bluuebunny/crossref_metadata_2025 huggingface dataset:
Tungsten patterning for 1:1 x-ray masks
Authors: Jurgensen C. W. , Kola R. R. , Novembre A. E. , Tai W. W. , Frackoviak J. , Trimble L. E. , Celler G. K.
Published: July 2002

A subtractive process to form subhalf micron, vertical-walled patterns in half-micron thick tungsten on x-ray masks has been developed. Electron-beam lithography was used to form resist patterns on a structure consisting of 300 Å Cr on 5000 Å W on 200 Å Cr on an approximately 1 μm thick poly-silicon or silicon nitride membrane. The Cr masking and etch-stop layers above and below the W layer are required because the resist and membrane materials etch rapidly in fluorine based W etching plasmas. Chromium was chosen for these layers because it has a high selectivity in the W etch (≊40:1), is compatible with the W deposition process, and can be patterned in an O2–Cl2 plasma which does not etch W or the membrane materials. Helium backside cooling at a pressure from 1 to 5 Torr controls membrane temperature during all plasma processing steps. Pure CBrF3 or CHF3 etch W slowly while simultaneously depositing polymer which produces sloping profiles where the base of the feature is wider than the initial mask width. Pure SF6 gives high etching rates but the fluorine radicals attach the W sidewall causing undercutting. Depositing polymer on the sidewall by adding CHF3 or CBrF3 to the SF6 reduces undercutting, but produces sloping profiles. The undercutting found with pure SF6 can be eliminated with vertical profiles by etching at low temperature or by adding N2 or Cl2 to the gas mixture to form low volatility reaction products with tungsten on the sidewall.
Patterning tungsten films with an electron beam lithography system at 50 keV for x-ray mask applications
Authors: Rhee K. W. , Ting A. C. , Shirey L. M. , Foster K. W. , Andrews J. M. , Peckerar M. C. , Ku Y.-C.
Published: July 2002

The application of electron beam lithography for the fabrication of x-ray masks is essential in the development of x-ray lithography technology. In this paper we present experimental results on the patterning of submicron (2–0.25 μm) features into a single-layer negative e-beam resist and then subsequent transfer of these patterns onto a 0.4 μm-thick tungsten film by reactive ion etching. To study the dependence of the proximity effect on the substrate material, a comparison of linewidths and sidewall profiles of electron beam resist images on silicon, silicon dioxide on silicon, and tungsten on silicon wafers has been established.
Near-field scanning optical microscopy II
Authors: Isaacson M. , Cline J. A. , Barshatzky H.
Published: July 2002

A brief survey of the principles of near-field optical imaging will be presented. Selected examples of super resolution imaging using visible reflected light will demonstrate that lateral resolution far smaller than the illumination wavelength can be achieved and that the technique is surface sensitive. In addition, we will demonstrate that subwavelength resolution can be achieved in the near-infrared spectral regime and that near-field scanning optical microscopy (NSOM) can be used in diagnostic inspection of hetrojunction laser modal emission patterns.
Proximity effect correction in electron-beam lithography: A hierarchical rule-based scheme—PYRAMID
Authors: Lee Soo-Young , Jacob Joseph C. , Chen Chung-Ming , McMillan Jo A. , MacDonald Noel C.
Published: July 2002

PYRAMID, a hierarchical, rule-based scheme for proximity effect correction in electron-beam lithography is proposed. The current implementation performs solely pattern modification, and uses a single dose for the entire circuit. Based on a digital image processing model of the physical lithographic process, a hierarchical correction procedure is employed in two parts, local correction and global correction. The local correction, fully implemented, is concerned with interactions between circuit components within a small window. The local correction itself is very systematic, using two levels of correction to minimize proximity effect caused by intrashape and intershape interactions, respectively. Rule tables are used to dictate correction modes for different situations. These tables, constructed a priori, are utilized to accelerate the correction process by minimizing the numerical calculation required during circuit correction. While the local correction ignores interactions between widely separated circuit elements, the global correction takes general characteristics of the entire circuit pattern into account to make adjustments to the local correction modes. This combination of local and global corrections permits the correction of arbitrarily sized circuit patterns in a small fraction of the time required by many previous approaches that are more computationally intensive. In addition, PYRAMID produces output circuit patterns that are decomposable into rectangles, allowing efficient representation of the circuit patterns, and maintaining compatibility with shaped electron-beam architectures. Furthermore, the hierarchical approach that has been employed permits us to develop and evaluate fast proximity correction schemes for new electron-beam architectures such as parallel beam lithography systems. Such system architectures may place severe constraints on the allowable dosage variation, e.g., constant dose, during exposure. Test patterns with a minimum feature size of 0.1 μm are presented along with corresponding correction times.
Dark current processes in thinned p-type HgCdTe
Authors: Blanks D. K.
Published: July 2002

Previous studies of p-type Hg1−xCdxTe indicate that diffusion is the dominant dark current mechanism for material with a 10 μm spectral cutoff (x=0.225) at 77 K [J. P. Omaggio, IEEE Trans. Electron Dev. 37, 141 (1990)]. This work demonstrates a 10X reduction of diffusion current in p-type HgCdTe upon thinning to a 10 μm thickness. Charge transient measurements applied to metal–insulator semiconductor (MIS) structures were used to determine dark currents over a temperature range of 40–110 K and electric fields of 0.5–1.4 V/μm for thick/thin pairs of p-type HgCdTe slices. Emperical fits to dark current measured in thick and thinned sister slices are compared to theoretical expressions for diffusion and tunnel current mechanisms.
Mercury cadmium telluride and related compounds: The last ten years and the next ten years
Authors: Freeman Charles F.
Published: July 2002

The series of workshops on the Physics and Chemistry of Mercury Cadmium Telluride (MCT) and related compounds has been in existence for about ten years now. It is worthwhile to take a look at its origins; the progress in these past ten years and some projections for the next ten years as we prepare to enter the 21st century.
Probing the surface chemistry of polycrystalline ZnO with scanning tunneling microscopy and tunneling spectroscopy
Authors: Rohrer Gregory S. , Bonnell Dawn A.
Published: July 2002

Scanning tunneling microscopy and spatially resolved tunneling spectroscopy have been used to examine polycrystalline ZnO surfaces in ultrahigh vacuum after bake-out, after a low temperature anneal that cleaned the surface, after a high temperature anneal, which segregated bismuth to the surface, after being dosed with O2 and H2O, and after exposure to air. The tunneling spectra depend both on the proximity to structural features, such as grain boundaries, and on the chemical composition of the surface. For example, the segregation of bismuth to the surface causes the tunneling spectra to have a p-type rectification. Our results also indicate that the rectification of tunneling spectra acquired in air is caused by surface hydration and that images of surfaces that have not been heated in vacuum have inferior resolution due to a reduction in the height of the apparent tunnel barrier. Spatially resolved tunneling spectroscopy has been used to demonstrate that surface hydration has a greater effect on the crystallite surfaces than on the grain boundary surfaces.
On the three-dimensional scanning tunneling microscopy formalism
Authors: Barniol N. , Pérez F. , Aymerich X.
Published: July 2002

The tunneling current using Bardeen formalism is calculated in a scanning tunneling microscope (STM). We take into account that the process is nonspecular tunneling, so the no conservation of the transverse wave number is considered. The tip is a three-dimensional box with free electrons inside and with the transversal dimensions in the atomic range. Note that with this description the allowed states inside the tip are quantified and that it is necessary for the electrons to have at least a minimum value for the energy in the parallel direction. The wave functions inside the sample are described as extended plane waves. Using a perturbative potential, the wave functions of the electrons inside and outside the tip are calculated. The matrix element to apply Bardeen formalism is calculated using the second Green’s identity which makes unnecessary the tip’s wave function outside it. Thus, instead of doing the integration on a tunnel surface, we have done the integration over the tip volume. Finally a discussion of the lateral resolution of the STM in terms of the transverse wave number is made.
A scanning tunneling microscope controlled field emission microprobe system
Authors: Chang T. H. P. , Kern D. P. , McCord M. A. , Muray L. P.
Published: July 2002

A novel approach based on scanning tunneling microscopy controlled field emission with microlens to form an exceptionally high brightness electron source and low aberration electron probe forming system has been explored. Electron optical studies of such a microsource have shown it to have a brightness two to three orders of magnitude greater than conventional field emission sources at energies in the low keV range and the ability to form an ultrahigh resolution probe with diameter in the 1 to 10 nm range in conjunction with additional microlenses. Encouraging preliminary experimental results have been obtained.
Low energy off-axis focused ion beam Ga+ implantation into Si
Authors: Steckl A. J. , Mogul H. C. , Novak S. W. , Magee C. W.
Published: July 2002

Off-axis focused ion beam (FIB) implantation of Ga+ has been performed at low energies to study the channeling effect. FIB implantations were performed at 3, 5, and 10 keV into crystalline (100) Si at tilt angles of up to 15° toward the 〈110〉 axis. The Ga atomic depth profile was measured using secondary ion mass spectrometry with a 2-keV-Cs+ primary beam incident at 60° from the sample normal, in order to minimize ion beam mixing effects during sputttering. The Ga depth profiles show significant reduction in channeling with implantation tilt angle. The fractions of the Ga dose found in the tail of distribution for the 5 keV implant were ∼16% and 10% for the 0° and 15° off-axis implantation, respectively. Corresponding values reported for 5-keV B+ implantation under the same conditions are ∼50% and 19%, respectively. Thus, low energy FIB Ga implantation is seen to not only have a much lower penetration depth than B, but also to produce more effective channeling suppression.
Ion irradiation induced effects in polyamidoimide
Authors: Merhari L. , Belorgeot C. , Moliton J. P.
Published: July 2002

The interaction between ion beam and polyamidoimide (PAI) is studied by means of low-temperature infrared spectroscopy. 200 keV Ar+ and 250 keV He+ beams with fluences ranging from 1013 ions cm−2 to 5×1016 ions cm−2 are found to induce atomic bond breaks leading to absorption bands at 2344, 2261, and 2125 cm−1 corresponding respectively to CO2, C=N=N and C=N–R vibrations. Shrinkage of the polymer along with a drastic decrease of the resistivity during Ar+ and He+ irradiation are observed. Speculations on the respective role of electronic processes and atomic collisions in the evolution of the polymer are made. No evidence of PAI modification through knock-on mechanism for fluences lower than 5×1015 ions cm−2 is noticed. In fact, our results would suggest a predominant role of the electronic processes for the low fluences (up to 5×1015 ions cm−2 ), whereas a degradation mechanism based on atomic collisions is more likely to take place for higher fluences. A theoretical mechanism of reactions based upon our Fourier transform infrared (FTIR) and secondary ion mass spectroscopies (SIMS) results, describing the chemical changes occurring in the PAI, is presented and briefly discussed.
Kinematic theory of ballistic electron emission spectroscopy of silicon–silicide interfaces
Authors: Stiles M. D. , Hamann D. R.
Published: July 2002

The electronic structure of the materials being measured has a strong effect on the spectroscopy of the interface between them measured by ballistic electron emission microscopy (BEEM). Specific calculations for CoSi2/Si(111) and NiSi2/Si(111) based on the calculated band structures of the materials illustrate some of the observable effects due to band structures, particularly of the overlayer. The BEEM spectra for CoSi2/Si(111) show a delayed onset due to a mismatch of the states near the conduction band minimum in the Si. The spectra for NiSi2/Si(111) show structure due to a decrease in the density of states in the NiSi2 at ∼1.8 eV above the Fermi level.
Ellipsometric profiling of HgCdTe heterostructures
Authors: McLevige W. V. , Arias J. M. , Edwall D. D. , Johnston S. L.
Published: July 2002

The application of ellipsometry in conjunction with step etching is demonstrated for determining compositional profiles of Hg1−xCdxTe heterostructures. Measurements of the ellipsometric ψ parameter can be directly correlated with composition, x, for 0.2<x<0.35, as long as the ellipsometric Δ parameter remains in the 146°–148° range. An approximate functional expression for the calibration of ψ versus x was determined to be ψ(x)=14.73–12.96x+2.726x2, and is expected to be reasonably accurate over the entire range from x=0 (HgTe) to x=1 (CdTe). The accuracy of this technique in practice is generally within ±0.01 in x value, with a depth resolution of ∼1000 Å.
An x-ray photoelectron spectroscopy study of bonding at II–VI/III–V heterovalent interfaces
Authors: Menke D. R. , Qiu J. , Gunshor R. L. , Kobayashi M. , Li D. , Nakamura Y. , Otsuka N.
Published: July 2002

In this paper in situ x-ray photoelectron spectroscopy (XPS) is used to study the nature of the bonding at ZnSe/GaAs and CdTe/InSb interfaces grown by molecular-beam epitaxy. X-ray photoelectron spectra support the transmission electron microscopy evidence that ZnSe/GaAs MIS capacitors exhibiting low interface state densities are associated with the formation of an interfacial layer of zinc blende Ga2Se3. An interfacial layer can be deliberately introduced by reacting an As deficient GaAs surface with an incident Se flux. A comparison of the Se 3d core level features from the ZnSe epilayer surface, a Se-reacted GaAs surface, and from separately grown Ga2Se3 epilayers, clearly indicate the same Se bonding characteristic for the Se-reacted layer, and the Ga2Se3 epilayer. A parallel XPS study of CdTe/InSb interfaces leads to the conclusion that there is a general tendency for the formation of a III–VI interfacial compound when forming a II–VI-on-III–V junction.
The molecular beam epitaxy growth of InGaAs on GaAs(100) studied by i
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u scanning tunneling microscopy and reflection high-energy electron diffraction
Authors: Snyder C. W. , Barlett D. , Orr B. G. , Bhattacharya P. K. , Singh J.
Published: July 2002

I n situ real space images and reflection high energy electron diffraction (RHEED) data for the initial stages of molecular beam epitaxy growth of highly strained InxGa1−xAs (0.3≤x≤0.6) on GaAs(100) are reported. RHEED patterns, specular intensity oscillations, and surface lattice constant data are recorded simultaneously during growth. From the RHEED analysis we divide the film evolution into two stages, corresponding to a largely unrelaxed and relaxed surface lattice constant. Scanning tunneling microscopy images of the surface of the film as it appeared during growth reveal that the initial phase has a rippled morphology. With further growth the film evolves to a distinctive three-dimensional island microstructure. Both of these characteristic morphologies are interpreted as manifestations of strain in the growing film.
Thermal expansion contributions to band gap and band offset temperature dependencies
Authors: Malloy Kevin J. , Van Vechten James A.
Published: July 2002

Using a thermodynamic approach, we examine the role thermal expansion plays in determining the temperature dependence of band gaps and band offsets. Because of the large variation in the standard volume of electrons (or, equivalently, variation in conduction-band deformation potential) with symmetry of the conduction band, most of the band-gap temperature variation can be ascribed to the valence band for the X gap, while the variation is more equitably divided between the conduction and valence band for the Γ band gap. The particulars of the AlAs/GaAs system are examined in detail, where we find evidence that X electrons have a larger electron–phonon entropy than Γ electrons, and that the lowest conduction-band offset exhibits considerable temperature variation.
Characterization of semiconductor materials and devices using acoustoelectric voltage measurement
Authors: Tabib-Azar M. , Abedin M. N. , Abbate Agostino , Das P.
Published: July 2002

During the past 20–25 years, the nondestructive surface acoustic wave (SAW) measurement technique has been developed and used to characterize the electrical properties of semiconductor materials and devices. Important semiconductor parameters such as carrier density, type and mobility, interface and fixed oxide charge densities, deep-level cross section and activation energy, and excess carrier generation and recombination lifetimes are all determined using SAW. In the majority of these experiments, separate medium structure is used where SAW is generated at the surface of a piezoelectric substrate like LiNbO3. SAW in the piezoelectric materials is accompanied by a decaying electric field which interacts with the free carriers of a semiconductor placed nearby. The spatial resolution that is usually achieved in these measurements is on the order of the SAW wavelength or the extrinsic Debye length, whichever is shorter. Variety of semiconductors are characterized using SAW including: silicon, GaAs, AlxGa1−xAs, InAs, GaP, HgxCd1−xTe, CdTe, InP, CdS, and InAs. More recently, high Tc ceramic superconductors have also been studied. The most important aspect of the SAW technique is that it is nondestructive and it has very high sensitivity in studying high resistivity materials. Here, we present a review of the SAW technique discussing its application in quantitative characterization of semiconductor materials and devices.
Growth of uniform HgCdTe by metalorganic chemical vapor deposition system
Authors: Murakami S. , Sakachi Y. , Nishino H. , Saito T. , Shinohara K. , Takigawa H.
Published: July 2002

Hg1−xCdxTe growth was studied, evaluating the uniformity in terms of the composition, thickness, and surface morphology. Growth was done on a 3 in. GaAs substrate in a vertical reactor using metalorganic chemical vapor deposition featuring a rotating susceptor with multiple nozzles. In a simulation based on the results of our experiment, we found that eight nozzles are needed to grow an epilayer having a compositional variation (Δx) within 0.002. Hg1−xCdxTe was grown using eight nozzles after a CdTe (111)B buffer layer was grown on a 3 in. GaAs (100) wafer. The maximum variation in x(Δx) was 0.010, and the mean value (x̄) was 0.264 over the full surface of the 3 in. diam wafer. The thickness variation (Δd) was 0.7 μm, and the mean value (d̄) 5.7 μm. An evaluation of the surface morphology showed a specular surface with small triangular pits. The etch pit density was 2.6–7.4×106 cm−2.
Patterned metal growth from dimethylaluminum hydride
Authors: Zhu Nongfan , Cacouris Ted , Scarmozzino Rob , Osgood Richard M.
Published: July 2002

We report on a two-step process for the patterning and growth of aluminum films from the metallorganic source gas dimethylaluminum hydride (DMAlH). In particular, ultraviolet light from a cw or pulsed laser source is used to generate a seed layer for selective chemical vapor deposition of aluminum conductors. The dependence of growth selectivity on the temperature and substrate material, the influence of the seed-layer thickness on film growth, and the process parameters such as temperature and pressure, that yield high purity aluminum, are presented. This technique has been applied to two applications with different materials requirements: final metallization of a complementary metal–oxide-semiconductor gate array in silicon, and electrode formation for GaAs/AlGaAs integrated optical modulators.
X-ray mask development based on SiC membrane and W absorber
Authors: Chaker M. , Boily S. , Diawara Y. , El Khakani M. A. , Gat E. , Jean A. , Lafontaine H. , Pépin H. , Voyer J. , Kieffer J. C. , Haghiri-Gosnet A. M. , Ladan F. R. , Ravet M. F. , Chen Y. , Rousseaux F.
Published: July 2002

We report a detailed description of x-ray mask technology based on SiC membrane and tungsten absorber. Amorphous SiC films were prepared using either a 100 kHz plasma-enhanced chemical vapor deposition (PECVD) system (allowing a high throughput) or a laser ablation deposition (LAD) technique. The PECVD a-SixC1−x:H films have a maximum Si–C bond density at x=0.5, a hydrogen content of 27 at. % and a high-compressive stress (1 GPa). The LAD films are stoichiometric, hydrogen-free, and under high-compressive stress (1.4 GPa). In order to achieve the tensile stress range (20–40 MPa) required for membrane fabrication, we developed a well-controlled rapid thermal annealing (RTA) process. At 633 nm, the resulting PECVD and LAD membranes have an optical transparency of 75% and 40%, respectively, and their corresponding biaxial Young’s moduli are 250±30 and 360±60 GPa. A novel approach using RTA for ‘‘fine tuning’’ of the tungsten stress is also proposed. Low stress (≤10 MPa) is obtained for W layers initially under compressive stress lower than 300 MPa. Finally, using an e-beam patterning process based on a single resist layer and reactive ion etching for the pattern transfer, x-ray masks with linewidths down to 100 nm were developed.
Nanometer metal–oxide semiconductor field effect transistor structures for studying electron transport
Authors: Jin Gongjiu , Tang Y. S. , Thoms S. , Wilkinson C. D. W. , Gundlach A. M.
Published: July 2002

Nanostructures including quantum wires and rings based on polycrystalline silicon gate metal–oxide semiconductor field effect transistor system were fabricated for fundamental studies of electron transport. Gate configurations were defined by electron beam lithography and dry etching using whole 3 in. wafers. A good low-field electron mobility (∼1.5 m2 V−1 s−1) in the inversion channel has been obtained at 4.2 K. Clear steplike quantized conductance has been observed at 4.2 K in the wires fabricated.
Arrayed miniature electron beam columns for high throughput sub-100 nm lithography
Authors: Chang T. H. P. , Kern D. P. , Muray L. P.
Published: July 2002

In recent years, considerable progress has been made on an approach based on a novel concept which combines scanning tunneling microscope, microfabricated lenses, and field emission technologies to achieve microminiaturized low-voltage electron beam columns with performance surpassing the conventional column. High throughput lithography is a potentially very important application for these microfabricated columns which measure only millimeters in dimensions. This is to be achieved using an array of these minicolumns in parallel in a multibeam mode with one or more columns per chip. The low-voltage operation is attractive because proximity effect corrections may not need to be applied. In addition, an arrayed microcolumn system also has the potential of reducing the cost of the overall system through the compaction of the mechanical system. The throughout advantages for such an arrayed system based on different beam forming optics and pattern generation approaches will be discussed. In addition to lithography, a wide range of other applications for such an arrayed system such as testing, metrology, storage, etc., can also be considered.
Epitaxial CoSi2 formation on Si(001) from an amorphous Co75W25 sputtered layer
Authors: La Via F. , Reader A. H. , Duchateau J. P. W. B. , Naburgh E. P. , Oostra D. J. , Kinneging A. J.
Published: July 2002

The formation of epitaxial CoSi2 on (001) Si using the solid state reaction between an amorphous Co75W25 sputtered layer and Si has been studied. Auger electron spectroscopy depth profiling, Rutherford backscattering spectrometry, x-ray diffraction, transmission electron microscopy, and resistivity and mobility measurements on Van der Pauw structures have been used to investigate the interaction between the amorphous alloy and Si. By employing anneals in vacuum between 500 and 600 °C for 60 or 120 min, Co diffuses out of the alloy into the substrate to form CoSi2. X-ray diffraction measurements indicate that the greater part (about 75%) of the disilicide film is epitaxial. The CoSi2 film is unstrained at the growth temperature. At room temperature a tetragonal distortion of the silicide lattice is noted, which results from cooling from the growth temperature, and is caused by the difference in the thermal expansion coefficients of Si and CoSi2. After a selective etch to remove the remaining amorphous alloy, a second anneal at a higher temperature has been performed to improve the quality of the silicide. As a result of the second anneal, the Rutherford backscattering channeling minimum yield and the residual resistivity of the film decrease to values of about 25% and 2.6 μΩ cm, respectively. Only the epitaxial (A type) orientation of CoSi2 could be detected after the second anneal by x-ray pole figure measurements. Both the vertical and the lateral distortions in the silicide lattice, measured at room temperature, appear to decrease during this anneal. The Debye temperature, obtained from electrical measurements, increases from 382 K, after Co outdiffusion, to 412 K after the second anneal.
Ohmic contact study for quantum effect transistors and heterojunction bipolar transistors with InGaAs contact layers
Authors: Chen W. L. , Cowles J. C. , Haddad G. I. , Munns G. O. , Eisenbeiser K. W. , East J. R.
Published: July 2002

Two ohmic contact systems for quantum effect devices and heterojunction bipolar transistors (HBTs) were investigated and compared. Ni/Ge/Au/Ti/Au and Pd/Ge/Ti/Al were characterized for diffusion length after annealing and specific contact resistivity on chemical beam epitaxially grown In0.53Ga0.47As. It was found, in general, that the diffusion length could be controlled by varying the total metal thickness and that the specific contact resistivity maintained reasonably low values as long as the compositional ratio of each system remained constant. The diffusion length for Ni/Ge/Au/Ti/Au ranged from 1000 to 2000 Å and that of Pd/Ge/Ti/Al was ∼300 Å. In both cases the specific contact resistivity on n-type InGaAs was 5×10−7 Ω cm2. Furthermore, the Pd/Ge/Ti/Al was applied to p-type InGaAs and showed a specific contact resistivity of 3×10−6 Ω cm2. Finally, both systems were used to fabricate an InGaAs/InP hot electron transistor and an InAlAs/InGaAs HBT with excellent direct-current results.
Geometrical growth rate nonuniformity effects on reflection high-energy electron diffraction signal intensity decay
Authors: van der Wagt Jan P. A. , Bacher Kenneth L. , Solomon Glenn S. , Harris James S.
Published: July 2002

We have discovered a method to use the physical positioning of one or more effusion cells in a molecular-beam epitaxy system to cancel out linear growth rate variations along the area sampled by the reflection high-energy diffraction (RHEED) beam. This cancellation, seen for example by growing with two Ga cells at the correct flux ratio, allows RHEED oscillations to continue for 250 periods where only about 20 oscillation periods are obtained with either source alone. An unrotated growth was performed to measure the nonuniformity from a single source and the results were used in a simple simulation of the RHEED response. The simulated decay and beat pattern agree well with experiment.
Well width dependence of electron transport in molecular-beam epitaxially grown InAs/AlSb quantum wells
Authors: Bolognesi C. R. , Kroemer H. , English J. H.
Published: July 2002

We present the results of a systematic study of the low-field electron transport as a function of the well width for InAs/AlSb quantum wells grown on nominally [100]-oriented, GaAs semi-insulating substrates. Both room-temperature and low-temperature mobilities are significantly reduced in narrow wells due to the dominance of interface roughness scattering. The mobility peaks for well widths around 125 Å, and then decays again, most probably due to the onset of scattering by misfit dislocations nucleated as the quantum well width exceeds the critical layer thickness imposed by the 1.3% lattice mismatch between InAs and AlSb.
Blue/green injection lasers and light emitting diodes
Authors: Xie W. , Grillo D. C. , Gunshor R. L. , Kobayashi M. , Hua G. C. , Otsuka N. , Jeon H. , Ding J. , Nurmikko A. V.
Published: July 2002

The p doping of molecular-beam epitaxially grown ZnSe by substitutional nitrogen using a plasma cell has enabled the fabrication of pn junction injection electroluminescent devices. The light emitting diode structures, including pulsed laser diodes described here, are grown on GaAs substrates and incorporate multiple quantum well structures as the active gain region. This article discusses optical properties as well as the x-ray and transmission electron microscopy (TEM) characterization of the quantum well device structures. The TEM imaging reveals low dislocation densities in both device configurations.
Inhomogeneous and wide range of barrier heights at metal/molecular-beam epitaxy GaAs(100) interfaces observed with electrical measurements
Authors: Chang S. , Raisanen A. , Brillson L. J. , Shaw J. L. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: July 2002

In situ internal photoemission, current–voltage, and capacitance–voltage measurements of electronic barrier heights at metal/molecular-beam epitaxy GaAs(100) interfaces indicate near-ideal behavior and large barrier heights for Au contacts but nonideal characteristics and barrier height inhomogeneity for Al contacts. The observed Au barrier heights of 0.98–1.10 eV are comparable among the three techniques employed and relatively uniform across the interface. Measurements indicate that Al barrier heights are laterally inhomogeneous. Analysis of internal photoemission results for the Al interface using a model of two parallel conduction channels yields good agreements with the experimental results. Fitting the model to the experimental results for different diodes prepared on the same surface yields a low electronic barrier of 0.37±0.05 eV and a high barrier of 0.72±0.04 eV. The former is consistent with our previous soft x-ray photoemission measurements and the latter agree with the value of reported Fermi-level ‘‘pinning.’’ In addition, the low barrier height increases with increasing duration of mechanical contact, indicating instability of the interface. Our results (1) confirm the wide range of barrier heights at metal/GaAs(100) interface observed previously, (2) demonstrate explicitly the existence of multiple contacts at metal/GaAs interfaces, and (3) suggest that differences in barrier heights in the literature are a direct result of local structural variation at the interface.
Study of partial strain release and surface states formed on the sidewall of InGaAs quantum-well wires
Authors: Tan I-Hsing , Mirin Richard , Yasuda Takashi , Hu Evelyn L. , Bowers John , Prater Craig B. , Hansma Paul K. , He Ming Yuan , Evans Anthony G.
Published: July 2002

Strained InGaAs/GaAs quantum-well wires (QWWs) with a lateral wire width of 105 nm and a pitch of 230 nm have been fabricated by holographic lithography and low-damage wet chemical etching. Partial strain release occurs on the sidewalls of the etched QWWs. The photoluminescence spectrum shows two well-resolved excitonic peaks for the QWWs; the lower-energy peak corresponds to the transition from the area close to the sidewall of the QWW and the higher-energy peak is from the center of the QWW. The expected band structure has been modeled, hence expected luminescence spectrum, solving both continuum elasticity equations as well as the four-band Luttinger Hamiltonian with strain. The etched QWWs were given different chemical treatments to test the sensitivity of both excitonic peaks to the quality of the sidewalls. It was found that the lower-energy peak is sensitive to the surface states formed on the sidewalls of QWWs. This sensitivity is believed to be useful in determining the best cleaning and low-damage treatments for subsequent regrowth steps.
Dynamic effects of coherent epitaxial strain and surface stability: Ge on Si(100)
Authors: Zinke-Allmang Martin
Published: July 2002

The clustering behavior of Ge thin films deposited on Si has been investigated by ion scattering and electron microscopy. From independent observations of the cluster height as a function of time and the cluster size distributions, postdeposit annealed Ge is shown to cluster according to an Ostwald ripening mechanism with an activation energy for clustering of 1.0±0.1 eV. Cluster formation during low deposition rates is subsequently studied. This permits an estimate of the limit for the applicability of the Ostwald ripening approach to the nonzero deposition rate regime. The first determination of the activation energy for surface diffusion on a Stranski–Krastanov layer is further reported. This result is based on independent measurements of the activation energy for cluster growth and cluster formation. Quantitative results include a Stranski–Krastanov layer thickness of Ge on Si(100) of 3.08±0.16 monolayer, the energy to remove a single Ge atom from a cluster of 0.16±0.1 eV, and an activation energy for surface diffusion of 0.84±0.14 eV.
Metal–semiconductor work function differences with HgCdTe and their effect on radiation-induced flatband voltage shifts
Authors: Strong Roger L.
Published: July 2002

Measurement of metal–semiconductor work function differences on HgCdTe has been made using Pt, Ni, Ta, W, and TiON capacitors with two different insulator thicknesses. These data indicate that the work function of Hg0.8Cd0.2Te is approximately 4.6 V. However, problems with charge trapping in the ZnS place this number in doubt. Results of radiation tests indicate that the work function is near 5.6 V. The effect of the metal work function on the radiation tolerance of metal–insulator–semiconductor devices was investigated. The radiation-induced flatband voltage shifts at 77 K correlated linearly with the known work functions of the metal gates.
Defect equilibrium in HgTe
Authors: Berding M. A. , Schilfgaarde M. van , Sher A.
Published: July 2002

Defects are a well-known source of problems in low xHg1−xCdxTe and Hg1−xZnxTe. To gain insight into the relative importance of various native point defects in these materials we have calculated the formation energy of native point defects in HgTe using a full-potential linearized muffin-tin orbital method. This method employs no shape approximation to the energy functional and permits the prediction of the lattice relaxations from first principles. In the present work, only breathing-mode relaxations were included. Formation entropies resulting from the change to the phonon spectrum upon formation of a defect were calculated using a valence force field model for the elastic contributions and a rigid ion model for the Coulomb contributions to the dynamical matrix. The energies and entropies were incorporated into mass-action equations to deduce the relative defect concentration. In agreement with experiments, we find mercury vacancies are the dominant defect to accommodate excess tellurium in the lattice when the material is equilibrated in the presence of mercury vapor; we predict that tellurium antisites are dominant in material equilibrated with tellurium solid. Of the defects that accommodate excess mercury, we find that mercury antisites may be more prevalent than previously thought. Extensions to the alloy are also discussed.
Shallow p
n
p profiling with a molecular ion probe
Authors: Ronsheim P. A. , Fitzgibbon G.
Published: July 2002

Accurate measurement of shallow pnp emitter depths requires secondary ion mass spectrometry analysis with optimized depth resolution. This work characterized depth resolution at different beam energies for monomer, dimer and trimer species from a N2O ion source, specifically for enhancing depth resolution of abrupt boron profiles in silicon. At high beam energies, (5.5 keV), the depth resolution of the trimer is favorable to that of the dimer, as the initial ion energy is split in thirds when the molecule disassociates. At sub-keV energies, the low velocity of the sputtering ion greatly increases the scattering cross section of the target, reducing the momentum transfer to the subsurface dopant species. At 2 keV/molecule, the trimer ion beam yields 0.67 keV/atom, and has significantly enhanced depth resolution compared to the dimer ion species.
Effects of substrate heating on the spatial uniformity of threshold current and emission wavelength in GaAs and InGaAs graded-index separate-confinement heterostructure quantum-well lasers grown by molecular-beam epitaxy
Authors: Chand Naresh , van der Ziel J. P. , Chu S. N. G. , Sergent A. M.
Published: July 2002

We show that if the active region of a quantum-well (QW) laser is grown at a high temperature such that the sticking coefficients of group III species are less than unity, the emission wavelength λ and threshold current density Jth are sensitive to the spatial variations in substrate growth temperature Ts despite the time average flux variations of less than 1% across the surface of a rotating 7.5 cm diam substrate in our molecular-beam epitaxy system. InGaAs strained QW lasers, in which the active region is grown at Ts < 580 °C at which In and Ga have unity sticking coefficients, have uniform Jth (212±4 A cm−2) and λ(989±1 nm) on a 5 cm diam substrate. These lasers were grown with In mounting. In contrast, GaAs QW lasers, which are grown at ∼700 °C with In mounting, have less uniform Jth (395±20 A cm−2) and λ(850±9 nm). This is the result of nonuniform substrate heating which is partly due to voids in the In back coating. This causes variations in GaAs growth rate because of the high temperature dependence of the Ga sticking coefficient at ∼700 °C. Uniformity of GaAs QW lasers deteriorates further if direct radiation heating of the substrate with In free mounting is used. With In free mounting, the Jth is minimum (245 A cm−2) in the center and increases monotonically to maximum (365 A cm−2) towards the edge of the wafer, suggesting the degradation of material quality towards the edge. Variation of λ in GaAs QW lasers is random or systematic depending upon whether they are grown with In mounting or In free mounting, respectively.
Rate constants for the etching of gallium arsenide by molecular iodine
Authors: Wong Kin-Chung , Ogryzlo Elmer A.
Published: July 2002

The etching of the (100) face of gallium arsenide with molecular iodine has been studied at I2 pressures between 0.10 and 1.25 Torr and in the temperature range from 270 to 330 °C. GaAs was found to be etched continuously at rates between 0.05 and 1.70 μm min−1 under these conditions. Although the etch rate appears to be first order with respect to I2 at pressures below 0.3 Torr, the order decreased at higher pressures. The data was analyzed in terms of two mechanisms, which have been proposed for the etching of semiconductors by halogen molecules. These are the ‘‘reversible dissociative adsorption’’ (RDA) mechanism, and the ‘‘surface site saturation’’ (SSS) mechanism. In the RDA mechanism the dissociative adsorption, which explains the nonlinear pressure dependence, occurs irreversibly at low pressure giving rise to first order kinetics with a first order rate constant (k1) which can be expressed in the following Arrhenius form: k1=104.7±0.2 μm min−1 Torr−1 exp[−(55±2) kJ mol−1/RT]. At higher pressures, the dependence on I2 changes to half order and the composite half order rate constant (k1/2) can be represented by the equation: k1/2=106.5±0.9 μm min−1 Torr−1/2 exp[−(69±10) kJ mol−1/RT]. On the other hand, the SSS mechanism involves the reversible physisorption of I2 on the GaAs surface (governed by an equilibrium constant K) followed by a rate controlling reaction of this physisorbed species leads to products (governed by the rate constant k4). The values obtained for these two constants are: K=10−4.8±0.7 Torr−1 exp[+(49±7) kJ mol−1/RT], and k4=109.2±0.4 μm min−1 exp[−(96±5) kJ mol−1/RT]. The etching is isotropic, and the major products are GaI3 and AsI3.
Quantitative analysis of semiconductor alloy composition during growth by reflection-electron energy loss spectroscopy
Authors: Nikzad Shouleh , Ahn Channing C. , Atwater Harry A.
Published: July 2002

Determination of alloy composition during epitaxial growth of GexSi1−x alloys has been demonstrated using reflection-electron energy loss spectroscopy (REELS) at reflection high-energy electron diffraction (RHEED) energies. Measurements of inelastic scattering intensities from Si K (1840 eV) and Ge L2,3 (1217 eV) core losses were performed using a conventional RHEED gun together with an electron energy loss spectrometer in a molecular beam epitaxy system. Comparison of ex situ composition measurements by Rutherford backscattering and energy dispersive x-ray spectroscopy in a transmission electron microscope indicate excellent agreement with composition determination by REELS, demonstrating the capability of REELS as a quantitative in situ analysis technique. Application of REELS to other semiconductors is discussed and initial results for III–V and II–VI semiconductor alloys (GaAs, CdTe, and ZnTe) are also presented.
α α′ α″ α‴ Poly-tetrafluoro-p-xylylene as an interlayer dielectric for thin film multichip modules and integrated circuits
Authors: Dabral S. , Zhang X. , Wu X. M. , Yang G.-R. , You L. , Lang C. I. , Hwang K. , Cuan G. , Chiang C. , Bakhru H. , Olson R. , Moore J. A. , Lu T.-M. , McDonald J. F.
Published: July 2002

α α′ α″ α‴ Poly-tetrafluoro-p-xylylene (PA-f ) has been evaluated as an interlayer dielectric for multichip modules and integrated circuits, and its properties are reported. It has a lower dielectric constant and higher thermal stability than parylene-n (PA-n). The as-deposited films have very low crystallinity. The crystallinity increases as the film is annealed. Thermogravimetric analysis has shown that these films lose weight at temperatures higher than 480 °C. A shrinkage in the films of ∼10% was observed when annealed in a vacuum at a temperature of 425 °C. The as-deposited film has a low dielectric constant of 2.38 and a volume resistivity of 1.3×1016 Ω cm. The refractive index at optical wavelengths was 1.3 for as-deposited samples and it increased with annealing temperature. The stress levels observed after annealing are also lower (20 MPa) than for PA-n (40 MPa). The hardness, as determined by a microindentor, of PA-f was 0.56 GPa in the bulk, but the surface hardness was ∼1.0 GPa. The conformal nature of these films permitted successful coating of micron-sized gaps having an aspect ratio of 1.5–2. Diffusion of Cu into PA-f is reported here and is contrasted with Cu/PMDA-ODA polyimide. Scanning electron microscopy of film cross sections shows microstructure changes above 350 °C. The low dielectric constant and high thermal stability of PA-f makes it a good insulator for high-speed interconnection applications.
Study of temperature dependent hydrogenation on near-surface strained quantum wells
Authors: Chang Ying-Lan , Krishnamurthy Mohan , Tan I-Hsing , Hu Evelyn L. , Merz James L. , Petroff Pierre M. , Frova A. , Emiliani V.
Published: July 2002

The incorporation of hydrogen by ion-gun irradiation into near-surface and deeply embedded In0.13Ga0.87As/GaAs strained quantum wells (QWs) has been studied by photoluminescence spectroscopy and transmission electron microscopy (TEM). Degradation in the free exciton luminescence and the appearance of hydrogen-related shallow or deep states have been observed within the near-surface QW after hydrogenation. This effect is more pronounced, the higher the hydrogen dose. In contrast, the deeply embedded QW is only slightly affected by the hydrogenation process even at high substrate temperature and hydrogen ion dose. TEM reveals hydrogen-induced plateletlike structure in the vicinity of the near-surface QW and of the GaAs buffer layer/GaAs substrate interface after room temperature and high temperature (250 °C) hydrogenation, respectively, which ascertain the extension and nature of the hydrogen-enriched regions throughout the whole material structure.
Fabrication of mesoscopic structures by channeled ion implantation for the study of boundary scattering of electrons
Authors: Hornsey R. I. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

The scattering of electrons from a boundary formed by ion implantation is discussed with reference to the lateral distribution of the implanted ions. A reduction in the lateral straggle is achieved by using channeled ions, but voids in the ion distribution still lead to the formation of a rough boundary. The specularity coefficient for such a boundary is measured using a transverse electron focusing device and the surface asperity parameter is calculated. It is shown that this value is significantly smaller than would be expected from the ion distribution and it is suggested that smoothing of the boundary is provided by the depletion around the implanted area.
Magnetron reactive ion etching of GaAs in a BCl3 discharge
Authors: McLane G. F. , Meyyappan M. , Lee H. S. , Cole M. W. , Eckart D. W. , Lareau R. T. , Namaroff M. , Sasserath J.
Published: July 2002

Magnetron reactive ion etching (MIE) of GaAs has been investigated using BCl3 as the etch gas. Etch rates are determined as a function of applied power density (0.16–0.80 W/cm2) and chamber pressure (2–6 mTorr). Patterned GaAs samples were etched anisotropically and exhibited smooth surfaces, with no indication of residues on surfaces or sidewalls. Transmission electron microscope measurements were performed to determine etch induced wafer damage. Schottky diode measurements on etched surfaces revealed minimal degradation of surface region electrical properties. Our results show that (MIE) in BCl3 is an attractive processing technique for GaAs device fabrication.
Molecular-beam epitaxial growth of arsenide/phosphide heterostructures using valved, solid group V sources
Authors: Johnson F. G. , Wicks G. W. , Viturro R. E. , LaForce R.
Published: July 2002

The first arsenide/phosphide heterojunctions grown by conventional molecular-beam epitaxy with solid-source valved crackers are reported. The use of needle valves to switch the group V fluxes allows Ga0.52In0.48P/GaAs heterojunctions to be grown with virtually no intermixing between layers. Photoluminescence from quantum wells as narrow as 40 Å has also been observed. For comparison, conventional mechanical shutters were used to switch the group V fluxes, and the resulting layers were severely intermixed. The relative incorporation coefficients of the arsenic and phosphorous group V species were found to be temperature dependent, but there was no difference as a result of switching from tetrameric to dimeric arsenic.