Papers

AVS2001 Session AS-WeA: Depth Profiling II

Wednesday, October 31, 2001 2:00 PM in Room 134

Wednesday Afternoon

Start	Invited?	Item
2:00 PM		AS-WeA-1 Multi-Technique Analysis of the Paint/Sealant Interface in Aircraft Structures S.J. Harris (British Aerospace, UK) The changes in environmental legislation in the early1990’s following the Montreal Agreement has resulted in the need for changes in the surface treatments used in the aerospace industry. This involves the removal of the CrVI ion from all processes and the use of low VOC (volatile organic content) or water based coatings. MaSSPS (or Materials System for Surface Protection and Sealing, a Brite-Euram project, BRPR CT-97-0538), incorporating 11 partners, aims to develop a fully integrated corrosion protection system using both of the above ideals. The system will consist of a Cr-free conversion coating, low VOC and water based, Cr-free primers, a Cr-free low density, fuel/water resistant, high adhesion sealant. The interaction of these new materials is complex and has to be understood in-order to avoid system failures in service. A key part of the airframe where these new materials will be used is the aircraft’s fuel tank. This is an integral part of the wing and, therefore, the coatings and sealants will be subjected to a wide range of temperatures, fuel and fuel/water mixtures and exposure to fungi that live at the fuel/water interface. This paper will discuss one of the many problems associated with a system of this kind. The challenge is to develop analytical methods to explore the surfaces and interfaces and understand their modes of failure. The surface analytical techniques used in the project are briefly described., which include XPS, ToF-SIMS, in-situ SEM tensile testing, AFM and µTA. The work will be described in a case by case basis rather than a discussion on individual surface analytical results.
2:40 PM		AS-WeA-3 Fourier Modulus Brings Charging Samples, Auger Depth Profiles, Linear Least Squares and Factor Analysis Together D.J. Pocker, M.A. Parker (IBM Storage Technology Division); R.E. Davis (IBM Microelectronics Division) The shifting of Auger spectra has frustrated the extraction of chemically distinct depth profiles from charging samples using Linear Least Squares (LLS) or Factor Analysis (FA) methods. It is shown here that normal LLS or FA of the moduli (or magnitudes) of Fourier transforms of profile spectra readily yields such chemically distinct depth profiles. This approach applies equally to ESCA measurements and to line scans, maps and time sequence spectra. There are two requirements: The spectral energy window must be wide enough to capture the whole peak over its whole range of shifts. And, any given shifted spectrum cannot have stationary spectra or differently shifted spectra of other constituents superimposed on it.
3:00 PM		AS-WeA-4 Determination of the Depth Scale in Sputter Depth Profiling S. Hofmann (Max-Planck-Institute for Metals Research, Germany) Determination of the sputtered depth in depth profiling with high accuracy is a difficult task in quantitative depth profiling. Usually, a linear interpolation is performed between two pionts, one corresponding to the unsputtered surface (zero sputtering time), and the other to the crater depth after sputtering (maximum sputtering time) or to a previously determined marker depth (interface, delta layer etc.).¹ This simple two point method contains a principal uncertainty because of the generation of a native oxide layer when the sample is brought back to air. In addition, this method does not take into account a composition dependency of the sputtering rate, which is particularly important in interface profiling.² Furthermore, the change of the sputtering rate caused by the initial build up of the collisional cascade, and by compound formation, e.g. in reactive ion sputtering, is neglected. Using multilayer interfaces as markers, depth profiling of multilayers can markedly reduce the initial transient effect. Comparison of profiling results on Ni/Cr, Ta/Si, SiO2/Ta2O5, and GaAs/AlAs multilayers show how preferential sputtering and compound formation influence the sputtering time/depth relation. In sputter depth profiling with AES, simultaneous recording of two signals of the same element with low and high electron energies, combined with quantitative evaluation of the intensity scale, can be used to inrinsically determine the depth scale. ¹ ISO Technical Report 15969 to be published 2001 ² S. Hofmann, Sputter Depth Profile Analysis of Interfaces, Rep. Prog. Phys. 61 (1998) 827.
3:40 PM		AS-WeA-6 ARXPS Analysis of Nitrogen Distribution and Chemistry in Nitrided Gate Oxides A.C. Ferryman, J.E. Fulghum (Kent State University) Rapid and reliable characterization of thin, nitrided gate oxide films remains a priority for the semiconductor industry. In this study we evaluate a variety of methods for the analysis of angle-resolved XPS data from nitrided gate oxides. The films have previously been characterized using SIMS depth profiling, and vary in oxide thickness and nitrogen location. Methods based on both ARXPS analysis of core-level photoelectron spectra and on inelastic background analysis will be compared. Trade-offs between rapid data acquisition and high energy resolution N chemistry analysis will be evaluated with respect to ARXPS results. The effect of variation in the electron attenuation length value at shallow angles will be discussed for oxide thickness measurements.
4:00 PM		AS-WeA-7 Characterizing Nanometer Oxy-nitride Films with ESCA Low Energy Sputter Depth Profiles J.H. Gibson (Physical Electronics); E.L. Principe (Applied Materials); J.F. Moulder, D.G. Watson (Physical Electronics); A. Hegedus (Applied Materials) Nanometer thick oxy-nitride films were used to evaluate low energy ESCA sputter depth profiling as a method to determine composition and elemental distribution within ultra thin films. Many previously published studies have focused on the use of angle resolved ESCA measurements to determine the composition of these films. The uncertainties of generating depth distribution information from angle resolved ESCA measurements are the topic of much debate and research. ESCA low energy sputter depth profiling provides a direct measurement of elemental distributions within ultra thin films and may be a valuable tool for thin film development and interpreting angle resolved ESCA measurements. Low energy sputter depth profiles and angle resolved ESCA measurements from 2 nm thick SiON films will be presented. The use and limitations of these complementary approaches for characterizing ultra thin films will be discussed.
4:40 PM		AS-WeA-9 Reconstruction of Buried Polymer Interfaces Observed by Sum-Frequency Generation L.J. Richter, P.T. Wilson, K.A. Briggman, J.C. Stephenson, W.E. Wallace (National Institute of Standards and Technology) The structure of polymer interfaces determines many in service properties such as adhesion. Linear vibrational spectroscopies (FTIR, ATIR, and Raman) are some of the most widely accepted and utilized diagnostics of bulk polymer systems but typically do not have sufficient specificity to probe interfaces. Vibrationally resolved sum-frequency generation (VR-SFG), a non-linear optical technique, is uniquely interface specific as it is dipole forbidden in media with inversion symmetry. We have developed a novel microcavity technique that allows selective characterization of the buried interfaces of polymer/polymer and polymer/dielectric thin film systems. We have applied the technique to the study of the buried interface between polystyrene (PS) and a hydrogen silsesquioxane (HSQ) spin-on-glass (Dow Corning FOx). The as-spun HSQ film is hydrophobic, with a water contact angle >90°. UV-ozone treatment of the as-spun HSQ results in a hydrophilic surface, with a water contact angle <10°. The structure of the PS/hydrophobic HSQ interface, as reflected in the VR-SFG spectra of the pendant phenyl groups, is very similar to that recently reported for the PS/air interface [K.A. Briggman, et al. J. Phys. Chem. B 105, 2785 (2001)]. On the hydrophilic surface, the PS 'reconstructs'. The reconstruction of the interface can be correlated with changes in the adhesion of the thin PS film to the HSQ.