bluuebunny/crossref_metadata_2025 huggingface dataset:
In search of high-performance resists for 50 kV shaped-beam exposure
Authors: Tan Z. C. H. , Stivers T. , Lem H. , DiGiacomo N. , Wood D.
Published: July 2002

A search was made to find a high-performance resist to manifest the high-resolution advantage of 50 kV electron-beam exposure. Four resists were evaluated: Shipley SAL-601, AT&T/OCG CAMP-6, IBM KRS, and IBM TNS. All resists were found to have high contrast ≳3 and were capable of resolving <0.25 μm line/space pairs at 3000 Å thickness. With the exception of TNS, the resists demonstrate a high bulk sensitivity of <15 μC/cm2 at 50 kV. The IBM KRS resist was found to have the highest figure of merit. It was capable of resolving less than 0.10 μm line/space at 4000 Å thickness. Furthermore, at 8000–10 000 Å, a resolution of ≤0.25 μm was obtained with a steep profile. The dry etch resistance of the resist relative to chrome was 2.4:1. This resist is not environmentally sensitive and needs no postexposure bake treatment. If KRS is made commercially available, it will be an outstanding resist for modern electron-beam/x-ray mask making and direct write for device fabrication.
Spectroscopic study of the CuO chains in YBa2Cu3O7−x
Authors: Edwards Hal , Derro D. J. , Barr A. L. , Markert J. T. , de Lozanne A. L.
Published: July 2002

We interpret our previously published results obtained using a technique called current-imaging tunneling spectroscopy (CITS) to study the detailed electronic structure of the CuO chains in the high-temperature superconductor YBa2Cu3O7−x near the Fermi level. Our CITS data comprise sequences of 32 simultaneously obtained images taken at bias voltages ranging from −78 to 72 mV. Cross sections of the CITS data, normalized-conductance analysis, and logarithmic-derivative analysis allow us to examine in detail the behavior of electronic modulations along the CuO chains and the energy gap in the CuO chains of YBa2Cu3O7−x. This new analysis lends a strong foundation to our previous interpretation of the CITS data [H. L. Edwards et al., Phys. Rev. Lett. 75, 1387 (1995)].
Low temperature chemically assisted ion-beam etching processes using Cl2, CH3I, and IBr3 to etch InP optoelectronic devices
Authors: Eisele K. M. , Daleiden J. , Ralston J.
Published: July 2002

Chemically assisted ion-beam etching processes have been examined using Cl2, CH3I, and IBr3 for application in manufacturing optoelectronic devices. Although the etch rate was one of the properties compared, more attention was directed towards clean, smooth surfaces and exact reproduction of the desired geometry. The main effort was directed towards etching of laser mirrors, which require perpendicular sides of the structure with respect to the substrate plane. It was found that a low substrate temperature of 0 to 10 °C is the key for obtaining the desired surface quality and that a perpendicular sidewall can only be obtained by tilting the semiconductor wafer. This is in contrast to GaAs where temperature and beam energy strongly determine the angle of the structure walls relative to the wafer plane.
A multilayer inorganic antireflective system for use in 248 nm deep ultraviolet lithography
Authors: Cirelli R. A. , Weber G. R. , Kornblit A. , Baker R. M. , Klemens F. P. , DeMarco J. , Pai C. S.
Published: July 2002

We propose a novel technique for reducing substrate reflections in 248 nm deep ultraviolet (DUV) lithography. The method we have developed utilizes a multilayer scheme comprised of layers of silicon rich oxide. Deposition of the film stack is carried out on a production ready PE-CVD tool in one continuous operation. The combining of multiple layers allows a gradual change in absorption thereby minimizing the reflection coefficient at the resist/ARC interface. The method of operation of these films is one of total absorption rather than the more common destructive interference method of a single layer film which relies on very tight thickness control. Absorption of the combined films is high enough to be effective on even the most highly reflective substrates such as aluminum. Furthermore, this technique does not require the ARC films to be tuned in their optical constants to accommodate the underlying substrate. We have successfully patterned wafers with feature sizes as small as 200 nm with no appreciable change in line width due to the underlying topography. The multilayer ARC system has been successfully integrated into the gate level of a 0.25 μm design rule device with excellent results. A description of the films used, their optical properties, and results from experimental data, as well as numerical simulations, will be reported.
Three dimensional electron optical modeling of scanning tunneling microscope lithography in resists
Authors: Dobisz E. A. , Koops H. W. P. , Perkins F. K. , Marrian C. R. K. , Brandow S. L.
Published: July 2002

Three dimensional electron optical simulations were used to model scanning tunneling microscope (STM) lithography in resists under field emission conditions. This work focuses on the effect of resists, as dielectric layers, between the tip and conducting substrate on the operation of the STM. Simulations were run for resist thicknesses of 1–50 nm, which are comparable to our experiments, and tip–resist separations of 1–20 nm. Simulations were run for a ‘‘best’’ tip of radius 10 nm and a typical tip of radius 50 nm. The results show that the presence of a resist layer dramatically reduces the range of stable STM operation, which is observed experimentally. For a given tip–substrate distance and fixed tip–substrate voltage, the interposition of the dielectric layer expels electric field and causes the electric field at the tip to increase. Although the tip will retract from the substrate, the tip–resist distance is less than the prior tip–bare substrate distance, for the same tip–sample voltage and same electric field at the tip. The effect increases with resist thickness. For a 25 nm thick resist layer, the STM will operate a factor of 2 closer to the resist than a bare substrate. In addition, the energy of the electrons entering the resist is 50% less than the applied tip–substrate bias. Estimates of spot size based upon emission centered about the tip–sample axis are ≤15 nm, which is consistent with the best experimental results.
How practical is 193 nm lithography?
Authors: Rothschild M. , Burns J. A. , Cann S. G. , Forte A. R. , Keast C. L. , Kunz R. R. , Palmateer S. C. , Sedlacek J. H. C. , Uttaro R. , Grenville A. , Corliss D.
Published: July 2002

The use of 193 nm ArF lasers to extend optical projection lithography to its limits was proposed as early as the mid 1980s. Since then steady progress has been made in this area, and the last two years in particular have witnessed an exponentially growing interest in and commitment to its development. At present, 193 nm lithography is a leading candidate for printing 0.18 and 0.13 μm devices. This article reviews the state of development of this technology at Lincoln Laboratory. Significant progress has been made in most areas: qualification of optical materials, characterization of a prototype large-field projection system, development of photoresist processes, and the fabrication of complementary metal-oxide semiconductor devices.
Direct aerial image measurements to evaluate the performance of an extreme ultraviolet projection lithography system
Authors: Fields C. H. , Oldham W. G. , Ray-Chaudhuri A. K. , Krenz K. D. , Stulen R. H.
Published: July 2002

We report the application of direct aerial image monitoring to measure the performance of an extreme ultraviolet lithography (EUVL) test bed. There are several issues which might limit the possibility of performing image monitoring experiments on EUVL systems. These issues include: source flux, signal-to-noise ratios, and EUV scanning aperture fabrication. We report the results of initial aerial image scans of equal lines and spaces as well as preliminary measurements of scatter produced by the EUV camera.
Fabrication of lateral resonant tunneling devices with heterostructure barriers
Authors: Randall John N. , Broekaert T. P. E. , Smith B. D. , Beam E. A. , Seabaugh A. C. , Jovanovic D.
Published: July 2002

Lateral resonant tunneling devices that employ heterostructure charge barriers are candidates to replace complementary metal–oxide–semiconductor devices as the basic device type that will drive integrated circuit technology in the next century. We present progress in lateral resonant tunneling device technology including the first lateral resonant tunneling transistor that has heterostructure barriers to be fabricated with planar processing techniques. The devices produced to date are limited to cryogenic operation; however, they do demonstrate that lateral resonant tunneling devices can be fabricated with etch and regrowth techniques and suggest the possibility of an integrated circuit technology that may be scaled down to less than 10 nm and would operate at room temperature.
A heavy ion implanted pocket 0.10 μm n-type metal–oxide–semiconductor field effect transistor with hybrid lithography (electron-beam/deep ultraviolet) and specific gate passivation process
Authors: Benistant F. , Tedesco S. , Guegan G. , Martin F. , Heitzmann M. , Dal’zotto B.
Published: July 2002

We present a 0.10 μm n-type metal–oxide–semiconductor process to achieve devices with reduced short channel effect (SCE) and good current drive capability. Full compatible chemical amplified resist process between deep ultraviolet and electron-beam lithography allowed us to use hybrid lithography at gate level. For the first time, we show that the conventional gate reoxidation is a limiting step to process integration because of the bird’s beak formation at the poly-gate edge. Consequently, this process is replaced by a low thermal oxide deposition. In addition, indium and gallium pocket implantations have been realized to improve the SCE control.
Propagation effects of partial coherence in optical lithography
Authors: Socha R. J. , Neureuther A. R.
Published: July 2002

A method based on optimal expansions is described for making an order of magnitude speed up in the analysis of partial coherence effects of scattering in optical lithography, inspection, and alignment. This method expands the incident mutual intensity from the illumination into coherent nonuniform plane waves whose effects can be added incoherently. For three-dimensional structures, the CPU time is reduced by an order of magnitude over the uniform plane wave approach of Abbe. For two-dimensional structures, the number of simulations with the decomposition technique has been found to be about three times smaller than with Abbe’s approach. The method has been incorporated into TEMPEST and shown to give accurate results and reduced CPU time in applications of imaging an attenuated phase shift mask, patterning of gates over an active area well in silicon, and inspection of a trench in silicon dioxide, where the CPU time savings are most significant due to large NA’s and high σ’s. Results for an embedded phase shift mask show the need to generalize Hopkin’s method to include effects of the dependence of the diffraction efficiencies on the angle of incidence. The inclusion of partial coherence in regions of topography scattering show beneficial imaging effects in that reflective notching is reduced as σ is increased.
Optical design of a combined ion and electron beam system for nanotechnology
Authors: de Jager P. W. H. , Kruit P.
Published: July 2002

Nanometer sized structures can be fabricated with an ion beam in several ways, but they would be destroyed if ions were used for observation of the newly made structures. Therefore, they must be observed with an electron beam or scanning probe microscope. A system is developed based on a scanning transmission electron microscope in which both an ion beam and an electron beam can be focused on the specimen. Several design concepts are discussed. In the chosen design, the ion beam is brought on the optical axis of the microscope by means of a 90° deflector which is also used as part of an energy filter. The particles are focused on the specimen by a combined electrostatic and magnetic objective lens. The smallest structure size that can be achieved, is determined by the aberrations of the lenses in the system and the interactions of the ions with each other in the beam (Coulomb interactions) and with the specimen (proximity effect). The system is optimized for these effects resulting in a design which should allow a smallest structure size of 7 nm when using Ar ion sputtering. The spatial resolution when using the electron beam to observe these structures is designed to be 0.6 nm.
Characterization and application of a low-profile metal–semiconductor–metal detector for low energy backscattered electrons
Authors: Meier G. D. , Fresser H. S. , Prins F. E. , Kern D. P.
Published: July 2002

A metal–semiconductor–metal (MSM) detector for low energy backscattered electrons has been developed and tested. The effects of detector symmetry, finger spacing, and detection area on signal to dark current ratio were studied in order to determine an optimized detector geometry. The detector assembly consisting of Ni-GaAs MSM structures with low dark current densities was mounted in a scanning electron microscope on a special sample holder which enabled the test of the detector under conditions which can be expected in electron beam microcolumn applications. With this experimental setup, backscattered electron images of alignment marks of 50-nm-thick Au on a Si substrate were obtained. The signal to noise performance of the device has been compared to a commercial Everhart–Thornley detector. It is demonstrated that MSM detectors can be used as backscattered electron detectors in microcolumns.
Electron beam induced damage of silicon germanium
Authors: Paul Douglas J. , Ryan Joseph M. , Pepper Michael , Broers Alec N. , Whall Terry E. , Fernández Juan M. , Joyce Bruce A.
Published: July 2002

The effect of electron beam irradiation damage to pseudomorphic modulation-doped SiGe two dimensional hole gas (2DHG) was investigated. For typical poly(methylmethacrylate) type processes with electron energies of 40 keV and doses of 2 C/m2, the material properties were not significantly altered. For 300 keV irradiated electrons, the resistivity of the material increased as the dose of electrons was increased. For 100 keV and higher electron irradiation energies, the material became more resistive as the irradiation energy was increased. The 2DHG material became highly resistive at low temperatures and froze out at between 20 and 30 K. Annealing at 400 °C to 500 °C on 40 keV samples with 2 C/m2 doses could return the resistivity of the material at 300 K to the non-irradiated value, but the large increase in resistivity for annealing temperatures above 500 °C suggests that the irradiation produced a significant number of defects which accelerated the relaxation of the strained Si0.87Ge0.13 channel by thermal processing. A number of narrow channel devices were fabricated in high mobility modulation-doped Si/SiGe two dimensional electron gas material and investigated at 4.2 K using the electron beam irradiation to locally damage material into an insulting state. Fluctuations were found in a number of devices with patterned widths below 0.5 μm.
Studies on correction accuracy of proximity effect for the pattern area density method in electron beam direct writing
Authors: Kasuga Takashi , Konishi Morikazu , Oda Tatsuji , Moriya Shigeru
Published: July 2002

This article describes the correction accuracy of the pattern area density method for 0.2 μm rule patterning, carrying out simulation and experiments. To enhance the μm correction accuracy at the boundary zone of the different pattern densities, a novel technique using the gradient vectors of the pattern density is proposed and its capability for sub-0.15-μm pattern fabrication is demonstrated.
Fabrication of laterally selected Si doped layer in GaAs using a low-energy focused ion beam/molecular beam epitaxy combined system
Authors: Yanagisawa Junichi , Nakayama Hiromasa , Wakaya Fujio , Yuba Yoshihiko , Gamo Kenji
Published: July 2002

A buried conductive layer in GaAs was formed using a low-energy focused ion beam (FIB) and molecular beam epitaxy (MBE) combined system. The sheet carrier density of the structure was measured as a function of ion dose ranging from 2×1012 to 5×1013 cm−2 and postrapid thermal annealing time at 800 °C. It was shown that implanted Si ions at an ion energy of 200 eV and an ion dose of 2×1012 to 1×1013 cm−2 can be fully activated by choosing an optimum annealing condition. Present results suggest the possibility of fabricating a high quality two-dimensional electron gas (2DEG) layer in the laterally selected area in GaAs and GaAs/AlGaAs systems.
Development of ion sources for ion projection lithography
Authors: Lee Y. , Gough R. A. , Kunkel W. B. , Leung K. N. , Perkins L. T. , Pickard D. S. , Sun L. , Vujic J. , Williams M. D.
Published: July 2002

Multicusp ion sources are capable of generating ion beams with low axial energy spread as required by the ion projection lithography (IPL). Longitudinal ion energy spread has been studied in two different types of plasma discharge: the filament discharge ion source characterized by its low axial energy spread, and the rf-driven ion source characterized by its long source lifetime. For He+ ions, longitudinal ion energy spreads of 1–2 eV were measured for a filament discharge multicusp ion source which is within the IPL source requirements. Ion beams with larger axial energy spread (∼7 eV) were observed in the rf-driven source. A double-chamber ion source has been designed which combines the advantages of low axial energy spread of the filament discharge ion source with the long lifetime of the rf-driven source. The energy spread of the double chamber source is approximately 2 eV.
Misfit dislocations in strained InxGa1−xAs heterostructure on patterned GaAs (001) substrate
Authors: Zeng W. , Jiang S. S. , Ferrari C. , Gennari S. , Salviati G. , Jiang J. H.
Published: July 2002

〈110〉 60° and 〈100〉 edge misfit dislocations in In0.06Ga0.94As heterostructures grown on patterned GaAs (001) substrates with relatively low misfit f(f=0.0043) have been investigated. The reduction of 〈110〉 misfit dislocation density on mesas is observed by cathodoluminescence, while the 〈100〉 misfit dislocation density on mesas observed by synchrotron radiation double crystal topography remains unchanged. The critical thickness is calculated by modifying the Matthews mechanical equilibrium theory introduced by Chidambarrao et al. The calculated results can be applied to both the nonpatterned area and the sidewalls of the mesa. The critical thickness of one side of the mesa is larger than that of nonpatterned areas. The critical thickness of both sides of mesas is dependent on the angle between the sidewall and (001) GaAs. This is likely due to different values of cos φ/sin ψ, which determines the values of the friction force FF with different sidewall angles. It is suggested that the 〈100〉 misfit dislocations are generated by climb and they can cross mesas by climbing along 〈100〉 directions.
Investigation of improved regrown material on InP surfaces etched with methane/hydrogen/argon
Authors: Yu D. G. , Chen C.-H. , Keller B. P. , Holmes A. L. , Hu E. L. , Baars S. P. Den
Published: July 2002

In this work, we study the hydrogen introduced into InP during methane/hydrogen/argon reactive ion etching (RIE) to determine its effect on metalorganic chemical vapor deposition regrowth. We replace hydrogen with deuterium and confirm that deuterium is introduced into the substrate during methane/deuterium/argon RIE with secondary ion mass spectrometry. During regrowth, the deuterium diffuses from deep within the material and clusters at the regrowth interface, strongly indicating the presence of defects. To further understand the role of hydrogen, we investigate the separate effects of ion damage and hydrogenation on subsequent regrowth. We find that photoluminescence of regrown quantum wells is greatly improved on argon ion damaged substrates which have been additionally exposed to hydrogen at −150 V for 3 min. These experiments illustrate that hydrogen interacts with defects in InP, preventing their propagation during regrowth, and improving the photoluminescence quality of regrown quantum wells.
Theoretical investigation of structural instabilities of Fe layers on face-centered-cubic Cu
Authors: Nordström Lars , Singh David J.
Published: July 2002

Calculations of structural stabilities for thin iron layers as grown on Cu(001) are reported. It is found that a free-standing fcc(001) monolayer is unstable with respect to 3×1 and 4×1 distortions. The former instability is directly related to the Pitsch transformation from fcc(001) to bcc(110), and calculations along the path find bcc(110) as the stable structure. Inclusion of the Cu substrate in the calculation tends to stabilize fcc(001). The calculated instabilities are of similar form to the superstructures observed for Fe grown on Cu(001). The relation to the experimental situation is discussed.
Comparative study of tantalum and tantalum nitrides (Ta2N and TaN) as a diffusion barrier for Cu metallization
Authors: Min Kyung-Hoon , Chun Kyu-Chang , Kim Ki-Bum
Published: July 2002

Tantalum (Ta) and tantalum nitride films (Ta2N and TaN) of about 50 nm thickness were reactively sputter deposited onto (100) Si substrate by using dc magnetron sputtering and their diffusion barrier properties in between Cu and Si were investigated by using sheet resistance measurement, x-ray diffraction, Auger electron spectroscopy, and Secco etching. With increasing amounts of nitrogen in the sputtering gas, the phases in the as-deposited film have been identified as a mixture of β-Ta and bcc-Ta, bcc-Ta, amorphous Ta2N, and crystalline fcc-TaN. Diffusion barrier tests indicate that there are two competing mechanisms for the barrier failure; one is the migration of Cu into the Si substrate and another is the interfacial reaction between the barrier layer and the Si substrate. For instance, we identified that elemental Ta barrier failure occurs initially by the diffusion of Cu into the Si substrate through the barrier layer at 500 °C. On the other hand, the Ta2N barrier fails at 700 °C by the interfacial reaction between Ta2N and Si substrate instead of the migration of Cu into the Si substrate. For the case of TaN, the barrier failure occurs by the migration of Cu into the Si substrate at 750 °C. It is also demonstrated that the diffusion barrier property is enhanced as the nitrogen concentration in the film is increased.
Contactless capacitance–voltage and photoluminescence characterization of ultrathin oxide–silicon interfaces formed on hydrogen terminated (111) surfaces
Authors: Hashizume Tamotsu , Koyanagi Satoshi , Hasegawa Hideki
Published: July 2002

Electronic properties of the interfaces between Si and ultrathin (≲10 Å) oxides formed by various low-temperature processes were characterized in contactless fashion, using contactless capacitance–voltage and photoluminescence surface state spectroscopy techniques together with x-ray photoelectron spectroscopy measurement. Hydrogen (H) terminated Si(111) surfaces were used as the initial surface. Ultrathin oxides were formed at low temperatures by chemical oxidation processes (hot HNO3, H2SO4+H2O2), long-time air exposure, and low-temperature oxidation processes below 350 °C. The initial H-terminated surfaces showed presence of Fermi-level pinning at E0=EV+0.65 eV due to high density of amphoteric discrete state probably originating from Si dangling bonds. On the other hand, all the ultrathin oxide–Si interfaces exhibited very limited capacitance variations with voltage at low capacitance levels similar to GaAs metal–insulator–semiconductor systems, and indicated that the Fermi level is pinned near the hybrid orbital charge neutrality level EHO due to presence of interface states with narrow U-shaped continuous distributions. Low-temperature oxidation at 350 °C slightly weakens such pinning. The present work indicates difficulty of realizing unpinned ultrathin oxide–silicon interface by low-temperature processes.
InP/InGaAs single heterojunction bipolar transistors grown by solid-source molecular beam epitaxy using a phosphorus valved cracker
Authors: Chen W. L. , Chin T. P. , Woodall J. M. , Haddad G. I.
Published: July 2002

In this work, InP/InGaAs single heterojunction bipolar transistors (SHBTs) with excellent performance were grown by solid-source molecular beam epitaxy using a phosphorus valved cracker. The maximum dc and differential current gain are ∼27 and 32 with breakdown voltages Vceo∼6 V and Vcbo∼10 V for the SHBT with a 5000 Å InGaAs collector layer doped at 4×1016 cm−3. The ideality factors for Ib and Ic are ∼1.12 and 1.07 and the transistors also show very uniform current gain down to 10−10 A range. For high frequency performance, the maximum fT and fmax are around 80 and 125 GHz for the SHBT with an emitter area of 32 μm2.
Solid source molecular beam epitaxy of low threshold 1.55 μm wavelength GaInAs/GaInAsP/InP semiconductor lasers
Authors: Johnson F. G. , King O. , Seiferth F. , Stone D. R. , Whaley R. D. , Dagenais M. , Chen Y. J.
Published: July 2002

We report the growth and characterization of 1.55 μm wavelength GaInAsP based semiconductor lasers grown by solid source molecular beam epitaxy. Quaternary compositions were reproducible over time. Photoluminescence and x-ray diffraction spectra indicate abrupt quantum well interfaces. Separate confinement heterostructure laser diodes with four quantum wells had threshold current densities as low as 580 A/cm2 and 275 A/cm2 for unstrained Ga0.47In0.53As and strained Ga0.27In0.73As0.8P0.2 wells, respectively. These results are as good as the best results reported for similar lasers grown by any growth technique.
X-ray mask distortion correction technology using pattern displacement simulator
Authors: Uchiyama S. , Oda M. , Matsuda T.
Published: July 2002

A new method to correct x-ray mask distortion was developed. This method uses the correction method of previous analysis of distortion and transformation of coordinates (PAT) and a simulator to calculate pattern displacement caused during backetching. The key advantages of using PAT with a simulator are that no extra time, substrates, or labor are required to fabricate send-ahead masks. Using this correction method, it was confirmed that the 3σ value of the pattern placement error was reduced to below 76 nm. This indicated that PAT with a pattern displacement simulator was as useful for improving the pattern placement accuracy of x-ray masks as PAT with send-ahead masks. In addition, analysis of the remaining error made it clear that the correction error was mainly caused by the lack of e-beam writing accuracy.
Fabrication of x-ray lithography masks with optical lithography
Authors: LaTulipe D. , Maldonado J. R. , Mitchell P. , Leduc R. , Babich I.
Published: July 2002

We describe a technique to fabricate (1×) x-ray masks utilizing an optical reduction tool (SVGL Micrascan II). A special 1× x-ray mask chuck was constructed to fit the optical tool. The technique takes advantage of the relatively flat x-ray mask substrates and the required low throughput which allows replication without compromising the printing tool depth of focus and the resist process. The potential advantages of this technology are: (1) improved placement accuracy relative to conventional e-beam tools; (2) no (e-beam) proximity effects; and (3) lower post processing data volumes. The placement distortion and the critical dimension uniformity obtained in the 1× daughter masks on a 22×32 mm field are similar in magnitude to x-ray masks fabricated with e-beam lithography utilizing product specific emulation techniques. Furthermore, the distortion seen is believed to be due primarily to the known distortion of the Micrascan tool lenses. This suggests that it may be possible to use the results of lens distortion characterization to adjust the pattern of the reticle so as to correct for the lens distortion. Lens correction in combination with product specific emulation may allow the fabrication of daughter masks with near-zero placement errors, suitable for sub-250 nm product applications.
Physics and chemistry of silicon wafer bonding investigated by infrared absorption spectroscopy
Authors: Weldon M. K. , Chabal Y. J. , Hamann D. R. , Christman S. B. , Chaban E. E. , Feldman L. C.
Published: July 2002

Silicon wafer bonding is achieved by joining two particle-free silicon wafers and annealing to elevated temperatures (∼1100 °C). We have used multiple internal transmission infrared absorption spectroscopy to probe the interface between the wafers upon initial joining and also during subsequent annealing steps. For atomically flat hydrophobic wafers (H passivated), we observe a pronounced shift in the Si–H stretching frequency due to the physical interaction (van der Waals attraction) that occurs when the surfaces come into intimate contact. The hydrogen eventually disappears at high temperatures (1000 °C) and Si–Si bonds are formed between the two surfaces. For hydrophilic wafers (oxide passivated), we initially observe three to five monolayers of water at the interface (providing the initial attraction through H bonding), as well as the presence of hydroxyl groups that terminate the oxide at low temperature. Upon moderate heating (<400 °C), the water trapped at the interface dissociates and leads to the formation of additional oxide. Between 400 and 800 °C, the hydroxyl groups disappear, resulting in a corresponding increase in oxide and the formation of Si–O–Si bridging linkages across the two surfaces.
Effect of silicon processing on giant magnetoresistance
Authors: Burkett S. L. , Yang J. , Pillai D. , Parker M. R.
Published: July 2002

The primary objective of this study is to determine the effect of silicon wafer processing parameters on giant magnetoresistance (GMR). Thermally oxidized silicon wafers serve as substrates for alternating layers of NiFeCo and Cu (2.0–2.5 nm). SiO2 films prepared in the laboratory are loaded into the sputtering chamber along with commercially oxidized wafers for comparison purposes. Four process parameters are systematically varied—oxidation method, postoxidation anneal (POA), oxide thickness, and oxidation temperature. Preliminary results indicate the two most influential processing parameters are the method of oxidation (dry oxygen or wet steam) and a POA. In contrast, GMR values do not seem to vary greatly for various oxidation or POA temperatures in the range 800–1000 °C. We present GMR results of NiFeCo/Cu multilayers on oxidized silicon substrates formed by various processing methods. GMR is observed for all films, with the magnitude of the effect increasing for substrates oxidized by ‘‘wet’’ methods and oxidized substrates that include a POA (1000 °C, nitrogen atmosphere, 20 min) previous to sputter deposition of the multilayers. Our data suggest that the GMR of the multilayer stack is sensitive to changes at the Si–SiO2 interface.
Silicon dioxide passivation of InP/InGaAs metal-semiconductor-metal photodetectors
Authors: Kollakowski St. , Schade U. , Böttcher E. H. , Kuhl D. , Bimberg D. , Ambrée P. , Wandel K.
Published: July 2002

We report on passivation and antireflection coating of InP/InGaAs metal-semiconductor-metal photodetectors by low-temperature deposited silicon dioxide. The passivating performance of silicon dioxide films applied by nonreactive radio frequency magnetron sputtering and remote plasma enhanced chemical vapor deposition are comparatively investigated. Different wet chemical treatments of the InP surface prior to deposition including sulfur passivation are performed and their influences on the device performance are presented. Under optimized deposition conditions and pretreatments, both processes result in a stable and reproducible surface passivation as reflected by a drastic reduction of excessive leakage currents and photocurrent gain. The improvement of the device characteristics due to the silicon dioxide coating is attributed to a substantial lowering of the density of interface states at the insulator-InP interface as compared to nonpassivated devices.
Distributed generator with extended interaction on field emitter arrays
Authors: Zakharchenko Yu. F. , Sinitsyn N. I. , Gulyaev Yu. V.
Published: July 2002

A possibility for designing a distributed microwave generator on field emitter arrays has been studied which involves a waveguide interaction system as a circular distributed resonator. This generator was shown to be able of operating in the millimeter wavelength band with low voltages and beam current densities and to provide an efficiency to 20%. The electrical tuning of the generator in frequency can achieve 30% for one of its versions.
Characterization of lateral thin-film-edge field emitter arrays
Authors: Johnson B. R. , Akinwande A. I. , Murphy D.
Published: July 2002

Measurements on arrays of lateral thin-film-edge field emitters are described, including current–voltage characteristics and results obtained with a high voltage (10 kV) cathodoluminescent phosphor screen. These devices offer the potential for enhanced emitter lifetime compared to conventional microtips, because one of the gate electrodes protects the emitter edge from ion sputter damage. One goal of this work is to demonstrate the feasibility of a cathodoluminescent field emitter lamp for a high-brightness backlight in an avionics display.
New technique for nanocantilever fabrication based on local electrochemical etching: Applications to scanning force microscopy
Authors: Hoummady M. , Farnault E. , Fujita H. , Kawakatsu H. , Masuzawa T.
Published: July 2002

We propose a new method to fabricate a nanocantilever with a mechanical oscillating ball on its end. The method is based on local electrochemical etching in a very thin electrolyte liquid layer. It allows fabrication of a very sharp tip as well as a ball tip that can be used in dynamic mode control of atomic force microscopy. The oscillating part measures 50 nm in diameter; the diameter of the ball tip is 1.5 μm. Because of the small mass of the oscillating ball and the small size of the threadlike neck, the estimated resonance frequency is around 300 MHz. This technique will help to increase the force gradient sensitivity in dynamic mode control of atomic force microscopy.
Microwave modulated photoluminescence as a contactless probe of interface states
Authors: Inglefield C. E. , DeLong M. C. , Taylor P. C. , Geisz J. F. , Olson J. M.
Published: July 2002

Microwave modulated photoluminescence (MMPL) is a developing spectroscopy in which the sample is subjected to continuous optical pumping and chopped microwave electric fields. The signal detected in an MMPL experiment is the change in the photoluminescence spectrum of the sample due to the presence of microwave electric fields, which increase the kinetic energy of the free carriers. In order to investigate the effects of interfaces on this measured quantity, two types of GaAs samples have been compared. The first type of sample was grown such that the GaAs epilayers are exposed, while in the second type the GaAs is “capped” by a layer of higher band gap material. Several pairs of such samples have been studied. The MMPL results are consistent with the following mechanism: an increase in the kinetic energy of the free carriers that results from the presence of the microwave fields allows more free carriers to reach the interface or surface of the GaAs layer before recombining. The presence of a greater number of nonradiative recombination paths in the samples with a bare GaAs surface than at the GaAs/capping-layer interface is therefore seen experimentally as an increase in the photoluminescence quenching by the microwave electric fields. The potential usefulness of MMPL as a probe of non-radiative recombination and as an indicator of interface quality is illustrated by a quantitative estimate of surface/interface non-radiative recombination.
Patterning of Langmuir–Blodgett film with ultrahigh vacuum-scanning tunneling microscope/atomic force microscope
Authors: Hamanaka H. , Ono T. , Esashi M.
Published: July 2002

We performed a patterning of a stearic acid Langmuir–Blodgett (LB) film on a Si substrate with ultrahigh vacuum scanning probe microscope. The patterning was carried out with a conducting Si cantilever probe by applying positive or negative bias voltages to the sample. When a negative bias (−10 V) was applied, one monolayer of the LB film was extracted. On the other hand, when a positive sample bias (+10 V) was applied, the scanned area was protruded. This extraction mechanism is explained in terms of the force caused by permanent and induced dipole moments. Further, SiO2 was selectively deposited on the patterned area using SiCl4 and H2O.
Studies of field related effects in the fabrication process on graphite using a scanning tunneling microscope
Authors: Wang Chen , Li Xiaodong , Shang Guangyi , Qiu Xiaohui , Bai Chunli
Published: July 2002

The surface modification process with low energy electron beams, generated with a scanning tunneling microscope, is investigated using graphite as an example. By analyzing the cross-sectional profiles, it is shown that local transport properties could play a vital role in determining the characteristics of the fabricated craters. In addition, the observed asymmetry in the contours of the as-produced craters is proposed to be correlated with the geometry of the tip apex region. It is therefore suggested that one look into the roles of low energy electrons, together with the effects of strong electric field, in the fabrication process.
Fabrication of metal field emitter arrays on polycrystalline silicon
Authors: Kim II Hwan , Lee Chun Gyoo , Kim Yeo Hwan , Park Byung Gook , Lee Jong Duk
Published: July 2002

Cone-shaped metal field emitter arrays were fabricated on a single heavily doped polysilicon layer. From the observation of the metal field emitter fabricated on the single-polysilicon layer, it was noticed that the irregular shape of the gate aperture was caused by the large grain size of heavily doped polysilicon after oxidation. Therefore, in order to obtain a good shape, the double layers of polysilicon where one was heavily doped and the other was not doped were used. The undoped polysilicon layer was consumed for the gate oxide layer and the doped polysilicon layer was used to serve as a conducting cathode layer. The small grain size of the undoped polysilicon after oxidation led to an improved shape of the gate aperture which rendered a stable emission characteristic.
Design and characterization of a high numerical aperture lens system for scanned laser lithography
Authors: Allen P. C. , Bohan M. J. , Buck P. D.
Published: July 2002

Over the past decade, three generations of scan lens systems have been developed, culminating in a 33×, 364 nm, 0.8 numerical aperture lens system for 0.25 μm generation mask writing. The specifications and design performance of this latest lens from Tropel are compared with measurements made on a lens test bench and on a scanned laser writing system. A full-width at half-maximum spot size of 270 nm, and linearity performance under 20 nm have been measured. CD linearity data shows deviations less than 20 nm down to 0.3 μm feature sizes. Corner rounding data shows marked improvement over previous generation imaging optics with a minimum radius of 253 nm. These lens distortion and resolution measurements confirm that the new lens system has the imaging performance required for 0.25 μm generation masks.
Novel technique for improving pattern placement in membrane mask making
Authors: Perkins F. Keith , Marrian Christie R. K. , Peckerar Martin C.
Published: July 2002

Pattern placement errors pose a serious problem in the manufacture of masks for proximity x-ray lithography. Many of these errors are attributable to long term drifts in beam position relative to external fiducials. To address this problem we have developed a technique based on through-the-membrane monitoring of the electron beam position. This technique uses as a detector a reverse biased Schottky diode with high bandwidth and gain. In use this detector is mounted near the back surface of the membrane. An accurately patterned overlayer on the detector provides the fiducial reference. The overlayer is designed to modulate the electron-hole pair current generated in the diode by absorbing the incident beam. Position information is obtained by analyzing the image created from recording the digitized diode current during patterning. The phase in a Fourier transform of the data at the spatial frequency of the patterned absorber gives a measure of the position of the incident beam. Changes in the observed phase from one frame to the next can then be used to correct position errors of the beam in real time. We report results from tests of various components of this system. Initial results indicate that the system will be sufficiently fast and accurate for use in pattern placement correction for 130 nm ground rule mask production.
Revisiting phase shifting masks in x-ray lithography
Authors: Khan Mumit , Bollepalli Srinivas , Cerrina Franco
Published: July 2002

In this article, we describe a framework for selecting the materials for phase shift masks (PSMs) in x-ray lithography to yield the optimal exposure latitude. Traditional design of PSMs involves choosing the thickness of the material to produce a π phase shift, as in the case of clear phase shifting masks, or to produce the sufficient contrast needed for imaging with a requisite phase shift to improve linewidth control, as in the cases of attenuated phase shifting masks and half-tone phase shifting masks. We instead find the optical constants of a theoretical material that yield optimal exposure latitude, and try to find combinations or alloys of various materials that have the requisite optical constants.
Blanked aperture array for parallel electron beam lithography
Authors: Winograd G. I. , Pease R. F. W. , McCord M. A.
Published: July 2002

The blanked aperture array (BAA) is a technique for improving the throughput of electron beam lithography tools by utilizing a much larger fraction of the electron source current than single probe forming systems. The fabrication of a BAA employs standard MEMS processing. Equations are derived which optimize the blanker performance under specified constraints on source emittance and brightness and blanker modulation frequency. An electron optics column is designed to illuminate the BAA and image it onto the target. For 0.1 μm lithography at 50 kV, an objective working distance of 30 mm and a 5 mrad convergence angle, a total current of 1 μa can be delivered to the target before beam blurring due to Coulomb interactions becomes unacceptable. An electron source of brightness 2×106 A/cm2/Ω and emittance 24 μm mrad can deliver this current through a 660 beamlet BAA at a 100 MHz modulation rate.
Fabrication of in situ Ohmic contacts patterned in three dimensions using a focused ion beam during molecular beam epitaxial growth
Authors: Sazio P. J. A. , Jones G. A. C. , Linfield E. H. , Ritchie D. A.
Published: July 2002

Focused ion beam doping during molecular beam epitaxial (MBE) growth is a novel technique that allows the in situ fabrication of unique three-dimensional semiconductor structures with doping profiles unobtainable using standard planar lithography. Conventional MBE growth uses a thermal Si effusion cell as the dopant source during two-dimensional layer growth of III–V semiconductor material. In the technique described here, a scanning Si focused ion beam (FIB) has been added onto the growth chamber to introduce the dopant atoms selectively in a maskless lithographic process. As the FIB is rastered in the xy plane under computer control during crystal growth in the z direction, it is possible to generate specific three-dimensional dopant patterns embedded within the semiconductor. Furthermore, the patterned semiconductor crystal requires no post growth anneal as the dopant ions are decelerated by a retarding electric field on the sample. The dopant is thus deposited on the epilayer surface rather than impinging at high energy, minimizing crystal damage. In this article, we report the successful fabrication and electrical measurements of highly doped GaAs/AlGaAs structures, directly written by focused ion MBE (FIMBE). The scanning Si FIB has been used to form both lateral and vertical, low resistance Ohmic contacts to two-dimensional electron gases at low temperatures. Lateral patterning was initially exploited to form extended contacts to an electrostatically induced electron gas. This was achieved by FIMBE using both selective modulation doping (forming two-dimensional electron gas sheet contacts to the induced gas) and selective n+ doping directly in the quantum well. Field-effect transistor action and Shubnikov de Haas oscillations were observed, thus demonstrating that the conventionally difficult constraint of self-alignment in undoped GaAs/AlGaAs field-effect transistor structures can be eliminated. Vertical patterning was used to form degenerately doped n+ columns embedded within a conventional high electron mobility transistor structure. The resulting I–V characteristics, recorded at room temperature and at 1.5 K in the presence of a 5 T magnetic field, will be discussed. The ability to introduce specific doping within a structure opens the possibility of forming three-dimensional integrated conducting pathways which would not be possible by any other means.
Characterizing partial coherence uniformity in a deep ultraviolet step and repeat tool
Authors: Watson G. Patrick , Cirelli Raymond A. , Mkrtchyan Masis , Travers Richard J.
Published: July 2002

In recent literature the partial coherence uniformity of a lithography tool has been suspected to be a cause of critical dimension control and pattern placement problems. A direct measurement of the uniformity of partial coherence has been developed to determine the magnitude and distribution of this problem. Apertures have been fabricated that block illumination everywhere except for a small angular range and in one quadrant. The illumination reaching the wafer plane of the stepper is measured with a photodetector on the wafer chuck designed to measure exposure uniformity. The intensity distribution can vary across a chip field by as much as ±20% for large off-axis illumination (OAI) angles. However, if no aperture is inserted, the field is uniform to within ±1.5%. The consequences of this nonuniformity are surprisingly subtle; at best focus, there is no difference between the aerial image of a feature with or without the uneven angular distribution. The combination of defocus with the nonuniform OAI leads not only to image shifts, but to feature dimension variations as well.
Origin of stress distribution in sputtered x-ray absorber film
Authors: Iba Yoshihisa , Kumasaka Fumiaki , Aoyama Hajime , Taguchi Takao , Yamabe Masaki
Published: July 2002

To eliminate distortion in x-ray masks, not only lower average stress but also uniformity of the stress distribution in the x-ray absorber film are very important. We investigated the cause of stress distribution in sputtered x-ray absorber films both theoretically and experimentally. Our investigation clarified that stress distribution is determined by the distribution of the average velocity of sputtered and working gas atoms and/or the arrival frequency of incident working gas atoms when arriving at the wafer in sputtering systems. These determinants are strongly influenced by the geometry of the sputtering apparatus, i.e., the shape of the erosion area of the target and the substrate-to-target distance. We obtained a good uniformity of stress by optimizing the sputtering equipment configuration taking the erosion area of the target into consideration. Two ways to accomplish this are by adjusting the gap between the target and the substrate and by achieving uniformity of the erosion area.