ToF - SIMS

Bond contacts in electronic components that become detached. Thin-film-based laser mirrors whose values for the damage thresholds do not meet the requirements. Clouding in optical components and substrates. Protective coatings that delaminate from surfaces. These are all examples of problems for which analytical microstructure diagnostics methods are used to clarify the causes and to minimize or eliminate defect risks. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) offers outstanding possibilities for these tasks, particularly when it comes to surface analysis, and is superior to many other methods.

Methods such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) including energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectrometry (FTIR) or Raman spectroscopy are valuable for materials research. However, they are generally not sufficient for the challenges described above or can only answer partial aspects. Because the detection sensitivity is insufficient. Because surface sensitivity is lacking. Or because individual elements, can be detected, but compounds can’t.

ToF-SIMS eliminates many of these disadvantages. The method provides detailed elemental and molecular information about the surface, thin films and interfaces of the sample and enables a complete three-dimensional analysis. At the Fraunhofer IMWS, the method is used with state-of-the-art equipment for microstructure elucidation in various material classes (e.g. semiconductors, coatings, plastics, glass, ceramics, paints), based on the many years of experience of our scientific team in cooperation with industry. This enables the Fraunhofer team to offer viable nanoanalytical solutions for defect analysis and for the characterization of materials, also in combination with other methods. The technique offers a very high surface sensitivity (information depth < 1 nm), a very high detection sensitivity for almost all elements (even very light elements such as hydrogen, lithium and boron) as well as the possibility of detecting chemical compounds in addition to elements.

In time-of-flight secondary ion mass spectrometry, the sample to be analyzed is bombarded with a primary ion beam. Secondary ions are released from the uppermost atomic layers of the sample. These pass through a time-of-flight mass spectrometer in which they are exposed to an electrostatic field, and are recorded by a detector at the end of the trajectory. In this field, ions of different masses move at different speeds: light ions fly through the field faster and reach the detector sooner, while heavy ions are slower and arrive at the detector later. The differences in flight time allow conclusions to be drawn about the mass of the ions, which in turn allows statements to be made about which element is involved.

Due to the very low primary ion currents used, which generally only ablate the top 1-2 atomic layers, the surface analysis is virtually non-destructive. However, information about deeper sample areas can also be generated easily and with high sensitivity using ablative ion bombardment. Lateral resolutions in the < 100 nm range and depth resolutions even in the sub-nm range are possible. The ToF-SIMS device used at the Fraunhofer IMWS also offers the possibility of carrying out depth profiling even in organic sample setups, by using a special ion source.