bluuebunny/crossref_metadata_2025 huggingface dataset:
Broad-area electron-beam-assisted etching of silicon in sulfur hexafluoride
Authors: Ortega Martinez R. , Verhey T. R. , Boyer P. K. , Rocca J. J.
Published: July 2002

Silicon etching rates up to 250 Å/min have been observed in an electron-beam-generated He plus SF6 plasma. The etch rate was found to increase linearly with electron beam current density and to be practically independent of the electron acceleration voltage in the range investigated (170–260 V). Profiles of the resulting features show that etching is anisotropic with a vertical-to-horizontal ratio of 2.5 to 3.
Direct writing through resist exposure using a focused ion beam system
Authors: Ochiai Y. , Kojima Y. , Matsui S.
Published: July 2002

A focused ion beam (FIB) system, fully computer controlled and containing a mounting stage with a laser interferometer, is used to investigate the accuracy of resist exposure fabrication and the mark detection. Fabricated patterns in poly(methylmethacrylate) (PMMA) and chloromethylated polystyrene (CMS) resists on both Si and SiO2 substrates showed good pattern width accuracy. This appears to be because of the absence of the proximity effect in ion beam exposure and the stability of both the Au–Si–Be liquid metal ion source and the FIB system itself. The authors examine the use of Si, Be, and Au FIB’s for the detection of alignment marks covered with PMMA and CMS resists. Detection of marks covered with PMMA resist was possible because of the resist sputter etching produced by the FIB irradiation. For marks covered with CMS resist, the addition of a differential amplifier enabled successful detection here as well.
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u ellipsometry of thin-film deposition: Implications for amorphous and microcrystalline Si growth
Authors: Collins R. W. , Yang B. Y.
Published: July 2002

Real-time ellipsometric characterization of the nucleation of hydrogenated amorphous silicon (a-Si:H) prepared by plasma-enhanced chemical vapor deposition (PECVD) on smooth, dense metal, and crystalline Si substrates is reviewed. The experimental results for photoelectronic quality a-Si:H from pure SiH4 on Mo and Cr are consistent with the Volmer–Weber nucleation mode, with a separation of 40–50 Å between nucleation centers. For c-Si substrates, a new interpretation suggests that nucleation occurs on the same scale, but the geometry in the first monolayer is disklike. A well-defined lobe and cusp in the data can be ascribed to surface smoothening by diffusion that results upon coalescence of these structures. For films from a pure SiH4 plasma, the rates of coalescence and relaxation of substrate-induced surface roughness on thick films are consistent with a diffusion length of ∼80 Å for the adsorbed precursors. For films prepared from a SiH4-depleted plasma, the average surface diffusion length is reduced by at least a factor of 2. New results for the growth of μc-Si:H on a-Si:H films reveal an induction period of several minutes for the nucleation of microcrystallites. During this period a structurally defective 40–80 Å amorphous layer is deposited. Such a layer is expected to influence the properties of photoelectronic devices and compositionally modulated materials that use thin μc-Si:H.
Oxygen plasma etching resistance of plasma polymerized organometallic film
Authors: Yamada H. , Satoh T. , Itoh S. , Hori M. , Nakamura M. , Morita S. , Hattori S.
Published: July 2002

The oxygen plasma etching resistance of plasma polymerized organometalic film was measured. The films were deposited by downstream plasma deposition using gaseous mixtures of an organic monomer (C3H6) and a metal-containing monomer tetramethyltin or tetramethylsilane. By changing the flow-rate ratio of both monomers, the metal content of the film was reproducibly varied from 0% to 27%. It was found that the O2 reactive ion etching rate depended on metal content in polymer, discharge power density, and oxygen gas pressure. High oxygen plasma etching resistance was obtained for films which contained even a few percent of metal. From the results of electron spectroscopy for chemical analysis and Auger electron spectroscopy measurements, it was observed that the metal-oxidized layer was formed on the surface during oxygen plasma etching.
Molecular-beam epitaxial growth and interface characteristics of GaAsSb on GaAs substrates
Authors: Yano M. , Ashida M. , Kawaguchi A. , Iwai Y. , Inoue M.
Published: July 2002

We report the growth by molecular-beam epitaxy of GaAsSb crystals on GaAs (100) substrates. The composition of the alloyed crystals has been strongly dependent on the growth condition, especially on the substrate temperature and the arrival rates of arsenic and antimony molecules. Raman scattering measurements have been performed to characterize the grown layers, GaAsSb, and GaSb on GaAs substrates. In the GaSb/GaAs grown at relatively high temperatures, we observe the variation of composition near the heterointerface.
GaAs/GaP strained-layer superlattices grown by atomic layer epitaxy
Authors: Ozeki M. , Kodama K. , Sakuma Y. , Ohtsuka N. , Takanohashi T.
Published: July 2002

We grew (GaAs)m(GaP)n strained-layer superlattices using pulsed jet epitaxy, a new type of atomic layer epitaxy. We investigated growth procedures for the heteroepitaxy and proposed a growth mechanism which includes adsorption, desorption, and decomposition of TMGa molecules on the surface. Structural analyses were carried out using x-ray rocking curves and Raman scattering measurements, and showed that growth of superlattices was completely controlled to within one atomic layer even for a monolayer (GaAs)1(GaP)1 superlattice. The photoluminescence and reflectance measurements suggest that (GaAs)1(GaP)1 has a direct energy band structure differing from the other superlattices (GaAs)m(GaP)n (m,n=2,3,4,5) and from alloy crystal GaAs0.5P0.5.
Spatial filtering for depth of focus and resolution enhancement in optical lithography
Authors: Fukuda Hiroshi , Terasawa Tsuneo , Okazaki Shinji
Published: July 2002

Spatial filtering at the lens pupil can achieve amplitude superposition for multiple images along the light axis and phase control between them. This enhances depth of focus while maintaining high resolution capability in optical lithography. Compared to conventional methods, three times larger depth of focus is expected for hole patterns with 20% improved resolution limit. For general pattern features, a 1.5–1.7 times larger depth of focus is expected at Rayleigh’s resolution limit.
Ballistic electron emission in silicide–silicon interfaces
Authors: Hasegawa Y. , Kuk Y. , Tung R. T. , Silverman P. J. , Sakurai T.
Published: July 2002

Ballistic electron emission microscopy (BEEM) of the NiSi2/Si(111) interface has been carried out under ultrahigh vacuum conditions. Atomically resolved scanning tunneling microscopy (STM) images of this surface show an unreconstructed (1×1) structure with Si adatoms that tend to form trimers. STM and BEEM-current images are taken simultaneously for type-A and -B interfaces. The BEEM currents measured for types A and B differ by less than 10% of the total BEEM current. The results may originate from field pinching between two domains.
Deformations and nonlinearity in scanning tunneling microscope images
Authors: Libioulle L. , Ronda A. , Taborelli M. , Gilles J. M.
Published: July 2002

We perform here a complete determination of the relation between applied voltage and displacement for a tripod piezoceramic scanning tunneling microscope (STM) scanner unit. The absolute calibration is obtained in two steps. First the gap between two capacitor plates is modified by the expansion of the piezoelectric tube driven at various voltages and frequencies. Second, we image by STM some well-known surfaces: an optical diffraction grating and highly oriented pyrolytic graphite for large and atomic scales, respectively. For the voltage versus expansion relation we consider both nonlinearity sources, which induce relevant image deformations: static hysteresis and time-retarded response or creep. This characterization of the scanning unit in the STM operating conditions (voltage and frequencies) allows a suitable image restoration.
Visualization of the dynamics in surface reconstructions
Authors: Besenbacher F. , Jensen F. , Lægsgaard E. , Mortensen K. , Stensgaard I.
Published: July 2002

By means of scanning tunneling microscopy we have been able to visualize in real-time and space dynamical processes on metal and semiconductor surfaces, such as the nucleation and growth of oxygen induced reconstructions on Cu surfaces. It is shown that although there are strong similarities in the final oxygen induced reconstructions, the growth modes are dramatically different, and that the information obtained from observations of dynamical processes may be crucial for a subsequent understanding of the static surface structure.
Ballistic electron emission microscopy investigation of SiGe nanostructures fabricated using reactive-ion etching
Authors: Couillard J. G. , Davies A. , Craighead H. G.
Published: July 2002

We have applied ballistic electron emission microscopy (BEEM) to microfabricated semiconductor structures in order to study the damage effects of dry etching. Structures were defined in Si0.92Ge0.08 using electron-beam lithography and reactive-ion etching. A gold Schottky contact was deposited on the surface, and the transport properties of the metal–semiconductor interface were then characterized using BEEM. BEEM current versus voltage spectra were fit with a two parameter model to determine the local Schottky barrier heights and transmission probabilities of adjacent etched and unetched regions. BEEM enables us to nondestructively examine the electrical nature of the etched surface with nanometer resolution. The results show a lower average barrier height in the etched regions compared to that of the unetched regions, consistent with macroscopic results. This technique also enables us to observe the distribution of local barrier heights with microscopic resolution much higher than conventional techniques.
Surface atomic structure and bonding of GaAs(110)-p(1×1)–Bi (1 ML)
Authors: Bowler Ann M. , Hermanson John C. , LaFemina John P. , Duke C. B.
Published: July 2002

The surface atomic and electronic structure of GaAs(110)-p(1×1)–Bi (1 ML) has been examined using a tight-binding total-energy (TBTE) model. Two structural candidates were considered; the epitaxial continued-layer structure (ECLS) and the epitaxial on-top structure (EOTS). The TBTE computations indicate that the ECLS is more stable than the EOTS by ∼0.06 eV/surface atom/unit cell in agreement with a recent low-energy electron diffraction (LEED) intensity analysis which selected the ECLS as the best-fit structure. The predicted TBTE structural parameters for the ECLS are in good agreement with the best-fit LEED results. The energy difference between the ECLS and EOTS is much smaller for the Bi/GaAs interface than for the Sb/GaAs interface (∼0.11 eV/surface atom/unit cell) in agreement with the proposition that the relative stability of the ECLS and EOTS is a function of the overlayer-substrate mismatch; with the EOTS being favored for larger overlayer-substrate mismatch. The primary difference between the bonding of Bi and Sb to the GaAs(110) surface is the occurrence of s–p hybridization in the Bi derived surface states. Both the Bi s and p states hybridize with the substrate atom orbitals and change the character of the adsorbate–substrate bonding. We find that both the ECLS and EOTS have similar surface electronic structures; the energies and dispersions of the predicted surface bound states for both structures are in good agreement with photoemission data.
Heterojunction band offset: A local feature
Authors: Priester C. , Allan G. , Lannoo M.
Published: July 2002

After an extensive compilation of calculated band offsets obtained from a self-consistent tight-binding description, it is shown how these results can be recovered by the use of a local description based on the molecular model of the semiconductor band structures. This local description allows us to explain the mechanism which relates the band offset modification to the chemical structure of the interface.
Effect of interfacial bond type on the electronic and structural properties of GaSb/InAs superlattices
Authors: Hemstreet L. A. , Fong C. Y. , Nelson J. S.
Published: July 2002

We have investigated the effects of interfacial bond configuration on the electronic and structural properties of thin (001)GaSb/InAs superlattices by using state-of-the-art ab initio molecular dynamics techniques to calculate the electronic and structural properties of two twelve-atom model GaSb/InAs superlattices which have been constructed to contain only In–Sb (model 1) or Ga–As (model 2) interface bonds, respectively. We find the strain at the the interface to be different in the two cases. In model 1, the In and Sb atoms at the interface move away from each other toward the InAs and GaSb layers, respectively, increasing the interfacial separation (4.3% greater than in bulk InSb) and compressing the back bonds to the atoms in the layer below the interface. In model 2 the Ga and As atoms move toward each other, decreasing the interplanar separation at the interface (3.2% smaller than in bulk GaAs) and stretching the back bonds to the neighboring Sb and In atoms, respectively. We calculate the valence band offset for the Ga–As bonded structure to be 0.15 eV smaller than that for the model containing only In–Sb bonds. This smaller band offset leads to more mixing of As p character into the highest lying valence band of the superlattice and results in a 0.015 eV smaller spin-orbit splitting at the valence band edge of the Ga–As bonded structure. This result is consistent with the 0.05 eV larger band gap observed for Ga–As bonded structures in recent photoconductivity measurements made on both Ga–As and In–Sb bonded samples grown by molecular-beam epitaxy.
Development of an ultrahigh vacuum atomic force microscope for investigations of semiconductor surfaces
Authors: Kageshima M. , Yamada H. , Nakayama K. , Sakama H. , Kawazu A. , Fujii T. , Suzuki M.
Published: July 2002

A new atomic force microscope (AFM) adapted for ultrahigh vacuum operation is described. This AFM utilizes the optical beam deflection method to detect the cantilever displacement. Both the laser diode and the photodiode sensor are contained within the vacuum chamber. An inchworm motor mechanism is used for the tip–sample approach. Up to eight cantilevers are stored in the chamber and can be used without breaking vacuum. The vacuum system is equipped with a sample heater, an evaporation cell, a gas inlet valve, and a low-energy electron diffraction system, for observing semiconductor surfaces. Imaging of a graphite surface and a clean Si (111) surface with step structures have been obtained.
Focused-ion-beam damage-etch patterning for isolation of quantum structures in AlGaAs/GaAs
Authors: Templeton I. M. , Fallahi M. , Charbonneau S. , Champion H. G. , Allard L. B.
Published: July 2002

A damage-nucleated wet crystallographic etch technique has been developed for AlGaAs. The etch extends beyond the initial patterned region, and is thus able to remove peripheral damage. GaAs is not appreciably affected at the dose required, and hence a GaAs layer may be used as an etch stop. The technique is readily applicable to the generation of quantum wires and dots. Photoluminescence studies of several preliminary dot structures in quantum well material show signals whose strength varies with dot size and with dose.
Molecular-beam epitaxy growth of Bi epilayers and Bi–CdTe superlattices
Authors: DiVenere A. , Yi X. J. , Hou C. L. , Wang H. C. , Chen J. , Ketterson J. B. , Wong G. K. , Meyer J. R. , Hoffman C. A. , Bartoli F. J.
Published: July 2002

The successful growth of Bi epilayers, and for the first time Bi–CdTe superlattices, by molecular-beam epitaxy (MBE) on CdTe (111)B substrates is reported. X-ray diffraction shows several orders of satellites indicative of the abruptness of the interfaces. Initial analysis by high-resolution transmission electron microscopy shows sharp interfaces, although stacking faults are evident in the growth of CdTe on Bi. The growth of Bi layers exhibits streaked reflection high-energy electron diffraction patterns with clear Kikuchi lines. This is the first direct evidence for the layer by layer growth of Bi on CdTe by MBE. A detailed characterization of the electron and hole densities and mobilities in epilayers with a range of thicknesses has been obtained from a hybrid mixed conduction analysis of the magneto-transport data. Temperature dependences of the minority electron concentrations at ≥150 K have yielded the first convincing evidence for a semimetal to semiconductor transition in Bi thin films, at a thickness between 200 and 300 Å.
High aspect ratio polyimide etching using an oxygen plasma generated by electron cyclotron resonance source
Authors: Juan W. H. , Pang S. W.
Published: July 2002

High aspect ratio etching of polyimide in an O2 plasma generated by an electron cyclotron resonance (ECR) source was investigated. The dependence of etch rate, profile, and selectivity on microwave power, rf power, pressure, etch time, and gas composition were characterized. Etch rate was found to increase with microwave and rf power. Etch anisotropy increases with rf power but decreases with pressure and etch time. With 750 W microwave power, 300 W rf power, and 0.5 mTorr pressure, the polyimide etch rate was 0.91 μm/min and the anisotropy was 0.92. Etch selectivity between polyimide and the Ti mask was 3150:1 at 50 W and 536:1 at 300 W rf power. Compared to reactive ion etching, etching using an ECR source provides etch rate that is typically 10× faster and etch selectivity that is 4–6× higher. High aspect ratio (≳15:1) structures in polyimide that were 50 μm deep and 3 μm wide have been obtained using an O2 plasma generated by an ECR source.
Electron spectroscopy for chemical analysis on surface germylation process
Authors: Yoshida Yasuhiro , Kubota Shigeru , Koezuka Hiroshi , Fujioka Hirofumi
Published: July 2002

The surface germylation process is an improved method to realize the fine pattern of ultra large scale integration and overcome the problems in conventional surface imaging resist technologies such as removability of the patterned resist. The surface germylation process is evaluated with electron spectroscopy for chemical analysis. After the germylation, the germanium is observed at the resist surface. The germanium introduced into the resist film is oxidized by oxygen dry etching and condensed at the resist surface. The density of the germanium introduced correlated to the etching resistance of the resist. The diffusion of the germylation agent into the resist film, which depends on the deep ultraviolet (UV) dose, is necessary to give the germanium oxide layer at the resist surface. In the near surface at the germylation layer at the deep UV dosed resist film, the germylation occurs completely to every reaction site in the resist film.
Exploring native nuclear pore complex structure and conformation by scanning force microscopy in physiological buffers
Authors: Goldie K. N. , Panté N. , Engel A. , Aebi U.
Published: July 2002

We have used the scanning force microscope to image the cytoplasmic and nuclear faces of the nuclear pore complex (NPC) in physiological buffer environment. In agreement with previous electron micrographs recorded from dehydrated specimens, we have been able to reproducibly distinguish a high degree of asymmetry between the nuclear and cytoplasmic surfaces of the nuclear pore complex. Very much like seen in the electron microscope, the cytoplasmic face of the nuclear pore complex appears ‘‘donutlike’’ with a massive, ∼18 nm high annulus surrounding the membrane pore. In contrast, the nuclear face of the pore complex looks like a ∼36 nm high ‘‘dome’’ in the scanning force microscope, which in the electron microscope is resolved into a tenuous ring from which eight thin filaments emanate that are joined distally by a terminal ring, thus forming a ‘‘basket’’ or ‘‘fishtrap.’’ In addition, we were able to visualize distinct structural changes occurring upon mechanical manipulation of the nuclear pore complex periphery with the scanning tip. These preliminary data provide us with the intriguing future possibility to directly correlate NPC structure with function.
Hydrogen desorption from Si: How does this relate to film growth?
Authors: Greenlief C. Michael , Armstrong Michael
Published: July 2002

The desorption of hydrogen from the Si(100) surface is investigated. The hydrogen coverage is generated by the adsorption of atomic hydrogen, by the thermal decomposition of disilane, or during silicon epitaxy using silane in a rapid thermal chemical vapor deposition reactor. Temperature programmed desorption studies are then used to help yield information about the hydrogen surface coverage and the desorption kinetics of hydrogen. The desorption order of hydrogen is first order, consistent with previously reported single crystal studies. However, the activation energy for desorption of hydrogen from surfaces generated during Si epitaxy with SiH4 is considerably different. The activation energy for hydrogen desorption from these epitaxially grown layers is 49±3 kcal/mol. The presence of monatomic steps on the surface, which are created during the temperature quench, is believed to play a role in this difference of activation energies. Single crystal, ultra-high vacuum based studies using atomic hydrogen and disilane adsorption and desorption are used to gain further insight into this phenomena.
Band discontinuities at heterojunctions between crystalline and amorphous silicon
Authors: Van de Walle Chris G. , Yang L. H.
Published: July 2002

We present a theoretical investigation of the band lineups between crystalline and amorphous silicon, based on the first-principles pseudopotential method and the model-solid theory. We find that the offsets are very sensitive to the hydrogen content of the material; the valence-band offset for a junction with unhydrogenated a-Si is −0.25 eV, while for hydrogenated a-Si with a hydrogen content of 11% the offset becomes 0.20 eV. Consequences for the interpretation of experimental data are discussed.
Field emitter arrays on nanotube carbon structure films
Authors: Gulyaev Yu. V. , Chernozatonskii L. A. , Kosakovskaja Z. Ja. , Sinitsyn N. I. , Torgashov G. V. , Zakharchenko Yu. F.
Published: July 2002

We present the finding of newly performed experiments of considerable field emission from the films consisting of nanotube carbon structures. Density of emission current was up to 1–3 A/cm2, while in 20–100 V/μm electric field it was 0.1–1 mA/mm2.
Performance characteristics of a dual focus x-ray alignment microscope
Authors: Feldman M. , Liu L. , Phani S. , Zhang C.
Published: July 2002

We report a dual focus alignment microscope which we have implemented on our Anorad x-ray exposure tool. The microscope uses an Olympus 50×, 0.55 numerical aperture extra-long-working distance objective and newly developed optics to obtain simultaneous images of the mask and wafer. The images are nearly diffraction limited, have high brightness, uniform intensity to 5% full width at half-maximum, and are telecentric. They may be viewed either sequentially or superimposed on a charge coupled device video camera. We have used conventional image processing techniques to locate individual vertical and horizontal x-ray mask and oxide level wafer features to about 15 nm, 3σ. This is much less than the 500 nm optical resolution of the microscope. The dual focus imaging avoids the very precise high-speed mechanical motion conventionally required to refocus the microscope objective. In addition, vibration induced offsets are eliminated by acquiring the mask and wafer images simultaneously. These offsets can be serious in systems in which the mask and wafer are locked together, even if the vibration is at a level which causes negligible deterioration of the resolution. We have observed that waveform errors of λ/20, much better than required for diffraction limited performance, lead to image distortions of about 25 nm. These distortions can be corrected either in software or by using very high-quality optics. We expect consideration of all these effects will be required to align far below the optical resolution.
Vapor phase SiO2 etching and metallic contamination removal in an integrated cluster system
Authors: Ma Y. , Green M. L. , Feldman L. C. , Sapjeta J. , Hanson K. J. , Weidman T. W.
Published: July 2002

Vapor phase pregate oxide surface preparation was studied in a high vacuum cluster tool. SiO2 was etched with anhydrous vapor hydrogen fluoride and methanol vapor. The oxide etch rate can be well controlled by varying wafer temperature, chamber pressure, and gas flow rates. A standard error of 5% in oxide etch rate has been achieved. Particles generated are less than ten per 125 mm wafer at an oxide etch rate of 60 Å/min. Atomic force microscopy measurements reveal no added Si surface microroughness attributable to vapor hydrogen flouride (HF) etching. Trace metallic contaminants such as iron and chromium were reduced with UV/Cl2 based processes. A combination of vapor HF etching followed by UV/Cl2 metal removal is an effective pregate oxide surface preparation.
Fabrication of sub-30 nm masks for x-ray nanolithography
Authors: Haghiri-Gosnet A. M. , Vieu C. , Simon G. , Carcenac F. , Madouri A. , Chen Y. , Rousseaux F. , Launois H.
Published: July 2002

For the study of the ultimate resolution limits of x-ray nanolithography, i.e., the contact printing of features smaller than 30 n m, the biggest task is the production of x-ray nanomasks. The fabrication of such conventional masks with features as small as 12 nm for isolated dots and 25 nm for isolated lines is reported. High-energy electron beam lithography, using a transmission electron microscope operating at a voltage of 200 kV was carried out in a 400-nm-thick single resist layer with an electron probe of 1 nm in diameter. The ability of gold plating to enter very narrow structures is demonstrated here: 12 nm width absorber features with a thickness of 360 nm are obtained. We demonstrate that sub-30 nm features can be routinely produced with aspect ratios as high as 15 with a good process latitude.
Multiple-layer blank structure for phase-shifting mask fabrication
Authors: Pierrat Christophe , Siegrist Theo , deMarco John , Harriott Lloyd , Vaidya Sheila
Published: July 2002

A multiple-layer blank structure with two shifter layers coated on a quartz substrate is proposed for the fabrication of phase-shifting masks. The thickness of these shifter layers is such that they induce a 180° phase shift of light compared to air. On top of these shifter layers, an opaque layer is coated. The top shifter layer is patterned during the fabrication of the phase-shifting mask. The bottom shifter layer is patterned only to repair missing shifter defects. But the main purpose of this bottom layer is to act as an etch layer or give an end point during the repair of the phase defects or during the fabrication of the mask. Using yttrium fluoride etch stop/end point layer (bottom shifter layer), we have demonstrated the feasibility of multiple-layer blanks. This layer acts as an etch stop during the patterning of the main shifter layer and has a good refractive index match to that of quartz. The phase-shifting masks made using this multiple-layer blank structure have shown lithographic performances comparable to those of standard phase-shifting masks.
Cross-sectional imaging of semiconductor device structures by scanning resistance microscopy
Authors: Nxumalo J. N. , Shimizu D. T. , Thomson D. J.
Published: July 2002

Scanning resistance microscopy (SRM) is a scanning probe microscopy technique that performs localized contact resistance profiling over a semiconductor surface. Experimental results show that this technique can localize p-n junctions with a lateral spatial resolution of less than 35 nm. Here we present results from SRM imaging of a metal–oxide–semiconductor field-effect transistor and silicon on insulator cross sections. These results were obtained with a constant current SRM imaging technique. We also show that doped diamond tips can overcome some wear and resolution problems observed with metal tips.
Systematic investigations of nanostructuring by scanning tunneling microscopy
Authors: Köning R. , Jusko O. , Koenders L. , Schlachetzki A.
Published: July 2002

Scanning tunneling microscopes allow the formation of structures, by the application of voltage pulses between tip and sample whose dimensions are in the range of some nanometers. Systematic investigations have been carried out on the Si(111)-7×7 using W and Au tips in order to better understand the physics of the underlying deposition process. Therefore the voltage pulse, current, and z-piezo voltage were measured as a function of time. Above a threshold voltage, which depends on the pulse duration and the tunneling current, too, hills were created in the range between 5 and 25 nm. The surface structure was preserved up to the hills. Further, there is a linear dependence of the diameter on the pulse amplitude and pulse duration. A fit of the data gives a slope of (0.1±0.02) nm/s for tungsten tips and (0.45±0.14 nm/s) for gold tips, respectively. In addition, there is also a logarithmically dependence of the diameter upon the tunneling current for both tip materials. The results obtained are discussed with reference to the formation mechanisms published to date. None provide a satisfying explanation of our results.
Quantum transport: Silicon inversion layers and InAlAs–InGaAs heterostructures
Authors: Vasileska D. , Eldridge T. , Ferry D. K.
Published: July 2002

Using a real-time Green’s functions formalism, we investigate the influence of depletion charge scattering on the room temperature mobility in scaled silicon metal-oxide-semiconductor field-effect transistors and low-temperature transport in In0.4Al0.6As-In0.4Ga0.6As modulation doped heterostructures. Our simulation results suggest that depletion charge scattering, which is usually ignored, has considerable impact on the electron transport in silicon inversion layers near the threshold gate voltage, even at room temperature. We also find that the weighting coefficients a and b (for the inversion and depletion charge densities) strongly depend on the substrate doping and deviate from that reported in the literature. In the case of modulation doped heterostructures, the low-temperature mobility is limited by alloy and Coulomb scattering. Intersubband scattering considerably affects the broadening of the states which, in turn, leads to mobility reduction.
Heteroepitaxy of CdTe on {211} Si using crystallized amorphous ZnTe templates
Authors: Dhar N. K. , Wood C. E. C. , Gray A. , Wei H. Y. , Salamanca-Riba L. , Dinan J. H.
Published: July 2002

CdTe films were grown by molecular-beam epitaxy on As-passivated nominal {211} Si substrates using thin interfacial ZnTe buffer layers. ZnTe layers were grown by the following two growth methods: (1) migration enhanced epitaxy (MEE) directly on Si and (2) MEE on 80 Å templates of crystallized amorphous ZnTe buffers deposited directly on Si. CdTe films thicker than 8 μm had threading dislocation densities in the range of 2.5 to 4×106 cm−2 and 1 to 2×106 cm−2 for methods (1) and (2), respectively. Double crystal x-ray rocking curve peak widths decreased from 550 to 120 arcsec as CdTe film thickness increased from 3 μm to 9 μm for samples grown by method (1), and for samples grown by method (2), peak widths decreased from 300 to 84 arcsec in the same thickness range. CdTe film grown on vicinal {211} Si substrates misoriented by 5° toward [111] with ZnTe buffer layer prepared by method (2) had a dislocation density of 8×105 cm−2 and an x-ray peak width of 72 arcsec.
Molecular beam epitaxy of high-quality, nonstoichiometric multiple quantum wells
Authors: Melloch M. R. , Lahiri I. , Nolte D. D. , Chang J. C. P. , Harmon E. S. , Woodall J. M. , Li N. Y. , Tu C. W.
Published: July 2002

Multiple quantum wells (MQWs) have been grown at low substrate temperatures by molecular beam epitaxy so as to incorporate excess arsenic. This excess arsenic precipitates and preferentially coarsens to the lower band gap well regions with anneal. Despite the excess arsenic, these AlAs/GaAs MQW structures exhibit sharp excitonic features that are comparable to those exhibited by stoichiometric MQW structures grown at standard temperatures. In addition to the sharp excitonic transitions, these MQWs possess ultrafast recombination lifetimes making them attractive for photorefractive, electro-optic sampling, and saturable absorption applications.
Micropatterned polycrystalline diamond field emitter vacuum diode arrays
Authors: Kang W. P. , Davidson J. L. , Howell M. , Bhuva B. , Kinser D. L. , Kerns D. V. , Li Q. , Xu J. F.
Published: July 2002

Electron field emission from an array of patterned pyramids of polycrystalline diamond for vacuum diode applications has been investigated. High current emission from the patterned diamond microtip arrays was obtained at low electric fields. An emission current from the diamond microtips of 0.1 mA was observed for a field of <10 V/μm. Field emission for these diamond microtips exhibits significant enhancement in total emission current compared to silicon emitters. Moreover, field emission from patterned polycrystalline diamond pyramidal tip arrays is unique in that the applied field is found to be lower compared to that required for emission from Si, Ge, GaAs, and metal surfaces. The fabrication process utilizes selective deposition of diamond film in a silicon cavity mold and subsequent creation of free standing polycrystalline diamond diaphragm with diamond pyramidal microtip array. The processing techniques are compatible with integrated circuit fabrication technology.
Scanning tunneling microscopy based on the conductivity of surface adsorbed water. Charge transfer between tip and sample via electrochemistry in a water meniscus or via tunneling?
Authors: Heim M. , Eschrich R. , Hillebrand A. , Knapp H. F. , Guckenberger R. , Cevc G.
Published: July 2002

Thanks to the recently discovered high conductivity of molecular thin water films one can investigate poor conductors and even hydrophilic insulators in the scanning tunneling microscope (STM). Tip approach experiments have looked into the question of whether a permanent water meniscus between the tunneling tip and sample surface must be present while scanning across a water covered surface. For glow discharged Pt/C, gold and freshly cleaved mica we investigated whether the current increases continuously when approaching the tip or if jumps in the current distance behavior can be observed. Jumps in the current-distance curves indicate the buildup of a water meniscus. We found that the tendency of adsorbed water on Pt/C to build up a water bridge between tip and sample is very high at humidities above 55%. When the tip was retracted, the water bridge was pulled out to a length of several tens of nanometers. On gold no comparable effects were observed up to 75% relative humidity. In the case of mica, where surface adsorbed water is the only charge transmitter across the sample, the current was found to increase exponentially with decreasing tip–sample distance. This implies that STM imaging that uses the conductivity of thin surface adsorbed water is based on the tunneling effect and not on a permanent water bridge.
Structure and interfacial stability of (111)-oriented InAsSb/InAs strained-layer multiquantum well structures
Authors: Theiring Scott C. , Pillai Manoj R. , Barnett Scott A. , Wessels Bruce W.
Published: July 2002

Biaxially strained InAsxSb1−x/InAs (111)-oriented multiquantum well structures with x≈0.8 have been grown by metalorganic vapor phase epitaxy. The quality of the multiquantum well structures was assessed by double-crystal x-ray diffraction (θ–2θ scans) and kinematical computer simulations. The x-ray diffraction pattern of an InAs0.79Sb0.21/InAs multiquantum well film showed eight orders of satellite peaks, with a low diffuse background, indicating that excellent (111)-oriented structures can be achieved. The simulations modeled the compositional broadening of the interfaces, layer thickness fluctuations, and lattice spacing fluctuations of the compositionally modulated structures. The simulations indicated that the InAs/InAsSb interfaces were compositionally broadened over at least 0.5 nm, and that the layer thickness fluctuations of the highest quality structure were below the detection limit of 0.1 nm. Segregation of the antimony during deposition appears to be the primary cause of the compositional broadening. Simulations indicated that the layer thickness fluctuations increased with deposition rate, from less than 0.1 nm at a deposition rate of 8.4 nm/min to 1.2 nm at a deposition rate of 24 nm/min. The increase in the interface roughness was attributed to changes in surface reaction kinetics due to a shift in the III/V ratio at higher growth rates.
Electron beam lithography for 0.13 μm manufacturing
Authors: McCord Mark A.
Published: July 2002

General requirements for the use of electron beam lithography in direct write manufacturing of silicon integrated circuits are discussed. 50 keV is suggested as an optimum beam energy, since this is the minimum beam energy that can achieve high aspect ratio structures (4:1) in single layer resists in a manufacturing environment. Higher beam energies result in an inefficient exposure process requiring larger currents; this combination will lead to excessive resist and wafer heating. Lower voltages will require the use of top surface imaging or multilayer resists, which have concerns of processing complexity, resist charging, and defects. At 50 keV, some form of proximity correction is required to achieve reasonable control of critical dimensions. While one of the principle arguments for low voltage lithography is that it avoids the need for proximity correction, proximity correction is a solvable problem for large chips and is therefore a less risky approach than developing a reliable surface imaging resist technology. From a quick review of available resists and recent resist progress, it appears that a sensitivity of 5 μC/cm2 at 50 kV is the best that will be achieved in the next several years. Neglecting overheads, for a design point of 40 8 in. wafers/h, a peak beam current of 13 μA for a raster scan or projection tool is required. One of the major challenges of designing a tool with such high beam currents is controlling space charge effects so that there is minimal impact on lithographic quality. After discussing the characteristics of various high speed electron beam writers that have been made to date, it will be concluded that there are two types of systems that have the best chance of meeting all of the requirements—a projection system such as SCALPEL, and a multibeam system with hundreds of independently blanked beamlets. These systems minimize space charge effects by spreading out the electrons through a larger volume of space, allowing a larger total beam current. However, in order to make these systems a commercial reality, a great deal of innovation, research, and development are still required.
Nanoscale colloidal particles: Monolayer organization and patterning
Authors: Sato T. , Hasko D. G. , Ahmed H.
Published: July 2002

The monolayer deposition of nanoscale colloidal particles (Au citrate sols) was demonstrated by employing an aminofunctional silane [3-(2-Aminoethlyamino) propyltrimethoxysilane] as a coupling agent. The compatibility of this colloidal Au deposition method with conventional electron beam lithography techniques was examined, and the two-dimensional patterning of the Au colloidal monolayer was demonstrated. Using this fabrication method, a proposal for a single electron device structure based on nanoscale (2 nm diameter) gold colloidal particles was made.
Force modulation atomic force microscopy recording for ultrahigh density recording
Authors: Hosaka S. , Koyanagi H. , Kikukawa A. , Miyamoto M. , Nakamura K. , Etoh K.
Published: July 2002

We propose force modulation atomic force microscopy (FM)-(AFM) pit recording and demonstrate the possibility of achieving ultrahigh density recording with high speed readout. A minimum pit size of around 10 nm in diameter is formed by cold plastic deformation of the polycarbonate disk surface at a force of over 40 nN. Using a prototype of the rotation type FM-AFM pit recording system, an ultrahigh recording density of 1.2 Tb/in.2 and a readout speed of 1.25 Mb/s are demonstrated in 1/2(2,7) code recording.
Investigation of existing defects and defect generation in device-grade SiO2 by ballistic electron emission spectroscopy
Authors: Wen H. J. , Ludeke R.
Published: July 2002

Degradation processes initiated by defect generation in device-grade SiO2 were studied by locally injecting hot electrons from a scanning tunneling microscope tip into Pd/SiO2/p-Si(100) metal–oxide semiconductor (MOS) structures. An analysis of the emerging collector current in the Si substrate, a technique known as ballistic electron emission microscopy, provides electron transport information, from which the oxide defect generation process was studied. The charging of the defects resulted in shifts of threshold energies for electron transport across the oxide. A novel sheet charge model was developed to assess the in-depth distribution and charge densities in the oxide from field-induced threshold shifts obtained from experiment. An as-fabricated MOS system with an oxide thickness of 71 Å was investigated and found to contain existing electron traps of charge densities in the range (0.7–2.8)×1013 e/cm2 that are distributed within a 30 Å region adjacent to the metal/oxide interface. Further stressing was performed at zero oxide bias with increasing tip voltages of up to −10 V. New electron traps characterized by charge densities of (1.9–3.6)×1013 e/cm2 and located within 40 Å of the SiO2/Si interface were generated when the kinetic energy of the electrons injected into the SiO2 conduction band exceeded 1.9 eV. This energy threshold is in very good agreement with the hydrogen-release energy that is frequently invoked to explain oxide degradation.
Field emission of nitrogen doped diamondlike carbon films deposited by plasma enhanced chemical vapor deposition
Authors: Park Kyu Chang , Moon Jong Hyun , Chung Suk Jae , Jang Jin
Published: July 2002

The N doping effect on the electrical conductivity and electron emission property for diamondlike carbon (DLC) films deposited by plasma enhanced chemical vapor deposition (PECVD) has been studied. The electrical conductivity can be widely varied by n-type doping of the DLC. The relationship between the prefactor of conductivity and the conductivity activation energy satisfy the Meyer–Neldel relation: σ0=σ00 exp(AEa) with A=19 eV−1 and σ00=9×10−8 S/cm. The emission current for heavily N doped DLC films is much higher than that of undoped DLC even though the lightly N doped film shows much smaller current.
Temperature effect on surface flatness of molecular beam epitaxy homoepitaxial layers grown on nominal and vicinal (111)B GaAs substrates
Authors: Guerret-Piecourt Christelle , Fontaine Chantal
Published: July 2002

For the first time a comparison is made between the surface characteristics of layers simultaneously grown on nominal and on vicinal (111)B substrates under the 1×1 reconstruction regime which provides flat surfaces for both orientations. The influence of growth temperatures, 600 and 700 °C, on surface characteristics is thoroughly reviewed based on an atomic force microscopy study. This study yields additional insight into results already reported on growth mechanisms occurring along these two orientations for the 19×19 growth regime. For the nominal (111)B layers, it will be shown that monoatomic steps at the surfaces define large atomically flat plateaus at both temperatures. At 600 °C, growth will be shown to proceed mainly through the development of two-dimensional nuclei, which are limited in size to a critical value and can coalesce by a proximity effect. These nuclei will be shown to be much smaller at 700 °C, thereby turning the step flow into the main mechanism occurring at that temperature. For the vicinal orientation, monoatomic-stepped and step-bunched surfaces grown at 600 and 700 °C, respectively, will be obtained under our 1×1 growth conditions, the same as in the 19×19 regime.
Effects of gas distribution on polysilicon etch rate uniformity for a low pressure, high density plasma
Authors: Khater Marwan H. , Overzet Lawrence J. , Cherrington Blake E.
Published: July 2002

The geometry of low pressure inductively coupled plasma sources is usually considered to be a main factor in determining both the plasma and processing uniformity over large area wafers. We demonstrate experimentally that the gas flow distribution can have a major impact on both the plasma density and etch rate uniformity at low pressures where one might expect diffusion to make gas flow distribution less important. 150 mm polysilicon on oxide wafers were etched in SF6/Ar (1:1) plasmas between 6 and 20 mTorr. Using a single gas inlet produced polysilicon etch rates that varied by 30% along the gas flow direction, but were highly uniform perpendicular to the gas flow direction. A gas distribution ring, on the other hand, produced highly uniform etch rates with variations less than 4% overall using the same source. Langmuir probe measurements of the ion saturation current spatial profiles in argon and SF6 discharges demonstrated significant gradients across the reactor for a single gas inlet with the largest current density near the inlet.
EL5: One tool for advanced x-ray and chrome on glass mask making
Authors: Sturans M. A. , Hartley J. G. , Pfeiffer H. C. , Dhaliwal R. S. , Groves T. R. , Pavick J. W. , Quickle R. J. , Clement C. S. , Dick G. J. , Enichen W. A. , Gordon M. S. , Kendall R. A. , Kostek C. A. , Pinckney D. J. , Robinson C. F. , Rockrohr J. D. , Safran J. M. , Senesi J. J. , Tressler E. V.
Published: July 2002

The state-of-the-art for mask making continues to be driven by 1× x-ray masks. The IBM EL4+ e-beam mask writer at the Advanced Mask Facility in Burlington, Vermont, was originally designed for 0.35 μm ground rules (GRs) direct write at 50 kV, but delivered at 75 kV operation to achieve 0.25 μm GR performance for 1× mask making. Over the next 2 years, with optimization and improvements in each of the subsystems, its performance was enhanced beyond the 0.18 μm GR requirements. It is clear, however, that for 0.13 and 0.1 μm GR mask manufacturing, a new tool is required. It has also become apparent that because of the very high development and tool build costs, and small number of required x-ray mask makers, the same technology must be applicable for chrome on glass (COG) mask making. Based on the experience with EL4+, IBM is designing an EL5 tool which will provide the 0.13/0.1 μm GR performance for 1×, and easily convert to 4× COG exposure for 9 in. glass as well as 300 mm wafer direct write operation. As with previous IBM EL series e-beam systems, it is anticipated that EL5 performance will be extendable beyond 0.1 μm GR.