask–substrate gap and the tilt angle, and it can be calculated by simple geometry. The shift can be into any azimuthal direction. The experimental results are consistent with the calculated shift. In our experiments we typically used gaps of 3 μm and tilts of 5.7° (0.1 rad) to achieve a shift of the order of 300 nm. There are a number of advantages and new lithography features that can be accessed using the assembly-tilting technique. For example, various double-exposure schemes, some of which are designed to achieve extremely fine lines or unique patterns, are easily accomplished by the assembly-tilting technique. Moreover, if a mask and substrate contain appropriate alignment marks, viewed optically at normal incidence, and a small misalignment is measured, this can be corrected by tilting the entire assembly rather than by moving the mask relative to the substrate.
Two-dimensional dopant profiling of ultrashallow junctions by electron holography
Authors: Thesen Alexander E. , Frost Bernhard G. , Joy David C.
Published: December 2002

Electron holography using a transmission electron microscope equipped with a Moellenstedt biprism has emerged as a viable technique for creating two-dimensional voltage maps of semiconductor devices. We are presenting an introduction to this dopant profiling method. Practical details are given on sample preparation, instrumentational considerations, and data interpretation.
Electrode modification by electron-induced patterning of self-assembled monolayers
Authors: Kaltenpoth G. , Völkel B. , Nottbohm C. T. , Gölzhäuser A. , Buck M.
Published: December 2002

Gold electrodes were coated with self-assembled monolayers of 1-1′-biphenyl-4-thiol(C6H5–C6H4–SH, BPT) and 1-octadecanethiol (CH3–(CH2)17–SH, ODT) and patterned by proximity printing with stencil masks using electron energies of 300 eV and area doses of 40 000 μC/cm2 (BPT) as well as 10 000 μC/cm2 (ODT). The subsequent copper deposition in an electrochemical cell revealed that e-beam patterned alkanethiol behaves opposite to that of e-beam patterned biphenyl. ODT acts as a “positive template” leading to copper deposition only on the irradiated parts. BPT on the other hand acts as a “negative template,” where the irradiated and therefore cross-linked biphenyl layer exhibits a blocking behavior, and hence copper is only deposited on the nonirradiated parts. The influence of the deposition potential and the copper ion concentration of the electrolyte on the process has been investigated to find the optimal parameters for producing nanostructures with high selectivity.
Acid catalyst mobility in resist resins
Authors: Stewart Michael D. , Tran Hoang Vi , Schmid Gerard M. , Stachowiak Timothy B. , Becker Darren J. , Willson C. Grant
Published: December 2002

In a chemically amplified resist absorbed photons generate stable catalyst molecules instead of directly switching resist solubility via photochemical reaction. This allows for much lower exposure doses to be used in imaging. Some catalyst mobility is necessary to achieve amplification since the catalyst must move from reaction site to reaction site, but a mobile catalyst can blur the deposited aerial image. Catalyst molecules that are free to move in exposed regions are also free to move into adjacent unexposed regions. Understanding acid catalyst diffusion in photoresist resins is complicated by the constantly changing chemical environment the diffusing catalyst experiences as the resist undergoes chemical reactions. The diffusing catalyst promotes chemical reactions which change the properties of its surrounding resin. In addition, it is possible a transient material state is generated by volatile reaction byproducts and their desorption from the film. In most photoresist systems it is impossible to separate reaction and diffusion effects. This work describes studies of acid diffusion in polymers that are close structural analogs to reactive photoresist resins but do not react with the diffusing acidic catalyst. The purpose of this study into nonreactive polymer is to gain insight into the more complex, reactive systems. In addition, experiments with polymeric photoacid generators are reported. These materials provide added insight into acid transport in photoresist materials.
Thermal modeling of extreme ultraviolet and step and flash imprint lithography substrates during dry etch
Authors: Weisbrod E. J. , Dauksher W. J. , Zhang D. , Rauf S. , Mangat P. J. S. , Ventzek P. L. G. , Smith K. H. , Clemens S. B. , Martin C. J. , Engelstad R. L.
Published: December 2002

Lithographic mask development requires that attention be paid to all aspects of mask manufacturing. As feature sizes and tolerable errors decrease, processes must be investigated for their effect on final mask quality. One potential area of concern for both extreme ultraviolet lithography (EUVL) and step and flash imprint lithography (SFIL) is temperature control during pattern transfer via dry etch. In particular, the etch tool fixturing for 6 in.×6 in.×0.25 in. (6025) plates used in EUVL development typically do not have provisions for backside helium (He) cooling, and this may allow the substrate to reach an unacceptably high temperature. This article presents the results of thermal finite element modeling and compares them with temperature data gathered during dry etch. Additionally, fused silica wafers were modeled as they are being used in SFIL template development and can also be used to evaluate the effects of backside He cooling. Substrates were etched in inductively coupled plasma and/or reactive ion etch processes. In situ measurements were made using adhesive temperature strips applied to the substrates that provided both transient and steady state temperature information. Results showed 6025 plate temperatures remained within acceptable limits for typical etch process times. Fused silica wafers did not reach temperatures of concern when backside He cooling was incorporated.
Low energy electron microscopy study of In on Si(111)
Authors: Pavlovska A. , Bauer E. , Giessen M.
Published: December 2002

The structural phase transitions in the multiphase system indium (In) on Si(111) are studied as a function of coverage at different temperatures between −100 and 550 °C by low energy electron microscopy (LEEM) and low energy electron diffraction (LEED). All phase transitions observed with increasing In coverage are first order. Nucleation of a new phase starts only after the previous phase is completed. At high temperatures only a disordered monolayer with high atomic density forms. When In is deposited at room temperature on a (√3×√3)-R30°–In surface four new phases are observed: a (2×1), a near coincidence (1.5√3×1.5√3), a “(1×1)-R30°” and a (6×6) phase. At room temperature and up at least to 400 °C a double layer forms. Below 120 °C this layer is compressed and ordered in two coexisting structures, (√7×√3) and “(1×1)-R30°”. Above 120 °C it shows a (1×1) LEED pattern, which is attributed to a disordered layer on the Si(111)-(1×1) surface. A third monolayer with the packing density of a slightly compressed In(111) plane is unstable at room temperature against formation of three-dimensional crystals but becomes stable during growth at temperatures below about −80 °C. Three-dimensional crystals grow at room temperature on the double layer in the Stranski–Krastanov mode. These crystals are primarily (100)-oriented and are bounded by the equilibrium planes known from bulk crystals, including the reconstructed (100) surface, which is no longer reconstructed above 120 °C.
Growth shapes of Ag crystallites on the Si(111) surface
Authors: Tang W. X. , Man K. L. , Huang Hanchen , Woo C. H. , Altman M. S.
Published: December 2002

Kinetically limited growth shapes of Ag crystallites on the Si(111) surface have been studied by low energy electron microscopy and diffraction. Triangular hexagons are predominant with the (111) plane parallel to the substrate. The major side facets are determined by facet diffraction spot analysis to be {100}. Absence of facet diffraction spots from the minor side facets suggests that they may be the more steeply inclined {11̄1} or {12̄1} orientations. Preliminary evidence is also obtained that codeposition of In causes the steeper side facets to dominate the growth shape.
Low energy electron microscopy/diffraction study on growth of Ge on Si(113) surface
Authors: Yasue T. , Koshikawa T. , Bauer E.
Published: December 2002

We studied the growth process of Ge on a Si(113) surface by low energy electron microscopy (LEEM) combined with low energy electron diffraction (LEED). It is demonstrated that the transition from layer growth to island growth can be detected by the variation of the (00) spot intensity. The (00) spot intensity showed a minimum at around a coverage of 4.4 monolayer at about 560 °C. Three-dimensional (3D) clusters form preferentially at the step bunches at the same coverage followed by the formation of 3D islands. This means that the reduction of the (00) spot intensity is caused by the formation of 3D clusters while the growth of 3D islands whose center part shows bright contrast corresponds to the recovery of (00) intensity. The LEED patterns of the 3D islands show many spots originating from facets. The energy dependence of the spot positions reveals that the 3D islands have {15x} side facets.
Comparison of stigmatically focusing magnetic prisms of square versus round symmetries
Authors: Kan H.-C. , Dürkop T. , Phaneuf R. J.
Published: December 2002

Based on the results of electron optical simulations, we report on a comparison of the performance of stigmatically focusing magnetic prisms designed with two different symmetries. One type consists of a set of square inner pole pieces surrounded with rectangular outer pole pieces, which is similar to the magnetic prism in Tromp’s design [R. M. Tromp et al., Surf. Rev. Lett. 5, 1189 (1995)]. The other type consists of a set of nested round inner and outer pole pieces, which is similar to the magnetic prism we constructed for our low energy electron microscope [H. C. Kan, D. Auerbach, and R. J. Phaneuf, Rev. Sci. Instrum. (submitted)]. One interesting difference is that the square pole piece prism produces a strong linear dependence of the focal point position on the impact parameter in the deflection dimension, compared to what is seen in the performance of round pole pieces. This linear dependence produces asymmetric distortion in the imaging in the deflection dimension.
Interference pattern formation from an array of coherent laser beams
Authors: Liu Y. , Barhen J. , Braiman Y. , Zhong J. X.
Published: December 2002

We present numerical analysis of interferometric patterns formed by multiple sources. Multiple beams can be achieved either from a synchronized laser array or by splitting a coherent light source. We assume Gaussian form for each beam, and all the beams are combined at the near field. The condition for achieving periodic structures with the feature size significantly smaller than λ/4 is obtained. Multiple beam interference has the potential of achieving smaller feature size, less power requirement, and more flexibility than the conventional two-beam interferometric lithography method.
Characterization of extreme ultraviolet lithography mask defects by actinic inspection with broadband extreme ultraviolet illumination
Authors: Park Mincheol , Yi Moonsuk , Mirkarimi Paul , Larson Cindy , Bokor Jeffrey
Published: December 2002

We present our study on actinic detection of defects on extreme ultraviolet (EUV) lithography mask blanks with broadband EUV illumination from a synchrotron light source. A mirror blank was substituted for the monochromator grating in the synchrotron beamline. This increases the spectral bandwidth that is taken from the broadband synchrotron beam by 1 order of magnitude, leading to a commensurate increase in the total available flux. The detection sensitivity of this actinic inspection system is able to reach approximately 20 nm in equivalent defect size. This has been determined through cross correlation experiments done with commercial visible-light inspection tools. Experimental results also show that this broadband EUV inspection system has a capability of detecting phase defects with 5 nm surface height.
Correcting for global space charge by positive ion generation
Authors: Crane Trevor , Campbell Colin , Pickard Dan , Han Liqun , Takahashi Kimitoshi , Meisburger W. Dan , Pease R. Fabian
Published: December 2002

In proposed high throughput electron beam projection systems there are surprisingly serious problems due to the first and third order lens action of the global space charge of the beam. Computer simulations [e.g., Takahashi et al., J. Vac. Sci. Technol. B 19, 2572 (2001)] show it may be possible to eliminate the deleterious effects of global space charge in these systems by introducing positive ions into the optical column. We have checked these claims experimentally on a scaled system designed to enhance global space charge effects. In our system, global space charge produces a first order focus shift of 5.4 mm and a field curvature of 2.2 mm. Introducing 4 mTorr of argon corrects the focus shift to 1 mm and reduces the field curvature to 1.3 mm, and we observed similar results with 7 mTorr of hydrogen. Introducing helium had no effect. Our experiment provides no significant information on stochastic Coulomb effects, although simulations indicate that these have little effect (e.g., Takahashi, ibid.).
Fabrication of x-ray masks using evaporated electron sensitive layers for back patterning of membranes
Authors: Awad Yousef , Lavallee Eric , Beauvais Jacques , Drouin Dominique , Yang Pan , Turcotte David , Mun Lau Kien
Published: December 2002

A process aimed at fabricating proximity x-ray lithography masks is presented. In this technique, the Ta absorber layer is deposited and patterned on the back side of the membrane and nonspin-coated electron sensitive layers were used in order to achieve high resolution patterning of this absorber. The advantages gained by this approach include a reduction of the membrane temperature during the plasma etching step of the absorber patterns without using any cooling gas. This temperature reduction results from the direct contact of the membrane with a cooling plate. This approach also allows increased protection of the absorber patterns from contamination during exposure of the mask. A third advantage is that the smooth surface of the mask exposed to the wafer in the x-ray lithography stepper may also make it possible to reduce the gap between wafer and mask, thus achieving increased resolution with the x-ray lithography process.
Ultraviolet and direct ultraviolet inspection of next generation lithography reticles
Authors: Pettibone Don , Dayal Aditya , Veldman Andrei , Stokowski Stan
Published: December 2002

The optical inspection of next generation lithography (NGL) patterned reticles, multilayer-coated blanks, and uncoated substrates is particularly challenging. The difficulties arise not only because of the higher sensitivity necessary at the smaller design rules, but also due to the specifics of the NGL mask materials and structures. Our research program is investigating the theoretical and practical operational limitations facing optical inspections of patterned and unpatterned NGL masks. We are constrained by the necessity to inspect only in reflected light, limitations in mask contrast, and interference effects caused by partially coherent illumination. We present inspection results and images of several types of NGL masks, blanks and substrates obtained on high resolution ultraviolet (UV) and direct ultraviolet (DUV) optical mask inspection systems. While electron projection lithography (EPL) stencil masks can be inspected in reflection, limited transmission through the mask suggests that subsurface defects will be detected with reduced sensitivity, compared to defects on the surface. For unpatterned inspections, we have demonstrated UV system sensitivity to 88 nm PSL spheres on quartz substrates and 117 nm PSLs on silicon substrates. On extreme ultraviolet masks we have achieved DUV system sensitivity down to defects as small as 80 nm in size, both in die-to-die inspections and in simulated die-to-database inspections. In addition to advancing the development of optical inspection systems for NGL reticles, these inspection results provide feedback to NGL mask developers.
Testing extreme ultraviolet optics with visible-light and extreme ultraviolet interferometry
Authors: Goldberg Kenneth A. , Naulleau Patrick , Bokor Jeffrey , Chapman Henry N. , Barty Anton
Published: December 2002

Optics for extreme ultraviolet (EUV) lithography arguably have the most strict fabrication tolerances of any optical systems fabricated to date, and the development of EUV lithography pushes advanced optical fabrication techniques toward never before realized levels of figure accuracy and finish quality. As EUV lithography advances toward viability, the need for ultrahigh-accuracy wave front metrology tools has never been greater. To enable the development of diffraction-limited EUV optical systems, visible-light and EUV interferometries must work in close collaboration. We present a detailed comparison of EUV and visible-light wave front measurements performed across the field of view of a lithographic-quality projection optical system designed for use in the Engineering Test Stand developed by the Virtual National Laboratory and the EUV Limited Liability Company. The comparisons reveal that the present level of root mean square agreement lies in the 0.3–0.4 nm range, with an agreement of 0.15±0.03 nm, excluding astigmatism. Astigmatism is the most significant aberration component for the alignment of this optical system; it is also the dominant term in the discrepancy, and the aberration with the highest measurement uncertainty. With EUV optical systems requiring total wave front quality in the λEUV/50 (0.25 nm) range, and even higher surface-figure quality for the individual mirror elements (∼0.1 nm), improved accuracy through future comparisons, and additional studies, are required.
Beam alignment for scanning beam interference lithography
Authors: Chen Carl G. , Heilmann Ralf K. , Joo Chulmin , Konkola Paul T. , Pati G. S. , Schattenburg Mark L.
Published: December 2002

By interfering two small diameter Gaussian laser beams, scanning beam interference lithography (SBIL) is capable of patterning linear gratings and grids in resist while controlling their spatial phase distortions to the nanometer level. Our tool has a patterning area that is up to 300 mm in diameter. The motive for developing SBIL is to provide the semiconductor industry with a set of absolute metrology standards, but the technology is easily adaptable to other important applications such as the making of high precision optical encoders. In this article, we describe a system for carrying out automated beam alignment for SBIL. Our design goals require tight alignment tolerances, where beam position and angle alignment errors must be controlled to ∼10 μm and ∼10 μrad, respectively. We describe our system setup, and discuss the so-called iterative beam alignment principle, focusing specifically on deriving a mathematical formalism that can guide the development of similar systems in the future. Repeatability experiments demonstrate that our system fulfills the alignment requirements for nanometer-level SBIL writing.
Electromigration in passivated Cu interconnects studied by transmission x-ray microscopy
Authors: Schneider G. , Meyer M. A. , Denbeaux G. , Anderson E. , Bates B. , Pearson A. , Knöchel C. , Hambach D. , Stach E. A. , Zschech E.
Published: December 2002

Time-resolved x-ray microscopy studies of the electromigration in inlaid Cu line/via structures were performed on focused-ion-beam-prepared cross sections of an advanced interconnect layer system. Multiple x-ray images were recorded at 1.8 keV photon energy while stressing the passivated Cu structures with an applied current. The image sequences show that void formation is a dynamic process, with voids being observed to nucleate and grow within the Cu via and migrate towards the via sidewall. Correlation of the real time x-ray microscopy images with postmortem high voltage transmission electron and scanning electron micrographs indicates that the void nucleation occurs at grain boundaries in the copper, and that the voids migrate along these grain boundaries during electromigration. By taking multiple images at different viewing angles, the three-dimensional arrangement of an interconnect stack with Cu line / via structures was reconstructed. In future studies time-resolved tomography will be used to visualize void dynamics within the volume, thereby identifying pathways for Cu diffusion.
Reversal imprinting by transferring polymer from mold to substrate
Authors: Huang X. D. , Bao L.-R. , Cheng X. , Guo L. J. , Pang S. W. , Yee A. F.
Published: December 2002

A reversal imprinting technique was developed in this study. A polymer layer was first spin coated on a patterned hard mold, and then transferred to a substrate under an elevated temperature and pressure. The reversal imprinting method offers an advantage over conventional nanoimprinting by allowing imprinting onto substrates that cannot be easily spin coated, such as flexible polymer substrates. Another unique feature of reversal imprinting is that three different pattern-transfer modes can be achieved by controlling the degree of surface planarization of the mold after spin coating the polymer resist as well as the imprinting temperature. “Embossing” occurs at temperatures well above the glass transition temperature (Tg) of a polymer; “inking” occurs at temperatures around Tg with nonplanarized polymer coating surface on the mold; and “whole-layer transfer” occurs at temperatures around Tg but with a somewhat planarized surface. These three imprinting modes have been quantitatively correlated with the surface planarization of the mold after polymer coating and the imprinting temperature.
High-resolution transfer printing on GaAs surfaces using alkane dithiol monolayers
Authors: Loo Yueh-Lin , Hsu Julia W. P. , Willett Robert L. , Baldwin Kirk W. , West Ken W. , Rogers John A.
Published: December 2002

We describe a transfer printing technique for directly patterning thin gold films onto GaAs surfaces. This additive transfer process is mediated by the presence of an alkane dithiol monolayer on the wafer surface. The transferred patterns are chemically bound to the wafer surface and they exhibit strong adhesion (i.e., they easily pass Scotch tape adhesion tests.) A variety of gold patterns with a wide range of feature sizes can be printed onto GaAs (100), (110), (211)A, and (211)B using this approach.
Liquid immersion lens technology applied to laser voltage probing of 130 nm process technology devices
Authors: Nataraj Nagamani , Deslandes Herve , Lo William , Eiles Travis , Pardy Patrick
Published: December 2002

Liquid immersion lens technology has been applied to internal-node, through-silicon probing of 130 nm integrated circuits. A 100×, 1.3 numerical aperture (NA) objective with 100 μm working distance was specifically designed for this application. An optical resolution of 500 nm is achieved using 1064 nm wavelength light, ≈30% improvement over the standard, air immersion, 0.85 NA lens currently used. Significant improvements in wave form quality were also achieved. A >2× signal to noise ratio improvement is demonstrated on 130 nm technology devices. Probing of 90 nm technology devices indicate that laser voltage probing with liquid immersion lens technology and phase-sensitive detection is extensible to this process node.
Scanning tunneling microscopy of endohedral metallofullerene Lu–C82 on C60 film
Authors: Shi Bo-Rong , Wang Xue-Sen , Huang Houjin , Yang Shi-He , Bachmann A. , Cue Nelson
Published: December 2002

Endohedral metallofullerene Lu–C82 molecules adsorbed on C60 film have been investigated by an ultra-high-vacuum scanning tunneling microscopy. The C60 film was obtained by depositing 2–3 ML of C60 molecules on a highly oriented pyrolytic graphite surface. The as-deposited Lu–C82 molecules were observed to form various structures on the C60 film. The nucleation behavior of Lu–C82 was compared with that of Nd–C82 and Tb–C82 on the C60 film. These structures were explained based on the interactions of Lu–C82–C60, Lu–C82–Lu–C82, and Lu–C82 scanning tunneling microscopy tip.
Photoresponse characteristics of n-ZnO/p-Si heterojunction photodiodes
Authors: Choi Y. S. , Lee J. Y. , Im S. , Lee S. J.
Published: December 2002

We report on the photoresponse behavior of n-ZnO/p-Si photodiodes. Semiconducting n-ZnO films have been deposited on p-Si substrates at 480 °C using various Ar/O2 ratios, 2:1, 4:1, and 6:1, to fabricate n-ZnO/p-Si photodiodes. As a laser of 670 nm wavelength illuminated the photodiodes, a maximum responsivity of 0.286 A/W and a maximum quantum efficiency of 53% were obtained at a reverse bias of 5 V from a diode prepared with an Ar/O2 ratio of 6:1. The response time of the photodiode was as short as 35 ns as measured using pulse modulation of the illuminating laser.
Radio-frequency discharge cleaning of silicon-capped Mo/Si multilayer extreme ultraviolet optics
Authors: Graham Samuel , Steinhaus Charles , Clift Miles , Klebanoff Leonard
Published: December 2002

Remote oxygen and hydrogen radio-frequency (rf) discharge cleaning experiments have been performed to explore their potential for cleaning carbon-contaminated extreme ultraviolet optics. The samples consisted of silicon wafers coated with 100 Å sputtered carbon, as well as bare Mo/Si multilayer mirrors (Si terminated). The samples were exposed for 3 h to rf plasma discharges at 100, 200, and 300 W. The carbon removal and surface oxidation rates were evaluated using sputter through depth profiling Auger spectroscopy. Reflectivity changes and surface roughness measurements were performed using at-wavelength reflectometry (13.4 nm) and atomic force microscopy, respectively. Data show that excited rf O2 consistently removes carbon at a rate approximately six times faster than excited rf H2 for a given discharge power and pressure. rf O2 also induces loss of reflectivity that is related to the growth of SiO2 on the optic surface. rf H2 shows a much lower oxidation rate of the optic surface. In spite of the lowered oxidation risk, reflectivity loss in Mo/Si multilayers was still observed, although this loss is not related to surface oxidation.
Probing surface and bulk chemistry in resist films using near edge x-ray absorption fine structure
Authors: Lenhart Joseph L. , Jones Ronald L. , Lin Eric K. , Soles Christopher L. , Wu Wen-li , Fischer Daniel A. , Sambasivan Sharadha , Goldfarb Dario L. , Angelopoulos Marie
Published: December 2002

The performance of chemically amplified photoresists is extremely sensitive to interfacial and surface phenomena, which cause deviations in the pattern profile near an interface. Striking examples include T-topping or closure near the air/resist interface and footing or undercutting near the resist/substrate interface. One focus of our research is to identify mechanisms that cause lithographic patterns to deviate near interfaces. Near edge x-ray absorption fine structure (NEXAFS) is a powerful tool that can be developed and adapted to probe for detailed chemical information near lithographically relevant interfaces. NEXAFS showed that our model resist films exhibited significant surface segregation of the photo acid generator (PAG) at the air interface. The PAG surface mole fraction was 20–70 times greater than the bulk mole fraction and the amount of surface segregation was dependent on the polarity of the polymer. NEXAFS also revealed that the PAG surface fraction was reduced after a postexposure bake. In the absence of delay times between processing steps, the PAG surface enhancement led to a faster deprotection reaction rate near the air interface relative to the bulk. However, when significant postexposure delay times were incorporated into the processing, NEXAFS showed that the surface deprotection reaction was incomplete after postexposure baking. Comparison of carbon K-edge, and oxygen K-edge NEXAFS spectra showed that the incomplete surface reaction was localized at the air interface. While delay effects have previously been linked to deterioration of resist performance, NEXAFS proved to be a valuable tool for providing detailed chemical specificity about the resist surface composition and deprotection kinetics.
Extendibility of proximity x-ray lithography to 25 nm and below
Authors: Toyota Eijiro , Washio Masakazu
Published: December 2002

Extendibility of proximity x-ray lithography (PXL) relates to three technical issues. They are the minimum proximity gap usable for steppers, the maximum allowable gap by exposure methods, and overall blur effect. The minimum usable gap gs (μm) for steppers is presumed to be gs=W1/2, where W (nm) is the design rule (half pitch). The maximum allowable gap g is expressed as g=αW2/λ, where λ is the average wavelength and α is a coefficient, which depends on the exposure methods using 1× masks or 2× masks. In the article, we have verified the equation (g=αW2/λ) by simulation for one- and two-dimensional patterns, and determined the α values for each exposure method. For the blur effect, we evaluated the sigma values using a simple model. As a result, we concluded that PXL can be used by 25 nm and most probably by 18 nm design rule by changing the exposure methods corresponding to the progress of the design rule generations.
Quantum dot with independently tunable tunneling barriers fabricated using an atomic force microscope
Authors: Nemutudi R. , Smith C. G. , Ford C. J. B. , Appleyard N. J. , Pepper M. , Ritchie D. A. , Jones G. A. C.
Published: December 2002

We fabricate independently tunable tunneling barriers on a GaAs/AlGaAs heterostructure using a conducting tip of an atomic force microscope (AFM). In a humid ambient, a negatively biased AFM tip induces an oxide beneath it, which oxide depletes a shallow two-dimensional electron gas (2DEG). We exploit the depletion property of the oxide and use it to electrically isolate different regions of the 2DEG. In particular, we manipulate the tip movement to generate two oxide patterns whose combined geometry defines two quantum point contacts, in series, with a quantum dot between them. Our device not only permits independent tuning of the transmission probability of each quantum point contact, but it also allows us to observe Coulomb-blockade oscillations when both contacts are tuned into the tunneling regime.
Prospects for photolithography at 121 nm
Authors: Liberman V. , Rothschild M. , Murphy P. G. , Palmacci S. T.
Published: December 2002

We have evaluated several subsystems that would be required for lithography at 121 nm: radiation sources, optics, ambient control, and resists. Dense plasma sources can generate significant power, >0.5 J of 121 nm radiation per pulse. An extensive survey of commercially available LiF, as well as specially grown LiF, shows that transmission losses are ∼20% per cm, a value which is at least 5× too high if LiF is to be used as lens material. At present it is not clear whether there is a fundamental limitation to LiF transparency at 121 nm, but the main source of absorption arises from lithium oxide or hydroxide in the crystal. Polymers, fluorinated or not, exhibit very high absorption at 121 nm, indicating that ultrathin resists or bilayer resists will have to be used at 121 nm. However, the photochemistry at 121 nm is probably not much different from that at longer wavelengths. The resists are sensitive, ∼1 mJ/cm2 required dose, and they have high contrast at 121 nm. Finally, we have also performed preliminary patterning experiments. Using contact printing with a phase shifting mask we have printed 45 nm features in an ultrathin photoresist.
Single-electron parametron memory cell
Authors: Emiroglu E. G. , Durrani Z. A. K. , Hasko D. G. , Williams D. A.
Published: December 2002

A single-electron parametron memory cell, based on two conducting islands separated by a multiple tunnel junction, has been realized in highly doped silicon-on-insulator. A memory cell with integrated read-out electrometers was fabricated using a combination of high-resolution electron beam lithography and reactive ion etching. The layout and operation of the memory cell is based on a proposal by Korotkov and Likharev, but modified in order to simplify fabrication. The operation of the electrometer, and the cell polarization characteristics are investigated by low temperature electrical measurements. Memory operation is indicated by current hysteresis in the electrometer characteristics with appropriate gate bias voltages.
Tunable distributed-feedback laser gratings for telecom applications, manufactured by electron-beam lithography
Authors: Rishton S. A. , Pezeshki B. , Zou S. , Yoffe G. , Henschel W.
Published: December 2002

A wide-range tunable laser component has been developed, based on a closely spaced array of 12 distributed feedback (DFB) grating lasers, 3 nm apart in wavelength, fabricated by electron-beam lithography. Coarse wavelength selection is achieved by selecting the appropriate laser stripe with a microelectromechanical system tilt mirror. We describe the application of direct-wire e-beam lithography to array DFB grating manufacture, with accurate multiple wavelengths and phase shifts required to optimize the spectral characteristics of the laser. The grating pitch is approximately 0.24 μm, but must be controlled to better than 0.01 nm. We have used an averaging technique with relatively coarse address unit and pixel size to fabricate multiple-pitch gratings without rescaling. This allows the use of a conventional thermal-field-emission Gaussian-beam system, at high throughput appropriate for manufacturing.
Growth dynamics of titanium silicide nanowires observed with low-energy electron microscopy
Authors: Bennett P. A. , Ashcroft B. , He Zhian , Tromp R. M.
Published: December 2002

We report in situ low-energy electron microscopy observations of spontaneous nanowire (NW) formation during deposition of Ti on Si(111) at T∼850 °C. The NWs are oriented primarily along {110} directions, with typical dimensions 50 nm wide, 20 nm high, and several microns long. The NW shape persists even at temperatures high enough to shrink the wires, suggesting that these are equilibrium shapes. During growth, the NW advances at both ends at a constant rate, independent of NW length or collisions with steps, which pile up at the ends. We argue that the rate-limiting kinetic step during growth is the reaction of silicide at the island ends. NWs that intersect during growth do not fuse, and will separate upon annealing. Occasionally, they form a temporary junction that connects and disconnects in an oscillating cycle.
Photoelectron emission microscopy of ultrathin oxide covered devices
Authors: Ballarotto V. W. , Breban M. , Siegrist K. , Phaneuf R. J. , Williams E. D.
Published: December 2002

Photoelectron emission microscopy (PEEM) has been used to investigate simple device structures buried under ultrathin oxides. In particular, we have imaged Au–SiO2 and p-type Si–SiO2 structures and have demonstrated that PEEM is sensitive to these buried structures. Oxide overlayers ranging up to 15.3 nm were grown by systematically varying the exposure time of the structures to a plasma-enhanced chemical-vapor deposition process. The change in image contrast as the oxide thickness increases was used to quantify the inelastic mean-free path of low-energy photoelectrons (∼1 eV) in amorphous silicon dioxide. For Au structures we find that the dominant mean-free path for photoelectrons in the overlying oxide is about 1.18±0.2 nm. Yet, we find a residual observable signal from the buried Au structure through roughly 13 oxide attenuation lengths. The signal attenuation from the Au can be explained by the spread of the photoelectron energies and the energy dependence of the electron–phonon interaction. Similar intensity attenuation behavior is also seen from heavily p-doped silicon (1020 cm−3) regions, but the signal is only observable through roughly 3.0 nm of oxide, and the signal from the 1018 cm−3 regions is not detectable through the thinnest oxide layer of approximately 2.5 nm. Here, the energy spread (∼2.0 eV) is more narrowly distributed about the phonon loss energies, leading to the observed attenuation behavior from heavily p-doped silicon.
In situ emission microscopy of field emitter cathode arrays
Authors: Mulhollan G. A. , Jamison K. D. , Kordesch M. E.
Published: December 2002

Emission microscopes have been used to image devices used for cold cathodes, in situ. The use of emission microscopy in the evaluation of these materials and devices is described.
Comparing ionized physical vapor deposition and high power magnetron copper seed deposition
Authors: Stout P. J. , Zhang D. , Rauf S. , Ventzek P. L. G.
Published: December 2002

A computational modeling comparison is made between ionized physical vapor deposition (IPVD) and high power magnetron (HPM) deposition of copper. For the comparison the point of view of the feature scale is stressed where the two reactors are distinguishable by the magnitude and ratio of specie (Cu,Cua,Cu+,Ar+) flux, the angular distribution of the specie, and the energy of the ions incident on the feature surface. The HPM is characterized for the conditions studied by a metal flux content made up almost entirely of copper athermals, an Ar+ ion flux about four times the Cu metal flux, decreasing Cu+ fraction and increasing Cu athermal flux to surface with increasing target power, and both no sputter and sputter regimes at the wafer possible. The IPVD reactor is characterized for the conditions studied by a Cu metal flux with a large neutral fraction but significant ions and athermals, an Ar+ ion flux on the order of the Cu metal flux, and only a sputter regime at the wafer possible. An increase in target power increases the deposition rate and decreases the Cu+ fraction in both systems. In IPVD the bottom coverage increases and the side wall coverage decreases due to a decrease in the sputter rate and an increase in the Cu neutral and athermal fraction. In HPM bottom coverage is reduced with increasing target power due to the lower Cu+ fraction. An increase in wafer power decreases the deposition rate in both systems by increasing the sputter rate. A lower ion current to the wafer for IPVD versus HPM gives the ions a higher energy at the wafer for the same power. In HPM lower energy ions are sufficient for the same sputtering rate versus IPVD due to the higher ion/neutral fraction. With no wafer bias HPM has thicker bottom versus IPVD since no sputtering of the feature bottom is occurring and the more focused athermals (versus neutrals) are less shadowed to the feature bottom. The IPVD side wall deposits have more thickness variation than HPM due to the large Cu neutral component in IPVD. An increase in wafer power increases side wall coverage and decreases feature bottom coverage in both systems as metal deposited at feature bottom is redeposited to the sidewalls. For increased coil power in IPVD the Cu+ fraction increases and the Cu neutral fraction decreases. Both bottom and side wall coverage increase as more Cu enters the feature as focused ions.
Near-surface deep-trap and bulk deep-trap states in InxGa1−xAs/GaAs
Authors: Halder N. C. , Genareau Kimberly
Published: December 2002

Field-effect studies have been performed to investigate the near-surface deep-trap and bulk deep-trap states in molecular-beam epitaxy-grown InxGa1−xAs (where x=0.1) on n+ GaAs. We have measured the isothermal capacitance transients for the major trap levels in the range of 77–380 K in the reverse-bias field of −1 to −3.8 V/cm. The results of our investigation indicate a distinct effect on the deep level spectra due to the applied field, suggesting a definitive way to identify the near-surface deep traps from the bulk deep traps, and vice versa. The two major deep traps identified in the present investigation further display a transition from one state to another, from near-surface to bulk state in the high-field region, when the applied reverse-bias field is increased from −3.0 to −3.8 V/cm. “Field” means “normalized” field, F(norm)=F(appl)×10−5.