bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-consistent solutions of electronic wave functions at GaAs–AlxGa1−xAs interfaces
Authors: Rajakarunanayake Y. , McGill T. C.
Published: July 2002

We report the first study of the self-consistent electronic wave functions at a heavily doped GaAs–AlxGa1−xAs interface. The doping densities in the GaAs are between 1017 and 1019 cm−3. These doping densities are characteristic of tunnel structure devices. The Schrödinger equation is solved self-consistently in the Hartree approximation. Some of the more important results of our calculations include the fact that there is only a single subband level in the well for a wide range of biases. This level is also fairly loosely bound (bound by a few meV) in spite of the fact that the notch at the interface is on the order of a 100 meV. In accumulation layers, the potential at the interface is somewhat similar to the non-self-consistent one. However, in depletion layers the self-consistent potential can be substantially different from the one obtained in the Thomas–Fermi approximation.
Implant and impurity redistribution during ion induced TaSi2 formation
Authors: Galuska A. A.
Published: July 2002

The formation of TaSi2 by 121Sb+ bombardment of Ta films on 〈100〉 Si was examined as a function of ion dose, temperature during implantation, and postimplantation rapid thermal annealing. The redistribution of Sb, C, and O was determined during the various treatments. In addition, the influence of this redistribution on silicide formation was evaluated. Ion induced TaSi2 growth exhibited a linear dose dependence that was weakly influenced by substrate temperature (200–400 °C) during ion bombardment. Under these conditions, TaSi2 growth was dominated by atomic mixing rather than radiation enhanced diffusion. Interfacial carbon layers were readily dispersed by ion bombardment, and did not greatly influence TaSi2 growth. In contrast, O and Sb segregated to the surface and the TaSi2/Si interface during ion bombardment. These O- and Sb-rich layers inhibited both Si diffusion and subsequent TaSi2 growth. Postimplant annealing resulted in the buildup of both interfacial C and O. Complete silicide formation was only accomplished at temperatures (1000 °C) sufficient for Si diffusion through the interfacial barriers and Sb surface depletion. Film characterization was performed using Rutherford backscattering spectrometry, secondary ion mass spectrometry, scanning electron microscopy, and x-ray diffraction.
Geometrical design of an alignment mark for focused ion beam implantation in GaAs using Monte Carlo simulation of ion trajectories
Authors: Morita Tetsuo , Miyauchi Eizo , Arimoto Hiroshi , Takamori Akira , Bamba Yasuo , Hashimoto Hisao
Published: July 2002

The geometrical features of an alignment mark for a precisely aligned focused ion beam (FIB) implantation in GaAs were studied. To optimize the shape etched on a GaAs wafer for various implantation conditions such as incident ion energy, beam diameter 2b, and ion species in addition to the sidewall angle θ and etched depth, intensity profiles of secondary electrons from the alignment mark were calculated by the Monte Carlo method. It was confirmed that the calculated results agreed with the experimental ones. The optimum depth dopt for an FIB alignment mark is given by dopt=2b tan θ regardless of the incident ion energy (80–200 keV) or the ion species (Si and Be). Fine pattern doping can be performed using this optimized mark.
Performance of a 20–200 kV focused-ion-beam system with a new optical design concept
Authors: Aihara R. , Sawaragi H. , Morimoto H. , Hosono K. , Sasaki Y. , Kato T. , Hassel Shearer M.
Published: July 2002

A computer controlled focused-ion-beam system (JIBL-200S) with a new optical design concept has been developed. The JIBL-200S has good focusing properties over a wide-accelerating voltage range. A double-mode optical system has been provided in order to improve the focusing properties for the low-accelerating voltage region. In this system the two einzel lenses are operated in the decel mode (central electrode positive) for beam accelerating voltages above 100 kV and in the accel mode (central electrode negative) below 100 kV. This reduces a chromatic aberration for the low energy beams. The beam diameter for a Ga ion was measured using a knife edge and Faraday cup. As a result, compared to the conventional mode of operation, the beam size is improved to 0.09 from 0.15 μm at 75 kV and to 0.13 μm from 0.20 μm at 50-kV-accelerating voltage by changing the operating mode. The writing performance was also evaluated by the use of a vernier pattern writer on a Si substrate coated with chloromethylated polymethylstyrene resist exposed with 250-keV-Si++ ions. Overlay accuracies of 0.183 μm in the X axis and 0.243 μm in the Y axis 3σ were obtained.
A Monte Carlo simulation of electron beam lithography used to create 0.5-μm structures on GaAs
Authors: Cummings K. D. , Resnick D. J.
Published: July 2002

We have used a positive trilevel resist structure on GaAs to verify our general purpose calculations of electron beam lithography. The model uses a single-scattering Monte Carlo simulation of electron–solid interactions, a simple dissolution rate versus energy model for the resist, and a string model for resist development. The spot size of the electron beam was varied from 0.2 to 0.4 μm in diameter. Experimental results on scanning electron microscopy linewidths and wall profiles are in good agreement with the simulation. Using the model, we have determined the change in process latitude with increasing spot size. However, we find that the lithography process is still able to create 0.5-μm lines even with large (0.4-μm) spots.
Reflection high-energy electron diffraction oscillations during growth of metallic overlayers on ideal and nonideal metallic substrates
Authors: Purcell S. T. , Arrott A. S. , Heinrich B.
Published: July 2002

Oscillations in the intensity of reflection high-energy electron diffraction (RHEED) patterns are observed for Fe, Ni, Au, and Mn overlayers epitaxially grown in various combinations on Fe, Ni, Au, Ag, and Ru substrates. Fe whickers are nearly ideal substrates for the study of RHEED and RHEED oscillations during growth. Oscillations for metals and semiconductors show similar dependence on temperature, diffraction angles, and surface impurities.
Sample geometry effects in rapid thermal annealing
Authors: Ruggles G. A. , Hong S. N. , Wortman J. J. , Sorrell F. Y. , Ozturk M. C.
Published: July 2002

Sample geometry has been shown to be a significant factor in determining the actual temperature of samples annealed in thermocouple controlled rapid thermal processing systems. Temperature differences of nearly 25 °C have been observed between full 4 in. wafers and quarter wafers under identical annealing conditions. Some of the geometry effects observed can affect the validity of temperature measurements in pyrometer controlled systems as well. The changes in sample temperature can be measured directly via thermocouples, and indirectly via secondary ion mass spectrometry (SIMS) and resistivity mesurements of ion implanted samples. Smaller samples are observed to heat up faster, and obtain a slightly higher maximum temperature than larger samples. Based on computer modeling this effect is attributed to the absorption of reflected/scattered radiation in addition to that directly incident on the sample. Small samples placed on top of full wafers during annealing are observed to heat up more slowly than the underlying wafer. This effect is likely due to imperfect thermal contact between the samples during the anneal. Small boron implanted samples annealed on top of whole wafers such that the implanted side is in contact with the whole wafer appear to experience a slight reduction in boron outdiffusion, similar to the reduced As outdiffusion observed for comparable anneals of GaAs wafers. In order to correctly compare reported temperature data from the literature, these geometry effects must be taken into consideration.
Electrodeposition of low stress gold for x-ray mask
Authors: Chiu Shih-Liang , Acosta R. E.
Published: July 2002

In order to maintain the dimensional accuracy of an x-ray mask, the residual stress of the absorber must be kept low (in the low range of 108 dyn/cm2 ). The absorber material studied in this paper is pure gold electroplated from a proprietary plating solution. Stress of the gold deposits is measured by holographic interferometry of bending disk/beam experiments. The effects of temperature, current density, thickness, pH, and pulse plating on the stress of the gold are investigated. The aging behavior of the plating solution is also discussed. The stress of electroplated gold does not show a strong dependence on the current density (1–5 mA/cm2 ). However, aging of the plating solution changes the stress of the gold deposits, especially for those obtained at a current density of ∼1 mA/cm2. Pulse plating produces stress levels similar to those given by dc plating, over a wide range of on-current-density, on-time, and off-time. Moreover, the pH of the solution does not affect the stress of gold when the current density is greater than 1 mA/cm2. Hence a plating solution and process has been found that produces low stress gold (≤4×108 dyn/cm2) over a wide range of operating conditions and shows no adverse effects upon aging over an extended period of time.
Design of a high resolution focused ion beam system using liquid metal ion source
Authors: Zhou Li , Orloff Jon
Published: July 2002

We have made a Monte Carlo simulation to design a high resolution ion beam column with a liquid metal ion source (LMIS), which employs Koehler illumination. The use of Koehler illumination is one of the few ways to avoid the problem caused by the non-Gaussian current density profile, which is due to the stochastic angular broadening of the ion beam near the source. Thus we can predict a 20 nm beam spot size with 1 nm edge sharpness and about 1 pA of ion current on the target plane at 100 keV beam energy with a Ga LMIS.
An investigation of the properties of cubic GaN grown on GaAs by plasma-assisted molecular-beam epitaxy
Authors: Strite S. , Ruan J. , Li Z. , Salvador A. , Chen H. , Smith David J. , Choyke W. J. , Morkoç H.
Published: July 2002

We present the first comprehensive investigation of the bulk properties, both optical and structural, of cubic GaN as grown by plasma-assisted molecular-beam epitaxy on vicinal (100) GaAs substrates. X-ray measurements determined the crystal structure of GaN/GaAs to be cubic with a lattice constant of 4.5 Å. High resolution transmission electron microscopy revealed a high density of planar defects propagating along the GaN {111} planes. The majority of the defects originated from disordered regions at the GaN/GaAs interface. The optical properties of the films were investigated by cathodoluminescence which revealed a broad midgap peak as well as several sharp emission peaks just below the expected band gap. The data imply that the room temperature band gap of cubic GaN is approximately 3.45 eV.
Transport and optical properties of semiconductor quantum wires
Authors: Forchel A. , Menschig A. , Maile B. E. , Leier H. , Germann R.
Published: July 2002

We have fabricated III–V semiconductor quantum wires which display a variety of novel transport and optical phenomena. For the definition of structures with widths down to 40 nm high resolution electron beam lithography and dry etching have been used. For the observation of dimensionality dependent effects in optical spectra buried quantum wires have been developed by overgrowth of dry etched structures and implantation induced intermixing. The physical properties of the nanometer structures have been analyzed by magnetotransport studies and emission spectroscopy.
Growth in ultrahigh vacuum and structural characterization of FeSi2 on Si(111)
Authors: Lagomarsino S. , Scarinci F. , Giannini C. , Castrucci P. , Savelli G. , Derrien J. , Chevrier J. , Le Thanh V. , Grimaldi M. G.
Published: July 2002

FeSi2 films grown in ultrahigh vacuum on Si (111) substrates by solid phase epitaxy (SPE) have been characterized by several in situ and ex situ structural techniques: reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD), and Rutherford backscattering (RBS). The results on a film a few hundred angstroms thick confirm that the FeSi2 which forms in these conditions is the semiconducting β phase and that an epitaxial growth takes place with the (202) and/or (220) FeSi2 planes parallel to the Si (111) planes. The lattice mismatch measurements in films as thin as 100 Å indicate that the films are little or no elastically strained, at least at a FeSi2 growth temperature of 600 °C.
Increased range of Fermi-level stabilization energy at metal/melt-grown GaAs(100) interfaces
Authors: Chang S. , Vitomirov I. M. , Brillson L. J. , Rioux D. F. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: July 2002

We report a room temperature soft x-ray photoemission spectroscopic study of electronic barrier formation and chemistry at Al, Ag, and Au contacts with horizontal Bridgman-grown GaAs(100) surfaces, prepared by etching, heat-cleaning in situ, and As-capping. As reported previously, we observe a pronounced chemical reaction with formation of dissociated Ga for Al, a minimal interface reaction for Ag, and interdiffusion for Au. However, we find significant differences in the interface electronic barrier heights between the present metal/melt-grown GaAs(100) contacts and those made on cleaved (110) surfaces as well as on melt-grown (100) surfaces. We obtain Schottky barrier heights of 0.62, 0.85, and 1.03 eV respectively for Al, Ag, and Au/GaAs interfaces covering a range of 0.41eV—in contrast to the 0.2–0.3 eV range obtained earlier for both cleaved (110) and heat-cleaned (100) surfaces as well as the 0.7 eV range observed for metal/molecular beam epitaxy GaAs(100) interfaces. This intermediate behavior underscores the dependence of barrier height variation on different growth and interface processing techniques.
Kinetics and mechanism of silicon dioxide deposition through thermal pyrolysis of tetraethoxysilane
Authors: Raupp Gregory B. , Shemansky Frank A. , Cale Timothy S.
Published: July 2002

Intrinsic silicon dioxide deposition rate dependences from tetraethoxysilane (TEOS) thermal pyrolysis were measured in an experimental cold wall low-pressure chemical vapor deposition reactor designed to minimize reactant depletion and gas-phase reactions. The apparent activation energy of 90 kJ mol−1±16 kJ mol−1 over the range of temperatures from 873 to 1073 K is significantly lower than that typically measured in commercial or development-scale hot wall reactors. The reaction rate exhibits a first order dependence on TEOS pressure. Film deposition proceeds without a nucleation-induced incubation period. Interpretation of deposited film profiles in high aspect ratio trenches through rigorous ballistic transport-reaction simulation reveals that deposition most likely occurs through a heterogeneous mechanism in which strong readsorption of the byproducts of TEOS decomposition inhibits silicon dioxide deposition.
Photoemission spectroscopic techniques to assess physical and chemical properties of mercury cadmium telluride
Authors: Seelmann-Eggebert M.
Published: July 2002

The contribution of photoemission to the understanding of electronic, chemical, and structural properties of HgCdTe is reviewed. Angle integrated and angle resolved techniques of x-ray photoelectron spectroscopy are discussed and their potential for characterizing the surface region of processed compound semiconductor materials is explored with respect to depth compositional profiling and with respect to assessing the crystalline surface structure. Each technique is exemplified by an experimental application to HgCdTe.
Influence of oxygen on the formation of ripples on Si
Authors: Elst K. , Vandervorst W. , Alay J. , Snauwaert J. , Hellemans L.
Published: July 2002

An extensive study of the ripple formation on Si is presented. The ripples are characterized with atomic force microscopy (AFM) as a function of sputter depth and also the effect of the introduction of oxygen gas near the sample is investigated. Based on these results, a two-step model is proposed for the formation of the ripples on Si. The first step relates to the formation of small topography (seeds) caused by the heterogeneity of the internal layer. The second step relates to the rapid development of these seeds into the regular ripple structure. The driving force for the latter is the surface oxidation of the different faces of the ripples. The validity of the separation in two steps is additionally checked by studying the effect of deliberately roughened samples. The chemically induced topography with a height of no more than 10 nm is shown to move forward the transient region quite severely suggesting that the origin of the roughness does not have any influence on the subsequent ripple formation. Interestingly enough, the AFM pictures of the ripple development reveal that the random distribution of the original topography gradually evolves into a structure aligned in a direction normal to the incident beam. The shape of the final structure is not linked with the original topography indicating that it is dictated by ion beam induced effects. The importance of the bulk heterogeneity compared with the surface oxidation is explored using argon bombardment in combination with O2 flooding. As expected on the basis of the proposed model, no ripples were formed when bombarding an unetched sample but large ripples were generated when starting from the rough samples.
GaAs surface control during metalorganic vapor phase epitaxy by reflectance anisotropy spectroscopy
Authors: Reinhardt F. , Richter W. , Müller A. B. , Gutsche D. , Kurpas P. , Ploska K. , Rose K. C. , Zorn M.
Published: July 2002

GaAs(001) surfaces are studied during metalorganic vapor phase epitaxy by reflectance anisotropy spectroscopy (RAS). In analogy to RAS spectra measured from GaAs(001) surfaces under ultrahigh vacuum conditions which were simultaneously controlled by reflection high-energy electron diffraction or low-energy electron diffraction certain surface reconstructions can be assigned to specific RAS spectra. Arsenic-rich disordered (4×4), centered (4×4), and (2×4) like surfaces are identified during deoxidation of the substrate at pregrowth heating. After starting growth the RAS signal shows oscillations the period of which corresponds to the growth of 1 ML of GaAs. This is verified by postgrowth layer thickness measurements. A (4×4) reconstructed surface before growth turns out to be the necessary condition for the appearance of these monolayer oscillations in the RAS signal.
Cross-sectional scanning tunneling microscopy on heterostructures: Atomic resolution, composition fluctuations and doping
Authors: Salemink H. W. M. , Johnson M. B. , Albrektsen O.
Published: July 2002

Cross-sectional scanning tunneling microscopy on semiconductor structures is evolving into a technique to analyze structural, chemical, and electronic properties on the atomic and nanometer scale in all spatial dimensions, in particular, in the lateral and in-depth spatial dimensions of the structure. This technique has been used on the ultrahigh vacuum cleaved (110) plane of (001)-grown AlGaAs/GaAs heterostructures. Measurements of (i) interface roughness, alloy fluctuations, and ordering; (ii) the variation of electronic properties over an interface as well as fluctuations within the alloy; and (iii) the distribution of individual dopant sites are reported on.
Detection of anomalous defect-enhanced diffusion using advanced spreading resistance measurements and analysis
Authors: Weinzierl S. R. , Hillard R. J. , Heddleson J. M. , Rai-Choudhury P. , Mazur R. G. , Osburn C. M.
Published: July 2002

Advanced spreading resistance measurements and analysis techniques are used to determine the dopant profiles in two ultra-shallow silicon metal–oxide–semiconductor source/drain structures which were germanium preamorphized prior to implant. Although the two structures differ only slightly in their anneal temperature and time, there is a significant difference in the metallurgical junction depths of the implants. It is proposed that the difference in junction depths is related to defect-enhanced transient diffusion.
Dead-time-free selective dry etching of GaAs/AlGaAs using BCl3/CHF3 plasma
Authors: Takenaka Hiroshi , Oishi Yoshiro , Ueda Daisuke
Published: July 2002

A dead-time-free selective dry etching of GaAs/AlGaAs using mixed plasma of BCl3 and CHF3 has been developed. The selectivity of the etching for GaAs/AlGaAs is strongly dependent on the flow ratio R, where R=(flow of CHF3)/(flow of CHF3+ flow of BCl3). It was also found that the angle of the sidewall can be varied from overhanging to tapered by controlling R. No undercutting was observed. Complete vertical recess structures with sub-quarter micrometer width were obtained at R=40% where a selectivity of 30 was attained. The roughness of the etched surface was also strongly dependent on R. A smooth etched surface was obtained where R was larger than 40% even for bulk GaAs. Complete square-shaped vertical recessed structures with sub-quarter micrometer width were obtained in a GaAs/AlGaAs epitaxial wafer. This etching process is very applicable for the fabrication of GaAs/AlGaAs heterojunction devices such as the GaAs modulation doped field-effect transistor and the heterojunction bipolar transistor.
Fabrication of n-metal–oxide semiconductor field effect transistor with Ta2O5 gate oxide prepared by plasma enhanced metalorganic chemical vapor deposition
Authors: Kim Sun-Oo , Kim Hyeong Joon
Published: July 2002

n-metal–oxide semiconductor field effect transistors (MOSFETs) were fabricated with plasma enhanced metalorganic chemical vapor deposited Ta2O5 gate oxide on Czochralski grown Si wafers using localized oxidation of silicon isolation technology by the conventional Si-based process. The Ta2O5 gate oxide n-MOSFETs showed excellent electrical characteristics such as subthreshold swing of 68–74 mV/dec, transconductance of 4 μS/μm for 4 μm gate length, and carrier mobility of 400 cm2/V s at the saturation region. The large Cox of the gate oxide with the high dielectric constant, εr=20–25, allowed the higher drain current of the device. During the whole process of n-MOSFET fabrication, the cross sectional transmission electron microscopy analysis of the Ta2O5/Si interface showed SiO2 interfacial oxide formation of about 35 Å thick. The Ta2O5 gate oxide n-MOSFET showed good performance compared to the high-temperature silicon oxide gate devices and thus has great potential for applications in the electronic devices.
Sulfide passivation of III–V semiconductors: The starting electronic structure of a semiconductor as a factor in the interaction between its valence electrons and the sulfur ion
Authors: Bessolov Vasily N. , Ivankov Andrey F. , Lebedev Mikhail V.
Published: July 2002

In the experiments on GaAs, InP, and GaP treated in aqueous solutions of Na2S:9H2O, it has been shown that in the process of sulfide passivation of III–V semiconductors a significant role is played by both the starting electronic structure of the semiconductor surface (prior to sulfidizing) and the energy state of the sulfur ion in solution. A model of the interaction of the sulfur ion in a solution with the valence electrons of a III–V semiconductor in the course of the sulfidizing process has been suggested and verified. During the interaction process, a change takes place in the electrochemical potential (Fermi level) of the semiconductor, which affects the electron work function at the surface. Between various semiconductors the amount of this change in the work-function value varies in proportion to the negative of the starting electron work-function value in the untreated semiconductor and depends on the treatment temperature. In a semiconductor such that its starting work-function value is equal to the effective electronegativity of the sulfur ion in solution, the work function will not be changed by sulfidization. The effective electronegativity of the sulfur ion in solution depends on the ionicity of the chemical bonds of the semiconductor being treated.
Scaling of Si and GaAs trench etch rates with aspect ratio, feature width, and substrate temperature
Authors: Bailey A. D. , van de Sanden M. C. M. , Gregus J. A. , Gottscho R. A.
Published: July 2002

The scaling of etch rates with feature dimensions is an important issue in the fabrication of microelectronic and photonic devices. Because etch rates depend on circuit layouts and design rules, considerable effort is spent to modify processes each time changes in design are made. Knowing how etch rates scale with design parameters should accelerate the introduction of new designs into manufacturing while minimizing the cost of doing so. Recently it has been shown that etch rates for a variety of conditions scale with the depth/width or aspect ratio and not on width or depth alone. While various mechanisms might be responsible for such scaling, isolating one mechanism from another is not straight forward. Nonetheless, it is important to understand the underlying mechanisms so that differences in etch chemistry and etch reactor design can be accounted for when scaling plasma processes from one design or reactor to another. To assess the effects of etch chemistry alone, the trench etch rates of Si and GaAs are compared under constant plasma conditions. Substrate temperature is varied to further assess the relative importance of surface vs transport phenomena during the etching process.

At higher temperatures, both Si and GaAs trench etch rates scale only with aspect ratio in an Ar/Cl2 electron cyclotron resonance plasma. The results are consistent with an ion-neutral synergy model based on Langmuir adsorption kinetics where the scaling can be explained by the aspect ratio dependence of the neutral reactant transport into the trench: charging effects, ion shadowing, and Knudsen transport are not consistent with the data. At −45 °C, the etch rate no longer scales with aspect ratio alone, but now also depends on trench width. The data at this lower temperature are well described by a model incorporating the deposition of an etch inhibiting layer. While the trench etch rates for GaAs and Si scale in similar ways with aspect ratio and trench width, the dependence on feature dimensions of the Si etch rate is much stronger than that for GaAs at all substrate temperatures because the steady-state surface coverage of Cl is smaller for Si. This results in a greater sensitivity to the incoming, aspect ratio dependent, neutral fluxes. The implications of the models on the goal of aspect ratio independent etching are also discussed.
Chemical vapor deposition TiN process for contact/via barrier applications
Authors: Paranjpe Ajit , IslamRaja Mazhar
Published: July 2002

Chemical vapor deposition (CVD) TiN is an attractive replacement for PVD TiN as a barrier and glue layer for subhalf-micron contacts and vias. CVD TiN films have been deposited in a commercial reactor via the thermal decomposition of tetrakis-dimethyl-amino-titanium (TDMAT) precursor in an N2 ambient. The deposition can be characterized by a simple Arrhenius rate expression with a half-order dependence on TDMAT concentration and an activation energy of 0.53 eV. Designed experiments show that the deposition transitions from being kinetically limited at high TDMAT flow rates and low temperatures to transport limited at the other extreme. In the kinetically limited regime, the deposition rate increases with increasing TDMAT mole fraction and increasing temperature. Step coverage simulations have been performed by coupling SPEEDIE (a profile evolution program) with the Arrhenius rate expression. Experimental and simulated step coverages show good agreement over a wide range of process conditions. Step coverage improves with increasing deposition rate and decreasing temperature. Adequate deposition rates (≳400 Å/min) with good deposition uniformity and high step coverage (50%–85%) can be achieved. Film stress and roughness are mostly invariant with process conditions. These films are close to stoichiometric (i.e., 1:1 Ti:N ratio), but contain up to 30% carbon. Exposure of these films to air causes rapid oxidation with a steady state concentration of 15%–20% oxygen after 24 h of air exposure.

The high carbon concentration results in high film resistivity (5000 μΩ cm), which doubles after 24 h of air exposure due to oxidation of the film. Film resistivity decreases and film stability improves with increasing N2 flow rate. Electrical characterization of two process variants have been performed. The first provides a film with 85% step coverage with a resistivity of 5600 μΩ cm, while the second process achieves a lower resistivity of 3700 μΩ cm and a lower step coverage of 50%. Electrical performance of both films is similar. Contact induced diode leakage is lower for CVD TiN compared to PVD TiN. Contact resistance for 100–200 Å CVD TiN is comparable or lower than 500 Å PVD TiN. A 100 Å CVD TiN barrier is adequate; 300 Å CVD TiN is too thick because of high film resistivity. An Al–Cu/100–300 Å CVD TiN/Si stack shows lower resistance increase after 450–500 °C, 30 min N2 anneal compared to a Al–Cu/200 Å PVD TiN/Si stack indicating that CVD TiN is a superior barrier and is more inert than PVD TiN.
Alignment of a multilayer-coated imaging system using extreme ultraviolet Foucault and Ronchi interferometric testing
Authors: Ray-Chaudhuri A. K. , Ng W. , Cerrina F. , Tan Z. , Bjorkholm J. , Tennant D. , Spector S. J.
Published: July 2002

Multilayer-coated imaging systems for extreme ultraviolet (EUV) lithography at 13 nm represent a significant challenge for alignment and characterization. The standard practice of utilizing visible light interferometry fundamentally provides an incomplete picture since this technique fails to account for phase effects induced by the multilayer coating. Thus the development of optical techniques at the functional EUV wavelength is required. We present the development of two EUV optical tests based on Foucault and Ronchi techniques. These relatively simple techniques are extremely sensitive due to the factor of 50 reduction in wavelength. Both techniques were utilized to align a Mo–Si multilayer-coated Schwarzschild camera. By varying the illumination wavelength, phase shift effects due to the interplay of multilayer coating and incident angle were uniquely detected.
Adsorption and reaction of NO on Si(111) studied by scanning tunneling microscopy
Authors: Röttger B. , Kliese R. , Neddermeyer H.
Published: July 2002

By using scanning tunneling microscopy, low-energy electron diffraction, and Auger electron spectroscopy adsorption and reaction of NO on Si(111)7×7 at 860 K and the effect of subsequent annealing to 1230 K have been studied. The latter results are compared with those obtained on a surface which has been heated to 1260 K during NO exposure. In both cases the previously described ‘‘8×8’’ structure has been obtained. At 860 K etching of Si and formation of oxynitride islands are found at the same time. In scanning tunneling microscopy the 8×8 structure appears as a rather regular array of protrusions in a mean distance of 8/3 aSi. No indications of the previously proposed coincidence lattice structure [A. G. Schrott and S. C. Fain, Jr., Surf. Sci. 123, 204 (1982)] are seen in the scanning tunneling microscopy results.
Selective wet etching of lattice-matched InGaAs/InAlAs on InP and metamorphic InGaAs/InAlAs on GaAs using succinic acid/hydrogen peroxide solution
Authors: Fourre Hervé , Diette Frédéric , Cappy Alain
Published: July 2002

A selectivity study of the etching of lattice matched (LM) InGaAs/InAlAs on InP and metamorphic (MM) InGaAs/InAlAs on GaAs in succinic acid: hydrogen peroxide solutions is reported. Selectivities as high as 70 and 1030 are, respectively, obtained for the LM and MM InGaAs on InAlAs. Observations and measurements with an atomic force microscope of narrow recess and under-resist etch on LM InP materials are also presented. The ability of these solutions for fabrication of InGaAs/InAlAs heterojunction field effect transistors is discussed.
Tetramethoxysilane as a precursor for focused ion beam and electron beam assisted insulator (SiOx) deposition
Authors: Lipp S. , Frey L. , Lehrer C. , Frank B. , Demm E. , Pauthner S. , Ryssel H.
Published: July 2002

Focused ion beams are intensively used for device modification by local material removal and ion beam induced metal deposition. With shrinking dimensions on modern multilayer devices, the need for ion beam induced insulator deposition is increasing. In this article, tetramethoxysilane as a precursor for ion beam induced deposition has been investigated. The influence of beam parameters dwell time and loop time on the material deposition rate will be discussed and compared to model calculations. For optimized scanning conditions, a maximum deposition rate of 0.33 μm3/nC was found. Insulating films were also deposited using an electron beam. The chemical composition and electrical properties of these films were compared with the films deposited by the ion beam. For electron beam deposition, the resistivity of the deposited films was 1×106 Ω cm which is two orders of magnitude higher than for ion beam deposited film.
Neutral shadowing in circular cylindrical trench holes
Authors: Abraham-Shrauner Barbara , Chen Wenjing
Published: July 2002

The neutral flux in the plasma etching of semiconductor wafers has been derived analytically for a simplified model for a circular cylindrical trench hole (circular via). The neutral molecules obey a Maxwellian distribution function and mutual collisions are neglected in the trench. Scattering of the neutrals with the sidewalls and trench bottom is ignored. The flux vector is given at each point on the etching profile surface. The flux vector reduces to the expression previously determined at the center of the trench. Etching profiles of the trench are displayed for neutral flux-limited etch rates.
Magnetic behavior of FexNi(1−x) and CoxNi(1−x) pseudomorphic films
Authors: Wu S. Z. , Schumann F. O. , Mankey G. J. , Willis R. F.
Published: July 2002

We set out to compare the ferromagnetic behavior of FexNi(1−x) and CoxNi(1−x) films of varying stoichiometry epitaxially grown on Cu(100). The thickness chosen was 5 ML over a wide alloy composition range. Using a scaling law for the thickness vs Curie temperature, we extrapolate the bulk fcc film thickness and plot the bulk fcc Curie temperature as a function of composition. The results suggest (a) that the Invar effect is quenched in these ultrathin pseudomorphic fcc films of FexNi(1−x) alloys and (b) the magnetic phase of Fe atoms is the low-spin ferromagnetic phase. The CoxNi(1−x) films show the expected monotonic decrease in Tc with increasing Ni content.
Adsorption and decomposition of C60 molecules on Si(111) surfaces
Authors: Chen Dong , Workman Richard K. , Sarid Dror
Published: July 2002

Adsorption of C60 molecules on Si(111)-(7×7) has been studied using scanning tunneling microscopy under ultrahigh vacuum conditions at a variety of temperatures and coverages. At submonolayer coverages, isolated C60 molecules were found to adsorb preferentially in the areas near the three midadatoms within a half unit cell of (7×7) symmetry. At monolayer coverage, the adsorbate–adsorbate interaction changes the molecular bonding sites and causes the local ordering of the C60 adlayer. Thermal annealing to temperatures above 800 °C causes the decomposition of C60 molecules on the Si surface and the formation of SiC clusters.
Surface and interface effects on ellipsometric spectra of crystalline Si
Authors: Bell K. A. , Mantese L. , Rossow U. , Aspnes D. E.
Published: July 2002

We present the first systematic investigation of the differences among reference-quality ellipsometrically measured pseudodielectric function 〈ε〉 spectra of crystalline Si, which are nominally used to approximate the bulk dielectric function of this material. In addition to the expected influence of residual overlayers, we identify surface-local-field and energy-derivative effects, the latter representing shifts between bulk and measured critical point energies, as well as changes in excited-carrier lifetimes due to the surface. Model calculations indicate that these four effects account for nearly all differences among spectra studied, although a second-energy-derivative component appears at the E1 transition in some cases. The isotropic contribution to the surface-local-field effect is observed for the first time.
Novel C60–DDME complex thin film with electrical bistable properties
Authors: Ouyang M. , Xue Z. Q. , Wang K. Z. , Wu Q. D. , Qiang D.
Published: July 2002

A novel C60–DDME complex thin film was prepared by a new modified vacuum deposition technique. Stable and reproducible electrical bistable properties are observed in the C60–DDME thin films. The structure and spectroscopy characteristics of the complex C60–DDME thin film are considerably different from those of both DDME and C60 thin films, as is revealed by high resolution scanning electron microscopy, x-ray diffraction, and ultraviolet-visible absorption spectra.
Novel effects in inorganic As50Se50 photoresists and their application in micro-optics
Authors: Lyubin V. , Klebanov M. , Bar I. , Rosenwaks S. , Eisenberg N. P. , Manevich M.
Published: July 2002

Some novel properties of one-layer inorganic As50Se50 photoresists are demonstrated. The photosensitivity of the photoresists increases drastically (1000 times and more) upon exposure to short intense light pulses. The exposure characteristics can be changed from steep to gently sloped ones. The photoresists can be used effectively in both negative and positive modes. Combination of these properties with good optical properties such as a high refractive index, high transparency in the IR and high resolution, makes As50Se50 photoresists attractive for application in nonconventional optics. Close packed spherical and cylindrical microlens arrays for IR based on the As50Se50 photoresists are fabricated and tested. The advantage of this technique is in the elimination of thermal reflow and plasma etching that are commonly used.
Fabrication and characterization of silicon field emitter arrays with focusing electrode by the chemical mechanical polishing process
Authors: Lee Jin Ho , Song Yoon-Ho , Kang Seung-Youl , Kim Sang Gi , Cho Kyoung Ik , Yoo Hyung Joun
Published: July 2002

We have fabricated silicon field emitter arrays with focusing electrodes by chemical mechanical polishing (CMP) process. After the formation of very sharp tips, the gate electrodes were formed by a CMP process. A very high etching selectivity (>100:1) between the gate electrode and the gate dielectric was used for preventing the tip to be etched off during the CMP. The dishing problem during the CMP process of the gate electrode was solved by forming an oxide masking layer on top of the gate electrode. After the formation of the extracting (first) gate electrode, the second electrode for focusing the electron beam was formed. By the CMP process, a clear-cut gate electrode was easily obtained which was aligned exactly to the tip. The equipotential contours and electron trajectories were simulated for a single emitter that has an extracting gate and a focusing electrode using a two-dimensional finite element method.
GaInAsP/InP distributed feedback lasers grown directly on grated substrates by solid-source molecular beam epitaxy
Authors: Hwang W.-Y. , Baillargeon J. N. , Chu S. N. G. , Sciortino P. F. , Cho A. Y.
Published: July 2002

Successful growth of 1.3 and 1.55 μm GaInAsP/InP multiquantum well lasers directly on a distributed feedback (DFB) grating substrate using all solid-source molecular beam epitaxy was demonstrated. A 1.12 μm wavelength GaInAsP planarization layer with a nominal thickness of 500–650 Å was first grown on the DFB gratings at an elevated temperature to create a smooth surface for subsequent layer growth. Transmission electron micrograph showed smooth interfaces after the growth of this GaInAsP planarization layer. Low threshold current density and high quantum efficiency were obtained from these index-coupled DFB lasers.
Artifacts in low-energy depth profiling using oxygen primary ion beams: Dependence on impact angle and oxygen flooding conditions
Authors: Wittmaack K.
Published: July 2002

The depth resolution and the accuracy of depth calibration in sputter profiling of boron delta distributions in silicon have been investigated using 1 keV O2+ ion bombardment at impact angles θ between 2° and 62° (to the surface normal) in combination with secondary ion mass spectrometry. The effect of jet-type oxygen flooding during sputter erosion was studied at 62°. For θ up to 34°, the depth resolution was essentially independent of θ (full width at half maximum, FWHM, 2.9 nm, decay length 1.4 nm) and also independent of depth (for deltas located between 40 and 190 nm). However, the well-known peak shift due to the initial short-term change in erosion rate was a factor of 2.7 larger at 34° than at 2° (3.5 vs 1.3 nm). As θ exceeded about 36°, two other types of artifacts were observed during bombardment in vacuum, (i) a severe profile broadening and (ii) a large long-term change in erosion rate which gave rise to crater-depth dependent peak shifts of the deltas (erosion rate reduced for 41°<θ<62°, but enhanced for 36°<θ<40°). Both effects became more severe as the sputtered depth became larger. In accordance with the previous surface topography investigations, the observed changes of the matrix ion signals provide evidence for a rapid onset of bombardment induced surface roughening, or ripple formation, starting at depths as low as about 15 nm. The artifacts were most severe at angles between 47° and 52°, in which case, at a depth of 190 nm, the FWHM increased to as much as 13 nm. In parallel, the erosion rate, averaged over depth intervals of 41–51 nm, decreased continuously by up to 23%. As a result, the 41 nm boron delta appeared to be shifted towards the surface by as much 6 nm. The very large changes in erosion rate invalidate depth calibration procedures based on final crater-depth measurements. At 62°, the depth profiling artifacts were significantly enlarged by oxygen flooding, notably at intermediate pressures, at which ripples grew so rapidly that the FWHM of boron deltas located at a depth of only 88 nm amounted to 13 nm. Even at the highest tolerable oxygen pressure (5×10−6 hPa), the FWHM was a factor of about 2 larger than at normal or near-normal beam incidence in vacuum. Furthermore, the decreasing erosion rate gave rise to an apparent 4 nm shift of the 41 nm delta towards the surface. We conclude that 1 keV O2+ bombardment at oblique incidence (36°<θ<62°) always gives rise to rapid ripple growth in vacuum and apparently also with oxygen flooding. Accurate depth profiles cannot be obtained under these conditions.
Enabling in situ atomic-scale characterization of epitaxial surfaces and interfaces
Authors: Smathers J. B. , Bullock D. W. , Ding Z. , Salamo G. J. , Thibado P. M. , Gerace B. , Wirth W.
Published: July 2002

A custom designed sample handling system which allows the integration of a commercially available scanning tunneling microscope (STM) facility with a commercially available molecular beam epitaxy (MBE) facility is described. No customization of either the STM imaging stage or the MBE is required to implement this design.
Scanning tunneling microscopy studies of formation of 8×5 reconstructed structure of Ga on the Si(001) surface
Authors: Nakada Yoshinobu , Aksenov Igor , Okumura Hajime
Published: July 2002

The behavior of Ga on the Si(001) 2×1 surface has been studied for Ga coverage of 0.8 monolayers and annealing temperatures in the range 623–863 K by means of scanning tunneling microscopy. Annealing at the lowest annealing temperature Ta leads to the formation of the Ga 2×2 phase, which is a result of self-arrangement of Ga dimers, as well as irregular Ga clusters. An increase in Ta to 673 K results in the formation of a partially ordered metastable Ga 5×2 phase, whereas further increase in Ta leads to the transformation of the 5×2 structure into 8×n (n=4,5) structure, the degree of order of which gradually increases with an increase in the annealing temperature. At Ta=833 K the surface is uniformly covered by the periodically aligned arrays of 8×5 units, this 8×5 structure is believed to consist of the ordered double-layered Ga clusters having 24–26 Ga atoms in the first layer and four Ga atoms in the second layer. The 8×5 units are out of registry with the underlying Si surface in one direction, this uncoupling from the surface is believed to be caused by Ga–Ga interactions. Further increase in Ta up to 863 K results in the evaporation of the Ga atoms from the surface giving rise to the redimerization of the Si and Ga atoms and reappearance of the Ga 2×2 phase.
Investigation of thickness effects on AlN coated metal tips by in situ I–V measurement
Authors: Kang D. H. , Zhirnov V. V. , Wojak G. J. , Preble E. A. , Choi W. B. , Hren J. J. , Cuomo J. J.
Published: July 2002

The effects of the aluminum nitride coating thickness on molybdenum emitter tips were investigated by an in situ I–V measurement technique inside a typical magnetron sputtering system. AlN was deposited on Mo tips using a dc-modulated 1 kW power source at 200 °C. Each I/V measurement was carried out immediately following a 15 s AlN deposition. Significantly improved field emission was observed as well as a strong emission thickness dependence, which we attribute to the influence of space charge.
Experimental comparison of off-axis illumination and imaging interferometric lithography
Authors: Chen Xiaolan , Brueck S. R. J.
Published: July 2002

Imaging interferometric lithography (IIL) has been proposed recently to extend optical lithography (OL) to the linear systems resolution limit of optics. In this work, a comparison of IIL and OL with off-axis illumination (OAI) is presented with both numerical simulations and experimental verification. In OAI, the optical modulation transfer function decreases at higher spatial frequencies as a result of the inclusion of the same low frequencies in more than one of the incoherently related offset exposures. Pupil plane filters avoid this multiple counting of the low frequency components and improve the pattern fidelity. Different filters provide different tiling of spatial frequency space and result in significant differences in the final patterns. Results of different tiling schemes for both OAI and IIL approaches are discussed. Overall, IIL provides the most robust imaging results.