In static SIMS, dedicated to the analysis of the top monolayer, the primary ion dose is kept below 112 ions/cm2 and the mass spectrum reveals MOLECULAR information. In dynamic SIMS mode, the primary ion dose is not limited and exceeds 112 ions/cm2. In this mode, ELEMENTAL and ISOTOPIC information can be obtained from the mass spectrum. It allows surface, "bulk" and 2D/3D analysis.

The ionization yield of most elements varies by decades, depending on the chemical environment. This property is used in SIMS instruments to increase the sensitivity of the technique: a dynamic SIMS instrument must be equipped with Oxygen and Cesium primary ion beams in order to enhance, respectively, positive and negative secondary ion intensity by 2 to 3 orders of magnitude compared to the use of noble gas ions. Oxygen gas can also be flooded onto the surface to oxidize it and increase positive ion emission.

When sending keV ions onto a solid surface, three important phenomena occur simultaneously: 

• the sputtering of mainly the top monolayer atoms, induced by the collision cascade,
• the ionization of a small fraction of the secondary particles,
• the primary ion implantation in the solid (and associated change of composition, surface work function, etc...). 

Starting from the surface (or going through an interface), the concentration of the implanted primary species (oxygen or cesium) will vary, and then reach an equilibrium (after a few nm, depending on the conditions). As soon as this is achieved, reliable quantification is possible with reference standard samples, using Relative Sensitivity Factors.

One of the main applications of dynamic SIMS is the analysis of trace element depth distribution (for example, dopant in semiconductors). Impact ion energy is adjusted depending on the applications. Low energy (down to 200-300 eV) is used to reduce atomic mixing due to the collision cascade and improve depth resolution to the nanometer level. High energy (up to 20-30 keV) is chosen to go deeper (10-20 microns), faster (µm per min), and improve detection limits and image resolution.

The Cameca IMS 7f magnetic sector SIMS can cater to Depth Profiling with high sensitivity - down to parts per billion atomic concentration - and 2D or 3D imaging of trace elements. It is widely used for dopant implant dose matching, junction depth measurement, process development (characterization of implant, deposition, annealing,...), failure and light element analysis.

The Cameca IMS 1280 is based on a double focusing mass spectrometer with a large radius magnetic sector (585 mm). It is particularly suited for minerals studied in geology where complex materials contain many different species at trace levels. This results in a large number of mass interference that makes trace element analysis impossible without High Mass Resolution capability. Moreover, the need for in-situ analyses at continuously decreasing scales - which are not achievable with conventional technique (TIMS or ICP-MS) - has led to the development of a new generation of SIMS instruments providing High Sensitivity at High Mass Resolution.

Another important feature of the IMS 1280 is the multi-collector system equipped with 5 moveable detectors (Electron Multiplier or Faraday Cup) to perform high accuracy isotope ratio analyses from lithium to lead in multi-collection mode. It also increases the throughput of the instrument by reducing the total acquisition time.

The NanoSIMS 50 & 50L multi-detector instruments but also more oriented for ultra fine feature analysis in Materials, Geology, Planetary and Life sciences. This instrument would be ideal also for cosmic dust analysis. Among the unique new features offered by the NanoSIMS 50 are:

• the ability to extend the SIMS analysis to extremely small areas or volumes (50 nm size in cesium, 150 nm in oxygen) while maintaining extremely high sensitivity at High Mass Resolution. This derives from the revolutionary coaxial optical design of the ion gun and secondary ion extraction, and from a new design of the magnetic sector mass analyzer.
• the capability to measure up to 5 (NS50) or 7 (NS50L) masses (ions) in parallel, ensuring perfect isotopic ratio from the same small volume, or perfect image superimposition

In the area of quadrupole SIMS, the SIMS 4550 is the benchmark instrument with top performances in depth profiling.
Some of the key points ensuring its success are:

• Reference performances in high depth resolution analysis. This derives mainly from: 
  • Oxygen and cesium Floating Low energy Ion Gun technology (FLIG), exceeding by far the performance of conventional or extraction floating ion columns used in other conventional SIMS. The performance in cesium beam has been impressively improved with the adaptation of the CAMECA Microbeam high brightness ion source, now common on all our SIMS range.
  • A total flexibility concerning the primary ion angle of incidence, even in unattended chained analysis.
  • A low field of extraction of the quadrupole analyzer facilitating the use of low energy primary ions.
• Reference performances in automation and reproducibility for metrology, deriving mainly from:
  • a superior redesign of the quadrupole analyzer optics (extraction, transfer, gating, post-acceleration),
  • a user-friendly chain analysis software and a renowned ease of use of the instrument, reducing the need for highly-trained operators,
  • ultra stable ion sources and electronics for unattended overnight measurements.
• Easy insulator analysis thanks to:
  • the low extraction field of the quadrupole,
  • a low energy electron flood gun for charge compensation,
  • unique OCE (Optical Conductivity Enhancement) for SiGe analysis.

Finally, the unique Checkerboard capability allows the operator to check the validity of the results, remove artifacts from sample inhomogeneity or dusts, without having to re-run the analysis. This adds greatly to the throughput of the instrument, reproducibility and reliability of the results.

- We refer you also to the ‘Applications’ area at our main web www.xtronix.ch
- Ref.  www.cameca.fr