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Electron Imaging and Holography Facility

Electron Imaging and Holography Facility / Equipment / SEM-FIB / Principle of Focused Ion Beam

Principle of Focused Ion Beam

The construction of a Focused Ion Beam(FIB) workstation is similar to that of an electron microscope. The probe is fixed on a multi-axis tilt stage located in a high-vacuum chamber. The ion column is connected to this chamber. Inside the column ions are generated, accelerated and focused. A liquid metal ion source acts as ion source (in most cases gallium or indium ions). It consists of a metal-coated tungsten needle.

Applying an electrical field the ions are extracted from the metal surface by field transmission.
A characteristic of liquid metal ion sources is their extremely high intensity (approx. 106A/cm²sr) and a small emission area (approx. 10nm). This small emission area is the basis for the strong focusing of the ion beam by the ion optical system integrated in the ion column.

The ion column contains all elements required for the acceleration, focusing and deflection of the ion beam. The ions are accelerated to an energy of 30 keV and focused through electrostatic lenses to a beam diameter of a minimum 7nm. Ion densities are within the range of 3-10A/cm²

The scanning of the ion beam over the sample surface is computer-aided. Due to the interaction of the impinging ions with the surface secondary electrons are generated. Just like in electron microscopes, the secondary electrons are detected by means of a secondary electron detector and used to produce an image. Thus, high-resolution ion-beam induced secondary electron images can be generated.

When the ions hit the sample surface, not only secondary electrons are emitted but due to their mass ions are also implanted, defects generated and sample material removed. This sputter erosion enables local removal of material by means of focused ion beams in a direct writing mode.

Focused ion beam workstations are equipped with gas injection devices which enable gaseous media to be injected close to the sample surface.

Etch gases, on the one hand, (e.g. iodine, chlorine) increase the etch rates for certain materials and avoid redeposition of etched material. On the other hand, adding metallo-organic compounds enables the deposition of ion beam-induced conductive materials.

Read about applications of the Focussed Ion Beam