bluuebunny/crossref_metadata_2025 huggingface dataset:
Modifications in the Si valence band after ion-beam-induced oxidation
Authors: Alay J. L. , Vandervorst W.
Published: July 2002

The changes undergone by the Si surface after oxygen bombardment have special interest for acquiring a good understanding of the Si+-ion emission during secondary ion mass spectrometry (SIMS) analysis. For this reason a detailed investigation on the stoichiometry of the builtup surface oxides has been carried out using in situ x-ray photoemission spectroscopy (XPS). The XPS analysis of the Si 2p core level indicates a strong presence of suboxide chemical states when bombarding at angles of incidence larger than 30°. In this work a special emphasis on the analysis and interpretation of the valence band region was made. Since the surface stoichiometry or degree of oxidation varies with the angle of incidence, the respective valence band structures also differ. A comparison with experimentally measured and theoretically derived Si valence band and SiO2 valence band suggests that the new valence bands are formed by a combination of these two. This arises from the fact that Si–Si bonds are present on the Si-suboxide molecules, and therefore the corresponding 3p–3p Si-like subband, which extends towards the Si Fermi level, forms the top of the respective new valence bands. Small variations in intensity and energy position for this subband have drastic implications on the intensity of the Si+-ion emission during sputtering in SIMS measurements. A model combining chemically enhanced emission and resonant tunneling effects is suggested for the variations observed in ion emission during O+2 bombardment for Si targets.
Investigation of the core–clad interface of coherent fiber optic devices using secondary ion mass spectrometry, surface analysis by laser ionization, and transmission electron microscopy
Authors: Kurz E. A. , Becker C. H. , Wu K. J. , Becker O. , Sommer B.
Published: July 2002

In fiber optics, the efficiency of light transmission depends on the perfection of total internal reflection at the interface between the core and clad of the fibers. Any loss due to light scattering at this interface can reduce the efficiency of light transmission. In this investigation, secondary ion mass spectrometry, surface analysis by laser ionization, and transmission electron microscopy have been used to characterize the interface between the core and clad of various glass systems used in coherent fiber optic devices. Interfaces with highly efficient, total internal reflection result from ‘‘compatible’’ glass combinations. Such systems have been found to have interface diffusion zones considerably narrower than systems exhibiting poor compatibility.
Angle-resolved self-ratio measurements on ion-implanted depth profiles by synchrotron x-ray fluorescence spectrometry
Authors: Schmitt W. , Rothe J. , Hormes J. , Gries W. H.
Published: July 2002

Centroid depth determinations by angle-resolved self-ratio x-ray fluorescence spectrometry on ion-implanted depth profiles have been carried out at a synchrotron radiation source using ‘‘white’’ radiation. For ion implants of phosphorus in silicon wafers at the 1016 cm−2 level, the results are very satisfactory. The wafer temperature can be kept to a tolerable level if the low-energy component is preabsorbed in a suitable filter (foil) and if additionally the specimen is placed in an environment of helium at atmospheric pressure. The helium atmosphere is indispensable also for avoidance of the deposition of adventitious carbon on the specimen surface. Extrapolating from the results obtained so far, one can conclude that (with the specimen properly mounted in a helium atmosphere) centroid depth measurements should be possible also at a few times 1014 cm−2 dose density level.
Si(100)2×1+Sb surfaces studied with photoemission and optical spectroscopy
Authors: Cricenti A. , Bernhoff H. , Purdie D. , Reihl B.
Published: July 2002

Applying in situ combination of angle-resolved photoelectron spectroscopy and k-resolved inverse photoemission to Si(100):Sb-1×1 and Si(100):Sb-2×1 surfaces, we have determined the surface band gaps between the Sb-derived filled and empty surface states at several points of the surface Brillouin zone. The values of the surface band gaps are compared with optical surface excitations obtained by means of surface differential reflectivity.
Metal overlayers on self-organized molecular assemblies. IV. Ion scattering spectroscopy of the Ag/CH3 interface
Authors: Herdt G. C. , Czanderna A. W.
Published: July 2002

Ion scattering spectroscopy (ISS) of vacuum deposited Ag on octadecanethiol (ODT, HS(CH2)17CH3) organized molecular assemblies (OMAs) provides a means of studying interfacial structure at metal/organic interfaces under controlled conditions. The OMAs were self-assembled onto gold films on silicon 〈100〉 substrates. ISS compositional depth profiles of the Ag/CH3 interface were performed at a number of temperatures between 113 and 293 K. Results from these experiments show clearly that Ag penetrates rapidly through ODT above ∼200 K. The changes in ISS Ag peak intensities as a function of time and temperature provide evidence for the formation of Ag clusters at the ODT/Au interface after penetration of Ag. Changes in deposition rate between 0.003 and 0.015 nm/s yielded little difference in corresponding ISS depth profiles. Over a range of ion beam current densities from 0.06 to 2.0 μA/cm2, scaled compositional depth profiles were found to be comparable within experimental error.
Secondary ion mass spectrometry relative sensitivity factors for Ru, Rh, Pr, Eu, Tm, Lu, Re, Os, and Ir
Authors: Wilson R. G. , Stevie F. A. , Chryssoulis S. L. , Irwin R. B.
Published: July 2002

The elements Ru, Rh, Pr, Eu, Tm, Lu, Re, Os, and Ir have been successfully implanted into Si, and, in some cases, GaAs, in order to quantify secondary ion mass spectrometry (SIMS). SIMS relative sensitivity factors have been determined for these elements for both oxygen and cesium primary bombardment and positive and negative secondary ions, respectively. Molecular ions were also monitored based on data from other studies and some poor secondary atomic ion yield for certain elements, e.g., Re. Relative ion yield enhancement for certain molecules is discussed. Relevance to geological applications is noted for the elements Ru, Rh, Os, and Ir.
Capillary arrays with variable channel density: An improved gas injection system
Authors: Scheinowitz D. A. , Werner K. , Radelaar S.
Published: July 2002

A new design concept has been studied for capillary array collimators used for the injection of gases, e.g., in gas source molecular-beam epitaxy. So far, the conventional designs suffer from either poor uniformity or low efficiency in precursor consumption (ratio of flux impinging on substrate to total emitted flux). The key feature of our new design is that the surface channel density is not homogeneous across the array but radius dependent instead, with the density of channels increasing towards the source array edge. In this way the steep decrease of the flux away from the beam center, which is a characteristic feature of conventionally designed arrays, is compensated. The numerical analysis shows that with the improved design, a high degree of uniformity (≳99%) can be achieved while at the same time the efficiency is increased by more than one order of magnitude compared to conventional capillary arrays.
Amorphous Si:B films: Microstructure and electrical properties
Authors: Yang G.-R. , Soss S. R. , Nason T. C. , Ma X.-F. , Cocoziello A. , Tong B. Y. , Zhu Y. T. , Du J. , Tjew K. F.
Published: July 2002

The properties of and potential uses for thin films of amorphous Si:B alloys are summarized. The films were deposited by low-pressure chemical vapor deposition of silane and diborane. The boron content of the samples was controlled by regulating the reaction of diborane and silane gases during the deposition. The alloy and its oxides possess many desirable properties for microelectronic applications, including high microhardness, resistance to chemical etching, high and tailorable conductivity, ease of oxidation, and (for the oxide) high resistivity and dielectric strength. The microstructural stability of the films is excellent. The volume fraction of crystallinity of the as-deposited films was reduced dramatically by increasing the boron content, as was crystallization upon annealing. Transport at low temperatures is seen to be dominated by hopping. The linear oxidation rate was observed to be radically enhanced by the presence of large amounts of boron. The electrical properties of the oxides were seen to be comparable to SiO2. Using a simple model relating the physical mode of boron incorporation in the amorphous network, mechanisms for the crystallization inhibition, the oxidation enhancement, and the electrical properties are discussed. These are consistent with stoichiometric and spectroscopic properties of the alloy and its oxides.
Thin-oxide degradation along feature edges during reactive ion etching of polysilicon gates
Authors: Markus K. , Osburn C. M. , Magill P. , Bobbio S. M.
Published: July 2002

Enhanced leakage current through the gate oxide insulator and degraded oxide breakdown voltages were observed following hexode reactive ion etching and magnetically enhanced reactive ion etching (MERIE) of poly-Si electrodes over thin gate oxides. The degradation was seen to occur along the edges of the etched poly-Si gates and was not aggravated by the amount of poly-Si charge collection area (antenna) over a thick field oxide. Defect densities ranging from 0.02 to 0.3 per meter of perimeter were observed so that significant yield losses could be expected in deep submicron ultralarge scale integrated circuit chips. Interestingly the defect density, as measured at a fixed voltage, was not markedly affected by the gate oxide thickness down to 7 nm. Comparisons of results from the two etching systems showed that the degradation was three times greater in MERIE than with the hexode.
Characterization of etch-induced damage for Si etched in Cl2 plasma generated by an electron cyclotron resonance source
Authors: Sung K. T. , Pang S. W.
Published: July 2002

A Cl2 plasma generated by a multipolar electron cyclotron resonance source is used for Si etching, and the effects of etch-induced damage are studied using Schottky diodes and metal–oxide–semiconductor (MOS) capacitors to investigate the effects of dry etching on device performance. The Schottky diode characteristics improved with increasing microwave power when the self-induced bias voltage was kept at −150 V, but degraded with increasing microwave power at −50 V. The diode characteristics were close to an ideal diode when low rf power, high Cl2 percentage, and close source distance were used. Varying the sample temperature during etching from −130 to 350 °C has no effect on the Schottky diode characteristics. The damaged layer was removed by reactive chlorine radicals and by wet etching. After removing 60 nm from the dry-etched surface, the Schottky diode performance was comparable to that of an ideal diode. Annealing at 800 °C in Ar for 5 min has similar effects. When the oxide was etched and MOS capacitors were fabricated on the etched oxide, no electrical degradation was observed. When Si was etched and the etched surface was oxidized to form MOS capacitors. The breakdown field was found to decrease with high microwave power, high rf power, and low Cl2 concentration. However, dry etching has no influence on fixed charge density, and the interface state density only increases slightly from 1.2 to 2.5×1010 cm−2.
Magnetron enhanced reactive ion etching of GaAs in CH4/H2/Ar: Surface damage study
Authors: McLane G. F. , Buchwald W. R. , Casas L. , Cole M. W.
Published: July 2002

An investigation was performed of surface region etch-induced damage of GaAs magnetron reactive ion etched in CH4/H2/Ar gas mixtures. Transmission electron microscope measurements revealed the presence of etch-induced defects which extended 4.3, 7.2, and 8.7 nm below the surface for Ar concentrations of 0%, 10%, and 20%, respectively, in the gas mixture. Auger electron spectroscopy measurements showed that etching produced an As-deficient surface region extending approximately 10 nm below the surface. The amount of As deficiency increased with Ar concentration, but was relatively unaffected by postetch annealing at 400  °C for 30 s. Changes in Schottky barrier surface potential Φb upon etching and subsequent annealing can be explained by a combination of H passivation effects and As removal from the surface, whereas changes in Schottky barrier diode ideality factor n can be explained by the presence of etch-induced surface region defects such as donorlike As vacancies and deep level recombination centers, both of which are passivated by H.
Plasma impedance and microwave interferometric measurements of electron concentrations in dual-frequency powered sulfur hexafluoride plasmas
Authors: Jaiprakash V. C. , Thompson B. E.
Published: July 2002

Recent literature shows that dual frequency rf power can give better characteristics in both plasma etching and plasma deposition. The key features of the powering system used in our experimental studies on a parallel plate plasma system is that the high frequency (HF) is an exact multiple of the low frequency (LF), and that the power from both is supplied to the same electrode. These features make it much easier to measure the plasma voltage and current waveforms with an oscilloscope. We examined 100 kHz plus 12.2 MHz discharges at 0.35 Torr with LF power from 0% to 100% of the total power of 0.05 to 0.6 W/cm2. The plasma impedance for the HF signal tended to be largest at times when the magnitude of the low frequency signal’s voltage was the largest which may be due to additional loss of electrons by extraction out of the plasma. Because of the time-varying HF impedance, we could alter when HF power was dissipated within the low frequency cycle by changing the matching network settings to effectively tune into the low or high impedance times. This effect shows that the process characteristics of the plasma might depend on the matching of the dual frequency systems for the same time-averaged HF power and LF power readings. In general as we increased the percentage of LF power, the electron concentrations decreased. No sudden changes of any plasma characteristics were observed while going through the full range of percentage LF power.
Auger electron spectroscopy of laser deposited a-C, a-C:H, microcrystalline diamond
Authors: Kovarik Peter , Bourdon E. B. D. , Prince R. H.
Published: July 2002

Auger electron spectroscopy has been used to characterize carbon films produced by a pure laser process [E. D. B. Bourdon, P. Kovarik, and R. H. Prince, Diamond Relat. Mater. 2, 425 (1993); E. D. B. Bourdon and R. H. Prince, U.S. Patent Application Ser. No. 821416 (filed 14 January 1992) Canadian Patent Application Ser. No. 2059185-4 (filed 10 January 1992)]. The analysis of the resulting spectra has been extended from the usual chemical element identification to qualitative carbon bond characterization. The data collection was performed in N(E) mode followed by deconvolution to isolate the true Auger peak. A multiple Gaussian fit was then used to approximate the density of states components and identify the electron pair contributions. This process was used to identify the components of highly oriented pyrolitic graphite (HOPG) and chemical vapor deposited diamond spectra before application to the laser-deposited materials a-C, a-C:H, and microcrystalline diamond. The HOPG and a-C spectra were compared and components affected by the sp3 content and short-range order identified. The a-C:H spectrum was observed to contain a C–H component and a satellite peak associated with the ‘‘shake-off’’ process of the C–H system. Heating of the sample reduced these features as hydrogen was expelled, and the film approached the a-C structure. The analysis of the microcrystalline diamond spectrum showed a more complex system containing contributions from diamond and SiC.
High temperature behavior of reactively sputtered AlN films on float glass substrates
Authors: Arbab M. , Finley J. J.
Published: July 2002

Thin AlN films were deposited on the air side of float glass substrates by reactive direct-current magnetron sputtering of an aluminum target in Ar–N2 gas mixtures, and at 4 kW of power. These films were characterized by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy (XPS). For nitrogen partial flow rates fN2, of 0.3 or higher, and for thicknesses of up to 800 Å, the gas composition does not affect the composition and morphology of the as-deposited films significantly. On the other hand, the morphology of films deposited on float glass and heated in air to 700 °C has a strong dependence on the composition of the working gas: films that are formed at low values of fN2 craze, while those deposited at high N2 partial pressures remain continuous upon heating but develop a wavy morphology. XPS/inert gas depth profiling analyses of the coated float glass samples revealed the formation of a thin layer with an N/Al ratio less than that of the as-deposited film at the interface, suggesting the interfacial oxidation of the film by the float glass substrate, as well as strong film–substrate adhesion. While the sputtering conditions influence the morphology of the heated samples, the high thermal expansion coefficient of the soda-lime-silica float glass, and its viscous flow, appear to be the cause of film deformations at high temperatures. Also upon heating, a graded oxy–nitride layer forms on the surfaces of these films. The thickness of both of the above oxidized layers depends on the temperature and duration of the heating schedule.
Preferential sputtering of silicon from metal silicides at elevated temperatures
Authors: Hedlund C. , Carlsson P. , Blom H.-O. , Berg S. , Katardjiev I. V.
Published: July 2002

It has been shown that at elevated temperatures silicon is preferentially sputtered from Ti and Co silicides during low energy Ar ion bombardment. The Si sputtering yield under these conditions is shown to substantially exceed that of pure Si, as well as that it is a function of the ion current density. On the other hand, the sputtering yield of the metal is found to be substantially smaller than that at lower temperatures under the same conditions. These effects have been studied both experimentally and numerically using the dynamic T-DYN program. It is shown that the increased Si sputtering yield is partly due to the so-called sputter yield amplification effect (which is a purely ballistic effect independent of temperature), while its sustenance with dose is caused by thermal and ion beam induced diffusion and segregation of Si at the surface.
Biased magnetron sputter deposition of corrosion resistant Al–Zn alloy thin films
Authors: Li L. , Nowak W. B.
Published: July 2002

The reason for the high corrosion resistance of Al–Zn films is unclear. To relate this behavior to the structure and fabrication we have studied films deposited by dc biased magnetron sputtering onto Fe–Cr substrates. Changes of composition, structure, and electrochemical polarization behavior of resultant films were measured as a function of experimental parameters, including on-axis and off-axis substrate positions. The films, 1.6–4 μm thick, were deposited with a chamber Ar pressure of 10 mTorr (1.33 Pa), substrate temperature of 22–90 °C, and substrate bias of −60 to −380 V. Transmission electron photomicrographs of thin alloy films exhibited polycrystalline structure comprising one or two phases depending on film composition. Lower bias (−60 V) tends to produce two phases. Reflection high-energy electron diffraction photomicrographs also presented polycrystal ring patterns. Energy-dispersive x-ray spectroscopy analysis of as-deposited films revealed that Al vapor flux was more likely than Zn to go axially. The enrichment of Al in the on-axis films increased dramatically with increasing substrate bias. The bias effect was small in off-axis films. The enrichment of Al in films also varied with target composition. Film surface morphology and cross sections were examined with scanning electron microscopy: zinc-rich targets and lower biases led to porous structures. Higher biases (−380 V) and Al-rich targets led to dense columnar structures. Transmission electron microscopy images showed a reduction of average grain size with increasing substrate bias. The deposited thin films presented active–passive transitions in potentiodynamic tests. Step passivity was observed on porous films but not on dense films. Alloy films had higher corrosion resistance than corresponding bulk material as a result of reduced grain size and better chemical uniformity, which enhances the films’ passive behavior.
Modification of surface condition and irradiation effects of synchrotron radiation on photoexcited etching of SiC
Authors: Terakado Shingo , Ogura Masayoshi , Suzuki Shigeo , Nakao Masao , Tanaka Kenichiro
Published: July 2002

Photoexcited etching of SiC film by synchrotron radiation excitation was investigated from both measurements of total electron yield (TEY) spectra and dependence of the etch rate on irradiated photon energy. We found from TEY spectra that the content of Si near the surface was decreased and that of C was increased upon exposing the SiC surface to reactive species. In the etching experiment with changing irradiated photon energy, we also found that the etch rate showed a photon energy dependence similar to that of photoabsorption of SiC. We concluded that photoexcited etching of SiC was realized based on the progress of the etching of the irradiated region being closely related to the photoabsorption of constituent elements of SiC, and by the slight etching of the nonirradiated region covered by the C-rich fluorinated layer.
Formation of chromium oxide on 316L austenitic stainless steel
Authors: Ohmi Tadahiro , Nakagawa Yoshinori , Nakamura Masakazu , Ohki Atushi , Koyama Tomoyuki
Published: July 2002

The new technology using electrochemical buffed 316L austenitic stainless steel was developed to form an oxide scale as a passivation film which consists of an outer surface that is a perfect chromium oxide (Cr2O3) layer of several tens nanometers thickness, and an inner part that contains iron and nickel oxides. This technology first makes the stainless steel surface feature a very fine grain structure and introduces Cr to the stainless steel surface through grain-boundary diffusion. Then a weak oxidizing ambience or a strong reductive ambience is created to perform oxidation to form a perfect Cr2O3 film. Growth behavior of Cr2O3 film was analyzed with x-ray photoelectron spectroscopy by varying each parameter of moisture, concentration, temperature, and duration of thermal treatment in ambience. The corrosion resistance of this film showed an excellent characteristic compared with the conventional electropolished surface. This shows a possibility of its application to specialty gas handling in semiconductor device manufacturing.
Strain measurements of SiGeC heteroepitaxial layers on Si(001) using ion beam analysis
Authors: Sego S. , Culbertson R. J. , Smith David J. , Atzmon Z. , Bair A. E.
Published: July 2002

The strain in SiGeC heteroepitaxial films grown on Si(001) substrates by chemical vapor deposition is quantified using ion channeling. Rutherford backscattering spectrometry was used to quantify the Ge concentration as well as the film thickness, nuclear resonance elastic ion scattering was used to quantify the C concentration, and ion channeling was utilized to measure film quality and C substitutionality. Channeling angular scans across an off-normal major axis were used to quantify the strain. The results confirm that addition of C compensates for the strain introduced by Ge.
Electric field control of plasma and macroparticles in cathodic arc deposition as a practical alternative to magnetic fields in ducts
Authors: Yin Y. , McKenzie D. R.
Published: July 2002

Plasma transportation and ion losses in a cathodic arc fitted with a curved magnetic macroparticle filter are studied for different magnetic field configurations. A planar Langmuir probe was used to carry out ion saturation current measurements along the axis of the duct, so that the losses of ions could be quantified. The losses of ions were found to depend sensitively on the magnetic field configuration in the prefilter region. The potential of the duct wall was measured as a function of distance to the cathode and the results were used to locate the effective anode of the discharge. The location of the effective anode was determined by the magnetic field configuration and affected the running stability of the arc. The conditions which provided the best efficiency of plasma transport also gave the least stable running conditions. The use of an electric field as a macroparticle filter was studied and higher deposition rates for coatings of comparable quality were found to be deposited onto a substrate held parallel to the drift velocity of the plasma to which a negative bias was applied.
Low dielectric constant, fluorine-doped SiO2 for intermetal dielectric
Authors: Denison D. R. , Barbour J. C. , Burkhart J. H.
Published: July 2002

Shrinking device geometry has produced a need for lower dielectric constant materials for intermetal dielectric to reduce circuit RC time constants and intertrace ‘‘cross-talk’’ capacitance and reduce power consumption at high frequency. One such material is F-doped SiO2. This study utilized an electron cyclotron resonance high-density oxygen plasma source to produce SiO2 from a mixture of SiH4 and SiF4, O2, and Ar. The total silicon gas flow was held constant and the ratio of SiH4 to SiF4 was varied from 0% to 100%. The fluorine content was measured using nuclear resonance analysis (NRA) with the reaction 19F(p,αγ)16O. A comparison of the NRA data and the ratio of the Fourier transform infrared Si–F absorbance near 934 cm−1 to the Si–O peak near 1080 cm−1 gives a proportionality constant of 144. The refractive index and dielectric constant were determined as a function of fluorine content. The dielectric constant decreased linearly from 4.0 at zero F to 3.55 at 10.5 at. % F and the refractive index decreased from 1.474 to 1.417. Film stress, thermal stability, moisture absorption, and electrical breakdown were also measured. Film stress decreased from 150 to 70 MPa compressive as the F content increased.
Surface barrier detection in plasma-enhanced chemical vapor deposition oxides
Authors: Peavey Jerris , Dawson Robert , Lowell John
Published: July 2002

The performance standards of plasma-enhanced chemical vapor deposition (PECVD) oxides increase as device sizes shrink and densities increase for ULSI. Future PECVD dielectric quality may be compromised by the effects of contaminants and/or charged ionic species that are present in the gaseous ambient which the wafers are exposed to. As a result of being left at the oxide/silicon interface, these gaseous ambient defects such as metallic ions can adversely effect reliability and performance. Moreover different types of PECVD oxides require different deposition chemistries and are grown to differing thicknesses making it difficult to apply a single C–V test. In this article, the problem is addressed by detecting, nondestructively, such residual interfacial charge postprocessing on product wafers rather than the traditional test wafers. For the first time the effects of mobile ions and interface states at the oxide/silicon interface and in the as-processed films for various PECVD oxides will be shown using no electrical test methods before and after anneal. Charge effects and approximate generation lifetime estimates are separated out from the total charge measurement using passive high-injection surface photovoltage. Thus one can passively examine the induced surface barrier height and interface charge for any PECVD oxide type at any thickness. This technique is demonstrated for several types of single-oxide samples. The charge effects (if any) in PECVD oxides as-deposited with or without rapid thermal annealing treatments are illustrated.
Degradation of zinc sulfide phosphors under electron bombardment
Authors: Swart H. C. , Sebastian J. S. , Trottier T. A. , Jones S. L. , Holloway P. H.
Published: July 2002

ZnS phosphor powders have been subjected to electron bombardment (2 keV, 2 mA/cm2) at a residual gas pressure of 1.2×10−8 Torr and oxygen pressures of 10−6 Torr. Auger electron spectroscopy and cathodoluminescence (CL), both excited by the same electron beam were used to monitor changes in surface state and luminous efficiency during electron bombardment. A direct correlation between the surface reactions and the degradation of CL brightness was observed. Both C and S were depleted from the surface during electron bombardment. The postulated mechanism for the electron stimulated reactions on the phosphor surface is electron beam dissociation of molecular species to atomic species which subsequently react with C to form volatile compounds (COx, CH4, etc.) and with ZnS to form a nonluminescence layer of either ZnO or ZnSO4. The growth in thickness of the nonluminescence surface layer is directly responsible for the degradation in CL brightness.
Novel approach for the preparation of metal colloid monolayers on modified surfaces
Authors: Rubin Shai , Bar Georg , Taylor Thomas N. , Cutts Russell W. , Zawodzinski Thomas A.
Published: July 2002

The morphology of Au colloid monolayers on modified silicon oxide surfaces (glass, silicon wafer, and ITO slides) has been studied. These monolayers were prepared by a new method described here. We also demonstrate several applications of this colloid monolayer surface. The preparation route creates a rough metal surface, the morphology of which can be easily controlled. The colloid monolayers are prepared in two steps: (1) modification of the substrates with starburst dendrimers; (2) noble metal colloid deposition onto the dendrimer layer. Au particles of approximately 28 nm in diameter were deposited onto the dendrimer-modified surfaces. The spontaneous adsorption of the dendrimers to the silicon oxide surface was proven by x-ray photoelectron spectroscopy, contact angle, and grazing angle Fourier transform infrared spectroscopy. The thickness of the dendrimer layer has been calculated to be in the range of d=14–25 Å. The structure and properties of the resulting particle arrangement have been studied by atomic force microscopy (AFM) and ultraviolet (UV-vis) spectroscopy. AFM data show that the colloids spontaneously form continuous films on the dendrimer-modified surfaces. The noble metal particles are well isolated, confined to a single layer, and aggregation does not occur on the surface. UV-vis spectroscopic data show that the microstructure controls the optical properties of the layer. The article demonstrates the practical applications of this rough metal surface as a platform for surface-enhanced Raman scattering and electrochemistry.
X-ray photoelectron spectroscopy study of TiC films grown by annealing thin Ti films on graphite
Authors: Miller S. , Berning G. L. P. , Plank H. , Roth J.
Published: July 2002

Thin Ti films with thicknesses in the range between 200 and 300 Å were evaporated onto graphite substrates under UHV conditions. The samples were annealed up to temperatures of 1470 K. After reaching steady state, subsequent x-ray photoelectron spectroscopy analysis showed formation of different TiCx phases dependent on the annealing temperature. For temperatures lower than 600 K, little carbide formation occurs in the metal film; a mixed metal–carbide phase forms only at the metal–graphite interface. At higher temperatures, the concentration ratio x of carbidic C to Ti ranges from about 0.6 at 750 K to about 0.95 at 1200 K and higher annealing temperatures. It was observed that the binding energies of the Ti 2p electrons rise continuously with increasing concentration ratio of carbidic C to Ti. Depth profiles were made to investigate chemical phases in the Ti film, as well as at the interface. It is illustrated from the profiles that formation of carbide proceeds from the metal–graphite interface, as well as from surface segregated carbon and advances into the Ti layer from both sides.
Plasma nitriding combined with a hollow cathode discharge sputtering at high pressures
Authors: Benda M. , Vlček J. , Cibulka V. , Musil J.
Published: July 2002

The article describes a new plasma nitriding system with an auxiliary cathode the surface of which is furnished with holes of diameter ∅ and depth d. The auxiliary cathode fulfills two functions: (i) it intensifies the nitriding discharge by hollow cathode discharges generated in the holes and (ii) strongly sputters its material. The sputtered material is transferred onto the surface of nitrided steel sample where it forms a surface layer of nitrides from deposited material. As the material of the auxiliary cathode can be different from that of samples to be nitrided, the surfaces of nitrided substrates can be improved by an addition of selected materials, such as Mo, Cr, Ti, V, etc. The main attention is devoted to the investigation of transfer of the material from the auxiliary cathode onto the surface of nitrided steel samples. It was found that conditions under which a maximum quantity of this material is transferred depend on dimensions of holes in the auxiliary cathode, potential of treated substrates, and on argon content in N2+H2+Ar mixture. The plasma nitriding was carried out at a high pressure of 1067 Pa and a substrate temperature T of 550 °C for a time of 2.5 h. Detailed measurements of elemental depth profiles and structure of nitrided steel samples, carried out by means of glow discharge optical emission spectroscopy and x-ray diffraction, respectively, are given.
Transparent conducting ZnO thin films prepared by XeCl excimer laser ablation
Authors: Hiramatsu Mineo , Imaeda Koichi , Horio Noriaki , Nawata Masahito
Published: July 2002

Highly conductive and transparent aluminum- and gallium-doped zinc oxide (ZnO:Al and ZnO:Ga) thin films in place of indium tin oxide films have been prepared by using XeCl excimer laser ablation at relatively low temperatures. The impurity content of Al or Ga in the ZnO target was optimized on the basis of the measurements of resistivity, carrier concentration, and Hall mobility of the deposited transparent conducting ZnO films. The effects of substrate temperature on the properties of ZnO films were investigated. The crystalline, electrical and optical properties of the films were found to depend directly on substrate temperature during deposition. The minimum resistivity of 1.4×10−4 Ω cm was obtained for the ZnO:Al film prepared at a substrate temperature of 300 °C using a ZnO target with an Al2O3 content of 1% by weight (wt %). Moreover, the ZnO:Al film prepared at a substrate temperature of 100 °C showed a low resistivity value of 2.5×10−4 Ω cm. As for the ZnO:Ga film, on the other hand, the minimum resistivity value was 2.7×10−4 Ω cm for the film deposited at 300 °C using a ZnO target with a Ga2O3 content of 7 wt %. Furthermore, plasma etching of ZnO films employing a mixture of CH4 and H2 was carried out, and it was found that a small amount of CH4 gas enhanced the etching of ZnO films.
Plasma etching of dielectric films with novel iodofluorocarbon chemistries: Iodotrifluoroethylene and 1-iodoheptafluoropropane
Authors: Karecki S. M. , Pruette L. C. , Reif R.
Published: July 2002

The use of two novel etch chemistries belonging to the iodofluorocarbon family, iodotrifluoroethylene and 1-iodoheptafluoropropane, has been investigated in a dielectric etch application. These substances are being explored as potential alternatives to perfluorocompounds, a fully fluorinated class of etchants that is presently in widespread use in dielectric etch processes. Whereas perfluorocompounds have global warming properties once emitted into the atmosphere, iodofluorocarbons such as those discussed in this work are presently believed not to possess long-term environmental impacts. Under the conditions tested, the two iodofluorocarbons discussed in this work have both been found to etch silicon dioxide films readily. Note that 1-iodoheptafluoropropane has also been found to be capable of etching silicon nitride films under these conditions. An Applied Materials Precision 5000 etch tool was used in this work.
Thermodynamic theory for preferred orientation in carbon and cubic BN
Authors: McKenzie D. R. , Bilek M. M. M.
Published: July 2002

The applications of thermodynamic theory to preferred orientations based on minimization of the Gibbs free energy is discussed in order to address the difficulties raised in recent work by Cardinale et al. [G. F. Cardinale et al., J. Vac. Sci. Technol. A 15, 196 (1997)]. We find that the preferred orientation of the cubic form of BN with the 〈111〉 direction lying in the stress plane is correctly described by the theory provided that the term linear in stress is included. We also describe how the predictions of this theory for the hexagonal forms of BN and for glassy carbon under compressive stress conditions are reconciled with measurement by allowing for reductions in the elastic constant s44 caused by imperfections.
Proposal for a new UV-light generating device based on cold electron emission
Authors: Nicolaescu Dan , Filip Valeriu , Okuyama Fumio
Published: July 2002

A new device intended for UV-light generation and based on cold electron emission is proposed and analyzed theoretically. The device operation is based on the excitation by the field emitted electrons of the surrounding nitrogen (N2) molecules, which in turn emit UV light. The device should operate at low pressures compatible with field emission. The proposed device involves electrons moving in crossed electric E and magnetic B fields. Equations for the electron time evolution (both radial and angular position) are obtained. When moving inside the device, the electron has a periodical cycloid-like trajectory which is always confined between two coaxial cylinders. The inner cylinder has the same radius and position with the circular array of emitters used for electron generation. The position of the outer cylinder (and so the width of the confinement zone) is controlled by E and B. The described analytical-numerical approach is used to analyze the device operation as function of model parameters.
Blistering mechanism for the crater formation at Ta/Si interface by sputtering with oxygen ion beam
Authors: Kim Kyung Joong , Moon Dae Won , Jung Kyung-Hoon , Jeon Il Cheol
Published: July 2002

Irregular interface artifacts were observed in secondary ion mass spectroscopy depth profiling of a Ta thin film on Si by O2+ ion beam. They were correlated with the formation of an abnormal surface topography. Volcano-type round craters were developed by sputtering with a 7 keV oxygen ion beam at an incidence angle of 45°. The surface topographic development on a Ta thin film was negligible before approaching the interface. However, scanning electron microscopy study as a function of sputter depth showed that the craters were developed abruptly near the interface. A blistering mechanism is proposed for the crater formation. The buildup of compressive stress caused by volume increase of the Ta layer near the interface due to oxidation is suggested to be a driving force for the crater formation.
Direct observation of Na and O impurities at grain surfaces of CuInSe2 thin films
Authors: Niles David W. , Al-Jassim Mowafak , Ramanathan Kannan
Published: July 2002

The authors use field-emission Auger electron spectroscopy to investigate the spatial nature of trace Na and O impurities in thin films of photovoltaic-grade CuInSe2 thin films. They give the first direct proof that Na and O reside at grain surfaces and not in the grain interiors of CuInSe2 (CIS) thin films, and discuss the improvement in photovoltaic conversion efficiency of CIS with Na.
Optical and mechanical consequences of microstructural alteration of alpha platinum dioxide films
Authors: Maya L. , Anovitz L. M. , Thundat T. , Yust C. S.
Published: July 2002

The microstructure of sputtered alpha platinum dioxide consists of a porous random assembly of platelets. A sweeping motion with very light pressure, by either a sharp or blunt object, leaves a track clearly visible, in reflected light, that stands in contrast to the opaque brown background of the intact film. Microstructural analysis utilizing atomic force microscopy revealed a flattening of the platelets in the affected areas. High reflectivity of the flattened portion is apparently a consequence of the relatively high refractive index of this material. X-ray diffraction by the flattened platelets shows a significant enhancement of the intensity of the 001 reflection corresponding to the alignment of the crystals parallel to the substrate. The work required to flatten the platelets along a microscopic track was deduced from sensitive friction force measurements. Electrical resistivity of the flattened film is moderately lower than that of the intact film. The phenomenon described here might be of importance for data storage or for alignment in lithographic reproduction of multilevel electronic circuits.
Metastable deexcitation spectroscopy study of oxygen adsorption on a polycrystalline titanium surface
Authors: Kurahashi Mitsunori , Yamauchi Yasushi
Published: July 2002

Adsorption of oxygen on a polycrystalline titanium surface at room temperature has been studied by metastable deexcitation spectroscopy in conjunction with ultraviolet photoelectron spectroscopy and Auger electron spectroscopy. From the analysis of the obtained spectra, we have shown the following. (1) With increasing oxygen exposure at <2 L, the surface density of states decreases substantially 1–2 eV below the Fermi level (EF) but it undergoes a small change at around the EF. (2) The TiO2 phase appears on the outermost titanium surface at around 5 L. It grows with increasing oxygen exposure, but it is a minor phase even at >100 L.
Computer study of boron segregation at the Si(100)–2×1 and Si(111)–3×3 surfaces
Authors: Zavodinsky V. G. , Kuyanov I. A. , Chukurov E. N.
Published: July 2002

Energetics of the boron substitution near the Si(100)–2×1 and Si(111)–3×3 surfaces have been studied using the semi-empirical cluster AM1 method at substitutional positions at the Si(100)–2×1 surface. It has been found that in the both cases boron prefers to be in the second layer, that is it occupies substitutional positions that are bonded with dimers of the Si(100)–2×1 surface and S5 sites under adatoms of the Si(111)–3×3 surface. The energies, counting from the fourth bulk-like layer, for the Si(100)–2×1 and Si(111)–3×3 surfaces are −1.3 and −2.1 eV, respectively. These values may be interpreted as corresponding segregation enthalpies.
Particle growth in a sputtering discharge
Authors: Samsonov D. , Goree J.
Published: July 2002

Submicron to micron size particles are produced in the gas phase of sputtering discharges. These particles can contaminate thin films grown by sputter deposition. On the other hand, particle production in a discharge can be desirable when used for manufacturing fine powders. Here, experimental results are presented demonstrating particle production in an argon discharge, using a variety of target materials. The rate of particle growth varied widely, depending on the target material. Particles grown to 300 nm–5 μm, usually have one of two different shapes. Compact particles with a nearly spherical shape were produced by sputtering graphite, titanium, tungsten, and stainless steel targets, while filamentary-shaped fractal particles formed when sputtering aluminum and copper targets. Particle growth was also observed for a target made of an insulating material.
Bi/Sb superlattices grown by molecular beam epitaxy
Authors: Cho Sunglae , Kim Yunki , DiVenere Antonio , Wong George K. , Ketterson John B. , Hong Jung-Il
Published: July 2002

Epitaxial Bi/Sb superlattices have been grown by molecular beam epitaxy on CdTe(111)B substrates. The superlattice modulation wavelength was in the range of 20–200 Å. Structural properties have been investigated using in situ reflection high-energy electron diffraction (RHEED), θ−2θ x-ray diffraction (XRD) analysis, and high-resolution transmission electron microscopy (TEM). The streaked RHEED patterns of Bi on Sb (or Sb on Bi) with clear Kikuchi lines indicate layer-by-layer growth with good epitaxial layer quality. The narrow XRD rocking curves for the central and the satellite peaks suggest that the interfaces are very sharp and that the superlattice periods do not fluctuate, which is demonstrated in this article by cross-sectional TEM.
Improved GaN growth using a quasihot wall metal-organic chemical vapor epitaxy reactor
Authors: Chung S. R. , Chen J. C. , Worchesky T. L.
Published: July 2002

A systematic study of the growth of GaN was carried out using different metal-organic chemical vapor deposition reactor configurations. The results, as obtained from thickness, mobility, x-ray diffraction, and photoluminescence measurements, indicate that the quasihot wall reactor produces better quality GaN than the conventional reactor. In particular, a high quality GaN epilayer can be obtained with very low ammonia (NH3) flow rates, or low V/III ratios, by using the quasihot wall reactor. These results are discussed in the context of adduct formation and ammonia decomposition upon GaN growth.
Versatile and economical specimen heater for ultrahigh vacuum applications
Authors: Bryant K. W. , Bozack M. J.
Published: July 2002

This note describes a simple, molded, filament-encapsulated specimen heater made from magnesium phosphate base ceramic cement that is compatible with high temperature (>1000 °C) operation in ultrahigh vacuum.
Graphite macroparticle filtering efficiency of three different magnetic filter designs used in the filtered cathodic vacuum arc deposition of tetrahedral amorphous carbon films
Authors: Hakovirta M. , Walter K. C. , Wood B. P. , Nastasi M.
Published: July 2002

The graphite macroparticle filtering efficiency of three different magnetic filter designs (straight duct, toroidal duct, and 90° free-standing solenoid) used in the filtered cathodic vacuum arc deposition of tetrahedral amorphous carbon (ta-C) films was investigated. The particle contents in the coatings were measured using scanning electron microscopy (SEM) technique. In addition, during the ta-C deposition, long time exposure photographs were taken to see the graphite macroparticle trajectories and thus to qualitatively evaluate the filtering performance of different magnetic filters. The particle density measurements from the SEM images show that the filtering efficiency of the 90° free-standing solenoid design is 13 times better than the filtering efficiency of the straight duct design. However, the toroidal duct design had only 3 times higher filtering efficiency compared to the straight duct design.
Establishing the relationship between process, structure, and properties on titanium nitride films deposited by electron cyclotron resonance assisted reactive sputtering. II. A process model
Authors: Carney Carl , Durham Delcie
Published: July 2002

Research has been conducted to investigate ways to make thinner, yet more cohesive TiN films. Physical vapor deposition techniques were used in conjunction with electron cyclotron resonance to deposit TiN films on substrates of Inconel 718. This investigation has focused on the relationship between film deposition parameter interactions, and the resulting film microstructure and mechanical response. Previous parts of this investigation have quantified the differences in Meyer hardness and grain orientation of these deposited TiN films as a function of systematically varied deposition conditions. This part of the research develops a model that explores the connection between deposition conditions, film texture, and mechanical integrity. This model describes the relationship between the triad of (1) deposition conditions, (2) texture metrics that include fractal exponent, crystal orientation, and grain size, and (3) mechanical response, as measured by Meyer hardness and root-mean-square roughness.