bluuebunny/crossref_metadata_2025 huggingface dataset:
Thin film stress from nonspherical substrate bending measurements
Authors: Fahnline D. E. , Masters Christine B. , Salamon N. J.
Published: July 2002

The usual formula for finding thin film deposition stress from the curvature of substrate wafers assumes small out-of-plane deflections and spherical bending. These are significant limitations because deposition stress often produces large deflections and ellipsoidal surfaces ranging from almost spherical to almost cylindrical depending on the film and substrate materials and on the deposition conditions. The present paper examines a nonlinear bending model proposed by Harper and Wu as well as by Masters, Salamon, and Fahnline and its usefulness for calculating deposition stress for both spherical and nonspherical bending. Algebraic solutions of the model predict spherical bending for small deflections and ellipsoidal bending for large deflections even for isotropic films and substrates. An initial experimental test of the nonlinear theory confirms its usefulness with data obtained by measuring the ellipsoidal and spherical curvatures of thin Ta films direct current magnetron deposited on different thickness and size polycarbonate wafers.
Interfacial forces
Authors: Israelachvili Jacob
Published: July 2002

The past few years have witnessed tremendous advances in experimental and theoretical techniques for probing both the static and dynamic properties of surfaces at the ångstrom level. Here we review how these advances have furthered our fundamental understanding of adhesion−particularly those processes that contribute to energy dissipation during adhesion and separation (loading–unloading cycles), and friction−particularly how the dynamic (e.g., viscous and rheological) properties of liquids in ultrathin films differ from the bulk liquid properties, and how this affects the friction forces of lubricated contacts. The emphasis will be on ‘‘ideal’’ surfaces and interfaces, i.e., surfaces that are molecularly smooth, and interfacial films that are no more than a few molecular layers thick.
Frequency effects in silane plasmas for plasma enhanced chemical vapor deposition
Authors: Howling A. A. , Dorier J.-L. , Hollenstein Ch. , Kroll U. , Finger F.
Published: July 2002

It is now generally recognized that the excitation frequency is an important parameter in radio-frequency (rf) plasma-assisted deposition. Very-high-frequency (VHF) silane plasmas (50–100 MHz) have been shown to produce high quality amorphous silicon films up to 20 Å/s [H. Curtins, N. Wyrsch, M. Favre, and A. V. Shah, Plasma Chem. Plasma Processing 7, 267 (1987)], and therefore the aim of this work is to compare the VHF range with the 13.56 MHz industrial frequency in the same reactor. The principal diagnostics used are electrical measurements and a charge coupled device camera for spatially resolved plasma-induced emission with Abel inversion of the plasma image. We present a comparative study of key discharge parameters such as deposition rates, plasma uniformity, ion impact energy, power transfer efficiency, and powder formation for the rf range 13–70 MHz.
Dynamics of ion-assisted etching in the Si(100)/XeF2/Ar+ system on a time scale 100 μs–1000 s
Authors: Joosten G. J. P. , Vugts M. J. M. , Spruijt H. J. , Senhorst H. A. J. , Beijerinck H. C. W.
Published: July 2002

To investigate the reaction layer dynamics of ion-assisted etching we have measured the time response of product formation in an ultrahigh vacuum beam-surface experiment on a time scale ranging from 100 μs to 1000 s. Both the step function response and the delta function response are investigated. For the latter the pseudorandom cross correlation method is used. The system investigated is the classic Si(100)/XeF2/Ar+ example, at low flux conditions of 0.6 ML/s XeF2 and 0.04 ML/s Ar+ ions at 1 keV energy. We observe a consistent picture of the fourfold action of the bombarding ions. First, on a 1 ms time scale and shorter, the release of tightly bound intermediate radical species such as SiF and SiF2 by physical sputtering, i.e., by momentum of the impinging ions, is the main effect. Second, on a time scale of 40 ms, we observe ion-enhanced formation of SiF4, most likely by the influence of ion bombardment on a rate limiting step in the reaction chain such as the formation of SiF4 from SiF3. Third, on a time scale of 4 s, there is a redistribution of intermediate SiFx products in the reaction chain, both in depth profile and in absolute density. Finally, on an even longer time scale, detectable after some 10 s at an ion bombardment of 0.04 ML/s, the production of vacancies and/or broken bonds as reactive sites deep in the substrate becomes important, as observed by a long-term enhanced etch rate after switching off the ion beam. The results are consistent with a model that for low temperatures (T<600 K) the disproportionation reaction, 2 SiF3→SiF4+SiF2, is the rate limiting step, while at high temperatures (T≳700 K) the reaction step leading from SiF2 to SiF3 plays this role.
Outgassing behavior on aluminum surfaces: Water in vacuum systems
Authors: Chen J. R. , Huang J. R. , Hsiung G. Y. , Wu T. Y. , Liu Y. C.
Published: July 2002

Several different effects of water in vacuum systems were studied. An outgassing rate measurement system was used to measure outgassing rates for different venting conditions. Both diffusion and desorption phenomena were observed. The drier the venting gas, the more significant the diffusion behavior. From the pressure buildup tests, it was shown that the increasing H2O partial pressure is much less than that of the other gases. More effective surface pumping for water vapor than for the other gases is thought to be the reason. For the outgassing behaviors mentioned, an effort was made to describe the phenomenon quantitatively by using simple models. In addition to the behavior in the static vacuum, water vapor also shows an interesting behavior in the dynamic vacuum. A few results will be discussed.
Inelastic electron scattering study of metallic oxidation: Synergistic effects involving electrons during the low temperature oxidation of Ni(111)
Authors: Li Wei , Stirniman M. J. , Sibener S. J.
Published: July 2002

Oxygen adsorption and oxide growth on Ni(111) has been investigated at 120 K by high resolution electron energy loss spectroscopy (HREELS). We have found that an electron beam can stimulate nickel oxide growth at all incident electron energies examined, spanning the range from 5 eV to 2 keV. When electron irradiation is absent, oxidation occurs extremely slowly on this surface at low temperatures, resulting in mainly chemisorbed oxygen. We demonstrate that HREELS is capable of simultaneously monitoring oxide growth and characterizing the chemical nature of the oxygen/nickel interface, providing a useful complement to our earlier Auger spectroscopy based study of electron stimulated oxidation of this interface. We propose a model for the observed effect in which electrons create oxide nucleation centers on the Ni(111) surface in the presence of chemisorbed oxygen. This model allows us to quantitatively account for the data, including extraction of the relevant cross sections.
Surface analysis of carbon on ozone treated metals
Authors: Momose T. , Maeda Y. , Asano K. , Ishimaru H.
Published: July 2002

To reduce gas desorption, especially dynamic gas desorption, of ultrahigh vacuum materials, it is necessary to reduce carbon on the surface and in the rear surface layer which deteriorates dynamic gas desorption coefficient. To eliminate carbon, an ozone treatment was applied to metal surfaces. The surfaces of aluminum, copper, and stainless steel without any treatment were exposed to 250 ppm ozone using air with flow rates of 1 ℓ/min for 24 or 48 hours. The samples were shown to decrease carbon levels, especially on Cu and Al surfaces, as detected by Auger electron spectroscopy (AES). In addition, no carbon was detected in the rear surface layers as detected by sputter profiling. The detectability of AES is on the order of 10−2 monolayers or approximately 3×1013 carbon atoms/cm2. The thickness of the oxidized layer was 6.3, 8.1, and 3.0 times the native oxide layer for Cu (120 Å), Al (170 Å), and stainless steel (60 Å), respectively. X-ray photoelectron spectroscopy shows (1) the ratio (O/Al) is 1.5 for the treated and 1.4 for the nontreated samples; (2) 24 at. % of Cu2+ is included in the treated but 78 at. % of Cu and Cu+ for the nontreated samples; (3) the oxide component excluding hydroxide is 29 at. % for the treated and 3 at. % for nontreated samples. The treated surfaces show low carbon adsorption characteristics: little carbon was detected by AES on copper and aluminum treated surfaces stored in a covered glass dish for more than four days and on an ozonized copper surface stored in aluminum foil for more than 100 days.
Spatiotemporal powder formation and trapping in radio frequency silane plasmas using two-dimensional polarization-sensitive laser scattering
Authors: Dorier J.-L. , Hollenstein Ch. , Howling A. A.
Published: July 2002

Powder formation studies in deposition plasmas are motivated by the need to reduce contamination in plasma and films. Models of the forces acting upon particles in radio frequency (rf) discharges suffer from a lack of quantitative experimental data to which to compare in the case of silane-containing plasmas. In this work, a cross section of the parallel-plate capacitor discharge is illuminated by a polarized beam-expanded laser, and global spatiotemporal scattered light and extinction are recorded by charge-coupled device cameras. Spatially regular periodic bright/dark zones due to constructive/destructive Mie interference are visible over large regions of the powder layers, which shows the uniform nature of particle growth in silane plasmas. For particles trapped in an argon plasma, and for steady-state conditions in silane, spatial size segregation is demonstrated by fringes that reverse according to the polarization of scattered light. The method allows a self-consistent estimation of particle size and number density throughout the discharge volume from which strong particle Coulomb coupling (Γ≳40) is suggested as influencing powder dynamics. An adjustment to the plasma emission profile must be made for extinction by the powder. This global diagnostic improves the understanding of particle growth and dynamics in silane rf discharges and provides experimental input for testing the validity of models.
Alpha-particle gas-pressure sensor
Authors: Buehler M. G. , Bell L. D. , Hecht M. H.
Published: July 2002

An approximate model was developed to establish design curves for the saturation region and a more complete model developed to characterize the current–voltage curves for an alpha-particle pressure sensor. A simple two-parameter current–voltage expression was developed to describe the dependence of the ion current on pressure. The parameters are the saturation-current pressure coefficient and μ/D, the ion mobility/diffusion coefficient. The sensor is useful in the pressure range between 0.1 and 1000 mb using a 1-μCi 241Am source. Experimental results, taken between 1 and up to 200 mb, show the sensor operates with an anode voltage of 5 V and a sensitivity of 20 fA/mb in nitrogen.
Enhanced ignition of cold cathode gauges through the use of radioactive isotopes
Authors: Welch K. M. , Smart L. A. , Todd R. J.
Published: July 2002

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory comprises vacuum systems that range in pressure from 10−4 to 10−11 Torr. For cost savings associated with commonality, it is desirable to use one ultrahigh vacuum (UHV)-compatible high vacuum gauge throughout the accelerator. Work was done with radioactive isotopes to enhance ignition of inverted magnetron gauges at very low pressures (i.e., <10−10 Torr). Tests were initially conducted using cobalt-coated copper washers with a nickel flash to prevent oxidation. Solid nickel washers were also activated and tested. Problems with these sources will be discussed. Finally, an americium source was tested. The UHV-compatible americium sources yielded average ignition times of about 10 min at 4×10−11 Torr. The addition of the americium source produced a gauge suitable for operation at UHV pressures, and as a consequence for all of the RHIC.
Correlation of antenna charging and gate oxide reliability
Authors: Gabriel Calvin T. , Nariani Subhash R.
Published: July 2002

Antenna structures are commonly used to study charging, and the resultant metal–oxide–semiconductor gate oxide damage, from plasma processing. Degradation of various device parameters, such as gate leakage and threshold voltage, have been correlated with high levels of charging. However, there has been little work done to correlate charging with reduced device reliability. In this study, we use antenna structures and accelerated life testing of application specific integrated circuit devices on the same wafers to show that oxide damage from charging measured by antennas does not necessarily correlate with reliability degradation. Depending on how the antenna is designed, the measured oxide damage results from a combination of process-induced charging and initial gate oxide quality. When initial oxide quality is high, then charging which does not degrade oxide reliability can occur. However, for initially defective oxide, the same process-induced charging can degrade reliability. As shown in this study, the key to distinguishing between the two is in the antenna design. Failures of simple antenna structures having a large antenna area ratio and small gate oxide area did not correlate with degraded oxide reliability. However, failures of antenna test structures having a relatively small antenna area ratio and a relatively large gate oxide area did correlate with reliability, probably by highlighting pre-existing defects in the gate oxide which induced the early reliability failures. Together, these two types of antenna structures can help differentiate between excessive plasma damage and intrinsic weakness in the gate oxide.
Dynamics and structure of chemisorbed CO on Cu(110): An electron-stimulated desorption ion angular distribution study
Authors: Ahner Joachim , Mocuta Dan , Ramsier R. D. , Yates John T.
Published: July 2002

The adsorption of CO on a Cu(110) surface has been studied in the temperature range between 32 K and 200 K by the ESDIAD (electron-stimulated desorption ion angular distribution) technique. Here a desorbing neutral excited CO* species is spatially imaged. At coverages up to θ=0.2, a pronounced anisotropy in the librational motion of CO adsorbed in the atop configuration has been observed. The higher amplitude of libration is along the copper atom rows ([11̄0]-direction). Large changes in the observed CO* pattern in the low temperature range between 32 K and 70 K give an indication of a shallow potential well and the thermal population of the higher librational levels. With increasing CO coverage three distinct ESDIAD patterns are observed. Starting from a single normal beam with an elliptical cross-section having the major axis in the [11̄0]-direction for coverages up to 0.2 monolayer (ML), a transformation of the ESDIAD pattern into two separated beams is observed for a coverage of about 0.5 ML, indicating a tilting of the molecules in the [11̄0]-directions. With further CO coverage increase, an additional central beam grows with a slight elliptical broadening in the [001]-direction. Based on ESDIAD and digital low-energy electron diffraction measurements, a linear-chain model for CO adsorption on atop sites of Cu(110) is proposed.
Surface chemistry study of water vapor and oxygen on Ni3(Al, Ti)(100) and Ni3Fe surfaces
Authors: Chia W. J. , Chung Y. W.
Published: July 2002

The interaction of water vapor with the Ni3(Al, Ti)(100) and polycrystalline Ni3Fe surfaces, with and without the presence of oxygen, was studied with Auger electron spectroscopy, photoemission, thermal desorption, and isotope scavenging. Water dissociates to produce atomic hydrogen above 200 K on the Ni3Fe surface. Preadsorbed or coadsorbed oxygen on both Ni3(Al, Ti) and Ni3Fe surfaces suppresses hydrogen production due to water dissociation. This suppression process occurs more efficiently on Ni3Fe than Ni3(Al, Ti).
First-principles calculations of the atomic and electronic structure of the Sb–Ge(111)(2×1) surface
Authors: Takeuchi Noboru
Published: July 2002

We perform first-principles calculations to determine the atomic and electronic properties of the Sb–Ge(111)(2×1) surface. The Sb atoms are located on top positions forming zigzag chains. In agreement with x-ray diffraction experiments, we found that the substrate Ge lattice exhibits only small distortions, and the Sb chain is slightly tilted. Structural parameters are in excellent agreement with x-ray diffraction, x-ray standing waves, and surface extended x-ray absorption fine structure experiments.
X-ray photoelectron spectroscopy investigations of the interaction of cells with pathogenic asbestoses
Authors: Seal S. , Krezoski S. , Petering D. , Barr T. L. , Klinowski J. , Evans P.
Published: July 2002

Recently we have expanded our chemical characterization of complex silicates (e.g., amphiboles and sheet silicates) to include their interactions with select biocells. In this regard we are beginning to simulate features related to certain infamous, and still not completely understood, deleterious environmental maladies, such as silicosis and asbestosis. It has been recognized that the surfaces of the silicates and interfaces with the cells may play particularly active roles in these processes, thus leading to the need for x-ray photoelectron spectroscopy (XPS) investigations of the surface chemistry. The present research describes examinations of the interactive chemistry of rat tumor cells grown on various asbestoses, before, during, and after interaction, followed by both cell/silicate separation and unique freeze drying. The former permits separate analysis of the two systems, while the latter documents features induced during the separation process. Aspects detected by XPS include some of the features of the cells, plus the cell induced alterations in the Si, Mg, and Fe chemistry of the silicates and also changes in the relative amount and chemistry of the cellular iron. The latter studies were confirmed by atomic absorption spectroscopy. Supporting results have also been achieved with Fourier transform infrared spectroscopy. The various XPS shift patterns are shown to be consistent with differences between the different silicates, e.g., amphiboles such as cummingtonite, both before and after reaction with similar rat cells. These unique investigations may eventually lead to suggestions for general mechanisms for these environmentally induced diseases.
Patterned self-assembled monolayers of ferrocene and methyl terminated alkanethiols on gold: A combined electrochemical, scanning probe microscopy, and surface science study
Authors: Bar G. , Rubin S. , Taylor T. N. , Swanson B. I. , Zawodzinski T. A. , Chow J. T. , Ferraris J. P.
Published: July 2002

We prepared patterned self-assembled monolayers (SAMs) consisting of hexadecanethiol (16AT) and ferrocenyldodecanethiol (12FAT). The samples were characterized by scanning electron microscopy, lateral force microscopy (LFM), Auger electron spectroscopy, x-ray photoelectron spectroscopy (XPS), electrochemistry and contact angle measurements. LFM images exhibit contrast even between surface regions of quite similar hydrophobicity. The 12FAT regions undergo irreversible chemical changes and become electrochemically inactive upon long exposure to the laboratory atmosphere. These chemical changes can be monitored by LFM, XPS, contact angle measurements and electrochemistry. The LFM images of the exposed and contaminated samples show a reversed frictional contrast relative to the LFM images of the fresh samples and to the LFM images of the exposed but ethanol-rinsed sample. Based on these observations, the mechanism of the LFM image contrast is discussed and other driving forces, arising not only from differences in hydrophobicity, but also from basic material properties such as elasticity, packing and contamination, are suggested.
Molecular beam epitaxy growth and characterization of GaN and AlxGa1−xN on 6H-SiC
Authors: Sinharoy S. , Augustine G. , Rowland L. B. , Agarwal A. K. , Messham R. L. , Driver M. C. , Hopkins R. H.
Published: July 2002

We have investigated the growth of undoped and doped GaN and AlGaN films on both on-axis and 3.5° off-axis 6H-SiC substrates. Scanning electron microscopy showed that the films were smooth and crack free. The typical x-ray rocking curve half-width of the GaN (0002) peak using Cu Kα x rays was found to be between 9 and 15 arcmin for a 1 μm film. The crystalline quality improved with increasing thickness. The best films were obtained at the highest growth temperature (800 °C) with a 40–50 nm AlN buffer layer grown at the same temperature. The n-type doping up to 4.0×1020 cm3 was accomplished with silicon, with a 40%–50% activation rate. A calibration curve correlating the n-type carrier concentration in the film with the Si effusion cell temperature was established. The undoped AlxGa1−xN film (x≊0.1) was found to be n type, with a carrier concentration of 7.0×1018/cm3.
Characterization of ultrathin SiO2 films grown by rapid thermal oxidation
Authors: Hu Y. Z. , Tay S. P. , Wasserman Y. , Zhao C. Y. , Hebert K. J. , Irene E. A.
Published: July 2002

The time-temperature product during gate dielectric formation is very important in controlling the extent of vertical diffusion profiles in active devices as well as the extent of lateral diffusion in traditional isolation schemes. Rapid thermal oxidation (RTO) appears to be an attractive processes for use in the fabrication of ultrathin SiO2 films. Ultrathin film metrology requirements continue to increase as device features shrink below 0.35 μm. Subangstrom 3σ-measurement performance on gate oxides is required for 64 Mbit to 1 Gbit dynamic random access memory and high performance microprocessors. Precision single wavelength ellipsometry (SWE) has been used to measure the values of Δ and Ψ for ultrathin RTO films. We employ Fowler–Nordheim (FN) tunneling current oscillations as an independent method for determining ultrathin film thicknesses. Combining the Δ and Ψ values from SWE and the thickness from FN, a value of the pseudorefractive index of 1.894 at a wavelength of 632.8 nm is used to determine oxide thickness in the ultrathin film regime. Multiple wavelength spectroscopic ellipsometry in the photon energy range of 2.0–5.0 eV using the Bruggeman effective medium approximation has shown that the best fit optical model is a two layer model: pure oxide and interface layer. A comparison of these techniques is discussed and presented in this article.
Carbon contamination in an etching reactor using electron cyclotron resonance plasma and the effect of a N2 addition
Authors: Miwa Kazuhiro , Aoyama Masaaki , Higuchi Kenichi , Inoue Minoru , Kojiri Hidehiro , Nagase Kunihiko
Published: July 2002

In a TiN etching process using electron cyclotron resonance (ECR) plasma of BCl3 and Cl2 gas mixture, the decline of TiN etch rate was observed after the erosion of the photoresist surface with the ECR plasma, but we could prevent the decline by the addition of N2 to the etching gas mixture. Carbon was detected by x-ray photoelectron spectroscopy (XPS) on the TiN surface (on which there was no photoresist) etched in the reactor with the ECR plasma after the erosion of the photoresist. The TiN surface was contaminated by carbon in the reactor during the etching process. N2 gas was added to reduce carbon contamination. In fact, after the photoresist was eroded with the N2 added ECR plasma, carbon was hardly detected by the XPS on the sample surface etched in the reactor and the TiN etch rate did not decline. Therefore, we concluded that carbon contamination on the TiN surface originated from the erosion of the photoresist with the ECR plasma causing the decline of the TiN etch rate. The effect of N2 addition must be attributed to the reaction between nitrogen radical in the N2 added ECR plasma and carbon in the reactor.
Femtosecond photoemission study of electron relaxation in two-dimensional layered electron systems
Authors: Xu S. , Miller C. C. , Cao J. , Mantell D. A. , Mason M. G. , Muenter A. A. , Parkinson B. A. , Miller R. J. D. , Gao Y.
Published: July 2002

By using the femtosecond two photon photoemission technique, we directly measured the lifetimes of photoexcited electrons in two layered materials, graphite and SnS2. The inverse lifetimes of photoexcited electrons in these two-dimensional layered materials exhibit linear energy dependence, i.e., 1/τ∝(E−EF), instead of quadratic, i.e., 1/τ∝(E−EF)2 as predicted by Fermi liquid theory. This can be explained with the layered electron gas theory, according to which the electron-plasmon interaction is strong, even for electrons at low excitation energies, due to the formation of plasmon band in layered electron systems. Furthermore, our observations in SnS2 also suggest that in layered semiconductors, photogenerated electron-hole pairs will recombine directly by emitting plasmons, and this causes the lifetimes of the conduction band electrons to be much shorter than those in three-dimensional semiconductors.
Transmission electron microscopy study of granular Fe–Mg films made by gas evaporation
Authors: Meng-Burany X. , Phillips J. , Hadjipanayis G.
Published: July 2002

Fe–Mg granular films with different Fe content were made using thermal evaporation. It is found that the Fe content, the magnetic properties, and microstructures of the Fe–Mg films vary with the amount of argon pressure used during the evaporation. The highest coercivity, Hc, was obtained in a film with about 60 wt % Fe, containing Fe particles with a size 13–15 nm. In all the films examined, Fe nanoparticles with a size of a few to 20 nm were observed to lay on Mg layered crystals which were as large as hundreds of nanometers.
Atomic-level investigation of the growth of Si/Ge by ultrahigh vacuum chemical vapor deposition
Authors: Lin D.-S. , Miller T. , Chiang T.-C.
Published: July 2002

Si and Ge films can be prepared under ultrahigh vacuum conditions by chemical vapor deposition using disilane and digermane as source gases. These gases offer a high sticking probability, and are suitable for atomic layer epitaxy. Using synchrotron radiation photoemission spectroscopy and scanning tunneling microscopy, we have examined the surface processes associated with the heteroepitaxial growth of Ge/Si. The measured surface-induced shifts and chemical shifts of the Si 2p and Ge 3d core levels allow us to identify the surface species and to determine the surface chemical composition, and this information is correlated with the atomic features observed by scanning tunneling microscopy. Issues related to precursor dissociation, attachment to dangling bonds, diffusion, surface segregation, growth morphology, and pyrolytic reaction pathways will be discussed.
Scanning tunneling microscope study of Sb/Si(111)-53×53 structure
Authors: Park Kang-Ho , Ha Jeong Sook , Yun Wan Soo , Lee El-Hang , Yi Jae-Yel , Park Seong-Ju
Published: July 2002

We have investigated Sb overlayer structures on Si(111) with low energy electron diffraction and scanning tunneling microscope (STM). The Sb/Si(111)-53×53 structure was constructed via the desorption of Sb from the saturated 2×1 surface at elevated temperature (700–750 °C). Its atomic structure and formation process were extensively studied with STM images, considering the structural stability. This Sb structure could be described in terms of the site selective replacement of outermost Si atoms with Sb atoms in the dimer-adatom-stacking fault 5×5 structure, which is generated by both the saturation of dangling bonds and strain due to the large lattice mismatch.
Study of poly(ether sulfone)/metal interfaces by high energy x-ray photoelectron spectroscopy and x-ray absorption spectroscopy
Authors: Tegen N. , Morton S. A. , Watts J. F.
Published: July 2002

The metallization of high-temperature polymers like poly(ether sulfone) (PES) is important, especially for microelectronic purposes. The adhesion of metals to these polymers can be greatly improved by using ion implantation. The low ion doses required to improve adhesion, however, make it difficult to determine the mechanism of the adhesion enhancement. This work studies the buried interfaces of ion implanted and as-deposited metal films (Al, Fe, and Cu) on PES. The U.K. Synchrotron Radiation Source at Daresbury Laboratory was used to provide tuneable photon energies in the range of 2100 eV up to 4600 eV. Thus, the interface can be probed to greater depth than usual without being destroyed by peeling or sputter profiling. Adhesion improvement as measured by mechanical testing can, thus, be linked to the chemical changes occurring at the interface of the system. These findings are complemented by additional x-ray absorption spectroscopy (NEXAFS studies) of spincoated PES films. These experiments are designed to give a deeper understanding of the interaction of individual metal atoms with the polymer surface.
Electrical-stress simulation of plasma-damage to submicron metal–oxide–silicon field-effect transistors: Comparison between direct current and alternating current stresses
Authors: Trabzon L. , Awadelkarim O. O.
Published: July 2002

The study reported herein is aimed at establishing signatures of metal–oxide–silicon field-effect transistors (MOSFETs) damage induced by alternating current (ac) stressing applied at conditions that simulate plasma processing environment and the comparison of the ac stress induced damage to damage from an equivalent direct current (dc) stress. We also examine the response of stress induced damage to annealing that emulates postmetallization annealing in complementary metal–oxide–silicon processing. We apply sinusoidal and dc voltage stress signals to 0.5 μm n- or p-MOSFETs with 90-Å-thick gate oxides and anneal the stressed transistors in forming gas ambient (6% H2 and 94% N2) at 400 °C for 30 min. We assess damage on MOSFETs by measuring transconductance, threshold voltage, and subthreshold swing. We find out that the onset of damage to devices subjected to ac stressing occurs at voltage amplitudes as low as 6 V, whereas in dc stressing damage becomes significant only at voltages larger than 10 V. We also show that the forming gas annealing is able to eliminate both types of damage and recover transistor characteristics. It is proposed that carrier hopping is primarily responsible for oxide current and, hence, device damage observed following the ac stress in contrast to Fowler–Nordheim tunneling current which causes the damage produced by our dc stress.
Operational experience of novel vacuum chambers incorporating massive titanium-sublimation pumping in the Cornell electron–positron storage ring interaction region
Authors: Kersevan Roberto , Li Yulin , Mistry Nariman B.
Published: July 2002

New vacuum chambers have recently been installed in the interaction region of the Cornell electron-positron storage ring (CESR) in order to improve the pumping and reduce the operating pressure of the collider in the vicinity of the (CLEO) detector as the beam currents are increased by a large factor. Lost-particles generated by the beams interacting with the residual gas are a major source of background in CLEO and could lead to radiation damage of sensitive components such as the new silicon vertex detector electronics installed around a two-centimeter radius beryllium beampipe. This article shows how titanium-sublimation pumps are used as an inexpensive and efficient way to attain pressures in the low nanotorr range in the face of large outgassing induced by intense synchrotron radiation. Laboratory measurements of pumping speed in these chambers using calibrated leaks are compared against performance in the ring. A history of the dynamic pressure rise in the ring (Torr/mA) since the most recent start-up of CESR will also be shown.
Cold cathode gauges for ultrahigh vacuum measurements
Authors: Kendall B. R. F. , Drubetsky E.
Published: July 2002

Nine cold cathode gauges have been evaluated on ion-pumped ultrahigh vacuum systems operating at pressures down to the 10−11 Torr range. The test gauges included magnetrons, inverted magnetrons, and double inverted magnetrons from four different manufacturers as well as experimental variable-geometry gauges built especially for this project. Spinning-rotor and extractor gauges were used for calibration. The investigation covered repeated calibration over the 10−10 to 10−4 Torr range, stability over periods of up to 35 000 h of low pressure operation, tests for discontinuities in the current-pressure characteristics, stray magnetic field measurements, susceptibility to external magnetic fields, outgassing effects, and starting behavior at very low pressures. Our conclusion is that modern cold-cathode gauges are capable of giving far more accurate results than were possible with earlier Penning-type designs. Because of their extremely low outgassing rates, and their relative freedom from x-ray and electron stimulated desorption errors, they may in practice give results at low pressures which are more accurate than those obtained with typical hot-cathode gauges.
Plasma fluorination of polyimide thin films
Authors: Endo Kazuhiko , Tatsumi Toru
Published: July 2002

The surface of polyimide films was fluorinated and a CF3 surface layer formed. The dielectric constant of the polyimide films decreased to a minimum of 2.5 as the treatment time increased. The leakage current of the polyimide films was also decreased significantly by the fluorination. The measurement of electrical properties and secondary ion mass spectroscopy revealed that the fluorine atoms diffused into the polyimide films from the fluorinated surface layer. The current–voltage characteristics indicated that reduction in the leakage current was due to fewer ionic impurities. This confirms that the fluorine diffused into the polyimide and it eliminated impurity ions.
Improved growth and thermal stability of Parylene films
Authors: Ganguli Seshadri , Agrawal Hemant , Wang Bin , McDonald Jack F. , Lu Toh -M. , Yang G.-R. , Gill William N.
Published: July 2002

Experimental results for the deposition of low dielectric constant Parylene-N and Parylene-F films are explained by a mechanism based on bulk phase diffusion reaction in the film. The deposition rate of Parylene-F decreases significantly as time increases and ultimately achieves steady state. Very favorable agreement with experiments at a substrate temperature of −10 °C is obtained for parylene-F with a rate constant of kf=5×10−5/s, and a diffusion coefficient Df=1.3×10−8 cm2/s. In contrast, the much higher rate constant at room temperature for Parylene-N films is kf=0.16/s and the predicted deposition rate is constant after a very small period of time (tss<4/kf=25 s). This prediction is confirmed by the experiments. The model predicts correctly that low deposition temperatures improve both the deposition rate and thermal stability of Parylene films. Our experiments confirm this prediction and one obtains both high growth rates and high molecular weight films at lower deposition temperatures. Furthermore, experiments show that the longer chains formed at low temperatures significantly improve the thermal stability of the films. The deposition rate also can be improved by using higher reactor pressures. However, the pressure that can be employed is limited to about 100 mTorr to maintain high quality films. At liquid nitrogen temperature (77 K), the deposition rate is three orders of magnitude larger than the film deposition rate at room temperature. The increased monomer concentration on the substrate due to higher condensation leads to this increased deposition rate.
Electron stimulated desorption study of the MgO(100)–D2O system
Authors: Colera I. , González R. , Soria E. , de Segovia J. L. , Román E. L. , Chen Y.
Published: July 2002

A study of the MgO(100)–D2O system at 300 K by electron stimulated desorption (ESD) over the energy range up to 600 eV is presented. Auger electron spectroscopy is used as a complementary technique. ESD of the nearly perfect clean surface shows O+ desorbed ions as the main desorbed species with small amounts of H+ and F+ contaminants. The adsorption of D2O produces a dramatic decrease of the O+ intensity in the ESD spectrum and new signals corresponding to D+ and OD+ ions are observed. There is a first energy threshold at about 30 eV for D+ and H+ desorbed ions and a second one at 55 eV for O+ desorbed ions. The desorption of these ions corresponds to a primary excitation of the O 2s (24 eV) and Mg 2p (55 eV) core levels, respectively. The ion kinetic energy distribution of the desorbed O+ ion from the clean surface has two peaks at energies of 6 and 9 eV. The ion kinetic energy distribution of the D+ desorbed ions also shows a bimodal structure with most probable kinetic energies of 3 and 6.5 eV at 150 eV incident electron energy. The ion kinetic energy distribution of the H+ desorbed ions from the H contamination correlates quite well with that of the D+ desorbed ions both in shape and in energy. The most probable kinetic energy of the OD+ is about 3 eV. From these experiments, we propose an adsorption model with the D2O dissociated as OD+D. The D species bonds to O surface ions to form OsurfD radicals, and the OD species bonds to Mg surface ions. Since the experiments were performed at D2O constant pressure there is a large increase of the D+ intensity due to ESD of the D from OD species. The final equilibrium of the adsorbed species is a consequence of the D2O adsorption and ESD desorption rates.
Characterizing flat panel display materials using quadrupole-based secondary ion mass spectrometry
Authors: Novak Steven W.
Published: July 2002

We have successfully used quadrupole-based secondary ion mass spectrometry (SIMS) to address numerous problems in flat panel display materials. This technique is well suited to address certain problems with these materials because of its combination of sensitivity, spatial resolution, and especially the ability to depth profile dielectric layers and structures on glass substrates. Measuring Na or other alkali element diffusion into layers deposited on glass substrates is difficult by SIMS because small amounts of charge buildup on the sample surface can cause rapid migration of the alkalis within the layers. We have developed an analysis protocol that minimizes migration of Na within SiO2 layers and will show some results of utilizing this technique for examining alkali element distributions in SiO2 and In–Sn oxide layers deposited on glass. We have also used O bombardment to measure Tb doping in electroluminescent ZnS display material. Using Cs bombardment we can analyze H, C, O, and N impurities in amorphous and crystalline silicon thin film transistor structures on glass substrates. The combination of low energy Cs bombardment at high incidence angles and an ultrahigh vacuum chamber yield low detection limits for these elements with excellent depth resolution. We have also used Cs bombardment to measure ion-implanted O and F distributions in electroluminescent ZnS. These elements have been investigated as charge compensators for Mn and Tb doping. SIMS offers a means to precisely calibrate the amounts of dopants within the electroluminescent layer.
Structural and optical properties of alkali halide multilayer LiF:NaF films
Authors: Somma F. , Montereali R. M. , Santucci S. , Lozzi L. , Passacantando M. , Cremona M. , Mauricio M. H. P. , Nunes R. A.
Published: July 2002

Alkali halide multilayer films containing a large concentration of color centers created by low energy (3–12 keV) electron beams in a thin dielectric layer of controlled depth, represent a good and simple way to obtain new optically active materials. This work presents a study of multilayer LiF:NaF films, grown by physical evaporation. The structural and morphological characterization of the samples have been performed using x-ray diffraction, scanning electron microscopy, atomic force microscopy, and x-ray photoemission spectroscopy depth profile techniques. The visible photoluminescence of optically active defects was measured by excitation with an Argon laser. Controlling the deposition and coloration parameters it is possible to obtain new photoluminescent materials with predesigned optical features.
Novel simple and complementary metal-oxide-semiconductor-compatible membrane release design and process for thermal sensors
Authors: Leclerc Stéphane , Antaki Robert , Currie John F.
Published: July 2002

A novel approach to the design and fabrication of released membrane thermal sensors has been developed. Its advantages are to facilitate processing over the suspended membranes after their liberation, and to allow the design of 1 μm to 100’s of μm deep cavities under the membrane. It consists in sacrificial etching of a layer up to an open silicon area hidden under the membrane, followed by front-side bulk micromachining of silicon under the membrane, to the depth desired. This approach is compatible to complementary metal-oxide-semiconductor commercial fabrication, and only needs one protective coarse lithography step and a few etching without alignment. This approach may be used in the fabrication of low temperature heated membrane gas sensors and thermal pressure sensors, as of thermal sensors in general, since thermal isolation may be optimized to high values.
Composition control by current modulation in dc-reactive sputtering
Authors: Nyberg T. , Nender C. , Berg S.
Published: July 2002

Control of the reactive sputtering process can be carried out by controlling either the flow of the reactive gas or the power supplied to the target. In the flow control mode it is well known that the reactive sputter deposition process exhibits a pronounced hysteresis effect. In this article we show that such a behavior is also observed in the power supply control mode. It is normally not possible to obtain stable operation of the system inside the hysteresis region. To achieve this, a feedback control system has to be used. In this way films with arbitrary compositions can be fabricated. Intermediate compositions, however, can also be obtained by varying the power fed to the sputtering target. Variation in film composition can be obtained by repeatedly switching the target power so that the process switches between the metal- and compound-sputtering modes. With this approach, it is possible to obtain any arbitrary stoichiometry of the film by choosing the correct ratio between the time in the metal mode and the time in the compound mode. In this article we present the physical background as well as experimental findings concerning operation in the power control mode.
Numerical study on near field imaging of fluorescence decay of near-surface molecule cluster
Authors: Xiao Mufei
Published: July 2002

We apply a recently established rigorous field propagator formalism to solve the electromagnetic radiation from a cluster of molecules, treated as point dipoles, near a metallic surface. For a given dipole lifetime in free space, we describe numerically the fluorescence decay of the molecules. Two-dimensional optical near field images above a group of random distributed near-surface molecules are presented at different moments during the decay. Complications and possible enhancements in the images are demonstrated and discussed.
Valence band x-ray photoelectron spectroscopic investigation of surface cleanliness of aluminum metal and its alloys
Authors: Havercroft Nathan J. , Sherwood Peter M. A.
Published: July 2002

Aluminum and its alloys are used in many practical situations. The surface preparation and treatment of these materials can significantly impact their practical applications. This article presents valence band and core x-ray photoelectron spectroscopy (XPS) data on these materials, showing in particular how the valence band region can provide an indication of differences in surface composition unobtainable in the core XPS region, or by other surface analytical probes. Surface chemistry is often vital to certain industrial applications. In this article the surface chemistry of stearate based lubricants is discussed, and the changes in the surface chemistry that results when these lubricants are applied to aluminum metal and alloy surfaces is discussed. It is possible to interpret the valence band region by comparison with spectra calculated from molecular orbital calculations, and it can be seen that stearic acid and stearates have a very characteristic valence band. The lubricants can be seen to tenaciously hold onto the surface of metal and alloys after application.
A numerical simulation of the evolution of nanometer-scale surface topography generated by ion milling
Authors: Winningham Thomas A. , Zou Zhong , Douglas Kenneth , Clark Noel A.
Published: July 2002

Ion milling has been used to transfer the nanometer scale, periodic pattern of a protein crystal (“S-layer”) into the supporting substrate. At the same time, etch pits, attributable to the presence of surface contamination, evolve in random areas of the substrate not covered by the S-layer (“off-S-layer”). Using the theory of ripple topography proposed by Bradley and Harper, a computer simulation of hole formation based on curvature dependent sputtering and surface self-diffusion has been formulated. To determine the validity of this model as applied to the patterning process, profiles of actual etch pits have been obtained using atomic force microscopy, and the simulation has been used to evolve these profiles in time. Even with a number of simplifying assumptions in place, the model simulates the experimental data quite well.
Measurements of epitaxially grown Pt/CaF2/Si(111) structures by ballistic electron emission microscopy and scanning tunneling microscopy
Authors: LaBella V. P. , Shusterman Y. , Schowalter L. J. , Ventrice C. A.
Published: July 2002

The hot electron transport properties and growth morphology of ultrathin Pt/CaF2/Si(111) metal-insulator-semiconductor structures have been characterized in situ by ballistic electron emission microscopy (BEEM) and scanning tunneling microscopy (STM). Platinum thicknesses from submonolayer to 50 Å and CaF2 thicknesses from 2 to 10 ML have been characterized. The STM images of the Pt/CaF2/Si(111) structures show the atomic steps of the underlying CaF2 morphology, as well as the formation of Pt nodules, which nucleate at step edges and defect sites. Some BEEM spectra show an anomalous peak near 2 eV, which has not been observed in previous studies of other metal/CaF2/Si(111) structures. The localized nature of this peak indicates that it results from an interaction between the ballistic electrons and fluorine vacancies at the Pt–CaF2 interface.
Analysis of B–SiO2 films by highly charged ion based time-of-flight secondary ion mass spectrometry and elastic recoil detection
Authors: Schenkel T. , Hamza A. V. , Barnes A. V. , Schneider D. H. , Walsh D. S. , Doyle B. L.
Published: July 2002

B–SiO 2 films formed by chemical vapor deposition on silicon substrates were analyzed by time-of-flight secondary ion mass spectrometry using slow Xe44+ and Th70+ as primary ions. Boron concentrations of 2×1021 cm−3 determined directly from positive secondary ion spectra agree with results from elastic recoil detection measurements, indicating strong decoupling of positive secondary ion production probabilities from elemental ionization potentials in the intense electronic sputtering induced by highly charged ions. Results demonstrate advantages of highly charged ions for quantitative analysis of surface near layers of materials.