SIMS2015 Session ST-SuA: SIMS XX Sunday Afternoon Tutorial Session

This lecture will provide an introduction to the fundamentals of secondary ion mass spectrometry, based on the classical sputtering theory, on the results of computer simulations of sputtering by atoms and clusters, and on the numerous experimental studies aimed at elucidating the mechanisms of SIMS that have been published over the years. Recent book chapters and review articles will serve as a reference for this tutorial [1-5]. A selection of topics will be presented, and illustrated with examples in direct connection with the everyday experience of the SIMS analysts: • Energy deposition, damage and sputtering processes induced by atoms and clusters; • Emission of fragments, intact molecules and clusters; • Influence of the sample nature on the emission; • Ionization of atoms and molecules; • Matrix and substrate effects; • Information depth; … [1] A. Delcorte, Sputtering and ionization basics, in The Encyclopedia of Mass Spectrometry, Volume 5: Elemental and Isotope Ratio Mass Spectrometry, Beauchemin and Matthews (Eds); Elsevier Science, 2010. pp 397-411. [2] H. M. Urbassek, Status of cascade theory, Chapter 3 in ToF-SIMS: Materials Analysis by Mass Spectrometry (2nd Edition), J. Vickerman and D. Briggs (Eds); IM Publications, Chichester, 2013. pp 67-86. [3] A. Delcorte, Fundamentals of Organic SIMS: Insights from Experiments and Models, Chapter 4 in ToF-SIMS: Materials Analysis by Mass Spectrometry (2nd Edition), J. Vickerman and D. Briggs (Eds); IM Publications, Chichester, 2013. pp 87-123. [4] B. J. Garrison, Z. Postawa, Computational view of surface based organic mass spectrometry, Mass Spectrometry Reviews, 2008, 27, 289-315. [5] A. Delcorte, O. A. Restrepo, B. Czerwinski, Cluster SIMS of organic materials: Theoretical Insights, Chapter 2 in Cluster Secondary Ion Mass Spectrometry: Principles and Applications (First Edition), Ch. M. Mahoney (Ed), John Wiley & Sons, Inc. 2013. pp 13-55.

During the past two decades, the ability of SIMS to obtain spatially resolved (3D) molecular information from organic materials has developed rapidly thanks to the development of new cluster ion sputter sources. Large gas cluster ion sources, the current state of the art, have opened a wide range of application areas from cell analysis to organic electronic devices. This tutorial will provide a guide for practical organic depth profiling and 3D SIMS imaging.

Organic depth profiling

- A brief history (from Ar₁ to Ar₅₀₀₀).

- Which materials can be profiled?

- Definitions (sputter rate, sputtering yield, depth resolution).

- The role of operating conditions (projectile type, cluster size, beam energy, angle of incidence, sample temperature, sample rotation).

- Operational modes and practical considerations (1-beam, 2-beam, non-interlaced, interlaced, dose ratio).

- Quantitative organic depth profiling.

3D imaging

- Topographical correction.

- Distortions (e.g. different sputtering yields).

- Analysis of organic/inorganic heterogeneous materials.

Outlook

- International standardisation.

- Advances and future capability.

Current ToF-SIMS instrumentation enables facile data collection which can result in large data sets. This is particularly true of image and depth profiling data sets which can contain thousands to millions of spectra. Each spectrum can contain hundreds of peaks, the intensities of which encode information about about surface composition, molecular conformation and more. This is further complicated by the fact that many of the peak intensities within a given spectrum are correlated since they originate from fragments of the same surface molecules. Multivariate analysis (MVA) methods present a set of mathematical routines that can be applied to complex data sets in order to simplify their interpretation. MVA methods have been successfully applied in many ToF-SIMS studies and have been shown to be useful tools to summarize and characterize ToF-SIMS data. The successful application of MVA methods requires proper planning, data collection, and data processing. In this tutorial I will provide an overview of how to apply MVA methods to ToF-SIMS data and suggest guidelines that can help navigate the seas of SIMS data. I will also highlight resources available to learn more about using MVA with ToF-SIMS data.

*Short historical overview of dynamic SIMS

*Analytical perspective: comparison of dynamic SIMS with complementary depth profiling techniques

*Instrumental aspects of SIMS depth profiling for different types of SIMS tools (i.e. mass spectrometers: quadrupole, magnetic sector, Time-of-Flight)

*Choice of primary and secondary parameters (primary species, impact energy and angle, current density, secondary species, analysed area restriction i.e. ‘gating’, mass resolution) and implications for depth profiling

*Quantification aspects: depth- and concentration calibration in homogenous matrices and more complicated multilayer systems, design of calibration standards, complementary external techniques for absolute quantification

*Depth resolution in SIMS depth profiling: definition, different mechanisms for degradation of depth resolution (collisional cascade mixing, chemical segregation, ion-beam induced roughness), optimization of primary impact conditions

*Charge compensation in thin dielectric films: optimization of electron impact conditions and/or surface coating, considerations for small metrology areas

*Metrology aspects: considerations for SIMS depth profiling in small metrology areas, reproducibility, automation of data acquisition and data processing for high volume (e.g. full wafer) analysis