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Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS)

Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is a surface analytical technique that focuses a pulsed beam of primary ions onto a sample surface, producing secondary ions in a sputtering process. Analyzing these secondary ions provides information about the molecular, inorganic and elemental species present on the surface. For example, if there were organic contaminants, such as oils adsorbed on the surface, TOF-SIMS would reveal this information, whereas other techniques may not, particularly at very low levels. Since TOF-SIMS is a survey technique, all the elements in the periodic table, including H, can generally be detected. Moreover, this analysis can provide mass spectral information; image information in the XY dimension across a sample; and also depth profile information in the Z direction into a sample.

The surface sensitivity of TOF-SIMS makes it a good first pass at problem solving to give an overview of what types of species are present on a sample. Other techniques can then be used to obtain additional information. TOF-SIMS is also a technique that can detect species at significantly lower levels than traditional surface analysis techniques such as XPS and Auger.

EAG has been offering Time-of-Flight Secondary ion Mass Spectrometry commercially longer than any other company and our expertise is second to none. This is particularly crucial for TOF-SIMS, where the data sets can be extremely complex and may require more interpretation or data processing than other methods. The imaging capabilities of TOF-SIMS can provide elemental and molecular information from defects and particles on the micron scale. TOF-SIMS can also be used for depth profiling and complements dynamic SIMS. The advantages for profiling are its small areas capabilities and also its ability to do survey depth profiles without selecting specific elements of interest. More recently, cluster ion beams enable the profiling of organic materials whilst maintaining structurally significant information.

At EAG, we use TOF-SIMS to assist customers with quality control, failure analysis, troubleshooting, process monitoring, and research and development. For example, the information we provide when investigating wafer surface contamination issues can help determine the specific source of the problem, such as pump oils or component outgassing, or it may indicate problems with the wafer-processing step itself (e.g. etch residue). We make sure you have person-to-person service throughout the process, so that you fully understand the test results and their implications.

Ideal Uses
  • Surface microanalysis of organic and inorganic materials
  • Mass spectra direct from surfaces
  • Ion imaging of surfaces
  • Survey depth profiling
Technical Specifications

Signal Detected: Molecular and elemental species
Elements Detected: Full periodic table coverage, plus molecular species
Detection Limits: 107 – 1010 at/cm2; sub-monolayer
Depth Resolution: 1-3 monolayers (Static mode)
Imaging/Mapping: Yes
Lateral Resolution/Probe Size: ~0.20µm

  • Specific molecular information on thin (sub-monolayer) organic films/contaminants
  • Surface analysis that allows more complete characterization of a surface
  • Excellent detection limits (ppm range) for most elements
  • Quantitative element analysis on Si and GaAs
  • Probe size ~0.2 µm for imaging
  • Insulator and conductor analysis
  • Non-destructive
  • Survey depth profiling
  • Organic/molecular depth profiling
  • Whole wafers up to 200mm
  • Ar cluster ion beams can also be used to clean contaminated or excessively handled surfaces prior to analysis
  • Usually not quantitative without standards
  • Samples must be vacuum compatible
  • It can be too surface sensitive:
    • Sample packaging and prior handling may impact quality of results
    • Analysis order is important, surface-damaging tests should be done after TOF-SIMS
  • Very surface specific — only examines top few monolayers