AVS1997 Session AS-TuP: Aspects of Applied Surface Science
Tuesday, October 21, 1997 5:30 PM in Room Exhibit Hall 1
Tuesday Afternoon
Time Period TuP Sessions | Topic AS Sessions | Time Periods | Topics | AVS1997 Schedule
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AS-TuP-1 Simultaneous Quantitative Thickness Mapping and Chemical Analysis of Thin Films, an Integrated Approach.
C.J. Blomfield (Kratos Analytical Limited, United Kingdom); A. Wirth, V. Vishnyakov, M. Rignall (Sheffield Hallam University, United Kingdom); P. Statham, M. Thornton (Oxford Instruments, United Kingdom); A. Walker (Kratos Analytical Limited, United Kingdom) Chemical analysis and the thickness measurements of surface films, less than a few nanometers to greater than several micrometers, produced e.g. by corrosive or tribological action, often provide important information regarding the nature of the process producing the film. Similarly a knowledge of the chemistry, thickness and integrity of surface engineered coatings provides valuable information regarding suitability for service. At the present time there are a number of well established techniques which can be used to produce images (both chemical and topographical maps). Techniques such as Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and secondary ion spectrometry (SIMS), that examine depth information from a few nanometers do not in general have the same corresponding range of lateral resolution. Additionaly Auger electron spectroscopy (AES) generally provides surface elemental data whilst differences in surface chemical composition are usually studied by imaging X-ray photoelectron spectroscopy (IXPS). "Bulk" elemental information is usually obtained using energy and wavelength dispersive X-ray (E/WDX) methods of analysis. In an attempt to overcome some of the shortcomings listed above the authors will describe the construction of a piece of equipment, combining surface chemical analysis and energy dispersive X-ray methods, in which we ultimately hope to achieve the non-destructive acquisition of quantifiable thickness data in the range from 1 nanometer to 5µm from real materials of engineering importance. Examples of data obtained will be presented. |
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AS-TuP-2 Surface Morphology and Crystallization of Amorphous Ni88P12 Film
S.Z. Dong, J. Yang, Q. Cai, H.X. Li, J.F. Deng (Fudan University, P.R. China) The structure of the amorphous film and the transformation process between amorphous phase and crystalline are interesting but still not clear. In this study, the morphology and the structure of amorphous Ni88P12 alloy film have been investigated by using STM, AFM, SEM, XRD and XPS before and after oxidation, reduction or crystallization. The film were prepared on Si(100) substrate by electroless plating from solution at 363K. The results show that the amorphous Ni88P12 alloy film prepared is an assembly of micrometer scale grains and each of which consists of nanoparticles. The crystallites formed on the amorphous film surface when the film was treated by an oxidation-reduction cycle at the temperature lower than that at which the crystallization of the film completed. After heat treatment, many honeycomb-like hollows with the size of several micrometers appear on the surface due to the effect of stress in the film. Two types of grains, prism-like and roundish, have been found on the surface after oxidation-reduction cycle treatment of the film. They should develop from Ni3P and Ni nuclei separately. The morphological feature of the crystallites was also observed by SEM with temperature. The nanoparticles in the amorphous alloy gathered graduately into big lumps during the crystallization process and finally transform into larger grains after complete crystallization. |
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AS-TuP-3 Auger Lineshape Analysis for MoCr Films
P. Peng, B. Huang, W. Ho (Tsinghua University, China) By the features of high localization of the Auger electrons and the small escape depth of the Auger electrons, AES was used in depth profile analysis of MoCr film with different stoichiometric to detect the local electron states and bonding states and the density of states[DOS] of valence band. After smoothing and background subtraction of the Auger integral spectra, the changes of the Auger line shape with the variation of the contents of Cr and Mo are drawn, and the result of curve fitting shows that Cr and Mo are not simply mixed together to form the MoCr film,there are some electrons transferring between Cr and Mo. Using Gaussian function to fit the curves and with area normalization according to the contents of Cr and Mo to each Auger peak, careful analysis demonstrates that the DOS of Mo N2,3 level increases. The orbital levels of M4,5,N1,N2,3 and the position of valence band of Mo shift. There are some 3d electrons of Cr transferring to 4d orbitals of Mo. To decompose the Auger Mo M4,5,N2,3,N2,3 peak into M4,N2,3,N2,3 and M5,N2,3,N2,3,We obtained the DOS of N2,3 level by self-deconvolution of the above peaks. Furthermore, we obtained the DOS of Mo valence band from Mo M5N2,3V peaks by the same way for each depth profile. Keyword: Auger lineshape analysis, MoCr film, Local density of states. |
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AS-TuP-4 Quantitative Analysis of Sputtered α- and α+ß- Brass Surfaces by Using Auger Electron Spectroscopy with Principal Component Analysis-Target Factor Analysis
G.E. Hammer (The Goodyear Tire & Rubber Company) Previous quantitative analyses of ion sputtered brass alloy surfaces have indicated preferential sputtering of the zinc with a possible effect of crystalline structure in going from the pure face-centered cubic α-phase to the mixed α plus body centered cubic ß-phase. The application of principal component analysis-target factor analysis allows the use of the more surface sensitive MVV Auger transitions despite the complete overlap of the MVV peaks from copper and zinc. Quantitative analysis of these signals confirms the occurrence of preferential sputtering, including the phase dependence. Specifically, the zinc/copper concentration ratio from the surface vs the bulk shows a discontinuity as the bulk composition changes from the α to the α+ß phase. |
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AS-TuP-5 Electrochemical Impedance Spectroscopy-Based Sensor to Detect Corrosion Under Paint Coatings
G.D. Davis, C.M. Dacres, M.B. Shook (DACCO SCI, INC.) An in-situ corrosion sensor, based on electrochemical impedance spectroscopy (EIS), is being developed to monitor the health of painted metal structures. EIS is commonly used to study corrosion of painted metals in the laboratory, but has not been suitable for field inspection as it typically requires immersion in an electrolyte with external counter and reference electrodes. The corrosion sensor eliminates the need for the electrolyte used in conventional three-electrode EIS and enables in-situ analyses of metal/coating systems. Two versions of the corrosion sensor are being tested: an attached electrode permanently applied to the topcoat and a probe which is pressed against the top coat during inspection. The impedance spectra obtained by the sensor and conventional laboratory measurements are identical, indicating that the sensor has negligible effect on the interaction of the painted metal with the environment and that the sensor, itself, is stable with time and exposure. In immersion (acidic and saline solutions), humidity, and salt fog exposures, the measurements show that the coated metal degrades with a distinct signature having well defined regions of water uptake by the coating, incubation of corrosion, and intense interfacial degradation. Correlations were made between EIS and corrosion rate measurements determined by dc potentiodynamic polarizations. Accelerated exposure tests showed that the sensor readily detects the early stages of interfacial degradation well before any visual indication of corrosion appears. The ability to detect and quantify material degradation from its earliest stages in the laboratory and field suggests that one application would be the correlation of paint performance in accelerated tests and field or ambient exposures. Another is to monitor critical structures to permit needs-based maintenance. |
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AS-TuP-6 An Interfacial Study of Fiber/Matrix Adhesion in Ceramic/Ceramic Composites
C.L. Weitzsacker, J. Helmuth, L.T. Drzal (Michigan State University) Ceramic/ceramic composites find many uses in high temperature applications. Examples of these are components in gas turbine engines, automotive and aircraft components such as brakes, clutches and sensors, and aerospace components such as heat shields and nozzles. As it has been identified in other types of composites, adhesion at the fiber/matrix interface is an important determiner of the mechanical properties of the composite. In the system of interest, Nextel312/Blackglas, the adhesion between the fiber and matrix was found to be too strong, resulting in lower strength composites. A BN coating treatment was investigated to allow controlled debonding to occur between the fiber and matrix, improving composite strength and toughness. As received, desized and BN coated fibers and their fractured composites were analyzed by XPS to characterize each surface and determine the mechanism of the coating during fracturing. Auger spectroscopy was also used to characterize the fracture surfaces. The results of this study and the challenges of utilizing XPS and AES to investigate this system will be discussed. |
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AS-TuP-7 The Effectiveness of Modified Pregate Oxidation Wet Cleans for Removal of Airborne Organic Contamination*
G.C. Nelson, R.J. Simonson, M.J. Kelly (Sandia National Laboratories) Experiments were conducted to evaluate the effectiveness of modified wet cleaning procedures for the removal of molecular contamination prior to gate oxidation. Contaminant concentrations on hydrophobic and hydrophilic Si(100) surfaces were monitored using TOF-SIMS. Hexamethyldisilizane (HMDS) and dioctyl phthalate (DOP) were chosen as contaminant challenges based on measurements of airborne contamination deposited onto wafers stored in the fab at the Sandia microelectronics development laboratory and in standard wafer carriers. The removal of HMDS and DOP by dilute SC1 (NH4OH + H2O2) when used alone was compared with the removal by complete pregate cleaning sequences which incorporated dilute SC1 chemistries. HMDS and DOP have significantly different adsorption behaviors, but both can be effectively removed using dilute SC1 chemistires as part of the full pregate cleaning sequence. The combination of these results with results previously obtained for the removal of particle contamination indicates that the SC1 step can in fact be significantly diluted without sacrificing the overall effectiveness of the pregate clean sequence for removal of both particles and molecular contaminants. *Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000. This work was funded through a cooperative research and development agreement with SEMATECH |
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AS-TuP-8 Work Function Reduction by Sc, Ba and O co-adsorption on W Surface
T. Yaguchi, S. Sasaki, N. Matsuzaki (Hitachi, Ltd., Japan) Scandate impregnated cathodes (Sc-type cathodes) are studied as low operating temperature cathodes. They can be used at 850C which is much lower than operating temperatures of M-type cathodes. To optimize Sc-type cathode surfaces, information abo Sc and Ba depositions were held in a UHV chamber and work functions were measured in another UHV chamber. A sample can be transferred between the two chambers without exposing to the air. Sc was evaporated with an electron beam evaporation source. For Sc deposition could be reduced the work function to 3.3eV from the value of a poly W clean surface(4.5eV). This value became still lower to 1.4eV by 0.7 layer Ba deposition. This is 0.8eV lower than that of an only Ba adsorbed surface, and is as low as
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AS-TuP-9 Sodium Contamination of Photooxidatively Self-Cleaning Films on Soda Lime Glass and its Prevention
Y. Paz (The Technion-IIT, Israel); G.N. Binyamin (University of Texas, Austin) In the context of studying the feasibility of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, photocatalytic films of TiO2 were formed by a sol-gel process on (a) soda lime glass (b) sodium depleted soda lime glass and (c) fused silica. The hypothesis that out-diffusion of sodium oxide from the soda lime glass into the titanium dioxide layer during the calcination step causes a lower photoefficiency in films on glass was tested and proven. Sodium degrades the photoefficiency by preventing, when the concentration of sodium is high, the formation of the anatase phase and at all concentrations, by introducing basic surface sites and bulk recombination centers. The depth profile of sodium in titania films on glass was measured by XPS. The sodium concentration at the air-contacting outer surface was higher than the concentration in the TiO2 bulk and in the glass / titania interface, demonstrating that the TiO2 films have a higher affinity for sodium ions than the soda lime glass itself. Sodium transport to the TiO2 layer can be retarded by forming a blocking layer at the glass / titania interface. Such layer is produced when the TiO2 precursor film is calcined on a hydrogen glass, formed upon extraction of the sodium from the glass surface with hot sulfuric acid. |
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AS-TuP-10 High Resolution Imaging and Depth Profiling with Resonance Ionization Mass Spectrometry
H.F. Arlinghaus, X.Q. Guo, T.J. Whitaker (Atom Sciences, Inc.) The extremely high element specificity and sensitivity of resonance ionization is valuable for imaging and depth profiling ultratrace elements in samples especially where the complexity of the matrix is frequently a serious source of interferences. We have built a time-of-flight sputter-initiated resonance ionization nanoprobe instrument capable of quantitatively imaging and depth profiling trace elements with submicron spatial and few nanometer depth resolution. For sputtering, this instrument utilizes a liquid metal gallium ion gun, a mass-filtered microbeam ion gun, and a mass-filtered low energy sputtering ion gun. Combining a low energy sputtering ion gun for eroding the sample and a pulsed high energy ion beam for analysis yields unprecedented depth resolution for surface or near surface analyses without loss of sensitivity. Using the liquid metal ion gun, submicron images of trace elements in complex samples as well as depth profiles on submicron devices can be obtained. In our presentation, we will describe the nanoprobe's capability to solve a number of analysis problems and illustrate the technique's salient characteristics and potentials with data of relevance to semiconductor research and drug delivery effectiveness. Results presented will include: a) high resolution Ge and B depth profiles on approximately one micrometer spot size; b) submicron Cu trace element images obtained from Cd precipitates in CdZnTe films; and c) boron trace element images in tissue samples with subcellular resolution. Dynamic range and depth resolution, imaging capabilities, quantitation accuracy, and limitations will be discussed in detail. Part of this material is based upon work supported by the National Science Foundation under Grant No. DMI-9460624 and National Institute of Health under Contract No. 5-R44-CA-54627-03. |
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AS-TuP-11 Scanning PhotoElectron Microscopy Studies at the Advanced Light Source
S. Seal, T. Warwick (Lawrence Berkeley National Laboratory); A. Garcia, H.W. Ade (North Carolina State University); J. Delinger (University of Michigan); B.P. Tonner, T.L. Barr (University of Wisconsin, Milwaukee); N. Sobczak (Foundry Research Institute, Poland) The development of third generation synchrotron radiation soft x-ray sources has led to new opportunities for the use of combined x-ray spectroscopy and microscopy to study the chemistry of surfaces and interfaces of complex materials. This development furthers the field of surface science by exploring spatial variations across a surface on a scale previously inaccessible to x-ray measurements. We have developed a new Scanning PhotoElectron zone-plate Microscope (SPEM) which provides spatially resolved X-ray Photoelectron Spectroscopy (XPS) analysis of features as small as 0.2 micron. As an example study we have examined the interfacial properties and surface chemistry of the systems formed by adding liquid drops of select Al-Ti alloys to graphite substrates. The observed image contrast of various phases present in the system is due to chemical shift of core levels of the atomic species involved. A variety of chemical states were revealed in the XPS measurements, suggesting the formation of separate regions composed of elemental metals, alloys and carbides. Acknowledgments: This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S.Department of Energy, under Contracts No. DE-AC03-76SF00098 and DE-FG02-92ER45468. |
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AS-TuP-12 Effects of HF Attack on the Surface and Interface Microchemistry of W Tips for use in the STM Microscope: A Scanning Auger Microscopy (SAM) Study
E. Paparazzo, L. Moretto, S. Selci, M.F. Righini, I. Farne (Consiglio Nazionale delle Ricerche, Italy) Although it is well known that the presence of surface tungsten oxides on W tips hinders the achievement of reproducible atomic resolution in STM imaging, and that HF successfully removes these oxides, a detailed knowledge of chemical change produced by acid attack is still lacking. We have performed SAM analysis on W tips prepared electrochemically which were subsequently subjected to HF attack. The surface chemistry was explored in several microscopic regions of the tip apex, from the vertex to the trunk base, and compared with the microchemical composition of untreated tips. Auger intensity ratios measured in survey spectra and averaged over prolonged Ar etch profiling show that HF lowers the content of tungsten oxides by a factor of circa 3. Both imaging and spot analysis with a submicron spatial resolution reveal that oxidic species accumulate mostly at the vertex. We explain this by recalling that the vertex has a higher surface-to-volume ratio than other regions of the tip. W(NVV) and W(MNN) spectra recorded in the fixed-analyzer-transmission mode reveal the presence of oxidic species with components at 160 and 1722 eV, respectively, which are several eV lower than the W metal levels. The kinetic energy separation between the two transitions allows a non-destructive distribution analysis over the depths 8 to 30 Å, respectively, below the surface. We emphasize that the chemical and surface sensitivities of electron-induced Auger spectra contribute valuable though often neglected features to the microanalytical potential of SAM. A reproducible atomic resolution is attained on a UHV cleaved Si(111) surface by an STM microscope equipped with the HF-treated tip. |
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AS-TuP-13 Whole-Wafer Contaminant Distribution by TOF-SIMS Analysis
P. Lindley, F. Radicati, L.A. McCaig, I.A. Mowat (Charles Evans & Associates) Wafers can be contaminated by molecular contaminants from a variety of sources including cleanroom air, gases, ultra-pure water, process chemicals, and outgassing from FAB construction materials or wafer storage materials. Although HEPA and ULPA filters remove particles, they have litttle or no effect on Airborn Molecular Contaminants. Filters of this type have even been shown to contribute outgassed contaminants. There can be differences in the distribution of many contaminants on the final wafer surface. This work investigates the lateral distribution of contaminants over a whole wafer with TOF-SIMS analysis using a whole-wafer sample stage and automated analysis capabilities. Contaminant type and distribution on the surface of prime and reclaimed wafers are compared. The effect of contact with sponge material during cleaning processes and exposure to different cleaning process chemicals are also investigated. |
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AS-TuP-14 Automated (Unattended) Surface Analysis by TOF-SIMS
D.F. Reich, B.W. Schueler, R.A. Register, H. Xiao, P. Coveney, A. Huesemann (Physical Electronics) Automated analysis (of any kind) is an important way of increasing sample analysis throughput in commercial environments. An unattended mode of operation for TOF-SIMS has been developed on commercial instrumentation, initially for surface analysis of hard disks (data storage) and also of 150 and 200mm diameter silicon wafers. Such applications are ideally suited to automation, because characterization of such samples requires that a measurement be made repeatedly at different points on the sample surface. At each successive analysis point the primary ion beams are auto-aligned to the mass spectrometer's acceptance area, removing the effect of sample height variations. If images are required at each analysis point, a mass spectrum is acquired for sufficient time for an automatic mass calibration to be made. If no imaging is required the mass spectrum is auto-calibrated at the end of the run, removing the need for a separate, pre-calibration stage. Data is then acquired for a preset time, during which multiple pre-set images may also be acquired. At the end of the acquisition, the data set is stored to disk with incremental filenames. Following this, a report on species of interest in the mass spectrum is generated. For quantitative analysis of trace species on wafer surfaces, relative sensitivity factors are automatically invoked in the report. At the end of the multi-point analysis, a full data table is reported. The time required for auto-tuning and moving to the next sample position is approximately 1 minute per point. Thus, for mapping of organic contaminants on a silicon wafer, or variations in lube chemistry on a hard disk it is possible to analyze approximately 30 points per hour, because the acquisition time can be kept to 1 minute per point. For surface metal detection sensitivities of ~ 1 x 109 atoms/cm2 (Fe on Si) approximately 6 points per hour can be analyzed. Data illustrating the mapping of both organic and inorganic species over whole wafers and disks will be shown. |
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AS-TuP-15 Comparison of TOF-SIMS and Thermal Desorption GC-MS in the Evaluation of Molecular Contamination on Silicon Wafers
P. Lindley (Charles Evans & Associates); M. Kendall (Surface Science Laboratories); L.A. McCaig, I.A. Mowat (Charles Evans & Associates) Time of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS) and Thermal Desorption-GC-MS are two techniques used to examine molecular surface contamination, such as acids, bases, dopants and condensible organic compounds. This type of contamination, also referred to as airborne molecular contamination (AMC), is of increasing importance in semiconductor processing, particularly as device sizes shrink. It is also relevant for the disk drive and optical component industries. Thermal desorption coupled with dynamic sampling GC-MS has been used to study compounds that outgas from various types of samples, including construction materials, shipping containers and wafers. The technique's ability to separate the components of outgassing mixtures, combined with mass spectral identification of individual components, makes it a valuable tool to assess contaminants, particularly those with lower or intermediate boiling points. TOF-SIMS is a UHV technique in which the surface of the sample is directly analyzed. Its extreme surface sensitivity and ability to determine the distribution of species on a surface make it valuable for the study of higher boiling compounds, as well as polar species that are not easily desorbed for GC-MS. In this work, organic contamination on the surface of silicon wafers is investigated using both TD-GC-MS and TOF-SIMS analyses. The type of data obtained and the contaminant species seen are compared for the two techniques. In addition to analysis of the wafers themselves, wafer storage container materials are also investigated as a source of organic contamination. |