Volume 17, Issue 4, July 1999
- papers from the 45th national symposium of the american vacuum society
- biomaterial interfaces
- electronic materials and processing
- magnetic interfaces and nanostructures
- manufacturing science and technology
- nanometer-scale science and technology
- partial pressure measurements and process control
- plasma science and technology
- selected energy epitaxy
- surface science
- thin films
- vacuum metallurgy
- vacuum technology
- applied surface science/vacuum technology
- applied surface science/biomaterial interfaces/surface science
- biomaterial interfaces/appl. surf. sci./micro-electro-mechanical systems/nanometer-scale sci. & technol./surf. sci.
- electronic materials and processing/plasma science and technology
- electronic materials and processing/selected energy epitaxy
- electronic materials and processing/plasma science and technology/selected energy epitaxy
- magnetic interfaces and nano structures/electronic materials and processing
- magnetic interfaces and nanostructures/nanometer-scale science and technology
- nanometer-scale science and technology/applied surface science
- nanometer-scale science and technology/electronic materials and processing/surface science
- micro-electro-mechanical systems/plasma science and technology
- micro-electro-mechanical systems/vacuum technology
- organic electronic materials/electronic materials and processing
- organic electronic materials/applied surface science/electronic materials and processing
- surface science/nanometer-scale science and technology
- vacuum metallurgy/thin films
Index of content:
- PAPERS FROM THE 45TH NATIONAL SYMPOSIUM OF THE AMERICAN VACUUM SOCIETY
- APPLIED SURFACE SCIENCE
17(1999); http://dx.doi.org/10.1116/1.581778View Description Hide Description
The present study continues our x-ray photoelectron spectroscopy(XPS) or electron spectroscopy for chemical analysis investigations of silicate systems, particularly those in contact with biological materials. In the present case, the investigations are extended to a detailed analysis for a wide variety of soil samples extracted from different locations around the world. The samples were selected from relatively pristine sites, pressed into wafers, and were examined without further modification. All of the materials were insulators and therefore analysis required extensive use of the electron flood gun. Careful XPSchemical shift assignments have been achieved for many silicate minerals. These have been exploited in the present study along with the detailed XPSanalysis of organofunctional groups rendered by Beamson and Briggs. As a result, a fairly detailed simultaneous nondestructive description is provided of the surface of both the humus and silt components of these soil samples. Substantial variations in the composition are demonstrated and questions are raised about our classifications of fertility.
17(1999); http://dx.doi.org/10.1116/1.582038View Description Hide Description
There has been a considerable effort in the past decade to incorporate nitrogen into in order to improve the electrical properties of ultrathin (2–10 nm) gate oxides. Process conditions affect the nitrogen concentration, coordination, and depth distribution which, in turn, affect the electrical properties.X-ray photoelectron spectroscopy(XPS) is particularly well suited to obtaining the nitrogen coordination and, to a lesser extent, the nitrogen concentration in thin oxynitride films. To date, at least four different nitrogen coordinations have been reported in the XPS literature, all having the general formula: where and In this article we review the XPS literature and report on a fifth nitrogen coordination, with a nitrogen binding energy of Next nearest neighbor oxygen atoms shifted the peak roughly 0.1 eV per oxygen atom. We also discuss results from a novel approach of determining the nitrogen areal density by XPS, the accuracy of which is dependent on the depth distribution of nitrogen. Secondary ion mass spectrometry is used to determine the depth N distribution, while nuclear reactionanalysis is used to check the N concentration measured by XPS.
Valence band x-ray photoelectron spectroscopic studies to distinguish between oxidized aluminum species17(1999); http://dx.doi.org/10.1116/1.581779View Description Hide Description
The determination of the detailed chemical nature of oxidized aluminum species is an essential requirement for the study of many important practical aspects associated with aluminum metal and its compounds. While thick oxidized films of aluminum metal can be easily characterized by x-ray powder diffraction when the films are crystalline, thin amorphous films are very difficult to characterize. In this article, a study of the valence band x-ray photoelectron spectrum of aluminum oxides, hydroxides, and oxyhydroxides is reported using monochromatic aluminum X radiation. The valence band spectra obtained are shown to have significant differences for different oxidized aluminum species, and can be well understood by comparison with spectra generated from cluster and band structure calculations. This study compliments earlier published studies from this research group using achromatic radiation, and demonstrates how the use of monochromatic X radiation allows a more conclusive distinction to be made among oxidized aluminum species.
17(1999); http://dx.doi.org/10.1116/1.581780View Description Hide Description
The matching configuration in an ionic interface is more stringent relative to metallic systems due to the polarity concern. This configuration has to satisfy both geometric and electrostatic requirements. We study the growth of several different thin films, including MgO, SrO, NiO, and on single crystalline MgO(001) and (001) substrates by molecular beam epitaxy. These oxides have different structures (rocksalt, perovskite, and spinel) and lattice misfits (small, and large, Using high energy electron diffraction, we observed some specific orientation relations between these structures. The interface of a rocksalt/rocksalt only shows a direct matching configuration. However, the interface of rocksalt/perovskite shows two different matching configurations, direct on and rotation of the film relative to the substrate. This difference results from the relative ionic arrangements of these materials. It further implies that a more general matching rule may exist in other ionic interfaces depending on the relative ionic symmetry. A calculation based on Ewald sum is also included.
17(1999); http://dx.doi.org/10.1116/1.581781View Description Hide Description
The optical properties and structural characteristics of copperdopedcoatings, prepared using the sol-gel method, were determined from spectroscopy ellipsometry, optical transmission and x-ray diffraction measurements.Coatings with 8 and 25 at. wt % of copper were analyzed. The samples were heat treated in air and under a CO atmosphere at various temperatures. The x-ray data show that samples thermally treated in air have an amorphous structure. In the coatings with 25 wt % of copper and annealed in the reducing atmosphere, there is precipitation of copper particles with nanometer sizes. The effective complex index of refraction of the coatings is deduced from the ellipsometric data using the Forouhi–Bloomer and Maxwell–Garnett expressions for samples with amorphous and composite structures, respectively. The optical transmission measurements indicate that ions are present in oxidized samples. The optical density spectra from reduced samples were analyzed with the Mie theory. There is a good agreement between the results from the different measurements.
Role of surface chemistry on the nature of passive oxide film growth on Fe–Cr (low and high) steels at high temperatures17(1999); http://dx.doi.org/10.1116/1.581782View Description Hide Description
High temperature materials degradation or protection of Fe–Cr alloys are often related to the nature of their oxide scale formation. Breakdown of passive oxide films leads to localized corrosion. Various alloying elements are often incorporated in these alloys to prevent high temperature oxidation. The addition of selected alloying elements is cumbersome and not always cost effective. In this article, we investigate the role of rare earth oxide coatings on high temperature corrosion prevention of both low and high Cr steel. An in situ high temperature oxidation setup has been built to study the oxidation kinetics of both coated and uncoated low and high Cr steels under ambient pressure and dry air. Reduction in scale growth kinetics is observed in the presence of coating. While scanning electron microscopy and x-ray diffraction are employed to study the structure and morphology of the oxide films, x-ray photoelectron spectroscopy and Auger electron spectroscopy are used to study the surface chemistry of the oxide layer. This article relates some of these data to explain the nature of scale growth kinetics (linear or logarithmic or parabolic) observed in both low and high Cr steels.
Improvements to the analysis of x-ray photoelectron spectra using a maximum entropy method for deconvolution17(1999); http://dx.doi.org/10.1116/1.581783View Description Hide Description
X-rayphotoelectron spectra are typically broadened by the inclusion of contributions from the exciting X radiation, as well as the spectrometer itself. A procedure for removal of much of this broadening using a version of the maximum entropy method is described. This method uses a nonlinear functional (the spectral “entropy” or information content) to stabilize the noise amplification problem inherent to deconvolution of real data. A less ambiguous solution is therefore obtained compared to previous approaches which use linear estimates. This algorithm avoids the subjective nature of many previous deconvolution methods by assuming that the informational uncertainty is always maximized within the constraint of the data provided. This large scale, nonlinear optimization problem can be solved on a fast personal computer using a sequential quadratic programming algorithm. For spectra with adequately high signal/noise, the linewidths produced approach the limiting core hole lifetime values. The method is applied to study the extended growth of an oxide layer on clean polycrystalline aluminumsurfaces following exposure to water vapor. For the early growth stages, the spectral detail is comparable to recent synchrotron-based studies where one or more precursor phases are detected at the interface prior to the nucleation of the extended oxide film. In a related study of the oxidation of gold–aluminum alloy surfacefilms, the evolution of the gold–aluminum near-surface phase could be followed through changes in the and the spectra. From the latter, the surface oxides grown on the alloy surface are seen to differ distinctly from those on pure aluminum.
17(1999); http://dx.doi.org/10.1116/1.581784View Description Hide Description
We present an evaluation of the consistency of calculated and measured electron inelastic mean free paths (IMFPs) for seven elemental solids (Al, Si, Ni,Cu,Ge, Ag, and Au). These solids were selected because, for each, there were two or more independent IMFP calculations and two or more IMFP measurements by elastic-peak electron spectroscopy. We found that the calculated IMFPs for each element showed a high degree of consistency and that there was greater scatter among the measured IMFPs. Comparison of the measured IMFPs with the calculated IMFPs showed generally good agreement. The greatest consistency in the comparisons was found for Ni,Cu, Ag, and Au. Recommended values of the IMFPs for these four elements can be obtained from a simple formula (used to fit the calculated IMFPs for each element) for electron energies between 50 and
17(1999); http://dx.doi.org/10.1116/1.581908View Description Hide Description
The demand for submicron lateral analysis, as a result of decreasing material size, has been met by the development of liquid metal ion gun (LMIG) sources capable of achieving spot sizes less than 50 nm. The trade-off, however, is the reduction in ion beam current at the sample. Therefore, highly sensitive detection techniques are required. Our technique, sputter-initiated resonance ionization spectroscopy (SIRIS), incorporates resonant ionization of sputtered neutral particles with time-of-flight mass detection. The two major advantages this approach has over conventional secondary ion mass spectrometry are that analysis of neutrals generally increases the detection efficiency by at least two orders of magnitude, and that resonance ionization nearly eliminates mass interferences. Additionally, analysis of neutrals substantially removes matrix effects, which is crucial for quantitative surface analysis.Sputtering is achieved with a gallium LMIG, a mass-filtered microbeam ion gun, and a mass-filtered low-energy sputtering ion gun. Submicron lateral resolution and few nanometer depth resolution have been obtained by eroding the sample with the low-energy ion gun while analyzing with the LMIG. In our presentation, we will describe the SIRIS technique and its dynamic range for quantitative analysis and imaging capabilities as they pertain to semiconductor research. In particular, Ge and B depth profiles on near 1 μm spot size and Cu trace element images obtained from Cd precipitates in CdZnTe films will be presented.
17(1999); http://dx.doi.org/10.1116/1.581785View Description Hide Description
Secondary ion mass spectrometry(SIMS) supported the development of deep trench capacitors in dynamic random access memory. SIMS is done efficiently by analyzing thousands of cells in parallel and the approach described in this article is scaleable to the multi-Gbit generation. By projecting out fundamental values using geometrical formalisms, the behavior of contaminants and dopants in sub-micrometer geometries is understood without the need for small-area measurements. This array-profiling approach is used to quantify and partition halogen, alkali, and transition-metalcontaminants among deep trench and other processing sectors. The deposition of self-limiting layers of arsenic during polysilicon fill of the deep trench is explored in detail. The doping of the trench sidewalls, either through angle ion implants or by drive in of doped-glass deposition, is quantified.
Nitrogen incorporation and trace element analysis of nanocrystalline diamond thin films by secondary ion mass spectrometry17(1999); http://dx.doi.org/10.1116/1.581786View Description Hide Description
Nitrogen has been successfully incorporated into nanocrystallinediamondfilms produced by a microwave plasma-enhanced chemical vapor deposition method. High mass resolution secondary ion mass spectrometry(SIMS) characterization shows that the density of the incorporated nitrogen, monitored via can be as high as depending on the ratio of to in the reactant gas and on the substrate temperature used for the film preparation. SIMS depth profiles demonstrate that the incorporated nitrogen is uniform within the diamondfilms (about 1.5 μm thick) except at the surfaces and at the interface between film and substrate. Furthermore, the SIMSanalyses reveal that alkali elements such as Na, K, and Li appear to be contaminants at the surface of nanocrystallinediamondfilms produced using a or discharge, but are bulk impurities only for the films prepared using a plasma. These alkali impurities can play an important role in electronic properties such as electron field emissions of nanocrystallinediamondthin films.
- BIOMATERIAL INTERFACES
Atomic force microscopy observation of human lymphoid cells chronically infected with the human immunodeficiency virus17(1999); http://dx.doi.org/10.1116/1.581787View Description Hide Description
The interaction between lymphocyte cell and human immunodeficiency virus (HIV) has been studied at membrane level by atomic force microscopy(AFM) in the repulsive regime of contact mode. Morphological characteristics of noninfected lymphoid cells and HIV infected cells were easily imaged from fixed and dried cell preparations. After HIV exposure we observed a decrease in surface protrusions (lost of microvilli) and the creation of many dips. Some particles, presumably of viral origin (120–130 nm size), were also observed in proximity of the cellsurface. Similar changes have been observed by AFM on cells exposed to intense electromagnetic field thus indicating that such cells undergo modifications of their morphology upon suffering from an external agent.
- ELECTRONIC MATERIALS AND PROCESSING
17(1999); http://dx.doi.org/10.1116/1.581788View Description Hide Description
Semiconductor wafer bonding has increasingly become a technology of choice for materials integration in microelectronics, optoelectronics, and microelectromechanical systems. The present overview concentrates on some basic issues associated with wafer bonding such as the reactions at the bonding interface during hydrophobic and hydrophilic wafer bonding, as well as during ultrahigh vacuum bonding. Mechanisms of hydrogen-implantation induced layer splitting (“smart-cut” and “smarter-cut” approaches) are also considered. Finally, recent developments in the area of so-called “compliant universal substrates” based on twist wafer bonding are discussed.
Reduced carbon contaminant, low-temperature silicon substrate preparation for “defect-free” homoepitaxy17(1999); http://dx.doi.org/10.1116/1.581789View Description Hide Description
A low-temperaturecleaning technique incorporating an ultraviolet light–ozone treatment with conventional hydrogen-passivation techniques is shown to yield a low concentration of surfacecontaminants: 0.01 monolayer. An additional advantage is that no ultrahigh vacuum prebaking treatments are required for substrates receiving this treatment prior to epitaxy.Epitaxialsilicon layers deposited onto substrates receiving the present technique are characterized by a threading dislocation density on the order of which is considerably lower than the order measured for films receiving more conventional preparation techniques. The results of this study suggest that aqueous solutions are a significant source of surfacecarbon and that residual carbon on the siliconsurface before epitaxy contributes to the generation of threading dislocations in Si homoepitaxialfilms.
Process optimization of dielectrics chemical mechanical planarization processes for ultralarge scale integration multilevel metallization17(1999); http://dx.doi.org/10.1116/1.581909View Description Hide Description
The requirements of gap-fill and global planarization for interlayer dielectric films obtain more and more importance as the size of the integrated circuits shrinks. Typical dimensions are 0.35 μm for gaps between 0.7 μm high aluminuminterconnect lines with an aspect ratio of 2:1. The push of leading edge ultralarge scale integration manufacturing technologies toward the formation of sub 0.1 μm feature sizes places extreme performance demands on the processes and equipment used. At submicron linewidths, the depth-of-focus was limiting technology and chemical mechanical planarization (CMP) became a necessary tool for feature sizes of 0.35 μm and below. Thus, CMP emerged quickly and has become quite sophisticated [R. DeJule, Semicond. Int. 11, 15 (1996)]. Also, in order to fill the small feature sizes high-density plasma chemical vapor deposition (HDP–CVD) of insulators gained increasing attention in the semiconductor world. Due to the uniform thickness of the HDP intermetal dielectric (see Fig. 1) the polishing time is shortened, pad wear is reduced, and thus, increasing the intervals between pad dressing. An increased throughput, as well as extended CMP stability and repeatability can be achieved. A saving in processing time as compared to standard techniques up to 35% is possible. In this article we describe the major dependencies of machine parameters versus experimental results for different CMP processes.
17(1999); http://dx.doi.org/10.1116/1.581790View Description Hide Description
Chemical mechanical polishing (CMP) is considered to be the enabling technology for meeting the planarization requirements in <0.35 μm feature sized multilevel semiconductor device fabrication. CMP of tungsten is done in order to planarize and remove excess tungsten in the process to form inter-level contacts. Considerable importance is given to the role played by the passive oxide film formation on the surface during tungsten CMP. In this study, x-ray photoelectron spectroscopy(XPS) is used to understand the oxide growth mechanism in tungsten.Tungsten wafers are polarized to different anodic potentials in static solutions of KIO3 and two commonly used oxidizers in CMP. XPS measurements are employed to probe the chemical and stoichiometric changes in the surface oxide filmstreated under these conditions. These results are then compared with the electrochemical polarization results.
Low damage dry etching of III–V materials for heterojunction bipolar transistor applications using a chlorinated inductively coupled plasma17(1999); http://dx.doi.org/10.1116/1.581791View Description Hide Description
Etching of InGaAs and InP in inductively coupled plasma(ICP) using was studied for heterojunctionbipolar transistor (HBT) applications. Low sample temperature was used to minimize etching isotropy and to reduce group V element desorption. The low ion energy etching process results in a damaged layer thickness of a few Å. Auger electron spectroscopy results on InP demonstrate a very thin layer of nonstoichiometric material. The nature of the etching mask impacts the surface contamination: local contamination effects due to sputtering are observed. For such low ion energy process, the sample preparation before ICPetching is shown to be very important for surface roughness, as observed by atomic force microscopy. Various preparation schemes have been investigated, before ICPetching, for reduction of the surface degradation resulting from ICPetching. It is shown that the best results in terms of roughness and etch-rate are obtained with a silicon nitride mask and surface oxidation by ultraviolet ozonization before a wet desoxidation immediately preceding the ICPetching. An ICP process was used successfully for partly etching the base mesa of HBT structures. No significant difference with wet etching was observed in terms of induced damage and HBT current gain.
Comparison of morphology and interfacial composition of Pd ultrathin films on 6H–SiC and 4H–SiC at different annealing temperatures17(1999); http://dx.doi.org/10.1116/1.581792View Description Hide Description
Pd/SiC Schottky diode has been applied as a chemical sensor for hydrogen and hydrocarbon gases at high temperatures. The diffusion and interfacial reactions between the metalthin film and SiC substrate are known to alter the electrical properties of the device. In this work, the morphology and interfacial composition of Pd ultrathin films on 6H–SiC and 4H–SiC are investigated after thermal annealing using atomic force microscopy and x-ray photoelectron spectroscopy. The Pd ultrathin films of about 3 nm thickness are deposited by radio frequency sputtering. The SiC substrates are 3.5° tilted, Si-face, and n-type, 6H–SiC and 4H–SiC, and the Pd thin film deposition and annealing conditions are identical for both samples. The samples are annealed consecutively from 100 to 600 °C in air for 30 min. The Pd ultrathin film on 6H–SiC and 4H–SiC has a good uniformity as deposited, and there are no significant morphological changes for either sample at the low annealing temperatures. At 300 °C, a nanofeatured layer and were formed on both samples. The irregularly shaped cracks on the Pd nanofeatured layer are observed on 4H–SiC substrate, while the Pd on 6H–SiC exhibits a uniform nanofeatured layer. The interaction between Pd and 4H–SiC is more enhanced than between Pd and 6H–SiC. At 500 and 600 °C, Pd on both 4H–SiC and 6H–SiC substrates becomes nanosize clusters. reacted with SiC to form PdSi at 500 °C for Pd/4H–SiC, and at 600 °C for Pd/6H–SiC. The surface composition and morphology of Pd/6H–SiC and Pd/4H–SiC are almost identical after annealing at 600 °C. The Schottky barrier heights are 1.4 and 1.7 eV for Pd as deposited on 6H–SiC and 4H–SiC, respectively. No significant changes in Schottky barrier height are found on either Pd/6H–SiC or Pd/4H–SiC after annealing.
17(1999); http://dx.doi.org/10.1116/1.581793View Description Hide Description
We have investigated the electron field emissioncharacteristics of BN and CN on highly conductive siliconthin filmsdeposited by End-Hall ion source and electron cyclotron resonance plasma source-assisted physical vapor deposition. The thermal processing and surface laser modification effects on the field emission properties were investigated. Current density-field emission characteristics were tested in a high vacuum environment. Mg-doped BNthin films on silicon exhibited a turn-on field as low as 25 V/μm and a current density higher than 1 A/cm2. The deposition of a thin BN layer on copper lithium (CuLi) metallic substrate yields surfaces with a 75 V/μm onset field and a current density 1000 times higher than that obtained from uncoated surfaces. Under high vacuum laser annealing BNcoated CuLi showed no enhancement but more stable emission characteristics. Our results show also that pulsed ultraviolet laser irradiation of CN films in vacuum results in an increase of the field emissioncurrent densities and a reduction in threshold field values. The turn-on fields of the irradiated surfaces depend strongly upon the energy density of the laser beam. In addition, the electroconductivity properties of BN and CN surface mapping have been performed using scanning tunneling field emission microscopy. The surface topography mapping and its correlation to the field emission properties were investigated. Preliminary results on surface mapping suggest that the surface relief plays some role in field emission enhancement.
17(1999); http://dx.doi.org/10.1116/1.581794View Description Hide Description
An overview of the steady state electrical properties of tin dioxide varistors is presented. The varistors are manufactured in two ways: (1) a ceramic route by mixing and compaction of tin dioxide powder with various dopants and (2) a sol-gel method, where dopants are dispersed in their aqueous solutions. For a quantitative agreement with the experimental data, the electronic defect states in the bulk of the tin dioxide grains and at the grain boundary interfaces are studied. Scanning electron microscope and x-ray diffraction are employed to study the morphological and structural aspects of tin dioxide varistors. The effect of various sintering temperatures on their nonohmic or nonlinear characteristics was also investigated. The varistors prepared by the sol-gel method showed high nonlinearity, high density, and high threshold voltage properties than the ones produced by the ceramic route. This is probably due to a finer grain structure and a better densification of dopants along the grain boundaries.