New Developments in Secondary Ion Mass Spectrometry
Authors: Werner HW 
Published: March 2009

A growing awareness by mankind can be found these days of the limitations of our planet's resources of both energy and materials. It is now realized that only a responsible policy for energy and material consumption can prevent too rapid exhaustion of these resources. Fortunately, new technologies and materials are available which make it possible to design new devices and components of tiny dimensions, resulting in a considerable reduction of material and energy consumption. These new (technological) elements, because of their ever decreasing dimensions, need special techniques for analytical guidance throughout the whole cycle of production and testing.

A number of thin-film analytical techniques are available, not only for these special type of analyses but also for a much broader range of applications. The developments in one of these techniques, secondary ion mass spectrometry (SIMS), will be the main topic of this paper. A brief comparison of the principle features of SIMS and other beam techniques—Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), etc.—with the classical discharge excitation techniques, such as arc, spark, and glow discharge-excitation, will be made.

The following different lines of development in SIMS will be discussed: 1. The increasing use of quadrupole mass spectrometers, mostly used in combination with other thin-film analysis techniques, and problems encountered in point analysis and elemental mapping (imaging), using ion microprobes, where a fine ion beam scans the surface to be imaged, or ion microscopes, where an image of the bombarded area is produced using the ion optics of the mass spectrometer. 2. The need to detect cluster ions XnYm+—important for organic SIMS analysis, depth profiling, and fundamental studies—which has led to the development of mass spectrometers with a large mass range. High mass resolution instruments (5000 and up) are required for the identification, by means of mass defects, of constituents of layers or interfaces, or both, that emit ions or cluster ions with the same mass number. 3. Methods for quantitative analysis with SIMS, using positive or negative atomic ions or molecular ions, developed for a large number of matrices. However, some caution is always necessary because of the possibility of artifacts not yet taken into account. 4. The combination of SIMS with other thin-film analysis techniques being used more and more, in many cases, to facilitate the solution of practical analytical problems caused by the complementary information available—for example, the element range, limit of detection, peak coincidences, and ease of interpretation. 5. Quantitative, routine depth profiling of many elements, including hydrogen, as reported by many authors. Reliable depth profiles will only be obtained, however, when the many artifacts inherent to ion bombardment are taken into account. 6. Different applications of SIMS—for example, the investigation of nonplanar samples, insulating materials, thin-film sandwich structures, organic materials, and biological materials.