Investigation and optimization of the emission parameters of alloy liquid metal ion sources

Liquid metal ion sources (LMIS) are one of the key elements in focused ion beam (FIB) technology. For special tasks, alloy LMIS are needed which have to be operated in the most cases at elevated temperatures. For the adjustme nt of an optimal beam performance in a FIB system, the source parameters. t emperature of the ion emitter and the energy spread of the different ion sp ecies used are of fundamental importance. Emitters wetted with Au73Ge27, Au 77Ge14Si9 and Co36Nd64 alloys were investigated with respect to the influen ce of the source temperature on the emission current-extraction voltage cha racteristics, the mass distribution, as well as the energy spread of the di fferent emitted ions using an equipment containing an ExB mass filter and a retarding field energy analyser. The energy spread significantly determine s the available FIB spot size and depends also on the emission current, the charge state, and the mass of ions or clusters. The axial angular intensit y and the resulting target current of the FIB were measured as a function o f the source parameters. Two operating regimes were found. Either one works in a high stable target current mode with lower resolution (emission curre nt similar to 10 mu A), or in the high resolution, high chromatic angular i ntensity mode (emission current a few mu A), with a reduced target current and less current stability, both at source temperatures some 10 K above the melting point. (C) 2000 Elsevier Science B.V. All rights reserved.