Focused Ion Beam
A Focused Ion Beam ( Abbr: FIB English for " a focused ion beam ," German also focused ion beam system ) is a device for surface analysis and editing. If the amount of material in the foreground, ie the method is also ion thinning. When scanning the surface of the object under examination by the ion beam is used primarily as an imaging method, then one speaks of a focused-ion -beam microscope.
- 6.1 Manufacturer
- 6.2 Further information
Working principle
The operating principle is similar to that of the FIB scanning electron microscope (SEM). Instead of electrons, ions, usually gallium or helium used. The ion beam is focused in analogy to the SEM with the aid of electrostatic and magnetic lenses in a point and line by line on the surfaces. In this case, contact of secondary electrons from the surface are detected and allow an image of the surface. In addition, the intensity of the beam passing through the sample and the light reflected from the sample beam can be measured.
The ions are typically accelerated by voltages of 2 to 50 kV. The FIB beam current can be controlled by the different sized apertures ( typically 1 Pa to 1.3 uA ). This produces large currents for the " rough " of material are used, small currents due to the better resolution for fine polishing and imaging.
For use frequently gallium because of the good producibility of ions using a liquid metal ion source (English liquid metal ion source, LMIS ). Gallium is heated by means of a tungsten needle to the melting point and obtained in a field-emission process of the ion beam. So-called plasma - FIB that work with xenon ions reaching very high beam currents of 1.3 uA. In addition, helium or neon are common.
Theoretically can be accomplished with a focused-ion -beam microscope due to the smaller De Broglie wavelength of the ions, a finer resolution than the use of electrons. In reality, the resolution of SEM and FIB but through the interaction region with the sample and limited by lens aberrations of the beam focusing ability is limited. The higher resolution of the helium ion microscope can not be explained directly by the smaller wavelength, since even the wavelength of the electrons ( at 10kV is this 12 pm ) very much smaller than the achievable resolution (~ 1 nm). FIB gallium, which are primarily designed for material removal and thus for high maximum currents (eg 60 nA), reach even the smallest aperture (1 pA) "only" resolutions of about 5-10 nm
Interaction of the ion beam
Interaction with the (sample ) surface
Due to the higher mass of the ions (as opposed to electrons) the interaction of the ion beam with the surface is significantly stronger, since, according to the laws of the elastic impact much more energy is transferred to the surface atoms. This is minimized by the use of light ions such as helium or specifically used (in the case of gallium, for example) to edit materials in the nanometer scale. It is then further surface processes, such as the storage of the primary ion and the amorphization of the surface.
Furthermore, can, by analogy with crystal Wachtumsstrukturen, form so-called mining structures. For example, chains of screw dislocations are visible as spirals.
Interaction with process gases
Process gases are directed through the sample, for example, complex organic platinum compound MeCpPtMe3, and structures can be built. The adsorbed on the surface of the process gases (in this case platinum in the example) is split and a volatile content through the ion beam in a non-volatile part. The platinum is thus only at points on the scans of the beam, deposited, as the process gas without the energy input of the beam does not split and verflüchtet again. In addition to platinum is also deposited on the surface of carbon, which originates from the organic platinum compound complex. The carbon content in the growing layer is up to 40 percent. By means of additional injection of water can be reduced by the reaction between the oxygen in the water with the carbon of the carbon content in the layer. It can also be deposited or tungsten, pure carbon, Siliziumdoxid and many other materials.
Other process gases such as, for example, water, iodine, xenon difluoride, or increase the etching selectivity and allow a selective etching, or a better removal of the materials, since the redeposition ( re-deposition ) is inhibited. With iodine can be aluminum and etched with xenon difluoride silicon oxide. Water is used for acceleration of the removal of carbon. The reaction between the oxygen of the water and the carbon caused the formation of carbon dioxide which is filtered off.
Applications
Applies the FIB technology in the semiconductor industry, mainly for the failure analysis, and in research. Where samples for further examination to be prepared (e.g., for examination by transmission electron microscopy, TEM), or manufactured structures, which can be investigated further. The possibility to produce cross-sections in materials and thereby generate extremely small mechanical or thermal disturbances make it possible to assess sensitive layers in the Materials Research better.
Furthermore, the manipulative effect of an ion beam can be specifically used for ion implantation, for example, in semiconductor structures. A concrete application is the structuring of feedback gratings on laser diodes by rasterized implantation of dopants.
Crossbeam and DualBeam
If a FIB system combined with an electron microscope, you get a "dual beam" ( two-beam ) or "cross beam" system ( with crossed beams ), which enable the simultaneous observation and processing of materials. This makes it possible to pinpoint defects ( eg, individual transistors in ICs ) to prepare or interesting points on a sample.