Volume 18, Issue 4, July 2000
- papers from the 46th national symposium of the american vacuum society
- applied surface science ii
- biomaterial interfaces
- electronic materials and processing
- electronic materials and processing i
- electronic materials and processing ii
- flat panel displays
- magnetic interfaces and nanostructures
- manufacturing science and technology
- nanometer-scale science and technology
- nanometer-scale science and technology i
- nanometer-scale science and technology ii
- plasma science and technology
- plasma science and technology i
- plasma science and technology ii
- surface science
- surface science i
- surface science ii
- surface science iii
- thin films
- vacuum metallurgy
- vacuum technology
- applied surface science/magnetic interfaces and nanostructures/vacuum metallurgy
- flat panel displays/vacuum technology
- flat panel displays/organic electronic materials/electronic materials and processing
- magnetic interfaces and nano structures/electronic materials and processing
- magnetic interfaces and nanostructures/nanometer-scale science and technology
- micro-electro-mechanical systems/magnetic interfaces and nanostructures
- manufacturing science and technology/plasma science and technology
- emerging opportunities and issues in nanotubes and nanoelectrics/...
- organic electronic materials/electronic materials and processing/applied surface science
- plasma science and technology/surface science
- surface science 1/electronic materials and processing
- surface science 2/electronic materials and processing/nanometer-scale science and technology
- surface science 3/electronic materials and processing
- thin films/vacuum metallurgy
- thin films/micro-electro-mechanical systems
- vacuum metallurgy/thin films
- vacuum metallurgy/magnetic interfaces and nanostructures/applied surface science
Index of content:
- PAPERS FROM THE 46TH NATIONAL SYMPOSIUM OF THE AMERICAN VACUUM SOCIETY
- APPLIED SURFACE SCIENCE
18(2000); http://dx.doi.org/10.1116/1.582472View Description Hide Description
Capacitance due to geometric influence of the finite tip shape and influence of distant surface points can lead to artifacts in scanning Kelvin probe microscopy (SKPM) images. These artifacts appear as features in the SKPM image which are due only to tip/surface geometry and not to true surface potential variations. They can also cause blurring of real features. Such effects are most prominent for samples with rich topography. We present here a method for identifying and removing these artifacts, and demonstrate it for a gold sample with rich topography relative to the nearly flat surface potential fluctuations.
Secondary ion mass spectrometry and x-ray photoelectron spectroscopy correlation study of nitrided gate oxide18(2000); http://dx.doi.org/10.1116/1.582299View Description Hide Description
Reliability of dielectric films such as silicon dioxide in the metal–oxide semiconductor gate insulator has become a key issue as devices shrink in size. Many of the problems associated with reduction in both the width and thickness of the gate oxide can be controlled with the addition of nitrogen. Nitrogen incorporation into the oxide has been shown to have significantly better charge trapping properties, less interface state generation, and more resistance to continued oxidation and incorporation of impurities. The nitrogen also acts as a barrier to diffusion of dopants from the silicon substrate. The amount of nitrogen present and its location in the oxide control the extent to which each of these properties is exhibited. The concentration and distribution of nitrogen in gate oxides was studied using secondary ion mass spectrometry(SIMS) and x-ray photoelectron spectroscopy(XPS). The SIMS analysis used Cs ion bombardment and detection of the cluster to reduce the matrix effects associated with profiling from silicon oxide into silicon. A procedure was developed for XPS to provide the necessary signal to noise required for these low nitrogen concentrations. In addition to comparing the concentrations and spatial resolution of the nitrogen in the gate oxide, repeatability studies were also performed for each technique.
18(2000); http://dx.doi.org/10.1116/1.582300View Description Hide Description
The rapid introduction of copper metallization for semiconductor devices has prompted increased research into focused-ion-beammicromachining of copper. Studies with the aim of increasing the material removal rate of Cu by focused-ion-beammicromachining have been complicated by variable micromachining behavior apparently resulting from differing Cufilm morphologies produced by the various Cudeposition procedures. This work examined the micromachining behavior of thin copperfilms produced by physical-vapor deposition(PVD) and electroplating, as well as single-crystalcopper samples. PVDcopperfilms were found to be preferentially textured along 〈111〉, with a columnar grain structure. Channeling effects within this type of grain structure provide a geometric enhancement of the material removal rate of 30% when the sample normal is tilted 12° from the incident ion beam, regardless of sample rotation. Single-crystal (111) copper was found to exhibit similar material removal rate enhancement (averaged over 360° rotation) when tilted 12°, verifying that the etching enhancement observed in the PVDfilms is directly related to their 〈111〉 texture. Compared to the PVDfilm, electroplated (EP) copperthin films contained a significantly more random grain orientation. Consequently, the EP films did not exhibit any appreciable variation in material removal rate beyond the expected cosine dependence when tilted with respect to the incident beam normal. Micromachining of the electroplated films, which have larger randomly oriented grains, results in grain decoration due to preferential etching producing severe micromachining-induced topography.
Oxide-free phosphate films on copper probed by core and valence-band x-ray photoelectron spectroscopic studies in an anaerobic cell18(2000); http://dx.doi.org/10.1116/1.582301View Description Hide Description
This article reports the results of a study of the formation of phosphate films formed directly on the surface of metallic copper without the presence of an oxide layer. The experiments were performed using aqueous electrochemical treatment in an anaerobic electrochemical cell designed to allow an oxide-free metal surface to be exposed to electrochemical treatment without having to expose the electrode to the atmosphere. The electrochemical treatment was performed using negative voltages (versus a saturated calomel electrode) in 5 M orthophosphoric acid. When the experiments were performed outside the anaerobic cell with as-received metallic copper, the treatment leads to the removal of oxide to leave a metallic surface with negligible amounts of oxide. In the anaerobic cell, however, a film consisting of a mixture of Cu(I) metalphosphate and orthophosphate is formed directly bonded to the metal. When this film is exposed to air for ten days, the surfacefilm, still directly bonded to the metal, is oxidized to Cu(II) orthophosphate, this film remaining in a stable condition. The surface chemistries were identified by valence-band photoemission interpreted by cluster calculations. The work illustrates how, by starting with an oxide-free metal surface and performing the treatment in an inert environment in an anaerobic electrochemical cell, one can achieve unusual surface chemistries.
18(2000); http://dx.doi.org/10.1116/1.582302View Description Hide Description
We report a systematic study of the Mn and core-level photoemission and satellite structures for Mn model compounds. Charge transfer from the ligand state to the metal state is observed and is distinguished by prominent shake-up satellites. We also observe that the Mn multiplet splitting becomes smaller as the Mn oxidation state increases, and that electron correlation reduces the branching ratio of the states in the Mn spectra. In addition, as the ligand electronegativity decreases, the spin-state purity is lost in the spectra, as evidenced by peak broadening. Our results are best understood in terms of the configuration–interaction model including intrashell electron correlation,charge transfer, and final-state screening.
X-ray photoemission spectroscopy and scanning tunneling spectroscopy study on the thermal stability of thin films18(2000); http://dx.doi.org/10.1116/1.582303View Description Hide Description
In this work the surface electronic and structural properties of about 150 nm thick films,deposited in high vacuum by thermal evaporation onto Si substrates, have been studied in ultrahigh vacuum (UHV) by means of x-ray photoemission spectroscopy(XPS) and scanning tunneling microscopy (STM)/spectroscopy. After deposition these films have been annealed in atmospheric oven for 24 h at different temperatures (300 and 500 °C) to stabilize the film morphology. XPS measurements to follow W O peaks and the valence band, have been performed on these samples both as prepared and after a re-annealing in UHV at temperatures ranging from 50 to 350 °C. The UHV re-annealing procedure strongly modifies the W peak of both the as deposited and the 300 °C/24 h treated samples, and produces an increase of metallic states at the Fermi edge. Instead, the 500 °C/24 h sample, after heating in UHV shows substantial stability of the nearly stoichiometric phase. Using STM in UHV we have investigated the morphology of the samples at room temperature and after the annealing at elevated temperatures up to 350 °C. In particular, we have taken curves on typical grains of the polycrystalline sample. Our findings on the electronic structure of samples close to the Fermi level are in agreement and allow a clearer understanding of the findings from the parallel XPS study.
Consistent, combined quantitative Auger electron spectroscopy and x-ray photoelectron spectroscopy digital databases: Convergence of theory and experiment18(2000); http://dx.doi.org/10.1116/1.582304View Description Hide Description
Auger Electron Spectroscopy(AES) and x-ray photoelectron spectroscopy(XPS) have many aspects in common. Therefore, tests of aspects for one spectroscopy, applicable to the other, should be validated for both. Digital databases of elemental spectra for both AES and XPS have thus been measured using an electron spectrometer that has been fully calibrated for its intensity and energy axes. These databases of true spectra give absolute Auger electron yields and relative photoelectron yields. The AES data are measured for both 5 and 10 keV electron beam energies, whereas the XPS data are measured for both Al and Mg unmonochromated x rays at the magic angle. In addition to these we have measured reflected electron energy loss spectroscopy (REELS) data to provide a third database. The combination of these databases allows a refinement of the theories to obtain an overall convergence between theory and experiment. Improvements to the theory have been obtained by identifying three classes of parameter, those (i) for both AES and XPS, such as electron transport, the methodology of evaluation of peak areas, and the spectrometer response function, (ii) for AES only, such as the electron ionization cross section, backscattering, and specific electron backgrounds, and (iii) for XPS only, such as the photon-ionization cross section. Additionally, the use of REELS data for background subtraction seems significantly better than the use of any one single Tougaard universal cross section in the determination of the AES and XPS intensities in the databases. The formalism for quantitative analysis in AES and XPS, using relative sensitivity factors, has been revised to develop an accurate matrix-less formalism that is very simple for use by the analyst. This formalism, involving “average matrix sensitivity factors” rather than “pure element sensitivity factors,” has the same accuracy as the matrix formalism but its simplicity permits ready extension to systems beyond binary.
18(2000); http://dx.doi.org/10.1116/1.582475View Description Hide Description
We present measurements of initial adsorption probabilities, as well as its coverage dependence, of CO on oxygen terminated ZnO(0001). The impact energies of the CO and surfaces temperature have been varied. The shape of the coverage dependent adsorption probability curves indicates the presence of precursor mediated adsorption. The heat of adsorption has been determined to by assuming a pre-exponential factor of
Compositional heterogeneity in ceria-based mixed oxides observed by x-ray photoelectron spectroscopy18(2000); http://dx.doi.org/10.1116/1.582305View Description Hide Description
It is argued that compositional heterogeneity in certain reducible mixed oxides, like can be inferred from a variation in the metals ratio, as measured by x-ray photoelectron spectroscopy, between fully oxidized and partially reduced states of the oxide, provided that the characteristic linear dimension of the heterogeneity is at least as large as the typical electron inelastic mean-free path. The argument is supported by experimental results from two examples involving mixed phases, one in which the length scale is 100 nm and the other in which the domains are too small for detection by standard x-ray diffraction.
Characterization of zirconia coatings deposited by inductively coupled plasma assisted chemical vapor deposition18(2000); http://dx.doi.org/10.1116/1.582306View Description Hide Description
Thin films of zirconia have been deposited by an inductively coupled plasma assisted chemical vapor deposition reactor from a tetra (tert-butoxy)–zircon precursor diluted in Ar and gas mixture. An independent rf generator is used to carefully control the substrate negative bias voltage during the deposition. Zirconia thin films, with thickness up to 10 μm were deposited on Si(100) polished wafers under different plasma conditions. Correlation between deposition parameters and microstructure has been established showing that the ion bombardment has a large influence on the coating characteristics. In particular, the possibility of tailoring mechanical properties of the films by controlling the applied dc bias voltage is discussed.
18(2000); http://dx.doi.org/10.1116/1.582307View Description Hide Description
Adequate die-to-lead frame adhesion is necessary for lead-on-chip (LOC) package integrity during and after the manufacturing process. Inadequate adhesion may result in a variety of defects such as die adhesion failure, marginal wire bond, broken wire, and bent leads, which ultimately lead to electrical failure [Mallik, USPatent No. 4,835,120 (May 1989); M. Amagai and E. Kawasaki, Mater. Res. Symp. Proc. 338, 185 (1994)]. Adhesion between the LOC tape and the polyimide passivation is affected by the surfaceproperties of both materials. Understanding the relationships between these properties helps engineers eliminate inadequate adhesion at die attach and continuously improve the manufacturing process. To this end, die that exhibit inadequate adhesion at die attach are analyzed and compared with die that exhibit adequate adhesion characteristics. To focus on the surface chemistry and physical properties of the passivation layer, x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, atomic force microscopy(AFM), and surface energy are used. Molecular concentrations and orientations are investigated and related to inadequate adhesion at die attach.
Identification of surface chemical functional groups correlated to failure of reverse osmosis polymeric membranes18(2000); http://dx.doi.org/10.1116/1.582308View Description Hide Description
The goal of this study is to identify the causes of membrane failure observed during a 15-month operation of a low pressure reverse osmosis (RO) membrane pilot plant to treat a highly organic surface water from the Hillsborough River in Tampa, Florida, using various surface analytical techniques. Three different commercial RO membranes, made of cellulose acetate or polyamide, were used in this pilot study, and all of these membranes showed performance deterioration presumably due to membrane fouling and degradation at given experimental conditions. In order to elucidate the mechanisms of membrane failure, scanning electron microscopy with energy dispersive spectrometry (SEM/EDS), x-ray photoelectron spectroscopy(XPS), and Fourier transform infrared spectroscopy(FTIR) were performed on the surface of the polymeric RO membranes used. More specifically, molecular composition including surface functional groups were identified from XPSanalysis, confirmed by FTIR, and correlated to membrane failure. In addition, surface morphology and fouling layer composition were determined by SEM/EDS. The results indicated that the cellulose acetate membrane was biologically damaged, while the polyamide membrane was compromised by chlorine oxidation. The biodegradation of cellulose acetate was evidenced by the presence of nitrogen on XPS and FTIR scans. Chlorine uptake shown in XPS and FTIR scans of used polyamide membranes was a good indicator of chemical degradation. This study demonstrated that XPS, combined with FTIR and SEM/EDS, is a valuable diagnostic tool for failure analysis of polymeric RO membranes and provides valuable information to aid the manufacturers in designing better membranes for reverse osmosis.
Self-assembled monolayers for polymer and protein cationization with time-of-flight secondary ion mass spectrometry18(2000); http://dx.doi.org/10.1116/1.582309View Description Hide Description
Detection of cationized polymers and proteins with time-of-flightsecondary ion mass spectrometry has been achieved using novel substrates consisting of carboxylic acid terminated self-assembledmonolayers(SAMs) with silver ion substituted headgroups. However, other metal ions (Na,Cu, Tl, or Li) as SAM headgroups can be used as well. Polymers were deposited on the metal ion derivatized SAMs by spin coating while proteins were adsorbed onto the substrates. Control experiments carried out on nonsubstituted and methyl-terminated SAMs suggest that only metal ions in close proximity to the polymer can cationize the molecules and their fragments. Both cationized fragments and whole molecular species were observed for 1 kD polyethyleneoxide and low molecular weight proteins (<2 kD).
- APPLIED SURFACE SCIENCE II
Sputter deposition and annealing of Ta, and composite films and their application in next generation lithography masks18(2000); http://dx.doi.org/10.1116/1.582310View Description Hide Description
Ta and Ta composites with other elements have been developed as low stress absorbers for x-ray mask technology. These thin films are often produced in small quantities by sputter deposition from targets of pure Ta with chips of the minor elements placed on the target to create the composites. For membrane-mask manufacturing it is important that absorber films have uniform composition, thickness, and low, uniform stress to assure that image size and pattern placement errors are minimal. Since sputteredfilms containing Ta often have highly compressive stress, several methods have been used to reduce the final stress, including careful control of sputtering conditions, deposition of layered films with different stresses, and thermal annealing. Much data has been reported regarding the effects of thermal annealing of Tafilms but less information is available on multiple element films such as and Previous reports on these materials have generally not discussed the behavior of these films under long term, higher volume manufacturing conditions. During the last several years IBM has been engaged in development and fabrication of refractoryx-ray membrane masks using Ta composites as absorber materials.Films were sputter deposited from hot isostatically pressed powder targets of Ta, Si, and B using an S-gun magnetron cluster deposition system. This article reports on the deposition and annealing of these films and their application to membrane-mask fabrication in a manufacturing environment. The effects of deposition parameters such as dc power, argon gas pressure, and substrate composition on film stress, composition, and density are discussed. The results of nitrogen annealing on and films are presented. Absorber film quality data and its impact on image size, image placement, and defect density of some x-ray masks is presented.
- BIOMATERIAL INTERFACES
Model for detection of immobilized superparamagnetic nanosphere assay labels using giant magnetoresistive sensors18(2000); http://dx.doi.org/10.1116/1.582476View Description Hide Description
Commercially available superparamagneticnanospheres are commonly used in a wide range of biological applications, particularly in magnetically assisted separations. A new and potentially significant technology involves the use of these particles as labels in magnetoresistive assay applications. In these assays, magnetic bead labels are used like fluorescent labels except that the beads are excited and detected with magnetic fields rather than with photons. A major advantage of this technique is that the means for excitation and detection are easily integrable on a silicon circuit. A preliminary study of this technique demonstrated its basic feasibility, and projected a sensitivity of better than [Baselt et al., Biosensors Bioelectronic 13, 731 (1998)]. In this article we examine the theoretical signal to noise ratio of this type of assay for the special case of a single magnetic bead being detected by a single giant magnetoresistive (GMR)detector. Assuming experimentally observed and reasonable parameters for the magnetic label and the sensitivity of the GMRdetector, the signal to noise ratio is calculated to be greater than 5000:1 for detection of a single 1 μm diameter magnetic microsphere immobilized on the surface of a GMRsensor. Based on this large signal to noise ratio, the detection format should be applicable to more complicated assays where linear quantification is required or to assays requiring significantly smaller beads. Detection of microsphere labels approaching 10 nm may be possible upon further technological advances.
- ELECTRONIC MATERIALS AND PROCESSING
18(2000); http://dx.doi.org/10.1116/1.582311View Description Hide Description
We demonstrate the selective area growth of GaN on -masked AlN/Si(111) and GaN/AlN/Si(111) wafers by chemical beam epitaxy (CBE) using triethyl gallium and ammonia. We investigated the selective nucleation process on Si wafers with oxide and nitride masks. The selectivity of the nucleation process was monitored in real time using time-of-flightmass spectroscopy of recoiled ions (TOF-MSRI). Our results show that TOF-MSRI peaks from mask-corresponding elements (Si and O or N) remain unchanged during GaN regrowth on continuous layers or nitridated Si(111) within the condition range we explored. The selective growth was confirmed by ex situscanning electron microscopy analysis. We also found that, depending on the growth conditions, CBE can be used for selective growth of both microcolumnar and planar GaNfilms. Room temperature photoluminescence studies revealed that both types of films are optically active, which could potentially lead to novel device concepts and applications.
18(2000); http://dx.doi.org/10.1116/1.582312View Description Hide Description
Au/Pt/GaN Schottky diode rectifiers were fabricated with reverse breakdown voltage up to 550 V on vertically depleting structures and >2000 V on lateral devices. The figure-of-merit where is the on-state resistance, had values between 4.2 and 4.8 The reverse leakage currents and forward on-voltages were still somewhat higher than the theoretical minimum values, but were comparable to SiC Schottky rectifiers reported in the literature. These devices show promise for use in ultrahigh-power switches.
18(2000); http://dx.doi.org/10.1116/1.582313View Description Hide Description
Plasma-induced etch damage can degrade the electrical and optical performance of III–V nitride electronic and photonic devices. We have investigated the etch-induced damage of an inductively coupled plasma(ICP)etch system on the electrical performance of mesa-isolated GaNpn-junction diodes. GaN positive-insulating-negative mesa diodes were formed by ICPetching under different plasma conditions. The reverse leakage current in the mesa diodes showed a strong relationship to chamber pressure, ion energy, and plasma flux. Plasma induced damage was minimized at moderate flux conditions (⩽500 W), pressures ⩾2 mTorr, and at ion energies below approximately −275 V.
18(2000); http://dx.doi.org/10.1116/1.582314View Description Hide Description
n- and p-type GaN was exposed to inductively coupled plasma of Ar, or as a function of source power (0–1000 W) and rf chuck power (20–250 W). For n-GaN, there was a strong reduction in diode reverse breakdown voltage and an increase in forward and reverse currents, while for p-GaN the reverse breakdown voltage increased. These results are consistent with creation of point defects with shallow donor nature that increase the conductivity of initially n-type GaN or decrease the conductivity of p-type GaN. Annealing at 750 °C under produced significant recovery of the electrical properties, while wet etch removal of 500–600 Å of the surface produced a full recovery. For completed n-type mesa diodes exposed to Ar or discharges, the low bias forward currents increased by several orders of magnitude. The exposed surfaces became deficient in all cases.
Effect of discharge treatment on AlGaN/GaN high electron mobility transistor ohmic contacts using inductively coupled plasma18(2000); http://dx.doi.org/10.1116/1.582315View Description Hide Description
The contact resistance of Ti/Al/Pt/Au metallization on AlGaN/GaN high electron mobility transistors was measured as a function of plasma exposure conditions prior to metaldeposition.Inductively coupled plasma discharges were used to create nitrogen-deficient near-surface regions in the AlGaN/GaN structures. At modest ion fluxes and low ion energies (125 eV), there was no detectable surface roughening of the AlGaN. Under optimized conditions, the plasma treatment reduces the ohmic contact resistance by a factor of approximately 3.