Long-life bismuth liquid metal ion source for micromachining application

Liquid metal ion sources (LMIS) are widely used in focused ion beam (FIB) technology for micromachining and surface treatment, and thus LMIS have been broadly developed. Key features of a LMIS for 3D-microfabrication of materials are long life-time, high brightness, stable ion current and a highly effective milling ability for the material to be modified. The most widely used LMIS with such properties is the Ga LMIS, being the working horse of FIB today. A very successful approach to increase the material removal rate, according to sputter theory, is the use of heavier ions and their clusters. We have produced a new long-life (about 1000 h) Bi LMIS with a good beam performance. The investigation of the sputtering rate of NiTi shape memory alloys using Ga and Bi LMIS shows that, for the same experimental conditions, the material removal rate with using of Bi ions without a mass separator is about 5 times larger compared to Ga ions. The sputter threshold dose is nearly one magnitude lower than that of Ga. For many applications this means a drastical reduction of working time. This sputter enhancement is particularly pronounced for target materials with large atomic masses. Furthermore, the roughness induced by the cluster projectile impact is much less pronounced than that generated by the atomic projectiles and the penetration depth is smaller, leading to less contamination of the target