bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic force microscopy of mercury iodide crystal growth from porous media at room temperature
Authors: Henderson D. O. , Tung Y. S. , Mu R. , Ueda A. , Collins W. E. , Burger A. , Chen K. T. , Frazier D. O.
Published: July 2002

A real time observation of the growth of agglomerates of pyramidal crystallites of mercuric iodide on a porous glass surface using tapping mode atomic force microscopy is reported. Crystallites are observed to grow from the pores (5.0 nm diameter) onto the surface of the porous glass impregnated with mercuric iodide. Immediately after fracturing the impregnated porous glasses, topographical images reveal a surface with a root mean square roughness of 75–130 nm over a 5 μm×5 μm area, which is typical for surfaces of fractured porous glass. After 3 h, 60–90 nm pyramidal structures with a high aspect ratio (pyramid base to height) begin to appear on the surface. Some of the pyramidal structures agglometrate and form structures much larger and higher than the surrounding ones. The bottom of some of these agglomerated pyramids form equilateral triangles with dimensions of 300–500 nm, exhibiting a preferred orientation on the surface. 6 h after fracturing, micrometer-size crystallites are observed. Most of the pyramidal structures are no longer observed and mostly needlelike features are covering the surface. Step heights consistent with multiples of the c axis of α-mercuric ioide are observed on the micrometer-sized crystallites. Some pyramidal structures are observed between the large crystallites, with sizes comparable to the early stage pyramidal structures. Raman and electronic spectra are also reported for mercuric iodide confined in porous glasses. The Raman spectra have peaks located at 39 and 141 cm−1, indicating that the confined mercuric iodide is stabilized in the yellow, orthorhombic (β phase) at room temperature. Confinement of mercuric iodide in pores with radii smaller than 3.75 nm results in the appearance of a new band at 145 cm−1 in the Raman spectra, suggesting the presence of a new or modified β phase of mercuric iodide. Further evidence supporting the presence of a new phase of mercuric iodide is found in the electronic spectra where an energy gap of 2.7 eV is observed, and lies between the energy gaps of the red, tetragonal, α phase (2.2 eV) and the yellow, orthorhombic β phase (3.1 eV) of mercuric iodide. The atomic force microscopy measurements provide a unique method for real time monitoring of the crystal growth and morphology changes of nanocrystalline mercuric iodide, while the spectroscopy provides insight to the phonon structure and energy gaps of the confined material.
Atomic force microscopy study of mercuric iodide surfaces
Authors: Tung Y. S. , Henderson D. O. , Mu R. , Collins W. E. , Chen K. T. , George M. A. , Burger A.
Published: July 2002

Mercuric iodide HgI2 is a layered material consisting of alternating sequences of I–Hg–I atoms stacked along the c axis and bonded through van der Waals forces. The dynamics of surface structure modifications of a freshly cleaved crystal of α-HgI2 have been investigated by tapping mode atomic force microscopy. Layer-by-layer removal of HgI2 is observed and is attributed to the tapping tip interactions with the relatively soft mercuric iodide surface and also to the relatively high vapor pressure of HgI2. The step heights between the layers are found to be either 6 or 12 Å corresponding to one or two layers of HgI4 tetrahedra. The effect of the tip modification is characterized by continuously scanning the same area for 1 h (41 scans) which produce craters ∼120 nm in depth. Three consecutive scans separated by 1 h intervals and imaged in the same area with a minimized tapping force reveal the effects of evaporation and the intrinsic instability of this surface under ambient conditions. Comparison of the images collected with 1 h intervals between consecutive scans and the 41 consecutive scans with no delay allows for decoupling the evaporation and tip induced etching processes on the (001) surface of HgI2. Friction force images revealed two distinct areas with different friction on the (001) surface. The area of high friction was found to have an atomically resolved periodicity of 4.4 Å which corresponds to the lattice spacing of the a or b planes. The areas of low friction exhibited a periodicity of 5.5 Å and this spacing was attributed to a defect induced distortion of the a or b lattice constant.
Scanning tunneling microscopy and spectroscopy on thin Fe3O4 (110) films on MgO
Authors: Jansen R. , van Kempen H. , Wolf R. M.
Published: July 2002

Thin Fe3O4 (110) films, grown by molecular-beam epitaxy on MgO, have been studied by scanning tunneling microscopy and spectroscopy. A 500-Å-thick film was cleaned prior to the measurements by annealing at 850 K under ultrahigh vacuum. Tunneling images show the onset of the formation of the one-dimensional row reconstruction, which was previously also observed on surfaces of bulk single crystals cleaned by ion bombardment and subsequent annealing. Spectroscopic current–voltage curves reveal different behavior depending on the location of the tip above the row reconstruction. Most notably, when probing the filled states at negative sample bias, a larger current was found on top of the rows as compared to a tip position between two rows.
Optical emission spectra of microwave oxygen plasmas and fabrication of SiO2 films
Authors: Chau T. T. , Kao K. C.
Published: July 2002

The optical emission spectra of microwave oxygen plasmas under various gas pressures have been investigated. At the gas pressure of 0.01 Torr the plasma-generated particles are mainly excited atomic oxygen and ionic molecular oxygen species. As the gas pressure is increased to a value higher than 0.2 Torr, the plasma contains excited atomic oxygen with emission peaks at 777 and 844 nm and a new emission peak at 759 nm. When the gas pressure reaches 2.9 Torr, only a single emission peak at 759 nm appears. To the best of our knowledge, the optical emission spectra peak at 759 nm has not been reported before. This peak is thought to be due to the presence of excited molecular oxygen species. At low gas pressures, the concentrations of atomic oxygen and ionic molecular oxygen increase linearly with increasing input power to the plasma, while there is no such input power dependence for excited molecular oxygen. SiO2 films have also been fabricated by means of oxidation of silicon wafers in microwave oxygen plasmas at two gas pressures, 0.01 and 2.2 Torr. It is found that the SiO2 films grown at 0.01 and 2.2 Torr have properties similar to those of thermally grown oxide, and that the films grown at 0.01 Torr have a lower value of interface trap density (≊9×10−10 eV−1 cm−2) and a smaller leakage current. Atomic oxygen species are found to be the main species to contribute to the oxidation of silicon in microwave oxygen plasmas.
Amplification and surface topography in synchrotron radiation induced dry etching of Si with XeF2
Authors: Streller U. , Li B. , Krause H.-P. , Schwentner N.
Published: July 2002

The topography of Si(100) surfaces is investigated by scanning electron microscopy after generating replicas using photoinduced dry etching with radiation predominantly in the wavelength range between 105 and 122 nm. XeF2 and Ar mixtures provide high selectivity with a structural resolution of about 100 nm. Pores and grains indicate that single photons initiate chain reactions with an amplification of 3×105. The overall quantum efficiency of removed Si atoms per incident photon above unity leads to a probability for stimulation of a reaction per incident photon of 6×10−5. Addition of O2 increases the amplification factor, reduces the excitation probability, and causes a reduced selectivity at high irradiation intensity.
High-temperature scanning tunneling microscopy study of the Li/Si(111) surface
Authors: Olthoff S. , Welland M. E.
Published: July 2002

A study of the topographical changes of Li/Si(111) during annealing has been conducted using a high-temperature scanning tunneling microscope. Depending on the Li coverage and postdeposition annealing temperature the surface exhibited a variety of structures replacing the initial (7×7) reconstruction during in situ investigations. In addition to the previously observed (3×1) structure a coexistence phase with domains of (n×n) (n=5,7,9), a (4×4) structure, and a faceting transition were imaged. Distinct differences were noticed on the Li/Si(111)-(3×1) surface compared to the corresponding Na structure. Moreover, the dynamic properties of the morphological transformations were revealed by a high-temperature scanning tunneling microscope.
Nanoscale roughening of Si(001) by oxide desorption in ultrahigh vacuum
Authors: Gray Struan M. , Johansson Mikael K.-J. , Johansson Lars S. O.
Published: July 2002

We have used scanning tunneling microscopy, Auger electron spectroscopy, and low-energy electron diffraction to investigate the surface of Si(001) prepared by low-temperature thermal decomposition of an oxide layer and subsequent annealing in ultrahigh vacuum. Such a surface is found to roughen on the mesoscopic length scale and consists of 3000-Å-wide voids of 2×1 reconstructed Si(001) surrounded by square-based pyramidal structures which are 200–300 Å high and have a cusplike cross section. Atomic scale imaging and spectroscopy of the sides of the pyramids reveals a wide variety of vicinal surfaces as well as higher angle facets such as (3×2) reconstructed (113). The structure formed is independent of the original oxide thickness and is shown to be qualitatively different from that caused by deliberate carbon contamination of the surface. We propose that the pyramids are created by kinetic effects acting on the surface disorder caused by the oxide removal and represent a fundamental instability of the Si(001) surface. This has implications for molecular-beam epitaxy growth and device fabrication, as well as offering a lithography-free method of making Si nanostructures and a way of studying vicinal surfaces without complex sample preparation.
Surface generation lifetime of MeV implanted Si
Authors: Lowell John
Published: July 2002

The use of high-energy (≳0.5 MeV) ion implantation potentially has distinct advantages for deep-submicron, ultralarge-scale integrated devices. Most reports on this technique focus on the formation and characterization of bulk properties at a depth of 1 μm or greater. In contrast, studies of the surface properties of MeV implanted wafers are few. Those that exist depend on C–V or C–t structures and do not provide in situ, on-wafer measurements of surface properties such as surface charge and generation lifetime of minority carriers on the processed material. This is important since it is important to observe the relationship between dose, formation of buried layers, use of hydrogen denuding cycles, and defect gettering on the surface carrier properties at a common energy level. For this study we report on the application of optical surface/interface charge analysis by time resolved surface photovoltage to both quantify and qualify surface charge and the interface generation lifetime characteristics on MeV implanted surfaces.
Sputter depth profiling of surface potentials in silicon semiconductors
Authors: Smith H. E. , Harris W. C.
Published: July 2002

This work is a study of depth-dependent changes in surface electrical potential observed during secondary ion mass spectroscopy (SIMS) sputter profiling of doped, recrystallized silicon semiconductor samples. These changes are measured indirectly, using spectrometer energy filtration to detect changes in secondary ion energy as changes in signal transmission. The effect is caused by carrier-depleted zones in samples containing n-p junctions, which become reverse-biased diodes due to the ion bombardment-induced surface charge. These profiles are qualitatively similar to spreading resistance probe (SRP) profiles and are indicative of the dynamic carrier profile as erosion removes the overlying doped silicon, as in the concept of an on-bevel SRP carrier profile. However, the amount of biasing surface charge is highly dependent on bombardment and instrumental conditions, so the same sample can be made to exhibit much different potential profiles. By optimizing these conditions, the signals can give useful information about the sample carrier profile at the same time that the SIMS dopant profile is directly measured.
Depth profiling of B through silicide on silicon structures, using secondary ion-mass spectrometry and resonant postionization mass spectrometry
Authors: De Bisschop P. , Gomez J. , Geenen L. , Vandervorst W.
Published: July 2002

This article presents a comparison of Cameca IMS 4f secondary ion-mass spectrometry (SIMS) measurements and resonant postionization mass spectrometry (RIMS) measurements of boron depth profiles in silicide/silicon samples (mainly CoSi2/Si). The emphasis of the comparison was on the shape of the profiles obtained with both techniques. For the SIMS data, we used a quantification procedure including a correction for sensitivity differences in both matrices. The RIMS sensitivity in CoSi2, TiSi2, and Si was explicitly compared using special test samples and shown to be identical to within 15%. Finally, we present preliminary results of the application of SIMS and RIMS to a number of CoSi2/Si samples with an unknown B profile. After application of the correction procedures, both techniques appear to produce nearly identical profile shapes in case of polycrystalline CoSi2 samples. For epitaxially grown crystalline CoSi2, however, differences sometimes remain, depending on the temperature of the second silicidation anneal used. Absolute quantification of the RIMS profiles could be achieved through the use of an internal implantation standard.
Application of a genetic algorithm to doping profile identification
Authors: Kuzmicz W.
Published: July 2002

This work describes a new approach to C–V dopant profiling by means of nonlinear least squares inverse modeling. It is shown that a genetic algorithm can replace standard nonlinear minimization procedure in identification of doping profile parameters. The most important advantages of the genetic algorithm are its ability to avoid local minima and often faster convergence in ‘‘difficult’’ cases. Practical implementation of the genetic algorithm is described in detail, and experimental results are shown.
Two-dimensional junction profiling by selective chemical etching: Applications to electron device characterization
Authors: Spinella C. , Raineri V. , La Via F. , Campisano S. U.
Published: July 2002

We present recent developments of the sample preparation technique used to obtain the delineation of a two-dimensional junction profile by transmission electron microscopy analysis. The technique is based on the selective chemical etching of doped regions in silicon by a HF:HNO3 chemical mixture. The role of crystallographic defects and the influence of the substrate doping (n or p type) is explained by taking into account the free carriers present at the solid/solution interface during the silicon dissolution process. This information allows us to identify some crucial aspects of the sample preparation method, and two-dimensional junction profiles can also be obtained in the case of samples doped with boron. The high spatial resolution of the technique allows us to resolve several features of the doping profiles which are not detectable with other techniques and to characterize a wide range of electron devices.
CERA-V: Microwave plasma stream source with variable ion energy
Authors: Balmashnov A. A.
Published: July 2002

A microwave plasma stream source with variable ion energy operated under low magnetic field electron cyclotron resonance conditions has been developed. A two mode resonant cavity (TE111, E010) was used. It was established that overdense plasma creation (TE111) and high energy in-phase space localized electron plasma oscillations (E010) in a decreased magnetic field lead to the potential for ion energy variation from 10 to 300 eV (up to 1 A of ion current, and a plasma cross section of 75 cm2, hydrogen) by varying the TE111, E010 power, the value of the magnetic field, and pressure. The threshold level of E010-mode power was also determined. An application of this CERA-V source to hydrogenation of semiconductor devices without deterioration of surface layers by ions and fast atoms is under investigation.
Schottky barrier height measurement on NiSi2/Si(100) by capacitance microscope
Authors: Khang Y. , Mang K. M. , Booh K. H. , Kuk Y.
Published: July 2002

Many different growth structures of nickel silicide on the Si(001) are present as functions of coverage and temperature. Conflicting results in macroscopic Schottky barrier height measurements are due to the fact that one of many phases may dominate carrier transport through the interface barrier. Scanning capacitance microscopy and spectroscopy were performed on NiSi2/Si(100) to measure the spatial variation of Schottky barrier height. From the intercept in an 1/C2 vs V plot, a local Schottky barrier height can be deduced.
Antimony doped GaAs: Role of the isoelectronic dopant in defect evolution
Authors: Paskova T. , Valcheva E. , Yakimova R.
Published: July 2002

Metalorganic vapor phase epitaxial GaAs:Sb layers and Schottky barrier structures based on them have been investigated regarding defect evolution versus doping level. Three types of defects are considered such as surface morphology imperfections, structural defects in the epilayers, and interface defects at the Schottky barriers. A correlation between the defect behavior in the layers and the Schottky structures has been observed. It has been shown that an optimal Sb doping region exists where the defect density decreases compared with the undoped and highly Sb doped samples. The dominating defects in the Schottky barrier interface are dislocation-related states which can be effectively influenced by the isoelectronic doping.
Prospect and challenges of ArF excimer laser lithography processes and materials
Authors: Ohfuji T. , Ogawa T. , Kuhara K. , Sasago M.
Published: July 2002

Practical chemically amplified resists for 193 nm lithography will be realized from newly developed polar alicyclic base polymers. Their resist performance is likely to be equal to that of resists used for 248 nm lithography, since a 193 nm resist basically follows the same physical rules as a conventional resist. Top surface imaging with a combination of 193 nm exposure and bi-functional silyation reagent B(DMA)MS was used to produce 0.12 μm L&S patterns. This resolution corresponds to a k1 factor of 0.34. Therefore, the use of dry-developed resists, which provide excellent resolution and a generous process margin, will help extend the use of 193 nm lithography. However, resolution enhancement techniques must still be developed to improve the process window.
Fabrication of InP-based wavelength division multiplexing arrayed waveguide filters using chemically assisted ion beam etching
Authors: Youtsey C. , Adesida I. , Soole J. B. D. , Amersfoort M. R. , LeBlanc H. P. , Andreadakis N. C. , Rajhel A. , Caneau C. , Koza M. A. , Bhat R.
Published: July 2002

Chemically assisted ion beam etching using Cl2 has been used to fabricate InP-based arrayed waveguide filters that demonstrate full polarization independence and excellent performance characteristics. The process is carried out at elevated temperatures of approximately 250 °C to avoid difficulties associated with the low volatility of indium chlorides at lower temperatures. Optimization of the process for smooth, vertical etching is discussed. InP regrowth is successfully carried out on the etched InGaAsP guides, and measurements of the fabricated devices are presented. The adaptation of the process for angled etching is also demonstrated.
Fabrication of subwavelength, binary, antireflection surface-relief structures in the near infrared
Authors: Wendt J. R. , Vawter G. A. , Smith R. E. , Warren M. E.
Published: July 2002

Subwavelength, binary surface-relief structures are artificial materials with an effective index of refraction that can be tailored by varying the duty cycle of the binary pattern. These structures have the significant advantage of requiring only a single lithography and etch step for fabrication. We demonstrate a specifically designed antireflection structure in a material system (GaAs) and at a wavelength (975 nm) directly integrable with GaAs-based vertical cavity surface-emitting lasers and which exhibits strong polarization-dependent properties. Fabrication is performed using electron beam lithography and reactive-ion-beam etching. The observed reflectivity is 2% for TE polarization and 23% for TM polarization, a difference in reflectivity of over a factor of 10 for the two polarizations.
Fabrication of quantum nanostructures for the measurement of thermoelectric phenomena
Authors: Hannan M. , Grundbacher R. , Adesida I. , Giannetta R. W.
Published: July 2002

Fabrication of nanostructures has been carried out for the study of thermal and thermoelectric transport properties. The study was done on an electron waveguide, defined as a double-bend quantum structure in a two-dimensional electron gas, using a current heating technique. Seebeck and Peltier effects are observed in this structure.
Limit of resolution of a standing wave atom optical lens
Authors: Behringer R. E. , Natarajan Vasant , Timp G. , Tennant D. M.
Published: July 2002

Using a Gaussian standing wave at λ=589 nm as an atom optical lens, we have focused a thermal atomic sodium beam. We have examined the limits of the resolution of this focusing technique, and have made structures with linewidths of 13 nm and contrast of 6:1 with a short focal length atom optical lens. While numerical simulations predict that smaller structures should be attainable with shorter focal lengths, we find that the resolution deteriorates for focal length shorter than f≊16 μm.
Precision optical aspheres for extreme ultraviolet lithography
Authors: Kania D. R. , Gaines D. P. , Sweeney D. S. , Sommargren G. E. , Fontaine B. La , Vernon S. P. , Tichenor D. A. , Bjorkholm J. E. , Zernike F. , Kestner R. N.
Published: July 2002

We have demonstrated significant advances in the production of aspheric optics for extreme ultraviolet lithography. An optic has been fabricated with an aspheric departure of 1.5 μm, a figure error of 0.7 nm rms, and a nanoroughness of 0.25 nm rms. Further improvements are required in the figure and nanoroughness to reach high throughput and near diffraction limited performance in an extreme ultraviolet lithography system.
Micro-objective lens with compact secondary electron detector for miniature low voltage electron beam systems
Authors: Liu W. , Ambe T. , Pease R. F.
Published: July 2002

The low voltage scanning electron microscope appears to be attractive for the examination of ultrathin film such as surface contamination. However, achieving high resolution and high secondary electron detection efficiency at, say 100 eV landing energy, meets serious electron optical challenges. We describe a very low aberration micro-objective lens that is combined with an efficient secondary electron detector to address this issue. The objective lens comprises a mirco-einzel lens followed by a retarding region (from 10 000 to 100 V) and a final electrode just above the sample to minimize the electric field at the sample surface. The retarding field (a) lowers aberration of the objective lens and (b) accelerates the secondary electrons to improve the detection. Using computer modeling we have optimized the design to minimize the primary beam diameter and maximize secondary electron collection. For a landing energy of 100 eV the minimum beam diameter is about 10 nm at 96 μm working distance when the beam energy spread is 0.1 eV. About 50% of secondary electrons can be collected by the compact p-n junction detector micromachined to serve also as the bottom electrode of the einzel lens. The depletion region extends from 0.25 to 5 μm at zero bias and experimental results indicate a current gain of more than 2000.
Modified mask methods for pattern accuracy enhancement in electron beam lithography
Authors: Sohda Yasunari , Someda Yasuhiro , Nakayama Yoshinori , Saitou Norio
Published: July 2002

In projection-type lithography, delineated resist patterns differ from original mask shapes. In this article, aperture modification methods are investigated to enhance the pattern accuracy of electron beam cell projection lithography. The modified aperture is easily fabricated by decreasing the mask thickness. Although electrons penetrate the mask, enough high scattering contrast can be obtained. In dot delineation, star-shape apertures make better square dots near the resolution limit. In line-and-space delineation, dividing the pattern into small patterns of lower resolution reduces the electron current. This decreases Coulomb effects. In addition, Monte Carlo simulation results also confirm these results. As a result, these methods are expected to be important in the application of projection-type charged particle lithography.
Divot defect repair on a deep ultraviolet SiNx halftone mask
Authors: Nakamura H. , Komano H. , Sugihara K. , Koike T. , Higashikawa I.
Published: July 2002

Divot defect repair on deep ultraviolet SiNx halftone masks in the case of 0.275 μm (on a wafer) line and space patterns was investigated experimentally. The problem regarding imaging is the difficulty of area recognition due to low contrast of halftone masks without the focused ion beam (FIB) irradiation damage. It is overcome by means of limiting the total FIB dose for imaging and by means of image processing with an image filter. Opaque carbon (C) film deposition on a divot defect was found to improve the performance of a defective area. The degree of the improvement was not perfect but allowable for practical use. It was also found that there were other factors that make the performance of the repaired area worse than the nondefective area, except for missing of the phase shift effect.
Sub-100 nm focused ion beam lithography using ladder silicone spin-on glass
Authors: Suzuki Kohei , Yamashita Motoji , Kawakami Nobuyuki , Yoshikawa Akihisa , Nakaue Akimitsu
Published: July 2002

Focused ion beam lithography using ladder silicone spin-on glass (LS-SOG) as a negative-tone resist was investigated. The use of 200 keV Be2+ ion and tetramethylammoniumhydroxide developer resulted an in 80-nm-width line pattern with a vertical profile. The pattern collapse during the development was avoided by the use of fluorocarbon-based solvent. The development mechanism of LS-SOG was investigated by using nuclear magnetic resonance and gel permeation chromatography analysis.
Quantitative depth profiling of boron in shallow BF+2-implanted silicon by using laser-ionization sputtered neutral mass spectrometry
Authors: Higashi Yasuhiro , Maruo Tetsuya , Homma Yoshikazu , Miyake Masayasu
Published: July 2002

Boron depth profiles in low-energy BF+2-implanted silicon were measured using laser-ionization sputtered neutral mass spectrometry and secondary-ion mass spectrometry. The laser-ionization sputtered neutral mass spectrometry measurements provided more accurate boron profiles in the ultrashallow regions (below 20 nm) than the secondary-ion mass spectrometry measurements. A pileup of boron atoms in the region below 5 nm after annealing was revealed by laser-ionization sputtered neutral mass spectrometry.
Hydrogen-induced reconstruction of the GaP(001) surface studied by scanning tunneling microscopy
Authors: Watanabe A. , Shimaya H. , Naitoh M. , Nishigaki S.
Published: July 2002

We report results of a scanning tunneling microscopy investigation on the reconstruction of GaP(001) surfaces. We have observed a 4×2 structure, accompanied locally with c(8×2) domains, at a surface prepared by using ion sputtering and annealing method. On the contrary, both 2×4 [with local c(2×8)] and 4×2 [with local c(8×2)] structures are obtained by hydrogenation followed by annealing. The former consists of a unit structure of three P dimers plus one dimer vacancy, whereas the latter is a parallel arrangement of zig–zag-chained structures along the [110] direction. It has been shown that the surface hydrogenation before annealing induces new types of reconstruction.
Etch-mask of pyrolytic-photoresist thin-film for self-aligned fabrication of smooth and deep faceted three-dimensional microstructures
Authors: Porkolab G. A. , Hsu Shih-Hsiang , Hryniewicz John V. , Lin Wenhua , Chen Y. J. , Agarwala Sambhu , Johnson F. G. , King Oliver , Dagenais M. , Stone D. R.
Published: July 2002

Etch-mask thin-film material that is particulate-free and topographically smooth has been created from a standard photoresist spun onto standard semiconductor substrates such as gallium arsenide, indium phosphide, and silicon, and then pyrolyzed by exposing to a temperature of 300 °C in air atmosphere for 1 min on a standard laboratory hot-plate. The resulting pyrolytic-photoresist thin-film is chemically inert to many standard organic solvents including the solvent of photoresist itself and to many inorganic reagents used in semiconductor processing. Therefore the pyrolytic-photoresist can be patterned by sulfur hexafluoride reactive ion etching via a standard photoresist mask. Upon stripping the standard photoresist in a mixture of 1:1/acetone:developer agitated ultrasonically, the remaining patterned pyrolytic-photoresist performs as an excellent etch-mask in chemically assisted ion beam etching and reactive ion etching systems. Thus it can be a key material in the multilayer masking technique used to sculpt self-aligned three-dimensional microstructures with deep and smooth facets which are needed for example for photonic integrated circuits and micro-electro-mechanical systems.
Computer simulations of porous silicon formation
Authors: Weng Y. M. , Qiu J. Y. , Zhou Y. H. , Zong X. F.
Published: July 2002

A computer simulation has been carried out to study the dynamics of pore formation in porous silicon. Porous structures were generated by a simple three-dimensional Monte Carlo calculation, based on a modified percolation model for pore growth in lightly and heavily doped silicon substrates. The results are consistent with recent observations. As an approximate guide, the type formed morphology was shown to depend mainly on the doping level of the substrate. A strong dependence of the average porosity on the doping level of the substrate is also predicted.
Reactive-ion etching of WSix in CF4+O2 and the associated damage in GaAs
Authors: Chan Yi-Jen , Su Chao-Shin , Sung Kuo-Tung
Published: July 2002

Assessments of WSix reactive-ion etching in terms of the different CF4 to O2 flow rate ratio were characterized. Based upon the evaluations from etching rates, side-wall profiles, surface roughness, and damages, we observed that the optimum etching condition was at a ratio of 10:1. The recovery of reactive-ion-etching-treated GaAs damaged layers through the thermal treatment was also investigated as a function of the annealing temperatures and duration times. These parameter evaluations were for the purpose of achieving a high performance GaAs metal–semiconductor field-effect transistor.
Silicon structures for in situ characterization of atomic force microscope probe geometry
Authors: Jarausch K. F. , Stark T. J. , Russell and P. E.
Published: July 2002

Atomic force microscopy (AFM) is increasingly relied on to image and measure micron and submicron scale surface features. Consistent interpretation of AFM information is, however, difficult if the geometry of the probe is not known. In this work, the fabrication of funnel-like structures and their use in probe characterization were developed from a proof of concept to readiness for field testing. The specifications that determine the structure’s sensitivity to probe shape were identified. The fabrication was tailored to yield large reproducible arrays (>100×100 structure). The geometry of the structures was characterized using low voltage scanning electron microscopy (SEM) techniques. Testing in intermittent contact mode has shown that the structures are stable even at high forces for multiple scans under various conditions. An algorithm was developed that calculates the probe geometry from an image of the structure. The sensitivity of the structures to probe shape was tested by comparing SEM images of probe shape to the probe geometry calculated from the AFM images of the structures. From this analysis it was determined that the structures are sensitive to the cone angle of the probe to within 5° and to the probe radius to within 50 nm.
Ammonia nitridation of thermal polyoxide to eliminate epitaxial ambient induced dielectric pinhole formation
Authors: Fultz W. W. , Neudeck G. W.
Published: July 2002

The incorporation and distribution of nitrogen in ammonia nitrided thermal polyoxide (NPOX) dielectric films and their degradation durability to reduced pressure, dichlorosilane (SiH2Cl2)–HCl–H2 ambient during epitaxial lateral overgrowth (ELO) indicated that the surface nitrogen concentration had no effect. However, a bulk nitrogen concentration as low as 8 at. % significantly reduced the formation of ELO ambient induced pinholes in 250 Å polyoxide films. After 40 min of ELO ambient stress the electrical yield was raised from 0%, for the control polyoxide dielectric capacitors, to 84% for NPOX dielectric capacitors. Analyses of the failed devices suggest that active pinhole generation still exists, however, the bulk nitrogen concentration dramatically reduces the frequency and rate at which these dielectric defects are produced.
Relaxation of the step profile for different microscopic mechanisms
Authors: Liu Da-Jiang , Fu Elain S. , Johnson M. D. , Weeks John D. , Williams Ellen D.
Published: July 2002

Theoretical and experimental studies of the rate of decay of metastable structures are compared quantitatively. The effect of decay mechanism, size, and periodicity of the structure on the rate of decay is evaluated within both a coarse-grained step-based model and a continuum model. For high-amplitude structures, the decay scales with size (N) and time as (t/Nα)−β. The exponents α and β depend on the mass transport mechanism. The size scaling is α=4 for locally conserved diffusive flux and α=2 for locally nonconserved flux. The time scaling exponent is β=1/5 for diffusive limited mass transport and β=1/4 for step attachment limited mass transport. Experiments were performed on metastable structures of controlled sizes 3–5 nm in height, prepared by direct current heating on Si(111). Quantitative agreement with theoretical predictions of both scaling (α=4.3±0.5, β=0.2−0.3) and absolute rate of decay were obtained.
Schwoebel barriers on Si(111) steps and kinks
Authors: Kodiyalam S. , Khor K. E. , Das Sarma S.
Published: July 2002

Motivated by our previous work using the Stillinger–Weber potential, which shows that the [2̄11] step on the relaxed 1×1 Si(111) has a Schwoebel barrier of 0.61±0.07 eV, we calculate here the same barrier corresponding to two types of kinks on this step—one with rebonding between upper and lower terrace atoms (type B) and the other without (type A). From the binding energy of an adatom, without additional relaxation of other atoms, we find that the Schwoebel barrier must be less than 0.39 eV (0.62 eV) for the kink of type A (type B). Such a bound is argued to be a robust feature following from the presence of rebonding at the step edge or kink site. From the true adatom binding energy we determine the Schwoebel barrier to be 0.15±0.07 eV (0.50±0.07 eV) for the kink of Type A (B). The decrease in the Schwoebel barrier is roughly consistent with our previous estimates of its upper bound of 0.05 eV. However, as the true binding energy plots show discontinuities due to significant movement of atoms at the kink site, we speculate on the possibility of multi-atom processes having smaller Schwoebel barriers.
Reduction of visible defect densities in molecular beam epitaxy grown GaAs using a high-capacity, low flux transient Ga source with novel crucible inserts
Authors: Sacks R. N. , Patterson George A. , Stair Kathleen A.
Published: July 2002

A new design of large capacity crucible with novel inserts has been evaluated with respect to visible defect density, layer uniformity, and flux transient. The crucible was tested in a commercially available furnace with two independently controlled heater windings. The inserts were two disks, each having a different set of holes, stacked inside the crucible and permitting no line of sight between the Ga melt and the substrate. The source was tested side-by-side with a similar furnace equipped with a commercially available crucible and conical insert set designed for low shutter transient and low flux drift. Defect densities were measured on epitaxial layer structures having a total of 1 μm of GaAs. The new design showed significantly lower total defect densities than a control growth with the standard cell, producing as few as ∼1/3 the defects (43±6 vs 155/cm2). Flux transients were the same with the two sources (<2%). Uniformity was tested by using photoluminescence to measure the thickness of GaAs quantum wells across a 75 mm diameter wafer. While the old design produces a center-to-edge decrease in thickness of ∼2.5%, the new source produces a decrease in thickness of ∼6.5%.
Microscopic processes during electron cyclotron resonance microwave nitrogen plasma-assisted molecular beam epitaxial growth of GaN/GaAs heterostructures: Experiments and kinetic modeling
Authors: Bandić Z. Z. , McGill T. C. , Hauenstein R. J. , O’Steen M. L.
Published: July 2002

A set of δ-GaNyAs1−y/GaAs strained-layer superlattices grown on GaAs (001) substrates by electron cyclotron resonance (ECR) microwave plasma-assisted molecular beam epitaxy (MBE) was characterized by ex situ high resolution X-ray diffraction (HRXRD) to determine nitrogen content y in the nitrided GaAs monolayers as a function of growth temperature T. A first order kinetic model is introduced to quantitatively explain this y(T) dependence in terms of an energetically favorable N for As anion exchange and thermally activated N-surface desorption and surface segregation processes. The nitrogen surface segregation process, with an estimated activation energy Es∼0.9 eV appears to be significant during the GaAs overgrowth of GaNyAs1−y layers, and is shown to be responsible for strong y(T) dependence.
Work function measurements of diamond film surfaces
Authors: Mackie W. A. , Plumlee Jason E. , Bell A. E.
Published: July 2002

We report on the growth and subsequent work function measurements of diamond film covered surfaces. Diamond films were grown via a thermal chemical vapor deposition technique. The feed gas mixture used was 1% CH4/99% H2. Raman spectroscopy was used to verify diamond growth. Electron emission was investigated and work function values obtained in field emission as well as thermionic emission modes. However, we primarily report on a unique way to ascertain the absolute work function of diamond surfaces using the field emission retarding potential technique. This experimental method readily lends itself to these types of investigations where values can be determined apart from thermal or field effects. This method gives a diamond surface work function of 4.15±0.05 eV.
Predicting in-plane distortion from electron-beam lithography on x-ray mask membranes
Authors: Laird D. L. , Engelstad R. L. , Puisto D. M. , Acosta R. E. , Cummings K. D. , Johnson W. A.
Published: July 2002

To produce x-ray masks useable for 0.25 μm lithography and beyond, all sources of mask distortion must be minimized. In order to facilitate the fabrication of high-quality masks, the phenomenon of changes in resist stress during e-beam exposure has been studied. Finite element modeling was employed to determine the effects of various geometric and material properties on final image quality. Additionally, writing patterns and multipass exposure were also studied. The results indicate that the stress relief phenomenon can be controlled in a well-designed system.
Defect-free x-ray masks for 0.2-μm large-scale integrated circuits
Authors: Okada I. , Saitoh Y. , Sekimoto M. , Ohkubo T. , Matsuda T.
Published: July 2002

The x-ray mask fabrication process we developed can be used to make and maintain essentially defect-free masks consisting of Ta absorbers on SiN membrane. The surface of the deposited SiN substrates is polished to make them as smooth as possible. As Ta is chemically stable, mask fabrication processes are frequently followed with a wet-cleaning process using a strong acid solution. Inspection of resist patterns printed on a wafer confirms that there are less than 20 printable defects per mask, and there are no defects on the back surface. The inspection and repair are repeated until the mask is defect free. Defects caused by mask handling and x-ray exposure are immediately washed up by wet cleaning with strong acid. The resulting x-ray masks have been used in large-scale integrated circuits fabrication, and fully functional devices have been obtained.
Near-surface dopant passivation after wet-chemical preparation
Authors: Ley L. , Ristein J. , Schäfer J. , Miyazaki S.
Published: July 2002

Recent advances in wet-chemical surface treatment of silicon has resulted in unreconstructed, hydrogen terminated Si(111) surfaces with extremely low surface recombination velocity of only 0.25 cm/s [E. Yablonovitch et al., Phys. Rev. Lett. 57, 249 (1986)]. This points towards a surface free of surface states that normally pin the Fermi level EF on Si(111) somewhere near midgap depending on the surface reconstruction. This expectation is not borne out, however, by experiment. Using Si 2p core level spectra, we find consistently a surface Fermi level position near midgap for 16 heavily doped n- and p-type samples. Checks for surface photovoltage and ion concentrations sufficient to induce the observed band bending were negative. All samples attain their bulk Fermi level position at the surface after annealing to about 400 °C, a temperature at which the surface hydrogen coverage is unchanged as monitored by ultraviolet excited photoemission. Above 400 °C, hydrogen starts to desorb from the surface and only with the onset of the 7×7 reconstruction does EF move back towards midgap. We suggest that the initial position of EF near midgap is due to a hydrogen induced passivation of dopants that leaves an intrinsic surface layer. Annealing at ∼400 °C reactivates the dopants by breaking the B–H and P–H complexes as is known from plasma passivation. The necessary passivation depth has been calculated as a function of bulk doping yielding values of the order of one micrometer.
Comparative scanning tunneling microscopy observation of a homologous series of n-alkyloxy-cyanobiphenyles
Authors: Walzer K. , Hietschold M.
Published: July 2002

In scanning tunneling microscopy (STM) experiments liquid crystals (LC) do often serve as model substances for organic adsorbates on solid substrates. Especially, the group of alkyl-cyanobiphenyle (nCB, n=number of carbon atoms in the alkyl chain) liquid crystals has been in the center of interest for a long time. In this work we present STM results of adsorbate studies of the closely related molecules of the alkyloxy-cyanobiphenyle type (nOCB, with n=5,7,8). Under the influence of the electric field at the STM tip apex these LC molecules form well-ordered structures, which are determined by the atomic structure of the substrate surface. This molecular ordering of a thin adsorbate layer above the substrate is investigated by STM. The results on OCBs are compared with data from x-ray diffraction studies and with results of STM measurements of the closely related 8 CB. Both highly oriented pyrolytic graphite and molybdenum disulfide have been used as substrates.
Pt:SnO2 thin films for gas sensor characterized by atomic force microscopy and x-ray photoemission spectromicroscopy
Authors: Cricenti A. , Generosi R. , Scarselli M. A. , Perfetti P. , Siciliano P. , Serra A. , Tepore A. , Almeida J. , Coluzza C. , Margaritondo G.
Published: July 2002

SnO2 thin films have been grown by radio frequency reactive sputtering method in order to be used as a gas sensor. Subsequently Pt has been added to the SnO2 films to increase the sensitivity to carbon monoxide gas. Two different substrates have been used: rough and mechanically polished alumina. The morphology of the film has been characterized by atomic force microscopy, whereas the chemical composition was analyzed by x-ray photoemission spectromicroscopy. Pt:SnO2 clusters with widths of 500–600 nm were observed on the rough alumina, whereas on the mechanically polished alumina, the Pt:SnO2 film was smoother. X-ray photoemission spectromicroscopy measurements show for Pt:SnO2 films on rough alumina substrates different charging in different areas of the sample. The response curve to carbon monoxide is 30% higher for rough alumina.
Nonlinear characteristics induced by carrier accumulation in InAs/GaAs superlattice cap layer on GaAs/GaAlAs multi-quantum well structure
Authors: Matsui Y. , Kusumi Y.
Published: July 2002

Nonlinear characteristics induced by accumulation of photogenerated carriers in a cap layer on a GaAs/GaAlAs multi-quantum well (MQW) structure can be observed at 300 K under weak photoexcitation (2.5 mW/cm2). Photoinduced currents (PIC) are measured for various structures of cap layer. Negative differential properties are observed in the relations between PIC and forward bias voltage for the MQW structures with a cap layer including InAs/GaAs short period superlattice. The phenomenon is reduced in the case of a cap layer including an InGaAs alloy and disappears in the case of that composed of only GaAs. These experimental results are explained reasonably considering the capability of the cap layer to accumulate photogenerated carriers.
Atomic structure of the steps on Si(001) studied by scanning tunneling microscopy
Authors: Komura T. , Yoshimura M. , Yao T.
Published: July 2002

We have studied atomic structures of the steps on Si(001) surface, using scanning tunneling microscopy. Freezing of dimer buckling on an upper terrace near the SA steps is clearly observed, which also affects atomic arrangements near the step. Both types of the rebonded and the nonrebonded SB steps are observed. The scanning tunneling microscopy image of the rebonded SB step shows a characteristic feature in which two markedly bright spots are observed in the empty state. It is found that one bright protrusion corresponds to the dimer at the end of the upper terrace, and another corresponds to the rebonded atoms at the lower terrace. The feature might be related to the lattice strain and the charge transfer by the rebonding.
Layer-by-layer etching of HgI2 films and crystals by scanning force microscopy
Authors: Lang H. P. , Erler B. , Rossberg A. , Piechotka M. , Kaldis E. , Güntherodt H.-J.
Published: July 2002

Thin films and single crystals of mercuric iodide (α-HgI2) have been investigated by scanning force microscopy. During the scan process, material evaporation is observed proceeding by hole formation and etching at steps. The ratio of etched volume per second and per interaction area between tip and mercuric iodide step edges is found to be constant for hole formation on an HgI2 crystal and for etching at a screw dislocation on HgI2 films. An estimate for the loading of the SFM tip gives a value comparable to the critical resolved shear stress in this material.
Atomic-hydrogen-induced Ag cluster formation on Si(111)-√
3×√3–Ag surface observed by scanning tunneling microscopy
Authors: Oura Kenjiro , Ohnishi Hideaki , Yamamoto Yasuji , Katayama Itsuo , Ohba Yasuyuki
Published: July 2002

The scanning tunneling microscope has been used to study structural transformation of the Si(111)-√3×√3(R30°)–Ag surface caused by atomic hydrogen adsorption. Atomically resolved scanning tunneling microscope images reveal a structure model for exchange adsorption of hydrogen and silver atoms. It has been shown that the proposed model can well explain various experimental results reported so far on this system.