Nanofabrication with a mass-separated FIB

In the last two decades focused ion beams (FIB) have become a very useful tool for many tasks in micro- as well as in nano-technology. Probe sizes of less than 10 nm and current densities of more than 10 Acm-2 are now available and allow to use these beams for many applications. Integrated circuit repair and modification, failure analysis, TEM specimen preparation, lithographic mask repair or FIB lithography as well as the writing maskless implantation are the main application in microelectronic research and industry. Especially, in R&D the FIB is very advantageous because of its high spatial resolution and its flexibility varying dose, energy and pattern design on one chip, or even in one structure detail. Therefore also in the field of basic and applied research the FIB became more important, including plasmonics, photonics and nano-optics.
Most of the FIB systems employ a Ga liquid metal ion source (LMIS). Due of the broad spectrum of applications with Ga beams many cases suffer from the impurity incorporation. For special purposes like writing ion implantation or ion mixing in the µm- or nm range different ion species are needed. Therefore alloy liquid metal ion sources (LMIS) are used and the FIB column must be equipped with a mass separation, namely an ExB mass filter system.
The assembly of a modern FIB system is presented and the development and investigation of different alloy LMIS`s working with other materials than Ga as well as their corresponding application in FIB nano-fabrication will be dicussed.
The energy distribution of the ions from an alloy LMIS is one of the determining factors for the performance of an FIB column. Different source materials like Au73Ge27, Au82Si18, Au77Ge14Si9, Co36Nd64, Er69Ni31, and Er70Fe22Ni5Cr3 were investigated with respect to the energy spread of the different ion species as a function of emission current, ion mass and emitter temperature. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-100 and later in the improved IMSA-OrsayPhysics machine especially for writing implantation to fabricate nm pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi2 nano-structures. Also the Co-FIB was applied to modify thin magnetic multi-layers in the nm-scale. Additionally, the possibility of varying the current density of the FIB by changing the pixel dwell-time was used to investigate the radiation damage and the dynamic annealing in Si and SiC at elevated implantation temperatures. Furthermore, a broad spectrum of ions was employed to study the sputtering process depending on temperature, angle of incidence and ion mass on a couple of target materials using the volume loss method. Especially this technique was used for the fabrication of various kinds of micro-tools and other 3D devices. A nano-hole was made into an AFM tip acting as an aperture in a single ion implantation project.
The presented examples underline useful application possibilities to different tasks of nanotechnology (or nanofabrication) applying FIB tools equipped with a mass separation system to chose from a broad spectrum of ion species the desired one.