bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of a velocity selected, pulsed source of hyperthermal (1–10 eV) neutral metal atoms for thin film growth studies
Authors: Knowles Matthew P. , Leone Stephen R.
Published: July 2002

The laser-induced vaporization by back-illumination technique is shown to generate well characterized, repetitively pulsed beams of hyperthermal neutral Co atoms with kinetic energies ranging from 1 to 10 eV. At a repetition rate of 10 Hz, and a distance of 0.53 m, 2×1011 Co atoms/cm2 per pulse are produced with less than 2×107 ions/cm2 per pulse, These beams can be used as an ultrahigh vacuum deposition source for thin film growth studies. The hyperthermal beam is deposited on polished Si(100) wafers and particulates deposited by the beam are detected using ex situ scanning electron microscopy. A mechanical chopper allows tunable velocity selection of the fast neutral atoms and is shown to eliminate particulates from the beam. Line-of-sight time-of-flight quadrupole mass spectrometry is used to measure kinetic energy distributions. Applications of the novel hyperthermal neutral atom source to kinetic energy enhanced neutral epitaxy are discussed.
Plasma-enhanced chemical vapor deposition of boron nitride thin films from B2H6–H2–NH3 and B2H6–N2 gas mixtures
Authors: Andújar J. L. , Bertran E. , Polo M. C.
Published: July 2002

Highly transparent and stoichiometric boron nitride (BN) films were deposited on both electrodes (anode and cathode) of a radio-frequency parallel-plate plasma reactor by the glow discharge decomposition of two gas mixtures: B2H6–H2–NH3 and B2H6–N2. The chemical, optical, and structural properties of the films, as well as their stability under long exposition to humid atmosphere, were analyzed by x-ray photoelectron, infrared, and Raman spectroscopies; scanning and transmission electron microscopies; and optical transmittance spectrophotometry. It was found that the BN films grown on the anode using the B2H6–H2–NH3 mixture were smooth, dense, adhered well to substrates, and had a textured hexagonal structure with the basal planes perpendicular to the film surface. These films were chemically stable to moisture, even after an exposition period of two years. In contrast, the films grown on the anode from the B2H6–N2 mixture showed tensile stress failure and were very unstable in the presence of moisture. However, the films grown on the cathode from B2H6–H2–NH3 gases suffered from compressive stress failure on exposure to air; whereas with B2H6–N2 gases, adherent and stable cathodic BN films were obtained with the same crystallographic texture as anodic films prepared from the B2H6–H2–NH3 mixture. These results are discussed in terms of the origin of film stress, the effects of ion bombardment on the growing films, and the surface chemical effects of hydrogen atoms present in the gas discharge.
Radial distributions of ion velocity, temperature, and density in ultrahigh-frequency, inductively coupled, and electron cyclotron resonance plasmas
Authors: Nakano Toshiki , Samukawa Seiji
Published: July 2002

Spatially resolved velocity distribution functions of metastable chlorine ions are measured in ultrahigh-frequency (UHF) plasma and compared with those in electron cyclotron resonance (ECR) plasma and inductively coupled plasma (ICP). In UHF plasma, ion velocity distribution function (IVDF) perpendicular to the surface normal of a wafer exhibits approximately no acceleration of ions to the side wall of a plasma reactor as the measuring point becomes radially far from the center of the reactor, even at 14 cm from the center where IVDF’s are shifted evidently in ECR plasma and ICP. This indicates that an almost flat profile of plasma potential is realized along the radius of the reactor in UHF plasma. As a consequence, metastable chlorine ion temperature remains low and almost constant over a radius of 14 cm in UHF plasma. Relative density of metastable chlorine ions in UHF plasma increases toward the side wall of the reactor. In contrast to this, the density exhibits a maximum in the center of the reactor and decreases towards the side wall in ECR plasma and ICP. The increased densities near the side wall in UHF plasma imply increased plasma production off the symmetry axis of the reactor, which makes UHF plasma uniform in a wider region than in ECR plasma and ICP. The effect of the discharge frequency on radial distribution of metastable chlorine ion density is also discussed.
Characterization and modeling of a Helicon plasma source
Authors: Cheetham A. D. , Rayner J. P.
Published: July 2002

An experimental and theoretical investigation of a Helicon plasma source has been completed as a precursor to the development of an automatic system for controlling the operation of such sources. The number density in an argon plasma has been observed over a parameter space defined by the input variables of filling pressure (1–100 μbar), magnetic field (0–450 G) and rf power (0–1250 W). Four distinct modes of operation have been identified, namely: electrostatic, inductive, Helicon and high pressure Helicon modes. A global model of the source has been modified to include the effect of radial confinement by the axial field. Comparisons with the experimental results show that the model generally can predict the plasma density to within 15%–20% for both the inductive and Helicon modes. It is found that the ratio of the ion cyclotron radius compared with the radius of the plasma is a useful measure of the amount of confinement. An alternative measure based on the product of the ion cyclotron frequency and the collision time for momentum transfer does not lead to satisfactory agreement between the global model and the experimental observations. The modified global model appears to describe the behavior of the plasma well enough to allow the development of a conventional control system that can be used within each of the modes. The model, however, is unable to predict the locations of the mode jumps within the parameter space.
Deposition of molybdenum thin films by an alternate supply of MoCl5 and Zn
Authors: Juppo Marika , Vehkamäki Marko , Ritala Mikko , Leskelä Markku
Published: July 2002

Molybdenum thin films were deposited onto both soda lime glass and Al2O3 film by an alternate supply of MoCl5 and Zn. Zinc was used as a reducing agent. The film growth was performed over a temperature range of 400–500 °C in order to study the temperature effect on the growth. In addition to the growth temperature, the purge length after zinc was also seen to have a considerable effect on the growth. The films were analyzed by energy dispersive x-ray spectroscopy, scanning electron microscopy, elastic recoil detection analysis, x-ray diffraction and four point resistance measurements in order to determine their chemical and physical characteristics.
In situ observations of nucleation and coalescence stages in Ge growth on Si surfaces using transmission electron microscope combined with molecular beam epitaxy chamber
Authors: Hiroyama Yuichi , Tamura Masao
Published: July 2002

Nucleation and defect formation processes were observed for the heteroepitaxial growth of Ge on Si(100), (110), and (111) substrates, using an ultra-high-vacuum transmission electron microscope (TEM) combined with a conventional molecular beam epitaxial growth chamber. Successive plan-view TEM images clearly showed that the changes in the radius of Ge islands as a function of film thicknesses depend on the orientations of Si substrates. The behavior of the misfit-strain relaxation in Ge islands was found to be independent of the substrate orientations. The formation of threading dislocations was shown by discontinuity in the moiré fringes between the coalesced Ge islands at 50 monolayer (ML) deposition. Twins and stacking faults, respectively, were also observed in Ge islands on (110) and (111) substrates in the early stages of 25–50 ML growth.
Diagnostics and modeling in a pure argon plasma: Energy balance study
Authors: Kelkar U. M. , Gordon M. H. , Roe L. A. , Li Y.
Published: July 2002

A self-consistent pseudo-one-dimensional (zero-dimensional with diffusion) plasma model and optical emission spectroscopy are used in tandem to investigate the power coupling efficiency for a pure argon microwave plasma. The self-consistent model is developed by simultaneously solving the Boltzmann equation (for the non-Maxwellian electron energy distribution function), electron number density balance equation, energy balance equation, and the excited state rate equations in a collisional-radiative model. The absolute line emission intensity is utilized to obtain number densities of three argon excited states [4p (7147 Å), 5p (4300 Å), and 5d (6043 Å)] in a 5 Torr, 680 W input power argon discharge. The absolute continuum emission from the plasma was utilized to determine the maximum electron number density. A comparison of the numerical and experimental data indicates that only 2%–5% (10–35 W) of the input power is deposited in the plasma. A control volume heat transfer analysis validates this claim. The experimentally determined energy balance shows that the remaining input power (645–670 W) bypasses the plasma and is dissipated in the reactor cooling systems.
Deep anisotropic etching of silicon
Authors: Aachboun S. , Ranson P.
Published: July 2002

We are interested in etching very deep anisotropic trenches (∼100 μm) with high aspect ratios (depth/width) (∼20–50) and high etch rates (∼5 μm/min). A high density plasma helicon reactor using SF6/O2 chemistry and a cryogenic chuck has been used for etching very narrow trenches from 1.2 to 10 μm wide on n-type Si wafers with a SiO2 mask. The first results show significant features that demonstrate the feasibility of this method. Two-micron-wide trenches have been etched to a depth of 80 μm at an average etch rate of 2.7 μm/min. The resulting profiles are highly anisotropic and selectivity of Si/SiO2 is remarkably high (>500).
Comparison of Cl2 and F2 based chemistries for the inductively coupled plasma etching of NiMnSb thin films
Authors: Hong J. , Caballero J. A. , Lambers E. S. , Childress J. R. , Pearton S. J.
Published: July 2002

Plasma etching chemistries based on BCl3/Ar, BCl3/H2 and NF3/Ar were studied for patterning NiMnSb Heusler alloys thin films and associated Al2O3 barrier layers in an inductively coupled plasma tool. Using BCl3/Ar discharges, high etch rates (⩾1 μm/min) were achieved either at high source power [(1000 W) or high direct current (dc) self bias (−300 V)] and etch rates showed a strong dependence upon source power, ion energy, and gas composition. Hydrogen addition to the BCl3 created new species (HCl) in the plasma, leading to faster etch rates for NiMnSb than in the case of Ar addition. Selectivities of ⩾8 for NiMnSb over Al2O3 were obtained in BCl3-based discharges. On the other hand, NF3/Ar discharges provided a narrow process window for the etching of NiMnSb and the etch rates were much lower compared to those with BCl3. The surfaces of NiMnSb etched with NF3/Ar was smoother (root-mean-square surface roughness of 1.4 nm measured by atomic force microscopy) than the surfaces produced with BCl3/Ar. In terms of near-surface chemistry, NF3/Ar produced Mn enrichment, indicating the existence of involatile Mn etch products, whereas Mn deficiency was obtained under the same conditions with BCl3/Ar.
Effects of moisture on Fowler–Nordheim characterization of thin silicon-oxide films
Authors: Peterson Charles A. , Workman Richard K. , Sarid Dror , Vermeire Bert , Parks Harold G. , Adderton Dennis , Maivald Peter
Published: July 2002

A conducting-tip atomic force microscope was used as a Fowler–Nordheim characterization tool of thin silicon oxides. The system was operated under a controlled environment using novel cantilevers fabricated from platinum/iridium wire and nickel foil. With this tool, humidity-dependent field-induced oxidation of the samples and variations in the tunneling current due to uneven water layer coverage were investigated. It is shown that baking the samples and characterizing them under a dry environment alleviates problems arising from the humid environment.
Metalorganic chemical vapor deposition of barium strontium titanate thin films with a more coordinatively saturated Ti precursor, Ti(dmae)4(dmae=dimethylaminoethoxide)
Authors: Lee Jung-Hyun , Kim Joo-Young , Shim Jae-Young , Rhee Shi-Woo
Published: July 2002

A more coordinatively saturated Ti precursor [Ti(OCH2CH2NMe2)4, Ti(dmae)4] (dmae=dimethylaminoethoxide) has been synthesized and characterized by 1H variable temperature nuclear magnetic resonance (NMR) and mass spectrometry. Ti(dmae)4 exists as a monomer in the liquid state. Chemical vapor deposition of barium strontium titanate (BST) thin films with direct liquid injection of Ba(tmhd)2-PMDT (tmhd=2,2,6,6-tetramethyl-3, 5-heptanedionate, PMDT=pentamethyl diethylenetriamine), Sr(tmhd)2-PMDT, and Ti(dmae)4 was studied. Ba and Sr incorporation into the BST film was almost constant (Ba/(Ba+Sr)=0.5) at a deposition temperature (Ts) range of 420–500 °C, and the amount of Ti incorporation was substantially higher than that of Ti(tmhd)2(i-OPr)2(i-OPr=isopropoxide,tmhd=tetramethyl-heptanedionate) or Ti(tmhd)2(mpd) (mpd=methylpentanediol). The hump and the hazy appearance detected in the BST film deposited with the previous Ti precursors were not detected with the new Ti precursor. The step coverage and properties of the BST films deposited with this new titanium source were also studied.
Modulated structures and metastable dopant concentrations in silicon annealed with Q-switched laser pulses
Authors: Cullis A. G.
Published: July 2002

Radiation pulses from Q-switched lasers can be used to transiently melt and modify the near surface regions of solids. Indeed the annealing is of such short duration that new, extremely rapid solidification phenomena are now amenable to study. Most work has probed the basic crystal growth behavior of elemental Si. This process is often strongly influenced by the presence of high concentrations of impurities: either growth instabilities or metastable, supersaturated solid solution formation may occur. At the highest resolidification rates (≳10 m/s) the recrystallization interface can break down with the formation of an amorphous solid phase. This paper describes the various processes which can occur and identifies limiting behavior in high speed crystal growth.
SiO2/InP interfaces with reduced interface state density
Authors: Wager J. F. , Clark M. D. , Jullens R. A.
Published: July 2002

By employing a new InP surface preparation procedure based upon KOH/methanol, the interface state density of plasma-enhanced chemically vapor deposited SiO2/InP structures has been significantly reduced. Capacitance–voltage characteristics of these structures exhibit unusual nonequilibrium behavior which appears to be assoicated with the formation of a p-type inversion layer and with the presence of interface traps with very slow response times. This surface preparation procedure yields an InP native oxide which has no detectable In2O3 and is contaminated with K.
The application of Doppler shift laser fluorescence spectroscopy for the detection and energy analysis of particles evolving from surfaces
Authors: Husinsky Wolfgang
Published: July 2002

Doppler shift laser fluorescence spectroscopy (DSLFS) has been developed in the last few years as a powerful tool to measure densities and energy distributions of neutral particles. Its main application described in this paper is the study of particles ejected from surfaces under impact of atoms, ions or electrons. Complications and controversies in the interpretation of DSLFS spectra will be discussed. The major achievements and applications of the method over the last few years will be presented. One of the most important results has been a deeper insight into the composition of the particle fluxes ejected from surfaces under ion beam bombardment in respect to the degree of surface oxidation. This has been possible due to the fact that DSLFS enables us to measure the densities and energy distributions of neutral particles in specific electronic states. As a direct consequence, a large amount of information on sputtered excited atoms has recently been obtained by DSLFS.
An electron beam lithography system for submicron VHSIC device fabrication
Authors: King H. J. , Merritt P. E. , Otto O. W. , Ozdemir F. S. , Pasiecznik John , Carroll A. M. , Cavan D. L. , Eckes W. , Lin L. H. , Veneklasen L. , Wiesner J. C.
Published: July 2002

A direct write electron beam lithography system has been constructed which is capable of writing 0.5 μm VHSIC patterns at a rate of 4 to 25 four−inch wafer levels per hour. The several key subsystems which permit this increase in performance over existing systems are (1) A variable shaped beam which exposes rectangular or triangular shapes from 0.5 to 2.0 μm in size at a current density up to 200 A/cm2; (2) an all digital, 100 MHz pattern generator with optical couplers for high speed, low noise data processing; (3) a unique deflection system with specially designed 18 bit digital to analog converters and ultralinear amplifiers; (4) a mechnaical state capable of 10 cm/s speed and 0.8 g acceleration, under microprocessor control, providing write-while-moving capability and synchronization with the pattern generator; and (5) a wafer handler system for cassette-to-cassette input/output; and (6) a complimentary software package which constructs files with the necessary data compaction for rapid transmission and proximity correction for proper exposure.
High resolution distortion measurements of electron-beam transmission masks
Authors: Zapka W. , Nehmiz P. , Bohlen H.
Published: July 2002

Electron-beam proximity printing (EBP) is a step-and-repeat lithography technique which uses masks. Stringent requirement for submicron lithography is the capability to compensate for ever present linear and nonlinear mask distortions. We have demonstrated that a slight modification of the EBP system converts this into a high resolution mask metrology tool, i.e., enabled us to measure absolute distortions of our e-beam transmission mask in the EBP lithography tool itself. Resolution of these measurements was ±50 nm. Relative mask distortion data as deduced from our results coincided with separate experimental results from overlay experiments.
A combined electron and ion beam lithography system
Authors: Cleaver J. R. A. , Ahmed H.
Published: July 2002

In scanning beam microfabrication processes, including resist exposure, direct maskless ion implantation, and micromachining, ions and electrons have complementary roles. It is advantageous to have, within a single scanning beam machine, finely focused and precisely coregistered beams of both ions and electrons. The requirement for the ion beam and the electron beam to have a common axis and to be focused at the target by a high resolution lens with short working distance can be met both by solely electrostatic and by combined magnetic and electrostatic lenses. Such lenses, and complete probe-forming systems incorporating them, are considered.
Summary Abstract: Internal photoemission studies of (GaIn)As, (AlIn)As Schottky diodes and (GaIn)As/(AlIn)As heterojunction grown by molecular beam epitaxy
Authors: Hsieh K. H. , Wicks G. , Calawa A. R. , Eastman L. F.
Published: July 2002

We report the first internal photoemission studies of GaInAs and AlInAs Schottky diodes in the infrared region. The photoresponses exhibit very high external quantum yield (about 1.22%) and high speed response (rise time smaller than 115 ps). Internal photoemission response has also been observed for the first time for a GaInAs/AlInAs heterojunction diode, due to the conduction band discontinuity at the interface. An internal barrier height of 0.4 eV was obtained.
Proposals and experiments on large area exposure in synchrotron radiation lithography
Authors: Tanino H. , Hoh K. , Hirata M. , Atoda N. , Ichimura S.
Published: July 2002

Novel methods are proposed to enlarge the vertical (normal to the plane of electron orbit) width of the exposed area in synchrotron radiation (SR) lithography. They are the shaping of the cross section of the SR beam by a fixed toroidal mirror with specified parameters and the superposition of the reflected SR beams from fixed planar mirrors onto the upper and lower peripheries of the straight beam. An experimental verification is presented and merits and demerits of these methods are compared with other methods including novel radiation sources proposed by us recently.
0.5 μ SWAMI/NMOS process technology with electron beam lithography
Authors: Liu E. David , Chiu Kuang Y. , Rissman Paul , Choong Hsia
Published: July 2002

This paper describes the process design and device characteristics of NMOS transistors with 0.5  μ mask layout in both channel width and channel length. Direct write electron beam lithography was used to fabricate submicron features. SWAMI (side wall masked isolation) and oxide spacer techniques were used to reduce both 2 Δ W and 2 Δ L to less than 0.3  μ with 6500 Å field oxide and 200 Å gate oxide. The device characteristics show that the threshold voltage of a 0.5  μ transistor is about 0.8 V, while the punch through and breakdown voltages are greater than 6.5 V. Short channel and narrow channel effects will also be presented.
Submicron pattern fabrication by focused ion beams
Authors: Kato T. , Morimoto H. , Saitoh K. , Nakata H.
Published: July 2002

A focused ion beam (FIB) technology has many advantages for submicron structure fabrication and other maskless processes. In order to develop 4–16 M(D) RAM, the FIB technology is strongly desired for its capability of submicron lithography without proximity effects.
Nanometer metal-oxide-semiconductor field-effect transistors: A flexible tool for studying inversion layer physics
Authors: Mankiewich P. M. , Howard R. E. , Jackel L. D. , Skocpol W. J. , Tennant D. M.
Published: July 2002

The fabrication of multiterminal silicon MOSFET’s containing channel segments as narrow as 30 nm is described. These can be used for a variety of fundamental studies of quantum transport. In particular, in 100-nm channels, spatially localized voltage measurements can be made probing the scattering effects of a single electron trap.
Oxygen reactive ion etching of organosilicon polymers
Authors: Watanabe F. , Ohnishi Y.
Published: July 2002

The relationship between etching characteristics and silicon content for organosilicon polymers has been studied. Under oxygen reactive ion etching (O2-RIE) conditions, the etching rate for the polymers became constant after an initial rapid decrease. An etching kinetic study was carried out to account for this behavior. It is confirmed from electron spectroscopy for chemical analysis (ESCA) data that a protective layer, which has high resistance against O2-RIE, is formed on the polymer surface and that most silicon atoms exist in the form of SiO2 at the protective layer surface. The etching rate for the polymers in a steady state is inversely proportional to the silicon content. The etching rate for quartz glass is in good agreement with the value extrapolated from this relationship. These results suggest that the rate determining step in the etching process is the sputtering of SiO2 formed by the polymer oxidation. Furthermore, for a polymer with a lower silicon content than a threshold value, the protective layer is porous, so that the underlying polymer is attacked by radical species during O2-RIE. The threshold silicon content is about 0.15 g/cm3.
Fast electron pattern generator–high resolution: A variable shaped beam system for submicron writing
Authors: de Chambost E. , Frichet A. , Chartier M. , The H. Ta , Trotel J.
Published: July 2002

Fast electron pattern generator–high resolution (FEPG-HR) is a variable shaped electron beam system, derived from FEPG, specially designed for submicron direct writing, while keeping the multipurpose capabilities. Quarter-micron linewidth is expected, thanks to a high demagnification of the stencil, reduction of the space charge effect, improvements in accurate metrology, and automatic calibration.
Effect of Sn in plasma copolymerized methylmethacrylate and tetramethyltin resist on plasma development for x-ray irradiation
Authors: Hori Masaru , Hattori Shuzo , Yoneda Takashi , Morita Shinzo
Published: July 2002

Plasma copolymerized methylmethacrylate and tetramethyltin [PP(MMA–TMT)] was prepared using an inductively coupled gas flow-type reactor. The atomic ratio of tin to carbon (Sn : C) in PP(MMA–TMT) was varied from 0 to 0.15 by changing the gas flow rate ratio of both TMT and MMA monomers. The characteristic of PP(MMA–TMT) as a resist was evaluated in dry lithography processes, in which the resist was exposed to radiation of CuKα (main wavelength: 1.54 Å) and x-ray imaged pattern in the resist was developed by Ar–20% O2 mixture gas plasma using a parallel plate electrode-type reactor. The sensitivity of positive resist was defined by the minimum dose rate that the resist in the exposed part was etched off when the remaining thickness at the unexposed part became about 38% of the initial film thickness under the plasma development. PP(MMA–TMT) resist showed the highest sensitivity of 8 J/cm2 at Sn : C of 0.046. The molecular structure of PP(MMA–TMT) film was investigated by electron spectroscopy for chemical analysis (ESCA) and infrared (IR) analysis and discussed in relation to its quality as a resist.
The role of gas phase reactions, electron impact, and collisional energy transfer processes relevant to plasma etching of polysilicon with H2 and Cl2
Authors: Krogh Ole , Wicker Tom , Chapman Brian
Published: July 2002

Plasma etching of silicon with H2 and Cl2 was simulated with mixtures of H2, Cl2, and SiCl4. The gas phase chemistry was elucidated by varying power and pressure. The cross sections for production of H (3p2P) atoms were probed through the emission response to pressure variations. Addition of rare gases to a hydrogen plasma identified qualitatively major energy transfer paths between the rare gas metastables and the H2/H system. We conclude that dissociation of hydrogen molecules and excitation of hydrogen atoms are separate electron impact collisional events that constitute the main excitation route in a hydrogen plasma. We find further that the role of metastable H atoms in the 2s2S state at 10.19 eV is minor, and that the direct dissociative excitation in a single electron impact at 16.57 eV is insignificant. The occurrence of state specific collisional energy exchange has limiting consequences for any actinometric method.
Anomalous I–V characteristics of semiconductor heterojunction diodes due to transmission resonance
Authors: Zohta Yasuhito , Tsuda Kunio , Hiraoka Yoshiko Someya
Published: July 2002

As sizes of semiconductor devices are reduced, quantum mechanical properties of electrons play an important role. For small heterojunction diodes including a potential barrier, the influence of transmission resonance on current–voltage characteristics is discussed. The diodes have been prepared using a GaAs–AlxGa1−xAs system by MBE. A preliminary result shows the anomalous I–V curve which is presumed to be due to transmission resonance.
A process dependent study of Al/Si/Cu very large scale integration metallization. I. Spectroscopic properties
Authors: Hong C. , Hance R. L. , Pyle R. E.
Published: July 2002

Spectroscopic characterization of samples of sputter-deposited Al/Si/Cu very large scale integration metallization 1.3 μ thick having 1 wt. % Si and 0.0, 0.2, 0.4, and 0.8 wt. % Cu with and without a forming gas (N2/H2) 450 °C anneal for 1 h was performed as a function of deposition temperatures of 100, 163, 263, 363, and 463 °C. Secondary ion mass spectroscopic depth profiles of the metallization samples show a unique redistribution of the Si from the bulk to the metal/oxide interface at deposition temperatures between 263 and 363 °C. These data are correlated with scanning electron microscope micrographs of Si module precipitation on the silicon dioxide substrate surface after removal of the Al by an Al-specific wet etch. In a subsequent paper, electrical and mechanical characterization results of these same metallization samples will be reported from resistivity and Knoop hardness measurements.
Mobility anisotropy and magnetoresistance at an (InAs)1(GaAs)1–InP heterointerface grown on a (001) vicinal InP substrate
Authors: Yamada Syoji , Fukui Takashi , Saito Hisao
Published: July 2002

Lateral monolayer superlattices (LMSLs) of (InAs)1(GaAs)1 were successfully grown on (001) vicinal InP substrates by metal-organic chemical vapor deposition. The formation of a periodic structure in the lateral [110] direction was confirmed by x-ray diffraction. In an electronic measurement using (InAs)1(GaAs)1 LMSL–InP heterojunctions, an in-plane mobility anisotropy as well as a modified two-dimensional subband structure were observed. The latter is that at least two Shubnikov–de Haas fundamental frequencies are always observed even in the sample having a sufficiently low sheet electron density. Possible origins including a formation of a lateral periodic potential were discussed with respect to the results obtained.
InSb growth on Sb(111) single crystals studied by angle-resolved photoemission
Authors: Sporken R. , Louette P. , Caudano R. , Barth J. , Ghijsen J. , Johnson R. L. , Richter H. W.
Published: July 2002

We have studied the interface formation at 550 K between Sb(111) and evaporated indium with angle-resolved photoemission using synchrotron radiation. At ultralow coverages (0.007–0.02 ML), simultaneous formation of small In clusters, and two-dimensional growth of InSb is detected. At higher coverages, the formation of an epitaxial layer of InSb is observed. The valence-band energy distribution curves exhibit pronounced angular variations which are consistent with the formation of a highly ordered InSb(111) overlayer.
Confined states and stability of GaAs–AlAs superlattices
Authors: Batra Inder P. , Ciraci S. , Nelson J. S.
Published: July 2002

Self-consistent calculations performed on small superlattices provide evidence for confined states. Superlattices investigated contained n layers each of GaAs and AlAs in the [001] orientation. For n=4, an analysis of the self-consistent charge distribution shows electron confinement in the AlAs region. The highest valence-band state is always localized in the GaAs region giving a staggered band alignment for this superlattice. The calculated valence band offset is about 0.3 eV. The tendency towards nonstaggered band lineup is noted since Γc6(GaAs), which for n=2 superlattice lies above Xc6(AlAs) continues to shift down towards it when n is varied from 2 to 4. In large superlattices, both electrons and holes are confined in the GaAs region. We have also studied the stability of the ordered phases in epitaxially grown Ga1−xAlxAs alloys. Our total energy calculations suggest that the ordered structure (GaAs)1–(AlAs)1 is favored over the disordered one. However, the ordered structure has a negative heat of formation (metastable) and segregation into constituents is suggested.
Long-lifetime, reliable liquid metal ion sources for boron, arsenic, and phosphorus
Authors: Clark W. M. , Seliger R. L. , Utlaut M. W. , Bell A. E. , Swanson L. W. , Schwind G. A. , Jergenson J. B.
Published: July 2002

Operation of liquid–metal ion sources based on palladium alloys that contain boron, arsenic, and phosphorus (singly or in combination) was studied. These sources, when run on refractory metal needles and heater ribbons, have exhibited high angular intensity (1.5–5 μA/sr), long lifetime (>150 h), low energy spread (<15 eV), and stable operation with extracted currents down to 2 μA.
An automatic mask alignment technique using moiré interference
Authors: Uchida Yoshiyuki , Hattori Shuzo , Nomura Tsutomu
Published: July 2002

This paper deals with an automatic and precise alignment technique for x-ray lithographic masks, using two pairs of moiré gratings, with their respective moiré signals 180° out of phase with each other. The moiré signals are detected in the 0th order beams, and the difference between these two signals are used to control the alignment of an x–y stage through a stepping motor. Experiments were carried out by using a transmission grating pitch of 200 μm, a displacement corresponding to one step of the stepping motor as 28 nm, a pulse frequency of 15 Hz and a response time of 0.13 s. With these parameters a precision better than 120 nm was obtained. Experiments were carried out by using a reflection grating of 25 μm pitch. The minimum displacement corresponding to one step of the stepping motor was 14 nm. The resolution of the A/D converters was 12 bits and the response time was 1.2 s. With these parameters a control reproducibility better than 32 nm was obtained. Improvement in the control precision by an order of magnitude is expected by using a pair of quadruple gratings, a combined unit of four matched photodiode and PZT controllers. The design considerations of a suitable x-ray lithographic mask alignment system are given.
Nanolithography with an acid catalyzed resist
Authors: Umbach C. P. , Broers A. N. , Willson C. G. , Koch R. , Laibowitz R. B.
Published: July 2002

Poly(p-t-butyloxycarbonyloxystyrene) resist shows great potential for electron-beam nanolithography, particularly as a negative resist. The resist has been used to fabricate structures with linewidths as narrow as 18 nm. The resist can be processed in both positive and negative modes depending upon the developing solvent, and linewidths <40 nm have been obtained in both cases. The exposure mechanism is based upon a new resist design principle incorporating an acid catalyst. The sensitivity of the resist can be at least six times higher than that of polymethylmethacrylate (PMMA) exposed under the same conditions (i.e., 50 kV, thin membrane substrates). The exposure distribution for the resist in the negative mode has been determined, confirming its resolution potential. These data indicate that the increase in sensitivity realized through incorporation of a gain mechanism in the resist chemistry is not achieved at a large loss in resolution. In its negative mode, the resist exhibits adequate ion etch resistance for device fabrication. The resist compares favorably with other negative resists for nanolithography with regards to both resolution, and its ability to be cleanly removed by rf plasma oxidation after serving as an ion etch mask.
Magnetically enhanced reactive ion etching of silicon in bromine plasmas
Authors: El-Masry Ahmed M. , Fong F-O. , Wolfe J. C. , Randall John N.
Published: July 2002

Reactive ion etching of single-crystal and polycrystalline silicon in bromine has been studied at 2-mTorr pressure in a magnetically enhanced reactor. Effective voltage thresholds for silicon and thermal SiO2 etching are observed at −50- and −175-V cathode bias, respectively. The selectivity of silicon with respect to SiO2 exhibits a sharp peak between these thresholds, attaining, at −100 V, a value of 225 for p-type and lightly doped n-type material. The corresponding etch rate is 65 nm/min. The etch rate doubles for n+-polysilicon and the peak selectivity is 450. Etching is anisotropic over the entire doping range. Application of the −100-V process to high-resolution trench and polysilicon gate fabrication is discussed.
Plasma etching with a microwave cavity plasma disk source
Authors: Hopwood J. , Dahimene M. , Reinhard D. K. , Asmussen J.
Published: July 2002

A tunable resonant-cavity microwave plasma disk source is applied to etching very large scale integrated circuit compatible profiles in crystalline silicon. Anisotropic etching downstream from the plasma is demonstrated without the use of large, potentially damaging wafer biases. Etch rate and degree of anisotropy are determined as a function of process chamber pressure, microwave power, and wafer bias. Etch rates from 200 to 490 Å/min and degrees of anisotropy approaching 0.9 are obtained for pressures from 0.3 to 2 mTorr. Microwave power is varied from 150 to 200 W, and the wafer bias is varied from −10 to −50 V with a flowing mixture of 16 standard cm3/min (sccm)of CF4 and 4 sccm O2. Results are discussed in terms of simple microwave plasma etching theory and previously reported plasma characteristics.
Experimental conditions for uniform anisotropic etching of silicon with a microwave electron cyclotron resonance plasma system
Authors: Hopwood J. , Reinhard D. K. , Asmussen J.
Published: July 2002

The etch rate uniformity of a SF6 +Ar plasma is studied for various discharge geometries using an electron cyclotron resonant microwave plasma disk reactor operating at 2.45 GHz. At a distance of 10 mm below the 9-cm-diam plasma source 2-in. (5-cm) wafers can be etched uniformly in a free-fall diffusion dominated discharge. The effect of the ratio of SF6 to Ar on vertical and lateral etch rates was investigated and correlated with the 704-nm F* emission line intensity and positive ion flux to the surface. Surface contamination and impurity implantation in etched silicon are documented using Auger electron spectroscopy.
Composition depth profiles of oxidized silicon and sputtered GaAs from angle-resolved x-ray photoelectron spectroscopy
Authors: Bussing T. D. , Holloway P. H. , Wang Y. X. , Moulder J. F. , Hammond J. S.
Published: July 2002

An inverse Laplace transform method has been used to extract composition depth profiles from angle-resolved x-ray photoelectron spectroscopy data from oxidized Si and Ar+ bombarded GaAs. An iterative procedure determines a least-squares curve fit of the data using the Laplace transforms of step functions, which are summed to yield the composition profiles. For a sample of native oxide on a Si wafer, the composition profile defines the thickness and chemical layering of the various silicon oxide states. For GaAs sputtered with 1.5-, 3.0-, and 5.0-keV Ar+, the composition depth profiles show a surface composition near the bulk ratio, a subsurface As depletion, the extent of which increases with increasing ion energy, then a return to the bulk composition at greater depth. These As composition profiles result from preferential sputtering caused by surface segregation enhanced by sputter-assisted diffusion in the near surface region.
Thickness measurement of titanium and titanium silicide films by infrared transmission
Authors: Lee Jen-Jiang , Lee Chang-Ou , Ernst Stephen
Published: July 2002

A nondestructive, noncontact, optical method was successfully developed to measure thicknesses of titanium and titanium silicide thin films by observing infrared transmissions. These transmissions can be substantial for film thicknesses of up to 850 Å in titanium and 1000 Å in titanium silicide. The technique provides a convenient and reliable means for in-line process monitoring of a Ti-salicide (titanium self-aligned silicide) process module for gate, source, and drain formation in integrated circuits. A linear relationship between absorbance and film thickness was obtained for titanium and titanium silicide films. This behavior can be explained very well by the classical wave propagation theory of metallic films.
Soft x-ray core level photoemission study of the Cs/InP interface formation
Authors: Kendelewicz T. , Soukiassian P. , Bakshi M. H. , Hurych Z. , Lindau I. , Spicer W. E.
Published: July 2002

The room temperature formation of the Cs/InP interface has been studied with soft x-ray core level photoemission spectroscopy. The line shape analysis of the Cs 4d core level indicates that at submonolayer coverages Cs is bonded at both In and P sites. This is deduced from a large (1 to 0.55 eV) coverage-dependent splitting of the Cs 4d into two doublets. The broadening at coverages close to a monolayer is consistent with the growth of an out registry overlayer as observed before for the Cs/GaAs interface. The energy shift of the substrate core level spectra indicates that the interface Fermi level stabilizes at about 0.8 eV above the valence band maximum which corresponds to relatively large (small) band bending for n-type (p-type) InP(110). This result is unexpected due to the small work function of Cs. The line shape and intensity analysis of the spectra indicates the formation of a laterally uniform overlayer and the lack of any noticeable chemical reaction.
Bonding of As and Se to silicon surfaces
Authors: Bringans R. D. , Olmstead Marjorie A.
Published: July 2002

Photoemission core level spectroscopy results obtained for the bonding of monolayers of As atoms to the Si(111) and Si(100) surfaces, are reviewed and compared to similar measurements for thin layers of Se atoms. For As-terminated Si surfaces, a single, ordered, passivating monolayer is formed. For Se films deposited at room temperature on Si(100) surfaces, on the other hand, SiSi2 compound formation occurs after annealing to 300 °C. After annealing to higher temperatures, a submonolayer of Se atoms in bridge sites remains.
Fabrication of surface acoustic wave devices by using x-ray lithography
Authors: Yoshioka Nobuyuki , Sakai Atsushi , Morimoto Hiroaki , Hosono Kunihiro , Watakabe Yaichiro , Wadaka Shusou
Published: July 2002

Surface acoustic wave (SAW) devices with 0.6 ∼ 1.7 μm pattern size (fo=287.5∼812.5 MHz) designed as band-pass filters (BPF) were fabricated by using x-ray lithography. An x-ray stepper SX-5 with a conventional source (Pd terget), high sensitive x-ray resist chlorinated polymethylstyrene (CPMS) (negative) and EBR-9 HS (positive), and a low-distortion x-ray mask with W–Ti alloy absorber were used. The SAW BPF devices were fabricated by forming Al transducer patterns on an LiNbO3 substrate. The Al film was chemically etched with an acid etchant. The frequency characteristic of the fabricated SAW BPF devices was evaluated. As a result, it is confirmed that the SAW BPF devices satisfied the superior specification, with a center frequency of f0± 2 MHz, an insertion loss of < 15 dB and a band width of 30 MHz. It is thus demonstrated that the x-ray lithography has the potential for use in the fabrication of submicron SAW devices.
Electron scattering effects in master mask fabrication by single layer process for submicron x-ray lithography
Authors: Gentili M. , Lucchesini A. , Lugli P. , Messina G. , Paoletti A. , Santangelo S. , Tucciarone A. , Petrocco G.
Published: July 2002

A single layer process in electroplated master mask making is discussed. The results of a Monte Carlo simulation are utilized in order to calculate the proximity function and compare theory with experimental test patterns. Silicon membranes are utilized (2 μm thick) and the variables investigated are resist thickness (10 000 and 5000 Å), metallic layer plating base (varying thickness) and electron accelerating voltage (20–40 kV). The results show quantitatively how high resolution patterns mainly depend on forward scattering in the resist (thus on resist thickness) and backscattering from the metallic layer. In particular, 500 Å of Au plating base may hinder the possibility of high resolution, which can be improved by lowering either the thickness or the Z of the metallic layers. Finally the possibility of obtaining high-contrast master masks down to 0.3 μm linewidth by a single layer process is demonstrated.
Silicon etching in a direct current glow discharge of CF4/O2 and NF3/O2
Authors: Blom H.-O. , Berg S. , Nender C. , Norström H.
Published: July 2002

The effect of adding oxygen to a dc discharge containing CF4 and NF3, when etching polysilicon, have been studied. It is shown that the increase in atomic fluorine concentration observed in rf discharges is absent in the measurements performed in a dc discharge. This is probably due to the inefficient dissociation of the gas molecules in a dc discharge. This indicates that oxidation reactions in the gas phase are limited. In the dc discharge it is possible to separate several mechanisms that act on the silicon surface. In the case of CF4, the added oxygen helps in keeping the silicon surface clean from polymer formation. This results in an observed maximum in etching rate and yield. For NF3 there is no need for a ‘‘cleaning’’ of the silicon surface. The rate and yield decreases monotonically for increasing oxygen concentrations.
Use of two-dimensional protein crystals from bacteria for nonbiological applications
Authors: Pum D. , Sára M. , Sleytr U. B.
Published: July 2002

This paper gives an overview on the structure, chemistry, self-assembly, and technical application potentials of crystalline bacterial cell surface layers (S layers). These structures represent ideal model systems for studying self-assembly processess on the nanometer level. Since S layers reveal no pore size distribution they can be used for the production of a completely new type of ultrafiltration membrane. Chemical modification allows specific adaption of the S-layer surface either for ultrafiltration purposes or for coating with monolayers of biologically active molecules (e.g., enzymes). As supports for covalent attachment of macromolecules, S-layer membranes might be usable for specific and rapid determination of substances by enzymatic or immunogenic methods. S-layer structures can also be used as supports for Langmuir–Blodgett films. Finally it can be expected that as the architecture and function of more complex biological systems, particularly membranes, become better known, novel concepts will influence the design and fabrication of molecular machines and electronic devices.
Comparison of disilane and hydrogen adsorption on Si(111)-7×7
Authors: Uram K. J. , Jansson U.
Published: July 2002

Multiple internal reflection (MIR) infrared spectroscopy has been used to study the adsorption of H and Si2H6 on the Si(111)-7×7 surface at 200 and 400 K. Both adsorbates react with the Si(111)-7×7 surface to yield a variety of silicon hydrides with similar temperature dependence. Adsorption of atomic hydrogen at 400 K produces three different monohydrides with characteristic vibrational frequencies of 2076, 2086, and 2095 cm−1. At 200 K hydrogen adsorption produces a surface dihydride with a stretching frequency of 2119 cm−1 and a trihydride with a stretch frequency of 2143 cm−1 in addition to the three surface monohydrides. Adsorption of Si2H6 on Si(111)-7×7 at 400 K yields a single absorption feature centered at 2096 cm−1 attributed to surface SiH species. The broad featureless spectrum is indicative of surface disorder due to the deposition of additional surface silicon atoms from the adsorbed disilane. At 200 K the adsorption of Si2H6 yields a sharp vibrational feature at 2154 cm−1 over a broad background centered at 2126 cm−1 characteristic of a surface trihydride species (SiH3). The temperature dependence of the formation of surface hydrides is similar for both adsorbates. Lower adsorption temperatures favor the formation of higher hydrides. Differences are observed in the sequential appearance of absorption bands for adsorption of atomic hydrogen as opposed to the coverage-independent vibrational spectra observed for the adsorption of Si2H6.
Frequency-domain analysis of time-dependent reflection high-energy electron diffraction intensity data
Authors: Turner G. W. , Nechay B. A. , Eglash S. J.
Published: July 2002

A technique has been developed for computerized acquisition and frequency-domain analysis of dynamic reflection high-energy electron diffraction (RHEED) intensity data obtained during growth by molecular-beam epitaxy (MBE). This technique allows the rapid, accurate determination of the frequency of RHEED oscillations, not only when these oscillations are well resolved, but also when the growth conditions yield oscillations that are too poorly resolved to permit frequency analysis by conventional procedures. The new technique has been used to study transients in the growth of AlGaAs on GaAs substrates and also to investigate the heteroepitaxial growth of GaAs on Si.