bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of pattern dimension accuracy in electron-beam lithography
Authors: Saitou Norio , Okazaki Shinji , Murai Fumio , Ozasa Susumu , Konishi Tadao
Published: July 2002

The etched pattern dimension accuracy for an e-beam lithography system is determined by machine-, resist process-, and proximity effect-related errors. This paper reports mainly on analysis of such machine-related errors, though process-related and proximity effect-related errors are also discussed. In a variably shaped vector writing system, machine-related errors occur from four sources: (i) beam dimension and shape errors, (ii) dose change, (iii) beam edge resolution, and (iv) deflection distortion. Each error includes several inherent causes. The Hitachi e-beam lithography system, the HL-600, makes use of such variably shaped vector writing techniques. In the context of this system, then, the authors have made separate determination of each error through experiments. Beam dimension and shape error was found to be 0.045 μm, dose change dependent error was 0.02 μm, beam resolution dependent error was 0.03 μm, and deflection distortion dependent error was 0.05 μm. The major causes for each error have also been identified. It was seen that the maximum overall dimension error was 0.06 μm inside a field and 0.08 μm in a mask.
A novel negative electron-beam resist with high resolution and high dry-etching durability: Chloromethylated poly-2-isopropenylnaphthalene
Authors: Atoda N. , Doi H. , Kokubun K.
Published: July 2002

Molecular parameters and lithographic performances evaluated with a 20 kV electron beam of a newly developed negative resist, chloromethylated poly-2-isopropenylnaphthalene (CM-IPN), are presented. IPN polymers with narrow molecular weight distribution (MWD) were obtained by anionic polymerization. Subsequent chloromethylation can enhance sensitivity with slight broadening of MWD. Observed contrast (γ) values of ∼2 are almost independent of sensitivity. The reactivity evaluated as Mw ⋅ D0 (Mw, molecular weight; D0, gelation dose) is about 0.18. Linewidth patterns of 0.1 μm or less with an aspect ratio of 5 can be delineated. High dry-etching durability and excellent thermal stability owing to aromatic rings and the high glass transition temperature (230 °C) are also confirmed.
Nucleation and growth of GaAs on Ge and the structure of antiphase boundaries
Authors: Petroff P. M.
Published: July 2002

Using an ultrahigh vacuum (UHV) scanning transmission electron microscope equipped with a molecular beam epitaxy chamber, the formation of the GaAs/Ge interface produced by deposition of GaAs on Ge substrate thin films with (111) or (110) or (100) orientations has been investigated. Three-dimensional nucleation and growth of facetted GaAs epitaxial islands are characteristic of this interface. The formation energy and orientation of antiphase boundaries are obtained from the structure analysis of these ultrathin films.
Molecular-beam epitaxy growth mechanisms on GaAs(100) surfaces
Authors: Farrell H. H. , Harbison J. P. , Peterson L. D.
Published: July 2002

A significant liability in the use of molecular-beam epitaxy (MBE) to grow device grade compound semiconductor materials is the cost entailed by the necessity of using ultrahigh vacuum and high-growth temperatures. The commercial feasibility of this process could be considerably enhanced if growth temperatures could be cut by one-half or more. In addition, lower growth temperatures could make feasible the growth of semiconductor layers by MBE on top of previously processed structures without degrading or destroying those structures from the high temperatures currently needed for semiconductor growth. An understanding of the detailed atomic nature of this growth process would be valuable in tailoring existing, or developing new techniques towards this end. In the previous papers in this series, we have developed atomic models for various structures on the GaAs(100) (and related) surfaces used in MBE growth. In this paper, we combine those models to suggest an actual mechanism whereby molecular-beam epitaxy occurs. This proposed mechanism is highly suggestive in terms of improving growth techniques by, for example, varying the incident flux of the constituent species or by using monochromatic light during the growth process. It is foreseen that the implementation of such variations at specific points during the growth cycle may allow substantial reduction in substrate temperature or otherwise improve MBE growth on compound-semiconductor surfaces.
Three-dimensional Monte Carlo calculation by a supercomputer
Authors: Hasegawa Shinya , Iida Yasuo , Hidaka Toshiharu
Published: July 2002

A Monte Carlo program suited for a parallel pipeline computer has been developed. About 100 times faster simulation than that obtainable with a general purpose computer with 10 MIPS handling capacity was achieved. Thanks to high computation speed, restriction on objective structures for simulation was practically eliminated. A three-dimensional Monte Carlo program simulates the backscattered electron signals from a contact hole which could not previously be calculated in a reasonable computation time.
High speed zone plate alignment systems
Authors: Feldman M. , Wong G. G. , Cheng M.
Published: July 2002

Zone plate alignment is routinely used in x-ray exposure tools and in optical step and repeat cameras. As with any alignment technique, the time taken to acquire and analyze the alignment data must be added to the wafer exposure time. This paper describes a technique in which the data may be acquired very rapidly by scanning the focused zone plate spot over a system of slits. For step and repeat systems this may be done during the time the table is moving to the next site. We have obtained alignments of 0.1 μ (3σ) by scanning across slits. In addition, we have developed analog circuitry which extracts the centroid of the focused spot in a few microseconds. With this circuit, the precision of spot location is <1% of the spot width. The combination of these two techniques should minimize the overhead in wafer exposure arising from the alignment process.
Effect of thin-film structures upon monochromatic optical autofocus systems
Authors: Lavine J. M.
Published: July 2002

In order to understand the focal properties of an autofocus system employing a monochromatic beam of light, a program was developed which solves Maxwell’s equations at non-normal incidence. This program was then used to calculate the focal dependence of the s and p polarizations upon thin-film structures. Calculations made at 815 nm and 79° are in good agreement with measurements. Unpolarized measurements made at 815 nm and 79° and calculations at normal incidence and other wavelengths point out the dependence of optical autofocus systems on thin-film configurations and the general requirement of a different offset for each thin-film structure.
An apparatus for batch fabrication of micromechanical elements by ion beam machining
Authors: Davies S. T. , Bowen D. K.
Published: July 2002

An apparatus has been constructed for ion beam milling of micromechanical structures. A 3 cm Kaufman type source is used to provide argon ion current densities and energies of up to 25 mA/cm2 and 1.5 kV, respectively. Stencil masks prepared by chemical milling are used to produce an array of microbeams allowing batch fabrication of micromechanical elements by scanning the mask or workpiece. Algorithms have been developed for computer control of workpiece position, orientation, and rotation. Computer control of beam current and energy has also been implemented. A database of sputtering yields and redeposition rates allows optimum operating conditions to be selected for a given application. Investigations include micromachining of refractory metals, milling of slots, holes, and grooves, and surface texturing, polishing, and figuring micromechanical structures.
Moiré alignment technique for the mix and match lithographic system
Authors: Nomura Tsutomu , Kimura Seiichiro , Uchida Yoshiyuki , Hattori Shuzo
Published: July 2002

This paper represents theoretical and experimental results using the moiré alignment technique to projection photolithography, as part of the mix and match lithographic system to go with the proximity x-ray lithography. Such a system is advantageous because the same alignment marks on the wafer are used both for photo- and x-ray lithography. The moiré signals are detected at the reverse image point of reflected beams from the moiré interference field between the wafer marks and the projection image of reticle marks through a reduction lens on the wafer marks. The basic experimental values agreed with theoretical results calculated from a grating pitch of 4 μm on the wafer. This paper also represents an alignment method which permits both fine and rough alignment simultaneously by using single alignment optical system eventually giving a wide alignment zone. These moiré alignment techniques were applied to an actual step-and-repeat photolithographic system, resulting in outstanding precision.
Fabrication and characterization of ultrashort gate length GaAs field-effect transistors
Authors: Tiberio R. C. , Wolf E. D. , Anderson S. F. , Schaff W. J. , Tasker P. J. , Eastman L. F.
Published: July 2002

We have fabricated GaAs metal–semiconductor field-effect transistors (MESFET’s) and GaAs/AlGaAs modulation-doped field-effect transistors (MODFET’s) with gate lengths of 50 and 100 nm. A JEOL 5DIIU electron-beam lithography system was used in the fabrication of these nanometer transistors. This system has demonstrated a 30-nm overlay accuracy and liftoff metal lines as narrow as 25 nm. The electrical measurement results showed a room temperature extrinsic transconductance (gm) of 540 mS/mm for the 100-nm MESFET’s and over 600 mS/mm for the 100-nm MODFET’s. The MESFET also exhibited a small signal gain of 16 dB at 18 GHz at the low-noise bias point which is the highest ever reported for a MESFET. A significant short channel effect, however, has also been observed in these very short gate transistors. In this paper, transistor fabrication will be discussed and electrical results will be presented.
On the effects of Ga in the formation of reactive interfaces
Authors: Taleb-Ibrahimi A. , Jezequel G. , Ludeke R.
Published: July 2002

We have studied the effects of heat treatments on the chemical and electronic properties of GaAs(110) surfaces covered with V or Pd to thicknesses of about 3 Å. The annealing improves the surface stoichiometry and reduces excess Ga generated during the deposition. Particularly for p-type surfaces and coverages <1 Å, the anneal reduces the position of the Fermi level by as much as 0.3 eV, which indicates that deposition and post-treatment affect the nature and energetics of defect/impurity levels. This rules out the possibility that Schottky barrier heights are universally determined by a single-intrinsic defect. Exchanged Ga does not appear to influence the position of the Fermi level for interfaces with reactive metals. Ga itself, deposited separately on clean GaAs(110) surfaces, appears to form a fixed donor level ∼250 meV above the valence band maximum (VBM) over a broad coverage range. Beyond a coverage of ∼5 Å the Fermi levels on n- and p-type GaAs essentially merge to a value of 0.63 eV above the VBM, indicating that this metal forms a conventional Schottky barrier.
Calculation of image profiles for contrast enhanced lithography
Authors: Babu S. V. , Barouch E. , Bradie B.
Published: July 2002

Simultaneous bleaching of a contrast enhancing film (CEF) and the underlying positive photoresist is considered in the absence of any interface or substrate reflectivity. The intensity transmitted by the CEF is determined as a function of exposure time exactly using the absorptivity of the film in Dill’s model equations. Corresponding to this time dependent transmitted intensity, the concentration profiles in the positive photoresist have been expressed exactly in closed form. Relations, that implicitly define the developed image profile, are derived assuming that the resist development can be approximated by a two state process. Furthermore, they are solved numerically for a polysilane–AZ2400 resist system and a model CEM-388–resist combination proposed by Mack. The predicted image profiles are in excellent agreement with the experimentally determined profiles of Hofer et al., for the polysilanes, and the predictions of prolith for the model system of Mack.
Luminescence of (Al,Ga)As and GaAs grown on the vicinal (511)B-GaAs surface by molecular-beam epitaxy
Authors: Towe E. , Fonstad C. G. , Le H. Q. , Hryniewicz J. V.
Published: July 2002

Experimental characteristics and evidence of differences in the optical properties of multiple quantum well structures grown on (511)B-  and (100)-GaAs substrates are presented. It is shown that residual background impurities do not behave in the same manner for similar structures grown on the two surfaces. It is also shown that the hole effective mass in the (511)B-based structures is different from that in similar structures on (100) surfaces.
Fabrication of a gated gallium arsenide heterostructure resonant tunneling diode
Authors: Kinard W. B. , Weichold M. H. , Kirk W. P.
Published: July 2002

Techniques used to fabricate a gated resonant tunneling diode (GRTD) are presented. Molecular-beam epitaxy (MBE), image reversal contact photolithography, liftoff metallization, anisotropic reactive ion etching, isotropic liquid etching, and a resulting self-aligned gate metal deposition technique were used to realize this effort. The physical sizes of the fabricated GRTDs were 2, 4, and 6 μm in diameter. The electrical size of the channel within the vertical resonant tunneling diode, however, was controlled by a simple, self-aligned rectifying electrode at the well region. Arrays of devices were fabricated to enhance detection while retaining small geometries. The results from these first devices indicate that an in situ transition from a two-dimensional resonant tunneling diode (RTD) to a zero-dimensional quantum dot is feasible using this design. Improvements in the design are realizable from straightforward modifications in the MBE material.
Scanning optical microscopy
Authors: Kino G. S.
Published: July 2002

Two types of scanning optical microscopes are described, the real-time scanning optical microscope and the Mirau correlation microscope. These microscopes give excellent depth definition of the order of 0.4 μm between half-power points, and can be used for optical cross sectioning. They are particularly useful for separate measurements of the top and bottom widths of trenches in photoresist at the low submicron level.
Scanning tunneling spectroscopy of graphite using an oxidized silicon tip
Authors: Venkateswaran N. , Sattler K. , Müller U. , Kaiser B. , Raina G. , Xhie J.
Published: July 2002

We report I–V characteristics of an ‘‘oxidized silicon tip on graphite’’ system realized by using a scanning tunneling microscope operating in air at room temperature. Of the 18 tips used, 2 have shown staircases in the I–V curves. We show that Coulomb blockade of electrons trapped in the oxide layer of the silicon tip causes this effect.
Nonuniform strain profiles in cubic CdS/GaAs films measured by reflection high energy electron diffraction and Raman spectroscopy
Authors: Sinha Kislay , Menéndez José , Niles David W. , Höchst Hartmut
Published: July 2002

We report a study of the strain relaxation in zinc-blende CdS films grown on GaAs by molecular beam epitaxy. We use Raman spectroscopy to determine the depth dependence of the strain profile. This dependence is compared with the instantaneous surface strain relaxation measured by reflection high energy electron diffraction during growth. The Raman results show that the strain profile determined by RHEED remains largely ‘‘frozen’’ in the final sample. It is only near the heterostructure interface, where the strain is large, that evidence of additional relaxation is found in the Raman spectrum.
Fast proximity effect correction: An extension of PYRAMID for circuit patterns of arbitrary size
Authors: Jacob Joseph C. , Lee Soo-Young , McMillan Jo A. , MacDonald Noel C.
Published: July 2002

Previously, we introduced PYRAMID, a hierarchical pattern shape modification scheme for proximity effect correction in electron-beam lithography, which enabled rapid correction of circuit patterns with linewidths down to 0.1 μm. However, it was limited to relatively small circuit patterns only. This article describes an extension of PYRAMID for circuit patterns of arbitrary size, as well as additional improvements to the previous implementation. PYRAMID is a fast hierarchical pattern modification scheme that can be conceptually partitioned into two phases: local correction to account for circuit components separated by small distances (approximately 1 μm) and global correction for circuit components separated by larger distances. PYRAMID supports input circuits composed of arbitrarily partitioned rectangles, as well as 135° angle path inputs. Also, a segmented mode of operation allows a large circuit to be corrected one segment at a time, thereby reducing computer memory requirements. Experimental results showing the successful correction of a relatively large test pattern (with linewidths as small as 0.1 μm) in 200 nm PMMA resist are provided along with correction times as a function of the number of circuit components.
Effects of interface stoichiometry on the structural and electronic properties of Ga1−xInxSb/InAs superlattices
Authors: Chow D. H. , Miles R. H. , Hunter A. T.
Published: July 2002

We report an investigation of the effects of interface layer composition on the structural and electronic properties of Ga1−xInxSb/InAs superlattices, which are of interest for infrared detector applications. Shutter sequencing during growth of a series of Ga0.75In0.25Sb (8 ML)/InAs (13 ML) superlattices by molecular-beam epitaxy has been employed to select structures with GaInAs-like interfaces, InSb-like interfaces, and intermediate choices of interfacial composition. Comparison of x-ray diffraction scans from the superlattices confirms that a superlattice with GaInAs-like interfaces has a 1.6% smaller average interatomic spacing in the growth direction than a sample with InSb-like interfaces, in near agreement with expected interfacial bond length differences. Hall measurements of intrinsic carrier concentrations at high temperatures indicate an increase in superlattice energy gap when interfaces are switched from InSb-like to GaInAs-like, consistent with intuitive expectations. Low temperature Hall measurements suggest that both the type and the level of background doping in Ga1−xInxSb/InAs superlattices may depend upon interfacial composition.
Effect of electron cyclotron resonance generated hydrogen plasmas on carbon incorporation and interfacial quality of GaAs and AlGaAs grown by metalorganic molecular-beam epitaxy
Authors: Abernathy C. R. , Wisk P. W. , Pearton S. J. , Ren F.
Published: July 2002

The authors have investigated the effect of in situ hydrogen plasmas generated by electron cyclotron resonance on growth rate and carbon incorporation in GaAs and AlGaAs grown by metalorganic molecular-beam epitaxy using triethylgallium and trimethylamine alane. Carbon backgrounds in GaAs grown at 500 °C were found to increase with increasing microwave power over the range 100–200 W and also with increasing H2 flow at 175 W. Hydrogen plasmas did not significantly increase the growth rate for either GaAs or AlGaAs even at growth temperatures as low as 375 °C. As at higher temperatures, carbon levels were not reduced in GaAs grown at low temperatures though some improvement was observed for AlGaAs grown at 375 °C. Plasmas were found to be much more effective for cleaning substrates prior to growth. At 500 °C, low microwave powers and moderate exposure times were found to produce the lowest levels of interfacial C, O, and Si contamination.
Growth modes and relaxation mechanisms of strained InGaAs layers grown on InP(001)
Authors: Gendry M. , Drouot V. , Santinelli C. , Hollinger G. , Miossi C. , Pitaval M.
Published: July 2002

Reflection high-energy electron diffraction and transmission electron microscopy were used to study the growth mode and relaxation of InxGa1−xAs layers, grown by molecular-beam epitaxy, mismatched relative to their In0.53Ga0.47As/InP(001) substrates, as a function of In composition and growth temperature (450 and 525 °C). Weakly mismatched (≊1%) layers grow layer-by-layer and relax through a regular cross-grid type 60° misfit dislocation network. Strongly mismatched (≊3%) layers begin to grow layer-by-layer, then grow with coherent three dimensional (3D) islands and relax through a tangled array of short edge dislocations. For an intermediate mismatch (≊2%), a 3D growth mode is observed at high-temperature (525 °C) which leads to a tangled dislocation array; lowering the growth temperature to 450 °C forces a two-dimensional growth mode producing a regular network of 60° and edge dislocations.
Characterization of point defect generation at silicon surfaces using gold diffusion
Authors: Graupner R. K. , Van Vechten J. A. , Harwood P.
Published: July 2002

The utility of observations of Au diffusion for the characterization of point defect generation and annihilation rates at surfaces and of vacancy distributions and diffusivity in the substrate is demonstrated. Particularly noted are the effects of ambient gases and surface finish on the diffusion process and on the resultant distributions of electrically active Au. Au was deposited on commercial float-zone Si in a vacuum system after the Si had reached the diffusion temperature (1233 K) and had been annealed in various ways. Contrary to a previously published report, electrically active Au with a one-sided profile is found when the Au is deposited and annealed in a vacuum. Previously reported two-sided profiles for electrically active Au are obtained when millitorr levels of O2 are present in the ambient gas during diffusion or during a preanneal prior to Au deposition. It is concluded that the polished or etched silicon surfaces lack the imperfections needed to make them effective sources or sinks for vacancies or self-interstitials, but that surface roughening caused by O2-induced evaporation of SiO is sufficient to create very effective sources or sinks.
Investigation of the laser-Al2O3(112̄0) surface interaction using excitation by pairs of picosecond laser pulses
Authors: Hamza Alex V. , Hughes Robert S. , Chase L. L. , Lee H. W. H.
Published: July 2002

The lifetime of a laser-induced surface excitation on Al2O3(112̄0) that leads to detectable emission of neutral or positively charged particles and further to optical surface damage is measured to be a ∼200 ps by varying the delay between pairs of 80 ps pulses at 1064 nm. The dependence of the emission threshold fluence on the time delay between laser pulses suggests a low order absorption process.
Growth of p- and n-type GaAs/(AlGa)As double barrier resonant tunneling devices on (311)A and (111)B substrate orientations
Authors: Harrison P. A. , Hayden R. K. , Henini M. , Valadares E. C. , Hughes O. H. , Eaves L.
Published: July 2002

A series of n-type and p-type double barrier resonant tunneling structures grown by molecular-beam epitaxy on different GaAs surface orientations have been investigated. Under identical growth conditions, Si incorporates preferentially as a donor for growth on (N11)B and as an acceptor on (N11)A surfaces (N=1,2,3). We report the observation of hole resonant tunneling through p-type Si-doped GaAs/AlAs double barrier structures on the (311)A GaAs surface. The high quality of the layers and interfaces allows us to observe six well-defined resonant peaks in the current–voltage characteristics. The positions of the resonances are compared with an envelope function calculation of the energies of the bound hole states in a (311)A GaAs quantum well. The (311)A plane has biaxial symmetry and, by using angle-resolved magnetotunneling spectroscopy, we are able to observe the pronounced anisotropy with respect to the crystalline axes of the confined hole states in the valence band quantum well. The I(V) curves for the (311)A orientation are compared with those of similar Be-doped structures grown on the (100)-oriented surface. We also report measurements on double barrier resonant tunneling devices based on n-GaAs/(AlGa)As with [Al]=0.4 and grown on the (111)B GaAs surface.
Quantum wells, excitons, and lasers at blue-green wavelengths in ZnSe-based heterostructures
Authors: Nurmikko Arto V. , Gunshor Robert L. , Kobayashi Masakazu
Published: July 2002

Recent developments were reviewed in ZnSe-based quantum wells and heterostructures with emphasis on physics and engineering towards light emitter applications at blue-green wavelengths. To illustrate current progress, examples are given of both diode laser and light emitting diode device research.
(511) and (711) GaAs epilayers prepared by molecular-beam epitaxy
Authors: Young K. , Kahn A. , Phillips J. M.
Published: July 2002

The surface structure, morphology, and crystallinity of high Miller index (511) and (711) GaAs epitaxial layers prepared by molecular-beam epitaxy are studied with electron diffraction, scanning electron micorscopy, Raman scattering, and Rutherford backscattering. All A- and B-(511) and (711) surfaces exhibit an ordered array of steps with (100) terraces and (111) risers. The (511)-B layers exhibit the smoothest surface morphology, and the best surface and bulk crystallinity among these layers.
Photoluminescence spectroscopy of near-surface quantum wells: Electronic coupling between quantized energy levels and the sample surface
Authors: Sobiesierski Z. , Westwood D. I. , Woolf D. A. , Fukui T. , Hasegawa H.
Published: July 2002

Photoluminescence (PL) measurements have been used to examine the influence which the proximity of the sample surface bears on the radiative recombination occurring within a near-surface quantum well (QW). The InxGa1−xAs/GaAs system exhibits dramatic attenuation in PL intensity for surface barriers below 75 Å in thickness, without any significant shift in PL peak energy. However, as the GaAs surface barrier is reduced to zero, both In0.26Ga0.74As/GaAs and In0.1Ga0.9As/GaAs QWs reveal the development of an additional PL feature at an energy which coincides with that expected for direct band-to-band recombination within the strained InxGa1−xAs layer. PL measurements for chemically etched Al0.3Ga0.7As/GaAs near-surface QWs also show a lack of shift in PL peak energy, as the outer layer is thinned gradually.
Tunable generation of microscopic and mesoscopic step arrays on non-(100)-oriented GaAs: A new route to quantum wire structures by epitaxial growth
Authors: Ploog Klaus H. , Nötzel Richard , Ilg Matthias
Published: July 2002

The evolution of ordered steps and facets on III–V semiconductor surfaces is used to directly synthesize quantum wire structures by molecular beam epitaxy (MBE). The existence of macrosteps on (311)A GaAs with a periodicity of 32 Å and a step height of 10 Å during MBE allows us to produce alternating thicker and thinner channels of GaAs in an AlAs matrix. The accumulation of steps by step bunching on (210) GaAs makes feasible the fabrication of mesoscopic step arrays in a GaAs/AlAs multilayer structure having a periodicity which is comparable to the exciton Bohr radius. Finally, a fraction of a strained InAs monolayer on (311)A GaAs is sufficient to change the surface morphology reversibly from corrugated to flat. After evaporation of the InAs the corrugation appears again. This opens a new way to tune and manipulate surface and interface corrugations on high-index semiconductor surfaces. The existence of the GaAs quantum wire structures and the tunability of their shape is confirmed by reflection high-energy electron diffraction, atomic force microscopy, high-resolution electron microscopy, and by the distinct electronic properties.
Generation and applications of compressive stress induced by low energy ion beam bombardment
Authors: McKenzie D. R.
Published: July 2002

Compressive stress is a widespread phenomenon in films subjected to ion beam bombardment. A thermodynamic treatment of materials under a general stress is used to show that preferred orientation will occur as a result of free energy minimization in a biaxial stress field. The equilibrium between structural phases of materials is also affected by stress. Thermodynamics is used to calculate the equilibrium between graphite and diamond under biaxial stress. Recent molecular dynamics studies of the mechanism of compressive stress generation are reviewed in which the phenomena of focused collision sequences and thermal spikes are studied. Experimental work shows compressive stress is linked to preferred orientation in hexagonal boron nitride films and to stabilization of high pressure phases such as cubic BN and tetrahedral amorphous carbon films, in agreement with the thermodynamic analysis.
Integrated electrostatically resonant scan tip for an atomic force microscope
Authors: Kong L. C. , Orr B. G. , Wise K. D.
Published: July 2002

The atomic force microscope (AFM) has become a practical tool for mapping surface features with a resolution better than 10 nm. As such, in recent years the demand from industry for the AFM has increased significantly. For the AFM to be a practical instrument, however, its operation must be user friendly and its performance must be consistent. The essential element of an AFM is a microprobe which uses a cantilever mounted with a sharp stylus as a force sensor. For reproducible measurements, it is crucial that the physical dimensions of the cantilever and its stylus be consistent. Typical dimensions of the cantilever are 100–200 μm in length, 20–50 μm in width, and 0.5–1.2 μm in thickness. Typical stylus dimensions include a height of at least 3 μm and a radius of tip curvature of less than 100 nm. Silicon micromachining techniques were applied to fabricate microprobes with built-in alternating-current excitation of the polysilicon cantilevers in our previous work. This article presents a compatible process for the formation of a fine grained polysilicon stylus on the cantilever and an optical port for fiber-optic interferometry readout. The process demonstrates the feasibility of integrating both electronic drive and sensing circuitry onto the microprobe for future use in multichannel AFM systems.
Molecular-beam epitaxial growth mechanisms of (Al,Ga)As on vicinal GaAs surfaces: Self-organization and step bunching
Authors: Krishnamurthy M. , Lorke A. , Wassermeier M. , Williams D. R. M. , Petroff P. M.
Published: July 2002

The growth mechanisms of (Al,Ga)As lateral superlattices (LSL) on GaAs(100) and GaAs (110) vicinal surfaces were studied using transmission electron microscopy (TEM) and Monte Carlo simulations. In GaAs(100) surfaces, spontaneous formation of a LSL from (AlAs)1(GaAs)1 short period superlattices is explained by a vertical exchange reaction model. This mechanism may be the underlying cause of poor lateral segregation in conventional fractional layer (Al,Ga)As LSL. Growth on vicinal GaAs(110) surfaces leads to periodic faceting. Cross-sectional TEM images were compared with simulation of a step-flow model to understand the process of step bunching and the evolution of periodic microfacets.
Characterization of high quality GaInP/GaAs superlattices grown on GaAs and Si substrates by gas source molecular beam epitaxy
Authors: Jelen C. , Slivken S. , He X. G. , Razeghi M. , Shastry S.
Published: July 2002

We report an analysis of the heteroepitaxial interfaces in high quality GaInP–GaAs superlattices grown simultaneously on GaAs and Si substrates by gas source molecular beam epitaxy. These two superlattices have been studied using high resolution x-ray diffraction measurements. Sharp superlattice satellites, with very little broadening, are observed within a 6° range for the sample on GaAs. Photoluminescence peaks with full widths at half-maximums of 5 and 7 meV are obtained at 4 K for samples with 58 Å wells on GaAs and Si, respectively. Room temperature exciton absorption is observed in the photovoltage measurements for a superlattice grown on Si substrate. The thicknesses determined by x-ray analysis are consistent with those obtained by a Kronig–Penny model fitting of the photovoltage spectroscopy.
Realization of three-dimensionally confined structures via one-step in situ molecular beam epitaxy on appropriately patterned GaAs(111)B and GaAs(001)
Authors: Rajkumar K. C. , Madhukar A. , Chen P. , Konkar A. , Chen L. , Rammohan K. , Rich D. H.
Published: July 2002

The realization of three-dimensionally confined GaAs/AlGaAs structures on GaAs (111)B and GaAs (001) substrates via one step in situ molecular beam epitaxy is reported. Growth is carried out on nonplanar patterned substrates with crystallographically equivalent mesa top edges. Equivalent side facets evolve during growth and completely surround the mesa top. Adatom migration from these facets to the mesa top result in shrinkage of the mesa top area leading to mesa pinch-off. Scanning and transmission electron microscopy provide evidence for the realization of structures with lateral linear dimensions ≲500 Å. Cathodoluminescence images from the (111)B structures attest to their high optical quality.
Shallow trench isolation for ultra-large-scale integrated devices
Authors: Blumenstock K. , Theisen J. , Pan P. , Dulak J. , Ticknor A. , Sandwick T.
Published: July 2002

A new process to form shallow trench isolation for ultra-large-scale integrated devices is presented. This technique utilizes chemical mechanical polish steps to provide a virtual planar surface at the end of processing for isolations of various size, ranging from 0.5 μm to several hundred μm. Superior uniformity has been obtained on wafers of 8 in. diam processed in a productionlike environment. Good device isolation also has been found.
Three-dimensional thermal analysis of high density triple-level interconnection structures in very large scale integrated circuits
Authors: Gui Xiang , Dew Steven K. , Brett Michael J.
Published: July 2002

A three-dimensional thermal model of generic multilevel interconnection systems in very large scale integrated (VLSI) circuits is presented. The temperature distributions are quantitatively studied using the transmission-line matrix modeling method. The temperature increase of a triple-level parallel and crossing interconnection-line scheme is found to be several times higher than that of a single-level parallel line structure if the same magnitude of current density in the 106 A/cm2 range is maintained. More than 50% of the temperature rise occurs across the Si substrate; the treatment of which as a perfect heat sink in many previous thermal analyses of metallization structures is, therefore, inadequate. The large thermal gradients within the SiO2 insulators between different metallization levels can be eliminated and the temperature rise can be significantly reduced if the SiO2 interlevel and passivation dielectrics are replaced by a material with much higher thermal conductivity. Lower temperatures would be beneficial for improving electromigration lifetime and reducing thermal stress voiding in high density VLSI multilevel interconnections.
Optimization of contacts and mobilities for (001) oriented two-dimensional hole gases
Authors: Cheng T. S. , Johnston D. , Middleton J. , Strickland K. , Hughes O. H. , Harris J. J. , Foxon C. T. , Mellor C. J.
Published: July 2002

A series of conventional and novel (AlGa)As/GaAs two-dimensional hole gas (2DHG) structures have been grown on (001) oriented surfaces. The samples were grown following an identical growth regime so as to render them comparable. The effects of variation in spacer layer width, growth interruption at the (AlGa)As/GaAs interface, variation in continuous and δ-doped beryllium density and of the subsequent contacting procedures, together with the use of As2 instead of As4 during growth, have been studied. The results are compared with theoretical analysis and an improved procedure for producing and contacting high mobility 2DHGs is described.
Si-indiffusion and O-outdiffusion processes at Si/SiO2/GaAs-oxides/GaAs structures: Implications in SiO2 formation and GaAs regrowth
Authors: Jiménez I. , Sacedón J. L.
Published: July 2002

The formation of SiO2/GaAs structures from reduction of substrate oxides has been studied by x-ray photoemission spectroscopy. GaAs oxides reduction is induced by Si deposition and subsequent high-temperature annealing. The deposition of Si on oxidized GaAs surfaces promotes the reduction of the GaAs oxides and the formation of SiO2, Si diffusion being the predominant process. This mechanism allows one to obtain SiO2 thicknesses up to 15 Å. Over this limit Si diffusion is negligible, Si nucleates on top of the Si dioxide layer, and a substantial amount of GaAs oxides can remain unreduced between the SiO2 layer and the GaAs substrate. Subsequent annealing to 870 K produces the disappearance of the GaAs oxides together with loss of Si atoms. A process based on breakage of the Ga–O bonds with Ga atoms remaining between SiO2 and the substrate, and oxygen atoms diffusing through the SiO2 to the outer surface, is consistent with the experimental results. The oxygen atoms react with the outer Si layer, showing an etchant behavior, and the Ga and As atoms supplied by their oxides recombine to form GaAs.
Problems relevant to the use of optical pyrometers for substrate temperature measurements and controls in molecular beam epitaxy
Authors: Nouaoura M. , Lassabatere L. , Bertru N. , Bonnet J. , Ismail A.
Published: July 2002

In molecular beam epitaxy an optical pyrometer is frequently used to determine substrate and epilayer temperatures during the growth of semiconductors. This implies a calibration of the pyrometer and a correct analysis of its indications. In this article we discuss problems presented by this calibration. We first compare the temperatures measured on the sample holder and on several substrates (GaAs, InAs, GaSb) attached to it. Then we present examples of temperature variations recorded during the growth of AlSb and GaSb on GaSb or GaAs substrates. GaSb epilayers thicker than 0.1 μm induce a 40°–60° decrease of the measured temperature. AlSb deposition on GaSb produces temperature oscillations. We discuss these variations in terms of apparent and true temperature variations.
Grain growth in copper films exposed to magnetically enhanced plasmas
Authors: Naeem Munir D. , Rossnagel Stephen M. , Rajan Krishna
Published: July 2002

The effects of low-energy plasma bombardment have been quantified for the first time. The plasma effects on thin copper films (∼50 nm) have been studied by exposing these films to magnetically enhanced Ar plasmas. The Cu films deposited by different techniques were exposed to plasmas by systematically varying the exposure time and the rf power. The microstructural changes (grain size) in the films were studied using transmission electron microscopy. Grain growth is observed in thin Cu films when the films are exposed to low-energy (63–114 eV) Ar plasmas. rf power is shown to have a strong influence on the microstructure of Cu films. The microstructural changes in sputtered and evaporated films are quite significant whereas the plasma bombardment has less effect on chemical vapor deposited films. These changes occur very rapidly and cannot be attributed solely to the thermal effects especially at low rf powers (300–500 W). The effect of temperature, however, becomes significant at 700 W. The initial microstructure of the film also plays a role in grain growth during plasma exposure.
End point control via optical emission spectroscopy
Authors: Litvak Herbert E.
Published: July 2002

We have studied the use of optical emission spectroscopy for end point detection in two dry etch applications: SiO2 contact etch in both parallel plate (diode) and high density plasma reactors, and high selectivity poly-Si over SiO2 etch in a chemical downstream reactor, where chemiluminescence is the source of optical emission. We show that useful end point results can be achieved in these processes, using a conventional monochromator/photomultiplier approach, in conjunction with appropriate signal conditioning and end point detection algorithms. Use of a background-correction channel is effective in removing signal drift in the SiO2 contact etch, while use of a large optical aperture is effective in dealing with the very low levels of emitted light in the downstream etch. Important aspects of the signal conditioning and end point detection algorithms are described.
Electron-beam microcolumns for lithography and related applications
Authors: Chang T. H. P. , Thomson M. G. R. , Kratschmer E. , Kim H. S. , Yu M. L. , Lee K. Y. , Rishton S. A. , Hussey B. W. , Zolgharnain S.
Published: July 2002

Lithography with an array of miniaturized scanning electron-beam columns presents one of the most promising high-throughput possibilities for fabrication of devices with feature sizes less than 100 nm. With scanning electron beams no mask is required and the necessary resolution and alignment of overlay structures are realizable. With arrays of microcolumns, the lithography throughput of a single column can be multiplied. The approach can also be used for a number of lithography related applications such as metrology, inspection, testing, etc. We review the status of the microcolumn program and discuss opportunities and challenges of this approach to high-throughput nanolithography and related applications. Special emphasis is given to lithography in the 100 nm regime.
Atomic-scale structure of InAs/InAs1−xSbx superlattices grown by modulated molecular beam epitaxy
Authors: Lew A. Y. , Yu E. T. , Zhang Y. H.
Published: July 2002

We present cross-sectional scanning tunneling microscopy (STM) studies of the atomic-scale structural and electronic properties of InAs/InAs1−xSbx superlattices grown by modulated molecular-beam epitaxy. In this technique the Group V composition is controlled by rapid modulation of the Group V beams rather than adjustment of the Group V flux ratios. A superlattice sample was grown at 475 °C consisting of 52 Å InAs1−xSbx alternating with 172 Å InAs for 30 periods on a GaSb (001) substrate. The InAs1−xSbx alloy layers consisted nominally of 7.8 Å InAs alternating with 5.2 Å InSb for four periods. X-ray diffraction was used to determine an average composition of InAs0.76Sb0.24 for the alloy layers. Constant-current STM images of the superlattice exhibit clear, electronically induced contrast between the InAs layers and InAs0.76Sb0.24 layers, and also reveal ordering within the InAs0.76Sb0.24 layers. Interfaces between the InAs layers and the InAs0.76Sb0.24 layers appear sharp, though there is evidence of more atomic intermixing at the InAs-on-InAs0.76Sb 0.24 interface. Significant variation in composition within individual InAs0.76Sb 0.24 alloy layers and apparent Sb incorporation from the InAs0.76Sb0.24 layers into the surrounding InAs layers are also observed.
Characteristics of gap fill and planarization of fluorinated polyimide FPI-45M films
Authors: Wang Shi-Qing , Zhao Bin
Published: July 2002

Cross sectional scanning electron microscopy was used to characterize the gap fill and planarization properties of DuPont experimental fluorinated polyimide FPI-45M films in Al–Cu metal gaps (0.25 to 2.0 μm in width) and over Al–Cu metal lines/spaces (0.50/0.50 to 50/100 μm in lines/spaces). It was found that the gap fill and planarization properties were dependent on the orientation of the lengthwise direction of the Al–Cu metal gaps and lines/spaces relative to the radius. Slightly enhanced fill is observed when gaps are parallel to the local radius. Planarization over small lines/spaces is identical regardless of their orientations. However, for large lines/spaces, planarization values are significantly higher when the line/space orientation is 90° relative to the radius than those oriented 0° relative to the radius.
Dual tunneling-unit scanning tunneling microscope for length measurement based on crystalline lattice
Authors: Zhang Haijun , Higuchi Toshiro , Nishioki Nobuhisa
Published: July 2002

A dual tunneling-unit scanning tunneling microscope (DTU STM) was developed for nm order length measurement with wide scan range. The crystalline lattice of highly oriented pyrolitic graphite (HOPG) was used as reference scale. A reference unit was set up on top of a test unit. The reference sample holder and the probe tip of test unit were attached to one single XYscanner on either surface, while the test sample holder was open. This enables simultaneous acquisition of wide images of HOPG and test sample. The length in test sample image was measured by counting the number of HOPG lattices. An inchworm actuator and an impact drive mechanism were introduced to roughly position probe tips. The XY scanner was designed to be elastic to eliminate image distortion. Some comparison experiments using two HOPG chips were carried out in air. The DTU STM is confirmed to be a stable and more powerful device for length measurement which has nanometer accuracy when covering a wide scan range up to several micrometers, and is capable of measuring comparatively large and heavy samples.
Effect of annealing temperature on electrical stability of radio frequency magnetron sputtered silicon oxides
Authors: Jelenkovic Emil V. , Tong K. Y.
Published: July 2002

Silicon oxides were rf magnetron sputtered on p-type silicon wafers, and annealed in the temperature range from 700 to 1000 °C for furnace annealing and from 950 to 1050 °C for rapid thermal annealing. The annealed oxides in metal–oxide–semiconductor structures were stressed with a constant current. Stability was monitored by midgap voltage and interface states density. The optimum condition to achieve the best electrical stability was furnace annealing at about 900 °C. It gives the least value of generated interface states and trapped charge after the electrical stress. A close relation between positive charge trapping and interface states generation is observed.
Molecular beam epitaxy of highly mismatched In0.73Ga0.27As on InP for near-infrared photodetectors
Authors: Kochhar R. , Hwang W.-Y. , Micovic M. , Mayer T. S. , Miller D. L. , Lord S. M.
Published: July 2002

We demonstrate that high-quality lattice-mismatched In0.73Ga0.27As:InP photodetectors for use at 2.2 μm can be grown by molecular beam epitaxy using compositionally graded buffer layers. By investigating various growth conditions, we found that the quality of the active layer material depends on the thickness of the compositionally graded buffer layers and the substrate temperature during the growth of the compositionally graded buffer layers and active layers. The best device performance was obtained from a sample with a 1.0 μm compositionally graded buffer grown at a substrate temperature of 350 °C combined with active layers grown at 400 °C. The typical room temperature dark current at a reverse bias of 1 V for 100×100 μm2 photodetectors on this sample was 2 mA/cm2. This dark current is a factor of 10 better than that of commercially available devices fabricated from material grown using vapor phase epitaxy.
New metal etching method for reducing electron shading damage
Authors: Tabara Suguru
Published: July 2002

This study proposes a new metal etching method for reducing electron shading damage using an inductively coupled plasma (ICP) etcher. Electron shading damage is caused by the same mechanism as in “notch” formation. Namely, negative charge-up of the sidewall of the photoresist by electrons due to the difference between electron and ion motion in the plasmas. We can therefore assume that an etching process with no notch will have low electron shading damage. The notch-free overetching process using low inductive power in an ICP etcher was found to have low and uniform electron shading damage. We also present an evaluation method for electron shading damage using a metal–nitride–oxide–silicon capacitor with a comblike antenna.