bluuebunny/crossref_metadata_2025 huggingface dataset:
On the electronic structure of clean, 2×1 reconstructed silicon (001) surfaces
Authors: Mönch W. , Koke P. , Krueger S.
Published: July 2002

Surface photovoltage spectroscopy with clean 2×1 reconstructed Si(001) surfaces revealed indirect transitions from the bulk valence band into a band of empty surface states at (0.59 ± 0.04) eV above it. Chemisorption of atomic hydrogen is known to finally produce a Si(001)− 1×1:H structure and was found to remove these surface states and to decrease the ionization energy by (0.34 ± 0.01) eV. This result proves the 2×1 reconstructed Si(001) surface to be ionic and buckled with the outward relaxed surface atoms being negatively charged, since Si–H bonds are partly polar with the hydrogen being negatively charged and thus tending to increase the ionization energy of the surface. Theoretical predictions based on a model with asymmetric dimers as building blocks of the 2×1 reconstruction are in good agreement with the experimental results. Furthermore, on the clean Si(001) surface an additional donor-type surface state at (0.29±0.04) eV above the valence band edge was found with a density of approximately 1011 cm−2. It is most probably caused by some kind of surface defect.
Energy spreading in the hydrogen field ionization source
Authors: Hanson G. R. , Siegel B. M.
Published: July 2002

The application of field ionization as a tool for routine submicron fabrication will depend critically upon the characteristics of the source; the angular intensity and the energy spread of the ions. The chromatic aberration coefficient of the ion optical system, the angular aperture, and the energy spread combine to set the limit of spot size and current density for very-high-resolution probes with sources of energy widths even as low as 1 eV. It is known that the various molecular species produced by hydrogen field ionization are indentifiable by the energy distribution, and because the mass of the ion will determine the particle range in resists at any given energy, energy measurements carry further importance in the development of the probe-forming system. In order to characterize the source-energy widths and mass species as a function of beam current, angular intensity, and surface characteristics of the emitter tip, we have designed and operated a unitized, positionable intermediate image filter lens with a demonstrated resolution of 0.1 eV at 3.5 kV and acceptance half-angles of less than 9 mrad. At angular intensities less than 10 μA/sr, 90% of the field ions from bright site emission of fields of 1.5 V/Å occur within an energy width of 1.2–1.9 eV. This narrow spread shows that only H2+ is being produced. The beam current and angular intensity from a single bright site can be increased by raising the source gas pressure and the applied field (5% increase in voltage). That energy broadening occurs at high intensities is demonstrated by the fact that at 3.5 μA/sr [0.5 nA emitted through 50 μm aperture subtending a half-angle (ϑ1/2) of 0.0067 rad], 90% of ions appear within 1.9 eV (0.94 eV FWHM), while at 18 μA/sr (2.5 nA, ϑ1/2 of 0.0067 rad), 90% of ions appear within 2.2 eV (0.98 eV FWHM) where a tail develops on the low-energy side causing a broadening of the energy distribution. The impact of field emitter surface configuration on source angular intensity and reliability are discussed.
Magnetron sputtering with additional ionization effect by electron beam
Authors: Adachi R. , Takeshita K.
Published: July 2002

The effects of electron beam ionization on the adhesion strength, plasma potential, and crystallinity of Cu films deposited on a glass substrates has been studied. (AIP)
An XPS study of the oxidation of AlAs thin films grown by MBE
Authors: Taylor J. Ashley
Published: July 2002

AlAs films grown by MBE and cleaned with light Ar+ sputtering have been oxidized with various exposures of O2 and H2O at room temperature and studied with XPS. Analysis of XPS at various exposures of the disordered AlAs surfaces showed the formation of an Al2O3 layer with the loss of As leaving what has tentatively been assigned as As0 within and on the Al2O3 layer. Oxidation of the As was not observed until after heavy O2 exposures (∠1011L). The rate of Al2O3 formation on the disordered AlAs film was found to be approximately comparable to that on metallic Al. Oxide formation by H2O exposure was found to be about four times faster than with O2.
Stress measurement in thin films by geometrical optics
Authors: Rossnagel S. M. , Gilstrap P. , Rujkorakarn R.
Published: July 2002

A simple variation of the Newton’s rings experiment is proposed for quick, relatively accurate stress measurements. The method involves depositing a thin film on a small circular thin substrate, in this case a common microscope cover slip (18 mm diam × 0.18 mm). The thin film then deforms the cover slip into roughly a paraboloid shape. The focal length of this ‘‘spherical mirror’’ is determined optically by reflecting parallel light from its surface onto a screen. Any magnification or contraction of the image of the film is indicative of distortion of the substrate due to film stress. Such magnification, whether greater or less than 1, immediately determines the sign of the stress. This method described for measuring stresses in the film is simple, fast and inexpensive, requiring only a laser, mirrors and a diverging lens. (AIP)
Ion beam synthesis of cubic boron nitride
Authors: Shanfield S. , Wolfson R.
Published: July 2002

Thin films containing cubic phase boron nitride have been synthesized using an ion beam extracted from a borazine (B3H3H6) plasma.We report on x-ray diffractometry, hardness tests, and Auger analysis of the deposited films. The x-ray diffractometer peak corresponding to cubic phase boron nitride was detected while peaks corresponding to hexagonal phase were usually absent. Consistent with the presence of cubic phase indicated by the x-ray analysis, the indentation hardness of boron nitride-coated substrates was higher than the same uncoated substrates. Auger compositional profiles indicated a film stoichiometry corresponding to boron nitride and suggested that the deposition method produced an intermixing layer between the boron nitride film and the substrate.
The effects of reaction parameters on the deposition characteristics in Al2O3 CVD
Authors: Park Chul-Soon , Kim Jae-Gon , Chun John S.
Published: July 2002

Deposits of aluminum oxides (Al2O3) have been formed by a chemical vapor deposition (CVD) technique involving the application of gas mixtures of AlCl3, CO2, and H2 onto TiN coated cemented carbide substrates. The relationships between the deposition rate and various reaction parameters such as the gas flow rate, the deposition temperature, the composition of reactant gases, and the system pressure were studied. The CVD of Al2O3 is a thermally activated process and limited by the surface chemical reaction. The apparent activation energy is about 36 kcal/mol at 50 Torr and decreases with the increasing system pressure. The dependence of the deposition rate on the reactant gas composition is affected by the variation of the relative contents of the aluminum donor and the oxygen donor. At a low AlCl3 mole fraction, the deposition rate increases with the AlCl3 mole fraction; however, at higher AlCl3 mole fractions than 1.0×10−2 the deposition rate is mainly influenced by the H2O-forming reaction between CO2 and H2.
A tabletop relativistic electron beam generator
Authors: Matsuzawa Hidenori
Published: July 2002

A compact, tabletop relativistic electron beam generator has been designed and constructed. Electron beam pulses of 1.8 kA, FWHM of 30 ns, and 380 kV were obtained. (AIP)
Quantitative determination of the intensities of known components in spectra obtained from surface analytical techniques
Authors: Nelson G. C.
Published: July 2002

Linear least-squares methods have been used to quantitatively decompose experimental data obtained from surface analytical techniques into its separate components. The mathematical procedure for accomplishing this is described and examples are given of the use of this method with data obtained from Auger electron spectroscopy [both N(E) and derivative], x-ray photoelectron spectroscopy, and low energy ion scattering spectroscopy. The requirements on the quality of the data are discussed.
A wavy versus straight interface in the explosive welding of aluminum to steel
Authors: Szecket A. , Inal O. T. , Vigueras D. J. , Rocco J.
Published: July 2002

Waveless, explosively welded interfaces between aluminum and steel are seen to be devoid of intermetallic formation and maintain integrity with heat exposures of up to 8 h at 550 °C. Microhardness determinations as well as tensile testing of the samples indicate the interface to be a zone of higher hardness than the weaker of the bonded materials (Al-1100) and of extremely high adhesion strength. The hardness profiles taken were utilized to determine the difference in the energy deposited at the wavy and waveless interface as well as the presence of extraneous byproducts of these energies in the respective interfaces. The study conclusively shows the superior characteristics of the waveless interface for this weld and its resistance to intermetallic formation that would lead to the consequential deterioration of the associated adhesion properties of these transition joints.
Aluminum plasma etching process using vacuum systems without cold traps
Authors: Bachmann P.
Published: July 2002

A suitable vacuum pump system used in plasma or RIE-mode dry etching of Al and Al alloys with CCl4/Cl2 enables to operate without LN2 cold traps. A Roots pump plus rotary vane pump combination, both using inert fluid lubricant, pumps and exhausts all occurring volatile products. Condensing solid AlCl3 is quantitatively removed from the backing pump sealing fluid by means of a high speed, main stream oil purification system via an Al2O3 deep bed filter. Maintenance of the pump system is limited to just changing the Al2O3 filter elements, each time after etching of 4000 4 in. wafers. No decomposition of the sealing fluid could be observed. Any fluid remaining when exchanging the filter elements can practically be recovered by centrifuging.
Chemical changes in chromium silicide thin films as a result of laser trimming as determined by SAM and XPS
Authors: Masters Richard G.
Published: July 2002

Scanning Auger microscopy (SAM), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to characterize the various chemical changes which can occur as a result of laser trimming of passive circuit devices fabricated from chromium silicide (CrSi) thin films. A sample matrix consisting of CrSi deposited on various sustrates, including silicon (Si), glass (SiO2), and silicon nitride (Si3N4), and subsequently coated with SiO2, was analyzed. Comparisons were made between trimmed and untrimmed samples. Results indicated a variance in the oxide content of the CrSi film and the oxidation state of the Cr, dependent upon the substrate material. These results were obtained from Auger elemental maps, and line scans of the depassivated laser kerfs and XPS spectra of trimmed and untrimmed sheet films. SEM micrographs taken of the glass overcoat indicate that the laser beam leaves the glass physically unaltered, transforming only the underlying chromium silicide.
Ceramic microstructure and adhesion
Authors: Buckley Donald H.
Published: July 2002

When a ceramic is brought into contact with a ceramic, a polymer, or a metal, strong bond forces can develop between the materials. The bonding forces will depend upon the state of the surfaces, cleanliness and the fundamental properties of the two solids, both surface and bulk. Adhesion between a ceramic and another solid are discussed from a theoretical consideration of the nature of the surfaces and experimentally by relating bond forces to the interface resulting from solid state contact. Surface properties of ceramics correlated with adhesion include orientation, reconstruction, and diffusion as well as the chemistry of the surface specie. Where a ceramic is in contact with a metal their interactive chemistry and bond strength is considered. Bulk properties examined include elastic and plastic behavior in the surficial regions, cohesive binding energies, crystal structures, and crystallographic orientation. Materials examined with respect to interfacial adhesive interactions include silicon carbide, nickel–zinc ferrite, manganese–zinc ferrite, and aluminum oxide. The surfaces of the contacting solids are studied both in the atomic or molecularly clean state and in the presence of selected surface contaminants.
Applications of Monte Carlo simulation in the analysis of a sputter-deposition process
Authors: Motohiro T.
Published: July 2002

Practicality of the Monte Carlo (MC) method developed for the analysis of the particle transport process in sputter-deposition was examined. Titanium film thickness distributions on both faces of a planar substrate facing and not facing a planar-magnetron-type target were compared with corresponding calculated profiles. The results show that sufficient performance of the MC method can be obtained in the usual sputtering condition up to the argon pressure beyond which the majority of particles are transported by the thermal diffusion process.
Infrared absorption measurement of the overtone of the wagging mode of hydrogen on W(100)
Authors: Chabal Y. J.
Published: July 2002

The infrared absorption of H chemisorbed on W(100) has been studied as a function of coverage. We find that, in addition to the fundamental symmetric stretch absorption, the overtone absorption of the wagging mode can also be measured as the coverage approaches saturation. These assignments are confirmed by isotopic mixture experiments. The strong enhancement of the overtone absorption is correlated with the p(1×1) structure of the top W layer (unreconstructed) and is believed to result from a strong coupling of the wag motion to bands of surface states located at the Fermi level. This coupling provides an efficient vibrational decay mechanism through the production of electron-hole pairs.
The role of thin films in integrated solid-state sensors
Authors: Wise K. D.
Published: July 2002

This paper reviews recent developments in integrated solid-state sensors, with emphasis on the important roles played by thin films in these device structures. Most such sensors employ transducers and custom interface circuits on a common substrate, with fabrication based on the processes associated with integrated circuits. Specific examples are used to illustrate the important electrical, mechanical, thermal, optical, and chemical properties of thin films in integrated sensors. Recently proposed undercut polysilicon film structures are discussed as an alternative to traditional bulk structures for measuring parameters such as pressure and flow. A multielectrode intracortical recording array under development for closed-loop neural prostheses is also described. This microprobe can be realized with high yields, with recording sites spaced as close as a few microns, and with substrate widths of less than 50 μm. A thin-film silicon thermal imager utilizes thin dielectric windows and polysilicon thermopiles to realize a broadband infrared detector which does not require cooling and which can be realized with effective element spacings less than 200 μm.
Photochemical vapor deposition of silicon nitride films
Authors: Padmanabhan R. , Miller B. J.
Published: July 2002

A low temperature photochemical vapor deposition method utilizing mercury sensitization was used to deposit thin silicon nitride films. The chief advantages of the photochemical process are the low deposition temperatures, conformal coverage, reduction of electromagnetic radiation and charged species, and ability to tailor stoichiometry for specific applications. The effects of process variables upon the optical characteristics of nitride films were studied in this investigation. These properties were found to be variable over a wide range. Refractive index was strongly dependent upon the deposition temperature and ammonia/silane ratio, with higher temperatures and lower gas ratios yielding denser films, but at reduced deposition rates. The etch rate of these films was strongly influenced by the annealing temperature, with lower rates resulting at higher temperatures, consistent with increased densification and decreased pinhole densities. Electrical properties of typical films, including dielectric constant, breakdown strength, and mobile ion concentration were also determined.
Noncontact electrical characterization of epitaxial HgCdTe
Authors: Jones C. E. , Boyd M. E. , Konkel W. H. , Perkowitz S. , Braunstein R.
Published: July 2002

It is important to be able to nondestructively characterize (‘‘screen’’) the electrical properties of those areas of HgCdTe epitaxial material that will later be made into devices. This paper compares several noncontact techniques for measuring resistivity, carrier concentration, and mobility with the standard Hall-effect technique. The noncontact techniques examined are far-infrared reflection, Raman scattering, eddy–current absorption, and electroreflectance. Of these techniques, far-infrared reflection was found to be the best noncontact technique for measuring resistivity, carrier concentration, and mobility. Resistivity values were within a factor of 2 of Hall-effect values, while carrier concentration and mobility values that depend on an assumed effective mass were within a factor of 3. In Raman scattering, interference between the free-carrier plasmon–phonon mode and other modes makes it an inaccurate method for estimating carrier concentration. Eddy–current absorption is useful for quickly measuring epitaxial layer resistivities to within a factor of 3 of Hall-effect values, while electroreflectance gives a relative value for the surface doping density, which is useful in layer profiling.
Time-dependent local-density-response theory for strongly charged metal surfaces
Authors: Gies P. , Gerhardts R. R.
Published: July 2002

We present a microscopic calculation of nonlocal effects on the optical response of strongly charged metal surfaces. Exchange and correlation effects are included within the time-dependent local-density-functional theory. We use the jellium model for the ionic background, and consider, for computational reasons, a thin metal slab. The background density is given by the Wigner–Seitz radius rs=3, and the surface charge is varied from −2.4 to 23.9 × 10−3 ‖e‖/Å2. In the long-wavelength limit, i.e., to lowest order in the (small) ratio of Fermi velocity to velocity of light, the nonlocal effects can be summarized in two surface-response functions. Our slab calculation yields a good approximation for the surface-response functions of a semi-infinite system. We show results for the relative deviation of the reflectance from its classical value and the power absorptance as a function of frequency for differently charged surfaces. They agree qualitatively with our previous results obtained in the conventional random-phase approximation. At high positive surface charges, the power absorption is drastically diminished, since certain surface excitations are suppressed. We discuss the relevance of these findings for experiments in nonaqueous electrolytic cells.
Selection and analytical monitoring of backing pump fluids in semiconductor processes
Authors: Kuhn Monika , Bachmann Paul
Published: July 2002

Fluids in backing pumps must fulfill the following tasks: sealing, lubricating, protection against corrosion, and the transportation of heat. In semiconductor processes, additional demands are made on a pump fluid. It must be resistant to reactive substances. For the different processes, such as etching, chemical vapor deposition, etc., different classes of fluids have proved to be effective in practice. This makes specific adaptation to a process possible. Regular control of the fluid is necessary to achieve safe operation. In general, the quality of a fluid is controlled by determining its viscosity, the total acid number and total base number, and its ash content, and an optical evaluation is made. With pump fluids coming from semiconductor processes, specific analytical problems arise which require special treatment and analysis. Filtration, extraction , adsorption, and degassing are good methods for treatment. The determination of decomposition products of the fluid and substances from the process chamber can be effected with the help of infrared spectroscopy. In addition, mass spectroscopy, elementary analysis, and other chemical methods can be helpful in evaluating a pumping fluid.
Dissociative chemisorption of H2 on Ni surfaces: Incident kinetic energy dependence and the characteristics of the potential energy surface
Authors: Lee Chyuan-Yih , DePristo Andrew E.
Published: July 2002

This paper demonstrates that the dependence of the dissociative sticking probability on incident kinetic energy can be changed significantly without materially changing the activation barrier. The presence of a potential well in the entrance channel and the detailed curvature of the potential energy surface also influence this dependence.
Chemical erosion of graphite by hydrogen impact: A summary of the database relevant to diamond film growth
Authors: Hsu W. L.
Published: July 2002

It is now established that diamond can be grown by vapor deposition, a condition where graphite is the more thermodynamically stable state. This supposed contradiction of thermodynamics is explained by the recognition that hydrogen is more likely to chemically erode graphite than diamond. In most diamond growth environments, hydrogen gas must be kept above a certain concentration (>95% of the mixture) to deposit films with nearly no graphitic component. This paper discusses the chemical interactions of hydrogen with graphite. The discussion is primarily based on the database collected from studies in the fusion research community. The studies cover interactions using both energetic and low-energy atomic hydrogen. Kinetic models have also been developed which can explain reasonably well the observed interaction characteristics. The majority of the interaction studies used graphite as the target material for hydrogen; a few were also carried out with carbon and diamond films.
Tunneling microscopy of steps on vicinal Ge(001) and Si(001) surfaces
Authors: Griffith J. E. , Kubby J. A. , Wierenga P. E. , Becker R. S. , Vickers J. S.
Published: July 2002

Tunneling images of vicinal Si(001) and vicinal Ge(001) are presented. When these surfaces are cut with a tilt about [11̄0], we find that a large fraction of the steps are straight double steps. A Ge(001) surface cut with a tilt about a line deviating from [11̄0] exhibits monoatomic steps, some of which have many kinks.
Scanning tunneling microscope tip structures
Authors: Nicolaides Ruth , Liang Yong , Packard William E. , Fu Zhou-Wu , Blackstead Howard A. , Chin K. K. , Dow John D. , Furdyna Jacek K. , Hu Wei Min , Jaklevic Robert C. , Kaiser William J. , Pelton Alan R. , Zeller Mary V. , Bellina Joseph
Published: July 2002

Studies of electrochemically etched tungsten scanning tunneling microscope tips, using scanning electron microscopy, show that (i) the tips are often convolved or bent if the mass of the tungsten wire submerged in the etchant is large (an effect ascribed to surface plastic flow), (ii) bent tips nevertheless often produce good quality scanning tunneling microscopy images of Au films in air, but (iii) tips, once crashed clumsily into the Au films, no longer produce images.
The molecular drag pump: Principle, characteristics, and applications
Authors: Duval P. , Raynaud A. , Saulgeot C.
Published: July 2002

The molecular drag pump (MDP) was invented in the 1920s, forgotten during a long time, and was recently reintroduced as a high-vacuum pump competing against the turbomolecular pumps and the Roots blowers. The present paper reviews the MDP principle of operation, with an emphasis on the drum type, and its theory. In order to enhance the performances of the original Holweck’s pump, the modern MDP’s are oil-free multigroove pumps with a variable channel optimized for high compression ratio (109) and high discharge pressure (up to 50 mbar). With a base pressure in the 10−7 mbar pressure range, MDP’s can be used to evacuate small volumes under clean conditions (oil free) in applications like mass spectrometry or UHV system, as well as to pump the corrosive by-products in plasma etching.
Application of reflectance difference spectroscopy to molecular-beam epitaxy growth of GaAs and AlAs
Authors: Aspnes D. E. , Harbison J. P. , Studna A. A. , Florez L. T.
Published: July 2002

We perform an accuracy analysis of several possible reflectance–difference (RD) configurations that are compatible with standard molecular-beam epitaxy (MBE) growth chambers, and describe in detail an optical-bridge system that can determine relative changes in RD signals as small as 5×10−5 under standard growth conditions. Using this system, we determine the RD response of GaAs for changes in surface conditions at different wavelengths and correlate these to simultaneously measured reflection high-energy electron diffraction (RHEED) intensities. Maximum anisotropies are found at 2.0–2.5 and 3.5 eV for Ga on GaAs and Al on AlAs, respectively, providing a way of spectrally distinguishing Ga–Ga and Al–Al dimers for surface-chemical investigations, and suggesting that these photon energies are also optimal for modifying growth by light. At photon energies well removed from these anisotropy maxima, RD signals follow changes in surface structure, as RHEED. Our RD-RHEED correlations provide insight concerning crystal growth by MBE and establish a common experimental link between MBE and non-UHV methods of crystal growth where RHEED cannot be used. Finally, our results illustrate various possibilities of using reflectance difference spectroscopy to investigate surface structure, surface chemistry, and surface dynamics.
Electron cyclotron resonance plasma stream source for plasma enhanced chemical vapor deposition
Authors: Popov O. A. , Waldron H.
Published: July 2002

An electron cyclotron resonance (ECR) plasma stream source at a frequency of 2.45 GHz was explored and utilized for SiO2 film chemical vapor deposition (CVD). It was found that for high and uniform plasma stream density the large limiting ring and magnetic fields higher than 930 G are required in the ECR plasma chamber. Plasma densities of(4–6)×1010 cm−3 in nitrogen and (6–8)×1011 cm−3 in argon with uniformities of ±5% over an area of 12 cm in diameter were achieved at distances of 30 to 50 cm from the source limiting ring at a microwave power range of 500 to 600 W. The etch of thermal silicon dioxide and polysilicon with CF4 showed uniformity better than ±1% over 5-in. wafers at a distance of 19 cm. SiO2 films were deposited in a mixture of 15% SiH4/N2 and O2 at substrate temperatures of 30 to 200 °C. Room-temperature ECR films had characteristics better than those obtained in conventional plasma enhanced CVD films deposited at 300 °C. ECR films deposited at 200 °C had properties which approach those of thermal silicon oxide.
Characterization of supported metal oxide particles by variable angle x-ray photoelectron spectroscopy
Authors: Berge Peter ten , Young Vaneica , Bates Stanley R.
Published: July 2002

The preliminary results of a newly developed method to determine the particle size distribution of a solid supported dispersed phase are presented. It is based on a modification of a theoretical model proposed by Kuipers et al. and employed intensity data obtained using variable angle x-ray photoelectron spectroscopy (VAXPS). The heart of the computer program generated is a nonlinear least-squares algorithm based on the Marquardt-Levenberg procedure. The test calculations show that the average particle size diameter of particles in heterogeneous catalysts can be determined with an accuracy of 16%. Comparison of particle size distributions obtained from transmission electron microscopy and VAXPS shows significant differences, which can partly be explained by fundamental differences of the techniques. The method appears to be a promising approach, which we hope to improve in the near future.
A versatile spectrometer system for quantitative surface and in-depth analysis with secondary ion and secondary neutral mass spectroscopy, Auger electron and x-ray photoelectron spectroscopy
Authors: Sander P. , Altebockwinkel M. , Storm W. , Wiedmann L. , Benninghoven A.
Published: July 2002

Recently, secondary neutral mass spectrometry (SNMS) has proved to be a fast and accurate technique for quantitative surface and bulk analysis of trace elements and multicomponent materials. The lack of sufficient chemical information urges the need of combination of this method with complementary analytical techniques such as secondary ion mass spectroscopy (SIMS), Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS). We describe a fully computerized surface analytical instrument, in which electron-beam SNMS, SIMS, AES, and XPS have been implemented for the first time in the same UHV system. We particularly discuss aspects of depth resolution, as obtained with each of the methods, and the need of a flexible computer-based control and data acquisition system for reliability and flexibility of the analytical instrumentation. Typical applications to depth profiles of multicomponent semiconductor materials include analysis of amorphous hydrogenated carbon (a-C:H) layers on germanium and of copper contacts on mercury cadmium telluride (CdxHg1−xTe).
Scanning tip microscope for study of electrical inhomogeneity on submicron scale
Authors: Mera Yutaka , Yanagisawa Hironori , Uota Masahiko , Maeda Koji
Published: July 2002

Spatial variations of sample resistance in electrically inhomogeneous samples were detected by modulating the tip–sample distance and measuring the demodulated signal of reciprocal current, which is proportional to the tunnel resistance. In contrast to featureless maps of sample resistance in Au film, maps in a fiber reinforced metal sample exhibited resistive regions which have no corresponding structures in the topography and are considered to originate in the highly insulating whiskers contained in the sample.
Surface hydrogen–palladium studies using a new photopyroelectric detector
Authors: Mandelis Andreas , Christofides Constantinos
Published: July 2002

A new hydrogen gas trace detection principle based on a photopyroelectric solid-state sensor has been developed. The sensor was made of thin commercially available polyvinylidene fluoride (PVDF) pyroelectric film, sputter coated with palladium (Pd). An infrared laser beam (800 nm) served to produce ac voltages due to the photopyroelectric effect. Exposure to hydrogen gas was shown to produce a differential signal between the Pd and reference electrodes. Accumulated experimental evidence has led us to tentatively attribute the detection principle to the adsorption, dissociation, and absorption of hydrogen molecules on the Pd surface, which caused a shift on the PVDF pyroelectric coefficient, due to electrostatic interactions of H+ ions with the PVDF polar molecular system at the Pd–PVDF interface. A quantitative interpretation of the hydrogen partial pressure dependence of the differential signal has been achieved using simple gas-solid interaction theory and the combination of the Langmuir isotherm with photopyroelectric theory. The new detector could become an excellent tool for surface science studies under ultrahigh vacuum, especially at low temperatures where other sensors do not exhibit good performance.
Thin films for micromechanical sensors
Authors: Burns D. W. , Guckel H.
Published: July 2002

Thin films compatible with integrated circuit and batch processing technologies are utilized in the fabrication of cost-effective, high performance integrated micromechanical sensors. These films are used as structural layers, sacrificial layers, passivation layers, oxidation barriers, masking layers, and for electrical interconnection in the formation of microminiature pressure sensors, accelerometers, and force sensors. Low-pressure chemical vapor deposition (LPCVD) polysilicon, LPCVD silicon nitride, and thin films of single crystal silicon are examples of structural layers. Highly controlled surface preparation, deposition conditions, and post-deposition temperature cycles are required to achieve uniform mechanical and thermal properties, low defect density and high stability. Young’s modulus, Poisson’s ratio, and internal stress are the most important properties to control for micromechanical devices. These properties become increasingly significant as multiple thin film or composite microstructures become important. Control and repeatability of these properties are essential in the design, fabrication and successful performance of micromechanical sensors and microstructures.
Raman scattering of amorphous germanium clusters and ultrathin films
Authors: Fortner J. , Yu R. Q. , Lannin J. S.
Published: July 2002

The near surface vibrational states of amorphous (a-) Ge supported semiconductor clusters are reported from in situ Raman scattering. A combination of multichannel detection and interference enhanced Raman scattering from multilayer structures has provided a means to study the vibrational states of an amorphous solid at coverages less than a monolayer. The deposition of a-Ge by direct current magnetron sputtering onto disordered C trilayer structures in UHV results in a Raman spectrum that is related to the phonon density of states by a smoothly varying coupling parameter. The Raman spectra are observed to exhibit significant changes in the width of the high frequency TO (transverse optic-like) band, as well as a substantial shift of the TO peak position to lower frequencies. These results indicate increased near surface structural disorder with decreasing cluster size. Support for this is provided by hydrogen chemisorption and by ultraviolet photoelectron spectroscopy (UPS) difference spectra that indicate a reduced coordination with decreasing cluster size.
Electric fields in a microwave-cavity electron-cyclotron-resonant plasma source
Authors: Hopwood J. , Wagner R. , Reinhard D. K. , Asmussen J.
Published: July 2002

A disk-shaped electron cyclotron resonant (ECR) plasma is generated inside a 2.45 GHz, cylindrical microwave cavity. The microwave electric field pattern within the cavity is measured using a microcoaxial probe while a plasma is ignited. TE211, TE311, and hybrid electromagnetic modes are identified. The radial component of the electric field adjacent to the cavity wall varies in strength from 7 to 46 kV/m. Double Langmuir probe density measurements show little variation in the plasma ion density among the various cavity modes, but discharge stability is clearly dependent on the alignment of cavity electric field patterns with the ECR magnetic field. Emission spectroscopy is used to measure the spatial distribution of ions in the ECR zones (where Langmuir probe measurements are not practical) and the distribution of fluorine radicals in SF6/Ar discharges. Peak ion densities in the ECR region are estimated at 1012 cm−3 in Ar at 9×10−4 Torr with 250 W of microwave input power.
Charge–transfer screening and the dynamics of electronically stimulated adsorbate dissociation and desorption
Authors: Burns A. R. , Jennison D. R. , Stechel E. B.
Published: July 2002

We present examples of substrate screening effects on two electronically stimulated surface processes: (1) The dissociation of NO2 on clean Pt(111); and (2) the desorption of NO from clean and O-covered Pt(111). For each set of experiments, we discuss quantum-resolved data obtained by time-of-flight laser resonance-ionization on the directly desorbed NO products. Two dominant NO2 dissociation channels have been assigned to 3b−12 and 1a−22 excitations on the basis of threshold measurements and lifetime arguments. Screening occurs through substrate charge transfer into the hybridized antibonding 6a1 molecular level. The 1a−22 channel has more NO vibrational and rotational internal energy than the 3b−12 channel due to the greater 6a1 charge density. However, screening is only partial, thus the internal excitations are a small fraction of those observed in gas phase photodissociation. The specific desorption yield from the 5σ−1 excitation of NO with coadsorbed O (≤0.75 ML) is enormously enhanced (>100×), while the vibrational excitation is reduced from that on the clean surface. Both effects are due to reduced charge transfer into the 2π antibonding molecular level. It is the 2π electron density that is utilized in the excitation decay.
Detection of odd symmetry shear modes at metal surfaces by inelastic electron scattering: Experiment and theory
Authors: Erskine J. L. , Jeong E.-J. , Yater J. , Chen Y. , Tong S. Y.
Published: July 2002

High resolution inelastic electron scattering measurements and full multiple-scattering calculations for Ni(100) and Ag(100) surfaces are presented and used to characterize, for the first time, shear horizontal surface phonon modes. Implications of these new capabilities for studies of surface structure, reconstruction, thin film epitaxy, and for exploring selectron rules that govern inelastic electron scattering are discussed.
Sputter-initiated resonance ionization spectroscopy: A matrix-independent sub-parts-per-billion sensitive technique applied to diffusion studies in SiO2–InP interfaces
Authors: Arlinghaus H. F. , Spaar M. T. , Thonnard N.
Published: July 2002

Sputter-initiated resonance ionization spectroscopy (SIRIS) is a very selective and extremely sensitive technique to analyze semiconductor materials. In the SIRIS technique, the abundant neutral atoms released by the sputtering process are ionized by precisely tuned laser beams and counted in a mass spectrometer. The resonance ionization spectroscopy (RIS) process virtually eliminates isobaric and other interferences and reduces matrix effects dramatically. Depth profiles of Si and In were measured in unannealed and rapid-thermal annealed SiO2–InP samples using the SIRIS and secondary ion mass spectrometry (SIMS) techniques. The results show diffusion process of In through the SiO2 layer and of Si into the InP substrate, as well as the matrix independence of the SIRIS technique. A detection limit, defined as 2 standard deviation above background, of In in Si was measured at 300 parts per trillion (ppt) with a 0.75 μA, 0.8 μs wide ion beam pulse and less than 3 min analysis time at 30 Hz repetition rate. Therefore, a detection limit in the low ppt range could be achieved with a 5 μA ion beam current and 25 min analysis time.
Substrate temperature dependence of subcutaneous oxidation at Si/SiO2 interfaces formed by remote plasma-enhanced chemical vapor deposition
Authors: Kim S. S. , Stephens D. J. , Lucovsky G. , Fountain G. G. , Markunas R. J.
Published: July 2002

We have previously reported that subcutaneous oxidation reactions between process gases and Si surfaces occur during deposition of thin films of SiO2 by remote plasma-enhanced chemical vapor deposition (remote PECVD) [G. G. Fountain, S. V. Hattangady, R. A. Rudder, R. J. Markunas, G. Lucovsky, S. S. Kim, and D. V. Tsu, J. Vac. Sci. Technol. A 7, 576 (1989) and G. Lucovsky, S. S. Kim, D. V. Tsu, G. G. Fountain, and R. J. Markunas, J. Vac. Sci. Technol. B 7, 861 (1989)]. We find that the rate of this oxidation process is substrate temperature (Ts) dependent, increasing with increasing Ts. The rate of SiO2 deposition by remote PECVD decreases with increasing Ts and the combination of oxide deposition and subcutaneous oxidation serves to establish limits on the deposition temperature, and oxide thickness for gate-quality SiO2 films on cleaned and characterized Si surfaces. This paper describes the subcutaneous oxidation process, the nature of the oxide films, and the effects of subcutaneous oxidation on interfacial electrical properties of the Si/SiO2 interfaces in metal–oxide-semiconductor (MOS) structures.
Reactive graphite etch and the structure of an adsorbed organic monolayer—a scanning tunneling microscopy study
Authors: Rabe Jürgen P. , Buchholz Stefan , Ritcey Anna M.
Published: July 2002

Two types of surface interactions of the basal plane of graphite with an organic ambient have been investigated with the scanning tunneling microscope: (1) At the bulk interphase between octylcyanobiphenyl and graphite local surface reactions have been observed with a threshold tip bias of −1.7 V and lifetimes of the reaction products on the order of 1 s. At more negative bias between −2.5 and −4 V the reactions become more intense resulting in localized graphite etch. While a crystalline adsorbate phase of octylcyanobiphenyl is very rarely observed on the flat graphite surface, it occurs more readily after the etching procedure, indicating a lack of nucleation sites on the pristine graphite. (2) A monolayer of a mixed cellulose ether (laurylmethyl) transferred onto graphite by the Langmuir–Blodgett technique has been imaged in the tip bias range of +10 mV to +1 V with a resolution of better than 1 nm. From the images one can determine the conformation of the individual polymer molecule. The polymer is found to be extended over several tens of nanometers and characteristic kinks along the chain are observed, indicative of a conformation which results from the adsorption of a twisted ribbon.
Scanning tunneling microscopy/spectroscopy of a-Si:H/SiNx interface of thin film transistors
Authors: Nejoh H.
Published: July 2002

In the deviation of current/voltage characteristics for staggered thin film transistors (TFTs) operating above threshold, previous authors have neglected amorphous silicon and gate insulator (silicon nitride) interface effects. I show that is not sufficient for explaining common TFT behavior. A corrugation at the a-Si/SiNx interface was found. The corrugation width of the a-Si/SiNx interface and the accumulation layer width perpendicular to the interface is comparable for a-Si TFT. The mean free path of free electrons traveling along with this interface is reduced, namely, the mobility decreases. The localized density of states (DOS) in this corrugated interface decreases areal charge density of electrons in extended states so that drain current decrease. These localized DOS trap electrons so that even above threshold the gate-induced electrons could not move, namely, the gate threshold voltage of TFT increases.
Characterization of epitaxial thin films by x-ray diffraction
Authors: Segmüller Armin
Published: July 2002

X-ray diffraction has been used to characterize thin epitaxial films. A new method, grazing-incidence diffraction, with the probing direction parallel to the interface is discussed and applied to several examples. The strain in thin copper films deposited on the basal plane of sapphire was determined in two directions: perpendicular to the interface by symmetric Bragg reflection and parallel to it by grazing-incidence diffraction. Finally, measurements of the lattice strain due to the excitation of electrons from DX centers in heavily tin-doped GaAlAs films on GaAs substrates at low temperature on a triple-crystal diffractometer are presented.
Hot filament activated chemical vapor deposition of boron nitride
Authors: Rye Robert R.
Published: July 2002

Using a hot filament (≊1400 °C) to activate borazine (B3N3H6) molecules for subsequent reaction with a direct line-of-sight substrate, transparent boron nitride films as thick as 25 000 Å have been grown for substrate temperatures as low as 100 °C. The minimum temperature is determined by radiative heating from the adjacent hot filament. The low temperature BN films show no indication of crystallinity with x-ray diffraction (XRD), but the opaque BN deposit produced on the hot filament is identified by XRD as polycrystalline h-BN. X-ray photoelectron spectra (XPS) show the films to have a B:N ratio (within experimental error) of 1:1 with no other XPS detectable impurities above the 0.5% level. Both Raman and infrared (IR) spectroscopy are characteristic of h-BN with small amounts of hydrogen detected as N–H and B–H bands in the IR spectrum. The important feature of this method is the separation and localization of the thermal activation step at the hot filament from the surface reaction and film growth steps at the substrate surface. This allows both higher temperature thermal activation and lower temperature film growth.
Comparison of sputter-initiated resonance ionization spectroscopy and laser atomization resonance ionization spectroscopy to localize tin-labeled deoxyribose nucleic acid
Authors: Arlinghaus H. F. , Thonnard N. , Spaar M. T. , Sachleben R. A. , Brown G. M. , Foote R. S. , Sloop F. V. , Peterson J. R. , Jacobson K. B.
Published: July 2002

Resonance ionization spectroscopy (RIS) is becoming recognized as an emerging field with wide applications. RIS is an analytical technique providing extreme element sensitivity and selectivity by detecting ionization produced from lasers tuned to excited states of the analyte. Using either sputter-initiated RIS (SIRIS) or laser atomization RIS (LARIS), it is possible to localize and quantify with micrometer spatial resolution ultratrace concentrations of a selected element at or near the surface of solid samples. The sensitivity and selectivity of the RIS process is especially valuable for trace element analysis in biological media, where the complexity of the matrix is frequently a serious source of interference. We have compared both the SIRIS and LARIS technique to determine their characteristics to localize and quantify Sn-labeled deoxyribose nucleic acid (DNA). We will present (a) data showing differences between SIRIS and LARIS response as a function of atomization parameter, substrate and analyte, and (b) the detection and resolution (spatial and isotopic) of subattomole quantities of Sn-labeled DNA bands. Both techniques have the potential of making a strong contribution to DNA sequencing.
Low resistance indium tin oxide films on large scale glass substrate
Authors: Oyama T. , Hashimoto N. , Shimizu J. , Akao Y. , Kojima H. , Aikawa K. , Suzuki K.
Published: July 2002

Preparation of low resistance indium tin oxide (ITO) films on large scale glass substrate has been studied for architectural applications. Coatings were carried out by a plasma enhanced deposition technique using sintered ITO pellets as the starting material and high deposition rate of more than 4000 Å/min was achieved. Scanning tunneling microscopy observation revealed that surface morphology of the thick (about 1 μm) film was strongly dependent on the substrate temperature. Crystallinity and electrical properties were also dependent on the temperature and closely related to the surface morphology. The films deposited on 125 °C substrate were composed of a mixture of amorphous and polycrystalline phases and showed a hazy appearance caused by light scattering at the rough surface. The polycrystalline ITO films with a clean and transparent appearance as well as the minimum resistivity of 1.7 × 10−4 Ω cm were obtained on 180 °C substrate. Coatings on architectural size glass substrate (1.8 m×3.2 m) were carried out and minimum sheet resistance of less than 1.25 Ω/sq was obtained. Sheet resistance less than 2 Ω/sq was observed over 88% of the surface area. The transparency and durability of the film were confirmed to be enough for practical use.