bluuebunny/crossref_metadata_2025 huggingface dataset:
The step coverage of undoped and phosphorus-doped SiO2 glass films
Authors: Levin R. M. , Evans-Lutterodt K.
Published: July 2002

The step coverage of undoped and phosphorous-doped SiO2 glass films has been studied. Various parameters which play a role in determining the quality of the step coverage are briefly discussed. The step coverage capability of various deposition processes is evaluated. The processes compared are: atmospheric-pressure CVD, low-temperature, low-pressure CVD (Silox), mid-temperature, low-pressure CVD (TEOS) and plasma-enhanced CVD. The parametric dependence of the step coverage obtained in the deposition of undoped glass by use of the mid-temperature low-pressure technique is reported. It is demonstrated that the quality of the step coverage is strongly dependent on the deposition conditions. It improved with increasing TEOS flow rate and molecular residence time in the reactor. Addition of nitrogen, oxygen, or phosphine/nitrogen mixture to the TEOS causes a deterioration in the step coverage capability of the deposition process. The step coverage of this particular process is independent of the deposition temperature in the range 650–780 °C.
Effects of strain and layer thickness on the growth of InxGa1−xAs–GaAs strained-layer superlattices
Authors: Laidig W. D. , Peng C. K. , Lin Y. F.
Published: July 2002

The effects of strain and layer thickness on the growth of InxGa1−xAs–GaAs strained-layer superlattices (SLS’s) by molecular beam epitaxy (MBE) is investigated. Data are presented on two series of InxGa1−xAs–GaAs SLS’s with x∼0.38 and x∼0.28. All of the SLS’s were grown consecutively with all fluxes and growth conditions remaining constant throughout. The only variation in the sample growth within each series was the layer thickness (shutter timing), which ranged from ∼20 to ∼800 Å. The growth rate for all the SLS’s is found to be constant and in close agreement with that predicted from much thicker layers. X-ray diffraction analysis of the SLS’s shows substantial broadening of diffracted peaks on highly mismatched SLS’s with relatively thick layers, although diffraction patterns of thin-layer SLS’s and thick single layers of InxGa1−xAs remain sharp. Scanning electron microscopy indicates the broadening in x-ray diffraction peaks is accompanied by an increased presence of structural defects in thick-layer SLS’s.
Diffusion coatings of steels: Formation mechanism and microstructure of aluminized heat-resistant stainless steels
Authors: Bangaru N. V. , Krutenat R. C.
Published: July 2002

The effect of base-alloy composition on the microstructure and mechanical and thermal stabilities of aluminum diffusion coatings has been studied for 316, 310, and I800H stainless steels, by optical, microprobe, transmission/scanning transmission electron microscopy, and microhardness testing. In all the diffusion aluminized alloys, two distinct coating layers form: an outer aluminide layer and an inner, interdiffusion layer. The substrate austenite stability is the single most important parameter affecting the thickness, phase distribution, and microchemistry of these two layers. TEM/STEM analyses showed that the interdiffusion layer is a ‘‘natural composite’’ made up of a uniform dispersion of the hard nickel aluminide phase (B2) in a soft ferrite matrix. Formation of this layer involves ‘‘ferritization’’ of the substrate, a process akin to pearlitic transformation in carbon steels. The interdiffusion layer demonstrated high hardness with good mechanical integrity and its thermal stability with the substrate depends strongly on the ease of ferritization, which depends in turn on the degree of austenite stability of the substrate.
Silicon nitride film deposition by hot-wall plasma-enhanced CVD for GaAs LSI
Authors: Ishii Yasunobu , Aoki Tatsuo , Miyazawa Shintaro
Published: July 2002

Silicon nitride film deposition by a hot-wall plasma-enhanced chemical vapor deposition (CVD) was investigated for application to GaAs large scale integrated circuits (LSI) fabrication. Silicon nitride film properties related to deposition parameters were described. The in situ plasma-precleaning effect on adhesion to GaAs was also investigated. Annealing effects on silicon nitride films were considered as a GaAs annealing cap material for the postimplantation annealing. It was concluded that a hot-wall plasma-enhanced CVD together with argon-plasma precleaning was preferable to achieve reliable silicon nitride film deposition for GaAs devices. The optimum deposition conditions were NH3/SiH4 gas flow ratio of 6 to 9 at 380 °C substrate temperature under 2 Torr pressure.
Reduction of arsenic oxide contamination in molecular beam epitaxy vacuum chambers
Authors: Stall R. A. , Swaminathan V. , Schumaker N.
Published: July 2002

Molecular beam epitaxial films of GaAs and AlxGa1−xAs are degraded by the presence of arsenic oxide in the background gas spectrum. This memorandum discusses a technique for reducing the arsenic oxide contamination by baking the vacuum chamber under flow of H2. This technique is useful for an MBE system whose arsenic deposits have been oxidized from exposure to atmosphere. In a chamber which has been exposed to atmosphere for greater than 72 h, a 12 h bakeout under a 6 l/min flow of N2/4% H2 at 1 atm decreased the partial pressure of the arsenic oxides greater than 10× more than did an 18 h vacuum bakeout. Initial results on the improvement of films grown in chambers with high arsenic oxide backgrounds through the use of 5×10−7 Torr of H2 is reported.
A high speed EBL column designed to minimize beam interactions
Authors: Veneklasen Lee H.
Published: July 2002

The writing strategy and electron optical aspects of the Perkin–Elmer AEBLE 150 EBL system are discussed. For a specific submicron EBL writing task, an ‘‘optimum’’ area for a variable shaped beam is derived. For specific column properties, an optimum gun brightness is chosen to image the shape at maximum beam interactions limited current. The writing system takes advantage of a continuously moving stage to allow a moderate scan field, exploiting in-lens deflection to use a very large aperture angle with a 2 mm field. Experimental data indicates a current density of 100 A/cm2 in rectangular or triangular shapes up to 2  μm in size. Edge resolution is less than 0.15  μm for shapes containing less than 1.5  μA of current. A series of beam profiles taken with a 300 ns exposure cycle shows that the deflection systems will support high speed lithography on insensitive resists.
Diffusion barrier properties of thin selective chemical vapor deposited tungsten films
Authors: Shen B. W. , Smith G. C. , Anthony J. M. , Matyi R. J.
Published: July 2002

Diffusion barrier properties of selective chemical vapor deposited (CVD) tungsten to silicon and aluminum interdiffusion have been investigated using secondary ion mass spectroscopy, x-ray diffraction analysis, and scanning electron microscopy. Samples of titanium layered pure aluminum on selective CVD tungsten on cleaned silicon wafers were prepared and sintered between 450 and 520 °C. The Ti layered aluminum was used to increase the capacity for silicon to facilitate the outdiffusion from the substrate. Magnetron sputter deposited Ti:W samples were also included in the analysis for comparison purposes. The experimental results indicated that 73 nm of selective tungsten with sheet resistance of 1.5 Ω/⧠ was sufficient as a diffusion barrier for both aluminum and silicon at 450 °C for 30 min, but failed at 520 °C for 30 min. 33 nm thick selective tungsten with 7 Ω/⧠ sheet resistance failed to prevent interdiffusion of aluminum and silicon even at 450 °C for 30 min. 100 nm of Ti:W remained an excellent diffusion barrier for anneals up to 485 °C for 30 min, but did not prevent Si outdiffusion at 520 °C, 30 min. No aluminum penetration was seen in Ti:W samples up to 520 °C. A ternary Ti–W silicide was identified at sintering temperatures as low as 485 °C. A possible formation mechanism is herein proposed.
Mechanism of Schottky barrier formation: The role of amphoteric native defects
Authors: Walukiewicz W.
Published: July 2002

A correlation between the Fermi level pinning deduced from Schottky barrier heights and from electrical properties of irradiated III–V semiconductors is found. The correlation indicates that similar defects are responsible for the Fermi level stabilization in both cases. It is proposed that amphoteric native defects, i.e., the defects which change their electrical characteristics depending on the Fermi level position, play a dominant role in the processes leading to a Schottky barrier formation. A detailed analysis of metal–GaAs contacts shows that in this case the amphoteric defects responsible for the barrier heights are VGa (acceptor) and a donor complex AsGa+VAs. It is shown that for thick metal coverages two barriers are formed. A surface barrier determined by the charge associated with a native defect and the bulk barrier controlled by the bulk doping. The sum of the two barrier heights satisfies the Schottky condition for the interface, but it is the bulk barrier that determines the macroscopic electrical properties of the contact. The model explains the evolution of the Fermi level position at the interface observed for metal coverages varying in a broad range of thicknesses. The relationship of the present proposal to previous models of Schottky barriers is discussed.
Investigation of the liquid metal ion source cluster beam constituents and their role in the properties of the deposited film
Authors: François M. , Pourrezaei K. , Bahasadri A. , Nayak D.
Published: July 2002

A transverse magnetic field has been used to separate ion cluster beam constituents according to their charge to mass ratio. As a result, several circular spots were observed on a silicon wafer at a distance of 160 mm from the source. The charge to mass ratio of each spot was identified based on its location. The current profile of each spot as a function of total beam current was measured. The results indicate that for the source structure used in this study, clusters are present along the axis of the beam, even at 60 μA current. However, their relative abundance is significantly increased as current is increased. The Auger electron spectroscopy of each spot confirms that the large clusters are the necessary species for film deposition. No significant deposition was observed for the Au++, Au+, Au+2, etc., due to sputter etching. The deposited film is due to large clusters, which in the absence of energetic ions shows cornflake type morphology as opposed to granular morphology observed in the presence of energetic ions. The film deposited in the presence of energetic ions shows excellent adhesion to the substrate and overall integrity. However, the film deposited in the absence of energetic ion does not have sufficient film integrity.
Hot-jet etching of Pb, GaAs, and Si
Authors: Geis M. W. , Efremow N. N. , Pang S. W. , Anderson A. C.
Published: July 2002

Hot-jet etching is a new dry-etching technique which uses a directed flux of radicals to achieve anisotropic etching. The radicals are obtained by the thermal decomposition of a comparatively unreactive source gas in a heated jet. Pb, GaAs, and Si have been etched with this technique using CH3 (methyl), Cl, and F radicals, respectively. Methyl radicals have been derived from several source gases including n-butane, dimethyl ether, and acetone. Atomic fluxes of Cl and F have been obtained by decomposing Cl2 and SF6. Etching rates as high as 10 μm min−1 have been obtained using a Cl flux on GaAs. Since there is no sputtering component during etching, very high differential etching rates, in excess of 1000, have been obtained between Si and SiO2. Since these radicals are very reactive, both the material of the hot jet and its operating temperature are important parameters. Jets formed from alloys of Re and W operating at temperatures near 2700 K have been used to etch GaAs with a Cl flux. Jets formed from W operating near 3200 K and Ir operating near 2000 K have been used to obtain F from SF6 to etch Si.
Reversibility of Fermi level pinning
Authors: Chiang T. T. , Spindt C. J. , Spicer W. E. , Lindau I. , Browning R.
Published: July 2002

By depositing monolayer coverage of Ag on freshly cleaved, clean GaAs(110) surface, the surface Fermi level was found to pin at 0.45±0.05 eV above valence band maximum (VBM) for p-GaAs and 0.65±0.05 eV above VBM for n-GaAs, due to the formation of midgap electronic states. Upon annealing to 500 °C, the Ag on the surface clustered into islands and the surface Fermi level moved back to within 0.2 eV of the bulk position [conduction band minimum (CBM) and VBM for n and p types, respectively]. Further deposition of Ag on the annealed surface moved the surface Fermi level back to the previously pinned positions. The surface Fermi level movement was monitored using Ga 3d and As 3d photoemission signals. The Ag clustering was seen both by a dramatic decrease in the Ag 4d photoemission signal and by scanning Auger microscopy. Scanning electron microscopy also revealed that the Ag clustering formed hemispherical-like islands with a size distribution up to ∼500 Å in diameter. The average island separation is about a few thousand angstroms (∼2000 Å). As a comparison with a reactive metal, similar annealing experiments were performed for monolayer coverage of Al on GaAs. For the Al case, the metal remained unclustered after annealing and the surface Fermi level remained pinned.
Optical studies of molecular-beam epitaxy growth of GaAs and AlAs
Authors: Aspnes D. E. , Harbison J. P. , Studna A. A. , Florez L. T. , Kelly M. K.
Published: July 2002

We discuss the first real-time optical spectroscopic measurements of (001) GaAs and AlAs surfaces during crystal growth by molecular-beam epitaxy. In these experiments, reflectance–difference spectroscopy (RDS) is used to enhance the typically low sensitivity of optical probes to surface phenomena. Comparison of reflectance–difference and reflection high-energy electron diffraction (RHEED) signals upon interruption of the As flux during otherwise normal growth of GaAs and AlAs shows that RD signals are sensitive to either surface chemistry or surface structure according to wavelength. The spectral dependence of the chemical component is sufficiently pronounced so that Al-terminated surfaces can be distinguished from Ga-terminated surfaces. We use this spectral capability to assess the competition between codeposited Al and Ga for the same surface-bonding sites. We also report the first observation of the RD analog of RHEED oscillations, that is, oscillations in the RD response upon initiation of growth. These are seen to occur under both chemically and structurally sensitive conditions. The initial heteroepitaxial growth of GaAs on AlAs shows very complicated energy and time dependences that extend over a number of monolayers. These results suggest that systematic investigations of the optical properties of growth surfaces will lead to a new understanding of the fundamental mechanisms of crystal growth.
Native oxide formation on CdTe
Authors: Choi S. S. , Lucovsky G.
Published: July 2002

We report studies of the chemical bonding of Cd and Te atoms to O atoms in air grown native oxides of CdTe. We find that the oxide grown in laboratory air on CdTe{100} surfaces: (i) always contains both Te–O and Cd–O bonds which we have detected, respectively, by x-ray photoelectron spectroscopy and x-ray Auger electron spectroscopy, and (ii) is soluble in deionized water. Based on these two observations and comparisons with the results of previous studies of native oxide formation of both CdTe and (Cd,Hg)Te, we conclude that the CdTe air grown native oxide is a compound oxide of the form CdxTeyOx, probably CdTeO3, and not a mixture of the elemental oxides, CdO and TeO2.
Scanning ion beam techniques for the examination of microelectronic devices
Authors: Cleaver J. R. A. , Kirk E. C. G. , Young R. J. , Ahmed H.
Published: July 2002

A scanning ion microscope has been applied to the examination of microcircuits. Highly localized sputtering with the ion beam can be used for cutting microsections, positioned with submicrometer accuracy, across selected features of semiconductor devices and integrated circuits. These sections can subsequently be examined with the ion beam in the same instrument. The secondary electron signal resulting from ion impact can depend on the voltage distribution over the specimen. Combination of voltage contrast imaging with sectioning gives voltage information from buried features of circuits.
Molecular-beam epitaxial growth and characterization of pseudomorphic InAs/In0.52Al0.48 As quantum wells
Authors: de Miguel J. L. , Meynadier M.-H. , Tamargo M. C. , Nahory R. E. , Hwang D. M.
Published: July 2002

The evolution of the structural and optical quality of molecular-beam epitaxial (MBE) grown InAs/In0.52Al0.48As pseudomorphic quantum wells with increasing well thickness has been analyzed by transmission electron microscopy (TEM) and photoluminescence measurements. TEM was used to assess the commensurability of the samples as well as to confirm the build up of stress as the InAs layer is made thicker. Under our growth conditions, intense intrinsic photoluminescence is observed for InAs layers as thick as 30 Å. Beyond this thickness a deterioration of the photoluminescence characteristics occurs due to roughening of the interfaces rather than to relaxation of the InAs lattice.
Dynamical method for the thermomechanical study of thin membranes
Authors: Berry B. S. , Pritchet W. C. , Uzoh C. E.
Published: July 2002

An apparatus has been built for the dynamic mechanical analysis of thin membranes, such as those of interest for x-ray lithographic masks. Frequency and damping measurements have been made over the temperature range 100–700 K, using vibrational modes in the range 1–10 kHz. The measurements are made at pressures below 10−5 Torr to remove atmospheric loading and damping effects and thereby reveal the intrinsic membrane behavior. Stress and differential thermal expansion results are presented for B-doped Si membranes and a PMDA/ODA polyimide membrane, prepared on Si wafers. Annealing behavior observed during thermal cycling of the Si(B) membranes has led to the discovery that the membrane stress can be varied reversibly over a wide range by the introduction and removal of hydrogen.
The application of reactive ion etching in producing free-standing microstructures and its effects on low-temperature electrical transport
Authors: Kwong Y. K. , Lin K. , Hakonen P. , Parpia J. M. , Isaacson M.
Published: July 2002

We have developed a reliable method of fabricating free-standing metallic microstructures with dimensions down to 50 nm. This technique is compatible with virtually any metal and can be used to fabricate samples that should be low-dimensional with respect to both electron and phonon transport. Unlike earlier schemes that effect substrate removal from the front, our technique calls for reactive-ion etching (RIE) from the reverse side of a Si3N4 membrane substrate, onto which microstructures have been previously patterned by standard methods. By carefully controlling the etching times, the extent of invasive damage of the etch on the microstructures is minimized. We have also performed resistance measurements for etched and unetched Al films on bulk substrates to characterize the effect of etching damage and its consequence on low-temperature transport. By measuring the low-field magnetoresistance (MR), the inelastic scattering rate and its dependence on temperature can be determined by fitting data to theoretical models. For short etch times, we have found that RIE does not alter the low-frequency electrical transport properties of these supported films in any significant fashion. The only discernible difference between the etched and the unetched samples appears to be a small, temperature-independent contribution to the inelastic rates, which can be attributed to surface damage. Thus, we conclude that our technique can be used to effectively decouple microstructures from substrate effects without introducing appreciable process related artifacts.
Optical system for a low-energy focused ion beam
Authors: Aihara R. , Kasahara H. , Sawaragi H. , Shearer M. H. , Thompson W. B.
Published: July 2002

A low-energy focused ion beam (FIB) would be a very useful tool for shallow doping with low damage density to the substrate. For a low-energy FIB, an optical system using a retarding field is advantageous because of a low chromatic aberration coefficient which could not be reduced with a conventional column. Some evaluations were made for an optical column with a retarding electrode for practical use. The secondary electron trajectories within the equipotential space were calculated by the surface-charge method, and some secondary-electron images were observed with an experimental column having a retarding electrode.
A single-filament effusion cell with reduced thermal gradient for molecular-beam epitaxy
Authors: Mattord T. J. , Kesan V. P. , Neikirk D. P. , Streetman B. G.
Published: July 2002

A molecular-beam source utilizing single-filament construction to generate a reproducible and uniform beam of elemental molecules is presented. The filament design is constructed to conform to the shape of pyrolytic boron nitride crucibles utilized in molecular-beam epitaxy (MBE) systems, and to minimize the thermal gradient between the crucible opening and the crucible bottom which is inherent in Knudsen cell technology. The design also improves heat transfer, efficiency, and flux response of the cell. We show that this cell exhibits a better flux response than typical commercially available effusion cells and successfully prevents source material redistribution, thus providing for long-term flux stability and reproducibility in certain materials used in MBE. No increase in background impurity concentration in epitaxial AlGaAs films was observed, when compared to films grown using a standard Varian effusion cell. This cell is currently installed and being used as an aluminum source in a Varian GEN II system.
Can atomic force microscopy tips be inspected by atomic force microscopy?
Authors: Hellemans Louis , Waeyaert Koen , Hennau Frans , Stockman Lieve , Heyvaert Ilse , Van Haesendonck Chris
Published: July 2002

An attempt has been made to image prospective tips by atomic force microscopy. The apex of mounted diamond fragments and of traditional metallic tips was investigated by the same diamond probe. The peculiar tip–tip configuration allowed to search for the effect of sample rotation on the images. Identical images were obtained when the diamond stylus scanned different etched tungsten tips, illustrating an interchange in the roles of tip and sample.
The fabrication of metal–oxide–semiconductor transistors using cerium dioxide as a gate oxide material
Authors: Frangoul A. G. , Sundaram K. B. , Wahid P. F.
Published: July 2002

Cerium dioxide was employed as a gate insulator for an enhancement-type n-channel metal–oxide–semiconductor (MOS) transistor. Cerium was evaporated in a tungsten boat and immediately oxidized for oxide uniformity. The use of CeO2 as a gate oxide in MOS transistor yielded a low positive threshold voltage with negligible interface charge effects. This resulted in the transistor performing as an enhancement type device.
High efficiency beamline for synchrotron radiation lithography
Authors: Kaneko Takashi , Saitoh Yasunao , Itabashi Seiichi , Yoshihara Hideo
Published: July 2002

A highly efficient beamline for synchrotron radiation (SR) lithography has been developed for our compact storage ring (Super-ALIS). Two toroidal mirrors are employed to increase the x-ray intensity on the wafer and to vertically expand the exposure area. Astigmatism is intentionally introduced in these mirrors to increase their converging and collimating abilities. The first mirror converges SR beams with a divergence angle of 2°. The second mirror, which is controlled by a microcomputer, collimates the beam and oscillates to produce an exposure area of 25×25 mm2. An improved vacuum evaporation technique is used to coat the mirror surfaces with platinum, which increases the reflectivity to 50% at a wavelength of 8.34 Å. The resulting x-ray intensity on the wafer is 5 mW/cm2/100 mA. A uniform x-ray intensity distribution can be obtained by adjusting the scan speed of the second mirror and using an x-ray compensation filter. The resulting nonuniformity is improved to be less than ±4%. A reliable x-ray extraction system that consists of two Be windows and a SiN window permits exposure in an atmospheric environment.
Dry surface cleaning using CO2 snow
Authors: Sherman Robert , Grob John , Whitlock Walter
Published: July 2002

Controlled expansion of high purity carbon dioxide through a nozzle forms a high velocity ‘‘snow’’ stream that effectively removes both particulate and thin film contaminants from silicon wafer surfaces [W. Whitlock, Presented at the 20th Annual Meeting of the Fine Particle Society, Boston, MA, August 22, 1989 (unpublished); R. Sherman and W. Whitlock, J. Vac. Sci. Technol. B 8, 563 (1990)]. This process will clean surfaces leaving no detectable film residue as well as reduce adventitious (native) hydrocarbon surface content. This article discusses the performance of CO2 snow cleaning on a variety of materials typically encountered in a surface analysis laboratory. Cleaning tests were performed on metals (aluminum and copper sheets), semiconductors (Si and InP wafers), and insulators (ceramics, laser optics, glass plates, and polymers). Performance is judged primarily through x-ray photoelectron spectroscopy measurements with primary consideration given to reduction of surface hydrocarbons. These measurements are compared with samples which were cleaned with a conventional solvent process. The results indicate that CO2 snow cleaning is comparable to solvent cleaning in its effectiveness for removal of hydrocarbon films. Recommendations are made for the use of CO2 snow cleaning in both industrial and laboratory applications.
Reactive sputtering of InP in N2 and N2/O2 plasmas
Authors: Sundararaman C. S. , Lafontaine H. , Poulin S. , Mouton A. , Currie J. F.
Published: July 2002

The plasma etching of InP using nontoxic, fluorocarbon free, N2 and N2/O2 mixtures has been demonstrated. The etch rates as a function of pressure, power, and O2 content have been studied. Reactive sputtering appears to be the principal etching mechanism for both plasmas. These plasmas react with the InP substrate forming In2O3, InPO4 and probably nitride and oxynitrides of indium. N+2 and N+ ions are the dominant sputtering species in the N2 plasma, while addition of small quantities of O2(<2%) to the plasma appears to promote the formation of heavier ions like NO+ and NO+2 and easily sputterable NO compounds thereby dramatically increasing the etch rates. At higher O2 contents (≥4%) strong surface oxidation and formation of compounds containing the NO2 radical limit the sputtering rate. Both gas mixtures exhibit low etch rates but form very smooth surfaces.
Surface characterization of multilayer x-ray diffraction specimens
Authors: Burkhalter P. G. , Brown D. B. , Gilfrich J. V. , Konnert J. H. , D’Antonio P. , Rosenstock H. , Shirey L. M. , Thompson M. , Elings V.
Published: July 2002

Multilayer specimens of high-Z/low-Z alternating layer stacking have utility as efficient elements for the diffraction and reflection of x rays and ultraviolet radiation. Bielement multilayers of W/C and W/Si, prepared commercially on ultrasmooth substrates, have been characterized by atomic force microscopy (AFM) and by scanning tunneling microscopy to assess the smoothness and nature of the diffraction surface and by transmission electron microscopy to evaluate the uniformity of layering. The diffraction properties of these multilayers have been evaluated by measurements using crystal spectrometers, and by calculations using coherent Bragg diffraction atomic scattering and classical multilayer reflection theory based on stacking uniformity. We have found that the x-ray diffraction performance of W/Si multilayers to be better than W/C multilayers. In addition, the surface of the W/Si specimens were determined by atomic force microscopy to be smoother than W/C and that agreement exists with a roughness factor determined by analytical diffraction theory. The evaluation of multilayers will enhance our understanding of nanostructures, leading to improved diffraction structures.
Heating-current-induced step motion on Si(111) surface by scanning tunneling microscopy
Authors: Tokumoto H. , Miki K. , Murakami H. , Kajimura K.
Published: July 2002

Scanning tunneling microscopy has been made on stepped Si(111) surfaces cleaned by heating at 1200 °C with dc electric current flowing directly through a sample. Heating-current-induced step motion was observed: the step bunching for the current along the step-up direction; the atomic steps with regular spacing for the current along the step-down direction. This step transformation was reversible with respect to the current direction. These results are in good agreement with the recent results by reflection electron microscope [Surf. Sci. 213, 157 (1989)] and could be ascribed to the electromigration effect. On the other hand, the preliminary observation for the dc current flowing perpendicular to the step direction did not show the appreciable step transformation.
Desorption from oxide films made by plasma enhanced chemical vapor deposition using tetraethylorthosilicate
Authors: Tompkins Harland G. , Grivna Gordon , Cowden William G. , Leathersich Cathy
Published: July 2002

The dielectric stack of multilevel metal interconnections of integrated circuits contains various forms of dielectrics separating metal conductors. Silicon dioxide deposited by plasma enhanced chemical vapor deposition (PECVD) is one such dielectric. The formation of voids in some of the metal layers stimulated a study of the thermal desorption of H2O from oxide films. The films were deposited by plasma enhanced chemical vapor deposition using a tetraethylorthosilicate precursor. The total amount of H2O desorbed was measured as a function of two deposition variables, deposition substrate temperature, and deposition plasma power. The total amount of H2O desorbed could be reduced by either increasing the deposition substrate temperature or increasing the deposition plasma power.
Thermodynamics of the homogeneous and heterogeneous decomposition of trimethylaluminum, monomethylaluminum, and dimethylaluminumhydride: Effects of scavengers and ultraviolet-laser photolysis
Authors: Carlsson J.-O. , Gorbatkin S. , Lubben D. , Greene J. E.
Published: July 2002

Thermodynamic calculations, based upon free-energy minimization, have been used to determine the nature and the relative amounts of equilibrium product species following thermal decomposition of the Al-bearing metal-alkyl donor molecules trimethylaluminum Al(CH3)3, monomethylaluminum AlCH3, and dimethylaluminumhydride Al(CH3)2H at temperatures between 0 and 1250 °C. The calculations were carried out using initial total pressures of 760, 1, and 0.1 Torr (101 kPa, 133, and 13.3 Pa) and both homogeneous and heterogeneous decomposition were considered. The calculations were repeated for mixtures containing trimethylaluminum and the reducing agents H2, arsine AsH3, and silane SiH4 in order to investigate the effectiveness of these species in scavenging C-containing radicals. The effect of H2 on the decomposition of AlCH3 and Al(CH3)2H was also studied. The results are discussed and compared with available data from Al film growth experiments by pyrolytic chemical vapor deposition (CVD) and laser-induced photolytic CVD. Finally, the CVD phase diagram for solid product species was computed for reactant mixtures of Al2(CH3)6+AsH3+H2.
Oxygen addition effects in synchrotron radiation excited etching using SF6
Authors: Utsumi Yuichi , Takahashi Jun-ichi , Urisu Tsuneo
Published: July 2002

The effects of oxygen addition on the synchrotron radiation-excited etching of crystal Si, poly-Si, and SiO2 using SF6 reaction gas are investigated. Without oxygen, two phenomenologically classified reaction mechanisms are observed: gas phase and surface excitation mechanisms. With oxygen addition, the gas phase excitation mechanism disappears and only the surface excitation mechanism becomes dominant. Oxygen addition is extremely effective in the microfabrication of SiO2 line and space patterns using poly-Si as an etching mask. Its addition creates high selectivity between SiO2 and crystal Si. Furthermore, it is considered that the added oxygen removes some etching suppressing species generated on the poly-Si surface.
Photoemission study of low pressure chemical vapor deposited and reactively sputtered titanium nitride in W/TiN/Si
Authors: Kumar Sunil , Chopra D. R. , Smith Gregory C.
Published: July 2002

Low-pressure chemical vapor deposited (LPCVD) tungsten has been deposited onto LPCVD grown and reactively sputtered titanium nitride (TiN) films. The x-ray photoelectron spectroscopy depth profiles and the chemical analysis suggest that the chemical interaction of TiN with W and with the Si/SiO2 substrates tends to be minimal.
Experimental and theoretical study of image bias in x-ray lithography
Authors: Guo Jerry Z. Y. , Leonard Quinn , Cerrina Franco , Di Fabrizio E. , Luciani L. , Gentili M. , Gerold David
Published: July 2002

The successful application of x-ray lithography to a manufacturing process requires a detailed understanding of the image formation process. In a series of articles, a theoretical study of the optical processes involved in the definition of the image in proximity printing has been presented. In addition to the diffraction process, it is included here that the image formation in the very near field (microgaps) due to the guiding effects in the absorber which alters the boundary condition for diffraction and thus changes the final image pattern. Also presented here is an experimental study designed to verify the predictions of the models of image formation. Preliminary result shows a very large depth-of-focus for 0.25 μm features.
Nanostructure fabrication using lithium fluoride films as an electron beam resist
Authors: Langheinrich W. , Spangenberg B. , Beneking H.
Published: July 2002

Homogeneous and quasiamorphous lithium fluoride based films have been deposited as a new ultrahigh resolution electron beam resist. The exposure characteristics of this self-developing positive tone resist are discussed. Compared to other metal halide films, a high sensitivity is the most important advantage, while the resolution limit is also far below 10 nm. Concerning pattern transfer, the properties of this resist in various reactive ion etch processes and the capability for a lift-off process were investigated.
Large-area, free-standing gratings for atom interferometry produced using holographic lithography
Authors: Carter J. M. , Olster D. B. , Schattenburg M. L. , Yen A. , Smith Henry I.
Published: July 2002

Interferometers based on matter waves promise orders-of-magnitude improvements in metrology over laser-based systems by virtue of the fact that the de Broglie wavelengths of atoms are about 104 times shorter. To date, the required matched set of four aligned gratings for such atom interferometers has been made using electron beam lithography and, as a result, such gratings suffer from a lack of spatial-phase coherence. We report on processes we have developed for fabricating free-standing gratings over large areas using conventional holographic lithography and achromatic holographic lithography to achieve spatial periods of 200 and 100 nm, respectively (i.e., nominal linewidths of 100 and 50 nm, respectively).
Lateral forces during atomic force microscopy of graphite in air
Authors: Baselt David R. , Baldeschwieler John D.
Published: July 2002

Highly oriented pyrolytic graphite and boronated pyrolytic graphite were imaged in air by simultaneous normal and lateral force microscopy. A number of effects occurred when scanning over steps, including an increase in attractive forces from surface contamination which could be detrimental to the imaging of soft or weakly bonded samples. Contamination may also give rise to regions of high lateral force which do not seem to be associated with any topographic features. Finally, in atomic resolution images of graphite, atomic corrugation was clearer in the lateral cantilever deflection images than in the simultaneous topography and normal cantilever deflection images, demonstrating the high sensitivity of lateral force detection to topographic features.
Doping limits of C, Be, and Si in GaAs grown by solid source molecular-beam epitaxy with a thermally cracked As2 source
Authors: Malik R. J. , Nagle J. , Micovic M. , Harris T. , Ryan R. W. , Hopkins L. C.
Published: July 2002

The maximum doping limits for C, Be, and Si in GaAs grown by solid source molecular-beam epitaxy using As2 derived from a high temperature Ta cracker have been investigated. The C and Si-dopant fluxes were obtained from resistively heated filaments, whereas Be was evaporated from pyrolytic BN crucible in an effusion cell. The maximum electrical carrier concentrations determined by Hall measurements were 6, 20, and 1.6 × 1019 cm−3 for C, Be, and Si, respectively. The maximum carrier densities for Be and Si-doping were obtained at a relatively low growth temperature around 480 °C, whereas for C-doping, the optimum growth temperature is around 600 °C. This difference is attributed to the temperature dependence of the surface vacancy concentration ratio [VGa]/[VAs], which affects the incorporation of substitutional dopant atoms. Secondary ion mass spectrometry data shows substantial in-diffusion of Be concentrations above the solubility limit for a given growth temperature.
Effects of barrier thicknesses on the electron concentration in not-intentionally doped InAs–AlSb quantum wells
Authors: Nguyen Chanh , Brar Berinder , Kroemer Herbert , English John
Published: July 2002

We present the results of a study of the dependence of electron concentration in molecular-beam-epitaxy-grown not-intentionally doped InAs–AlSb quantum-well structures on the top barrier thickness in single-well structures and on the internal barrier thickness in multiwell structures. A contribution from surface donors was found to be dominant in single wells with thin top barriers. The bulk donor concentration in the AlSb barriers varied from 2 × 1015 to 1016 cm−3. Interface donors at the InAs–AlSb heterointerface were also found, with an energetic location below the Fermi level in the wells. They are primarily responsible for the increase of the carrier concentration with increasing temperature.
Recent developments in ohmic contacts for III–V compound semiconductors
Authors: Shen T. C. , Gao G. B. , Morkoç H.
Published: July 2002

Recent advances in the technology and understanding of ohmic contacts for a variety of III–V compound semiconductor material systems are reviewed. Special attention is focused on factors and critical issues involved in making low resistance and reliable ohmic contacts. The solid-phase regrowth mechanisms of key metallization systems are described. In addition, special techniques to improve the ohmic contacts are discussed. Finally, the reliability issues of ohmic contacts are addressed.
Tunneling spectroscopy on compensating surface defects induced by Si doping of molecular-beam epitaxially grown GaAs(001)
Authors: Pashley M. D. , Haberern K. W. , Feenstra R. M.
Published: July 2002

The compensating defects on the GaAs(001)-(2×4)/c(2×8) surface that are induced by Si doping have been studied by spatially resolved tunneling spectroscopy. Previous scanning tunneling microscopy studies have shown that as the Si doping level of molecular-beam epitaxially grown GaAs is increased, an increasing number of kinks form in the dimer-vacancy rows of the (2×4)/c(2×8) surface reconstruction. These kinks are believed to act as surface acceptors and result in pinning of the surface Fermi level. In this work, both voltage dependent imaging and spectroscopy show that negative charge is located at the kink sites. This confirms that they are surface acceptors. The spectroscopy is consistent with each acceptor being occupied by one electron. The surface Fermi level is found to be pinned near midgap. While no peak in the state density centered on the Fermi level is observed, gap states in the form of tails extending in from the band edges are observed near some kinks.
Characterization of chemically amplified resists for soft x-ray projection lithography
Authors: Kubiak Glenn D. , Kneedler Eric M. , Hwang Robert Q. , Schulberg Michelle T. , Berger Kurt W. , Bjorkholm J. E. , Mansfield W. M.
Published: July 2002

Sensitivity, lithographic performance, photoabsorption, and photodesorption of chemically amplified novolac-based resists have been studied at an exposure wavelength of 140 Å and are compared to poly(methylmethacrylate) (PMMA). Monochromatic exposures of the resists AZ PF514, AZ PN114, and SAL 601 yielded D0.9 values of 2.5–3 mJ/cm2 for 0.25 μm thick films. Contrast values ranged from 3 for AZ PN114 to 5 for SAL 601. Photoabsorption measurements of supported AZ PN114 films at 140 Å yield an absorption coefficient of 4.4±0.1 μm−1. Photodesorption of fragment ions induced by 140 Å radiation has been studied in PMMA and AZ PN114 using time-of-flight mass spectrometry. It is found that H+, CH2+, CH3+, H2O+, CHO+, C3H5+, and COOCH3+ dominate the ion mass spectra photodesorbed from PMMA, while H+, CH3+, H2O+, and CHO+ dominate the ion mass spectra for AZ PN114. The mass-integrated ion desorption yield from AZ PN114 is three times less than that measured for PMMA per photon or 90 times less when expressed per exposure. Lithographic performance of AZ PF514 and SAL 601 has been characterized using a multilayer-coated 20× Schwarzschild objective and a transmissive Ge/Si mask illuminated by a laser plasma source.
Model and simulation of scanning tunneling microscope tip/semiconductor interactions in p
n junction delineation
Authors: Chapman Richard , Kellam Mark , Goodwin-Johansson Scott , Russ John , McGuire G. E. , Kjoller Kevin
Published: July 2002

Scanning tunneling microscopy (STM) is an electrically sensitive technique with atomic resolution, making it a viable candidate for use in shallow junction delineation. It has been demonstrated that STM can be used to distinguish between n- and p-type semiconductors, yet the effects of STM tip and sample biases on the electronic structure of the silicon and, hence, on the tunneling current have not been extensively explored. A tunnel diode model has been proposed coupled with classical band bending to simulate these effects. The scanning of the tip across the junction was simulated using structure defining algorithms in pisces, a two dimensional device simulator. The tip electrode was moved incrementally across the silicon surface at a set height. pisces was called at each new tip location to produce a new structure file. The Poisson equation was solved by pisces at each tip location to determine band bending. Silicon surface potentials were extracted from the simulation and incorporated into the tunneling current calculations. Tunneling currents in the model depend on the density of empty states in the electron-receiving material, on the density of filled states in the electron-supplying material, and on the tunneling probability across the tip-to-semiconductor gap. The tunneling currents were then compared to experimental results.
Ion velocity distributions in helicon wave plasmas: Magnetic field and pressure effects
Authors: Nakano T. , Giapis K. P. , Gottscho R. A. , Lee T. C. , Sadeghi N.
Published: July 2002

Consideration of ion transport in high density, low pressure plasma systems is important for meeting process requirements in the manufacturing of ultra-large-scale integrated circuits. The ion energy and angular distributions at the boundary between the plasma and the wafer, the sheath, influence etching selectivity, linewidth control, plasma-induced damage, and microscopic etching uniformity. These distributions, in turn, are easily altered by changing the magnetic field profile and/or the neutral gas pressure. Using Doppler-shifted laser-induced fluorescence, metastable ion velocity distribution functions in helicon-wave-excited Ar plasmas are measured. Two magnetic field configurations are examined. For a magnetic ‘‘mirror,’’ where the field exhibits a maximum and a saddle point in the source, the plasma is observed to be asymmetric and nonuniform: this leads to broadened velocity distributions and significant ion drift from one region of the plasma to another. As the pressure is increased in the mirror field configuration, the transverse ion ‘‘temperature’’ exhibits a maximum as a function of pressure and, when etching is ion-flux limited, either decreasing or increasing the pressure should result in improved linewidth control. The plasma is more symmetric when the magnetic field is reversed in the source and again downstream. With this double cusp configuration, the transverse ion temperature decreases monotonically with pressure, and improved linewidth control in the ion-flux limit would be obtained by operating at higher pressure.
Structural inheritance from polycrystalline underlayers in the growth of double-layered aluminum films
Authors: Tsukada Mitsuo , Ohfuji Shin-ichi
Published: July 2002

Experimental evidence of the inherited strong <111≳ orientation from the room-temperature- evaporated Al underlayer is presented for the Al upperlayers evaporated at temperatures higher than the Al recrystallization temperature, in the double-layered Al films. By contrast, Al films evaporated on an amorphous SiO2 substrate at high temperatures exhibit a remarkable weakening of the <111≳ fiber texture. Crystallographic characteristics of the Al films were evaluated by rocking curves in the x-ray diffraction measurement. Inheritance of the strong preferential orientation observed for the double-layered structures suggests that the Al upper- layers grow in a layer-by-layer process during the deposition at high temperatures through the surface migration of Al atoms.
Field emission device modeling for application to flat panel displays
Authors: Kesling W. Dawson , Hunt Charles E.
Published: July 2002

A computer model has been developed for determining the electrical characteristics of field emission devices. Numerical techniques are employed to determine the electric field distribution and electron trajectories in the modeled device. Using the electron trajectories and emission current density determined from the Fowler–Nordheim equation, electrode currents are found. The current–voltage characteristics are constructed using superposition of electric field solutions. Simulation results are presented for a single vertical triode of a field emission flat panel display. The cathode tip has a radius of curvature of 20 nm and is centered in a 2 μm diam gate aperture. The anode is typically biased at 400 V and spaced 0.2 mm from the cathode. Simulation results indicate turn-on at 75 V and 0.1 μA emitted at a gate drive of 95 V. Gate current is negligible. Peak-to-peak gate drive for a 1000 line field emission display having 100:1 contrast ratio is found to be less than 50 V for such a structure.