Secondary Ion Mass Spectrometry (SIMS)
Description of method
SIMS is a surface-sensitive method for in-depth profiling and microrange analysis on layer systems and bulk materials of conducting, semiconducting and insulating solid samples. Sample material is sputtered by means of an ion beam. Part of the sputtered material consists of positive or negative ions. These secondary ions are separated in a mass spectrometer according to their mass-to-charge ratio and thus enable the identification of all the chemical elements present.
Features of SIMS
- In-depth profiling permits the determination of in-depth concentration gradients, since due to the removal of sample material the time profile of a measurement can be allocated to a distribution in depth (depth resolution a few nm).
- Lateral element distributions can be determined by making use of the imaging properties of the spectrometer arrangement or using a very fine-focussed ion beam for sputtering. The lateral resolution is in the range of 0,1 - 3 µm.
- A microrange analysis with high lateral position resolution is possible using a fine-focussed primary ion beam. The analysed areas are generally 250 x 250 µm², but can be reduced down to the 20 x 20 µm2 range. The depth range covered is a few nm.
- Isotopic abundance analyses can be performed with high precision.
- For bulk- and trace element analysis (e.g. on semiconductor materials) SIMS is used due to its generally low detection limits in the ppb range.
- The quantification of element concentrations uses standards with a known concentration of the relevant elements. The detection limits range from ppm to ppb, and a depth allocation within a few nm is simultaneously possible.
- Suitable samples are solids and powders. The maximum sample size should be 1 x 2 cm2 and the minimum sample size should not be below 1 x 3 mm2, the maximum sample thickness is 6 mm.
- Tof-SIMS from ION-TOF, ion microprobe, time of flight mass spectrometer (max. mass resolution of 10 000 (M/ D M)),
Bi primary ion source,
Cs and EI (O2, Xe, Ar) sputter source, 250-2000eV
- SIMSLAB 410 from Thermoquest, quadrupole mass spectrometer (max. mass resolution of 300 (M/ D M)),
postionization by electron beam,
duoplasmatron and Ga primary ion source with fine focussing,
possibility of SNMS and SIMS
Depth profiles of element distributions; quantitative concentration determination of trace elements if matrix-adapted standard reference materials (e.g. Si or GaAs) are available.
Metals, alloys, semiconductors, superconductors, insulators, glasses and ceramics as bulk materials or thin-film systems.