bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of phase-shifting masks with shifter overcoat
Authors: Kostelak R. L. , Garofalo J. G. , Smolinsky G. , Vaidya S.
Published: July 2002

Phase-shifting masks have demonstrated the potential to extend the application of existing optical lithography tools by simultaneously enhancing their resolution, depth of focus, and exposure latitude. This paper identifies a processing sequence for the fabrication of phase-shifting masks using spin-on-glass (SOG) as a shifter overcoat. The SOG is applied uniformly, range of 11 nm, across conventional 5-in. mask substrates. A selective wet etch for patterning the SOG is also demonstrated. Using this processing sequence, alternate aperture, phase-shifting masks are fabricated, and both focus and exposure latitude are evaluated. Additionally, the role of shifter wall angle and level-to-level alignment on the sized rim shifter are explored. It was found that a 45° shifter wall angle resulted in ∼10% degradation in the aerial image of a 0.35-μm feature as compared with a vertical wall angle, and an alignment error of 0.25 μm on the reticle resulted in pattern placement errors of 0.06 μm. In order to circumvent second level lithography constraints several self-aligned schemes have been proposed. Two previously published techniques are reviewed and their implications on the shifter overcoat mask are discussed. Finally, having identified several of the limitations related to the overcoat process, issues related to the fabrication of phase-shifting masks with the shifter material beneath the chromium are defined.
X-ray mask distortion from arbitrary integrated circuit patterns: Closed-form and finite-element calculation
Authors: Yanof Arnold W.
Published: July 2002

Distortions in x-ray masks continue to be a critical problem for x-ray lithographic technology because upcoming integrated circuit (IC) generations demand ever-tightening requirements on the accuracy of pattern placement. In this work, elastic theory of plane stress is applied to calculate distortions arising from arbitrary patterned areas on an infinite mask membrane exactly. Distortions due to rectangular features of finite size are obtained in closed form. This analysis is used to model the structures in real x-ray masks, such as interconnect level masks, where square pads, long runners, and gratings are typical. A particular issue discussed herein is the question of stress concentration at the ends of a long rectangular feature. Here the in-plane distortion increases logarithmically with the aspect ratio of the feature. For arrays of long rectangular features, the distortion increases in accordance with the aspect ratio of the whole array. The model predictions agree with experimental data for actual x-ray masks having arrays of rectangular features, and with numerical calculations based on finite-element analysis. In order to treat actual complex IC masks having finite-sized membranes, a numerical method combining both finite-element and exact calculation is developed.
Effect of thermal treatment on the mechanical and structural properties of gold thin films
Authors: Malek C. Khan , Kebabi B. , Charai A. , de la Houssaye P.
Published: July 2002

Low-stress (<50 MPa) gold films 0.7- and 2-μm thick were deposited by electroplating from a cyanide solution at 40 °C at a current density of 2.5 mA/cm2. Thin gold films under higher stress were electron-beam evaporated at room temperature or sputtered at a power of 150 W under 2-Pa argon gas. The stress dependence of these films on the post-deposition annealing temperature up to 200 °C was investigated, using an interferometric method at room temperature. The stress evolution is discussed in relationship to the thermally induced changes in the structure and the microstructure of the various films investigated by transmission electron microscopy.
Electron impact reactions of triphenylsulfonium salt resist sensitizers in the solid state
Authors: Haller Ivan , Stewart Kevin J.
Published: July 2002

To elucidate the mechanism of electron beam exposure of triphenylsulfonium salt sensitized resists, films of triphenylsulfonium hexafluoroantimonate or triflate in various polymers and in the pure solid state were exposed to pulses of electrons. The composition of the resulting pulses of gaseous products was analyzed by Fourier transform mass spectrometry. Components of product mixtures were identified by using both electron impact and chemical ionization techniques. The main volatile products of triphenylsulfonium under electron impact are diphenyl sulfide, benzene, and biphenyl. The yield of benzene is much larger from triphenylsulfonium salts dissolved in polymer than in the pure solid state. This implies rapid hydrogen-abstraction reactions by the intermediate phenyl radicals from matrices with available aliphatic hydrogens. The product distributions observed from several polymer solvents, and their dependence on electron energy, show few other rapid reactions between the matrix and the primary products. No volatile products arising from the anions were observed. This indicates that acidic products formed in the electron stimulated decomposition reactions of triphenylsulfonium salts are retained dissolved in the polymer under high vacuum conditions. Thus under electron beam exposure, as in deep-UV exposure, it is the subsequent acid-catalyzed reactions of the resin that are responsible for the high sensitivity of onium–salt resists.
X-ray photoelectron spectroscopy and infrared study of the processing of a silylated positive photoresist
Authors: Haring Ruud A. , Stewart Kevin J.
Published: July 2002

Liftoff processes are being used in microelectronics technology for various metallization steps. In a typical application, a photoresist is spun on top of a soluble polymer, exposed, developed, silylated, and cured. Subsequently, the silylated resist acts as a stencil mask for O2 reactive ion etching (RIE) pattern transfer into the underlying polymer. The generation of debris, leading to etch residues (‘‘grass’’), is a major concern during this process step. The goal of this work is to follow the various process steps that the resist is subjected to, and in particular to determine the effect of ultraviolet (uv) hardening on the silylated resist. We used the complementary techniques of x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectrophotometry (FTIR) to obtain information on the chemical composition in the surface region and in the bulk of the film. In contrast to conventional baking, uv hardening appears to induce a substantial carbon depletion in the top layer. The aromatic structure of the novolac-type resist is diminished and the surface exhibits higher siloxane concentration. It is inferred that under O2 RIE patterning, this layer is quickly converted to an etch resistant (sub) oxide and less silicon containing debris is generated in the process than in the case of a baked silylated layer.
A top antireflector process for improved linewidth control and alignment
Authors: Brunner T. A. , Lyons C. F. , Miura S. S.
Published: July 2002

Thin film interference plays a destructive role in optical photolithography in two regards. (1) Large linewidth variations can occur from tiny changes in the thickness of resist or underlying thin films. (2) Asymmetric flow of resist over alignment mark topography can cause optical fringes which result in poor alignment signal profiles. In this paper, a new approach is described which can address both of these issues. A thin, low index, transparent film analogous to a lens antireflector (AR) coat is placed on top of the photoresist film before exposure. The ideal top antireflector (TAR) film would have thickness T=λ/(4n′) and n′=(n)1/2 where n and n′ are the refractive indices of resist and TAR, respectively. Experimental results are presented which show how various TAR layers can improve linewidth control and reduce notching as lines are patterned over topographic steps. In addition, simulations are presented which demonstrate how a TAR layer can improve the alignment signal, for certain types of alignment systems. The TAR process has great potential for high volume, economical semiconductor manufacturing.
Quantum lithography
Authors: Maluf Nadim I. , Pease R. Fabian W.
Published: July 2002

The edge definition and the interior filling of pattern features are commonly performed using the same exposing beam regardless of the feature size. Separating the two processes, as first proposed by Fulton et al. [Appl. Phys. Lett. 42, 752 (1983)], improves the efficiency of the mask making process and adds ‘‘smartness’’ to the substrate, i.e., the pattern generating tool need only provide the minimum information; the substrate and process are configured to convert the minimum information into the necessary pattern. We describe an improved level of smartness on substrates: we view the mask as a bitmapped lattice of independent pixel elements (pels), each having a given shape and carrying the relevant edge information; the desired pattern would be generated by selectively addressing a subset of the lattice and modifying the optical properties of its pels. The feature edges are effectively ‘‘quantized’’ in the sense that they can exist only in some specific places. In the edge definition step, a very fine grid whose edges are within the specifications on edge positional accuracy and precision, is inscribed on the mask blank by its manufacturer using a high resolution and high precision lithographic technique. The pitch is such that the size of the resulting tiles equals the minimum feature size of the pattern to be delineated. The limitation on the grid width is that it is not imaged by the optics upon the exposure of the mask. Once the grid is defined, the pattern can be customized by the user simply by tagging those tiles that constitute the pattern. We describe here the general principles, advantages, fabrication, and exposure of ‘‘quantum lithography’’ masks.
A servo guided X–Y–theta stage for electron beam lithography
Authors: Kendall Rodney , Doran Sam , Weissmann Erwin
Published: July 2002

This paper describes a high precision X–Y–theta stage for use inside the variable axis immersion lens of IBM’s EL3+ direct write e-beam lithography systems. X–Y stages typically use some form of rail and bearing combination to provide guidance along the X and Y axes. The planar stage presented in this paper has no X or Y guide rails or bearings, instead both guidance and positioning are provided by the simultaneous operation of three mechanical drives controlled by closed-loop velocity, position, and theta servos. The control requirements, architecture, and performance of the servo electronics is discussed. The design and materials constraints imposed by having to operate inside a magnetic lens are discussed and stage performance data is presented. Servo guided stages eliminate the need for precise alignment of guide rails and bearings, while the kinematic nature of the design results in low sensitivity to temperature variations and reduces the need for extreme mechanical tolerances.
Review of the status of computational solid-state physics
Authors: Sher A. , van Schilfgaarde M. , Berding M. A.
Published: July 2002

The current status of ab initio methods to study the properties of solids is reviewed. During the past ten years, a wealth of calculations have established that many properties of solids can be accurately calculated from first principles. Recent advances in methods now make it possible to treat a number of practical problems in materials science within tolerable times and costs.
The reaction of amorphous Co–Zr layers with Si(100) and SiO2 substrates by annealing in vacuum and NH3
Authors: Duchateau J. P. W. B. , Kuiper A. E. T. , Willemsen M. F. C. , Torrisi A. , van der Kolk G. J.
Published: July 2002

The reaction of amorphous Co–Zr films with Si(100) and SiO2 substrates has been investigated using in situ Rutherford backscattering spectrometry, Auger electron spectroscopy and x-ray diffraction. For this purpose, CoxZr1−x (x=0.5 or 0.6) films were deposited on a substrate and annealed in vacuum or NH3. During annealing of an amorphous Co–Zr film on Si in vacuum at a temperature lower than 600 °C, Co reacts with Si, forming CoSi2 next to the substrate. Above 600 °C, the layer reacts completely with Si and the following structure develops: (ZrSi2+CoSi2)/CoSi2/Si. Annealing the same structure in NH3 above 600 °C causes two reactions to occur simultaneously: (i) CoSi2 formation at the film/substrate interface, and (ii) nitridation of the film surface, forming ZrN, which stops the diffusion of Si to the surface. It was found that a fraction of the CoSi2 grains was aligned with the Si(100) substrate, irrespective of the annealing ambient. This fraction increases with increasing annealing temperature. When annealing below 600 °C in NH3, an oxide layer between the surface nitride layer and the interface silicide layer develops, retarding the formation of the nitride and silicide layer. On SiO2 the situation is complex since Zr reacts with SiO2 above 600 °C, resulting in a ZrO2 toplayer with underneath a Co–Si layer after annealing in vacuum. In NH3 an oxygen-containing layer between the substrate and the ZrN top layer is formed.
Photoelectrochemical i
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u observation of n-MoS2 in aqueous solutions using a scanning tunneling microscope
Authors: Sakamaki Kenji , Hinokuma Kohichiroh , Fujishima Akira
Published: July 2002

A scanning tunneling microscope under potentiostatic control in visible light illumination was used in aqueous solutions to investigate an in situ dynamical light-induced morphological transformation of n-MoS2, a representative layer-type semiconductor electrode. In a KCl solution, light-induced corrosion originated from ‘‘layer-island’’ structures, island edges, and depressions, all of which served as active reaction sites. The electrode surface was then morphologically transformed by photoelectrochemical processes into a stable van der Waals’ surface. Additionally, the effect of I− ions on the suppression of photocorrosion of n-MoS2 was investigated.
p-buffer layer dependent drift mobility profiles in GaAs metal–semiconductor field-effect transistors
Authors: Steiner Klaus , Uchitomi Naotaka
Published: July 2002

Mobility profiles in WnX-LDD (lightly doped drain region) and WNX-BPLDD (buried p-type buffer lightly doped drain region) GaAs metal–semiconductor field-effect transistor (MESFET) with various p-buffer layers are discussed. The mobility profiles are evaluated using frequency dependent admittance studies. A slightly doped p-buffer layer seems to have no influence on the carrier concentration while there is a significant modification of the mobility profile at lower gate voltages. The channel drift mobility in BPLDD-MESFETs with heavily implanted p-buffer layers is degraded over the whole gate voltage swing. Mg-p-type implants have no effect on the carrier profile near its peak while the tail region is shifted to higher gate voltages. However, to observe a significant sharpening of the channel electron concentration profile a certain amount of Mg implantation dose seems to be necessary.
Resonant inverse photoemission of Sb multilayers on GaAs(110) and InP(110) surfaces
Authors: Hu Yongjun , Jost M. B. , Weaver J. H.
Published: July 2002

The coverage- and structure-dependent empty electronic states of Sb multilayers on nearly unrelaxed GaAs(110) and relaxed InP(110) have been investigated using inverse photoemission (IPES) and low energy electron diffraction. Two significant Sb-derived empty states, termed features A and B, are used to characterize the evolution of ordered, metastable Sb multilayers and the ordered first monolayer. Feature A appears ∼0.30 and ∼0.35 eV above EF for ordered metastable Sb multilayers on p-GaAs(110) and p-InP(110), respectively, while feature B appears at 2.0 eV for 1 ML of ordered Sb. Feature A resonates for photon energies of IPES near ℏωp=15.9 eV because radiative decay of a plasmon within the Sb film provides a decay channel that competes with the inverse photoemission channel. This resonance occurs for thicknesses greater than ∼3.5 ML for GaAs(110) and ∼2 ML for InP(110) for overlayers annealed at 475 K following Sb growth at 300 K. Structural studies reveal that the resonance features of IPES are correlated with metastable structures of the Sb layers. Very gradual relief of strained-layer structures, coherent with (110) surfaces, may contribute to the existence of metastable phases for coverages below ∼10 ML. For Sb/GaAs(110), the metastable structures consist of long-range-ordered (110) domains with Sb crystallites between them. For Sb/InP(110), the metastable structures may be associated with a fairly continuous, periodic distribution of atomically corrugated (110) domains along [001], and the plane defined by the Sb zig–zag chains is not parallel to the unrelaxed (110) surface. These metastable structures may provide various coupling conditions for the momenta of the photon and the electron-excited Sb plasmons.
The passivation of ZnSe(100) surfaces via As capping
Authors: Farrell H. H. , Tamargo M. C. , Shibli S. M. , Chang Yeh , McNeill J.
Published: July 2002

The use of amorphous As layers to protect compound semiconductor surfaces when transferred in air among ultrahigh vacuum systems has been demonstrated for III–V materials containing As and group III metals such as Ga. We have extended this passivation, or capping, technique to a new class of materials: the II–VI semiconducting compounds, typified by ZnSe. This capping procedure allows transfer among noninterconnecting systems resulting in clean, highly ordered, and stoichiometric surfaces suitable for heteroepitaxial growth, other fabrication procedures, and fundamental studies.
Fine pattern definition with atomic intermixing induced by focused ion beam and its application to x-ray mask fabrication
Authors: Kanayama Toshihiko , Komuro Masanori , Hiroshima Hiroshi , Itoh Junji , Atoda Nobufumi , Tanoue Hisao , Tsurushima Toshio
Published: July 2002

Mixing of double-layered Al-on-Au and Al-on-W structures by a focused ion beam (FIB) has been used to define fine patterns in Au and W layers and to demonstrate that the mixing spread is less than 0.1 μm. Since the mixed Al–Au alloy and Au have higher sputtering yield than Al, etching with 4-keV Xe ions engraves the FIB-defined pattern in the Au layer. This process yielded 0.2-μm-wide grooves in 20-nm Al/0.3-μm Au with a 50-keV Ga+ FIB of ∼5×1015/cm2. In the Al/W, Al is removed in H3PO4 leaving the mixed Al–W alloy, which acts as a durable mask in SF6 reactive ion etching of W with a selectivity of ∼80. This process enables the Ga+ FIB to define patterns less than 0.1 μm in 20-nm Al/0.3–0.5-μm W with a sensitivity of ∼1×1015/cm2. To demonstrate applicability of the above processes, patterns of x-ray masks were fabricated and transferred with synchrotron radiation to poly-methyl-methacrylate. Backscattering measurements of He ions and x-ray diffraction verify mixing occurs within the range of the ion. The process performance and its relation with the mixing kinetics are also discussed.
Fabrication of open and buried quantum wires using a removable mask applicable for multiple processing steps
Authors: Menschig A. , Kübler P. A. , Prins F. E. , Rudeloff R. , Hommel J. , Schweizer H.
Published: July 2002

We have carried out detailed investigations on dry etch selectivity, ion penetration depths, and adhesion properties for a wide variety of materials to find a suitable combination for the fabrication of multiple process masks (MPM). A combination of Al2O3, TiO, and Pt yield the best results for the use in the In0.53Ga0.47As/InP system. Using this type of MPM for different fabrication processes, we have realized wires by deep dry etching (i.e., open wires) and also buried wires either by deep dry etching with an additional overgrowth or by ion implantation. All three kinds of wires show characteristic size effects in magnetotransport experiments.
Development of the field emission electron gun integrated in the sputter ion pump
Authors: Yamazaki Y. , Miyoshi M. , Nagai T. , Okumura K.
Published: July 2002

A field emission electron gun (FEG) integrated in a rotationally symmetric sputter ion pump (SIP) has been developed. By integrating the FEG into the SIP, a high vacuum condition at the cathode can be easily obtained. The gun chamber and its evacuation system can be very simple and small. Working pressure of 5×10−9 Torr is easily obtained in our experimental setup. Furthermore, the 15 mT axial magnetic field of SIP is superimposed on the cathode. The magnetic field forms the magnetic field immersed FEG, resulting in the reduction of the spherical aberration by one-half. As an experimental result, a probe current of 6 nA with a 0.1 μm probe diameter at 1 kV beam voltage was successfully obtained with the two lens optical system.
Nanofabrication techniques for 100 nm-scale silicon metal oxide semiconductor field effect transistor
Authors: Reeves C. M. , Hohn F. J. , Wind S. J. , Lii Y. T. , Newman T. H. , Bucchignano J. J. , Klaus D. P. , Chiong K. N.
Published: July 2002

In this paper we report on an exploratory metal oxide semiconductor field effect transistor (MOSFET) device which we are currently investigating which requires 100 nm lithography at all critical levels to achieve a completely fully scaled 100 nm device structure. The device also incorporates a novel trench isolation scheme whereby the isolation trenches are etched after the gate electrodes have been formed leading to a butted gate configuration. The device further incorporates fully overlapped contacts to the gate, source, and drain regions in order to provide maximum contact area. We believe that this structure will provide a good basis for exploring the density and performance limits of 100 nm-scale devices. We describe here the structure of the proposed device and then we propose a suitable method of fabrication. This is followed by a demonstration of suitable nanofabrication techniques which are based, in each case, on high resolution electron beam lithography and precision reactive ion etching. Finally, we assess the feasibility of integrating these techniques in order to realize the proposed device.
First step towards application of high-temperature superconductors for planar magnetic lenses
Authors: Adriaanse J. P. , van der Mast K. D. , van Zuylen P.
Published: July 2002

The feasibility of high-temperature superconductors for applications in particle optics is discussed. Although high Tc superconducting coils and wire are not available yet, we conclude that thin films are very promising for ironless magnetic lenses due to their high maximum current density and because they can be very accurately patterned. However, a stack of 10–100 layers will be needed to fulfil the field strength and rotational symmetry requirements. Initial experimental results obtained with a superconducting YBa2Cu3O7−x film patterned with a 50-turn spiral-shaped coil are presented. The maximum critical current density obtained in the 50-turn spiral was 104 A/cm2 at 30 K. The best way to stack the films would be a multilayer fabrication process, but this is not yet available. As an intermediate step, we developed a pattern suitable for face-to-face stacking and we propose an alignment technique based on capacitive position sensors.
Synthesis of electron and ion optical columns
Authors: Szilagyi M.
Published: July 2002

The basic ideas of a systematic procedure for the automatic design of electron and ion optical columns with given focusing and deflection properties and minimum aberrations are outlined. The concept of synthesis is thoroughly explained. Optical columns can be synthesized either from given elements or in their entirety. The procedures are based on two different approaches: (1) Seeking the appropriate potential distributions in the form of spline functions with the subsequent reconstruction of the electrodes. (2) Using an a priori given multipurpose multielectrode system, the electrode potentials of which are selected so that the given constraints are satisfied and the aberrations are minimized. The first practical calculations show quite promising results.
Study of palladium silicide formed using a focused ion beam machine
Authors: Balakrishnan Sridhar , Corelli John C. , Rajan Krishna
Published: July 2002

This paper deals with the formation, growth kinetics, and some electrical properties of palladium silicide formed by using the direct implantation of palladium ions into (100) and (111) Si using a focused ion beam machine. The activation energy for growth of the silicide formed has been determined by two different techniques and has been found to be significantly lower than normally reported values for thermal formation by thin-film annealing of the same silicide. Results from an extensive microstructural study have been presented for a variety of implantation and follow-up anneal conditions. Finally, some data for Schottky diodes made using this novel technique have been presented.
Lift-off patterning of ion-beam sputter deposited silicon nitride oxidation masks
Authors: Bosseboeuf A. , Bouchier D. , Fourrier A.
Published: July 2002

A single-step image reversal lift-off process is used to delineate micron wide patterns in silicon nitride films deposited at room temperature by reactive ion-beam sputtering. Edges of lines perpendicular to the plane of incidence of the ion-beam on the target during deposition were found to be asymmetrical. This result is explained by the tilting of angular distributions of sputtered nitrogen and silicon. It is further demonstrated that these films can be used as masks for the local oxidation of silicon without pattern degradation and with a weak penetration of oxide under the silicon nitride mask edge (known as the bird’s beak). Film-induced stress has no influence on the bird’s beak configuration.
Impurity-induced mechanism of periodic structures excitation on solidifying melt surface
Authors: Vladimirov V. V. , Gabovich M. D. , Soloshenko I. A. , Khomich V. A. , Tsyolko V. V.
Published: July 2002

The instability of solidification process occurring under the cooling of a metal melt is shown to be able to initiate short-wave periodical structures on the surface provided the impurity concentration in the melt is sufficiently high. The experiments were carried out using titanium (plus yttrium) and copper (plus tin) targets melted by means of an ion beam. The mechanism of this phenomenon is associated with the solidification front instability caused by the constitutional supercooling of the liquid phase due to the impurities forced out into the latter under front motion. A dispersion equation for the solidification waves on the interphase boundary is derived for the thin melt case, its solutions are investigated as functions of the impurity concentration and heat transfer regime. The calculated values of the structure periods and excitation criteria are in good accordance with the experimental data. In our opinion, the short-wave structures occurring on the solidified surface of liquid metal ion source [A. Wagner, T. Venkatesan, P. M. Petroff, and D. Barr, J. Vac. Sci. Technol. 19, 1186 (1981)] may be caused by the above mentioned instability of the melt solidification process. In course of ion source operation, the impurities are produced by the cathode sputtering of the extractor [G. S. Galovich and A. Wagner, J. Vac. Sci. Technol. B 6, 2108 (1988)].
The image potential in scanning tunneling microscopy of semiconductor surfaces
Authors: Huang Z.-H. , Weimer M. , Allen R. E.
Published: July 2002

A semiclassical screening theory for semiconductors is used to treat the image potential throughout a one-dimensional metal-vacuum-semiconductor junction in the absence of surface states. The image interaction due to induced surface charge at the semiconductor-vacuum interface produces an effective band bending in the semiconductor interior, whose influence on electron tunneling through the junction is investigated. In particular, we examine the effect of this extra potential on STM measurements of the apparent tunneling barrier at unpinned semiconductor surfaces, and consider n-type, H-terminated Si(111) as a specific example. In the instance where tip-induced band bending may be neglected, we find the role of the image potential in metal-vacuum semiconductor tunneling to be qualitatively similar to its role in metal-vacuum-metal tunneling: The experimentally determined barrier height—obtained from the logarithmic derivative of the tunneling current with respect to tip–sample separation—deviates little from the electron affinity of the semiconductor, while the theoretical barrier height exhibits a stronger dependence on the vacuum gap width. The origin of this behavior appears to lie in the fact that while the image interaction in the semiconductor may be long range, the image induced tunneling barrier is not.
Growth of As overlayers on vicinal Si(100) surfaces
Authors: Alerhand O. L. , Wang J. , Joannopoulos J. D. , Kaxiras Efthimios
Published: July 2002

First-principles total-energy calculations are used to study the structure of As overlayers deposited on a stepped Si(100) surface. It is predicted that deposition of As at low substrate temperatures allows the As to grow directly on top of the Si surface, while growth at high temperatures results in a rearrangement of the surface as if the As replaced the original top Si layer. This result explains the sublattice orientation dilemma in GaAs-on-Si epitaxy.
Low-energy cathodoluminescence spectroscopy studies of III–V superlattice interdiffusion: Optical emission properties of diffusion associated defects
Authors: Viturro R. Enrique , Olmsted Brian L. , Houde-Walter Susan N. , Wicks Gary W.
Published: July 2002

We report a direct optical observation of process-specific diffusion-related deep levels associated with interdiffusion in AlGaAs/GaAs superlattice structures. We have used low-energy cathodoluminescence spectroscopy (CLS) to investigate the formation and evolution of deep levels for intrinsic, under As overpressure, and Si induced layer intermixing. The spatial distribution of these deep levels strongly correlates with the extent of superlattice intermixing, as measured by secondary ion mass spectroscopy (SIMS) and photoluminescence spectroscopy (PLS). The measured cathodoluminescence emission energies and intensities reveal the important role of impurities in the mechanism of interdiffusion at III–V semiconductor superlattices. In particular, our experimental results strongly suggest that the larger interdiffusion rate of the Si induced layer intermixing process is related to the formation of a deep level associated with an optical emission at 1.3 eV. These results indicate the potential of the low-energy cathodoluminescence technique for studying deep level formation and deep level inhomogeneities in semiconductor structures.
Dynamical strain at semiconductor interfaces: Structure and surface-atom vibrations of GaAs(110) and GaAs(110)–p(1×1)–Sb
Authors: Godin T. J. , LaFemina John P. , Duke C. B.
Published: July 2002

The dynamical force fields of the clean GaAs(110) surface, an isolated Sb chain, and the GaAs(110)–p(1×1)–Sb(1-ML) interface have been computed utilizing tight-binding total energy models that have been used successfully to describe the atomic and electronic structure of the clean and adsorbed cleavage faces of the tetrahedrally coordinated compound semiconductors. Since the main consequences of the different chemical bonding in these two cases are manifested in changes in the force field associated with the dynamics of the top-layer atoms, we explore these consequences using a restricted dynamical model in which only the top-layer atoms are allowed to vibrate. The resulting vibrational energies are in remarkably good agreement with experimental measurements, and hence afford a vehicle to obtain quantitative relationships between the nature of the surface chemical bonds and the vibrational energies of the surface atomic species.
Shubnikov–de Haas oscillations and quantum Hall effect in modulation-doped HgTe–CdTe superlattices
Authors: Hoffman C. A. , Meyer J. R. , Arnold D. J. , Bartoli F. J. , Lansari Y. , Cook J. W. , Schetzina J. F.
Published: July 2002

We have investigated quantum oscillations in the magneto-transport properties of HgTe–CdTe superlattices grown by molecular-beam epitaxy. Modulation doping was achieved by incorporating either indium donors or arsenic acceptors into the CdTe barriers. In a p-type sample, quantized plateaus were observed in the Hall conductivity down to i=3 conduction channels. Since the structure contained 200 periods, this implies that the quantized holes populated only a small fraction of the total superlattice volume. A mixed conduction analysis of the nonoscillating component of magneto-transport data provided confirming evidence for the presence of a two-dimensional hole gas with the appropriate density in addition to the superlattice holes. Previous reports of the quantum Hall effect in HgTe–CdTe also yielded i far less than the total number of superlattice wells. In contrast, an n-type sample from the present study displayed a single quantum Hall plateau at i≊140, indicating that in this case most of the 200 superlattice periods contributed to the conduction. We argue that this represents the first observation of the quantum Hall effect associated with carriers distributed throughout the interior of a HgTe–CdTe superlattice.
X-ray photoelectron diffraction from the HgCdTe(111) surface
Authors: Herman G. S. , Friedman D. J. , Tran T. T. , Fadley C. S. , Granozzi G. , Rizzi G. A. , Osterwalder J. , Bernardi S.
Published: July 2002

The surface polarity of a mercury cadmium telluride (MCT) (111) crystal surface has been determined by x-ray photoelectron diffraction (XPD). Emission from the core levels of Hg, Cd, and Te gave reproducible photoelectron diffraction patterns with considerable fine structure. Comparisons between experiment and single scattering cluster calculations via R factors very well distinguished the different kinds of lattice sites of Cd, Hg, and Te, and also permitted unambiguously assigning a cationic termination to the sample studied. This is thus a demonstration of the capability of XPD to study the type of termination involved at MCT and other compound semiconductor surfaces.
Fabrication of optical beamwidth transformers for guided waves on InP using wedge-shaped taper structures
Authors: Zengerle R. , Brückner H.-J. , Koops H. W. P. , Olzhausen H.-J. , Zesch G. , Kohl A. , Menschig A.
Published: July 2002

A waveguide device is proposed for spot-size transformation of an optical beam from the 1 μm range to about 8 μm using a wedge-shaped taper. The structure can be entirely integrated on an InP-based optoelectronically integrated circuit. It is shown by numerical simulation that the width of the thin end of the wedge has a major influence on the transformation loss of such a device. By using direct writing e-beam lithography and reactive ion etching as well as subsequent InP regrowth, we were able to produce the required structures. The beamwidth transformation capability is confirmed by optical measurements.
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u device electrical parameter adjustment and monitoring during remote plasma dry etching
Authors: Lishan David G. , Snider Gregory L. , Hu Evelyn L.
Published: July 2002

By monitoring device electrical parameters during remote plasma dry etching, we have demonstrated a novel method for in situ adjustment of saturation currents. Time-elapsed I-V curves and current-versus-time plots illustrate the low damage, controllable gate recess etching of a metal-semiconductor field-effect transistor device structure and two different high electron mobility transistors. Using a one-dimensional Poisson solver, simulations of conduction versus depth are made and discussed in relation to experimental results.
A lower bound on alignment accuracy and subpixel resolution in lithography
Authors: Gatherer Alan , Meng Teresa H.-Y.
Published: July 2002

In wafer alignment, subpixel resolution methods have been used in an attempt to increase the accuracy of the wafer positioning algorithm. These methods produce line positions that are between the pixels of the rasterized image of the alignment pattern. In this paper we provide a lower bound on the error variance of any alignment algorithm for a given alignment system and develop a method of ranking alignment patterns for their suitability for the task. We show that the use of a nonsymmetric alignment pattern will cause a decrease in accuracy unless information about the amplitude of the alignment pattern is known. An expression for the maximum useful subpixel resolution of any alignment system is derived and it is shown that with pixel resolution higher than this maximum value the subpixel methods produce no significant increase in accuracy. Examples of the use of the bound will be given.
Photoemission study of oxygen adsorption on ternary silicides
Authors: Horache E. , Fischer J. E. , Ruckman M. W.
Published: July 2002

Molecular oxygen adsorption on several ternary silicides (Ti4M4Si7, M=Ni,Co) and (TiFeSi2) is studied using photoemission. The valence band spectrum shows that the O2 dissociates on adsorption and suggests that an exposure of a few hundred langmuirs is sufficient to completely cover the surface with a layer of atomic oxygen. Si 2p core-level spectra show that oxygen bonds with the silicon and photoemission peaks from all oxidation states of silicon are observed. 3p core levels from the metallic elements like titanium do not show core-level components indicating the formation of metal–oxygen bonds. The bonding of oxygen to silicon could be due to silicon termination of the surface or maybe due to energetics which favor silicon–oxygen bond formation over metal–oxygen bond formation, the breaking of silicon–silicon bonds rather than silicon–metal bonds or the breaking of the fewest atomic bonds.
Effects of Au on NiGe(Au)W ohmic contacts to n-GaAs
Authors: Lustig Naftali
Published: July 2002

The contact resistance and thermal stability of NiGe(Au)W ohmic contacts are reported as a function of their Au content. The contact resistance, measured by the transmission line method, is found to decrease monotonically from a maximum of ∼0.8 Ω mm for the Au-free NiGeW contacts, to less than 0.15 Ω mm for NiGe(Au)W containing ∼60 Å of Au. The low Au content contacts are also found to be more stable than their Au-free counterparts when stressed at 400 °C for a number of hours. Possible mechanisms to explain these results are proposed.
Closed-ampoule diffusion of sulfur into Cd-doped InP substrates: Dependence of S profiles on diffusion temperature and time
Authors: Faur Mircea , Faur Maria , Honecy Frank , Goradia Chandra , Goradia Manju , Jayne Douglas , Clark Ralph
Published: July 2002

In order to optimize the fabrication of n+–p InP solar cells made by closed-ampoule diffusion of sulfur into p-InP:Cd substrates, we have investigated the influence of diffusion conditions on sulfur diffusion profiles. We show that S diffusion in InP is dominated by the P vacancy mechanism and is not characterized by a complementary error function as expected for an infinite source diffusion. The S diffusion mechanism in p-InP is qualitatively explained by examining the depth profiles of S, P, and In in the emitter layer and by taking into account the presence and composition of different compounds found to form in the In–P–S–O–Cd system as a result of diffusion.
Observation of protrusions and ring structures on MoS2 by scanning tunneling microscopy
Authors: Permana Haryani , Lee Sangho , Ng K. Y. Simon
Published: July 2002

Natural MoS2 was investigated by scanning tunneling microscopy operated in air. The atomic resolution image yields the hexagonal symmetry of the surface of the crystal with lattice constant of 3.1 Å, in agreement with the reported x-ray crystallographic value. Corrugations along the [110] cell diagonal show major and secondary peaks which have been reported to correspond to molybdenum atoms and sulfur atoms, respectively. A large-area image of MoS2 reveals protrusions and ring-type structures of similar sizes on the surface of the sample. The islands and ring-type structures may be due to vanadium and fluoride ions, which are found in low concentrations (0.03 and 0.5 at. %, respectively) in the MoS2 sample when investigated by secondary ion mass spectroscopy. The protrusions and ring-type structures were observed only at a higher bias voltage (−0.084 V), suggesting that the impurities are found in the molybdenum layer only. Low bias voltage (−0.003 V) does not show any indications of islands or ring structures, which suggests that there are no impurities on the sulfur layer.
Field effect on the deep levels and DX centers in AlxGa1−xAs/GaAs and InxGa1−xAs/GaAs
Authors: Halder N. C. , Echon E. A.
Published: July 2002

Field effect studies have been performed on the deep levels in molecular beam epitaxially grown AlxGa1−xAs (with x=0.385) and InxGa1−xAs (with x=0.1) on n+-GaAs. We have measured the isothermal and isofield capacitance transients for the major energy levels with the applied electric field [here, field means normalized field, F(norm)=F(appl)×10−5] in the range −0.5 to −5 V/cm. The results of our investigation suggest that the applied field has a distinct effect on thermal emission rate, capture cross section and activation energy. In particular, the Arrhenius plots showed a nonlinear behavior that could be associated with electron–phonon interactions. Furthermore, the activation energy versus field plots indicate a linear behavior, illustrating a complex nature of the deep levels some of which, E1 in AlxGa1−xAs and E3 in InxGa1−xAs, can be characterized as DX centers.
Ti/borophosphosilicate glass interfacial reactions and their effects on adhesion
Authors: Kottke M. , Travis E. O. , Rogers B. R. , Pintchovski F. , Fiordalice R.
Published: July 2002

The interfacial reaction of sputtered Ti films with borophosphosilicate glass (BPSG) sublayers has been studied using primarily Auger electron spectroscopy depth profiling techniques. Thin interfacial layers formed during rapid thermal annealing in N2 ambients were studied as a function of temperature, time, BPSG composition, and sublayer preclean treatment. A P-rich (phosphide) layer was found to accumulate at the Ti/BPSG interface during the reactions and in so doing inhibited the Ti/SiO2 reduction reaction. B accumulated only when the consumption of the entire Ti film neared completion. In some cases, adhesion failures could be generated following the deposition of an Al metallization over the reacted Ti/BPSG films. These failures were found to occur between the P-rich (phosphide) interfacial layer and the BPSG sublayer and could be prevented by backsputtering the BPSG prior to Ti depositon.
Growth over nonplanar substrates by organometallic molecular-beam epitaxy
Authors: Tamargo M. C. , Quinn W. E. , Hwang D. M. , Chen C. Y. , Kapon E. , Schiavone L. M. , Brasil M. J. S. P. , Nahory R. E.
Published: July 2002

We present the growth habits of GaAs and InGaAs quantum wells grown by organometallic-molecular-beam epitaxy (OM-MBE) on (100) GaAs substrates with micron-range corrugations aligned along the [011̄] direction. The growth habits resemble those obtained by molecular-beam epitaxy, but with several obvious differences, which are discussed on the basis of their different growth mechanisms. These differences reduce the importance of the geometric factors for OM-MBE which dominate in MBE. We observe lateral compositional variations in the InGaAs quantum well. The patterned samples exhibit enhanced luminescence efficiency compared to reference flat samples.
Low threshold (111)B GaAs quantum well lasers and applications to coherent blue–green sources
Authors: Fischer R. J. , Vakhshoori D.
Published: July 2002

We have studied the growth and properties of GaAs (111)B lasers for application to visible blue–green generators. Nearly featureless surface morphologies were obtained by growth at a temperature of 680 °C. Broad area current densities of 200 A/cm2 were obtained and ridge lasers 4×800 μm2 had threshold currents between 11 and 13 mA.
Temperature modulation molecular-beam epitaxy and its application to the growth of periodic index separate confinement heterostructure InGaAs quantum-well lasers
Authors: Hong M. , Wu M. C. , Chen Y. K. , Mannaerts J. P. , Chin M. A.
Published: July 2002

Solid-source molecular-beam epitaxy has been employed to grow periodic index separate confinement heterostructure InGaAs quantum-well lasers emitting at 980 nm. The 5 μm×750 μm device fabricated using a self-aligned process has far-field angles of 10° by 20°, a threshold current of 45 mA, an external differential quantum efficiency of 1.15 mW/mA (90%), and an output power of 620 mW, all measured at room temperature under cw operation. A record high fiber coupling efficiency of 51% has been achieved.
Intersubband absorption in Sb δ-doped molecular beam epitaxy Si quantum well structures
Authors: Lee Chanho , Wang K. L.
Published: July 2002

Strong electron intersubband infrared absorption near the 10 μm wavelength is observed in Sb δ-doped Si multiple quantum wells grown on (100) Si substrate. The structure used for measurements consists of five periods of Sb δ-doped Si quantum wells and undoped Si barriers. An infrared absorption of 82% is measured with a Fourier-transform infrared spectrometer using a waveguide structure with ten internal reflections. Sb δ-doped layers with sharp and high doping profiles for the quantum wells are obtained by modulating the substrate temperature between 300 and 600 °C during molecular beam epitaxy growth. Absorption peaks ranging from 5.8 to 8.1 μm are observed. The peak positions can be tuned by changing the doping concentration in the quantum wells. The observed polarization angle dependence agrees with the intersubband selection rule for (100) Si, i.e., X-like valley.
GaAs/AlGaAs quantum wells grown over epitaxial CoAl layers with molecular-beam epitaxy
Authors: Goodhue W. D. , Le H. Q. , Johnson G. D. , Bales J. W.
Published: July 2002

GaAs/AlGaAs quantum wells have been successfully grown over 10 nm thick epitaxial CoAl layers with molecular-beam epitaxy and characterized with transmission electron microscopy (TEM) and photoluminescence. Cross-sectional TEMs of the structures showed well-defined GaAs and AlGaAs epitaxial layers, and photoluminescence spectra taken at 77 K showed reasonably bright and narrow quantum-well (QW) exciton peaks compared to structures grown over GaAs. This preliminary work indicates the feasibility of growing epitaxial quantum wells over a CoAl layer. The ability to grow low-defect buried epitaxial metals together with InGaAs/AlGaAs or GaAs/AlGaAs QWs would enable the fabrication of a variety of unique electro-optical devices incorporating buried optical mirrors, Schottky barriers, and/or ohmic electrical contacts.
Enhancement of carrier concentration and spatial confinement in molecular-beam epitaxial Si and Be δ-doped GaAs by increasing As4/As2 flux ratio
Authors: Shih Y. C. , Block T. R. , Streetman B. G.
Published: July 2002

We report the effects of changing As4/As2 flux ratio from an As cracking source on Si and Be δ-doped GaAs grown by molecular-beam epitaxy. It is observed that the carrier concentration increases as the As4/As2 flux ratio increases. The spatial confinement of carriers in the δ-doped induced potential well is also enhanced using high As4/As2 flux ratio. These effects are attributed to the enhancement of dopant incorporation by As4 during the δ-doping growth period.