Alloy liquid metal ion sources for mass separated focused ion beams

During the last decades, the focused ion beam (FIB) became a very useful and versatile tool in the microelectronics industry, as well as in the field of research and development. For special purposes like writing ion implantation or ion mixing in the µm- or sub-µm range different ion species are needed. Therefore alloy liquid metal ion sources (LMIS) are used. 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 I, ion mass m and emitter temperature T. For singly charged ions the predicted dependence of the energy spread, DE µ I2/3 m1/3 T1/2 found for Ga could be confirmed. The alloy LMIS`s discussed above have been used in the Rossendorf FIB system IMSA-100 especially for writing implantation to fabricate sub-µm pattern without any lithographic steps. A Co-FIB was applied for the ion beam synthesis of CoSi2 micro-structures. Additionally, the possibility of varying the current density with the FIB by changing the pixel dwell-time was used for radiation damage investigations 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.
All these examples underline the importance of FIBs in modern research and the new possibilities opened up by a mass separated system applying a broad spectrum of ion species.